Chemical and Biological Studies on a Series of Lipid-Soluble (trans-(R,R)- and -(S,S)-1, 2-Diaminocyclohexane)platinum(II) Complexes Incorporated in Liposomes

cw-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 >95% and stability in normal saline at 4 °C was >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.