An Industry Perspective on the Utility of Short-Term Carcinogenicity Testing in Transgenic Mice in Pharmaceutical Development

International guidelines allow for use of a short-tern cancer bioassay (twenty-six weeks) in transgenic mice as a substitute for one of the two required long-term rodent bioassays in the preclinical safety evaluation of pharmaceuticals. The two models that have gained the widest acceptance by sponsors and regulatory authorities are the CB6F1-RasH2 mouse hemizygous for a human H-ras transgene and the B6.129N-TrP53 mouse heterozygous for a p53 null allele. The p53(+/-) models is of particular value for compounds with residual concern that genotoxic activity may contribute to tomorigenesis. The rasH2 model is an appropriate alternative without regards to evidence of genotoxic potential. Since results from a short-term bioassay can be obtained relatively early in drug development, there is the potential for more timely assessment of cancer risk for individuals in long-term clinical trials. Use of these models in preclinical safety evaluation also significantly reduces animal use, time, and manpower. Preliminary findings indicate that prediction of two-year bioassay outcomes based on data from chronic rat toxicity studies, together with early assessment of carcinogenic potential in short-term transgenic models may have the potential to increase the timeliness and efficiency of strategies for the identification of human carcinogenic hazards.