HALOHYDRIN INTERMEDIATES IN ACTIVATION OF BENZO[A]PYRENE

由化学致癌物引发的肿瘤被认为是由 与DNA的结合导致关键基因的激活/停用 原癌基因和抑癌基因。我们一直在研究 以环境致癌物苯并[a]芘(BaP)为模型 了解分子致癌机制。将BAP转换为 由细胞新陈代谢产生的强化学致癌物 中级IS 7R，8S-dihydroxy-9S，10R-epoxy-7，8，9，10-tetrahydroBP[(+)-anti-BPDE].一个 (-)-抗BPDE对映体也被制成，但这种代谢物有50倍 更少的生物活动。在过去的二十年里， BP的肿瘤被认为是环氧化物直接氧化的过程 烷基化DNA。然而，我们最近发现了一条新的途径 哪种氯离子既催化BPDE的加合物形成，又催化BPDE和 致癌物质的水解(被动解毒)。BPDE表单 许多加合物与DNA但诱导的加合物的同一性 肿瘤的起源尚未确定。构象研究已经 重点介绍了主要的反式(+)-抗和反式(-)-抗BPDE-dGuo 加合物，但不在次要的Dado和dCyd加合物上 进行，部分原因是糟糕的合成反应， 目前用于制造BPDE-DNA加合物。的一个重要方面 这项建议是对次要加法的分析，因为原则上， 即使是单一的加合物也可以被生物放大。这项研究 目的有三个：(一)研究氯离子催化的反应机理 通过体外模型系统形成加合物，(Ii)开发新的 BPDE-脱氧核苷加合物的合成方案及其应用 组装辅基修饰的寡聚脱氧核苷酸 用于构象研究的加合物，以及(Iii)分析 反应谱中dCyd加合物的存在和性质 BPDE和DNA。目标(I)将通过合成卤代氢化合物来实现 BPDE和与该中间体形成的加合物的比较 BPDE。我们还将研究溴化物和碘在加合物中的作用。 队形。关于致癌机制的一个重要问题 氯化物是否参与了肿瘤的启动特性 所有的亲电化学致癌物或反应是否 仅限于环氧化物。目标(二)将通过以下方式基本实现 改进合成加合物的方法。这将允许 次要修饰的寡核苷酸的合成及构象研究 加合物。目标(III)将通过分离的发展来实现 能够解析来自其他组件的dCyd加合物的系统 BPDE-DNA反应。这项工作的长期目标是确定 化学致癌物攻击DNA的机制，并评估 每种BPDE-DNA加合物的相对生物活性 是由致癌物质形成的。这些调查将提供 关于BPDE Adducts负责的必要信息 这一重要而无处不在的环境的生物活性 污染物。

Tumor initiation by chemical carcinogens is thought to result from binding to DNA that leads to activation/deactivation of critical proto-oncogenes and suppressor genes. We havebeen studying the environmental pro-carcinogen benzo[a]pyrene (BaP) as a model for understanding molecular carcinogenesis. BaP is converted into a potent chemical carcinogen by cellular metabolism and this intermediate is 7R,8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydroBP[(+)-anti-BPDE]. A (-)-anti-BPDE enantiomer is also made but this metabolite has 50-fold less biological activity. For the past two decades the initiation of tumors by BP has been viewed as a process in which epoxides directly alkylate DNA. However, we have recently discovered a new pathway in which chloride ions catalyze both adduct formation from BPDE and hydrolysis (passive detoxification) of the carcinogen. BPDE forms many adducts with DNA but the identity of the adduct that induces tumor initiation has not been determined. Conformational studies have focused on the major trans(+)-anti- and trans(-)-anti-BPDE-dGuo adducts but not on the minor dAdo and dCyd adducts have not been carried out, in part because of the poor synthetic reactions that are currently employed to make BPDE-DNA adducts. An important aspect of this proposal is the analysis of minor adducts since, in principle, even a single adduct could be biologically amplified. This research has three aims: (i) to study the mechanism of chloride-catalyzed adduct formation through in vitro model systems, (ii) to develop new synthetic schemes for making BPDE-deoxynucleoside adducts and use them to assemble oligodeoxynucleotides (ODNs) modified with the minor adducts for conformational studies, and (iii) to analyze the occurrence and properties of dCyd adducts in reaction profiles between BPDE and DNA. Aim (i) will be pursued by synthesizing halohydrins of BPDE and comparing adducts formed with this intermediate and from BPDE. We will also study the role of bromide and iodide in adduct formation. An important question concerning carcinogenesis mechanisms is whether chloride participates in the tumor initiation properties of all electrophilic chemical carcinogens or whether the reaction is confined to epoxides. Aim (ii) will be accomplished by substantially improving synthetic methods for making adducts. This will permit the synthesis and conformational study of ODNs modified with minor adducts. Aim (iii) will be accomplished by development of separation systems capable of resolving dCyd adducts from other components in BPDE-DNA reactions. The long term goal of this work is to determine the mechanism by which chemical carcinogens attack DNA, and to assess the relative biological activity of each of the BPDE-DNA adducts that are formed from the carcinogen. These investigations will provide necessary information concerning which BPDE adduct is responsible for the biological activity of this important and ubiquitous environmental contaminant.