MDB-93. A Transcriptome-Based Approach to Drug Repurposing for Aggressive Group 3 Medulloblastomas

Abstract BACKGROUND Medulloblastoma (MB) is the most common malignant brain tumor in children, representing 20% of pediatric brain tumors. International consensus has identified molecular subgroups: WNT, SHH, group 3 (G3), and group 4 (G4). Current treatments, guided by histologic tumor grade and stage, do not fully harness these subgroups, resulting in varying prognoses. G3MB particularly faces challenges with rapid recurrence and aggressive disease, necessitating focused intervention. METHODS We conducted differential expression analysis on MB patient datasets (GSE148389, GSE164677) to generate a G3MB gene expression signature. This gene expression signature was analyzed against the LINCS database, yielding candidate antineoplastic compounds. Candidates were filtered for blood-brain barrier permeability and FDA approval. Functional assays evaluated drug effects on cytotoxicity, clonogenicity, wound healing, cell cycle, and apoptosis in G3MB cell lines (HDMB03 and D425). RNA sequencing of treated cells identified differentially regulated pathways to infer mechanism, followed by in vitro validation. Mitochondrial function and membrane potential were measured by Seahorse and TMRM assays, respectively. RESULTS Eighty-one candidates passed filtering. The leading drug class identified was antidepressants. Based on MTT assays, the top four candidates were nortriptyline, simvastatin, fluoxetine, and sertraline. Nortriptyline (NT) emerged as the lead compound, with IC50 values of ~7uM (HDMB03) and ~11uM (D425). Amongst the four drugs, NT induced consistent anti-neoplastic effects on wound healing, colony formation, medullosphere generation, and apoptosis. Mechanistically, NT induced mitochondrial stress, escalated mitochondrial superoxide, and decreased mitochondrial membrane potential. CHRM3, a receptor antagonized by NT and upregulated in G3MB samples was downregulated by NT treatment. Western blotting confirmed the inhibition of CHRM3 downstream effectors. CONCLUSIONS Our pipeline identified cytotoxic compounds against G3MB, including NT, which we hypothesize induces mitochondrial stress via CHRM3 modulation. This approach offers repurposable FDA-approved candidates for high-risk G3MB, potentially reducing current treatment toxicity and improving outcomes.