Tumor suppressor p16(INK4A)/Cdkn2a alterations in 7, 12-dimethylbenz(a)anthracene (DMBA)-induced hamster cheek pouch tumors

A mechanistic evaluation of the Syrian hamster embryo cell transformation assay (pH 6.7) and molecular events leading to senescence bypass in SHE cells

The implementation of the Syrian hamster embryo cell transformation assay (SHE CTA) into test batteries and its relevance in predicting carcinogenicity has been long debated. Despite prevalidation studies to ensure reproducibility and minimise the subjective nature of the assay's endpoint, an underlying mechanistic and molecular basis supporting morphological transformation (MT) as an indicator of carcinogenesis is still missing. We found that only 20% of benzo(a)pyrene-induced MT clones immortalised suggesting that, alone, the MT phenotype is insufficient for senescence bypass. From a total of 12 B(a)P- immortalised MT lines, inactivating p53 mutations were identified in 30% of clones, and the majority of these were consistent with the potent carcinogen's mode of action. Expression of p16 was commonly silenced or markedly reduced with extensive promoter methylation observed in 45% of MT clones, while Bmi1 was strongly upregulated in 25% of clones. In instances where secondary events to MT appeared necessary for senescence bypass, as evidenced by a transient cellular crisis, clonal growth correlated with monoallelic deletion of the CDKN2A/B locus. The findings further implicate the importance of p16 and p53 pathways in regulating senescence while providing a molecular evaluation of SHE CTA -derived variant MT clones induced by benzo(a)pyrene.

Animal models of head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the most common oral cancer worldwide. Local bone invasion into the maxilla or mandible and metastasis to regional lymph nodes often result in a poor prognosis, decreased quality of life and shortened survival time for HNSCC patients. Poor response to treatment and clinical outcomes are the major concerns in this aggressive cancer. Multiple animal models have been developed to replicate spontaneous HNSCC and investigate genetic alterations and novel therapeutic targets. This review provides an overview of HNSCC as well as the traditional animal models used in HNSCC preclinical research. The value and challenges of each in vivo model are discussed. Similarity between HNSCC in humans and cats and the possibility of using spontaneous feline oral squamous cell carcinoma (FOSCC) as a model for HNSCC in translational research are highlighted.

Chemoprevention of oral cancer by lyophilized strawberries

BACKGROUND/AIM

Oral cancer represents approximately 2.5% of all cancers in the United States, with five- and 10-year survival rates of 62% and 51%. In the present study, lyophilized strawberries (LS) were evaluated for their potential to inhibit tumorigenesis in the hamster cheek pouch (HCP) model of oral cancer and for their ability to modify expression of several genes relevant to oral cancer development.

MATERIALS AND METHODS

HCPs were painted three times a week for six weeks with 0.2% 7,12-dimethylbenz(a)anthracene (DMBA). Hamsters were given 5% or 10% LS in their diet prior to, during, and after, or only after carcinogen treatment. Animals were sacrificed 12 weeks from the beginning of DMBA treatment and the number of total lesions and tumors was determined.

RESULTS

A significant difference (p<0.01-0.04) in the number of tumors was found between the LS-treated groups and the carcinogen controls. Histological examination of HCPs revealed a significant reduction in mild and severe dysplasia following 12 weeks of treatment with LS. Molecular analysis revealed that genes related to tumor development were modulated by LS.

CONCLUSION

These experiments support previous studies in HCP that demonstrated a chemopreventive activity by black raspberries and show, to our knowledge for the first time, that strawberries can inhibit tumor formation in an animal model of oral cancer.

Epigenetic mechanisms in oral carcinogenesis

Dysregulation of gene expression is a frequent occurrence in oral squamous cell carcinoma (OSCC). However, accumulating evidence suggests that in contrast to genetics, epigenetic modifications consisting of aberrant DNA methylation, histone modifications and altered expression of miRNAs induce OSCC tumorigenesis and perhaps play a more central role in the evolution and progression of this disease. The unifying theme among these three epigenetic mechanisms remains the same, which is aberrant regulation of gene expression. In this article, we provide a comprehensive review of the impact of epigenetics on oral tumorigenesis with a systematic report on aberrant DNA methylation, histone modifications and miRNA regulation in the pathogenesis of OSCC. We provide insights into recent studies on the prospect of biomarkers for early detection and indication of disease recurrence, and novel treatment modalities.

p16(INK4a)/CDKN2 expression and its relationship with oral squamous cell carcinoma is our current knowledge enough?

Oral squamous cell carcinomas (OSCC) are the most common malignancy of the oral cavity and their multistep development requires the accumulation of multiple genetic and epigenetic alterations. Inactivation of p16(INK4a), encoded by the CDKN2 gene has been widely associated with this type of tumors. The purpose of this review is to elucidate the relationship between p16(INK4a) expression and the different clinical and pathological aspects of OSCC, analyze the variation in results between studies, detailing the described genetic/epigenetic alterations that result in gene silencing and the relationship between p16(INK4a) and HPV infection.