Enhancement of the cytotoxic effects of pepleomycin by dibucain.

T he ability of dibucain, a local anesthetic, to enhance the cytotoxicity of and the repair of potentially lethal damage induced by pepleomycin or X-rays has been studied in exponential and plateau phase cultures of Chinese hamster cells. No enhancement of X-ray cytotoxicity or inhibition of repair from X-ray injury was observed, but dibucain produced very significant enhancement of pepleomycin effectiveness. In both cases the effects induced were larger in the exponentially growing cells than in the plateau phase cells. Greater than 20-fold increases in the cytotoxic effectiveness of pepleomycin, and greater than 10-fold differences in survival after the cells had been allowed to repair the potentially lethal damage induced by pepleomycin were observed when the cells were treated with dibucain. The possible mechanisms underlying this enhance ment are discussed.