INDUCTION OF INVASIVE SQUAMOUS-CELL CARCINOMAS IN THE FORESTOMACH OF (C3HXMSM)F1, MSM, AND C3H MICE BY N-METHYL-N-NITROSOUREA AND MUTATIONAL ANALYSIS OF THE H-RAS AND P53 GENES

Genetic analysis of tumors developing in Fl hybrids between geneticall y separate strains of mice makes it possible to search for loss of het erozygosity (LOH), information on which provides clues to finding tumo r-suppressor genes. For this purpose, however, reproducible carcinogen ic conditions for the organ of interest need to be first determined. I n the present study, a forestomach model of squamous cell carcinomas ( SCCs), induced in (C3H x MSM)F1 mice by N-methyl-N-nitrosourea (MNU), was established and mutational changes in the H-ras and p53 genes were examined in tumors. Male (C3H x MSM)F1, MSM and C3H mice were given M NU by i.g. intubation once a week at a dose of 0.03 mg/g body weight f or 10 weeks, then kept without further treatment. At experimental week s 38-46, markedly invasive SCCs were observed in the forestomach at in cidences of 9/14 (64.3%), 9/16 (56.3%), and 2/10 (20.0%), respectively . In the three strains of mice, DNA analysis of SCCs by PCR-SSCP analy sis followed by direct DNA sequencing revealed low incidences of point mutations in the H-ras (4/20, 20%) and p53 (3/20, 15%) genes. The res ults demonstrate the usefulness of the present animal experimental pro tocol for induction of high grade SCC in the forestomach of (C3H x MSM )F1 mice, and suggest the possibility that point mutations in the H-ra s or p53 genes may play some role in pathways leading to the developme nt of such lesions. (C) 1997 Elsevier Science Ireland Ltd.