Nelfinavir Down-regulates Hypoxia-Inducible Factor 1α and VEGF Expression and Increases Tumor Oxygenation: Implications for Radiotherapy

Nabendu Pore,Cameron J Koch,Anjali K Gupta,Sydney M Evans,George J Cerniglia,Amit Maity,Zibin Jiang,Stephen M Hahn,Eric J Bernhard

doi:10.1158/0008-5472.can-06-1239

Abstract

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.

Highlights

It was shown that protease inhibitors such as nelfinavir, currently used to treat HIV patients, can radiosensitize tumor cells, possibly via inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt signaling [1]
The PI3K/Akt pathway has been implicated in the regulation of both hypoxia-inducible factor 1a (HIF-1a) and vascular endothelial growth factor (VEGF) expression [8, 9, 30]
We show in the present study that nelfinavir, a drug known to inhibit PI3K/Akt signaling [1], decreases both VEGF and HIF-1a expression

Summary

Introduction

It was shown that protease inhibitors such as nelfinavir, currently used to treat HIV patients, can radiosensitize tumor cells, possibly via inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt signaling [1]. Doi:10.1158/0008-5472.CAN-06-1239 tion of PI3K subunits, overexpression of Akt, and mutations in the PI3K subunits [2,3,4] This pathway has been implicated in many cellular processes including cell proliferation, adhesion, migration, invasion, and apoptosis [4,5,6,7]. The level of HIF-1a is very low in normoxia in most cell lines but is induced by hypoxia. When both components are present, the heterodimer binds to the consensus sequence found in dozens of hypoxia-inducible genes that control a wide range of processes including angiogenesis (VEGF), glycolysis, glucose uptake (glut1), and tumor invasion and metastasis When both components are present, the heterodimer binds to the consensus sequence found in dozens of hypoxia-inducible genes that control a wide range of processes including angiogenesis (VEGF), glycolysis, glucose uptake (glut1), and tumor invasion and metastasis (reviewed in ref. 10)

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Results

Conclusion