Vascular Endothelial Growth Factor, Irradiation, and Axitinib Have Diverse Effects on Motility and Proliferation of Glioblastoma Multiforme Cells

Abstract

Glioblastoma multiforme (GBM) is the most common primary brain tumor. It is highly aggressive with an unfavorable prognosis for the patients despite therapies including surgery, irradiation, and chemotherapy. One important characteristic of highly vascularized GBM is the strong expression of vascular endothelial growth factor (VEGF). VEGF has become a new target in the treatment of GBM, and targeted therapies such as the VEGF-receptor blocker axitinib are in clinical trials. Most studies focus on VEGF-induced angiogenesis, but only very few investigations analyze autocrine or paracrine effects of VEGF on the tumor cells. In this study, we examined the impact of VEGF, irradiation, and axitinib on cell proliferation and cell motility in human GBM cell lines U-251 and U-373. VEGF receptor 2 was shown to be expressed within both cell lines by using PCR and immunochemistry. Moreover, we performed 24-h videography to analyze motility, and a viability assay for cell proliferation. We observed increasing effects of VEGF and irradiation on cell motility in both cell lines, as well as strong inhibiting effects on cellular motility by VEGF-receptor blockade using axitinib. Moreover, axitinib diminished irradiation induced accelerating effects. While VEGF stimulation or irradiation did not affect cell proliferation, axitinib significantly decreased cell proliferation in both cell lines. Therefore, the impairment of VEGF signaling might have a crucial role in the treatment of GBM.

Effects of Far-infrared Ray on Temozolomide-treated Glioma in Rats

“…Studies on phototherapy and/or irradiation in glioma are limited and diverse. Irradiation has been shown to increase cell motility, but it does not affect cell proliferation in glioma cell lines (10). Radiation-induced VEGF can also increase cell motility of glioma in vitro (22).…”

“…Also, glioblastoma stem-like cells secrete the pro-angiogenic VEGF-A factor in extracellular vesicles, which carry essential information that can adapt the microenvironment to the tumor's needs, inducing tumour-associated angiogenesis (20). VEGF can increase cell motility, but it does not affect cell proliferation in glioma cell lines (10). Overexpression of VEGF isoforms have been shown to drive vascularization, oxygenation, and growth but not progression to GBM in a human model of gliomagenesis (21).…”

“…Additionally, EGF activation of EGF receptor expressed on glioma cells leads to enhanced secretion of VEGF by glioma cells (9). VEGF has, thus, become a new target in the treatment of GBM (7,10).…”

A Vascularized Tumoroid Model for Human Glioblastoma Angiogenesis

“…The opposite result is observed for HDF supporting cells (Figure 2A), demonstrating the supporting role primary, serum-free cultured GBM cells have especially under hypoxia even without direct intracellular contact. GBM cells are known to secrete pro-angiogenic factors under hypoxia, such as VEGF and bFGF [32,33]. Futhermore, the addition of exogenous growth factors enhances this effect for cells cultured at normoxia but not at hypoxia suggesting that under hypoxia the GBM cells are already producing a significant amount of growth factors (Figure 3B).…”

“…2A), demonstrating the supporting role primary, serum-free cultured GBM cells have especially under hypoxia even without direct intracellular contact. GBM cells are known to secrete pro-angiogenic factors under hypoxia, such as VEGF and bFGF [35,36].…”