ANTINEOPLASTIC ACTIVITY OF STERICALLY STABILIZED ALKYLPHOSPHOCHOLINE LIPOSOMES IN HUMAN BREAST CARCINOMAS

New sterically stabilized liposomes derived from the antitumor agent h exadecylphosphocholine with reduced uptake by the mononuclear phagocyt e system and improved antitumor activities were developed and tested. The bilayer of such sterically stabilized liposomes consists of hexade cylphosphocholine, cholesterol and polyethylene glycol-linked phosphoe thanolamine. The measurement of carbon clearance in mice shows that th ese stabilized liposomes, in contrast to conventional alkylphosphochol ine liposomes, are not largely engulfed by the mononuclear phagocyte s ystem. Their therapeutic activity on experimental human breast carcino mas MaTu, MT-1 and MT-3 was tested in nude mice. Especially in the MaT u models the sterically stabilized hexadecylphosphocholine liposomes r esulted in significantly reduced tumor growth in comparison to convent ional hexadecylphosphocholine liposomes or free hexadecylphosphocholin e. The enhanced therapeutic efficacy of sterically stabilized hexadecy lphosphocholine liposomes is probably related to the extended circulat ion time of the formulation and its accumulation in tumors.