Human angiostatin inhibits murine hemangioendothelioma tumor growth in vivo.

Lannutti BJ; Gately ST; Quevedo ME; Soff GA; Paller AS Department of Pediatrics, Northwestern University Medical School, Chicago, Illinois 60611, USA.

Angiostatin inhibits angiogenesis and metastatic tumor growth; however, its usefulness in treating primary nonmetastasizing tumors is less well understood. We now report the effectiveness of human angiostatin administration in a mouse hemangioendothelioma model. Human angiostatin was administered to mice with s.c. hemangioendothelioma and associated disseminated intravascular coagulopathy (Kasabach-Merritt syndrome). Angiostatin significantly reduced tumor volume in comparison to nontreated controls, increased survival, and prevented the profound thrombocytopenia and anemia of Kasabach-Merritt syndrome. Apoptosis of tumor cells was induced by angiostatin, but tumor cell proliferation was not inhibited. These data suggest angiostatin as a novel treatment for nonmetastasizing vascular tumors and for Kasabach-Merritt syndrome.

Science 1999 Apr 30;284(5415):808-12

Effects of angiogenesis inhibitors on multistage carcinogenesis in mice.

Bergers G, Javaherian K, Lo KM, Folkman J, Hanahan D Department of Biochemistry and Biophysics and Hormone Research Institute, University of California, San Francisco, 513 Parnassus Ave, San Francisco, CA 94143-0534, USA

Solid tumors depend on angiogenesis for their growth. In a transgenic mouse model of pancreatic islet cell carcinogenesis (RIP1-Tag2), an angiogenic switch occurs in premalignant lesions, and angiogenesis persists during progression to expansive solid tumors and invasive carcinomas. RIP1-Tag2 mice were treated so as to compare the effects of four angiogenesis inhibitors at three distinct stages of disease progression. AGM-1470, angiostatin, BB-94, and endostatin each produced distinct efficacy profiles in trials aimed at preventing the angiogenic switch in premalignant lesions, intervening in the rapid expansion of small tumors, or inducing the regression of large

Recent Results Cancer Res 1998;152:341-52

Anti-angiogenesis therapy and strategies for integrating it with adjuvant therapy.

Harris AL ICRF Molecular Oncology Laboratory, John Radcliffe Hospital, Oxford, UK.

Tumor angiogenesis is critical for the growth of primary cancers above 1-2 mm in diameter. A major vascular growth factor is VEGF, and approaches to inhibit VEGF have shown encouraging results in pre-clinical studies. The mechanisms involved in switching on angiogenesis involve activation of oncogenes and upregulation of the hypoxia-sensing pathway. These provide novel targets for therapy. Many anti-angiogenic drugs are in clinical trial currently and there are problems in assessing these types of drugs if they only cause disease stabilisation. It will be important to develop methods to assess inhibition of vascular growth in vivo. New generations of anti-angiogenesis drugs such as endostatin of angiostatin, which are more potent, may cause tumor regression, but this has not yet been studied in patients. These approaches for advanced disease should be more successful when applied early in an adjuvant situation. This will also require careful monitoring of long-term toxicity.

Semin Cancer Biol, 1996 Jun, 7:3, 139-46

Regulation of angiogenesis by SPARC and angiostatin: implications for tumor cell biology.

Jendraschak E; Sage EH
Department of Biological Structure, University of Washington, School of Medicine, Seattle 98195-7420, USA.

The formation of blood vessels through endothelial cell proliferation from extant vasculature (angiogenesis) is a prerequisite for the remodeling, regeneration and repair of tissue. In pathological processes, angiogenesis is a major limiting step in tumor growth and is necessary for tumor formation at metastatic sites. Angiogenesis consists of a sequence of events that include (i) dissolution of the basement membrane, (ii) migration and (iii) proliferation of endothelial cells, (iv) formation of the vascular loop, and (v) formation of a new basement membrane. A variety of factors control and regulate these multiple steps during which the endothelium gives rise to new vessels. Growth factors such as vascular endothelial growth factor or platelet-derived growth factor act directly on endothelial cells and/or activate inflammatory cells (monocytes and T lymphocytes) which in turn synthesize angiogenic factors. SPARC (Secreted Protein Acidic and Rich in Cytsteine), in conjunction with other known angiogenic factors, might act pleiotropically during angiogenesis. Recently, angiostatin, a novel endogenous inhibitor of metastasis, has been reported. This protein, a cleavage product of plasminogen, most likely acts through inhibition of angiogenesis. Current research is focused on the angiogenic and antiangiogenic properties of SPARC and angiostatin and will provide us with a better understanding of how these important factors regulate angiogenesis.

Rev Med Interne 1998 Dec;19(12):904-13

[Tumoral angiogenesis: physiopathology, prognostic value and therapeutic perspectives].

[Article in French]
Andre T, Chastre E, Kotelevets L, Vaillant JC, Louvet C, Balosso J, Le Gall E, Prevot S, Gespach C
Inserm U482, hopital Saint-Antoine, Paris, France

INTRODUCTION: Angiogenesis activation plays a crucial role in tumoral growth and metastases dissemination. This review summarizes and analyzes current knowledge on molecular mechanisms related to angiogenesis and the prognostic value of its effectors. It also focuses on the therapeutical relevance of various drugs that might inhibit angiogenesic processes. CURRENT KNOWLEDGE AND KEY POINTS: Tumor angiogenesis involves complex interactions between tumoral, stromal, endothelial cells, fibroblasts and the extracellular matrix. Normal and malignant angiogenesis depends on the balance of proangiogenic and antiangiogenic factors. Endothelial cells are activated by growth factors, such as Vascular Endothelial Growth Factor (VEGF), and proliferate; they release proteases able to induce degradation of the basement membrane and extracellular matrix, and undergo migration and tubulogenesis. Angiostatin and endostatin are two powerful inhibitors of angiogenesis in experimental models. Assessment of intratumoral microvessel density and quantification of angiogenic factors, including VEGF, are of prognostic value in most cancers, particularly in breast cancer. However, the use of these prognosis markers in clinical practice is still controversial due to the lack of prospective studies and to technical limits inherent to the scoring and standardization of immunohistochemical methods. FUTURE PROSPECTS AND PROJECTS: Better understanding of the molecular basis of angiogenesis allows the development of new therapeutical strategies. Biochemical targets of antiangiogenic therapy are: the interaction between angiogenic factors and their receptors; the interaction of endothelial cells with the extracellular matrix; and intracellular signaling pathways. Angiogenesis inhibitors may not cause tumor regression, but inhibit cellular growth and produce "disease dormancy". Extensive phase I to III clinical trials involving antiangiogenesis therapy are in progress.

Proc Natl Acad Sci U S A, 1997 Sep, 94:20, 10868-72

The mechanism of cancer-mediated conversion of plasminogen to the angiogenesis inhibitor angiostatin.

Gately S; Twardowski P; Stack MS; Cundiff DL; Grella D; Castellino FJ; Enghild J; Kwaan HC; Lee F; Kramer RA; Volpert O; Bouck N; Soff GA
Department of Medicine, Division of Hematology/Oncology, Northwestern University School of Medicine, Chicago, IL 60611, USA.

Angiostatin, a potent naturally occurring inhibitor of angiogenesis and growth of tumor metastases, is generated by cancer-mediated proteolysis of plasminogen. Human prostate carcinoma cells (PC-3) release enzymatic activity that converts plasminogen to angiostatin. We have now identified two components released by PC-3 cells, urokinase (uPA) and free sulfhydryl donors (FSDs), that are sufficient for angiostatin generation. Furthermore, in a defined cell-free system, plasminogen activators [uPA, tissue-type plasminogen activator (tPA), or streptokinase], in combination with one of a series of FSDs (N-acetyl-L-cysteine, D-penicillamine, captopril, L-cysteine, or reduced glutathione] generate angiostatin from plasminogen. An essential role of plasmin catalytic activity for angiostatin generation was identified by using recombinant mutant plasminogens as substrates. The wild-type recombinant plasminogen was converted to angiostatin in the setting of uPA/FSD; however, a plasminogen activation site mutant and a catalytically inactive mutant failed to generate angiostatin. Cell-free derived angiostatin inhibited angiogenesis in vitro and in vivo and suppressed the growth of Lewis lung carcinoma metastases. These findings define a direct mechanism for cancer-cell-mediated angiostatin generation and permit large-scale production of bioactive angiostatin for investigation and potential therapeutic application.

Biochem Biophys Res Commun, 1997 Jul, 236:3, 651-4

Suppression of tumor growth with recombinant murine angiostatin.

Wu Z; OReilly MS; Folkman J; Shing Y
Department of Surgery, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA

Angiostatin, a 38 kDa internal fragment of plasminogen, is an antiangiogenic endothelial cell inhibitor. It regresses several primary and metastatic tumors in mice. To produce recombinant angiostatin for further structural and functional studies, the mouse angiostatin gene preceded by a sequence including a signal peptide of plasminogen was introduced into baculovirus. Recombinant murine angiostatin was purified from the culture medium of angiostatin baculovirus-infected insect cells (yield = 1 mg/liter) with a single-step of lysine-Sepharose chromatography. The angiostatin baculovirus-infected insect cells expressed and secreted a 52 kDa polypeptide that demonstrated all of the biological activities of angiostatin. A partial amino acid sequence of the NH2-terminus of the secreted protein revealed that the signal peptide was recognized and properly cleaved in insect cells. The recombinant murine angiostatin potently inhibited the proliferation of bovine capillary endothelial cells in vitro (half maximal inhibition = 50 ng/ml) and suppressed the growth of primary Lewis lung carcinoma in vivo (6 mg/kg/day, T/C = 0.08).
EXS, 1997, 79:, 273-94

Angiostatin: an endogenous inhibitor of angiogenesis and of tumor growth.

OReilly MS
Department of Surgery, Children's Hospital, Boston, Massachusetts, USA

Angiostatin, an internal fragment of plasminogen, is a potent inhibitor of angiogenesis, which selectively inhibits endothelial cell proliferation. When given systemically, angiostatin potently inhibits tumor growth and can maintain metastatic and primary tumors in a dormant state defined by a balance of proliferation and apoptosis of the tumor cells. We identified angiostatin while studying the phenomenon of inhibition of tumor growth by tumor mass and have elucidated one mechanism for this phenomenon. In our animal model, a primary tumor almost completely suppresses the growth of its remote metastases. However, after tumor removal, the previously dormant metastases neovascularize and grow. When the primary tumor is present, metastatic growth is suppressed by a circulating angiogenesis inhibitor. Serum and urine from tumor-bearing mice, but not from controls, specifically inhibit endothelial cell proliferation. The activity copurifies with a 38 kD plasminogen fragment which we have sequenced and named angiostatin. Human angiostatin, obtained from a limited proteolytic digest of human plasminogen, has similar activities. Systemic administration of angiostatin, but not intact plasminogen, potently blocks neovascularization and growth of metastases and primary tumors. We here show that the inhibition of metastases by a primary mouse tumor is mediated, at least in part, by the angiogenesis inhibitor angiostatin.

Cancer Res, 1996 Nov, 56:21, 4887-90

Human prostate carcinoma cells express enzymatic activity that converts human plasminogen to the angiogenesis inhibitor, angiostatin.

Gately S; Twardowski P; Stack MS; Patrick M; Boggio L; Cundiff DL; Schnaper HW; Madison L; Volpert O; Bouck N; Enghild J; Kwaan HC; Soff GA
Division of Hematology/Oncology, Northwestern University School of Medicine, Chicago, Illinois 60611, USA.

Angiostatin is an inhibitor of angiogenesis and metastatic growth that is found in tumor-bearing animals and can be generated in vitro by the proteolytic cleavage of plasminogen. The mechanism by which angiostatin is produced in vivo has not been defined. We now demonstrate that human prostate carcinoma cell lines (PC-3, DU-145, and LN-CaP) express enzymatic activity that can generate bioactive angiostatin from purified human plasminogen or plasmin. Affinity purified PC-3-derived angiostatin inhibited human endothelial cell proliferation, basic fibroblast growth factor-induced migration, endothelial cell tube formation, and basic fibroblast growth factor-induced corneal angiogenesis. Studies with proteinase inhibitors demonstrated that a serine proteinase is necessary for angiostatin generation. These data indicate that bioactive angiostatin can be generated directly by human prostate cancer cells and that serine proteinase activity is necessary for angiostatin generation.

J Biol Chem, 1996 Nov, 271:46, 29461-7

Kringle domains of human angiostatin. Characterization of the anti-proliferative activity on endothelial cells.

Cao Y; Ji RW; Davidson D; Schaller J; Marti D; Söhndel S; McCance SG; OReilly MS; Llinás M; Folkman J
Departments of Surgery and Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA

Recently we have identified angiostatin, an endogenous angiogenesis inhibitor of 38 kDa which specifically blocks the growth of endothelial cells (O'Reilly, M. S., Holmgren, L., Shing, Y., Chen, C. , Rosenthal, R. A., Moses, M., Lane, W. S., Cao, Y., Sage, E. H., and Folkman, J. (1994) Cell 79, 315-328; Folkman, J. (1995) Nat. Med. 1, 27-31). Angiostatin was shown to represent an internal fragment of plasminogen containing the first four kringle structures. We now report on the inhibitory effects of individual or combined kringle structures of angiostatin on capillary endothelial cell proliferation. Recombinant kringle 1 and kringle 3 exhibit potent inhibitory activity with half-maximal concentrations (ED50) of 320 nM and 460 nM, respectively. Also, recombinant kringle 2 displays a significant inhibition, although decreased compared with both kringle 1 and kringle 3. In contrast, kringle 4 is an ineffective inhibitor of basic fibroblast growth factor-stimulated endothelial cell proliferation. Among the tandem kringle arrays, the recombinant kringle 2-3 fragment exerts inhibitory activity similar to kringle 2 alone. However, relative to kringle 2-3, a marked enhancement in inhibition is observed when individual kringle 2 and kringle 3 are added together to endothelial cells. This implies that it is necessary to open the cystine bridge between kringle 2 and kringle 3 to obtain the maximal inhibitory effect of kringle 2-3. An increased (<2-fold) inhibitory activity is observed for the kringle 1-3 fragment (ED50 = 70 nM) compared with kringle 1-4 (ED50 = 135 nM). These data indicate that the anti-proliferative activity of angiostatin on endothelial cells is shared by kringle 1, kringle 2, and kringle 3, but probably not by kringle 4 and that more potent inhibition results when kringle 4 is removed from angiostatin. Thus, in view of the variable lysine affinity of the homologous domains, it would appear that lysine binding capability does not correlate with the relative inhibitory effects of the kringle-containing constructs. However, as we also demonstrate, appropriate folding of kringle structures is essential for angiostatin to maintain its full anti-endothelial activity.

J Biol Chem, 1997 Nov, 272:46, 28823-5

Angiostatin-converting enzyme activities of human matrilysin (MMP-7) and gelatinase B/type IV collagenase (MMP-9).

Patterson BC; Sang QA
Department of Chemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.

Angiostatin is one of the most potent inhibitors of angiogenesis. Reports have shown that metalloelastase, pancreas elastase, plasmin reductase, and plasmin convert plasminogen to angiostatin. However, the cleavage sites of plasminogen by those enzymes have not been determined. Here we demonstrate that two members of the human matrix metalloproteinase (MMP) family, matrilysin (MMP-7) and gelatinase B/type IV collagenase (MMP-9), hydrolyze human plasminogen to generate angiostatin fragments. The cleavage sites have been determined. The 58-kDa bands derived from plasminogen by MMP-7 and MMP-9 both have the N-terminal sequence KVYLSEXKTG, which corresponds to that of angiostatin. This N terminus is identical to that of the starting plasminogen itself and corresponds to residues 97-106 of prepro-plasminogen. The 42- and 38-kDa bands generated by MMP-7 both have the N-terminal sequence VVLLPNVETP, which corresponds to the amino acid sequence 467-476 of prepro-plasminogen, between kringle domain 4 and 5. MMP-9 cleaves plasminogen to generate a 42-kDa fragment with the N-terminal sequence PVVLLPNVE, 1 residue upstream of the MMP-7 cleavage site. These results indicate that MMP-7 and MMP-9 may regulate new blood vessel formation by cleaving plasminogen and generating angiostatin molecules.

J Biol Chem, 1997 Aug, 272:33, 20641-5

Generation of angiostatin by reduction and proteolysis of plasmin. Catalysis by a plasmin reductase secreted by cultured cells.

Stathakis P; Fitzgerald M; Matthias LJ; Chesterman CN; Hogg PJ
Centre for Thrombosis and Vascular Research, School of Pathology and Department of Haematology, Prince of Wales Hospital, University of New South Wales, Sydney NSW 2052, Australia.

Extracellular manipulation of protein disulfide bonds has been implied in diverse biological processes, including penetration of viruses and endotoxin into cells and activation of certain cytokine receptors. We now demonstrate reduction of one or more disulfide bonds in the serine proteinase, plasmin, by a reductase secreted by Chinese hamster ovary or HT1080 cells. Reduction of plasmin disulfide bond(s) triggered proteolysis of the enzyme, generating fragments with the domain structure of the angiogenesis inhibitor, angiostatin. Two of the known reductases secreted by cultured cells are protein disulfide isomerase and thioredoxin, and incubation of plasmin with these purified reductases resulted in angiostatin fragments comparable with those generated from plasmin in cell culture. Thioredoxin-derived angiostatin inhibited proliferation of human dermal microvascular endothelial cells with half-maximal effect at approximately 0.2 microg/ml. Angiostatin made by cells and by purified reductases contained free sulfhydryl group(s), and S-carbamidomethylation of these thiol group(s) ablated biological activity. Neither protein disulfide isomerase nor thioredoxin were the reductases used by cultured cells, because immunodepletion of conditioned medium of these proteins did not affect angiostatin generating activity. The plasmin reductase secreted by HT1080 cells required a small cofactor for activity, and physiologically relevant concentrations of reduced glutathione fulfilled this role. These results have consequences for plasmin activity and angiogenesis, particularly in the context of tumor growth and metastasis. Moreover, this is the first demonstration of extracellular reduction of a protein disulfide bond, which has general implications for cell biology.

Cancer Res, 1997 Apr, 57:7, 1329-34

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