Abstract 3769: Metabolic activation of batracylin and N-acetylbatracylin to reactive metabolites that bind protein and DNA: Possible role in toxicity

Abstract

Abstract Batracylin (NSC 320846, BAT) is a heterocyclic arylamine and topoisomerase II inhibitor shown to be active in murine tumor models, but with demonstrated species differences in toxicity associated with metabolism to N-acetylbatracylin (NBAT) by N-acetyltransferase (NAT). BAT is a preferential substrate of human NAT2. Accordingly, production of NBAT should be subject to population variability as a function of NAT2 polymorphisms. A phase I clinical trial of BAT in patients with advanced cancer and slow acetylator NAT2 phenotypes to reduce the risk of NBAT-related toxicity found a dose-limiting toxicity (DLT) of cystitis/hemorrhagic cystitis. In subsequent in vitro and in vivo preclinical studies to elucidate metabolic pathways that might contribute to BAT toxicity, we found oxidative metabolites and thiol conjugates of BAT and NBAT (MM Ames et al, Cancer Res 2011;71(8 Suppl):Abstract nr 1303). Since these data are consistent with metabolic activation of BAT to potentially toxic metabolites, we assessed formation of reactive intermediates as measured by covalent binding (CB) to protein and DNA or by formation of glutathione conjugates. Radiolabeled BAT and NBAT were incubated with 3-MC-induced rat (r), human (h) and dog (d) liver microsomes (LM), as well as with recombinant human cytochromes P450 (CYPs) with or without added DNA. NADPH-dependent BAT protein and DNA CB were detected in all microsomal preparations (see table below). NADPH-dependent NBAT protein CB was detected in all microsomal preparations except hCYP1B1. NADPH-dependent NBAT DNA CB was detected in all microsomal preparations except 3MC-rLM. We also detected a glutathione conjugate of mono-hydroxy BAT by lc/ms/ms analysis when BAT was incubated with hLM in the presence of glutathione and NADPH. Thus, CYP-catalyzed oxidation of BAT yields reactive metabolites that that bind protein and DNA and may contribute to drug-related DLT. Supported in part by NCI Contract N01-CM-52206. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3769. doi:1538-7445.AM2012-3769