Abstract 5190: Oncoprotein SET determines the radiosensitivity of hepatocellular carcinoma cell and antagonizing SET augments the effects of radiotherapy via reactivating PP2A-mediated Akt downregulation

Abstract

Abstract Background: SET is a novel oncoprotein with growing evidence suggesting its roles in promoting the survival of hepatocellular carcinoma (HCC) and other types of malignant disease. Notably, pre-clinical data suggesting SET overexpression in cancer cell leaded to the development of resistance to various anti-cancer medications, and antagonizing SET reversely enhanced therapeutic efficacy. Radiotherapy (RT) is a commonly used anti-cancer modality, but its role for the treatment of HCC is largely limited for the concern of endogenous radioresistance. In this report, we explored the role of SET regarding the radiosensitivity of HCC cells. Furthermore, we explored whether SET serve as a valid target to enhance RT against HCC. Method: A panel of HCC cell lines, including Hep3B, PLC5, HA22T and HA59T, were used for in vitro experiments, and the PLC5 subcutaneous xenograft mice model was used for in vivo testing. HCC cells and tumors were treated with RT and/or SET antagonist and harvested for subsequent experiments. The viability of cancer cells were assessed by sub-G1, colony and sphere formation assay. Molecular events were determined by western blot and PP2A activity. Result: Through manipulating the expression of SET in cancer cells, we showed the crucial role of SET in mediating the effects of RT in HCC cells. Using colony formation and hepatosphere formation assay, we showed that RT significantly reduced the number and size of both tumor colony and sphere formed by Hep3B and PLC5 cells. In contrast, ectopic expression of SET in Hep3B and PLC5 cells abolished the effects of RT. More importantly, SET-knockdown oppositely potentiated the RT-induced growth inhibition in HCC cells. Based on our findings, we hypothesized that targeting SET may exert potential to enhance RT for the treatment of HCC. In order to validate our hypothesis, we tested the effects of RT in combine with a novel SET antagonist, EMQA, developed and characterized in our previous works. As expected, we found that EMQA significantly potentiated the anti-HCC effects of RT in vitro and in vivo. Moreover, we found that antagonizing SET to restore PP2A-mediated p-Akt downregulation was responsible for the synergism between EMQA and RT. Conclusion Oncoprotein SET plays a critical role in affecting the radiosensitivity of HCC cells. Using SET antagonist plus RT showed promising results in pre-clinical HCC models, and yields further investigation. Citation Format: Man-Hsin Hung, Chao-Yuan Huang, Chih-Ting Shih, Min-Hsien Tsai, Yung-Jen Hsiao, Tzu-I Chao, Feng-Shu Hsieh, Chung-Wai Shiau, Kuen-Feng Chen. Oncoprotein SET determines the radiosensitivity of hepatocellular carcinoma cell and antagonizing SET augments the effects of radiotherapy via reactivating PP2A-mediated Akt downregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5190. doi:10.1158/1538-7445.AM2017-5190