The clinical role of EZH2 in radiation resistance has not been reported DAPT concentration before. However, several studies have suggested the possible involvement of EZH2 in radiation resistance. Recent evidence from Hung’s group suggests that enhanced expression of EZH2 promotes breast CSC expansion through impairment of the DNA damage repair protein Rad51 and the activation of RAF1-ERK-β-catenin signaling [11].

They showed that EZH2-mediated downregulation of DNA damage repair leads to accumulation of recurrent RAF1 gene amplification in breast CSCs, which activates p-ERK-β-catenin signaling to promote CSC expansion. They further revealed that targeting EZH2 downstream activation pathways such as RAF1-ERK signaling with the MEK inhibitor AZD6244 could prevent

breast cancer progression by eliminating CSCs. They further showed that HIF1α, a known mediator of radioresistance in breast cancer, activates the EZH2 gene and increases EZH2 expression under hypoxic conditions [11]. Other studies have also supported the possible PRIMA-1MET in vitro role for EZH2 in modulating radiation response. Dong et al demonstrated that overexpression of Bmi-1, another PcG protein similar to EZH2, elicits radioprotective effects in keratinocytes by mitigating the genotoxic effects of radiation through epigenetic mechanisms [15]. In another study, EX 527 nmr pharmacologic inhibition of EZH2 induced radiation sensitivity in atypical teratoid/rhabdoid tumors in vitro [16], and silencing EZH2 with RNAi enhanced radiation sensitivity in lung cancer cells [17]. Collectively, these data together with our current findings that EZH2 is associated with local out failure in IBC patients support the hypothesis that EZH2 has a significant role in promoting resistance to radiation treatment. However, it remains unknown which, if any, of the known mechanisms of EZH2 activity actually modulates resistance to radiation therapy. We and others have provided evidence that breast CSCs are resistant

to radiation through upregulation of stem cell self renewal pathways including β-catenin and Notch signaling [3,4] and other studies have shown that CSCs contribute to radioresistance by preferential activation of the DNA damage checkpoint response and increased DNA repair capacity and by maintaining low ROS levels [18,19]. EZH2 has been shown to promote CSC expansion and maintenance [11,20] and to impair DNA repair via downregulation of Rad51 [11,21]. These findings seem paradoxical given that downregulation of Rad51 is expected to increase radiosensitivity but CSC expansion has been linked with radiation resistance. Further studies are warranted to elucidate this paradox by examining how EZH2 activates radiation resistance mechanisms in breast cancer cells.