Role of O6-alkylguanine in nitrosamine-induced cancers

说明(申请人提供)：烟草特有的亚硝胺，NNK和NNN，在实验室中是致癌物质，是潜在的人类致癌物质。NNN被代谢成DNA吡氧丁基化试剂，而NNK被代谢成DNA吡氧丁基化和甲基化中间体。DNA的吡氧丁基化可生成多种DNA加合物，其中之一是O6-[4-氧-4-(3-吡啶)丁基]鸟嘌呤(O6-pobG)。我们以前的研究表明，这种突变加合物可以被O6-烷基鸟嘌呤-DNA烷基转移酶(AGT)修复。人类AGT变异体修复O6-pobG的能力有很大差异，这表明修复能力降低的人患烟草相关癌症的风险可能会增加。然而，目前还不清楚O6-pobG在吡氧丁基亚硝胺的诱变和致癌特性中所起的整体作用。这项赠款研究的中心假设是，O6-pobG在不修复时，对烟草特有的亚硝胺NNK和NNN的诱变和致癌活性有显著贡献。我们计划通过追求以下特定目标来验证我们的中心假设：1)确定O6-pobG的形成和持久性是否与A/J小鼠NNN和NNKOAc的肺癌致癌特性有关。2)通过AGT对人肝修复体积较大的O6-烷基鸟嘌呤加合物相对于O6-镁加合物的能力。3)确定其他修复途径是否参与致突变的O6-pobG的整体修复，并确定这些途径是否影响吡啶氧丁基化试剂的诱变性质。总而言之，这些目标将确定O6-pobG的形成和修复在吡啶氧丁基亚硝胺的诱变和致癌性能中的重要性。这些研究将为分子流行病学研究奠定基础，以确定无法修复这种突变加合物的个人是否面临与烟草相关的癌症风险增加的风险。

DESCRIPTION (provided by applicant): Tobacco-specific nitrosamines, NNK and NNN, are carcinogenic in laboratory and are potential human carcinogens. NNN is metabolized to a DNA pyridyloxobutylating agent whereas NNK is metabolized to both DNA pyridyloxobutylating and methylating intermediates. Pyridyloxobutylation of DNA results in the formation of a variety of DNA adducts, one of which is O6-[4-oxo-4-(3-pyridyl)butyl]guanine (O6-pobG). Our previous studies indicate that this mutagenic adduct is repaired by O6-alkylguanine-DNA alkyltransferase (AGT). Human AGT variants differ substantially in their ability to repair O6-pobG, suggesting that individuals with reduced repair capacity may be at increased risk of tobacco-related cancers. However, it is unclear what the overall role O6-pobG makes in the mutagenic and carcinogenic properties of pyridyloxobutylating nitrosamines. The central hypothesis under investigation in this grant is that O6-pobG contributes significantly to the mutagenic and carcinogenic activity of the tobacco-specific nitrosamines, NNK and NNN, when not repaired. We plan to test our central hypothesis by pursuing the following specific aims: 1) Determine if O6-pobG formation and persistence are linked to the pulmonary carcinogenic properties of NNN and NNKOAc in A/J mice. 2) Phenotype human livers for their ability to repair bulky O6-alkylguanine adducts relative to O6-mG adducts by AGT. 3) Determine the involvement of other repair pathways in the overall repair of the mutagenic O6-pobG and determine whether these pathways affect the mutagenic properties of pyridyloxobutylating agents. Collectively, these aims will establish the importance of formation and repair of O6-pobG in the mutagenic and carcinogenic properties of pyridyloxobutylating nitrosamines. These studies will set the stage for a molecular epidemiological study to determine whether individuals who are unable to repair this mutagenic adduct are at increased risk of tobacco-related cancers.