Oral mucosal carcinogenesis in SENCAR mice

Abstract

Animal models of oral carcinogenesis have been developed but most use the hamster buccal pouch or rat oral mucosa. With completion of human and murine genome sequencing, the development of a mouse model of oral carcinogenesis may prove useful for future genomic studies of oral carcinogenesis. To achieve this objective, 30 SENCAR mice were initiated by brush application of palatal, buccal and tongue mucosa with 200 nmol 7,12-dimethylbenz[a]anthracene (DMBA) using 3 treatment regimens, and promoted by brush application with 5 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) for a total of 28 weeks. Alternatively, 5 mice were treated with 0.5% 4-nitroquinoline-1-oxide (4NQO) alone by brush application for 28 weeks. There were another 6 control mice treated with vehicle alone. The tumor samples were analyzed for the presence of H-ras codon 61 gene mutations using a mutant-allele-specific amplification-polymerase chain reaction (MASA-PCR) technique. The results showed that among the group of 24 mice initiated with DMBA for 2 or 6 weeks, a range of papilliferous lesions were seen on the buccal mucosa comprising papillomas, papillomas with dysplasia and 7 squamous cell carcinomas (SCC). In those 6 mice initiated with 1 week of DMBA, only papillomas developed. In the 5 mice treated with 4NQO, one developed papillomas with dysplasia and two had SCCs in the tongue mucosa but not the buccal mucosa. Both carcinogens induced codon 61 mutation of the H-ras gene at a high frequency. The results indicated that DMBA/TPA and 4NQO in SENCAR mice reliably produced preneoplastic and malignant oral cavity lesions, which resemble the multistages for human oral carcinogenesis, and targeted to site-specific zones of the oral mucosa, namely the buccal mucosa and tongue, respectively. These results show that SENCAR mice can be used as a unique model of oral carcinogenesis with the potential for detailed molecular studies of neoplastic progression to SCC.