Targeting A Mapk-Mir-124-Sox9 Axis Radiosensitizes Human Glioblastoma Cells

Glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor. Although genetic alterations and overexpression of genes in the RTK/RAS/MEK/ERK pathway (MAPK) is known to drive GBM aggressiveness, less is known about down-stream effector genes. We confirmed that EGFR amplified human GBMs display high levels of the transcription factor SOX9, a known barrier to neurogenesis and target of microRNA-124 (miR-124). Surprisingly, a subpopulation of SOX9-negative tumor cells expressed markers of mature neurons. Here, we demonstrate that the MEK inhibitor PD325901 depletes SOX9, reduces proliferation, and induces neurogenesis in a mouse GBM model and human GBM cells. We find that MAPK signaling regulates a large cluster of miRNAs in mouse neurosphere cultures, including miR-124. In addition, PD325901 effectively induced miR-124 levels in SOX9-expressing human GBMs. Using a doxycycline-regulable approach, we demonstrate that miR-124 overexpression depletes SOX9 levels and induces neurogenesis in a concentration- and time-dependent manner in human GBM tumorsphere cultures. Doxycycline treatment of athymic nude mice intracranially xenografted with human GBM cells resulted in reduced tumor growth, robust neuronal differentiation, and increased overall survival. Finally, we demonstrate that a brief 3-day treatment with PD325901 or doxycycline effectively radiosensitizes human GBM cells and extends overall survival of xenografted mice. Our work shows that the miR-124-SOX9 axis is a down-stream effector pathway that drives GBM aggressiveness. Long-term exposure to PD325901 is associated with adverse side-effects in patients. We propose that a priming regimen of the clinically relevant MEK inhibitor PD325901 should radiosensitize SOX9-expressing tumors in patients and result in reduced side-effects compared to continuous treatment protocols. Citation Format: Hanna Sabelstrom, Rahul Jandial, Ksenya Shchors, Selma Masic, Edith Yuan, Trenten Fenster, Supna Saxena, Allen Ho, Theodore P. Nicolaides, Robyn Wong, Stanislava Yakovenko, Mitchel H. Berger, Evan Y. Snyder, Johan Jakobsson, William A. Weiss, Anders I. Persson. Targeting a MAPK-miR-124-Sox9 axis radiosensitizes human glioblastoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1916.