Stereospecific deuterium substitution attenuates the tumorigenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).
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-(2)H(1)]NNK and (4S)-[4-(2)H(1)]NNK. Upon ip administration to groups of 20 female A/J mice, NNK and (4S)-[4-(2)H(1)]NNK exhibited similar lung tumorigenicity at three different doses, whereas (4R)-[4-(2)H(1)]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-(2)H(1)]NNK than in mice treated with NNK or (4S)-[4-(2)H(1)]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-(2)H(1)]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-(2)H(1)]NNK was the substrate for p2A4 and 2A5, respectively, whereas they were 1.3 +/- 0.1 and 1.1 +/- 0.1 when (4S)-[4-(2)H(1)]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-(2)H(1)]NNK relative to (4S)-[4-(2)H(1)]NNK is due to prochiral selectivity during p450-catalyzed metabolic activation.
Jalas
John R
JR
Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA.
McIntee
Edward J
EJ
Kenney
Patrick M J
PM
Upadhyaya
Pramod
P
Peterson
Lisa A
LA
Hecht
Stephen S
SS
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D002273:Carcinogens / Q000378:metabolism* / Q000633:toxicity*; D065637:Cytochrome P-450 CYP2A6; D004247:DNA / Q000378:metabolism; D018736:DNA Adducts / Q000032:analysis; D003903:Deuterium / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D008168:Lung / Q000187:drug effects / Q000201:enzymology; D008175:Lung Neoplasms / Q000139:chemically induced* / Q000473:pathology; D051379:Mice; D008805:Mice, Inbred A; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D015394:Molecular Structure; D009602:Nitrosamines / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D002273:Carcinogens; D018736:DNA Adducts; D009602:Nitrosamines; D006147:Guanine; C008450:7-methylguanine; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D004247:DNA; C008449:O-(6)-methylguanine; D003903:Deuterium; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6