Multidrug resistance in cancer chemotherapy.

Resistance to chemotherapy is the single most important reason for treatment failure in cancer patients. Over the past 15 years, we have gained significant insight into one of the mechanisms responsible for this process: multidrug resistance (MDR). Far from being a phenomenon limited to the laboratory, multidrug resistance has been identified in a wide variety of newly diagnosed and recurrent human tumors. A number of compounds can block p-glycoprotein and overcome MDR in vitro and in vivo. Current strategies to block MDR are discussed in this review. Future research in this area will focus on the identification of more selective and potent MDR reversing agents and the development of entirely new approaches to overcoming multidrug resistance such as monoclonal antibodies, immunotoxins, and gene therapy.