Background Art Pentavalent 99"Tc-meso-2,3-dimercaptosuccinic acid (99mTc (V)-DMSA) is a tumour imaging agent which has been used as an imaging agent for various cancers. Rhenium analogues 188 186Re (V)-2,3-dimercaptosuccinic acid (188 l86Re (V)-DMSA) have been synthesized and chemically characterized in order to develop a matching pair of radiopharmaceuticals consisting of 99mTc (V)-DMSA and 188sl86Re (V)-DMSA, for diagnosis and therapy of cancer. Both the 99mTc (V)-DMSA and 188, 186Re (V)-DMSA which have been tested in clinical studies have been prepared using 2,3-dimercaptosuccinic acid kits for 99mTc kidney scintigraphy which are commercially available from Amersham International PLC (Amersham, UK) and contain tin (II) as reducing agent for 99mTc. The resulting product inevitably contains substantial amounts of tin species.

99mTc (V)-DMSA and 188l86Re (V)-DMSA show similar tumour-targeting behaviour.

However, the rhenium complex as prepared using the commercially available kit exhibits much greater accumulation in the kidney than does the technetium analogue. For this reason, therapeutic or diagnostic applications of 188 l86Re (V)-DMSA have been very limited in comparison with 99mTc (V)-DMSA with only a few studies on therapy of the medullary carcinoma of thyroid having being reported. Attempts to modify pharmacologically high renal uptake of 188l86Re (V)-DMSA have been reported, but this objective has proven to be difficult to achieve.

There remains, therefore, a need for a clinically effective method of treatment of cancers using radiolabelled Re (V)-DMSA. Surprisingly, the present inventors have found that when substantially tin-free radiolabelled Re (V)-DMSA is administered to a mammal, renal uptake of the complex is substantially lower than when radiolabelled Re (V)-DMSA containing tin species is administered, and is in fact diminished to such an extent that the clinical use of radiolabelled Re (V)-DMSA becomes feasible.

Re (V)-DMSA which is substantially tin-free has been synthesised previously, but has not previously been administered to a mammal. It was therefore not known, prior to the present invention, that the presence of tin in a solution of Re (V)-DMSA administered to a mammal is responsible for the high renal uptake which has been observed previously.

Tin-free Re (V)-DMSA has been synthesised previously by reduction of Re (VII) species by, for example, triphenyl phosphine. However, this method of synthesis requires the use of organic solvent and/or high concentrations of strong acids or alkali and removal of the solvents and phosphorus-containing byproducts is necessary before the product can be used for therapeutic or diagnostic purposes. It is therefore impractical to synthesise tin-free Re (V)-DMSA for therapeutic or diagnostic use using triphenylphoshine as reductant.

Tc (V)-DMSA has been synthesised by the reduction of a Tc (VII) species by a S02- releasing reducing agent such as dithionite or metabisulfite under mildly alkaline conditions. Previous studies of attempts to reduce rhenium (VII) using dithionite have utilised similar conditions, including alkaline pH, as have hitherto been used successfully to reduce technetium (VII). However, under these alkaline conditions, yields of rhenium (V) have been poor. In contrast, the present inventors have discovered that excellent yields of Re (V)-DMSA may surprisingly be obtained by reducing Re (VII) with a SO2-releasing reducing agent under acidic reaction conditions which are quite different to those utilised for the preparation of Tc (V)-DMSA.

Summary of the Invention According to a first embodiment of the invention there is provided a method for the treatment of cancer in a mammal in need of said treatment, including the step of administering to said mammal an effective amount of a substantially tin-free solution of a therapeutic agent selected from the group consisting offre (V)-2,3-dimercaptosuccinic acid, 186Re (V)-2,3-dimercaptosuccinic acid and mixtures thereof.

According to a second embodiment of the invention there is provided a method for the diagnosis of cancer in a mammal including the step of administering to said mammal a diagnostically effective amount of a substantially tin-free solution of a diagnostic agent selected from the group consisting of 188Re (V)-2,3-dimercaptosuccinic acid, l86Re (V)-2,3- dimercaptosuccinic acid and mixtures thereof.

According to a third embodiment of the invention there is provided a method for diminishing the renal uptake in a mammal of a therapeutic agent selected from the group consisting of 188Re (V)-2,3-dimercaptosuccinic acid, 186Re (V)-2,3-dimercaptosuccinic acid and mixtures thereof, by administering to said mammal a substantially tin-free solution of said therapeutic agent.

According to a fourth embodiment of the invention there is provided a process for the preparation of substantially tin-free Re (V)-2,3-dimercaptosuccinic acid, including the step of reducing a solution of a rhenium (VII) species in the presence of at least a 105-fold molar excess of 2,3-dimercaptosuccinic acid with at least a 105-fold molar excess of a sulfur dioxide releasing reducing agent at a pH of not greater than 6, wherein said molar excesses are based on the number of moles of said rhenium (VII) species in said solution.

In a fifth embodiment, the invention also provides Re (V)-2,3-dimercaptosuccinic acid when prepared by the process of the fourth embodiment.

The invention further provides a substantially tin-free injectable composition including a radiolabelled Re (V)-2,3-dimercaptosuccinic acid, together with at least one physiologically acceptable carrier, diluent, excipient or adjuvant. Typically, the radiolabelled Re (V)-2,3- dimercaptosuccinic acid is a radiolabelled Re (V)-2,3-dimercaptosuccinic acid of the fifth embodiment.

The invention yet further provides a kit for preparation of a substantially tin-free injectable composition including a radiolabelled Re (V)-2,3-dimercaptosuccinic acid selected from the group consisting of 188Re (V)-2,3-dimercaptosuccinic acid and 186Re (V)-2, 3- dimercaptosuccinic acid, the kit including the radiolabelled Re (V)-2,3-dimercaptosuccinic acid in a suitable container and a physiologically acceptable diluent therefor in a separate container.

The invention still further provides the use of a substantially tin-free therapeutic agent selected from the group consisting of 188Re (V)-2,3-dimercaptosuccinic acid, 186Re (V)-2,3- dimercaptosuccinic acid and mixtures thereof, for the manufacture of a medicament for the treatment or diagnosis of cancer.

Detailed description of the invention In a process of the fourth embodiment, the sulfur dioxide releasing reducing agent may be a soluble dithionite, such as sodium dithionite, potassium dithionite or ammonium dithionite, a soluble bisulfite or metabisulfite such as sodium bisulfite, potassium bisulfite, lithium bisulfite, ammonium bisulfite, sodium metabisulfite, potassium metabisulfite, lithium metabisulfite or ammonium metabisulfite, or an aqueous solution of sulfur dioxide.

Usually, the sulfur dioxide releasing reducing agent is sodium dithionite or sodium metabisulfite.

The pH of the reaction medium is not greater than 6, and is typically in the range of 2-5, more typically from 2.7-4, still more typically from 3.5-4.

The molar excess of 2,3-dimercaptosuccinic acid, based on the number of moles of the rhenium (VII) species in the solution to be reduced, is typically in the range of from about 105 to about 108, more typically in the range of about 5x105 to about 5x107, still more typically in the range of about 5x105 to about 5x106. By"molar excess of 2,3- dimercaptosuccinic acid"is meant the ratio of the number of moles of 2,3- dimercaptosuccinic acid in the reaction medium, to the number of moles of rhenium (VII) species initially present.

The molar excess of sulfur dioxide releasing reducing agent, based on the number of moles of the rhenium (VII) species in the solution to be reduced, is typically in the range of

from about 105 to about 109, more typically in the range of about 5x105 to about 108, still more typically in the range of about 106 to about 107.

The rhenium (VII) species is typically a 188Re perrhenate or a 186Re perrhenate, or a mixture thereof. Sources of radiolabelled perrhenate are known to those of ordinary skill in the art. For instance, 188Re may be obtained from a 188W/l88Re generator.

The reaction temperature in a process of the fourth embodiment may be ambient or higher.

Typically, the reaction temperature is at least 30°, more typically at least 37°C, still more typically 50°C or above, and up to 90°C or more. It will be appreciated that for given amounts of the reactants, the reaction time required to achieve a maximum yield of the desired product is an inverse function of the reaction temperature. Excessive reaction times at a given temperatures should be avoided, as under some conditions the yield of the desired product first increases with time at a given temperature up to a maximum yield, then begins to decline after the maximum yield has been reached. Usually, the reaction time is not more than two hours, owing to the relatively short half life of 188Re and 186Re.

Given the teaching herein, persons of ordinary skill in the relevant filed can readily ascertain the approximate maximum yield obtainable with a given set of reaction conditions.

The process of the fourth embodiment may further include the step of separating the substantially tin-free Re (V)-2,3-dimercaptosuccinic acid from unreacted Re (VII) species by contacting the product of the reduction step with a basic anion exchange resin. Optionally, the product obtained from the process of the fourth embodiment may be dried, such as by lyophilisation, or it may be diluted with a suitable diluent such as sterile saline solution.

In the method of the first, second or third embodiments, the 188Re (V)-2,3- dimercaptosuccinic acid and/or 186Re (V)-2,3-dimercaptosuccinic acid administered is usually, but need not be, a product obtained by the process of the fourth embodiment.

Other methods for reducing Re (VII), utilising other reducing agents which do not contain tin, are possible and are known to persons of ordinary skill in the relevant field. For example, hydrogen bromide may be utilised as a reducing agent. In general, any soluble reducing agent having a reduction potential sufficiently high to be capable of reducing Re (VII) to Re (V) could be used. Some other reducing agents which may be used include thiocyanate, hypophosphorous acid, hydriodic acid and borohydride or other water-soluble hydride reducing agents. Alternatively, electrochemical reduction may be used.

Preferably, the reducing agent is a pharmaceutically acceptable reducing agent. In this respect, the process of the fourth embodiment is advantageous for the synthesis of l88Re (V)-2,3-dimercaptosuccinic acid and/or 186Re (V)-2,3-dimercaptosuccinic acid because the sulfur dioxide releasing reducing agents used are approved for use in foods as preservatives, for example, and thus have low toxicities.

In the method of the first embodiment, the therapeutic agent is typically administered in a dose of between about 10 and 500mCi, more typically between about 10 and 200 mCi, still more typically from about 30 to 200 mCi. In the method of the second embodiment, the diagnostic agent is typically administered in an amount of between about 1 and lOmCi. In the method of the third embodiment, the therapeutic agent is typically administered in a dose of between about 1 and 500mCi, more typically between about 1 and 200 mCi. The therapeutic agent may be administered with one or more substances which enhance or modulate uptake of the therapeutic agent. Such substances are known in the art and include meso-2,3-dimercaptosuccinic acid and sodium bicarbonate.

The therapeutic agent may be administered in a single dose, or the dose may be repeated once, twice or several times, depending on the stage of the disease being treated, the tumour response, and the degree of any myelotoxicity which is manifested after administration of the therapeutic agent. Appropriate dosages and treatment regimens will depend on the disorder being treated and the stage of the disorder. Given the teaching herein, a physician will readily determine the appropriate dosage and treatment regimen in any given situation.

In the method of the first or second embodiments, the cancer may be any cancer susceptible to treatment by 188Re (V)-2,3-dimercaptosuccinic acid and/or 186Re (V)-2,3- dimercaptosuccinic acid and includes conditions for which uptake of 99mTc (V)-2,3- dimercaptosuccinic acid is known. Examples of such cancers have been described in the literature and include medullary and insular carcinoma of the thyroid, head and neck tumours, amyloidosis, osteosarcoma, pancreatic neuroendocrine tumours, soft tissue tumours including lung cancer, brain tumours and hepatic carcinoma, and brain, liver and skeletal metastases, for example from breast carcinoma.

In the method of the first, second and third embodiments, the mammal is usually a human.

An injectable composition in accordance with the invention is typically a sterile aqueous solution, such as a solution in sterile saline solution. The concentration of radiolabelled Re (V) in such a solution is typically in the range of from 5xl0-8molar to 10-6 molar, and the specific activity of the solution is typically in the range of from 2mCi/mL to 1000mCi/mL, more typically from 2mCi/mL to 200mCi/mL.

Alternatively, the radiolabelled Re (V)-2,3-dimercaptosuccinic acid may be provided in the form of a kit, consisting of or including the radiolabelled Re (V)-2,3-dimercaptosuccinic acid in a suitable container, in dry form, optionally with one or more solid diluents, adjuvants, carriers or excipients, and a separate container of sterile diluent, such as saline, to be mixed with the radiolabelled Re (V)-2,3-dimercaptosuccinic acid before use. In such a kit, the dry Re (V)-2,3-dimercaptosuccinic acid may conveniently be a lyophilised solution obtained by the process of the fourth embodiment of the present invention. The radiolabelled Re (V)-2,3-dimercaptosuccinic acid is usually carrier-free.

Best Method and Other Methods for Carrying out the Invention A preferred process in accordance with the fourth embodiment of the present invention includes the step of reacting 188Re perrhenate solution with a solution of sodium dithionite in the presence of 2,3-dimercaptosuccinic acid at a pH in the range 3.5-4 at a temperature of 37°C for at least 1 hour, in which the 2,3-dimercaptosuccinic acid and sodium dithionite are present in amounts of about 1-2mg and 3mg, respectively, per lmCi of 188Re. An alternative preferred process involves reaction under essentially the same conditions, except that the pH is about 4 and the reaction is at a temperature of about 70°C for about 15 minutes.

At the end of the reaction time, the pH of the solution is adjusted to 8.5 and the product is separated from any unreacted perrhenate by passing the reaction mixture through a Bond ElutX (-NH2) column (Varian Associates) or similar, washing the column with water and eluting the desired product with 0.5M sodium hydroxide solution. The resulting solution may be diluted, if desired, with sterile saline solution, or it may be lyophilised and stored in a suitable container.

A preferred method in accordance with the first embodiment of the invention includes administering to a patient in need of treatment for cancer an amount of from 30-200mCi of a tin-free t88Re (V)-2,3-dimercaptosuccinic acid prepared by a preferred process of the fourth embodiment.

A preferred method in accordance with the second embodiment of the invention includes administering to a patient in need of diagnosis of cancer an amount of from 1-lOmCi of a tin-free 188Re (V)-2,3-dimercaptosuccinic acid prepared by a preferred process of the fourth embodiment. The body of the patient, or part of it suspected of including cancerous tissue is then imaged by techniques known in the art, the presence or absence of cancer being indicated by abnormal localisation of radiolabelled rhenium.

The invention will be further described by reference to the following examples, which are not to be construed, however, as limiting the disclosure herein.

Examples Synthesis of'88Re (V)-meso-2, 3-dimercaptosuccinic acid (I88Re (-DMSA) using Na2S204 or Na2S205 as reducing agents A mixture of 1-20mg DMSA and lmg L-ascorbic acid was suspended in lOOuJL of water in a first vial. 0.5mL of 188Re perrhenate solution (about 370 MBq) was added to a second vial containing 5-30 mg Na2S204 or Na2S205. The mixture was incubated at 25-90°C for 0.25-3 hours. The pH of the mixture was about 3.5-4. In some experiments the pH was altered by addition of appropriate amounts of 1M HCl or 1M NaOH. On completion of incubation, reaction mixtures were cooled to room temperature and the pH of the solution was adjusted to 8.5 with 1 M NaOH. If necessary, the 688Re (V)-DMSA product was

separated from unreacted perrhenate prior to biodistribution experiments by passing the reaction mixture through a Bond ElutO (-NH2) column (Varian Associates). The column was first activated by washing with 1mL methanol and 1mL saline. After the reaction mixture had been passed through the column, it was washed with 1 mL of water and the 188Re (V)-DMSA was eluted with 0.5mL 0.5M NaOH.

Yields of l88Re (V)-DMSA under various conditions are set out in Table 1 Table 1 Preparative conditions and yields for 188Re(V)-DMSA synthesized by Na2S2O4 or Na22O5 red@ Example DMSA, mg Na2S2O4, mg Na2S2O5, mg pH Time(hrs) Temperature, °C 188Re(V)D 1 1 5 - 3.5-4 2 25 2 1 12 - 3.5-4 2 25 3 130 - 4 2 25 4 10 30 - 3.5-4 2 25 5** 10 30 - 2.7 2 25 6 15 30 - 3.2 2 25 7 20 30 - 3.2 2 25 8 10 30 - 3.5-4 1 37 9 10 30 - 3.5-4 2 37 10 10 30 - 3.5-4 1 50 11 10 30 - 3.5-4 2 50 12 10 30 - 3.5-4 1 70 13 10 30 - 3.5-4 2 70 14 10 30 - 3.5-4 1 90 15 10 30 - 3.5-4 2 90 16 10 - 30 4 1 25 17 10 - 30 4 1 37 18 10 - 30 4 0.25 70 19 1 12 - 3.5-4 5 25 20 1 12 - 3.5-4 2 60 21 1 12 - 3.5-4 5 60 22 10 30 - 3.5-4 18 25 23 15 30 - 3.2 18 25 24 20 30 - 3.2 18 25 Comparative Examples *** 1 20 30 - 8.5 2 25 2 10 30 - 8.5 2 37 ** pH adjusted with 40µL 1M HCl<BR> *** pH adjusted with 100µL 1M NaOH

Biodistribution of'88Re (V)-DMSA a) Synthesis ofReV-DMSA by SnfID reduction 0.5 mL of l88Re perrhenate solution in normal saline was added to the vial of a kit commercially available from Amersham International PLC, Amersham, UK. The vial was gently shaken for 30 seconds. The pH of the mixture was about 2. The reaction mixture was equilibrated at 90°C for 30 min. In some experiments DMSA (9 mg) was added to the vial before addition of l88Re perrhenate in order to check the influence of excess of DMSA on biodistribution. b) Synthesis of l88Re (V !-DMSA using HBr reduction A mixture of 10mg DMSA and 1 mg L-ascorbic acid was suspended in 100pL of water in a first vial. 0.5 mL of 188Re perrhenate solution was added to a second vial containing 200 µL 7M HC1 and 200µL 48% HBr. The contents of both vials were combined, and the reaction mixture was incubated at 70°C for 60 min.

On completion of incubation, reaction mixtures obtained according to a) and b) were cooled to room temperature and the pH of the solution was adjusted to 8.5 with 1 M NaOH.

Chromatographically, the product of the reduction using the commercial kit (tin (II) reduction) was essentially indistinguishable from the product of the reduction using dithionite or metabisulfite or HBr.

Biodistribution studies in mice Samples of l88Re (V)-DMSA synthesised by methods a) and b) above, or by dithionite or metabisulfite reduction as described above were diluted with a sterile solution of 0.84% NaHC03 in normal saline and terminally sterilised by filtration through sterile 0.2 filter.

Female BALB/c mice (6-8 weeks old) were injected with lOOuJL of the product (activity 10 pCi/100pL) and sacrificed at various intervals. 5 animals per time point were sacrificed.

In a second study, to investigate the correlation between bone maturation and bone uptake of'88Re (V)-DMSA, adult animals (13-15 weeks old) were used.

Tables 2 to 4 set out the biodistribution of l88Re at various time intervals. It will be seen from a comparison of Table 2 with Table 3 or Table 4 that renal uptake of the products which were prepared without a tin-containing reducing agent was very substantially lower than the renal uptake of the product of reduction using the tin (II) reducing agent, although the biodistribution pattern of 188Re (V)-DMSA in other organs was much less affected.

Kidney uptake was decreased from 41.9% for tin (II) reduction to 2.18-2.95% injected dose per gram organ at 1 hour post-injection for the other reducing agents. Time dependencies of kidney uptake of l88Re (V)-DMSA samples using the different reducing agents were also different: in the presence of tin (II), l88Re (V)-DMSA tended to accumulate

in kidneys reaching maximum at 3 h post-injection, while 188Re (V)-DMSA prepared using other reducing agents was rapidly excreted.

Influence of excess 2.3-dimercaptosuccinic acid on biodistribution The data in Table 5 demonstrate that the changed renal uptake of l88Re (V)-DMSA prepared from tin-free reducing agents was not due to an excess of the ligand, 2,3- dimercaptosuccinic acid (DMSA). Biodistribution of l88Re (V)-DMSA synthesized via tin (II)-reduction in the presence of an additional 9 mg DMSA are presented in Table 5.

The concentration of DMSA in the product was 10 times higher than in commercial kit and was equal to that in many of the tin-free preparations. The presence of the DMSA excess lowered to some extent kidney uptake at 1 hour post-injection in comparison with the product obtained using the commercial kit as supplied (25.33 and 41.9% injected dose per gram organ, respectively). By 3 hours post-injection, however, kidney uptake had increased to 42.66%, showing the same trend as uptake of 188Re (V)-DMSA synthesized via tin (II) reduction without excess DMSA.

Bone uptake: influence of bone maturation Bone uptake of l88Re (V)-DMSA in young and mature mice is shown in Table 6. The reducing agent used did not substantially affect bone uptake. It will be seen from Table 6 that bone maturation, though incomplete in the 15 week old animals, resulted in about a 50% decrease in bone uptake in the 15 week old mice, compared to the 7 week old animals, whether the l88Re (V)-DMSA was obtained by tin (II) or Na2S204 reduction.

Absence of uptake of tin-free 188 Re (V)-DMSA in normal skeleton is a prerequisite to ensuring that when used in adult patients it will not deliver unnecessary dose to healthy bone, and, simultaneously, will display high tumour uptake according to its ability to accumulate in the sites with increased metabolism. Table 2. Biodistribution of 188Re (V)-DMSA synthesised by tin (II) reduction (% of injected dose per g of organltissue; mean of 5 animals) organ 0. 25h 1 h 3h 24h 48h 72h liver 4.34(0. 36) 4.43 (0.44) 5.14 (0.79) 5.11 (0.48) 5.26 (0.75) 4.64 (0.37) kidney 28.6 (2.62) 41.91 (4.51) 50.3 (5.78) 44.28 (4.72) 35.11 (5.01) 26.8 (4.58) muscle 1.38 (0.19) 0.68 (0.08) 0.48 (0.07) 0.27 (0.03) 0.24 (0.06) 0.27 (0.16) bone 8.52 (1.14) 7.85 (0.74) 5.4 (1.36) 3.27 (0.5) 2.3 (0.15) 2.17 (0.32) lungs 7. 92 (2.27) 3.91 (1.62) 2.75 (1.17) 1.58 (0.15) 1.77 (0.69) 2.0 (0.17) bllod 9.74(0. 58) 4.78 (0.6) 2.65 (0.46) 0.73 (0.06) 0.49 (0.07) 0.4 (0.11) bladder 6.07 (3.18) 1.99 (0.49) 1.54 (0.17) 1.28 (0.86) 0.73 (0.36) 3.08 (4.61) stomach 2.98 (0.23) 1.8 (0.18) 1.13 (0.31) 0.43 (0.1) 0.37 (0.05) 0.39 (0.06) GIT 1.98 (0.24) 1.64 (0.31) 1.47 (0.28) 0.64 (0.09) 0.71 (0.12) 0.47 (0.08) tail 5.0 (0.76) 4.17 (0.6) 3.07 (0.58) 2.5 (1.28) 1.39 (0.46) 1.19 (0.39) brain 0.32 (0.07) 0.18 (0.06) 0.13 (0.05) 0.04 (0.01) 0.04 (0.02) 0.03 (0.05) thyroid 5.13 (1.28) 3.52 (1.01) 2.53 (0.68) 0.97 (0.18) 0.86 (0.77) 2.61 (1.99) urine 811 (338) 588 (218) 4.87 (2.6) 2.69 (1.76) * GIT: Gastro-intestinal tract Table 3. Biodistribution of 188Re (V)-DMSA synthesised by Na2S204 reduction (% of injected dose per g of organltissue; mean of 5 animals) organ 0. 25h 1 h 3h 24h 48h 72h liver 1. 23 (0.06) 0.4 (0.05) 0.28 (0.02) 0.2 (0.02) 0.17 (0.02) 0.1 (0.04) kidney 8.62 (3.26) 2.18 (0.25) 1.63 (0.16) 1.24 (0.37) 0.78 (0.12) 0.12 (0.03) muscle 1.71 (0.5) 0.18 (0.05) 0.06 (0.04) 0.02 (0.02) 0.08 (0.06) 0.97 (1.11) bone 12.95 (1.77) 10.48 (1.28) 7.0 (1.01) 3.5 (0.53) 3.11 (0.58) 4.5 (1.12) lungs 3.53 (0.22) 0.53 (0.09) 0.21 (0.07) 0.05 (0.02) 0.07 (0.04) 0.01 (0.01) blood 4. 06 (0.42) 0.55 (0.1) 0.11 (0.03) 0.02 (0.01) 0.03 (0.05) 0.01 (0.15) bladder 6. 92 (4.37) 1.6 (1.13) 0.63 (0.37) 0.27 (0.1) 0.48 (0.37) 0.02 (0.02) stomach 2.68 (0.22) 0.9 (0.03) 0.5 (0.17) 0.22 (0.25) 0.05 (0.02) 0.02 (0.02) GIT 1.25 (0.08) 0.3 (0.07) 0.22 (0.05) 0.22 (0.12) 0.05 (0.02) 0.12 (0.03) tail 8.87 (4.32) 4.13 (0.56) 3.09 (1.17) 2.04 (1.65) 1.2 (0.42) 0.29 (0.1) brain 0.16 (0.03) 0.06 (0) 0.03 (0.01) 0.02 (0.01) 0.02 (0.02) 0 (0) thyroid 14.11 (11.3) 5.65 (2.31) 0.92 (0.21) 0.34 (0. 54) 0 (0) 0 (0) urine 2460 (1189) 500 (120)- Table 4. Biodistribution of 188Re (V)-DMSA synthesised by Na2S205 reduction or HBr reduction (% of injected dose per g of organltissue; mean of 5 animals) Na2S205-reduction HBr-reduction organ 1 h 3h 1 h 3h 24h liver 0. 51 (0.06) 0.33 (0.08) 1.15 (0.16) 0.78 (0.13) 0.22 (0.03) kidney 2.32 (0.18) 1.64 (0.4) 2.95 (0.52) 1.72 (0.18) 0.88 (0.05) muscle 0.16 (0.06) 0.06 (0.01) 0.4 (0.07) 0.14 (0.04) 0.02 (0.02) bone 10.36 (1.7) 7.59 (1.06) 12.01 (0.99) 8.56 (1.56) 2.94 (0.5) lungs 0. 66 (0.07) 0.21 (0.05) 1.34 (0.28) 0.65 (0.08) 0.06 (0.03) blood 0. 67 (0.08) 0.16 (0.04) 0.55 (0.1) 0.11 (0.03) 0.02 (0.01) bladder 3. 34 (2.38) 0.98 (0.89) stomach 1.89 (0.26) 1.04 (0.41) 12.17 (3.56) 6.44 (1.2) 0.03 (0.01) GIT 0.49 (0.08) 0.27 (0.15) 0.65 (0.08) 0.56 (0.02) 0.04 (0.01) tail 4.15 (0.72) 2.71 (0.89) 5.8 (0.55) 2.92 (0.37) 1.7 (0.58) brain 0.05 (0.01) 0.02 (0.01) 0.09 (0.04) 0.05 (0.02) 0.01 (0.01) thyroid 8.59 (2.22) 9.37 (2.79) 27.68 (16.3) 23.97 (6.9) 0.22 (0.25) urine 812 (119) 267 (120) 541 (278) 285 (141) 1.38 (0.26) Table 5. Influence of DMSA excess on biodistribution of 188Re (V)-DMSA synthesized via tin (II)-reduction (commercial kit plus 9 mg DMSA) in 6-8 weeks old BALB/c mice (% injected dose per gram organltissue; mean of 5 animals) 3horgan1h 3.42(0.1liver3.33(0.43) kidney 25. 33 (4.07) 42.66 (4.27) muscle 1.34 (0.66) 1.17 (0.63) bone 7.33 (2.32) 10.89 1. 64) lungs 3. 79 (0.93) 3.45 (0.38) blood 5.03 (0.25) 3.05 (0.26) bladder 3. 47 (2. 62) 3.16 (0.74) stomach 1.54 (0.38) 1.52 (0.47) GIT 1.41 (0.09) 1.55 0. 09) heart 1.7 (0.55) 1.25 (0.22) brain 0.12 (0.02) 0.12 (0.02) thyroid 2. 34 1. 59) 2.46 (0.54)

Table 6. Bone uptake of 188Re (V)-DMSA synthesized via tin (II)- and Na2S20s reduction in weeksold)andmature(13-15weeks)BALB/cmice(%injecteddoseper(6- 8 gram bone; mean of 5 animals) tin(II)-reudctionNa2S2O5-reduction Animal age, weeks 48h3h24h 24h 48h 7 5.4 1. 36) 3.27 (0.5) 2.3 (0.15) 7 (1. 01) 3.5 (0.53) 3.11 (0.58) 15 3.13 (0. 27 1.81 (0. 19 1.77 (0.28) 3.57 (0. 85 1.82 (0. 79 1.3 (0.18)