Part I. Investigations of DNA damage mechanisms of azinomycin analogs and the natural product leinamycin. Part II. Biologically relevant chemical reactions of 1,2-dithiole-3-thiones as cancer preventive agents

Part I. Azinomycin is known to cause DNA crosslink formation. It has been proposed that reaction at aziridine residue proceeds alkylation of DNA by epoxide of azinomycin. Because epoxides are known to be efficient DNA alkylation agents (eg. pluramycin), and it seems likely that naphthalene binds to DNA, we examined whether formation of epoxide adducts in azinomycin could occur independent of aziridine reaction. More importantly, the epoxide-only metabolite of azinomycin is formed in vivo and retains potent biological activities. We find the left half of azinomycin B, containing only the epoxide moiety of the natural product, modifies guanosines in DNA with high efficiency. UV-vis, DNA unwinding, viscosimetry and fluorescence experiments indicate the naphthalene ring intercalates into DNA. The sequence specificity of azinomycin analogs is also discussed. Relying on these results, we are able to provide insights about the DNA crosslinking properties of the natural product azinomycin B.;Leinamycin is a structurally novel antitumor agent that is bioactivated by reaction with cellular thiols. It has been shown that thiol attack on leinamycin triggers DNA damage by two unprecedented mechanisms. Herein, we provide evidence of an interesting bioactivation pathway in which hydrolysis of the 1,2-dithiolan-3-one 1-oxide heterocycle in leinamycin generates a reactive episulfonium ion species that alkylates DNA. DNA alkylation by leinamycin triggered by other nucleophiles was also investigated. In addition, leinamycin has a unique and previously unknown 18-membered macrocycle, its DNA-binding properties are both mechanistically interesting and biologically important. The results of UV-Vis DNA titration, DNA alkylation efficiency of ds-DNA vs. ss-DNA support for the noncovalent association of leinamycin with DNA. We have suggested the thialzole dieneone portion of leinamycin may bind DNA by intercalation. The sequence specificity of DNA alkylation by leinamycin supports the notion that this compound binds noncovalently to double stranded DNA via intercalation.;Part II. Because prevention is the most desirable approach for fighting cancer, we are investigating the biologically relevant chemical properties of chemoprotective agents. 1,2-Dithiole-3-thiones are a promising class of chemoprotective agents that operate through induction of phase II enzymes. Dithiolethiones are currently in clinical trials as cancer preventive agents. Oltipraz (5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione) has been used to protect against carcinogenic effects of aflatoxin and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, which are known mutagens. Elucidation of the chemical events underlying the selective induction of phase II enzymes is crucial for understanding existing chemoprotective agents and for development of novel anticarcinogenic agents. Our goal is to define the nature of the chemical reactions of dithiolethiones with thiols under mimics of physiological conditions. We find that dithiolethiones could mediate thiol dimerization and lead to other types of thiol modifications. Such modifications of protein thiol groups could be relevant to signal transduction processes involved in the cellular chemoprotective response.