Divergent Effects Of Braf Activation In Neural Stem And Progenitor-Like Glioblastoma Cells

Glioblastoma multiforme (GBM) are heterogeneous tumors that are refractory to radiation and traditional chemotherapeutics. Separate studies have identified populations of neural stem and progenitor -like GBM cells, however the contribution of these cells types to tumor progression and the response to targeted therapy are poorly understood. Small molecules (such as vemurafenib) targeting the most common MAPK-activating mutation, BRAFV600E, are currently entering clinical trials for treatment of high-grade glioma. Understanding the contribution of different cell types to treatment responses will be necessary for the design of effective adjuvant therapeutic strategies. We show that activating MAPK pathway gene mutations in GBM correlate with elevated expression levels of oligodendrocyte precursor (OPC) and neural stem cell (NSC)-associated genes. Cells expressing CD133 and NG2 coexist in human GBM and BRafV600E expressing mouse neurosphere cultures, and maintain some of their respective neural stem and progenitor-like properties. In isogenic mouse cells expressing BRafV600E, NG2+ cells expand rapidly and symmetrically, while rates of asymmetric division are unaffected in slow-proliferating CD133+ cells. Tracing of proliferation rate with the membrane-associated dye PKH-26 reveals heterogeneity in the proliferation rate of CD133+ cells, but not proliferative NG2+ cells. BRAF-targeted inhibition of human GBM cells with PLX4720, the tool compound of vemurafenib, reduces S-phase entry of NG2+ cells, yet CD133+ cells are less affected. Interestingly targeted inhibition of components of the asymmetric division machinery selectively disrupts G2-M progression in CD133+ cells. The functionally divergent populations of CD133-expressing NSC-like cells will likely be therapeutically problematic with mono-therapeutic approaches. These data point to a differential regulation of key cell cycle processes between CD133+ stem-like cells and NG2+ OPC-like cells, that will inform the intelligent design of compound treatment strategies. Note: This abstract was not presented at the meeting. Citation Format: Robin G. Lerner, Yuichiro Ihara, Kate Lewis, Amelie Griveau, Brian Reichhold, Dian Qu, Martin McMahon, David Rowitch, Charles D. James, Claudia Petritsch. Divergent effects of BRAF activation in neural stem and progenitor-like glioblastoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1944. doi:10.1158/1538-7445.AM2014-1944