STEM-13. IDENTIFICATION OF NOVEL TARGETS IN GLIOBLASTOMA STEM CELLS THROUGH CRISPR-Cas9 SCREENING

Glioblastoma is the most lethal primary brain tumor, with a median survival of less than 15 months despite maximal therapy. The therapeutic resistance and inevitable recurrence of glioblastoma are driven in large part by glioblastoma stem cells (GSCs). Identifying novel targets that inhibit GSC survival is critical to developing new and effective therapies for GBM and for advancing our understanding of molecular dependencies in GSCs. We therefore performed a CRISPR-Cas9 screen in patient-derived GSC lines to elucidate drivers of GSC viability. To identify candidate genes for the screen, we performed an in silico analysis, interrogating The Cancer Genome Atlas (TCGA). We first stratified by CpG island methylator phenotype (CIMP) status since glioma-CIMP (G-CIMP) tumors appear to have a distinct underlying biology and disease course. We selected genes that were upregulated in either non G-CIMP or G-CIMP tumors vs. normal brain tissue and further filtered this gene set by intersecting it with the list of genes for which higher expression was associated with worse survival in each group. We designed a CRISPR-Cas9 library targeting the selected 536 genes and performed a drop-out screen in five distinct patient-derived GSC lines for genes that are critical for survival and maintenance of GSCs. We then validated top hits by individual CRISPR knockout. Using CRISPR screening technology in patient-derived cell lines, we identified crucial dependencies in patient-derived GSCs. Further experiments will characterize the mechanism of these dependencies and assess their potential therapeutic relevance in pre-clinical models.