The suppression of hypoxia-inducible factor and vascular endothelial growth factor by siRNA does not affect the radiation sensitivity of multicellular tumor spheroids.

Background: The hypoxic microenvironment is closely associated with the radiation resistance of tumor cells. Hypoxia induces several genes such as hypoxia-inducible factor (HIF-1) and vascular endothelial growth factor (VEGF) to promote tumor cell growth and survival. The up-regulated expression levels of HIF-1 and VEGF in tumor cells also correlate with their resistance to radiation, suggesting t...