title: The influence of repair pathways on the cytotoxicity and mutagenicity induced by the pyridyloxobutylation pathway of tobacco-specific nitrosamines.
abstract: Tobacco-specific nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine, are considered to be human carcinogens. Both compounds are metabolized to pyridyloxobutylating intermediates that react with DNA to form adducts such as 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine, O(2)-[4-(3-pyridyl)-4-oxobut-1-yl]cytosine, O(2)-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxythymidine (O(2)-pobdT), O(6)-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O(6)-pobdG), and 4-hydroxy-1-(3-pyridyl)-1-butanone-releasing adducts. The role of specific DNA adducts in the overall genotoxic activity of the pyridyloxobutylation pathway is not known. One adduct, O(6)-pobdG, is mutagenic. To characterize the mutagenic and cytotoxic properties of pyridyloxobutyl DNA adducts, the impact of DNA repair pathways on the cytotoxic and mutagenic properties of the model pyridyloxobutylating agent, 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc), was investigated in Chinese hamster ovary cell lines proficient or deficient in O(6)-alkylguanine DNA alkyltransferase (AGT), deficient in both AGT and base excision repair (BER), or deficient in both AGT and nucleotide excision repair (NER). The repair of the four pyridyloxobutyl DNA adducts was determined in the same cell lines via sensitive LC-MS/MS methods. NNKOAc was more cytotoxic in the cell lines lacking AGT, BER, and NER repair pathways. It also induced more mutations in the hprt gene in the BER- and NER-deficient cell lines. However, AGT expression did not influence NNKOAc's mutagenicity despite efficient repair of O(6)-pobdG. Analysis of the hprt mutational spectra indicated that NNKOAc primarily caused point mutations at AT base pairs. GC to AT transition mutations were a minor contributor to the overall mutation spectrum, providing a rationale for the observation that AGT does not protect against the overall mutagenic properties of NNKOAc in this model system. The only adduct affected by the absence of effective NER was O(2)-pobdT. Slower repair of O(2)-pobdT in NER-deficient cells was associated with increased AT to TA transversion mutations, supporting the hypothesis that these mutations are caused by O(2)-pobdT. Together, these data support a hypothesis that the pyridyloxobutylation pathway generates multiple mutagenic and toxic adducts.
authors: Division of Environmental Health Sciences and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors: Li
authors: L
authors: Li
authors: Joana
authors: J
authors: Perdigao
authors: Anthony E
authors: AE
authors: Pegg
authors: Yanbin
authors: Y
authors: Lao
authors: Stephen S
authors: SS
authors: Hecht
authors: Bruce R
authors: BR
authors: Lindgren
authors: Joyce T
authors: JT
authors: Reardon
authors: Aziz
authors: A
authors: Sancar
authors: Elizabeth V
authors: EV
authors: Wattenberg
authors: Lisa A
authors: LA
authors: Peterson
mesh_terms: D000477:Alkylating Agents; D000818:Animals; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA; D005260:Female; D006801:Humans; D053858:Metabolic Networks and Pathways; D009152:Mutagenicity Tests; D009602:Nitrosamines / Q000378:metabolism* / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism; D014026:Nicotiana
chemical_list: D000477:Alkylating Agents; D009602:Nitrosamines; D004247:DNA; D013936:Thymidine; C008655:N'-nitrosonornicotine