Full kringles of plasminogen (aa 1-566) mediate complete regression of human MDA-MB-231 breast tumor xenografted in nude mice

Since kringle (K)5, not present in the angiostatin molecule, was shown to be a key functional domain possessing potent antiangiogenic activity, we have evaluated a new plasminogen-derived fragment, consisting of the N-terminal part of human plasminogen, that included the complete secondary structure of K1-5 (aa 1-566). In contrast to other fragments described to date, K1-5 includes cysteine residues at positions 543, 555 and 560 allowing the formation of the three disulfide bonds lying within K5. Vascular endothelial cell proliferation and migration assays revealed that a replication-defective adenovirus (AdK1-5(1-566)), expressing K1-5 (aa 1-566), was dose dependently more potent that AdK1-3(1-354), an adenovirus that expresses only the first three kringles. In contrast to AdK1-3(1-354), a single intratumoral injection of AdK1-5(1-566) into MDA-MB-231 breast human carcinoma tumors was followed by a total regression of 40% of the tumor and by significant arrest of tumor growth (90%), which was correlated with a drastic decrease of functional neovascularization into the tumors. Furthermore, systemic delivery of AdK1-5(1-566) in mice inhibited the lung invasion of melanoma B16-F10 cells by 87%. Our findings provide evidence that the full kringles of plasminogen (aa 1-566) may be much more potent than K1-3 (aa 1-354), for the suppression of angiogenesis, tumor growth and metastatic dissemination.