BIS-PLATINU COMPLEXES AS ANTITUMOR AGENTS

Background of the Invention This invention relates to bis-platinum complexes and their use as antitumor agents in humans and animals. It is known that Cisplatin, cis-[Pt(NH_) Cl_] is effective against several types of animal tumors and has been used successfully in treating certain types of malignancies in humans. A number of other platinum complexes have been tested for antitumor activity, e.g., increased life span for mice having implanted tumors such as L-1210 lymphoid leukemia.

An oligomeric platinum complex is disclosed in U.S. Patent 4,128,342 to Yolles. These complexes contain bridging halogen ligands as well as a number .of platinum ions in both therapeutic and non-therapeutic forms in the complex.

Three bis-platinum complexes were reported by Rochon et al., J. Clin. Hematology & Oncology, 12, 39-43 (May, 1982) . Two of those showed no activity against L-1210 lymphoid leukemia, while a third showed a low level of activity but also showed significant toxicity.

Gale et al., U.S. Patent 4,137,248, and Kidani et al., U.S. Patent 4,169,846, disclose mono eric complexes of [l,2-diaminocyclohexane]Pt(II) . The disclosures of the fore- going patents are incorporated herein by reference.

A need continues to exist for platinum complexes having appreciable water solubility to facilitate-intravenous injec¬ tion, along with significant antitumor activity and low toxicity.

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OBJECTS OF THE INVENTION One object o.f the present invention is to provide platinum antitumor agents having appreciable water solu¬ bility, significant antitumor activity and relatively low toxicity.

Another object of the invention is to provide plati¬ num antitumor agents having a high yield of therapeutic platinum in a form which is advantageous for intravenous administration. A further object of this invention is to provide a method of tumor therapy which avoids disadvantages in prior art methods.

SUMMARY OF THE INVENTION These and other objects of the invention can be achieved by a bis-platinum complex having the formula I

wherein A is a ligand having two pairs of platinum- coordinating acidic groups which are each independently a carboxylate, phenolate, sulfonate or phosphonate group, each said pair being capable of coordinating with a platinum ion to form a 5-10 membered chelate ring; Z is a water-solubilizing group; n is 0 or a positive inte¬ ger, with the proviso that n is 0 only when at least one of said platinum-coordinating acidic groups is sulfonate or phosphonate, or when at least one platinum ion is a Pt(IV) ion; and W\\ , ^~ _ _f R3, R4, R5 and Rς are each in¬ dependently H or a Cι_20 alkyl, C3--20 carbocyclic or heterocyclic aryl, aralkyl or alkaryl group, or together form one or more C1-30 alkylene, C3-20 carbocyclic or heterocyclic cycloalkylene, arylene, aralkylene or alkar¬ ylene groups; or a pharmaceutically acceptable salt thereof. In a method of use aspect, the present invention

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provides a method for tumor therapy in humans and ani¬ mals, comprising administering to a human or animal subject having a tumor an antitumor effective amount _: of the foregoing bis-platinum complex.

DETAILED DISCUSSION

The bis-platinum complexes of the invention each have a central ligand. A, which may also bear one or more water-solubilizing groups, Z. In general, A can be any organic group incorporating in its structure the aforementioned two pairs of platinum-coordinating acidic groups, in the proper geometry for forming two 5-10 membered chelate rings with platinum ions.

Suitable such ligands include, but are not limited to, mononuclear or polynuclear aromatic ring systems, the latter preferably dinuclear or trinuclear, each said aromatic ring being a substituted or unsubstituted car¬ bocyclic or heterocyclic aromatic ring. More specifi¬ cally, the aromatic ring system can be a benzene or naphthalene ring system, e.g.,

G

wherein G and G* are said pair of platinum-coordinating acid groups. Preferred such groups include those where- in G and G* are both carbox late groups and those where¬ in at least one G or G' is a phenolate oxygen. It will also be understood that carboxylate, sulfonate and phos¬ phonate groups need not be attached directly to the ring system, but can be separated therefrom, e.g., by short chains, preferably aliphatic, lower alkylene chains, consistent with the requirement that the chelate ring to platinum be 5-10 atoms in size.

The aromatic ring systems can include heteroatoms, preferably oxygen and/or nitrogen atoms, with ^' the nitro- gen atoms preferably having unshared electron pairs which are part of the pi-electron system of the aromatic ring, so that they are of low basicity and do not tend to compete with the acidic chelating functions for coordi¬ nation sites on the platinum ions. Highly nucleophilic heteroatoms, e.g., sulfur ^* , phosphorus and the like, are preferably avoided since they will tend to bind too tightly to platinum ions. Examples of such heteroaro- matic systems include, e.g., benzofuran, indole, chro- mene, benzopyran, indolizine and the like. The aromatic systems need not be fused ring systems but can also be, e.g., biphenyl, terphenyl ^" , diphenyl- methane, diphenylbutane and the like, as well as mixed fused and non-fused systems, e.g., phenylnaphthalene.

benzylnaphthalene, phenylbenzofuran, and the like.

Suitable ligands. A, can also include alicyclic ring systems, including mononuclear or polynuclear, substituted or unsubstituted, carbocyclic or heterθ cyclic alicyclic ring systems. Examples include cyclo¬ propane, cyclobutane, cyclohexane, cycloheptane and larger rings, linked or fused to other similar rings, optionally including non-nucleophiliσ heteroatoms, e.g., oxygen, and preferably- excluding non-aromatic nitrogen atoms and the aforementioned nucleophilic heteroatoms. Again, mixed fused and unfused ring assemblies can be used, including mixed alicyclic and aromatic ring systems, spirocyclic systems, and ring systems linked by one or more atoms in a chain, preferably an aliphatic alkylene moiety. A pair of platinum-coordinating acidic groups can both be located on the same atom on an ali¬ cyclic ring, e.g., in cyclobutane-1,1,3,3-tetracarboxyl- ate, and like structures , _r

Also suitable as ligands. A, are aliphatic groups bearing appropriately located pairs of platinum- coordinating acidic groups. Examples include 2,5-diσar- boxyadipate, 3,12-dicarboxytetradecanedicarbσxylate and the like.

It will be understood that many other variants can be used for the central ligand. A, and all such variants are included within the scope of this invention, provided that they meet the criteria generally set forth above. Any of the foregoing, ligands may be substituted by any non-interfering substitue ^' nts, e.g., alkyl, halogen, nitro, ether, ester, amide and the like, preferably con¬ taining not more than about 10 carbon atoms.

The chelate ring including each pair of platinum- coordinating acidic groups and its coordinated platinum ion, can be a 5-10 membered ring, but is preferably a 5- 8 membered ring, more preferably a 6-7 membered ring. Preferably, not more than one acidic coordinating group is sulfonate or phosphonate, and in such cases, it is

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not necessary to provide an additional water-solubiliz- ing group, Z, since sulfonate and phosphonate groups coordinate somewhat more loosely with platinum and are capable of dissociating relatively rapidly in water and serving as a solubilizing group. However, the presence of a water-solubilizing group, Z, is not excluded even when-one or more platinum-coordinating acidic groups is sulfonate or phosphonate.

It will be understood that the two chelate rings need not be the same size, and the two pairs of platinum- coordinating acidic groups in the l.igand. A, also need not be the same. In fact, it may be advantageous to have chelate rings which bind their respective platinum ions with significantly different binding constants, so that release of platinum will occur at different rates from the two chelate binding sites, thereby providing added flexibility in designing dose-response properties of potential therapeutic-utility.

Examples of this type of unsymmetrical chelation can include binding of one platinum ion by a salicylate- type chelation while the other platinum ion is bound by a dicarboxylate, e.g., phthalate-type, chelation, where¬ in both the chelating groups and the chelate ring size are varied; catechol-type chelation provides yet a smaller chelate ring and a tighter chelate binding; dicarboxylate chelation at, e.g., the 1,8-positions of a naphthalene ring system forms an 8-membered chelate ring., which can be combined with vicinal dicarboxylate chelation in a 7-membered ring to provide variation in chelate binding properties for a single bis-platinum complex. Other examples will be readily apparent to the ordinary skilled art worker.

Water-solubilizing groups, Z, improve the solubil¬ ity in water of the bis-platinum complexes -of the in- vention. One type of water-solubilizing group is an acidic function which can be converted to its' salt in

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alkaline solution, e.g., aqueous sodium bicarbonate. This renders the complex readily soluble in water and facilitates its dissolution in a sterile injection vehicle for intravenous infusion. The water solubility of Cisplatin is about 1 mg/ml in water. Bis-platinum complexes having equivalent potency to Cisplatin will advantageously have at least equivalent solubility. It will be understood that significantly more potent antitumor agents can be administered in more dilute solution and the requirement for water solubility is less critical. On the other hand, relatively high solubility in water can be most advantageous for anti¬ tumor agents, since it permits administration in a concentrated solution, i.e., in a small volume of injec- tion or infusion vehicle. This can be particularly advantageous where it is desirable to administer the antitumor agent in the vicinity of a tumor location, e.g., by intravenous or intraarterial administration over a relatively short period of time for maximum im- pact at the tumor site.

Preferably, the solubility of a complex according to the invention is at least about 1 mg/ml in water or dilute alkali, e.g., 1% NaHCθ3, more preferably at least about 10 mg/ml. For more potent complexes, a solubility of at least about 0.01 mg/ml is preferable, more prefer¬ ably at least about 0.1 mg/ml in water or dilute alkali. One useful and preferred type of water-solubilizing group is a phenolate, carboxylate, sulfonate or phos¬ phonate group similar to the platinum-coordinating acidic groups forming the chelate rings, preferably sulfonate or carboxylate. For example, where a tetracarboxylate is used as the ligand. A, the addition of a fifth car¬ boxylate group to the ligand provides a water-solubilizing function which permits facile dissolution of the complex in dilute aqueous bicarbonate. Where the group, Z, is an acidic function, the bis-platinum complex of the

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invention may be provided as a pharmaceutically accept¬ able salt thereof, e.g., a sodium, potassium, magnesium, or calcium salt, or the like.

Another suitable type of water-solubilizing group is a mono- or polyhydroxylic group, preferably a Cχ_i2 hydroxylic group. Convenient sources of such groups are derivatives of mono- or polysaccharides, e.g., ribityl, sorbityl, glucosyl and the like. These groups can be attached to the central portion of the ligand. A, by a variety of conventional reactions, including, but not limited to, condensation, alkylation, esterification, etherification and the like.

It is also possible for the water-solubilizing moiety, Z, to be incorporated directly in the ligand, A. For example, two phthalate groups can be joined to either end of a sugar derivative by means of any of the foregoing steps, whereby the water-solubilizing group, Z, links the two portions of the ligand. A, bearing the two pairs of platinum-coordinating acidic groups. Several such water-solubilizing groups, Z, can be present on the central ligand, A. Thus, rather than a single polyhydroxylic "tail", it may be advantageous to have several shorter hydroxylic substituents on the ligand. The number of such substituents is advantageously no larger than necessary to achieve suitable water solu¬ bility for the complex and this will vary as a function of the detailed structure of the ligand. A, and of the amine substituents coordinated to the platinum ions. Where n is a positive integer, it is preferably 1-4, _j more preferably 1-2 and most preferably 1.

It is often the case that Pt(II) complexes will have low solubility in water unless water-solubilizing groups are present. Where at least one of the platinum ions is a Pt(IV) ion, the water solubility of the com- plex will generally be sufficiently high so that addi¬ tional water-solubilizing groups, Z, will not' generally

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be necessary. Where "Pt" is other than Pt(II) ^' , it will be understood to include coordinated water molecules .and/or counterions to balance the charge of the complex. The complex may be isolated as a hydrate. The water-solubilizing groups, Z, can include more than one type of water-solubilizing function, e.g., combinations of carboxyl, sulfonate, phosphonate, pheno- late, hydroxyl, ether, ester groups and the like, on the same or different moieties, Z. Other equivalent water- solubilizing functions will be apparent to one of ordinary skill in the art, and such equivalents are included within the scope of the present invention..

The substituents on the a ine groups coordinated to the platinum ions, Ri-Rg, can each independently be hydrogen atoms, Cι_20 alkyl, C3-20 carbocyclic or _. hetero¬ cyclic groups, or pairs of substituents on the same or different amine nitrogen(s) can form one or more chains or rings, e.g., Cι_3o alkylene, C3--20 carbocyclic or hetero¬ cyclic, cycloalkylene, arylene, aralkylene or alkarylene rings. The amine groups coordinated to the two platinum ions need not be the same. As indicated above with respect to unsymmetrical chelation of the two platinum ions by the acidic functions on the ligand. A, there may be therapeutic advantages to using different amine coordinating groups on one platinum ion from those used to coordinate the other.

Examples of suitable amine coordinate groups in¬ clude, e.g., ammonia, lower alkylamines, including straight- chain and branch-chain amines, cyclic amines, e.g.,- pyrrolidine, piperidine, and the like; and diamines,ι e.g., ethylenediamine, 1,2,diaminocyclopentane and, preferably, 1,2-diaminocyclohexane. Also suitable are bidentate diamines having one amine function attached directly to an alicyclic ring, while the other is in the form of an a inomethyl substituent on the ring, e.g., 1- amino-2-aminomethylcyclohexane. This permits variation in the size of the chelate ring of bidentate amine sub-

stituents. The amine coordinating group(s) can- be chiral, and the invention includes complexes made with mixtures of diastereomers, racemic mixtures and/or pure enantiomers of such chiral amines. It will be understood that other chiral constituents, e.g., A and/or Z, of the bis-platinum complexes of the invention can also be present as mixtures of diastereomers and/or racemates or as pure enantiomers. It will some¬ times be the case that a single enantiomer or racemate will have improved therapeutic properties compared to other stereoisomers.

The bis-platinum complexes of the invention are conveniently prepared by reacting potassium tetrachloro- platinite with the amine components of the eventual • complex to form a diamino dichloroplatinite. Normally, this intermediate can be obtained as a precipitate from neutral aqueous solution. Advantageously, the dichloro complex is converted to the diaquo complex with silver nitrate, after which about two equivalents of the resultant diamino diaquo complex or about one equivalent of each of two diamino diaquo complexes are reacted with the- ligand. A, bearing the water-solubilizing group(s), whereupon the bis-platinum complex ordinarily forms as a precipitate, which is isolated and purified by conventional procedures, e.g., filtration, washing, drying, optionally including chromatography, recrystallization and the .like. The reactions are normally effected at about 0-40° C, preferably at room temperature, under analogous con¬ ditions to those disclosed in Kidani et al. Pt(IV) complexes are conveniently synthesized by oxidation of Pt(II) complexes, e.g., by reaction with hydrogen per¬ oxide, normally at about 20-80° C. It will be appreciated that, where one or both platinum ions are other than Pt(II) ions, e.g., Pt(IV) ions, additional counterions will be re- quired to balance the charge. These counterions will gener¬ ally be selected from halide, hydroxide, nitrate, azide, other pseudohalides or other organic or inorganic anions.

Oxidation of Pt(II) to Pt(IV) is described in, e.g.. Cotton et al, "Advanced Inorganic Chemistry", p. 854 (John Wiley, 1962).

An illustrative subclass of ligands. A, includes com- pounds having the formula II

L Q L'

Q- - ^ G -

wherein LGG' and L'GG' are each independently a bidentate ligand, G and G' being said pair of platinum-coordinating aci groups (acid form); and Q is a single bond or a divalent linking group. It will be understood that the water-solubili zing function, Z, can be incorporated in any of L, L' or Q, when required.

Suitable bidentate ligands, LGG' or L'GG*, include, e.g., phthalate, salicylate, catechol, ortho-hydroxysulfonate, and analogs wherein one or both G and G' functions are sulfonate or phosphonate.' Fused-ring, multiple-ring, hetero¬ cyclic ring, alicyclic ring and/or non-cyclic groups bearing a pair of coordinating groups, G and G', can also be used.

Some illustrative examples of linking .groups, Q, include -N=N-, -CO-, -SO2-, -NHC0-(CH2) _p -C0NH- (p is an integer from 0 to 30, preferably from 2 to 8), -NHCONH-(CH2>q-NHCONH- (q is an integer from 1 to 30, preferably from 1 to 8), - CR ¹ R ² ) _m -- (R ¹ and R ² are each independently H, Cι_20- alkyl, aryl, alkaryl, araJkyl, alkylidene, aralkylidene, quinoidal, and the like; m is an integer from 1 to 30), (Ar is arylene; Q' is a divalent linking group, e.g., a single bond, -NHCO-, -NHC0NH-, -CONH-, CH2, -CO-, -SO2- and the like), and -COO-R ³ -OOC- (R ³ is alkylene, arylene and the like). Illustrative ligands of formula II include the following representative examples. The first six examples show the acid form of the ligand, the solubilizing group, Z, and also illustrate a bis-Pt complex with 1,2-diaminocyclohexane ⁽ DACH) or other amine ligand. Ic will be understood that, _

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other solubilizing groups ana other amine ligands can be used, as set rorth herein. The remaining examples snow either the ligand A, alone, or A-(Z)n alone, omitting the PU RJ-RZR ³ ) (R R ⁵ R ^δ ) portions of the complex. IIA: (A-Z, Z = COOH)

An illustrative complex of this azo-linked _. (Q= -N=N-) mixed catechol/salicylate ligand with (DACH) Pt(II) is:

IIB : (A-Z _r Z = SO3H)

An illustrative complex of this azo-linked bis-salicylate ligand with [4-amino-5-aminomethyl-2-methylpyrimidineJ Pt(II) is

IIC: (A-Z ₂ , Z= COOH, n=2 )

An illustrative complex of this carbonyl-1 inked (Q= -CO-) bis-phthalate ligand with [5,6-diaminouracil]Pt(II) is

IID: (A-Z, Z= COOH)

An illustrative complex of this quinoidal methylene- linded bis-salicylate ligand with (3 ,4-diamino-5-pyrazolol] - Pt(II) is

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HE: (A-Z , Z= COOH)

An illustrative complex of this azo-linked (Q= -N=N-Ph-N=N-) mixed catechol/salic late ligand with [ethylenediamine]-= Pt(II) is

IIF: (A-Z , Z= CH2COOH)

An illustrative complex of this azophenylamide-1inked (Q= -NHC0-Ph-N=N-) aliphatic dicarboxylate/catechol ligand with [o-phenylenediamine]Pt(II) , in which the two chelate rings to the tetradentate ligand are 8-membered and 5-membered respectively, is

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^" VΪFO

*

IIG: ⁽ A-Z, Z= SO3H) the ligand is an azo-linked bis- dicarboxylate which forms 8-membered and 7-membered Pt chelate rings.

IIH: (A-Z ₂ , Z= SO-H, n=2) The ligand is a hexamethyiene- bis-urea-linked bis-catechol.

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Other representative types of tetradentate ligands. A, are illustrated by the following examples. Where no solu- bilizing group, Z, is present, and no platinum-coordinating group is sulfonate or phosphate, at least one Pt(IV) ion wil! be complexed with the ligand.

IIIA hexitolyl IIIB

IIIC HID

HIE IIIF

Complexes of, e.g., (DACH)P (II) , [4-amino-5-amino- methyl-2-methylepyrimidine]Pt(II) , [5,6-diaminpuracil]Pt (II), [3,4-diamino-5-pyrazolol]Pt(II) , [ethylenediamine]- Pt(II) and o-phenylenediamine]Pt(II) with, e.g., IIIA, HID, IIIF, cyclopentane-l,2,3,4,5-pentacarboxylic acid, 3-sulfohydroquinone-2,5-diacetic acid, pentane-1,2,3,4,5- pentacarboxylic acid, 2-sulfonaphthalene-l,4,5,8-tetra- carboxylic acid, bicyclo[2.2.2]-octane-2,3, ^" 5,6,7-penta- carboxylic acid, hydroquinone-2,5-diphosphonic, acid, 5-hydroxy-4-phosphonyloxysalicylic acid and

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butane-l,4-bis-(2-phosphonoacetic acid) are additional representative compounds according to the invention. Other representative compounds include complexes of Pt(IV) with the above diamine ligands and tetradentate ligands, and also with the tetradentate ligands IIA-H, IIIB, IIIC,

HIE, bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic acid, cyclobutane-l,2,3,4-tetracarboxylic acid, furan-2,3,4,5- tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic acid, 2,5-dihydroxyterephthaliσ acid, hydroquinone-2,5- diacetic acid, 2,4,5-trihydroxybenzoic acid, benzene-

1,2,4,5-tetracarboxylic acid, 4- (4-salicylylazo)phthalic acid and cyclohexane-l,2,4,5-tetracarboxylic acid.

The ligand. A, bearing the water-solubilizing group(s) Z, will often be commercially available. Alternatively, this ligand can be synthesized by methods which will be apparent to the ordinary skilled art worker.

The aromatic ligands can be prepared from the unsub- stituted mono- or polynuclear aromatic systems by con¬ ventional methods of aromatic substitution. Alternatively, platinum-coordinating acidic groups can be introduced by, e.g., oxidation of alkyl substituents, or a combination of acylation and oxidation to form carboxylates; sulfonation to form sulfonic acids; a combination of acylation, Baeyer- Villiger degradation and hydrolysis to form phenols; and phosphonation as described in Worms et al., "Phosphonic Acids and Derivatives", in "Organic Phosphorus Compounds", Vol. 7, pp. 1-487, Kosolapoff et al., Eds. (John Wiley, 1973) , and references therein.

Alicyclic ligands can be prepared, inter alia, by catalytic hydrogenation of corresponding aromatic ligands. Other methods for synthesizing the aromatic, alicyclic and/or non-cyclic ligands bearing the platinum-coordinating acidic groups can be readily devised using conventional synthetic methods such as those in, e.g., Harrison et al., "Compendium of Organic Synthetic Methods" (Wiley-

Interscience, New York, 1971); Houben-Weyl, "Die Methoden

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der Organischen Chemie"; Organic Syntheses (annual and collective) ; Theilheimer, "Synthetic Methods of Organic Chemistry"; Wagner and Zook, "Synthetic Organic Chemistry", and the like. Entry into the subclass of compounds with ligands having the formula II, wherein Q is azo, can be con¬ veniently gained by diazonium coupling, using conventional conditions. Many bidentate ligants, LGG' , L*GG* , bearing amino groups, are commercially available, and their behavior in diazonium coupling reactions is known from the dye art. Further derivatization of azo compounds, e.g., to introduce sulfonic acid solubilizing groups, is also known from this art.

Compounds of formula II, wherein Q is a bis-urea linking group, can be readily prepared by reaction of bidentate amine-substituted ligands with a polymethylene- diisocyanate, under conventional conditions. Alternatively, a diester can be used as a linking reagent, to give ligands wherein Q is a bis-amide. Acylation with bis-acid halides can be used to produce bis-ketones . Sulfuryl halide sulfonation or phosgene acylation can be used, to link protected bidentate ligands by sulfonyl or carbonyl groups, respectively.

Similarly, numerous amines suitable for use as amine coordinating groups will be commercially available and/or readily convertible into other groups from available starting materials, e.g., by methods such as those collected in, e.g., Harrison et al., supra, the other compendia indicated supra, and like sources. Bidentate diamino coordinating groups, e.g., 1,2- diaminocyclohexane, can be conveniently produced from the corresponding cyclic olefin, e.g. , cyσlohexene, by addition across the double bond, e.g. , by formation of an aziridine, followed by displacement with ^* an amine; or by reaction of the cyclic olefin with silver cyanate and iodine, followed by displacement of the iodo group by a second amine; or by epoxidation, opening with an amine, . „ conversion of the vicinal h drox l grou to a leaving f

group, e.g., a tosylate, followed by displacement with a second amine; and similar reactions for producing vici¬ nal substituents from olefinic starting materials. These reactions can obviously be applied to non-cyclic compounds as well.

Known compounds which can be used as the ligand. A, the complete ligand A-Z, the group, Z, or the amine NR1R2R3 and/or NR3R5R5 may often be found in compila¬ tions of organic compounds, together with syntheses or isolation procedures whereby they may be produced. Such compilations include, e.g., Beilstein's "Handbuch der organischen Chemie", Elsevier's "Encyclopedia of Organic

Chemistry", Heilbron's "Dictionary of Organic Compounds", Rodd's "Chemistry of Carbon Compounds", and the like. Other sources of known compounds include Chemical Abstracts, compound indices of chemical journals and computerized data bases. Even where a ^* desired component of the com¬ plex of the invention is not known, it will generally be readily synthesized from a known precursor using methods disclosed in the aforementioned compendia or readily. available to the skilled art worker.

The bis-platinum complexes of the invention are advantageously administered to patients, i.e., humans or animals having tumors susceptable to therapeutic treat- ment by platinum complexes, as sterile aqueous solutions. The solutions are preferably administered intravenously or intraarterially, although other forms of a'dministra- tion may be indicated in certain cases.

Solutions for intravenous injections will normally be sterile physiological solutions, which may also contain appropriate amounts of alkali, e.g., sodium bicarbonate, to convert complexes bearing acidic water- solubilizing groups to their salts. It is also possible to use pharmaceutically acceptable surfactants, e.g., naturally occurring constituents of blood which have surface active properties, e.g., salts of bile acids

such as deoxycholic acid, as dispersing and/or emulsifying agents. Such natural emulsifiers have been used to disperse antibiotics, e.g., amphotericin B, in aqueous injection media. Preferably, however, the water- solublizing group(s) will render the bis-platinum complex of the invention soluble in water without the use of such emulsifiers and/or surfactants. Suitable dos ^¬ age forms can also include oily or aqueous injectable pre¬ parations, e.g., for intramuscular or intraperitoneal in¬ jection, syrups and the like liquid preparations, and solid dosage forms, e.g., capsules, tablets and the like.

The effective amounts of the complex of the inven¬ tion which should be administered can be determined by conventional methods which will be apparent to the skilled clinician. Normally, the activity of the bis- platinum complex of the invention will be evaluated in a screen along with a known complex such as Cisplatin or the (DACH)Pt(H) complexes of Gale or Kidani. The relative potency and the therapeutic index, i.e., the ratio of thera¬ peutic effectiveness to toxicity, compared to that of the known analogue will normally determine the relative dosage compared to conventional dosages of the analoque for the type of malignancy being treated.

The treatment regimen can be varied in ways which are well known to the skilled clinician, as a functi/on of the type of malignancy being treated, the _^ condition of the patient, and the particular properties of the antitumor bis-platinum complex being administered. In¬ evitably, a certain amount of experimentation is required to determine the optimum dosages and treatment regimens, as is normally the case for antitumor therapy.

It will sometimes.be advantageous to administer the bis-platinum complex of the invention in combination with one or more agents that potentiate its antitumor activity or mitigate undesired side effects. Such synergistic effects have been disclosed in, e.g.. Gale

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et al., U.S. Patent 4,137,248, where a platinum complex was administered with cyσlophosphamide and 5-fluorouracil or hydroxyurea.

An antitumor effective dosage, e.g., an amount of the complex of the invention suitable for delivery of an equi¬ valent amount of diaminoplatinum ions to the amount of such ions released by the complexes of Gale or Kidani, will generally be in the range of about 0.1-500 mg/kg/dose. It is recognized that certain of the bis-platinum complexes having the formula shown above will have suf¬ ficiently high toxicity and/or sufficiently low thera¬ peutic indices as to be unsuitable for antitumor thera¬ py. However, these parameters can be readily determined by conventional screening tests, e.g., with L-1210 uri- ne leukemia cells implanted in mice, and such complexes can be avoided.

It should be noted that the ready solubility of the bis-platinum complexes of the invention in water is advantageous for oral administration. Depending on the stability, the potency, the bioavailability and the side effects of a particular compound, oral administration may be indicated.

Without being bound by any mechanism or theory, it is nevertheless considered likely that cis-diaminoplatinum complexes are fully or partially hydrolysed in the blood stream, in the tissues or even in solution, to generate the (diamine)Pt(II) or (dia ine)P (IV) moiety having water or chlorine in some or all of the remaining coordination sites. The bis-platinum complexes of the invention have, the advantage of being able to deliver two identical or different diaminoplatinum ions by sequential hydrolysis of the two pairs of platinum- coordinating groups from a symmetrical or unsymmetrical tetradentate carrier ligand. A, while at the same time being able to carry two diaminoplatinum -moieties in a single soluble complex.

As noted above, prior art platinum antitumor complexes generally have had a single Pt ion. The advantages of the

bis-platinum complexes of the invention include the possi¬ bility of tailoring the complex to deliver two sequential doses of diaminoplatinum ions at a chosen rate and with a theapeutically beneficial time delay. This could permit both quantitatively and qualitatively improved delivery of antitumor diaminoplatinum ions to tumor sites.

Without further elaboration, it is believed that one skilled in the art can., using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. In the following examples, all temperatures are set forth uncorrected in degrees Celsius; unless otherwise indicated, all parts and percentages are by weight.

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EXAMPLE 1 Preparation of benzenepentacarboxylatobis [(1,2- diaminocyclohexane) platinum(H) ]

An 8 gram portion of platinum metal was digested in 250 ml of aqua regia to form chloroplatinic acid. Potas¬ sium chloride (12 g) solution was added to immediately precipitate potassium hexachloroplatinate(IV) which was subsequently reduced to potassium tetrachloroplatinite (II) with 2 grams of hydrazine hydrochloride. To the red aqueous solution of potassium tetrachloroplatinite was added 6 ml of 1,2-diaminocyclohexane (Aldrich) and enough 0.5 N NaOH to adjust the pH to 7. After overnight stirring, 10 grams (64% yield) of dichloro(1,2-diaminocyclo- hexane)platinum was collected as a yellow precipitate. The commercial diaminocyσlohexane used in this synthesis was a mixture of cis and trans isomers and the platinum complex was therefore also an isomeric mixture. It should be noted that isomerically pure complex can be prepared from readily synthesized cis and trans isomers of diaminocyclohexane or from easily resolved pure enanticmers thereof, as prepared by the process of, e.g., U.S. Patent 4,169,846.

Dichloro(1,2-diaminocyσlohexane)platinum (lOg; 26.3 mmole) and silver nitrate (8.5g; 521 mmole) were reacted in 100 ml of deionized water overnight at room tempera¬ ture, protected from light. The insoluble silver chloride was filtered off on a glass frit and 3.6 g (12.1 mmole) of benzenepentacarboxylic acid (Pfalz 8 Bauer) dissolved in 100 ml of water was added to the filtrate and the pH of the solution was adjusted to 5 with sodium hydroxide. The mixture was allowed to stand at 40° for 2 hours and the yellow-white precipitate was collected and washed with water, ethanol, and ether and dried i^i vacuo to yield 6.2g (52%) of benzenepentacarboxylatobis[ (1,2- diaminocyclohexane)platinum(II) tetrahydrate] . Elemen-

tal analysis for C23H3oN θχoPt2' ^4H 2 ^0: Calculated C, 28.05; H, 3.89; N, 5.68; Found C, 27.89; H, 3.91; N, 5.64.

The infrared spectrum as a KBr pellet shows a major peak at 1600 cm~l, indicative of platinum-bound carboxyl groups and a small peak at 1700 cm~l, indicative of a free carboxyl group. The compound is insoluble in water and common organic solvents, but dissolves readily in 1% NaHCθ3« Thin layer chromatography of a bicarbonate solution of the compound on reverse phase silica gel plates eluted with methanol/water (2/1) gives a S Cl2 positive spot at Rf=0.85.

EXAMPLE 2 Antitumor activity of benzenepentacarboxylatobis- [(1,2-diamonocyclohexane) platinum(II) ]

The bis-platinum complex of Example 1, dissolved in 1% aHCθ3 solution, was screened against the murine tumor line L1210 leukemia over a dose range of 2.5-20 mg/kg and a dose schedule of daily x 7 and days 1, 5, and 9. The results are presented in Table I. A dose of 20 mg/kg was toxic on the daily x 7 schedule and 40 mg/kg was toxic on the days 1, 5, 9 schedule.

TABLE I

Dose Percent Increase int Lifespan ^a (mg/kg Daily x 7 Drugsi 1, 5 and 9

2.5 87 21

5.0. 117 43 10.0 61 135 20.0 — 193

^a Treatment was started 24 hours after inoculation of 1 x 10 ^δ L1210 cells in CDF^ mice. The drug was administered intraperitoneally.

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The test showed this compound to be active against the experimental murine tumor line L1210 leukemia. Its solubility of greater than 10 mg/ml in 1% NaHCθ3 solu¬ tion allows it to be readily administered to patients.- EXAMPLE 3

Preparation of hydroquinone-2,5-disulfonato bis[ (1,2-diaminocyclohexane) platinum(H) ]

To an aqueous solution of dinitrato (1,2-diamino- cyclohexane) platinum(II) , prepared according to Example 1, was added 1/2 equivalent of a solution of hydroquinone- 2,5-disulfonic acid dipotassium salt (Aldrich), to which an equivalent of potassium hydroxide was added to form the tetrapotassium salt. An immediate white precipitate formed which was collected, washed thoroughly with water and dried in vacuo. 0.9 grams of the sulfonic acid (2.6 meq) yielded 1.2 grams of the bisplatinum complex (56%). An infrared spectrum of the product had strong absorptions at 3200, 2920, 2830, 1590, 1410, 1170, 1160, 1060, 1010, 800 and 650 cm-1. The product dissolved in 1% NaHCθ3 solution.

By an analogous procedure, the hydroquinone-2,5- disulfonate bis-Pt(II) complexes of: [4-amino-5-aminomethyl-2-methylpyrimidine]Pt(II) , [5,6-diaminouracil]Pt(II) , [3,4-diamino-5-pyrazolol] Pt(II), [ethylenediamine]Pt(H) and [o-phenylenediamine] Pt(II) are prepared.

EXAMPLE 4 Prepration of benzenepentacarboxylatobis[ethylene- diamine] platinum(II) ]

Dichloro (ethylenediamine) platinum(H) was prepared from the reaction of potassium tetrachloroplatinate and ethylenediamine. The reactants were stirred in water at room temperature to give a yellow precipitate which was collected, washed with water and dried in vacuo over calcium chloride overnight. The product was then reacted with 1.9 equivalents of silver nitrate dissolved in water

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and the mixture was stirred for 12 hours, protected from light. Silver chloride was removed by filtration.

To the filtrate was added 1/2 equivalent of benzenepentacarboxylic acid dissolved in water. The pH of the solution was adjusted to 4.5 with I NaOH solution. The solution was warmed at 40°C for 1 hour and a tan precipitate formed, which was collected, washed and dried. In one preparation, 200mg of benzenepentacarboxylic acid (0.67 meq) yielded 250mg of product.

An infrared spectrum of the product had absorptions at 3200, 3100, 1700(sh), 1600, 1320, 1140, 1050 cm- ¹ . The shoulder at 1700 indicates unbound carboxyl group, while a stronger absorption at 1600 cm""l shows platinum-bound carboxylate groups.

The product dissolves in 1% NaHCθ3 solution.

By an analogous procedure, [ethylenediamine]Pt(II) complexes of IIA-H are prepared.

EXAMPLE 5 Preparation of aurintricarboxylatobis[(1,2-diamino- cyclohexane) platinum(II) ]

To 120 mg of aurintricarboxylic acid .(0.28 meq) (Aldrich) was added 1 ml of INNaOH to form a solution at pH=12. To this solution was added an aqueous solution of dinitrato (1,2-diaminocyclohexane) platinum (250 mg; 0.57 meq), prepared according to Example 1, and the pH was reduced to 5.7. An immediate red precipitate formed. After drying, 250 mgs (85% yield) was collected. An infrared spectrum of the product showed peaks at 3200, 3100, 2920, 2840, 1600(sh), 1560, 1360, 800 cm ^-1 . By an analogous procedure, the aurintricarboxylato complexes of

[4-amino-5-aminomethyl-2-methylpyrimidine]Pt(H), [5,6-diaminouracil]Pt(II) , [3,4-diamino-5-pyrazolol] Pt(II), [ethylenediamine]Pt(II) and [o-phenylenediamine] Pt(II) are prepared.

EXAMPLE 6 Preparation of 5,5' -carbonylbistrimellito bis [ (l,2-diaminocyclohexane)platinum(H) ]

5,5'-Carbonylbistrimellitic acid (223 mg; 0.5 meq) (Aldrich) was dissolved in water with the addition of 2 ml of IN NaOH. Dinitrato (1,2-diaminocyclohexane) platinum (500 mg; 1.1 meq) was added and the pH of the resulting mixture was maintained at 5. The mixture was kept at room temperature and after 30 minutes a white precipitate started to form. The product was collected by filtration, washed with water and dried in vacuo to yield 350 mg (63%) of product.

The product dissolves readily in 1% aHCθ3 solution. An infrared spectrum of the product had the following peaks: 3200, 3100, 2920, 2840, 1780(C=0), 1700(sh), 1580, 1380, 960, 800, 690 cm ^"1 .

By an analogous procedure, the 5,5'-carbonyl¬ bistrimellito complexes of

[4-amino-5-aminomethyl-2-methylpyrimidine]Pt(II) , [5,6-diaminouracil]Pt(H) , [3,4-diamino-5-pyrazolol]

Pt(II), [ethylenediamine]Pt(II) ,and [o-phenylenediamine] Pt(II) are prepared.

EXAMPLE 7 Preparation of 5-(2-carboxy-4,5-dihydroxyphenylazo) salicylatobis[ (1,2-diaminocyclohexane)platinum(II) ] 0.005 Mole of 5-aminosalicylic acid, in 35 ml of 0.5M HCl was cooled to 0°C, and treated with 0.0052 mole aNθ2 in 2 ml deionized water to form the diazonium salt. A suspension of the diazonium salt was transferred to an addition funnel and added over 70 minutes to an ice cooled solution of 3,4-dihydrozybenzoiσ acid (0.005 mole) in 47 ml of 0.5M aqueous NaHCθ3, with stirring, to produce a dark red product. The reaction mixture was diluted with 120 ml of cold water, and 14.5 ml of lM HCl was added, resulting in separation of solid product, which was filtered and vacuum dried.

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The azo-coupled catechol/salicylatewas dissolved in water with 2 equivalents of base, and reacted with 2 equivalents of dinitrato(l,2-diaminocyclohexane) platinum(II) , as in the procedure of Example 1, except that the pH was adjusted to 9.3 with IN NaOH. A reddish- brown precipitate formed (60% yield), which was very soluble in 1% NaHCθ3 solution.

The infrared spectrum had peaks at 3200, 3100, 2900, 2850, 1700, 1600, 1480, 1440(azo), 1380, 790 cm ^"1 -

By an analogous procedure, the azo-linked complexes mentioned above can be prepared.

EXAMPLE 8 Preparation of hydroquinone-2,5-diacetato bis[(1,2-diaminocyclohexane)platinum(IV) ] 2 ₇ 5-Hydroquinone-2,5-diacetic acid (125 mg; 0.55 meg) (Aldrich) was dissolved in water with the addition of NaOH. Dinitrato (1,2-diaminocyclohexane) platinum (500 mg; 1.15 meg) was added, and the pH of the resulting solution was adjusted to 7. After 1 hour at room temperature, a tan precipitate formed. The product, hydroquinone-

2,5-diacetato bis[ (1,2-diaminocyclohexane) platinum (II)] was collected, washed with water and dried to yield 200 mg (43%) . The infrared spectrum of the product had peaks at 3200, 3100, 2920, 2840, 1560, 1360, 1200, 1050, 1020 cm ^"1 .

The compound is insoluble in basic solutions. The compound was then suspended in water at 60° and 3 ml of 30% hydrogen peroxide was added dropwise to form a yellow solution. Unreacted starting material was filtered off and the filtrate was evaporated to 10% volume. Ethanol was then added to precipitate a yellow product. The infrared spectrum of this platinum (IV) compound had the following peaks: 3200, 3100, 2920, 2840, 1700, 1600, 1360, 690, 560 cm ^"1 .

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By an analogous procedure, Pt (IV) complexes corresponding to each of the Pt (II) complexes mentioned above can be prepared, as can Pt (IV) complexes of the tetradentate ligands IIA-H, IIIB, IIIC, HIE, bicyclo[2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic acid, cyclobutane-

1,2,3,4-tetracarboxylic acid, furan-2,3,4,5-tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic acid, 2,5- dihydroxyterephthalic acid, hydroquinone-2,5-diacetiσ acid, 2,4,5-trihydroxybenzoic acid, benzene-1,2,4,5- tetracarboxylic acid, 4-(4*-salicylylazo)phthalic acid, and cyclohexane-l,2,4,5-tetracarboxylic acid.

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The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of tKis invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and con- ditions.