Glioblastoma multiforme is characterized by vascular proliferation secondary to angiogenesis. Interleukin-8 (IL-8), a chemokine produced by activated endothelium, and tumor cells, has been shown to induce angiogenesis. Since angiogenesis is critical for continued glioma growth, understanding the functional response of the endothelial cells in glioblastomas to IL-8 is essential. Therefore, the hypothesis of this study is that glioblastoma derived endothelial cells (TuBEC) contribute to tumor vascularity by differential production and response to IL-8, as compared to normal brain-derived endothelial cells (BEC). Transwell Boyden chamber migration assays were performed to test the ability of BEC and TuBEC to migrate in response to IL-8. Results demonstrate that untreated TuBEC have a higher migration rate than normal BEC. In addition, IL-8 induced BEC migration but had no effect on TuBEC. We also demonstrated that IL-8 was able to induce MMP-2 mRNA expression in BEC in a dose-depended manner. Moreover, in untreated TuBEC, the MMP-2 mRNA expression was higher than in untreated BEC. To determine whether this lack of response in migration by the TuBEC was due to the endogenous production of IL-8, TuBEC and BEC were evaluated for IL-8 production using ELISA. The data show that TuBEC produce significantly higher amounts of IL-8 compared to BEC. To clarify whether the endogenously produced IL-8 was activating these cells in an autocrine manner, antibodies blocking the IL-8 receptors were utilized in the migration assay. Blocking either CXCR1 or CXCR2 partially reduced the migration of untreated TuBEC; whereas antibodies to both receptors further reduced migration in an additive manner. Further experiments that investigated the mechanism of constitutive production of IL-8 in the TuBEC, demonstrated that TGF-β1, a factor previously shown to inhibit Et-1 induced IL-8 production in the BEC, had no inhibitory effect in the production of IL-8 by TuBEC. These studies demonstrate that IL-8 functions in an autocrine manner in TuBEC, enabling angiogenesis to occur independently of stimulation or an outside source of growth factor. This is in contrast to normal BEC, where IL-8 production is highly regulated. Therefore, manipulation of the IL-8 response in TuBEC may represent a new target for anti-angiogenic therapy.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]