Validation of transgenic mice carrying the human prototype c-Ha-ras gene as a bioassay model for rapid carcinogenicity testing.

Carcinogenicity testing is indispensable for identifying environmental carcinogens and for evaluating the safety of drugs in the process of development. Conventional 2-year rodent bioassays are one of the most resource-consuming tests in terms of animals, time, and costs. Development of rapid carcinogenicity testing systems that can assess carcinogenicity within a short period has become a social demand and is essential to improve efficacy in the identification of environmental carcinogens as well as in the development of new drugs. In this review we introduce the rapid carcinogenicity testing system using transgenic (Tg) mice carrying the human prototype c-Ha-ras gene, namely rasH2 mouse (CB6F1-TgHras2 mouse is the same mouse). The studies have been conducted to validate the rasH2 mouse as a model for the rapid carcinogenicity testing system. Our current validation studies revealed that rasH2 mice are able to detect various types of mutagenic carcinogens within 6 months. The rasH2 mice may also be able to detect various nonmutagenic carcinogens. The validation studies also revealed that rasH2 mice are generally much more susceptible to both mutagenic and nonmutagenic carcinogens than control non-Tg mice. No significant tumor induction has been observed in rasH2 mice with either mutagenic or nonmutagenic noncarcinogens. More rapid onset and higher incidence of more malignant tumors can be expected with a high probability after treatment with various carcinogens in the rasH2 mice than in control non-Tg mice. The rasH2 mouse appears to be a promising candidate as an animal model for development of a rapid carcinogenicity testing system.