Tumor-Associated Angiogenesis and Tumor Growth

We evaluated the significance of the host kallikrein-kinin system in tumor angiogenesis and tumor growth using two rodent models genetically deficient in a kallikrein-kinin system. Inoculation of Walker 256 carcinoma cells into the s.c. tissues of the back of normal Brown Norway Kitasato rats (BN-Ki rats) resulted in the rapid development of solid tumors with marked angiogenesis. By contrast, in kininogen-deficient Brown Norway Katholiek rats (BN-Ka rats), which cannot generate intrinsic bradykinin (BK), the weights of the tumors and the extent of angiogenesis were significantly less than those in BN-Ki rats. Daily administration of B2 receptor antagonists significantly reduced angiogenesis and tumor weights in BN-Ki rats to levels similar to those in BN-Ka rats but did not do so in BN-Ka rats. Angiogenesis and tumor growth were significantly suppressed in B2 receptor knockout mice bearing sarcoma 180 compared with their wild-type counterparts. Immunoreactive vascular endothelial growth factor (VEGF) was localized in Walker tumor stroma more extensively in BN-Ki rats than in BN-Ka rats, although immunoreactive B2 receptor also was detected in the stroma to the same extent in both types of rats. Cultured stromal fibroblasts isolated from BN-Ki rats and BN-Ka rats produced VEGF in response to BK (10 -10 6 M), and this stimulatory effect of BK was abolished with a B2 receptor antagonist, Hoe140 (10 5 M). These results suggest that BK generated from kininogens supplied from the host may facilitate tumor-associated angiogenesis and tumor growth by stimulating stromal B2 signaling to up-regulate VEGF production mainly in fibroblasts.