Inhibition of hypoxia inducible factor-1α (HIF-1α) decreases vascular endothelial growth factor (VEGF) secretion and tumor growth in malignant gliomas

Introduction: Hypoxia inducible factor-1 alpha (HIF-1 alpha) regulates vascular endothelial growth factor (VEGF), the presumed principal mediator of angiogenesis in malignant gliomas, under normal physiologic conditions. We examined the effect of HIF-1 alpha on VEGF secretion, tumor growth, and angiogenesis in malignant gliomas. Methods: We examined 175 human gliomas for expression of HIF-1 alpha and its downstream-regulated proteins. HIF-1 alpha expression and VEGF secretion in glioma cell lines under normoxia and hypoxia were examined using ELISA and Western blot. Malignant glioma cell lines were transfected with dominant-negative HIF-1 alpha (DN-HIF-1 alpha) expression vector or siRNA constructs against the HIF-1 alpha gene. Growth studies were conducted on cells with the highest VEGF/HIF-1 alpha inhibition isolated from stable transfected cell lines. MIB-1-labeling index and microvascular density (MVD) measurements were performed on the in vivo tumors. Results: HIF-1 expression correlates with malignant glioma phenotype and was not confined to perinecrotic, pseudopalisading cells. VEGF and HIF-1 expression was high in glioma cell lines even under normoxia, and increased after exposure to hypoxia or growth factor stimulation. Cells transfected with DN-HIF-1 alpha or HIF-1 alpha siRNA demonstrated decreased HIF-1 alpha and VEGF secretion. In vivo but not in vitro growth decreased in response to VEGF and HIF-1 inhibition. HIF-1 siRNA studies showed decreased VEGF secretion and in vitro and in vivo growth of glioma cell lines. MVD was unchanged but MIB-1 proliferation index decreased for both types of HIF-1 inhibition. Conclusions: VEGF and HIF-1 alpha are elevated in malignant gliomas. HIF-1 alpha inhibition results in VEGF secretion inhibition. HIF-1 alpha expression affects glioma tumor growth, suggesting clinical applications for malignant glioma treatment.