Angiogenesis at the Interface between Basic and Clinical Research

The field of antiangiogenesis has shown a remarkably rapid evolution from the discovery at the bench to translation into the clinic. Currently a wide variety of compounds are in clinical trial as inhibitors of angiogenesis, and new compounds are being frequently added. The target cell of most angiogenesis inhibitors is the endothelial cell, with inhibitors that selectively affect a number of endothelial cell functions acquired during angiogenesis, including activation, proliferation, migration, invasion and survival. The endothelial cell may also be targeted by chemotherapeutic agents currently in use. The high doses and intermittent treatment schedules used to fight resistant tumor cells may be altered towards lower doses and chronic administration to obtain selective inhibition of angiogenic factor-stimulated endothelial cells as adjuvant therapy. Finally, gene therapy is a promising route for the delivery of novel protein inhibitors of angiogenesis, and is actively being investigated.

The role of heparin in angiogenesis

A series of experiments is described in which: (i) mast cells were found to accumulate at a tumour site before the ingrowth of new capillaries; (ii) heparin released by mast cells increased the migration of capillary endothelial cells in vitro; and (iii) heparin enhanced tumour angiogenesis in vivo. These experiments led to the discovery that protamine and platelet factor 4 are angiogenesis inhibitors. This finding suggests a central role for heparin or related glycosaminoglycans in the growth regulation of capillary blood vessels.

Retinopathy of prematurity: molecular pathology and therapeutic strategies

Retinopathy of prematurity (ROP) is an ischemia-induced proliferative retinopathy, which affects premature infants with low birth weight. It is a leading cause of visual impairment and blindness in children, and shares pathophysiological characteristics with other common ocular diseases such as diabetic retinopathy, central vein occlusion, and age-related macular degeneration. Pathologically similar inherited diseases such as Norrie disease suggest a possible genetic component in the susceptibility to ROP. The process of retinal neovascularization in ROP and in animal models of oxygen-induced retinopathy is complex, and involves angiogenic factors, such as vascular endothelial growth factor, and basement membrane components. Potential medical therapies for ROP, including modulators of angiogenic factors, inhibitors of basement membrane changes, endogenous inhibitors such as pigment epithelium derived factor, and anti-inflammatory drugs, have shown efficacy against neovascularization in several animal models. Some of these therapies are in clinical trials now for diabetic retinopathy and age-related macular degeneration, and in the future may prove efficacious for the treatment of ROP.

[The clinical perspective of angiogenesis inhibitors]

An important development in the treatment of cancer is the recognition that the tumour's microenvironment, notably its vasculature, may be an attractive target for therapy. In the eighties of the last century, the concept of angiogenesis (the formation of new blood vessels from existing vasculature) was developed. Angiogenesis is the driving force behind tumour growth and metastasis. Recent angiogenesis research has elucidated the role of growth factors (vascular endothelial growth factor (VEGF), epidermal growth factor), metalloproteinases and endogenous proteins such as angiostatin and endostatin. This new knowledge has led to the rapid development of several angiogenesis inhibiting strategies. Although these new strategies showed very promising results in preclinical animal studies, early clinical studies with individual angiogenesis inhibitors have shown no antitumour effect so far. However, in recent studies blocking VEGF in addition to conventional chemotherapy has led to an increase in disease-free survival time and in response rate to chemotherapy. Angiogenesis research has contributed to the knowledge of the biology of cancer, the design of modified clinical studies and the development of surrogate markers that can be used as pharmacodynamic end points in future studies.

Contrasting effects of VEGF gene disruption in embryonic stem cell-derived versus oncogene-induced tumors

Previous gene targeting studies have implicated an indispensable role of vascular endothelial growth factor (VEGF) in tumor angiogenesis, particularly in tumors of embryonal or endocrine origin. In contrast, we report here that transformation of VEGF-deficient adult fibroblasts (MDF528) with ras or neu oncogenes gives rise to highly tumorigenic and angiogenic fibrosarcomas. These aggressive VEGF-null tumors (528ras, 528neu) originated from VEGF(-/-) embryonic stem cells, which themselves were tumorigenically deficient. We also report that VEGF production by tumor stroma has a modest role in oncogene-driven tumor angiogenesis. Both ras and neu oncogenes down-regulated at least two endogenous inhibitors of angiogenesis [pigment epithelium derived factor (PEDF) and thrombospondin 1 (TSP-1)]. This is functionally important as administration of an antiangiogenic TSP-1 peptide (ABT-526) markedly inhibited growth of VEGF(-/-) tumors, with some ingress of pericytes. These results provide the first definitive genetic demonstration of the dispensability of tumor cell-derived VEGF in certain cases of 'adult' tumor angiogenesis, and thus highlight the importance of considering VEGF-independent as well as VEGF-dependent pathways when attempting to block this process pharmacologically.

Localization of Tie2 and phospholipase D in endothelial caveolae is involved in angiopoietin-1-induced MEK/ERK phosphorylation and migration in endothelial cells

Angiopoietin-1 (Ang1) and its receptor, Tie2, play critical roles in blood vessel formation. Ang1 triggers a variety of signaling events in endothelial cells leading to vasculogenic and angiogenic processes. However, the underlying mechanism for Ang1/Tie2 signaling is not fully understood. Here, we show that Tie2 and phospholipase D (PLD) are localized in the caveolae, specialized subdomains of the endothelial cell plasma membrane enriched with signaling molecules. Interestingly, Ang1 increased PLD activities in a dose- and time-dependent manner. Ang1-induced MEK/ERK activation was abrogated when PLD was inhibited, suggesting that PLD mediates Ang1-induced MEK/ERK activation. Moreover, PLD inhibitor, 1-butanol, inhibited Ang1-induced endothelial cell migration. Our results indicate that: (1) caveolae may be the platform for Tie2/PLD association in endothelial cells; (2) PLD is a new mediator of Ang1/Tie2-induced signaling pathway, and it participates in MAPK activation and endothelial cell migration.

Angiopoietin-2 induces human glioma invasion through the activation of matrix metalloprotease-2

A hallmark of highly malignant human gliomas is their infiltration of the brain. We analyzed a large number of primary human glioma biopsies and found high levels of expression of an angiogenic regulator, angiopoietin-2 (Ang2), in the invasive areas, but not in the central regions, of those tumors. In the invasive regions where Ang2 was overexpressed, increased levels of matrix metalloprotease-2 (MMP-2) were also apparent. Consonant with these features, intracranial xenografts of glioma cells engineered to express Ang2 were highly invasive into adjacent brain parenchyma compared with isogenic control tumors. In regions of the Ang2-expressing tumors that were actively invading the brain, high levels of expression of MMP-2 and increased angiogenesis were also evident. A link between these two features was apparent, because stable expression of Ang2 by U87MG cells or treatment of several glioma cell lines with recombinant Ang2 in vitro caused activation of MMP-2 and acquisition of increased invasiveness. Conversely, MMP inhibitors suppressed Ang2-stimulated activation of MMP-2 and Ang2-induced cell invasion. These results suggest that Ang2 plays a critical role in inducing tumor cell infiltration, and that this invasive phenotype is caused by activation of MMP-2.

Proangiogenic properties of human myeloma cells: production of angiopoietin-1 and its potential relationship to myeloma-induced angiogenesis

Patients with multiple myeloma (MM) have increased bone marrow (BM) angiogenesis; however, the proangiogenic properties of myeloma cells and the mechanisms of MM-induced angiogenesis are not completely clarified. The angiopoietin system has been identified as critical in the regulation of vessel formation. In this study we have demonstrated that myeloma cells express several proangiogenic factors, and, in particular, we found that angiopoietin-1 (Ang-1), but not its antagonist Ang-2, was expressed by several human myeloma cell lines (HMCLs) at the mRNA and the protein levels. In a transwell coculture system, we observed that myeloma cells up-regulated the Ang-1 receptor Tie2 in human BM endothelial cells. Moreover, in an experimental model of angiogenesis, the conditioned medium of HMCLs significantly stimulated vessel formation compared with control or vascular endothelial growth factor (VEGF) treatment. The presence of anti-Tie2 blocking antibody completely blunted the proangiogenic effect of XG-6. Finally, our in vitro results were supported by the in vivo finding of Ang-1, but not Ang-2, mRNA and protein expression in purified MM cells obtained from approximately 47% of patients and by high BM angiogenesis in patients with MM positive for Ang-1, suggesting that the angiopoietin system could be involved, at least in part, in MM-induced angiogenesis.

Osteopontin (Eta-1) and fibroblast growth factor-2 cross-talk in angiogenesis

The cytokine/extracellular matrix protein osteopontin (OPN/Eta-1) is an important component of cellular immunity and inflammation. It also acts as a survival, cell-adhesive, and chemotactic factor for endothelial cells. Here, subtractive suppression hybridization showed that serum-deprived murine aortic endothelial (MAE) cells transfected with the angiogenic fibroblast growth factor-2 (FGF2) overexpress OPN compared with parental cells. This was confirmed by Northern blotting and Western blot analysis of the conditioned media in different clones of endothelial cells overexpressing FGF2 and in endothelial cells treated with the recombinant growth factor. In vivo, FGF2 caused OPN expression in newly formed endothelium of the chick embryo chorioallantoic membrane (CAM) and of murine s.c. Matrigel plug implants. Recombinant OPN (rOPN), the fusion protein GST-OPN, and the deletion mutant GST-DeltaRGD-OPN were angiogenic in the CAM assay. Angiogenesis was also triggered by OPN-transfected MAE cells grafted onto the CAM. OPN-driven neovascularization was independent from endothelial alpha(v)beta(3) integrin engagement and was always paralleled by the appearance of a massive mononuclear cell infiltrate. Accordingly, rOPN, GST-OPN, GST-DeltaRGD-OPN, and the conditioned medium of OPN-overexpressing MAE cells were chemotactic for isolated human monocytes. Also, rOPN triggered a proangiogenic phenotype in human monocytes by inducing the expression of the angiogenic cytokines TNF-alpha and IL-8. OPN-mediated recruitment of proangiogenic monocytes may represent a mechanism of amplification of FGF2-induced neovascularization during inflammation, wound healing, and tumor growth.

Angiopoietin-1 inhibits vascular permeability, angiogenesis, and growth of hepatic colon cancer tumors

Angiopoietin (Ang)-1 and -2 are critical regulators of embryonic and postnatal neovascularization. Ang-1 activates the endothelial cell-specific tyrosine kinase receptor Tie-2, which in turn leads to enhanced endothelial cell survival and stabilization. The effects of Ang-1 on tumor angiogenesis remain controversial; although we have previously demonstrated that Ang-1 overexpression in colon cancer cells leads to a decrease in s.c. tumor growth, others have shown that Ang-1 may be proangiogenic. Few studies have addressed the role of the Angs in tumors growing in the organ of metastatic growth. We hypothesized that overexpression of Ang-1 may inhibit the growth of colon cancers growing in the liver by inhibition of angiogenesis. We also wanted to investigate the mechanisms by which Ang-1 affects angiogenesis in vivo. Human colon cancer cells (HT29) were stably transfected with an Ang-1 construct or an empty vector (pcDNA) and injected directly into the livers of nude mice. After 37 days, livers were harvested and weighed, and tumor sizes were measured. In an additional experiment, to validate the paracrine effect of Ang-1, various mixtures of control cells and Ang-1-transfected cells were injected into livers, and tumor growth was assessed. Direct effects of recombinant Ang-1 on angiogenesis were studied with an in vivo Gelfoam angiogenesis assay. The impact of Ang-1 on vascular permeability was investigated using an intradermal Miles assay with conditioned media from transfected cells. Liver weights (P < 0.05), tumor volumes (P < 0.05), vessel counts (P < 0.01), and tumor cell proliferation (P < 0.01) in the Ang-1 group were significantly lower than those in the control (pcDNA) group. Tumor vessels in the Ang-1 group developed a significantly higher degree of pericyte coverage (P < 0.02) than vessels in pcDNA tumors. In the cell mixture experiment, even as few as a 1:10 mixture of Ang-1-transfected cells/control cells resulted in a significant reduction of hepatic tumor volumes (P < 0.04). In the angiogenesis assay, vessel counts in Gelfoam implants were significantly decreased by the addition of Ang-1 (P < 0.01). Finally, conditioned medium from Ang-1-transfected cells decreased vascular permeability more than that from control cells (P < 0.05). Our results suggest that Ang-1 is an important regulator of angiogenesis and vascular permeability and that this effect may be secondary to increasing periendothelial support and vessel stabilization. Thus, Ang-1 could potentially serve as an antineoplastic or anti-permeability agent for patients with metastatic colorectal cancer.

The angiogenic factor CYR61 in breast cancer: molecular pathology and therapeutic perspectives

CYR61 (CNN1), a member of the cysteine rich 61/connective tissue growth factor/nephroblastoma overexpressed (CYR61/CTFG/NOV) family of growth regulators (CNN), is a pro-angiogenic factor that mediates diverse roles in development, cell proliferation, and tumorigenesis. We have recently shown that CYR61 is overexpressed in invasive and metastatic human breast cancer cells. Accordingly, elevated levels of CYR61 in breast cancer are associated with more advanced disease. Unfortunately, the exact mechanisms by which CYR61 promotes an aggressive breast cancer phenotype are still largely unknown. This review examines the functional role of CYR61 in breast cancer disease, presenting evidence that CYR61 signaling may play a major role in estrogen- as well as growth factor-dependent breast cancer progression. We also emphasize the functional significance of the molecular connection of CYR61 and its integrin receptor alpha(v)beta(3) enhancing breast cancer aggressiveness. Moreover, we describe experimental evidence that establishes a novel role for CYR61 determining the protection of human breast cancer cells against chemotherapy-induced apoptosis through its interactions with the integrin receptor alpha(v)beta(3). All these findings delineate a new noteworthy function of a CYR61/alpha(v)beta(3) autocrine-paracrine signaling pathway within both angiogenesis and breast cancer progression, which would allow a dual anti-angiogenic and anti-tumor benefit with a single drug.

Protective role of angiopoietin-1 in experimental pulmonary hypertension

Angiopoietin-1 (Ang-1), a newly discovered ligand of the endothelial-specific tyrosine kinase receptor Tie-2, has been found to promote cell survival, vascular maturation, and stabilization. We hypothesized that Ang-1 gene transfer to the pulmonary microcirculation would improve pulmonary hemodynamics and vascular remodeling in experimental pulmonary hypertension. Rat pulmonary artery smooth muscle cells were transfected with Ang-1 cDNA or null (pFLAG-CMV-1) vector. Syngeneic Fisher 344 rats were treated with monocrotaline (MCT) (75 mg/kg IP) with or without delivery of 5x10(5) Ang-1-transfected cells into the right jugular vein. After 28 days, plasmid-derived Ang-1 mRNA was consistently and robustly detected by reverse transcriptase-polymerase chain reaction in lungs from all animals receiving Ang-1 gene therapy. Tie-2 receptor expression was markedly downregulated in rats treated with MCT, and this was partially restored by gene therapy with Ang-1. Animals receiving MCT exhibited 77% mortality by 28 days. In contrast, in pAng-1-treated animals, the 28-day mortality was only 14% (P<0.0001). In addition, right ventricular systolic pressure was reduced from 52+/-1.3 mm Hg in the MCT-treated group to 38+/-1.3 mm Hg by Ang-1 gene transfer (P<0.01), whereas the measurement of right to left ventricular plus septal weight ratio was also reduced from 0.41+/-0.03 to 0.31+/-0.01 (P<0.05). Moreover, MCT resulted in increased apoptosis, mainly in the microvasculature, and reduced endothelial NO synthase mRNA expression, both of which were prevented by Ang-1 gene transfer. Thus, cell-based gene transfer with Ang-1 improved survival and pulmonary hemodynamics in experimental pulmonary hypertension by a mechanism involving the inhibition of apoptosis and protection of the pulmonary microvasculature.

[Molecular mechanisms of vasculogenesis and angiogenesis. What regulates vascular growth?]

The basic mechanisms governing how endothelial cells, periendothelial cells, matrix molecules and blood constituents interact with each other are discussed. The many insights gained from this basic knowledge are being extended to further understand physiological and pathological features of vascular sprouting and maintenance. Understanding these basic principles that drive angiogenesis and vasculogenesis will lead to a more specific therapy of many disorders in ophthalmology and other fields, such as arteriosclerosis, tumor growth, myocardial ischemia and tissue repair.

Vessel co-option: how tumors obtain blood supply in the absence of sprouting angiogenesis

The hypothesis that solid tumors are dependent on angiogenesis, the formation of new vessels, for outgrowth and metastasis has acquired a central position in cancer research and has since inspired many scientists for several decades. Among the various angiogenic stimuli that are secreted by tumor cells, members of the Vascular Endothelial Growth Factor (VEGF) family are most prominent. More recently it has become clear, however, that tumors may use alternative ways to obtain blood supply. Vessel co-option, the use of pre-existent vessels, was described first in the brain, one of the most densely vascularized organs in the body. Thus, brain tumors may develop without the need of an angiogenic switch to occur. Obviously, this way of blood supply will not be affected by angiogenesis inhibition. In addition, it is predicted that tumors with this type of behavior will be less visible in contrast-enhanced MRI. In this article we present our recently developed mouse brain model of vessel co-option in melanoma. The effects of expression of VEGF on tumor vascularity, and on MRI visualization of these brain lesions are described. Possible consequences of anti-angiogenesis therapy are discussed.

PDGF-D is a potent transforming and angiogenic growth factor

Platelet-derived growth factors (PDGFs) are important for normal tissue growth and maintenance. Overexpression of the classical PDGFs, PDGF-A and PDGF-B, has been linked to several diseases, including cancer, fibrotic disease and atherosclerosis. Recently, two novel PDGFs, PDGF-C and PDGF-D, were discovered. It has not yet been established whether PDGF-C and PDGF-D are linked to disease phenotypes like the classical PDGFs. PDGF-B, the cellular homologue of the viral simian sarcoma oncogene v-sis, is known to potently induce cellular transformation through activation of PDGF receptor (PDGFR)-beta. In this work, we have determined the transformation efficacy of PDGF-D in comparison with that of PDGF-C and PDGF-B. PDGF-D is a potent transforming growth factor for NIH/3T3 cells, and the transformed cells displayed stress fibre reorganization, increased proliferation rate, anchorage-independent growth in soft agar, ability to induce tumours in nude mice, and upregulation of vascular endothelial growth factor. Morphological analyses of the vasculatures from the PDGF-isoform-expressing tumours revealed marked differences suggesting differential signalling through the two PDGF receptors in tumour vessel development and remodelling. In summary, these results suggest that PDGF-D induce cellular transformation and promote tumour growth by accelerating the proliferation rate of the tumour cells, and by stimulation of tumour neovascularization.

Glomerular-specific alterations of VEGF-A expression lead to distinct congenital and acquired renal diseases

Kidney disease affects over 20 million people in the United States alone. Although the causes of renal failure are diverse, the glomerular filtration barrier is often the target of injury. Dysregulation of VEGF expression within the glomerulus has been demonstrated in a wide range of primary and acquired renal diseases, although the significance of these changes is unknown. In the glomerulus, VEGF-A is highly expressed in podocytes that make up a major portion of the barrier between the blood and urinary spaces. In this paper, we show that glomerular-selective deletion or overexpression of VEGF-A leads to glomerular disease in mice. Podocyte-specific heterozygosity for VEGF-A resulted in renal disease by 2.5 weeks of age, characterized by proteinuria and endotheliosis, the renal lesion seen in preeclampsia. Homozygous deletion of VEGF-A in glomeruli resulted in perinatal lethality. Mutant kidneys failed to develop a filtration barrier due to defects in endothelial cell migration, differentiation, and survival. In contrast, podocyte-specific overexpression of the VEGF-164 isoform led to a striking collapsing glomerulopathy, the lesion seen in HIV-associated nephropathy. Our data demonstrate that tight regulation of VEGF-A signaling is critical for establishment and maintenance of the glomerular filtration barrier and strongly supports a pivotal role for VEGF-A in renal disease.

Comparison of vascular endothelial growth factor and basic fibroblast growth factor on angiogenesis in SCID mice

Therapeutic angiogenesis is a promising approach to treat patients with cardiovascular disease, and will likely be critical to engineering large tissues. Many growth factors have been found to play significant roles in angiogenesis, and vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are the most extensively investigated angiogenic factors to date. However, the appropriate dose to obtain a desired response and the effectiveness of each factor, relative to the other, in promoting angiogenesis at a specific site in the body remains unclear. We have used alginate hydrogels as localized delivery vehicles for VEGF and bFGF, and compared the ability of these factors to promote new blood vessel formation in the subcutaneous tissue of severe combined immunodeficient (SCID) mice. We have found that the thickness of a granulation tissue layer formed around the gel and the number of blood vessels in the layer increased with the dose of VEGF in the gel, but the density of new blood vessels remained relatively constant. Sustained and localized delivery of bFGF from the gels, while similarly leading to an increase in the density of blood vessels in the granulation tissue, did not lead to as high of a blood vessel density as VEGF. The results of this study support previous studies demonstrating the utility of both VEGF and bFGF in promoting angiogenesis, and suggest VEGF is more appropriate for creating a dense bed of new blood vessels in this model.

Vascular growth factors and angiogenesis in cardiac surgery

Therapeutic angiogenesis, in the form of growth factor protein administration or gene therapy, has emerged as a new method of treatment for patients with severe, inoperable coronary artery disease. Improved myocardial perfusion and function after administration of angiogenic growth factors has been demonstrated in animal models of chronic myocardial ischemia. Recently, preliminary clinical trials using growth factor proteins or genes encoding these angiogenic factors have demonstrated clinical and other objective evidence of relevant angiogenesis. A recent study reported beneficial long-term effects of therapeutic angiogenesis using fibroblast growth factor (FGF)-2 protein in terms of freedom from angina and perfusion on single-photon emission computed tomographic imaging. Thus, therapeutic angiogenesis has the potential to extend treatment options to patients who are not optimal candidates for conventional methods of myocardial revascularization. However, endogenous antiangiogenic influences, intrinsic lack of response of patients with severe endothelial dysfunction, and other limitations will need to be overcome before angiogenesis becomes a standard therapy for the treatment of patients with severe coronary disease.

Use of adenovirus vectors for functional gene analysis in the chicken chorioallantoic membrane

The chicken chorioallantoic membrane (CAM) assay represents one of the most widely used in vivo screening assay for genes with angiogenic (blood vessel-inducing) or angiostatic (inhibition of vessel formation or their destruction) activities. Here we show that adenovirus gene transfer vectors infect cells in the CAM and lead to expression of the viral transgene. Furthermore, infection with an adenovirus vector containing the human vascular endothelial growth factor gene induced the formation of new blood vessels. This improved method saves a considerable amount of time in the identification of genes that can influence blood vessel formation because the expensive and time-consuming production and purification of recombinant protein can be omitted.

Cartilage-specific matrix protein, chondromodulin-I (ChM-I), is a strong angio-inhibitor in endochondral ossification of human neonatal vertebral tissues in vivo: relationship with angiogenic factors in the cartilage

Although cartilage contains many angiogenic factors during endochondral ossification, it is an avascular tissue. The cartilage-specific non-collagenous matrix protein chondromodulin-I (ChM-I) has been shown to be a strong angio-inhibitor. To elucidate whether ChM-I plays an essential role in angio-inhibition during endochondral ossification in man, we investigated the expression and localization of ChM-I in comparison with those of angiogenic factors and the endothelial cell marker CD34 in human neonatal vertebral tissues. Although invasion of CD34-positive endothelial cells was observed in primary subchondral spongiosa, expression of the marker of endothelial cells, CD34, was not found in neonatal vertebral cartilage matrix. Type II collagen was deposited in all matrices during endochondral ossification, whereas aggrecan was deposited in the matrix of hypertrophic cartilage, especially around lacunae. Vascular endothelial growth factor (VEGF), which is known to be a strong angiogenic factor, was localized in chondrocytes in mature to hypertrophic cartilage and also in bone marrow. Fibroblast growth factor-2 (FGF-2; basic fibroblast growth factor), which is also known to be a strong angiogenic factor, was localized in the cytoplasm of chondrocytes of mature cartilage in human vertebral cartilage tissues. Transforming growth factor (TGF)-beta has been reported to have many functions including angiogenesis, and TGF-beta1 was also localized in mature chondrocytes in endochondral tissues undergoing ossification. On the other hand, the novel cartilage-specific matrix protein ChM-I was localized in interterritorial regions of the matrix in mature to hypertrophic cartilage, especially around lacunae. In conclusion, these observations indicate that ChM-I may serve as a barrier against the angiogenic properties of VEGF, FGF-2 and TGF-beta1 during endochondral ossification, and this matrix molecule may play an essential role in determining the avascular nature of cartilage in vivo.

Vascular permeability factor/vascular endothelial growth factor induces lymphangiogenesis as well as angiogenesis

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF, VEGF-A) is a multifunctional cytokine with important roles in pathological angiogenesis. Using an adenoviral vector engineered to express murine VEGF-A(164), we previously investigated the steps and mechanisms by which this cytokine induced the formation of new blood vessels in adult immunodeficient mice and demonstrated that the newly formed blood vessels closely resembled those found in VEGF-A-expressing tumors. We now report that, in addition to inducing angiogenesis, VEGF-A(164) also induces a strong lymphangiogenic response. This finding was unanticipated because lymphangiogenesis has been thought to be mediated by other members of the VPF/VEGF family, namely, VEGF-C and VEGF-D. The new "giant" lymphatics generated by VEGF-A(164) were structurally and functionally abnormal: greatly enlarged with incompetent valves, sluggish flow, and delayed lymph clearance. They closely resembled the large lymphatics found in lymphangiomas/lymphatic malformations, perhaps implicating VEGF-A in the pathogenesis of these lesions. Whereas the angiogenic response was maintained only as long as VEGF-A was expressed, giant lymphatics, once formed, became VEGF-A independent and persisted indefinitely, long after VEGF-A expression ceased. These findings raise the possibility that similar, abnormal lymphatics develop in other pathologies in which VEGF-A is overexpressed, e.g., malignant tumors and chronic inflammation.

Placental growth factor (PlGF) and its receptor Flt-1 (VEGFR-1): novel therapeutic targets for angiogenic disorders

Efforts to therapeutically stimulate or inhibit vessel growth have been primarily focused on vascular endothelial growth factor (VEGF) and its receptor VEGFR-2 (Flk-1), while little attention has been devoted to the therapeutic potential for angiogenic disorders of placental growth factor (PlGF), a VEGF family member, and its receptor VEGFR-1 (Flt-1). However, recent developments and insights could shift that focus to P1GF and Flt-1. Indeed, PlGF stimulated angiogenesis and collateral growth in ischemic heart and limb with at least a comparable efficiency to VEGF and did not cause side effects associated with VEGF, such as edema or hypotension. An anti-Flt-1 antibody suppressed neovascularization in tumors and ischemic retina, and angiogenesis and inflammatory joint destruction in arthritis. The anti-Flt-1 antibody also reduced atherosclerotic plaque growth and vulnerability, but the atheroprotective effect was not due to reduced plaque neovascularization. The anti-inflammatory effects of the anti-Flt-1 antibody were attributable to a reduced mobilization of bone marrow-derived myeloid progenitors into the peripheral blood, a reduced mobilization/differentiation (and impaired infiltration) of Flt-1-expressing leukocytes into inflamed tissues, and a defective activation of myeloid cells. Thus, PlGF and Flt-1 constitute potential candidates for therapeutic modulation of angiogenesis and inflammation.

Release of regulators of angiogenesis following Hypocrellin-A and -B photodynamic therapy of human brain tumor cells

Photodynamic therapy (PDT) is an innovative strategy for the treatment of solid neoplasms of the brain. Aside from inducing cell death in tumor cells, PDT induces endothelial cell death and promotes formation of blood clots; however, exact mechanisms that trigger these phenomena remain largely unknown. We now used Western blotting to analyze secretion of regulators of angiogenesis to the supernatants of one glioma, one macrophage, and one endothelial cell line following Hypocrellin-A and -B photodynamic therapy. We observed induction of proangiogenic VEGF (vascular endothelial growth factor) and of antiangiogenic sFlt-1, angiostatin, p43, allograft inflammatory factor-1, and connective tissue growth factor. Release of thrombospondin-1 was diminished in a glioma cell line supernatant. Endostatin release was induced in glioma cells and reduced in macrophages and endothelial cells. These data show that a wide range of antiangiogenic factors are secreted by brain tumor cells following Hypocrellin photochemotherapy. However, VEGF release is also induced thus suggesting both favorable and deleterious effects on tumor outgrowth.

Angiopoietin-1 inhibits tumour growth and ascites formation in a murine model of peritoneal carcinomatosis

Angiopoietin-1 is an important regulator of endothelial cell survival. Angiopoietin-1 also reduces vascular permeability mediated by vascular endothelial growth factor. The effects of angiopoietin-1 on tumour growth and angiogenesis are controversial. We hypothesised that angiopoietin-1 would decrease tumour growth and ascites formation in peritoneal carcinomatosis. Human colon cancer cells (KM12L4) were transfected with vector (pcDNA) alone (control) or vector containing angiopoietin-1 and injected into the peritoneal cavities of mice. After 30 days, the following parameters were measured: number of peritoneal nodules, ascites volume, and diameter of the largest tumour. Effects of angiopoietin-1 on vascular permeability were investigated using an intradermal Miles assay with conditioned media from transfected cells. Seven of the nine mice in the pcDNA group developed ascites (1.3+/-0.5 ml (mean+/-s.e.m.)), whereas no ascites was detectable in the angiopoietin-1 group (0 out of 10) (P<0.01). Number of peritoneal metastases (P<0.05), tumour volume, (P<0.05), vessel counts (P<0.01), and tumour cell proliferation (P<0.01) were significantly reduced in angiopoietin-1-expressing tumours. Conditioned medium from angiopoietin-1-transfected cells decreased vascular permeability more than did conditioned medium from control cells (P<0.05). Our results suggest that angiopoietin-1 is an important mediator of angiogenesis and vascular permeability and thus could theoretically serve as an anti-neoplastic agent for patients with carcinomatosis from colorectal cancer.

Molecular approaches for the treatment of atherosclerosis

Advances in vascular biology and the study of molecular pathophysiology have enabled the design and initial testing of therapeutic principles for cardiovascular intervention at the level of gene expression. This approach can offer an avenue to greatly impact the onset and progression of vascular disease at its roots. Early translations of basic research into human clinical protocols might provide novel alternatives for patients without traditional therapeutic options and might provide means of improving and prolonging the success of standard therapies. As the understanding of the genetic basis of vascular disease continues to grow and the tools for in vivo genetic manipulation continue to improve, vascular gene therapies might someday become a part of routine patient care.

Anti-angiogenic agents for the treatment of brain tumors

It is accepted that novel therapeutic approaches are needed for the majority of patients with malignant brain tumors. The vascularity of many primary brain tumors and the encouraging preclinical studies suggest that antiangiogenic agents have the potential to become an important component of multimodality treatment of patients with brain tumors. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of brain tumor neovasculature. Neuroimaging techniques evaluating the angiogenic process and the impact of antiangiogenic agents will be an important tool for the rapid development of these novel therapeutic agents.

Angiogenesis by implantation of peripheral blood mononuclear cells and platelets into ischemic limbs

BACKGROUND

Peripheral blood mononuclear cells (PBMNCs), platelets, and polymorphonuclear leukocytes (PMNs) contain various angiogenic factors and cytokines.

METHODS AND RESULTS

Unilateral hindlimb ischemia was surgically induced in athymic nude rats, and fluorescence-labeled human blood cells (PBMNCs [10(7) cells]+platelets [10(9)] or PBMNCs [10(7)]+platelets [10(9)]+PMNs [10(7)]) were intramuscularly implanted into the ischemic limbs. Laser Doppler imaging revealed markedly increased blood perfusion in PBMNC+platelet-implanted limbs (44% increase, P<0.001) compared with control implantation of human umbilical vein vascular endothelial cells. The addition of PMNs to PBMNCs+platelets attenuated blood perfusion (27% decrease, P<0.01). Neocapillary densities were increased by implantation of PBMNCs+platelets or platelets alone (3.5-fold and 2.4-fold, respectively; P<0.001), whereas PMNs inhibited (32%, P<0.05) PBMNC+ platelet-mediated capillary formation. There was no incorporation of implanted PBMNCs into neocapillaries, whereas PBMNCs and platelets accumulated around arterioles after implantation. Cellular extract from PBMNCs+platelets, in which vascular endothelial growth factor (VEGF), basic fibroblast growth factor, platelet-derived growth factor-AB, and transforming growth factor-beta were detected, markedly stimulated tubule formation of human umbilical vein vascular endothelial cells. Anti-VEGF neutralizing antibody markedly inhibited tubule formation and in vivo vessel formation. Neutrophil elastase inhibitor blocked the antiangiogenic action of PMNs, whereas inhibitors of oxygen metabolites had no effect.

CONCLUSIONS

This study demonstrated that implantation of PBMNCs and platelets into ischemic limbs effectively induces collateral vessel formation by supplying angiogenic factors (mainly VEGF) and cytokines, suggesting that this cell therapy is useful as a novel strategy for therapeutic angiogenesis.

Peripheral actions of leptin and its involvement in disease

The discovery of leptin is broadening our understanding of the mechanisms underlying neuroendocrine function. To date, most investigations have focused on the effects of leptin on food intake control and body weight homeostasis with attention primarily focused on the central effects of leptin. However, the almost ubiquitous distribution of leptin receptors in peripheral tissues provides a fertile area for investigation and a more dynamic view of leptin is starting to unfold. Thus, leptin has generated enormous interest in the interaction as well as integration between brain targets and peripheral signals. The scientific evidence supporting the direct peripheral effects of leptin on angiogenesis, wound healing, lipolysis, blood pressure homeostasis, and satiety control is reviewed.

Expression of angiogenic and neurotrophic factors in the human amnion and choriodecidua

OBJECTIVE

Our objective was to identify the novel or differential expression of growth or development associated genes in the human gestational membranes that might play roles in pregnancy or in term or preterm parturition.

STUDY DESIGN

Complementary DNA arrays were probed with [alpha(33)P]dCTP-labeled-complementary DNA that was prepared from the RNA of reflected amnion and choriodecidua that represent term not-in-labor, term spontaneous labor, and preterm labor with and without chorioamnionitis (n = 4 per group). Differential expression (term not-in-labor vs term spontaneous labor or preterm labor with chorioamnionitis vs preterm labor without chorioamnionitis) was evaluated by Wilcoxon tests.

RESULTS

All 16 amnion samples expressed angiogenic factors (endothelin-2 and -3, vascular endothelial growth factor, and vascular endothelial growth factor-B) and neurotrophic factors (ephrin-A2, ephrin receptors-A2, -B1, -B3, -B4, and -B5, neuropilin-2, p75/nerve growth factor receptor and semaphorin-F). In both amnion and choriodecidua, the expression of vascular endothelial growth factor and the angiopoietin receptor, Tie-2, were greater with term spontaneous labor than with term not-in-labor (P <.05); increased VEGF receptor-2 (flk-1) expression was observed in term spontaneous labor choriodecidua (P <.05) but not amnion. Ephrin-A1 expression increased with term spontaneous labor in both tissues (P <.05). Semaphorin-F expression decreased with preterm labor with chorioamnionitis in choriodecidua (P <.05), although the trend was not significant in amnion (P =.1).

CONCLUSION

Neurotrophic and angiogenic factor genes are expressed in amnion and choriodecidual membranes. Several of the genes exhibit differential expression with labor at term or in association with infection preterm, which suggests roles in or associated with these processes.

Dual role of Ang2 in postnatal angiogenesis and lymphangiogenesis

The maturation of the vascular system and the adjustment of blood vessel density in tissues require the opposing processes of vessel growth and regression. A new study in this issue of Developmental Cell shows that Angiopoietin-2 (Ang2), a ligand for the endothelial Tie2 receptor tyrosine kinase, has a dual function in the processes of postnatal angiogenesis and vascular remodeling. Also, Ang2 signals are required for the proper development and function of the lymphatic vessels.

Recent advances in cutaneous angiogenesis

An understanding of the molecular basis of angiogenesis is key to the appreciation of many of the advances made in the field of neovascularization over the past two decades. The sequence of events involved in angiogenesis includes: (i) increased vascular permeability and leakage; (ii) degradation of basement membrane; (iii) endothelial cell proliferation and migration through the surrounding extracellular matrix; and (iv) maturation and stabilization of the newly formed vessel bed. This review provides an update on the molecular basis of such pathways in the skin, with particular emphasis on the endothelial cell-specific vascular endothelial growth factor and angiopoietins as modulators of angiogenesis that can be targeted in therapy of cutaneous disease.

Serum factors involved in human microvascular endothelial cell morphogenesis

Our previous studies have demonstrated that lipid and protein angiogenic factors operate in tandem to induce optimal angiogenic responses in vivo. This study was undertaken to clarify the nature of the substances in human serum that are responsible for its remarkable ability to promote capillary morphogenesis in vitro. The ability of dilute (2%) human serum to promote the morphogenic differentiation of human dermal microvascular endothelial cells on Matrigel supports was depleted by more than 50% by treatment of the serum with activated charcoal, a procedure that effectively removes biologically active lipid growth factors. The remainder of the activity within serum was lost on heating to 60 degrees C for 60 minutes, indicating the involvement of a protein in the response. The ability of charcoal-treated serum to promote capillary morphogenesis was completely restored by the addition of sphingosine 1-phosphate (SPP, 500 nmol/L), but other lipids thought to be released into serum during clotting were ineffective. In addition, basic fibroblast growth factor (bFGF) effectively restored the ability of heat-treated serum to promote endothelial cell morphogenesis, but other protein growth factors, including vascular endothelial growth factor and platelet-derived growth factor, were ineffective. Together, SPP and bFGF were as effective as whole serum in promoting capillary morphogenesis. Responses to purified SPP were entirely sensitive to the effects of preexposure of the cells to pertussis toxin, whereas responses to bFGF were entirely pertussis toxin-resistant. Consistent with our hypothesis that two distinct factors in serum play a role in promoting capillary morphogenesis, responses induced by serum were inhibited approximately 50% by preexposure of endothelial cells to pertussis toxin. We conclude that platelet-released SPP acts in conjunction with circulating bFGF to promote capillary formation by microvascular endothelial cells. Lipid and protein growth factors apparently exert complementary roles in the angiogenic response, as demonstrated by their ability to promote chemotaxis, angiogenic differentiation, and angiogenesis in vivo.

Angiopoietin-2 is required for postnatal angiogenesis and lymphatic patterning, and only the latter role is rescued by Angiopoietin-1

VEGF and Angiopoietin-1 requisitely collaborate during blood vessel development. While Angiopoietin-1 obligately activates its Tie2 receptor, Angiopoietin-2 can activate Tie2 on some cells, while it blocks Tie2 activation on others. Our analysis of mice lacking Angiopoietin-2 reveals that Angiopoietin-2 is dispensable for embryonic vascular development but is requisite for subsequent angiogenic remodeling. Unexpectedly, mice lacking Angiopoietin-2 also exhibit major lymphatic vessel defects. Genetic rescue with Angiopoietin-1 corrects the lymphatic, but not the angiogenesis, defects, suggesting that Angiopoietin-2 acts as a Tie2 agonist in the former setting, but as an antagonist in the latter setting. Our studies define a vascular growth factor whose primary role is in postnatal angiogenic remodeling and also demonstrate that members of the VEGF and Angiopoietin families collaborate during development of the lymphatic vasculature.

Correlation between interleukin 10 and vascular endothelial growth factor expression in human esophageal cancer

Interleukin 10 (IL-10) is an immunosuppressive cytokine produced by T-lymphocytes, and is a regulatory molecule for angiogenesis in various cancers. We examined IL-10 and vascular endothelial growth factor (VEGF) gene expression in 45 esophageal cancer patients who underwent surgical resection. Thirty-seven (82.2%) of the 45 esophageal cancers revealed IL-10 gene expression. VEGF121, VEGF165 and VEGF189 isoforms were detected in 93.3% (42/45), 55.6% (25/45) and 26.7% (12/45) of cases, respectively. IL-10 gene expression was significantly correlated with VEGF121 gene expression (P=0.0039, Fisher's test). The results suggested that IL-10 stimulates angiogenic factor gene expression.

Angiogenesis, thrombospondin, and ductal carcinoma in situ of the breast

Angiogenesis, the growth of new vessels from existing vasculature, plays an essential role in tumour development. The process involves interaction between a variety of cells, growth factors, and components of the extracellular matrix, regulated by pro-angiogenic and anti-angiogenic factors. This review profiles these factors, outlines the available methods for measuring new vessel formation, and discusses the importance of angiogenesis in breast cancer, with emphasis on ductal carcinoma in situ.

[Angiogenesis and bladder cancer: trendy prognostic factor or new therapeutic target?]

Tumor-associated angiogenesis is emerging as an important prognostic factor and represents a hopeful potential therapeutic target for the cancer treatment. Bladder tumors, as all solid tumors, require an active angiogenesis to support their growth and progression. The angiogenic phenotype observed within a tumor is determined in large part by the balance between stimulatory and inhibitory inputs to the endothelial cells. Clinically, the importance of the angiogenic response observed within a tumor should be considered as an independent prognostic factor for superficial as well as invasive bladder tumors. The analysis of the angiogenic response could in the future influence the therapeutic strategy. Angiogenesis also represents a promising new therapeutic target, and is at the moment intensively tested in experimental and clinical trials. In this article, we will first review the mechanism of angiogenesis, and then its implication in bladder cancer, and as a potential therapeutic target.

The role of vascular growth factors in hyperoxia-induced injury to the developing lung

Normal pulmonary vascular development is the result of a complex interplay of growth factors, including vascular endothelial growth factor (VEGF) and the angiopoietins. Injury to the developing lung, whether due to hyperoxia or mechanical ventilation, results in disordered vascular development, ranging from an apparent arrest of microvascular development in milder injury to extensive microvascular derangement in more severe injury. Alterations in vascular growth factors may participate in these injuries. During injury to the developing animal lung, VEGF abundance is markedly decreased. In models of post-injury recovery, up-regulation of VEGF accompanies the re-establishment of normal vasculature. Alterations in lung VEGF levels in human premature infants are less clear cut. However, among humans premature newborns who later go on to develop bronchopulmonary dysplasia (BPD), VEGF production is decreased in comparison to those newborns who recover. Other angiogenic factors, such as the CXC ELR+ chemokines, are also altered in injury to the developing lung, but their specific roles in vascular injury are less clear. Strategies that enhance microvascular integrity, whether through attenuating alterations in vascular growth factors or by other means, also improve the outcome of lung injury. Such therapies may eventually offer hope in human BPD.

The CXC chemokine cCAF stimulates precocious deposition of ECM molecules by wound fibroblasts, accelerating development of granulation tissue

BACKGROUND

During wound repair, fibroblasts orchestrate replacement of the provisional matrix formed during clotting with tenascin, cellular fibronectin and collagen III. These, in turn, are critical for migration of endothelial cells, keratinocytes and additional fibroblasts into the wound site. Fibroblasts are also important in the deposition of collagen I during scar formation. The CXC chemokine chicken Chemotactic and Angiogenic Factor (cCAF), is highly expressed by fibroblasts after wounding and during development of the granulation tissue, especially in areas where extracellular matrix (ECM) is abundant. We hypothesized that cCAF stimulates fibroblasts to produce these matrix molecules.

RESULTS

Here we show that this chemokine can stimulate precocious deposition of tenascin, fibronectin and collagen I, but not collagen III. Studies in culture and in vivo show that tenascin stimulation can also be achieved by the N-terminal 15 aas of the protein and occurs at the level of gene expression. In contrast, stimulation of fibronectin and collagen I both require the entire molecule and do not involve changes in gene expression. Fibronectin accumulation appears to be linked to tenascin production, and collagen I to decreased MMP-1 levels. In addition, cCAF is chemotactic for fibroblasts and accelerates their migration.

CONCLUSIONS

These previously unknown functions for chemokines suggest that cCAF, the chicken orthologue of human IL-8, enhances healing by rapidly chemoattracting fibroblasts into the wound site and stimulating them to produce ECM molecules, leading to precocious development of granulation tissue. This acceleration of the repair process may have important application to healing of impaired wounds.

[Angiogenesis--anti-angiogenesis. Significance for tumor growth and metastasis]

Angiogenesis plays an important role in the local growth and metastasis of a variety of malignant tumors. During the past three decades so-called angiogenesis factors have been discovered and characterized in more detail. These are the major contributors to angiogenesis. The term angiogenesis factors includes other functionally heterogeneous molecules. The best characterized angiogenesis factors are endothelial growth factors, such as "vascular endothelial growth factor" (VEGF), "fibroblast growth factor" (FGF), "platelet-derived growth factor" (PDGF), Angiogenin and interleukin-8 (IL-8). However, members of the family of matrix metalloproteinases are also included. The list of factors involved in angiogenessis and their receptors are increasing steadily as does the list of molecules with antiangiogenic capacity. The latter comprises the endogenous factors, Angiostatin, Endostatin, Thrombospondin-1 and 2, and chemical compounds, such as the Fumagillin derivative, AGM-1470, or inhibitors of matrix metalloproteinases. These have attracted more interest during the past years, since investigations on these molecules foster hope for new therapeutic strategies. Some of these antiangiogenic factors have already been used in various therapeutic approaches to influence tumor growth. While impressive results have been obtained in well controlled experimental animal models, the results of clinical studies in humans fall short of these successes. This is at least in part due to the fact that angiogenesis of tumors is a complex process based on the interaction of a variety of factors. The present article summarizes the current knowledge about tumor angiogenesis with a particular emphasis on antiangiogenic molecules. The presented data open new interesting therapeutic perspectives for future dermatology.

[Milk angiogenin (Review)]

Recent data on angiogenin, a multifunctional member of pancreatic RNase protein superfamily, are summarized. Advances in the investigation of angiogenin structure, function, and properties are analyzed. Potentialities in natural angiogenin production from inexpensive dairy by-products are demonstrated.