SYNTHESIS AND BIOLOGICAL STUDIES OF NEW LIPID-SOLUBLE CISPLATIN ANALOGS ENTRAPPED IN LIPOSOMES

A series of highly lipophilic platinum(II) complexes of the type cis-[(RNH2)2PtX2] have been synthesized, where R = ethyl, propyl, isopropyl, butyl, cyclopropyl, cyclopentyl, or neopentyl and X = either long-chain carboxylate, such as decanoate (C10), laurate (C12), myristate (C14), heptadecanoate (C17), stearate (C18), nonadecanoate (C19), or 2,2,3,3-tetramethylcyclopropylcarboxylate, or branched-chain carboxylate, such as neopentanoate, neohexanoate, neoheptanoate, neononanoate, or neodecanoate. These complexes have been characterized by elemental analysis, IR, and C-13 and Pt-195 NMR spectroscopic techniques. The platinum complexes were entrapped in multilamellar vesicles composed of dimyristoyl phosphatidylcholine (DMPC) and dimyristoyl phosphatidylglycerol (DMPG) at a 7:3 molar ratio and tested for antitumor activity. The entrapment efficiency of liposomal platinum (L-Pt) complexes ranged from 60 to 100 %. The percentage of T/C obtained after a single i.p. injection of the optimal dose of L-Pt complexes tested against L1210 leukemia ranged from 90 to 125 %. These L-Pt preparations did not show significant antitumor activity in mice.