Multidrug resistance.

Since we found verapamil as a multidrug resistance (MDR) reversing agent in 1981, many MDR reversing compounds have been reported. This type of drug must have strong effects with little side effects. We recently found MS-209 and PSC-833 as reversing agents. These two compounds interacted directly with P-glycoprotein, and showed a good MDR reversing effect in vitro and in vivo. MRK16, an antibody against P-glycoprotein, also showed a good therapeutic effect against drug resistant human tumors. MS-209, PSC-833 and the antibody against P-glycoprotein are interesting candidates for clinical use in the future.