Effect of calcium influx blocker verapamil on adriamycin-induced cytotoxicity in leukemia cells in vitro.

The effect of verapamil (calcium influx blocker) on adriamycin-induced cytotoxicity against sensitive and resistant subline of K 562 acute myelogenous human leukemia cells has been evaluated. Verapamil by itself at a concentration of 0.5 microgram/ml did not affect the cell growth. It was found that the nontoxic concentration of verapamil moderately enhanced adriamycin cytotoxicity against K 562 cells, showing enhancement ratio of 1.3-1.4 according to the schedule used. A significant enhancement of adriamycin cytotoxicity (enhancement ratio of 5.8) was observed when verapamil and adriamycin were administered simultaneously against resistant subline of K 562/ADM cells. The results obtained give grounds to assume that verapamil could be used to overcome drug resistance in tumor cells.