PP28. THERAPEUTIC COMPOUND DISCOVERY AND VALIDATION OF DRUGS TARGETING A RECURRENT GLIOBLASTOMA (GBM) PHENOTYPE USING LINCS COMPOUNDS VIA QUADRATIC ANALYSES

Abstract

Glioblastoma (GBM) is the most prevalent and aggressive of malignant primary brain tumours. Despite multi-modal therapy, including surgical resection, radiotherapy and chemotherapy, GBM continues to be uniformly lethal, with a median survival of 12–18 months from the time of diagnosis. The resistance to therapy and ultimate recurrence is thought to originate from a sub-population of cells residing in the initial tumour, identified as glioma-initiating or glioma-stem cells (GSC). These GSC have been shown to be intrinsically more invasive, with enhanced repair and drug-efflux pathways mediating resistance to chemo-radiation therapies. The purpose of this study was to use and validate a novel connectivity mapping procedure to identify candidate compounds targeting therapy-resistant and recurrent GBM. This procedure was developed by O’Reilly and colleagues (“QUADrATiC: A Scalable Approach to Repurposing FDA-approved therapeutics”, under review in Bioinformatics), and in this study, was performed on publicly available NCBI GEO microarray datasets. Based on the cancer stem cell theory whereby the resistant GSCs repopulate and are enriched in recurrent tumours, primary and recurrent GBM gene expression profiles were compared and the connections between the identified gene lists and drug responses were mapped. To validate that this connectivity mapping procedure is reliable at identifying effective treatments to target therapeutic resistance and recurrence, we tested one of the top ten compounds identified, rosiglitazone (rosi), a ligand of the peroxisome proliferator activated receptor gamma (PPARγ). The efficacy of rosi alone and in combination with the current standard of care therapies, temozolomide and radiation, at killing GSC was assessed in vitro using the clonogenic survival assay. Our data indicated that rosi significantly reduced survival of both non-stem glioma cells and GSC, alone and in combination with radiation and temozolomide. The p53 pathway was identified as a pathway by which rosi may induce permanent cell cycle arrest and cell death. Further work is ongoing to fully elucidate the downstream mechanisms of cell death. This work is proof-of-principle that the current connectivity mapping procedure can be instrumental in identifying more targeted therapeutic interventions for GBM resistance and prevent recurrence.