Vascular Endothelial Growth Factor 121 (VEGF121), a secreted glycoprotein member of the VEGF family and a VEGFA splice variant, lacks heparin-binding domains for free extracellular solubility. It binds VEGFR121 on vascular endothelial cells to exert robust pro-angiogenic effects, promoting endothelial cell proliferation, migration and tube formation to drive vasculogenesis and angiogenesis. Distinct from anti-proliferative/pro-apoptotic proteins, it inhibits endothelial cell apoptosis via survival signaling, sustaining vascular integrity and mediating tissue vascularization in development, wound repair and pathological angiogenesis.To test the effect of VEGF121 on cell apoptosis, HCT116 cells were seeded into triplicate wells of 96-well plates at a density of 5,000 cells/well and allowed to attach, replaced with serum-free overnight, then the medium was replaced with 5% serum standard DMEM  prior to the addition of various concentrations of recombinant human VEGF121. After incubated for 48h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 µl of CCK-8 solution was added to each well of the plate, then the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37 ℃. Cell viability was assessed by CCK-8(Cell Counting Kit-8 ) assay after incubation with recombinant VEGF121 for 48h. The result was shown in Figure 1. It was obvious that VEGF121 significantly decreased cell viability of HCT116 cells. The ED50 of recombinant human VEGF121 is 153 ng/mL.