Effects of {alpha}-deuterium substitution on the mutagenicity of 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)1

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a carcinogenictobacco specific nitrosamine, can be converted to electrophilicdiazohydroxide intermediates by metabolic hydroxylalion of eitherthe methylene carbon (carbon 4) or the methyl carbon attachedto the nitrosamine group. To investigate the relative importanceof these two processes in NNK mutagenesis, we synthesized 4,4-dideutero-4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone([4,4,-D₂]NNK)and 4-(trideuteromethylnitrosamino)-1-(3-pyridyl)-1-butanone([CD₃] NNK), and evaluated their mutagenic activities in Salmonellatyphimurium tester strains. In the presence of Aroclor inducedrat liver 9000 g supernatant, NNK and [4,4-D₂]NNK had comparablemutagenic activities towards S. typhimurium TA 1535 and TA 100,but [CD₃]NNK was inactive in both strains. These results suggestthat hydroxylation of the methyl group of NNK is more importantthan hydroxylation of carbon 4 in its activation to a mutagen.To test the inherent mutagenicity of 4-oxo-4-(3-pyridyl)butyldiazohydroxideand methyldiazohydroxide which would be formed by methyl hydroxylationor carbon 4 hydroxylation, respectively, we compared the mutagenicities,without activation, of the corresponding model compounds, 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanoneand carbethoxynitrosaminomethane (methylnitrosourethane). Bothcompounds were highly mutagenic toward S. typhimurium TA 1535and TA 100, but at doses of 4 x 10^–3 to 4 x 10^–4µmol/plate,only 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone wasmutagenic. These results are consistent with those obtainedwith the deuterium substituted compounds and indicate the importanceof 4-oxo-4-(3-pyridyl)butylation of DNA in NNK mutagenesis.