Role of local P450 enzymes in chemical carcinogenesis in mouse mammary gland

描述（由申请方提供）：长期目标是确定乳腺组织中化学致癌的机制。我们目前的重点是研究乳腺细胞色素P450（P450）酶在化学致癌物诱导的乳腺（MG）DNA加合物形成的作用，使用组织选择性基因敲除小鼠模型。微粒体细胞色素P450（P450）酶在化学原致癌物的代谢活化中起着关键作用。然而，很难确定在全身暴露于给定的原致癌物后，乳腺组织中大部分活化的致癌物或其DNA加合物是来自局部代谢还是来自肝脏;后一器官在原致癌物的代谢活化中通常比肝外靶组织活跃得多。对于原致癌物，如7，12-二甲基苯并[a]蒽（DMBA），问题变得更加复杂，因为它需要多个代谢活化步骤，考虑到肝或乳腺组织不仅对最终致癌物的形成，而且对中间代谢物，如DMBA-反式-3，4-二氢二醇（3，4-diol-DMBA），即最终致癌物的前体的形成的潜在贡献。我们的假设是，靶组织P450介导的代谢活化在DMBA诱导的乳腺（MG）DNA加合物的形成中起着重要作用;然而，这种靶组织贡献的程度将根据MG的发育阶段和生理状态而变化。为了验证这一假设，我们将通过条件性删除（或抑制）P450还原酶（Cpr）基因（所有微粒体P450酶活性所需的酶）来调节肝脏和肝外组织（包括MG）中的P450活性。在这项为期两年的试点项目研究中，我们将确定肝和肝外的相对贡献，（包括MG）P450酶在新开发的小鼠模型中对乳腺前致癌物DMBA及其中间代谢物3，4-二醇-DMBA的代谢活化中的作用，对P450活性具有组织特异性抑制，无论是在肝脏中单独（指定为肝-Cpr-无效小鼠），或在除肝外的所有组织中（指定为肝外-Cpr-低小鼠）（目的1）。此外，我们将开发和表征MG选择性Cpr无效模型（指定为MG-Cpr无效小鼠），用于直接测定MG P450酶在DMBA和3，4-二醇-DMBA诱导的MG DNA加合物形成中的作用（目的2）。从研究中获得的知识将改进流行病学研究的设计，这些研究试图将环境化学品暴露和/或P450酶的遗传多态性与人类乳腺癌的发病率联系起来。它也可能有助于设计基于机制的方法来预防乳腺癌。 公共卫生相关性：这项研究将进一步加深我们对环境化学物质诱导乳腺化学致癌机制的理解，并为基于机制的乳腺癌预防方法提供新的见解。

DESCRIPTION (provided by applicant): The long-term objective is to determine the mechanisms of chemical carcingensis in the breast tissue. Our current focus is to study the role of mammary cytochrome P450 (P450) enzymes in chemical carcinogen- induced DNA adduct formation in the mammary gland (MG) using tissue-selective gene knockout mouse models. It is well-documented that the microsomal cytochrome P450 (P450) enzymes play a critical role in the metabolic activation of chemical procarcinogens. However, it has been difficult to determine whether, following systemic exposure to a given procarcinogen, the bulk of the activated carcinogen, or its DNA adducts, in the breast tissue is derived from local metabolism or from the liver; the latter organ is generally much more active than extrahepatic target tissues in the metabolic activation of procarcinogens. The problem becomes even more complicated for procarcinogens, such as 7,12-dimethylbenz[a]anthracene (DMBA), that require multiple steps of metabolic activation, given the potential contributions of hepatic or breast tissues to the formation of not only the ultimate carcinogen, but also the intermediate metabolites, such as DMBA-trans-3,4-dihydrodiol (3,4-diol-DMBA), that are precursors to the ultimate carcinogen. Our hypothesis is that target-tissue P450- mediated metabolic activation plays an important role in DMBA-induced formation of DNA adducts in the mammary gland (MG); however, the extent of this target-tissue contribution will vary according to the developmental stages and physiological states of the MG. To test this hypothesis, we will modulate P450 activities in the liver and extrahepatic tissues (including MG) through conditional deletion (or suppression) of the gene for P450 reductase (Cpr), an enzyme required for the activity of all microsomal P450 enzymes. In this two-year pilot project study, we will determine the relative contributions of hepatic and extrahepatic (including the MG) P450 enzymes in the metabolic activation of DMBA, a mammary procarcinogen, and its intermediate metabolite 3,4-diol-DMBA, in newly developed mouse models with tissue-specific suppression of P450 activities, either in the liver alone (designated as liver-Cpr-null mouse), or in all tissues except the liver (designated as extrahepatic-Cpr-low mouse) (Aim 1). Furthermore, we will develop and characterize MG selective Cpr null models (designated as MG-Cpr-null mice), for direct determination of the role of MG P450 enzymes in the MG DNA-adduct formation induced by DMBA and 3,4-diol-DMBA (Aim 2). The knowledge gained from studies will improve the design of epidemiological studies that attempt to associate environmental chemical exposure, and/or genetic polymorphisms in P450 enzymes, with the incidence of breast cancer in humans. It may also help with designing mechanism-based approaches to the prevention of breast cancer. PUBLIC HEALTH RELEVANCE: This research will further our understanding of the mechanisms of chemical carcinogenesis in the mammary gland induced by environmental chemicals, and provide novel insights for mechanism-based approaches to the prevention of breast cancer.