RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63/085,510, filed on September 30, 2020. The entire teachings of this application are incorporated herein by reference.

BACKGROUND

[0002] Although combination drug therapy has a robust history for several important clinical applications, including antibiotic treatments, antiviral treatments and oncology therapeutics, combination drug therapy involving two drugs that target the same biological pathway is rarer. AMXT 1501 and difluoromethylomithine (DFMO) both target the polyamine metabolic pathway for the treatment of cancer.

[0003] Pharmaceutics is the scientific and technical field that aims to improve dose forms. One goal is to optimize dose forms that provide durable and potent engagement of biological targets over the desired treatment period. Additional goals are to provide dose products that have higher stability, more convenient handling properties, more convenient patient dosing scheduling and, especially for drug combinations, more consistent dosing of exact quantities and ratios of drug agents. AMXT 1501 and DFMO are currently administered separately.

[0004] Accordingly, there is a need for combination dosage forms of AMXT 1501 and DFMO.

SUMMARY

[0005] Provided herein is a combination (e.g., a combination dosage form) comprising difluoromethylomithine (DFMO), or an ionic form thereof, and a compound of the following structural formula:

or a protonated form thereof, wherein values for the variables (e.g., a, b, c, d, e, n, R _b R ₂ , X) are as described herein.

[0006] Also provided herein is a solid form (e.g., a crystalline solid form) comprising DFMO, or an ionic form thereof, and a compound of structural formula I, or a protonated form thereof, wherein values for the variables (e.g., a, b, c, d, e, n, R _b R ₂ , X) are as described herein.

[0007] Also provided herein is a pharmaceutical composition comprising a combination or solid form (e.g., solid form) described herein, and a pharmaceutically acceptable excipient. [0008] Also provided herein is a method of treating a cancer in a subject in need thereof, comprising administering to the subject a therapeutically effective amount of a combination, solid form or pharmaceutical composition described herein. Also provided herein is a combination, solid form or pharmaceutical composition described herein for use in treating a cancer. Also provided herein is use of a combination, solid form or pharmaceutical composition described herein for the manufacture of a medicament for the treatment of a cancer.

[0009] The AMXT 1501 -DFMO solid forms described herein have greatly increased melting point properties in comparison to their individual components. In addition, the combinations and solid forms provided herein are expected to provide one or more of the following advantages: (i) ion-pairing of AMXT 1501 with DFMO may enhance drug bioavailability, tissue and/or tumor targeting and/or pharmacokinetic activity against tumors; (ii) combination of two agents into one solid form may improve patient compliance; (iii) combination of two agents into one solid form may improve drug product handling and production feasibility; and (iv) combination of two agents into one solid form may reduce pill burden. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing will be apparent from the following more particular description of example embodiments.

[0011] FIG. 1 A is a mean plasma concentration versus time profile, and shows the mean plasma concentration of AMXT 1501 after a single dose (Day 1).

[0012] FIG. IB is a mean plasma concentration versus time profile, and shows the mean plasma concentration of AMXT 1501 after repeat dosing (Day 14).

[0013] FIG. 2 is a mean plasma concentration versus time profile, and shows the mean plasma concentration of DFMO after repeat dosing (Day 28).

[0014] FIG. 3 is a ^X H NMR spectrum, and shows the presence of both AMXT 1501 and DFMO in Lot 4-138. Data was obtained on a Varian instrument at 400 MHz in D ₂ O (residual HDO shift set to 4.79 ppm).

[0015] FIG. 4A is HPLC chromatograms, and shows the peaks generated by AMXT 1501 and DFMO under the HPLC conditions described in Example 1.

[0016] FIG. 4B is a graph, and shows the standard curve produced from HPLC analysis of standard solutions of AMXT 1501.

[0017] FIG. 4C is a graph, and shows the standard curve produced from HPLC analysis of standard solutions of DFMO.

[0018] FIG. 4D is a HPLC chromatogram, and shows the peaks produced from HPLC analysis of Lot 4-138.

[0019] FIG. 5 is x-ray pattern diffractograms, and shows the overlap of the x-ray diffraction patterns of Lot 4-138, DFMO and AMXT 1501.

[0020] FIG. 6A is a bright-field image, and shows the results of polarized light microscopy (PLM) analysis of Lot 4-138.

[0021] FIG. 6B is a polarized light image, and shows the results of PLM analysis of Lot 4-138.

[0022] FIG. 7 is a thermogram, and shows the results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of Lot 4-138.

[0023] FIG. 8A is a pH titration curve, and shows the results of the pH titration of DFMO HC1 H ₂ O (0. IM 2mL) with IM NaOH.

[0024] FIG. 8B is a charge state diagram, and shows the charge state of DFMO HC1 H ₂ O as a function of pH. [0025] FIG. 8C is a pH titration curve, and shows the results of the pH titration of AMXT 1501 4HC1 (0.05 M 2mL) with IM NaOH.

[0026] FIG. 8D is a charge state diagram, and shows the charge state of AMXT 1501 -4HC1 as a function of pH.

[0027] FIG. 9 is a thermogram, and shows the results of DSC and TGA of Test Solid 1 (Lot 5-9).

[0028] FIG. 10 is a thermogram, and shows the results of DSC and TGA of Test Solid 2 (Lot 5-11).

[0029] FIG. 11 is x-ray pattern diffractograms, and shows the overlay of the x-ray diffraction patterns of Test Solid 1, Test Solid 2 and DFMO HC1 H ₂ O.

DETAILED DESCRIPTION

[0030] A description of example embodiments follows.

Definitions

[0031] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents, unless the content and context clearly dictates otherwise.

[0032] Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and synonyms and variants thereof such as “have” and “include”, as well as variations thereof, such as “comprises” and “comprising”, are to be construed in an open, inclusive sense, e.g., “including, but not limited to.”

[0033] “About” means within an acceptable error range for the particular value, as determined by one of ordinary skill in the art. Typically, an acceptable error range for a particular value depends, at least in part, on how the value is measured or determined, e.g., the limitations of the measurement system. For example, “about” can mean within an acceptable standard deviation, per the practice in the art. Alternatively, “about” can mean a range of ± 20%, ± 10%, ± 5% or ± 1% of a given value. It is to be understood that the term “about” can precede any particular value specified herein, except for particular values used in the Examples.

[0034] “Alicyclic” refers to a non-aromatic, cyclic, hydrocarbon radical having the specified number of carbon atoms. Thus, “(C ₁ -C ₁₀ )alicyclic” refers to an alicyclic radical having from 1-10 carbon atoms. In some embodiments, alicyclic is (Ci-C ₂ 5)alicyclic, e.g., (Ci-C ₂₀ )alicyclic, (Ci-Ci ₅ )alicyclic, (Ci-Cio)alicyclic, (Ci-C ₆ )alicyclic or (Ci-C ₅ )alicyclic. “Alicyclic” can be saturated, or contain one or more units of unsaturation (e.g., carboncarbon double bonds). Examples of alicyclic include cycloalkyl, cycloalkenyl and cycloalkynyl. In some embodiments, alicyclic is saturated alicyclic. Examples of alicyclic include cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cycloheptyl, cyclooctyl, etc. [0035] “Aliphatic” refers to a non-aromatic, branched- or straight-chain, hydrocarbon radical having the specified number of carbon atoms. Thus, “(Ci-Ci ₅ )aliphatic” refers to an aliphatic radical having from 1-15 carbon atoms. In some embodiments, aliphatic is (C C ₅₀ )aliphatic, e.g., (Ci-C ₂₅ )aliphatic, (Ch-C^aliphatic, (C!-C ₁₀ )aliphatic, (C!-C ₅ )aliphatic or (Ci-C ₃ )aliphatic. “Aliphatic” can be saturated, or contain one or more units of unsaturation (e.g., carbon-carbon double bonds). Examples of aliphatic include alkyl, alkenyl and alkynyl. In some embodiments, aliphatic is saturated aliphatic, for example, (C!-C ₂₅ )saturated aliphatic, (Ch-C^saturated aliphatic, (Cx-Cw) saturated aliphatic or (C!-C ₅ )saturated aliphatic. In some embodiments, aliphatic is alkyl or alkenyl. In some embodiments, aliphatic is alkyl. [0036] “Alkyl” refers to a saturated, branched- or straight-chain, aliphatic radical. “(C ₁ -C ₁₅ )Alkyl” refers to a radical having from 1-15 carbon atoms in a branched or linear arrangement. In some embodiments, alkyl is (C ₁ -C ₅₀ )alkyl, e.g., (C!-C ₂₅ )alkyl, (Ci-Ci ₅ )alkyl, (Ci-Cio)alkyl, (Ci-C ₅ )alkyl or (Ci-C ₃ )alkyl. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, 2-methylpentyl, hexyl (e.g., n-hexyl), heptyl (e.g., n-heptyl), octyl (e.g., n-octyl), nonyl (e.g., n-nonyl), decyl (e.g., n-decyl), undecyl (e.g., n-undecyl), dodecyl (e.g., n-dodecyl), tridecyl (e.g., n-tridecyl), tetradecyl (e.g., n-tetradecyl), pentadecyl (e.g., n-pentadecyl), and the like. [0037] “Alkenyl” refers to a branched- or straight-chain, aliphatic radical having at least one (e.g., one, two, three, four, five, etc.) carbon-carbon double bond. “(C1-C15) Alkenyl” refers to a radical having from 1-15 carbon atoms and at least one carbon-carbon double bond in a branched or linear arrangement. In some embodiments, alkenyl is (Ci-C ₅₀ )alkenyl, e.g., (Ci-C ₂₅ )alkenyl, (Ci-Ci ₅ )alkenyl, (Ci-Cio)alkenyl, (Ci-C ₅ )alkenyl or (Ci-C ₃ )alkenyl.

Examples of alkenyl groups include vinyl, allyl, and the like.

[0038] “Alkoxy” refers to an alkyl radical attached through an oxygen linking atom, wherein alkyl is as described herein. Examples of alkoxy include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, and the like.

[0039] “Alkynyl” refers to a branched- or straight-chain, aliphatic radical having at least one (e.g., one, two, three, four, five, etc.) carbon-carbon triple bond. “(C ₁ -C ₁₅ )Alkynyl” refers to a radical having from 1-15 carbon atoms and at least one carbon-carbon triple bond in a branched or linear arrangement. In some embodiments, alkynyl is (Ci-C ₅₀ )alkynyl, e.g., (Ci-C ₂₅ )alkynyl, (Ch-C^alkynyl, (C!-C ₁₀ )alkynyl, (C!-C ₅ )alkynyl or (C ₁ -C ₃ )alkynyl. Examples of alkynyl groups include propargyl, and the like.

[0040] “Aryl” refers to a monocyclic or polycyclic (e.g., bicyclic, tricyclic), carbocyclic, aromatic ring system, and includes aromatic ring(s) fused to non-aromatic rings, as long as one of the fused rings is an aromatic hydrocarbon. “(C ₆ -Ci ₅ )Aryl” means an aromatic ring system having from 6-15 ring atoms. In some embodiments, aryl is (C ₆ -C ₂ 5)aryl, for example, (C ₆ -C ₂₀ )aryl, (C ₆ -C ₁₅ )aryl, (C ₆ -C ₁₂ )aryl or (C ₆ -C ₁₀ )aryl. Examples of aryl include phenyl, naphthyl, fluorenyl, and the like.

[0041] “Aryl sulfonyl” refers to an aryl radical attached through -S(O) ₂ - linking group, wherein aryl is as described herein.

[0042] “Carbalkoxyalkyl” refers to alkyl substituted with one or more (e.g., one) -C(O)- alkoxy, wherein alkyl and alkoxy are as described herein.

[0043] “Carboxyalkyl” refers to alkyl substituted with one or more (e.g., one) -CO ₂ H, wherein alkyl is as described herein.

[0044] “Cyano” refers to -CN.

[0045] “Heterocyclic” refers to a non-aromatic, cyclic, hydrocarbon radical wherein at least one carbon atom has been replaced with a heteroatom (e.g., N, S and/or O; N or O). “(C|-C|o)Heterocyclic” refers to a heterocyclic radical having from one to 10 atoms. In some embodiments, heterocyclic is (C!-C ₂₅ )heterocyclic, for example, (Cx-C^heterocyclic, (C Cio)heterocyclic, (Ci-C ₆ )heterocyclic, (Ci-C ₅ )heterocyclic or (Ci-C ₃ )heterocyclic.

“Heterocyclic” can be saturated or contain one or more units of unsaturation. In some embodiments, heteroaliphatic is heteroalkyl.

[0046] Combination,” as used herein, refers to a composition (e.g., pharmaceutical composition) comprising two or more active agents (e.g., AMXT 1501 and DFMO).

Typically, the two or more active agents are combined in the combination to provide a single dosage form of the active agents. Also typically, the two or more active agents in a combination target a single disease, disorder or condition, such as cancer. Examples of combinations include combinations comprising AMXT 1501, or a protonated or salt form thereof, and DFMO, or an ionic or salt form thereof, as well as any of the solid forms (e.g., crystalline forms, such as co-crystals and polymorphs) and salts (e.g., pharmaceutically acceptable salts) described herein. Combinations (e.g., solid forms, for example, crystalline forms, such as co-crystals and polymorphs; salts, such as pharmaceutically acceptable salts) comprising AMXT 1501, or a protonated or salt form thereof, and DFMO, or an ionic or salt form thereof, are also referred to herein as AMXT 1501 -DFMO combinations (e.g., solid forms, for example, crystalline forms, such as co-crystals and polymorphs; salts, such as pharmaceutically acceptable salts).

[0047] “Crystalline,” as used herein, refers to a homogeneous solid formed by a repeating, three-dimensional pattern of atoms, ions or molecules having fixed distances between constituent parts. The unit cell is the simplest repeating unit in this pattern. Notwithstanding the homogenous nature of an ideal crystal, a perfect crystal rarely, if ever, exists. “Crystalline,” as used herein, encompasses crystalline forms that include crystalline defects, for example, crystalline defects commonly formed by manipulating (e.g. , preparing, purifying) the crystalline forms described herein. A person skilled in the art is capable of determining whether a sample of a compound is crystalline notwithstanding the presence of such defects. Crystalline forms can be characterized by analytical methods such as x-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), nuclear magnetic resonance spectroscopy (NMR), single crystal x-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and/or any other suitable analytical techniques.

[0048] An XRPD pattern, DSC thermogram or TGA thermal curve that is “substantially in accordance” with one or more figures herein showing an XRPD pattern or DSC thermogram or TGA thermal curve, respectively, is one that would be considered by one skilled in the art to represent the same single crystalline form as the sample that provided the pattern or thermogram or thermal curve of one or more figures provided herein. Thus, an XRPD pattern or DSC thermogram or TGA thermal curve that is substantially in accordance may be identical to that of one of the figures or, more likely, may be somewhat different from one or more of the figures. For example, an XRPD pattern that is somewhat different from one or more of the figures may not necessarily show each of the lines of the diffraction pattern presented herein and/or may show a slight change in appearance or intensity of the lines or a shift in the position of the lines. These differences typically result from differences in the conditions involved in obtaining the data or differences in the purity of the sample used to obtain the data. A person skilled in the art is capable of determining if a sample of a crystalline form is of the same form as or a different form from a form disclosed herein by comparison of the XRPD pattern and/or DSC thermogram and/or TGA thermal curve of the sample and the corresponding XRPD pattern and/or DSC thermogram and/or TGA thermal curve disclosed herein.

[0049] It is to be understood that, unless otherwise indicated, any XRPD peak specified herein, with the exception of the XRPD peaks in the Figures or Examples, means the specified value ± 0.2 or less. For example, unless otherwise indicated, when an embodiment or a claim specifies a peak, in terms of 2-theta, at 20.0, this is to be understood to mean 20.0° ± 0.2° or less, that is a 2-theta angle of from 19.8° to 20.2°. In preferred embodiments, a 2- theta angle is the specified value ± 0.1° or less, in more preferred embodiments, ± 0.05° or less.

[0050] The crystalline forms provided herein can also be identified on the basis of differential scanning calorimetry (DSC) and/or thermogravimetric analysis (TGA). DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample is measured as a function of temperature. DSC can be used to detect physical transformations, such as phase transitions, of a sample. For example, DSC can be used to detect the temperature(s) at which a sample undergoes crystallization, melting or glass transition. It is to be understood that any temperature associated with DSC specified herein, with the exception of the DSC temperatures in the Figures or Examples, means the specified value ± 5 °C or less. For example, when an embodiment or a claim specifies an endothermic peak at 264 °C, this is to be understood to mean 264 °C ± 5 °C or less, that is a temperature of from 259 °C to 269 °C. In preferred embodiments, a DSC is the specified value ± 3 °C or less, in more preferred embodiments, ± 2 °C or less.

[0051] Thermogravimetric analysis (TGA) is a thermoanalytical technique in which the mass change of a substance is measured as a function of temperature or time in a controlled atmosphere. The record is a thermogravimetric curve which is a plot of the mass of the substance versus time or temperature, with the mass loss on the ordinate plotted downward and mass gains plotted upward relative to a baseline. The technique can be used to characterize weight loss or gain due to the sorption/desorption of volatiles, decomposition, oxidation and/or reduction. It is to be understood that any mass change (e.g., loss, gain) associated with TGA specified herein, with the exception of mass changes in the Figures or Examples, means the specified mass change ± 0.2%. For example, when an embodiment or a claim specifies 3.2% mass loss over a specified temperature range, this is to be understood to mean 3.2% ± 0.20%, that is mass loss of from 3.0% to 3.4%. In preferred embodiments, a mass change is the specified value ± 0.1%, in more preferred embodiments, the specified value ± 0.05%, in yet more preferred embodiments, the specified value ± 0.025%. In some embodiments, a mass change is the specified value ± 0.02%, for example, ± 0.01% or ± 0.005%.

[0052] Co-crystal” refers to a crystal composed of two or more different species in a defined stoichiometric ratio and associated with one another in a crystal lattice by noncovalent and nonionic interactions. Co-crystals include solvates and hydrates. In some embodiments, a co-crystal is not a solvate or hydrate.

[0053] Coformer” refers to a species that interacts noncovalently and nonionically with another species, typically, an active pharmaceutical ingredient, in a crystal lattice. Coformers include solvents and water, as well as pharmaceutically acceptable acids and bases identified herein as useful to form pharmaceutically acceptable salts, particularly those acids and bases having a pK _a difference from the other species in the crystal lattice of less than 2 and, preferably, of less than 1. In some embodiments, a conformer is not a solvent or water.

[0054] The term “salt” has its standard meaning in the art, and refers to a positively charged species (cation) and a negatively charged species (anion) that are complexed to one another through an ionic interaction. Generally, these salts do not involve covalent bonding between partner molecular components. Salts can be obtained by customary methods known to those skilled in the art, for example, by combining a compound with an inorganic or organic acid or base in a solvent or diluent, or from other salts by cation exchange or anion exchange.

[0055] The phrase “pharmaceutically acceptable” means that the substance or composition the phrase modifies is, within the scope of sound medical judgment, 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.

[0056] The term “pharmaceutically acceptable salt” refers to those salts which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of mammals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio. Pharmaceutically acceptable salts are well known in the art. An example list of pharmaceutically acceptable salts can be found in the Handbook of Pharmaceutical Salts: Properties, Selection and Use, P. H. Stahl and C. G. Wermuth editors, Weinheim/Zurich:Wiley-VCHA/VHCA, 2002, the relevant teachings of which are incorporated herein by reference in their entirety. Pharmaceutically acceptable salts include pharmaceutically acceptable acid addition salts and pharmaceutically acceptable base addition salts.

[0057] Examples of pharmaceutically acceptable acid addition salts are salts of an amino group formed with inorganic acids such as hydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid and perchloric acid, or with organic acids, such as acetic acid, oxalic acid, maleic acid, tartaric acid, citric acid, succinic acid or malonic acid or by using other methods used in the art, such as ion exchange. Other pharmaceutically acceptable acid addition salts include adipate, alginate, ascorbate, aspartate, benzenesulfonate, benzoate, bisulfate, borate, butyrate, camphorate, camphorsulfonate, cinnamate, citrate, cyclopentanepropionate, digluconate, dodecyl sulfate, ethanesulfonate, formate, fumarate, glucoheptonate, glycerophosphate, gluconate, glutarate, glycolate, hemisulfate, heptanoate, hexanoate, hydroiodide, hydroxybenzoate, 2-hydroxy-ethanesulfonate, hydroxymaleate, lactobionate, lactate, laurate, lauryl sulfate, malate, maleate, malonate, methanesulfonate, 2- naphthalenesulfonate, nicotinate, nitrate, oleate, oxalate, palmitate, pamoate, pectinate, persulfate, 2-phenoxybenzoate, phenyl acetate, 3 -phenylpropionate, phosphate, pivalate, propionate, pyruvate, salicylate, stearate, succinate, sulfate, tartrate, thiocyanate, p- toluenesulfonate, undecanoate, valerate salts, and the like. Either the mono-, di- or tri-acid salts can be formed, and such salts can exist in either a hydrated, solvated or substantially anhydrous form.

[0058] Other pharmaceutically acceptable acid addition salts include salts formed with hydrophobic carboxylic acids, such as those described in U.S. Patent No. 10,632,145, the entire content of which is incorporated herein by reference in its entirety. Hydrophobic carboxylic acids include those carboxylic acid-containing compounds having a water solubility of less than 10 g/L, e.g., less than 1 g/L, or less than 0.1 g/L, or less than 0.01 g/L in water, as determined at a temperature of 25° C and a pH of 7. Compendiums of the water solubility of carboxylic acid-containing compounds may be found in, e.g., Yalkowsky S H, Dannenfelser R M; The AQUASOL database of Aqueous Solubility. Fifth ed., Tucson, Ariz.: Univ. AZ, College of Pharmacy (1992); Yalkowsky S H et al; Arizona Data Base of Water Solubility (1989); and The Handbook of Aqueous Solubility Data, Second Edition, edited by Yalkowsky S H, He, Y, and Jain, P, CRC Press (2010). Specific examples of hydrophobic carboxylic acids include fatty acids, such as C ₈ -C ₁₈ straight chain hydrocarbon fatty acids, such as octanoic acid (also known as caprylic acid), nonanoic acid, decanoic acid (also known as capric acid), undecanoic acid, dodecanoic acid (also known as lauric acid), tridecanoic acid, tetradecanoic acid and hexadecanoic acid. Capric acid is a preferred hydrophobic carboxylic acid.

[0059] Pharmaceutically acceptable base addition salts include salts formed with inorganic bases, such as alkali metal, alkaline earth metal, and ammonium bases, and salts formed with aliphatic, alicyclic or aromatic organic amines, such as methylamine, trimethylamine and picoline, or N ⁺ ((Ci-C ₄ )alkyl) ₄ salts. Representative alkali or alkaline earth metal salts include sodium, lithium, potassium, calcium, magnesium, barium and the like. Further pharmaceutically acceptable base addition salts include, when appropriate, nontoxic ammonium, quaternary ammonium, and amine cations formed using counterions such as halide, hydroxide, carboxyl, sulfate, phosphate, nitrate, lower alkyl sulfonate and aryl sulfonate.

[0060] Compounds can also exist as “solvates” or “hydrates.” A “hydrate” is a compound that exists in a composition with one or more water molecules. A hydrate can include water in stoichiometric quantities, such as a monohydrate or a dihydrate, or can include water in random amounts. A “solvate” is similar to a hydrate, except that a solvent other than water, such as methanol, ethanol, dimethylformamide, diethyl ether, or the like replaces water. Mixtures of such solvates or hydrates can also be prepared.

[0061] “Ionic,” used herein, refers to a positively or negatively charged group. Examples of positively charged groups include protonated amino groups (e.g., NH ₄ ⁺ ). Examples of negatively charged groups include anions, such as carboxylate (CO ₂ ‘) and Cl". Ionic forms include anionic forms (having an overall negative charge), cationic forms (having an overall positive charge) and zwitterionic forms, where a molecule has separate negatively charged group(s) and positively charged group(s) rendering the overall charge zero.

[0062] Compounds may have asymmetric centers, chiral axes, and chiral planes (e.g., as described in: E. L. Eliel and S. H. Wilen, Stereo-chemistry of Carbon Compounds, John Wiley & Sons, New York, 1994, pages 1119-1190), and occur as racemic mixtures, individual isomers (e.g., diastereomers, enantiomers, geometrical isomers (including cis and trans double bond isomers), conformational isomers (including rotamers and atropisomers), tautomers, and intermediate mixtures, with all possible isomers and mixtures thereof being included, unless otherwise indicated.

[0063] When a disclosed compound is depicted by structure without indicating the stereochemistry, and the compound has one or more chiral centers, it is to be understood that the structure encompasses one enantiomer or diastereomer of the compound separated or substantially separated from the corresponding optical isomer(s), a racemic mixture of the compound, and mixtures enriched in one enantiomer or diastereomer relative to its corresponding optical isomer(s). When a disclosed compound is depicted by a structure indicating stereochemistry, and the compound has more than one chiral center, the stereochemistry indicates relative stereochemistry, rather than the absolute configuration of the substituents around the one or more chiral carbon atoms. “R” and “S” can be used to indicate the absolute configuration of substituents around one or more chiral carbon atoms. D- and L- can also be used to designate stereochemistry.

[0064] “Enantiomers” are pairs of stereoisomers that are non-superimposable mirror images of one another, most commonly because they contain an asymmetrically substituted carbon atom that acts as a chiral center.

[0065] “Diastereomers” are stereoisomers that are not related as mirror images, most commonly because they contain two or more asymmetrically substituted carbon atoms. [0066] “Racemate” or “racemic mixture,” as used herein, refer to a mixture containing equimolar quantities of two enantiomers of a compound. Such mixtures exhibit no optical activity (i.e., they do not rotate a plane of polarized light).

[0067] Percent enantiomeric excess (ee) is defined as the absolute difference between the mole fraction of each enantiomer multiplied by 100% and can be represented by the following equation: ee x 100%, where R and S represent the respective fractions of each enantiomer in a mixture, such that R + S = 1. An enantiomer may be present in an ee of at least or about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98%, about 99% or about 99.9%.

[0068] Percent diastereomeric excess (de) is defined as the absolute difference between the mole fraction of each diastereomer multiplied by 100% and can be represented by the following equation: represent the respective fractions of each diastereomer in a mixture, such that DI + (D2 + D3 + D4. . .) = 1. A diastereomer may be present in a de of at least or about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98%, about 99% or about 99.9%.

[0069] Compounds can also exist as isotopologues, differing from a disclosed structure only in the presence of one or more isotopically enriched atoms. For example, compounds produced by the replacement of a hydrogen with deuterium or tritium, or of a carbon with a ¹³ C- or ¹⁴ C-enriched carbon are within the scope of this disclosure. In all provided structures, any hydrogen atom can also be independently selected from deuterium ( ² H), tritium ( ³ H) and/or fluorine ( ¹⁸ F). Such compounds are useful, for example, as analytical tools, as probes in biological assays, or as therapeutic agents in accordance with the present disclosure.

[0070] As used herein, the term “combination of the disclosure” refers to any combination described herein comprising DFMO and a polyamine transport inhibitor (e.g., a compound of structural formula I or a subformula thereof), as well as isomers, such as stereoisomers (including diastereoisomers, enantiomers and racemates) and tautomers, isotopologues, inherently formed moi eties (e.g., polymorphs and/or solvates, such as hydrates), ionic forms and salts (e.g., pharmaceutically acceptable salts) of DFMO and/or the polyamine transport inhibitor.

[0071] “Pharmaceutically acceptable carrier” refers to a non-toxic carrier or excipient that does not destroy the pharmacological activity of an agent(s) with which it is formulated and is nontoxic when administered in doses sufficient to deliver a therapeutic amount of the agent(s). Pharmaceutically acceptable carriers that may be used in the compositions described herein include, but are not limited to, ion exchangers, alumina, aluminum stearate, lecithin, serum proteins, such as human serum albumin, buffer substances such as phosphates, glycine, sorbic acid, potassium sorbate, partial glyceride mixtures of saturated vegetable fatty acids, water, salts or electrolytes, such as protamine sulfate, disodium hydrogen phosphate, potassium hydrogen phosphate, sodium chloride, zinc salts, colloidal silica, magnesium trisilicate, polyvinyl pyrrolidone, cellulose-based substances, polyethylene glycol, sodium carboxymethylcellulose, polyacrylates, waxes, polyethylene-polyoxypropylene-block polymers, polyethylene glycol and wool fat.

[0072] Treatment” and “treating” refer to medical management of a disease, disorder, or condition of a subject. A treatment may improve or decrease the severity at least one symptom of a disease, disorder or condition; delay worsening or progression of a disease, disorder or condition; delay or prevent onset of additional associated diseases, disorders or conditions; or improve remodeling of lesions into functional (partially or fully) tissue.

[0073] A “therapeutically effective amount” or “effective amount” of a therapy refers to that amount sufficient to result in amelioration of one or more symptoms of the disease being treated in a statistically significant manner. When referring to an individual active ingredient administered alone, a therapeutically effective amount refers to that ingredient alone. When referring to a combination, a therapeutically effective amount refers to combined amounts of the active ingredients that result in the therapeutic effect, whether administered serially or simultaneously.

[0074] “Subject,” as used herein, refers to a mammal. In addition to warm-blooded animals, such as mice, rats, horses, cattle, sheep, dogs, cats, monkeys, etc., “subject” includes humans. In preferred embodiments, a subject is a human.

[0075] “Subject in need” refers to a subject at risk of, or suffering from, a disease, disorder or condition that is amenable to treatment in accordance with the present disclosure. In certain embodiments, a subject in need is a mammal, e.g., a human.

Polyamine Transport Inhibitors

[0076] AMXT 1501 acts as a potent blocker of polyamine uptake into cancer cells. Examples of other polyamine or polybasic drugs include inhibitors of the polyamine precursor-forming enzyme known as S-adenosylmethionine decarboxylase (AdoMetDC), such as MGBG. MGBG is a poly-cationic, charged molecule, and has been shown to be a potent inhibitor of S-adenosylmethionine decarboxylase. The S-adenosylmethionine decarboxylase inhibitor CGP-48664 is also a poly-cationic, poly-basic amine. Other polyamine transport inhibitors, such as Trimer PTI, are likewise useful for oncology therapy. AMXT 1501 is D-lys(palmitoyl)-spermine, and has the following structure: . g [0077] Various terminally di-alkylated polyamines, such as diethyl-norspermine (DENSPM), have also been explored as polyamine anti-metabolites for cancer treatment. This, and other, diethyl polyamine analogs have been shown to induce the polyamine degradation enzyme spermidine/spermine N ¹ -acetyl transferase (SSAT) in cancer cells.

DENSPM has the following structure: ^{H H H H} .

[0078] Further polyamine transport inhibitors are disclosed in U.S. Patent No. 10,632,145, the entire content of which is incorporated herein by reference.

[0079] In some embodiments, a polyamine transport inhibitor is a compound of the following structural formula:

(I), or a protonated form thereof, wherein: each of a, b and c is independently an integer from one to ten; each of d and e is independently an integer from 0 to 30; each X is independently carbon or sulfur; each n is independently 0 or 1 when the adjacent X is carbon, or 2 when the adjacent X is sulfur; and

Ri and R ₂ are each independently selected from hydrogen or straight or branched, saturated or unsaturated (Ci-C ₅₀ )aliphatic; carboxyalkyl; carbalkoxyalkyl; alkoxy; (Cx-Chojalicyclic; single- or multi-ring aryl aliphatic; aliphatic single- or multiring aromatic; single- or multi-ring heterocyclic; single- or multi-ring heterocyclic aliphatic; arylsulfonyl; or cyano; or

Ri-X(O) _n -, R ₂ -X(O) _n - or Ri-X(O) _n - and R ₂ -X(O) _n - are replaced by hydrogen. [0080] In some embodiments of a compound of structural formula I, R ₂ -X(O) _n - is replaced by hydrogen. In alternative embodiments, Rx-X(O) _n - is replaced by hydrogen. [0081] In some embodiments of a compound of structural formula I, each of a, b and c is independently an integer from one to five. In more specific embodiments, each of a, b and c is independently three or four. In yet more specific embodiments, a is three, b is four and c is three.

[0082] In some embodiments of a compound of structural formula I, d is an integer from one to five. In more specific embodiments, d is four.

[0083] In some embodiments of a compound of structural formula I, e is 0.

[0084] In some embodiments of a compound of structural formula I, each X is carbon.

[0085] In some embodiments of a compound of structural formula I, Ri and R ₂ are each independently selected from hydrogen or straight or branched, saturated or unsaturated (Ci- C ₅₀ )aliphatic or (C ₁ -C ₁₀ )alicyclic. In more specific embodiments, R| and R ₂ are each independently selected from straight or branched, saturated or unsaturated (C ₁ -C ₅₀ )aliphatic or (Ci-Cio)alicyclic. In yet more specific embodiments, Ri and R ₂ are each independently selected from (Ci-C ₂₅ )alkyl or (Ci-Cio)cycloalkyl.

[0086] Specific examples of a compound of structural formula (I) include the compounds listed in Table 7. In a particular embodiment, a polyamine transport inhibitor described herein (e.g., a compound of structural formula I) is AMXT 1501, or a protonated form thereof.

Combinations With DFMO

[0087] The combination of AMXT 1501 and DFMO has promise as a broadly-applicable, anti-cancer therapy for solid tumors. Together, the two agents target cancer cells’ polyamine metabolic pathway, an approach that has been shown to suppress tumor growth in both a poly amine- and a T-cell-dependent manner. DFMO inhibits the rate-limiting poly amine biosynthesis enzyme, ornithine decarboxylase (ODC). AMXT 1501 acts as a potent blocker of poly amine uptake into cancer cells. The combination of AMXT 1501 and DFMO produces a marked reduction in the tumor burden in multiple murine nonclinical models, including children’s cancers, neuroblastoma and diffuse intrinsic pontine glioma (DIPG).

Pharmacological benefits of the combination of AMXT 1501 and DFMO include reduction of solid tumor growth, and induction of an adaptive immune reactivity to primary tumors and their metastases, which suggests that the combination will produce a sustained affect against cancer in human patients. DFMO has the following structure:

[0088] In addition to AMXT 1501, other polyamine or polybasic drugs, especially those targeting the polyamine metabolic pathway, can be combined with DFMO to form ionic salt pairings. For example, treatment with DFMO has been shown to lead to greatly increased uptake of MGBG, a potent inhibitor of S-adenosylmethionine decarboxylase, by cancer cells. This observation led to clinical testing of DFMO and MGBG in combination for cancer therapy. Therefore, combination inhibition of the polyamine precursor-generating enzymes targeted by DFMO and MGBG, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC), respectively, is clinically desirable for oncology therapy.

[0089] DENSPM, and other diethyl polyamine analogs have been shown to induce the polyamine degradation enzyme spermidine/spermine bE-acetyltransferase (SSAT) in cancer cells. Induction of this polyamine degradation enzyme, together with inhibition of the polyamine producing enzyme, ODC, could also have usefulness for oncology therapy.

[0090] Accordingly, provided herein are combinations (e.g., pharmaceutical combinations) comprising difluoromethylomithine (DFMO), or an ionic form thereof, and a polyamine transport inhibitor (e.g., a compound of structural formula (I)), or a protonated form thereof.

[0091] Also provided herein are solid forms (e.g., crystalline solid forms, such as cocrystals or crystalline salts; amorphous solid forms) comprising DFMO, or an ionic form thereof, and a polyamine transport inhibitor (e.g., a compound of structural formula (I)), or a protonated form thereof. In some embodiments, the solid form is a crystalline solid form. In some embodiments, the crystalline form is characterized by an x-ray diffraction pattern substantially in accordance with that depicted in FIG. 5 or one of those depicted in FIG. 11. [0092] In some embodiments, the crystalline form is characterized by an x-ray powder diffraction pattern comprising peaks at two theta angles of 15.2, 19.2 and 19.6. In more specific embodiments, the x-ray powder diffraction further comprises at least one (e.g., one, at least two, two, at least three, three, at least four, four, at least five, five, at least six, six, at least seven, seven, eight) peak at a two theta angle selected from 9.8, 12.8, 14.3, 16.4, 21.2, 22.9, 23.5 or 25.0. [0093] In some embodiments, the crystalline form is characterized by an x-ray powder diffraction pattern comprising peaks at two theta angles of 18.9 and 19.0, and further comprising at least one (e.g., one, at least two, two, at least three, three, at least four, four, at least five, five, six) peak at a two theta angle selected from 9.8, 12.8, 14.3, 21.2, 22.9 or 23.5. [0094] In some embodiments, the crystalline form is characterized by an x-ray powder diffraction pattern comprising peaks at two theta angles of 9.8 and 14.3, and further comprising at least one (e.g., one, at least two, two, three) peak at a two theta angle of 16.4, 23.5 or 25.0. In more specific embodiments, the x-ray powder diffraction further comprises at least one (e.g., one, at least two, two, at least three, three, at least four, four, at least five, five, six) peak at a two theta angle selected from 12.8, 16.4, 21.2, 22.9, 23.5 or 25.0.

[0095] Also provided herein is a co-crystal comprising DFMO, or a salt thereof (e.g., a pharmaceutically acceptable salt thereof), and a polyamine transport inhibitor (e.g., a compound of structural formula (I)), or a salt thereof (e.g., a pharmaceutically acceptable salt thereof). In some embodiments, the co-crystal further comprises a coformer, such as HC1 and/or water.

[0096] Also provided herein is a salt e.g., a pharmaceutically acceptable salt) comprising DFMO, or an ionic (e.g., deprotonated) form thereof, and a polyamine transport inhibitor (e.g, a compound of structural formula (I)), or a protonated form thereof. In some embodiments, the salt comprises an ionic (e.g., deprotonated) form of DFMO and a protonated (e.g. , monoprotonated, diprotonated, triprotonated, tetraprotonated) form of the polyamine transport inhibitor.

[0097] It will be understood that DFMO, by virtue of its structure, may exist in anionic form, cationic form or zwitterionic form. Without wishing to be bound by any particular theory, it is believed that when DFMO forms a salt with a polyamine transport inhibitor in accordance with the present disclosure, the carboxylic acid of DFMO is deprotonated and the resulting carboxylate interacts ionically with a corresponding cation of the polyamine transport inhibitor (e.g., a protonated amine of AMXT 1501). In such salts, one or both of the amino groups of DFMO may also be protonated, and the resulting substituted ammonium group(s) may interact ionically with a corresponding anion(s), such as Cl".

[0098] It will also be understood that the ratio of DFMO, or an ionic form thereof, to a polyamine transport inhibitor, or a protonated form thereof, in the combinations of the disclosure can vary. For example, a salt described herein may comprise a single molecule of a protonated form of a polyamine transport inhibitor and one or more than one (e.g. , two, three, four) molecules of an ionic form of DFMO, such that, for example, two molecules of the DFMO may each be complexed with a single molecule of the polyamine transport inhibitor. The molar ratio of DFMO, or an ionic form thereof, to the polyamine transport inhibitor, or a protonated form thereof, in any of the combinations of the disclosure (e.g., cocrystal, salt) or compositions described herein can be from about one to one (1 : 1) to about 25 to one (25:1), e.g., from about one to one (1 : 1) to about 10 to one (10: 1), about two to one (2:1), about three to one (3: 1), about four to one (4: 1), about five to one (5:1), about six to one (6: 1), about seven to one (7: 1), about eight to one (8:1), about nine to one (9 : 1 ) or about ten to one (10: 1). In some embodiments, the molar ratio of DFMO, or an ionic form thereof, to the polyamine transport inhibitor, or a protonated form thereof, in any of the combinations of the disclosure (e.g., co-crystal, salt) or compositions described herein is from about 1 : 1 to about 10:1. In more specific embodiments, the molar ratio of DFMO, or an ionic form thereof, to the poly amine transport inhibitor, or a protonated form thereof, in any of the combinations of the disclosure (e.g., co-crystal, salt) or compositions described herein is about 8:1. In other embodiments, the molar ratio of DFMO, or an ionic form thereof, to the polyamine transport inhibitor, or a protonated form thereof, in any of the combinations of the disclosure (e.g., co-crystal, salt) or compositions described herein is about 4:1. In yet other embodiments, the molar ratio of DFMO, or an ionic form thereof, to the polyamine transport inhibitor, or a protonated form thereof, in any of the combinations of the disclosure (e.g., cocrystal, salt) or compositions described herein is about 3: 1. In yet other embodiments, the molar ratio of DFMO, or an ionic form thereof, to the polyamine transport inhibitor, or a protonated form thereof, in any of the combinations of the disclosure (e.g., co-crystal, salt) or compositions described herein is about 2: 1.

[0099] In addition, a combination of the disclosure (e.g., co-crystal, salt) may further comprise one or more additional molecules. For example, the combination may further comprise a conformer, such as a salt, or one or more additional ionic species. For example, a salt comprising an ionic form of DFMO complexed with a protonated form of a polyamine transport inhibitor as described above, may further comprise an additional ionic species (e.g., anionic species) complexed with DFMO, e.g., Cl".

[00100] Thus, in some embodiments, a salt further comprises an anion or cation of any of the pharmaceutically acceptable acids and bases identified herein as useful to form pharmaceutically acceptable salts, particularly those which have a pK _a difference of greater than or equal 2 compared to DFMO and/or the poly amine transport inhibitor in the salt. The salt may also or alternatively further be a solvate and/or hydrate, in which case one or more solvent and/or water molecules are also or alternatively, respectively, complexed to the salt. [00101] In some embodiments, a co-crystal further comprises a coformer, such as a pharmaceutically acceptable acid or base identified herein as useful to form pharmaceutically acceptable salts, particularly those acids and bases having a pK _a difference of less than 2 and, preferably of less than 1, compared to DFMO and/or the polyamine transport inhibitor in the co-crystal. In some embodiments, the coformer includes hydrochloric acid and/or water. [00102] In general, when preparing the combinations, the polyamine transport inhibitor may be provided in free base form or as a salt which includes one or more anions. Likewise, DFMO may be provided in a form wherein the carboxylate is protonated or as the carboxylate, which includes a cation. By virtue of the structure of DFMO the cation could be the substituted ammonium group of another molecule of DFMO. Alternatively, the cation could be a different cation. The salt form of the polyamine transport inhibitor may be referred to as an acid addition salt of the polyamine, while the salt form of the carboxylate may be referred to as a base addition salt of the carboxylic acid. These salts may be prepared by methods known in the art and disclosed herein.

[00103] In one process for preparing combinations of the disclosure, the combination of polyamine transport inhibitor and DFMO does not include any additional anions or cations. Such a combination may be prepared by combining the free base form of the polyamine transport inhibitor with the free acid form of DFMO. Thus, a convenient process for preparing a combination of the present disclosure is to combine a polyamine transport inhibitor in free base form with DFMO in free acid form in a solvent under proton transfer conditions to form, e.g., a salt of a positively charged polyamine transport inhibitor and a negatively charged carboxylate of DFMO. The salt can then be separated (e.g., isolated) from the solvent.

[00104] Thus, the present disclosure provides a method of making a combination of the disclosure, comprising: combining a polyamine transport inhibitor, or a salt thereof, and DFMO, or a salt thereof, in a solvent (e.g., a solvent that allows for proton transfer) to provide a mixture. In some embodiments, the method further comprises isolating a solid from the mixture, wherein the solid comprises a combination of the disclosure (e.g, a salt described herein).

[00105] Optionally, the method may further comprise any one or more (e.g, any two, any three, any four) of the following. The polyamine transport inhibitor and the DFMO may be combined in relative amounts so as to provide the desired stoichiometry. For example, if a 1 : 1 molar stoichiometry of polyamine transport inhibitor:DFMO is desired, then equal, or approximately equal, molar amounts of polyamine and hydrophobic carboxylic acid are combined in the solvent. Thus, in one embodiment, about 1 mole, e.g., 0.9-1.1 moles, of DFMO are combined with each 1 mole of polyamine transport inhibitor. If a 1 :2 molar stoichiometry of polyamine transport inhibitor:DFMO is desired, then exactly or about 2 moles, e.g., 1.8-2.2 moles, of DFMO are combined with each 1 mole of polyamine transport inhibitor. If a 1 :4 molar stoichiometry of polyamine transport inhibitor:DFMO is desired, then exactly or about 4 moles, e.g., 3.6-4.4 moles, of DFMO are combined with each 1 mole of polyamine transport inhibitor.

[00106] In the case where it is desirable to facilitate salt formation in the methods of making described herein, the solvent should facilitate proton transfer amongst the species in the reaction mixture, e.g., between DFMO and the polyamine transport inhibitor. For example, the solvent may be a pure polar protic solvent or it may be a mixture of solvents comprising a polar protic solvent. A suitable polar protic solvent is water, e.g., a water selected from deionized water and distilled water. Another suitable polar protic solvent is a lower-chain alcohol, e.g., methanol or ethanol.

[00107] Preferably, the mixture is a solution. In such embodiments, the components may be combined in any order so as to form a solution. For example, the polyamine transport inhibitor and the DFMO may be added to the solvent so as to provide the solution. In one embodiment, the polyamine transport inhibitor is dissolved in the solvent, and then the DFMO is gradually added to the solution of solvent and polyamine transport inhibitor.

[00108] The process may be performed in a batch or a continuous mode. In a batch mode, a container receives the full charge of solvent, polyamine transport inhibitor and DFMO, and the combination is formed in the container. The polyamine transport inhibitor, DFMO and solvent may be combined so as to provide a solution. Typically, the polyamine transport inhibitor, DFMO and solvent are combined at a temperature within the range of 10-30 °C, although other temperatures may be used. In a continuous mode, continuous flow techniques can be used for the production and isolation of the combinations described. Use of available flow apparatus, wherein solutions of the polyamine transport inhibitor in free base form in a suitable solvent such as methanol, are mixed with a co-solvent in which the combination is not soluble, such as acetonitrile, in a flow cell apparatus, allow for continuous production of the insoluble, or soluble form of the combination. [00109] After the combination is formed, the solvent can be separated from the combination to provide a residue (e.g, a solid residue) that is, or includes, the combination. When the solvent is volatile, then it may be removed from the solution by a process such as evaporation or distillation, so as to isolate the residue from the solution. As another option, a co-solvent (an example being acetonitrile) may be added to the solution, whereupon a precipitate comes out of solution, and the resulting solution is referred to as the supernatant. The co-solvent may also be referred to as a non-solvent, since the combination is not soluble in the non-solvent. The precipitate, also referred to as a residue, may be separated from the supernatant, e.g, by decantation, so as to isolate the residue from the solvent(s). As yet another option, the solution may be chilled to a temperature such that the combination is no longer soluble in the solvent(s) and thus forms a residue in the form of a precipitate. As in the case when a co-solvent is used to form the precipitate, the supernatant may be separated from the residue so as to isolate the residue from the solvent(s). Once the residue is formed, it or a portion thereof may be combined with additional components as described herein so as to form a pharmaceutical composition suitable for administration to a subject, e.g., by ingestion. Those additional components may include diluents, e.g., lactose and microcrystalline cellulose, disintegrants, e.g., sodium starch glycolate and croscarmellose sodium, binders, e.g., PVP and HPMC, lubricants, e.g,. magnesium stearate, and glidants, e.g., colloidal SiO ₂ . For example, a method described herein may further comprise formulating a combination into a composition (e.g., pharmaceutical composition), e.g., by forming a solid dosage form selected from a pill, a tablet, a capsule, a lozenge, a caplet, and a pastille, from the residue or a portion thereof. The combination so formulated may be in sterile form, so as to be used in the manufacture of a pharmaceutical agent.

[00110] As mentioned above, a protonated form of a polyamine transport inhibitor, such as a salt of a polyamine transport inhibitor, and/or an ionic form of DFMO may alternatively be used to prepare a combination of the disclosure.

[00111] An acid addition salt of a polyamine transport inhibitor may be formed by bringing the polyamine transport inhibitor into contact with a suitable inorganic or organic acid under conditions known to the skilled person. An acid addition salt may, for example, be formed using an inorganic acid. Suitable inorganic acids may be selected from the group consisting of hydrochloric acid, hydrobromic acid, sulphuric acid and phosphoric acid. An acid addition salt may also be formed using an organic acid. Suitable organic acids may be selected from the group consisting of trifluoroacetic acid, citric acid, maleic acid, oxalic acid, acetic acid, formic acid, benzoic acid, fumaric acid, succinic acid, tartaric acid, lactic acid, pyruvic acid, methanesulfonic acid, benzenesulfonic acid and paratoluenesulfonic acid. [00112] A base addition salt of a carboxylic acid (e.g., of DFMO) may be formed by bringing the carboxylic acid into contact with a suitable inorganic or organic base under conditions known to the skilled person. Suitable inorganic bases which form suitable base addition salts include the hydroxide form of any of lithium, sodium, potassium, calcium, magnesium or barium. Suitable organic bases which form suitable base addition salts include aliphatic, alicyclic or aromatic organic amines such as methylamine, trimethylamine and picoline, alkylammonias and ammonia.

Pharmaceutical Compositions

[00113] A combination of the disclosure can be administered to a subject in pure or substantially pure form (e.g., not in admixture with another solid or liquid). Typically, for administration to a subject, a combination of the disclosure is formulated with one or more pharmaceutically acceptable excipients. Thus, one embodiment is a composition (e.g., pharmaceutical composition) comprising a combination of the disclosure and a pharmaceutically acceptable excipient. The compositions described herein can be used in the methods described herein, e.g., to supply a combination of the disclosure for administration to a subject.

[00114] The compositions described herein may be formulated for administration by oral, parenteral (e.g., intramuscular, intraperitoneal, intravenous, intracerebroventricular, intraci sternal injection or infusion, subcutaneous injection, or implant), inhalation spray, nasal, vaginal, rectal, sublingual, or topical routes of administration. In preferred embodiments, the compositions described herein are formulation for oral administration.

[00115] The compositions described herein may be formulated into suitable dosage forms (e.g., unit dosage forms), e.g., containing pharmaceutically acceptable excipient(s) appropriate for the intended route of administration. Accordingly, some embodiments provide a dosage form (e.g., unit dosage form) comprising a composition described herein. [00116] Compositions described herein can be prepared by any of the methods well known in the art of pharmacy. For example, some methods include the step of bringing the active ingredient(s), e.g., a combination of the disclosure, into association with a pharmaceutically acceptable excipient(s). In general, compositions are prepared by uniformly and intimately bringing a combination of the disclosure into association with a liquid carrier or a finely divided solid carrier or both, and then, if necessary, shaping the product into the desired formulation. In the composition, the combination is included in an amount sufficient to produce the desired effect upon the process or condition of disease. For example, in some embodiments, the concentration of the combination in the composition is from about 0.001% to about 99%, from about 0.01% to about 98%, from about 0.1% to about 95%, from about 0.1% to about 50%, from about 0.1% to about 25%, from about 0.2% to about 20%, or from about 1% to about 10% w/w, w/v or v/v (e.g., w/w).

[00117] In one embodiment, the composition (e.g., pharmaceutical composition) is a solid dosage form, e.g., intended for oral use. For many reasons, an oral composition, and particularly a solid oral dosage form, is advantageous and convenient for both the patient and the medical practitioner responsible for developing the therapeutic regime. An oral composition avoids the complications, cost and inconvenience of administration via IV injection or infusion which must be done by a medical professional in a hospital or outpatient setting which exposes him or her to hospital-based infections and illnesses. In particular, patients undergoing treatment for cancer may be immunocompromised individuals and particularly susceptible to hospital-based infections and illnesses. An oral formulation, such as a pill or tablet, may be taken outside of a hospital setting, increasing the potential for subject ease of use and compliance. This permits a subject to avoid infection risks concomitant with IV administration and hospital visits. In addition, oral delivery may avoid the high concentration peak and rapid clearance associated with an IV bolus dose.

[00118] Examples of oral solid dosage forms include pills, tablets, capsules, granules, and microspheres, any of which may include an enteric coating to protect the composition from acid degradation by stomach environment, or to maximize delivery to intestinal sections where absorption may be enhanced. The solid dosage form may be chewable or swallowable, or have any suitable ingestible form. In one embodiment, the solid dosage form contains little or no water, e.g., less than 0.1 weight percent water, less than 0.2 weight percent water, less than 0.3 weight percent water, less than 0.4 weight percent water, less than 0.5 weight percent water, less than 1 weight percent water, less than 1.5 weight percent water, less than 2 weight percent water or less than 5 weight percent water.

[00119] For oral administration, the compositions are preferably provided in a solid dosage form, such as the form of pills, capsules, tablets and the like, containing from about 1 milligram to about 5,000 milligrams, for example, from about 1 milligram to about 2,500 milligrams, from about 1 milligram to about 1,000 milligrams, from about 50 milligrams to about 500 milligrams or from about 50 milligrams to about 350 milligrams, particularly about: 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, 300, 400, 500, 600, 750, 800, 900, or 1,000 milligrams, of active ingredient(s) (e.g., a combination of the disclosure).

[00120] In one embodiment, a solid dosage form contains about: 10 mg, or 20 mg, or 30 mg, or 40 mg, or 50 mg, or 60 mg, or 70 mg, or 80 mg, or 90 mg, or 100 mg, or 110 mg, or 120 mg, or 130 mg, or 140 mg, or 150 mg, or 200 mg, or 250 mg, or 300 mg, or 350 mg, or 400 mg, or 450 mg, or 500 mg, of a polyamine transport inhibitor, where that polyamine transport inhibitor will, however, be present in the solid dosage form in combination with DFMO. The amount of the polyamine transport inhibitor present in a solid dosage form may also be characterized in terms of a range of possible amounts, where lower and upper limits of the range are selected from the amounts just described, e.g., from about 10 mg to about 500 mg, or numbers in between, e.g., from about 50 to about 350 mg. A tablet or pill will typically have a total weight of at least 50 mg.

[00121] In one embodiment, the solid dosage form provides a therapeutically effective systemic plasma level of a polyamine transport inhibitor and/or DFMO for a period of at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 30, 36, or 48 hours. In further embodiments, the solid dosage form provides a therapeutically effective systemic plasma level of a polyamine transport inhibitor and/or DFMO for at least an 8-hour period. In further embodiments, the solid dosage form provides a therapeutically effective systemic plasma level of a polyamine transport inhibitor and/or DFMO for at least a 14-hour period. In further embodiments, the solid dosage form provides a therapeutically effective systemic plasma level of a polyamine transport inhibitor and/or DFMO for at least an 18-hour period. In further embodiments, the solid dosage form provides a therapeutically effective systemic plasma level of a polyamine transport inhibitor and/or DFMO for at least a 24-hour period. [00122] In one embodiment, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 25, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent of the peak plasma concentration for at least 4 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 75% of the peak plasma concentration for at least 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, or 24 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 75% of the peak plasma concentration for at least 4 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 75% of the peak plasma concentration for at least 6 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 75% of the peak plasma concentration for at least 10 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 50% of the peak plasma concentration for at least 6 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 50% of the peak plasma concentration for at least 12 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 50% of the peak plasma concentration for at least 18 hours. In certain embodiments, a solid dosage form provides a plasma level of a polyamine transport inhibitor and/or DFMO of at least 25% of the peak plasma concentration for at least 18 hours. In some embodiments, the peak plasma concentration is a therapeutically effective concentration. In further embodiments, the percentage of peak plasma concentration is therapeutically effective over the given time period.

[00123] Solid dosage forms may be prepared according to any method known to the art for the manufacture of such. Such compositions may contain one or more inert components, where exemplary inert components may be selected from the group of sweetening agents, flavoring agents, coloring agents and preserving agents.

[00124] Excipients for solid dosage forms are well known in the art, and are selected to provide various benefits including, for example, ease of administration to the subject, improved dosing compliance, consistency and control of drug bioavailability, assistance with enhanced bioavailability, improved API stability including protection from degradation, and to contribute to the ease of production of a robust and reproducible physical product. Excipients are commonly subdivided into various functional classifications, depending on the role that they are intended to play in the formulation. For solid dosage forms, common excipient roles and exemplary materials that fulfill that role are diluents, e.g., lactose and microcrystalline cellulose, disintegrants, e.g., sodium starch glycolate and croscarmellose sodium, binders, e.g., PVP and HPMC, lubricants, e.g., magnesium stearate, and glidants, e.g., colloidal SiO ₂ . Tablets and capsules often contain a diluent, filler and/or bulking agent, e.g., lactose. Excipients used to formulate the combinations described herein should typically avoid those containing reducing sugar components in order to prevent formation of Schiff- base addition products as degradants.

[00125] Excipients may be, for example, inert diluents, such as calcium carbonate, sodium carbonate, and lactose; granulating and disintegrating agents, such as com starch and alginic acid; binding agents, such as starch, gelatin or acacia; and lubricating agents, such as magnesium stearate, stearic acid and talc.

[00126] Tablets may be uncoated or they may be coated, e.g., with an enteric coating, by known techniques, in order to delay disintegration and absorption in the gastrointestinal tract and thereby provide a sustained action over a longer period. Compositions for oral use may also be formed as hard gelatin capsules wherein the combination described herein is mixed with an inert solid diluent, for example, calcium carbonate, or kaolin, or as soft gelatin capsules wherein the combination is mixed with water or an oil medium, for example, peanut oil, liquid paraffin, or olive oil.

[00127] Compositions described herein can also be in the form of aqueous suspensions, e.g., where a combination of the disclosure is in admixture with one or more excipients suitable for the manufacture of aqueous suspensions. Oily suspensions may be formulated by suspending the active ingredient in a suitable oil. Oil-in-water emulsions may also be employed. Dispersible powders and granules suitable for preparation of an aqueous suspension by the addition of water may also be used to provide a combination described herein in admixture with a dispersing or wetting agent, suspending agent and one or more preservatives.

[00128] Pharmaceutical compositions may be in the form of a sterile injectable aqueous or oleaginous suspension or a suppository for rectal administration. For topical use, creams, ointments, jellies, solutions or suspensions, etc., containing a combination described herein may be employed. Compositions may also be formulated for administration by inhalation or a transdermal patch by methods known in the art.

[00129] In some embodiments, a composition may further comprise one or more additional therapeutically active compounds, e.g., which are beneficially applied in the treatment of a disease, disorder or condition, such as cancer, experienced or potentially experienced by a subject receiving a combination of the disclosure.

[00130] As mentioned above, a composition may be formulated as a tablet, capsule or the like. For example, in one embodiment, a composition comprises from about 0.1% to about 50% of a combination of the disclosure; from about 0.1% to about 99.9% of a filler; from about 0% to about 10% of a disintegrant; from about 0% to about 5% of a lubricant; and from about 0% to about 5% of a glidant. For example, in one embodiment, a composition comprises from about 0.1% to about 50% of a combination of the disclosure; from about 0.1% to about 99.9% of a filler; from about 0% to about 10% of a disintegrant; from about 0% to about 5% of a lubricant; and from about 0% to about 5% of a glidant. Optionally, a composition (e.g., in unit dosage form) comprises from about 10 mg to about 300 mg of a polyamine transport inhibitor such as AMXT 1501, or a protonated form thereof, making up from about 2% to about 50% of the tablet content or capsule fill content, for example; from about 0% to about 10% of a disintegrant; from about 0% to about 5% of a lubricant; from about 0% to about 5% of a glidant; and from about 30% to about 98% of a filler. In another embodiment, a composition comprises a combination of the disclosure, from about 0.1% to about 10% of a binder, from about 0% to about 5% of a surfactant, from about 0% to about 10% of an intergranular disintegrant, and from about 0% to about 10% of an extragranular disintegrant.

[00131] Examples of binders, fillers, surfactants, disintegrants, lubricants, intergranular disintegrants, extragranular disintegrants and glidants are known in the art, and examples are disclosed herein, and include, a binder selected from copolyvidone, hydroxypropylcellulose, hydroxypropylmethylcellulose, and povidone; a filler selected from a sugar, a starch, a cellulose, and a poloxamer; a surfactant selected from polyoxyethylene sorbitan monooleate, a poloxamer, and sodium lauryl sulfate; an intergranular disintegrant selected from croscarmellose sodium, sodium starch glyconate, and crospovidone. Other examples include a disintegrant selected from povidone and crospovidone; a lubricant which is magnesium stearate; and a glidant which is silicon dioxide.

[00132] It may be advantageous to tune the drug ratio in the compositions described herein (e.g., comprising a co-crystal or salt comprising DFMO, or an ionic form thereof, and a compound of structural formula (I), such as AMXT 1501, or a protonated form thereof), e.g., by adding DFMO, or a pharmaceutically acceptable salt thereof, or AMXT 1501, or a pharmaceutically acceptable salt thereof. For example, MYC and RAS oncogenes are known to induce the polyamine metabolic pathway. The increased polyamine levels in tumors expressing MYC and RAS oncogenes are known to induce higher proliferative ability of the underlying tumor cells and provide the cells with a mechanism for immune system evasion. Thus, in some embodiments, a pharmaceutical composition described herein comprises a cocrystal or salt comprising DFMO, or an ionic form thereof, and a compound of structural formula (I), such as AMXT 1501, or a protonated form thereof, and further comprises DFMO, or a pharmaceutically acceptable salt thereof and/or a compound of structural formula (I), such as AMXT 1501, or a pharmaceutically acceptable salt thereof. [00133] Kits can also be used to provide tuning of the drug ratio in accordance with the present disclosure. In some embodiments, a kit comprises a combination of the disclosure and a separate composition comprising DFMO, or a pharmaceutically acceptable salt thereof. In some embodiments, a kit comprises a combination of the disclosure and a separate composition comprising a polyamine transport inhibitor (e.g., the same polyamine transport inhibitor provided in the combination in the kit, such as AMXT 1501 dicaprate), or a pharmaceutically acceptable salt thereof. In some embodiments, a kit comprises a combination of the disclosure and a separate composition comprising a polyamine transport inhibitor (e.g., the same polyamine transport inhibitor provided in the combination in the kit, such as AMXT 1501 dicaprate), or a pharmaceutically acceptable salt thereof, and a further separate composition comprising DFMO, or a pharmaceutically acceptable salt thereof.

Written instructions for administering the combination to a subject to treat a disease, disorder or condition described herein, such as cancer, can also be provided in a kit. In some embodiments, a kit comprises a combination of the disclosure and written instructions for administering the combination to a subject to treat a disease, disorder or condition described herein, such as cancer.

[00134] Preferably, the compositions provided herein do not have substantially doselimiting side effects, e.g., gastrointestinal side effects such as nausea, vomiting, diarrhea, abdominal pain, oral mucositis, oral ulceration, pharyngitis, stomatitis, and gastrointestinal ulceration.

Therapeutic Uses

[00135] Provided herein is a method of treating cancer in a subject (e.g., a subject in need thereof), comprising administering to the subject a therapeutically effective amount of a combination of the disclosure (e.g., a solid form and/or salt described herein) or a composition described herein comprising a combination of the disclosure.

[00136] A variety of cancers are amenable to treatment in accordance with the present disclosure. In some embodiments, the cancer comprises a solid tumor. In some embodiments, the cancer is a solid tumor cancer. In some embodiments, the cancer is a hematological cancer, e.g., a leukemia, lymphoma or myeloma. The cancer may be, for example, breast cancer, prostate cancer, colon cancer or lung cancer. Other cancers that may be treated by appropriate selection of the polyamine transport inhibitor include neuroblastoma, pancreatic, bladder, melanoma, skin cancer, non-Hodgkin lymphoma, kidney cancer, head and neck cancers including glioblastoma, leukemia and other blood cancers, ovarian and thyroid cancers. The cancer may be treated by polyamine transport inhibitors that are specific for oncogenes, e.g., MYC- and/or RAS-derived tumors.

[00137] Other cancers amenable to treatment in accordance with the present disclosure include Acute Lymphoblastic Leukemia (ALL); Acute Myeloid Leukemia (AML); Adrenocortical Carcinoma; Adrenocortical Carcinoma, Childhood; AIDS-Related Cancer (e.g., Kaposi Sarcoma, AIDS-Related Lymphoma, Primary CNS Lymphoma); Anal Cancer; Appendix Cancer; Astrocytomas, Childhood; Atypical Teratoid/Rhabdoid Tumor, Childhood, Central Nervous System; Basal Cell Carcinoma of the Skin; Bile Duct Cancer; Bladder Cancer; Bladder Cancer, Childhood; Bone Cancer (including Ewing Sarcoma, Osteosarcoma and Malignant Fibrous Histiocytoma); Brain Tumors/Cancer; Breast Cancer; Burkitt Lymphoma; Carcinoid Tumor (Gastrointestinal); Carcinoid Tumor, Childhood; Cardiac (Heart) Tumors, Childhood; Embryonal Tumors, Childhood; Germ Cell Tumor, Childhood; Primary CNS Lymphoma; Cervical Cancer; Childhood Cervical Cancer;

Cholangiocarcinoma; Chordoma, Childhood; Chronic Lymphocytic Leukemia (CLL); Chronic Myelogenous Leukemia (CML); Chronic Myeloproliferative Neoplasms; Colorectal Cancer; Childhood Colorectal Cancer; Craniopharyngioma, Childhood; Cutaneous T-Cell Lymphoma (e.g., Mycosis Fungoides and Sezary Syndrome); Ductal Carcinoma In Situ (DCIS); Embryonal Tumors, Central Nervous System, Childhood; Endometrial Cancer (Uterine Cancer); Ependymoma, Childhood; Esophageal Cancer; Childhood Esophageal Cancer; Esthesioneuroblastoma; Ewing Sarcoma; Extracranial Germ Cell Tumor, Childhood; Extragonadal Germ Cell Tumor; Eye Cancer; Childhood Intraocular Melanoma; Intraocular Melanoma; Retinoblastoma; Fallopian Tube Cancer; Fibrous Histiocytoma of Bone, Malignant, and Osteosarcoma; Gallbladder Cancer; Gastric (Stomach) Cancer; Childhood Gastric (Stomach) Cancer; Gastrointestinal Carcinoid Tumor; Gastrointestinal Stromal Tumors (GIST); Childhood Gastrointestinal Stromal Tumors; Germ Cell Tumors; Childhood Central Nervous System Germ Cell Tumors (e.g, Childhood Extracranial Germ Cell Tumors, Extragonadal Germ Cell Tumors, Ovarian Germ Cell Tumors, Testicular Cancer);

Gestational Trophoblastic Disease; Hairy Cell Leukemia; Head and Neck Cancer; Heart Tumors, Childhood; Hepatocellular (Liver) Cancer; Histiocytosis, Langerhans Cell; Hodgkin Lymphoma; Hypopharyngeal Cancer; Intraocular Melanoma; Childhood Intraocular Melanoma; Islet Cell Tumors, Pancreatic Neuroendocrine Tumors; Kaposi Sarcoma; Kidney (Renal Cell) Cancer; Langerhans Cell Histiocytosis; Laryngeal Cancer; Leukemia; Lip and Oral Cavity Cancer; Liver Cancer; Lung Cancer (Non-Small Cell and Small Cell); Childhood Lung Cancer; Lymphoma; Male Breast Cancer; Malignant Fibrous Histiocytoma of Bone and Osteosarcoma; Melanoma; Childhood Melanoma; Melanoma, Intraocular (Eye); Childhood Intraocular Melanoma; Merkel Cell Carcinoma; Mesothelioma, Malignant; Childhood Mesothelioma; Metastatic Cancer; Metastatic Squamous Neck Cancer with Occult Primary; Midline Tract Carcinoma With NUT Gene Changes; Mouth Cancer; Multiple Endocrine Neoplasia Syndromes; Multiple Myeloma/Plasma Cell Neoplasms; Mycosis Fungoides; Myelodysplastic Syndromes, Myelodysplastic/Myeloproliferative Neoplasms; Myelogenous Leukemia, Chronic (CML); Myeloid Leukemia, Acute (AML); Myeloproliferative Neoplasms, Chronic; Nasal Cavity and Paranasal Sinus Cancer; Nasopharyngeal Cancer; Neuroblastoma; Non-Hodgkin Lymphoma; Non-Small Cell Lung Cancer; Oral Cancer, Lip and Oral Cavity Cancer and Oropharyngeal Cancer; Osteosarcoma and Malignant Fibrous Histiocytoma of Bone; Ovarian Cancer; Childhood Ovarian Cancer; Pancreatic Cancer; Childhood Pancreatic Cancer; Pancreatic Neuroendocrine Tumors; Papillomatosis (Childhood Laryngeal); Paraganglioma; Childhood Paraganglioma; Paranasal Sinus and Nasal Cavity Cancer; Parathyroid Cancer; Penile Cancer; Pharyngeal Cancer; Pheochromocytoma; Childhood Pheochromocytoma; Pituitary Tumor; Plasma Cell Neopl asm/Mul tipi e Myeloma; Pleuropulmonary Blastoma; Pregnancy and Breast Cancer; Primary Central Nervous System (CNS) Lymphoma; Primary Peritoneal Cancer; Prostate Cancer; Rectal Cancer; Recurrent Cancer; Renal Cell (Kidney) Cancer; Retinoblastoma; Rhabdomyosarcoma, Childhood; Salivary Gland Cancer; Sarcoma (e.g., Childhood Rhabdomyosarcoma, Childhood Vascular Tumors, Ewing Sarcoma, Kaposi Sarcoma, Osteosarcoma (Bone Cancer), Soft Tissue Sarcoma, Uterine Sarcoma); Sezary Syndrome; Skin Cancer; Childhood Skin Cancer; Small Cell Lung Cancer; Small Intestine Cancer; Soft Tissue Sarcoma; Squamous Cell Carcinoma of the Skin; Squamous Neck Cancer with Occult Primary, Metastatic; Stomach (Gastric) Cancer; Childhood Stomach (Gastric) Cancer; T-Cell Lymphoma, Cutaneous (e.g., Mycosis Fungoides and Sezary Syndrome); Testicular Cancer; Childhood Testicular Cancer; Throat Cancer (e.g., Nasopharyngeal Cancer, Oropharyngeal Cancer, Hypopharyngeal Cancer); Thymoma and Thymic Carcinoma; Thyroid Cancer; Transitional Cell Cancer of the Renal Pelvis and Ureter; Ureter and Renal Pelvis, Transitional Cell Cancer; Urethral Cancer; Uterine Cancer, Endometrial; Uterine Sarcoma; Vaginal Cancer; Childhood Vaginal Cancer; Vascular Tumors; Vulvar Cancer; and Wilms Tumor and Other Childhood Kidney Tumors. [00138] Metastases of the aforementioned cancers can also be treated in accordance with the methods described herein. In some embodiments, the cancer is a metastatic cancer. [00139] In some embodiments, the cancer is a pediatric cancer. “Pediatric cancer” typically refers to cancer that occurs between birth and fourteen years of age.

[00140] In general, there is a myriad of therapeutic uses for the combinations of the disclosure in addition to use as an anti-cancer treatment. For example, polyamine transport inhibitors have been described to have antibiotic, antiviral, anti-inflammatory, anti-sepsis, anti-pain, anti-psychotic, anti-aging, and anti-heart damage activities, among others. Accordingly, also provided herein are methods of treating a disease, disorder or condition in a subject in need thereof, comprising administering to the subject a therapeutically effective amount of a combination of the disclosure (e.g., a solid form and/or salt described herein) or a composition described herein comprising a combination of the disclosure, wherein the disease, disorder or condition would benefit from treatment with an agent having antibiotic, antiviral, anti-inflammatory, anti-sepsis, anti-pain, anti-psychotic, anti-aging and anti-heart damage activity.

[00141] As described above, it may be advantageous to tune the drug ratio in accordance with the present disclosure. This can be done, e.g., by adding DFMO, or a pharmaceutically acceptable salt thereof, and/or AMXT 1501, or a pharmaceutically acceptable salt thereof, to a composition described herein. It is also or alternatively possible to tune the drug ratio by administering additional polyamine transport inhibitor and/or DFMO, or a pharmaceutically acceptable salt of the foregoing, to a subject. When additional polyamine transport inhibitor and/or DFMO, or a pharmaceutically acceptable salt of the foregoing, is administered to the subject, the polyamine transport inhibitor and/or DFMO, or a pharmaceutically acceptable salt of the foregoing, can be administered before, after or concurrently with the combination of the disclosure or composition described herein. Further, the additional polyamine transport inhibitor and/or DFMO, or a pharmaceutically acceptable salt of the foregoing, can be administered with any frequency, by any route and in any amount described herein in connection with the combinations and compositions described herein. Further, when additional polyamine transport inhibitor, or a pharmaceutically acceptable salt thereof, and additional DFMO, or a pharmaceutically acceptable salt thereof, is administered to a subject, the polyamine transport inhibitor, or a pharmaceutically acceptable salt thereof, and DFMO, or a pharmaceutically acceptable salt thereof, can be administered before, after or concurrently with one another. [00142] Thus, in some embodiments, a method further comprises administering DFMO, or a pharmaceutically acceptable salt thereof (e.g., a therapeutically effective amount of DFMO, or a pharmaceutically acceptable salt thereof), to the subject. In some embodiments, a method further comprises administering a poly amine transport inhibitor, or a pharmaceutically acceptable salt thereof (e.g., AMXT 1501 dicaprate; a therapeutically effective amount of a polyamine transport inhibitor, or a pharmaceutically acceptable salt thereof, such as AMXT 1501 dicaprate), to the subject.

[00143] In some embodiments, a method further comprises administering to a subject one or more additional therapies (e.g., therapeutically active compounds), e.g., which are beneficially applied in the treatment of a disease, disorder or condition, such as cancer, experienced or potentially experienced by a subject receiving a combination described herein. When a combination of the disclosure is administered with one or more additional therapies, the combination can be administered before, after or concurrently with the other therapy(ies). When co-administered concurrently, the combination and additional therapeutically active agent(s) can be in separate formulations or the same formulation. Alternatively, the combination and additional therapeutically active agent(s) can be administered sequentially, either at approximately the same time or at different times, as separate compositions. When the combination of the disclosure and the other therapy are administered as separate formulations or compositions, the combination and the other therapy can be administered by the same route of administration or by different routes of administration. A skilled clinician can determine appropriate timing for administration of each therapy being used in combination (e.g., timing sufficient to allow an overlap of the pharmaceutical effects of the therapies).

[00144] The compositions described herein may be administered by oral, parenteral (e.g., intramuscular, intraperitoneal, intravenous, intracerebroventricular, intracistemal injection or infusion, subcutaneous injection, or implant), inhalation spray, nasal, vaginal, rectal, sublingual, or topical routes of administration. In preferred embodiments, the compositions described herein are administered orally.

[00145] In the treatment of cancer, the combinations of the disclosure and compositions described herein will be administered at an appropriate dosage level, typically, from about 0.01 mg to about 1,000 mg (e.g., from about 0.01 mg to about 500 mg) per kg patient body weight per day, which can be administered in single or multiple doses. Human dose levels, especially those used for cancer chemotherapy, are alternatively expressed in units of mg/m ² /day. The dose may be higher or lower at the discretion of the attending health care professional, based, for example, on that person’s experience and knowledge in dealing with the specific medical condition being treated and the condition of the subject. Optionally, the dosage level will be from about 0.1 to about 250 mg/kg per day; or from about 0.5 to about 100 mg/kg per day. A suitable dosage level may be from about 0.01 to about 250 mg/kg per day, from about 0.05 to about 100 mg/kg per day, from about 0.1 to about 100 mg/kg per day, or from about 0.1 to about 50 mg/kg per day. Within this range the dosage may be, for example, from about 0.05 to about 0.5, from about 0.5 to about 5, from about 1 to about 50, or from about 5 to about 50 mg/kg per day. For most large mammals, the total daily dosage will typically be from about 1 milligram to about 5,000 milligrams, or from about 1 milligram to about 2,500 milligrams, or from about 1 milligram to about 1,000 milligrams. For oral administration, the compositions are preferably provided in a solid form or any of the unit dosage forms described herein.

[00146] The combinations may be administered as a single daily dose or in divided doses two to six times per day, or in sustained release form. The combinations may be administered on a regimen of 1 to 4 times per day, preferably once or twice per day (e.g., QD or BID), e.g., at the discretion of the attending health care professional.

[00147] It will be understood, however, that the specific dose level and frequency of dosage for any particular subject may be varied and will depend upon a variety of factors including the activity of the specific combination employed, the metabolic stability and length of action of the components of the combination, the age, body weight, general health, sex, diet, mode and time of administration, rate of excretion, drug combination, the severity of the particular condition, and the subject undergoing therapy.

EXAMPLES

[00148] The Examples and preparations provided below further illustrate and exemplify the subject matter described herein. It is to be understood that the following Examples are not intended to limit the scope of the subject matter described herein in any way. In the following Examples, molecules with a single chiral center, unless otherwise noted, exist as a racemic mixture. Those molecules with two or more chiral centers, unless otherwise noted, can exist as a racemic mixture of diastereomers. Single enantiomers/diastereomers may be obtained by methods known to those skilled in the art. The starting materials and various reactants utilized or referenced in the Examples may be obtained from commercial sources, or are readily prepared from commercially available organic compounds, using methods well known to those skilled in the art.

Example 1: Oral AMXT 1501 dicaprate in combination with DFMO [00149] Aminex Therapeutics is developing oral AMXT 1501 dicaprate in combination with oral DFMO for treatment of cancer patients (clinicaltrials.gov NCT03536728). The objective of this clinical trial is to determine the safety and tolerability of oral AMXT 1501 dicaprate in combination with DFMO in patients with advanced solid tumors. Interim data for the pharmacokinetic (PK) behavior of both agents in human subjects has been generated. Both AMXT 1501 dicaprate and DFMO have high water solubility. Due to low bioavailability of AMXT 1501 dicaprate, this agent appears to belong to Biopharmaceutics Classification System (BCS) Class 3.

[00150] Clinical Trial Outline. Aminex’ s clinical trial evaluating the combination of AMXT 1501 dicaprate and DFMO consists of two parts. All solid tumor types are eligible for the trial. Part 1 of the clinical trial evaluated the safety of escalating doses of AMXT 1501 dicaprate, given alone, for two weeks to patients with cancer, then given in combination with a fixed low dose of DFMO for an additional two weeks. This was followed by a two-week recovery period, using a standard 3+3 AMXT 1501 dicaprate dose escalation design. In Part 2 of the clinical trial, the AMXT 1501 dicaprate dose is fixed at 1,800 mg (calculated as the free base content of AMXT 1501 dicaprate), and the DFMO dose will be escalated, following a 3+3 dose escalation protocol design, to determine the maximum tolerated dose (MTD) and recommended Phase 2 dose (RP2D) for the combination. An expansion cohort will be included at the RP2D level to confirm safety and tolerability of the combination. In this clinical trial, AMXT 1501 dicaprate was delivered to fasted patients orally, once daily in enteric-coated capsules. DFMO was delivered orally twice daily in gel capsules. Additional patients will be treated by giving both agents twice daily (BID dosing schedule).

[00151] Interim plasma AMXT 1501 and DFMO concentration versus nominal time data are available from Cohorts 1 through 5 of Part 1 of the clinical trial (corresponding to dose levels of 80, 160, 400, 1,200, and 1,800 mg AMXT 1501 alone or in combination with DFMO at 250 mg BID). Twenty-one patients have been dosed in Part 1. Based on the interim pharmacokinetic data from Part 1, mean AMXT 1501 exposure following single or repeat PO dosing increased in a dose-dependent manner at dose levels of 160 mg AMXT 1501 and higher. [00152] Interim AMXT 1501 and DFMO Clinical Pharmacokinetic (PK) Data. Plasma levels of AMXT 1501 and DFMO were determined using GLP validated LC/MS ² bioanalytical methods. Blood samples from patients were collected over the first three days after a single dose of AMXT 1501 dicaprate on Day 1 of the study, and over a 24-hour period on Day 14 of the study after repeat dosing of AMXT 1501 dicaprate according to the study design. FIGs. 1A and IB show the resulting AMXT 1501 mean plasma levels from the study. Twenty patients were treated with the 500 mg/day DFMO (split twice daily) from Day 15-28 of the study. DFMO plasma levels were measured at various times post-dosing on Day 28 of the study, and the resultant DFMO plasma concentrations were determined using a validated LC/MS ² bioanalytical assay. Resulting DFMO plasma levels versus time for all 20 patients post-dosing are shown in FIG. 2. All these patients were treated with same DFMO dose and showed an AUC (n = 14) average of 11,417 hr*ng/mL, SD 4,870, for a percent CV of 43%.

[00153] At the highest AMXT 1501 dose provided to patients (Part 1, Cohort 5: 1,800 mg AMXT 1501), an average C _max of 794.25 ng/mL (SD 208.6, for a percent CV of 26%) was observed for plasma AMXT 1501 concentration after repeat dosing (Day 14; n = 4 patients). Plasma levels of AMXT 1501 were sustained over the 24-hour dosing time increment. An average AUC value of 14,225 hr*ng/mL (SD 5,017 hr*ng/mL, for a percent CV of 35%) was observed for the four patients in Part 1, Cohort 5.

[00154] Multiple positive murine efficacy studies have dosed AMXT 1501 dicaprate at 2.5 mg/kg by daily subcutaneous injections. PK assessment of this same dose in 4T1 breast cancer syngeneic tumor-bearing mice showed AMXT 1501 plasma C _max values reached 978 ng/mL, with AUC values of 8,270 hr*ng/mL. Importantly, in this mouse study, tumor retention of AMXT 1501 was 14 times higher than plasma, with AUC values of 152,000 hr*ng/mL. Although not wishing to be bound by any particular theory, the difference between the plasma AUC value and the tumor AUC value in mice, suggests that plasma AMXT 1501 levels observed in the clinical trial are an underestimation of tumor target engagement. Patients in Cohort 5 had AUC values 1.72 times higher than plasma levels observed in multiple efficacious mouse studies.

[00155] For PK characterization, it is generally assumed that the C _max parameter, the maximal plasma level of drug, tracks toxicological endpoints, while the parameter of AUC, measuring sustained plasma drug concentrations, tracks efficacy endpoints. PK data obtained in patients in Part 1 of the trial suggest robust AMXT 1501 plasma coverage, as reflected by the AUC values. Furthermore, sustained, 24-hour plasma levels of AMXT 1501 were observed over the dosing time increment. Given the modest Grades 1 and 2 adverse effects observed in these patients, mainly gastrointestinal in nature (nausea and diarrhea), it is presumed that plasma C _max values below 1,000 ng/mL AMXT 1501 are well-tolerated. Importantly, in vitro EC50 values for AMXT 1501 against cancer cells are 50 nM, which is equivalent to a 28 ng/mL plasma concentration of AMXT 1501.

[00156] Clinical Drug Ratios. Table 1 depicts the various molar ratios of AMXT 1501 to DFMO anticipated during Part 2 of the clinical trial. The optimum ratio of each agent will depend, for example, on tumor target susceptibility, drug tumor distribution and retention and genetic background of the patient and the tumor. Given its goal of demonstration of tolerability and maximally-achievable dose of the two drug agents, Aminex’s initial clinical trial dosed patients with a fixed, unit dose level of each agent. It is expected drug dosing for future clinical trials will be performed on the more precise mg/m ² unit basis. Dosing based on m ² , also known as Body Surface Area (BSA), tends to be more precise, given it adjusts dose to patient BSA, and indirectly to patient body weight.

Table 1: AMXT 1501 - DFMO Drug ratios in Aminex NCT03536728 First-in-Human Clinical Trial.

Example 2: Production of AMXT 1501 crystalline salt(s) with DFMO [00157] Four molar equivalents of DFMO monohydrochloride monohydrate in 50%

EtOH/H ₂ O (6 mL) formed a homogeneous solution upon heating. To this solution was added a homogeneous solution of 1 equivalent of AMXT 1501 free base in absolute EtOH (3 mL; formed with gentle heating), to produce a homogeneous solution at a slightly warm temperature. Flakes began forming after standing at 10 minutes at room temperature. After placing in a freezer, a mass of crystals formed. Filtration gave 61% yield of white solid (Lot#4-138), presuming the tetra-DFMO salt had formed. TLC in CH ₂ Cl ₂ /MeOH/NH ₄ OH (60:38:2) showed this white solid contained both AMXT 1501 and DFMO. ^X H NMR likewise showed the solid contained both AMXT 1501 and DFMO (FIG. 3).

[00158] ¹ H Nuclear Magnetic Resonance. Using the ^X H NMR data from the AMXT 1501-DFMO crystal (Lot#4-138) shown in FIG. 3, the ratio of AMXT 1501 to DFMO was estimated. The CHF ₂ integration intensity at 6.2 ppm is not expected to be highly accurate due to the long T1 time for CHF ₂ . Nevertheless, since this signal is sufficiently isolated, an estimation can be made. Integration of the signal for the terminal lipid chain methyl group of AMXT 1501 (at 0.65 ppm) as 3 protons sets the molar equivalent of AMXT 1501 associated with the crystals to 1. Summation of the integration of the triplet signal due to the -CHF ₂ for DFMO provides an estimated 7.92 molar ratio of DFMO to AMXT 1501 in these crystals.

[00159] High Performance Liquid Chromatography. HPLC analysis with ELSD detection using a gradient method was used to determine the amount of AMXT 1501 and DFMO in samples of Lot#4-138. Table 2 describes HPLC conditions used for the analysis. A standard curve was generated using injections of known amounts of AMXT 1501 4 HC1 and DFMO H ₂ O HC1. Comparisons of peak areas of each drug generated from injection of a sample of the AMXT 1501 - DFMO complex to the standard curve was based on the molecular weight of each material. For standard solutions used to prepare the standard curves, calculations were made based on the DFMO and AMXT 1501 free base forms. Chromatograms for standard solution sample injections are shown in FIG. 4 A. The standard curves generated from the chromatograms depicted in FIG. 4A are shown in FIGs. 4B and 4C for AMXT 1501 and DFMO, respectively. This analysis resulted in a measured 1 to 7.01 ratio of AMXT 1501 to DFMO in the Lot #4-138 crystalline material used to produce the chromatograph shown in FIG. 4D. The data and calculation used to arrive at the measured ratio are shown below. Table 2: HPLC conditions for AMXT 1501 and DFMO ratio determination.

AMXT-

1501 -4HC1

(714.9 g/mol) AMXT-1501:

- ► DFMO =

DFMO HC1 H ₂ O 1 :7.01

(236.7 g/mol)

[00160] Elemental Analysis. Elemental Analysis results from Lot #4-138 showed C, 44.31 and 44.43; H, 7.83 and 7.69; N, 14.10 and 13.99. These data support the molecular formula shown below, containing 8 moles of DFMO for each mole of AMXT 1501, and 4 equivalents of HC1:

Chemical Formula: C ₈ oH ₁₆₈ CI ₄ F ₁₆ N220 ₁₈ Molecular Weight: 2172.13 Elemental Analysis: C, 44.24; H, 7.80; Cl, 6.53; F, 13.99; N, 14.19; O, 13.26

[00161] X-Ray Powder Diffraction. The x-ray diffractometer used was a Rigaku Miniflex 6G, where 1 to 3 mg of each solid sample was placed on a sample holder and analyzed using the following parameters: Start Angle, 3.00 degree; Stop Angle, 40.00 degree; Step Width, 0.05 degree; Run Time, 5 minutes, collecting data at 45 kV and 15 mA.

[00162] The AMXT 1501 - DFMO crystalline complex (Lot #4-138), and the two individual drug agents present as crystalline forms had distinct XRPD diffraction patterns. The diffraction pattern of DFMO alone showed signals at 10 degrees 20 that are absent in the diffraction pattern of the AMXT 1501 - DFMO crystalline complex. The diffraction pattern from 14-19 degrees 20 in the diffraction pattern of the AMXT 1501 - DFMO crystalline complex is absent in the diffraction pattern from DFMO alone.

[00163] Polarized Light Microscopy. Lot#4-138 material was analyzed by PLM, which revealed the crystalline nature of the complex. FIGs. 6A and 6B show the bright-field and polarized light images, respectively, obtained from PLM analysis of the AMXT 1501 -DFMO combination.

[00164] Differential Scanning Calorimetry and Thermogravimetric Analysis. The

DSC data was collected on a TA Instrument DSC25, where an exact amount (1.0 - 2.0 mg) of solid sample was weighed on a hermetic aluminum pan, using an analytical balance. The pan was then sealed using a hermetic aluminum lid with pin hole. Each sample was analyzed using the following parameters: Equilibration temperature: 35°C; Ramping Step: 10.0°C; Maximum temperature: 400°C; N ₂ Purge Flow, 50 mL/min.

[00165] The TGA data was collected on a TA Instrument TGA Q500, where approximately 1 - 3 mg of each solid sample was placed on the thermogravimetric balance and analyzed using the following parameters: Equilibration Temperature: 25°C; Ramping Step: 10.0°C; Maximum Temperature: 400 °C; N ₂ Purge Flow, 60 mL/min.

[00166] The AMXT-1501 DFMO complex (Lot #4-138) has a high melting point at 234.0 °C, with minimal weight loss prior to 200 °C (FIG. 7). AMXT-1501 free base may contain solvent (MeOH up to 17.2%) which, when removed, improved crystallinity and provided a melting point of 94.0 °C. DFMO HC1 H ₂ O melted at 157.6 °C with weight loss equivalent to one water loss. DFMO HC1 H ₂ O was previously reported to have a melting point of 183 °C. These data show that the AMXT 1501 - 8DFMO complex has a higher melting point in comparison to each of its individual components. Higher melting solids have a distinct advantage in pharmaceutical products due to improved stability properties.

Example 3: pH Control during AMXT 1501 - 4DFM0 salt formation

[00167] More consistent control of the AMXT 1501 to DFMO ratio in the salt production was obtained with strict pH control of the starting aqueous solution containing the two drug molecules. Although not wishing to be bound by any particular theory, it is thought that, without strict pH control, DFMO HC1 H ₂ O itself crystallizes from EtOH and H ₂ O solvent mixtures, and carries variable amounts of AMXT 1501 in the precipitation process. It is hypothesized that addition of AMXT 1501 free base deprotonates DFMO HC1, which precipitates, carrying various amounts of AMXT 1501 free base with it.

[00168] To gain knowledge about the various charge states of the individual drugs in aqueous solution, each were titrated with IN NaOH while monitoring the pH change of the solution. As shown in FIG. 8A, several inflection points were observed with the DFMO HC1 H ₂ O solution titration. Although not wishing to be bound by any particular theory, it is theorized that the most acidic functional group of DFMO HC1 H ₂ O is the alpha carboxylate group of the amino acid portion of molecule, with a pKa of 6.6. This is a higher than expected pKa compared to acetic acid (4.75) or glycine (2.34), possibly due to the electronwithdrawing effects of the beta difluoro atoms of DFMO’ s alpha methyl substituent. An alternative explanation of the titration curve shown in FIG. 8A is the inflection at pH 6.6 is due to deprotonation of one of the ammonium groups of DFMO. In either case, as shown by the predicted charge state of DFMO in the diagram of FIG. 8B, ensuring DFMO’s carboxylic acid is in its deprotonated carboxylate form requires pH control of its solutions to near, or above, pH 7. Alternatively, as shown in FIG. 8B, in order for sufficient charge association between DFMO and AMXT 1501, one of DFMO’s two ammonium ions must be deprotonated to its amino form. This is further supported by the expectation that the alpha amino group of DFMO is less basic than its distal, delta amino group. Additional evidence for protonation of either amino group is the observation of substantial chloride in the elemental analysis results, implying several amino groups in the complex are in their ammonium forms. In either instance, the carboxylate is fully deprotonated at pH 7.

[00169] AMXT 1501 4HC1 in aqueous solution was also titrated with IM NaOH, and the resulting pH monitored. As shown in FIG. 8C, at pH values near, or less than 7, AMXT 1501 is in its nearly completely protonated tetra-ammonium charge state form. For these reasons, in order to form a solution of DFMO in its carboxylate charged form, while retaining AMXT 1501 in its fully ammonium charged form, requires dissolution at a pH value of near 7. Thus, a pH range of from about 6 to about 8 represents the optimum pH for ionic interactions of AMXT 1501 and DFMO in solution.

[00170] For Example 3, AMXT 1501 in its 4HC1 salt form was used. A homogeneous, foamy solution of 3.078 g (4.31 mmole) of AMXT 1501 4HC1 (MW 714.78 g/mole) was prepared in 20 mL of H ₂ O with slight warming. To this solution (pH 2) was added 4.3 mL of IN NaOH (1 equiv), resulting in a pH 10 solution by Whatman pH strips. A separate solution of 4.07 g (MW 236.64, 4 equiv) of DFMO HC1 H ₂ O was prepared in 20 mL of H ₂ O. The pH of the resulting DFMO solution was 5. These two solutions were mixed at room temperature and the resulting homogeneous solution was pH adjusted to pH 7 with portionwise additions of IM NaOH. A total of 5 mL IM NaOH were introduced, bringing the pH to 7.

[00171] Previous smaller scale experiments showed the unique formation of two separate, homogeneous clear layers when the above solution was treated with the anti-solvent acetonitrile. This was unexpected because acetonitrile is generally completely miscible with aqueous solutions. This observation was exploited in the current example by adding 50 mL of the co-solvent isopropanol to the above AMXT 150LDFMO pH 7 solution. Again, the resulting solution was completely clear. Addition of 100 mL of the anti-solvent acetonitrile caused the formation of much white precipitation. Shaking caused everything to go back into solution at room temperature. Storage overnight in a -10 °C freezer caused the formation of a white precipitate. Filtration yielded 1.524 g (24%) of a white solid after drying (Lot 5-9). [00172] The clear mother liquor was treated with an additional portion of 150 mL of acetonitrile, heated and decanted from a slight precipitate to give a warm clear solution. This was placed in a -10 °C freezer for two days, when the resulting white precipitate that formed was filtered and dried to give 2.822 g (45%) white solid (Lot 5-11). The pH of the mother liquor was measured to be 7.

[00173] TLC analysis of these two lots of crystals showed they both contained the two drug agents. TLC analysis of the mother liquor showed it contained predominately DFMO. [00174] Elemental analysis of these two samples was used to assess composition of these two solids. Results are shown in Tables 3A and 3B. Corresponding structural formulas consistent with the elemental analyses of Lot 5-9 and Lot 5-11 solids, respectively, appear below. Differences in elemental composition results are accounted for by differing amounts of HC1 and H ₂ O associated with the two crops of crystals.

Table 3A: Elemental analysis results for Lot 5-9 solid.

Cl- Cl- Cl- CI-

Cl- Cl- H2O

Chemical Formula: C ₆₆ H ₁₂₄ CI ₆ F ₈ N ₁₄ O ₁₁

Molecular Weight: 1534.38

Elemental Analysis: C, 43.84; H, 8.15; Cl, 13.86; F, 9.91 ; N, 12.78; O, 11.47

100175] HPLC Analysis of Lot 5-9 and Lot 5-11. Using the same HPLC method described in Example 2, the ratio of AMXT 1501 to DFMO for both the Lot 5-9 and Lot 5-11 materials were shown to be near 1 to 4, as expected for a stoichiometric association of DFMO’s carboxylate with AMXT 1501 ’s ammonium functional groups at a pH of 7. HPLC calibration curves and results for AMXT 1501 - xDFMO ratio analysis are shown in Table 4. In Table 4, Test Solid 1 is Lot 5-9 material and Test Solid 2 is Lot 5-11 material. Table 4: HPLC Calibration curves and results for AMXT 1501 - DFMO ratio analysis.

*The API concentrations were calculated as free base forms (HC1 or H ₂ O excluded).

[00176] XRPD, DSC and TGA of Lot 5-9 and Lot 5-11. Using the same XRPD, DSC and TGA conditions described in Example 2, AMXT 1501 -DFMO solids from Lots 5-9 and 5-11 were analyzed. The results from DSC and TGA of Lots 5-9 and 5-11 are shown in FIGs. 9 and 10, respectively. Lot 5-9 material (Test Solid 1) had a melting point of 155.20 °C and a weight loss of 6.0% at 200 °C, and was composed of 7.5% water. Lot 5-11 material (Test Solid 2) had a melting point of 155.65 °C and a weight loss of 4.5% at 200 °C, and was composed of 1.2% water. DFMO HC1 H ₂ O has a melting point of 157.6 °C, and is composed of 7.6% water. The results from XRPD analysis of Lots 5-9 and 5-11 are shown in Table 5 and FIG. 11.

Table 5: XRPD Peak Summary

[00177] Repeat crystallization studies at pH 7.5 and pH 7.8 resulted in solids shown to contain a ratio of 1 :3 AMXT 1501/DFMO by the HPLC methods described above. Table 6 summarizes these HPLC assay results.

Table 6: HPLC assay of obtained solids after crystallization at pH 7.5 and pH 7.8.

* Solids were analyzed with HPLC-ELSD assay in replicates.

**The API concentrations were calculated as free base forms (HC1 or H ₂ O excluded).

[00178] The ratio of polyamine transport inhibitor to DFMO is expected to vary according to the polyamine transport inhibitor: DFMO stoichiometry, together with the exact crystallization conditions utilized. Processes disclosed herein, such as precise pH control, together with optimized choice of solvent and anti-solvent pairs are very useful to form such materials. Furthermore, combination of any of the examples described herein would be expected to improve drug handling and stability properties and provide more convenient patient dosing formats and hence patient compliance. Various chemical analogs of the examples given herein would also be envisioned to form salts with DFMO.

Example 4: Complexes of DFMO with other polyamine transport inhibitors [00179] DFMO is complexed with other polyamine transport inhibitors, such as those in Table 7.

Table 7: Structures of example polyamine transport inhibitors.

REFERENCES

E Casero, R.A., Jr., Murray Stewart, T. & Pegg, A.E. Polyamine metabolism and cancer: treatments, challenges and opportunities. Nat Rev Cancer 18, 681-695 (2018).

2. Amidon, G.L., Lennernas, H., Shah, V.P. & Crison, J.R. A theoretical basis for a biopharmaceutic drug classification: the correlation of in vitro drug product dissolution and in vivo bioavailability. Pharm Res 12, 413-420 (1995).

3. Burns, M.R., Graminski, G.F., Weeks, R.S., Chen, Y. & O'Brien, T.G. Lipophilic lysine-spermine conjugates are potent polyamine transport inhibitors for use in combination with a polyamine biosynthesis inhibitor. J Med Chem 52, 1983-1993 (2009).

4. Gamble, L.D., et al. Inhibition of polyamine synthesis and uptake reduces tumor progression and prolongs survival in mouse models of neuroblastoma. Set TranslMed 11(2019).

5. Hayes, C.S., et al. Polyamine-blocking therapy reverses immunosuppression in the tumor microenvironment. Cancer Immunol Res 2, 274-285 (2014). Hayes, C.S., Burns, M.R. & Gilmour, S.K. Polyamine blockade promotes antitumor immunity. Oncoimmunology 3, e27360 (2014). Saulnier Sholler, G.L., et al. A Phase I Trial of DFMO Targeting Polyamine Addiction in Patients with Relapsed/Refractory Neuroblastoma. PLoS One 10, e0127246 (2015). Carbone, P.P., et al. Bioavailability study of oral liquid and tablet forms of alpha- difluoromethylomithine. Clin Cancer Res 6, 3850-3854 (2000). Na-Bangchang, K., et al. The pharmacokinetics of eflornithine (alpha- difluoromethylomithine) in patients with late-stage T.b. gambiense sleeping sickness. Eur J Clin Pharmacol 60, 269-278 (2004). Schultheiss, N. & Newman, A. Pharmaceutical Cocrystals and Their Physicochemical Properties. Cryst Growth Des 9, 2950-2967 (2009). Neubert, R. Ion pair transport across membranes. Pharm Res 6, 743-747 (1989). Neubert, R. & Dittrich, T. Ion pair approach of ampicillin using in vitro methods. Pharm Acta Helv 65, 186-188 (1990). Hatanaka, T., Kamon, T., Morigaki, S., Katayama, K. & Koizumi, T. Ion pair skin transport of a zwitterionic drug, cephalexin. J Control Release 66, 63-71 (2000). Ivaturi, V.D. & Kim, S.K. Enhanced permeation of methotrexate in vitro by ion pair formation with L-arginine. J Pharm Sci 98, 3633-3639 (2009). Benaouda, F., et al. Ion-Pairing with Spermine Targets Theophylline To the Lungs via the Polyamine Transport Sy stem. Mol Pharm 15, 861-870 (2018). Bello-Fernandez, C., Packham, G. & Cleveland, J.L. The ornithine decarboxylase gene is a transcriptional target of c-Myc. Proc Natl Acad Sci U S H 90, 7804-7808 (1993). Origanti, S. & Shantz, L.M. Ras transformation of RIE-1 cells activates capindependent translation of ornithine decarboxylase: regulation by the Raf/MEK/ERK and phosphatidylinositol 3-kinase pathways. Cancer Res 67, 4834-4842 (2007). Chang, B.K., Libby, P.R., Bergeron, R.J. & Porter, C.W. Modulation of polyamine biosynthesis and transport by oncogene transfection. Biochem Biophys Res Commun 157, 264-270 (1988). Soda, K. The mechanisms by which polyamines accelerate tumor spread. J Exp Clin Cancer Res 30, 95 (2011). 20. Metcalf, B.W., et al. Catalytic irreversible inhibition of mammalian ornithine decarboxylase (E.C.4.1.1.17) by substrate and product analogs. Journal of the American Chemical Society 100, 2551-2553 (1978).

21. Williams-Ashman, H.G. & Schenone, A. Methyl glyoxal bis(guanylhydrazone) as a potent inhibitor of mammalian and yeast S-adenosylmethionine decarboxylases. Biochem Biophys Res Commun 46. 288-295 (1972).

22. Seppanen, P. Some properties of the polyamine deprivation-inducible uptake system for methylglyoxal bis(guanylhydrazone) in tumor cells. Acta Chem ScandB 35, 731- 736 (1981).

23. Warrell, R.P., Jr., Coonley, C.J. & Burchenal, J.H. Sequential inhibition of polyamine synthesis. A phase I trial of DFMO (alpha-difluoromethylomithine) and methyl-GAG [methylglyoxal-bis(guanylhydrazone)]. Cancer Chemother Pharmacol 11, 134-136 (1983).

24. Stanek, J., et al. 4-Amidinoindan-l-one 2'-amidinohydrazone: a new potent and selective inhibitor of S-Adenosylmethionine decarboxylase. J Med Chem 36, 2168- 2171 (1993).

25. Libby, P.R., Henderson, M., Bergeron, R.J. & Porter, C.W. Major increases in spermidine/spermine-Nl -acetyltransferase activity by spermine analogues and their relationship to polyamine depletion and growth inhibition in L1210 cells. Cancer Res 49, 6226-6231 (1989).

26. Muth, A., et al. Polyamine transport inhibitors: design, synthesis, and combination therapies with difluoromethylornithine. J Med Chem 57, 348-363 (2014).

27. Gilmour, S.K., Alexander, E.T., Mariner, K., Donnelly, J. & Phanstiel, O. Polyamine Blocking Therapy Decreases Survival of Tumor-Infiltrating Immunosuppressive Myeloid Cells and Enhances the Anti-Tumor Efficacy of PD-1 Blockade. Mol Cancer Ther (2020).

[00180] The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.

[00181] While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims.