14-azacamptothecin: a potent water-soluble topoisomerase I poison.

On the basis of an analysis of luotonin A and its D-ring deaza analogue as topoisomerase I poisons and topoisomerase I-dependent cytotoxic agents, a novel analogue of the structurally related antitumor antibiotic camptothecin (CPT) was prepared. 14-Azacamptothecin was found to have much greater aqueous solubility than CPT, to inhibit topoisomerase I-mediated DNA relaxation more efficiently than CPT, and to stabilize the covalent binary complex to almost the same extent. 14-Aza CPT was found to be slightly less active than CPT in mediating cytotoxicity toward yeast expressing human topoisomerase I, possibly as a consequence of its greater off-rate from the CPT-topoisomerase I-DNA ternary complex.