Hepatocellular carcinoma (HCC) has been correlated with specific p53 mutations and exposure to aflatoxin B1 (AFB1). Individual response to liver carcinogens shows great variability. High risk factors include chronic infection with hepatitis B (HBV) and C viruses (HCV), while additional risk factors include exposure to tobacco smoke. Cytochrome P450 genes, such as CYP1A1, CYP1A2, CYP3A4, and CYP3A5 encode proteins that activate potent liver carcinogens into genotoxic epoxides. Heterocyclic aromatic amines (HAs) require additional activation by N,O-acetyltransferase (NAT2). Specific cytochrome P450 polymorphisms and NAT2 polymorphisms contribute to risk of specific cancers, such as breast, pancreatic and colon. However, determining the risk of P450 and NAT polymorphisms in HCC is complicated by many modifying factors that can lead to detoxification of metabolites. To determine whether P450 polymorphisms per se are sufficient to increase the genotoxicity of carcinogens, we have expressed the P450 genes in Saccharomyces cerevisiae (yeast), which lacks the detoxification enzymes. We previously observed that expression of specific P450 genes in yeast is sufficient to stimulate carcinogen-associated mutation and recombination, the transcriptional induction of DNA repair genes after AFB1 exposure, and AFB1-associated activation of the checkpoint gene Rad53 (CHK2). We propose to further screen CYP1A1, CYP1A2, CYP3A4 and CYP3A5 polymorphisms that are associated with increased cancer risk. In the first specific aim, we will determine whether a subset of CYP1A1 and CYP1A2 polymorphisms affect frequencies of genetic recombination and mutation and the DNA damage response to AFB1 and liver carcinogens. In the second specific aim, we will determine whether CYP1A2 and NAT2 polymorphisms affect the metabolic activation of HAs in yeast. In the third specific aim, we will develop an expression system for CYP3A4 and CYP3A5 in yeast that will enable us to detect metabolic activation of carcinogens mediated by CYP3A3 and CYP3A5 polymorphisms. These studies will thus provide a new strategy for determining the potential risk of cytochrome P450 polymorphisms in liver cancer. Ultimately, the information will aid public health practitioners and clinicians to identify which individuals are at highest risk for liver cancer, and guide prevention and early detection efforts.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Exploratory/Developmental Grants (R21)
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Cancer Etiology Study Section (CE)
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Thompson, Claudia L
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Ordway Research Institute, Inc.
United States
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Fasullo, Michael; Freedland, Julian; St John, Nicholas et al. (2017) An in vitro system for measuring genotoxicity mediated by human CYP3A4 in Saccharomyces cerevisiae. Environ Mol Mutagen 58:217-227
Freedland, Julian; Cera, Cinzia; Fasullo, Michael (2017) CYP1A1 I462V polymorphism is associated with reduced genotoxicity in yeast despite positive association with increased cancer risk. Mutat Res 815:35-43
Fasullo, Michael T; Sun, Mingzeng (2017) Both RAD5-dependent and independent pathways are involved in DNA damage-associated sister chromatid exchange in budding yeast. AIMS Genet 4:84-102
Fasullo, Michael; Smith, Autumn; Egner, Patricia et al. (2014) Activation of aflatoxin B1 by expression of human CYP1A2 polymorphisms in Saccharomyces cerevisiae. Mutat Res Genet Toxicol Environ Mutagen 761:18-26
Fasullo, Michael; Sun, Mingzeng; Egner, Patricia (2008) Stimulation of sister chromatid exchanges and mutation by aflatoxin B1-DNA adducts in Saccharomyces cerevisiae requires MEC1 (ATR), RAD53, and DUN1. Mol Carcinog 47:608-15