[Mechanism of resistance to antitumor agents--its involvement in blood-brain barrier].

Resistance of tumors to a variety of chemotherapeutic agents presents a major problem in cancer treatment. The gene responsible for multidrug resistance, termed mdr1, encodes a membrane glycoprotein (P-glycoprotein) that acts as a pump to transport various cytotoxic agents. The P-glycoprotein has been shown to bind anticancer drugs and several resistance-reversing agents including calcium channel blockers, and to be an ATPase. The P-glycoprotein was found to function in the blood-brain barrier. The physiological function of the P-glycoprotein in relation to therapy is discussed.