Chemically induced skin carcinogenesis in a transgenic mouse line (TG.AC) carrying a v-Ha-ras gene

A transgenic mouse line (TG.AC) created in the FVB/N strain, carries a v-Ha-ras gene fused to a zeta-globin promoter gene. These trangenic mice have the properties of genetically initiated skin and have been shown to be sensitive to 12-O-tetradecanoylphorbol-13-acetate (TPA), a well-described promoter of skin papillomas in the two-stage mouse skin tumorigenesis model. It was of interest to determine whether the TG.AC mouse strain was also responsive to other known promoters. Groups of heterozygous or homozygous TG.AC mice were treated topically, 2x/week, for up to 20 weeks with benzoyl peroxide (BPO), 2-butanol peroxide (2-BUP), phenol (PH), acetic acid (AA), TPA and acetone (ACN), the vehicle control. Skin papillomas were induced in all groups treated with TPA, BPO and 2-BUP. Papillomas were observed in some treatment groups as early as 3 weeks. The relative activity of the promoters was TPA > 2-BUP > BPO > PH = AA = ACN. No papillomas were observed in any of the uninitiated FVB/N mice treated in a similar manner and which served as treatment control groups. Studies to determine the sensitivity of TG.AC mice to TPA, indicated that a total dose of 25-30 micrograms of TPA administered in 3 or 10 applications, was sufficient to induce an average incidence of 11-15 papillomas per mouse. The papilloma incidence continued to increase and was maintained up to 15 weeks after TPA treatment was terminated. The short latency period and high incidence of papilloma induction indicate that TG.AC mice have a high sensitivity to known skin promoters. The TG.AC line should prove to be a sensitive model for identifying putative tumor promoters or complete carcinogens.