Use of slow Ca2+ channel blockers to enhance inhibition by taxol of growth of drug-sensitive and -resistant Chinese hamster ovary cells.

The toxicity of taxol for drug-sensitive and -resistant Chinese hamster ovary cells has been examined in tissue cultures in the presence and absence of drugs that are being used as slow Ca2+ channel blockers. Enhancement of toxicity was found to be greater in the case of taxol than of daunorubicin. Several blockers including pimozide and nimodipine were more effective as toxicity enhancers than verapamil. Studies of uptake of 14C-labeled daunorubicin revealed a poor correlation between the effectiveness of various drugs to enhance intracellular daunorubicin concentration and their toxicity to cells grown in tissue cultures.