Well-differentiated
squamous cell carcinomas were induced in hamster buccal pouch epithelium by twice weekly topical applications of
N-methyl-N-benzylnitrosamine (MBN) or 7,12-dimethylbenz[a]
anthracene (DMBA) over a period of 15 weeks. Each of the 22
tumors induced (14 MBN and eight DMBA) were evaluated by single-strand conformation polymorphism and
DNA sequencing to identify mutations in conserved exons (E5-E8) of the p53 tumor suppressor gene and
codons 12/13 and 61 of Ha-ras. In addition, Northern blot analysis of 10 MBN
tumors and five DMBA
tumors was performed to determine whether the mdm-2 gene was overexpressed, p53 mutations were detected in five of 14 (35%) MBN-induced
carcinomas and in two of eight (25%) DMBA-induced
carcinomas. Ha-ras mutations were detected in three of 14 (21%) MBN-induced
carcinomas and in three of eight (37%) DMBA-induced
carcinomas. One MBN-induced
carcinoma exhibited a mutation in both the p53 and Ha-ras genes. The majority (five of seven of p53/Ha-ras mutations induced by MBN were G->A transitions and two of these occurred at hamster p53
codon 248, which corresponds to human p53
codon 245, a known mutational
tumor 'hot spot'. A->T transversion at Ha-ras
codon 61 accounted for three of five (60%) DMBA-induced mutations. There was no evidence of mdm-2 overexpression in any of the
tumors evaluated. Overall, the results provide additional support for the validity of the hamster buccal pouch model of oral
carcinogenesis, as applied to sequential cellular and molecular analysis and
cancer chemoprevention studies.