Abstract 5739: Characterization of the metabolism and DNA adduct formation of 2-amino-9H-pyrido[2,3-b]indole in human hepatocytes

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Abstract 2-Amino-9H-pyrido[2-3-b]indole (AαC) is a heterocyclic aromatic amine (HAA) and considered to be a possible human carcinogen by the International Agency for Research on Cancer (IARC). Like other HAAs, AαC is metabolized in the liver and can undergo bioactivation to produce highly electrophilic derivatives that can form DNA adducts by covalent binding to DNA. Among the HAAs, AαC is of particular interest because it is present at high levels in tobacco smoke and ubiquitous in the environment. AαC was shown to form high levels of DNA adducts in primary cultured human hepatocytes. The adduct levels were higher than those formed by other HAAs such as 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) or 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and comparable to those derived from 4-aminobiphenyl (4-ABP), a known human carcinogen. An understanding of the metabolism of AαC and its potential to form DNA adducts would provide a better assessment of the human health risk posed by AαC. Indeed, the metabolism pathways of MeIQx, PhIP and AαC are different. These differences in metabolic processing of HAAs can lead to variable levels of DNA adducts formed in humans and impact the interindividual susceptibility towards these procarcinogens. Knowledge about the metabolism of AαC in humans is unknown. We have analyzed the role of human cytochromes P450, especially CYP1A2, in the metabolism of AαC and DNA adduct formation. The ring-oxidized 3-HO-AαC and 6-HO-AαC sulfate and glucuronide conjugates, AαC-N2-Gl, N2-acetyl-AαC and the glucuronide conjugates of 2-hydroxyamino-9H-pyrido[2,-3-b]indole (HONH-AαC) and the deoxyguanosine DNA adduct, dG-C8-AαC, were identified and quantified by liquid chromatography coupled with multistage mass spectrometry in human hepatocytes in primary culture. The levels of DNA adducts formed after a 24hr-treatment with AαC were (2 folds) lower when cells were pre-treated with furafylline, a specific CYP1A2 inhibitor; however, the levels of most of the metabolites formed were not significanly affected by furafylline. Our data suggests that CYPs other than CYP1A2 may be involved in AαC metabolism, while CYP1A2 is the main enzyme involved in the production of reactive metabolites leading to the formation of DNA adducts. The identification of CYPs and Phase II enzymes involved in AαC metabolism in human hepatocytes are under study to fully understand the health risk of AαC to humans. 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 5739. doi:1538-7445.AM2012-5739