The research goal of this revision proposal is related to Reducing Toxicity of Tobacco Products and Smoke, one of the four areas relevant to the Family Smoking Prevention and Tobacco Control Act. Specifically, we seek to gain a better understanding of the mechanisms underlying cigarette smoke (CS)-induced lung tumorigenesis in mouse models, in order to improve the utility of mouse models for testing the carcinogenicity of tobacco products. We propose to use two novel transgenic mouse models developed in the PI's laboratory to test the hypotheses that 1) suppression of hepatic cytochrome P450 (P450) family of biotransformation enzyme activity will lead to increased circulating and tissue levels of CS carcinogens and, consequently, increased lung DNA damage and tumorigenesis in mice exposed chronically to CS, and 2) CS-induced lung tumorigenesis depends on target-tissue bioactivation of tobacco carcinogens by P450 enzymes. The two mouse models, both targeting the cytochrome P450 reductase (CPR), an enzyme required for the activities of all microsomal P450 enzymes, are the liver-Cpr-null (LCN) mouse, in which Cpr expression is absent in hepatocytes, and the extra-hepatic Cpr-low (or xh-CL) mouse, in which Cpr expression, and thus P450 activities, in all extrahepatic tissues (including the lung) are greatly decreased.
Two Specific Aims are proposed.
In Aim 1, we will determine the impact of hepatic P450 activity on CS-induced lung tumorigenesis. We will compare LCN A/J and wild-type (WT) A/J mice for sensitivity to CS-induced lung tumorigenesis, and for levels of CS-induced lung DNA adducts formed by major tobacco carcinogens in vivo. The ability to show increased tumorigenic responses in tumor bioassays would make it more practical to apply the assays to testing of new """"""""reduced-toxicity"""""""" tobacco products, as well as for testing efficacy of lung tumor chemoprevention.
In Aim 2, we will determine whether CS-induced lung tumorigenesis in AJ mouse depends on P450-mediated bioactivation in the target tissue. We will compare xh-CL A/J and WT A/J mice for sensitivity to CS-induced lung tumorigenesis, and for levels of CS-induced DNA adducts in the lungs and livers. The anticipated results will resolve the controversy about whether the lung tumors observed in CS-exposed mouse models are derived from direct tumor initiation by CS, through genotoxic pathways that depend on P450- mediated bioactivation of procarcinogens, as opposed to increased promotion by CS of spontaneous tumors.
A better understanding of the mechanisms underlying the cigarette smoke-induced lung tumorigenesis in the mouse would increase confidence in the predictive value of the animal model for the human risks of developing lung cancer, which is the leading cause of cancer-related death in the U.S. General improvements in the sensitivity of the mouse models to cigarette smoke-induced lung tumorigenesis would make mouse lung tumor bioassays more applicable to the testing of various """"""""reduced-toxicity"""""""" tobacco products, as well as for testing efficacy of lung tumor chemoprevention.
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