EMBR-13. NOVEL SYNERGISTIC APPROACHES FOR TARGETED THERAPY OF MYC-DRIVEN MEDULLOBLASTOMA USING CRISPR/CAS9 GENE EDITING

INTRODUCTION: Resistance to chemotherapy is a common cause of treatment failure in cancer patients and a major problem facing current cancer research. Targeted modulation of oncogenic signaling pathways may be used to systematically characterize drug resistance mechanisms across tumor entities and may help to identify new therapeutic strategies. Since the transcription factor MYC is aberrantly activated in many cancers including pediatric malignant brain tumors, like medulloblastoma (MB), our study focused on MYC-related drug resistance. METHODS AND RESULTS: We performed high-throughput drug screening using our in-house semi-automated platform and identified the HDAC inhibitor Entinostat as a drug that shows promising effects in MYC-driven MB. Investigating genome-wide dCas9-based transcriptional activation screening, potential drug response modulators, mainly TGFB1/Erk/MKNK1 signaling including neural EGFL like 2 (NELL2), were discovered. For further validation, we stably overexpressed NELL2 in MYC-driven MB cells and treated overexpressing cells and the corresponding control cells with Entinostat. Using PI staining, cell cycle status was tracked. Entinostat treatment led to modest induction of cell death in MYC-driven MB control cells but only slightly increased cell death rate in MYC-driven MB cells with NELL2-overexpression. CONCLUSION: We report that the combination of genetic and pharmacological approaches is a powerful approach to study drug resistance. Our data suggest that activation of the TGFB1/Erk/MKNK1 signaling pathway desensitizes MYC-driven MB cells to Entinostat. Synergistic targeting of TGFB1/Erk/MKNK1 signaling and MYC could therefore provide a novel therapeutic option in this aggressive MB subtype.