TAMOXIFEN DECREASES DRUG EFFLUX FROM LIPOSOMES - RELEVANCE TO ITS ABILITY TO REVERSE MULTIDRUG-RESISTANCE IN CANCER-CELLS

Tamoxifen decreased the efflux of the fluorescent marker drug, chloroq uine, from phosphatidylcholine liposomes. Tamoxifen is a known structu ral-mimic of cholesterol, which were both found to be similarly effect ive in preventing drug release from liposomes. This ability of tamoxif en and cholesterol to decrease drug efflux in a concentration-dependen t manner is likely to arise from their known ability to decrease membr ane fluidity both in liposomes and also in cancer cells. The possible importance of the ability of tamoxifen to inhibit drug efflux from lip osomes in relation to its ability to reverse multidrug resistance in c ancer patients caused by the efflux of cytotoxic therapeutic agents, i s discussed.