ATP- and glutathione-dependent transport of chemotherapeutic drugs by the multidrug resistance protein MRP1

1 The present study was performed to investigate the ability of the multidrug resistance protein (MRP1) to transport different cationic substrates in comparison with MDR1-P-glycoprotein (MDR1). Transport studies were performed with isolated membrane vesicles from in vitro selected multidrug resistant cell lines overexpressing MDR1 (A2780AD) or MRP1 (GLC(4)/Adr) and a MRP1-transfected cell line (S1(MRP)). 2 As substrates we used H-3-labelled derivatives of the hydrophilic monoquaternary cation N-(4',4'-azo-n-pentyl)-21-deoxy-ajmalinium (APDA), the basic drug vincristine and the more hydrophobic basic drug daunorubicin. All three are known MDR1-substrates, 3 MRP1 did not mediate transport of these substrates per se. In the presence of reduced glutathione (GSH), there was an ATP-dependent uptake of vincristine and daunorubicin, but not of APDA, into GLC(4)/Adr and S1(MRP) membrane vesicles which could be inhibited by the MRP1-inhibitor MK571. 4 ATP- and GSH-dependent transport of daunorubicin and vincristine into GLC4/Adr membrane vesicles was inhibited by the MRP1-specific monoclonal antibody QCRL-3. 5 MRP1-mediated daunorubicin transport rates were dependent on the concentration of GSH and were maximal at concentrations greater than or equal to 10 mM. The apparent K-M value for GSH was 2.7 mM. Transport of daunorubicin in the presence of 10 mM GSH was inhibited by MK571 with an IC50 of 0.4 mu M. 6 In conclusion, these results demonstrate that MRP1 transports vincristine and daunorubicin in an ATP- and GSH-dependent manner. APDA is not a substrate for MRP1.