DNAR-14. EZH2 Inhibition As a Potential Therapeutic Avenue in the Treatment of Meningioma

High grade meningiomas provide challenges to treatment as these neoplasms are more likely to recur, exhibit invasion of brain parenchyma, and result in decreased long term survival. Recent works demonstrate the epigenetic modifier, EZH2, to be increased in higher grade meningiomas and to correlate with poor survival, along with loss of SMARCB1, a known antagonizer of EZH2. The selective targeting of EZH2 has shown promise in other malignancies with overexpression of or gain-of-function mutations in EZH2, leading to promising findings. Here we sought to investigate the effect of EZH2 inhibition on meningioma cell growth and viability, using a panel of in vitro and in vivo models. Human immortalized meningioma cell lines, mouse meningioma cell lines and a panel of human primary cell cultures with varying baseline protein expression of NF2, SMARCB1, and EZH2, were selected for investigation. Cells were treated with several small molecule inhibitors of EZH2 including the anti-viral agent ribavirin. Cell proliferation, cell cycle, and cell death processes were assessed. RNAseq and Western blots were used to assess downstream target effects after EZH2 inhibition. In vivo orthotopic xenograft models were used to assess survival. EZH2 inhibition via a panel of inhibitors significantly impairs meningioma cell proliferation, at varying IC50s, in all cell lines and primary cultures tested. Furthermore, EZH2 inhibition results in a reduction of Ki67+ cells, induction of cell cycle arrest, and apoptosis. Ribavirin (a known EZH2 inhibitor) -treated animals exhibited a significantly increased median survival (67 days) compared to controls (41 days; p=0.0009;) in an orthotopic convexity meningioma xenograft model. Furthermore, ribavirin treatment resulted in increased survival in an orthotopic skull base meningioma xenograft model. Our work demonstrates that EZH2 inhibition in meningioma results in decreased proliferation, induced cell cycle arrest and cell death, in vitro, while ribavirin treatment resulted in increased survival, in vivo, potentially via inhibition of EZH2. This work provides the framework for further investigation of EZH2 inhibition as targeted therapy in meningioma.