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

• Published in: Chemical research in toxicology Vol. 16; no. 6; pp. 794 - 806
• Main Authors: Jalas, John R, McIntee, Edward J, Kenney, Patrick M. J, Upadhyaya, Pramod, Peterson, Lisa A, Hecht, Stephen S
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.06.2003
• Subjects: Animals; Aryl Hydrocarbon Hydroxylases - metabolism; Carcinogens - metabolism; Carcinogens - toxicity; Cytochrome P-450 CYP2A6; Deuterium - chemistry; DNA - metabolism; DNA Adducts - analysis; Dose-Response Relationship, Drug; Female; Guanine - analogs & derivatives; Guanine - metabolism; Lung - drug effects; Lung - enzymology; Lung Neoplasms - chemically induced; Lung Neoplasms - pathology; Mice; Mice, Inbred A; Microsomes - enzymology; Mixed Function Oxygenases - metabolism; Molecular Structure; Nitrosamines - chemistry; Nitrosamines - metabolism; Nitrosamines - toxicity; Stereoisomerism; Structure-Activity Relationship
• ISSN: 0893-228X; 1520-5010
• DOI: 10.1021/tx034022l

Stereochemical determinants of the tumorigenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were investigated using the stereospecifically deuterated isotopomers (4R)-[4-2H1]NNK and (4S)-[4-2H1]NNK. Upon ip administration to groups of 20 female A/J mice, NNK and (4S)-[4-2H1]NNK exhibited similar lung tumorigenicity at three different doses, whereas (4R)-[4-2H1]NNK was 2-fold less tumorigenic at all three doses. In a parallel experiment, levels of O 6-methylguanine and 7-methylguanine were 2-fold lower in lung DNA of mice treated with (4R)-[4-2H1]NNK than in mice treated with NNK or (4S)-[4-2H1]NNK. To corroborate these in vivo data, the in vitro metabolism of these compounds was investigated using A/J mouse lung microsomes and Spodoptera frugiperda (Sf9)-expressed mouse cytochrome P450s 2A4 and 2A5. Kinetic isotope effects on the apparent V max (D V) for the product of NNK 4-hydroxylation, OPB, were 2.7 ± 0.2 and 2.8 ± 0.4 when (4R)- and (4S)-[4-2H1]NNK were incubated with mouse lung microsomes, respectively. The D V 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 and 1.1 ± 0.1 when (4S)-[4-2H1]NNK was the substrate for these respective enzymes. Analysis of an OPB derivative (10) for deuterium content by LC/MS confirmed the results from the kinetic assays and indicated that P450s 2A4 and 2A5 preferentially abstract the pro-R 4-hydrogen of NNK. The results obtained using Sf9-expressed P450s provide a rationale for the differences observed in the lung tumor and DNA adduct experiments, namely, that the attenuated tumorigenicity of (4R)-[4-2H1]NNK relative to (4S)-[4-2H1]NNK is due to prochiral selectivity during P450-catalyzed metabolic activation.