Modulation of mitoxantrone cytotoxicity by verapamil in human chronic myeloid leukemia cells.

Calcium channel-blocking agent verapamil has been established to be an effective drug to modulate the action of many anticancer drugs. In this study, we examined the effect of verapamil on the cytotoxicity of mitoxantrone in human chronic myeloid leukemia (CML) cells. Mitoxantrone alone exhibited dose-dependent inhibition of DNA biosynthesis in CML cells. The addition of verapamil (3.3 microM) enhanced the responsiveness of CML cells to mitoxantrone (1 microgram/ml) cytotoxicity indicated by significant increased inhibition of thymidine incorporation (p less than 0.001). The present study demonstrates the possible efficacy of verapamil in the chemotherapy of CML with mitoxantrone.