Post-radiation increase in VEGF enhances glioma cell motility in vitro

Abstract

BackgroundGlioblastoma multiforme (GBM) is among the most lethal of all human tumors, with frequent local recurrences after radiation therapy (RT). The mechanism accounting for such a recurrence pattern is unclear. It has classically been attributed to local recurrence of treatment-resistant cells. However, accumulating evidence suggests that additional mechanisms exist that involve the migration of tumor or tumor stem cells from other brain regions to tumor bed. VEGFs are well-known mitogens and can be up-regulated after RT. Here, we examine the effect of irradiation-induced VEGF on glioma cell motility.Materials and methodsU251 and LN18 cell lines were used to generate irradiated-conditioned medium (IR-CM). At 72 h after irradiation, the supernatants were harvested. VEGF level in IR-CM was quantified by ELISA, and expression levels for VEGF mRNA were detected by RT-PCR. In vitro cancer cell motility was measured in chambers coated with/without Matrigel and IR-CM as a cell motility enhancer and a VEGF antibody as a neutralizer of VEGF bioactivity. Immunoblots were performed to evaluate the activity of cell motility-related kinases. Proliferation of GBM cells after treatment was measured by flow cytometry.ResultsIrradiation increased the level of VEGF mRNA that was mitigated by pre-RT exposure to Actinomycin D. U251 glioma cell motility (migration and invasion) was enhanced by adding IR-CM to un-irradiated cells (174.9 ± 11.4% and 334.2 ± 46% of control, respectively). When we added VEGF antibody to IR-CM, this enhanced cell motility was negated (110.3 ± 12.0% and 105.7 ± 14.0% of control, respectively). Immunoblot analysis revealed that IR-CM increased phosphorylation of VEGF receptor-2 (VEGFR2) secondary to an increase in VEGF, with a concomitant increase of phosphorylation of the downstream targets (Src and FAK). Increased phosphorylation was mitigated by adding VEGF antibody to IR-CM. There was no difference in the mitotic index of GBM cells treated with and without IR-CM and VEGF.ConclusionsThese results indicate that cell motility can be enhanced by conditioned medium from irradiated cells in vitro through stimulation of VEGFR2 signaling pathways and suggest that this effect involves the secretion of radiation-induced VEGF, leading to an increase in glioma cell motility.

The role of the PI3K/AKT/mTOR pathway in brain tumor metastasis

“…[108] However, single agents targeting the PAM pathway have been reported to be an inefficient approach in MB and to increase invasion in the surviving fraction of GBM. [109] Therefore, new therapeutic approaches should be based on increasing the therapeutic window by targeting two different routes, namely the PAM and ERK pathways, or on combining PAM inhibitors with chemotherapeutic agents. [110] MicroRNAs have also been shown to play an important role in various CNS malignancies, and miR-142-5p and miR-25 are upregulated in all of them.…”

Irradiation enhances expression of cxcr4 in murine glioma cells via HIF-1α-independent pathway

“…8,9 In addition, glioma cell mobility was enhanced by adding irradiated-conditioned medium to nonirradiated cells. 3 We hypothesize that the enhanced invasive ability of irradiated glioma cells is mediated both directly via glioma cells themselves and indirectly via the increased expression of various mediators.…”

“…3,14 Clinical studies of patients with rectal cancer found that monotherapy with the anti-VEGF antibody bevacizumab upregulates SDF-1a and CXCR4 expression in tumour cells, and higher SDF-1a plasma levels during bevacizumab treatment were significantly associated with distant metastasis. 15 Simultaneous inhibition of both VEGF and SDF-1a/CXCR4 might enhance the efficacy of radiotherapy.…”

“…2 Radioresistance is therefore an important issue in glioma treatment. In glioma, vascular endothelial growth factor (VEGF) is upregulated by irradiation and promotes the motility of the glioma cell in vitro, 3 indicating that cytokines secreted by irradiated tumour cells play a role in radioresistance.…”

Redox-Mediated and Ionizing-Radiation-Induced Inflammatory Mediators in Prostate Cancer Development and Treatment

“…VEGF is critical for not only angiogenesis but also prostate-cancer-mediated osteoblastic activity (93). IR modulates VEGF expression through multiple mitogen activated protein kinases (MAPK)-dependent pathways (137) and enhances glioma cell motility through vascular endothelial growth factor receptor 2 (VEGFR2) signaling pathways (87). Since prostate cancer cells lack expression of specific VEGF receptors, especially VEGFR2, IR-induced VEGFs are more likely to promote prostate cancer progression indirectly through their functions in stromal cells, in particular, endothelial cell survival, and as a chemotactic agent within the tumor microenvironment (93).…”