P10.24.A TARGETING NON-GENETIC KINASE-DEPENDENT SIGNALING TO PREVENT GROUP 3 MEDULLOBLASTOMA RECURRENCE

Abstract BACKGROUND Brain tumors are the leading cause of cancer-related death in children, with medulloblastoma (MB) comprising 20-25% of cases. Proteogenomic profiling categorizes MB into four subgroups: Wingless (WNT), Sonic Hedgehog (SHH), Group 4 (G4), and Group 3 (G3), with G3 MB being the most aggressive one. Despite intensive chemoradiotherapy (CRT), which often leads to long-term side effects, G3 MB is prone to develop treatment-resistant relapse tumors, resulting in a five-year survival rate below 60%. Genomic analyses show that recurrent tumors retain their original genomic features, suggesting that changes in non-genomic signaling pathways drive relapse. Kinases, as central regulators of phosphorylation-driven signaling, can control pathways involved in proliferation, migration, and survival. We hypothesize that kinase-driven changes in signaling pathways underlie treatment resistance and tumor relapse in G3 MB. Understanding these adaptations will provide insights into novel therapeutic strategies for targeting recurrent MB. MATERIAL AND METHODS We used well-characterized MB cell lines and orthotopic intracerebellar patient-derived xenograft (PDOX) mouse models treated with a clinically relevant CRT regimen. Kinase activity changes were assessed via human phospho-kinase arrays, immunoblotting, and immunohistochemistry. The efficacy of kinase inhibitors in combination with CRT treatment was evaluated in vitro using viability, tumorsphere formation, and migration assays, and in vivo by assessing tumor progression and animal survival. RESULTS CRT-resistant G3 MB cells showed elevated activating phosphorylation of Src kinase and its downstream targets, with minimal changes in other key oncogenic kinases. Notably, upregulation of p-Src was not observed in CRT-treated SHH MB cells or normal human stem cells, suggesting a tumor- and subgroup-specific adaptation. G3 MB CRT-resistant cells demonstrated marked sensitivity towards repurposed FDA-approved brain-penetrant Src inhibitors, which significantly impaired their stemness and migratory potential in vitro and extended animal survival in the CRT PDOX animal model. CONCLUSION These results identify Src signaling as a subgroup-specific driver of therapy resistance and recurrence in G3 MB. Targeting this pathway may offer a promising therapeutic strategy to combat CRT resistance in recurrent G3 MB to ultimately improve patient outcomes. SUPPORT This work was supported by the Canadian Institute of Health Research (CIHR), Canadian Cancer Society (CCS), Cancer Research Society (CRS), and Natural Sciences and Engineering Research Council of Canada (NSERC).