Nelfinavir down-regulates hypoxia-inducible factor 1alpha and VEGF expression and increases tumor oxygenation: implications for radiotherapy

Cancer Res. 2006 Sep 15;66(18):9252-9. doi: 10.1158/0008-5472.CAN-06-1239.


The phosphatidylinositol 3-kinase (PI3K)/Akt pathway can increase vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1alpha (HIF-1alpha) expression. We examined the effect of nelfinavir, an HIV protease inhibitor that inhibits Akt signaling, on VEGF and HIF-1alpha expression and on angiogenesis, tumor oxygenation, and radiosensitization. Nelfinavir decreases VEGF expression under normoxia via the transcription factor Sp1, which regulates the proximal core VEGF promoter. Nelfinavir decreased Sp1 phosphorylation and decreased Sp1 binding to a probe corresponding to the proximal VEGF promoter in a gel shift assay. Nelfinavir also decreased the hypoxic induction of HIF-1alpha, which also regulates the VEGF promoter, most likely by decreasing its translation. The effect of nelfinavir on VEGF expression had the functional consequence of decreasing angiogenesis in an in vivo Matrigel plug assay. To determine the effect this might have on tumor radiosensitization, we did tumor regrowth assays with xenografts in nude mice. The combination of nelfinavir and radiation increased time to regrowth compared with radiation alone whereas nelfinavir alone had little effect on tumor regrowth. This radiosensitizing effect was greater than suggested by in vitro clonogenic survival assays. One possible explanation for the discordance is that nelfinavir has an effect on tumor oxygenation. Therefore, we examined this with the hypoxia marker EF5 and found that nelfinavir leads to increased oxygenation within tumor xenografts. Our results suggest that nelfinavir decreases HIF-1alpha/VEGF expression and tumor hypoxia, which could play a role in its in vivo radiosensitizing effect. These data support the use of nelfinavir in combination with radiation in future clinical trials.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Carcinoma, Squamous Cell / blood supply
  • Carcinoma, Squamous Cell / drug therapy
  • Carcinoma, Squamous Cell / metabolism*
  • Carcinoma, Squamous Cell / radiotherapy
  • Cell Line, Tumor
  • Down-Regulation / drug effects
  • Female
  • Head and Neck Neoplasms / blood supply
  • Head and Neck Neoplasms / drug therapy
  • Head and Neck Neoplasms / metabolism*
  • Head and Neck Neoplasms / radiotherapy
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / biosynthesis*
  • Hypoxia-Inducible Factor 1, alpha Subunit / genetics
  • Lung Neoplasms / drug therapy
  • Lung Neoplasms / metabolism*
  • Lung Neoplasms / radiotherapy
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Nelfinavir / pharmacology*
  • Neovascularization, Pathologic / drug therapy
  • Oxygen / metabolism*
  • Protease Inhibitors / pharmacology*
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / metabolism
  • Radiation Tolerance / drug effects
  • Random Allocation
  • Sp1 Transcription Factor / metabolism
  • Vascular Endothelial Growth Factor A / biosynthesis*
  • Vascular Endothelial Growth Factor A / genetics
  • Xenograft Model Antitumor Assays


  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Protease Inhibitors
  • Sp1 Transcription Factor
  • Vascular Endothelial Growth Factor A
  • Proto-Oncogene Proteins c-akt
  • Nelfinavir
  • Oxygen