Treatment with 50nM SU5416 reduces angiogenic potency of SB623 cell -conditioned medium. Following “starvation”, HUVECs were treated with SB623-CM with or without SU5416 for 30 minutes prior to culture to assess the role of VEGF in different steps of angiogenesis. The negative controls were cultured directly in OptiMEM. A and B) Cell death and cell proliferation were assessed after 7 days in culture by staininig for propidium iodide and Ki67, respectively. SB623 cell-CM significantly reduced cell death and increased proliferation (*p < 0.05 versus OptiMEM only control). However, this was partially reversed in the presence of SU5416 (#p < 0.05 SB623 CM versus SB623 CM + SU5416). C) HUVEC vascular tube formation was quantified at 16- and 40 hours after plating in RGF-basement gel. A representative phase contrast picture of vascular tube formation at 16 hours is shown here, revealing the reduction in complete tubes formed in the presence of SU5416 (p < 0.05 versus OptiMEM only control; #p < 0.05 versus SB623 CM + SU5416). D) Aortic rings were likewise pre-treated with or without SU5416 for 30 minutes prior to embedding in RGF gels with SB623-CM. The control aortic ring well was not pre-treated with SU5416 and was maintained in RGF-basement gel in OptiMEM. It is clear that in the presence of SU5416 there is no aortic sprouting. Plots show Mean ± SD.