YLL545 is an inhibitor of Vascular Endothelial Growth Factor Receptor 2 (VEGFR2). It inhibits VEGF-induced phosphorylation of VEGFR2 and the activation of downstream signaling mediators (such as phosphorylated STAT3 and phosphorylated ERK1/2) in human umbilical vein endothelial cells (HUVEC). Additionally, YLL545 suppresses HUVEC proliferation, migration, invasion, and angiogenesis. It also induces apoptosis and inhibits tumor growth in a mouse model of breast cancer.