Vascular endothelial growth factor: basic science and clinical progress

The role of VEGF receptors in angiogenesis; complex partnerships

Vascular endothelial growth factors (VEGFs) regulate blood and lymphatic vessel development and homeostasis but also have profound effects on neural cells. VEGFs are predominantly produced by endothelial, hematopoietic and stromal cells in response to hypoxia and upon stimulation with growth factors such as transforming growth factors, interleukins or platelet-derived growth factor. VEGFs bind to three variants of type III receptor tyrosine kinases, VEGF receptor 1, 2 and 3. Each VEGF isoform binds to a particular subset of these receptors giving rise to the formation of receptor homo- and heterodimers that activate discrete signaling pathways. Signal specificity of VEGF receptors is further modulated upon recruitment of coreceptors, such as neuropilins, heparan sulfate, integrins or cadherins. Here we summarize the knowledge accumulated since the discovery of these proteins more than 20 years ago with the emphasis on the signaling pathways activated by VEGF receptors in endothelial cells during cell migration, growth and differentiation.

Intravitreal Bevacizumab (Avastin) for Neovascular Age-Related Macular Degeneration

PURPOSE

To report the short-term safety, biologic effect, and a possible mechanism of action of intravitreal bevacizumab in patients with neovascular age-related macular degeneration (AMD).

DESIGN

Interventional, consecutive, retrospective case series.

PARTICIPANTS

Eighty-one eyes of 79 patients with subfoveal neovascular AMD.

METHODS

Patients received intravitreal bevacizumab (1.25 mg) on a monthly basis until macular edema, subretinal fluid (SRF), and/or pigment epithelial detachment (PED) resolved. Ophthalmic evaluations included nonstandardized Snellen visual acuity (VA), complete ophthalmic examination, fluorescein angiography, and optical coherence tomography (OCT).

MAIN OUTCOME MEASURES

Assessments of safety, changes in Snellen VA, OCT retinal thickness, and angiographic lesion characteristics were performed.

RESULTS

No significant ocular or systemic side effects were observed. Most patients (55%) had a reduction of >10% of baseline retinal thickness at 1 week after the injection. At 4 weeks after injection, 30 of 81 eyes demonstrated complete resolution of retinal edema, SRF, and PEDs. Of the 51 eyes with 8 weeks' follow-up, 25 had complete resolution of retinal thickening, SRF, and PEDs. At 1, 4, 8,and 12 weeks, the mean retinal thickness of the central 1 mm was decreased by 61, 92, 89, and 67 mum, respectively (P<0.0001 for 1, 4, and 8 weeks and P<0.01 for 12 weeks). At 4 and 8 weeks, mean VA improved from 20/200 to 20/125 (P<0.0001). Median vision improved from 20/200 to 20/80(-) at 4 weeks and from 20/200 to 20/80 at 8 weeks.

CONCLUSIONS

Short-term results suggest that intravitreal bevacizumab (1.25 mg) is well tolerated and associated with improvement in VA, decreased retinal thickness by OCT, and reduction in angiographic leakage in most patients, the majority of whom had previous treatment with photodynamic therapy and/or pegaptanib. Further evaluation of intravitreal bevacizumab for the treatment of choroidal neovascularization is warranted.

Evidence for the presence of a guanine quadruplex forming region within a polypurine tract of the hypoxia inducible factor 1alpha promoter

The promoter of the hypoxia inducible factor 1 alpha (HIF-1alpha) gene has a polypurine/polypyrimidine tract (-65 to -85) overlapping or adjacent to several putative transcription factor binding sites, and we found that mutagenesis of this region diminished basal HIF-1alpha expression. Oligonucleotides representing this region of the HIF-1alpha promoter were analyzed by electrophoretic mobility shift, chemical probing, circular dichroism, and DNA polymerase arrest assays. The guanine-rich strand was found to form a parallel, unimolecular quadruplex in the presence of potassium that was further stabilized by two known quadruplex binding compounds, the cationic porphyrin TmPyP4 and the natural product telomestatin, while TmPyP2, a positional isomer of TmPyP4, did not stabilize quadruplex formation. These data suggest that a quadruplex structure may form in a region of the HIF-1alpha promoter that regulates basal HIF-1alpha expression.

VEGFR-1 (FLT-1) activation modulates acute lymphoblastic leukemia localization and survival within the bone marrow, determining the onset of extramedullary disease

The presence of persistent circulating leukemia cells, or engrafted into extramedullary tissues, is a bad prognostic factor for patients with acute leukemia. However, little is known about the mechanisms that regulate the exit of leukemia cells from the bone marrow (BM) microenvironment. We reveal that vascular endothelial growth factor receptor 1 (FLT-1) modulates acute leukemia distribution within the BM, along VEGF and PlGF gradients, regulating leukemia survival and exit into the peripheral circulation. FLT-1 activation on acute lymphoblastic leukemia (ALL) cells results in cell migration and proliferation in vitro, whereas in vivo FLT-1-overexpressing cells accumulate in the BM epiphysis of nonobese diabetic-severe combined immunodeficient (NOD-SCID) recipients and are detected in circulation 2 weeks after inoculation. In turn, FLT-1 neutralization affects leukemia localization (now in the BM diaphysis), increases leukemia apoptosis, and impedes the exit of ALL cells, prolonging the survival of inoculated mice. We demonstrate further that FLT-1-induced cell migration involves actin polymerization and lipid raft formation. Taken together, we show that FLT-1 regulates the BM localization of ALL cells, determining their survival and exit into the circulation and ultimately the survival of inoculated recipients. FLT-1 targeting on subsets of acute leukemias may delay the onset of extramedullary disease, which may be advantageous in combinatorial therapeutic settings.

Angiostatin is directly cytotoxic to tumor cells at low extracellular pH: a mechanism dependent on cell surface-associated ATP synthase

Angiostatin, a proteolytic fragment of plasminogen, is a potent angiogenesis inhibitor able to suppress tumor growth and metastasis through inhibition of endothelial cell proliferation and migration. Previously, we showed that angiostatin binds and inhibits F(1)F(o) ATP synthase on the endothelial cell surface and that anti-ATP synthase antibodies reduce endothelial cell proliferation. ATP synthase also occurs on the extracellular surface of a variety of cancer cells, where its function is as yet unknown. Here, we report that ATP synthase is present and active on the tumor cell surface, and angiostatin, or antibody directed against the catalytic beta-subunit of ATP synthase, inhibits the activity of the synthase. We show that tumor cell surface ATP synthase is more active at low extracellular pH (pH(e)). Low pH(e) is a unique characteristic of the tumor microenvironment. Although the mechanism of action of angiostatin has not been fully elucidated, angiostatin treatment in combination with acidosis decreases the intracellular pH (pH(i)) of endothelial cells, leading to cell death. We also find that, at low pH(e), angiostatin and anti-beta-subunit antibody induce intracellular acidification of A549 cells, as well as a direct cytotoxicity that is absent in tumor cells with low levels of extracellular ATP synthase. These results establish angiostatin as an antitumorigenic and antiangiogenic agent through a mechanism implicating tumor cell surface ATP synthase. Furthermore, these data provide evidence that extracellular ATP synthase plays a role in regulating pH(i) in cells challenged by acidosis.

Vascular endothelial growth factor in the lung

Vascular endothelial growth factor (VEGF) is a pluripotent growth and permeability factor that has a broad impact on endothelial cell function. The lung tissue is very rich in this protein; many different lung cells produce VEGF and also respond to VEGF. VEGF is critical for the development of the lung and serves as a maintenance factor during adult life. In addition to the physiological functions of this protein, there is increasing evidence that VEGF also plays a role in several acute and chronic lung diseases, such as acute lung injury, severe pulmonary hypertension, and emphysema. Here we provide a comprehensive overview of the rapidly expanding literature.

New insights into nNOS regulation of vascular homeostasis

An important physiological response to changes in local or systemic oxygenation is the modulation of vascular tone, which is mediated in part by changes in the activities of the 3 NO synthase (NOS) isoforms. In arterial smooth muscle cells, acute hypoxia induces increased vascular tone, which is attenuated if hypoxia persists. In this issue of the JCI, Ward et al. demonstrate that changes in O2 concentration have effects on neuronal NOS enzymatic activity and gene expression that contribute to vascular homeostasis under conditions of acute and chronic hypoxia (see the related article beginning on page 3128).

VEGF as a predictive marker of rectal tumor response to preoperative radiotherapy

BACKGROUND

Neoadjuvant radiotherapy for rectal cancer may result in tumor downstaging or complete tumor regression leading to greater sphincter preservation. The identification of molecular predictive markers of tumor response to preoperative radiotherapy would provide an additional tool for selecting patients most likely to benefit from treatment. The aim of this study was to determine whether VEGF expression in preirradiation tumor biopsies is a useful predictive marker of tumor response in patients with rectal cancer undergoing preoperative radiotherapy.

METHODS

Immunohistochemistry for VEGF was performed on 59 preirradiation biopsies from patients with completely responsive (ypT0) or nonresponsive tumors after preoperative radiotherapy. VEGF positivity was evaluated using several scoring methods and the association between VEGF and tumor response was compared. The distribution of VEGF scores was obtained as well as the mean VEGF expression in the two response groups.

RESULTS

The mean VEGF expression in nonresponsive tumors (NR) was significantly greater than in completely responsive tumors (CR) (P = 0.0035). Nearly half (47%) of all CR tumors had a VEGF expression of 10% or less. Eleven tumors were negative (0% immunoreactivity) for the protein and all of these (100%) were complete responders. Fifty-two percent of the NR tumors had VEGF scores of 80% or greater. The four scoring methods used to determine the association between VEGF and tumor response each produced significant results (P < 0.05).

CONCLUSIONS

The results of this study indicate that VEGF assessed immunohistochemically from preirradiation tumor biopsies may be a useful marker of rectal tumor response to preoperative radiotherapy.

MAPKAPK-2-mediated LIM-kinase activation is critical for VEGF-induced actin remodeling and cell migration

Vascular endothelial growth factor-A (VEGF-A) induces actin reorganization and migration of endothelial cells through a p38 mitogen-activated protein kinase (MAPK) pathway. LIM-kinase 1 (LIMK1) induces actin remodeling by phosphorylating and inactivating cofilin, an actin-depolymerizing factor. In this study, we demonstrate that activation of LIMK1 by MAPKAPK-2 (MK2; a downstream kinase of p38 MAPK) represents a novel signaling pathway in VEGF-A-induced cell migration. VEGF-A induced LIMK1 activation and cofilin phosphorylation, and this was inhibited by the p38 MAPK inhibitor SB203580. Although p38 phosphorylated LIMK1 at Ser-310, it failed to activate LIMK1 directly; however, MK2 activated LIMK1 by phosphorylation at Ser-323. Expression of a Ser-323-non-phosphorylatable mutant of LIMK1 suppressed VEGF-A-induced stress fiber formation and cell migration; however, expression of a Ser-323-phosphorylation-mimic mutant enhanced these processes. Knockdown of MK2 by siRNA suppressed VEGF-A-induced LIMK1 activation, stress fiber formation, and cell migration. Expression of kinase-dead LIMK1 suppressed VEGF-A-induced tubule formation. These findings suggest that MK2-mediated LIMK1 phosphorylation/activation plays an essential role in VEGF-A-induced actin reorganization, migration, and tubule formation of endothelial cells.

Angiogenesis in non-small cell lung cancer: The prognostic impact of neoangiogenesis and the cytokines VEGF and bFGF in tumours and blood

BACKGROUND

Due to a dismal prognosis of advanced lung cancer, novel screening tools and more effective treatments are clearly needed. Lately, an increasing number of tumour-released angiogenic cytokines which affect vessel formation, tumour growth, invasion, and metastasis have been identified. Vascular endothelial growth factors (VEGFs) and basic fibroblast growth factor (bFGF) are among the most important angiogenic factors. Based on available literature, we have explored the mechanisms of angiogenesis and its prognostic significance in non-small cell lung cancer, estimated by microvessel density (MVD) and the presence of VEGF and bFGF in the tumour and blood from NSCLC patients.

METHODS

Several comprehensive Pubmed searches for the period January 1993 to May 2005 were performed using strategic combinations of the terms non-small cell lung cancer, angiogenesis, vascular endothelial growth factor, basic fibroblast growth factor, tumour expression, microvessel density, circulating, and serum.

RESULTS

NSCLC neoangiogenesis, as measured by MVD, and tumour expression of VEGF are poor prognostic factors for survival (MVD, HR 1.8-2.0; VEGF, HR 1.5). bFGF tumour expression is also associated with poor survival and more aggressive disease. When evaluating the prognostic impact of elevated VEGF levels in blood, 10 of 16 studies (63%) indicated a negative prognostic impact. Of five studies on the prognostic value of circulating bFGF, three studies reported a negative prognostic impact, while one indicated bFGF as a good prognostic factor and one was inconclusive.

CONCLUSION

Angiogenic factors are poor prognostic indicators for tumour aggressiveness and survival in NSCLC. Assessments of circulating levels of VEGF and possibly bFGF may be valuable future tools for treatment planning and monitoring of treatment effect and relapse. First, however, these blood tests need to be standardised and validated in large-scale prospective clinical trials.

Early cardiac hypertrophy induced by thyroxine is accompanied by an increase in VEGF-A expression but not by an increase in capillary density

Cardiac hypertrophy in response to hyperthyroidism is well known. However, the effects on cardiac microcirculation are still controversial in this model. The present study evaluated the effects of acute administration of two different thyroxine (T4) dose levels on the angiogenic response in the myocardium. Capillary density (CD), the CD to fiber density (FD) ratio (CD/FD), and intercapillary distance (ICD) were assessed, as was ventricle weight (VW) to body weight (BW) ratio (VW/BW). Collagen I and III messenger ribonucleic acid (mRNA) expression and VEGF-A expression were also determined by reverse transcriptase polymerase chain reaction (RT-PCR). Immunohistochemical detection of proliferating cell nuclear antigen (PCNA) expression in endothelial cell nuclei was also carried out. We simulated an acute hyperthyroidism situation in male Wistar rats by daily intraperitoneal injection of T4 (0.025 or 0.1 mg kg(-1) day(-1)) for 7 days. Hemodynamic parameters showed that T4 did not alter systolic blood pressure (SBP) but significantly increased heart rate (HR). Both T4 doses significantly increased VW. Morphologically, the higher T4 dose resulted in a 33% greater myocardial mass, which was not accompanied by alterations in collagen I and III mRNA expression. The CD and CD/FD parameters were significantly lower in the hyperthyroid rats treated with the higher dose than in the control animals, and PCNA-labeling analysis indicated total absence of marked capillary growth. However, although the acute treatment with T4 did not induce any alteration in capillary number and endothelial cell proliferation, the vascular endothelial growth factor (VEGF)-A mRNA and protein expression were significantly increased with the higher T4 dose. These data indicate that the cardiac hypertrophy induced by acute treatment with thyroid hormone precedes the angiogenic process, which probably occurs later.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Angiogenesis in gliomas: biology and molecular pathophysiology

Glioblastoma multiforme (GBM) is characterized by exuberant angiogenesis, a key event in tumor growth and progression. The pathologic mechanisms driving this change and the biological behavior of gliomas remain unclear. One mechanism may involve cooption of native blood vessels by glioma cells inducing expression of angiopoietin-2 by endothelial cells. Subsequently, vascular apoptosis and involution leads to necrosis and hypoxia. This in turn induces angiogenesis that is associated with expression of hypoxia-inducible factor (HIF)-1alpha and vascular endothelial growth factor (VEGF) in perinecrotic pseudopalisading glioma cells. Here we review the molecular and cellular mechanisms implicated in HIF-1-dependent and HIF-1-independent glioma-associated angiogenesis. In GBMs, both tumor hypoxia and genetic alterations commonly occur and act together to induce the expression of HIF-1. The angiogenic response of the tumor to HIF-1 is mediated by HIF-1-regulated target genes leading to the upregulation of several proangiogenic factors such as VEGF and other adaptive response molecules. Understanding the roles of these regulatory processes in tumor neovascularization, tumor growth and progression, and resistance to therapy will ultimately lead to the development of improved antiangiogenic therapies for GBMs.

Microarray expression profiles of angiogenesis-related genes predict tumor cell response to artemisinins

Artemisinin (ARS) and its derivatives are used for the second-line therapy of malaria infections with Plasmodium falciparum and P. vivax. ARSs also reveal profound antitumor activity in vitro and in vivo. In the present investigation, we correlated the mRNA expression data of 89 angiogenesis-related genes obtained by microarray hybridization from the database of the US National Cancer Institute with the 50% growth inhibition concentration values for eight ARSs (ARS, arteether (ARE), artesunate (ART), artemisetene, arteanuine B, dihydroartemisinylester stereoisomers 1 and 2). The constitutive expression of 30 genes correlated significantly with the cellular response to ARSs. By means of hierarchical cluster analysis and cluster image mapping expression, profiles were identified that determined significantly the cellular response to ART, ARE, artemether and dihydroartemisinylester stereoisomer 1. We have exemplarily validated the microarray data of six out of these 30 genes by real-time RT-PCR in seven cell lines. The fact that sensitivity and resistance of tumor cells could be predicted by the mRNA expression of angiogenesis-related genes indicate that ARSs reveal their antitumor effects at least in part by inhibition of tumor angiogenesis. As many chemopreventive drugs exert antiangiogenic features, ARSs might also be chemopreventive in addition to their cytotoxic effects.

Locally applied angiogenic factors--a new therapeutic tool for meniscal repair

Tears in the peripheral part of the menisci have a better healing potential than tears in the central part, because the central two-thirds of the menisci are avascular. The avascular status of the meniscus is maintained by the expression of antiangiogenic factors such as endostatin. The distribution of endostatin in the menisci correlates with the degree of vascularization. Endostatin immunostaining is strong in the avascular zone and reduced in the vascularized outer one-third. Endostatin interacts with signal transduction of the vascular endothelial growth factor (VEGF) by reducing VEGF-induced kinase (Erk1/2) phosphorylation. VEGF plays an important role in angiogenesis in fetal menisci and it is down-regulated in the adult meniscus. We hypothesized that healing of meniscal tears in the avascular zone can be promoted by the local application of the angiogenic factor VEGF. To evaluate this hypothesis a tear was created in the avascular zone of the medial meniscus in 18 merino sheep. The tear was then repaired with an uncoated suture (group 1), a suture coated with PDLLA (group 2), and by a suture coated with PDLLA/VEGF (group 3). After 6 weeks we observed increased factor VIII immunostaining in the VEGF-treated group. However, in this treatment group (VEGF/PDLLA) no meniscus healed. In the uncoated suture group and in the PDLLA-coated suture group partial healing was observed in three animals and complete healing in three animals, respectively. Factor VIII expression is normally restricted to vascular endothelial cells. In this study, however, single endothelial cells could be detected in the menisci of the VEGF/PDLLA group. This finding suggests that the application of VEGF might have stimulated proliferation of vascular endothelial cells but the application of VEGF was not successful in stimulating the more complex process of vasculogenesis. Further immunohistochemical examinations of the specimen have shown that in the VEGF/PDLLA group there is strong immunostaining against matrix metalloproteinase 13 (MMP-13). In vitro studies have shown that VEGF can stimulate chondrocytes to proliferate but also to express MMP-13 via HIF1-alpha induction. Since meniscal fibrochondrocytes express the VEGF receptor 2 (KDR) the induction of MMP expression might be another factor which inhibits healing despite increased angiogenesis. In conclusion, the local application of VEGF via PDLLA-coated sutures does not promote meniscal healing. A single growth factor might not always be a promising tool for the promotion of tissue repair. Further studies have to find out if growth factor combinations (VEGF and angiopoitin) might be more effective in stimulating vasculogenesis during meniscal healing.

A SNP in the flt-1 promoter integrates the VEGF system into the p53 transcriptional network

The VEGF system is essential for angiogenesis. VEGF overexpression frequently correlates with increased microvascularity and metastasis and decreased spontaneous apoptosis. Although a precise mechanism has not been established, studies suggest that VEGF expression is negatively regulated by p53, a master regulator and tumor suppressor. There are no reports of additional components of the VEGF signal transduction pathway being part of the p53 transcriptional network. A target of VEGF, the VEGF receptor 1/flt-1, can regulate growth and migration of endothelial cells and modulate angiogenesis. VEGF appears to be up-regulated in various cancers in which flt-1 may have a role in tumor progression and metastasis. We identified a C-to-T SNP upstream of the transcriptional start site in approximately 6% of the people examined. The SNP is located within a putative p53 response element. Only the promoter with the T SNP (FLT1-T) was responsive to p53 when examined with reporter assays or by endogenous gene expression analysis in cell lines with different SNP status. In response to doxorubicin-induced DNA damage, there was clear allele discrimination based on p53 binding at the FLT1-T but not FLT1-C promoters as well as p53-dependent induction of flt-1 mRNA, which required the presence of FLT1-T. Our results establish that p53 can differentially stimulate transcription at a polymorphic variant of the flt-1 promoter and directly places the VEGF system in the p53 stress-response network via flt-1 in a significant fraction of the human population. We suggest that the p53-VEGF-flt-1 interaction is relevant to risks in angiogenesis-associated diseases, including cancer.

Rapid on-membrane proteolytic cleavage for Edman sequencing and mass spectrometric identification of proteins

A method for the rapid limited enzymatic cleavage of PVDF membrane-immobilized proteins is described. This method allows the fast characterization of PVDF blotted proteins by peptide mass fingerprinting (Henzel, W. J., Billeci, T. M., Stults, J. T., Wong, S. C., Grimley, C., Wantanabe, C., Proc. Natl. Acad. Sci. USA 1993, 90, 5011-5015), LC-MS/MS, or N-terminal sequencing and has been demonstrated on a range of proteins using a full complement of proteolytic enzymes. This technique allows the generation of proteolytic fragments between 5 and 60 min (depending on the enzyme employed), which is significantly faster than previously reported on-membrane digestion methods. To date, this on-membrane rapid digestion protocol has aided in the identification and confirmation of mutation sites in over 200 recombinant proteins.

Angiogenesis as a therapeutic target

Inhibiting angiogenesis is a promising strategy for treatment of cancer and several other disorders, including age-related macular degeneration. Major progress towards a treatment has been achieved over the past few years, and the first antiangiogenic agents have been recently approved for use in several countries. Therapeutic angiogenesis (promoting new vessel growth to treat ischaemic disorders) is an exciting frontier of cardiovascular medicine, but further understanding of the mechanisms of vascular morphogenesis is needed first.

PPAR gamma represses VEGF expression in human endometrial cells: implications for uterine angiogenesis

Endometrial vasculature supports physiological uterine growth, embryonic implantation and endometrial pathology. Vascular endothelial growth factor (VEGF) is regulated by diverse developmental and hormonal signals, including eicosanoid ligands of PPARgamma. The action of natural and synthetic PPARgamma ligands on VEGF expression in primary and transformed human endometrial cell cultures was established by quantifying endogenous gene expression and transfected VEGF gene reporters. VEGF promoter-luciferase constructs were truncated and mutated to map functional sequences. Endometrial tissues and cells express PPARgamma protein. Treatment of transformed and primary endometrial cells with rosiglitazone, a synthetic PPARgamma agonist, or prostaglandin 15-deoxy-Delta12-14 J(2), a naturally occurring eicosanoid ligand, decreased VEGF protein secretion. In transiently transfected Ishikawa cells, rosiglitazone repressed VEGF gene promoter-luciferase activation with an IC(50) approximately approximately 50 nM. Truncated and mutated VEGF promoter constructs revealed that the PPARgamma-regulated domain is a direct repeat (DR)-1 motif -443 bp upstream of the transcriptional start site.

CONCLUSIONS

PPARgamma ligands repress VEGF gene expression via a PPARgamma-responsive element (PPRE) in the VEGF gene promoter. Agonists of this nuclear receptor might be exploited pharmacologically to inhibit pathological vascularization in complications of pregnancy, endometriosis and endometrial adenocarcinoma.

Antibody-based therapies for colorectal cancer

The recent successful development of novel monoclonal antibodies that target key components of biologic pathways has expanded the armamentarium of treatment options for patients with colorectal cancer. Two targets in particular--the process of new blood vessel development, or angiogenesis, and the epidermal growth factor receptor and its signaling pathway--are exploited by the newest monoclonal antibodies that are available for use in colorectal cancer patients. This clinical review focuses on the defining role of the two most clinically advanced novel agents, bevacizumab (Avastin; Genentech, Inc., South San Francisco, CA, http://www.gene.com) and cetuximab (Erbitux; ImClone Systems, Inc., New York, http://www.imclone.com), in colorectal cancer.

Molecularly targeted therapies in myelodysplastic syndromes and acute myeloid leukemias

Although there has been significant progress in acute myeloid leukemia (AML) treatment in younger adults during the last decade, standard induction therapy still fails to induce remission in up to 40% of AML patients. Additionally, relapses are common in 50-70% of patients who achieve a complete remission, and only 20-30% of patients enjoy long-term disease-free survival. The natural history of myelodysplastic syndrome (MDS) is variable, with about half of the patients dying from cytopenic complications, and an additional 20-30% transforming to AML. The advanced age of the majority of MDS patients limits the therapeutic strategies often to supportive care. To address these shortcomings, much effort has been directed toward the development of novel treatment strategies that target the evolution and proliferation of malignant clones. Presented here is an overview of molecularly targeted therapies currently being tested in AML and MDS patients, with a focus on FMS-like tyrosine kinase 3 inhibitors, farnesyltransferase inhibitors, antiangiogenesis agents, DNA hypomethylation agents, and histone deacetylase inhibitors.

Autologous fibrin matrices: A potential source of biological mediators that modulate tendon cell activities

The use of autologous fibrin matrices has been proposed as a therapeutic strategy for the local and physiological delivery of growth factors in the treatment of several clinical conditions requiring tendon healing or tendon graft remodelling. In the present work, we investigated the proliferation, synthesis of type-I collagen and angiogenic factors by tendon cells seeded on platelet-rich (PR) and platelet-poor (PP) matrices. Furthermore, in vivo cellular and vascular effects of each treatment were examined after infiltration in Achilles tendon in sheep. Results showed that the presence of platelets within the fibrin matrices increased significantly the proliferation of tendon cells. Additionally, cultured tendon cells synthesised type I collagen and angiogenic factors such as VEGF and HGF. The synthesis of VEGF, but not of HGF, was significantly higher when platelets were present within the matrix. In the sheep model, the injection of pre-clotted plasma within tendons increased cellular density and promoted neovascularization. These results indicate that administration of fibrin matrices is a safe and easy strategy that may open new avenues for enhancing tissue healing and remodelling and influences the process of regeneration in clinical situations characterised by a poor healing outcome.

A recombinant human RNASET2 glycoprotein with antitumorigenic and antiangiogenic characteristics

BACKGROUND

Human RNASET2 is a T2-RNase glycoprotein encoded by the RNASET2 gene, which is located on chromosome 6 (6q27). Deletion in 6q27 is associated with several human malignancies.

METHODS

A synthetic RNASET2 gene that was optimized for expression in the yeast Pichia pastoris was designed according to the cDNA sequence and was cloned under the control of the methanol-induced promoter fused to the alpha-mating secretion peptide. The recombinant protein was purified from the culture supernatant of transformed P. pastoris through an affinity Sepharose-concanavalin A column. Actin-binding activity was examined by membrane blotting using monoclonal mouse antiactin immunoglobulin M and by cross-linking in solution to G-actin using 1-[3-(dimethylamino)propyl]-3-ethyl-carboimide methiodide. The antiangiogenic activity of RNASET2 (from 0.5 microM to 10 microM) was assessed by a human umbilical vein endothelial (HUVE) cell assay in the presence of 1 microg/mL angiogenin, basic fibroblast growth factor (bFGF), or recombinant human vascular endothelial growth factor (VEGF). Cell colony formation was examined in human colon HT29 cancer cells to assess the antitumorigenic activity of RNASET2 or the enzymatic-inactivated RNASET2 (EI-RNASET2) (1 microM each). In an athymic mouse xenograft model, LS174T human cancer cells were injected subcutaneously. When tumors were palpable, the mice were treated for 3 weeks with RNASET2 (1 mg/kg), paclitaxel (10 mg/kg or 15 mg/kg), or a combination of the 2 drugs.

RESULTS

The recombinant RNASET2 was identified as a 27-kilodalton glycoprotein that possessed the ability to bind actin in vitro. RNASET2 significantly inhibited clonogenicity in HT29 cells. EI-RNASET2 produced a similar effect, suggesting that its antitumorigenic activity is unrelated to its RNase activity. In HUVE cells, RNASET2 inhibited angiogenin-, bFGF-, and VEGF-induced tube formation in a dose-dependent manner. In athymic mice, RNASET2 inhibited the development of an LS174T-derived xenograft by 40%. A synergistic effect was obtained with combined RNASET2 and paclitaxel treatments.

CONCLUSIONS

The current results suggested that RNASET2 represents a new class of antitumorigenic and antiangiogenic drugs, and the findings of this study emphasize the advantage of using agents like RNASET2 in combined therapy.

In vitro endothelial potential of human UC blood-derived mesenchymal stem cells

BACKGROUND

Human mesenchymal stem cells (MSC) possess powerful ex vivo expansion and versatile differentiation potential, placing themselves at the forefront of the field of stem cell-based therapy and transplantation. Of high clinical relevance is the endothelial differentiation potential of MSC, which can be used to treat various forms of ischemic vascular disease.

METHODS

We investigated whether human umbilical cord blood (UCB)-derived MSC are able to differentiate in vitro along an endothelial lineage, by using flow cytometry, RT-PCR and immunofluorescence analyzes, as well as an Ab array method.

RESULTS

When the cells were incubated for up to 3 weeks in the presence of VEGF, EGF and hydrocortisone, they began to express a variety of endothelial lineage surface markers, such as Flk-1, Flt-1, VE-Cadherin, vWF, VCAM-1, Tie-1 and Tie-2, and to secrete a specific set of cytokines. Differentiated cells were also found to be able to uptake low-density lipoprotein and form a tubular network structure.

DISCUSSION

These observations have led us to conclude that UCB-derived MSC retain endothelial potential that is suitable for basic and clinical studies aimed at the development of vasculature-directed regenerative medicine.

Osteoclastogenesis in the nonadherent cell population of human bone marrow is inhibited by rhBMP-2 alone or together with rhVEGF

During bone development and repair, angiogenesis, osteogenesis, and bone remodeling are closely associated processes that share some common mediators. In the present study nonadherent human bone marrow mononuclear cells under the induction of sRANKL and M-CSF, differentiated into osteoclasts with TRAP-positive staining, VNR expression, and Ca-P resorptive activity. The effects of various combinations of rhBMP-2 (0, 3, 30, and 300 ng/mL) and rhVEGF (0 and 25 ng/mL) on osteoclastogenesis potentials were examined in this experimental system. The percentages of TRAP-positive multiple nucleated cells represent osteoclast differentiation potential, and the percentages of resorptive areas in the Ca-P coated plates resemble osteoclast resorption capability. The presence of rhBMP-2 at 30 and 300 ng/mL showed inhibitory effects on osteoclast differentiation and their resorptive capability in the human osteoclast culture system. rhVEGF (25 ng/mL) enhanced the resorptive function of osteoclast whenever it was used alone or combined with 3 ng/mL rhBMP-2. However, rhVEGF-induced resorptive function was inhibited by 30 ng/mL and 300 ng/mL rhBMP-2 in a dose-dependent manner. Statistical analysis demonstrated that an interactive effect exists between rhBMP-2 and rhVEGF on human osteoclastogenesis. These findings suggested that an interactive regulation may exist between BMPs and VEGF signaling pathways during osteoclastogenesis; exact mechanisms are yet to be elucidated.

Vascular endothelial growth factor signalling in endothelial cell survival: a role for NFkappaB

Angiogenesis is the development of blood capillaries from pre-existing vessels. Vascular endothelial growth factor (VEGF) is a key regulator of vessel growth and regression, and acts as an endothelial survival factor by protecting endothelial cells from apoptosis. Many genes involved in cell proliferation and apoptosis are regulated by the nuclear factor kappa B (NFkappaB) transcription factor family. This study aimed to address the hypothesis that VEGF-mediated survival effects on endothelium involve NFkappaB. Using an NFkappaB-luciferase reporter adenovirus, we observed activation of NFkappaB following VEGF treatment of human umbilical vein endothelial cells. This was confirmed using electrophoretic mobility shift assay and found to involve nuclear translocation of NFkappaB sub-unit p65. However, NFkappaB activation occurred without degradation of inhibitory IkappaB proteins (IkappaBalpha, IkappaBbeta, and IkappaBepsilon). Instead, tyrosine phosphorylation of IkappaBalpha was observed following VEGF treatment, suggesting NFkappaB activation was mediated by degradation-independent dissociation of IkappaBalpha from NFkappaB. Adenovirus-mediated over-expression of either native IkappaBalpha, or of IkappaBalpha in which tyrosine residue 42 was mutated to phenylalanine, inhibited induction of NFkappaB-dependent luciferase activity in response to VEGF. Furthermore, VEGF-induced upregulation of mRNA for the anti-apoptotic protein Bcl-2 and cell survival following serum withdrawal was reduced following IkappaBalpha over-expression. This study highlights that different molecular mechanisms of NFkappaB activation may be involved downstream of stimuli which activate the endothelial lining of blood vessels.

Epidermal growth factor receptor and angiogenesis: Opportunities for combined anticancer strategies

Tumor-induced angiogenesis is essential for malignant growth. This mini review focuses on the role of vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF) and their receptors in this process, and the rationale to combine inhibitors of these growth factors as anticancer therapy. Concomitantly, targeting the VEGF(R) and the EGF(R) signaling pathway may circumvent the problem of acquired resistance to EGFR inhibitors. By targeting both pathways, the antiangiogenic effect may be more pronounced, which may lead to greater antitumor activity. Preliminary efficacy data from clinical trials encourage further exploration of this combined anticancer strategy.

Transgenic rabbits with increased VEGF expression develop hemangiomas in the liver: a new model for Kasabach-Merritt syndrome

Clinical studies have provided ample evidence that high (either systemic or local) levels of vascular endothelial growth factor (VEGF) are associated with several pathophysiological disorders, including hemangiomas. To investigate whether elevated VEGF expression could directly affect these disorders, we created a transgenic (Tg) rabbit model with increased hepatic expression of the human VEGF(165) transgene under the control of the human alpha-antitrypsin promoter. Tg rabbits exhibited marked hepatomegaly, with livers 2.5-fold heavier than those of control rabbits. Histological analysis revealed that the livers of Tg rabbits showed prominent dilation of the sinusoids and formed various-sized blood vessel networks, a feature of diffuse hemangiomas. Immunohistochemical staining revealed that the hepatocytes produced VEGF(165), whereas plasma VEGF(165) was not detected. Furthermore, Tg rabbits suffered from hemolytic anemia, thrombocytopenia and splenomegaly, which was associated with marked extramedullary hematopoiesis. The manifestations of Tg rabbits mimic many of the features of hemangiomatous disorders in humans such as the Kasabach-Merritt syndrome, and therefore this model may be potentially useful for the study of the pathogenesis and complications of hemangiomas as well as the investigation of angiogenesis inhibitors.

EWS–ETS oncoproteins: The linchpins of Ewing tumors

Ewing tumors, which comprise Ewing's sarcoma and peripheral primitive neuroectodermal tumors, are highly aggressive and mostly affect children and adolescents. Their molecular signature is a chromosomal translocation leading to the generation of EWS-ETS (or very rarely FUS-ETS) fusion proteins that are capable of transforming cells. These oncoproteins act as aberrant transcription factors due to the fusion of an ETS DNA binding domain to a highly potent EWS (or FUS) transactivation domain. Accordingly, many EWS-ETS target genes have been identified whose dysregulation could contribute to the development of tumor formation. Furthermore, EWS-ETS oncoproteins may impact on RNA splicing or affect other proteins through disturbing their ability to form functional complexes. The molecular knowledge gained so far from studying EWS-ETS oncoproteins has not only broadened our understanding of Ewing tumors but also improved the diagnosis of these highly undifferentiated tumors. In addition, several potential prognostic markers have been uncovered and novel therapies are suggested that may improve the still dismal survival rate of Ewing tumor patients.

Vascular endothelial growth factor stimulates a novel calcium-signaling pathway in vascular smooth muscle cells

BACKGROUND

Vascular endothelial growth factor (VEGF) is a potent vascular mitogen that selectively stimulates vascular smooth muscle cell (VSMC) migration through an unknown mechanism while having no effect on VSMC proliferation. It is known that VSMC migration and proliferation are dependent on the second messenger Ca2+ and, in particular, mitogen-stimulated Ca2+ influx. We hypothesized that the selective effect of VEGF on VSMC migration versus proliferation was a result of differential VEGF-stimulated Ca2+ signaling pathways.

METHODS

Primary cultured human aortic smooth muscle cells (VSMCs) were grown to subconfluency and assigned to the following experimental groups: no stimulation, stimulation with platelet-derived growth factor-BB (PDGF-BB) (20 ng/mL) as positive control, and stimulation with VEGF165 (40 ng/mL). Total increase in [Ca2+]cyt and intracellular calcium release was quantified with the use of a fura-2 fluorescence assay. Assays for the following receptors VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1) and PDGFR-beta were performed by immunoprecipitation, while PLCgamma1, Akt 1/2, and phospholamban B phosphorylation were assessed with Western immunoblotting.

RESULTS

VSMCs stimulated with VEGF165 exhibited no intracellular Ca2+ release, compared with a 75 +/- 30 nmol/L intracellular calcium release after PDGF-BB stimulation, (P < .02) VEGF165-stimulated VSMCs in Ca2+-containing media exhibited 192 +/- 26 nmol/L increase in [Ca2+]cyt, compared with 354 +/- 54 nmol/L increase after PDGF-BB stimulation (P < .02). VEGF165 did not phosphorylate PLCgamma1 after 1, 5, or 10 minutes of treatment. VEGF165 treatment did not result in PI3-K/Akt activation at 1-, 5-, or 10-minute time points. Calmodulin-dependent kinase II (CaMKII) was activated by both VEGF165 and PDGF-BB after 1 and 5 minutes of stimulation. The presence of the receptors VEGFR-1, VEGFR-2, and PDGFR-beta was confirmed in all experimental groups.

CONCLUSIONS

VEGF induces extracellular calcium influx but no intracellular calcium release in VSMCs. This lack of intracellular Ca2+ release stems from the inability of VEGF165 to activate the PLCgamma1 cascade and IP3 receptor-mediated Ca2+ release. The lack of PI3-K/Akt activation at these time points indicates a novel extracellular Ca2+ influx pathway sufficient to activate CaMKII. A paradigm relating extracellular Ca2+ influx to CaMKII activation and migration is suggested and may account for the selective effects of VEGF on VSMC migration.

Antagonistic functions of tetradecanoyl phorbol acetate-inducible-sequence 11b and HuR in the hormonal regulation of vascular endothelial growth factor messenger ribonucleic acid stability by adrenocorticotropin

Expression of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen and a potent angiogenic factor, is up-regulated by a variety of factors including hypoxia, growth factors, and hormones. In the adrenal cortex, regulation of VEGF expression by the pituitary hormone ACTH ensures the maintenance of the organ vasculature. We have previously shown that ACTH evokes a rapid and transient increase in VEGF mRNA levels in primary adrenocortical cells through transcription-independent mechanisms. We further demonstrated that the zinc finger RNA-binding protein Tis11b (tetradecanoyl phorbol acetate-inducible-sequence 11b) destabilizes VEGF mRNA through its 3'-untranslated region (3'-UTR) and that Tis11b is involved in the decay phase of ACTH-induced VEGF mRNA expression. In the present study, we attempted to determine the mechanisms underlying ACTH-elicited increase in VEGF mRNA levels in adrenocortical cells. We show that ACTH triggers an increase in the levels of the mRNA-stabilizing protein HuR in the cytoplasm and a concomitant decrease in the levels of HuR in the nucleus. This process is accompanied by an increased association of HuR with the nucleocytoplasmic shuttling protein pp32, indicating that ACTH induces HuR translocation from the nuclear to the cytoplasmic compartment. Leptomycin B, a specific inhibitor of CRM1-dependent nuclear export of pp32, significantly reduced ACTH-induced VEGF mRNA levels. Furthermore, RNA interference-mediated depletion of HuR in adrenocortical cells abrogated ACTH-induced VEGF mRNA expression. Finally, we show that Tis11b and HuR exert antagonistic effects on VEGF 3'-UTR in vitro. Although both proteins could bind simultaneously on VEGF 3'-UTR, Tis11b markedly decreases HuR-binding to this RNA sequence. Altogether, these results suggest that the RNA-stabilizing protein HuR is instrumental to ACTH-induced expression of VEGF mRNA and that the nuclear export of HuR is a rate-limiting step in this process. HuR appears to transiently stabilize VEGF transcripts after ACTH stimulation of adrenocortical cells, and Tis11b appears to subsequently trigger their degradation.

Cross-species vascular endothelial growth factor (VEGF)-blocking antibodies completely inhibit the growth of human tumor xenografts and measure the contribution of stromal VEGF

To fully assess the role of VEGF-A in tumor angiogenesis, antibodies that can block all sources of vascular endothelial growth factor (VEGF) are desired. Selectively targeting tumor-derived VEGF overlooks the contribution of host stromal VEGF. Other strategies, such as targeting VEGF receptors directly or using receptor decoys, result in inhibiting not only VEGF-A but also VEGF homologues (e.g. placental growth factor, VEGF-B, and VEGF-C), which may play a role in angiogenesis. Here we report the identification of novel anti-VEGF antibodies, B20 and G6, from synthetic antibody phage libraries, which block both human and murine VEGF action in vitro. Their affinity-improved variants completely inhibit three human tumor xenografts in mice of skeletal muscle, colorectal, and pancreatic origins (A673, HM-7, and HPAC). Avastin, which only inhibits the tumor-derived human VEGF, is approximately 90% effective at inhibiting HM-7 and A673 growth but is <50% effective at inhibiting HPAC growth. Indeed, HPAC tumors contain more host stroma invasion and stroma-derived VEGF than other tumors. Thus, the functional contribution of stromal VEGF varies greatly among tumors, and systemic blockade of both tumor and stroma-derived VEGF is sufficient for inhibiting the growth of tumor xenografts.

Regulators of angiogenesis and strategies for their therapeutic manipulation

Angiogenesis provides a mechanism by which delivery of oxygen and nutrients is adapted to compliment changes in tissue mass or metabolic activity. However, maladaptive angiogenesis is integral to the process of several diseases common in Western countries, including tumor growth, vascular insufficiency, diabetic retinopathy and rheumatoid arthritis. Understanding the process of capillary growth, including the identification and functional analyses of key pro- and anti-angiogenic factors, provides knowledge that can be applied to improve/reverse these pathological states. Initially, angiogenesis research focused predominantly on vascular endothelial growth factor (VEGF) as a main player in the angiogenesis cascade. It is apparent now that participation of multiple angiogenic factors and signal pathways is critical to enable effective growth and maturation of nascent capillaries. The purpose of this review is to focus on recent progress in identifying angiogenesis signaling pathways that show promise as targets for successful induction or inhibition of capillary growth. The strategies applied to achieve these contradictory tasks are discussed within the framework of our existing fundamental knowledge of angiogenesis signaling cascades, with an emphasis on comparing the employment of distinctive tactics in modulation of these pathways. Innovative developments that are presented include: (1) inducing a pleiotropic response via activation or inhibition of angiogenic transcription factors; (2) modulation of nitric oxide tissue concentration; (3) manipulating the kallikrein-kinin system; (4) use of endothelial progenitor cells as a means to either directly contribute to capillary growth or to be used as a vehicle to deliver "suicide genes" to tumor tissue.

Viral etiology of hepatocellular carcinoma and HCV genotypes in Taiwan

Etiologic variations of hepatocellular carcinoma (HCC) exist in different geographic areas of the world. Hepatitis B virus infection is associated with HCC. However, hepatitis C virus (HCV) infection plays an increasingly more important role in the development of HCC and is associated with more than 30% of HCC in Taiwan. The prevalence of HCV infection and HCV genotypes vary in different geographic areas. The prevalence of HCV genotype 1b (HCV-1b) was around 50-70% in Taiwan and even varied in different townships. In addition to host factors, HCV genotypes may be associated with the development of HCC. In our study, the prevalence of HCV-1b in patients with HCC was significantly higher than in those with liver cirrhosis and chronic hepatitis; multivariate analysis revealed that the disease severity was significantly correlated with age and HCV-1b. Furthermore, HCV-1b was associated with a lower response rate to interferon (IFN) therapy than HCV-2. Our study has demonstrated that mutations in the IFN sensitivity-determining region, spanning nucleotides 2,209-2,248 in the NS5A region, correlate with the sustained virological response to combination therapy with IFN and ribavirin in patients with chronic HCV-1b infection in Taiwan. A third-generation enzyme immunoassay for antibody to HCV can be used to predict viremia and monitor the virological response.

Vascular Endothelial Growth Factor (VEGF) Production by the Monkey Corpus Luteum During the Menstrual Cycle: Isoform-Selective Messenger RNA Expression In Vivo and Hypoxia-Regulated Protein Secretion In Vitro1

Experiments were designed to investigate the expression and regulation of vascular endothelial growth factor (VEGF) in the primate corpus luteum (CL) throughout the luteal life span in the natural menstrual cycle. Corpora lutea were collected during the early (ECL; Days 3-5 post-LH surge), mid (MCL; Day 6-8 post-LH surge), mid-late (MLCL; Days 10-12 post-LH surge), late (LCL; Days 14-16 post-LH surge), and very late (Days 17- 18 post-LH surge) luteal phase. Specific primers were designed to amplify mRNAs encoding VEGF isoforms 206, 189, 183, 165, 145, and 121. Only two cDNA products were obtained by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends; cloning and sequencing confirmed their 98% homology to the corresponding human VEGF 165 and 121 sequences. Semiquantitative RT-PCR assays indicated that VEGF 165 mRNA levels increased (P < 0.05) from ECL to MLCL but then declined (P < 0.05) by LCL. Although VEGF 121 mRNA levels were limited in ECL, they increased significantly in MCL (P < 0.05). Levels of VEGF protein, as measured by Western blot analysis, were two- to fourfold higher for VEGF 165 versus VEGF 121. Also, VEGF 165 levels were higher (P < 0.05) in ECL and MCL compared to those at later stages. During 2-day culture, preparations of dispersed luteal cells secreted VEGF into the media; the highest levels were observed in ECL and declined (P < 0.05) by LCL. Regardless of luteal stage, hypoxic conditions increased (P < 0.05) VEGF levels, whereas LH exposure increased (P < 0.05) progesterone, but not VEGF, in the media. These results are consistent with a dynamic, local regulation of VEGF production during the life span of the primate CL that is not directly controlled by LH.

[Overload damage to the Achilles tendon: the importance of vascularization and angiogenesis]

In the Achilles tendon, degenerative changes mostly occur in regions that are hypo- or avascular. Angiogenesis is mediated by angiogenic factors and recent studies have shown that vascular endothelial growth factor (VEGF) is highly expressed in degenerative Achilles tendons, whereas VEGF expression is nearly completely downregulated in healthy tendons. VEGF expression in tendon fibroblasts is regulated by the transcription factor hypoxia inducible factor 1 (HIF-1). Several factors are able to upregulate VEGF expression in tenocytes: hypoxia, inflammatory cytokines and mechanical load. Angiogenesis plays an important role in the tendinotic process. The neovessels are accompanied by small glutamate positive neural structures. This finding suggests that angiogenesis plays an important role in the pain experienced during the degenerative tendon disease. On the other hand, there is some evidence that HIF-1/VEGF induced angiogenesis has an effect on the material properties of the tendinotic tendon tissue. Since VEGF has the potential to stimulate the expression of matrix metalloproteinases and inhibits the expression of tissue inhibitors of matrix metalloproteinases (TIMP) in various cell types this cytokine might play a significant role in the pathogenetic processes during degenerative tendon disease. These experimental findings are in accordance with clinical results which show that eccentric training leads to a regression of neovessels and decrease of pain. Another strategy is the local administration of a sclerosing agent (Polidocanol) to destroy neovessles. Preliminary results show that both strategies are effective in reducing vascular density and pain.

A hypoxia-driven vascular endothelial growth factor/Flt1 autocrine loop interacts with hypoxia-inducible factor-1alpha through mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 pathway in neuroblastoma

Flt1, an "fms-like tyrosine kinase" receptor, has been suggested to play an active role in vascular endothelial growth factor (VEGF)-mediated autocrine signaling of tumor growth and angiogenesis. Here, we used a neuroblastoma model to investigate the role of VEGF/Flt1 signaling in hypoxia-mediated tumor cell survival, drug resistance, and in vivo angiogenesis. SK-N-BE2, a highly malignant neuroblastoma cell line resistant to hypoxia-induced apoptosis expresses active Flt1 but lacks VEGFR2 expression. We found that 24-hour hypoxia (<0.1% O2) alone (no serum deprivation) showed sustained activation of extracellular signal-regulated kinase 1/2 (ERK1/2) associated with bcl-2 up-regulation and resistance to etoposide-induced (5 mumol/L) apoptosis. Treatment with anti-VEGF and anti-Flt1 antibodies inhibited ERK1/2 activation, down-regulated bcl-2, and reversed the hypoxia-mediated drug resistance to etoposide. Similar results were obtained with U0126 and ursolic acid, specific and nonspecific inhibitors of ERK1/2, respectively. We confirmed the protective role of Flt1 receptor by small interfering RNA knockout and Flt1 overexpression studies. Subsequently, we found that inhibition of VEGF/Flt1 autocrine signaling led to reduced hypoxia-inducible factor-1alpha (HIF-1alpha) phosphorylation. Furthermore, the reduced phosphorylation was associated with down-regulation of basic fibroblast growth factor, a downstream target of the HIF-1alpha and VEGF pathways. Our findings suggested an expanded autocrine loop between VEGF/Flt1 signaling and HIF-1alpha. We investigated the angiogenic activity of the loop in an in vivo Matrigel plug assay. The hypoxia-treated conditioned medium induced a strong angiogenic response, as well as the cooption of surrounding vessels into the plugs; ursolic acid inhibited the angiogenesis process. We also found that three other Flt1-expressing neuroblastoma cell lines show hypoxia-mediated drug resistance to etoposide, melphalan, doxorubicin, and cyclophosphamide. Taken together, we conclude that a hypoxia-driven VEGF/Flt1 autocrine loop interacts with HIF-1alpha through a mitogen-activated protein kinase/ERK1/2 pathway in neuroblastoma. The interaction, in the form of an autocrine loop, is required for the hypoxia-driven cell survival, drug resistance, and angiogenesis in neuroblastoma.

Vascular morphogenesis in the primate ovary

Ovarian function is dependent on intense cyclical vascular morphogenesis and regression. The molecular and cellular pathways involved in the generation of new capillary networks in the ovary are now being elucidated. Focussing on the marmoset, the course of angiogenesis at different stages of follicular maturation and in the corpus luteum throughout the cycle and in early pregnancy have been quantified and major progress has been made in the evaluation of the role of vascular endothelial growth factor (VEGF). To study the physiological role of VEGF in follicular and luteal angiogenesis in detail, VEGF was inhibited during defined stages of the cycle in vivo. VEGF antagonist administered throughout the follicular phase of the cycle resulted in a marked decrease in endothelial cell proliferation in developing antral follicles, accompanied by a decline in granulosa cell proliferation, restriction of follicular growth and inhibition of ovulation. An outstanding feature in the ovary is the intense angiogenesis that occurs during the early luteal phase. VEGF inhibitors markedly suppressed this angiogenesis, resulting in a marked restriction in the development of the microvascular tree and suppression of plasma progesterone. These studies showed that VEGF is essential for normal follicular and luteal angiogenesis and function, and demonstrated how luteal angiogenesis in particular could serve as a sensitive bioassay for putative angiogenic antagonists. Antagonists of VEGF are potent tools for investigating the role of angiogenic factors within the ovary and may have applications to the treatment of reproductive disorders characterised by alterations in normal vascular structure or function.

Vascular endothelial growth factor increases the ultrafiltration coefficient in isolated intact Wistar rat glomeruli

Vascular endothelial growth factor (VEGF) is expressed by the podocytes of renal glomeruli, and has profound influences on systemic microvascular permeability and haemodynamics. We describe an extensive refinement of a model that permits evaluation of the ultrafiltration coefficient (LpA) of isolated mammalian glomeruli, in the absence of circulating and haemodynamic influences, and tested the hypothesis that VEGF influences glomerular LpA via an effect on endothelial cells. Glomeruli were isolated by sieving Wistar rat renal cortical tissue, and individually loaded onto a suction micropipette. Flowing perifusate containing 1% bovine serum albumin (BSA) was rapidly switched to an oncopressive perifusate containing 8% BSA, eliciting transglomerular fluid efflux. The rate of the resultant reduction in glomerular volume was used to calculate glomerular LpA (1.07 +/- 0.53 nl min(-1) mmHg(-1) (mean +/-s.d.), n= 51), which compares favourably with those reported in the same rat strain using different techniques. A significant relationship between LpA and initial glomerular volume (Vi) (r= 0.72, n= 41, P < 0.0001) necessitated correction of LpA for Vi. The initial rate of change of glomerular volume, normalized for Vi, showed a strong positive correlation with applied oncotic gradient (Pearson r= 0.59, n= 28, P < 0.001), as predicted by Starling's law of filtration. A 60 min exposure of glomeruli to 1 nm VEGF increased glomerular LpA/Vi (1.19 +/- 0.19 (n= 10) to 2.23 +/- 0.33 (n= 9) min(-1) mmHg(-1) (mean +/-s.e.m.); P < 0.02). Time- and concentration-dependent relations between VEGF and LpA/Vi were observed. The VEGF-induced elevation of LpA/Vi was blocked by the selective VEGF-R2 inhibitor ZM323881. We suggest that glomerular VEGF contributes to the high physiological permeability of mammalian glomeruli to water through an action on endothelial cells.

Silibinin inhibits angiogenesis via Flt-1, but not KDR, receptor up-regulation

BACKGROUND

Our previous study found that silymarin (SM) and its major pure component silibinin (SB) have anti-angiogenic effects via decreased vascular endothelium growth factor (VEGF) secretion of LoVo cells (colon cancer). We designed this consecutive study to evaluate the anti-angiogenic effects of SM/SB in vivo, and on VEGF receptor (VEGFR) gene expression.

MATERIALS AND METHODS

We used LoVo cells exposed to SM/SB in a modified chicken chorioallantoic membrane assay (CAM) to evaluate anti-angiogenic effects. We used EA.hy 926 cells (endothelial cells) exposed to SM/SB to evaluate the effect on VEGFR-1 (Flt-1) and VEGFR-2 (KDR), with 1-step, real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

In CAM, SM/SB showed a dose-dependent decrease on the vascular density index (VDI) induced by LoVo cells, as did thalidomide in a concentration of 10 microg/ml. Adding escalating dosages of VEGF successfully reversed this inhibitory effect. RT-PCR revealed that SB up-regulated Flt-1 mRNA expression of EA.hy 926 cells. SM had a similar trend, although the effect was not statistically significant (P = 0.19). Neither drug effected KDR mRNA expression.

CONCLUSION

We conclude that anti-angiogenic effects of SM/SB are associated with the up-regulation of VEGFR-1 (Flt-1) gene expression and that they are good candidates for combination therapy to treat colorectal cancer.

Recent advances in endometrial angiogenesis research

This review summarises recent research into the mechanisms and regulation of endometrial angiogenesis. Understanding of when and by what mechanisms angiogenesis occurs during the menstrual cycle is limited, as is knowledge of how it is regulated. Significant endometrial endothelial cell proliferation occurs at all stages of the menstrual cycle in humans, unlike most animal models where a more precise spatial relationship exists between endothelial cell proliferation and circulating levels of oestrogen and progesterone. Recent stereological data has identified vessel elongation as a major endometrial angiogenic mechanism in the mid-late proliferative phase of the cycle. In contrast, the mechanisms that contribute to post-menstrual repair and secretory phase remodelling have not yet been determined. Both oestrogen and progesterone/progestins appear to have paradoxical actions, with recent studies showing that under different circumstances both can promote as well as inhibit endometrial angiogenesis. The relative contribution of direct versus indirect effects of these hormones on the vasculature may help to explain their pro- or anti-angiogenic activities. Recent work has also identified the hormone relaxin as a player in the regulation of endometrial angiogenesis. While vascular endothelial growth factor (VEGF) is fundamental to endometrial angiogenesis, details of how and when different endometrial cell types produce VEGF, and how production and activity is controlled by oestrogen and progesterone, remains to be elucidated. Evidence is emerging that the different splice variants of VEGF play a major role in regulating endometrial angiogenesis at a local level. Intravascular neutrophils containing VEGF have been identified as having a role in stimulating endometrial angiogenesis, although other currently unidentified mechanisms must also exist. Future studies to clarify how endometrial angiogenesis is regulated in the human, as well as in relevant animal models, will be important for a better understanding of diseases such as breakthrough bleeding, menorrhagia, endometriosis and endometrial cancer.

Cold-induced expression of the VEGF gene in brown adipose tissue is independent of thermogenic oxygen consumption

To examine whether cold-induced vascular endothelial growth factor (VEGF) gene expression in brown adipose tissue involved generation of hypoxic oxygen levels by thermogenic processes, we cold-exposed wild-type mice, as well as uncoupling protein-1 (UCP1)-ablated mice in which no thermogenesis in brown adipocytes can be induced. Cold exposure stimulated VEGF expression in both wild-type and UCP1-ablated mice. Unexpectedly, the effect was 3-fold higher in UCP1-ablated animals, whereas cultured brown adipocytes from both genotypes responded identically to norepinephrine stimulation. These results demonstrate that generation of low oxygen levels does not contribute to cold-induced VEGF expression in brown adipose tissue, but the results are consistent with an adrenergic regulation of expression.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibition of coronary vasculogenesis is mediated, in part, by reduced responsiveness to endogenous angiogenic stimuli, including vascular endothelial growth factor A (VEGF-A)

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exposure prior to chick embryo incubation (GD 0) induces dilated cardiomyopathy, and reduces myocardial hypoxia, vascular endothelial growth factor A (VEGF-A) expression, and coronary vascularization. We investigated whether reduced coronary vascularization 1) occurs in the absence of changes in cardiac morphology and 2) is associated with altered secretion of VEGF-A and/or an antivasculogenic factor.

METHODS

Chicken eggs were treated with control (corn oil) or TCDD (0.075-0.3 pmol of TCDD/gm) on GD 5. In vivo cardiac morphology and artery number were determined on GD 10, while in vitro vascular outgrowth and VEGF-A secretion were determined from cardiac explants on GD 6. Effects of recombinant VEGF-A (rcVEGF-A), soluble flt-1 (sFlt-1) receptor plus rcVEGF-A, and control conditioned media were assessed in TCDD explants, while effects of TCDD-conditioned media was assessed in control explants.

RESULTS

TCDD reduced coronary artery number in vivo by 53 +/- 8% and induced a dose-related reduction in tube outgrowth in vitro, but had no effect on cardiac morphology. All TCDD doses reduced explant VEGF-A secretion equally (43 +/- 3%), compared to control. sFlt-1 blocked outgrowth in control cultures and blocked rcVEGF-A-mediated rescue of outgrowth in TCDD explants. Control conditioned media partially rescued outgrowth from TCDD explants, while conditioned media from TCDD explants had no effect on controls.

CONCLUSIONS

TCDD inhibition of coronary vascularization can occur in the absence of changes in cardiac morphology and is associated with reduced VEGF-A secretion but not an antivasculogenic factor. Since control media only partly rescues TCDD's inhibitory effect, we suggest that TCDD-exposed endothelial cells are less responsive to vasculogenic stimuli.

Absence of Adverse Effects in Cynomolgus Macaques Treated with CNTO 95, a Fully Human Anti-αv Integrin Monoclonal Antibody, Despite Widespread Tissue Binding

PURPOSE

CNTO 95 is a fully human anti-alphav integrin monoclonal antibody that inhibits macaque and rodent angiogenesis and inhibits human tumor growth in rodents. The purpose of these studies was to evaluate the preclinical safety of long-term administration of CNTO 95 in cynomolgus macaques.

EXPERIMENTAL DESIGN

The in vitro binding profiles of CNTO 95 to human and macaque tissues and the in vivo binding to macaque tissues was evaluated by immunohistochemistry. The preclinical safety of CNTO 95 (10 and 50 mg/kg, i.v.) was evaluated in macaques treated once per week for up to 6 months. Safety was evaluated by clinical observations, ophthalmic and physical examinations (including heart rate, blood pressure, and electrocardiogram), clinical pathology (including coagulation parameters), and comprehensive anatomic pathology. The effect of CNTO 95 (50 mg/kg, i.v.) on incisional wound healing was evaluated in macaques.

RESULTS

The tissue binding studies showed that CNTO 95 bound with mild to moderate intensity to macaque and human endothelial cells, epithelial cells, and vascular smooth muscle cells in most normal tissues examined. CNTO 95 showed strong to intense staining to the positive control tissue, human placenta. Despite the widespread binding to normal tissues, treatment of cynomolgus macaques with CNTO 95 produced no signs of toxicity and no histopathologic changes in any of the tissues examined (including ovaries and bone growth plates). CNTO 95 did not impair wound healing.

CONCLUSION

These studies show that CNTO 95 is safe and, unlike some other angiogenesis inhibitors, does not seem to inhibit normal physiologic angiogenesis.