SC-38 * IDENTIFICATION OF NOVEL THERAPEUTIC TARGETS FOR GLIOBLASTOMA STEM CELLS

Abstract

The prognosis for patients with glioblastoma (GBM) is poor. Recent evidence suggests that the cells driving GBM malignancy and possibly recurrence are GBM stem cells (GSCs), a small population of GBM cells capable of developing resistance to current therapeutics. To target GSCs, we hypothesized that specific protein kinases are essential to GSC survival. Knockdown of these essential kinases in GSCs will result in inhibition of both GSC and overall GBM tumor growth. To identify kinases essential for GSCs, we first performed a drop-out screen in U87MG human GBM cells using an shRNA library directed against human kinases. We then screened the candidate kinases in a GSC line, GS9-6/NOTCH1 + , and identified 39 kinases that are essential to GSCs. Among these, we elected to focus on casein kinase 1 epsilon (CSNK1E) and maternal embryonic leucine zipper kinase (MELK) for the following reasons: 1) multiple shRNAs targeting these kinases were revealed from our screen; 2) MELK is a known essential kinase for GSCs; 3) chemical inhibitors are available for these kinases. Further experiments revealed that knockdown of CSNK1E or MELK resulted in a significant decrease in viability in multiple GSC lines isolated from either established cell lines, such as LN229, LN18, and U251, or fresh tumor tissues, such as VTC001. To probe the mechanism by which these kinases are essential for GSCs, we measured the self-renewal and differentiation of these GSCs. We found that knockdown of MELK and CSNK1E significantly inhibited stem cell self-renewal and promoted differentiation of GS9-6/NOTCH1+ cells. Taken together, our research revealed that MELK and CSNK1E are essential to GSC survival, thereby becoming appealing drug targets. Future work will further evaluate MELK and CSNK1E as therapeutic targets by utilizing small molecule kinase inhibitors in an in vivo mouse model of GBM.