The synthesis and characterization of a group of platinum(IV) compounds containing the various isomeric forms of 1,2-diaminocyclohexane (DACH) are described. Antitumor tests with the new complexes, as well as with other platinum(II) compounds containing the DACH ligand, revealed that trans,cis-PtIV(SS-DACH)(OH)2Cl2, 7, is more active than its mirror image, trans,cis-PtIV(RR-DACH)(OH)2Cl2, 6, against L1210 leukemia implanted in mice. However, activity is dependent on the tumor model, and against B16 melanoma implanted in mice, the activities of the two enantiomers are reversed, with 6 being more active than 7. The results of the tests are discussed in light of the mechanism by which Pt(IV) compounds are believed to express their antitumor effects.

A series of novel platinum(IV) complexes of the type DACH-PtIV-trans-(Y)2-cis-X (where DACH = trans-(1R,2R)-, trans-(1S,2S)-, or cis-1,2-diaminocyclohexane; X = diacetate, oxalate, malonate, methylmalonate, cyclobutanecarboxylate (CBCA), or 1,1-cyclobutanedicarboxylate (CB-DCA); and Y = acetate or trifluoroacetate) has been synthesized and characterized by elemental analysis, IR, and 195Pt-NMR spectroscopy. The compounds have been tested against cisplatin-sensitive L1210/0 leukemia, cisplatin-resistant L1210/DDP leukemia, and M5076 reticulosarcoma cell lines in vivo. Most of these analogs displayed reasonable activity against L1210/0 cells (%T/C = 135 to > 700). There were no gross differences in activity between analogs containing isomers of DACH. Selected compounds were evaluated against L1210/DDP tumor models in which they demonstrated reduced but significant activity compared with activity in the L1210/0 model. Interestingly, complex 20, PtIV(trans-1R,2R-DACH)-trans-(acetate)2-methylmalonate, was highly active against M5076, although it had no activity against the L1210 lines. The results demonstrate that specific combinations of axial and equatorial carboxylate ligands, together with the DACH carrier ligand, can favorably modulate the antitumor properties of platinum complexes and enhance circumvention of cisplatin resistance.

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Acquired drug resistance is a major drawback of using cisplatin in the treatment of cancer; however, analogs containing the 1,2-diaminocyclohexane (DACH) ligand can overcome this resistance. DACH can exist as the trans-1R,2R, trans-1S,2S or cis isomer, and we have examined whether specific isomers coordinated to a platinum(IV) center can modulate antitumor activities in murine tumor models in vivo. Ten isomeric series of DACH-Pt(IV) complexes were synthesized, each series containing a different combination of axial and equatorial ligands and varying only by the isomeric form of the DACH ligand. Among the ten series, seven clearly indicated superiority of the (R,R)-DACH-Pt(IV) complex against leukemia L1210/0 cells, while in three the R,R and S,S configurations gave similar efficacies which were better than that of the corresponding cis analog. In three out of the ten series, the antitumor activities of the S,S and cis complexes were similar, in six the cis analogs were the least effective, and in the remaining one the cis analog was superior to S,S. One series of complexes with axial chloro ligands and an equatorial 1,1-cyclobutanedicarboxylato group, which had produced the efficacy ranking R,R > cis > S,S in the L1210/0 model, gave S,S > R,R > cis against cisplatin-resistant L1210/DDP cells, R,R = S,S > cis against B16 melanoma cells, and R,R = S,S = cis against M5076 reticulosarcoma cells. The results demonstrate that profound variation can occur in antitumor activities among isomeric forms of the DACH-Pt(IV) complex. However, the (R,R)-DACH-Pt(IV) complexes appear to be of greater interest overall.

cis-Bis(neodecanoato)(trans-(R,R)-1,2-diaminocyclohexane)platinum( II) [L-NDDP] is a liposome incorporated lipophilic cisplatin analogue that has shown promising antitumor activity against tumors resistant to cisplatin and liver metastases in mice. L-NDDP is currently under clinical evaluation. However, NDDP is an isomeric mixture of different species having various isomeric neodecanoic moities as liganded leaving groups. A series of new highly lipid-soluble cis-bis(neodecanoato)(trans-(R,R)- and -(S,S)-1,2-diaminocyclohexane)platinum(II) [Pt] complexes, using single isomers of neodecanoic acid, were synthesized and characterized by analytical and spectroscopic techniques (infrared and 195Pt NMR). Multilamellar vesicles (MLVs) composed of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) at a molar ratio of 7:3 were used as carriers of the Pt complexes. The efficiency of incorporation of the liposomal-platinum (L-Pt) preparations was greater than 95% and stability in normal saline at 4 degrees C was greater than 95% at day 14 in each case. The iv LD50 values of all L-Pt preparations tested were in the range of 62.3 to 104 mg/kg. The % T/C obtained after a single ip injection of the optimal dose of L-Pt preparations against L1210 leukemia was in the range of 150 to 253 (160 for cisplatin). When a multiple ip injection schedule was used (on days 1, 5, and 9) the L-Pt preparations of R,R complexes (1, 7, and 9) were more active than cisplatin at the optimal dose (% T/C = 257 for each vs 220 for cisplatin). The L-Pt preparations of R,R complexes were also markedly active against L1210 leukemia resistant to cisplatin (% T/C 355, 231, and 185 respectively vs 112 for cisplatin). These studies show that the single isomers of NDDP are comparable to the original isomeric mixture in terms of toxicity and biological activity.