A recombinant human angiostatin protein inhibits experimental primary and metastatic cancer.

Sim BK; OReilly MS; Liang H; Fortier AH; He W; Madsen JW; Lapcevich R; Nacy CA
EntreMed, Inc., Rockville, Maryland 20850, USA.

Endogenous murine angiostatin, identified as an internal fragment of plasminogen, blocks neovascularization and growth of experimental primary and metastatic tumors in vivo. A recombinant protein comprising kringles 1-4 of human plasminogen (amino acids 93-470) expressed in Pichia pastoris had physical properties (molecular size, binding to lysine, reactivity with antibody to kringles 1-3) that mimicked native angiostatin. This recombinant Angiostatin protein inhibited the proliferation of bovine capillary endothelial cells in vitro. Systemic administration of recombinant Angiostatin protein at doses of 1.5 mg/kg suppressed the growth of Lewis lung carcinoma-low metastatic phenotype metastases in C57BL/6 mice by greater than 90%; administration of the recombinant protein at doses of 100 mg/kg also suppressed the growth of primary Lewis lung carcinoma-low metastatic phenotype tumors. These findings demonstrate unambiguously that the antiangiogenic and antitumor activity of endogenous angiostatin resides within kringles 1-4 of plasminogen.

Cell, 1997 Mar, 88:6, 801-10

Macrophage-derived metalloelastase is responsible for the generation of angiostatin in Lewis lung carcinoma.

Dong Z; Kumar R; Yang X; Fidler IJ
Department of Cell Biology, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA

To determine the mechanism responsible for the in vivo production of angiostatin that inhibits growth and metastasis in Lewis lung carcinoma (3LL), we implanted 3LL variant cells into the subcutis of syngeneic C57BL/6 mice. The tumors were infiltrated by macrophages and expressed high levels of steady-state mRNA for metalloelastase (MME). Successive passages (more than three) of cultures established from the tumors resulted in complete depletion of macrophages; steady-state MME mRNA, elastinolytic activity, and production of angiostatin (in the presence of plasminogen) were correspondingly reduced. Coculture of macrophages with either 3LL cells or their conditioned media containing granulocyte-macrophage colony-stimulating factor resulted in secretion of MME and production of angiostatin by the macrophages, suggesting that angiostatin is produced by tumor-infiltrating macrophages whose MME expression is stimulated by tumor cell-derived granulocyte-macrophage colony-stimulating factor.

Nat Med, 1996 Jun, 2:6, 689-92

Angiostatin induces and sustains dormancy of human primary tumors in mice.

OReilly MS; Holmgren L; Chen C; Folkman J
Department of Surgery, Children's Hospital, Boston, Massachusetts, USA

There is now considerable direct evidence that tumor growth is angiogenesis-dependent. The most compelling evidence is based on the discovery of angiostatin, an angiogenesis inhibitor that selectively instructs endothelium to become refractory to angiogenic stimuli. Angiostatin, which specifically inhibits endothelial proliferation, induced dormancy of metastases defined by a balance of apoptosis and proliferation. We now show that systemic administration of human angiostatin potently inhibits the growth of three human and three murine primary carcinomas in mice. An almost complete inhibition of tumor growth was observed without detectable toxicity or resistance. The human carcinomas regressed to microscopic dormant foci in which tumor cell proliferation was balanced by apoptosis in the presence of blocked angiogenesis. This regression of primary tumors without toxicity has not been previously described. This is also the first demonstration of dormancy therapy, a novel anticancer strategy in which malignant tumors are regressed by prolonged blockade of angiogenesis.

Eur J Biochem, 1996 Mar, 236:2, 682-8

Limited plasmin proteolysis of vitronectin. Characterization of the adhesion protein as morpho-regulatory and angiostatin-binding factor.

Kost C; Benner K; Stockmann A; Linder D; Preissner KT
Haemostasis Research Unit, Kerckhoff-Klinik, Bad Nauheim, Germany.

The adhesion protein vitronectin is associated with extracellular matrices and serves as cofactor for plasminogen-activator inhibitor-1. Limited proteolysis by plasmin converts vitronectin into defined fragments which are detectable at sites of inflammation and angiogenesis. The loss and gain of binding functions of vitronectin fragments for macromolecular ligands was characterized in the present study. The initially generated 61--63-kDa vitronectin-(1--348)-fragment serves as typical binding component for plasminogen and binding function was lost upon carboxypeptidase B treatment indicating the importance of a C-terminal lysine. Complementary binding sites reside in isolated plasminogen kringles 1--3 (designated angiostatin) as deduced from direct binding and ligand blotting experiments. A synthetic vitronectin-(331--348)-peptide from the C-terminus of the 61--63-kDa fragment could mimic plasminogen and angiostatin binding. Also, the immobilized peptide bound tissue plasminogen-activator and mediated plasmin formation, comparable to fibrinogen-derived peptides. The 61--63-kDa vitronectin fragment was indistinguishable in its adhesive properties to intact vitronectin and bound active but not latent plasminogen-activator inhibitor-1. Late plasminolysis of vitronectin resulted in the processing of the N-terminal region of the protein with the generation of 42 kDa/35-kDa fragments that had Gly89 as new N-terminus and that were ineffective in promoting cell adhesion. Thus, at sites of cell-matrix interactions which become proteolytically modified by plasmin during inflammatory and angiogenic processes, vitronectin serves as plasminogen/angiostatin-binding factor. Due to this differential change in functions particularly at sites of deposition in the vascular system or at wound sites vitronectin is considered to be an important morpho-regulatory factor.

J Biol Chem, 1997 Sep, 272:36, 22924-8

Kringle 5 of plasminogen is a novel inhibitor of endothelial cell growth.

Cao Y; Chen A; An SSA; Ji RW; Davidson D; Llinás M
Laboratory of Angiogenesis Research, Department of Cell and Molecular Biology, Karolinska Institute, S-171 77 Stockholm, Sweden. yihai.cao@cmb.ki.se

Angiostatin is a potent angiogenesis inhibitor which has been identified as an internal fragment of plasminogen that includes its first four kringle modules. We have recently demonstrated that the anti-endothelial cell proliferative activity of angiostatin is also displayed by the first three kringle structures of plasminogen and marginally so by kringle 4 (Cao, Y., Ji, R.-W., Davidson, D., Schaller, J., Marti, D., Sohndel, S., McCance, S. G., O'Reilly, M. S. , Llinás, M., and Folkman, J. (1996) J. Biol. Chem. 271, 29461-29467). We now report that the kringle 5 fragment of human plasminogen is a specific inhibitor for endothelial cell proliferation. Kringle 5 obtained as a proteolytic fragment of human plasminogen displays potent inhibitory effect on bovine capillary endothelial cells with a half-maximal concentration (ED50) of approximately 50 nM. Thus, kringle 5 would appear to be more potent than angiostatin on inhibition of basic fibroblast growth factor-stimulated capillary endothelial cell proliferation. Appropriately folded recombinant mouse kringle 5 protein, expressed in Escherichia coli, exhibits a comparable inhibitory effect as the proteolytic kringle 5 fragment. Thus, kringle 5 domain of human plasminogen is a novel endothelial inhibitor that is sufficiently potent to block the growth factor-stimulated endothelial cell growth.

J Protein Chem, 1997 Oct, 16:7, 669-79

Limited proteolysis of angiogenin by elastase is regulated by plasminogen.

Hu GF
Center for Biochemical and Biophysical Sciences and Medicine, Harvard Medical School, Boston, Massachusetts 02115, USA. guofuhu@warren.med.harvard.edu

Human neutrophil elastase cleaves angiogenin at the Ile-29/Met-30 peptide bond to produce two major disulfide-linked fragments with apparent molecular weights of 10,000 and 4000, respectively. Elastase-cleaved angiogenin has slightly increased ribonucleolytic activity, but has lost its ability to undergo nuclear translocation in endothelial cells, a process essential for angiogenic activity. Cleavage appears to alter the cell-binding properties of angiogenin, despite the fact that it occurs some distance from the putative receptor-binding site, since the elastase-cleaved protein fails to compete with its native counterpart for nuclear translocation in endothelial cells. Plasminogen specifically accelerates elastase proteolysis of angiogenin. It does not enhance elastase activity toward ribonuclease A or the synthetic peptide substrate MeOSuc-Ala-Ala-Pro-Val-pNA. Plasminogen-accelerated inactivation of angiogenin by elastase might be a significant event in the process of angiogenin-induced angiogenesis since (i) angiogenin and plasminogen circulate in plasma at high concentrations, (ii) angiogenin, especially when bound to actin, activates tissue plasminogen activator to generate plasmin from plasminogen, and (iii) elastase cleaves plasminogen to produce angiostatin, a potent inhibitor of angiogenesis and metastasis. Interrelationships among angiogenin, plasminogen, plasminogen activators, elastase, and angiostatin may provide a sensitive regulatory system to balance angiogenesis and antiangiogenesis.

J Clin Invest, 1996 Feb, 97:3, 858-64

Apolipoprotein(a) kringle 4-containing fragments in human urine. Relationship to plasma levels of lipoprotein(a).

Mooser V; Seabra MC; Abedin M; Landschulz KT; Marcovina S; Hobbs HH Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.

Apo(a) is a large glycoprotein of unknown function that circulates in plasma as part of lipoprotein(a). Apo(a) is structurally related to plasminogen and contains at least 10 kringle (K)4 repeats (type 1-10), a K5 repeat and sequences similar to the protease domain of plasminogen. Plasminogen generates two biologically active peptides: plasmin and angiostatin, a kringle-containing peptide. As a first step in determining if apo(a) generates a similar kringle-containing peptide, human urine was immunologically examined. Fragments ranging in size from 85 to 215 kD were immunodetected using antibodies directed against epitopes in the K4-type 2 repeat, but not the K4-type 9 repeat or protease domain, NH2-terminal sequence analysis revealed sequences specific for the K4-type 1 repeat, confirming that the fragments are from the NH2 terminus of the K4 array. The amount of urinary apo(a) rose in proportion to the plasma lipoprotein(a) concentration. Even individuals with trace to no apo(a) in plasma had immunodetectable apo(a) fragments in their urine. Intravenous administration of the human urinary apo(a) into mice resulted in the urine. These findings suggest that the apo(a) fragments found in urine are formed extrarenally and then excreted by the kidney.

Curr Opin Oncol, 1996 Jan, 8:1, 60-5

Mechanisms and therapeutic implications of angiogenesis.

Bicknell R; Harris AL
Institute of Molecular Medicine, University of Oxford, UK

Angiogenesis is a key step in tumor growth and metastasis. Many angiogenic factors have been described, including vascular endothelial growth factor, basic fibroblast growth factor, and thymidine phosphorylase. More recently, a number of naturally occurring inhibitors of angiogenesis, including thrombospondin and angiostatin, have also been identified. The control of angiogenesis by inhibitors regulated by suppressor oncogenes or produced by tumors has emerged as an important mechanism. The development of quantitative assessment of vascular density in primary human tumors has produced a new independent marker of prognosis and could be helpful in selecting patients for antiangiogenic therapy. A large number of antiangiogenic agents are in development, however, new ways to assess their antitumor effects will be necessary for the treatment of advanced cancer. Stabilization of disease may occur by inhibiting new vessel growth, and thus, evidence for a decrease in blood supply should be sought by positron emission tomography scanning, magnetic resonance imaging, or other methods. Markers of angiogenesis in urine or blood will prove to be helpful in the monitoring of treatments.

Drugs 1999 Jul;58(1):17-38

The rationale and future potential of angiogenesis inhibitors in neoplasia

Gasparini G Division of Medical Oncology, Azienda Ospedali Riuniti Bianchi-Melacrino-Morelli,
Reggio Calabria, Italy. oncologiarc@diel.it

Malignant tumours are angiogenesis-dependent diseases. Several experimental studies suggest that primary tumour growth, invasiveness and metastasis require neovascularisation. Tumour-associated angiogenesis is a complex multistep process under the control of positive and negative soluble factors. A mutual stimulation occurs between tumour and endothelial cells by paracrine mechanisms. Angiogenesis is necessary, but not sufficient, as the single event for tumour growth. There is, however, compelling evidence that acquisition of the angiogenic phenotype is a common pathway for tumour progression, and that active angiogenesis is associated with other molecular mechanisms leading to tumour progression. Experimental research suggests that it is possible to block angiogenesis by specific inhibitory agents, and that modulation of angiogenic activity is associated with tumour regression in animals with different types of neoplasia. The more promising angiosuppressive agents for clinical testing are: naturally occurring inhibitors of angiogenesis (angiostatin, endostatin, platelet factor-4 and others), specific inhibitors of endothelial cell growth (TNP-470, thalidomide, interleukin-12 and others), agents neutralising angiogenic peptides (antibodies to fibroblast growth factor or vascular endothelial growth factor, suramin and analogues, tecogalan and others) or their receptors, agents that interfere with vascular basement membrane and extracellular matrix [metalloprotease (MMP) inhibitors, angiostatic steroids and others], antiadhesion molecules antibodies such as antiintegrin alpha v beta 3, and miscellaneous drugs that modulate angiogenesis by diverse mechanisms of action. Antiangiogenic therapy is to be distinguished from vascular targeting. Gene therapy aimed to block neovascularisation is also a feasible anticancer strategy in animals bearing experimental tumours. Antiangiogenic therapy represents one of the more promising new approaches to anticancer therapy and it is already in early clinical trials. Because angiosuppressive therapy is aimed at blocking tumour growth indirectly, through modulation of neovascularisation, antiangiogenic agents need to be developed and evaluated as biological response modifiers. Therefore, adequate and well designed clinical trials should be performed

Cancer Res 1999 Jul 15;59(14):3308-12

Liposomes complexed to plasmids encoding angiostatin and endostatin inhibit breast cancer in nude mice.

Chen QR, Kumar D, Stass SA, Mixson AJ
Department of Pathology and Greenebaum Cancer Center, University of Maryland, Baltimore 21201, USA.

Gene therapy transfer of angiostatin and endostatin represents an alternative method of delivering angiogenic polypeptide inhibitors. We examined whether liposomes complexed to plasmids encoding angiostatin or endostatin inhibited angiogenesis and the growth of MDA-MB-435 tumors implanted in the mammary fat pads of nude mice. We determined that plasmids expressing angiostatin (PCI-Angio) or endostatin (PCI-Endo) effectively reduced angiogenesis using an in vivo Matrigel assay. We then investigated the efficacy of these plasmids in reducing the size of tumors implanted in the mammary fat pad of nude mice. Both PCI-Angio and PCI-Endo significantly reduced tumor size when injected intratumorally (P < 0.05). Compared to the untreated control group, the mice treated with PCI-Angio and PCI-Endo exhibited a reduction in tumor size of 36% and 49%, respectively. In addition, we found that i.v. injections of liposomes complexed to PCI-Endo reduced tumor growth in the nude mice by nearly 40% when compared to either empty vector (PCI) or untreated controls (P < 0.05). These findings provide a basis for the further development of nonviral delivery of antiangiogenic genes.

Haematologica 1999 Jul;84(7):643-50

Therapeutic potentials of angiostatin in the treatment of cancer.

Cao Y Laboratory of Angiogenesis Research, Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77,
Stockholm, Sweden. yihai.cao@mtc.ki.se

The discovery of specific endothelial inhibitors such as angiostatin and endostatin not only increases our understanding of the functions of these molecules in the regulation of physiological and pathological angiogenesis, but also provides an important therapeutic strategy for cancer treatment. Recent studies have demonstrated that the angiostatin protein significantly suppresses the growth of a variety of tumors in mice. However, the dosages of angiostatin protein used in these animal studies seem to be too high for clinical trials. In addition, repeated injections and long-term treatment with angiostatin are required to reach its maximal antitumor effect. In this article, I will discuss several alternative approaches that may become feasible to move angiostatin therapy from animal experiments into the clinic. In particular, I will emphasize the therapeutic potentials of angiostatin gene therapy and more potent angiogenesis inhibitors that are related to angiostatin.

Oncologist 1998;3(2):II

Tumor Growth: A Putative Role for Platelets?

Verheul HM, Pinedo HM
Department of Medical Oncology, Free University Hospital, 1081 HV Amsterdam, The Netherlands.
[Record supplied by publisher]

Tumors do not grow without inducing a new vessel formation. The postulation of Dr. Folkman in 1971-that tumor growth is angiogenesis-dependent-has been widely accepted, more than two decades later. The question now becomes, "Is it possible to treat cancer by attacking its blood supply?" Many pharmaceutical companies directed their research to antiangiogenic therapy in the past years. Despite increasing knowledge of tumor-induced angiogenesis, the mechanism as to how antiangiogenic agents inhibit new vessel formation remains unknown. Even the mechanisms of two of the most potent preclinical antiangiogenic drugs, angiostatin and endostatin, are still unknown. Many factors are involved in new vessel formation and experimental models are not sophisticated enough to take into account all factors that play a role in spontaneously occurring tumors. Translational research from the clinic to the laboratory is warranted for the discovery of new potent antiangiogenic agents. Our translational angiogenesis research started two years ago, when we hypothesized that circulating concentrations of vascular endothelial growth factor (VEGF), an important angiogenic factor, if initially elevated, would decrease during therapy in cancer patients. Until then, several investigators tried to correlate serum concentrations of VEGF with the prognosis of cancer patients. Fascinatingly, we found a specific pattern of VEGF concentrations that correlated exactly with the platelet counts of these patients during therapy. No relationship with tumor burden was detected, indicating that circulating levels of VEGF are not influenced by tumor cells, but are mainly dependent on platelet contents. In addition, it was shown by others that thrombin activation of platelets causes VEGF release.What then is the role of circulating VEGF carried by platelets? VEGF has been shown to induce permeability, has mitogenic and chemotactic activity on endothelial cells, and also has procoagulatory activity. Platelets play a critical role in wound healing and, if they are activated, they release upon activation, in addition to VEGF, other growth factors that are involved in angiogenesis (e.g., platelet-derived endothelial cell growth factor, thrombospondin, and platelet factor 4). On the other hand, in the clinic it was found that platelet counts have prognostic significance for cancer patients and that coagulation abnormalities are regularly found in cancer patients. In preclinical studies the tumor-platelet interactions have been studied extensively and a relationship between metastasis formation and platelet-tumor interaction has been reported. We are currently investigating whether a specific tumor endothelium-platelet interaction can contribute to tumor-induced angiogenesis.Although these translational studies have no direct impact on clinical cancer therapy, oncologists should be aware of a potential role for platelets in cancer growth. For example, bone marrow-supportive agents, currently used in high-dose chemotherapy, contribute to platelet production and thereby may influence response to therapy. At this time we investigate in our hospital the pretreatment platelet counts in cancer patients, and we are studying how bone marrow-supportive agents during chemotherapy affect these counts in relation to the response to therapy. We would be pleased to learn of your observations.

Oncologist 1998;3(1):I

Apolipoprotein(a) kringle 4-containing fragments in human urine. Relationship to plasma levels of lipoprotein(a).

Mooser V; Seabra MC; Abedin M; Landschulz KT; Marcovina S; Hobbs HH Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.

Apo(a) is a large glycoprotein of unknown function that circulates in plasma as part of lipoprotein(a). Apo(a) is structurally related to plasminogen and contains at least 10 kringle (K)4 repeats (type 1-10), a K5 repeat and sequences similar to the protease domain of plasminogen. Plasminogen generates two biologically active peptides: plasmin and angiostatin, a kringle-containing peptide. As a first step in determining if apo(a) generates a similar kringle-containing peptide, human urine was immunologically examined. Fragments ranging in size from 85 to 215 kD were immunodetected using antibodies directed against epitopes in the K4-type 2 repeat, but not the K4-type 9 repeat or protease domain, NH2-terminal sequence analysis revealed sequences specific for the K4-type 1 repeat, confirming that the fragments are from the NH2 terminus of the K4 array. The amount of urinary apo(a) rose in proportion to the plasma lipoprotein(a) concentration. Even individuals with trace to no apo(a) in plasma had immunodetectable apo(a) fragments in their urine. Intravenous administration of the human urinary apo(a) into mice resulted in the urine. These findings suggest that the apo(a) fragments found in urine are formed extrarenally and then excreted by the kidney.

Curr Opin Oncol, 1996 Jan, 8:1, 60-5

Investment in Research as a National Priority.

Oncology Program, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-1904, USA.
curtg@pbmac.nci.nih.gov
[Record supplied by publisher]

The first time a nation made research a national priority was probably in 15th Century Portugal. While the Spanish built large galleons to ferry gold from the New World to Madrid, the Portuguese built small caravels to return with something more valuable: information. A National Navigational Institute was established in Sagres, where Prince Henry collated the raw data being delivered by the caravels: latitude, longitude, ocean depths, coastal landmarks, and current. Slowly, the caravels moved down the western coast of Africa, overcame the nautical and psychological obstacle of rounding the Horn, and slowly pushed up the Eastern coast. Each new voyage built on the incremental knowledge gleaned from the last and the certain knowledge of the ultimate goal. When Vasco DiGama reached India, the price of pepper in Venice plunged. A new route to the spice trade had been established, a route which did not require the payment of costly tributes at regular intervals along the land route, and a wealthy Empire which would last two centuries was established. The National Institutes of Health represent this nation's commitment to the importance of basic research. In the history of all mankind there has never been a greater, more consistent, and publically funded investment to understand the biology of human disease. Like the caravels, research laboratories and clinical trials have steadily moved forward with incremental progress toward a clearly visualized goal-the prevention and treatment of human disease. In the area of cancer research, we have clearly rounded the horn. The understanding of cancer at a basic level has now brought new targets for cancer treatment into sharper focus. We now understand cancer as a genetic disease. No longer do our therapies target a single cancer feature, uncontrolled growth. Instead, new vaccines like MART-1, gp100, p53 and ras peptides are targeting the cancer cell's ability to evade immune surveillance. Anti-angiogenesis agents like endostatin, Col-3, and angiostatin promise to inhibit the tumor's ability to make new blood vessels and convert cancer to a static, chronic disease. One advantage to these new angiogenesis inhibitors is their action against normal endothelial cells, rather than targeting the cancer itself. For this reason, the genetic plasticity of tumor cells, and their ability to develop drug resistance, is no longer relevant. The Clinton administration has recently announced its intention to add $4.7 billion to cancer research, essentially reaffirming the nation's initial investment of the National Cancer Act. The commitment could not have been better timed. When grants are funded at the 20th percentile, peer review does not work well. And when managed care makes clinical research nearly impossible, we erode the purpose of basic research and undermine the essence of our mission: the prevention and cure of human disease. The Administration's investment will prove to be wise. With the knowledge at hand, and the ability to translate this knowledge into new diagnostic, preventive and treatment approaches, we can begin to realistically vision cancer cures. A new era is at hand.