Potentiation of chemotherapeutic effect of vincristine in vincristine resistant tumor bearing mice by calmodulin inhibitor clomipramine.

Clomipramine, which is used as antidepressant and possesses calmodulin inhibitory activity, circumvented partly the vincristine resistance in vivo. Although vincristine alone at 30-200 micrograms/kg did not confer a significant therapeutic effect in vincristine resistant P388 leukemia (P388/VCR)-bearing mice, clomipramine at doses of 20 to 50 mg/kg administered daily for 10 d with vincristine enhanced the chemotherapeutic effect of vincristine in P388/VCR-bearing mice. Approximately a 30% increase in life span occurred. Although the circumvention of vincristine resistance was not achieved perfectly, it could be speculated that more than 98-99% of vincristine resistant tumor cells which could not be killed by vincristine alone could be killed by this approach.