HALOHYDRIN INTERMEDIATES IN ACTIVATION OF BENZO[A]PYRENE

化学致癌物引发肿瘤被认为是由于 与DNA结合，导致关键的 原癌基因和抑制基因。 我们一直在研究 环境致癌物苯并[a]芘（BaP）作为模型， 了解分子致癌作用。 BaP转化为 通过细胞代谢产生的潜在化学致癌物， 中间体 7 R，8 S-二羟基-9S，10 R-环氧-7，8，9，10-四氢BP [（+）-抗-BPDE]。 一 还制备了（-）-抗-BPDE对映体，但该代谢物具有50倍的 更少的生物活性。 在过去的二十年里， 肿瘤被认为是一个过程，其中环氧化物直接 烷基化DNA。 然而，我们最近发现了一种新的途径， 所述氯离子催化BPDE的加合物形成， 致癌物质的水解（被动解毒）。 BPDE表格 许多加合物与DNA，但身份的加合物，诱导 肿瘤的发生尚未确定。 构象研究 主要集中在反式（+）-抗-和反式（-）-抗-BPDE-dGuo 加合物，但不是对次要的dAdo和dCyd加合物还没有 进行，部分原因是由于不良的合成反应， 目前用于制备BPDE-DNA加合物。 的一个重要方面 该建议是次要加合物的分析，原则上， 甚至单个加合物也可以被生物放大。 本研究 目的有三：（i）研究氯催化的反应机理 通过体外模型系统形成加合物，（ii）开发新的 制备BPDE-脱氧核苷加合物的合成方案及其用途 组装用次要修饰的寡脱氧核苷酸（ODNs）， 加合物的构象研究，和（iii）分析 之间的反应曲线中dCyd加合物的存在和性质 BPDE和DNA。 目的（i）将通过合成式（I）的卤代醇来实现。 BPDE和比较用该中间体形成的加合物和由 BPDE。 我们还将研究溴化物和碘化物在加合物中的作用 阵 关于致癌机制的一个重要问题 氯是否参与了肿瘤的发生， 所有亲电化学致癌物或反应是否 仅限于环氧化物。 （二）实现目标的主要途径 改进加合物的合成方法。 这将允许 小分子修饰ODNs合成及构象研究 加合物 （iii）通过发展分离 能够将dCyd加合物与其他组分分离的系统， 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加合物负责的必要信息 这一重要且普遍存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.