Abstract 3314: DNA methylome analysis identifies epigenetic silencing of FHIT as a determining factor for radiosensitivity in oral cancer and its implication in treatment and outcome prediction
Authors: Lin Hon-Yi , Hung Shih-Kai , Lee Moon-Sing , Chiou Wen-Yen , Huang Tze-Ta , Tseng Chih-En , Shih Liang-Yu , Lin Ru-Inn , Lin Jora , Lai Yi-Hui , Chang Chia-Bin , Hsu Feng-Chun , Chen Liang-Cheng , Tsai Shiang-Jiun , Su Yu-Chieh , Li Szu-Chi , Lai Hung-Chih , Hsu Wen-Lin , Liu Dai-Wei , Tai Chien-Kuo , Wu Shu-Fen , Chan Michael W. 
Published: August 2015

Radioresistance is still an emerging problem for radiotherapy of oral cancer. Aberrant epigenetic alterations play an important role in cancer development, yet the role of such alterations in radioresistance of oral cancer is not fully explored. Using Illumina 27K methylation BeadChip microarray, we identified promoter hypermethylation of FHIT (fragile histidine triad) in radioresistant OML1-R cells, established from hypo-fractionated irradiation (5-Gy by 10 fractions) of parental OML1 radiosensitive oral cancer cells. Further analysis confirmed that transcriptional repression of FHIT was due to promoter hypermethylation and H3K27me3 as demonstrated by MBDcap-PCR, bisulfite pyrosequencing and ChIP-PCR. These phenomenon were partially attributed to overexpression of EZH2 and DNMT3a, 3b in OML1-R cells. In consistent with these observations, treatment of 5-azaDC, EZH2 inhibitor (GSK343) or depletion of EZH2 by lentiviral knockdown restored FHIT expression in OML1-R cells. Interestingly, knockdown of EZH2 also reversed histone modifications (increased of H3K4me3 and decreased of H3K27me3) and reduced promoter methylation of FHIT thus suggesting that H3K27me3 linked to DNA methylation in this loci. We also analyzed the expression of FHIT in primary human oral keratinocyte (HOK) and four other oral cancer cell lines (OCSL, SCC25, SAS, and SCC4). FHIT expression demonstrated a tight inverse relationship with its promoter methylation. Ectopic expression of FHIT restored radiosensitivity (single fraction, 10-Gy) in OML1-R cells and oral cancer cells (SAS, SCC25) showing epigenetic silencing of FHIT. These phenomenon may be due to restoration of Chk2 phosphorylation, induction of apoptosis and G2/M check point. Reciprocal experiments also showed that depletion of FHIT in OSCL cells, which highly express FHIT, slightly enhanced radioresistance. Clinically, bisulfite pyrosequencing and iummnohistochemistry revealed that promoter hypermethylation of FHIT inversely correlated with its expression. Patients with higher FHIT methylation (methylation&gt;10%, n = 22) are associated with lower locoregional control (P&lt;0.05) and overall survival rate (P&lt;0.05) than patients with lower FHIT methylation (n = 18). For patients treated with post-operative radiotherapy alone (n = 19), sub-group analysis also found that patients with higher FHIT methylation tend to have a 2-fold lower locoregional control rate (P = 0.0998). Further in vivo therapeutic experiments confirmed that treatment of 5-azaDC significantly resensitized radioresistant oral cancer cell xenograft tumors. These results show that epigenetic silencing of FHIT contributes partially to radioresistance and predicts clinical outcomes in irradiated oral cancer. The radiosensitizing effect of epigenetic interventions warrants further clinical investigation.

Citation Format: Hon-Yi Lin, Shih-Kai Hung, Moon-Sing Lee, Wen-Yen Chiou, Tze-Ta Huang, Chih-En Tseng, Liang-Yu Shih, Ru-Inn Lin, Jora Lin, Yi-Hui Lai, Chia-Bin Chang, Feng-Chun Hsu, Liang-Cheng Chen, Shiang-Jiun Tsai, Yu-Chieh Su, Szu-Chi Li, Hung-Chih Lai, Wen-Lin Hsu, Dai-Wei Liu, Chien-Kuo Tai, Shu-Fen Wu, Michael W. Chan. DNA methylome analysis identifies epigenetic silencing of FHIT as a determining factor for radiosensitivity in oral cancer and its implication in treatment and outcome prediction. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3314. doi:10.1158/1538-7445.AM2015-3314