Angiogenesis in cancer, vascular, rheumatoid and other disease

VE-Cadherin mediates endothelial cell capillary tube formation in fibrin and collagen gels

Various cell adhesion molecules mediate the diverse functions of the vascular endothelium, such as cell adhesion, neutrophil migration, and angiogenesis. In order to identify cell adhesion molecules important for angiogenesis, we used an in vitro model (Chalupowicz, Chowdhury, Bach, Barsigian, and Martinez, J. Cell Biol. 130, 207-215, 1995) in which human umbilical vein endothelial cell monolayers are induced to form capillary-like tubes when a second gel, composed of either fibrin or collagen, is formed overlying the apical surface. In the present investigation, we observed that a monoclonal antibody directed against the first extracellular domain of human vascular endothelial cadherin (VE-cadherin, cadherin 5) inhibited the formation of capillary tubes formed between either fibrin or collagen gels. Moreover, when added to preformed capillary tubes, this antibody disrupted the capillary network. In contrast, monoclonal antibodies directed against the extracellular domain of N-cadherin, the alphavbeta3 integrin, and PECAM-1 failed to inhibit capillary tube formation. During capillary tube formation, Western blot and RT-PCR analysis revealed no marked change in VE-cadherin expression. Immunocytochemical studies demonstrated that VE-cadherin was concentrated at intercellular junctions in multicellular capillary tubes. Thus, VE-cadherin plays a specific role in fibrin-induced or collagen-induced capillary tube formation and is localized at areas of intercellular contact where it functions to maintain the tubular architecture. Moreover, its function at tubular intercellular junctions is distinct from that at intercellular junctions present in confluent monolayers, since only the former was inhibited by monoclonal antibodies.

Two functional forms of vascular endothelial growth factor receptor-2/Flk-1 mRNA are expressed in normal rat retina

Vascular endothelial growth factor (VEGF) is an important mediator of ocular neovascularization by exerting its endothelial specific mitogenic effects through high affinity tyrosine kinase receptors. By screening a rat retina cDNA library, we have isolated a clone encoding the full-length prototypic form of the rat VEGF receptor-2/Flk-1, as well as a short form of the mRNA that encodes the complete seven N-terminal immunoglobulin-like extracellular ligand-binding domains, transmembrane region, NH2-terminal half of the intracellular kinase domain, and kinase insert domain but does not encode the COOH-terminal half of the intracellular kinase domain and carboxyl-terminal region. Both forms of mRNA are detected in rat retina, although the short form is expressed at a lower level. VEGF induced a biphasic increase of cytoplasmic calcium with both forms in HK 293 transfected cells, indicating that both forms of the VEGF receptor-2/Flk-1 are functional and that the COOH-terminal half of the intracellular kinase domain and carboxyl region of VEGF receptor-2/Flk-1 are not strictly necessary for either ligand binding or this biological activity.

Interleukin-6 produced by pancreatic carcinoma cells enhances humoral immune responses against tumor cells: a possible event in tumor regression

Production of interleukin-6 (IL-6) by human pancreatic carcinoma cells inversely correlates with potentials for blood-borne metastasis to the liver in nude mice. IL-6 cDNA was transfected to PCI-43, one of our cultured pancreatic carcinoma cell lines that does not produce IL-6 and generates numerous metastases to the liver. An IL-6 high-producer clone (PCI-43h) generated few metastases; IL-6 production thus has a direct effect on metastasis, whereas other transfectants (PCI-43l and PCI-43n), which are IL-6 low-, and IL-6 non-producers, respectively, did generate metastases. Tumor-reactive IgG, which mediated antibody-dependent cellular cytotoxicity (ADCC) in vitro, was detected in sera from recipient nude mice inoculated with PCI-43h but not in sera from mice given PCI-43l, PCI-43n or parent PCI-43. Tumor-reactive IgM was detected in sera from all mice, irrespective of inoculated PCI-43 species, with a slight augmentation being noted in PCI-43h-inoculated nude mice. Severe combined immunodeficiency (SCID) beige mice were then used as recipients for PCI-43 species, and tumorigeneity was examined by s.c. inoculation of a suboptimal number of PCI-43 transfectants (1 x 10(6)/0.1 ml). Only PCI-43h formed palpable masses in SCID beige mice, whereas it first grew to be palpable but subsequently became not palpable in nude mice, thereby revealing a dual action of tumor-derived IL-6. Thus, tumor-derived IL-6 confers growth promotion in SCID beige mice, while the same cytokine exhibits anti-tumorigenic functions, presumably through humoral immune responses, in nude mice.

Cancer treatment by targeted drug delivery to tumor vasculature in a mouse model

In vivo selection of phage display libraries was used to isolate peptides that home specifically to tumor blood vessels. When coupled to the anticancer drug doxorubicin, two of these peptides-one containing an alphav integrin-binding Arg-Gly-Asp motif and the other an Asn-Gly-Arg motif-enhanced the efficacy of the drug against human breast cancer xenografts in nude mice and also reduced its toxicity. These results indicate that it may be possible to develop targeted chemotherapy strategies that are based on selective expression of receptors in tumor vasculature.

Corticosteroids inhibit the expression of the vascular endothelial growth factor gene in human vascular smooth muscle cells

The vascular endothelial growth factor (VEGF) is a specific mitogen for vascular endothelial cells and enhances vascular permeability and edemagenesis. VEGF is also a major regulator of angiogenesis and may be a key target for inhibiting angiogenesis in angiogenesis-associated diseases. Among the extensively studied angiostatic compounds are several corticosteroids when used alone or in combination with heparin. In this study we present evidence for an additional mechanism of action of hydrocortisone, cortisone and dexamethasone in inhibiting edemagenesis or angiogenesis. In cultures of aortic human vascular smooth muscle cells these corticosteroids (1 x 10(-8) to 1 x 10(-12) M) abolished the platelet-derived growth factor-induced (PDGF) expression of the VEGF gene in a dose-dependent manner. In contrast, two precursors of corticosteroids, desoxycorticosterone or pregnenolone, did not affect PDGF-induced VEGF expression. Our findings indicate that the capacity of corticosteroids to reduce edema or to prevent new blood vessel formation may be attributed, at least in part to the ability of these agents to abolish the expression of VEGF.

Angiogenesis and prostate cancer: in vivo and in vitro expression of angiogenesis factors by prostate cancer cells

OBJECTIVES

Recently, it was confirmed that angiogenesis is important in the development and spread of a variety of human cancers, including prostate cancer (PCa). Tumor neovascularization is thought to be controlled by chemical signals, known as angiogenic factors (AF). To date, little is known regarding the existence and role of AF in PCa. We previously reported on vascular endothelial growth factor (VEGF) in PCa. Currently, we compare VEGF expression with that of interleukin-8 (IL-8), another putative regulator of angiogenesis. We evaluated the expression of these two important AF in PCa and explored the role of inflammatory cytokines IL-1 and tumor necrosis factor (TNF) in their regulation.

METHODS

Ex vivo studies involved previously reported immunohistochemical analysis for VEGF and recent evaluation of IL-8 expression and distribution in archival tissue samples of PCa, benign prostatic hyperplasia (BPH), and normal prostate tissue. In vitro studies used PCa cells (DU-145) grown in culture and stimulated with cytokines thought to induce VEGF and IL-8 (ie, IL-1 alpha, IL-1 beta, TNF-alpha, and TNF-beta). After 24 hours, with or without cytokines, cell culture supernatants were analyzed by enzyme-linked immunosorbent assay or radioimmunoassay for VEGF or IL-8 levels.

RESULTS

Immunohistochemical studies of prostate tissue showed that PCa cells stained positively for VEGF and IL-8. Benign prostatic hyperplasia and normal prostate cells displayed little staining for either AF. Low levels of VEGF and IL-8 were produced by unstimulated DU-145 cells. Induction of DU-145 cells with cytokines resulted in differential stimulation whereby TNF was the predominant inducer of VEGF, whereas IL-1 was the predominant inducer of IL-8.

CONCLUSIONS

Our results indicate that significant levels of VEGF and IL-8 are present in PCa, but not BPH or normal prostate cells in vivo. In vitro studies suggest that differential regulation of AF expression occurs in PCa. Because IL-1 and TNF are present in the PCa tumor microenvironment, it is likely that differential regulation of AF also occurs in human PCa and contributes to differential tumor growth and metastasis.

Tumor angiogenesis--a new therapeutic target in gliomas

Tumor growth is critically dependent on angiogenesis, which is sprouting of new vessels from pre-existing vasculature. This process is regulated by inducers and inhibitors released from tumor cells, endothelial cells, and macrophages. Brain tumors, especially glioblastoma multiforme, have significant angiogenic activity primarily by the expression of the angiogenic factor VEGF Anti-angiogenic therapy represents a new promising therapeutic modality in solid tumors. Several agents are currently under evaluation in clinical trials. The present review describes the principal inducers and inhibitors of angiogenesis in tumors and summarizes what is known about their mechanisms of action in relation to CNS tumors. Potential areas for clinical use are also discussed.

Gene transfer of human heme oxygenase into coronary endothelial cells potentially promotes angiogenesis

Heme oxygenase (HO-1) is a stress protein that has been suggested to participate in defense mechanisms against agents that induce oxidative injury such as hemoglobin/heme, hypoxia-ischemia and cytokines. Overexpression of HO-1 in endothelial cells (EC) might, therefore, protect against oxidative stress produced under these pathological conditions, by generation of CO, a vasodilator, and bilirubin, which has antioxidant properties that enhance blood vessel formation to counteract hypoxia-induced injury. A plasmid containing the cytomegalovirus promoter (pCMV) neomycin human HO-1 gene complexed to cationic liposomes, lipofectin, was used to transfect rabbit coronary microvessel EC. Cells transfected with human HO-1 gene demonstrated a twofold increase in HO activity and maintained a similar phenotype as in the nontransfected cells. Cell number in transfected cells with human HO-1 gene increased by about 45%, as compared to nontransfected or those transfected with control pCMV. Transfected and nontransfected EC revealed a similar response to basic fibroblast growth factor (bFGF) in capillary formation. However, transfected cells with the human HO-1 gene exhibited a twofold increase in blood vessel formation. The angiogenic response of EC to overexpression of HO-1 gene provides direct evidence that the inductive form of HO-1 following injury represents an important tissue adaptive mechanism for moderating the severity of cell damage produced in inflammatory reaction sites of hemorrhage, thrombosis and hypoxic-ischemia. Thus, HO-1 may participate in the regulation of EC activation, proliferation and angiogenesis.

Over-expression of human CD44s in murine 3T3 cells: selection against during primary tumorigenesis and selection for during micrometastasis

Human CD44 standard isoform (hCD44s) cDNA regulated by a high-expressing promoter was transfected into Balb/c 3T3 cells and the tumorigenic and metastatic capacities of the transfectants were investigated in nude mice at the subcutaneous site. One of three transfectants was tumorigenic. hCD44s expression was lost in the cells of large primary tumors using this tumorigenic clone. These tumors were extremely aggressive giving overt metastases and micrometastases to several sites including mesentery, stomach, liver, diaphragm, pancreas and lung. Micrometastatic cells re-expressed hCD44s, consistent with its importance for early steps in the metastatic cascade. hCD44s was not expressed in overt metastases; most probably the expression was lost during the outgrowth of micrometastases into overt metastatic tumors. Thus hCD44s expression in murine 3T3 cells does induce tumorigenicity in select cases, is not compatible with aggressive outgrowth of primary or secondary tumors, and is advantageous for early steps in metastatic spread. These results suggest that CD44s is an example of a novel type of 'metastasis' molecule that is disadvantageous for tumor growth and is only transiently advantageous during metastatic spreading of tumor cells to distant organs.

Podokinesis in endothelial cell migration: role of nitric oxide

Previously, we demonstrated the role of nitric oxide (NO) in transforming epithelial cells from a stationary to locomoting phenotype [E. Noiri, T. Peresleni, N. Srivastava, P. Weber, W.F. Bahou, N. Peunova, and M. S. Goligorsky. Am. J. Physiol. 270 (Cell Physiol. 39): C794-C802, 1996] and its permissive function in endothelin-1-stimulated endothelial cell migration (E. Noiri, Y. Hu, W. F. Bahou; C. Keese, I. Giaever, and M. S. Goligorsky, J. Biol: Chem. 272: 1747-1753, 1997). In the present study, the role of functional NO synthase in executing the vascular endothelial growth factor (VEGF)-guided program of endothelial cell migration and angiogenesis was studied in two independent experimental settings. First, VEGF, shown to stimulate NO release from simian virus 40-immortalized microvascular endothelial cells, induced endothelial cell transwell migration, whereas NG-nitro-L-arginine methyl ester (L-NAME) or antisense oligonucleotides to endothelial NO synthase suppressed this effect of VEGF. Second, in a series of experiments on endothelial cell wound healing, the rate of VEGF-stimulated cell migration was significantly blunted by the inhibition of NO synthesis. To gain insight into the possible mode of NO action, we next addressed the possibility that NO modulates cell matrix adhesion by performing impedance analysis of endothelial cell monolayers subjected to NO. The data showed the presence of spontaneous fluctuations of the resistance in ostensibly stationary endothelial cells. Spontaneous oscillations were induced by NO, which also inhibited cell matrix adhesion. This process we propose to term "podokinesis" to emphasize a scalar from of micromotion that, in the presence of guidance cues, e.g., VEGF, is transformed to a vectorial movement. In conclusion, execution of the program for directional endothelial cell migration requires two coexisting messages: NO-induced podokinesis (scalar motion) and guidance cues, e.g., VEGF, which imparts a vectorial component to the movement. Such a requirement for the dual signaling may explain a mismatch in the demand and supply with newly formed vessels in different pathological states accompanied by the inhibition of NO synthase.

Vascular endothelial growth factor increases release of gelatinase A and decreases release of tissue inhibitor of metalloproteinases by microvascular endothelial cells in vitro

The present study was designed to determine the influences of vascular endothelial growth factor (VEGF) on cell proliferation and the release of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) from human dermal microvascular endothelial cells. Treatment of cultures with 10 ng/ml or more of VEGF significantly increased cell proliferation. The effect of VEGF treatment on the levels of specific MMPs and TIMPs in the media was subsequently examined in cultures that were treated with 10 ng/ml VEGF. Zymography and Western blot analyses demonstrated that gelatinase A levels in the media were increased by VEGF treatment. Collagenase was detected by Western blots in both VEGF-treated and untreated culture media, but the levels were not significantly increased by the VEGF treatment. An ELISA assay confirmed that VEGF treatment significantly increased gelatinase A levels but did not significantly increase collagenase levels. Western blot and ELISA data showed that VEGF treatment significantly decreased TIMP-1 and TIMP-2 levels compared to untreated cultures. The data suggest that VEGF may modulate endothelial cell-derived MMP activity by: (1) increasing the abundance of gelatinase A; (2) disinhibiting gelatinase A by decreasing the abundance of TIMP-2; and (3) disinhibiting preexisting collagenase by reducing levels of TIMP-1. These actions could contribute to the ability of VEGF to promote endothelial cell invasion of new territory.

Expression of Tie2/Tek in breast tumour vasculature provides a new marker for evaluation of tumour angiogenesis

Endothelial receptor tyrosine kinases may play important roles in pathological vascular growth, particularly in tumours. In this study, immunohistochemistry was used to evaluate the expression of a novel endothelial receptor tyrosine kinase, Tie2/Tek, in the endothelium of vascular 'hotspots' in normal breast tissue (n = 10), benign breast lesions (n = 10) and in breast tumours (n = 123). Tie2 expression was detected in the endothelium of all breast tissues examined. However, the strongest expression of Tie-2 was seen in vascular 'hot spots' within the inflammatory infiltrate at the periphery of invasive tumours. Moreover, the proportion of Tie2-positive vessels (Tie2 counts/CD31 counts) was significantly higher in breast tumours than the proportion of Tie2-positive vessels in either normal breast tissue or benign breast lesions (P = 0.004 and 0.0001 respectively). These data are consistent with a role for Tie2 in tumour angiogenesis and demonstrate the potential use of Tie2 expression as a novel marker of the tumour vasculature.

Stimulation of tumour angiogenesis by proximal wounds: spatial and temporal analysis by MRI

We show here, using high-resolution magnetic resonance imaging, that injured tissue provides a favourable milieu for the neovascularization and growth of C6 glioma spheroids, implanted subcutaneously in nude mice. Moreover, the presence of micro-tumours in an injured tissue inhibited the healing process, leaving an open persistent wound. In correlation with the induced angiogenesis of implanted spheroids in the presence of proximal wounds, a shorter lag period was observed for initiation of tumour growth. This effect was restricted spatially and was observed only for wounds within 5 mm from the tumour. In such proximal wounds, angiogenesis was enhanced in the first days after injury, and vessel regression, which normally starts 4 days after injury, did not occur. Injury causing interference to tumour perfusion promoted tumour vascularization and growth even for more remote incisions, possibly by activating stress-induced angiogenesis. The kinetics of vascularization and growth of these wound-tumour systems sheds light on the clinical observations of increased probability of metastatic recurrence and stimulated regrowth of residual tumour in the site of surgical intervention. High-resolution magnetic resonance imaging could detect the aberrant angiogenic activity of these tumour-wound systems as early as 1 week after injury.

Isolation and characterization of the circulating form of human endostatin

Recently, fragments of extracellular proteins, including endostatin, were defined as a novel group of angiogenesis inhibitors. In this study, human plasma equivalent hemofiltrate was used as a source for the purification of high molecular weight peptides (10-20 kDa), and the isolation and identification of circulating human endostatin are described. The purification of this C-terminal fragment of collagen alpha1(XVIII) was guided by MALDI-MS and the exact molecular mass determined by ESI-MS was found to be 18 494 Da. N-terminal sequencing revealed the identity of this putative angiogenesis inhibitor and its close relation to mouse endostatin. The cysteine residues 1-3 and 2-4 in the molecule are linked by disulfide bridges. In vitro biological characterization of the native protein demonstrated no anti-proliferative activity on different endothelial cell types. These data indicate that human endostatin, which is a putative angiogenesis inhibitor, is present in the circulation.

Inhibition of vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation by a peptide corresponding to the exon 7-encoded domain of VEGF165

Vascular endothelial growth factor (VEGF) is a potent mitogen for endothelial cells (EC) in vitro and a major regulator of angiogenesis in vivo. VEGF121 and VEGF165 are the most abundant of the five known VEGF isoforms. The structural difference between these two is the presence in VEGF165 of 44 amino acids encoded by exon 7 lacking in VEGF121. It was previously shown that VEGF165 and VEGF121 both bind to KDR/Flk-1 and Flt-1 but that VEGF165 binds in addition to a novel receptor (Soker, S., Fidder, H., Neufeld, G., and Klagsbrun, M. (1996) J. Biol. Chem. 271, 5761-5767). The binding of VEGF165 to this VEGF165-specific receptor (VEGF165R) is mediated by the exon 7-encoded domain. To investigate the biological role of this domain further, a glutathione S-transferase fusion protein corresponding to the VEGF165 exon 7-encoded domain was prepared. The fusion protein inhibited binding of 125I-VEGF165 to VEGF165R on human umbilical vein-derived EC (HUVEC) and MDA-MB-231 tumor cells. The fusion protein also inhibited significantly 125I-VEGF165 binding to KDR/Flk-1 on HUVEC but not on porcine EC which express KDR/Flk-1 alone. VEGF165 had a 2-fold higher mitogenic activity for HUVEC than did VEGF121. The exon 7 fusion protein inhibited VEGF165-induced HUVEC proliferation by 60% to about the level stimulated by VEGF121. Unexpectedly, the fusion protein also inhibited HUVEC proliferation in response to VEGF121. Deletion analysis revealed that a core inhibitory domain exists within the C-terminal 23-amino acid portion of the exon 7-encoded domain and that a cysteine residue at position 22 in exon 7 is critical for inhibition. It was concluded that the exon 7-encoded domain of VEGF165 enhances its mitogenic activity for HUVEC by interacting with VEGF165R and modulating KDR/Flk-1-mediated mitogenicity indirectly and that exon 7-derived peptides may be useful VEGF antagonists in angiogenesis-associated diseases.

Myocardial angiogenesis as a possible mechanism for TMLR efficacy

Despite advances in the treatment of ischemic heart disease, there still exists a significant number of individuals for whom bypass surgery or angioplasty are not options. Transmyocardial laser revascularization (TMLR) is a promising technology that has already been shown to reduce symptoms in patients with chronic ischemic heart disease that is not amenable to conventional therapies. Although it appears that TMLR can provide symptomatic relief of angina in selected patients, the mechanism by which TMLR is thought to work is unclear. Recently it has been postulated that TMLR induces an angiogenic response and, perhaps, improves local perfusion to ischemic myocardial territories. A brief overview of the biology of myocardial angiogenesis is presented.

alphavbeta3 integrin mediates the cell-adhesive capacity and biological activity of basic fibroblast growth factor (FGF-2) in cultured endothelial cells

Fibroblast growth factor-2 (FGF-2) immobilized on non-tissue culture plastic promotes adhesion and spreading of bovine and human endothelial cells that are inhibited by anti-FGF-2 antibody. Heat-inactivated FGF-2 retains its cell-adhesive activity despite its incapacity to bind to tyrosine-kinase FGF receptors or to cell-surface heparan sulfate proteoglycans. Recombinant glutathione-S-transferase-FGF-2 chimeras and synthetic FGF-2 fragments identify two cell-adhesive domains in FGF-2 corresponding to amino acid sequences 38-61 and 82-101. Both regions are distinct from the FGF-receptor-binding domain of FGF-2 and contain a DGR sequence that is the inverse of the RGD cell-recognition sequence. Calcium deprivation, RGD-containing eptapeptides, soluble vitronectin (VN), but not fibronectin (FN), inhibit cell adhesion to FGF-2. Conversely, soluble FGF-2 prevents cell adhesion to VN but not FN, thus implicating VN receptor in the cell-adhesive activity of FGF-2. Accordingly, monoclonal and polyclonal anti-alphavbeta3 antibodies prevent cell adhesion to FGF-2. Also, purified human alphavbeta3 binds to immobilized FGF-2 in a cation-dependent manner, and this interaction is competed by soluble VN but not by soluble FN. Finally, anti-alphavbeta3 monoclonal and polyclonal antibodies specifically inhibit mitogenesis and urokinase-type plasminogen activator (uPA) up-regulation induced by free FGF-2 in endothelial cells adherent to tissue culture plastic. These data demonstrate that FGF-2 interacts with alphavbeta3 integrin and that this interaction mediates the capacity of the angiogenic growth factor to induce cell adhesion, mitogenesis, and uPA up-regulation in endothelial cells.

Mechanisms of metastasis

The metastatic spread of solid tumours is responsible directly or indirectly for most cancer-related deaths. Our understanding of the molecular genetic and biological events that contribute to tumor cell dissemination has increased considerably over the last decade. It is clear that close anatomic and temporal co-operation between cellular adhesion molecules, extracellular matrix (ECM)-degrading proteases and peptides inducing tumour vascularisation are essential components of the metastatic behaviour of cancer cells. Although this enhanced understanding may have little immediate impact on patient survival (about 50% of patients have established metastatic disease at first presentation), it has led to the development of novel anti-metastatic therapies targeting distinct molecules and steps in the metastatic cascade. Here we review the role of matrix-degrading enzymes, changes in cellular adhesive capacity and tumour angiogenesis during cancer spread, highlighting areas that are of emerging importance in the clinic.

Loss of ovarian function promotes angiogenesis in human ovarian carcinoma

We show here that elevated levels of gonadotropins (luteinizing hormone and follicle stimulating hormone), as found in menopause or after ovariectomy, promote growth of human ovarian carcinoma by induction of tumor angiogenesis. Human epithelial ovarian cancer tumors progressed faster in ovariectomized mice. This induced growth could be attributed to the elevated levels of gonadotropins associated with loss of ovarian function because direct administration of gonadotropins also was effective in promoting tumor progression in vivo. On the other hand, gonadotropins had no direct effect on the proliferation of human ovarian cancer cells in vitro. Using MRI, we demonstrated that ovariectomy significantly (P < 0.02) induces neovascularization of human ovarian carcinoma spheroids implanted in nude mice. Moreover, conditioned medium of gonadotropin-treated human ovarian carcinoma cells showed increased mitogenic activity to bovine endothelial cells, and this activity could be blocked by neutralizing antibodies against luteinizing hormone and against vascular endothelial growth factor. Accordingly, gonadotropin stimulation resulted in a dose-dependent-induced expression of vascular endothelial growth factor in monolayer culture as well as in the outer proliferating cells of human ovarian cancer spheroids. These results demonstrate the significance of the elevated levels of gonadotropins, as found in menopause and in all ovarian cancer patients, on the progression of ovarian cancer and could explain the protective effect of estrogen replacement therapy. Based on these results, we suggest that hormonal therapy aimed at lowering the circulating levels of gonadotropins may possibly prolong remission in ovarian cancer by extending tumor dormancy.

Hyaluronectin blocks the stimulatory effect of hyaluronan-derived fragments on endothelial cells during angiogenesis in vitro

Hyaluronic acid (HA) is a glycosaminoglycan of the extracellular matrix. Its fragmentation by the hyaluronidase, secreted by tumor cells, facilitates tumor invasion and the HA degradation products generated stimulate angiogenesis. We report here that the HA-binding protein hyaluronectin (HN) inhibits the stimulatory effect of HA-derived fragments on the proliferation and migration of endothelial cells in vitro, and hampers the organization of endothelial cells into capillary-like structures. Since HN strongly inhibits endothelial cell adhesion to immobilized HA, it is postulated that HN acts by impairing the binding to endothelial cells of HA fragments generated by hyaluronidase, thereby neutralizing the effect of HA degradation products on angiogenesis. Our results reveal a new mechanism by which the angiogenesis induced by HA fragments is modulated by HN.

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

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

Tranilast inhibits the proliferation, chemotaxis and tube formation of human microvascular endothelial cells in vitro and angiogenesis in vivo

1. First developed as an antiallergic drug, tranilast inhibits chemical mediator release from mast cells. In the present study, we examine the effects of tranilast on angiogenesis in vitro and in vivo and discuss the application of tranilast for angiogenic diseases. 2. Tranilast inhibited significantly the proliferation (IC50: 136 microM, 95% confidence limits: 134-137 microM) and vascular endothelium growth factor (VEGF)-induced chemotaxis (IC50: 135 microM, 95% confidence limits: 124-147 microM) of human dermal microvascular endothelial cells (HDMECs) at concentrations greater than 25 micrograms ml-1. No toxicity to HDMECs measuring by LDH release and no inhibitory effects on metalloproteinase (MMP)-2 and MMP-9 activity were observed even at 100 micrograms ml-1 (306 microM). 3. Tube formation of HDMECs cultured on the matrigel as an in vitro angiogenesis model was inhibited by tranilast in a concentration-dependent manner. The IC50 value and 95% confidence limits were 175 microM and 151-204 microM, respectively. 4. In vivo angiogenesis was induced in mice by the subcutaneous injection of matrigel containing 30 ng ml-1 VEGF and 64 micrograms ml-1 heparin. Tranilast was administered orally twice a day for 3 days. Tranilast dose-dependently suppressed angiogenesis in the matrigel and a significant change was observed at a dose of 300 mg kg-1. 5. These results indicate that tranilast is an angiogenesis inhibitor which may be beneficial for the improvement of angiogenic diseases such as proliferative diabetic retinopathy, age-related macular degeneration, tumour invasion and rheumatoid arthritis.

Establishment and characterization of a novel in vitro angiogenesis model using a microvascular endothelial cell line, F-2C, cultured in chemically defined medium

The behavior of vascular endothelial cells (EC) is an important factor in the processes involved in angiogenesis, but the regulatory mechanisms of angiogenesis, especially underlying the tubulogenesis by EC are not yet clear. Although a number of in vitro experimental models of tubulogenesis have been developed by use of cultured EC, most of those models are too complex to be easily handled and further, the culture media are usually supplemented with serum, creating problems in interpretation of experimental results. To generate a simple in vitro angiogenesis study model under serum-free culture conditions, we adapted a murine microvascular endothelial cell line, F-2, to a chemically defined medium, Cos Medium 001, and successfully established a subline of F-2, designated F-2C, which revealed a unique growth pattern. In Cos Medium 001, F-2C proliferates in a cobblestone pattern at an early growth stage, but, at a late growth stage, spontaneously differentiates to form three-dimensional honeycomblike tubular structures without the supplementation of any specific factors. The cell aggregation activity of F-2C in the presence of Ca2+ was much greater than that of F-2. The amount of subendothelial matrix deposited by F-2C was significantly higher than that by F-2, and increased prominently after the F-2C cells reached the differentiating stage of tubulogenesis. These findings indicate that F-2C is a new EC line in which tubulogenesis is spontaneously induced by the marked deposition of basement membrane analog to the subendothelial matrix and by the enhancement of presumable cadherin activity. We suggest that this cell line, F-2C, represents a simple and useful in vitro angiogenesis model.

PF4 inhibits thrombin-stimulated MMP-1 and MMP-3 metalloproteinase expression in human vascular endothelial cells

We investigated whether PF4 could regulate the constitutive and thrombin-stimulated expression of metalloproteinases (MMPs) in endothelial cells (EC). PF4 inhibited the increase in the expression of MMP-1 and MMP-3 promoted by thrombin or the thrombin receptor agonist peptide SFLLRNPNDKYEPF (SFLL..) by 50% but did not modify the constitutive expression of these MMPs. This inhibitory effect was not mediated through a direct interaction of PF4 with thrombin or with the MMPs themselves. The interaction of PF4 with heparan sulfates at the surface of the EC appeared to be implicated in the inhibition mechanism of MMP-1 but not in that of MMP-3. MMP-1 transcription levels remained unchanged after PF4 treatment, whereas the increase in MMP-3 transcription induced by thrombin or SFLL.. was inhibited by approximately 50%. Expression of the tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2 was not affected by PF4. The present data provide new evidence that the antiangiogenic properties of PF4 involve the inhibition of matrix breakdown and suggest that this property of PF4 could be especially relevant in the context of thrombin-regulated tissue remodelling.

Development of the kidney vasculature

Renal vascularization and nephrogenesis occur simultaneously following a tightly regulated developmental program influenced by growth factors, extracellular matrix components and cell membrane receptors. Both processes of angiogenesis and vasculogenesis probably participate in the formation of renal vessels. The origin and fate of the various renal vascular cells and the molecular mechanisms that initiate and guide intrarenal vascularization are fundamental questions that remain to be answered.

Does surgical removal of primary melanoma trigger growth of occult metastases? An analytical epidemiological approach

BACKGROUND

In several human tumor systems a potential role of surgical removal of the primary tumor upon metastatic tumor growth has been evaluated, as it has been in experimental models. The present study addresses the question of whether the removal of primary melanomas disinhibits growth of metastatic disease and results in more rapid progression.

METHODS

In a data set of 1224 primary cutaneous melanomas the risk of "thin" melanomas to develop metastases within 1 year was compared with the risk of matched pairs of "thick" melanomas to present metastases at the time of diagnosis. For this purpose, a pairwise matching procedure based on certain assumptions as to tumor volume and tumor doubling time has been applied.

RESULTS

When a long tumor doubling time is assumed (200, 400, or 800 days), the tumors removed seem to have a significantly higher risk of metastases to become clinically apparent within 1 year than the matched pairs of tumors to present metastatic disease at the time of diagnosis (chi-square < 0.01). When short tumor doubling time is assumed (50 or 100 days), the difference is not significant, but there also seems to be no benefit for the operated patients.

CONCLUSION

In the present data set there is evidence that surgery of primary melanoma may enhance tumor growth at metastatic sites.

Induction of Vascular Endothelial Growth Factor by Hypoxia Is Modulated by a Phosphatidylinositol 3-Kinase/Akt Signaling Pathway in Ha-ras-Transformed Cells Through a Hypoxia Inducible Factor-1 Transcriptional Element

Tumor angiogenesis, the development of new blood vessels, is a highly regulated process that is controlled genetically by alterations in oncogene and tumor suppressor gene expression and physiologically by the tumor microenvironment. Previous studies indicate that the angiogenic switch in Ras-transformed cells may be physiologically promoted by the tumor microenvironment through the induction of the angiogenic mitogen, vascular endothelial growth factor (VEGF). In this report, we show Ras-transformed cells do not use the downstream effectors c-Raf-1 or mitogen activated protein kinases (MAPK) in signaling VEGF induction by hypoxia as overexpression of kinase-defective alleles of these genes does not inhibit VEGF induction under low oxygen conditions. In contrast to the c-Raf-1/MAP kinase pathway, hypoxia increases phosphatidylinositol 3-kinase (PI 3-kinase) activity in a Ras-dependent manner, and inhibition of PI 3-kinase activity genetically and pharmacologically results in inhibition of VEGF induction. We propose that hypoxia modulates VEGF induction in Ras-transformed cells through the activation of a stress inducible PI 3-kinase/Akt pathway and the hypoxia inducible factor-1 (HIF-1) transcriptional response element.

Targeting by affinity-matured recombinant antibody fragments of an angiogenesis associated fibronectin isoform

The oncofetal fibronectin (B-FN) isoform is present in vessels of neoplastic tissues during angiogenesis but not in mature vessels. B-FN could therefore provide a target for diagnostic imaging and therapy of cancer. Phage display libraries have been used to isolate human antibody fragments with pan-species recognition of this isoform. We describe the use of these fragments in nude mice to target an aggressive tumor (grafted F9 murine teratocarcinoma). Imaging in real time was done by infrared photodetection of a chemically coupled fluorophore. The targeting was improved by use of affinity-matured fragments with low kinetic dissociation rates (koff = 1.5 x 10(-4) s-1) and also by engineering dimeric fragments via a C-terminal amphipathic helix.

Arterial wall neovascularization--potential role in atherosclerosis and restenosis

Neointimal formation and arterial wall remodeling are pivotal causes of luminal narrowing in atherogenesis and restenosis. Arterial remodeling refers to a series of dynamic structural changes that arteries may undergo in response to various stimuli, including changes in blood flow and pressure, and acute injury. The biological mechanisms involved in arterial remodeling are poorly understood and are currently a main target for research. We have recently focused on the role of the arterial wall microcirculation (ie, vasa vasorum) in arterial remodeling after injury. In the past, a correlation between arterial wall neovascularization and the accumulation of arterial plaque has been documented; however, the dynamic role of these microvessels in arterial repair and luminal narrowing has not been examined. The type of arterial injury, the nature of the lesion that develops, and the arterial compartment in which angiogenesis occurs may determine the role of the vasa vasorum in arterial narrowing. In this review, we highlight the data that link arterial wall neovascularization with lesion formation and the process of arterial remodeling.

In vitro angiogenesis is modulated by the mechanical properties of fibrin gels and is related to alpha(v)beta3 integrin localization

This study deals with the role of the mechanical properties of matrices in in vitro angiogenesis. The ability of rigid fibrinogen matrices with fibrin gels to promote capillarylike structures was compared. The role of the mechanical properties of the fibrin gels was assessed by varying concentration of the fibrin gels. When the concentration of fibrin gels was decreased from 2 mg/ml to 0.5 mg/ml, the capillarylike network increased. On rigid fibrinogen matrices, capillarylike structures were not formed. The extent of the capillarylike network formed on fibrin gels having the lowest concentration depended on the number of cells seeded. The dynamic analysis of capillarylike network formation permitted a direct visualization of a progressive stretching of the 0.5 mg/ml fibrin gels. This stretching was not observed when fibrin concentration increases. This analysis shows that 10 h after seeding, a prearrangement of cells into ringlike structures was observed. These ringlike structures grew in size. Between 16 and 24 h after seeding, the capillarylike structures were formed at the junction of two ringlike structures. Analysis of the alpha(v)beta3 integrin localization demonstrates that cell adhesion to fibrinogen is mediated through the alpha(v)beta3 integrin localized into adhesion plaques. Conversely, cell adhesion to fibrin shows a diffuse and dot-contact distribution. We suggest that the balance of the stresses between the tractions exerted by the cells and the resistance of the fibrin gels triggers an angiogenic signal into the intracellular compartment. This signal could be associated with modification in the alpha(v)beta3 integrin distribution.

Combined analysis of p53 and vascular endothelial growth factor expression in colorectal carcinoma for determination of tumor vascularity and liver metastasis

Recent studies have demonstrated that the p53 tumor suppressor gene plays an important role in controlling tumor angiogenesis. We examined the expression of p53 and vascular endothelial growth factor (VEGF), a well-characterized angiogenic inducer, together with microvessel density to investigate the role of p53 in the regulation of angiogenesis and its clinical significance in human colorectal carcinoma. Surgically resected specimens of 163 colorectal carcinomas were studied by immunohistochemical staining for p53 protein, VEGF and factor VIII-related antigen. Positive p53 protein accumulation and VEGF expression was found in 41.7% and 49.1% of tumors, respectively. p53 and VEGF staining status was identical in 65.6% of tumors. The incidence of p53- or VEGF-positive tumors was significantly higher in patients with venous invasion and liver metastases than in those without. The microvessel count (MVC) in p53- or VEGF-positive tumors was significantly higher than that in negative tumors, and MVC in both p53- and VEGF-positive tumors was significantly higher than that in the other subgroups. Neither synchronous nor metachronous hepatic metastases were found in patients with p53- and VEGF-negative tumors, while 52.2% of patients with both-positive tumors had liver metastases and had a poorer prognosis than those with both-negative tumors. Our findings suggest the presence of a p53-VEGF pathway regulating tumor angiogenesis in human colorectal carcinoma. Combined analysis of p53 and VEGF expression might be useful for predicting the occurrence of liver metastasis in patients with this disease.

A High Pretreatment Serum Vascular Endothelial Growth Factor Concentration Is Associated With Poor Outcome in Non-Hodgkin's Lymphoma

Vascular endothelial growth factor (VEGF ) is a secreted endothelial cell-specific mitogen, which is induced by hypoxia and is angiogenic in vivo. Recently, elevated serum concentrations of VEGF (S-VEGF ) have been reported in patients with cancers of various histologies. However, the prognostic significance of S-VEGF in human cancer is unknown and the origin of S-VEGF remains unsettled. We measured S-VEGF by enzyme-linked immunosorbent assay from sera taken from 82 patients with non-Hodgkin's lymphoma before treatment and stored for 9 to 15 years at −20°C. All but one of the patients had been followed-up for at least 5 years or until death. S-VEGF ranged from 15 to 964 pg/mL; median, 228 pg/mL; mean, 291 pg/mL. A higher than the median S-VEGF level was associated with a poor World Health Organization performance status, a high International Prognostic Index, a high serum lactate dehydrogenase level, and a large cell histology. Patients with lower than the median S-VEGF at diagnosis had a 71% 5-year survival rate in comparison with only 49% among those with a higher than the median S-VEGF. We conclude that a high pretreatment S-VEGF level is associated with poor outcome in non-Hodgkin's lymphoma.

The crystal structure of vascular endothelial growth factor (VEGF) refined to 1.93 A resolution: multiple copy flexibility and receptor binding

BACKGROUND

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific angiogenic and vasculogenic mitogen. VEGF also plays a role in pathogenic vascularization which is associated with a number of clinical disorders, including cancer and rheumatoid arthritis. The development of VEGF antagonists, which prevent the interaction of VEGF with its receptor, may be important for the treatment of such disorders. VEGF is a homodimeric member of the cystine knot growth factor superfamily, showing greatest similarity to platelet-derived growth factor (PDGF). VEGF binds to two different tyrosine kinase receptors, kinase domain receptor (KDR) and Fms-like tyrosine kinase 1 (Flt-1), and a number of VEGF homologs are known with distinct patterns of specificity for these same receptors. The structure of VEGF will help define the location of the receptor-binding site, and shed light on the differences in specificity and cross-reactivity among the VEGF homologs.

RESULTS

We have determined the crystal structure of the receptor-binding domain of VEGF at 1.93 A resolution in a triclinic space group containing eight monomers in the asymmetric unit. Superposition of the eight copies of VEGF shows that the beta-sheet core regions of the monomers are very similar, with slightly greater differences in most loop regions. For one loop, the different copies represent different snapshots of a concerted motion. Mutagenesis mapping shows that this loop is part of the receptor-binding site of VEGF.

CONCLUSIONS

A comparison of the eight independent copies of VEGF in the asymmetric unit indicates the conformational space sampled by the protein in solution; the root mean square differences observed are similar to those seen in ensembles of the highest precision NMR structures. Mapping the receptor-binding determinants on a multiple sequence alignment of VEGF homologs, suggests the differences in specificity towards KDR and Flt-1 may derive from both sequence variation and changes in the flexibility of binding loops. The structure can also be used to predict possible receptor-binding determinants for related cystine knot growth factors, such as PDGF.

Fibronectin modulates endothelial response to HIV type 1 Tat

The normal function of the endothelium is impaired in HIV-1 infection. Disturbances of the local cytokines as well as the release of HIV-1 Tat by infected mononuclear cells play a role in endothelial dysfunction. We studied the effects of Tat on the human endothelial ECV cell line. In this system, Tat inhibited cell proliferation only in the presence of fibronectin as a culture substrate, whereas it did not modulate plasminogen activator activity, cell migration, or synthesis of fibronectin. Because amino acids 49-57 contains a nuclear translocation sequence, we also evaluated the potential intracellular role of Tat in tat-transfected ECV cells. tat transfectants showed inhibition of cell growth, unaffected cell migration and plasminogen activator activity, and a significant induction of the expression of fibronectin.

Genomic organization of human and mouse genes for vascular endothelial growth factor C

We report here the cloning and characterization of human and mouse genes for vascular endothelial growth factor C (VEGF-C), a newly isolated member of the vascular endothelial growth factor/platelet-derived growth factor (VEGF/PDGF) family. Both VEGF-C genes comprise over 40 kilobase pairs of genomic DNA and consist of seven exons, all containing coding sequences. The VEGF homology domain of VEGF-C is encoded by exons 3 and 4. Exons 5 and 7 encode cysteine-rich motifs of the type C6C10CRC, and exon 6 encodes additional C10CXCXC motifs typical of a silk protein. A putative alternatively spliced rare RNA form lacking exon 4 was identified in human fibrosarcoma cells, and a major transcription start site was located in the human VEGF-C gene 523 base pairs upstream of the translation initiation codon. The upstream promoter sequences contain conserved putative binding sites for Sp-1, AP-2, and NF-kappaB transcription factors but no TATA box, and they show promoter activity when transfected into cells. The VEGF-C gene structure is thus assembled from exons encoding propeptides and distinct cysteine-rich domains in addition to the VEGF homology domain, and it shows both similarities and distinct differences in comparison with other members of the VEGF/PDGF gene family.

Target effector role of vascular endothelium in the inflammatory response: insights from the clinical trial of anti-TNF alpha antibody in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterised by chronic joint inflammation and infiltration by cells from the blood, especially activated T cells and macrophages, together with formation of new blood vessels. The overgrowth of the synovial lesion results eventually in destruction of cartilage and bone. Cytokines play a major role in RA, both in systemic inflammatory processes, such as induction of acute phase protein synthesis, and in the stimulation of new blood vessel development and recruitment of leucocytes to developing lesions. The focus for the interplay of many cytokines is the endothelium, the lining layer of the vasculature. This is the primary target for circulating mediators, and it controls the traffic of cells and molecules from the bloodstream into underlying tissues. Targeting the action of individual cytokines--for example, using antibody against tumour necrosis factor alpha (TNF alpha), has been shown to be very effective in the treatment of RA. Blockade of TNF alpha activity results in deactivation of the endothelium, manifested as reduced expression of adhesion molecules and chemoattractant cytokines, leading to diminished trafficking of inflammatory cells to synovial joints. In addition anti-TNF alpha decreases circulating levels of the potent angiogenic cytokine VEGF, suggesting that new blood vessel formation, and hence the supply of nutrients to the growing synovial lesion, is also affected. These observations lend further support to the hypothesis that interruption of a component of the cytokine network in RA may modulate disease progression, and point the way towards the development of new therapeutic strategies for the treatment of chronic inflammatory disease states.

Angiogenesis in the pathobiology and treatment of vascular and malignant diseases

Cardiovascular disease and cancer account for the majority of adult disease in the developed world. This review focuses on current concepts in the study of angiogenesis (new vessel formation) as related to these conditions and highlights the role of vascular endothelial growth factor. Developments in therapeutic angiogenesis have raised the possibility that pharmacologic or gene-directed interventions, based on the ability of vascular endothelial growth factor to promote new vessel formation, may soon gain clinical application for the treatment of occlusive vascular disease. Similarly, the future treatment of malignant disease is likely to involve antiangiogenic agents that, in preliminary animal work, have demonstrated an efficacy that is not limited by adverse affects. Aside from these potential applications, current investigations have enhanced our understanding of mechanisms involved in the development of atherosclerotic and malignant disease.