UNIDIRECTIONAL MEMBRANE UPTAKE OF THE ETHER LIPID ANTINEOPLASTIC AGENT EDELFOSINE BY L1210 CELLS

We have studied the cellular uptake of edelfosine octadecyl-2-O-methyl -rac-glycero-3-phosphocholine; ET-18-OCH3), a membrane active anticanc er drug of the ether lipid family, by L1210 murine leukemia cells. Ini tial unidirectional linear uptake velocity was 1.1 nmol/min per 2 x 10 (6) cells, at about 30 min it reached a steady-state phase of accumula tion of approximately 5 nmol/2 x 10(6) cells. Concentration studies in dicated no saturation kinetics from 0 to 40 muM. Studies with metaboli c inhibitors displayed no energy dependence. There was no effect of ch loroquine, monensin or cytochalasin B, which are known inhibitors of e ndocytosis. The inhibitory effect of lower temperature on uptake was m oderate in extent and compatible with passive diffusion. There was no efflux of drug from preloaded cells which indicates intense binding of incorporated drug to cells. In human serum, edelfosine bound to sever al protein components, primarily high density lipoprotein and albumin, and this may explain why cellular uptake was slowed considerably by t he presence of serum or albumin in the incubation medium. We conclude that the lipophilic ether lipid derivative edelfosine is taken up by p assive diffusion by the L1210 cell. It is tightly bound to cellular st ructures, probably by insertion into the membrane lipid bilayer.