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

Abstract

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.

Tumor microenvironment conditions alter Akt and Na+/H+ exchanger NHE1 expression in endothelial cells more than hypoxia alone: implications for endothelial cell function in cancer

“…TME treatment reduced proliferation signaling and induced PARP cleavage in the endothelial cells, a finding supported by earlier reports that HUVEC undergo caspase-dependent death upon deprivation of serum/nutrients [ 28 , 53 ], and by a recent report showing that HUVEC proliferation is reduced by acidic pH e [ 57 ]. The results also fit well with the downregulation of Akt, which normally favors cell proliferation and counteracts cell death via phosphorylation-mediated regulation of e.g.…”

Carbonic anhydrase 2 (CAII) supports tumor blood endothelial cell survival under lactic acidosis in the tumor microenvironment

“…Previous studies involving endothelial cells focused on either the effect of lactate [13] or acidity [12, 23] on angiogenesis. First, we demonstrated that lactate could support endothelial cell growth, evidenced by a dose-dependent increase in proliferation by both TECs and NECs with sodium lactate (Fig.…”

Extrinsic acidosis suppresses glycolysis and migration while increasing network formation in pulmonary microvascular endothelial cells

“…In addition to SLC-0111, we tested other CA inhibitors including acetazolamide (AZ; nonspecific CA inhibitor), benzolamide (nonspecific extracellular CA inhibitor) (20), and N-methyl-AZ (AZ analogue with no CA-inhibiting activity) (35). Unlike SLC- (30), human umbilical vein endothelial cell (11), and tumor cell (8) migration and human bone marrow-derived endothelial progenitor cell migration and Matrigel network formation (21). Our finding suggests that migration and network formation do not necessarily occur together, with distinct cellular mechanisms controlling the latter.…”