The vascular endothelial growth factor (VEGF)-VEGF receptor (R) system is deeply involved in angiogenesis and lymphangiogenesis[3]. KRN-633 inhibits tyrosine phosphorylation of VEGFR-1, VEGFR2, c-Kit, and PDGFR-β (IC50=11.7, 1.16, 8.01, 130 nM) in human umbilical vein endothelial cells. KRN-633 also inhibits the VEGF-driven proliferation of HUVECs (IC50=14.9 nM). KRN-633 suppresses capillary tube formation of endothelial cells. KRN-633 inhibits tumor growth in several tumor xenograft models with diverse tissue origins, including lung, colon, and prostate, in athymic mice and rats. KRN-633 also causes the regression of some well-established tumors and those that have regrown after the cessation of treatment. KRN-633 is well tolerated and has no significant effects on body weight or the general health of the animals. Histologic analysis of tumor xenografts treated with KRN-633 reveals a reduction in the number of endothelial cells in non-necrotic areas and a decrease in vascular permeability[4]. Reduction in the expression levels of VEGF and VEGF receptor-2 in the CL precedes the impairment of luteal circulation and a series of events leading to parturition (i.e., reduction of plasma progesterone, enhancement of myometrium contractility, and onset of parturition). Blocking of VEGF signaling by using the inhibitor of VEGFR tyrosine kinase KRN633 at mid-pregnancy caused a similar sequence of events and induced preterm birth[5]. In retinas of rats injected subcutaneously with KRN633 (10 mg/kg), simplified vasculature attributable to capillary regression and prevention of endothelial cell growth were seen, whereas no visible changes in the morphology of the retinal layers were observed[6].
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