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Promoter hypermethylation of tumor suppressor genes (TSGs) is a common featureof primary cancer cells. However, to date the somatic epigenetic events that occurin head and neck squamous cell carcinoma (HNSCC) tumorigenesis have not been well-defined.In the present study, we analyzed the promoter methylation status of the genesmutL homolog 1 (MLH1), Ras-association domain family member 1 (RASSF1A) and O-6-methylguanine-DNAmethyltransferase (MGMT) in 23 HNSCC samples, three control tissues and one HNSCCcell line (UM-SCC 33) using methylation-specific PCR (MSP). The expression ofthe three proteins was quantified by semi-quantitative immunohistochemical analysis.The cell line was treated with the demethylating agent 5-azacytidine (5-Aza) andthe methylation status after 5-Aza treatment was analyzed by MSP and DNA sequencing.Proliferation was determined by Alamar blue staining. We found that the MGMT promoterin 57% of the analyzed primary tumor samples and in the cell line was hypermethylated.The MLH promoter was found to be methylated in one out of 23 (4%) tumor sampleswhile in the examined cell line the MLH promoter was unmethylated. The RASSF1Apromoter showed methylation in 13% of the tumor samples and in the cell line.MGMT expression in the group of tumor samples with a hypermethylated promoterwas statistically significantly lower compared to the group of tumors with nomeasured hypermethylation of the MGMT promoter. After treatment of the cell linewith the demethylating agent 5-Aza no demethylation of the methylated MGMT andRASSF1A genes were determined by MSP. DNA sequencing verified the MSP results,however, increased numbers of unmethylated CpG islands in the promoter regionof MGMT and RASSF1A were observed. Proliferation was significantly (p&lt;0.05)reduced after treatment with 5-Aza. In summary, we have shown promoter hypermethylationof the tumor suppressor genes MGMT and RASSF1A in HNSCC, suggesting that thisepigenetic inactivation of TSGs may play a role in the development of HNSCC. 5-Azaapplication resulted in partial demethylation of the MGMT and RASSF1A TSGs andreduced proliferation of the tumor cells suggesting further evaluation of 5-Azafor HNSCC treatment.

oncology reports

Promoter methylation of MGMT, MLH1 and RASSF1A tumor suppressor genes in head and neck squamous cell carcinoma: Pharmacological genome demethylation reduces proliferation of head and neck squamous carcinoma cells