Smokeless tobacco products such as moist oral snuff are being promoted by the tobacco industry with a half billion dollars per year in advertising. It is likely that the prevalence of smokeless tobacco use will continue to increase in the U.S. Smokeless tobacco products are widely used in other parts of the world and are considered by the International Agency for Research on Cancer as causes of cancer of the oral cavity, esophagus and pancreas in humans. However, no previous study has reported the presence of a strong oral cavity carcinogen in these products.

N'-Nitrosonornicotine (NNN) occurs in significant amounts in smokeless tobacco products, generally being found at levels of 1 - 10 μg/g tobacco. Since NNN has a chiral center, it exists as (S)- and (R)- enantiomers. (S)-NNN is the major enantiomer in smokeless tobacco products. While racemic NNN (a 50:50 mixture of (S)- and (R)-NNN) has been previously shown to cause esophageal tumors in rats, the carcinogenicity of the individual enantiomers has not been reported. Based on our published metabolism and DNA binding studies of (S)-NNN, we hypothesized that it might be a more powerful carcinogen than (R)-NNN and, furthermore, that it might cause oral cancer.

Groups of 24 male F-344 rats were treated with either (S)-NNN (15 ppm), (R)-NNN (15 ppm), or racemic NNN (30 ppm) in the drinking water for 15-20 months. Necropsy of 20 rats treated with (S)-NNN demonstrated a 100% incidence of oral cavity tumors. More than 60 oral cavity tumors were observed, including benign and malignant tumors of the buccal mucosa, soft and hard palate, tongue, and pharynx. All rats also had esophageal tumors. (R)-NNN was significantly less carcinogenic than (S)-NNN. Racemic NNN also induced a high incidence of oral cavity and esophageal tumors.

The results of this study demonstrate for the first time the presence of a strong oral cavity carcinogen in smokeless tobacco. (S)-NNN is a prime target for elimination from these products as a positive step toward cancer prevention.

Citation Format: Stephen S. Hecht, Sandra James-Yi, Gerard O'Sullivan, Irina Stepanov, Mingyao Wang, Fekadu Kassie, Steven Carmella, Pramod Upadhyaya, Silvia Balbo. Induction of oral cavity cancer in rats by (S)-N'-nitrosonornicotine, a constituent of smokeless tobacco. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr CN06-01.