Abstract 849: Profiling signaling networks using reverse phase protein arrays: validating FOXM1 as a potential target to radiosensitize glioblastoma (GBM) stem cells

Abstract

Abstract Glioblastoma multiforme (GBM) continues to be the most frequently diagnosed and lethal primary brain tumor. Adjuvant chemo-radiotherapy remains the standard of care following surgical resection. In this study, using reverse phase protein arrays (RPPAs), we assessed the biological effects of radiation on signaling pathways to identify potential radiosensitizing molecular targets. We examined levels of 172 phosphorylated and non-phosphorylated proteins under conditions of Ionizing radiation (IR) in patient derived GBM stem cells and established U251, U87 GBM cell lines in vitro and in an in vivo orthotropic mouse model. We identified subsets of proteins with clearly concordant/discordant behavior between GBM cells in vitro and in vivo. In general, molecules involved in anti-apoptotic, cell-cycle, survival pathways, tumor metastasis and DNA repair were affected. Comparing in vivo and in vitro samples after IR, 9 proteins were commonly elevated; phospho(p)-STAT3, CDC2, CyclinB1, BAX, pEIF4BP1, pAKT, pRB, pMEK1, and FOXM1. Conversely, 4 other proteins were commonly decreased; pPRKCA, pPRKCD, pNDRG1 and pRPS6. Recent evidence of FOXM1 as a master regulator of metastasis and its important role in maintaining neural, progenitor, and GBM stem cells intrigued us to validate it as a radiosensitizing target. We show high expression of FOXM1 across different patient derived stem cells. When GBM stem cells (NSC11, GBAM1) were differentiated in serum, we observed a decrease in FOXM1 levels, attaining more differentiation markers. In both differentiated and un-differentiated GBM stem cells, treatment with IR resulted in an increase of FOXM1 expression. However, inhibition of FOXM1 was only seen to have an effect on un-differentiated GBM stem cells, and resulted in reduced cell viability, a significant reduction in clonogenicity, and anchorage-independent growth, along with enhanced radiosenstivity with IR. Importantly, the combination of IR with FOXM1 inhibition showed these same effects irrespective of serum-differentiation. These results clearly suggest, inhibition of FOXM1 leads to radiosensitization. Since GBM stem cells, which comprise a subpopulation of tumor cells, maybe responsible for therapeutic resistance, we show that FOXM1 inhibition stands as a potential cancer stem-cell specific chemo-radio therapeutic target for GBM. Citation Format: Uday Bhanu Maachani, Anita T. Tandle, Uma Shankavaram, Tamalee Meushaw, Philip J. Tofilon, Kevin A. Camphausen. Profiling signaling networks using reverse phase protein arrays: validating FOXM1 as a potential target to radiosensitize glioblastoma (GBM) stem 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 849. doi:10.1158/1538-7445.AM2014-849