Enhancement of vincristine- and adriamycin-induced cytotoxicity by verapamil in P388 leukemia and its sublines resistant to vincristine and adriamycin.

A calcium antagonist, verapamil, enhanced the cellular uptake and cytotoxicity of vincristine (VCR) in adriamycin-resistant P388 leukemia (P388/ADM) cells and also enhanced the cellular uptake and cytotoxicity of adriamycin (ADM) in vincristine-resistant P388 leukemia (P388/VCR) and P388/ADM cells. The enhancement of cytotoxicity and cellular uptake of VCR in P388 and P388/VCR cells has been reported previously. [1]. VCR and ADM resistance was circumvented by verapamil. A common transport mechanism for VCR and ADM, which is responsive to verapamil, seems to exist in VCR- and ADM-resistant cells. However, the enhancement of ADM cytotoxicity and cellular uptake by verapamil was not evident in P388 cells.