CYP1A1 and CYP1B1-Mediated Biotransformation of the Antitrypanosomal Methamidoxime Prodrug DB844 Forms Novel Metabolites Through Intramolecular Rearrangement

DB844 (CPD-594-12), N-methoxy-6-{5-[4-(N-methoxyamidino)phenyl]-furan-2-yl}-nicotinamidine, is an oral prodrug that has shown promising efficacy in both mouse and monkey models of second stage human African trypanosomiasisHowever, gastrointestinal (GI) toxicity was observed with high doses in a vervet monkey safety studyIn the current study, we compared the metabolism of DB844 by hepatic and extrahepatic cytochrome P450s to determine whether differences in metabolite formation underlie the observed GI toxicityDB844 undergoes sequential O-demethylation and N-dehydroxylation in the liver to form the active compound DB820 (CPD-593-12)However, extrahepatic CYP1A1 and CYP1B1 produced two new metabolites, MX and MYAccurate mass and collision-induced dissociation mass spectrometry analyses of the metabolites supported proposed structures of MX and MYIn addition, MY was confirmed with a synthetic standard and detection of nitric oxide (NO) release when DB844 was incubated with CYP1A1Taken altogether, we propose that MX is formed by insertion of oxygen into the amidine C'N to form an oxaziridine, which is followed by intramolecular rearrangement of the adjacent O-methyl group and subsequent release of NOThe resulting imine ester, MX, is further hydrolyzed to form MYThese findings may contribute to furthering the understanding of toxicities associated with benzamidoxime- and benzmethamidoxime-containing molecules© 2013 Wiley Periodicals, Incand the American Pharmacists Association J Pharm Sci 103:337-349, 2014