Inhibition of hypoxia inducible factor-1α (HIF-1α) decreases vascular endothelial growth factor (VEGF) secretion and tumor growth in malignant gliomas
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Hypoxia inducible factor-1α (HIF-1α) 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-1α on VEGF secretion, tumor growth, and angiogenesis in malignant gliomas.
We examined 175 human gliomas for expression of HIF-1α and its downstream-regulated proteins. HIF-1α 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-1α (DN-HIF-1α) expression vector or siRNA constructs against the HIF-1α gene. Growth studies were conducted on cells with the highest VEGF/HIF-1α inhibition isolated from stable transfected cell lines. MIB-1-labeling index and microvascular density (MVD) measurements were performed on the in vivo tumors.
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-1α or HIF-1α siRNA demonstrated decreased HIF-1α 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.
VEGF and HIF-1α are elevated in malignant gliomas. HIF-1α inhibition results in VEGF secretion inhibition. HIF-1α expression affects glioma tumor growth, suggesting clinical applications for malignant glioma treatment.
Keywordsangiogenesis brain tumor glioblastoma multiforme hypoxia inducible factor siRNA vascular endothelial growth factor
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This work was supported by a grant from the Western Institute of Biomedical Research. We wish to thank Elizabeth Jensen, M.D., for her help with the pathological interpretation, technical advice, and photography. We thank Kristin Kraus for her editorial guidance.
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