Summary

Angiogenesis plays a primary role in tumor growth and metastasis. Angiostatin, a proteolytic fragment containing the first four kringle domains of human plasminogen, can inhibit angiogenesis. The anti-angiogenic activities of kringle 1–5 (K1–5) and kringle 5 fragments of plasminogen are greater than angiostatin in inhibiting angiogenesis and angiogenesis-dependent tumor growth.To further optimize kringle fragment anti-angiogenic activities, mutations were created at the potential glycosylation sites Asn-289 and Thr-346 and the Lys binding site, Leu-532, at kringle 5, including K1–5N289A (replacing Asn by Ala at residue 289), K1–5T346A, K1–5L532R, K1–5N289A/T346A, K1–5T346A/ L532R, K1–5N289A/L532R, and K1–5N289A/T346A/L532R. Wild-type and mutant K1–5 proteins were expressed successfully by the Pichia pastoris expression system. Native K1–5 from proteolytic cleavage and wild-type K1–5 have similar activity in inhibiting basic fibroblast growth factor-induced endothelial cell proliferation. Among these mutated proteins, K1–5N289A/ T346A/L532R exhibited the greatest effect in inhibiting endothelial cell proliferation and in inducing endothelial cell apoptosis. Integrin αvβ3-mediated adhesion of K1–5N289A/ T346A/L532R to endothelial cells was more greatly enhanced when compared to wild type K1–5. Furthermore, K1–5N289A/ T346A/L532R was most potent in inhibiting basic fibroblast growth factor-induced angiogenesis in Matrigel assay in vivo.Angiogenesis- dependent tumor growth was inhibited by systemically injected K1–5N289A/T346A/L532R into mice. These results demonstrate that alteration of glycosylation and Lys binding properties could increase the anti-angiogenic action of K1–5, possibly via enhanced interaction with integrin αvβ3 in endothelial cells.