Promoter hypermethylation of GPX3 as a predictor for chemoresistance and survival in head and neck cancer patients

6027 Background: Resistance of cancer cells to cisplatin and its analogues is the major limitation in clinical application of cisplatin-based chemotherapy. The mechanisms by which cancer cells develop resistance to the drugs are still unclear, and there is no way currently to predict the drug resistance of individual tumors. By genome-wide scanning of hypermethylated genes on head and neck cancer cells, we identified glutathione peroxidase 3 (GPX3) as one of the strong candidates whose promoter hypermethylation may be associated with head and neck chemoresistance. In this study, we investigated the potential predictive value of GPX3 methylation for head and neck cancer chemoresistance and patient prognosis. Methods: Promoter methylation and expression of GPX3 gene in head and neck cancer cell lines were examined by plasmid cloning, bisulfite DNA sequencing, reverse transcription-PCR and Western blot. GPX3 methylation in primary cancer tissues was assessed by real-time methylation-specific PCR (MSP). Forty-six head and neck cancer cases, for which chemotherapy response and survival were known, were selected for analysis. Correlation of GPX3 methylation and chemoresistance was tested using two-sided Fisher’s Exact Test and its prediction for patient survival was assessed using Kaplan-Meier survival analysis. Results: Loss of GPX3 expression was observed in 4 of 8 head and neck cancer cell lines and was consistent with cisplatin resistance. Demethylating treatment of the cell lines negative for GPX3 expression significantly restored its expression. Bisulfite DNA sequencing showed that the 5’ flanking promoter region of GPX3 was heavily hypermethylated in all cell lines with expression-silencing of the gene. In the 46 head and neck cancer cases analyzed by MSP, 15 of 23 non-responding cases (65%) showed GPX3 methylation, while 4 of 23 complete and partial response cases (17%) contained low levels of GPX3 methylation (Relative Risk 3.343, two sided Fisher’s exact test, P=0.002). Kaplan-Meier survival analysis showed a relative risk of death of 1.942 in patients with GPX3 methylation. Conclusions: Our findings suggest that GPX3 methylation is a strong candidate predictor for chemoresistance and prognosis of head and neck cancer patients. No significant financial relationships to disclose.