Cross-reference to Related Applications

[0001] This application claims priority from International Patent Application No. PCT/AU2021/051203 filed 14 October 2021 and Australian Provisional Patent Application No. 2022900994 filed 13 April 2022, the entire contents of which are incorporated herein by cross-reference.

Technical Field

[0002] The present disclosure broadly relates to radiolabelled conjugates of trivalent arsenical compounds as defined herein and their preparation. The present disclosure further relates to the use of such radiolabelled conjugates in the diagnosis and treatment of conditions associated with cell death, such as neoplastic conditions, and methods of producing such radiolabelled conjugates.

Background of the Invention

[0003] Cancer is responsible for about 1 in 6 deaths globally and the economic cost is in the trillions of dollars annually. Tumours are characterized by an imbalance between rates of cellular proliferation and survival in a tissue, while successful treatment controls tumour growth by inhibiting tumour cell proliferation and/or promoting tumour cell death.

[0004] Chemotherapy, radiotherapy and immunotherapy are the mainstay of cancer therapies and are effective in many cases. When cancer is localised, it is amenable to potentially curative treatments such as surgery or synergistic combinations such as chemo-radiotherapy. However, once disease is disseminated, systemic therapies such as chemotherapy, targeted therapies or immunotherapy are required. Whilst the addition of external beam radiotherapy may be synergistic in patients with disseminated disease, it is often not possible to treat all sites of disease due to toxicity, and thus radiotherapy is reserved for palliative treatment of symptomatic sites of disease. Curative treatments remain in the minority for most cancer types. In addition, the efficacy of these treatment strategies is limited by the heterogeneity of the tumour, as certain populations of cancer cells become resistant to therapy.

[0005] There has been renewed interest in theranostics to improve curative rates for solid tumours. A theranostic employs a tumour marker to deliver a therapeutic isotope to the tumour. Theranostic approaches have proved successful in niche applications such as neuroendocrine tumours (Strosberg J, El-Haddad G, Wolin E, et al. Phase 3 Trial of (177)Lu-Dotatate for Midgut Neuroendocrine Tumors. N Engl J Med. 2017;376(2):125-135) and prostate carcinoma (von Eyben FE, Roviello G, Kiljunen T, et al. Third-line treatment and (177)Lu-PSMA radioligand therapy of metastatic castration-resistant prostate cancer: a systematic review. Ear J Nucl Med Mol Imaging. 2018;45(3):496-508), wherein the tumour markers are somatostatin receptor and prostate specific membrane antigen, respectively. However, theranostic approaches have traditionally been limited to niche applications and select tumour groups.

[0006] A promising diagnostic agent is the ⁶⁸ Ga labelled compound ⁶⁸ Ga-NODAGA-GSAO, which was disclosed in PCT application PCT/AU2020/050359. While ⁶⁸ Ga-NODAGA-GSAO could be prepared at room temperature, chelation of radioisotopes using other chelators can require heating, which could lead to radiolysis of the active agent. Radiolysis may also be a risk when trying to incorporate higher energy radioisotopes into a theranostic agent. Accordingly, it remains desirable to provide effective methods for preparing radiolabelled agents useful in the diagnosis and treatment of cancers.

Summary of the Invention

[0007] The present disclosure provides, inter alia, a process for preparing a radiolabelled trivalent arsenical compound, the process comprising a step of: a) adding a radioisotope to a trivalent arsenical compound comprising a bifunctional chelator in the presence of a low molecular weight thiol to form an adduct of a radiolabelled trivalent arsenical compound and a low molecular weight thiol. [0008] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (Y)

Formula (Y) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; and L is a bifunctional chelator; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof or derivative thereof. In some embodiments, L comprises DOTA, DTPA, NOD AGA, NOTA, DOT AGA, or sarcophagine.

[0009] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (II)

Formula (II) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. [0010] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (VI)

Formula (VI) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or ORf>. wherein R ₆ is a C _1-5 straight or branched alkyl group; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0011] In some embodiments of the processes described herein, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some embodiments, R ₅ is -NHCH ₂ COOH.

[0012] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (Ila)

Formula (Ila) wherein A is -As(OH) ₂ or an arsenoxide equivalent group, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0013] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (W)

Formula (W) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; and L is a bifunctional chelator; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof or derivative thereof. In some embodiments, the radioisotope is ¹⁷⁷ Lu. In some embodiments, L comprises DOTA, DTPA, NOD AGA, NOTA, DOT AGA, or sarcophagine. [0014] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (IV) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0015] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (VIII) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0016] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (IVa)

Formula (IVa) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; R? and R ₈ are in independently selected from H and methyl; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0017] In some embodiments of the processes described herein, the radioistotope is a therapeutic radioisotope and/or a radioisotope with a half-life of less than 4 days. In some embodiments, the radioisotope is ¹⁷⁷ Lu, ⁶⁸ Ga, ⁶⁴ Cu, ⁶⁷ Cu, ⁹⁰ Y, ¹⁸⁶ Re or ¹⁸⁸ Re. In some embodiments, the radioisotope is ¹⁷⁷ Lu.

[0018] In some embodiments of the processes described herein, the low molecular weight (LMW) thiol is selected from the group consisting of glutathione, cysteine, N-acetyl cysteine, y-glutamylcysteine, cysteinylglycine, homocysteine, thiocysteine, cysteamine, hydrogen sulfide, thiophenol, 2-butenethiol, furfurylthiol, 2-mercaptoethanol, methanethiol, ethanethiol, 1 -propanethiol, 2-propanethiol, allyl mercaptan, tert-butyl mercaptan, pentanethiols, thioacetic acid, coenzyme A, 2-mercaptoindole, furan-2-ylmethanethiol, 3-mercaptopropane-l,2-diol, 3- mercapto- 1 -propanesulfonic acid, 1 -hexadecanethiol, pentachlorobenzenethiol, mycothiol and bacillithiol. In some embodiments, the low molecular weight thiol is selected from the group consisting of glutathione, cysteine, N-acetyl cysteine and homocysteine. In some embodiments, the low molecular weight thiol is naturally or non-naturally occurring. In some embodiments, the concentration of low molecular weight thiol in the reaction mixture is about 0.01M or greater.

[0019] In some embodiments of the processes described herein, the low molecular weight thiol is not glutathione.

[0020] In some embodiments of the processes described herein, the radioisotope is added to the trivalent arsenical compound in the presence of a low molecular weight thiol and an antioxidant. In some embodiments, the antioxidant is ascorbic acid. In some embodiments, the concentration of the ascorbic acid in the reaction mixture is about 0.01M or greater.

[0021] In some embodiments of the processes described herein, the process takes place above room temperature. In some embodiments, the process takes place at a temperature between about 70°C and about 130°C.

[0022] In some embodiments of the processes described herein, the process further comprises a step of: b) treating the adduct formed in step a) with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the anions are phosphate anions.

[0023] In some embodiments of the processes described herein, the process further comprises a step of: c) purification of the radiolabelled trivalent arsenical compound formed in step b). In some embodiments, purification comprises solid phase extraction. In some embodiments, the solid phase extraction comprises silica as the mobile phase.

[0024] The present disclosure further provides an adduct of a radiolabelled trivalent arsenical compound and a low molecular weight thiol. In some embodiments, the present disclosure provides the adduct formed in step a) of the processes described herein. [0025] The present disclosure further provides a compound described herein. In some embodiments, the present disclosure further provides a compound according to Formula (III)

Formula (III) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; and Z is a therapeutic radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some embodiments, the compound comprises less than about 5% of the corresponding oxidized As(V) compound as determined by HPLC.

[0026] The present disclosure further provides a pharmaceutical composition comprising a compound of the disclosure together with a pharmaceutically acceptable carrier, excipient, diluent, vehicle and/or adjuvant. In some embodiments, the present disclosure provides a compound of Formula (III) together with a pharmaceutically acceptable carrier, excipient, diluent, vehicle and/or adjuvant.

[0027] The present disclosure further provides a method of treating a neoplastic condition in a subject comprising administering an effective amount of a compound or a pharmaceutical composition described herein to the subject. In some embodiments, the present disclosure provides a method of treating a neoplastic condition in a subject comprising administering an effective amount of a compound of Formula (III) or a pharmaceutical composition comprising a compound of Formula (III) together with a pharmaceutically acceptable carrier, excipient, diluent, vehicle and/or adjuvant. [0028] The present disclosure further provides a method of inducing cell death in a subject, comprising administering a compound or a pharmaceutical composition described herein to the subject. In some embodiments, the present disclosure provides a method of inducing cell death in a subject, comprising administering a compound of Formula (III) or a pharmaceutical composition comprising a compound of Formula (III) together with a pharmaceutically acceptable carrier, excipient, diluent, vehicle and/or adjuvant.

[0029] The present disclosure further provides the use of a compound described herein in the manufacture of a medicament for the treatment of a neoplastic condition. In some embodiments, the present disclosure provides the use of a compound of Formula (III) in the manufacture of a medicament for the treatment of a neoplastic condition.

[0030] The present disclosure further provides the use of a compound described herein in the manufacture of a medicament for inducing cell death. In some embodiments, the present disclosure provides the use of a compound of Formula (III) in the manufacture of a medicament for inducing cell death.

[0031] The present disclosure further provides a process for preparing a compound of Formula (III), comprising adding a therapeutic radioisotope to a compound according to Formula (IV) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

Brief description of the drawings

[0032] Exemplary embodiments of the present disclosure are described herein, by way of nonlimiting example only, with reference to the following drawings.

[0033] Figure 1 shows the model of action for the therapeutic radiolabelled compounds disclosed herein.

[0034] Figure 2 shows the HPLC chromatogram of ¹⁷⁵ Lu-NODAGA-GSAO labelled for 30 minutes at pH 5.0 at 80°C, (A) without 2,3-dimercapto-l-propanol (DMP) or (B) with preincubation with DMP as described in Example 2.

[0035] Figure 3 shows the HPLC chromatogram of ⁶³ Cu-NODAGA-GSAO labelled for 30 minutes at pH 5.0 at room temperature, (A) without DMP or (B) with pre-incubation with DMP as described in Example 2.

[0036] Figure 4 shows the HPLC chromatogram of ⁸⁹ Y-NODAGA-GSAO labelled for 30 minutes at pH 5.0 at 120°C as described in Example 2.

[0037] Figure 5 shows the percentage of labelling at different timepoints following formation of the isotope-NODAGA-GSAO complex for A) the ¹⁷⁵ Lu-labelled product obtained from incubation for 30 minutes at pH 5.0 at 80°C and B) the ⁶³ Cu-labelled product obtained from incubation for 30 minutes at pH 5.0 at room temperature.

[0038] Figure 6 is a radiometric HPLC chromatogram of the reaction product of Example 4 at the end of synthesis.

[0039] Figure 7 is a radiometric HPLC chromatogram of the reaction product of Example 4 1.5 hours after the end of synthesis.

[0040] Figure 8 is a radiometric HPLC chromatogram of the reaction product of Example 5a at the end of synthesis. [0041] Figure 9 is a radiometric HPLC chromatogram of the reaction product of Example 5a mixed with 1% DMP in DMSO.

[0042] Figure 10 is a radiometric HPLC chromatogram of the reaction product of Example 5b at the end of synthesis.

[0043] Figure 11 is a radiometric HPLC chromatogram of the reaction product of Example 5b mixed with 1% DMP in DMSO.

[0044] Figure 12 is a radiometric HPLC chromatogram of the reaction product of Example 5c at the end of synthesis.

[0045] Figure 13 is a radiometric HPLC chromatogram of the reaction product of Example 5c at the end of synthesis mixed with 1% DMP in DMSO.

[0046] Figure 14 is a radiometric HPLC chromatogram of the reaction product of Example 5c at 72 hours post-synthesis.

[0047] Figure 15 is a radiometric HPLC chromatogram of the reaction product of Example 5c at 72 hours post-synthesis mixed with 1% DMP in DMSO.

[0048] Figure 16 is a radiometric HPLC chromatogram of the reaction product of Example 5d at the end of synthesis.

[0049] Figure 17 is a radiometric HPLC chromatogram of the reaction product of Example 5d at the end of synthesis mixed with 1% DMP in DMSO.

[0050] Figure 18 is a schematic diagram of a radiolabelling system as used in Example 6.

[0051] Figure 19 is a radiometric HPLC chromatogram of the final product produced in Example 6. [0052] Figure 20 is a radiometric HPLC chromatogram of the final product produced in Example 6 (the same product as Figure 19) following reaction with DMP.

[0053] Figure 21 shows the biodistribution of ⁶⁸ Ga-NODAGA-GSAO (%ID/g) in healthy male rats at 1 and 2 hours post administration of ⁶⁸ Ga-NODAGA-GSAO.

[0054] Figure 22 shows the maximum intensity projection of ⁶⁸ Ga-NODAGA-GSAO PET CT scans performed a) 1 hour and b) 2 hours following tracer ( ⁶⁸ Ga-NODAGA-GSAO) administration.

[0055] Figure 23 shows anterior maximum intensity projections of ⁶⁸ Ga-NODAGA-GSAO PET at 8 time points following injection in patient 1.

[0056] Figure 24 shows anterior maximum intensity projections of ⁶⁸ Ga-NODAGA-GSAO PET at 8 time points following injection in patient 2.

[0057] Figure 25 shows anterior maximum intensity projections of ⁶⁸ Ga-NODAGA-GSAO PET at 8 time points following injection in patient 3.

[0058] Figure 26 shows anterior maximum intensity projections of ⁶⁸ Ga-NODAGA-GSAO PET at 8 time points following injection in patient 4.

[0059] Figure 27 shows biodistribution of ⁶⁸ Ga-NODAGA-GSAO in normal organs of patient 1 over time.

[0060] Figure 28 shows biodistribution of ⁶⁸ Ga NOD AGA GSAO in selected normal tissues and tumour for patient 1.

[0061] Figure 29 shows biodistribution of ⁶⁸ Ga NOD AGA GSAO in selected normal tissues and tumour for patient 2.

[0062] Figure 30 shows biodistribution of ⁶⁸ Ga NOD AGA GSAO in selected normal tissues and tumour for patient 3. [0063] Figure 31 shows biodistribution of ⁶⁸ Ga NOD AGA GSAO in selected normal tissues and tumour for patient 4.

[0064] Figure 32 shows the biodistribution in selected normal tissues (mean SUV ± SD) of ⁶⁸ Ga NOD AGA GSAO in subjects 1-4.

[0065] Figure 33 shows blood pool activity and uptake of ⁶⁸ Ga NOD AGA GSAO into tumour deposits in subjects 1-4.

[0066] Figure 34 shows anterior maximum projection intensity images of FDG-PET (Fig. 34A) performed 60 min after administration of 256 MBq of FDG (fluorodeoxyglucose), and CDI-PET (Fig. 34B) performed 60 min after administration of 205 MBq of ⁶⁸ Ga NODAGA GSAO ( ⁶⁸ Ga-CDI) in patient 3. The tumours were surgically excised, fixed and adjacent sections stained for apoptotic cells (Fig. 34C, brown TUNEL stain, a and b) or for morphology by haematoxylin and eosin (Fig. 34C, c and d).

[0067] Figure 35 shows radiochromatograms following the ¹⁷⁷ Lu-CDI (CDI = NODAGA GSAO) synthesis reaction of Example 11. The labelling of CDI with ¹⁷⁷ Lu was assessed by HPLC. (A) Synthesis of ¹⁷⁷ Lu-CDI in the presence of 0.002M ascorbic acid. (B) The proportion of ¹⁷⁷ LU-CDI VS radiolysed ¹⁷⁷ Lu-CDI at 1.5h following synthesis reaction. (C) Synthesis of ¹⁷⁷ LU-CDI in the presence of 0.01M ascorbic acid and 0.028M GSH. Region 1 represents free ¹⁷⁷ LU, region 2 represents radiolysed ¹⁷⁷ Lu-CDI, region 3 represents product of interest ( ¹⁷⁷ Lu- CDI).

[0068] Figure 36 shows absorbance chromatograms of ¹⁷⁵ Lu-CDI and ¹⁷⁵ Lu-CDI-GSH by HPLC. CDI was labelled with ¹⁷⁵ Lu at pH 5.0 for 30 min at 85°C in the presence of glutathione. The labelling of CDI was assessed by HPLC in the absence (A) or presence (B) of 0.0028M GSH using absorbance at 280nm. ¹⁷⁵ Lu-CDI elutes at ~13.9min and ¹⁷⁵ Lu-CDLGSH elutes at ~15.8-16.0min.

[0069] Figure 37 shows absorbance chromatograms of ¹⁷⁵ Lu-CDI in the presence of different small thiols by HPLC. CDI was labelled with ¹⁷⁵ Lu at pH 5.0 for 30 min at 85°C in the presence of cysteine (A), N-acetyl cysteine (B) or homocysteine (C). The labelling of CDI was assessed by HPLC using absorbance at 280nm. ¹⁷⁵ Lu-CDI elutes at ~13.9min, ¹⁷⁵ Lu-CDI-cysteine elutes at ~14.2-14.6min, ¹⁷⁵ Lu-CDI-N-acetyl cysteine elutes at ~19.8-20.2min, and ¹⁷⁵ Lu-CDI- homocysteine elutes at ~16.7min.

[0070] Figure 38 shows absorbance chromatograms showing 10-fold dilution of ¹⁷⁵ Lu-CDI- GSH dissociates GSH from ¹⁷⁵ Lu-CDI. CDI was labelled with ¹⁷⁵ Lu at pH 5.0 for 30 min at 85°C in the presence of glutathione and the synthesis product was diluted in 0.4M sodium acetate pH 5.0 buffer (A) or 0.5M Tris pH 9.0 buffer (B). The labelling of CDI was assessed by HPLC using absorbance at 280nm. ¹⁷⁵ Lu-CDI elutes at ~13.9min and ¹⁷⁵ Lu-CDI-GSH elutes at ~15.8-16.2min.

[0071] Figure 39 shows absorbance chromatograms showing pH dependent dissociation of GSH from ¹⁷⁵ Lu-CDI following 10-fold dilution in sodium phosphate buffer. CDI was labelled with ¹⁷⁵ LU at pH 5.0 for 30 min at 85°C in the presence of glutathione and the synthesis product was diluted in 0.4M sodium acetate buffer with pH of 7.0 (A) 8.0 (B) or 9.0 (C). The labelling of CDI was assessed by HPLC using absorbance at 280nm. ¹⁷⁵ Lu-CDI elutes at ~13.9min and ¹⁷⁵ LU-CDLGSH elutes at ~15.6-15.8min.

[0072] Figure 40 shows the chemical structure of NOD AGA GSAO (CDI) and ¹⁷⁷ Lu-CDI and the reaction conditions required for the optimal labelling of CDI with ¹⁷⁷ Lu.

[0073] Figure 41 shows absorbance chromatograms showing the results of the HLB cartridge elution step following loading of ¹⁷⁵ Lu-CDI + GSH. (A-B) CDI was labelled with ¹⁷⁵ Lu at pH 5.0 for 30 min at 85°C in the presence of glutathione and the synthesis product was diluted in 0.4M sodium acetate pH 9.0 buffer. The diluted product was loaded on a HLB cartridge and eluted using (A) 0.5mL ethanol (a) or 0.5mL acetonitrile (B). (C) CDI was labelled with ¹⁷⁵ Lu at pH 5.0 for 30 min at 85 °C in the absence of glutathione and the synthesis product was diluted in 0.4M sodium acetate pH 9.0 buffer. The diluted product was loaded on a HLB cartridge and eluted using 0.5mL ethanol. The elution of CDI from the HLB cartridge was assessed by HPLC using absorbance at 280nm. ¹⁷⁵ Lu-CDI elutes at ~14.4min and ¹⁷⁵ Lu-CDLGSH elutes at -15.6- 16.2min.

[0074] Figure 42 shows absorbance chromatograms following loading of ¹⁷⁵ Lu-CDI + GSH on the C18 cartridge. CDI was labelled with ¹⁷⁵ Lu at pH 5.0 for 30 min at 85°C in the presence of glutathione and the synthesis product was diluted in 0.4M sodium acetate pH 9.0 buffer. The diluted product was loaded on a C 18 cartridge. (A) The C18 cartridge was washed using 5mL normal saline followed by 2mL air. The flowthrough was collected and assessed by HPLC using absorbance at 280nm. (B) Following the wash, the C18 cartridge was eluted using 0.5mL ethanol. The eluate was collected and assessed by HPLC using absorbance at 280nm. ¹⁷⁵ Lu- CDI elutes at ~14.5min and ¹⁷⁵ Lu-CDI-GSH elutes at ~15.6-16.2min.

[0075] Figure 43 shows mean %IA (A) and concentration (B) for selected tissues / organs.

[0076] Figure 44 shows maximum intensity projection images of FDG PET and eight sequential CDI PET scans for participant 1 (Example 12). All images are scaled from SUV 0 to 7. The tumor is arrowed on the FDG PET and CDI PET performed at 59 minutes post CDI injection.

[0077] Figure 45 shows mean SUV of the blood pool (A) and tumor (B) and tumour to blood pool ratio (C).

[0078] Figure 46 shows Mean SUV (A) and tumour to blood ratio (B) of the right cervical (neck) and right axillary squamous cell carcinoma lymph node metastases. Representative axial non contrast CT and fused CDI PET CT images (SUV 0 - 7) of the right axillary (top) and right cervical (neck) squamous cell carcinoma lymph node metastases (C). Representative histological sections of the right axillary (top row) and right cervical (neck, bottom row) squamous cell carcinoma lymph node metastases stained with TUNEL (left, TUNEL positive cells stain brown, arrowheads) and haematoxylin and eosin (right) (D).

Detailed description of the invention

Definitions

[0079] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, typical methods and materials are described. [0080] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or" comprising", will be understood to imply the inclusion of a stated step or element or integer or group of steps or elements or integers, but not the exclusion of any other step or element or integer or group of elements or integers. Thus, in the context of this specification, the term "comprising" means "including principally, but not necessarily solely".

[0081] In the context of this specification, the terms "a" and "an" refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0082] In the context of this specification, the term "about" is understood to refer to a range of numbers that a person of skill in the art would consider equivalent to the recited value in the context of achieving the same function or result.

[0083] In the context of this specification, reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0084] As used herein, the term "and/or" means "and" or "or" or both.

[0085] The term "subject" as used herein refers to any mammal, including, but not limited to, livestock and other farm animals (such as cattle, goats, sheep, horses, pigs and chickens), performance animals (such as racehorses), companion animals (such as cats and dogs), laboratory test animals and humans. Typically the subject is a human.

[0086] As used herein the terms "treating", “treatment”, "treating", “reduce”, “reducing”, “prevent” "preventing" and "prevention" and the like refer to any and all applications which remedy, or otherwise hinder, retard, or reverse the progression of, an infection or disease or at least one symptom of an infection or disease, including reducing the severity of an infection or disease. Thus, the terms “treat”, "treating", “treatment”, do not necessarily imply that a subject is treated until complete elimination of the infection or recovery from a disease. Similarly, the terms “prevent”, "preventing", “prevention” and the like refer to any and all applications that prevent the establishment of an infection or disease or otherwise delay the onset of an infection or disease.

[0087] The term "optionally" is used herein to mean that the subsequently described feature may or may not be present or that the subsequently described event or circumstance may or may not occur. Hence the specification will be understood to include and encompass embodiments in which the feature is present and embodiments in which the feature is not present, and embodiments in which the event or circumstance occurs as well as embodiments in which it does not.

[0088] As used herein the terms "effective amount” and "effective dose" include within their meaning a non-toxic but sufficient amount or dose of a compound to provide the desired effect. The exact amount or dose required will vary from subject to subject depending on factors such as the species being treated, the age and general condition of the subject, the severity of the condition being treated, the particular compound being administered and the mode of administration and so forth. Thus, it is not possible to specify an exact “effective amount” or "effective dose". However, for any given case, an appropriate “effective amount” or "effective dose" may be determined by one of ordinary skill in the art using only routine experimentation.

[0089] In the context of the present specification, the term "arsenoxide" refers to the group - As=O. The groups written -As=O and -As(OH) ₂ are to be considered synonymous.

[0090] As used herein, the term "arsenoxide equivalent" refers to any dithiol reactive species that shows essentially the same affinity towards dithiols as -As=O or As(OH) ₂ , and the term includes, for example, groups comprising a transition element, and any trivalent arsenical that is either hydrolysed to -As=O or -As(OH) ₂ when dissolved in aqueous medium (such as cell culture buffers and the fluids contained in the organism being treated). Typically, arsenoxide equivalent includes dithiol reactive entities, such as As, Ge, Sn and Sb species. Arsenoxide equivalents are expected to exhibit identical or substantially identical activity to that of the corresponding arsenoxide.

[0091] The term "bifunctional chelator" refers to a chemical moiety which comprises a chelating moiety capable of binding a metal or other ion, for example a radionuclide, as well as a chemically reactive functional group for attachment to a further chemical entity. In the context of the present application, the term "bifunctional chelator" refers to both the relevant chemical compound before chelation with a metal or other ion and/or before reaction at the reactive functional group, as well as once chelated to a metal or other ion and/or attached to a further chemical entity by way of the reactive functional group, the relevant definition being readily apparent from context. When not chelating a metal or other ion, a bifunctional chelator is suitable for chelating a metal or other ion. Non-limiting examples of chelators suitable for use in the compounds, processes, and methods of the present disclosure include 2, 2', 2", 2'"- ( 1 ,4,7, 10-tetraazacyclododecane- 1 ,4,7, 10-tetrayl)tetraacetic acid (DOTA), diethylenetriaminepentaacetic acid (DTPA), 2-(4,7-bis(carboxymethyl)-l,4,7-triazonan-l- yl)pentanedioic acid (NOD AGA), 2, 2 ',2”-( 1,4, 7 -triazacyclononane- 1, 4, 7-triyl)triacetic acid (NOTA), 2-(4,7,10-tris(carboxymethyl)-l,4,7,10-tetraazacyclododecan- l-yl)pentanedioic acid (DOTAGA), and 3,6,10,13,16,19-hexazabicyclo[6.6.6]icosane (sarcophagine).

[0092] A “therapeutic radioisotope” is, in the context of the present disclosure, understood to refer to any radioisotope that has a therapeutic effect, in particular a therapeutic effect in promoting cell death, for example, for the treatment of a neoplastic condition, such as a tumour or cancer. As used herein, a “neoplastic condition” refers to a condition characterised by abnormally high levels of cell proliferation. Such promotion of cell death is to a therapeutically useful degree. Typically, the therapeutic isotope is an alpha or beta emitter. In some embodiments, the therapeutic isotope is an alpha emitter, for example ²²⁵ Ac, ²¹¹ At, ²¹³ Bi and/or ²²³ Ra. In some embodiments, the therapeutic isotope is a beta emitter, for example, ¹⁷⁷ Lu, ⁶⁷ Cu, ⁹⁰ Y, ¹⁸⁶ Re and/or ¹⁸⁸ Re. Any suitable therapeutic isotope may be selected, and in particular a therapeutic isotope having the appropriate radius of energy delivery (i.e., cell kill radius) may be selected for particular in vivo biology and the particular desired therapeutic use, for example depending on tumour size/radius and/or the pattern of dispersion of dead and dying cells within the tumour. [0093] The terms "C ₁ -C ₅ -alkyl", or the like, as used herein, refer to saturated, straight- or branched-chain hydrocarbon radicals containing between one and three, one and six or one and twelve carbon atoms, respectively. Examples of C ₁ -C ₅ -alkyl radicals include but are not limited to methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, isopentyl and neopentyl.

[0094] By "pharmaceutically acceptable salt" it is meant those salts which, within the scope of sound medical judgement, are suitable for use in contact with the tissues of humans and lower animals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio. Reference to a compound herein shall be understood to include its pharmaceutically acceptable salts unless specified otherwise or otherwise understood from context.

Processes for Preparing a Radiolabelled Trivalent Arsenical Compound

[0095] The present disclosure relates to a process for preparing a radiolabelled trivalent arsenical compound employing the use of low molecular thiols as protectants against radiolysis during synthesis. The present inventors have discovered a problem particular to the radiolabelling of As(III)-containing compounds, specifically that employing the heated conditions typically used to chelate radioisotopes or attempting to chelate highly energetic radioisotopes results in oxidation of the arsenic atom to As(V). However, the inventors have also discovered that when radiolabelling of As(III)-containing compounds is performed, the inclusion of one or more low molecular weight (LMW) thiols can unexpectedly provide a protective effect on the oxidation state of the arsenic atom. Unlike typical radical scavengers and antioxidants, which act by rapidly interacting with formed radicals to minimize radiolysis, LMW thiols behave more like protecting groups and form an adduct with As(III) that shields the atom from oxidation. Notably, the present inventors have further discovered that the formed adduct can be conveniently deprotected by treatment with anions, such as phosphate anions.

[0096] Accordingly, provided herein is a process for preparing a radiolabelled trivalent arsenical compound, the process comprising adding a radioisotope, preferably a therapeutic radioisotope as described herein, to a trivalent arsenical compound in the presence of a low molecular weight thiol to form an adduct of the radiolabelled conjugate and the low molecular weight thiol. It is to be understood that the trivalent arsenical compound comprises a bifunctional chelator, thereby enabling the formation of a radiolabelled conjugate when the arsenical compound is reacted with a radioisotope. Further, it is to be understood that the trivalent arsenical compound comprises a trivalent arsenic atom (e.g., As(III)).

[0097] As used herein, the phrase “added to” indicates that the radioisotope is reacted with the trivalent arsenical compound in the presence of the LMW thiol, regardless of in which order the components are added to or combined in a reaction mixture. For example, the trivalent arsenical compound may be combined with the LMW thiol prior to adding the radioisotope, the radioisotope may be added to the trivalent arsenical compound simultaneously with the LMW thiol, or the radioisotope may be added to the trivalent arsenical compound prior to combining with the LMW thiol.

[0098] In some embodiments, the radiolabelled trivalent arsenical compound comprises a trivalent arsenical compound selected from 4-(A-(S-glutathionylacetyl)amino)phenylarsenous acid (GSAO), 4-(A-(S-penicillaminylacetyl)amino) phenylar sonous acid (PENAO) and 4-(A- (S-cysteinylacetyl)amino)phenylarsonous acid (CYSAO) which have been radiolabelled with a radioisotope using a bifunctional chelator. Suitable bifunctional chelators are described herein and may include, but are not limited to, DOTA, DTPA, NODAGA, NOTA, DOTAGA, and sarcophagine. Accordingly, in some embodiments, the radiolabelled trivalent arsenical compound comprises a trivalent arsenical compound selected from GSAO, PENAO, and CYSAO, which is conjugated to a bifunctional chelator selected from DOTA, DTPA, NODAGA, NOTA, DOTAGA, and sarcophagine.

[0099] Certain radiolabelled trivalent arsenical compounds disclosed herein are based on 4-(A- (S-glutathionylacetyl)amino)phenylarsenous acid (GSAO), 4-(A-(S- penicillaminylacetyl)amino) phenylarsonous acid (PENAO) and 4-(A-(S- cysteinylacetyl)amino)phenylarsonous acid (CYSAO) which have been radiolabelled with a radioisotope using a bifunctional chelator. In particularly preferred embodiments, the bifunctional chelator is 2,2'-(7-(l-carboxy-4-((2,5-dioxopyrrolidin-l-yl)oxy)-4-oxobu tyl)- l,4,7-triazonane-l,4-diyl)diacetic acid (NODAGA), as shown in Formula (I) and Formula (la) below. [0100] GSAO is a trivalent As(III) peptide, which has been found to activate the mitochondrial permeability transition pore. GSAO is toxic to proliferating cells and inhibits angiogenesis in vivo (Don AS, Kisker O, Dilda P et al (2003) A peptide trivalent arsenical inhibits tumor angiogenesis by perturbing mitochondrial function in angiogenic endothelial cells. Cancer Cell 3:497-509), but is nontoxic to quiescent endothelial cells in vitro. Conjugation of the y- glutamyl residue of GSAO with therapeutic radioisotopes, as in the present disclosure, results in loss of its anti- angiogenic effect and the ability to target dying cells. When the plasma membrane integrity has been compromised the GSAO conjugate enters and binds to intracellular proteins, predominantly 90 kDa heat-shock proteins (Hsp90) (Park D, Don AS, Massamiri T et al (2011) N on-invasive imaging of cell death using an Hsp90 ligand. J Am Chem Soc 133:2832-2835); this protein is highly abundant in the cytosol, is only accessible when cell membrane integrity is compromised during cell death and is up-regulated in many malignancies (Hahn JS. The Hsp90 chaperone machinery : from structure to drug development. BMB Rep. 2009;42(10):623-30). The As(III) motif of GSAO cross-links the unpaired thiols of Cys597 and Cys598 of Hsp90 forming a stable cyclic dithioarsinite which is effectively irreversible in the cell cytosol. The radiolabelled compounds of embodiments of the present disclosure do not target a transitory cell death process, recognise both apoptotic and necrotic forms of cell death, and the cellular target is abundant and the binding irreversible. Like GSAO, PENAO and CYAO are impermeable to viable cells when a reporter group such as a fluorophore or radioisotope chelate is conjugated to the primary amine. Conjugated PENAO and CYAO, like GSAO, enter and label dying/dead cells. These characteristics are especially advantageous for providing a targeted therapeutic agent targeting areas of cell death.

[0101] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (X)

Formula (X) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; Z is a radioisotope; and L is a bifunctional chelator chelating Z; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some embodiments, Z is a therapeutic radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days. In some embodiments, L comprises DOTA, DTPA, NODAGA, NOTA, DOTAGA, or sarcophagine. In some embodiments, L comprises NODAGA. In some embodiments, L comprises DOTA.

[0102] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (X)

Formula (X) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; Z is a therapeutic radioisotope; and L is a bifunctional chelator chelating Z; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0103] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound according to Formula (X) is a compound according to Formula (Xa), or pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

Formula (Xa) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0104] In some embodiments of the compounds of Formula (X) or (Xa), L comprises NODAGA. In some embodiments of the compounds of Formula (X) or (Xa), L comprises DOTA.

[0105] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (Z)

Formula (Z) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; Z is a radioisotope; and L is a bifunctional chelator chelating Z; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some embodiments, Z is a therapeutic radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days. In some embodiments, L comprises DOTA, DTPA, NODAGA, NOTA, DOTAGA, or sarcophagine. In some embodiments, L comprises NODAGA. In some embodiments, L comprises DOTA.

[0106] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (Z)

Formula (Z) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; Z is a therapeutic radioisotope; and L is a bifunctional chelator chelating Z; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0107] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound according to Formula (Z) is a compound according to Formula (Za), or pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

Formula (Za) wherein R ₇ and R ₈ are independently selected from H and methyl; A is -As(OH) ₂ or an arsenoxide equivalent group; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. [0108] In some embodiments of the compounds of Formula (Z) or (Za), L comprises NODAGA. In some embodiments of the compounds of Formula (Z) or (Za), L comprises DOTA.

[0109] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (I)

Formula (I) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; and Z is a radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some preferred embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some preferred embodiments, R ₅ is -NHCH ₂ COOH. In some embodiments, Z is a therapeutic radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days.

[0110] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (I)

Formula (I) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or ORf>. wherein R ₆ is a C _1-5 straight or branched alkyl group; and Z is a therapeutic radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some preferred embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some preferred embodiments, R ₅ is -NHCH ₂ COOH.

[0111] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (la):

Formula (la) or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In preferred embodiments, A is an arsenoxide group As(OH) ₂ .

[0112] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (V) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; and Z is a radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some preferred embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some preferred embodiments, R ₅ is -NHCH ₂ COOH. In some embodiments, Z is a therapeutic radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days.

[0113] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound of Formula (V) is a compound according to Formula (Va): or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In preferred embodiments, A is an arsenoxide group As(OH) ₂ .

[0114] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (III)

Formula (III) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; and Z is a radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some preferred embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some preferred embodiments, both R ₇ and R ₈ are H. In other preferred embodiments, R ₇ and R ₈ are both methyl. In some embodiments, Z is a therapeutic radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days.

[0115] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (III)

wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; and Z is a therapeutic radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some preferred embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some preferred embodiments, both R ₇ and R ₈ are H. In other preferred embodiments, R ₇ and R ₈ are both methyl.

[0116] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (Illa): or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In preferred embodiments, A is an arsenoxide group As(OH) ₂ .

[0117] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound is a compound according to Formula (VII)

Formula (VII) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; and Z is a radioisotope, or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some preferred embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some preferred embodiments, both R ₇ and R ₈ are H. In other preferred embodiments, R ₇ and R ₈ are both methyl. In some embodiments, Z is a therapeutic radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days.

[0118] In some embodiments of the processes described herein, the radiolabelled trivalent arsenical compound of Formula (VII) is a compound according to Formula (Vila):

Formula (Vila) or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In preferred embodiments, A is an arsenoxide group As(OH) ₂ .

[0119] In compounds suitable for use in the present disclosure, the arsenoxide group (- AS(OH) ₂ ) can typically be replaced by an arsenoxide equivalent.

[0120] In some embodiments of the radiolabelled trivalent arsenical compounds of Formulas (X), (Xa), (Z), (Za), (I), (la), (III), (Illa), (V), Va), (VII), and (Vila), Z is a therapeutic radioisotope selected from ²²⁵ Ac , ²¹¹ At, ²¹³ Bi, ²²³ Ra. ¹⁷⁷ Lu, ⁶⁷ Cu, ^Cu, ⁹⁰ Y, ¹⁸⁶ Re and ¹⁸⁸ Re, for example selected from ¹⁷⁷ Lu, ⁶⁷ Cu, ⁶⁴ Cu, ⁹⁰ Y, ¹⁸⁶ Re and ¹⁸⁸ Re. In some embodiments, Z is selected from ¹⁷⁷ Lu, ⁶⁷ Cu, ⁹⁰ Y, ¹⁸⁶ Re and ¹⁸⁸ Re. In some preferred embodiments, Z is ¹⁷⁷ Lu, ⁶⁷ Cu, ⁶⁴ Cu or ⁹⁰ Y, for example ¹⁷⁷ Lu, ⁶⁷ Cu or ⁹⁰ Y. In particularly preferred embodiments, Z is ¹⁷⁷ LU or ⁶⁷ Cu. In particular embodiments wherein Z is a rhenium (Re) isotope, such as ¹⁸⁸ Re or ¹⁸⁶ Re, or other therapeutic isotopes as necessary, Z may refer to the therapeutic isotope in any suitable form for incorporation into the compounds of the present disclosure, for example as a tricarbonyl, for example rhenium tricarbonyl. In preferred embodiments, L is a bifunctional chelator known to chelate a therapeutic radioisotope, for example ¹⁷⁷ Lu, ⁶⁷ Cu, or ⁹⁰ Y, with a high affinity. In some preferred embodiments, the therapeutic isotope also functions as a diagnostic isotope, i.e., has a diagnostic emission to enable imaging of the compound, in particular where the therapy has been delivered and or/how much therapeutic compound has been delivered to the desired location, and/or calculation of radiation dose to tumour and normal tissue to determine probability of tumour kill and also normal tissue toxicity. For example, the therapeutic isotope may be positron emitting and be imaged by positron emission tomography. In some embodiments, imaging may be carried out by single photon imaging (SPECT). In some embodiments, nuclear medicine (‘gamma camera’) may be used to image the radioisotope. The particular type of imaging suited to a given isotope and application will be readily apparent to a skilled person.

[0121] In some embodiments of the radiolabelled trivalent arsenical compounds of Formulae (X), (Xa), (Z), (Za), (I), (la), (III), (Illa), (V), (Va), (VII), and (Vila), Z is not ⁶⁴ Cu.

[0122] In some embodiments of the radiolabelled trivalent arsenical compounds of Formulas (X), (Xa), (Z), (Za), (I), (la), (III), (Illa), (V), (Va), (VII), and (Vila), Z is a radioisotope with a half-life of less than 4 days. Incorporation of a radioisotope which has a half-life of less than 4 days in radiolabeled compounds of the present disclosure allows assessment of cell death to be undertaken on a practical and clinically relevant time scale. Z may be, for example, ⁿ C, ⁶⁴ Cu, ¹³ N, ¹⁵ 0, { A1 ¹⁸ F} ²⁺ , ⁶⁸ Ga, ⁸⁹ Zr. ⁸² Rb or ⁹⁹ Tc. In preferred embodiments, Z has a half-life of less than 1 day, for example less than 12 hours, for example less than 8 hours, for example less than 6 hours, for example less than 4 hours, or for example less than 2 hours. In preferred embodiments, the compounds of the present disclosure are suitable for use in Positron Emission Tomography (PET). In particularly preferred embodiments, Z is ⁶⁸ Ga. ^6S Ga has a half-life of 68 minutes, meaning it is particularly useful for visualisation of cell death byway of PET; the use of such a short-lives positron emitting radioisotope allows imaging on a practical and clinically relevant timescale (i.e. long waits are not required following administration for images to be obtained). In addition, such a short half-life permits, in some instances, frequent serial and quantitative imaging. That is, repeated imaging may be conducted, allowing accurate changes in cell death over a time to be recorded, for example before and after administration of a chemotherapeutic agent or other treatment which induces cell death, such as radiotherapy, targeted therapy or immunotherapy or combinations thereof. Repeated measurements of the same subject allows more accurate assessment of cell death than single measurements made with reference to a standard value or image derived from a different subject. In contrast, the use of isotopes with much longer half- lives would require waits of multiple weeks between administration and imaging if any changes in cell death are to be visualised. In some alternative preferred embodiments, Z is { A1 ¹⁸ F} ²⁺ Such a radioisotope is particularly advantageous as ¹⁸ F is widely available, and has a half-life (109.7 minutes) which is both short enough to be particularly useful in Positron Emission Tomography, as described above, but also long enough to facilitate production and distribution of products containing the radioisotope without substantial decay.

[0123] According to some preferred embodiments of the compounds of Formulas (X), (Xa), (Z), (Za), (I), (la), (III), (Illa), (V), (Va), (VII), and (VIla), Z may be, for example, ¹⁷⁷ Lu, ⁶⁷ Cu, ⁶⁴ Cu, ⁹⁰ Y, ¹⁸⁶ Re or ¹⁸⁸ Re. In some embodiments, Z may be, for example, ¹⁷⁷ Lu, ⁶⁷ Cu, ⁹⁰ Y, ¹⁸⁶ Re or ¹⁸⁸ Re. In some preferred embodiments, Z is ¹⁷⁷ Lu, ⁶⁷ Cu, ⁶⁴ Cu or ⁹⁰ Y. In some embodiments, Z is ¹⁷⁷ Lu, ⁶⁷ Cu or ⁹⁰ Y, or, in some embodiments, Z is ¹⁷⁷ Lu, ⁶⁷ Cu or ⁶⁴ Cu. In particularly preferred embodiments, Z is ¹⁷⁷ Lu or ⁶⁷ Cu. ¹⁷⁷ Lu is a decaying radioactive atom that emits beta particles, which are negatively charged electrons, with a maximum energy of 497 keV that travel -1,800 pm in biological tissue. Tumour cells have diameters of 10-20 pm, so ¹⁷⁷ Lu beta particles can travel the width of several tumour cells. Labelling of dying and dead tumour cells with a ¹⁷⁷ Lu labelled compound according to embodiments of the present disclosure therefore delivers therapeutic radiation to adjacent, viable tumour cells. ¹⁷⁷ Lu has a half-life of 6.7 d, which is well suited for a therapeutic isotope. ⁶⁷ Cu has been proven to be clinically useful for the treatment of cancer. ⁹⁰ Y is used in a wide range of applications in radiation therapy, including as treatment strategy for certain forms of cancer. In some embodiments, Z is not ⁶⁴ Cu.

[0124] In particularly preferred embodiments, the compound according to Formula (I) is ¹⁷⁷ Lu- NODAGA-GSAO (i.e. the compound of Formula (I) wherein Z is ¹⁷⁷ Lu, R ₁ - R ₄ are H, R ₅ is - NHCH ₂ COOH, and A is As(OH) ₂ ) or ⁶⁷ Cu-NODAGA-GSAO (i.e. the compound of Formula I wherein Z is ⁶⁷ Cu, R ₁ - R ₄ are H, R ₅ is -NHCH ₂ COOH, and A is As(OH) ₂ ). Such embodiments provide the advantages of being readily synthesised via the processes disclosed herein and providing radioisotopes useful for treatment of cancers in a targeted manner.

[0125] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (Y)

Formula (Y) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or ORf>. wherein R ₆ is a C _1-5 straight or branched alkyl group; and L is a bifunctional chelator; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof or derivative thereof.

[0126] In some embodiments of the processes described herein, the compound according to Formula (Y) is a compound according to Formula (Ya)

Formula (Ya)

[0127] In some embodiments of the compounds of Formula (Y) or (Ya), L comprises DOTA, DTPA, NODAGA, NOTA, DOTAGA, or sarcophagine. In some embodiments of the compounds of Formula (Y) or (Ya), L comprises NODAGA. In some embodiments of the compounds of Formula (Y) or (Ya), L comprises DOTA.

[0128] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (Y) which is a compound according to Formula (II)

Formula (II) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or OR ₆ , wherein R ₆ is a C _1-5 straight or branched alkyl group; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0129] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (Y) which is a compound according to Formula (VI)

Formula (VI) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₅ is -NHCH ₂ COOH, OH or ORf>. wherein R ₆ is a C _1-5 straight or branched alkyl group; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0130] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (W)

Formula (W) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; and L is a bifunctional chelator; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof or derivative thereof.

[0131] In some embodiments of the processes described herein, the compound according to Formula (W) is a compound according to Formula (Wa)

Formula (Wa)

[0132] In some embodiments of the compounds of Formula (W) or (Wa), L comprises DOTA, DTPA, NODAGA, NOTA, DOTAGA, or sarcophagine In some embodiments of the compounds of Formula (W) or (Wa), L comprises NODAGA. In some embodiments of the compounds of Formula (W) or (Wa), L comprises DOTA. [0133] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (W) which is a compound according to Formula (IV)

Formula (IV) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some embodiments, both R ₇ and R ₈ are H. In other preferred embodiments, R ₇ and R ₈ are both methyl.

[0134] In some embodiments of the processes described herein, the trivalent arsenical compound is a compound according to Formula (W) which is a compound according to Formula (VIII)

Formula (VIII) wherein A is -As(OH) ₂ or an arsenoxide equivalent group; each of R ₁ , R ₂ , R ₃ and R ₄ is independently selected from H, X, OH, NH ₂ , CO, SCN, -CH ₂ NH, -NHCOCH ₃ , -NHCOCH ₂ X or NO, and X is a halogen; R ₇ and R ₈ are in independently selected from H and methyl; or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. In some embodiments, each of R ₁ , R ₂ , R ₃ and R ₄ are H. In some embodiments, both R ₇ and R ₈ are H. In other preferred embodiments, R ₇ and R ₈ are both methyl.

[0135] Compounds of Formula (Y) are useful in the synthesis of Formula (X). Similarly, compounds of Formula (W) are useful in the synthesis of Formula (Z). In particular, compounds according to Formula (II) (or Formula (IV)) are useful in the synthesis of compounds according to Formula (I) (or Formula (III)), by radiolabelling of the NODAGA group. Similarly, compounds according to Formula (VI) (or Formula (VIII)) are useful in the synthesis of compounds according to Formula (V) (or Formula (VII)), by radiolabelling of the DOTA group. Such a synthesis is represented schematically below in Scheme 1, exemplified by NODAGA-GSAO as the starting material and ¹⁷⁷ Lu as the radioisotope.

(trivalent arsenical compound) (radiolabelled trivalent arsenical compound)

Scheme 1

[0136] In preferred embodiments of the compounds of Formula (Y) or Formula (II), each of R ₁ , R ₂ , R ₃ and R ₄ are H. In further preferred embodiments, R ₅ is -NHCH ₂ COOH. In particularly preferred embodiments, the trivalent arsenical compound is a compound according to Formula (Ila)

Formula (Ila) wherein A is as defined for Formula (II); or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. [0137] In some embodiments of the compounds of Formula (Y) or Formula (VI), each of R ₁ , R ₂ , R ₃ and R ₄ are H. In further embodiments, R ₅ is -NHCH ₂ COOH. In particularly preferred embodiments, the trivalent arsenical compound of Formula (VI) is a compound according to Formula (Via)

Formula (Via) wherein A is as defined for Formula (VI); or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0138] In preferred embodiments of the compounds of Formula (W) or Formula (IV), each of R ₁ , R ₂ , R ₃ and R ₄ are H. In particularly preferred embodiments, the trivalent arsenical compound is a compound according to Formula (IVa)

wherein R ₇ , R ₈ and A are as defined for Formula (IV); or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof.

[0139] In some embodiments of the compounds of Formula (W) or Formula (VIII), each of R ₁ , R ₂ , R ₃ and R ₄ are H. In particularly preferred embodiments, the trivalent arsenical compound of Formula (VIII) is a compound according to Formula (Villa)

Formula (Villa) wherein R ₇ , Rs and A are as defined for Formula (VIII); or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof. [0140] In preferred embodiments of the compounds disclosed herein, A is an arsenoxide group AS(OH) ₂ .

[0141] In the compounds disclosed herein, the arsenoxide group (-As(OH) ₂ ) can typically be replaced by an arsenoxide equivalent.

[0142] In particular embodiments, the present disclosure provides a process for preparing a compound according to Formula (I) comprising mixing a radioisotope having a half-life of less than 4 days with a compound according to Formula (II) in the presence of a low molecular weight thiol, wherein the compound of Formula (I) or Formula (II) may be any of those described above. Similarly, the present disclosure provides a process for preparing a compound according to Formula (III) comprising mixing a radioisotope having a half-life of less than 4 days with a compound according to Formula (IV) in the presence of a low molecular weight thiol, wherein the compound of Formula (III) or Formula (IV) may be any of those described above. Further, the present disclosure provides a process for preparing a compound according to Formula (V) comprising mixing a radioisotope having a half-life of less than 4 days with a compound according to Formula (VI) in the presence of a low molecular weight thiol, wherein the compound of Formula (V) or Formula (VI) may be any of those described above. Further still, the present disclosure provides a process for preparing a compound according to Formula (VII) comprising mixing a radioisotope having a half-life of less than 4 days with a compound according to Formula (VIII) in the presence of a low molecular weight thiol, wherein the compound of Formula (VII) or Formula (VIII) may be any of those described above. In some embodiments, the radioisotope having a half-life of less than 4 days is ⁶⁸ Ga.

[0143] In particular embodiments, the present disclosure provides a process for preparing a compound according to Formula (I) comprising mixing a therapeutic radioisotope with a compound according to Formula (II) in the presence of a low molecular weight thiol, wherein the compound of Formula (I) or Formula (II) may be any of those described above. Similarly, the present disclosure provides a process for preparing a compound according to Formula (III) comprising mixing a therapeutic radioisotope with a compound according to Formula (IV) in the presence of a low molecular weight thiol, wherein the compound of Formula (III) or Formula (IV) may be any of those described above. Further, the present disclosure provides a process for preparing a compound according to Formula (V) comprising mixing a therapeutic radioisotope with a compound according to Formula (VI) in the presence of a low molecular weight thiol, wherein the compound of Formula (V) or Formula (VI) may be any of those described above. Further still, the present disclosure provides a process for preparing a compound according to Formula (VII) comprising mixing a therapeutic radioisotope with a compound according to Formula (VIII) in the presence of a low molecular weight thiol, wherein the compound of Formula (VII) or Formula (VIII) may be any of those described above. In some embodiments, the therapeutic radioisotope is ¹⁷⁷ Lu.

[0144] In some embodiments, the process takes place at room temperature, i.e. without heating, for example in some embodiments wherein Z is ⁶⁷ Cu. In some embodiments, the process takes place with heating, for example in some embodiments wherein Z is ¹⁷⁷ Lu. In such embodiments, the heating may be to a temperature of, for example, at least about 60°C, for example from about 60°C to about 80°C, for example about 80°C, for example in embodiments wherein Z is ¹⁷⁷ Lu or, in some embodiments, the heating may be to a temperature of, for example, at least about 80°C, for example from about 80°C to about 150°C, for example about 120°C, for example in embodiments wherein Z is ⁹⁰ Y. In some embodiments, the process takes place at a temperature between about 50°C and about 150°C. In some embodiments, the process takes place at a temperature between about 60°C and about 140°C. In some embodiments, the process takes place at a temperature between about 70°C and about 130°C. In some embodiments, the process takes place at a temperature between about 80°C and about 120°C. In some embodiments, the process takes place at a temperature between about 90°C and about 110°C. In some embodiments, the process takes place at a temperature of about 100°C.

[0145] In some embodiments, the process occurs at a pH of at least about 5.0, for example about 5.0, for example in embodiments wherein Z is ¹⁷⁷ Lu. In some particular preferred embodiments wherein Z is ¹⁷⁷ Lu, the process occurs at a temperature from about 60 to about 80°C, at a pH of at least about 5.0, for example about 5.0, optionally for a time period of about at least 20 minutes, for example about 30 minutes. Desired pH levels may be achieved by use of any suitable buffer, for example sodium acetate buffer.

[0146] The present disclosure provides a process for preparing a compound according to Formula (I), Formula (III), Formula (V), or Formula (VII) comprising adding a radioisotope (e.g., a therapeutic radioisotope) Z to a compound according to Formula (II), Formula (IV), Formula (VI), or Formula (VIII) respectively. The compound according to Formula (II) Formula (IV), Formula (VI), or Formula (VIII) may, according to some embodiments, be optionally mixed with a buffer, wherein the buffer may have a pH of, for example, at least about 5.0, for example about 5.0. In some embodiments, the mixing is carried out at room temperature, i.e. without heating, and in some alternative embodiments, the mixing is carried out with heating, as described above. In some embodiments, the process comprises eluting the radioisotope (e.g., a therapeutic radioisotope) onto a strong cation exchange column, and eluting the strong cation exchange column into a compound according to Formula (II), Formula (IV), Formula (VI), or Formula (VIII). In some embodiments, the compounds according to Formula (I), and Formula (II) are compounds according to Formula (la) and Formula (Ila) respectively. Similarly, in some embodiments, the compounds according to Formula (III) and Formula (IV) are compounds according to Formula (Illa) and Formula (IVa) respectively. Further, in some embodiments, the compounds according to Formula (V) and Formula (VI) are compounds according to Formula (Va) and Formula (Via) respectively. Further still, in some embodiments, the compounds according to Formula (VII) and Formula (VIII) are compounds according to Formula (Vila) and Formula (Villa) respectively.

[0147] As described hereinabove, the present disclosure further provides a process for preparing a compound according to Formula (X) or Formula (Z), comprising mixing a radioisotope (e.g., a therapeutic radioisotope) with a compound according to Formula (Y) or Formula (W) in the presence of a low molecular weight thiol, wherein the compounds of Formula (X), Formula (Y), Formula (Z) or Formula (W) may be any of those described above. In some embodiments, the mixing is carried out at room temperature, i.e. without heating, and in some alternative embodiments, the mixing is carried out with heating, as described above. The present disclosure provides a process for preparing a compound according to Formula (X) or Formula (Z) wherein Z is ¹⁷⁷ Lu, ⁶⁴ Cu or ⁶⁷ Cu, such as ¹⁷⁷ Lu or ⁶⁷ Cu comprising adding ¹⁷⁷ Lu or ⁶⁷ Cu to a compound according to Formula (Y), optionally mixed with a buffer, wherein the buffer has, in some embodiments, a pH of at least about 5.0, for example about 5.0. In some embodiments, the mixing is carried out at room temperature, i.e. without heating, for example in some embodiments wherein Z is ⁶⁷ Cu or ⁶⁴ Cu, such as ⁶⁷ Cu. In some alternative embodiments, the mixing is carried out with heating, as described above, for example in some embodiments wherein Z is ¹⁷⁷ Lu. [0148] In some embodiments of the processes described above, the radioisotope (e.g., a therapeutic radioisotope) is added to the compound according to Formula (II) (or Formula (Ila) or Formula (Y) as described herein), Formula (IV) (or Formula (IVa) or Formula (W) as described herein), Formula (VI) (or Formula (Via) as described herein), or Formula VIII (or Formula Villa as described herein), in the presence of one or more antioxidants. In particular embodiments, the one or more antioxidants comprise ascorbic acid. In some embodiments of the processes described above, the radioisotope (e.g., a therapeutic radioisotope) is added to the compound according to Formula (II) (or Formula (Ila) or Formula (Y) as described herein), Formula (IV) (or Formula (IVa) or Formula (W) as described herein), Formula (VI) (or Formula (Via) as described herein), or Formula VIII (or Formula Villa as described herein), in the presence of one or more protectants against radiolysis. In some embodiments of the processes described herein, the radioisotope (e.g., a therapeutic radioisotope) is added to the compound according to Formula (II) (or Formula (Ila) or Formula (Y) as described herein), Formula (IV) (or Formula (IVa) or Formula (W) as described herein), Formula (VI) (or Formula (Via) as described herein), or Formula VIII (or Formula Villa as described herein), in the presence of glutathione. Without wishing to be bound by theory, it is thought that glutathione may function both as an antioxidant and as a protectant in reducing radiolytic breakdown of NODAGA-GSAO during synthesis which produces oxidised NODAGA-GSAO. As demonstrated in Examples 4 and 5 below, the presence of an antioxidant such as ascorbic acid, and/or the presence of glutathione, and in particular the presence of both ascorbic acid and glutathione, especially in high concentrations, reduced radiolytic breakdown of NODAGA-GSAO during synthesis and protected against the formation of oxidised NODAGA- GSAO. Accordingly, in preferred embodiments, the radioisotope (e.g., a therapeutic radioisotope) is added to the compound according to Formula (II) (or Formula (Ila) or Formula (Y) as described herein) in the presence of one or more antioxidants and/or one or more protectants against radiolysis, for example in the presence of glutathione, for example in the presence of ascorbic acid and glutathione.

[0149] In particular embodiments, the one or more antioxidants and/or the one or more protectants, such as ascorbic acid and/or glutathione, may each be present in the reaction mixture in a concentration of about 0.0075 M or greater, for example about 0.01 M or greater, for example about 0.0125 M or greater, for example about 0.015 M or greater, for example about 0.0175 M or greater, for example about 0.02 M or greater. In some embodiments, the one or more antioxidants and/or the one or more protectants, such as ascorbic acid and/or glutathione, may each be present in the reaction mixture in a concentration of up to about 0.1 M. In some embodiments, the one or more antioxidants and/or the one or more protectants, such as ascorbic acid and/or glutathione, may each be present in the reaction mixture in a concentration of between about 0.0075 M to about 0.1 M. In some embodiments, the one or more antioxidants and/or the one or more protectants, such as ascorbic acid and/or glutathione, may each be present in the reaction mixture in a concentration of between about 0.01 M to about 0.1 M. In some embodiments, the one or more antioxidants and/or the one or more protectants, such as ascorbic acid and/or glutathione, may each be present in the reaction mixture in a concentration of between about 0.015 M to about 0.1 M. In some embodiments, the one or more antioxidants and/or the one or more protectants, such as ascorbic acid and/or glutathione, may each be present in the reaction mixture in a concentration of between about 0.02 M to about 0.1 M. Where multiple antioxidants and/or protectants are present, such concentrations may, according to some embodiments, relate to each of the separate antioxidants and/or protectants, for example to each of ascorbic acid and/or glutathione independently. The concentration of “in the reaction mixture” refers to the concentration in which the relevant component is present when the therapeutic radioisotope is reacted with the compound according to Formula (II) (or Formula (Ila) or Formula (Y) as described herein), Formula (IV) (or Formula (IVa) or Formula (W) as described herein), Formula (VI) (or Formula (Via) as described herein), or Formula VIII (or Formula (Villa) as described herein).

[0150] The present inventors have also found that, in addition to glutathione (GSH), other low molecular weight thiols may act as protectants against radiolysis of trivalent arsenical compounds more generally during synthesis of radiolabelled conjugates of the arsenical compound. As used herein, the term "low molecular weight thiols" or "LMW thiols" refers to a class of compounds well known in the art for their extensive involvement in the maintenance of cellular redox homeostasis and the protection of cells from a variety of reactive chemical and electrophilic species (Wang et al., Bioessays. 2015; 37(12): 1262-7; Pivato et al., Arch Biochem Biophys. 2014;560:83-99.). The present inventors have shown that various LMW thiols form stable adducts with NODAGA-GSAO. Adduct formation is believed to be the result of weak covalent bonds between trivalent arsenic and thiols, thereby reducing (preferably preventing) radiolytic oxidation of As(III) to As(V). Thus, the present disclosure also relates to an adduct of a radiolabelled trivalent arsenical compound and a low molecular weight thiol. [0151] Suitable LMW thiols for use in the present disclosure may include natural and synthetic thiols. Preferably, the LMW thiols are monothiols, which can be more readily dissociated from the arsenical compound after radiolabelling than LMW thiols with two or more thiol groups. Examples of suitable LMW thiols may include but are not limited to glutathione, cysteine, N- acetyl cysteine, γ-glutamylcysteine, cysteinylglycine, homocysteine, thiocysteine, cysteamine, hydrogen sulfide, thiophenol, 2-butenethiol, furfurylthiol, 2-mercaptoethanol, methanethiol, ethanethiol, 1 -propanethiol, 2-propanethiol, allyl mercaptan, tert-butyl mercaptan, pentanethiols, thioacetic acid, coenzyme A, 2-mercaptoindole, furan-2-ylmethanethiol, 3- mercaptopropane-l,2-diol, 3-mercapto-l-propanesulfonic acid, 1 -hexadecanethiol, pentachlorobenzenethiol, mycothiol and bacillithiol. In an embodiment, the low molecular weight thiol is a thiol-containing amino acid, which may be a naturally or non-naturally occurring amino acid, such as cysteine or homocysteine. In an embodiment, the low molecular weight thiol is selected from glutathione, cysteine, N-acetyl cysteine and homocysteine. In an embodiment, the low molecular weight thiol is glutathione. In an embodiment, the low molecular weight thiol is selected from cysteine, N-acetyl cysteine and homocysteine. In another embodiment, the low molecular weight thiol is cysteine. In yet another embodiment, the low molecular weight thiol is N-acetyl cysteine. In still another embodiment, the low molecular weight thiol is homocysteine. Other suitable LMW thiols will be apparent to those skilled in the art.

[0152] In some embodiments of the processes described herein, the low molecular weight thiol is not glutathione. Thus, in some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound as described herein, the process comprising a step of adding a radioisotope to a trivalent arsenical compound comprising a bifunctional chelator in the presence of a low molecular weight thiol to form an adduct of a radiolabelled trivalent arsenical compound and a low molecular weight thiol, with the proviso that the low molecular weight thiol is not glutathione.

[0153] In other embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound as described herein, the process comprising a step of adding a radioisotope to a trivalent arsenical compound comprising a bifunctional chelator in the presence of glutathione to form an adduct of a radiolabelled trivalent arsenical compound and glutathione. [0154] In a preferred embodiment, the arsenical compound is a compound according to Formula (Y) (or Formula (Ya)), more preferably a compound of Formula (II) (or Formula (Ila)) as described herein. In another preferred embodiment, the arsenical compound is a compound according to Formula (W) (or Formula (Wa)), more preferably a compound of Formula (IV) (or Formula (IVa)) as described herein. It is to be understood that where the arsenical compound used in the process is, for example, of Formula (Y) or Formula (II), the resulting radiolabelled compound will be a corresponding compound of Formula (X) or Formula (I), respectively. Other suitable trivalent arsenical compounds will be identifiable by those skilled in the art. As demonstrated in Example 11 below, the presence of a LMW thiol, optionally together with an antioxidant such as ascorbic acid, especially in high concentrations, reduced radiolytic breakdown of NODAGA-GSAO during synthesis of the radiolabelled conjugate relative to the degree of radiolytic breakdown in the absence of LMW thiol. Preferably, the LMW thiols is added in molar excess relative to the trivalent arsenical compound, e.g., in a molar ratio of about 1:1, 2:1, 3:1, 4:1, 5:1, 10:1 or more. In some embodiments, the molar ratio of the LMW thiol to the trivalent arsenical compound is between about 10:1 and about 20000: 1. In some embodiments, the molar ratio of the LMW thiol to the trivalent arsenical compound is between about 500:1 and about 10000:1. In some embodiments, the molar ratio of the LMW thiol to the trivalent arsenical compound is between about 1000:1 and about 7000:1. In some embodiments, the molar ratio of the LMW thiol to the trivalent arsenical compound is between about 1000: 1 and about 5000: 1. In some embodiments, the molar ratio of the LMW thiol to the trivalent arsenical compound is between about 1000:1 and about 3000:1.

[0155] In some embodiments, the LMW thiol may be present in the reaction mixture in a concentration of between about 0.0075 M to about 0.1 M. In some embodiments, the LMW thiol may be present in the reaction mixture in a concentration of between about 0.01 M to about 0.1 M. In some embodiments, the LMW thiol may be present in the reaction mixture in a concentration of between about 0.015 M to about 0.1 M. In some embodiments, the LMW thiol may be present in the reaction mixture in a concentration of between about 0.02 M to about 0.1 M.

[0156] LMW thiols may be particularly useful for preventing radiolysis of a trivalent arsenical compound, such as a compound of Formula (Y) or Formula (W) as described herein, when reacted with ¹⁷⁷ Lu. For example, significant radiolysis occurs during the synthesis of ¹⁷⁷ Lu- NODAGA-GSAO as compared to the synthesis of ⁶⁸ Ga-NODAGA-GSAO, which can be prepared at room temperature under alternate conditions without significant radiolysis (see, e.g., Examples 6 and 11). Without wishing to be bound by theory, it is considered that elevated temperature during synthesis of the radiolabelled arsenical compound (e.g., 85°C for synthesis of ¹⁷⁷ LU-NODAGA-GSAO versus ambient temperature of synthesis of ⁶⁸ Ga-NODAGA- GSAO) and/or the high activity of beta radiation derived from ¹⁷⁷ Lu ( ⁶⁸ Ga has relatively low beta energy) may result in increased radiolysis of trivalent arsenical compounds when ¹⁷⁷ Lu is added. Further, though ⁶⁸ Ga-NODAGA-GSAO was successfully synthesized at room temperature (see Example 6), incorporation of a radioisotope into an alternate bifunctional chelator (e.g., DOTA) may require heating to proceed. Accordingly, the processes disclosed herein provide access to radiolabelled trivalent arsenical compounds that could not be effectively prepared based on methods known in the art.

[0157] The present inventors have also found that an adduct of a radiolabelled trivalent arsenical compound and low molecular weight thiol as described herein may be dissociated (or, in other words, the radiolabelled trivalent arsenical compound "deprotected") by treatment of the adduct with anions, such as phosphate anions. Phosphate anions form weak bonds with thiols, thus treatment of an adduct as disclosed herein with phosphate anions (preferably using a biocompatible phosphate anion source, such as sodium phosphate buffer) may cause dissociation of the LMW thiol from the arsenical compound. Preferably, the adduct is treated with an excess of anions to deprotect the radiolabelled compound. In a preferred embodiment, dissociation of the LMW thiol may be achieved by diluting a reaction mixture comprising the adduct with sodium phosphate buffer. The pH of the buffer may also affect the degree of dissociation of the radiolabelled arsenical compound and LMW. For example, greater dissociation of GSH from ¹⁷⁷ Lu-NODAGA-GSAO was demonstrated in Example 11 with increased pH. Preferably, the buffer pH is greater than 7.0, more preferably greater than 8.0, most preferably 9.0. Thus, the process for preparing a radiolabelled trivalent arsenical compound as described herein may further comprise treating an adduct of a radiolabelled trivalent arsenical compound and a low molecular weight thiol as described herein with anions, preferably phosphate anions, to dissociate the radiolabelled trivalent arsenical compound and low molecular weight thiol, i.e., to deprotect the radiolabelled compound.

[0158] The process may further comprise a purification step to separate the radiolabelled compound from the LMW thiol and/or any free radioisotope. In particular, the present inventors have found that solid phase extraction using silica as the stationary phase (e.g., using C18 cartridge) may be particularly useful for the removal of residual radioisotope and LMW thiol from the radiolabelled compound. Suitable solvents for use as in mobile phase may include, but are not limited to, ethanol and acetonitrile. Accordingly, in some embodiments, the processes described herein further comprise a step of purifying the radiolabelled trivalent arsenical compound. In some embodiments, the purification comprises solid phase extraction. In some embodiments, the solid phase extraction comprises silica as the mobile phase.

[0159] The processes described herein may be used to prepare radiolabelled compounds as described herein, wherein Z is a radioisotope which is not limited to a therapeutic radioisotope. Z may be a therapeutic radioisotope as described herein or Z may be an alternative radioisotope. In some embodiments, Z is a radioisotope with a half-life of less than 4 days, for example less than 1 day, for example less than 4 hours, for example less than 2 hours. Z may, in some embodiments, be a radioisotope suitable for use as an imaging agent, such as in positron emission tomography. In some embodiments, Z is ⁶⁸ Ga. Such embodiments may find use in preparing compounds useful in imaging cell death. Z may be as described in PCT application no. PCT/AU2020/050359 (published as W02020206503).

[0160] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound, wherein the process comprises adding a radioisotope to a trivalent arsenical compound comprising a bifunctional chelator in the presence of a low molecular weight thiol to form an adduct of the radiolabelled conjugate and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days.

[0161] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound of Formula (X), wherein the process comprises: adding a radioisotope to a compound of Formula (Y) in the presence of a low molecular weight thiol to form an adduct of the compound of Formula (X) and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the compound of Formula (X) is a compound of Formula (Xa). In some embodiments, the compound of Formula (Y) is a compound of Formula (Ya). In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days.

[0162] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound of Formula (Z), wherein the process comprises: adding a radioisotope to a compound of Formula (W) in the presence of a low molecular weight thiol to form an adduct of the compound of Formula (Z) and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the compound of Formula (Z) is a compound of Formula (Za). In some embodiments, the compound of Formula (W) is a compound of Formula (Wa). In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days.

[0163] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound of Formula (I), wherein the process comprises: adding a radioisotope to a compound of Formula (II) in the presence of a low molecular weight thiol to form an adduct of the compound of Formula (I) and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the compound of Formula (I) is a compound of Formula (la). In some embodiments, the compound of Formula (II) is a compound of Formula (Ila). In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days. [0164] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound of Formula (V), wherein the process comprises: adding a radioisotope to a compound of Formula (VI) in the presence of a low molecular weight thiol to form an adduct of the compound of Formula (V) and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the compound of Formula (V) is a compound of Formula (Va). In some embodiments, the compound of Formula (VI) is a compound of Formula (Via). In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days.

[0165] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound of Formula (III), wherein the process comprises: adding a radioisotope to a compound of Formula (IV) in the presence of a low molecular weight thiol to form an adduct of the compound of Formula (III) and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the compound of Formula (III) is a compound of Formula (Illa). In some embodiments, the compound of Formula (IV) is a compound of Formula (IVa). In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days.

[0166] In some embodiments, the present disclosure provides a process for preparing a radiolabelled trivalent arsenical compound of Formula (VII), wherein the process comprises: adding a radioisotope to a compound of Formula (VIII) in the presence of a low molecular weight thiol to form an adduct of the compound of Formula (VII) and the low molecular weight thiol. In some embodiments, the process further comprises treating the adduct with anions to disassociate the radiolabelled trivalent arsenical compound and low molecular weight thiol. In some embodiments, the process further comprises purifying the radiolabelled trivalent arsenical compound. In some embodiments, the compound of Formula (VII) is a compound of Formula (Vila). In some embodiments, the compound of Formula (VIII) is a compound of Formula (Villa). In some embodiments, the radioisotope is a therapeutic radioisotope. In some embodiments, the radioisotope has a half-life of less than 4 days.

Compounds, Adducts, Pharmaceutical Compositions, and Methods of Use

[0167] In a further aspect, the present disclosure provides a radiolabelled trivalent arsenical compound prepared by any of the processes disclosed herein. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (X) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (Xa) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (Z) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (Za) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (I) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (la) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (V) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (Va) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (III) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (Illa) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (VII) as defined hereinabove. In some embodiments, the present disclosure provides a compound of Formula (Vila) as defined hereinabove.

[0168] The present disclosure also provides a radiolabelled trivalent arsenical compound that is substantially free of the corresponding As(V) compound (i.e., the oxidized form of the radiolabelled trivalent arsenical compound). Accordingly, in some embodiments, the present disclosure provides a compound of Formula (X), (Xa), (Z), (Za), (I), (la), (V), (Va), (III), (Illa), (VII), or (Vila), as defined hereinabove, having a purity of at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, or at least about 99% as determined by HPLC. In some embodiments, the present disclosure provides a compound of Formula (X), (Xa), (Z), (Za), (I), (la), (V), (Va), (III), (Illa), (VII), or (Vila), as defined hereinabove, having a purity of at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, or at least about 99% as determined by DMP assay (e.g., as described in Example 2). In some embodiments, the disclosure provides a compound of Formula (X), (Xa), (Z), (Za), (I), (la), (V), (Va), (III), (Illa), (VII), or (Vila), as defined hereinabove, comprising less than about 15%, less than about 14%, less than about 13%, less than about 12%, less than about 11%, less than about 10%, less than about 9%, less than about 8%, less than about 7%, less than about 6%, less than about 5%, less than about 4%, less than about 3%, less than about 2%, or less than about 1% of the corresponding oxidized As(V) compound as determined by HPLC. In some embodiments, the disclosure provides a compound of Formula (X), (Xa), (Z), (Za), (I), (la), (V), (Va), (III), (Illa), (VII), or (Vila), as defined hereinabove, comprising less than about 10% of the corresponding oxidized As(V) compound as determined by HPEC. In some embodiments, the disclosure provides a compound of Formula (X), (Xa), (Z), (Za), (I), (la), (V), (Va), (III), (Illa), (VII), or (Vila), as defined hereinabove, comprising less than about 5% of the corresponding oxidized As(V) compound as determined by HPEC.

[0169] In a further aspect, the present disclosure provides a trivalent arsenical compound useful in the preparation of a radiolabelled trivalent arsenical compound according to any of the processes disclosed herein. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (Y) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (Ya) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (W) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (Wa) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (II) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (Ila) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (VI) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (Via) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (IV) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (IV a) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (VIII) as defined hereinabove. Accordingly, in some embodiments, the present disclosure provides a compound of Formula (Villa) as defined hereinabove. [0170] The present disclosure further provides an adduct of a radiolabelled trivalent arsenical compound disclosed herein and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (X) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Xa) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Z) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Za) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (I) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (la) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (V) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Va) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (III) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Illa) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (VII) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Vila) and a low molecular weight thiol. In some embodiments, the low molecular weight thiol is glutathione, cysteine, N-acetyl cysteine, or homocysteine. In some embodiments, the low molecular weight thiol is glutathione. In some embodiments, the low molecular weight thiol is cysteine. In some embodiments, the low molecular weight thiol is N-acetyl cysteine. In some embodiments, the low molecular weight thiol is homocysteine.

[0171] The present disclosure further provides an adduct of a trivalent arsenical compound disclosed herein and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Y) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Ya) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (W) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Wa) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (II) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Ila) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (VI) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Via) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (IV) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (IV a) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (VIII) and a low molecular weight thiol. In some embodiments, the present disclosure provides an adduct of a compound of Formula (Villa) and a low molecular weight thiol. In some embodiments, the low molecular weight thiol is glutathione, cysteine, N-acetyl cysteine, or homocysteine. In some embodiments, the low molecular weight thiol is glutathione. In some embodiments, the low molecular weight thiol is cysteine. In some embodiments, the low molecular weight thiol is N- acetyl cysteine. In some embodiments, the low molecular weight thiol is homocysteine.

[0172] The present disclosure further provides pharmaceutical compositions and/or therapeutic formulations, that is, compounds of the present disclosure present together with a pharmaceutical acceptable carrier, excipient, diluent and/or vehicle.

[0173] For medical use, salts of the compounds according to the present disclosure may be used and they include pharmaceutically acceptable salts, although other salts may be used in the preparation of the compound or of the pharmaceutically acceptable salt thereof. By pharmaceutical acceptable salt it is meant those salts which, within the scope of sound medical judgement, are suitable for use in contact with the tissues of humans and lower animals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio.

[0174] Pharmaceutically acceptable salts are well known in the art.

[0175] For instance, suitable pharmaceutically acceptable salts of the compounds of the present disclosure may be prepared by mixing a pharmaceutically acceptable acid such as hydrochloric acid, sulfuric acid, methanesulfonic acid, succinic acid, fumaric acid, maleic acid, benzoic acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid, tartaric acid, or citric acid with the compounds of the present disclosure. Suitable pharmaceutically acceptable salts of the compounds of the present disclosure therefore include acid addition salts.

[0176] For example, S. M. Berge et al describe pharmaceutically acceptable salts in detail in J. Pharmaceutical Sciences, 1977,66 : 1-19. The salts can be prepared in situ during the final isolation and purification of the compounds of the present disclosure, or separately by reacting the free base function with a suitable organic acid. Representative acid addition salts include acetate, adipate, alginate, ascorbate, asparate, benzenesulfonate, benzoate, bisulfate, borate, butyrate, camphorate, camphorsulfonate, citrate, cyclopentanepropionate, digluconate, dodecylsulfate, ethanesulfonate, fumarate, glucoheptonate, glycerophosphate, hemisulfate, heptonate, hexanoate, hydrobromide, hydrochloride, hydroiodide, 2-hydroxy-ethanesulfonate, lactobionate, lactate, laurate, lauryl sulfate, malate, maleat, malonate, methanesulfonate, 2- naphthalenesulfonate, nicotinate, nitrate, oleate, oxalate, palmitat, pamoate, pectinate, persulfate, 3 -phenylpropionate, phosphate, picrate, pivalate, propionate, stearate, succinate, sulfate, tartrate, thiocyanate, toluenesulfonate, undecanoate, valerat salts, and the like. Representative alkali or alkaline earth metal salts include sodium, lithium potassium, calcium, magnesium, and the like, as well as nontoxic ammonium, quaternary ammonium, and amine cations, including, but not limited to ammonium, tetramethylammonium, tetraethylammonium, methylamine, dimethylamine, trimethylamine, triethylamine, ethylamine, and the like.

[0177] The present disclosure also provides prodrugs. Typically, prodrugs will be functional derivatives of the compounds of the present disclosure which are readily converted in vivo to the required (active) compounds of the present disclosure, such as imaging, therapeutic and/or diagnostic agents.

[0178] Typical procedures for the selection and preparation of prodrugs are known to those of skill in the art and are described, for instance, in H. Bundgaard (Ed), Design of Prodrugs, Elsevier, 1985.

[0179] Intermediates and final products can be worked up and/or purified according to standard methods, e.g., using chromatographic methods, distribution methods, (re-) crystallization, and the like. The compounds, including their salts, may also be obtained in the form of solvates, in particular hydrates. In the context of the present disclosure, solvates refer to those forms of the compounds according to the present disclosure which, in the solid or liquid state, form a complex by coordination with solvent molecules. Hydrates are a specific form of the solvates in which the coordination is with water. Crystals of the present compounds may, for example, include the solvent used for crystallization. Different crystalline forms may be present.

[0180] The present disclosure also relates to those forms of the process of preparing compounds according to the present disclosure in which a compound obtainable as an intermediate at any stage of the process is used as starting material and the remaining process steps are carried out, or in which a starting material is formed under the reaction conditions or is used in the form of a derivative, for example in a protected form or in the form of a salt, or a compound obtainable by the process according to the present disclosure is produced under the process conditions and processed further in situ.

[0181] Single or multiple administrations of the compounds or pharmaceutical compositions can be carried out with dose levels and patterns being selected by the treating physician. Regardless, the compounds or pharmaceutical compositions of the present disclosure should provide a quantity of the compound sufficient to effectively treat the patient.

[0182] One skilled in the art would be able, by routine experimentation, to determine an effective, non-toxic amount of the compounds or pharmaceutical compositions used in the present disclosure which would be required to treat or prevent the disorders and diseases disclosed herein.

[0183] A compound of the present disclosure may be administered in a dose of, for example, up to 800 pg. In some particular embodiments, a compound of the present disclosure may be administered in a dose of, for example, up to 700 pg, for example up to 600 pg, for example up to 500 pg, for example up to 400 pg, for example up to 300 pg, for example up to 250 pg, for example up to 200 pg, for example up to 150 pg, for example up to 100 pg, for example up to 50 pg. In some preferred embodiments, a compound of the present disclosure is administered in a dose of up to 200 pg. In some embodiments, the compound of the present disclosure is administered in a dose of less than 50pg, for example 10 to 50 pg. [0184] Whilst the compounds of the present disclosure may be administered alone, it is generally preferable that the compound be administered as a pharmaceutical composition/formulation. In general pharmaceutical formulations of the compounds of the present disclosure may be prepared according to methods which are known to those of ordinary skill in the art and accordingly may include a pharmaceutically acceptable carrier, excipient, diluent, vehicle and/or adjuvant.

[0185] The carriers, excipients, diluents, vehicles and adjuvants must be "acceptable" in terms of being compatible with the other ingredients of the formulation, and not deleterious to the recipient thereof.

[0186] In some embodiments, pharmaceutical compositions of the present disclosure comprise a compound according to the present disclosure, as well as one or more further components selected from ascorbic acid, sodium, phosphate, acetate and chloride. In some embodiments, the pharmaceutical compositions comprises all such components. In a preferred form the pharmaceutical composition of a compound of the present disclosure comprises an effective amount of a compound according to the present disclosure, together with the pharmaceutically acceptable carriers, diluents and/or adjuvants as shown in Example 5 for a composition comprising ⁶⁸ Ga-NODAGA-GSAO.

[0187] The pharmaceutical compositions of the present disclosure may be administered by standard routes.

[0188] In particularly preferred embodiments, the compound or pharmaceutical composition of the present disclosure is administered intravenously. For administration as an injectable solution or suspension, non-toxic parenterally acceptable diluents or carriers can include, Ringer's solution, isotonic saline, phosphate buffered saline, ethanol and 1, 2-propylene glycol.

[0189] In Examples 4-8 of the present disclosure, biodistribution of compounds disclosed herein, radiolabelled with ⁶⁸ Ga have been shown to have favourable human biodistribution characteristics, with high uptake in tumours and low uptake in normal tissues, and with no observed adverse events. Low uptake in normal tissues minimises side effects of treatment with compounds according to embodiments of the present disclosure. [0190] When in situ at an area of high cell death such as a tumour, radiation emitted by the therapeutic radioisotope is of a range that affects multiple surrounding cells. Compounds according to the present disclosure labelled with therapeutic radioisotopes label dying and dead cells such as tumour cells with high specificity and sensitivity and are thus useful for providing therapeutic radioisotopes specifically to areas of high cell death, such as tumours. In particular, radiolabelled conjugates as described herein can be used in treating conditions associated with high levels of cell death, for example neoplastic disorders, for example tumours or for example cancer. Since the compounds of the present disclosure are targeted to areas of high cell death and cell turnover, such as tumours, they may be advantageously used to selectively enhance tumour cell death by delivering therapeutic isotopes to tumours, such that therapeutic radiation is consequently delivered to viable tumour cells adjacent to dying/dead cells; these adjacent cells may be relatively resistant to other treatment given that they are not already committed to cell death. Induction of death in adjacent cells by the radioisotope may then also further promote binding of the radiolabelled compound of the present disclosure, consequently causing further cell death in adjacent cells. This may create a positive-feedback mechanism for treating conditions such as tumours. Compounds according to the present disclosure also find use in “amplifying” approaches to therapy, wherein an initiator event causing cell death, such as a therapy such as radiotherapy, chemotherapy, immunotherapy or targeted therapy, is carried out, which increases the number of dying cells in a target area, and a radiolabelled compound of the present disclosure is also administered, which binds to said dying cells (whether before, after or concurrently with the initiator therapy). The binding of the radiolabelled compound of the present disclosure to the dying cells causes further cell death in adjacent cells, as discussed above, thus amplifying the effects of the initiator therapy, such as radiotherapy, chemotherapy, immunotherapy or targeted therapy.

[0191] For example, compounds of the present disclosure may be administered in combination (including at different times) with another therapy, such as a further radiopharmaceutical, such as a further targeted radiopharmaceutical, in order to reduce the dose required of the other therapy by virtue of further cell death also being induced by the compound of the present disclosure. Compounds of the present disclosure may also enhance the efficacy of a therapy by extending its efficacy, for example by inducing cell death in cells which are not targeted by another targeted therapy; for example, in circumstances wherein a subject is suffering from two different subsets of cancer which express different markers and a targeted therapy is only targeted to one such subset, compounds of the present disclosure may be used to induce cell death in those cells not targeted by the alternative targeted therapy. As such, the present disclosure provides methods for reducing the dose of a therapy required to effectively treat a condition and/or enhancing the effectiveness of a therapy, for example of a radiopharmaceutical such as a targeted radiopharmaceutical, comprising administering the therapy in combination with a compound according to the present disclosure. Such administration in combination may include administering the therapy and the compound of the present disclosure at different times or concurrently.

[0192] In such treatments, the target is the area of cell death, such as the tumour itself, rather than an area adjacent to a tumour, providing a treatment having high specificity. This mechanism provides a particularly efficient and targeted means of treating conditions such as tumours. Radiolabelled compounds according to embodiments of the present disclosure may further advantageously target all sites of disease whilst sparing normal tissues, which is particularly helpful in the treatment of non-localised cancers. The radiolabelled conjugates of the present disclosure may, in some embodiments, advantageously provide a valuable pantumour treatment, since dying/dead tumour cells are present in all solid tumours.

[0193] As noted above, compounds of the present disclosure radiolabelled with ⁶⁸ Ga are shown by Examples 6-8 of the present application to have very low levels of activity in all organs except the urinary tract that is the route of excretion, with the dose limiting organ being the urinary bladder. This is in common with the radionuclides used for treatment of neuroendocrine tumours and there are established protocols for management of this. Importantly, targeting of the compound to cell death in healthy tissues such as bone marrow, lymph nodes and the gastrointestinal tract is minimal, if at all. Dying cells in normal tissues are cleared rapidly by macrophages, unlike dying/dead cells in tumours that persist for days to weeks, which may be why targeting to cell death in healthy tissues is minimal. High uptake of the compound within tumours with high basal cell death is also demonstrated by the Examples of the present disclosure (Example 8). This greatly minimises potential side-effects of the therapeutic compounds.

[0194] The present disclosure provides compounds and compositions according to the present disclosure for use in the treatment of neoplastic conditions, including tumours and cancers, for example solid tumours. The cancer may include cancers which do not necessarily comprise solid or discrete tumours, for example leukaemia or lymphoma. Said treatment is by delivery of a therapeutic radioisotope to an area of cell death and, in response to delivery of the therapeutic isotope, induction/enhancement of cell death in surrounding cells. When administered intravenously, the compounds of the present disclosure will target dying cells present in high levels, such as in tumours (which have high rates of cell death and turnover); as a consequence, radiation from the therapeutic radioisotope will be delivered to adjacent, viable cells, causing death of surrounding tumour cells. Such cell death induced by compounds of the present disclosure may cause further binding of compound of the present disclosure, thus causing further cell death in a positive-feedback mechanism; compounds of the present disclosure may be administered to a subject multiple times (i.e. in multiple cycles), to provide increased cell death across the multiple cycles, for example with each administration cycle.

[0195] The present disclosure further provides methods of treating the above-mentioned conditions comprising administration of a therapeutically effective amount of a compound described herein to a subject. The present disclosure further provides use of the compounds described herein in such methods, and use in the manufacture of medicaments for the treatment of such conditions. Said treatments may be by way of the compounds of the present disclosure comprising a therapeutic isotope inducing cell death, in particular in cells surrounding dying cells which the compounds selectively label.

[0196] Use of the compounds of the present disclosure and methods of treatment provided herein, for example of the conditions described above, include administration of an effective amount of a compound or pharmaceutical composition described herein to a subject.

[0197] In some embodiments, such methods comprise administering an effective amount of a compound or a pharmaceutical composition of the present disclosure in two or more cycles, wherein efficacy of the administration against the neoplastic condition increases across the two or more cycles. An increase in efficacy of the administration against the neoplastic condition across the two or more cycles may include overall increases in efficacy from the first to a later cycle, even if the efficacy in each individual cycle is not greater than the immediate previous cycle. In some preferred embodiments, the efficacy of the administration against the neoplastic condition increases with each of the two or more cycles, i.e. the efficacy of each administration is greater than in the immediately previous cycle. “Cycles” will be understood to refer to separate, repeated administrations, which may or may not be interspersed by other steps, such as administration of other therapies. An increase in efficacy of the administration against the neoplastic condition across the two or more cycles arises due to the positive feedback mechanism associated with the compounds of the present disclosure discussed above; compounds may exhibit a self-amplifying effect, where cell death caused by compounds of the present disclosure in turn attracts more compound, which in turn induces more cell death. As such, subsequent cycles of administration of a compound of the present disclosure may have increased efficacy against the neoplastic condition by virtue of increased uptake of the compound in dying cells, due to increased levels of cell death caused by previous administration(s). “Increased efficacy” may be understood as higher levels of cell death in the target area (such as a tumour) caused by administration of the compound for a given amount of compound, relative to previous administration(s).

[0198] Particularly advantageously, and in contrast to other therapeutic approaches, it is possible to increase uptake of the radiolabelled compounds according to embodiments of the present disclosure by initial, concurrent or subsequent (typically initial or concurrent)administration of an initiator therapy which induces cell death, such as chemotherapy, radiotherapy, immunotherapy and/or targeted therapy, which by killing some cells, such as tumour cells, will increase uptake of radiolabelled compounds of embodiments of the present disclosure, but also have a synergistic effect with the internal radiation delivered. This mode of action is depicted in Fig. 1 (wherein ‘CDF refers to a radiolabelled compound comprising a therapeutic radioisotope according to the present disclosure). This results in a positive feedback mechanism, with a self-amplifying cascade of tumour cell kill; each cycle of treatment results in more cell death that will amplify radiolabelled compound uptake in the subsequent treatment cycle and so forth, providing exponential feedback killing of residual adjacent viable tumour cells. Compounds of the present disclosure may accordingly be delivered in multiple cycles, optionally together with multiple cycles of an initiator therapy, to provide increased cell death across the multiple cycles. An increase in cell death across the multiple cycles may include overall increases in cell death from the first to a later cycle, even if the cell death in each individual cycle is not greater than the immediate previous cycle. In some preferred embodiments, the cell death associated with an administration increases with each of the two or more cycles, i.e. the cell death associated with each administration is greater than in the immediately previous cycle. This represents a new paradigm in multimodal therapy, with the potential to transform combination therapy approaches in all malignancies. According to some embodiments, the radiolabelled compound of embodiments of the present disclosure, i.e., the therapeutic, in combination with sensitising chemotherapy, radiotherapy, immunotherapy and/or targeted therapy will generate a self-amplifying cascade of tumour cell kill - a new concept for a therapeutic.

[0199] Accordingly, the present disclosure further provides methods of treating a condition as described above, the method comprising a) optionally carrying out a treatment for said condition on a subject in need thereof; and b) administering a therapeutically effective amount of a compound described herein to the subject. The treatment of step a) is a treatment other than administering a compound or composition of the present disclosure. The treatment of step a) preferably induces some cell death, in particular in a desired location such as a tumour or cancer, or other site of a neoplastic condition. Step a) may be carried out concurrently with step b), or step b) may be carried out after step a). Steps a) and/or b) may be repeated. In some embodiments, step b) is repeated in two or more cycles, i.e. is carried out two or more times; such embodiments provide a self-amplifying treatment as discussed above. In some such embodiments, efficacy of the administration against the neoplastic condition increases across the two or more cycles, for example with each cycle, as discussed above, in particular the amount of cell death induced by each treatment comprising step a) and/or b) may increase across the two or more cycles, for example with each cycle. In some embodiments, step a) is carried out to initiate or initially increase cell death in a target area, such as a neoplastic site such as a tumour, and step b) is carried out multiple times, wherein the compound administered in step b) is taken up by dying cells resulting from step a), and further cycles of step b) further amplify the treatment effect as described above. In some embodiments, both steps a) and b) are carried out in multiple steps, whether in alternating steps or in any other order. . The therapy of step a) may, in some embodiments, be selected from chemotherapy, radiotherapy, immunotherapy and targeted therapy. The present disclosure further provides compounds as described herein, comprising a therapeutic radioisotope, for use in such methods, use of said compounds in such methods, and use of said compounds in the manufacture of medicaments for treatment of the conditions described above wherein the treatment may comprise such methods. [0200] The present disclosure further relates to a method of inducing cell death in a subject, whether in treatment of a neoplastic condition or otherwise, comprising administering a compound or a pharmaceutical composition according to the present disclosure. Such methods may be methods as described herein for treating neoplastic or other conditions, mutatis mutandis. In some embodiments, the compound or composition of the present disclosure is administered to a subject in multiple cycles, wherein the amount of cell death induced increases across the multiple cycles, for example with each cycle, due to the self-multiplying effect discussed above. Such increase in cell death may be for a given amount of compound or composition administered, relative to a previous administration.

[0201] The therapeutic compounds of the present disclosure may be used for theranostic treatment of the conditions discussed herein, by use of a therapeutic isotope which also provides emissions capable of imaging. For example, the therapeutic isotope may be a positron emitting isotope which may be imaged by use of positron emission tomography. In some embodiments, the therapeutic isotope may be ¹⁷⁷ Lu, ⁶⁷ Cu, ⁶⁴ Cu ⁹⁰ Y, ¹⁸⁸ Re or ¹⁸⁶ Re, all of which may be imaged. A therapeutic isotope which may also be used in imaging/diagnosis allows use of the compounds of the present disclosure in theranostic methods (i.e. methods combining therapy and diagnosis/identification of target conditions such as cancers/tumours). For example, a therapeutic compound according to the present disclosure may be administered and imaging subsequently carried out to visualise where the compound has been delivered, and, in some embodiments, how much compound has been delivered, such as how much of the compound has been delivered to a target location. In some embodiments, calculation of radiation dose to tumour and normal tissue to determine probability of tumour kill and also normal tissue toxicity may be carried out with use of a theranostic compound. Since compounds of the present disclosure selectively label dying cells, visualisation of cell death by imaging of the therapeutic agent may further be used to assess changes in cell death in response to delivery of the therapeutic compounds, i.e. to monitor efficacy of the treatment. Such theranostic compounds of the present disclosure therefore allow both treatment and visualisation or monitoring of treatment with a single compound.

[0202] Therapeutic compounds of the present disclosure may also be used in combination with administration of a separate diagnostic agent, for example an imaging agent, for example an imaging agent which is targeted to neoplastic cells such as tumour cells, and which may be imaged, for example, by positron emission tomography (PET) scanning. Such a diagnostic may be used before administration of the therapeutic compounds disclosed herein, to visualise the presence of a condition, for example in the form of visualising cell death, for example in the form of tumours having high levels of cell death, and/or after treatment with compounds of the present disclosure to visualise changes in response to said treatment, for example changes in cell death. Alternatively or in addition, the diagnostic agent may be administered together with the therapeutic agent. A suitable diagnostic agent for use in such theranostic approaches is the ⁶⁸ Ga labelled compound ( ⁶⁸ Ga-NODAGA-GSAO) described in Examples 4-8 of the present application, and disclosed in PCT application PCT/AU2020/050359, the disclosure of which is incorporated herein by reference. The compounds of PCT/AU2020/050359 and methods disclosed therein may be used for imaging cell death together with treatment by administration of therapeutic compounds labelled with therapeutic radioisotopes as described herein. For example, the ⁶⁸ Ga labelled compound described in the present examples may be administered before and/or after treatment with compounds labelled with therapeutic radioisotopes as described herein, and visualised by PET, to monitor efficacy of the treatment. Diagnostic compounds of PCT/AU2020/050359, in particular ⁶⁸ Ga-NODAGA-GSAO, exhibit good biodistribution, low normal organ uptake, advantageous imaging characteristics, favourable radiation dosimetry, are non-invasive in use, and/or have a short half-life suitable for sequential repeated imaging by Positron Emission Tomography and imaging on a clinically relevant and practical timescale. The diagnostic agent may, in some embodiments, be administered intravenously.

[0203] In the context of the present disclosure, the term “diagnostic compound” may refer to a separate diagnostic compound, or to a therapeutic compound of the present disclosure which may also function as a diagnostic compound by way of imaging of the compound, i.e. a “theranostic compound”. The meaning of such terms will be readily apparent from context of use.

[0204] When administered intravenously, theranostic compounds of the present disclosure, and imaging compounds of PCT/AU2020/050359, will target dying cells and may be visualised by virtue of their radiolabelling, thus providing information on the levels of cell death in different parts of a subject, for example in response to some other therapy causing cell death. The compounds may be used to provide a measure of cell death at a single point in time, i.e. by conducting a single PET scan or other appropriate imaging technique. In some embodiments, more than one administration and/or scan may be carried out, for example, before and after a therapy is administered, to assess the changes in levels of cell death before and after therapy and to determine whether or not treatment is successful. Successful treatment of neoplastic conditions, such as a tumour, or such as cancer following administration of the therapeutic compounds of the present disclosure and/or another therapy can be determined by visualisation of increased levels of cell death at the site of the neoplastic condition by use of imageable compounds.

[0205] Diagnostic compounds, whether theranostic as described herein or a separate diagnostic compound, such as those described in PCT/AU2020/050359, may be used to tailor or alter the treatment applied, for example the intensity or duration of treatment. The measure of cell death may indicate that a therapeutic regime is or is not proving effective; where it is ineffective, an alternative dose, or an alternative treatment may be adopted. Where it is effective, treatment may be continued if required, or reduced/discontinued if required. For example the treatment dose of therapeutic compounds according to the present disclosure or some other therapy may be adjusted accordingly dependent on the level of cell death. For example, identification of patients in whom there is little or no tumour cell death following therapy would indicate the need for either an increase in the dose or duration of treatment (escalation) or a change to more intensive or multimodal therapies in order to maximise the chance of cure or disease control. Conversely, accurately assessing response early on in the course of treatment would allow a reduction in either the duration or intensity of treatment in cancer patients who are responding well in order to avoid treatment related morbidity and mortality (de-escalation) without compromising the chance of cure or disease control. An assessment of therapy success, such as by way of cell death, may cause the adoption of a new therapy, where the measure of cell death following an initial therapeutic approach suggests that the initial approach is not successful.

[0206] Use of a theranostic compound of the present disclosure comprises administering a compound of the present disclosure to a subject. Use of separate diagnostic compounds such as those disclosed in PCT/AU2020/050359 together with the therapeutic compounds of the present disclosure includes administration of an effective amount of the diagnostic compound to a subject. Such uses may further comprise conducting an imaging method on the subject following administration of the diagnostic compound (for example the theranostic compound), for example conducting PET on the subject following administration of the diagnostic compound, for example immediately after administration of the diagnostic compound. In alternative embodiments, any suitable imaging method other than PET may be used to image the diagnostic compound. In some embodiments, especially wherein the compound is a theranostic compound, nuclear medicine (gamma camera) or PET may be used to image the compound, depending on the isotope used. In some embodiments, single photon imaging (SPECT) is used to image the isotopes. The particular type of imaging suited to a given isotope and application will be readily apparent to a skilled person.

[0207] In some embodiments, PET scans are carried out after a time interval of at least 10 minutes, for example at least 20 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, or at least 1 hour following administration of the diagnostic or theranostic compound, for example about 1 hour following administration of the diagnostic compound. In some embodiments, multiple PET scans may be carried out at various times following administration. For example, the diagnostic compound may be administered, and a PET scan may be carried out immediately following administration, as well as at about 30 minutes, about 1 hour, about 2 hours and about 3 hours following administration. Alternatively, the therapeutic compound of the present disclosure may, in some embodiments, take some time before its effects are shown; visualisation of effectiveness, such as by way of cell death, by use of a diagnostic compound or use of a theranostic compound, such as by a PET scan, may therefore take place a longer time after administration of the therapeutic or theranostic compound, for example, at least or about 1 day, 3 days, 5 days, 1 week, 2 weeks, 1 month, 2 months, or more following administration of the therapeutic or theranostic compound. In some such embodiments wherein a separate diagnostic compound is used, a diagnostic compound may be administered prior to the scan.

[0208] In some embodiments, a method of treatment comprises administration of a therapeutic radiolabelled compound according to the present disclosure, such as for the treatment of a neoplastic condition, and administration of a separate diagnostic agent, such as disclosed in PCT/AU2020/050359, to visualise the effectiveness of the therapeutic compound, such as effectiveness in inducing cell death. The therapeutic compound may be administered to a subject together with, prior to or subsequent to administering a diagnostic compound. PET scans may be carried out following administration of the diagnostic compound to visualise the cell death-inducing activity of the therapeutic compound. [0209] In some particular embodiments, the present disclosure provides a method of assessing a response of a subject to a treatment of a neoplastic condition, comprising: administering a therapeutic compound of the present disclosure; and visualising cell death. In some embodiments, the therapeutic compound comprises a therapeutic radioisotope capable of being imaged for visualising cell death, i.e the compound is a theranostic compound. In some embodiments, the method comprises administering a separate diagnostic compound for visualising cell death, for example as disclosed in PCT/AU2020/050359, for example ⁶⁸ Ga- NODAGA-GSAO. In one particular embodiment, the cell death is visualised by conducting positron emission tomography on the subject. In one particular embodiment, cell death is visualised by way of nuclear medicine (‘gamma camera’) on the subject. In some embodiments, imaging may be carried out by single photon imaging (SPECT). In successful therapy, the assessment will show success of the therapy when a high level of cell death is visualised in the desired location. In some embodiments, a diagnostic compound is administered and/or cell death is also visualised prior to administration of the therapeutic compound, to allow comparison between the level of cell death before and after administration of the therapeutic compound. In such instances, an increase in the level of cell death between the two visualisations may indicate successful therapy. Conversely, low levels of cell death or a decrease in cell death may indicate unsuccessful or sub-optimal therapy.

[0210] In the above methods, visualisation of cell death (and optionally administration of a separate diagnostic compound) may take place, for example, about 1 day, about 2 days, about 3 days, about 1 week, about 2 weeks, about 3 weeks, about 4 weeks, about 5 weeks and/or about 6 weeks following administration of the therapeutic compound of the present disclosure. In some embodiments, visualisation of cell death takes place within 7 days of administration of the therapeutic compound. In some embodiments, visualisation of cell death takes place at least 4 weeks following administration of the therapeutic compound. In some embodiments, visualisation of cell death takes place more than once following administration of the therapeutic compound. For example, in some embodiments, visualisation of cell death takes place both within 7 days of and at least 4 weeks following administration of the therapeutic compound.

[0211] In the above methods, wherein a separate diagnostic compound is administered in order to visualise cell death, visualisation of cell death, for example by positron emission tomography, may take place, for example, at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, at least 1 hour or at least 90 minutes following administration of the diagnostic compound. For example, the diagnostic compound may be administered, and visualisation may be carried out, for example, immediately following administration, or about 30 minutes, about 1 hour, about 90 minutes, about 2 hours or about 3 hours following administration of the diagnostic compound.

[0212] The present disclosure relates to the above methods, compounds according to the present disclosure for use in such methods, use of compounds of the present disclosure in such methods, and use of compounds according to the present disclosure in the manufacture of a medicament for use in such methods.

[0213] This disclosure may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this disclosure relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0214] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0215] The present disclosure will now be described with reference to the following specific examples, which should not be construed as in any way limiting the scope of the disclosure. Examples

EXAMPLE 1

Synthesis of NODAGA-GSAO

[0216] a) GSAO was prepared using the process described in ParkD, Don AS, Massamiri T et al (2011 ) Non-invasive imaging of cell death using an Hsp90 ligand. J Am Chem Soc 133:2932- 3835; 4-(A-(bromoacetyl)amino)phenylarsonic acid (BRAA) was synthesized from p-arsanilic and bromoacetyl bromide, and BRAA reduced to 4-(N-(bromoacetyl)amino) phenylarsonous acid (BRAO). BRAO was coupled to glutathione (GSH) to produce GSAO. The GSAO was resolved from unreacted BRAO and GSH by C18 chromatography.

[0217] b) Sodium bicarbonate and ultrapure water were purged with nitrogen for 30 minutes prior to use. The reaction setup and purification were performed under an inert atmosphere of nitrogen. GSAO obtained from step a) (20.0 mg, 36.5 pmol) was dissolved in 0.1 N sodium bicarbonate (7.4 mL) at 4°C and stirred for 10 minutes.

[0218] c) NODAGA-NHS (2,2'-(7-(l-carboxy-4-((2,5-dioxopyrrolidin-l-yl)oxy)-4- oxobutyl)- 1,4, 7 -triazonane- l,4-diyl)diacetic acid mono-N-hydroxy succinimide ester) obtained from CheMatech (Dijon, France) (34.5 mg, 47.0 pmol) was dissolved in anhydrous dimethylformamide (DMF) (1 mL) and added to the reaction mixture obtained in step b) dropwise over 1 hour.

[0219] d) The reaction mixture was stirred for 4 hours, acidified by the addition of 1 M hydrochloric acid (1 mL), shock- frozen in liquid nitrogen, and freeze-dried.

NODAGA-GSAO purification

[0220] e) The residue resulting from step d) was redissolved in deaerated water (4 mL), filtered (0.45 pm), and purified by reverse phase high-performance liquid chromatography (RP- HPLC). A gradient of 2-20 % mobile phase B (0.2% trifluoroacetic acid (TFA) in acetonitrile) in mobile phase A (0.2% TFA in ultrapure water) was applied from 0 to 25 minutes. NOD AGA- GSAO was eluted at 20.6 minutes. The sample was collected by hand and each fraction was instantly purged with nitrogen.

[0221] HPLC was carried out on a Shimadzu LC-20 series LC system with two LC-20AP pumps, a SIL-10AP autosampler, an SPD-20A UV/VIS detector, and a Shimadzu ShimPack GIS-C18 column (150 x 10.0 mm i.d., 5pm, 4mL/min ¹ ) (System A). Shimadzu LabSolutions Software (Ver. 5.73) was used for data acquisition and processing.

[0222] f) The pooled fractions were frozen at -20 °C and freeze-dried to give 7.3 mg of white powder (21.6% yield).

[0223] g) NODAGA-GSAO was dispensed in aliquots of 54 pg per 100 μL water and stored at -80°C.

[0224] h) The purity of the compound (>95%) was verified by injecting a solution of NODAGA-GSAO (5 μL; approx. 17 mM, in water) onto liquid chromatography-mass spectrometry (LC-MS) at 2-2-50% mobile phase B (0.1% formic acid (FA) in acetonitrile) in mobilephase A (0.1% FA in mass spectrometry-grade water ) over 0-5-45 minutes. NODAGA- GSAO eluted at 19.4 minutes.

[0225] LC-MS was conducted using an Agilent system (Santa Clara, CA, USA) consisting of a 1260 series quarternary pump with an inbuilt degasser, 1200 series autosampler, thermostated column compartment, diode array detector, fraction collector, a 6120 series single-quadrupole mass spectrometer, and an Agilent Zorbax Eclipse XDB-C18 column (150 x 4.6 mm i.d., 5 pm) at 30 °C (System B). The drying gas flow, temperature, and nebulizer were set to 12 L/min, 350°C, and 35 psi respectively. Agilent OpenLAB Chromatography Data System (CDS) ChemStationEdition (C.01.05) was used for data acquisition and processing. Electrospray ionization (ESI) was used to analyse aliquots (5 μL) in positive ion mode with a 3500 V capillary voltage. Nuclear magnetic resonance (NMR) spectroscopy ( ^X H and ¹³ C) spectra were recorded in 5 mm Pyrex tubes (Wilmad, USA) using a Varian 400-MR NMR spectrometer (Lexington, MA, USA) at a frequency of 399.73 MHz ( ^X H) or 100.51 MHz ( ¹³ C) at 24 °C operated with VnmrJ 3.1 software (Agilent Technologies, Santa Clara, CA, USA). The spectral data are reported in ppm (δ) and referenced to residual solvent (deuterated dimethyl sulfoxide [DMSO-d ₆ ] 2.50/39.52 ppm).

[0226] i) Absorbance was measured at 210 and 254 nm and the respective area under the curve (AUC) was used to determine compound purity as a percent of total AUC compared to background.

EXAMPLE 2

Labelling of NODAGA-GSAO with ¹⁷⁵ Lutetium ( ¹⁷⁵ Lu), ⁶³ Copper ( ⁶³ Cu) and ⁸⁹ Yttrium ( ⁸⁹ Y)

[0227] Before labelling with radioisotopes, binding conditions using stable isotopes were evaluated. In particular, ¹⁷⁵ Lu, ⁶³ Cu and ⁸⁹ Y were used in place of ¹⁷⁷ Lu, ⁶⁷ Cu and ⁹⁰ Y respectively. These experiments determined the optimal binding conditions and function as proof of concept for the radioisotopes.

[0228] Labelling of NODAGA-GSAO (62 μM) obtained in Example 1 was carried out in 0.4M sodium acetate (Sigma Aldrich) buffer at various pH levels and temperatures, as indicated below. Stable isotope ¹⁷⁵ Lu (as lutetium (III) chloride), ⁶³ Cu (as copper(II) sulphate pentahydrate) or ⁸⁹ Y (yttrium(III) chloride) (Sigma Aldrich) were added at a 1.2-fold molar ratio relative to NODAGA-GSAO and the mixture incubated for 30 minutes.

[0229] All experiments were performed on an Agilent (Santa Clara, CA, USA) 1260 Infinity Quaternary LC and analysed using the Agilent OpenLab CDS ChemStation Edition software. The analytical column was an Alltima HP C18 150 x 4.6 mm 5 pm particle size (Hichrom, Berkshire, UK). The column was equilibrated in a mixture of 0.1% (v/v) trifluoroacetic acid (Sigma Aldrich) in MiliQ water (mobile phase A) and acetonitrile (mobile phase B; 98/2, v/v) (Unichrom, Thermo Fisher Scientific). Samples (100 μL) were loaded on the column using the autosampler at room temperature and products were eluted using a gradient of 2-20-70-2-2% mobile phase B in mobile phase A over 0-18-28-28-33 min at a flowrate of 0.6 mL/min. Absorbance was measured at 210 nm and 280 nm. [0230] The extent of labelling was determined as the percentage of the area under the curve (AUC) of the labelled CDI peak (time to peak, 13.9-14.1) over the total AUC compared to background.

[0231] The pH-dependent labelling of NODAGA-GSAO with stable isotopes following incubation at room temperature (63Cu), 80°C (89Y), or 85°C (175Lu) for 30 min is shown in Table 1 below. Data are from one or two (average ± S.D. of the two measurements) experiments.

Table 1

[0232] Time- and temperature-dependent labelling of NODAGA-GSAO with ¹⁷⁵ Lu or ⁸⁹ Y at pH 5 is shown in Table 2 below (N.D. = not determined). Data are from one or two (average ± S.D. of the two measurements) experiments.

Table 2 ¹⁷⁵ Lu

[0233] Binding of ¹⁷⁵ Lu with NODAGA-GSAO was found to be suboptimal at pH 4.0 or 4.5, but efficient at pH > 5.0. Binding at pH 5.0 was found to be inefficient (7.76%) with 30 minutes incubation at room temperature, but increasing the temperature to 60-80°C enhanced labelling in a temperature- and time-dependent manner, and maximum labelling was found following a 30 minute incubation at 80°C.

[0234] To ensure that the observed elution peaks constituted ¹⁷⁵ Lu-NODAGA-GSAO, the labelled products were pre-incubated with DMP for 15 min at room temperature and assessed by HPLC. The dithiol of DMP engages the As(III) hydroxyl groups of NODAGA-GSAO to form a five-membered ring structure that right-shifts the elution peak, as shown in Scheme 2 below.

Scheme 2

[0235] The HPLC chromatogram of ¹⁷⁵ Lu-NODAGA-GSAO labelled for 30 minutes at pH 5.0 at 80°C is shown in Fig. 2, (A) without DMP or (B) with pre-incubation with DMP as described above. Time to peak of relevant elution peaks are indicated. Data are representative of 2 independent experiments. Incubation of ¹⁷⁵ Lu-NODAGA-GSAO with DMP shifted the time for elution of the compound from 13.9 to 25.0 min, confirming that the compound contains active As(III) targeting moiety.

⁶³ Cu

[0236] Labelling with ⁶³ Cu was found to be near 100% for all pH conditions tested with incubation at room temperature.

[0237] Incubation of the ⁶³ Cu-NODAGA-GSAO product with DMP confirmed that it contained active As(III). Chromatograms of ⁶³ Cu-NODAGA-GSAO by HPLC labelled for 30 minutes at pH 5.0 at room temperature is shown in Fig. 3, (A) without DMP or (B) with preincubation with DMP as described above.

89Y

[0238] With ⁸⁹ Y, labelling was found to be ineffective at pH 4.0 or 4.5 and reached maximal values at pH > 5.0, up to about 60% NODAGA-GSAO labelling, at 80°C. A modest increase in labelling at 120°C occurred, but by-product generation was observed at 120°C. An HPLC chromatogram of ⁸⁹ Y-NODAGA-GSAO labelled for 30 minutes at pH 5.0 at 120°C is shown in Fig. 4.

EXAMPLE 3

Stability of labelled NODAGA-GSAO products

[0239] The in vitro stability of the complexed product is an important determinant for the potential clinical use of a therapeutic compound. Post-labelling stability was assessed by incubation of the ¹⁷⁵ Lu- and ⁶³ Cu-labelled NODAGA-GSAO products at room temperature.

[0240] The percentage of labelling at different time-points following formation of the isotope- NODAGA-GSAO complex was measured. Results are shown in Fig. 5 for A) the ¹⁷⁵ Lu-labelled product obtained from incubation for 30 minutes at pH 5.0 at 80°C and B) the ⁶³ Cu-labelled product obtained from incubation for 30 minutes at pH 5.0 at room temperature. At certain time points, aliquots were taken and the labelling (black circles) of NODAGA-GSAO were assessed by HPLC. Data are from one or two (average ± S.D. of the two measurements) experiments.

[0241] For ¹⁷⁵ LU-NODAGA-GSAO, the labelling slightly decreased over time but remained -90% after 14 days of storage. In addition, the loss of labelling coincided with increased levels of by-products (4-7.5% of total AUC).

[0242] NODAGA-GSAO chelated with ⁶³ Cu was highly stable for up to four days and only a minor amount of a single by-product was formed (< 1% of total AUC). The by-products observed with ¹⁷⁵ Lu-NODAGA-GSAO but not ⁶³ Cu-NODAGA-GSAO are likely due to the heating during reaction with ¹⁷⁵ Lu. Considering the half-life of the radioisotopes and the time of treatment following product synthesis, ¹⁷⁵ Lu- and ⁶³ Cu-labelled NODAGA-GSAO display sufficient stability to pursue therapeutic evaluation.

[0243] The above results demonstrate that NODAGA-GSAO can be efficiently labelled with isotopes of Lu and Cu; therapeutic radioisotopes with an established clinical role in radiation oncology. Furthermore, high in vitro stability of ¹⁷⁵ Lu- and ⁶³ Cu-labelled NODAGA-GSAO has been demonstrated. By employing the unique properties of NODAGA-GSAO, these conjugates provide a promising therapeutic approach for targeting dying and dead tumour cells and provides a novel means of delivering therapeutic radiation to adjacent viable tumour cells.

EXAMPLE 4

Labelling of NODAGA-GSAO with ¹⁷⁷ Lutetium ( ¹⁷⁷ Lu)

[0244] Following labelling of NODAGA-GSAO with stable isotopes as described in Example 2, NODAGA-GSAO was successfully labelled with radioisotope ¹⁷⁷ Lu at a specific activity of 500 MBq/54 pg NODAGA-GSAO (~2 GBq/216 pg NODAGA-GSAO).

Synthesis

[0245] First, [ ¹⁷⁷ Lu]LuC13 was diluted to form a stock solution. 1.0 mL of 0.04 M HCL was added to a vial of 0.5 mL ¹⁷⁷ LUC1 (no carrier added) (ANSTO). All [ ¹⁷⁷ Lu]LuC13 was then transferred to into a 10 mL evacuated vial. A further 1.5 mL of 0.04 M HC1 was used to rinse the residual [ ¹⁷⁷ Lu]LuC13 into the evacuated vial to give a solution of [ ¹⁷⁷ Lu]LuC13 with 5.0 GBq in 5.0 mL (radioactive concentration = 1 GBq/mL). A vent needle with syringe attached was inserted to equilibrate the pressure.

[0246] A vial of NODAGA-GSAO prepared as Example 1 (54 pg in 100 μL, 0.06 pmol) was thawed and the contents pipetted into an Eppendorf tube. 100 μL of 0.25M ascorbic acid was then added, followed by 250 μL of sodium acetate binding buffer (CFLCOONa • SELO, 1.5 M, pH 4.5, MW 136.08). 0.25 M ascorbic acid was obtained by dissolving 44 mg ascorbic acid (Merck 100468) in 1 mL Ultrapure water. The overall concentration of ascorbic acid in the reaction mixture was 0.0056 M. [0247] The sodium acetate buffer was obtained by dissolving 10.21 g CHsCOONa • 3H ₂ O (Merck 106267) in 40 mL Ultrapure water, adjusting to pH 5.0 with glacial acetic acid, and adding Ultrapure water to give a total volume of 50 mL.

[0248] Ultrapure water was then drawn into a syringe so that the total volume of water, NODAGA-GSAO, ascorbic acid, and binding buffer (and ethanol or glutathione when used in Example 5 below) was 4 mL. The filled syringe was then used to draw the contents of the Eppendorf tube and transfer into an evacuated vial. 500 μL of ¹⁷⁷ LuC13 solution was then added. A vent needle was inserted to equilibrate pressure with a syringe, and the vial wrapped with Parafilm to prevent aerosol contamination. The vial was then incubated for 30 minutes at 85°C.

[0249] Approximately 0.4 mL of the reaction vial contents was then withdrawn for analysis. 200 μL was placed into an autosampler vial with insert and HPLC analysis performed. 200 μL was also placed into an autosampler vial with insert containing 10 μL DMP:DMSO and HPLC analysis performed. DMP:DMSO was obtained by dissolving 5 μL 2,3 -Dimercapto- 1 -propanol (DMP) (Sigma DI 129) in 495 μL DMSO). Results are shown in Figures 6 and 7. pH was also measured using paper.

Post-synthesis purification

[0250] The contents of the reaction vial was withdrawn into a syringe and loaded onto an Oasis PRiME HLB cartridge (335 mg sorbent, primed with 1 mL ethanol and 10 mL water for injection) at approximately ~1 mL.min ¹ , purged with air and waste collected in a waste vial. The reaction vial was further rinsed with 10 mL normal saline and load onto the Oasis PRiME HLB cartridge at approximately ~1 mL.min ¹ , purged with air and waste collected in the waste vial.

[0251] The product was eluted off the Oasis PRiME HLB cartridge with 0.5 mL ethanol and purged with air, collecting product into product vial. The Oasis PRiME HLB cartridge was further rinsed with 9.5 mL normal saline at approximately ~1 mL.min ¹ and purged with air, collecting into a product vial. [0252] Activity was measured in the waste vial, Oasis PRiME HLB cartridge and product vial.

[0253] Approximately 0.4 mL of the product vial was withdrawn for analysis. Approximately 200 μL was placed into an autosampler vial with insert and HPLC analysis performed. Approximately 200 μL was also placed into an autosampler vial with insert containing 10 μL DMP:DMSO and HPLC analysis performed (2,3-Dimercapto-l-propanol (DMP) (Sigma DI 129) solution for HPLC was obtained by dissolving 5 μL DMP in 495 μL DMSO), as above. pH was also measured using paper.

[0254] HPLC parameters are provided below:

Solutions

A: trifluoroacetic acid (TFA)/H ₂ 0

B: acetonitrile (ACN)

C: H ₂ O

D: MeOH

Gradients

Table 3: Analysis gradient Table 4: Clean Gradient

Results

[0255] NODAGA-GSAO was successfully labelled with ¹⁷⁷ Lu at 500 MBq/~51 |ag NOD AGA - GSAO. Radiochromatograms of the reaction product before post-synthesis purification are shown in Figure 6 and Figure 7, of the reaction product at the end of synthesis (Figure 6) and at 1.5 hours after the end of synthesis (Figure 7). Region 2 is oxidised NODAGA-GSAO. Region 3 is ¹⁷⁷ Lu-NODAGA-GSAO.

[0256] The chromatograms show that very low amounts of free Lu- 177 are present in the reaction product, even before any post-synthesis purification is carried out. Whilst NODAGA- GSAO was successfully labelled with ¹⁷⁷ Lu as described above, radiolysis occurred during synthesis, producing oxidised NODAGA-GSAO, as shown in Figures 6 and 7. Following synthesis, no further radiolysis occurs, suggesting that both heat and free radical generation are required for radiolysis. Accordingly, methods for reducing radiolysis were investigated as described below.

EXAMPLE 5

Labelling of NODAGA-GSAO with ¹⁷⁷ Lutetium ( ¹⁷⁷ Lu) with reduction of radiolysis

[0257] As demonstrated in Example 4 above, presence of ascorbic acid during labelling of NODAGA-GSAO with ¹⁷⁷ Lu incompletely prevented radiolysis. Several methods for further prevention of radiolysis were investigated: a) ethanol

[0258] The method as described in Example 4 was used to prepare ¹⁷⁷ Lu-NODAGA-GSAO, except that during synthesis, lOOμL of ethanol was added to NODAGA-GSAO instead of 100 μL M ascorbic acid.

[0259] Radiochromatograms of the reaction product before post-synthesis purification are shown in Figures 8 and 9. A radiochromatogram of the reaction at the end of synthesis is shown in Figure 8. A radiochromatogram of the product mixed with 1% DMP in DMSO is shown in Figure 9. Region 1 is oxidised NODAGA-GSAO. Region 2 is ¹⁷⁷ Lu-NODAGA-GSAO. Region 3 is a cyclic dithioarsinite complex of DMP with the As(III) atom of NODAGA-GSAO.

[0260] As can be seen from the chromatograms, radiolabelling was achieved in the presence of ethanol. However, ethanol provided minimal protection from radiolysis. A proportion of the reaction was still able to form a cyclic dithioarsinite complex with DMP. b) high concentration ascorbic acid

[0261] The method as described in Example 4 was used to prepare ¹⁷⁷ Lu-NODAGA-GSAO, except that during synthesis, 500 pF of 0.25 M ascorbic acid instead of 100 μL ascorbic acid was added to NODAGA-GSAO. The overall concentration of ascorbic acid in the reaction mixture was 0.023 M.

[0262] Radiochromatograms of the reaction product before post-synthesis purification are shown in Figures 10 and 11. A radiochromatogram of the reaction at the end of synthesis is shown in Figure 10. Region 2 is oxidised NODAGA-GSAO. Region 3 is ¹⁷⁷ Lu-NODAGA- GSAO. A radiochromatogram of the product mixed with 1% DMP in DMSO is shown in Figure 11. Region 2 is oxidised NODAGA-GSAO. Region 3 is a cyclic dithioarsinite complex of DMP with the As(III) atom of NODAGA-GSAO.

[0263] As seen in the radiochromatograms, increasing amounts of ascorbic acid provided some additional protection against radiolysis. c) high concentration ascorbic acid and glutathione

[0264] The method as described in Example 4 was used to prepare ¹⁷⁷ Lu-NODAGA-GSAO, except that during synthesis, 500 μL of ascorbic acid instead of 0.25 M 100 pF ascorbic acid was added to NODAGA-GSAO, as well as 500 μL 0.25 M glutathione (obtained by dissolving 77 mg L-Glutathione Reduced (Sigma G4251-25G) in 1 mF Ultrapure water). The overall concentration of each of the glutathione and the ascorbic acid in the reaction mixture was 0.023 M.

[0265] Radiochromatograms of the reaction product before post-synthesis purification are shown in Figures 12 -15. A radiochromatogram of the reaction at the end of synthesis is shown in Figure 12. Region 2 is oxidised NODAGA-GSAO. Region 3 is ¹⁷⁷ Lu-NODAGA-GSAO. A radiochromatogram of the product at the end of synthesis mixed with 1% DMP in DMSO is shown in Figure 13. Region 2 is oxidised NODAGA-GSAO. Region 3 is a cyclic dithioarsinite complex of DMP with the As(III) atom of NODAGA-GSAO. A radiochromatogram of the product at 72 hours post synthesis is shown in Figure 14. Region 2 is ¹⁷⁷ Lu-NODAGA-GSAO. A radiochromatogram of the product at 72 hours post synthesis mixed with 1% DMP in DMSO is shown in Figure 15. Region 1 is a cyclic dithioarsinite complex of DMP with the As(III) atom of NODAGA-GSAO.

[0266] As seen in the radiochromatograms, a combination of high concentration of ascorbic acid and glutathione almost completely prevented radiolysis, both during and up to 72 hours post-synthesis. Importantly, ascorbic acid and glutathione are biocompatible compounds. d) reduced concentration of glutathione

[0267] The method as described in Example 5c) above was used to prepare ¹⁷⁷ Lu-NODAGA- GSAO, except that during synthesis, 100 pF instead of 500 pF 0.25 M glutathione was used. The overall concentration of glutathione in the reaction mixture was 0.0056 M.

[0268] Radiochromatograms of the reaction product before post-synthesis purification are shown in Figures 16 and 17. A radiochromatogram of the reaction at the end of synthesis is shown in Figure 16. Region 2 is oxidised NODAGA-GSAO. Region 3 is ¹⁷⁷ Lu-NODAGA- GSAO. A radiochromatogram of the product mixed with 1% DMP in DMSO is shown in Figure 17. Region 2 is oxidised NODAGA-GSAO. Region 3 is ¹⁷⁷ Lu-NODAGA-GSAO. Region 4 is a cyclic dithioarsinite complex of DMP with the As(III) atom of NODAGA-GSAO.

[0269] Reducing the concentration of glutathione resulted in an increase in radiolysis of NODAGA-GSAO. Additionally, there was a component of NODAGA-GSAO which appeared not to form a cyclic dithioarsinite complex of DMP with the As(III) atom.

EXAMPLE 6

Radiolabelling of NODAGA-GSAO with ⁶⁸ Ga

[0270] ⁶⁸ Ga was used to radiolabel NODAGA-GSAO in place of a therapeutic isotope, as described in PCT application PCT/AU2020/050359 and depicted in Scheme 3 below. Such compounds are useful in imaging of cell death, for example for monitoring the progress of a condition associated with cell death, for example a neoplastic condition such as a tumour or cancer, or for monitoring effectiveness of a treatment. Such imaging may be carried out for example by way of positron emission tomography.

NODAGA-GSAO ⁶⁸ Ga-NODAGA-GSAO

Scheme 3

[0271] The methods and procedures of the following Examples described in relation to ⁶⁸ Ga may be applied to compounds comprising a therapeutic radioisotope as described herein mutatis mutandis. However, labelling with ¹⁷⁷ Lu or ⁶⁷ Cu may be carried out without steps a) to c), g) and h) and below (i.e. without use of a SCX column; the radioisotope is added to the NODAGA-GSAO without initial cation exchange).

[0272] a) The barrel of a BondElute SCX column was cut so that when inserted the barbed female luer thread rested just above the column media to create a cartridge (hereafter referred to as the SCX cartridge). The barbed female luer thread should be fitted firmly and securely into the cut barrel of the BondElute SCX column to create a sealed cartridge that is air- and liquid-tight.

[0273] b) The SCX cartridge was primed with 1 mL 5.5 M HC1 and then flushed with 10 mL of water.

[0274] c) The SCX cartridge was purged with air.

[0275] d) Ascorbic acid solution (0.25 M) was obtained by dissolving 44 mg of ascorbic acid in 1 mL water (Water Ultrapur, Merck).

[0276] e) A sodium acetate buffer (1.5 M CH ₃ COONa-3H ₂ O, pH4.5) was obtained by dissolving 10.21 g CH ₃ COONa-3H ₂ O in water (Water Ultrapur, Merck). The pH was adjusted to pH 4.5 with glacial acetic acid and water was added to a total volume of 50 mL.

[0277] f) One vial of 54 pg NODAGA-GSAO obtained in Example 1 was thawed and mixed with 100 μL of ascorbic acid solution (used as a free radical scavenger since GSAO is sensitive to radiolysis and oxidation), 250 μL of sodium acetate buffer, and 3.5 mL water and the mixture transferred to a 10 mL evacuated glass reaction vial.

[0278] g) The ⁶⁸ Ga was eluted according to the supplier's instructions onto the primed SCX cartridge.

[0279] h) The SCX cartridge was purged with air. [0280] i) The contents of the SCX cartridge were eluted into the reaction vial with 500 μL of the NaCl/HCl elution mixture followed by 0.5 mL air, using B. Braun Sterican needles to minimize leaching of metal ions from the needles. The contents of the reaction vial were briefly mixed and allowed to react at room temperature for 10 minutes.

[0281] j) 3 mL of phosphate buffer was added to the reaction vial. The contents of the reaction vial were withdrawn with a 10 mL syringe and passed through a 0.22 pm filter into a new sterile vial yielding the final product for injection. No post-purification of the product was performed as ⁶⁸ Ga-NODAGA-GSAO was not significantly retained on C-18 cartridges and a suitable biocompatible post-purification cartridge/solvent system has not been identified. Despite this, the method described produced ⁶⁸ Ga-NODAGA-GSAO of high radiochemical purity and specific activity, exceeding current release requirements for ⁶⁸ Ga radiopharmaceuticals.

[0282] k) A sterile, closed radiolabelling system is used for the above procedure, as is preferred for preparation for human use and also for minimization of the risk of radioactive contamination to the operator and environment (Fig. 18). This may also be automated using a radiochemistry synthesis module.

Purity of ⁶⁸ Ga-NODAGA-GSAO

[0283] 1) Radiochemical purity of ⁶⁸ Ga-NODAGA-GSAO (approximately 100 μL sample of the final product obtained in step h) above) was assessed by HPLC system C at 9-9-60% mobile phase B (acetonitrile) in mobile phase A (0.1% TFA in ultrapure water) over 0-6-10 minutes using radiometric detection. The AUC of ⁶⁸ Ga-NODAGA-GSAO peak over the sum of all radiometric peaks greater than three times background was used to determine radiochemical purity. Absorbance was also measured at 210 and 280 nm; however, the molar quantities were below the limits of reliable absorbance detection and were therefore not used for assessment of purity. ⁶⁸ Ga-NODAGA-GSAO was eluted with a retention time of approximately 3 minutes and 55 seconds., as shown in the radiometric HPLC chromatogram of the final product in Fig. 19: region 1 is corresponds to ⁶⁸ Ga, region 2 corresponds to oxidation products, and region 3 corresponds to ⁶⁸ Ga-NODAGA-GSAO. The release criterion used for radiochemical purity of ⁶⁸ Ga-NODAGA-GSAO in the final product was >91% (European Pharmacopeia (2016) 01/2013:2482 Gallium (68Ga) Edotreotide injection correct 8.6. European Pharmacopeia, 9 ^th edn, pp 1150-1152).

[0284] m) Further assessment of the radiochemical purity of ⁶⁸ Ga-NODAGA-GSAO was performed by reacting 200 μL of the final product with 5 μL of DMP/DMSO solution at room temperature with occasional agitation for 10 minutes. Approximately 100 μL of this mixture was assessed by HPLC system C at 9-9-60 % mobile phase B (acetonitrile) in mobile phase A (0.1% TFA in ultrapure water) over 0-6-10 minutes using radiometric detection. The DMP- ⁶⁸ Ga-NODAGA-GSAO peak (with a retention time of approximately 9 minutes and 30 seconds) over the sum of all radiometric peaks greater than three times background should be >91%; as DMP binds with very high affinity to the phenylarsonous moiety of ⁶⁸ Ga-NODAGA- GSAO this will abolish the usual ⁶⁸ Ga-NODAGA-GSAO peak with a retention time of approximately 3 minutes and 55 seconds and result in a new peak with a retention time of approximately 9 minutes and 30 seconds. This provides specific information about the radiochemical purity of the active GSAO and is able to distinguish between ⁶⁸ Ga-NODAGA- GSAO and other products, such as oxidized degradation products of GSAO. However, this is not included in the required release criteria to minimise loss of product due to decay. The Radiometric HPLC chromatogram obtained is shown in Fig. 20: region 1 corresponds to unchelated ⁶⁸ Ga, region 2 corresponds to oxidation products, and region 3 corresponds to DMP- ⁶⁸ Ga-NODAGA-GSAO.

[0285] n) Assessment of colloidal contaminants was performed by instant thin-layer chromatography developed in 0.9% NaCl. Colloidal contaminants remained at the origin while ⁶⁸ Ga-NODAGA-GSAO had Rf >0.5. The release criterion used for colloid contaminants with total radioactivity with Rf > 0.5 was > 90%.

[0286] o) Half-life was determined by a minimum of four measurements over 10 minutes performed on a dose calibrator. The release criterion used was a calculated half-life between 64 and 72 minutes (the half-life determination is required to confirm the absence of significant ⁶⁸ Ge breakthrough). Sterility and pyrogenicity testing

[0287] p) Sterility and pyrogenicity were initially tested in an appropriately accredited laboratory on three serial syntheses to confirm that for the process sterility and pyrogenicity are within pharmacopoeia guidelines (European Pharmacopeia (2016) 01/2013:2482 Gallium ⁶⁸ Ga Edotreotide injection correct 8.6. European Pharmacopeia, 9 ^th edn, pp 1150-1152). Subsequent random testing of preparations is performed at regular intervals.

EXAMPLE 7

Pharmaceutical formulation of ⁶⁸ Ga-NODAGA-GSAO

[0288] A composition was prepared containing ingredients in the amounts listed in Table 5 below.

Table 5

EXAMPLE 8

Biodistribution of ⁶⁸ Ga-NODAGA-GSAO

[0289] Biodistribution was studied in ten healthy male rats (Lewis, Liverpool Hospital Animal Facility) aged 6-8 weeks. Five rats were administered with ⁶⁸ Ga-NODAGA-GSAO. The rats were housed singly in a cage with impervious absorbent matting and at 1 hour post administration 5 rats were sacrificed by lethal carbon dioxide overdose. Immediately post mortem, blood was sampled via cardiac puncture. Two of the 5 rats were then imaged by PET CT (GE Discovery 710). The PET CT scan comprised a CT scan (80kVp, 20mA, helical mode, reconstructed slice thickness of 0.625mm) followed by a PET scan (2 bed positions, 7.5 min/bed position, 256 x 256 reconstruction matrix, slice thickness 3.27mm).

[0290] All of the rats were then dissected, organs sampled and weighed and counted in a gamma counter, and the cpm value converted to MBq using a known standard. The activity in the remaining carcass was measured in a dose calibrator.

[0291] Biodistribution studies were performed in a further 5 rats at two hours following ⁶⁸ Ga- NODAGA GSAO administration.

[0292] Injected activity was corrected by measuring residual activity left in the syringe after injection in a dose calibrator. To correct for any dose extravasated at the injection site the tail was harvested and the activity in the tail was subtracted from the administered activity. All calculations were decayed corrected using the injection time as the reference.

[0293] Biodistribution was expressed as %ID/g and %ID/organ. %retained activity was the sum total of all activity in all individually harvested organs as well as the activity in the remaining carcass as a percentage of the injected dose. % recovered activity was the sum total of all activity in all individually harvested organs as well as the activity in the remaining carcass and excreted activity in the impervious matting as a percentage of the injected dose.

Results

[0294] The rats weighed an average of 170g (range 120 - 229g, standard deviation 32.2g). The average injected activity was 27.3MBq (range 18.9 - 38.6MBq, standard deviation 7.4MBq).

[0295] For the 1 hour biodistribution group, the mean uptake time was 62.6 (range 60 - 65) minutes and for the 2 hour biodistribution group the mean uptake time was 122.2 (range 120 - 126) minutes. [0296] Fig. 21 shows the organ biodistribution of ⁶⁸ Ga-NODAGA-GSAO (%ID/g) in healthy male rats at 1 and 2 hours post administration of ⁶⁸ Ga-NODAGA-GSAO.

[0297] As seen in Fig. 21, the highest concentration of ⁶⁸ Ga-NODAGA-GSAO is in the kidneys, and the organs with the greatest uptake of ⁶⁸ Ga-NODAGA-GSAO are the kidneys, liver and small bowel. The high renal and hepatic uptake is consistent with renal excretion and hepatic metabolism while the small bowel uptake is likely to reflect uptake within dead and dying small bowel epithelial cells.

[0298] At 1 hour 32.4% (range 24.9 -38.2%, SD 5.6%) of injected activity was retained and at 2 hours 21.4% (range 11.2-32.1%, SD 7.5%) of injected activity was retained within the animal. Overall mean total recovered activity at 1 hour was 84.9% (range 55.3-107.9%, SD 19.0%) and at 2 hours total recovered activity was 75.3% (range 50.0-120.9%, SD 27.2%) of injected activity.

Imaging

[0299] PET CT images demonstrated findings concordant with the quantitative biodistribution data. Fig. 22 shows the maximum intensity projections of ⁶⁸ Ga-NODAGA-GSAO PET CT scans performed a) 1 hour and b) 2 hours following tracer ( ⁶⁸ Ga-NODAGA-GSAO) administration. The images performed one hour after tracer administration demonstrate a high concentration of tracer in the kidneys (arrows i) in Fig. 22 a) and b)), with lower levels of uptake in the liver (arrows ii)). There is residual blood pool activity in the mediastinum (arrow iii)) similar to that of the liver. In the images performed 2 hours after administration (Fig. 22b) there is again a high concentration of tracer in the kidneys with lower levels of uptake in the liver. There is no longer visible blood pool activity in the mediastinum. In both the sets of images there is uptake in the small bowel (arrow iv)) and in the physes (arrow v)) likely due to specific uptake at sites of high physiological cell death. EXAMPLE 9

Radiation Dosimetry

[0300] The biodistribution data derived above was used to estimate human radiation dosimetry using the methods described by Stabin for a standard adult male (Stabin and Siegel 2003). The %ID/g for a given standard male organ was extrapolated from the rat biodistribution data using the following equation:

[0301] Mono-exponential clearance curves for each organ and total remaining tissues were fitted using tools in OLINDA/EXM software. Given the rapid excretion of ⁶⁸ Ga-NODAGA-GSAO it was assumed that all excretion was via urine (i.e. urinary half clearance time was calculated using a mono-exponential fit and was assumed to be 1 - % total retained activity at each time point). For the voiding bladder model it was assumed that patients would void 1 hour following administration.

[0302] Whole body effective dose was estimated at 2.13E-02 mSv/MBq. Assuming an injected activity of 150MBq this results in a whole body effective dose of 3.2mSv, a dose lower than from a diagnostic CT scan of the abdomen and lower than FDG-PET CT. Estimated human individual organ doses are listed in Table 6 below (ULI = upper large intestine, LLI = lower large intestine).

Table 6

Discussion

[0303] As shown in the above-described experiments, ⁶⁸ Ga-NODAGA-GSAO has advantageous imaging characteristics, with relatively little interference from physiologic renal and hepatic activity. In addition, the rapid clearance suggests that imaging between 1 and 2 hours post injection is feasible and thus well suited to using ⁶⁸ Ga (clinically for ⁶⁸ Ga-based somatostatin receptor expression imaging, imaging is performed at 45-90 minutes following injection). Of note from the ⁶⁸ Ga-NODAGA-GSAO PET/CT images (Fig. 22) is the visualisation of uptake within small and large bowel and also in the physes of the long bones, which may represent uptake in areas of high rates of physiologic cell death. The imaging appearances are confirmed by the measured distribution, and in contrast to some other organs (especially the liver and kidneys) uptake is higher at the 2 hour time point then at one hour post-injection, suggesting that the uptake in bowel may represent specific binding rather than non-specific tracer diffusion.

[0304] The estimated human radiation dosimetry is favourable, with an estimated total body effective dose of 0.021mSv/MBq which, assuming a standard injected dose of 150MBq, would deliver a total dose whole body effective dose of 3.2mSv. The dose limiting organ is the urinary bladder wall with a dose of 0.32mSv/MBq.

[0305] These combined results suggest that ⁶⁸ Ga-NODAGA-GSAO may be a promising agent for in vivo imaging of dead and dying cells and first in human studies are warranted.

EXAMPLE 10

Human studies

[0306] The following patients were administered between 200 and 207MBq 200 MBq of ⁶⁸ Ga- NODAGA-GSAO:

1. 66 year old male patient with squamous cell carcinoma of the oesophagus

2. 73 year old female with metastatic ovarian carcinoma

3. 66 year old male with metastatic cutaneous squamous cell carcinoma

4. 81 year old female with invasive ductal breast carcinoma.

[0307] All subjects tolerated the study well with no related or unrelated serious adverse events or adverse events. There were no significant changes in any clinical, laboratory or electrocardiographic parameters.

Biodistribution

[0308] The biodistribution data demonstrates prompt intravascular distribution of ⁶⁸ Ga-NODAGA-GSAO with rapid initial clearance, followed by a second slower phase of clearance from the blood pool. There is rapid renal uptake and excretion. [0309] For patient 1), the % injected dose (%ID) excreted in urine by 2 hours averaged 30% (range 19 - 38%) and by 3 hours averaged 48% (range 21 - 71%). Imaging findings from this subject are shown in Fig. 23, which shows anterior maximum intensity projections of ⁶⁸ Ga- NODAGA-GSAO PET at 8 time points; anterior maximum projection of the FDG PET is shown underneath for comparison. The location of the tumour is arrowed at each time point. Low levels of tracer uptake are seen in the remaining organs which gradually declines over time (apart from the testis and large bowel). No hepatobiliary excretion is evident. There is almost absent activity within the brain, suggesting that it does not cross the blood brain barrier to any extent. Imaging finding from patients 2-4 are similarly shown in Fig. 24 (patient 2) Fig. 25 (patient 3), Fig. 26 (patient 4).

[0310] Fig. 27 shows biodistribution of ⁶⁸ Ga-NODAGA-GSAO in normal organs over time in patient 1. In blood there is an initial rapid decrease in concentration, followed by a second slower phase of clearance. Most of the organs demonstrate an early peak followed by a gradual decline, similar to the second phase of blood clearance, except for the large bowel and testes which demonstrate an initial increase in concentration up to approximately 40 minutes following administration and then a slow decline. This may be due to higher physiologic rates of cell death in these two organs. Note that the urinary bladder wall was evaluated separately.

[0311] Patterns of biodistribution in organs and tissues were consistent across subjects 1-4 (as shown in Figure 32). All demonstrated rapid distribution of ⁶⁸ Ga NODAGA GSAO through the blood pool following injection, with rapid renal uptake and excretion. At Ih post injection, the kidneys had the highest concentration of ⁶⁸ Ga NODAGA GSAO (4.85 ± 0.70; mean SUV ± SD, SUV = Standard Uptake Value) with relatively low levels of ⁶⁸ Ga NODAGA GSAO in the other tissues and organs, which cleared over time. The large bowel has the next highest concentration of ⁶⁸ Ga NODAGA GSAO (3.00 ± 0.62), followed by the blood pool (2.31 ± 0.37) and stomach (2.05 ± 1.34).

[0312] Figures 28-31 show biodistribution of ⁶⁸ Ga NODAGA GSAO in selected normal tissues and tumour for patients 1-4 respectively. Note that Tumour 2 is only applicable in patients 3 and 4, so is blank in Figures 28 and 29. Figure 32 shows the biodistribution in selected normal tissues (mean SUV ± SD) of subjects 1-4. Radiation dosimetry

[0313] The whole-body effective dose was estimated by drawing representative spherical volumes of interest within the organs, estimating the %ID/g for each organ and then calculating the %ID/organ using the organ weights from a standard adult phantom.

[0314] The effective whole -body dose from ⁶⁸ Ga NODAGA GSAO for subjects 1-4 ranged from 2.16 x 10’ ² to 3.38 x 10’ ² mSv/MBq, giving an estimated effective whole -body dose ranging from 13.5 - 15.9 mSv for the protocol used in the first in human study. Detailed organ dosimetry for ⁶⁸ Ga NODAGA GSAO is shown for the four subjects (Tables 7 - 10). In all cases, the urinary bladder was the dose limiting organ. For subsequent human studies, fewer time points will be required, reducing the need for low dose CTs which will reduce the overall radiation dose. The dose is at level that is comparable to many routine medical imaging procedures using ionising radiation including x-ray computed tomography (CT), SPECT/CT and PET/CT scans.

[0315] For subjects 1-4, radiation dosimetry was calculated using Olinda/EXM based on the organ biodistribution discussed above. Urinary excretion was modelled based on measurement of activity in collected urine samples and urinary volume was measured from the images.

[0316] Tables 7-10 show the estimate for radiation dosimetry for subjects 1-4 of 200MBq of ⁶⁸ Ga NODAGA GSAO for individual organs and for the whole body in mSv / MBq (EDE cont. = effective dose equivalent contribution, ED Cont. = effective dose contribution). The estimated whole-body dose from the one (1) low dose CT and two (2) ultra-low dose CTs was 9.2mSv.

[0317] Table 7 shows the estimate for radiation dosimetry for subject 1. The overall estimated radiation dose to subject 1 was 14.5mSv. Table 7

[0318] Table 8 shows the estimate for radiation dosimetry for subject 2. The overall estimated radiation dose to subject 2 was 13.9 mSv.

Table 8

[0319] Table 9 shows the estimate for radiation dosimetry for subject 3. The overall estimated radiation dose to subject 3 was 13.5 mSv.

Table 9

[0320] Table 10 shows the estimate for radiation dosimetry for subject 4. The overall estimated radiation dose to subject 4 was 15.9 mSv.

Table 10 too

[0321] The biodistribution and kinetics of ⁶⁸ Ga-CDI was used to estimate ¹⁷⁷ Lu-CDI dosimetry. Two models were used, a conservative model assuming only physical decay (and no biological clearance) beyond 3 hours post-injection (the last imaging time point in the first- in-human study of ⁶⁸ Ga-CDI) and a model based on combined physical decay and biological clearance by extrapolation of the ⁶⁸ Ga-CDI organ clearance curves. Based on the physical decay only model the renal dose was estimated at 0.98 mGy/MBq while with the combined physical decay and biological clearance model the estimated renal dose was 0.36 mGy/MBq. These are similar to measured renal doses from ¹⁷⁷ Lu-dotatate and ¹⁷⁷ Lu-PSMA. Based on these estimations and comparability of renal dose to ¹⁷⁷ Lu-dotatate and ¹⁷⁷ Lu-PSMA, the initial microdose level of 177Lu-CDI will be approximately 2.0 GBq.

Tumour uptake

[0322] Fig. 33 shows blood pool activity and uptake of ⁶⁸ Ga NODAGA GSAO into tumour deposits in subjects 1-4 (note: in patients 3 and 4, there are two tumour deposits, and these have been analysed separately). Whilst blood pool and clearance are reproducible, tumour uptake and clearance vary by tumour type.

[0323] Across subjects 1-4, tumour uptake was variable depending on tumour histology, with high levels of uptake seen in squamous cell carcinoma of the oesophagus (SUVmean 3.8) and metastatic cutaneous squamous cell carcinoma (SUVmean 4.1) and lower uptake seen in metastatic ovarian carcinoma (SUVmean 1.9) and breast carcinoma (SUVmean 1.8). Note that in subjects 3 and 4 there were two tumour deposits and these have been analysed separately. It is not unexpected that different tumour histology will have differing rates of de novo cell death. To confirm this, histological correlation of tumour cell death with tumour uptake of ⁶⁸ Ga NODAGA GSAO was performed on two tumour deposits in patient 3 (one with high uptake of ⁶⁸ Ga NODAGA GSAO SUVmean 4.1 in the right axilla and the other with low uptake of ⁶⁸ Ga NODAGA GSAO SUVmean 2.7 in the right upper anterior cervical triangle) (Fig. 34).

[0324] Dissected tumours were fixed in formalin, embedded in paraffin and 4 pm thick sections were cut. Adjacent sections were stained for apoptotic cells using TUNEL (Abeam, Cat#206386) or morphology using haematoxylin and eosin. For TUNEL staining, sections were deparaffinized in xylene, rehydrated in decreasing concentrations of ethanol and permeabilized with Proteinase K for 20 min at room temperature. The endogenous peroxidase activity was quenched with 3% H ₂ O2for 5 min. Apoptotic cells were labelled with biotinylated terminal deoxynucleotidyl transferase at 37 °C in a humidified chamber for 2 h followed by a 30 min incubation with streptavidin-HRP conjugate. HRP-positive cells were developed using diaminobenzidine and sections counterstained with methyl green (Sigma). Whole sections were imaged using PowerMosaic scanning at lOx magnification on a Leica DM6000D microscope.

[0325] Fig. 34 shows anterior maximum projection intensity images of FDG-PET (Fig. 34A) performed 60 min after administration of 256 MBq of FDG (Fluorodeoxyglucose), and CDL PET (Fig. 34B) performed 60 min after administration of 205 MBq of CDI ( ⁶⁸ Ga NODAGA GSAO) in a 66 year old male with metastatic cutaneous squamous cell carcinoma (patient 3). The FDG-PET demonstrates two intensely metabolically active nodal metastases, one in the right axilla and the other in the right upper anterior cervical triangle. These are thought to represent synchronous nodal metastases from two different cutaneous squamous cell carcinomas (previously resected). The CDLPET ( ⁶⁸ Ga NODAGA GSAO) demonstrates intense uptake in the right axillary nodal metastasis (SUVmean = 4.1) and mild uptake in the right anterior cervical triangle nodal metastasis (SUVmean = 1.7). The tumours were surgically excised, fixed and adjacent sections stained for apoptotic cells (Fig. 34C, brown TUNEL stain, a and b) or for morphology by haematoxylin and eosin (Fig. 34C, c and d). Arrows in the TUNEL staining point to areas of extensive apoptosis.

[0326] Note that those tumours with high uptake have uptake up to 2 fold greater than blood pool, and the uptake is greater than uptake in all other organs except for the renal tract which is the route of excretion. This high level of uptake within some tumours combined with the low level of activity within normal tissues and organs demonstrates the potential for use of ⁶⁸ Ga NODAGA GSAO as an effective imaging agent.

Discussion

[0327] The interim analysis of the first four patients in this first in human study of ⁶⁸ Ga- NODAGA-GSAO demonstrates it is safe, well-tolerated and without adverse effects. The biodistribution and imaging characteristics are favourable with only low levels of activity in most normal organs. The urinary tract is the only route of excretion. Uptake into dead and dying cells in the tumour is seen and ⁶⁸ Ga-NODAGA-GSAO tumour uptake variable consistent with varying tumour histologies, and has been demonstrated histopathologically to correlate with the proportion of dead and dying cells within the tumour. The effective whole-body dose from 68Ga NODAGA GSAO ranged from 2.16 x 10-2 to 3.38 x 10-2 mSv/MBq, giving an estimated effective whole -body dose ranging from 4.3 - 6.8mSv for ad administered activity of 200 MBq. This is comparable to many other diagnostic radiopharmaceuticals used for PET/CT and SPECT/CT as well as for effective whole -body dose from other radiologic procedures such as x-ray computed tomography (CT).

EXAMPLE 11

Prevention of radiolysis using low molecular weight thiols

Materials

[0328] Lutetium(III) chloride, 2,3-dimercaptopropanol (DMP), sodium acetate, L-glutathione (GSH), sodium phosphate dibasic dihydrate, sodium phosphate monobasic dihydrate, dimethyl sulfoxide, and trifluoroacetic acid were purchased from Sigma Aldrich. Acetonitrile and ethanol were of high-performance liquid chromatography (HPLC) grade and purchased from Unichrom, Thermo Fisher Scientific. The radioisotope Lutetium ¹⁷⁷ (Lu ¹⁷⁷ ) was acquired from the Australian Nuclear Science and Technology Organisation (ANSTO).

Synthesis of CDI

[0329] 4-(N-(S-glutathionylacetyl)amino)phenylarsonous acid was dissolved in 0.1 N sodium bicarbonate and (2,2'-(7-(l-carboxy-4-((2,5-dioxopyrrolidin-l-yl)oxy)-4-oxob utyl)-l,4,7- triazonane-l,4-diyl)diacetic acid) (NODAGA-NHS, Chematech) was dissolved in anhydrous dimethylformamide (DMF) and added to the reaction mixture dropwise over 1 h. The reaction mixture was stirred for 4 h, acidified by the addition of 1 N hydrochloric acid, shock-frozen in liquid nitrogen and freeze-dried. The residue was re-dissolved in de-aerated water and purified by HPLC to provide NOD AGA GSAO (CDI). The purity was confirmed by liquid chromatography and mass spectroscopy and 100 μL aliquots (54 pg) stored at -80 °C.

Labelling of CDI with ¹⁷⁷ Lu and protection with GSH

[0330] Labelling of CDI (54 pg) with ¹⁷⁷ Lutetium ( ¹⁷⁷ Lu) was performed in 0.083 M sodium acetate buffer at pH 5.0. ¹⁷⁷ Lu (500 MBq) and ascorbic acid (0.002 M) were added and the mixture was incubated at 85°C for 30 min. In a similar reaction, CDI was labelled with ¹⁷⁷ Lu in the presence of 0.01 M ascorbic acid and 0.028 M GSH. The extent of labelling was determined by radiation counts as the percentage of the area under the curve (AUC) of the labelled CDI peak ( ¹⁷⁷ Lu-CDI: time to peak -19 min; ¹⁷⁷ Lu-CDI-GSH: time to peak -21 min) over the total AUC compared to background.

Labelling of CDI with ¹⁷⁵ Lu and protection with GSH

[0331] Labelling of CDI (54 pg) with ¹⁷⁵ Lutetium ( ¹⁷⁵ Lu) was performed in 0.4 M sodium acetate buffer at pH 5.0. ¹⁷⁵ Lu (1.2-fold molar ratio relative to CDI) and GSH (0.0178 M) were added and the mixture was incubated at 85 °C for 30 min. The extent of labelling was determined by absorbance as the percentage of the area under the curve (AUC) of the labelled CDI peak ( ¹⁷⁵ Lu-CDI: time to peak -14.1-14.4 min; ¹⁷⁵ Lu-CDI-GSH: time to peak, -16.4-16.8 min) over the total AUC compared to background.

Post-synthesis dissociation of GSH and clean-up

[0332] Following synthesis of ¹⁷⁵ Lu-CDI-GSH, the product was diluted 10-fold in a 0.5 M tris(hydroxymethyl)aminomethane (Tris) pH 9.0 or 0.4 M sodium phosphate pH 7.0-9.0 buffer and incubated at room temperature for 30 min. A Waters Oasis PRIME HLB Plus Short Cartridge or Waters Corp Sep-Pak tC18 Plus Light Cartridge was primed with 1 mL ethanol, 2 mL air, 10 mL water, 4 mL air at a rate of <2 mL/min. The diluted ¹⁷⁵ Lu-CDI-GSH product was slowly loaded on a HLB or C18 cartridge followed by 2 mL air, and the flowthrough was collected for HPLC analysis. The HLB/C18 cartridge was washed with 5 mL normal saline (0.9% NaCl), flushed with 2 mL air, and the flowthrough was collected for HPLC analysis. The product ( ¹⁷⁵ Lu-CDI) was eluted with 0.5 mL ethanol or acetonitrile and 2 mL air, followed by washing with 4.5 mL normal saline and 2 mL air.

High performance liquid chromatography

[0333] The experiments using the radioisotope ¹⁷⁷ Lu were performed on a Shimadzu LC-20 series LC system with two LC-20AP pumps, an SPD-20A UV/VIS detector and analysed using the LabLogic Laura software (version 4.2.11.129 SP2). Experiments using ¹⁷⁵ Lu were performed on an Agilent (Santa Clara, CA, USA) 1260 Infinity Quaternary LC and analysed using the Agilent OpenLab CDS ChemStation Edition software. The analytical column was an Alltima HP C18 150 x 4.6 mm 5 pm particle size (Hichrom, Berkshire, UK). The column was equilibrated in a mixture of 0.1% (v/v) trifluoroacetic acid in MiliQ water (mobile phase A) and acetonitrile (mobile phase B; 98/2, v/v). Samples (100 μL) were loaded on the column using the autosampler at room temperature. Products were eluted using a gradient of 2-20-70- 2-2% mobile phase B in mobile phase A over 0-18-28-38-42 min ( ¹⁷⁷ Lu) or 0-18-28-32-33 min ( ¹⁷⁵ LU) at a flowrate of 0.6 mL/min. Absorbance was measured at 210 nm, 256 nm, and 280 nm and radioactivity was detected using a LabLogic Dual Scan-RAM.

Results

Labelling of CDI with ¹⁷⁷ Lu

[0334] Although CDI could effectively be labelled with the radioisotope ¹⁷⁷ Lu under the above-described labelling conditions supplemented with 0.002 M ascorbic acid (an antioxidant for stabilization of metal-labelled radiopharmaceuticals ¹⁴ ), HPLC analysis of the product revealed two distinct ¹⁷⁷ Lu-CDI peaks indicative of significant radiolysis of CDI during synthesis (Figure 35A). Further analysis of ¹⁷⁷ Lu-CDI following a 1.5 h incubation at room temperature did not show an increase in radiolysis (Figure 35B), suggesting that both heat and free radical generation are required for radiolysis. Labelling CDI with ¹⁷⁷ Lu in the presence of 0.01 M ascorbic acid and 0.028 M GSH prevented radiolysis during and up to 72 h post CDI labelling (Figure 35C). The addition of GSH during synthesis shifted the time of elution of ¹⁷⁷ LU-CDI ( ¹⁷⁷ LU-CDI in the absence of GSH elutes at ~19 min; ¹⁷⁷ Lu-CDI in the presence of GSH elutes at ~21 min), indicating the formation of an adduct between CDI and GSH (CDI- GSH).

Formation of adducts of CDI with cysteine, N-acetyl cysteine and homocysteine

[0335] The observation that GSH prevents radiolysis via adduct formation suggested other small molecule thiols could also be used to prevent radiolysis. Experiments using the stable isotope ¹⁷⁵ LU as proof of principle and products were analysed by HPLC using absorbance detection. ¹⁷⁵ Lu-CDI and ¹⁷⁵ Lu-CDLGSH were synthesized using the reaction conditions of ¹⁷⁷ LU-CDI in the absence of ascorbic acid which interfered with detection by absorbance. Supporting the data obtained using ¹⁷⁷ Lu-CDI, the elution time of ¹⁷⁵ Lu-CDI (~13.9min; Figure 36A) shifted to -15.8-16.0 min in the presence of GSH ( ¹⁷⁵ Lu-CDI-GSH; Figure 36B). HPLC analysis revealed that substitution of GSH for cysteine in the synthesis reaction resulted in an adduct between ¹⁷⁵ Lu-CDI and cysteine that elutes at 14.2-14.6 min (Figure 37A). Similarly, in the presence of N-acetyl cysteine or homocysteine adduct formation was observed by the shift in elution time to -19.8-20.2 min (Figure 37B) or -16.7 min (Figure 37C), respectively. Together, these results demonstrate adduct formation of Lu-CDI with cysteine, N-acetyl cysteine and homocysteine.

Dissociation of GSH from Lu-CDI

[0336] Using a 5-fold molar excess of GSH (0.0018 M) over ¹⁷⁵ Lu-CDI, a 10-fold dilution of the synthesis product in 0.4 M sodium acetate buffer pH 5.0 could partially dissociate GSH from ¹⁷⁵ LU-CDI (Figure 38A), indicating that dilution of the product could disrupt adduct formation. As phosphate anions can from very weak bonds with thiols (Jones et al., Adv Synth Catal. 2020;362:2801-2846), it was reasoned that a vast excess of phosphate anion over Lu- CDI-GSH in the deprotection step would displace GSH from CDI. Indeed, 10-fold dilution of ¹⁷⁵ LU-CDI-GSH in a 0.5 M Tris pH 9.0 buffer revealed a complete dissociation of GSH as only a ¹⁷⁵ LU-CDI was observed (Figure 38B). Ten-fold dilution in 0.4 M sodium phosphate buffer with pH 7.0, 8.0, or 9.0 revealed a pH-dependent dissociation of GSH of 50%, 90% and 100%, respectively (Figures 39A-C). This result supports the phosphate anion as the active species in the deprotection of CDI. In summary, following synthesis of ¹⁷⁵ Lu-CDI-GSH, GSH could be effectively dissociated by 10-fold dilution in a 0.4 M sodium phosphate pH 9.0 buffer (Figure 40).

Post-synthesis clean-up

[0337] To remove any excess of free ¹⁷⁷ Lu and GSH from the end-product, post-purification clean up protocol using a HLB or C18 cartridge was employed. Cartridges were primed by flushing with 1 mL 100% EtOH, followed by 2 mL of air, 10 mL of Ultrapure water/MiliQ, 2 mL of air, and a further 2 mL of air. [0338] . The diluted ¹⁷⁵ Lu-CDI product in 0.4 M sodium phosphate pH 9.0 buffer was subsequently loaded on the HLB cartridge. HPLC analysis of the flowthrough revealed the binding of ¹⁷⁵ Lu-CDI to the HLB cartridge whereas GSH could be detected in the flowthrough. However, upon elution of ¹⁷⁵ Lu-CDI from the HLB cartridge using either 0.5 mL ethanol or acetonitrile no ¹⁷⁵ Lu-CDI could be detected in the eluate (Figure 41A-B). In contrast, ¹⁷⁵ Lu- CDI eluted using 0.5 mL ethanol following a synthesis reaction in the absence of GSH (Figure 41C), suggesting that GSH interferes with elution of ¹⁷⁵ Lu-CDI from the HLB cartridge.

[0339] To assess whether the C 18 cartridge could be suitable for post-synthesis clean up, ¹⁷⁵ Lu- CDI was synthesized in the presence of GSH, the product diluted 10-fold in 0.4 M sodium phosphate pH 9.0 buffer and the product loaded on the C18 cartridge. Whereas only a small fraction of ¹⁷⁵ Lu-CDI was detected in the flowthrough during the washing step (Figure 42A), ¹⁷⁵ LU-CDI could be eluted from the C18 cartridge using 0.5 mL ethanol (Figure 42B), demonstrating that the C18 cartridge but not HLB cartridge can be used for effective postsynthesis clean-up of Lu-CDI.

Discussion

[0340] The synthesis reaction with ¹⁷⁷ Lu-CDI resulted in significant radiolysis of CDI that was not observed during synthesis of ⁶⁸ Ga-CDI (Shon et al., Preclinical assessment of [68Ga]Ga- Cell Death Indicator (CDI): a novel hsp90 ligand for positron emission tomography of cell death. Curr Radiopharm. 2021). Whereas ⁶⁸ Ga-CDI is synthesized at room temperature, the reaction to generate ¹⁷⁷ Lu-CDI requires a temperature of 85°C. That suggests the combination of significant heat and radioactivity are responsible for the radiolysis of CDI. Alternatively, the radiolysis could be explained by the high activity of beta radiation derived from ¹⁷⁷ Lu in contrast to the relatively low beta energy that is generated by ⁶⁸ Ga. The radiolytic effects could be prevented by the addition of GSH in the synthesis reaction. CDI contains a trivalent arsenical that forms weak covalent bonds with thiols such as GSH (Donoghue et al. Protein Sci. 2000;9:2436-45; Spuches et al. Inorg Chem. 2005;44:2964-72), thereby preventing radiolytic oxidation of As(III) to As(V) during ¹⁷⁷ Lu labelling. HPLC analysis revealed a shift in the time of elution of ¹⁷⁷ Lu-CDI, indicative of a ¹⁷⁷ Lu-CDI-GSH adduct. The adduct formation was also observed using ¹⁷⁵ Lu-CDI via absorbance detection. In similar fashion, cysteine, N-acetyl cysteine, and homocysteine have been shown to form a complex with ¹⁷⁵ Lu-CDI and could substitute for GSH.

[0341] The deprotection of ¹⁷⁷ Lu-CDI was achieved using an excess of phosphate anions. The GSH adduct can effectively be dissociated using a dilution of ¹⁷⁵ Lu-CDI-GSH in sodium phosphate pH 9.0 buffer. To test the mechanism of GSH displacement by phosphate anion, a 50-fold molar excess of GSH over ¹⁷⁵ Lu-CDI was used to simulate radiolysis protection and the effects of product dilution into sodium phosphate buffer at different pH was examined. As anticipated, the dissociation of GSH was dependent on the buffer pH where only 50% dissociation was observed using pH 7.0 and 90% using pH 8.0. An advantage of using a sodium phosphate buffer is that it is human compatible.

[0342] Unexpectedly, a significant difference was observed in the utility of the HLB cartridge versus the C18 cartridge for the post-synthesis clean-up. Although CDI has a stronger binding affinity to the HLB material compared to the C 18 silica, ¹⁷⁵ Lu-CDI did not elute from the HLB cartridge in the presence of GSH using either ethanol or acetonitrile. Presumably, the presence of GSH interferes with the binding to and/or elution of ¹⁷⁵ Lu-CDI from the HLB cartridge. In contrast, ¹⁷⁵ Lu-CDI was successfully eluted from the C18 cartridge using ethanol, although a small fraction of ¹⁷⁵ Lu-CDI was lost during the washing step of the cartridge, likely due to the lower binding affinity of ¹⁷⁵ Lu-CDI for the C18 silica.

In summary, CDI can be efficiently labelled with ¹⁷⁵ Lu in the presence of GSH. The addition of GSH to the synthesis reaction creates a CDLGSH adduct which protects CDI from oxidation by free radical generation when labelled with ¹⁷⁷ Lu. In addition, a post-synthesis clean up protocol involving dissociation of GSH from Lu-CDI using phosphate anions and clearance of the free GSH from the product using a C18 cartridge was developed, which resulted in a human compatible radiopharmaceutical.

EXAMPLE 12

In-human study of 68Ga-CDI

[0343] This study aimed to assess the first-in-human biodistribution, radiation dosimetry, safety and tumor uptake of ⁶⁸ Ga-CDI. Material and methods

Subjects

[0344] This open label, single arm interventional study recruited subjects with histologically or cytologically confirmed solid malignancy with at least one measurable lesion >2 cm. The study was approved by the South Eastern Sydney Local Health District Human Research Ethics committee (2019/ETH04821) and all subjects signed an informed consent form. The study is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12621000641897) and is registered with the Therapeutics Goods Administration of the Department of Health, Australian Government under the Clinical Trials Notification scheme (CT-2018-CTN-00827-1). Within 28 days of undergoing the study subjects were screened to ensure they met inclusion and exclusion criteria and written consent obtained. The full inclusion and exclusion criteria are shown in Table 11. Although not an inclusion criteria for participation in this study, all patients also underwent an FDG PET CT between 3 - 11 days prior to CDI PET CT as part of standard of care.

Table 11. Inclusion and exclusion criteria ⁶⁸ Ga-CDI PET CT Protocol and monitoring

[0345] Subjects were encouraged to be well orally hydrated prior to ⁶⁸ Ga-CDI administration, otherwise there was no preparation required. Two intravenous cannulas were placed (one for administration of ⁶⁸ Ga-CDI and the other blood sampling during the study). Immediately prior to ⁶⁸ Ga-CDI administration clinical assessment of participants was performed, vital signs (blood pressure, heart rate, respiratory rate, arterial oxygen saturation and temperature) measured and a 12-lead electrocardiogram (ECG) obtained and QTc calculated according to Bazett’s formula to confirm eligibility. ⁶⁸ Ga-CDI was administered as an intravenous bolus. The mean and standard deviation of the administered mass of ⁶⁸ Ga-CDI was 40.1 ± 5.8 pg (range, 32.8 - 48.8 pg). The mean and standard deviation of administered activity was 205 ± 4.1 MBq (range 200 - 221 MBq) of ⁶⁸ Ga-CDI.

[0346] Eight serial PET scans were then performed from skull vertex to the proximal femora. The first PET scan commenced immediately following administration of ⁶⁸ Ga-CDI, with subsequent scans commencing at approximately 7, 17, 29, 47, 64, 120 and 180 minutes after administration (+/- 5 minutes). All scans were performed on a Phillips ingenuity TF 128 PET CT scanner (Philips Medical Systems, Cleveland) with acquisition times increasing for each subsequent scan ranging from 30 s / bed (immediately after administration) to 240 s / bed (at 180 minutes after administration) to compensate for excretion and decay. All PET scans were reconstructed using CT attenuation correction with a time of flight, list-mode, blob-based, ordered subsets maximum likelihood expectation maximization algorithm (BLOB-OS-TF) (reconstructed voxel size 4 x 4 x 4 mm).

[0347] Immediately prior to the scan commencing at approximately 47 minutes post administration a low-dose, non-contrast CT of the same region was performed for attenuation correction and localisation (of the first six scans during which time the patient had not moved) (44 - 120 mAs, 120-140 kV adjusted for body weight and body mass index, iDose 3 iterative reconstruction, reconstructed voxel size 1.17 x 1.17 x 3 mm). Ultra-low dose non-contrast CT (25 mAs, 100 kV, filtered back projection reconstruction, reconstructed voxel size 1.17 x 1.17 x 3 mm) was performed for attenuation correction immediately prior to the 120 minute and 180 minute PET scans. [0348] During and immediately following completion of the scanning protocol, subjects were clinically assessed for adverse reactions and vital signs measured. Blood was collected for venous radioactivity measurements at 1, 2 and 3 hours following ⁶⁸ Ga-CDI administration. Subjects were asked to void between 1.5 to 2 h and 2.75 to 3 h after ⁶⁸ Ga-CDI administration, urine collected, the volume measured, and an aliquot counted in a gamma counter to determine activity concentration. Following completion of the scanning protocol, ECG was recorded, and blood collected for biochemical and haematological assessment.

Post CPI PET CT Monitoring

[0349] On the day following the ⁶⁸ Ga-CDI PET CT subjects were clinically assessed for adverse reactions, vital signs, ECG obtained, and blood collected for biochemical and haematological assessment. Clinical follow-up was also performed seven days later for assessment of adverse reactions.

Analysis ⁶⁸ Ga-CDI PET CT scans

[0350] For analysis of uptake and biodistribution in normal tissues and organs, spherical volumes of interest (VOIs) were drawn on the Digital Imaging and Communications in Medicine (DICOM) ⁶⁸ Ga-CDI-PET emission data on a workstation (IntelliSpace Portal, V5.0.2.60000, Philips Medical System, Best, The Netherlands) by an experienced nuclear medicine physician over clearly tumor-free regions of organs. VOI diameter varied depending on organ size but where possible was at least 10mm. Spherical VOIs were also drawn over all tumor deposits greater than 10 mm in diameter. These VOIs were replicated across all time points and the mean, maximum and standard deviation of the activity concentration (Bq/mL) of all VOIs at each time point was recorded. Activity concentration was used to calculate the % injected activity (%IA) for organs and tissues based on the masses of source organs for standard phantom male and female models (Stabin & Siegel, Health Phys. 2003;85:294-310). Mean, maximum and standard deviation of the SUV for each VOI was also a calculated from the activity concentration using the slope intercept stored with the DICOM CDI PET emission data. Radiation dosimetry calculations

[0351] Activity concentrations derived above were entered into OLINDA/EXM 1.1 and biexponential curves fitted using the curve fitting tools within OLINDA/EXM 1.1 (Stabin et al., J Nucl Med. 2005;46:1023-1027). A urinary bladder filling and voiding model was derived. Organ and total body effective dose were calculated using ICRP publication 103 weighting factors (the 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP. 2007;37:1-332).

Histological correlation

[0352] In one subject, who proceeded to surgical excision of the tumor deposits 1 day after the ⁶⁸ Ga-CDI PET scan, histological correlation of the tumor deposits were undertaken using haematoxylin and eosin staining and TUNEL staining to specifically identify dead and dying cells. Representative samples of the formalin fixed surgical specimens (following completion of all clinical analysis and excess to that required for archival purposes) from the right axillary and right cervical nodal masses were selected and provided by the reporting clinical pathologist. The tissues were fixed, rehydrated with ethanol and xylene and embedded in paraffin. A series of 4 pm thick sections were cut and stained with Haematoxylin and Eosin. Apoptotic cells were stained using the TUNEL assay kit HRP-DAB (Abeam, Cat#206386, Cambridge, MA, USA) according to manufacturer’s protocol. Briefly, 4 pm sections of paraffin embedded tumor were deparaffinized in xylene and rehydrated in decreasing concentrations of ethanol. Tumor sections were permeabilized with Proteinase K for 20 min at room temperature. The endogenous peroxidase activity was quenched with 3% H ₂ O2 for 5 min. Apoptotic cells were labelled with biotinylated Terminal deoxynucleotidyl Transferase (TdT) at 37°C in humidified chamber for 2 h followed by a 30 min incubation with streptavidin-HRP conjugate. HRP positive cells were developed using diaminobenzidine (DAB) and specimens were counterstained with Methyl Green (Sigma, St Louis, MO, USA). The entire tumor section was imaged using PowerMosaic scanning at 10X magnification on a Leica DM6000D microscope. Results

Subjects

[0353] Five participants were recruited to this study, three females and two males, ranging in age from 52 to 81 years (Table 12).

Table 12. Participant characteristics

Safety and Tolerability

[0354] [ ⁶⁸ Ga]Ga-CDI was well tolerated. There were no adverse or clinically detectable pharmacologic effects in any of the 5 subjects. No significant changes in vital signs or the results of laboratory studies or electrocardiograms were observed.

Biodistribution and imaging

[0355] Following ⁶⁸ Ga-CDI administration, there is rapid distribution in the blood pool, with rapid renal uptake and excretion. Of the organs and tissues, the greatest amount of activity is within the blood pool with on average 12.2%, 8.8% and 7.7% IA remaining in the blood pool at 1, 2 and 3 hours respectively. The highest concentration of activity is within the kidneys with an average SUV of 5.3, 4.9, and 4.0 at 1, 2 and 3 hours post injection respectively (Figure 43). The remaining organs demonstrated lower activity concentrations and there was a progressive decline in activity in all organs over time. By 90 minutes, 39 ± 18% of total activity has been excreted in urine.

[0356] Serial PET imaging demonstrates rapid distribution in the blood pool, renal uptake and excretion with low levels of physiologic uptake in the remaining organs. Representative images of one participant are shown in Figure 44 (images of the remaining participants are in Supplemental Data).

Tumor Uptake

[0357] Tumor uptake is variable depending on tumor histology. High uptake is seen in squamous cell carcinoma of the oesophagus (SUVmax 5.7) and metastatic cutaneous squamous cell carcinoma (SUVmax 6.5), moderate uptake in metastatic colorectal carcinoma (SUVmax 4.4) and lower uptake in metastatic ovarian carcinoma (SUVmax 2.7) and breast carcinoma (SUVmax 2.5). In contrast to normal tissues and organs, tumor in 4 of the 5 patients demonstrated prolonged retention throughout the duration of imaging, with a commensurate increase in tumor to blood as blood pool activity progressively declined (Figure 45).

Radiation Dosimetry

[0358] The average effective dose is 2.17E-02 ± 4.61E-03 mSv/MBq. Average organ doses are shown in Table 13. In all cases, the dose limiting organ was the urinary bladder wall (2.79E- 01 ± 1.11E-01 mSv/MBq) followed by the kidneys (4.89E-02 ± 3.55E-03 mSv/MBq).

Table 13

Histological correlation

[0359] Subject 3 presented with a nodal mass in the right axilla, biopsy of which demonstrated squamous cell carcinoma, thought to be metastatic from a previously excised cutaneous primary. During pre-operative assessment prior to resection of the right axillary nodal metastatic disease, CT and FDG PET CT demonstrated further nodal metastatic disease in the right upper neck. Given the anatomical location and clinical history (the subject previously had multiple cutaneous squamous cell carcinomas resected from the head, neck and trunk), the treating surgeon considered that this was likely to represent metastatic disease from a different cutaneous primary to that responsible for the right axillary nodal metastatic disease. The patient proceeded to right lateral neck dissection and right axillary dissection 1 day after the ⁶⁸ Ga-CDI PET study. Representative sections of the right axillary nodal metastases demonstrated many more TUNEL positive cells than the right cervical nodal metastases. Corresponding haematoxylin and eosin-stained sections demonstrated that the TUNEL positive cells corresponded to squamous cell carcinoma and adjacent normal lymphoid tissue did not demonstrate TUNEL staining. The number of TUNEL positive cells correlated with the intensity of ⁶⁸ Ga-CDI uptake (Figure 46).

Discussion

[0360] This first-in-human study reports on a novel radiopharmaceutical, ⁶⁸ Ga-CDI, for imaging of cell death that is safe, well tolerated, has dosimetry similar to clinical ⁶⁸ Ga radiopharmaceuticals, and demonstrates excellent biodistribution and imaging characteristics. ⁶⁸ Ga-CDI overcomes most of the limitations encountered with previous attempts at molecular imaging of cell death and creates opportunities for personalised treatment based on near real time imaging of treatment-induced cell death in cancer.

[0361] This study utilised dosimetry methodology employed for other ⁶⁸ Ga radiopharmaceuticals currently in clinical practice. Walker et. al. reported the dosimetry of ⁶⁸ Ga dotatate in 6 patients and found that the mean effective dose was 2.57E-02 mSv/MBq and renal dose was 9.21E-02 mSv/MBq (Walker et al., J Nucl Med. 2013;54:855-860.). A study comprising 4 subjects found ⁶⁸ Ga PSMA had a mean effective dose of 2.3E-02 mSv/MBq, renal dose of 2.6E-01 mSv/MBq and a urinary bladder dose of 1.3E-01 mSv/MBq (Afshar- Oromieh et al., Eur J Nucl Med Mol Imaging. 2016;43:1611-1620). Another study of ⁶⁸ Ga PSMA dosimetry which included 5 subjects reported an effective dose of 2.37E-02 mSv/MBq, renal dose of 1.21E-01 mSv/MBq and urinary bladder dose of 1.64E-01 mSv/MBq (Pfob et al., Eur J Nucl Med Mol Imaging. 2016;43: 1962-1970). In summary, compared to both ⁶⁸ Ga dotatate and ⁶⁸ Ga PSMA, ⁶⁸ Ga-CDI has a slightly lower effective dose and renal dose but a slightly higher urinary bladder dose, and is therefore well suited for routine and repeated human use. [0362] Aside from the renal tract, which is the route of excretion, physiologic uptake of ⁶⁸ Ga-CDI is low. In comparison, the activated caspase 3/7 agent, ¹⁸ F-ICMT, has high levels of uptake in the hepatobiliary system and bowel as it undergoes both hepatobiliary and renal excretion (Challapalli et al., J Nucl Med. 2013;54:1551-1556). Similarly, many annexin V radiopharmaceuticals demonstrate very high physiologic uptake in the kidneys (49.7% IA) and liver (13.1 % IA), and prolonged retention (Kemerink et al., J Nucl Med. 2003;44:947-952). The biodistribution characteristics of ⁶⁸ Ga-CDI translate to ideal imaging characteristics with minimal or no interference from physiologic uptake, whereas high physiologic uptake observed with other cell death imaging radiopharmaceuticals especially in the hepatobiliary system and bowel makes abdominal and pelvic imaging suboptimal. Furthermore, as CDI is labelled with ⁶⁸ Ga it enables short interval serial PET for near real time, quantitative dynamic assessment of treatment-induced changes in tumor cell death.

[0363] While acceptable dosimetry, good biodistribution and imaging characteristics are important, for a cell death imaging agent to be successful it must have the sensitivity to quantitively detect tumor cell death. ⁶⁸ Ga-CDI detects constitutive tumor cell death with levels of [ ⁶⁸ Ga]Ga-CDI uptake varying between different tumor types but also within tumors of the same histological subtype. In addition, ⁶⁸ Ga-CDI tumor uptake correlated with histological tumor cell death assessed by TUNEL on operative specimens. The ability to detect constitutive tumor cell death indicates the exquisite sensitivity of ⁶⁸ Ga-CDI for imaging tumor cell death. In contrast, previous radiopharmaceuticals for imaging cell death did not reliably detect tumor cell death even after treatment. For example, the caspase ligand ¹⁸ F-ICMT did not detect an increase in cell death in a proof-of-concept study. This was attributed to the low abundance and spatial and temporal heterogeneity of the target and that response may occur by mechanisms independent of caspase 3/7 activation (Dubash et al., Eur J Nucl Med Mol Imaging. 2018;45:2285-2299). It has been suggested that a long integration would be required to overcome these limitations (Gammon et al., Mol Imaging Biol. 2020;22:1310-1323). [ ⁶⁸ Ga]Ga-CDI resolves these limitations. Firstly, hsp90 is highly abundant, constituting up to 1-2% of total cellular protein content, and is often upregulated in malignancy (Whitesell & Lindquist, Nat Rev Cancer. 2005;5:761-772), making it an ideal target for imaging cell death when cell membrane integrity is compromised during death. Secondly, it is a spatially and temporally stable target, as once a cell is committed to death the target is accessible and stable until the cellular debris is cleared by physiologic mechanisms, which may take several weeks. Finally, in contrast to previous cell death imaging radiopharmaceuticals which have specifically targeted aspects of apoptosis, ⁶⁸ Ga-CDI detects different forms of cell death and there is increasing evidence of the importance of non-apoptotic cell death in malignancy (Galluzzi et al., Cell Death Differ. 2018;25:486-541.

[0364] The disclosure of PCT application no. PCT/AU2020/050359 (published as W02020206503) is incorporated herein by reference.

EXAMPLE 13

Radiolabelling of NODAGA-GSAO with ¹⁷⁷ Lu

[0365] ¹⁷⁷ Lu-NODAGA-GSAO was prepared by incubating NODAGA-GSAO with ¹⁷⁷ Lu in ammonium acetate buffer (pH = 5) for 30 minutes at 100°C in the presence of one or more radioprotectants. No pre-purification or post-purification procedures were performed. Results are shown in Table 14.

Table 14.

[0366] Consistent with the results of Example 5, a combination of a high concentration of ascorbic acid and glutathione almost completely prevented radiolysis.

Radiolabelling of DOTA-GSAO and NODAGA-GSAO with ⁶⁸ Ga

[0367] ⁶⁸ Ga-DOTA-GSAO and ⁶⁸ Ga-NODAGA-GSAO were prepared by incubating the trivalent arsenical compound (DOTA-GSAO or NODAGA-GSAO) with ⁶⁸ Ga in ammonium acetate buffer (pH from about 4 to 4.5) for 10-15 minutes. Results are shown in Table 15. Table 15.

[0368] Attempts to synthesize ⁶⁸ Ga-DOTA-GSAO under heated conditions with or without the radioprotectants ethanol and ascorbic acid did not result in the desired product with high purity or activity. On the basis of the present inventors’ work, inclusion of a low molecular weight thiol would be expected to minimize radiolysis of the compound under the heated conditions necessary to incorporate a radioisotope into the DOTA chelator. While radiolysis proved an issue in the preparation of ⁶⁸ Ga-DOTA-GSAO, replacement of the chelator with NOD AGA and performing the radiolabelling step under the room temperature conditions described in Example 6 afforded ⁶⁸ Ga-NODAGA-GSAO with minimal radiolysis.