P18.04.A Cay10603, HDAC6 inhibitor, enhances radiosensitivity in meningioma via supressing the nuclear beta-catenin accumulation

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Abstract Background Meningioma is the most frequent primary central nervous system tumour (PCNST) which account ca 36% of all PCNST. Due to the lack of efficient chemotherapy for meningioma, radiotherapy often become a first-line treatment especially when the tumour is not operable. Radiotherapy plays a crucial role in local control but its efficacy is restricted by radioresistance and by normal tissue radiation tolerance. Therefore, developing and evaluating potential radiosensitisers to enhance therapeutic efficacy are needed.Histone deacetylase (HDACs) expression is generally increased in many cancer types and regulate the expression of numerous proteins involved in tumorigenesis. Targeting HDAC using HDAC inhibitor (HDACi) represent promising radiosensitisers that affect various biological processes, such as cell survival, apoptosis, and DNA repair. Material and Methods We investigated whether pre-treatment with the hydroxamate-based HDAC6 inhibitor, Cay10603, impacts radiation-induced DNA double-strand break (DSB) induction, cell survival, cell cycle arrest, and cell death using immunocytochemistry, clonogenic assay, and flow cytometry in meningioma cell lines. Low concentration (100 nM) of Cay10603 was treated 24 hr prior to high energy x-ray irradiation (2 Gy) by a medical linear accelerator (LINAC). To investigate the nuclear localisation of beta-catenin, subcellular fractionation and Western Blotting were conducted. Results We found that tumour cells survival was synergistically decreased after combination treatment of Cay10603 and radiation. Combination therapy induced DNA damage with activation of histone gH2AX and increased G2/M arrest compared to drug or radiation alone. Both apoptotic and necrotic cell death were increased after combination therapy. To focus on the mechanisms of action of HDAC6 inhibition followed by radiation, we further investigated nuclear localisation of beta-catenin levels. The results showed the both beta-catenin and c-myc expression in the nucleus was suppressed after combination therapy. Conclusion In meningioma cells, radiotherapy in combination with HDAC6 inhibitor reduces the nuclear localisation of beta-catenin and synergistically decreases cell survival. Our findings demonstrate a potential therapeutic strategy of Cay10603 to improve the radiosensitisation for meningioma cells.