The emergence of multidrug resistant tumours during the course of chemotherapeutic treatment of cancer patients is a major obstacle in cancer chemotherapy. Although several mechanisms may contribute to the appearance of multidrug resistance phenotype (MDR) in tumour cells, reduced drug accumulation and the ability of cells to undergo apoptosis are thought to be very important in expression of MDR. The work in this thesis focuses on the mechanism responsible for the reduced drug accumulation in tumour cells, mainly the multidrug resistance protein (MRP1). / The molecular mechanism underlying the binding and efflux of drugs by the MRP1 is currently not well understood. Several studies have now demonstrated that the cysteinyl leukotriene C$ sb4$ (LTC$ sb4$) and other glutathione (GSH) S-conjugated anions are substrates for the MRP. To learn more about MRP-drug interactions, we characterized the binding of MRP to a non-glutathione photoactive quinoline compound (abbreviated, ASA-AQ) (Chapter II). Since MRP mediated multi-drug resistance can be modulated by the anionic quinoline LTD$ sb4$ cysteinyl leukotriene receptor antagonist (MK571), we speculated that other quinoline-based compounds are likely to interact with MRP. In Chapter III, we show that MDR cells that express MRP1 are more resistant to the antimalarial drug, chloroquine. We also show that. chloroquine is a substrate for MRP1 drug efflux. / Taken together, the results of this thesis describe the interactions of MRP1 with a quinoline-based photoactive drug and the antimalarial drug chloroquine.

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