Vascular endothelial growth factor receptor 2 (VEGFR2, also known as KDR and FLK1) is a receptor tyrosine kinase that regulates angiogenesis, vascular development, and embryonic hematopoiesis in response to VEGF isoforms A, C, and D. VEGFR2 kinase inhibitor I is a potent, cell-permeable inhibitor of mouse VEGFR2 kinase (IC50 = 70 nM). It has little or no effect against receptors for platelet-derived growth factor, epidermal growth factor, or insulin-like growth factor (IC50 > 100 μM).