The cancer chemotherapeutic agent amsacrine, 4'-(9-acridinylamino)-methanesulfon-m-anisidide (mAMSA), is thought to effect cytotoxicity by inhibiting the ATP-dependent enzyme topoisomerase II in the act of its duplex strand-passing action. Upon protein denaturation, the arrested "cleavable complex" that results gives rise to double- and single-strand breaks… (More)