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Chem Res Toxicol. 2012 Oct 15;25(10):2167-78. doi: 10.1021/tx300245w. Epub 2012 Sep 13.

Formation and repair of pyridyloxobutyl DNA adducts and their relationship to tumor yield in A/J mice.

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Division of Environmental Health Sciences and ‡Masonic Cancer Center, University of Minnesota , Minneapolis, Minnesota 55455, USA.


The nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a known human carcinogen. It generates methyl and pyridyloxobutyl DNA adducts. The role of the methyl DNA adducts has been well-established in the tumorigenic properties of NNK. However, the role of the pyridyloxobutyl DNA adducts is unclear. Four pyridyloxobutyl DNA adducts have been characterized: 7-[4-3-(pyridyl)-4-oxobut-1-yl]guanine (7-pobG), O²-[4-3-(pyridyl)-4-oxobut-1-yl]-cytodine (O²-pobC), O²-[4-3-(pyridyl)-4-oxobut-1yl]thymidine (O²-pobdT), and O⁶-[4-3-(pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O⁶-pobdG). Mutagenic O⁶-pobdG is thought to contribute to the tumorigenic properties of the pyridyloxobutylation pathway. It is repaired by O⁶-alkylguanine-DNA alkyltransferase (AGT). To explore the role of O⁶-pobdG formation and repair in the tumorigenic properties of NNK, A/J mice were given single or multiple doses of the model pyridyloxobutylating agent 4-(acetoxymethyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc) in the presence or absence of the AGT depletor, O⁶-benzylguanine. Levels of the four pyridyloxobutyl DNA adducts were measured in the lung at 8, 48, or 96 h following treatment and compared to the lung tumorigenic activity of these treatments. AGT depletion had only a modest effect on the levels of O⁶-pobdG and did not increase tumor formation. Three pyridyloxobutyl DNA adducts, 7-pobG, O²-pobdT, and O⁶-pobdG, persisted in lung DNA at significant levels for up to 96 h post-treatment, suggesting that all three adducts may contribute to the tumorigenic properties of NNK.

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