K6/ODC transgenic mice as a sensitive model for carcinogen identification.

Ornithine decarboxylase (ODC), an important enzyme in the polyamine biosynthetic pathway, is aberrantly regulated in many epithelial tumors of rodents and humans. In murine skin, it has been shown that ODC overexpression provides a sufficient condition for tumor promotion. Therefore, we hypothesized that K6/ODC transgenic mice in which ODC overexpression was targeted to hair follicle keratinocytes might provide a sensitive model for identifying genotoxic carcinogens. Ten known carcinogens or noncarcinogens have been tested in the model so far and results are highly concordant with 2-year rodent bioassays (100% concordant). More importantly, each of two chemicals tested that is recognized as a human carcinogen was identified as a carcinogen in K6/ODC transgenic mice. In addition, 7, 12-dimethylbenz(a)anthracene (DMBA) dose response studies indicated that even at a very low dose, 2 nmol, a high percentage of mice (50%) had already developed tumors 8 weeks after treatment. We conclude that the K6/ODC transgenic mouse model is very sensitive to topical application of genotoxic carcinogens and could therefore be a useful mouse model for carcinogen identification and chemical risk assessment.