MDB-40. TRANSCRIPTOME-BASED DRUG REPURPOSING IN GROUP 3 MEDULLOBLASTOMA

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. MB is divided into four molecular subgroups (SHH, WNT, Group 3 [G3], and Group 4 [G4]), each defined by unique genetic and molecular features. G3MB is the most aggressive subgroup, with the lowest five-year survival. Features conferring high risk to G3MB include frequent metastases at diagnosis, MYC amplification, and chromosome i17q. Outcomes for G3MB patients remain dismal, partly due to a lack of G3MB-specific therapies, defining an important gap in MB research. To address this gap, we employed a strategy of comparing the G3MB transcriptomic signature against a repository of chemical perturbagens (LINCS) to identify FDA-approved, blood-brain barrier penetrant drugs capable of reverting the disease signature to a more normal cerebellum-like state. Following preliminary in silico and in vitro screening, we identified four drugs - fluoxetine, sertraline, simvastatin, and nortriptyline - that passed screening criteria and demonstrated cytotoxicity against HDMB03 cells at low micromolar doses. Each compound also inhibited clonogenicity, impaired wound healing, and impeded cell migration and invasion. Further, each compound induced apoptosis as evidenced by annexin V and propidium iodide staining. Western blotting confirmed both dose- and time-dependent increases in the expression of key apoptotic markers. Since nortriptyline possessed the best cytotoxicity profile against HDMB03 cells, we interrogated the transcriptome of HDMB03 cells treated with nortriptyline to identify cancer-related pathways inhibited by drug treatment. Our data revealed strong inhibition of E2F transcription factors, which are critical to cancer cell cycle progression and proliferation. Notably, five of the six E2F transcription factors as well as a panel of E2F target genes (HN1, KIF4A, CDCA3, CDCA8, and SSRP1) are all specifically upregulated in G3MB. This study highlights the promise of drug discovery and repurposing using subgroup-specific transcriptomes, which may deliver effective treatments expeditiously to high-risk patients.