Suppression of angiogenesis and tumor growth by the inhibitor K1-5 generated by plasmin-mediated proteolysis

Adiponectin inhibits the growth and peritoneal metastasis of gastric cancer through its specific membrane receptors AdipoR1 and AdipoR2

Adiponectin, a circulating peptide hormone produced in adipose tissue, has been shown to be reduced in the plasma of patients with cancer, suggesting that this adipokine may be mechanically involved in the pathogenesis of adiposity-related carcinogenesis. In this study, we examined the expression of adiponectin receptors (AdipoR1 and AdipoR2) and assessed the function of adiponectin in gastric cancer. All of the six gastric cancer cell lines significantly expressed mRNA and protein of both receptors with variable levels. Addition of 30 microg/mL adiponectin potently induced apoptosis and inhibited the proliferation of AZ521 and HCG27. Down-regulation of either AdipoR1 or AdipoR2 by specific siRNA significantly suppressed the growth inhibitory effects of adiponectin in both cell lines. Moreover, a local injection of adiponectin markedly inhibited the growth of AZ521 inoculated subcutaneously in nude mice. Similarly, the continuous intraperitoneal infusion of adiponectin effectively suppressed the development of peritoneal metastasis of AZ521. Adiponectin negatively regulates the progression of gastric cancer cells possibly through both AdipoR1 and AdipoR2. Although adiponectin was already reported to have antiangiogenic effects, our results suggest that the antitumor effect of adiponectin was, at least partially, dependent on the direct effects on tumor cells.

Kringle 5 of human plasminogen, an angiogenesis inhibitor, induces both autophagy and apoptotic death in endothelial cells

Inhibition of endothelial cell proliferation and angiogenesis is emerging as an important strategy in cancer therapeutics. Kringle 5 (K5) of human plasminogen is a potent angiogenesis inhibitor. Previous studies have shown K5 exposure promotes caspase activity and apoptosis in endothelial cells. Here we report that K5 treatment evokes an autophagic response in endothelial cells that is specific and initiated even in the absence of nutritional stress. Endothelial cells exposed to K5 up-regulated Beclin 1 levels within a few hours. Furthermore, progressively increasing amounts of antiapoptotic Bcl-2 were found to be complexed with Beclin 1, although total levels of Bcl-2 remained unchanged. Prolonged exposure to K5 ultimately led to apoptosis via mitochondrial membrane depolarization and caspase activation in endothelial cells. Knocking down Beclin 1 levels by RNA interference decreased K5 induced autophagy but accelerated K5-induced apoptosis. These studies suggest that interfering with the autophagic survival response can potentiate the antiangiogenic effects of Kringle 5 in endothelial cells.

Plasminogen fragment K1-5 improves survival in a murine hepatocellular carcinoma model

BACKGROUND

The prognosis of patients with hepatocellular carcinoma (HCC) remains poor, and new alternative treatments are needed.

AIMS

To comparatively test the angiostatic and antitumour effects of adenoviral gene transfer of angiostatin (PlgK1-4, amino acids 1-440) and full kringles 1-5 (PlgK1-5, amino acids 1-546) in a model of subcutaneously transferred HCC in mice.

METHODS

PlgK1-4 and PlgK1-5 were generated from human WtPlg cDNA and used for adenovirus construction. Vector function and angiostatic effects were confirmed in vitro and in vivo. Antitumoral efficacies of intratumoral vector injections were studied in a model of subcutaneously transferred HCC model.

RESULTS

Cell supernatants containing PlgK1-4 and PlgK1-5 reduced endothelial tube formation in vitro by about 30%, whereas WtPlg exerted no inhibitory effect. Endothelial cell infiltration in vivo was decreased by about 60%, but not in AdWtPlg-treated animals. Intratumoral treatment of subcutaneous HCC tumours inhibited growth by 40% for AdPlgK1-4 and 63% for AdPlgK1-5 in surviving mice 12 days after initiation of treatment, whereas treatment with AdWtPlg even led to accelerated growth. Although PlgK1-4 and PlgK1-5 have similar inhibitory effects on intratumoral microvessels, PlgK1-5 markedly improved the survival time compared with PlgK1-4.

CONCLUSION

PlgK1-5 and PlgK1-4 effectively inhibited HCC growth. As PlgK1-5 could also prolong the survival time, inducing complete tumour elimination in half of the AdPlgK1-5-treated mice, PlgK1-5 might be the most potential plasminogen fragment for treatment of experimental HCC.

Antiangiogenic plasma activity in patients with systemic sclerosis

OBJECTIVE

Systemic sclerosis (SSc; scleroderma) is a systemic connective tissue disease with an extensive vascular component that includes aberrant microvasculature and impaired wound healing. The aim of this study was to investigate the presence of antiangiogenic factors in patients with SSc.

METHODS

Plasma samples were obtained from 30 patients with SSc and from 10 control patients without SSc. The samples were analyzed for the ability of plasma to affect endothelial cell migration and vascular structure formation and for the presence of antiangiogenic activity.

RESULTS

Exposure of normal human microvascular dermal endothelial cells to plasma from patients with SSc resulted in decreased cell migration (mean +/- SEM 52 +/- 5%) and tube formation (34 +/- 6%) compared with that in plasma from control patients (P < 0.001 for both). SSc plasma contained 2.9-fold more plasminogen kringle 1-3 fragments (angiostatin) than that in control plasma. The addition of angiostatin to control plasma resulted in inhibition of endothelial cell migration and proliferation similar to that observed in SSc plasma. In vitro studies demonstrated that granzyme B and other proteases contained in T cell granule content cleave plasminogen and plasmin into angiostatin fragments.

CONCLUSION

Plasminogen conformation in patients with SSc enables granzyme B and granule content protease to limit the proangiogenic effects of plasmin and increase the levels of antiangiogenic angiostatin. This increase in angiostatin production may account for some of the vascular defects observed in patients with SSc.

Therapeutic Targets of Multiple Angiogenic Factors for the Treatment of Cancer and Metastasis

Like any growing healthy tissues, tumors build up their blood vessels by three mechanisms: angiogenesis, vasculogenesis, and intersucception. Vascular endothelial growth factor-A (VEGF-A) is one of the key factors responsible for stimulation and maintenance of the disorganized, leaky, and torturous tumor vasculature. In addition to VEGF-A, tumors produce multiple other factors to stimulate blood vessel growth. These include members in the platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), VEGF-C, insulin-like growth factor (IGF), angiopoietin (Ang), and hepatocyte growth factor (HGF) families. Recent studies show that these angiogenic factors can also promote lymphangiogenesis and potentially lymphatic metastasis. Understanding the roles of individual and combined angiogenic factors in promoting tumor angiogenesis is crucial for defining therapeutic targets and antiangiogenic drug development for the treatment of cancer.

Differential binding of plasminogen, plasmin, and angiostatin4.5 to cell surface beta-actin: implications for cancer-mediated angiogenesis

Angiostatin4.5 (AS4.5) is the product of plasmin autoproteolysis and consists of kringles 1 to 4 and approximately 85% of kringle 5. In culture, cancer cell surface globular beta-actin mediates plasmin autoproteolysis to AS4.5. We now show that plasminogen binds to prostate cancer cells and that the binding colocalizes with surface beta-actin, but AS4.5 does not bind to the cell surface. Plasminogen and plasmin bind to immobilized beta-actin similarly, with a Kd of approximately 140 nmol/L. The binding is inhibited by epsilon-aminocaproic acid (epsilonACA), indicating the requirement for a lysine-kringle domain interaction. Using a series of peptides derived from beta-actin in competitive binding studies, we show that the domain necessary for plasminogen binding is within amino acids 55 to 69 (GDEAQSKRGILTLKY). Substitution of Lys61 or Lys68 with arginine results in the loss of the ability of the peptide to block plasminogen binding, indicating that Lys61 and Lys68 are essential for plasminogen binding. Other actin peptides, including peptides with lysine, did not inhibit the plasminogen-actin interaction. AS4.5 did not bind actin at concentrations up to 40 micromol/L. Plasminogen, plasmin, and AS4.5 all contain kringles 1 to 4; however, kringle 5 is truncated in AS4.5. Isolated kringle 5 binds to actin, suggesting intact kringle 5 is necessary for plasminogen and plasmin to bind to cell surface beta-actin, and the truncated kringle 5 in AS4.5 results in its release from beta-actin. These data may explain the mechanism by which AS4.5 is formed locally on cancer cell surfaces and yet acts on distant sites.

Liposome-mediated gene transfer of K1-5 suppresses tumor development and improves the prognosis of hepatocellular carcinoma in mice

It has been reported that kringle 1-5 (K1-5) has a potent and specific antiangiogenic activity. In the present study, we investigated the antitumor effect of gene transfer of K1-5 for hepatocellular carcinoma in mice. Inhibitory effect by the media of Cos-1 cells containing K1-5 on bovine capillary endothelial (BCE) cell proliferation was evaluated by a tetrazolium-based assay. For tumor growth, intrahepatic metastasis, and survival studies, intravenous injection of liposome-K1-5 cDNA complexes was performed to nude mice implanted with three hepatoma cell lines into the liver. Production of K1-5 was investigated by immunohistochemistry and Western blotting. The number of vessels in the tumor was counted in 0.125 mm2 fields. Expression of vascular endothelial growth factor (VEGF) and angiopoietin (Ang)-1 and -2 in tumors was investigated by Western blotting. Serum ALT levels and body weight of the mice were measured. Proliferation of BCE cells was inhibited by 44% in the media containing K1-5. Gene transfer of K1-5 suppressed tumor growth of the three hepatoma cell lines, respectively. In the K1-5-treated group, survival period was prolonged and the number of intrahepatic metastases was reduced. Expression of K1-5 protein was detected on hepatoma cells and hepatocytes. The number of vessels in tumor tissues was decreased by K1-5 transfection. Expression of angiopoietin-2 in tumor tissues was suppressed by K1-5 transfection. Serum ALT levels and body weight of mice were not influenced by K1-5 transfection. These findings suggest that antiangiogenic gene therapy with K1-5 cDNA will be a safe and effective strategy to suppress the growth of hepatocellular carcinoma.

Simultaneous metal chelate affinity purification and endotoxin clearance of recombinant antibody fragments

Endotoxins are frequent contaminants of recombinant proteins produced in Escherichia coli. Due to their adverse effects, endotoxins have to be removed from recombinant proteins prior their use in cell-based assays or parenteral application. Reduction of endotoxin to less than 10 EU mg(-1) is, however, one of the most problematic steps during protein purification from E. coli and often associated with substantial loss of biological materials. The present paper describes the use of a single step procedure enabling metal chelate affinity purification and endotoxin clearance from antibody fragments produced in E. coli using a non-ionic detergent. Endotoxin content was as low as 5 to 9 EU mg(-1) with a recovery of antibody fragments of over 90%. Non-ionic detergent treatment did not compromise integrity and functionality of these multimeric molecules. Furthermore, recombinant antibody fragments did not stimulate endotoxin-sensitive cell lines confirming the low endotoxin content. In conclusion, this one-step protocol is a rapid, cost effective and automation-compatible procedure suitable for recombinant antibody fragments.

Adeno-associated virus-mediated expression of apolipoprotein (a) kringles suppresses hepatocellular carcinoma growth in mice

Hepatocellular carcinoma (HCC) constitutes more than 90% of all primary liver cancers. HCC is a hypervascular tumor that develops from dedifferentiation of small avascular HCC and is therefore a good target for anti-angiogenic gene therapy. Recent studies have identified apolipoprotein(a) [apo(a)] kringles LK68 and LK8 (LKs) as having a potential antiangiogenic and anti-tumor activity, and the current study evaluates the therapeutic potential of gene therapy with recombinant adeno-associated virus carrying genes encoding LKs (rAAV-LK) in the treatment of hypervascular HCC. We generated rAAV-LK to obtain persistent transgene expression in vivo, which is essential for anti-angiogenic therapy. The rAAV-produced LKs substantially inhibited proliferation and migration of human umbilical vein endothelial cells (HUVECs) in vitro, validating their anti-angiogenic potential. Intramuscular administration of rAAV-LK gave 60% to 84% suppression (P < .05) of tumor growth in mice bearing subcutaneously transplanted HCC derived from Huh-7 and Hep3B cells, respectively. Histological and immunohistochemical analyses of HCC tumor sections showed that a single administration of rAAV-LK gave rise to persistent expression of LKs that inhibited tumor angiogenesis and triggered tumor apoptosis, and, thus, significantly suppressed tumor growth. The administration of rAAV-LK provided a significant survival benefit (P < .05), and 3 of 10 rAAV-LK-treated mice were still alive without visible tumors and without clinical symptoms 188 days after treatment. In conclusion, rAAV-LK is a potential candidate for anti-angiogenic gene therapy in the treatment of HCC.

Gene transfer of kringle 1-5 suppresses tumor development and improves prognosis of mice with hepatocellular carcinoma

BACKGROUND & AIMS

Recent studies indicate that kringle 1-5 has a potent and specific antiangiogenic activity. Here, we investigated the antitumor effect of kringle 1-5 gene transfer on hepatocellular carcinoma in mice.

METHODS

The inhibitory effect of kringle 1-5 protein on proliferation of bovine capillary endothelial cells was evaluated by a tetrazolium-based assay. To study tumor growth, intrahepatic metastasis, and survival, liposome/kringle 1-5 complementary DNA complexes were injected intravenously in nude mice preimplanted with 1 of 3 hepatoma cell lines into the liver. Production of kringle 1-5 was tested by immunohistochemistry and Western blotting. Intratumoral vessel density was quantified. Expression of vascular endothelial growth factor, angiopoietin-1, and angiopoietin-2 in tumors was examined by Western blotting. Serum alanine aminotransferase and alpha-fetoprotein levels and body weights were measured.

RESULTS

Proliferation of bovine capillary endothelial cells was inhibited by purified kringle 1-5 in a dose-dependent manner. Gene transfer of kringle 1-5 caused a significant reduction in vessel density with suppression of tumor growth of the 3 hepatoma cell lines and serum alpha-fetoprotein levels, prolonged the survival period, and reduced the number of intrahepatic metastases. Among the analyzed angiogenic factors, kringle 1-5 reduced angiopoietin-2 expression levels. Expression of kringle 1-5 protein was detected on hepatoma cells and hepatocytes in the liver. However, it did not alter serum alanine aminotransferase levels and body weights, suggesting kringle 1-5 lacks severe side effects.

CONCLUSIONS

Antiangiogenic gene therapy with kringle 1-5 complementary DNA is a promising safe and effective strategy for suppression of growth of hepatocellular carcinoma.

From gene profiling to diagnostic markers: IL-18 and FGF-2 complement CA125 as serum-based markers in epithelial ovarian cancer

We used an oligonucleotide-based DNA microarray to identify potential markers in 39 primary cultures of ovarian cancer specimens compared with 11 primary cultures of normal ovarian epithelia. Differential gene expression of IL-18 and FGF-2 was validated on a subset of samples by quantitative PCR and by IHC, using an independent tissue array of 90 cores of 20 normal ovarian surface epithelia and 70 EOCs representing different grades and pathologies of ovarian disease. We further compared, by ELISA, these two markers with CA125 in sera from 25 cancer-free and 47 ovarian cancer patients. IL-18 and FGF-2 proteins were significantly elevated in tumor tissues (p<0.04) and sera (p<0.05) from patients with ovarian cancer. In combination, the three markers (IL-18, FGF-2, and CA125) showed similar sensitivity in scoring for ovarian cancer (35/45 patients) compared to that of CA125 alone (37/45) and significantly improved the specificity of detection (20/25 patients) compared to each marker individually (15/25 for CA125; 18/25 FGF-2; 16/25 for IL-18). In conclusion we show that a combination of the three serum markers (IL-18, FGF-2 and CA125) is associated with EOC, with higher specificity than CA125 alone. Prospective studies with a large cohort of susceptible ovarian cancer patients will be required to expand these findings.

Specific conformational changes of plasminogen induced by chloride ions, 6-aminohexanoic acid and benzamidine, but not the overall openness of plasminogen regulate, production of biologically active angiostatins

The overall conformation of plasminogen depends upon the presence of anions and molecules such as AHA (6-aminohexanoic acid) and BZ (benzamidine). The purpose of the present study was to determine the effect of conformation on the initial and secondary cleavages of plasminogen to generate active angiostatins. Plasminogen was digested with the physiologically relevant neutrophil elastase in one of the four Tris/acetate buffers: buffer alone or buffer plus NaCl, AHA or BZ. The initial cleavage of Glu1-plasminogen was much slower in the tight NaCl-induced alpha-conformation, fastest in the intermediate BZ-induced beta-conformation and intermediate both in the control and in the AHA-induced open gamma-conformation. Although the buffer system determined the relative amounts of the initial cleavage products, the same four cleavage sites were utilized under all conditions. A fifth major initial cleavage within the protease domain was observed in the presence of BZ. N-terminal peptide cleavage required for angiostatin formation occurred as either the initial or the secondary cleavage. Angiostatins were generated fastest in the presence of BZ and slowest in the presence of NaCl. Both the initial and secondary cleavages were affected by the modifying agents, indicating that they influence the conformation of both Glu-plasminogen and the initial cleavage products. The angiostatins produced under the different conditions inhibited proliferation of human umbilical-vein endothelial cells. These results suggest that plasminogen conversion into active angiostatins is dependent more on the specific conformation changes induced by the various modifying reagents rather than on the overall openness of the molecule.

Adiponectin in relation to childhood myeloblastic leukaemia

Adiponectin, an adipocyte-specific secretory protein known to induce apoptosis, has been reported to be inversely related to breast and endometrial cancers and recently found to inhibit proliferation of myeloid but not lymphoid cell lines. We hypothesised that adiponectin may be inversely associated with acute myeloblastic leukaemia (AML), but not with acute lymphoblastic leukaemia of B (ALL-B) or T (ALL-T) cell origin in children. Blood samples and clinical information were collected over the period 1996–2000 from 201 children (0–14 years old) with leukaemia (22 AML, 161 ALL-B and 18 ALL-T cases) through a national network of childhood Hematology-Oncology units in Greece and from 201 controls hospitalised for minor pediatric ailments. Serum adiponectin levels were measured under code, at the Beth Israel Deaconess Medical Center, Boston, MA, USA using a radioimmunoassay procedure. Each of the three leukaemia groups was compared with the control group through multiple logistic regression. Odds ratios (OR) and 95% confidence intervals (95% CI) for an increase of adiponectin equal to 1 s.d. among controls were estimated controlling for gender, age, as well as for height and weight, expressed in age–gender-specific centiles of Greek growth curves. Adiponectin was inversely associated with AML (OR=0.56; 95% CI, 0.34–0.94), whereas it was not significantly associated with either ALL-B (OR=0.88; 95% CI, 0.71–1.10) or ALL-T (OR=1.08; 95% CI, 0.67–1.72). Biological plausibility and empirical evidence point to the importance of this hormone in the pathogenesis of childhood AML.

Expression of recombinant kringle 1-5 domains of human plasminogen by a prokaryote expression system

Kringle1-5 (K1-5), a proteolytic fragment containing five kringle domains of human plasminogen generated by plasmin-mediated proteolysis, has been already identified by Cao et al. with relation to anti-angiogenesis and proliferation of endothelial cells. To investigate anti-angiogenesis activity of recombinant human K1-5 (rhK1-5) expressed in Escherichia coli BL21, the cDNA of human K1-5 obtained from cloning vector pUC57-K1-5 by PCR, was inserted into an expression vector pET30(+) to construct a prokaryotic expression vector pET-K1-5. Recombinant K1-5 efficiently expressed in E. coli BL21 after IPTG induction was monitored by SDS-PAGE and Western blotting with an anti-angiostatin monoclonal antibody and an anti-hexahistidine tag antibody. The expressed K1-5 accounted for approximately 32% of the total bacterial proteins as estimated by densitometry, and existed mainly as inclusion bodies. The inclusion bodies were washed, lysed, purified, and refolded to a purity of 96% as estimated by capillary electrophoresis and the final purification yield of K1-5 in E. coli system was approximately 5.8 mg/L. Purified K1-5 protein was tested on chicken embryo chorioallantoic membranes (CAMs), and a large number of newly formed blood vessels were significantly regressed. In the present study, we demonstrated that bacterial-expressed K1-5 effectively inhibited angiogenesis of the chicken embryo in a dose-dependent manner through CAM assay. In addition, the rhK1-5 potently inhibited endothelial cell proliferation but not non-endothelial cells. For the first time, these findings demonstrate that the rhK1-5 produced by a prokaryote expression system effectively inhibited angiogenesis of the chicken embryo in a dose-dependent manner and specially suppressed in vitro the proliferation of human umbilical vein endothelial cells. This fact derived from the present study further suggests the rhK1-5 can be used for anti-angiogenesis therapy of cancer.

Gene transfer for the treatment of neovascular ocular disease (an American Ophthalmological Society thesis)

PURPOSE

As vasoproliferative diseases account for a substantial fraction of worldwide blindness and share the activation of the angiogenic pathway as a common etiology, the expression of antiangiogenic proteins offers a promising means of treatment. This study was designed to develop viral vectors, harboring angiostatic genes, for the study and treatment of experimental proliferative ocular disease. A variety of methods (in vitro, ex vivo tissue, and in vivo) were employed to model the process of proliferation and test the effectiveness of these reagents.

METHODS

Antiangiogenic genes included single genes as well as hybrid genes that fused the active elements of different genes. Genes studied included the soluble vascular endothelial growth factor receptor (sKDR), soluble neuropilin (sNRP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1), plasminogen gene fragments (Kringle 1-3, 1-4, and 1-5), and soluble receptors for advanced glycosylation end products (sRAGE) genes, as well as the Endo:Ang, MIG:IP10, and Endo:Kringle5 fusion genes. All genes were cloned into a lentiviral vector system and were used to produce replication deficient lentiviral particles. These viral particles were used to transduce a variety of ocular cells and tissues to test viral transfer efficiency and transgene expression. In vivo systems were employed to explore the potential of these genes as antiangiogenic agents in models of corneal and retinal neovascular disease.

RESULTS

Recombinant lentiviral particles, capable of transducing cell lines germane to eye disease (ocular endothelial, epithelial, and fibroblast cells), were successfully produced. These vectors were demonstrated to be effective in long-term transformation of cells and tissues. In vivo experiments confirmed that at least three different potentially angiostatic genes were successful in aborting the angiogenic process in the ocular models tested.

CONCLUSIONS

Lentiviral vectors are a viable means to deliver angiostatic genes to tissues of the eye. Some angiostatic genes appear to have a stronger and longer-lasting effect than others in modulating the angiogenic pathway.

A branched histidine/lysine peptide, H2K4b, in complex with plasmids encoding antitumor proteins inhibits tumor xenografts

BACKGROUND

In this study we investigated whether a particular branched HK polymer, H2K4b, was an effective in vivo carrier of plasmids expressing the antiangiogenic kringle 1-5 or the tumor suppressor p53.

METHODS

H2K4b was synthesized on a solid-phase peptide synthesizer. Distribution, optimization and time course studies were done in tumor-bearing nude mice by systemically administering H2K4b in complex with a luciferase-expressing plasmid. We examined the amount of tumor angiogenesis in C6 with MDA-MB-435 xenografts utilizing the carmine dye. The ability of H2K4b to carry luciferase plasmids to different tissues was compared with several liposomal carriers. Medium from cells transfected with mKr1-5 was tested for its capacity to inhibit angiogenesis with an in vivo Matrigel assay. We then determined if systemically delivered H2K4b in complex with plasmid encoding mKr1-5 inhibited tumor growth; we also compared the antitumor activity of HK polyplexes containing hKr1-5, mKr1-5, and p53 plasmids.

RESULTS

H2K4b carried the luciferase-expressing plasmid in order of descending efficacy to these tissues: lung, spleen, tumor, and liver. Compared to DOTAP-containing liposomes, H2K4b was a more effective carrier of a luciferase-containing plasmid to extrapulmonary tissues. We then determined that mKr1-5 in complex with H2K4b reduced MDA-MB-435 tumor growth by approximately 50% compared to the control group (P < 0.01). Similarly, H2K4b/mKr1-5 polyplexes reduced the growth of C6 xenografts. In MDA-MB-435 xenografts, p53- and Kr1-5-expressing plasmids in complex with H2K4b had comparable antitumor activity.

CONCLUSION

H2K4b demonstrates potential as a carrier of plasmids encoding antiangiogenic and/or tumor suppressor proteins in a tumor-bearing mouse model.

Vascular endothelial growth factor-a promotes peritumoral lymphangiogenesis and lymphatic metastasis

Metastases are commonly found in the lymphatic system. The molecular mechanism of lymphatic metastasis is, however, poorly understood. Here we report that vascular endothelial growth factor (VEGF)-A stimulated lymphangiogenesis in vivo and that overexpression of VEGF-A in murine T241 fibrosarcomas induced the growth of peritumoral lymphatic vessels, which occasionally penetrated into the tumor tissue. As a result of peritumoral lymphangiogenesis, metastases in lymph nodes of mice were detected. VEGF-A-overexpressing tumors contained high numbers of infiltrating inflammatory cells such as macrophages, which are known to express VEGF receptor (VEGFR)-1. It seemed that in the mouse cornea, VEGF-A stimulated lymphangiogenesis through a VEGF-C/-D/VEGFR-3-independent pathway as a VEGFR-3 antagonist selectively inhibited VEGF-C-induced, but not VEGF-A-induced, lymphangiogenesis. Our data show that VEGF-A contributes to lymphatic mestastasis. Thus, blockage of VEGF-A-induced lymphangiogenesis may provide a novel approach for prevention and treatment of lymphatic metastasis.

Plasminogen kringle 5-engineered glioma cells block migration of tumor-associated macrophages and suppress tumor vascularization and progression

Angiostatin, a well-characterized angiostatic agent, is a proteolytic cleavage product of human plasminogen encompassing the first four kringle structures. The fifth kringle domain (K5) of human plasminogen is distinct from angiostatin and has been shown, on its own, to act as a potent endothelial cell inhibitor. We propose that tumor-targeted K5 cDNA expression may act as an effective therapeutic intervention as part of a cancer gene therapy strategy. In this study, we provide evidence that eukaryotically expressed His-tagged human K5 cDNA (hK5His) is exported extracellularly and maintains predicted disulfide bridging conformation in solution. Functionally, hK5His protein produced by retrovirally engineered human U87MG glioma cells suppresses in vitro migration of both human umbilical vein endothelial cells and human macrophages. Subcutaneous implantation of Matrigel-embedded hK5His-producing glioma cells in nonobese diabetic/severe combined immunodeficient mice reveals that hK5His induces a marked reduction in blood vessel formation and significantly suppresses the recruitment of tumor-infiltrating CD45+ Mac3+ Gr1- macrophages. Therapeutically, we show in a nude mouse orthotopic brain cancer model that tumor-targeted K5 expression is capable of effectively suppressing glioma growth and promotes significant long-term survival (>120 days) of test animals. These data suggest that plasminogen K5 acts as a novel two-pronged anticancer agent, mediating its inhibitory effect via its action on host-derived endothelial cells and tumor-associated macrophages, resulting in a potent, clinically relevant antitumor effect.

Vasculostatin, a proteolytic fragment of brain angiogenesis inhibitor 1, is an antiangiogenic and antitumorigenic factor

Brain angiogenesis inhibitor 1 (BAI1) is a transmembrane protein with unknown function expressed primarily in normal but not tumoral brain. The finding of thrombospondin type 1 repeats in its extracellular domain suggested an antiangiogenic function, but the mechanisms by which a transmembrane receptor could inhibit angiogenesis remained unexplained. Here we demonstrate that BAI1 is proteolytically cleaved at a conserved G-protein-coupled receptor proteolytic cleavage site (GPS), releasing its 120 kDa extracellular domain. We named this secreted fragment Vasculostatin as it inhibited migration of endothelial cells in vitro and dramatically reduced in vivo angiogenesis. Both constitutive and doxycycline-induced expression of Vasculostatin elicited dose-dependent suppression of tumor growth and vascular density in mice, implicating Vasculostatin in the regulation of vascular homeostasis and tumor prevention. Generation of a soluble antiangiogenic factor by cleavage of a pre-existing transmembrane protein represents a novel mechanism for regulating vascular homeostasis and preventing tumorigenesis. Modulation of this cleavage or delivery of Vasculostatin may constitute novel treatment modalities for cancer and other diseases of aberrant angiogenesis, especially in the brain.

Cotargeting tumor and tumor endothelium effectively inhibits the growth of human prostate cancer in adenovirus-mediated antiangiogenesis and oncolysis combination therapy

Tumor-endothelial interaction contributes to local prostate tumor growth and distant metastasis. In this communication, we designed a novel approach to target both cancer cells and their "crosstalk" with surrounding microvascular endothelium in an experimental hormone refractory human prostate cancer model. We evaluated the in vitro and in vivo synergistic and/or additive effects of a combination of conditional oncolytic adenovirus plus an adenoviral-mediated antiangiogenic therapy. In the in vitro study, we demonstrated that human umbilical vein endothelial cells (HUVEC) and human C4-2 androgen-independent (AI) prostate cancer cells, when infected with an antiangiogenic adenoviral (Ad)-Flk1-Fc vector secreting a soluble form of Flk1, showed dramatically inhibited proliferation, migration and tubular formation of HUVEC endothelial cells. C4-2 cells showed maximal growth inhibition when coinfected with Ad-Flk1-Fc and Ad-hOC-E1, a conditional replication-competent Ad vector with viral replication driven by a human osteocalcin (hOC) promoter targeting both prostate cancer epithelial and stromal cells. Using a three-dimensional (3D) coculture model, we found that targeting C4-2 cells with Ad-hOC-E1 markedly decreased tubular formation in HUVEC, as visualized by confocal microscopy. In a subcutaneous C4-2 tumor xenograft model, tumor volume was decreased by 40-60% in animals treated with Ad-Flk1-Fc or Ad-hOC-E1 plus vitamin D3 alone and by 90% in a combined treatment group, compared to untreated animals in an 8-week treatment period. Moreover, three of 10 (30%) pre-established tumors completely regressed when animals received combination therapy. Cotargeting tumor and tumor endothelium could be a promising gene therapy strategy for the treatment of both localized and metastatic human prostate cancer.

Bacillolysin MA, a Novel Bacterial Metalloproteinase That Produces Angiostatin-like Fragments from Plasminogen and Activates Protease Zymogens in the Coagulation and Fibrinolysis Systems

We isolated a novel protease that converts plasminogen to angiostatin-like fragments (BL-angiostatins) from a culture of Bacillus megaterium A9542 through a single-step chromatography on CM-cellulose. The protease, designated bacillolysin MA (BL-MA), belongs to a family of neutral metalloproteinases based on the nucleotide sequence of its gene. At an enzyme:substrate ratio of 1:540, BL-MA cleaved human plasminogen mainly at Ser441-Val442 to form BL-angiostatin and miniplasminogen with a K(m) of 3.0 +/- 0.8 microM and a k(cat) of 0.70 +/- 0.09 s(-1). The resulting BL-angiostatins inhibited the proliferation, migration, and tube formation of vascular endothelial cells at concentrations of 1-10 microg/ml. Although BL-MA failed to activate plasminogen, it increased urokinase-catalyzed activation of plasminogen caused by production of miniplasminogen, which is highly susceptible to activation. In addition, BL-MA was active in converting prourokinase, prothrombin, coagulation factor X, and protein C to their active forms. BL-MA enhanced both the clotting of human plasma and clot dissolution in the presence of prourokinase. Thus, BL-MA affects blood coagulation and fibrinolysis systems and can be used to produce angiostatin-like plasminogen fragments and active serine proteases of human plasma.

Evidence of human thrombomodulin domain as a novel angiogenic factor

BACKGROUND

Thrombomodulin is an anticoagulant, endothelial-cell-membrane glycoprotein. A recombinant thrombomodulin domain containing 6 epidermal growth factor-like structures exhibits mitogenic activity. This study explored the novel angiogenic effects of the recombinant domain using in vitro and in vivo models.

METHODS AND RESULTS

Human recombinant thrombomodulin containing 6 epidermal growth factor-like structures (TMD2) and TMD2 plus a serine and threonine-rich domain (TMD23) were prepared using the Pichia pastoris expression system. Combined with purified TMD2 or TMD23, thrombin effectively activated protein C. TMD23 had higher activity than TMD2 in stimulating DNA synthesis in cultured human umbilical vein endothelial cells. Additionally, TMD23 stimulated chemotactic motility and capillarylike tube formation in human umbilical vein endothelial cells, an effect mediated through phosphorylation of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase and the phosphatidylinositol-3 kinase/Akt/endothelial nitric oxide synthase pathway. TMD23 also stimulated endothelial cell expression of matrix metalloproteinases and plasminogen activators, which mediated extracellular proteolysis, leading to endothelial cell invasion and migration during angiogenesis. Furthermore, TMD23-containing implants in rat cornea induced ingrowth of new blood vessels from the limbus. With the murine angiogenesis assay, TMD23 not only induced neovascularization coinjected with Matrigel and heparin but also enhanced angiogenesis in Matrigel containing melanoma A2058 cells in nude mice.

CONCLUSIONS

The recombinant thrombomodulin domain TMD23 enhanced the angiogenic response in vitro and in vivo, suggesting that thrombomodulin fragments may play a role in the formation of new vessels. These findings may provide a new therapeutic option for treating ischemic diseases.

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.

Antiangiogenic activity of a domain deletion mutant of tissue plasminogen activator containing kringle 2

OBJECTIVE

The thrombolytic therapy drug, Reteplase, is a domain deletion mutant of tissue plasminogen activator (tPA), comprising the kringle 2 and protease (K2P) domains. Some kringle domains of hemostatic proteins are antiangiogenic and promote apoptosis. The objective of this study was to investigate whether K2P is an angiogenesis inhibitor because of the presence of kringle 2.

METHODS AND RESULTS

K2P inhibited basic fibroblast growth factor-induced human endothelial cell proliferation and migration. Inhibition was not dependent on the protease activity of K2P because similar results were obtained with catalytically inactivated K2P. Purification of the kringle 2 domain derived from elastase cleavage of K2P at the Arg275-Ile276 bond revealed that inhibition was mediated by this domain. In addition, K2P inhibited angiogenesis in vivo and increased endothelial cell apoptosis.

CONCLUSIONS

Wound healing and angiogenesis are severely compromised by K2P. These data provide new mechanistic insights into the bleeding complications observed in some patients while undergoing thrombolytic therapy with this drug. In addition, we identify the kringle 2 domain of tPA as a novel target for antiangiogenic therapy.

Antiangiogenic cancer therapy

Like most embryonic tissues, tumors have the ability to build up their own blood vessel networks. However, the architecture of tumor vessels is fundamentally different from that found in healthy tissues. Tumor vessels are usually irregular, heterogeneous, leaky, and poorly associated with mural cells. Endothelial cells in tumor vessels are also disorganized and express imbalanced surface molecules. These unusual features may provide some molecular and structural basis for selective inhibition or even destruction of tumor vessels by angiogenesis inhibitors. In animal tumor models, several angiogenesis inhibitors seem to inhibit tumor angiogenesis specifically without obvious effects on the normal vasculature. As a result, these inhibitors produced potent antitumor effects in mice. Excited by these preclinical studies, more than 60 angiogenesis inhibitors are being evaluated for their anticancer effects in human patients. Although the ultimate outcome of antiangiogenic clinical trials remains to be seen, several early observations have reported some disappointing results. These early clinical data have raised several important questions. Can we cure human cancers with angiogenesis inhibitors? Have we found the ideal angiogenesis inhibitors for therapy? What is the difference between angiogenesis in an implanted mouse tumor and in a spontaneous human tumor? What are the molecular mechanisms of these angiogenesis inhibitors? Should angiogenesis inhibitors be used alone or in combinations with other existing anticancer drugs? In this review, we will discuss these important issues in relation to ongoing antiangiogenic clinical trials.

PDGF-BB induces intratumoral lymphangiogenesis and promotes lymphatic metastasis

Cancer metastases are commonly found in the lymphatic system. Like tumor blood angiogenesis, stimulation of tumor lymphangiogenesis may require the interplay of several tumor-derived growth factors. Here we report that members of the PDGF family act as lymphangiogenic factors. In vitro, PDGF-BB stimulated MAP kinase activity and cell motility of isolated lymphatic endothelial cells. In vivo, PDGF-BB potently induced growth of lymphatic vessels. Expression of PDGF-BB in murine fibrosarcoma cells induced tumor lymphangiogenesis, leading to enhanced metastasis in lymph nodes. These data demonstrate that PDGF-BB is an important growth factor contributing to lymphatic metastasis. Thus, blockage of PDGF-induced lymphangiogenesis may provide a novel approach for prevention and treatment of lymphatic metastasis.

Endothelial Cell Surface ATP Synthase-Triggered Caspase-Apoptotic Pathway Is Essential for K1-5-Induced Antiangiogenesis

We have recently reported the identification of kringle 1-5 (K1-5) of plasminogen as a potent and specific inhibitor of angiogenesis and tumor growth. Here, we show that K1-5 bound to endothelial cell surface ATP synthase and triggered caspase-mediated endothelial cell apoptosis. Induction of endothelial apoptosis involved sequential activation of caspases-8, -9, and -3. Administration of neutralizing antibodies directed against the alpha- and beta-subunits of ATP synthase to endothelial cells attenuated activation of these caspases. Furthermore, inhibitors of caspases-3, -8, and -9 also remarkably blocked K1-5-induced endothelial cell apoptosis and antiangiogenic responses. In a mouse tumor model, we show that caspase-3 inhibitors abolished the antitumor activity of K1-5 by protecting the tumor vasculature undergoing apoptosis. These results suggest that the specificity of the antiendothelial effect of K1-5 is attributable, at least in part, to its interaction with the endothelial cell surface ATP synthase and that the caspase-mediated endothelial apoptosis is essential for the angiostatic activity of K1-5. Thus, our findings provide a mechanistic insight with respect to the angiostatic action and signaling pathway of K1-5 and angiostatin.

Adiponectin-induced antiangiogenesis and antitumor activity involve caspase-mediated endothelial cell apoptosis

Obesity is a risk factor for the development of many severe human diseases such as cardiovascular disorders, diabetes, and cancer, which are tightly linked to angiogenesis. The adipose tissue produces several growth factors/hormones including leptin, tumor necrosis factor alpha, and adiponectin. It has been found that adiponectin levels are reduced in obesity. Here, we report a unique function of adiponectin as a negative regulator of angiogenesis. In vitro, adiponectin potently inhibits endothelial cell proliferation and migration. In the chick chorioallantoic membrane and the mouse corneal angiogenesis assays, adiponectin remarkably prevents new blood vessel growth. Further, we demonstrate that the antiendothelial mechanisms involve activation of caspase-mediated endothelial cell apoptosis. Adiponectin induces a cascade activation of caspases-8, -9, and -3, which leads to cell death. In a mouse tumor model, adiponectin significantly inhibits primary tumor growth. Impaired tumor growth is associated with decreased neovascularization, leading to significantly increased tumor cell apoptosis. These data demonstrate induction of endothelial apoptosis as an unique mechanism of adiponectin-induced antiangiogenesis. Adiponectin, as a direct endogenous angiogenesis inhibitor, may have therapeutic implications in the treatment of angiogenesis-dependent diseases.

Treatment of colorectal and hepatocellular carcinomas by adenoviral mediated gene transfer of endostatin and angiostatin-like molecule in mice

AIM AND METHOD

In this study, we explored the responsiveness of different tumour entities (colorectal carcinoma (CRC), hepatocellular carcinoma (HCC), and the murine Lewis lung carcinoma (LLC)) to angiostatic antitumour treatment with two recombinant adenoviral vectors encoding angiostatin-like molecule (AdK1-3) and endostatin (Adendo).

RESULTS

AdK1-3 and Adendo exerted inhibitory biological functions on endothelial cell proliferation, migration, and tube formation in vitro. AdK1-3 inhibited significantly endothelial cell infiltration in vascular endothelial growth factor embedded Matrigel plugs in mice whereas Adendo showed only minor effects. Both AdK1-3 and Adendo induced similar antitumour effects in the LLC tumour model in immune competent C57BL/6 mice but AdK1-3 had stronger inhibitory effects in athymic mice. Furthermore, AdK1-3 inhibited tumour growth in a murine CRC and human HCC model but was ineffective in a human CRC model. In contrast, Adendo did not reduce tumour progress in either of these tumour models although AdK1-3 and Adendo effectively reduced intratumoral microvessel density in LLC tumours.

CONCLUSION

Our data demonstrate that angiostatic gene therapy may form a feasible strategy for the treatment of established hepatocellular carcinomas and that in vivo antitumour efficacy of angiostatic proteins is tumour specific.

Identification and Characterization of a Novel Angiostatin-binding Protein by the Display Cloning Method

Angiostatin is a potent anti-angiogenic protein. To examine the angiostatin-interacting proteins, we used the display-cloning method with a T7 phage library presenting human cDNAs. The specific T7 phage clone that bound to the immobilized angiostatin was isolated, and a novel gene encoding the displayed polypeptide on the isolated T7 phage was identified. The displayed angiostatin-binding sequence was expressed in E. coli as a soluble protein and purified to homogeneity. This novel angiostatin-binding region interacted specifically to angiostatin with a dissociation constant of 3.4 x 10(-7) M. A sequence analysis showed that the identified sequence was a part of the large ORF of 1,998 amino acids, whose function has not yet been characterized. A Northern analysis indicated that the gene containing the angiostatin-binding sequence was expressed differentially in the developmental stages or cell types.

Nonlysine-analog plasminogen modulators promote autoproteolytic generation of plasmin(ogen) fragments with angiostatin-like activity

We recently discovered several nonlysine-analog conformational modulators for plasminogen. These include SMTP-6, thioplabin B and complestatin that are low molecular mass compounds of microbial origin. Unlike lysine-analog modulators, which increase plasminogen activation but inhibit its binding to fibrin, the nonlysine-analog modulators enhance both activation and fibrin binding of plasminogen. Here we show that some nonlysine-analog modulators promote autoproteolytic generation of plasmin(ogen) derivatives with its catalytic domain undergoing extensive fragmentation (PMDs), which have angiostatin-like anti-endothelial activity. The enhancement of urokinase-catalyzed plasminogen activation by SMTP-6 was followed by rapid inactivation of plasmin due to its degradation mainly in the catalytic domain, yielding PMD with a molecular mass ranging from 68 to 77 kDa. PMD generation was observed when plasmin alone was treated with SMTP-6 and was inhibited by the plasmin inhibitor aprotinin, indicating an autoproteolytic mechanism in PMD generation. Thioplabin B and complestatin, two other nonlysine-analog modulators, were also active in producing similar PMDs, whereas the lysine analog 6-aminohexanoic acid was inactive while it enhanced plasminogen activation. Peptide sequencing and mass spectrometric analyses suggested that plasmin fragmentation was due to cleavage at Lys615-Val616, Lys651-Leu652, Lys661-Val662, Lys698-Glu699, Lys708-Val709 and several other sites mostly in the catalytic domain. PMD was inhibitory to proliferation, migration and tube formation of endothelial cells at concentrations of 0.3-10 microg.mL(-1). These results suggest a possible application of nonlysine-analog modulators in the treatment of cancer through the enhancement of endogenous plasmin(ogen) fragment formation.

Matrix metalloproteinases and matrikines in angiogenesis

Neoangiogenesis, the formation of new blood capillaries from pre-existing vessels, plays an important role in a number of physiological and pathological processes, particularly in tumor growth and metastasis. Extracellular proteolysis by matrix metalloproteinases or other neutral proteinases is an absolute requirement for initiating tumor invasion and angiogenesis. Cryptic segments or pre-existing domains within larger proteins, most of them belonging to the extracellular matrix, can be exposed by conformational changes and/or generated by partial enzymatic hydrolysis. They can positively or negatively regulate important functions of endothelial cells including adhesion, migration, proliferation, cell survival and cell-cell interactions. Such regulations by cryptic segments and proteolytic fragments led to the concept of matricryptins and matrikines, respectively. Matrix metalloproteinases and matrikines in conjunction with other pro- or anti-angiogenic factors might act in concert at any step of the angiogenesis process. A number of matrikines have been identified as potent anti-angiogenic factors, which could provide a new alternative to anti-proteolytic strategies for the development of anti-angiogenic therapeutic molecules aimed at inhibiting tumor growth and metastasis. Some of them are currently being investigated in clinical trials.

Kringle 5 peptide–albumin conjugates with anti-migratory activity

Three peptide fragments of the kringle 5 region of plasminogen and their respective N- and C-terminus maleimido derivatives conjugated to Cys34 of human serum albumin were evaluated in vitro using a human umbilical vein endothelial cell (HUVEC) migration assay and a human plasma stability assay. The N-terminus maleimido derivative of the 64 to 74 segment of kringle 5 conjugated to human serum albumin possessed remarkable anti-migratory activity.

Cell Surface-Dependent Generation of Angiostatin4.5

Angiostatin4.5 (AS4.5) is a naturally occurring human angiostatin isoform, consisting of plasminogen kringles 1-4 plus 85% of kringle 5 (amino acids Lys78 to Arg529). Prior studies indicate that plasminogen is converted to AS4.5 in a two-step reaction. First, plasminogen is activated to plasmin. Then plasmin undergoes autoproteolysis within the inner loop of kringle 5, which can be induced by a free sulfhydryl donor or an alkaline pH. We now demonstrate that plasminogen can be converted to AS4.5 in a cell membrane-dependent reaction. Actin was shown previously to be a surface receptor for plasmin(ogen). We now show that beta-actin is present on the extracellular membranes of cancer cells (PC-3, HT1080, and MDA-MB231), and beta-actin can mediate plasmin binding to the cell surface and autoproteolysis to AS4.5. In the presence of beta-actin, no small molecule-free sulfhydryl donor is needed for generation of AS4.5. Antibodies to actin reduced membrane-dependent generation of AS4.5 by 70%. In a cell-free system, addition of actin to in vitro-generated plasmin resulted in stoichiometric conversion to AS4.5. Annexin II and alpha-enolase have been reported to be plasminogen receptors, but we did not demonstrate a role for these proteins in conversion of plasminogen to AS4.5. Our data indicate that membrane-associated beta-actin, documented previously as a plasminogen receptor, is a key cell membrane receptor capable of mediating conversion of plasmin to AS4.5. This conversion may serve an important role in regulating tumor angiogenesis, invasion, and metastasis, and surface beta-actin may also serve as a prognostic marker to predict tumor behavior.

Anti-tumor activity of a combination of plasminogen activator and captopril in a human melanoma xenograft model

Angiostatin, a proteolytic fragment of plasminogen consisting of the first 3 or 4 kringle domains, reduces tumor growth by specifically inhibiting tumor angiogenesis. Angiostatin is generated in vitro in a 2-step process. First, plasminogen is converted to plasmin by plasminogen activators. Next, plasmin excises the angiostatin fragment from plasminogen, a process requiring molecules that are able to donate a free sulfhydryl group. In this study, we investigated whether stimulation of in vivo angiostatin generation by administration of plasminogen activator and a free sulfhydryl group donor (FSD) has anti-tumor activity. First, we determined the optimal conditions for in vitro angiostatin generation by incubating murine plasma with different concentrations of plasminogen activator and/or the FSD captopril. Angiostatin generation was monitored by western blot analysis. Our results were extrapolated to the in vivo situation by administering the optimal dose of tissue-type plasminogen activator (tPA, i.v. injection 3 times/week) and captopril (in drinking water) to mice and analyzing the presence of angiostatin in the circulation. Angiostatin was readily detectable in mice receiving both tPA and captopril, but not in mice receiving either one of the agents. Finally, the anti-tumor activity of the tPA/captopril treatment was tested in a human melanoma xenograft model. Administration of tPA alone had only a marginal effect on tumor growth. Captopril alone reduced tumor growth by about 60%, whereas treatment with both captopril and tPA resulted in 83% inhibition of tumor growth.

From the cradle to the clinic: VEGF in developmental, physiological, and pathological angiogenesis

Formation of new blood vessels, which is fundamental in embryonic development, occurs through a combination of angiogenesis and vasculogenesis. Angiogenesis also plays a vital role postnatally, especially in reparative processes such as wound and fracture healing. Some of these events, especially in fracture healing, recapitulate processes observed in developmental angiogenesis. However, dysregulated angiogenesis is well documented to underlie a number of pathological disorders, including rheumatoid arthritis (RA). The vascular endothelial growth factor (VEGF)/VEGF receptor system is the best characterized regulator of angiogenesis. VEGF is expressed in a range of cells in response to soluble mediators (such as cytokines and growth factors), cell-bound stimuli (such as CD40 ligand), and environmental factors (such as hypoxia). As a consequence, this molecule is vital in the modulation of physiological and pathological angiogenesis. This review will focus in particular on the role played by VEGF in embryogenesis and skeletal growth, in fracture healing (in which increased angiogenesis is likely to be beneficial in promoting union), and in RA (in which excessive angiogenesis is thought to play a significant role in disease pathogenesis). In the not-too-distant future, targeting VEGF may prove to be of benefit in the treatment of diseases associated with excessive or aberrant angiogenesis, such as malignancies and RA.

Tracking angiogenesis induced by skin wounding and contact hypersensitivity using a Vegfr2-luciferase transgenic mouse

The vascular endothelial growth factor-2 (VEGFR2) gene is transcriptionally regulated during angiogenesis. The ability to monitor and quantify VEGFR2 expression in vivo may facilitate a better understanding of the role of VEGFR2 in different states. Here we describe a transgenic mouse, Vegfr2-luc, in which a luciferase reporter is under control of the murine VEGFR2 promoter. In adult mice, luciferase activity was highest in lung and uterus, intermediate in heart, skin, and kidney, and lower in other tissues. Luciferase expression in these tissues correlated with endogenous VEGFR2 mRNA expression. In a cutaneous wound-healing model, Vegfr2-luc expression was induced in the wound tissue. Histologic and immunohistochemical studies showed significant macrophage infiltration into the wound and induction of Vegfr2-luc expression in endothelial and stromal cells. Dexamethasone significantly suppressed Vegfr2-luc expression and macrophage infiltration into the wound, resulting in delayed healing and impaired angiogenesis. In a skin hypersensitivity reaction produced by treatment with oxazolone, Vegfr2-luc expression was induced in the ear. Treatment by dexamethasone markedly suppressed Vegfr2-luc expression and leukocyte infiltration in the ear and was correlated with reduced dermal edema and epidermal hyperplasia. The Vegfr2-luc model will be valuable in monitoring the ability of drugs to affect angiogenesis in vivo.

Coelectrotransfer to skeletal muscle of three plasmids coding for antiangiogenic factors and regulatory factors of the tetracycline-inducible system: tightly regulated expression, inhibition of transplanted tumor growth, and antimetastatic effect

We describe an approach employing intramuscular plasmid electrotransfer to deliver secretable forms of K1-5 and K1-3-HSA (a fusion of K1-3 with human serum albumin), which span, respectively, five and three of the five kringle domains of plasminogen. A tetracycline-inducible system (Tet-On) composed of three plasmids coding, respectively, for the transgene, the tetracycline transcriptional activator rtTA, and the silencer tTS was employed. K1-3-HSA and K1-5, produced from C2C12 muscle cells, were found to inhibit endothelial cell (HMEC-1) proliferation by 30 and 51%, respectively. In vivo, the expression of the transgene upon doxycycline stimulation was rapid, stable, and tightly regulated (no background expression) and could be maintained for at least 3 months. Blood half-lives of 2.1 and 3.7 days were found for K1-5 and K1-3-HSA, respectively. The K1-5 protein was secreted from muscle into blood at a level of 45 ng/ml, which was sufficient to inhibit MDA-MB-231 tumor growth by 81% in nude mice and B16-F10 melanoma cell lung invasion in C57BL/6 mice by 73%. PECAM-1 immunostaining studies revealed modest tumor vasculature in mice expressing K1-5. In contrast, K1-3-HSA, although secreted into blood at much higher level (250 ng/ml) than K1-5, had no effect on tumor growth.

Inhibition of tumor angiogenesis by angiostatin: from recombinant protein to gene therapy

Tumor growth, local invasion, and metastatic dissemination are dependent on the formation of new microvessels. The process of angiogenesis is regulated by a balance between pro-angiogenic and anti-angiogenic factors, and the shift to an angiogenic phenotype (the "angiogenic switch") is a key event in tumor progression. The use of anti-angiogenic agents to restore this balance represents a promising approach to cancer treatment. Known physiological inhibitors include trombospondin, several interleukins, and the proteolytic break-down products of several proteins. Angiostatin, an internal fragment of plasminogen, is one of the more potent of this latter class of angiogenesis inhibitors. Like endostatin, another anti-angiogenic peptide derived from collagen XVIII, angiostatin can induce tumor vasculature regression, leading to a complete cessation of tumor growth. Inhibitors of angiogenesis target normal endothelial cells, therefore the development of resistance to these drugs is unlikely. The efficacy of angiostatin has been demonstrated in animal models for many different types of solid tumors. Anti-angiogenic cancer therapy with angiostatin requires prolonged administration of the peptide. The production of the functional polypeptides is expensive and technical problems related to physical properties and purity are frequently encountered. Gene transfer represents an alternative method to deliver angiostatin. Gene therapy has the potential to produce the therapeutic agent in high concentrations in a local area for a sustained period, thereby avoiding the problems encountered with long-term administration of recombinant proteins, monoclonal antibodies, or anti-angiogenic drugs. In this review we compare the different gene therapy strategies that have been applied to angiostatin, with special regard to their ability to provide sufficient angiostatin at the target site.

Interaction of plasminogen-related protein B with endothelial and smooth muscle cells in vitro

Plasminogen-related protein B (PRP-B) closely resembles the N-terminal plasminogen activation peptide, which is released from plasminogen during conversion to plasmin. We have previously demonstrated that the steady-state level of mRNA encoding PRP-B is increased within tumor tissues, and that recombinant PRP-B antagonizes neoplastic growth when administered systemically to mice harboring tumors, but no insights into the cell targets of PRP-B have been presented. Employing serum-free medium optimized for culturing human endothelial or smooth muscle cells, we show that recombinant PRP-B inhibits basic fibroblast growth factor-dependent cell migration for both cell types, as well as tube formation of endothelial cells. Comparison with the angiogenesis inhibitors angiostatin and endostatin revealed similar results. Recombinant PRP-B is effective in promoting cell attachment of endothelial and smooth muscle cells, and antibody interference experiments reveal that the interaction of recombinant PRP-B with endothelial cells is mediated at least in part by alpha(v)-containing integrins. Inhibition of angiogenesis in vivo by PRP-B was demonstrated in the chicken chorioallantoic membrane assay. PRP-B and other antiangiogenic molecules may elicit metabolic perturbations in endothelial cells as well as perivascular mesenchymal cells such as smooth muscle cells and pericytes.

Upregulation of Cdc2 and cyclin A during apoptosis of endothelial cells induced by cleaved high-molecular-weight kininogen

We (8) reported that the cleaved high-molecular-weight kininogen (HKa) and its domain 5 (D5) inhibited angiogenesis. Further studies (15) revealed that D5 could inhibit cell proliferation and induce apoptosis of proliferating endothelial cells, which together may represent a critical part of antiangiogenic activity of HKa and D5. In the present study, we further examined the effect of HKa on cell cycle progression and cell viability. We report that HKa induced a significant upregulation of Cdc2 and cyclin A in proliferating endothelial cells, concurrent with a marked increase of Cdc2 activity. The increased expression of Cdc2 and cyclin A by HKa was not associated with an apparent change in cell cycle profiles of basic fibroblast growth factor-stimulated proliferating cells, but closely correlated with a marked increase of apoptosis, suggesting that the elevated Cdc2 activity is involved in HKa-induced apoptosis of proliferating endothelial cells. Our results support an emerging hypothesis that Cdc2 and cyclin A are important regulators for cell cycle as well as for apoptosis.

Gene therapy for bladder cancer using E1B-55 kD-deleted adenovirus in combination with adenoviral vector encoding plasminogen kringles 1-5

Mutations or loss of heterozygosity of p53 are detected in approximately 50% of bladder cancers. E1B-55 kD-deleted adenovirus has been shown to kill tumour cells with defective p53 function while sparing normal cells. Here, we examined the cytolytic effect and replication of E1B-55 kD-deleted adenovirus, designated Ad5WS1, on human bladder cancer cell lines with various p53 status. Ad5WS1 caused more severe cytolytic effect and replicated more efficiently in J82 and TCC-SUP bladder cancer cells carrying mutant p53 compared with TSGH-8301 and BFTC-905 bladder cancer cells retaining wild-type p53. Introduction of dominant negative p53 into BFTC-905 cells rendered them more susceptible to Ad5WS1-induced cytolysis. Furthermore, cells susceptible to lysis caused by Ad5WS1 were not attributable to their greater infectability by adenovirus. Finally, Ad5WS1 suppressed the growth of TCC-SUP bladder tumour xenografts, which could be augmented when combined with replication-defective adenoviral vector encoding kringles 1-5 of plasminogen (K1-5), an angiogenic inhibitor. Taken together, our results show that E1B-55 kD-deleted adenovirus replicates and hence lyses bladder cancer cells with mutant p53 much more efficient than those with wild-type p53. Thus, E1B-deleted adenovirus may have therapeutic potential, especially in combination with adenoviral vector expressing K1-5, for the treatment of bladder cancer.

Immortalization of bovine capillary endothelial cells by hTERT alone involves inactivation of endogenous p16INK4A/pRb

Recent studies show that stable expression of the human telomerase catalytic subunit, hTERT, alone can lead several types of normal human somatic cells to bypass replicative senescence and become immortal. The molecular mechanisms by which telomerase immortalizes cells are not fully understood, although a key function of telomerase is to maintain a critical length of telomeres in order to preserve the stability and integrity of the genome. Here we report that stable transfection of hTERT alone was sufficient to allow bovine capillary endothelial (BCE) cells to bypass senescence and acquire immortality. Surprisingly, telomere lengths in these stable transfectants were progressively shortened during an increasing number of population doublings (PDLs), despite high telomerase activity. The expression of the cyclin-dependent kinase inhibitors (CDKIs) p16INK4A and p21CIP1/WAF1 was concomitantly repressed, and the retinoblastoma protein (pRb) was maintained in a hyperphosphorylated state in the telomerase-expressing cells. Re-expression of p16INK4A in these cells by either treatment with a demethylating agent or by adenovirus-mediated expression reinduced a senescence-like phenotype, suggesting that the inactivation of p16INK4A was due to DNA methylation and was crucial for the immortalization process. In agreement with this finding, the expression levels of the prototypic DNA methyltransferase DNMT1 were elevated in the hTERT-positive cells.

Different inhibitors of plasmin differentially affect angiostatin production and angiogenesis

Plasmin is a broad-spectrum serine proteinase, which is presumed to cleave many extracellular proteins and affect angiogenesis. In the present work, we studied the effect of two different inhibitors of plasmin (epsilon-aminocaproic and alpha(2)-antiplasmin) on angiogenesis in vivo using the chicken embryo chorioallantoic membrane assay, and in vitro using human umbilical vein endothelial cells. Epsilon-aminocaproic acid inhibited, while alpha(2)-antiplasmin induced, angiogenesis, as well as human umbilical vein endothelial cell proliferation, migration and tube formation on matrigel in a dose-dependent manner. Since plasmin has been implicated in the production of angiostatin, we studied the effect of the two plasmin inhibitors on angiostatin protein amounts in the chicken embryo chorioallantoic membrane. In this tissue, the 38- and 45-kDa isoforms of angiostatin are differentially affected by the two inhibitors: epsilon-aminocaproic acid increased, while alpha(2)-antiplasmin decreased the amounts of both isoforms. These data suggest that plasmin may have an antiangiogenic role in vivo through generation of angiostatin. Moreover, plasmin inhibitors differentially affect in vivo angiogenesis, depending on the mechanism by which they inhibit plasmin activity.

Expression of Kringle 5 Domain of Human Plasminogen in Pichiapastoris

The kringle 5 domain of plasminogen exhibits potent inhibitory effect on endothelial cell proliferation. It can also cause cell cycle arrest and apoptosis of endothelia cell specifically, and shows promise in antiangiogenic therapy. It has been prepared via both proteolysis of native plasminogen and recombinant DNA methodologies. When expressed in E. coli, recombinant, kringle 5 deposited mainly as inactive, insoluble inclusion bodies and the refolding yield was also low. In the present study, human kringle 5 encoding gene was cloned into secretory plasmid pPIC9K and then integrated into Pichia pastoris genome for expression. On methanol induction, biologically active recombinant kringle 5 was expressed and secreted into the culture medium by the integrated Pichia pastoris with the expression level around 30mg/L of yeast culture. After a simple and economical three-step purification protocol, namely precipitation, DEAE ion exchange chromatography, and gel filtration, the recombinant kringle 5 was purified to homogeneity, with the yield of 7.5 mg/liter yeast culture.

The angiogenesis inhibitor protease-activated kringles 1-5 reduces the severity of murine collagen-induced arthritis

During rheumatoid arthritis there is enlargement and increased cellularity of the synovial lining of joints, before invasion by the synovium of the underlying cartilage and bone. This increased tissue mass requires a network of blood vessels to supply nutrients and oxygen. Disruption of synovial angiogenesis is thus a desirable aim of antiarthritic therapies. Protease-activated kringles 1-5 (K1-5) is an angiogenesis inhibitor related to angiostatin. In common with angiostatin, K1-5 contains the first four kringle domains of plasminogen, but also encompasses the kringle 5 domain, which confers enhanced antiangiogenic activity when compared with angiostatin. The purpose of the present study was to assess the effect on murine arthritis of K1-5. Arthritis was induced in DBA/1 mice by a single injection of bovine collagen. Treatment with K1-5 was commenced on the day of arthritis onset and continued for 10 days, until the end of the experiment. Daily intraperitoneal administration of K1-5 (2 mg/kg body weight) significantly reduced both paw swelling and clinical score (a composite index of the number of arthritic limbs and the severity of disease). The clinical efficacy of this treatment was reflected by a reduction in joint inflammation and destruction, as assessed histologically. These data suggest that antiangiogenic therapies, which block formation of new blood vessels and hence reduce synovial expansion, might be effective in treating rheumatoid arthritis.

Angiogenesis and hepatic colorectal metastases

Angiogenesis is a critical step in the metastatic cascade of colorectal cancer. Several angiogenesis inhibitors have been evaluated in animal models and have shown efficacy, but challenges remain in using these drugs effectively in the clinical setting. Although several of these angiogenesis inhibitors are currently being evaluated in clinical trials, alone or in combination with cytotoxic chemotherapy, early results suggest that angiogenesis inhibitors alone, when used for advanced disease, have minimal activity. It is likely that this class of drugs will prove more efficacious when used either in the setting of minimal disease as agents that may promote tumor dormancy or in combination with other conventional forms of therapy. In addition, strategies such as metronomic therapy have been proposed whereby lower doses of cytotoxic chemotherapy, given more frequently, may act via an antiangiogenic mechanism [67,68]. Another challenge is identifying methods of assessing response to antiangiogenic therapy. To date, traditional methods of identifying response to treatment have not proven effective. Several investigators are working toward identifying circulating endothelial or tumor-associated factors that may be useful in following treatment. Novel imaging techniques are also being evaluated with enhanced CT and MRI, and newer modalities. Hepatic colorectal metastases provide an opportune setting in which to accomplish these challenges because the high incidence of disease and the ability to measure tumor with a variety of techniques lend themselves to evaluation of antiangiogenic therapy.

A truncated plasminogen activator inhibitor-1 protein blocks the availability of heparin-binding vascular endothelial growth factor A isoforms

We have made deletions of the porcine plasminogen activator inhibitor-1 (PAI-1) gene to obtain recombinant truncated PAI-1 proteins to examine functions of the PAI-1 isoforms. We previously reported that one recombinant truncated protein, rPAI-1(23), induces the formation of angiostatin by cleaving plasmin. The rPAI-1(23) protein is also able to bind urokinase plasminogen activator and plasminogen and then reduce the amount of plasmin that is formed. We have now prepared three different truncated rPAI-1 proteins and demonstrate that PAI-1 conformations control the release of heparin-binding vascular endothelial growth factor (VEGF) isoforms. The rPAI-1(23) isoform can regulate the functional activity of heparan sulfate-binding VEGF-A isoforms by blocking the activation of VEGF from heparan sulfate. The rPAI-1(23) conformation induced extensive apoptosis in cultured endothelial cells and thus reduced the number of proliferating cells. The rPAI-1(23) isoform inhibited migration of VEGF-stimulated sprouting from chick aortic rings by 65%, thus displaying a role in anti-angiogenic mechanisms. This insight into anti-angiogenic functions related to PAI-1 conformational changes could provide potential intervention points in angiogenesis associated with atherosclerotic plaques and cancer.