The activity of mammalian topoisomerase I is inhibited by acidic phospholipids. We investigated the effect of psychotropic drugs and local anesthetics on cardiolipin-inhibited calf thymus DNA topoisomerase I activity. Chlorpromazine, promethazine, and imipramine, which interact with phospholipids, suppressed the inhibitory effect of cardiolipin. The present results suggest that relaxation of DNA supercoiling is involved in the cytotoxic action of these drugs.
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