Carcinogen-DNA Adducts: Topology, Conformation and Repair (Renewal)

描述（由申请人提供）：一类非平面，扭曲的多环芳烃（PAHs），称为峡湾地区化合物，是非常有效的肿瘤致癌物；它们包括二苯并[a， 1]芘，它最近被认为是迄今发现的最具致瘤性的多环芳烃。这些污染物作为各种燃料的燃烧产物被释放到环境中，并污染粮食作物。它们在食品和城市空气中的低浓度下具有生物活性，对一般人群有害。峡湾多环芳烃的非凡致癌性的来源仍然未知。然而，最近有研究表明，它们在代谢激活二醇环氧化物后产生的一些大体积DNA加合物对核苷酸切除修复（NER）有抗性，NER是细胞对这种DNA损伤的主要防御。这些加合物对DNA修复的抵抗被认为是母体化学物质异常致瘤性的关键原因，因为它们会引起引发癌症的突变。然而，每一个环境峡湾多环芳烃产生一个复杂的混合物的立体异构体鸟嘌呤和腺嘌呤DNA加合物。此外，每种加合物的NER易感性可能随DNA碱基序列而变化。在这众多的病变中，导致癌症的关键的抗修复细胞仍未被发现。我们广泛的长期目标是，与我们的实验合作者N. Geacintov教授一起工作，使用创新和最先进的建模方法确定耐ner加合物及其特征：我们假设耐ner加合物是由多环芳烃修饰DNA的结构、动态和热力学性质决定的。选择用于详细研究的峡湾多环芳烃有二苯并[a， 1]芘、苯并[g]芘和苯并[c]菲；我们研究了它们的加合物通过完善的环氧二醇代谢激活途径产生。这些多环芳烃分别代表了6,5和4环的芳香系统，这是诱导肿瘤的最佳范围。我们的目的是研究许多二醇环氧化物加合物的三个亲本多环芳烃在选定的序列，我们假设会改变他们的ner敏感性。我们进一步旨在确定在核小体（细胞环境中染色质结构的基本单位）的组蛋白环境中组织病变的特征特性和NER易感性。这是在染色质背景下阐明复杂NER机制功能的重要的第一步。我们将与我们的实验合作者N. Geacintov教授携手合作：人类细胞提取物的NER数据，包括含有病变的核小体，将为我们的发现与实验观察直接联系起来提供锚点，我们的分析将指向重要的预测，这些预测将在他的实验室进行测试。我们的研究将提供下一代多环芳烃暴露的生物标志物，通过我们对多环芳烃机制的理解，促进设计更好的耐多环芳烃化疗药物，并提高我们对环境中多环芳烃衍生的加合物进行基因毒性筛选的能力。

DESCRIPTION (provided by applicant): A category of non-planar, twisted polycyclic aromatic hydrocarbons (PAHs), termed fjord region compounds, are extremely potent tumorigens; they include dibenzo[a,l]pyrene which has recently been cited as the most tumorigenic PAH yet identified. These pollutants are released into the environment as combustion products of a variety of fuels, and they contaminate food crops. They are biologically active at the low concentrations present in foods and urban air and are hazardous to the population at large. The origin of the extraordinary carcinogenic potencies of fjord PAHs remains unknown. However, it has recently been shown that several of the bulky DNA adducts that they produce after metabolic activation to diol epoxides, are resistant to nucleotide excision repair (NER), the principal cellular defense against such DNA lesions. Resistance to DNA repair of these adducts is deemed a critical cause for the extraordinary tumorigenicity of the parent chemicals, as they cause the mutations which initiate cancer. However, each environmental fjord PAH gives rise to a complex mixture of stereoisomeric guanine and adenine DNA adducts. Furthermore, the NER susceptibility of each such adduct may vary with DNA base sequence. In this multitude of lesions, the key repair-resistant ones that lead to cancer remain unidentified. Our broad, long-term objective is, working in tandem with our experimental collaborator Prof. N. Geacintov, to identify the NER-resistant adducts and their characteristics using innovative and state-of-the-art modeling methods: we hypothesize that NER-resistance is governed by the structural, dynamic and thermodynamic properties of the PAH-modified DNA. The fjord PAHs selected for detailed study are dibenzo[a,l]pyrene, benzo[g]chrysene, and benzo[c]phenanthrene; we investigate their adducts produced via the well established diol epoxide metabolic activation pathway. These PAHs represent aromatic systems of 6, 5, and 4 rings, respectively, a range optimal for the induction of tumors. We aim to investigate the many diol epoxide adducts of the three parent PAHs in selected sequences that we hypothesize will alter their NER-susceptibilities. We further aim to determine the characteristic properties and NER susceptibilities of lesions when organized within the histone protein environment of the nucleosome, the basic unit of chromatin structure in the cellular environment. This is an essential first step towards elucidating the functioning of the complex NER machinery in the context of chromatin. We will work hand-in-hand with our experimental collaborator Prof. N. Geacintov: NER data with human cell extracts and including lesion- containing nucleosomes will provide anchors for directly linking our findings with the experimental observations, and our analyses will point to important predictions that will be tested in his laboratory. Our studies will provide the next-generation of biomarkers for PAH exposure, facilitate design of better NER- resistant chemotherapeutics through our gained understanding of NER mechanisms, and advance our capability for genotoxic screening of adducts derived from PAHs present in our environment. PUBLIC HEALTH RELEVANCE: Our work will advance cancer prevention: it will yield novel capability for efficient screening of polycyclic aromatic hydrocarbons to determine their cancer-initiating potency, and provide next-generation biomarkers for PAH exposure that much better signal cancer susceptibility. In addition, design of more efficacious cancer chemotherapeutic agents will be facilitated.