Tumor Suppressor P16(INK4A)/Cdkn2a Alterations in 7, 12-dimethylbenz(a)anthracene (DMBA)-induced Hamster Cheek Pouch Tumors

The prevalence of p16(INK4A)/Cdkn2a genetic alterations in human oral cancers indicates that the p16 gene could be a potent and appropriate target for novel intervention. While chemically induced hamster cheek pouch (HCP) tumors are regarded as an appropriate surrogate model for human oral cancers because of their similarities to human oral cancers in both histology and genetics, little is known about the genetic events in the p16 gene in the HCP tumor model. The purpose of this study was to evaluate chemically induced HCP tumor specimens for potential inactivating p16 alterations. HCP tumors were induced with 7, 12-dimethylbenz(a)anthracene (DMBA), and DNA extracted from 34 such specimens were analyzed for homozygous/hemizygous deletions, aberrant methylation of 5' CpG islands, and point mutations using real-time multiplex PCR, methylation-specific PCR, and direct sequencing/cold single strand conformation polymorphism (SSCP), respectively. Homozygous deletions, hemizygous deletions, aberrant methylation of 5'-CpG islands, and point mutation were identified in 11, 4, 9, and 1 of 34 specimens, respectively. While the overall incidence of p16 alterations was 70.6% (24 of 34 specimens), the majority of inactivating events (67.6%) stemmed from deletion or methylation, which is consistent with the observations found in human oral SCCs. Our results show the resemblance between chemically induced HCP tumors and their human counterparts in p16 genetic alterations, and strongly support the use of DMBA-induced HCP tumor model in evaluating novel p16-targeted therapy and prevention of human oral SCCs.