304 NF2 Loss-of-Function and Hypoxia Together Drive Radioresistance in Grade 2 Meningiomas

INTRODUCTION: Grade 2 meningiomas (G2Ms) are associated with an aggressive natural history characterized by recurrence and resistance to radiation therapy. Histopathological necrosis is associated with worse progression-free survival (PFS) following radiation therapy in G2Ms. We seek to understand the molecular pathophysiology of radiation resistance and to identify molecular biomarkers and therapeutic targets for radioresistant G2M. METHODS: We performed genetic sequencing and histopathological analysis of 121 G2Ms. Using the IOMM-Lee meningioma cell line, we investigated the role of tumor hypoxia and genes of interest in radio-resistance through lentivirally targeted gene knockdown and clonogenic survival assays following exposure to ionizing radiation. Transcriptional profiling of cells in in vitro and in 38 patient G2Ms was performed using RNA sequencing. RESULTS: NF2 loss of function mutations were significantly associated with tumor necrosis in G2Ms (p = 0.0026). Patients with NF2mutation and spontaneous necrosis had worse post-radiation PFS compared to NF2 wildtype patients without necrosis (p = 0.035). In the setting of hypoxia, NF2 knockdown significantly increased radio-resistance in vitro (p < 0.001). Gene set enrichment analysis on in vivo and in vitro data and functional assays revealed downregulation of apoptosis and upregulation of cell proliferation in NF2-deficient and necrotic group compared to control. Integration of differentially expressed genes in both NF2-deficient cells in vitro and human necrotic tumors identified shared upregulation of HES1, XDH, NOG, IGFBP3, ALOXE3, THSB1, and TRIML2, suggesting these genes may represent targets for radio-sensitization or biomarkers of radio-resistance. CONCLUSIONS: NF2 loss-of-function in the setting of hypoxia confers radiation resistance through a transcriptional program that promotes proliferation and DNA repair. Targeting molecular pathways identified by transcriptional profiling may improve local control in patients with radioresistant G2M.