Antitumor effects of alkylphosphocholines in different murine tumor models: use of liposomal preparations.

Hexadecylphosphocholine (HPC) and its analogs with a longer alkyl chain (C18 and C20) were examined for antineoplastic activity in the murine tumor models P388 leukemia, B 16 melanoma, the mammary carcinoma C3H and Ca 755, and the human MT-1 mammary tumor in nude mice. The maximum tolerated doses were determined and found to be higher in mice than in rats. The toxicity of the alkylphosphocholines increases with chain length. The murine mammary carcinoma C3H and the human MT-1 mammary carcinoma showed response to HPC whereas the classical screening models did not respond to the synthetic lipids. Furthermore, HPC showed activity in a mitoxantrone-resistant P388 leukemia. Treated/control values between 120 and 160% in survival time could be obtained following a daily application of the lipid. Examination of the activity of possible cleavage products of HPC gave no information about the mechanism of action of the used etherlipids. Liposomes with encapsulated mitoxantrone, formed from alkylphosphocholines, cholesterol and dicetylphosphate had the same activity against P388 mouse leukemia as the free drug. The hemolytic activity of the three lipids tested in vivo was assumed to be related to toxic deaths of single animals; hemolytic activity was observed to be sometimes independent of schedule and dose.