title: Analysis of pyridyloxobutyl DNA adducts in F344 rats chronically treated with (R)- and (S)-N'-nitrosonornicotine.
abstract: NNN (1) is an esophageal carcinogen in rats. 2'-Hydroxylation of NNN is believed to be the major bioactivation pathway for NNN tumorigenicity. (S)-NNN is preferentially metabolized by 2'-hydroxylation in cultured rat esophagus, whereas there is no preference for 2'-hydroxylation versus 5'-hydroxylation in the metabolism of (R)-NNN. 2'-Hydroxylation of NNN generates the reactive intermediate 4-oxo-4-(3-pyridyl)butanediazohydroxide (8), resulting in the formation of pyridyloxobutyl (POB)-DNA adducts. On the basis of these observations, we hypothesized that (S)-NNN treatment would produce higher levels of POB-DNA adducts than that by (R)-NNN in the rat esophagus. We tested this hypothesis by treating male F344 rats with 10 ppm of (R)-NNN or (S)-NNN in drinking water. After 1, 2, 5, 10, 16, or 20 weeks of treatment, POB-DNA adducts in esophageal, liver, and lung DNA were quantified by HPLC-ESI-MS/MS. In the rat esophagus, (S)-NNN treatment generated levels of POB-DNA adducts 3-5 times higher than (R)-NNN treatment, which supports our hypothesis. 7-[4-(3-Pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua, 14) was the major adduct detected, followed by O2-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O2-POB-dThd, 11) and O2-[4-(3-pyridyl)-4-oxobut-1-yl]cytosine (POB-Cyt, 15). O6-[4-(3-Pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O6-POB-dGuo, 10) was not detected. The total POB-DNA adduct levels in the esophagus were 3-11 times higher than those in the liver for (R)-NNN and 2-6 times higher than those for (S)-NNN. In contrast to the esophagus and liver, (R)-NNN treatment produced more POB-DNA adducts than (S)-NNN treatment in the rat lung, which suggested an important role for cytochrome P450 2A3 in NNN metabolism in the rat lung. In both the liver and lung, O2-POB-dThd was the predominant adduct and accumulated during the experiment. The results of this study demonstrate that individual POB-DNA adducts form and persist in the esophagi, livers, and lungs of rats chronically treated with NNN enantiomers and demonstrate that (S)-NNN produces higher levels of POB-DNA adducts in the esophagus than (R)-NNN, suggesting that (S)-NNN is more tumorigenic than (R)-NNN to the rat esophagus.
authors.affiliation: Department of Medicinal Chemistry, and The Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Lao
authors.forename: Nanxiong
authors.initials: N
authors.lastname: Yu
authors.forename: Fekadu
authors.initials: F
authors.lastname: Kassie
authors.forename: Peter W
authors.initials: PW
authors.lastname: Villalta
authors.forename: Stephen S
authors.initials: SS
authors.lastname: Hecht
mesh_terms: D000284:Administration, Oral; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D018736:DNA Adducts / Q000032:analysis* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004947:Esophagus / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008168:Lung / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008175:Lung Neoplasms / Q000139:chemically induced*; D008297:Male; D015394:Molecular Structure; D009602:Nitrosamines / Q000008:administration & dosage / Q000737:chemistry / Q000633:toxicity*; D011725:Pyridines / Q000032:analysis* / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: D018736:DNA Adducts; D009602:Nitrosamines; D011725:Pyridines; C008655:N'-nitrosonornicotine