Enhanced therapeutic effects of liposome-associated 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine.

The ether-lipid 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH3) has anticancer activity, but systemic toxicity has restricted its therapeutic use. In this report "free" ET-18-OCH3 and a stable, well-characterized, liposome-based formulation of ET-18-OCH3 (ELL-12) were compared for in vivo toxicity in normal mice and for therapeutic efficacy in three mouse tumor model systems. The entrapment of ET-18-OCH3 in liposomes decreased the acute toxicity of ET-18-OCH3 after i.v. administration. The maximum tolerated dose for a single i.v. dose of free ET-18-OCH3 was found to be approximately 25 mg/kg, whereas the maximum tolerated dose for ELL-12 was approximately 200 mg/kg. ELL-12 was much less hemolytic in vivo than ET-18-OCH3. The therapeutic efficacy of free ET-18-OCH3 and ELL-12 was investigated against i.p. P388 leukemia, Lewis lung cancer lung metastases, and B16/F10 melanoma (lung tumor nodules) in mice. Although ET-18-OCH3 had some anticancer activity, it was found that ELL-12 was more effective than ET-18-OCH3 in all three tumor models at lower and nontoxic dose schedules. These results suggest that association of ET-18-OCH3 in stable, well-characterized liposomes transforms it into an effective antitumor agent.