The vascular-disrupting agent, combretastatin-A4-phosphate, enhances neurogenic vasoconstriction in rat small arteries

Combretastatin-A4-phosphate (CA4P/CA4), an anti-cancer drug, induces tumour hypoxia by destabilizing the cytoskeleton in tumour endothelial cells. Hypertensive side effects have been observed. We hypothesized that CA4P/CA4 lead to endothelial dysfunction followed by increased vasoconstriction. Mesenteric small arteries and femoral arteries isolated from male Wistar rats were mounted in microvascular myographs for isometric tension recordings and electrical field stimulation (EFS). Immunoblotting of endothelial nitric oxide synthase (eNOS) was performed on human umbilical vein endothelial cells (HUVECs). CA4P failed per se to change vascular tone. In femoral arteries, endothelial cell removal, l-nitro-arginine (l-NNA, an inhibitor of eNOS) and CA4P enhanced phenylephrine-induced vasoconstriction, while in mesenteric arteries only l-NNA leftward shifted concentration–response curves for phenylephrine. CA4P enhanced vasoconstriction induced by low frequency (0.5–4 Hz) EFS in femoral arteries, but not in mesenteric arteries. Neurogenic contractions were inhibited by prazosin, an α1-adrenoceptor antagonist. In mesenteric arteries, CA4P and l-NNA inhibited vasorelaxation induced by vanadate, a tyrosine phosphatase inhibitor. CA4P did not affect acetylcholine-induced relaxation. In HUVECs, CA4P increased phosphorylation at eNOS-Thr495, a negative regulatory site, while the positive phosphorylation site eNOS-Ser1177 was not affected. CA4 neither influenced the actions of phenylephrine, vanadate nor acetylcholine in femoral and mesenteric arteries. In conclusion, our findings suggest that CA4P, but not CA4, enhances sympathetic adrenergic vasoconstriction probably by increasing eNOS-Thr495 phosphorylation, in a tissue selective manner. These findings encourage further investigation to show that the hypertension and regional organ ischemia induced by CA4P can be avoided by concomitant treatment with an α1-adrenoceptor antagonist.