Bepridil enhances adriamycin-induced DNA biosynthesis inhibition in human myeloid leukemia cells

The utilization of drug response modulators, based on their physico-chemical properties to augment the cytotoxic response of anticancer drugs is now gaining importance. We present in this communication, investigations performed to assess the antitumor activity of Adriamycin (ADR), on chronic myeloid leukemia (CML) cells, and the effect of bepridil, a calcium channel blocker on the ADR cytotoxicity. Inhibition of 3H-thymidine incorporation into DNA was used as an index of the cytotoxic effects of drugs when utilised alone or in combination. The combination of bepridil (1 and 5 micrograms/ml) and ADR (5 and 10 micrograms/ml) indicated a significant (P less than 0.001) enhancement in the DNA biosynthesis inhibition in CML cells, as compared to those samples exposed to ADR alone. The observed inhibition of DNA biosynthesis was found to be totally reversible, partially reversible and completely irreversible when the CML cells were exposed to bepridil alone, ADR alone and ADR plus bepridil, respectively. Bepridil was found to be highly lipid soluble at physiological pH, and this property could be responsible for the modulation of the ADR activity observed in this study. Results obtained, though preliminary due to the small sample size, clearly indicate a necessity for a detailed evaluation of bepridil effects, which would lead to higher therapeutic gains in anticancer chemotherapy in the clinic.