MEDB-21. SOX2(+) cells: the perpetrators of medulloblastoma relapse

Pediatric brain tumors are the number one cause of cancer-related death in children, with medulloblastoma being the most common type. While survival in patients with medulloblastoma has dramatically improved since chemotherapy was added to standard of care protocols, still 30% of tumors will recur. As recurrent disease in medulloblastoma patients in considered uniformly lethal, it is key to identify the cells allowing tumor relapse, and their targetable regulators. By analyzing single cell transcriptomic data, we uncovered a population of SOX2 labeled astrocyte like cells resistant to SMO inhibitors in clinical trials. Using SOX2-enriched medulloblastoma cultures, we observed that SOX2(+) cells rely on non-canonical GLI signaling to propagate medulloblastoma. Therefore, in vivo inhibition of SHH signaling using functionally different GLI inhibitors depleted the SOX2(+) cell pool, what led to less aggressive tumors that lacked the ability to further engraft. Stressing the translational relevance of our findings, a clinically relevant GLI inhibitor not only exhausted SOX2(+) cells driving tumor relapse, but increased overall survival in mice harboring medulloblastoma. Our results emphasize the importance of using targeted therapies that deplete SOX2(+) cells to prevent medulloblastoma recurrence.