Vascular Endothelial Growth Factor A (VEGF-A) is produced by a wide variety of cell types, including tumor and vascular cells. VEGF-A is a mediator of vascular growth, vascular permeability, and plays a role in stimulating vasodilation via nitric oxide-dependent pathways. VEGF-A has several alternatively spliced isoforms, with one being VEGF-121. The VEGF-121 isoform is a secreted protein that acts on receptors VEGFR-1 and VEGFR-2 to modulate endothelial cell function.