Stereospecific Deuterium Substitution Attenuates the Tumorigenicity and Metabolism of the Tobacco-Specific Nitrosamine 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

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• 作者：John R. Jalas ; Edward J. McIntee ; Patrick M. J. Kenney ; Pramod Upadhyaya ; Lisa A. Peterson ; and Stephen S. Hecht
• 刊名：Chemical Research in Toxicology
• 出版年：2003
• 出版时间：June 2003
• 年：2003
• 卷：16
• 期：6
• 页码：794 - 806
• 全文大小：170K
• 年卷期：v.16,no.6(June 2003)
• ISSN：1520-5010

文摘

Stereochemical determinants of the tumorigenicity and metabolism of the tobacco-specificnitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were investigated usingthe stereospecifically deuterated isotopomers (4R)-[4-²H₁]NNK and (4S)-[4-²H₁]NNK. Upon ipadministration to groups of 20 female A/J mice, NNK and (4S)-[4-²H₁]NNK exhibited similarlung tumorigenicity at three different doses, whereas (4R)-[4-²H₁]NNK was 2-fold lesstumorigenic at all three doses. In a parallel experiment, levels of O⁶-methylguanine and7-methylguanine were 2-fold lower in lung DNA of mice treated with (4R)-[4-²H₁]NNK thanin mice treated with NNK or (4S)-[4-²H₁]NNK. To corroborate these in vivo data, the in vitrometabolism of these compounds was investigated using A/J mouse lung microsomes andSpodoptera frugiperda (Sf9)-expressed mouse cytochrome P450s 2A4 and 2A5. Kinetic isotopeeffects on the apparent V_max (^DV) for the product of NNK 4-hydroxylation, OPB, were 2.7 ± 0.2and 2.8 ± 0.4 when (4R)- and (4S)-[4-²H₁]NNK were incubated with mouse lung microsomes,respectively. The ^DV values for OPB formation were 3.2 ± 0.2 and 2.2 ± 0.2 when (4R)-[4-²H₁]NNK was the substrate for P450s 2A4 and 2A5, respectively, whereas they were 1.3 ± 0.1 and1.1 ± 0.1 when (4S)-[4-²H₁]NNK was the substrate for these respective enzymes. Analysis ofan OPB derivative (10) for deuterium content by LC/MS confirmed the results from the kineticassays and indicated that P450s 2A4 and 2A5 preferentially abstract the pro-R 4-hydrogen ofNNK. The results obtained using Sf9-expressed P450s provide a rationale for the differencesobserved in the lung tumor and DNA adduct experiments, namely, that the attenuatedtumorigenicity of (4R)-[4-²H₁]NNK relative to (4S)-[4-²H₁]NNK is due to prochiral selectivityduring P450-catalyzed metabolic activation.