title: Suppression of angiogenesis and tumor growth by the inhibitor K1-5 generated by plasmin-mediated proteolysis.
abstract: Proteolytic enzymes are involved in generation of a number of endogenous angiogenesis inhibitors. Previously, we reported that angiostatin, a potent angiogenesis inhibitor, is a proteolytic fragment containing the first four kringle modules of plasminogen. In this report, we demonstrate that urokinase-activated plasmin can process plasminogen to release an angiogenesis inhibitor, K1-5 (protease-activated kringles 1-5). K1-5 inhibits endothelial-cell proliferation with a half-maximal concentration of approximately 50 pM. This inhibitory effect is endothelial-cell-specific and appears to be at least approximately 50-fold greater than that of angiostatin. A synergistic efficacy of endothelial inhibition was observed when angiostatin and kringle 5 (K5) were coincubated with capillary endothelial cells. The synergistic effect is comparable to that produced by K1-5 alone. Systemic treatment of mice with K1-5 at a low dose significantly blocked the fibroblast growth factor-induced corneal neovascularization, whereas angiostatin had no effect at the same dose. K1-5 also suppressed angiogenesis in chicken embryos. Systemic administration of K1-5 at a low dose at which angiostatin was ineffective significantly suppressed the growth of a murine T241 fibrosarcoma in mice. The antitumor effect correlates with the reduced neovascularization. These findings suggest that the plasmin-mediated proteolysis may be involved in the negative switch of angiogenesis.
mesh_terms: D043168:Angiostatins; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002642:Chick Embryo; D020256:Choroidal Neovascularization / Q000378:metabolism; D016510:Corneal Neovascularization / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects; D005341:Fibrinolysin / Q000378:metabolism*; D005354:Fibrosarcoma; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000378:metabolism* / Q000473:pathology; D010446:Peptide Fragments / Q000494:pharmacology; D010958:Plasminogen / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured