HALIDE CATALYSIS OF EPOXIDE/DNA ADDUCT FORMATION

多环芳烃(PAH)和许多其他重要化学品 致癌物被代谢激活为亲电环氧化物， 烷基化DNA。它们对原癌基因的突变激活作用 反应是化学反应的初始步骤之一。 致癌。认为环氧化物是直接烷基化试剂的观点 在我们的二十年里主导了我们对肿瘤模拟的概念。然而， 我们已经发现，卤化物既催化形成 苯并[a]芘二醇环氧化物(BPDE)-DNA加合物和四氢呋喃。初步 体外研究表明，氯水化合物来源于环氧化物 都是中间体。我们在此应用程序中打算做的是 确定(I)多环芳烃和非多环芳烃是否通常发生卤化物催化 多环芳烃环氧化物，(Ii)其他卤化物(碘化物和溴化物)是否催化 加合物的形成，(Iii)如果卤化物催化在体内发生，以及(Iv) 致癌环氧化物的空间性质是否有助于 它们经历卤化物催化的程度。在没有卤化物离子的情况下， 酸催化下BPDE-DNA加合物的形成及四氢呋喃的产率 几乎完全是反式产物(参照9，10-位 碳氢化合物部分)。卤化物催化导致大量的 顺式产物形成增加，这是对受累的诊断 这些阴离子。我们将测试卤化物催化是否普遍 通过研究一系列化合物参与致癌的环氧化物反应 碳氢化合物(BADE、DMBADE、MCDE和环氧苯乙烯)和测定 卤化物催化其反应的程度。我们将决定 除了氯化物，碘化物和溴化物是否能够 催化加合物的形成。用于水解的产品比例将为 在介质和内部细胞中测定，以及在 CHO细胞。致癌环氧化物的氯丙醇。这些数据将 使我们能够确定细胞培养中是否形成氯醇 媒介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合物的研究 海湾地区存在不同程度的障碍。卤化物系中的催化作用 致癌环氧化物的反应有几个重要的含义。 先前关于DNA体外结合的研究需要重新解释 取决于使用的氯化物的量。这将是特别的 重要的是在获得大量顺式加合物的地方。 此外，我们对致癌启动机制的看法将具有 如果体内发生了大量的卤化物催化作用，就会发生变化。 这项研究和我实验室的其他工作的长期目标之一 是对启动机制有一个完整的理解，因为 如果我们要找到合理的方法，这将是至关重要的 预防致癌损害和由此产生的肿瘤。

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.