Susceptibility of transgenic mice carrying human prototype c-Ha-ras gene in a short-term carcinogenicity study of vinyl carbamate and ras gene analyses of the induced tumors.

To determine if hemizygous transgenic mice carrying the human c-Ha-ras gene (CB6F1-Tg Hras2 mice (Hras2 mice)) are susceptible to the carcinogenic potential of known murine carcinogens, male and female Hras2 mice and their non-transgenic CB6F1 littermates (non-Tg mice) were each given a single intraperitoneal injection of 60 mg of vinyl carbamate (VC)/kg body weight or saline (vehicle control) and monitored for 16 wk without further treatment. At necropsy, grossly visible tumors were fixed for histopathologic diagnosis and, when of sufficient size, portions were frozen for subsequent molecular analysis. Nine of 31 male and nine of 29 female Hras2 mice treated with VC died within 16 wk as a result of lung tumor burden. At the termination of the study, lung tumors (alveolar-bronchiolar epithelial neoplasms and hemangiosarcomas) and focal alveolar-bronchiolar hyperplasias were present in both sexes of Hras2 and non-Tg mice treated with VC; there were significantly more proliferative lung lesions in Hras2 than non-Tg mice. Splenic hemangiosarcomas and squamous cell tumors of the forestomach were induced in male and female VC-treated Hras2 mice but not in VC-treated non-Tg mice. Polymerase chain reaction-single-strand conformation polymorphism analysis and DNA sequencing of the induced lung tumors revealed point mutations at codon 61 of the transgene in two of 29 lung tumors (one of 16 in males and one of 13 in females) from VC-treated Hras2 mice; no mutations in murine Ki-ras were found in these tumors. Point mutations at codons 12 and 61 of the murine Ki-ras gene were observed, however, in one of 10 and six of 10 lung tumors respectively, from VC-treated non-Tg mice. These findings indicate that Hras2 mice are highly sensitive to pulmonary neoplasms and splenic and lung hemangiosarcomas after treatment with VC. The molecular analyses suggest that point mutations of the transgene and the murine Ki-ras gene do not play a major role in VC induction of pulmonary neoplasms in these transgenic mice.