Preface [Hot topic:Drug Resistance in Cancer Therapy (Guest Editor: Jian-Ting Zhang)]

Despite the success es in us e of anticancer agents in appr opriate combinations to treat human cancer s, resistance to chemotherapy fr equently occurs and is a major obstacle in success ful cancer treatment. Extensive studies with tumor cell lines have revealed that multidr ug resistance ( MD R) can develop and it may be one of the major caus es in clinical cancer chemotherapy failure. A dvances in elucidating the molecular mechanisms of the M DR phenotype indicated that existence of one or more dr ug ef flux pumps on the plas ma membranes of cancer cells is a f requent caus e of MDR. The use of thes e drug eff lux pumps is the f irs t line of defense system of cancer cells agains t anticancer dr ugs . These dr ug pumps include but not limit to P- glycoprotein (Pgp or ABCB1), multidr ug resistance ass ociated pr otein 1 (M RP1 or ABCC1), and br eas t cancer r es istance pr otein (BCRP or ABCG2). All thr ee pr oteins belong to the large superfamily of ATP- binding cassette ( ABC) tr ansporters w hich include various transporters with a wide variety of substrates. The current challenge is the successful development of modulators that can inhibit the function of these transporters to enhance efficacy of cancer chemotherapy. This special issue of Current Medicinal Chemistry-Anticancer Agents is devoted to reviews by experts on recent development in the studies of these proteins regarding the aspects of their drug binding sites, modulators, and our understanding of three dimensional structures of ABC proteins which may be useful for future rational drug designs. It is my pleasure to serve as the guest editor for this special issue and I would like to thank all the contributors for their insightful and stimulating reviews.