PHYSICAL AND CHEMICAL INTERACTIONS OF BPDE AND DNA

化学致癌物引发肿瘤被认为是由于 与DNA结合，导致关键原核生物的激活/失活， 癌基因和抑制基因。 我们一直在研究 前致癌物苯并（a）芘（BaP），作为理解的模型 分子致癌作用 苯并（a）芘被转化为一种强效化学物质 致癌物质通过细胞代谢，这种中间体是7 R，8 S- 二羟基-9S，10 R-环氧-7，8，9，10-四氢BP（（+）-抗-BPDE）。 A（-）- 还制备了抗BPDE对映体，但该代谢物具有比抗BPDE对映体低50倍的 生物活性 这两种立体异构体都与DNA结合形成 主要和次要加合物和构象研究受到阻碍， 仅微克量非均匀改性的 DNA用于研究。 由于致癌物质的生物学特性， 非致癌性立体异构体可能是由于 构象，本研究的一个目标是合成足够的 大量的主要和次要BPDE加合物来实现这些 问题研究 另一个目标是表征重要的次要加合物，如 如通过顺式打开BPDE加合物以进行这些反应而形成的那些， 问题研究 另一个目标是表征重要的次要加合物，如 如通过BPDE环氧化物的顺式打开和dCyd烷基化形成的那些 产品，因为它们可能是负责的诱变性能 致癌物质 我们的具体目标是（i）合成BPDE修饰的 脱氧核苷酸和BPDE修饰的寡脱氧核苷酸（ODN），（ii） 对改性单体和低聚物进行构象研究， (iii)研究了顺式加合物的形成机理，并（iv）分析了 结构和表征DNA中dCyd加合物的存在。 的 方法将是合成BPDE-脱氧核苷，并将它们 转化为位点特异性致癌物修饰的ODNs ODN将由 使用顺式和反式脱氧核苷的BPDE修饰的dGuo和dAdo 衍生自（+）-和（-）-反立体异构体的加合物。 合成 将开发用于制备BPDE-dCyd加合物的方法，并且这 致癌物修饰的脱氧核苷也将用于构建ODN 含有单一的特定部位的损伤。 构象将是 通过UV、CD、荧光和NMR光谱以及X射线进行评价 结晶学 我们将研究的机制和性质的 卤素催化形成与DNA的顺式加合物。 我们还将 完成DNA中dCyd加合物的表征和发生， 以评估它们对苯并（a）芘生物效应的重要性。 的 这项工作的长期目标是确定相对生物学 所形成的每种BPDE-DNA加合物的活性，以便 评估哪一个（或多个）可能是肿瘤启动的原因 这是一种重要的、普遍存在的环境污染物。

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 have been 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. Both of these stereoisomers bind to DNA to form major and minor adducts and conformational studies have been hampered by the availability of only microgram quantities of heterogeneously modified DNAs for study. Since the biological properties of the carcinogenic and non-carcinogenic stereoisomers may result from differences in conformation, one goal of this research is to synthesize sufficient quantities of both the major and minor BPDE adducts to carry out these studies. Another goal is to characterize important minor adducts, such as those formed by cis opening of the BPDE adducts to carry out these studies. Another goal is to characterize important minor adducts, such as those formed by cis opening of the BPDE epoxide and dCyd alkylation products, since they may be responsible for the mutagenic properties of the carcinogen. Our specific aims are to (i) synthesize BPDE-modified deoxynucleotides and BPDE-modified oligodeoxynucleotides (ODNs), (ii) carry out conformational studies on the modified monomers and oligomers, (iii) study the mechanism of cis adduct formation, and (iv) analyze the structure and characterize the occurrence of dCyd adducts in DNA. The approach will be to synthesize BPDE-deoxynucleosides and incorporate them into site-specific, carcinogen-modified ODNs. The ODNs will be made with BPDE-modified dGuo and dAdo employing cis and trans deoxynucleoside adducts derived from both the (+)- and (-)-anti-stereoisomers. Synthetic methods for making BPDE-dCyd adducts will be developed, and this carcinogen-modified deoxynucleoside will also be used to construct ODNs containing a single, site-specific lesion. Conformations will be evaluated by UV, CD, fluorescence, and NMR spectroscopies and by X-ray crystallography. We will study the mechanism and properties of the halogen-catalyzed formation of cis adducts with DNA. We will also complete the characterization and occurrence of dCyd adducts in DNA, in order to assess their importance to the biological effects of BaP. The long term goal of this work is to determine the relative biological activity of each of the BPDE-DNA adducts that are formed, in order to assess which one(s) may be responsible for the tumor initiating properties of this important and ubiquitous environmental contaminant.