Angiostatin binds ATP synthase on the surface of human endothelial cells

The antitumoral effect of endostatin and angiostatin is associated with a down-regulation of vascular endothelial growth factor expression in tumor cells

Endostatin and angiostatin are known as tumor-derived angiogenesis inhibitors, but their mechanisms of action are not yet completely defined. We report here that endostatin and angiostatin, delivered by adenoviral vectors, reduced in vitro the neovessel formation in the mouse aortic ring assay by 85 and 40%, respectively. We also demonstrated in vivo that both endostatin and angiostatin inhibited local invasion and tumor vascularization of transplanted murine malignant keratinocytes, and reduced by 50 and 90% the development of highly vascularized murine mammary tumors. This inhibition of tumor growth was associated with a reduction of tumor vascularization. Expression analysis of vascular endothelial growth factor (VEGF) carried out in the mouse aortic ring model revealed a 3- to 10-fold down-regulation of VEGF mRNA expression in endostatin-treated rings. A similar down-regulation of VEGF expression at both mRNA and protein levels was also observed in the two in vivo cancer models after treatment with each angiogenesis inhibitor. This suggests that endostatin and angiostatin effects may be mediated, at least in part, by their ability to down-regulate VEGF expression within the tumor. This work provides evidence that endostatin and angiostatin act on tumor cells themselves.

The role of Grp 78 in alpha 2-macroglobulin-induced signal transduction. Evidence from RNA interference that the low density lipoprotein receptor-related protein is associated with, but not necessary for, GRP 78-mediated signal transduction

The low density lipoprotein receptor-related protein (LRP) is a scavenger receptor that binds to many proteins, some of which trigger signal transduction. Receptor-recognized forms of alpha(2)-Macroglobulin (alpha(2)M*) bind to LRP, but the pattern of signal transduction differs significantly from that observed with other LRP ligands. For example, neither Ni(2+) nor the receptor-associated protein, which blocks binding of all known ligands to LRP, block alpha(2)M*-induced signal transduction. In the current study, we employed alpha(2)-macroglobulin (alpha(2)M)-agarose column chromatography to purify cell surface membrane binding proteins from 1-LN human prostate cancer cells and murine macrophages. The predominant binding protein purified from 1-LN prostate cancer cells was Grp 78 with small amounts of LRP, a fact that is consistent with our previous observations that there is little LRP present on the surface of these cells. The ratio of LRP:Grp 78 is much higher in macrophages. Flow cytometry was employed to demonstrate the presence of Grp 78 on the cell surface of 1-LN cells. Purified Grp 78 binds to alpha(2)M* with high affinity (K(d) approximately 150 pm). A monoclonal antibody directed against Grp 78 both abolished alpha(2)M*-induced signal transduction and co-precipitated LRP. Ligand blotting with alpha(2)M* showed binding to both Grp 78 and LRP heavy chains in these preparations. Use of RNA interference to silence LRP expression had no effect on alpha(2)M*-mediated signaling. We conclude that Grp 78 is essential for alpha(2)M*-induced signal transduction and that a "co-receptor" relationship exists with LRP like that seen with several other ligands and receptors such as the uPA/uPAR (urinary type plasminogen activator or urokinase/uPA receptor) system.

Angiogenesis as a target for cancer therapy

Antiangiogenic drugs are unique for having highly specific targets while carrying the potential to be effective against a wide variety of tumors. Moreover, some of the major limitations of cytotoxic therapies likely will be avoided by this entirely new class of anticancer weapons. After the realization of the potential advantages of antiangiogenic therapy, the field of angiogenesis research is growing exponentially. Still, there is much to learn about the machinery that tumors use to recruit new blood vessels, and the results of the clinical trials will show the best way to apply that knowledge for cancer therapy.

Transport ATPases in biological systems and relationship to human disease: a brief overview

Interest in the field of transport ATPases has grown dramatically during the past 20 years and gained considerable visibility for several reasons. First, it was shown that most transport ATPases can be lumped into only a few categories designated simply as P, V, F, and ABC types, the latter consisting of a large superfamily. Second, it has been shown that many transport ATPases have a clear relevance to human disease. Third, the field of transport ATPases has become rather advanced in the study of the reaction mechanisms and structure-function relationships associated with several of these enzymes. Finally, the Nobel committee recently recognized major accomplishments in this field of research. Here, the author provides a brief discussion of transport ATPases that are present in biological systems and their relevance or possible relevance to human disease.

Clinical translation of angiogenesis inhibitors

Angiogenesis inhibitors are a new class of drugs, for which the general rules involving conventional chemotherapy might not apply. The successful translation of angiogenesis inhibitors to clinical application depends partly on the transfer of expertise from scientists who are familiar with the biology of angiogenesis to clinicians. What are the most common questions that clinicians ask as they begin to test angiogenesis inhibitors in cancer clinical trials?

Mechanisms and future directions for angiogenesis-based cancer therapies

Targeting angiogenesis represents a new strategy for the development of anticancer therapies. New targets derived from proliferating endothelial cells may be useful in developing anticancer drugs that prolong or stabilize the progression of tumors with minimal systemic toxicities. These drugs may also be used as novel imaging and radiommunotherapeutic agents in cancer therapy. In this review, the mechanisms and control of angiogenesis are discussed. Genetic and proteomic approaches to defining new potential targets on tumor vasculature are then summarized, followed by discussion of possible antiangiogenic treatments that may be derived from these targets and current clinical trials. Such strategies involve the use of endogenous antiangiogenic agents, chemotherapy, gene therapy, antiangiogenic radioligands, immunotherapy, and endothelial cell-based therapies. The potential biologic end points, toxicities, and resistance mechanisms to antiangiogenic agents must be considered as these therapies enter clinical trials.

Plasmin-induced migration of endothelial cells. A potential target for the anti-angiogenic action of angiostatin

Angiostatin, a plasminogen fragment containing 3-4 N-terminal kringle domains, is a potent inhibitor of tumor-induced angiogenesis, but its mechanism of action is unclear. Angiostatin is a ligand for integrin alphavbeta(3) but does not induce stress fiber formation upon integrin binding, suggesting that angiostatin is a potential integrin antagonist. Plasmin, the parent molecule of angiostatin and a major extracellular protease, induces platelet aggregation, migration of peripheral blood monocytes, and release of arachidonate and leukotriene from several cell types. In the current study, we found that plasmin specifically bound to alphavbeta(3) through the kringle domains and induced migration of endothelial cells. In contrast, angiostatin did not induce cell migration. Notably, angiostatin, anti-alphavbeta(3) antibodies, RGD-peptide, and a serine protease inhibitor effectively blocked plasmin-induced cell migration. These results suggest that plasmin-induced migration of endothelial cells requires alphavbeta(3) and the catalytic activity of plasmin and that this process is a potential target for the inhibitory activity of angiostatin.

The interaction between epidermal growth factor and matrix metalloproteinases induces the development of sweat glands in human fetal skin

BACKGROUND

The development of sweat glands is a very complicated biological process involving many factors. In this study, we explore the interrelationship among epidermal growth factor (EGF), matrix metalloproteinase 2 (MMP-2), matrix metalloproteinase 7 (MMP-7), and the development of sweat glands in human embryos. Furthermore, we hope to elucidate the mechanism(s) underlying the induction of epidermal stem cells into sweat gland cells.

MATERIALS AND METHODS

Skin biopsies of human embryos obtained from spontaneous abortions at different gestational ages from 11 to 31 weeks were used in this study. The dynamic expression of EGF, MMP-2, MMP-7, and keratin-7 (K7) in developing sweat gland cells or extracellular stroma surrounding the sweat gland cells was examined with SP immunohistochemical methods. The localization of the cellular sources of MMP-2 and MMP-7 was examined with in situ hybridization.

RESULTS

At 14-20 weeks of gestation, a gradual increase in EGF immunoreactivity was observed not only in developing sweat gland buds but also in extracellular stroma surrounding the buds, and the expression intensity of EGF peaked at 20-22 weeks of gestational age. All mRNA-positive buds or cells in developing sweat glands contained corresponding immunoreactive proteins. Positive immunostaining for K7 appeared in early sweat gland buds at 14-16 weeks of gestation, and from then on, the positive signal of K7 was concentrated in developing sweat gland cords or cells.

CONCLUSIONS

The morphogenesis of sweat glands in human fetal skin begins at 14-16 weeks of gestational age, and is essentially complete by 24 weeks. There is a close relationship among EGF, extracellular matrix remodeling, and morphogenesis of the sweat glands. EGF is one of the inducers in the development and maturity of sweat gland buds or cells.

Novel targets for lung cancer therapy: part II

Lung cancer is the second most common form of cancer in the United States, and although it accounts for 15% of all cancers, it is the most lethal, accounting for approximately 28% of cancer deaths. In 2002, it is estimated that 177,000 new cases of lung cancer will be diagnosed in the United States, and an estimated 160,000 men and women will die from the disease. This mortality rate is greater than that attributable to colorectal, breast, and prostate cancer combined. Systemic treatments for lung cancer with standard chemotherapy agents are still relatively ineffective. Agents targeting novel proliferative and survival pathways in lung cancer are needed to improve treatment outcomes. In recent years, numerous agents inhibiting aberrant processes in tumor cells have undergone clinical evaluation. This review is the second of a two-part series that summarizes pertinent preclinical and clinical information on novel drugs that target critical abnormalities in lung cancer. In this article, agents that were developed to inhibit various aspects of tumor protein trafficking and protein degradation, cell cycle regulation, angiogenesis, and antigenicity are described. Future approaches to treatment are suggested.

Regulation of endothelial cell survival and apoptosis during angiogenesis

The process of angiogenesis plays an important role in many physiological and pathological conditions. Inhibition of endothelial cell (EC) apoptosis providing EC survival is thought to be an essential mechanism during angiogenesis. Many of the angiogenic growth factors inhibit EC apoptosis. In addition, the adhesion of ECs to the extracellular matrix or intercellular adhesion promotes EC survival. In contrast, increasing evidence suggests that the induction of EC apoptosis may counteract angiogenesis. In this review, we focus on the regulation of EC survival and apoptosis during angiogenesis and especially on the effects and intracellular signaling promoted by angiogenic growth factors, endogenous angiogenic inhibitors (such as angiostatin, endostatin, and thrombospondin-1), and the adhesion to the extracellular matrix. Furthermore, we discuss the effects of cross talk between adhesion molecules and growth factors. Understanding the molecular mechanisms involved in the regulation of EC survival and apoptosis may provide new targets for the development of new therapies to enhance angiogenesis in the case of tissue-ischemia (eg, the neovascularization of myocardium) or to inhibit angiogenesis in the case of neovascularization-dependent disease (eg, tumor, diabetic retinopathy).

The X-ray crystallographic structure of the angiogenesis inhibitor angiostatin

Angiogenesis inhibitors have gained much public attention recently as anti-cancer agents and several are currently in clinical trials, including angiostatin (Phase I, Thomas Jefferson University Hospital, Philadelphia, PA). We report here the bowl-shaped structure of angiostatin kringles 1-3, the first multi-kringle structure to be determined. All three kringle lysine-binding sites contain a bound bicine molecule of crystallization while the former of kringle 2 and kringle 3 are cofacial. Moreover, the separation of the kringle 2 and kringle 3 lysiner binding sites is sufficient to accommodate the alpha-helix of the 30 residue peptide VEK-30 found in the kringle 2/VEK-30 complex. Together the three kringles produce a central cavity suggestive of a unique domain where they may function in concert.

Interaction of the C-terminal domain of p43 and the alpha subunit of ATP synthase. Its functional implication in endothelial cell proliferation

Human p43 is associated with macromolecular tRNA synthase complex and known as a precursor of endothelial monocyte-activating polypeptide II (EMAP II). Interestingly, p43 is also secreted to induce proinflammatory genes. Although p43 itself seems to be a cytokine working at physiological conditions, most of the functional studies have been obtained with its C-terminal equivalent, EMAP II. To gain an insight into the working mechanism of p43/EMAP II, we used EMAP II and searched for an interacting cell surface molecule. The level of EMAP II-binding molecule(s) was significantly increased in serum-starved tumor cells. Thus, the EMAP II-binding molecule was isolated from the membrane of the serum-starved CEM cell. The isolated protein was determined to be the alpha subunit of ATP synthase. The interaction of EMAP II and alpha-ATP synthase was confirmed by enzyme-linked immunosorbent assay and in vitro pull down assays and blocked with the antibodies raised against EMAP II and alpha-ATP synthase. The binding of EMAP II to the surface of serum-starved cells was inhibited in the presence of soluble alpha-ATP synthase. EMAP II inhibited the growth of endothelial cells, and this effect was relieved by soluble alpha-ATP synthase. Anti-alpha-ATP synthase antibody also showed an inhibitory effect on the proliferation of endothelial cells mimicking the activity of EMAP II. These results suggest the potential interaction of p43/EMAP II with alpha-ATP synthase and its role in the proliferation of endothelial cells.

Angiostatin gene transfer as an effective treatment strategy in murine collagen-induced arthritis

OBJECTIVE

To determine the efficacy of local therapy with human angiostatin gene in murine collagen-induced arthritis (CIA).

METHODS

DBA/1 mice were immunized with bovine type II collagen. Before the onset of arthritis, NIH3T3 fibroblasts, transduced with angiostatin-expressing retroviral vectors or control vectors, were transplanted into the knee cavity. The incidence of arthritis in the knee joints was evaluated histologically based on pannus formation and cartilage destruction. Paws were evaluated macroscopically for redness, swelling, and deformities and immunologically for levels of interleukin-1 beta. Angiogenesis in paws and knee joints was studied by immunohistochemistry using anti-CD31 antibody and measurement of von Willebrand factor levels.

RESULTS

Pannus formation and cartilage erosion were dramatically reduced in knees transplanted with angiostatin-expressing cells. In addition, the onset of CIA in the ipsilateral paws below the knees injected with the angiostatin gene was significantly prevented. Furthermore, angiostatin gene transfer inhibited arthritis-associated angiogenesis.

CONCLUSION

Local production of angiostatin in the knee was able to prevent the onset of CIA not only in the knee injected with genetically engineered cells, but also in the uninjected ipsilateral paw. This suggests that transfer of the angiostatin gene, and potentially also its protein, may provide a new, effective approach to the treatment of rheumatoid arthritis.

Mechanism of the F(1)F(0)-type ATP synthase, a biological rotary motor

The F(1)F(0)-type ATP synthase is a key enzyme in cellular energy interconversion. During ATP synthesis, this large protein complex uses a proton gradient and the associated membrane potential to synthesize ATP. It can also reverse and hydrolyze ATP to generate a proton gradient. The structure of this enzyme in different functional forms is now being rapidly elucidated. The emerging consensus is that the enzyme is constructed as two rotary motors, one in the F(1) part that links catalytic site events with movements of an internal rotor, and the other in the F(0) part, linking proton translocation to movements of this F(0) rotor. Although both motors can work separately, they must be connected together to interconvert energy. Evidence for the function of the rotary motor, from structural, genetic and biophysical studies, is reviewed here, and some uncertainties and remaining mysteries of the enzyme mechanism are also discussed.

Neutrophils as a key cellular target for angiostatin: implications for regulation of angiogenesis and inflammation

Angiostatin effectively blocks tumor angiogenesis through still poorly understood mechanisms. Given the close association between immune and vascular regulation, we investigated the effects of angiostatin on angiogenesis-associated leukocytes. Angiostatin inhibited the migration of monocytes and, even more markedly, neutrophils. Angiostatin blocked chemotaxis of neutrophils to CXCR2 chemokine receptor agonists (IL-8, MIP-2, and GROalpha), formyl-Met-Leu-Phe (fMLP), and 12-O-tetradecanoylphorbol 13-acetate, and repressed fMLP-induced mitochondrial activity. Two different angiostatin forms (kringles 1-4 and 1-3) were effective, whereas whole plasminogen had no effect. IL-8, MIP-2, and GROalpha induced intense angiogenic reactions in vivo, but no angiogenic response to these factors was observed in neutropenic mice, demonstrating an essential role for neutrophils. Angiostatin potently inhibited chemokine-induced angiogenesis in vivo, and consistent with in vitro observations, both angiostatin forms were active and whole plasminogen had little effect. Angiostatin inhibition of angiogenesis in vivo was accompanied by a striking reduction in the number of recruited leukocytes. In vivo, the inflammatory agent lipopolysaccharide also induced extensive leukocyte infiltration and angiogenesis that were blocked by angiostatin. Neutrophils expressed mRNAs for ATP synthase and angiomotin, two known angiostatin receptors. These data show that angiostatin directly inhibits neutrophil migration and neutrophil-mediated angiogenesis and indicate that angiostatin might inhibit inflammation.

Inhibition of human endothelial cell proliferation by ShIF, a vacuolar H(+)-ATPase-like protein

ShIF is a bone marrow stroma cell-derived factor originally identified to support proliferation of bone marrow cells in vitro. This protein shares high sequence homology to the yeast vacuolar H(+)-ATPase subunit, Vph1p, and the 116 kDa proton pump of the rat and bovine synaptic vesicle, Vpp1. We examined the function of ShIF in the proliferation of human umbilical vein endothelial cells (HUVEC). ShIF inhibited HUVEC proliferation in a dose-dependent manner. Recombinant ShIF added at 10 and 20 ng/ml inhibited HUVEC proliferation by 21.6 and 44.3%, respectively and increasing the concentration of ShIF to 100 ng/ml inhibited proliferation by as much as 55.5%. When HUVEC cells were cultured at various concentrations of ShIF in the presence of anti-ShIF antibody, the inhibitory effects of ShIF to HUVEC proliferation were abrogated by 89-91% indicating that the activity of ShIF to HUVEC was specific. HUVEC cultured in the presence of ShIF and bafilomycin, a specific inhibitor of ATPase, resulted to a 90% growth inhibition. Thus, ShIF may act as an antagonist to the ATPase complex by disrupting the production of cellular ATP thereby decreasing the ability of HUVEC to proliferate.

Disordered cellular migration and angiogenesis in cd39-null mice

BACKGROUND

Nucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39 is the major ectonucleotidase of endothelial cells and monocytes and catalyzes phosphohydrolysis of extracellular nucleoside diphosphates (NDP) and triphosphates (NTP, eg, ATP and UTP). Deletion of cd39 causes perturbations in the hydrolysis of NTP and NDP in the vasculature. Activation of P2 receptors appears to influence endothelial cell chemotactic and mitogenic responses in vitro. Therefore, aberrant regulation of nucleotide P2 receptors may influence angiogenesis in cd39-null mice. Methods and Results- In control mice, implanted Matrigel plugs containing growth factors were rapidly populated by monocyte/macrophages, endothelial cells, and pericytes, with the development of new vessels over days. In cd39-null mice, migrating cells were completely confined to the tissue-Matrigel interface in a clearly stratified manner. Absolute failure of new vessel ingrowth was consistently observed in the mutant mice. Linked to these findings, chemotaxis of cd39-null monocyte/macrophages to nucleotides was impaired in vitro. This abnormality was associated with desensitization of nucleotide receptor P2Y-mediated signaling pathways.

CONCLUSIONS

Our findings demonstrate a role for NTPDase1 and phosphohydrolysis of extracellular nucleotides in the regulation of the cellular infiltration and new vessel growth in a model of angiogenesis.

Mitochondrial coupling factor 6 is present on the surface of human vascular endothelial cells and is released by shear stress

BACKGROUND

We showed that mitochondrial coupling factor 6 (CF6), an endogenous inhibitor of prostacyclin synthesis, is present in the systemic circulation as a pressor substance in rats. We investigated the possibility of vascular endothelial cells as a source of circulating CF6.

METHODS AND RESULTS

We used 2 cultured endothelial cell lines, human umbilical vein endothelial cells (HUVECs) and ECV 304 cells (transformed HUVECs), for this study. Immunofluorescence microscopy of both ECV 304 and HUVECs confirmed the surface-associated immunoreactivity of anti-CF6 antibody on the plasma membrane. The concentration of CF6 in the medium increased gradually with time in both ECV 304 and HUVECs in static conditions. Exposure of ECV 304 and HUVECs to a fluid shear stress enhanced the release of CF6: In ECV 304, the concentration of CF6 in the medium (ng. well(-1). 6 hours(-1)) was 2.1+/-0.8 at baseline, 4.3+/-0.8 after shear at 15 dynes/cm(2), and 57.7+/-8.4 after shear at 25 dynes/cm(2). CF6 contents in the cell homogenate and mitochondria were both significantly increased after exposure of ECV 304 to 6-hour shear at 15 dynes/cm(2), whereas they were unchanged after shear stress at 25 dynes/cm(2). The ratio of CF6 to GAPDH mRNA was enhanced significantly, by 1.8+/-0.2-fold, after 6-hour shear stress at 25 dynes/cm(2). Flow cytometry analysis revealed that the surface-associated CF6 was significantly increased in a 3-hour static condition after the previous exposure of the cells to shear stress for 3 hours.

CONCLUSIONS

Vascular endothelial cells are a source of CF6, and shear stress regulates the release of the surface-associated CF6.

Genetic identity and differential expression of p38.5 (Haymaker) in human malignant and nonmalignant cells

Previous studies from our laboratory revealed a novel protein of 38.5 kD on the surface of malignant cell lines of hematopoetic origin that exhibit susceptibility to naive natural killer (NK) cell-mediated lysis. In contrast, p38.5 was not detected on the surface of NK cell-resistant carcinoma cell lines or normal cells. We now report that this protein is differentially expressed, intracellularly, in malignant cell lines of both hematopoetic and epithelial origin compared with nonmalignant cells. To characterize p38.5 further, we used a previously developed antipeptide antibody (anti-11-mer) to probe cDNA expression libraries and subsequently performed 5' extension by rapid amplification of cDNA ends (RACE). Sequence analyses of these cDNA clones reveal open reading frames (ORFs) that include the previously identified 11-mer peptide from purified, native p38.5 and that have identical sequences to a gene of unknown function on chromosome 19. Nucleotide sequence data obtained from these cDNA clones, as well as analysis of the genomic sequence, permitted design of primers for reverse transcriptase-polymerase chain reaction (RT-PCR) that resulted in a cDNA clone encoding an ORF of 361 amino acids; the clone was identical to a sequence encoded by an unpublished mRNA in GenBank. Anti-p38.5 antibody against the 11-mer peptide encoded in exon 5 and against a 25-mer peptide encoded in exon 1 both reacted with the same protein in immunoprecipitation studies, providing further evidence of identity. RT-PCR and Northern blot analyses both demonstrated p38.5 gene transcripts in normal cells, nonmalignant cell lines and malignant cell lines of epithelial as well as hematopoietic origin. Semiquantitative studies revealed a greater level of p38.5 gene transcription in malignant cell lines compared with nonmalignant cells. Immunoblot analyses of protein expression confirmed and extended the latter studies by revealing substantially greater levels of the 38.5 kD protein in whole cell extracts of malignant cell lines compared with nonmalignant cells. Quantitative differences in detection of the 38.5 kD protein and mRNA in NK susceptible- hematopoietic malignancies compared with NK resistant-carcinomas were not observed. These experiments suggest that the p38.5 gene (Haymaker) is widely expressed in human cells of different tissue origins but that elevated expression is associated with the malignant phenotype.

Specific interaction of angiostatin with integrin alpha(v)beta(3) in endothelial cells

Angiostatin, the N-terminal four kringles (K1-4) of plasminogen, blocks tumor-mediated angiogenesis and has great therapeutic potential. However, angiostatin's mechanism of anti-angiogenic action is unclear. We found that bovine arterial endothelial (BAE) cells adhere to angiostatin in an integrin-dependent manner and that integrins alpha(v)beta(3), alpha(9)beta(1), and to a lesser extent alpha(4)beta(1), specifically bind to angiostatin. alpha(v)beta(3) is a predominant receptor for angiostatin on BAE cells, since a function-blocking antibody to alpha(v)beta(3) effectively blocks adhesion of BAE cells to angiostatin, but an antibody to alpha(9)beta(1) does not. epsilon-Aminocaproic acid, a Lys analogue, effectively blocks angiostatin binding to BAE cells, indicating that an unoccupied Lys-binding site of the kringles may be required for integrin binding. It is known that other plasminogen fragments containing three or five kringles (K1-3 or K1-5) have an anti-angiogenic effect, but plasminogen itself does not. We found that K1-3 and K1-5 bind to alpha(v)beta(3), but plasminogen does not. These results suggest that the anti-angiogenic action of angiostatin may be mediated via interaction with alpha(v)beta(3). Angiostatin binding to alpha(v)beta(3) does not strongly induce stress-fiber formation, suggesting that angiostatin may prevent angiogenesis by perturbing the alpha(v)beta(3)-mediated signal transduction that may be necessary for angiogenesis.

Mitochondrial coupling factor 6 as a potent endogenous vasoconstrictor

We demonstrated recently that coupling factor 6, an essential component of the energy-transducing stalk of mitochondrial ATP synthase, suppresses the synthesis of prostacyclin in vascular endothelial cells. Here, we tested the hypothesis that coupling factor 6 is present on the cell surface and is involved in the regulation of systemic circulation. This peptide is present on the surface of CRL-2222 vascular endothelial cells and is released by these cells into the medium. In vivo, the peptide circulates in the vascular system of the rat, and its gene expression and plasma concentration are higher in spontaneously hypertensive rats (SHRs) than in normotensive controls. Elevation of blood pressure with norepinephrine did not affect the plasma concentration of coupling factor 6. Intravenous injection of recombinant peptide increased blood pressure, apparently by suppressing prostacyclin synthesis, whereas a specific Ab to coupling factor 6 decreased systemic blood pressure concomitantly with an increase in plasma prostacyclin. Interestingly, the antibody's hypotensive effect could be abolished by treating with the cyclooxygenase inhibitor indomethacin. These findings indicate that mitochondrial coupling factor 6 functions as a potent endogenous vasoconstrictor in the fashion of a circulating hormone and may suggest a new mechanism for hypertension.

Adhesion events in angiogenesis

Recent work from several laboratories indicates that the coordination of endothelial cell adhesion events with growth factor receptor inputs regulates endothelial cell responses during angiogenesis. Analyses of the signaling pathways downstream of integrins, cadherins and growth-factor receptors are providing an insight into the molecular basis of known anti-angiogenic strategies, as well as into the design of novel therapies.

Angiostatin enhances B7.1-mediated cancer immunotherapy independently of effects on vascular endothelial growth factor expression

Tumors must develop an adequate vascular network to meet their increasing demands for nutrition and oxygen. Angiostatin, a multiple kringle (1-4)-containing fragment of plasminogen, is an effective natural inhibitor of tumor angiogenesis. Here we show that gene transfer of angiostatin into small (0.1 cm in diameter) solid EL-4 lymphomas established in syngeneic C57BL/6 mice led to reduced tumor angiogenesis and weak inhibition of tumor growth. In contrast, when angiostatin gene therapy was preceded by in situ gene transfer of the T-cell costimulator B7.1, large (0.4 cm in diameter) tumors were rapidly and completely eradicated, whereas B7.1 and angiostatin monotherapies were ineffective. Combined gene transfer of B7.1 and angiostatin generated potent systemic antitumor immunity that was effective in eradicating a systemic challenge of 10(7) EL-4 cells. Gene transfer of angiostatin expression plasmids led to overexpression of angiostatin in tumors, increased apoptosis of tumor cells, and decreased density of tumor blood vessels, which may allow the immune system to overcome tumor immune resistance. The latter effects were not the result of a decrease in vascular endothelial growth factor expression, as tumoral vascular endothelial growth factor expression increased slightly after angiostatin gene transfer, presumably in response to increasing hypoxia. These results suggest that combining immunogene therapy with a vascular attack by angiostatin is a particularly effective approach for eliciting antitumor immunity.

Therapeutic effects of viral vector-mediated antiangiogenic gene transfer in malignant ascites

Malignant ascites is a common complication of advanced intraabdominal neoplasms for which standard treatments are suboptimal. Evidence suggests that tumor-mediated angiogenesis and enhanced vascular permeability in the peritoneal wall due to high levels of vascular endothelial growth factor play a fundamental role in the pathogenesis of malignant ascites. To explore the advantage of viral vector-mediated "targeted antiangiogenic therapy" in ascites formation, we constructed and administered adenoviral vectors encoding several different antiangiogenic proteins (angiostatin, endostatin, platelet factor 4, and a fusion protein between angiostatin and endostatin) alone or in combination intraperitoneally in mice with peritoneal carcinomatosis from breast cancer (TA3 cells) and ovarian cancer (SKOV-3 i.p. and ES-2 cell lines) to explore the potential of additive or synergistic activity. Our data demonstrated statistically significant downregulation of ascites formation, tumor growth, vascularity, and prolongation of animal survival after intraperitoneal treatment with antiangiogenic adenoviral vectors in three different ascites tumor models. Combined treatment proved to be more effective than treatment with one vector alone. Reduced ascites formation was accompanied by decreased microvascular density in the peritoneal wall and increased apoptosis of tumor cells after administration of antiangiogenic vectors in vivo. Of interest was the observation that AdPF4 caused a significant decrease in the level of VEGF secreted by tumor cells both in vitro and in TA3 ascites tumor-bearing animals in vivo. These data suggest that adenoviral vector-mediated delivery of genes encoding antiangiogenic proteins may represent a potentially new treatment modality for malignant ascites.

Targeting tumor angiogenesis with gene therapy

A recent target of cancer gene therapy is tumor angiogenesis. An appealing feature of gene therapy targeting the tumor vasculature is that it is readily accessible, particularly when the carrier and its gene are administered systemically. Several gene-based viral and nonviral therapies that target tumor angiogenesis have demonstrated the "proof of principle" of antiangiogenic therapy in preclinical models. The utility of antiangiogenic gene therapy in a clinical setting will depend in large part on developing vectors with minimal toxicity and with increased in vivo transfection efficiency. In this review, we discuss the current status and future directions of antiangiogenic gene therapy.

The hemostatic system and angiogenesis in malignancy

Coagulopathy and angiogenesis are among the most consistent host responses associated with cancer. These two respective processes, hitherto viewed as distinct, may in fact be functionally inseparable as blood coagulation and fibrinolysis, in their own right, influence tumor angiogenesis and thereby contribute to malignant growth. In addition, tumor angiogenesis appears to be controlled through both standard and non-standard functions of such elements of the hemostatic system as tissue factor, thrombin, fibrin, plasminogen activators, plasminogen, and platelets. "Cryptic" domains can be released from hemostatic proteins through proteolytic cleavage, and act systemically as angiogenesis inhibitors (e.g., angiostatin, antiangiogenic antithrombin III aaATIII). Various components of the hemostatic system either promote or inhibit angiogenesis and likely act by changing the net angiogenic balance. However, their complex influences are far from being fully understood. Targeted pharmacological and/or genetic inhibition of pro-angiogenic activities of the hemostatic system and exploitation of endogenous angiogenesis inhibitors of the angiostatin and aaATIII variety are under study as prospective anti-cancer treatments.

Antiangiogenic agents and their promising potential in combined therapy

One of the most promising strategies for treating cancer is the addition of antiangiogenic therapy to therapeutic regimens. Angiogenesis, or the growth of new blood vessels from preexisting vessels, is essential both for the growth of a primary tumor and for successful metastasis. As a result of intense research in this field, a number of antiangiogenic agents have been identified and have demonstrated varying degrees of success in inhibiting the growth of solid tumors and metastases in preclinical and clinical studies. The real potential of antiangiogenic agents for cancer therapy resides in strategic combinations with each other, with chemotherapy, with radiation, and with tumor-targeting agents, such as radioimmunotherapy. Along with this new opportunity to develop synergistic therapy comes the challenging complexities of the physiologic systems regulating angiogenesis. These multifaceted systems could intimidate investigators seeking to take advantage of the potential synergy in combined cancer therapy. To aid in these efforts, this overview of key antiangiogenic agent mechanisms, combination strategies and initial studies of the potential synergy with chemotherapy, radiation and radioimmunotherapy is presented.

Angiostatin effects on endothelial cells mediated by ceramide and RhoA

Angiostatin is a cleavage product of plasminogen that has anti-angiogenic properties. We investigated whether the effects of angiostatin on endothelial cells are mediated by ceramide, a lipid implicated in endothelial cell signaling. Our results demonstrate that angiostatin produces a transient increase in ceramide that correlates with actin stress fiber reorganization, detachment and death. DNA array expression analysis performed on ceramide-treated human endothelial cells demonstrated induction of certain genes involved in cytoskeleton organization. Specifically, we report that treatment with angiostatin or ceramide results in the activation of RhoA, an important effector of cytoskeletal structure. We also show that treatment of endothelial cells with the antioxidant N-acetylcysteine abrogates morphological changes and cytotoxic effects of treatment with angiostatin or ceramide. These findings support a model in which angiostatin induces a transient rise in ceramide, RhoA activation and free radical production.

Endothelial cell surface F1-F0 ATP synthase is active in ATP synthesis and is inhibited by angiostatin

Angiostatin blocks tumor angiogenesis in vivo, almost certainly through its demonstrated ability to block endothelial cell migration and proliferation. Although the mechanism of angiostatin action remains unknown, identification of F(1)-F(O) ATP synthase as the major angiostatin-binding site on the endothelial cell surface suggests that ATP metabolism may play a role in the angiostatin response. Previous studies noting the presence of F(1) ATP synthase subunits on endothelial cells and certain cancer cells did not determine whether this enzyme was functional in ATP synthesis. We now demonstrate that all components of the F(1) ATP synthase catalytic core are present on the endothelial cell surface, where they colocalize into discrete punctate structures. The surface-associated enzyme is active in ATP synthesis as shown by dual-label TLC and bioluminescence assays. Both ATP synthase and ATPase activities of the enzyme are inhibited by angiostatin as well as by antibodies directed against the alpha- and beta-subunits of ATP synthase in cell-based and biochemical assays. Our data suggest that angiostatin inhibits vascularization by suppression of endothelial-surface ATP metabolism, which, in turn, may regulate vascular physiology by established mechanisms. We now have shown that antibodies directed against subunits of ATP synthase exhibit endothelial cell-inhibitory activities comparable to that of angiostatin, indicating that these antibodies function as angiostatin mimetics.

Intracellular Ca(2+) signaling in endothelial cells by the angiogenesis inhibitors endostatin and angiostatin

Intracellular signaling mechanisms by the angiogenesis inhibitors endostatin and angiostatin remain poorly understood. We have found that endostatin (2 microg/ml) and angiostatin (5 microg/ml) elicited transient, approximately threefold increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). Acute exposure to angiostatin or endostatin nearly abolished subsequent endothelial [Ca(2+)](i) responses to carbachol or to thapsigargin; conversely, thapsigargin attenuated the Ca(2+) signal elicited by endostatin. The phospholipase C inhibitor U-73122 and the inositol trisphosphate (IP(3)) receptor inhibitor xestospongin C both inhibited endostatin-induced elevation in [Ca(2+)](i), and endostatin rapidly elevated endothelial cell IP(3) levels. Pertussis toxin and SB-220025 modestly inhibited the endostatin-induced Ca(2+) signal. Removal of extracellular Ca(2+) inhibited the endostatin-induced rise in [Ca(2+)](i), as did a subset of Ca(2+)-entry inhibitors. Peak Ca(2+) responses to endostatin and angiostatin in endothelial cells exceeded those in epithelial cells and were minimal in NIH/3T3 cells. Overnight pretreatment of endothelial cells with endostatin reduced the subsequent acute elevation in [Ca(2+)](i) in response to vascular endothelial growth factor or to fibroblast growth factor by approximately 70%. Intracellular Ca(2+) signaling may initiate or mediate some of the cellular actions of endostatin and angiostatin.

Antiangiogenesis signals by endostatin

Endostatin is a potent endogenous angiogenesis inhibitor that induces regression of tumors in mice. Neither an extracellular receptor for endostatin nor intracellular signals that result in the regression of tumor vascular beds have been identified. We demonstrate that endostatin, but not angiostatin, at comparable concentrations to those used in in vivo animal trials, rapidly down-regulates many genes in exponentially growing endothelial cells. These include immediate early response genes, cell cycle-related genes, and genes regulating apoptosis inhibitors, mitogen-activated protein kinases, focal adhesion kinase, G-protein-coupled receptors mediating endothelial growth, a mitogenic factor, adhesion molecules, and cell structure components. Suppression of both apoptosis inhibitors and cell proliferation genes may have a limited contribution to the antiangiogenesis process because endostatin induces neither apoptosis nor growth inhibition, unless studied under reduced serum conditions. In contrast, the antimigratory effect of endostatin was rapid and potent even under serum-supplemented conditions. Endostatin caused gene suppression and migration arrest exclusively in endothelial cells, most profoundly in microvascular endothelial cells. The c-myc null fibroblasts obtained by targeted homologous recombination showed an attenuated migration rate compared with isogenic parental cells, whereas the introduction of the c-myc gene into endothelial cells abrogated the antimigratory effect of endostatin. Inhibition of E-box-driven transcription by overexpressing max or mad suppressed endothelial migration. Thus, rapid down-regulation of genes by endostatin neither restores proliferating endothelial cells to their resting states nor induces apoptosis; rather, it potently inhibits endothelial cell migration partly via suppression of c-myc expression.

Angiomotin: an angiostatin binding protein that regulates endothelial cell migration and tube formation

Angiostatin, a circulating inhibitor of angiogenesis, was identified by its ability to maintain dormancy of established metastases in vivo. In vitro, angiostatin inhibits endothelial cell migration, proliferation, and tube formation, and induces apoptosis in a cell type-specific manner. We have used a construct encoding the kringle domains 1--4 of angiostatin to screen a placenta yeast two-hybrid cDNA library for angiostatin-binding peptides. Here we report the identification of angiomotin, a novel protein that mediates angiostatin inhibition of migration and tube formation of endothelial cells. In vivo, angiomotin is expressed in the endothelial cells of capillaries as well as larger vessels of the human placenta. Upon expression of angiomotin in HeLa cells, angiomotin bound and internalized fluorescein-labeled angiostatin. Transfected angiomotin as well as endogenous angiomotin protein were localized to the leading edge of migrating endothelial cells. Expression of angiomotin in endothelial cells resulted in increased cell migration, suggesting a stimulatory role of angiomotin in cell motility. However, treatment with angiostatin inhibited migration and tube formation in angiomotin-expressing cells but not in control cells. These findings indicate that angiostatin inhibits cell migration by interfering with angiomotin activity in endothelial cells.

Pharmacological aspects of targeting cancer gene therapy to endothelial cells

Targeting cancer gene therapy to endothelial cells seems to be a rational approach, because (a) a clear correlation exists between proliferation of tumor vessels and tumor growth and malignancy, (b) differences of cell membrane structures between tumor endothelial cells and normal endothelial cells exist which could be used for targeting of vectors and (c) tumor endothelial cells are accessible to vector vehicles in spite of the peculiarities of the transvascular and interstitial blood flow in tumors. Based on the knowledge on the pharmacokinetics of macromolecules it can be concluded that vectors targeting tumor endothelial cells should own a long blood residence time after intravascular application. This precondition seems to be fulfilled best by vectors exhibiting a slight anionic charge. A long blood residence time would allow the formation of a high amount of complexes between tumor endothelial cells and vector particles. Such high amount of complexes should enable a high transfection rate of tumor endothelial cells. In view of their pharmacokinetic behavior nonviral vectors seem to be more suitable for in vivo targeting tumor endothelial cells than viral vectors. Specific binding of nonviral vectors to tumor endothelial cells should be enhanced by multifunctional ligands and the transduction efficiency should be improved by cationic carriers. Effector genes should encode proteins potent enough to induce reactions which eliminate the tumor tissue. To be effective to that degree such proteins should induce self-amplifying antitumor reactions. Examples for proteins which have the potential to induce such self-amplifying tumor reactions are proteins endowed with antiangiogenic and antiproliferative activity, enzymes which convert prodrugs into drugs and possibly also proteins which induce embolization of tumor vessels. The pharmacological data for such examples are discussed in detail.

Mitochondrial polypeptides of the oxidative phosphorylation pathway as potential new targets for anti-cancer therapy

We have analyzed our own results on upregulated gene expression in human and monkey lymphomas as well as the data published on expression levels of genes in various cancer cells. The analysis suggests an important role of particular subunits of oxidative phosphorylation (OXPHOS) proteins in malignant transformation of the cell. It opens a possibility of designing new anti-cancer drugs aimed at specific inhibition of the expression of definite mitochondrial OXPHOS proteins' subunits including those of NADH-dehydrogenase 4, cytochrome c oxidase 1, and cytochrome b.

Angiogenesis: regulators and clinical applications

Angiogenesis is a fundamental process in reproduction and wound healing. Under these conditions, neovascularization is tightly regulated. Unregulated angiogenesis may lead to several angiogenic diseases and is thought to be indispensable for solid tumor growth and metastasis. The construction of a vascular network requires different sequential steps including the release of proteases from "activated" endothelial cells with subsequent degradation of the basement membrane surrounding the existing vessel, migration of endothelial cells into the interstitial space, endothelial cell proliferation, and differentiation into mature blood vessels. These processes are mediated by a wide range of angiogenic inducers, including growth factors, chemokines, angiogenic enzymes, endothelial specific receptors, and adhesion molecules. Finally, when sufficient neovascularization has occurred, angiogenic factors are down-regulated or the local concentration of inhibitors increases. As a result, the endothelial cells become quiescent, and the vessels remain or regress if no longer needed. Thus, angiogenesis requires many interactions that must be tightly regulated in a spatial and temporal manner. Each of these processes presents possible targets for therapeutic intervention. Synthetic inhibitors of cell invasion (marimastat, Neovastat, AG-3340), adhesion (Vitaxin), or proliferation (TNP-470, thalidomide, Combretastatin A-4), or compounds that interfere with angiogenic growth factors (interferon-alpha, suramin, and analogues) or their receptors (SU6668, SU5416), as well as endogenous inhibitors of angiogenesis (endostatin, interleukin-12) are being evaluated in clinical trials against a variety of solid tumors. As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.

Pharmacokinetics and whole body distribution of elastase derived angiostatin (K1-3) in rats

In the current study, we determined short-term pharmacokinetics and whole body distribution of elastase derived angiostatin [angiostatin(k1-3)] in rats after i.v. injection of radiolabelled protein. Since in gamma-camera studies, no tumor specific angiostatin(k1-3) accumulation was observed, general pharmacokinetics were studied in tumor free rats. By one-compartment model fitting of the data, Km 7.3 +/- 1.7 microg x ml(-1), Vmax 0.94 +/- 0.19 microg x min(-1), V, 10.9 +/- 2.5 ml and intrinsic clearance (Vmax/Km) 0.128 ml x min(-1) were calculated. Of the injected dose (I.D.) of angiostatin(k1-3), 12.1 +/- 2.1% per gram tissue was present in the kidneys 10 min after injection. Accumulation of angiostatin(k1-3) was detectable in spleen, liver, lungs and heart 10 min after injection. Sixty minutes after injection, kidney associated angiostatin(k1-3) had decreased, whereas in stomach and small intestines a small increase was seen. Immunohistochemical analysis demonstrated specific staining of interstitial cells of the kidney, liver Kupffer cells and endothelium of larger blood vessels of the lungs. Renal clearance of angiostatin(k1-3) and/or fragments is a major route of elimination, whereas lack of accumulation of radioactivity in the faeces indicates little hepatic elimination or hepatic elimination followed by enterohepatic cycling of the protein's degradation products. Instant blood coagulation at the site of vascular activation and the occurrence of respiratory problems upon administration of higher doses of angiostatin(k1-3) warrants further investigation of the protein's potential side effects. The data presented can be applied to study the relation between angiostatin(k1-3) treatment regimens, blood concentration levels, anti-tumor activity and harmful effects.

Extracellular ATP formation on vascular endothelial cells is mediated by ecto-nucleotide kinase activities via phosphotransfer reactions

Cell surface ecto-nucleotidases are considered the major effector system for inactivation of extracellular adenine nucleotides, whereas the alternative possibility of ATP synthesis has received little attention. Using a TLC assay, we investigated the main exchange activities of 3H-labeled adenine nucleotides on the cultured human umbilical vein endothelial cells. Stepwise nucleotide degradation to adenosine occurred when a particular nucleotide was present alone, whereas combined cell treatment with ATP and either [3H]AMP or [3H]ADP caused unexpected phosphorylation of 3H-nucleotides via the backward reactions AMP --> ADP --> ATP. The following two groups of nucleotide-converting ecto-enzymes were identified based on inhibition and substrate specificity studies: 1) ecto-nucleotidases, ATP-diphosphohydrolase, and 5'-nucleotidase; 2) ecto-nucleotide kinases, adenylate kinase, and nucleoside diphosphate kinase. Ecto-nucleoside diphosphate kinase possessed the highest activity, as revealed by comparative kinetic analysis, and was capable of using both adenine and nonadenine nucleotides as phosphate donors and acceptors. The transphosphorylation mechanism was confirmed by direct transfer of the gamma-phosphate from [gamma-32P]ATP to AMP or nucleoside diphosphates and by measurement of extracellular ATP synthesis using luciferin-luciferase luminometry. The data demonstrate the coexistence of opposite, ATP-consuming and ATP-generating, pathways on the cell surface and provide a novel mechanism for regulating the duration and magnitude of purinergic signaling in the vasculature.

Downregulation of microglial activation by apolipoprotein E and apoE-mimetic peptides

Apolipoprotein E plays an important role in recovery from acute brain injury and risk of developing Alzheimer's disease. We demonstrate that biologically relevant concentrations of apoE suppress microglial activation and release of TNFalpha and NO in a dose-dependent fashion. Peptides derived from the apoE receptor-binding region mimic the effects of the intact protein, whereas deletion of apoE residues 146-149 abolishes peptide bioactivity. These results are consistent with the hypothesis that apoE modulates microglial function by binding specific cell surface receptors and that the immunomodulatory effects of apoE in the central nervous system may account for its role in acute and chronic neurological disease.

Kringle 1-4 of hepatocyte growth factor inhibits proliferation and migration of human microvascular endothelial cells

NK4 composed of the N-terminal hairpin and subsequent four-kringle domains of hepatocyte growth factor (HGF) is bifunctional, acting as a competitive antagonist for HGF and an angiogenesis inhibitor. In this study, we determined whether or not four-kringle domains of HGF (K1-4) have anti-angiogenic activity. For this purpose, we prepared recombinant K1-4 and NK4, using the baculovirus expression system. Although NK4 antagonized HGF-induced DNA synthesis of rat hepatocytes, cell scattering of MDCK cells and the c-Met/HGF receptor tyrosine phosphorylation in endothelial cells, K1-4 failed to antagonize HGF-induced DNA synthesis, cell scattering and the c-Met/HGF receptor tyrosine phosphorylation in endothelial cells, thus, indicating that K1-4 lacks HGF-antagonist activity. However, endothelial proliferation and migration induced by HGF was inhibited by K1-4, similar to the case seen with NK4. Furthermore, K1-4 inhibited the proliferation and migration of human dermal microvascular endothelial cells induced by vascular endothelial growth factor or by basic fibroblast growth factor. We propose that kringle 1-4 of HGF inhibits angiogenic responses in endothelial cells, independently of HGF-c-Met signaling pathways.

Angiostatin generation by cathepsin D secreted by human prostate carcinoma cells

Angiostatin, a potent endogenous inhibitor of angiogenesis, is generated by cancer-mediated proteolysis of plasminogen. The culture medium of human prostate carcinoma cells, when incubated with plasminogen at a variety of pH values, generated angiostatic peptides and miniplasminogen. The enzyme(s) responsible for this reaction was purified and identified as procathepsin D. The purified procathepsin D, as well as cathepsin D, generated two angiostatic peptides having the same NH(2)-terminal amino acid sequences and comprising kringles 1-4 of plasminogen in the pH range of 3.0-6.8, most strongly at pH 4.0 in vitro. This reaction required the concomitant conversion of procathepsin D to catalytically active pseudocathepsin D. The conversion of pseudocathepsin D to the mature cathepsin D was not observed by the prolonged incubation. The affinity-purified angiostatic peptides inhibited angiogenesis both in vitro and in vivo. Importantly, procathepsin D secreted by human breast carcinoma cells showed a significantly lower angiostatin-generating activity than that by human prostate carcinoma cells. Since deglycosylated procathepsin D from both prostate and breast carcinoma cells exhibited a similar low angiostatin-generating activity, this discrepancy appeared to be attributed to the difference in carbohydrate structures of procathepsin D molecules between the two cell types. The seminal vesicle fluid from patients with prostate carcinoma contained the mature cathepsin D and procathepsin D, but not pseudocathepsin D, suggesting that pseudocathepsin D is not a normal intermediate of procathepsin D processing in vivo. The present study provides evidence for the first time that cathepsin D secreted by human prostate carcinoma cells is responsible for angiostatin generation, thereby causing the prevention of tumor growth and angiogenesis-dependent growth of metastases.

Effects of microenvironmental extracellular pH and extracellular matrix proteins on angiostatin's activity and on intracellular pH

Antiangiogenic agents target migratory and proliferative endothelial cells (EC) in the process of forming new vessels, resulting in growth inhibition or cell death. Here we have shown that the antiangiogenic activity of angiostatin on EC is enhanced in culture when the microenvironmental extracellular pH (pH(e)) is reduced to levels similar to that of many tumors. In a migration/scratch assay and during tube formation, angiostatin in combination with reduced pH(e) synergistically resulted in an increased EC death--an effect not seen with either stimulus individually. Lowering of pH(e) decreased intracellular pH (pH(i)), and a further lowering of pH(i) occurred when low pH(e) was combined with angiostatin. These data suggest that low pH(e) plays a role in the relative specificity and efficacy of angiostatin for tumor neovasculature and indicate roles for both pH(e) and pH(i) in the mechanism of angiostatin action. A receptor for angiostatin, the alpha-subunit of ATP synthase, was found on the surface of EC. We show that cell surface receptor distribution is increased on Matrigel, a basement-like matrix, as opposed to fibronectin or RGD peptide substrates, and redistributed to a more punctuate appearance at low pH(e). Furthermore, positive cell surface histochemical staining for alpha-ATP synthase was blocked by preincubation with angiostatin. These data indicate that substrate and pH(e) are critical parameters in the evaluation of this antiangiogenic substance, and probably for others as well.

Kringle 1 of human hepatocyte growth factor inhibits bovine aortic endothelial cell proliferation stimulated by basic fibroblast growth factor and causes cell apoptosis

Hepatocyte growth factor (HGF), also known as scatter factor, is a mesenchymal or stromal-derived mediator with angiogenic activity. There are four kringle domains in its amino terminus. They display considerable sequence similarity with those of angiostatin, an angiogenesis inhibitor. We now describe that the recombinant kringle1 of HGF (HGFK1) inhibits bovine aortic endothelial (BAE) cell proliferation stimulated by basic fibroblast growth factor in a dose-dependent manner, with an ED(50) of approximately 0.7 microg/ml, while ED(50) of angiostatin is 3 microg/ml. Treatment of BAE cell with HGFK1 caused cell apoptosis. This report thus constitutes the first demonstration that kringle1 of HGF is a selective inhibitor for BAE cell proliferation stimulated by bFGF.