AG-028262, a novel selective VEGFR tyrosine kinase antagonist that potently inhibits KDR signaling and angiogenesis in vitro and in vivo

2578 Vascular endothelial growth factor (VEGF) and its receptors play key roles in tumor angiogenesis, growth, and metastasis. AG-028262 is a next-generation small molecule inhibitor designed to block the ATP kinase domain of human VEGFR2 (KDR, Flk-1) while sparing other related non-VEGF receptors. In enzymatic assays, AG-028262 had pM affinity for KDR, but ≥ nM affinities for other kinases, such as FGFR1 and Lck. In cellular assays, AG-028262 inhibited KDR autophosphorylation in response to VEGF stimulation with an IC50 of 0.34 nM, but was 568 and 1338-fold less potent for inhibiting related RTKs such as PDGFR-β and FGFR1, respectively. In human umbilical vein endothelial cells (HUVEC), AG-028262 inhibited VEGF-mediated survival with an IC50 of 0.73 nM compared to an IC50 of 154 nM for inhibiting bFGF-mediated survival. AG-028262 induced apoptosis in HUVECs concomitant with inhibition of cellular signaling downstream of KDR. AG-028262 also lacked anti-proliferative activity in vitro against many tumor cell lines at concentrations up to 10 μM. In vivo, oral administration of AG-028262 led to marked antitumor efficacy in several human tumor xenograft models, including MV522 carcinoma, U87 glioblastoma, and H526 lung carcinoma, and in the syngeneic Lewis lung carcinoma model. Immunohistochemistry studies showed that the compound significantly reduced microvessel density in tumors. PK/PD studies in A375 human melanoma xenografts and in the rat retina demonstrated potent and selective inhibition of KDR in vivo. In summary, AG-028262 is a potent and selective VEGF receptor tyrosine kinase inhibitor with marked antiangiogenic properties that may have utility in cancer therapy.