Doxorubicin resistance circumvention by verapamil in B16 melanoma cells.

We present data on the cellular drug pharmacokinetic alterations correlated with the circumvention of doxorubicin resistance by verapamil in a B16 melanoma cell line. An increased drug uptake, a decreased drug efflux and a different intracellular drug distribution appear to be responsible for the enhancement of doxorubicin cytotoxicity induced by treatment with verapamil in drug-resistant cells. However, doxorubicin pharmacokinetics and cytotoxicity were not affected by verapamil in doxorubicin-sensitive melanoma cells.