The aim of the proposed research is to discover and develop unique, non-intercalative inhibitors of DNA topoisomerase II as potential antineoplastic agents. Prior studies on synthetic topoisomerase II agents led to a model pharmacophore that assimilated the structural elements of many intercalative and non-intercalative classes of agents. Based on these studies, the prototype agent azatoxin was designed. Azatoxin is a potent inducer of topoisomerase II -bound DNA strand breaks. Studies of structure-activity relationships of azatoxin and related compounds as well as consideration of work published by others has helped to refine the model.
The specific aims are to synthesize unique structural classes of topoisomerase II-directed agents that (1) incorporate the anthracycline-epipodophyllotoxin/azatoxin/qunotoxin nuclei (2) possess the DNA intercalation-minor groove binding motif proposed in their model and (3) that possess the potential to undergo significant structural alteration upon bioreduction or glutathione conjugation and/or by hypoxic conditions (4) that are non-intercalative and have the potential for photoactivated crosslinking to DNA while bound to the cleavable complex and (5) that possess defined conformational relationships between the minor groove binding and DNA intercalation domains in their model. Finally, in an attempt to provide new information on the mechanism of topoisomerase II poison cytotoxicity, they will compare the sensitivity of the alpha and beta isozymes of topoisomerase II to the different analogs, quantitate the levels of single and double strand DNA breaks and possibly through a collaboration, the intensity of drug-induced in vitro cleavage activity in the ras protooncogene.
