p53 and Ha-ras mutations in chemically induced hamster buccal pouch carcinomas

Abstract

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.

Mdm2: keeping p53 under control

“…Examples are chemically induced squamous cell carcinomas of the bucal pouch in hamster where seven of 22 tumors contained p53 mutations but none showed overexpression of Mdm2 mRNA (Chang et al, 1996) and pancreatic duct adenocarcinomas where ®ve of 19 tumors contained higher Mdm2 mRNA levels but none had p53 mutations (Chang et al, 1995). This kind of tumor type speci®city also suggests that p53 mutation and Mdm2 overexpression are phenotypically not equivalent, although one cannot exclude that this speci®city is rather a re¯ection of the type of mutations occurring in di erent tumors (point mutations for p53 versus gene ampli®cations for Mdm2).…”

Chemopreventive potential of 3-[2,6-bis(4-fluorophenyl)-3-methylpiperidin-4-ylideneamino]-2-thioxoimidazolidin-4-one on 7,12-dimethylbenz[a]anthracene (DMBA) induced hamster buccal pouch carcinogenesis

“…Squamous cell carcinomas induced by the application of 7,12-dimethylbenz[a]anthracene (DMBA) to the cheek pouch of the Syrian hamsters are morphologically and histologically similar to human tumours [10,11]. In addition, hamster tumours express many metabolic and molecular markers that are expressed in human oral cancer [12][13][14].…”

p53 polymorphisms associated with mutations in and loss of heterozygosity of the p53 gene in male oral squamous cell carcinomas in Taiwan

“…The most prevalent types of p53 mutation found in Taiwanese OSCCs were G:C to A:T transitions and G:C to T:A transversions. Studies have demonstrated that these types of mutations are the most common mutations observed in animals treated with NNK or other tobacco nitrosamines (Belinsky et al, 1991;Oreffo et al, 1993;Ronai et al, 1993;Chang et al, 1996). Evidence from the literature also indicates that NNK-associated DNA adducts, in addition to being repaired by the nucleotide excision repair pathway, are also repaired by base excision repair (Cloutier and Castonguay, 1998).…”