PHOSPHATIDYLCHOLINE AND PHOSPHATIDYLETHANOLAMINE BEHAVE AS SUBSTRATESOF THE HUMAN MDR1 P-GLYCOPROTEIN

The multidrug resistant cell line CEM/VBL300 and the parental CEM T-ly mphoblastic cell line from which it was derived were used to study the accumulation of fluorescent phospholipid analogs of phosphatidylcholi ne (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS). T he fluorescent analogs NBD-PC, NBD-PE, and NBD-PS and [H-3]PC were del ivered in liposomes prepared by ethanol injection. Fluorescence micros copy demonstrated decreased accumulation of the NBD-PC analog in the m ultidrug resistant cell line compared to the parental cell line. Verap amil enhanced NBD-PC accumulation in the resistant eels. Similar resul ts were obtained with insect cells expressing high levels of recombina nt human MDR1. Elimination of NBD fluorescence on the outer leaflet of the plasma membrane with dithionite permitted quantification of the i nternal cellular fluorescence by FAGS analysis. The drug resistant CEM /VBL300 cells accumulated approximately 10% the amount of NBD-PE and 2 0% the amount of NBD-PC compared to CEM drug sensitive cells. No diffe rence in internal accumulation of NBD-PS was found between the drug re sistant and drug sensitive cell lines. The internal accumulation of NB D-PE and NBD-PC was enhanced by the MDR reversal agents verapamil, cyc losporin A, and SDZ PSC 833 in the CEM/VBL300 cells but not in the CEM cells. The increased accumulation was dose dependent, and the relativ e potency of the reversal agents paralleled their ability to circumven t multidrug resistance. In addition, the monoclonal antibody UIC2 dire cted against the P-glycoprotein produced similar results. The evidence presented here suggests that PC and PE but not PS behave as substrate s for human MDR1 P-glycoprotein.