Research Papers:

Acidic pH reduces VEGF-mediated endothelial cell responses by downregulation of VEGFR-2; relevance for anti-angiogenic therapies

Seraina Faes, Emilie Uldry, Anne Planche, Tania Santoro, Catherine Pythoud, Nicolas Demartines and Olivier Dormond _

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Oncotarget. 2016; 7:86026-86038. https://doi.org/10.18632/oncotarget.13323

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Seraina Faes1, Emilie Uldry1, Anne Planche1, Tania Santoro1, Catherine Pythoud1, Nicolas Demartines1, Olivier Dormond1

1Department of Visceral Surgery, University Hospital of Lausanne, Switzerland

Correspondence to:

Olivier Dormond, email: [email protected]

Keywords: acidity, VEGF, angiogenesis, sunitinib, endothelium

Received: April 22, 2016     Accepted: November 06, 2016     Published: November 12, 2016


Anti-angiogenic treatments targeting the vascular endothelial growth factor or its receptors have shown clinical benefits. However, impact on long-term survival remains limited. Solid tumors display an acidic microenvironment that profoundly influences their biology. Consequences of acidity on endothelial cells and anti-angiogenic therapies remain poorly characterized and hence are the focus of this study. We found that exposing endothelial cells to acidic extracellular pH resulted in reduced cell proliferation and migration. Also, whereas VEGF increased endothelial cell proliferation and survival at pH 7.4, it had no effect at pH 6.4. Furthermore, in acidic conditions, stimulation of endothelial cells with VEGF did not result in activation of downstream signaling pathways such as AKT. At a molecular level, acidity significantly decreased the expression of VEGFR-2 by endothelial cells. Consequently, anti-angiogenic therapies that target VEGFR-2 such as sunitinib and sorafenib failed to block endothelial cell proliferation in acidic conditions. In vivo, neutralizing tumor acidity with sodium bicarbonate increased the percentage of endothelial cells expressing VEGFR-2 in tumor xenografts. Furthermore, combining sodium bicarbonate with sunitinib provided stronger anti-cancer activity than either treatment alone. Histological analysis showed that sunitinib had a stronger anti-angiogenic effect when combined with sodium bicarbonate. Overall, our results show that endothelial cells prosper independently of VEGF in acidic conditions partly as a consequence of decreased VEGFR-2 expression. They further suggest that strategies aiming to raise intratumoral pH can improve the efficacy of anti-VEGF treatments.

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