Dermal Carcinogenicity in Transgenic Mice: Relative Responsiveness of Male and Female Hemizygous and Homozygous Tg.AC Mice to 12-O-Tetradecanoylphorbol 13-Acetate (TPA) and Benzene

Abstract

Assessment of the carcinogenic potential of chemical agents continues to rely primarily upon the chronic rodent bioassay, a resource-intensive exercise. Recent advances in transgenic technology offer a potential resource conserving approach to carcinogen detection. Incorporation of oncogenes with known roles in the development of neoplasms into the genomes of laboratory rodents may provide new models with the potential of quickly and accurately separating carcinogenic from noncarcinogenic chemicals. The insertion of the v-Ha-ras oncogene into the genome of FVB/N mice imparts the qualities of genetically initiated skin in the transgenic mouse line designated as Tg.AC. The skin of either hemizygous (animals carrying the transgene on 1 allele) or homozygous (transgene copies on both alleles) Tg.AC mice promptly responds to the application of nongenotoxic carcinogens, such as the classical tumor promoting phorbol esters, with the development of squamous papillomas. Tumor production generally begins after 8-10 applications of 2.5 μg/mouse (3 times/wk) of 12-O-tetradecanoylphorbol 13-acetate (TPA). Maximal tumor response is usually in evidence within 20 wk. If this transgenic mouse line is to be useful in the identification of carcinogenic chemicals, experimental protocols must be systematically optimized. Experiments were conducted to compare the relative responsiveness of male and female hemizygous and homozygous Tg.AC mice to the dermal application of TPA and the known human leukemogen, benzene. Results revealed shipment-related variabilities in the relative responsiveness of hemizygous male and female mice to the application of the proliferative agent. Homozygous mice of both sexes were more reliable and uniform in responsiveness to both TPA and benzene. Therefore, our standard protocol for the conduct of bioassays with the Tg.AC mouse line specifies the use of homozygous males and/or females.

Keywords

Tg.AC mice transgenic rodent lines short-term carcinogenicity tests dermal papillomas benzene TPA

References

1. Hansen L and Tennant RW (1994). Focal transgenic expression associated with papilloma development in v-Has-ras transgenic Tg.AC mice. Mol. Carcinog.. 9: 143–156.

2. Holden HE , Stoll RE , Spalding JW , and Tennant RW (1998). Hemizygous Tg.AC transgenic mouse as a potential alternative to the 2-year mouse carcinogenicity bioassay: Evaluation of husbandry and housing factors. J. Appl. Toxicol.. 18: 19–24.

3. Leder A , Kuo A , Cardiff RD , Sinn E , and Leder P (1990). v-Ha-ras transgene abrogates the initiation step in mouse skin tumorigenesis: Effects of phorbol esters and retinoic acid. Proc. Nail. Acad. Sci. USA. 87: 9178–9182.

4. Spalding JW , Momma J , Elwell MR , and Tennant RW (1993). Chemically induced skin carcinogenesis in a transgenic mouse line (Tg.AC) carrying a v-Has-ras gene. Carcinogenesis. 14: 1335–1341.

5. Tennant R (1997). Identifying carcinogens–A strategy for use of abbreviated models. Toxicol. Pathol.. 25: 240–241.

6. Tennant RW , French JE , and Spalding JW (1995). Identifying chemical carcinogens and assessing potential risk in short-term bio-assays using transgenic mouse models. Environ. Health Perspect.. 103: 942–950.

7. Tennant RW , Spalding J , and French JE (1996). Evaluation of transgenic mouse bioassays for identifying carcinogens and noncarcin-ogens. Mutat. Res.. 365: 119–127.

8. Thompson KL , Rosenzweig BA , and Sistare FD (1998). An evaluation of the hemizygous transgenic Tg.AC mouse for carcinogenicity testing of pharmaceuticals. II. A genotypic marker that predicts tumorigenic responsiveness. Toxicol. Pathol. 26: 548–555 (this issue).