O6.10 GLIOMA CELL VEGFR-2 EXPRESSION IMPAIRS CHEMOTHERAPEUTIC AND ANTIANGIOGENIC TREATMENTS IN PTEN-DEFICIENT GLIOBLASTOMA

BACKGROUND: Given the recent failure of bevacizumab (BEV) in extending overall survival of patients with newly diagnosed glioblastoma, tissue biomarkers predicting response to antiangiogenic treatments are urgently needed. Here, we hypothesized that loss of the tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a prerequisite for glioma cell expression of vascular endothelial growth factor receptor (VEGFR)-2 in glioblastoma defining a more aggressive glioblastoma subgroup prone to develop evasive resistance towards antiangiogenic treatments including BEV. METHODS AND RESULTS: Besides its ubiquitous expression on endothelial cells, immunohistochemical analysis of 59 glioblastoma tissues showed glioma cell-bound VEGFR-2 expression was restricted to PTEN-deficient tumor specimens and detectable in 20% of all specimens examined, most pronounced in infiltration zones. In glioma cells, pharmacological and RNAi-mediated inhibition of VEGFR-2 signaling revealed proproliferative, antiinvasive and chemoprotective functions for VEGFR-2 in several experimental paradigms comprising flow cytometry-based cell cycle analyses, in vitro proliferation and invasion assays, organotypic brain slice culture assays, and an MRI-monitored orthotopic mouse model. VEGFR-2-dependent cellular effects were concomitant with activation of three potent resistance factors: 'kappa-light-chain-enhancer' of activated B-cells (NF- Kappa B), protein kinase B (AKT/PKB), and N-myc downstream regulated gene (NDRG)1. Two-photon in vivo microscopy demonstrated that glioma cell expression of VEGFR-2 hampers antiangiogenesis and favors a proinvasive response to treatment with BEV. CONCLUSIONS: Glioma cell expression of VEGFR-2, next to its expression on vessels, indicates a particularly aggressive glioblastoma subgroup prone to develop early resistance to chemotherapy with temozolomide or antiangiogenic treatment with BEV. Loss of PTEN can serve as a readily available surrogate marker to identify those tumors upfront by routine neuropathological methods.