HALIDE CATALYSIS OF EPOXIDE/DNA ADDUCT FORMATION

多环芳烃（PAH）和许多其他重要的化学品 致癌物被代谢活化为亲电环氧化物， 烷基化DNA。 原癌基因的突变激活， 化学反应是化学反应的初始步骤之一。 致癌作用 认为环氧化物是直接烷基化剂的观点， 在过去的20年里，肿瘤模仿一直是我们的主流概念。 然而，在这方面， 我们已经发现卤化物可以催化 苯并[a]芘二醇环氧化物（BPDE）-DNA加合物和四醇。 初步 体外研究表明，衍生自环氧化物的氯醇 是中间体。 在本申请中，我们建议做的是 确定（i）卤化物催化是否通常与PAH和非PAH一起发生， PAH环氧化物，（ii）其他卤化物（碘化物和溴化物）是否催化 加合物形成，（iii）如果卤化物催化发生在体内，和（iv） 致癌环氧化物的空间特性是否有助于 在一定程度上，它们经历卤化物催化。在没有卤离子的情况下， 酸催化形成BPDE-DNA加合物和四元醇， 几乎完全是反式产品（参考9，10-位置 烃部分）。 卤化物催化导致显著的 顺式产物形成增加，这是参与的诊断 这些阴离子。 我们将测试卤化物催化是否通常 参与致癌的环氧化物反应， 碳氢化合物（BADE，DMBADE，MCDE和氧化苯乙烯），并确定 卤化物催化其反应的程度。 我们将确定 除了氯化物之外，碘化物和溴化物是否能够 催化加合物形成。 水解的产物比率为 在培养基和细胞内测定，以及 CHO细胞。 致癌环氧化物的氯代醇。 这些数据将 使我们能够确定氯乙醇是否在细胞培养中形成 介质以及它们是否参与体内加合物的形成。 最后，我们将确定空间拥挤在稳定性中的作用 通过对一系列多环芳烃环氧化物的研究， 在海湾地区受到不同程度的阻碍。 卤化物催化 致癌环氧化物的反应有几个重要的含义。 以前的体外DNA结合研究需要重新解释 这取决于所使用的氯化物的量。 这一点尤其 重要的是获得大量顺式加合物。 此外，我们对致癌起始机制的看法将具有 如果体内发生大量的卤化物催化作用， 这项研究和我实验室其他工作的长期目标之一是， 是发展一个完整的理解启动机制， 这将是至关重要的，如果我们要发现合理的方法， 防止致癌性损伤和由此产生的肿瘤。

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.