ABSTRACT
The mdr 1-type P-glycoprotein can confer multidrug resistance to tumor cells by actively pumping a wide variety of drugs from the cells. To counteract this drug resistance, P-glycoprotein-blocking agents are currently administered to patient during chemotherapy. However, this may also affect the normal physiological functions of the mdr 1-type P-glycoprotein. The P-gp is a transmembrane efflux transporter found on the luminal side of the capillary cells that comprise the blood-brain barrier. Recent insights recognize P-glycoprotein, as an important element of the blood-brain barrier (BBB), play an important role for mdr 1a P-glycoprotein in the blood-brain barrier. Studies in mice, which lack P-gp in the BBB 〔mdr1a (-/-) mice〕, have contributed significantly to these insights. In addition, the potential of new therapeutic approaches in the near future as well as their limitations will be clearified.