Abstract
Glioblastomas (GBM) are brain tumors with a poor prognosis despite treatment that combines surgical resection and radio-chemotherapy. These tumors are characterized by abundant vascularization and significant cellular heterogeneity including GBM stem-like cells (GSC) which contribute to tumor aggressiveness, resistance, and recurrence. Recent data has demonstrated that GSC are directly involved in the formation of new vessels via their transdifferentiation into Tumor Derived Endothelial Cells (TDEC). We postulate that cellular stress such as ionizing radiation (IR) could enhance the transdifferentiation of GSC into TDEC. GSC neurospheres isolated from 3 different patients were irradiated or not and were then transdifferentiated into TDEC. In fact, TDEC obtained from irradiated GSC (TDEC IR+) migrate more towards VEGF, form more pseudotubes in MatrigelTM in vitro and develop more functional blood vessels in MatrigelTM plugs implanted in Nude mice than TDEC obtained from non-irradiated GSC. Transcriptomic analysis allows us to highlight an overexpression of Tie2 in TDEC IR+. All IR-induced effects on TDEC were abolished by using a Tie2 kinase inhibitor, which confirms the role of the Tie2 signaling pathway in this process. Finally, by analyzing Tie2 expression in patient GBMs by immunohistochemistry, we demonstrated that the number of Tie2+ vessels increases in recurrent GBM compared with matched untreated tumors. In conclusion, we demonstrate that IR potentiates proangiogenic features of TDEC through the Tie2 signaling pathway, which indicates a new pathway of treatment-induced tumor adaptation. New therapeutic strategies that associate standard treatment and a Tie2 signaling pathway inhibitor should be considered for future trials.
Highlights
The primitive tumors of the central nervous system represent ~2–3% of all human cancers
The expression of VEGFR2, the main VEGF receptor, was not significantly different between GBM stem-like cells (GSC), GBM differentiated cells (GDC) and Tumor Derived Endothelial Cells (TDEC) obtained from SRA5 and SRB1
We quantified the number of human CD31 (hCD31)+ vessels in all plugs and detected more hCD31+ vessels in plugs with TDEC ionizing radiation (IR)+ compared to plugs with TDEC IR(Fig. 3c). All these data show that IR potentiates in vitro and in vivo proangiogenic features of TDEC obtained from GSC
Summary
The primitive tumors of the central nervous system represent ~2–3% of all human cancers. The formation of vessels connected to the tumor develops prematurely during tumor progression This vascularization, abundant, is morphologically and functionally abnormal and contributes to the establishment of hypoxia within the tumor, which helps in GSC stemness maintenance. It has been shown that endothelial cells and GSC establish connections, which are important for GSC stemness maintenance[9]. The vessels of tumor xenografts formed by the injection of GSC in immunocompromised mice were primarily composed of human endothelial cells[11]. This new mechanism of glioma-associated neovascularization could contribute to the failure of the anti-angiogenic therapies (anti-VEGF), which is mainly associated with enhanced invasiveness[14]
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