Hypertension During Vascular Endothelial Growth Factor Inhibition: Focus on Nitric Oxide, Endothelin-1, and Oxidative Stress

Angiogenesis inhibition with humanized antibodies targeting vascular endothelial growth factor (VEGF) or orally active small tyrosine kinase inhibitors targeting VEGF receptors has become an established treatment modality for various forms of cancer. A common side effect of angiogenesis inhibition is the development of sometimes severe hypertension, which simultaneously appears to be predictive for a favorable antitumor response.Since VEGF increases the expression and activity of endothelial nitric oxide synthase, it has been assumed that the mean blood pressure (MAP) rise during angiogenesis inhibition is caused by a decrease in nitric oxide bioavailability. Yet, the results from experimental and clinical studies exploring this possibility are conflicting. Recent studies provided evidence that the MAP rise during angiogenesis inhibition rather is mediated by activation of the endothelin-1 (ET-1) axis, which, among others, induces oxidative stress. Nevertheless, conclusive evidence for the involvement of reactive oxygen species in the MAP rise could not be obtained so far.The mechanism underlying activation of the ET-1 axis during angiogenesis inhibition is unclear, and this activation was not anticipated in view of studies showing that VEGF stimulates both the expression and production of ET-1 by endothelial cells.In fact, this activation of the ET-1 axis may support the use of ET receptor antagonists for the treatment of angiogenesis inhibition-induced hypertension, especially because ET receptor stimulation in vascular smooth muscle cells results in VEGF production and mitogenesis in a mitogen-activated protein kinase pathway-dependent manner.