Abstract 1303: Characterization of the metabolite profile for batracylin and N-acetylbatracylin in rat and human models of invitro and in vivo metabolism: Elucidation of pathways that might contribute to batracylin toxicity

Abstract

Abstract Batracylin (NSC 320846, BAT) is a heterocyclic arylamine and topoisomerase II inhibitor that was shown to be active in several murine tumor models. Pharmacology and toxicology studies demonstrated marked species differences in sensitivity to the toxic effects of BAT attributed to metabolism to N-acetylbatracylin (NacBAT) by N-acetyltransferase (NAT). It was subsequently shown that BAT is a preferential substrate for human NAT2; thus production of NacBAT is likely subject to population variability as a function of known NAT2 polymorphisms. A phase I clinical trial of BAT in patients with advanced cancer and slow acetylator NAT2 genotypes to reduce the risk of toxicity due to NacBAT is ongoing and a potentially dose-limiting toxicity of cystitis/hemorrhagic cystitis was observed in several patients. In order to determine if this toxicity is due to BAT, NacBAT, and/or other metabolites, we investigated the in vitro metabolism of BAT and NacBAT in human (h) and rat (r) liver microsomes (LM) and hepatocytes, and the in vivo metabolism of BAT and NacBAT in rats. 14C-BAT and differentially deuterated (d3- and d4-) BAT were provided to facilitate metabolic profiling. d3- and d4- NacBAT were generated in situ. BAT, NacBAT and their metabolites were detected and quantified by HPLC with diode array, fluorescence, radiochemical and mass spectrometry as appropriate. The goals of these investigations were to obtain a detailed metabolic profile for BAT in rats and humans and to elucidate pathways that might contribute to BAT toxicity. In NADPH-fortified microsomal preparations, loss of BAT was accompanied by formation of one hydroxylated metabolite in hLM and three hydroxylated metabolites in rLM. The single hydroxylated metabolite found in incubations of NacBAT with hLM was attributed to deacetylation by microsomal carboxlesterase. Six mono- and di- hydroxy NacBAT metabolites were found in incubations of NacBAT with rLM. Hydroxylation sites were identified with deuterated BAT and NacBAT. Incubation with recombinant cytochomes P450 (CYPs) identified rCYP1A1, rCYP1A2, hCYP1A1 and hCYP1B1 as the major CYP isoforms that metabolize BAT and NacBAT. Glucuronide conjugates of BAT and NacBAT were identified in rat and human hepatocyte incubations. NacBAT, hydroxylated BAT and NacBAT, and glucuronide conjugates were detected in in vivo metabolism and pharmacokinetic studies with BAT and NacBAT in rats. Finally, thiol-containing adducts, consistent with metabolic activation of BAT, were identified in kidney and urine samples from in vivo metabolism and pharmacokinetic studies with rats. In conclusion, we characterized the in vitro and in vivo metabolism of BAT and identified a pathway for metabolic activation of BAT to potential toxic metabolites. Supported by NCI Contract N01-CM-52206. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1303. doi:10.1158/1538-7445.AM2011-1303