HALIDE CATALYSIS OF EPOXIDE/DNA ADDUCT FORMATION

环氧化物/DNA 加合物形成的卤化物催化

基本信息

批准号：
2155791
负责人：
Thomas Meehan
金额：
$ 12.83万
依托单位：
UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
依托单位国家：
美国
项目类别：
财政年份：
1994
资助国家：
美国
起止时间：
1994-08-01 至 1999-07-31
项目状态：
已结题

项目摘要

Polycyclic aromatic hydrocarbons (PAH) and many other important chemical carcinogens are metabolically activated to electrophilic epoxides that alkylate DNA. Mutational activation of proto-oncogenes by these reactions constitutes one of the initial steps in chemical carcinogenesis. The view that epoxides are direct alkylating agents has dominated our concepts of tumor imitation for our two decades. However, we have discovered that halides catalyze both the formation of benzo[a]pyrene diol epoxide (BPDE)-DNA adducts and tetrols. Preliminary in vitro studies demonstrate that cholorhydrins derived from the epoxides are intermediates. What we propose to do in this application is to determine (i) whether halide catalysis generally occurs with PAH and non- PAH epoxides, (ii) whether other halides (iodide and bromide) catalyze adduct formation, (iii) if halide catalysis occurs in vivo, and (iv) whether steric properties of carcinogenic epoxides contribute to the extent that they undergo halide catalysis. In the absence of halide ions, the acid-catalyzed formation of BPDE-DNA adducts and tetrols yields almost exclusively trans products (with reference to the 9,10-positions of the hydrocarbon moiety). Halide catalysis results in a substantial increase in cis product formation which is diagnostic for the involvement of these anions. We will test whether halide catalysis is generally involved in carcinogenic epoxide reactions by studying a series of hydrocarbons (BADE, DMBADE, MCDE, and styrene oxide) and determining the extent to which halides catalyze their reactions. We will determine whether iodide and bromide are, in addition to chloride, capable of catalyzing adduct formation. Product ratios for hydrolysis will be determined in media and inside cells as well as for adduct formation in CHO cells. Chlorohydrins of the carcinogenic epoxides. These data will allow us to determine whether chlorohydrins are formed in cell culture media and whether they are involved in adduct formation in vivo. Finally, we will determine the role of steric crowding in the stability and properties of chlorohydrins by studying a series of PAH epoxides with varying degrees of hindrance in the bay region. Halide catalysis in the reactions of carcinogenic epoxides has several important implications. Previous studies on DNA binding in vitro will need to be re-interpreted depending on the amount of chloride used. This will be particularly important where substantial amounts of cis adducts were obtained. Furthermore, our view of carcinogenesis initiation mechanisms will have to be altered if significant amounts of halide catalysis occur in vivo. One of the long term goals of this study and other work in my laboratory is to develop a complete understanding of initiation mechanisms since this will be essential if we are to discover rational approaches to preventing carcinogenic damage and the tumors that result from it.

多环芳烃（PAH）和许多其他重要化学物质致癌物被代谢激活为电代环氧化物，这些环氧化物烷基化DNA。这些原始基因的突变激活反应构成化学的初始步骤之一致癌作用。环氧化物是直接烷基化剂的观点在我们二十年的时间里，我们统治了我们肿瘤模仿的概念。然而，我们发现卤化物催化了两者的形成苯并[A] pyrene二醇环氧（BPDE） - DNA加合物和四元。初步的体外研究表明，源自环氧化物的胆汁氢蛋白是中间体。我们建议在此申请中做的是确定（i）PAH和非 - 是否通常发生卤化物催化 PAH环氧化物，（ii）其他卤化物（碘化物和溴）是否催化加合物形成，（iii）如果卤化物催化发生在体内，并且（iv）致癌环氧化物的空间特性是否有助于他们经历卤化物催化的程度。在没有卤化离子的情况下， BPDE-DNA加合物和四元组的酸催化形成产生几乎完全跨产品（参考9,10位置碳氢化合物部分）。卤化物催化导致实质性增加CIS产品形成，这是诊断的参与这些阴离子。我们将测试卤化物催化是否通常是通过研究一系列的致癌环氧化物反应碳氢化合物（Bade，Dmbade，McDe和氧化苯乙烯），并确定卤代催化其反应的程度。我们将确定除氯化物外，碘化物和溴是否能够催化加合物的形成。水解产品比率将是在媒体和内部细胞中确定以及在 CHO细胞。致癌环氧化物的氯氢蛋白。这些数据将允许我们确定在细胞培养中是否形成氯氢蛋白媒体以及它们是否参与体内加合物形成。最后，我们将确定空间拥挤在稳定中的作用通过研究一系列具有带有氯氢蛋白的特性海湾地区的障碍程度不同。卤化物催化致癌环氧化物的反应具有几种重要的含义。先前对体外DNA结合的研究将需要重新解释取决于使用的氯化物量。这尤其是在获得大量的顺式加合物的地方重要。此外，我们对癌变发起机制的看法将具有如果体内发生大量卤化物催化，则会改变。这项研究的长期目标之一以及我的实验室中的其他工作是为了完全了解起始机制，因为如果我们要发现合理的方法，这将是至关重要的防止致癌损伤及其肿瘤。