Kallikrein-binding protein inhibits growth of gastric carcinoma by reducing vascular endothelial growth factor production and angiogenesis.

Kallikrein-binding protein (KBP) has been identified as an endogenous angiogenic inhibitor. We previously showed that KBP inhibited rat retinal neovascularization by down-regulation of vascular endothelial growth factor (VEGF) in endothelial cells. However, its antiangiogenic potential for inhibition of gastric carcinoma and the effect on VEGF in tumor cells have not been elucidated. The present study was designed to investigate the effect of KBP on growth of gastric carcinoma and the possible molecular mechanism. Recombinant KBP dose dependently inhibited proliferation and induced apoptosis of endothelial cells, but no effect on proliferation and apoptosis of SGC-7,901 gastric carcinoma cells. I.p. injection of KBP resulted in growth inhibition of both heterotopic and orthotopic gastric carcinoma xenografts at 61.4% and 52.3%, respectively. Microvessel density in tumor tissues treated with KBP was significantly decreased, suggesting that KBP suppressed tumor growth by antiangiogenesis. The expression and release of VEGF, a major angiogenic stimulator, were down-regulated by KBP in SGC-7,901 cells and gastric carcinoma xenografts. RNA levels of VEGF in SGC-7,901 cells were also decreased by KBP, thus suggesting the regulation at the transcriptional level. Therefore, hypoxia-inducible factor 1alpha (HIF-1alpha), a crucial transcriptional factor for VEGF expression, was examined in SGC-7,901 cells treated by KBP. KBP reduced HIF-1alpha protein level and nuclear translocation, which may be responsible for the down-regulation of VEGF transcription. Down-regulation of VEGF expression and release in tumor cells through inhibiting HIF-1alpha, thus attenuating the paracrine effect of VEGF on endothelial cell proliferation and vascular permeability in tumor tissues, may represent a novel mechanism for the antiangiogenic and antitumor activity of KBP.