THE QUINOLINE-BASED DRUG, N-(4-[1-HYDROXY-2-(DIBUTYLAMINO)ETHYL] QUINOLIN-8-YL)-4-AZIDOSALICYLAMIDE, PHOTOAFFINITY LABELS THE MULTIDRUG-RESISTANCE PROTEIN (MRP) AT A BIOLOGICALLY RELEVANT SITE

MRP is a member of the ABC trafficking proteins thought to mediate the transport of glutathione S-conjugates and amphiphilic natural product s. However, unlike P-glycoprotein, the biochemical mechanism by which MRP mediates the resistance to cytotoxic drugs is not clear, In this r eport, we describe the interactions of a quinoline-based drug, N-{4-[1 -hydroxy-2-(dibutylamino)ethyl] quinolin-8-yl}-4-azidosalicylamide (IA AQ), with MRP. Our results demonstrate the ability of IAAQ to photoaff inity label a 190 kDa protein in resistant Small Cell Lung Cancer cell s (H69/AR) but not in the parental H69 cells. The photoaffinity labeli ng of the 190 kDa protein with IAAQ was both saturable and specific. T he identity of the 190 kDa protein, as MRP, was confirmed by immunopre cipitation with the monoclonal antibody, QCRL-1. Furthermore, a molar excess of LTC4, MK 571 or vinblastine inhibited the photoaffinity labe ling of MRP with IAAQ in intact cells and plasma membranes, Cell growt h and drug transport studies showed H69/AR cells to be less sensitive to and to accumulate less IAAQ than the parental H69 cells. In additio n, MK 571 and doxorubicin increased the sensitivity to and the accumul ation of IAAQ in H69/AR cells. Together, the results of this study sho w for the first time the direct binding of unaltered cytotoxic drug to MRP. Moreover, given the structural similarities between IAAQ and MK 571, we suggest that MK 571 modulates MRP-mediated resistance by direc t binding to MRP. (C) 1997 Academic Press.