Human CYP2A and respiratory tract xenobiotic toxicity

 描述(申请人提供)：肺癌是美国癌症相关死亡的主要原因，而接触烟草烟雾(TS)是最重要的致死因素。然而，尽管人们对烟草致癌作用和潜在的致癌机制已经了解很多，但人们对TS的致癌机制知之甚少。TS是一种实际的复杂环境混合物，许多人每天都会接触到这种混合物。体内特定致癌物及其生物活性在TS诱导的肺肿瘤发生中的作用，或在TS致癌前引起的病理变化，如肺部炎症，在很大程度上是未知的；但这些知识对于设计有效的TS诱导的肺毒性的化学预防和评估新烟草产品的安全性至关重要。这笔赠款的长期目标是确定呼吸道细胞色素P450(P450或CYP)酶在环境化学品的代谢激活和毒性中的作用，重点是在呼吸道选择性表达的人类酶CYP2A13。我们的中心假设是，CYP2A13在烟草相关肺癌的发生中起着至关重要的作用。细胞色素P4502A13在一种主要的烟草致癌物质4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(Nnk)诱导的肺肿瘤发生中的作用已经得到了充分的证实，例如，我们对该基因人源化的小鼠的研究。CYP2A13还能激活许多其他TS毒物/致癌物。对CYP2A13*2等位基因的流行病学研究进一步支持了CYP2A13在人类吸烟者患肺癌风险中的重要作用。合乎逻辑的下一步是直接确定CYP2A13在TS诱导的肺肿瘤形成中的作用。因此，我们将确定由小鼠和人的CYP2ABFS基因簇编码的人CYP2A13和其他P450酶在环境烟草烟雾(ETS)诱导的肺肿瘤形成(AIM 1)和肺部炎症(AIM 2)中的体内作用；后者与肿瘤的启动和肿瘤的促进有关。在目标1中，我们将检验一种假设，即在慢性暴露于ETS的小鼠中，小鼠Cyp2abf的缺失和人CYP2A13的加入将导致肺肿瘤形成程度和肺组织中O6-甲基鸟嘌呤(O6-mG)DNA加合物水平的相应变化。在目标2中，我们将测试ETS成分的独特亚群依赖于CYP2A/B/F/S酶进行生物激活的假说，使ETS能够在体内引起肺部炎症。我们的目标是将CYP2A13确立为肺癌风险评估的有效遗传标记物和化学预防的合理分子靶点。

 DESCRIPTION (provided by applicant): Lung cancer is the leading cause of cancer-related death in the U.S., and tobacco smoke (TS) exposure is the most important contributing factor. However, while much has been learned about the tumorigenic effects and the underlying mechanisms of many individual tobacco carcinogens, relatively little is known about the mechanisms of carcinogenesis induced by TS, the actual complex environmental mixture that many people are exposed to on a daily basis. The in vivo contribution of specific carcinogens and their bioactivation to TS-induced lung tumorigenesis, or to TS-induced pathologic changes that precede carcinogenesis, such as lung inflammation, is largely unknown; but such knowledge is critical for designing effective chemoprevention for TS-induced lung toxicity and for assessing the safety of new tobacco products. The long-term objective of this grant has been to determine the role of respiratory tract cytochrome P450 (P450 or CYP) enzymes in the metabolic activation and toxicity of environmental chemicals, with a focus on CYP2A13, a human enzyme selectively expressed in the respiratory tract. Our central hypothesis is that CYP2A13 plays a vital role in tobacco-related lung carcinogenesis. The ability of CYP2A13 to mediate lung tumorigenesis induced by a major tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is now well-documented, e.g., by our studies of CYP2A13-humanized mice. CYP2A13 also bioactivates many other TS toxicants/carcinogens. Epidemiologic studies of the CYP2A13*2 allele further support an important role of CYP2A13 in lung cancer risk in human smokers. A logical next step is to directly determine the role of CYP2A13 in TS-induced lung tumorigenesis. Thus, we will determine the in vivo role of human CYP2A13 and other P450 enzymes encoded by the mouse and human CYP2ABFS gene cluster in environmental tobacco smoke (ETS)-induced lung tumorigenesis (Aim 1) and lung inflammation (Aim 2); the latter is linked with both tumor initiation and tumor promotion. In Aim 1, we will test the hypothesis that deletion of mouse Cyp2abfs and addition of human CYP2A13 will lead to corresponding changes in the extent of lung tumorigenesis and the levels of O6-methylguanine (O6-mG) DNA adduct in the lung, in mice exposed chronically to ETS. In Aim 2, we will test the hypothesis that unique subsets of ETS constituents, which depend on CYP2A/B/F/S enzymes for bioactivation, enable ETS to cause lung inflammation in vivo. Our goal is to establish CYP2A13 as a valid genetic marker for lung cancer risk assessment and a logical molecular target for chemoprevention.