Abstracts of the 32nd Annual Meeting of the United Kingdom Environmental Mutagen society, 12–15 July 2009 at the University of Leeds, UK

Mutagenesis vol. 24 no. 6 pp. 523–552, 2009 doi:10.1093/mutage/gep046 Abstracts of the 32nd Annual Meeting of the United Kingdom Environmental Mutagen Society, 12–15 July 2009 at the University of Leeds, UK 1. Mechanisms of acrylamide carcinogenicity in relation to human risk Frederick A. Beland National Center for Toxicological Research, Jefferson, Arkansas, USA Acrylamide, a water-soluble a,b-unsaturated amide, is a contaminant in baked and fried starchy foods, including French fries, potato chips, and bread, as a result of Maillard reactions involving asparagine and reducing sugars. Other dietary sources of acrylamide include coffee, Postum coffee substitute, olives, and certain breakfast cereals. Acrylamide is carcinogenic in laboratory animals; however, there is controversy over the mechanism of tumor induction. Acrylamide undergoes cytochrome P450-catalyzed oxidation to glycidamide, a reactive epoxide that could be responsible for the carcinogenicity of acrylamide. To obtain information regarding the mechanisms of tumor induction by acrylamide, we have compared the carcinogenicity of acrylamide and glycidamide in two-year chronic bioassays with B6C3F1 mice and F344 rats, and in neonatal bioassays with B6C3F1 mice. The results strongly support a critical role for glycidamide in the carcinogenicity of acrylamide. Further support for this supposition was obtained by assessing mutation induction and DNA and hemoglobin adduct formation in the same experimental models used for the carcinogenicity bioassays. These data have been incorporated in physiologically based pharmacokinetic models to predict DNA adduct levels and carcinogenic risk in humans due to dietary exposure to acrylamide. 2. Mouse cytochrome P450 (Cyp) knockout, knock-in, and ‘humanised’ CYP lines are useful for environmental mutagenesis and cancer studies Daniel W Nebert1, Jake Shi1, Marian L Miller1 and Nadine Dragin2 1 University Cincinnati Medical Center, Cincinnati, OH, 45267-0056, USA; 2CNRS UMR 8162, Université Paris-Sud, Hôpital Marie Lannelongue, 92350 Le Plessis-Robinson, France Numerous studies relevant to mouse Cyp knockout, knock-in, and ‘humanised’ lines with regard to environmental mutagenesis and cancer have been carried out [e.g. Refs. 1–7]. Mouse genes knocked out include: Cyp1a1, Cyp1a2, Cyp1b1, Cyp2e1, Cyp2j5, Cyp3a cluster, Cyp7a1, Cyp7b1, Cyp8b1, Cyp19a1, Cyp24a1, Cyp26b1, Cyp27a1 and Cyp46a1. Humanised mouse lines include: hCYP1B1, hCYP1A1_1A2, hCYP2D6, hCYP2C18_2C19, hCYP2E1 and hCYP3A4. Double- and triple-knockouts of Cyp genes, mouse lines carrying two hCYP genes, and lines carrying one hCYP gene plus one hXRR (xenobiotic-related receptor) gene have also been created. Tumorigenesis studies are mostly associated with all three genes in the Cyp1 family, Cyp2e1, and Cyp8a1 (overexpression). Examples of CYP detoxication, as well as metabolic activation, are tissue- or cell-specific. In response to daily oral benzo[a]pyrene (BaP) at 125 mg/ kg/day, Cyp1(þ/þ) wild-type mice remain healthy for their normal lifetime whereas Cyp1a1(-/-) knockout mice die at
28 days with immunosuppression; Cyp1a1/1b1(-/-) mice do not show immunotoxicity or early death––suggesting that CYP1B1 in immune cells is both necessary and sufficient for BaP metabolic activation leading to immunosuppression. In response to daily oral BaP at 12.5 mg/kg/day, Cyp1(þ/þ) and Cyp1b1(-/-) mice remain healthy whereas Cyp1a1(-/-) mice now survive until 20–25 weeks; at 10-12 weeks Cyp1a1(-/-) mice develop adenocarcinoma of the proximal small intestine (PSI) and show highly elevated compensatory CYP1B1 expression. At this 12.5 mg/kg/day oral BaP dose, Cyp1a1/ 1b1(-/-) mice do not develop PSI tumors, indicating that CYP1B1 (metabolic activation of BaP) might be causative in BaP-induced PSI tumorigenesis. On the other hand, Cyp1a1/ 1b1(-/-) mice develop squamous cell carcinoma of the preputial gland duct (PGD). Hence, the same route-of-administration of a polycyclic aromatic hydrocarbon (BaP) results in one target tissue (PSI) developing cancer if one gene (Cyp1a1) is missing and another target tissue (PGD) developing cancer if two genes (Cyp1a1, Cyp1b1) are absent, all genotypes having a constant C57BL/6J genetic background. Reference 1. Gonzalez, FJ. (2003) Role of gene knockout and transgenic mice in the study of xenobiotic metabolism, Drug Metab. Rev., 35, 319–335. 2. Derkenne S, Curran CP, Shertzer HG, Dalton TP, Dragin N, Nebert DW. (2005) Theophylline pharmacokinetics: comparison of Cyp1a1(-/-) and Cyp1a2(-/-) knockout mice, humanized hCYP1A1_1A2 knock-in mice lacking either the mouse Cyp1a1 or Cyp1a2 gene, and Cyp1(þ/þ) wildtype mice. Pharmacogenet. Genomics, 15, 503-511. 3. Cheung C, Ma X, Krausz KW, Kimura S, Feigenbaum L, Dalton TP, Nebert DW, Idle JR, Gonzalez FJ. (2005) Differential metabolism of 2-amino-1methyl-6-phenylimidazol[4,5-b]pyridine (PhIP) in mice humanized for CYP1A1 and CYP1A2. Chem. Res. Toxicol., 17, 1667-1674. 4. van Herwaarden AE, Wagenaar E, van der Kruijssen CM, van Waterschoot RA, Smit JW, Song JY, van der Valk MA, van Tellingen O, van der Hoorn JW, Rosing H, Beijnen JH, Schinkel AH. (2007) Knockout of cytochrome P450 3A yields new mouse models for understanding xenobiotic metabolism. J. Clin. Invest., 117, 3583–3592. 5. Shi Z, Chen Y, Dong H, Amos-Kroohs RM, Nebert DW. (2008) Generation of ‘humanized’ hCYP1A1_1A2_Cyp1a1/1a2(-/-) mouse line harboring the poor-affinity aryl hydrocarbon receptor. Biochem. Biophys. Res. Commun., 376, 775–780.. 6. Uno S, Endo K, Ishida Y, Tateno C, Makishima M, Yoshizato K, Nebert DW. (2009) CYP1A1 and CYP1A2 expression: comparing ‘humanized’ mouse lines and wild-type mice; comparing human and mouse hepatomaderived cell lines. Toxicol. Appl. Pharmacol., 237, 119–126. 7. Dong H, Dalton TP, Miller ML, Chen Y, Uno S, Shi Z, Shertzer HG, Bansal S, Avadhani NG, Nebert DW. (2009) Knock-in mouse lines expressing either mitochondrial or microsomal CYP1A1: Differing responses to dietary benzo[a]pyrene as proof-of-principle. Mol. Pharmacol., 75, 555–567. 3. Nuclear receptor (CAR/PXR) humanised mouse models to study non-genotoxic hepatocarcinogenesis Clifford R. Elcombe1, Jillian Ross1, Nico Scheer2, Anja Rode2 and C. Roland Wolf1 1 CXR Biosciences, Dundee, UK; 2TaconicArtemis GmbH, Cologne, Germany PB is a non-genotoxic carcinogen that in mice induces hepatomegaly (characterised by hypertrophy and hyperplasia) and, following long-term treatment, hepatocellular tumours, possibly due to its ability to increase cell proliferation. The relevance of these tumours to human health is controversial due Ó The Author 2009. Published by Oxford University Press on behalf of the UK Environmental Mutagen Society. All rights reserved. For permissions, please e-mail: . 523 Abstracts to the lack of a clear molecular mechanism and suitable humanlike models. PB has been shown to activate the murine and human constitutive androstane receptors (CAR) and pregnane X receptors (PXR). CAR (...truncated)