title: O6-methylguanine is a critical determinant of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone tumorigenesis in A/J mouse lung.
abstract: The relative importance of the two alpha-hydroxylation pathways in the tumorigenicity of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), was examined in the A/J mouse lung. Methyl hydroxylation, which results in DNA pyridyloxobutylation, was investigated with 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc) and N'-nitrosonornicotine. Methylene hydroxylation, which leads to DNA methylation, was studied by using acetoxymethyl-methylnitrosamine (AMMN). The tumorigenic activities of these compounds were compared to that of 10 mumol NNK at doses that yielded similar or greater adduct levels 24 h after exposure. The methylating agent AMMN was more tumorigenic than the pyridyloxobutylating agents, NNKOAc and N'-nitrosonornicotine. NNKOAc enhanced the tumorigenic activity of AMMN when the two compounds were given in combination. These results suggested that DNA methylation was more important than DNA pyridyloxobutylation in A/J mouse lung tumor induction by NNK and that pyridyloxobutylation enhanced the activity of the methylation pathway. However, the tumorigenicity of 10 mumol NNK could not be reproduced by AMMN +/- NNKOAc at doses that yielded similar levels of DNA adducts 24 h after exposure. Therefore, a second study was conducted in which the persistence of O6-methylguanine in lung DNA following various doses of NNK or AMMN +/- NNKOAc was compared to the tumorigenicity of these treatments. A strong correlation was observed between lung tumor yield and levels of O6-methylguanine at 96 h for NNK and AMMN +/- NNKOAc (r = 0.98). The ability of NNKOAc to increase the tumorigenic activity of AMMN was attributed to its ability to enhance the persistence of O6-methylguanine in lung DNA. These results demonstrate that the formation and persistence of O6-methylguanine are critical events in the initiation of A/J mouse lung tumors by NNK. They also suggest that DNA pyridyloxobutylation by NNK can increase the persistence of this promutagenic base in lung DNA.
authors.affiliation: Division of Chemical Carcinogenesis, American Health Foundation, Valhalla, New York 10595.
authors.forename: L A
authors.initials: LA
authors.lastname: Peterson
authors.forename: S S
authors.initials: SS
authors.lastname: Hecht
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000378:metabolism / Q000633:toxicity*; D004247:DNA / Q000378:metabolism*; D004128:Dimethylnitrosamine / Q000031:analogs & derivatives / Q000378:metabolism / Q000633:toxicity; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006900:Hydroxylation; D008175:Lung Neoplasms / Q000139:chemically induced*; D008745:Methylation; D051379:Mice; D009602:Nitrosamines / Q000378:metabolism / Q000633:toxicity*
chemical_list: D002273:Carcinogens; D009602:Nitrosamines; C014659:methyl(acetoxymethyl)nitrosamine; D006147:Guanine; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D004247:DNA; C008449:O-(6)-methylguanine; D004128:Dimethylnitrosamine