Abstract
Novel small molecules for glioblastoma are urgently needed, given the dearth of advances that have yielded better overall/progression-free survival since the Stupp Protocol (2005). One strategy is to utilize the latest drug screening paradigms and molecularly characterized patient-derived organoids with the goal of repurposing FDA-approved drugs. We utilized high-throughput in vitro screening with/without temozolomide (TMZ) to identify drugs that selectively target GBM or enhance TMZ efficacy. So far, a total of 166 FDA-approved drugs were evaluated across 12 genomically diverse patient-derived GBM xenograft models cultured under organoid/explant-like conditions. Cells were plated in 384-well, treated with 10 µM of each drug ± TMZ (IC(30)), and viability assessed in quadruplicate. Negative controls for eliminating off-target effects included non-transformed/non-neoplastic human astrocytes, fibroblasts, and neural stem cells. Hits were selected using t-tests with FDR correction. Follow-up validation was performed and synergistic interactions evaluated using SynergyFinder. >60% of drugs demonstrated control cytotoxicity or TMZ sensitization, emphasizing the importance of these controls. However, 28 drugs sensitized only GBM to TMZ (≤11 sensitizers/patient), of which 11 drugs were also effective in ≥2 samples. Separately, up to 12 drugs per sample showed GBM-selective cytotoxicity (≤50% viability) as monotherapies. Three agents - decitabine, raloxifene, and gefitinib – the targets of which are upregulated in GBM, demonstrated selective toxicity in ≥6 GBM models and collectively covered all 12. As a single agent, avapritinib significantly reduced viability in all GBM lines – especially of interest given its preliminary efficacy in pediatric high-grade glioma. Viability did not appear to correlate with PDGFRA-mutation status. This screen has demonstrated significant value in identifying possible new GBM therapeutics. By incorporating normal control cells, we identified compounds with tumor-specific activity and TMZ sensitization. Further in vitro and in vivo experiments are in progress. These findings nominate several drug candidates for rapid clinical evaluation in GBM.