Abstract 1369: Inhibition of Notch- and EGFR signaling reduces cell viability and angiogenesis in glioblastoma multiforme

Abstract The high-grade glioma, Glioblastoma Multiforme (GBM), is the most prevalent and aggressive brain tumour in adults with a median survival of fifteen months. Thus new therapeutic targets are urgently needed. GBM is characterized by extensive vascularisation why targeting angiogenesis has promising potential in improving the treatment of GBM patients. Aberrant EGFR signaling is another characteristic of GBM, and increased EGFR downstream signaling is believed to correlate with poor prognosis. However, little is known of the involvement of EGFR signaling in GBM angiogenesis. Notch signaling is known for its role in angiogenesis during foetal development and in other cancers, but the importance of Notch signaling in GBM angiogenesis is yet to be elucidated. Recently, it has been shown, that crosstalk between Notch- and EGFR signaling occurs in cancer cells, and aberrant EGFR signaling may therefore play a functional role in GBM angiogenesis through crosstalk with Notch signaling. The aim of this study was to investigate the effect of combined Notch- and EGFR inhibition on GBM cell viability and on ability of GBM cells to induce angiogenesis in endothelial cells. In vitro assays of GBM angiogenesis were established using two patient derived GBM cell cultures, one expressing the mutated EGFR, the EGFRvIII, and one expressing wild type EGFR. The functional relevance of EGFR- and Notch signaling in GBM cells was tested using the tyrosine kinase inhibitor Iressa for EGFR inhibition, and the gamma-secretase inhibitor DAPT for Notch inhibition. We show that combined inhibition of EGFR- and Notch signaling caused additive inhibition of cell viability of both cell cultures in vitro. Abrogated EGFR/Notch signaling in GBM cells further reduced angiogenesis in endothelial cells exposed to conditioned media from treated GBM cells. Moreover, when GBM cells were treated with the inhibitors, this inhibited phosphorylation and activation of the two survival signalling pathways ERK and Akt, and abrogated secretion and expression of the most prominent angiogenic factor - VEGF. The presented results indicate that EGFR- and Notch signaling play a functional role in GBM angiogenesis and that combined treatment with drugs targeting both the EGFR- and Notch pathway could prove beneficial over single drug therapy in targeting both the tumorigenic and angiogenic potential of GBM cells. Citation Format: Mikkel Staberg, Signe Regner Michaelsen, Louise Stobbe Olsen, Mette Kjølhede Nedergaard, Mette Villingshøj, Hans Skovgaard Poulsen. Inhibition of Notch- and EGFR signaling reduces cell viability and angiogenesis in glioblastoma multiforme. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1369. doi:10.1158/1538-7445.AM2015-1369

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