The 121 amino acid isoform of vascular endothelial growth factor is more strongly tumorigenic than other splice variants in vivo

Molecularly Imprinted Nanomedicine for Anti-angiogenic Cancer Therapy via Blocking Vascular Endothelial Growth Factor Signaling

The VEGF-VEGFR2 (VEGF = vascular endothelial growth factor) signaling has been a promising target in cancer therapy. However, because conventional anti-angiogenic therapeutics suffer from drawbacks, particularly severe side effects, novel anti-angiogenic strategies are much needed. Herein, we report the rational engineering of VEGF-targeted molecularly imprinted polymer nanoparticles (nanoMIP) for anti-angiogenic cancer therapy. The anti-VEGF nanomedicine was prepared via a state-of-the-art molecular imprinting approach using the N-terminal epitope of VEGF as the template. The nanoMIP could target the two major pro-angiogenic isoforms (VEGF165 and VEGF121) with high affinity and thereby effectively block the VEGF-VEGFR2 signaling, yielding a potent anti-angiogenic effect of "killing two birds with one stone". In vivo experiments demonstrated that the anti-VEGF nanoMIP effectively suppressed tumor growth via anti-angiogenesis in a xenograft model of human colon carcinoma without apparent side effects. Thus, this study not only proposes an unprecedented anti-angiogenic strategy for cancer therapy but also provides a new paradigm for the rational development of MIPs-based "drug-free" nanomedicines.

Adenoviral vectors for cardiovascular gene therapy applications: a clinical and industry perspective

Abstract

Despite the development of novel pharmacological treatments, cardiovascular disease morbidity and mortality remain high indicating an unmet clinical need. Viral gene therapy enables targeted delivery of therapeutic transgenes and represents an attractive platform for tackling acquired and inherited cardiovascular diseases in the future. Current cardiovascular gene therapy trials in humans mainly focus on improving cardiac angiogenesis and function. Encouragingly, local delivery of therapeutic transgenes utilising first-generation human adenovirus serotype (HAd)-5 is safe in the short term and has shown some efficacy in drug refractory angina pectoris and heart failure with reduced ejection fraction. Despite this success, systemic delivery of therapeutic HAd-5 vectors targeting cardiovascular tissues and internal organs is limited by negligible gene transfer to target cells, elimination by the immune system, liver sequestration, off-target effects, and episomal degradation. To circumvent these barriers, cardiovascular gene therapy research has focused on determining the safety and efficacy of rare alternative serotypes and/or genetically engineered adenoviral capsid protein-modified vectors following local or systemic delivery. Pre-clinical studies have identified several vectors including HAd-11, HAd-35, and HAd-20–42-42 as promising platforms for local and systemic targeting of vascular endothelial and smooth muscle cells. In the past, clinical gene therapy trials were often restricted by limited scale-up capabilities of gene therapy medicinal products (GTMPs) and lack of regulatory guidance. However, significant improvement of industrial GTMP scale-up and purification, development of novel producer cell lines, and issuing of GTMP regulatory guidance by national regulatory health agencies have addressed many of these challenges, creating a more robust framework for future adenoviral-based cardiovascular gene therapy. In addition, this has enabled the mass roll out of adenovirus vector-based COVID-19 vaccines.

Key messages

First-generation HAd-5 vectors are widely used in cardiovascular gene therapy.

HAd-5-based gene therapy was shown to lead to cardiac angiogenesis and improved function.

Novel HAd vectors may represent promising transgene carriers for systemic delivery.

Novel methods allow industrial scale-up of rare/genetically altered Ad serotypes.

National regulatory health agencies have issued guidance on GMP for GTMPs.

How VEGF-A and its splice variants affect breast cancer development - clinical implications

BACKGROUND

Altered expression levels and structural variations in the vascular endothelial growth factor (VEGF) have been found to play important roles in cancer development and to be associated with the overall survival and therapy response of cancer patients. Particularly VEGF-A and its splice variants have been found to affect physiological and pathological angiogenic processes, including tumor angiogenesis, correlating with tumor progression, mostly caused by overexpression. This review focuses on the expression and impact of VEGF-A splice variants under physiologic conditions and in tumors and, in particular, the distribution and role of isoform VEGF165b in breast cancer.

CONCLUSIONS AND PERSPECTIVES

Many publications already highlighted the importance of VEGF-A and its splice variants in tumor therapy, especially in breast cancer, which are summarized in this review. Furthermore, we were able to demonstrate that cytoplasmatic VEGFA/165b expression is higher in invasive breast cancer tumor cells than in normal tissues or stroma. These examples show that the detection of VEGF splice variants can be performed also on the protein level in formalin fixed tissues. Although no quantitative conclusions can be drawn, these results may be the starting point for further studies at a quantitative level, which can be a major step towards the design of targeted antibody-based (breast) cancer therapies.

Anti-Angiogenic Treatments Interact with Steroid Secretion in Inflammatory Breast Cancer Triple Negative Cell Lines

Human inflammatory breast cancer (IBC) is a highly angiogenic disease for which antiangiogenic therapy has demonstrated only a modest response, and the reason for this remains unknown. Thus, the purpose of this study was to determine the influence of different antiangiogenic therapies on in vitro and in vivo steroid hormone and angiogenic growth factor production using canine and human inflammatory breast carcinoma cell lines as well as the possible involvement of sex steroid hormones in angiogenesis. IPC-366 and SUM149 cell lines and xenotransplanted mice were treated with different concentrations of VEGF, SU5416, bevacizumab and celecoxib. Steroid hormone (progesterone, dehydroepiandrostenedione, androstenedione, testosterone, dihydrotestosterone, estrone sulphate and 17β-oestradiol), angiogenic growth factors (VEGF-A, VEGF-C and VEGF-D) and IL-8 determinations in culture media, tumour homogenate and serum samples were assayed by EIA. In vitro, progesterone- and 17β-oestradiol-induced VEGF production promoting cell proliferation and androgens are involved in the formation of vascular-like structures. In vivo, intratumoural testosterone concentrations were augmented and possibly associated with decreased metastatic rates, whereas elevated E1SO4 concentrations could promote tumour progression after antiangiogenic therapies. In conclusion, sex steroid hormones could regulate the production of angiogenic factors. The intratumoural measurement of sex steroids and growth factors may be useful to develop preventive and individualized therapeutic strategies.

VEGFA's distal enhancer regulates its alternative splicing in CML

Enhancer demethylation in leukemia has been shown to lead to overexpression of genes which promote cancer characteristics. The vascular endothelial growth factor A (VEGFA) enhancer, located 157 Kb downstream of its promoter, is demethylated in chronic myeloid leukemia (CML). VEGFA has several alternative splicing isoforms with different roles in cancer progression. Since transcription and splicing are coupled, we wondered whether VEGFA enhancer activity can also regulate the gene's alternative splicing to contribute to the pathology of CML. Our results show that mutating the VEGFA +157 enhancer promotes exclusion of exons 6a and 7 and activating the enhancer by tethering a chromatin activator has the opposite effect. In line with these results, CML patients present with high expression of +157 eRNA and inclusion of VEGFA exons 6a and 7. In addition, our results show that the positive regulator of RNAPII transcription elongation, CCNT2, binds VEGFA's promoter and enhancer, and its silencing promotes exclusion of exons 6a and 7 as it slows down RNAPII elongation rate. Thus our results suggest that VEGFA's +157 enhancer regulates its alternative splicing by increasing RNAPII elongation rate via CCNT2. Our work demonstrates for the first time a connection between an endogenous enhancer and alternative splicing regulation of its target gene.

Exploring the Intracrine Functions of VEGF-A

Vascular endothelial growth factor A (VEGF-A or VEGF) is a highly conserved secreted signalling protein best known for its roles in vascular development and angiogenesis. Many non-endothelial roles for VEGF are now established, with the discovery that VEGF and its receptors VEGFR1 and VEGFR2 are expressed in many non-vascular cell-types, as well as various cancers. In addition to secreted VEGF binding to its receptors in the extracellular space at the cell membrane (i.e., in a paracrine or autocrine mode), intracellularly localised VEGF is emerging as an important signalling molecule regulating cell growth, survival, and metabolism. This intracellular mode of signalling has been termed “intracrine”, and refers to the direct action of a signalling molecule within the cell without being secreted. In this review, we describe examples of intracrine VEGF signalling in regulating cell growth, differentiation and survival, both in normal cell homeostasis and development, as well as in cancer. We further discuss emerging evidence for the molecular mechanisms underpinning VEGF intracrine function, as well as the implications this intracellular mode of VEGF signalling may have for use and design of anti-VEGF cancer therapeutics.

Expression of vascular endothelial growth factor (VEGF) in equine sarcoid

BACKGROUND

Sarcoids are the mostcommon skin tumors in horses, characterized by rare regression, invasiveness and high recurrence following surgical intervention and Delta Papillomaviruses are widely recognized as the causative agents of the disease. In order to gain new insights into equine sarcoid development, we have evaluated, in 25 equine sarcoids, by immunohistochemistry and western blotting analysis, the expression levels of VEGF, Ki67 and bcl-2. Moreover, we have measured microvessel density and specific vessel parameters.

RESULTS

All sarcoid samples showed a strong and finely granular cytoplasmatic staining for VEGF in the majority (90%) of keratinocytes, sarcoid fibroblasts and endothelial cells. Numerous small blood vessels, immunostained with Von Willebrand factor, often appeared irregular in shape and without a distinct lumen, with mean values of microvessel area and perimeter lower than normal. Moreover, in all sarcoid samples, Ki67 immunoreactivity was moderately positive in 5-10% of dermal sarcoid fibroblasts, while Bcl2 immunoreactivity was detected in 52% of the sarcoid samples, with a weak staining in 20-50% of dermal sarcoid fibroblasts. Biochemical analysis was consistent with immunohistochemical results.

CONCLUSIONS

This study has provided evidence that in equine sarcoid: VEGF was strongly expressed; the increased number of vessels was not associated with their complete maturation, probably leading to a hypoxic condition, which could increase VEGF synthesis; the levels of sarcoid fibroblasts proliferation were very low. Concluding, VEGF may have a role in equine sarcoid development, not only through the increase of angiogenesis, but also through the control of sarcoid fibroblast activity.

Malignant pericytes expressing GT198 give rise to tumor cells through angiogenesis

Angiogenesis promotes tumor development. Understanding the crucial factors regulating tumor angiogenesis may reveal new therapeutic targets. Human GT198 (PSMC3IP or Hop2) is an oncoprotein encoded by a DNA repair gene that is overexpressed in tumor stromal vasculature to stimulate the expression of angiogenic factors. Here we show that pericytes expressing GT198 give rise to tumor cells through angiogenesis. GT198+ pericytes and perivascular cells are commonly present in the stromal compartment of various human solid tumors and rodent xenograft tumor models. In human oral cancer, GT198+ pericytes proliferate into GT198+ tumor cells, which migrate into lymph nodes. Increased GT198 expression is associated with increased lymph node metastasis and decreased progression-free survival in oral cancer patients. In rat brain U-251 glioblastoma xenografts, GT198+ pericytes of human tumor origin encase endothelial cells of rat origin to form mosaic angiogenic blood vessels, and differentiate into pericyte-derived tumor cells. The net effect is continued production of glioblastoma tumor cells from malignant pericytes via angiogenesis. In addition, activation of GT198 induces the expression of VEGF and promotes tube formation in cultured U251 cells. Furthermore, vaccination using GT198 protein as an antigen in mouse xenograft of GL261 glioma delayed tumor growth and prolonged mouse survival. Together, these findings suggest that GT198-expressing malignant pericytes can give rise to tumor cells through angiogenesis, and serve as a potential source of cells for distant metastasis. Hence, the oncoprotein GT198 has the potential to be a new target in anti-angiogenic therapies in human cancer.

Stage-Dependent Expression of an Angiogenic Agent and Vascular Organization in Experimental Skin Tumor Development

Increased angiogenesis and expression of antibodies to vascular endothelial growth factor (VEGF), an angiogenic agent, have been shown in the tumor development of many tissues. Areas of skin expressing VEGF and total volume of vessels expressing laminin in the wall were measured in chemical carcinogen-exposed mice using CAS-200 morphometry apparatus having a sensitivity exceeding 99% and reproducibility exceeding 99%. The area of VEGF expression was increased in carcinogen-exposed skin, dysplasia and in well-differentiated squamous cell carcinomas, but decreased in squamous cell carcinomas with decreased degree of differentiation. The vessel volume increased prior to the formation of tumors in carcinogen-exposed skin as well as in highly malignant neoplasms. In well-differentiated squamous cell carcinomas with an expansive growth pattern, the vessels were parallel to the basal membrane, in moderately differentiated tumors the vessels were in the direction of tumor invasion, and in poorly differentiated tumors, active angiogenesis consisted of numerous, enlarged vessels within the tumor. This study showed increased VEGF expression and number of vessels occurring in early stages of skin tumor development, pointing to a role of angiogenesis in chemical risk assessment and in cancer prevention. Altered vessel structure and vessel arrangement were distinct in later stages of tumor growth and in malignant neoplasms, pointing to the utility of detailed vessel analysis in neoplasm characterization.

Molecular underpinnings of corneal angiogenesis: advances over the past decade

The cornea is maintained in an avascular state by maintaining an environment whereby anti-angiogenic factors take the upper hand over factors promoting angiogenesis. Many of the common pathologies affecting the cornea involve the disruption of such equilibrium and the shift towards new vessel formation, leading to corneal opacity and eventually-vision loss. Therefore it is of paramount importance that the molecular underpinnings of corneal neovascularization (CNV) be clearly understood, in order to develop better targeted treatments. This article is a review of the literature on the recent discoveries regarding pro-angiogenic factors of the cornea (such as vascular endothelial growth factors, fibroblast growth factor and matrix metalloproteinases) and anti-angiogenic factors of the cornea (such as endostatins and neostatins). Further, we review the molecular underpinnings of lymphangiogenesis, a process now known to be almost separate from (yet related to) hemangiogenesis.

AdVEGF-All6A+ Preconditioning of Murine Ischemic Skin Flaps Is Comparable to Surgical Delay

Background:

Surgical flap delay is commonly used in preconditioning reconstructive flaps to prevent necrosis. However, staged procedures are not ideal. Pharmacologic up-regulation of angiogenic and arteriogenic factors before flap elevation poses a nonsurgical approach to improve flap survival.

Methods:

Male Sprague Dawley rats were divided into control (n = 16), surgical delay (Delay), AdNull, AdEgr-1, and AdVEGF (n ≥ 9/group) groups. Delay rats had a 9 cm × 3 cm cranial based pedicle skin flap incised 10 days prior to elevation. Adenoviral groups received 28 intradermal injections (10⁹ pu/animal total) throughout the distal two thirds of the flap 1 week prior to elevation. At postoperative day (POD) 0 flaps were elevated and silicone sheeting was placed between flap and wound bed. Perfusion analysis in arbitrary perfusion units of the ischemic middle third of the flap using laser Doppler imaging was conducted preoperatively and on POD 0, 3, and 7. Clinical and histopathologic assessments of the skin flaps were performed on POD 7.

Results:

AdVEGF (50.8 ± 10.9 APU) and AdEgr-1 (39.3 ± 10.6 APU) perfusion levels were significantly higher than controls (16.5 ± 4.2 APU) on POD 7. Delay models were equivalent to controls (25.9 ± 6.8 APU). AdVEGF and Delay animals showed significantly more viable surface area on POD 7 (14.4 ± 1.3 cm², P < 0.01 and 12.4 ± 1.2 cm², P < 0.05, respectively) compared with Controls (8.7 ± 0.7 cm²).

Conclusions:

AdVEGF preconditioning resulted in flap survival comparable to surgical delay. Adenoviral preconditioning maintained perfusion levels postoperatively while surgical delay did not.

RNA-seq analysis reveals significant effects of EGFR signalling on the secretome of mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) contribute to breast cancer progression by releasing soluble factors that sustain tumor progression. MSCs express functional epidermal growth factor receptor (EGFR) and breast cancer cells secrete EGFR-ligands including transforming growth factor-α (TGFα). Using RNA-sequencing, we analysed the whole transcriptome of MSCs stimulated with TGFα. We identified 1,640 highly differentially regulated genes: 967 genes up-regulated with Fold Induction (FI)≥1.50 and 673 genes down-regulated with FI≤0.50. When highly regulated genes were categorized according to GO molecular function classification and KEGG pathways analysis, a large number of genes coding for potentially secreted proteins or surface receptors resulted enriched following TGFα treatment, including VEGFA, IL6, EREG, HB-EGF, LIF, NGF, NRG1, CCL19, CCL2, CCL25 and CXCL3. Secretion of corresponding proteins was confirmed for selected factors. Finally, we identified 4,377 and 4,262 alternatively spliced genes in untreated and TGFα-treated MSCs, respectively. Among these, an unannotated splice variant of VEGFA coding for a secreted VEGF protein of 172 aminoacids (VEGFA₁₇₂), was found only in MSCs stimulated with TGFα. These findings suggest that EGFR activation in MSCs leads to a significant change in the expression of a wide array of genes coding for secreted proteins that can significantly enhance tumor progression.

MDA-MB-231 breast cancer cells overexpressing single VEGF isoforms display distinct colonisation characteristics

Background:

Vascular endothelial growth factor (VEGF) is a multifunctional cytokine that has important roles in angiogenesis. Our knowledge of the significance of VEGF isoforms in human cancer remains incomplete.

Methods:

Bioluminescence imaging and transcriptomic analysis were used to study the colonisation capacity of the human breast cancer cells MDA-MB-231 controlling or overexpressing the VEGF165 or VEGF189 isoform (named cV-B, V165-B and V189-B, respectively) in nude mice.

Results:

When injected into the bloodstream, V189-B cells induced less metastasis in the lungs and bone than V165-B and cV-B control cells, consistent with longer survival of these mice and delay in tumour uptake in the mice injected with a V189-B clone. Histological analysis confirmed that there were less αSMA-positive cells in the lungs of the mice injected with V189-B. In vitro V189-B cells decreased both cell invasion and survival. Using transcriptomic analysis, we identified a subset of 18 genes expressed differentially between V189 and V165 cell lines and in 120 human breast tumours. V165 was associated with poor prognosis, whereas V189 was not, suggesting a complex regulation by VEGF isoforms. Our results showed a negative correlation between the expression pattern of VEGF189 and the levels of expression of seven genes that influence metastasis.

Conclusion:

Our findings provide the first evidence that VEGF isoforms have different effects on breast cancer cell line colonisation in vivo.

Alternative splicing of VEGFA, APP and NUMB genes in colorectal cancer

AIM

To investigate alternative splicing in vascular endothelial growth factor A (VEGFA), amyloid beta precursor protein (APP), and Numb homolog (NUMB) in colorectal cancer (CRC).

METHODS

Real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and PCR-restriction fragment length polymorphism analyses were performed to detect the expression of VEGFA, APP, and NUMB mRNA in 20 CRC tissues and matched adjacent normal tissues, as well as their alternative splicing variants.

RESULTS

qRT-PCR analysis revealed that the expression of APP, NUMB, and VEGFA165b mRNA were significantly downregulated, while VEGFA mRNA was upregulated, in CRC tissues (all P < 0.05). PCR-restriction fragment length polymorphism analysis revealed that the expression of VEGFA165a/b in CRC tissues was significantly higher than in adjacent normal tissues (P < 0.05). Compared with adjacent normal tissues, the expression of NUMB-PRR(S) in CRC tissues was significantly decreased (P < 0.05), and the expression of NUMB-PRR(L) was increased (P < 0.05).

CONCLUSION

Alternative splicing of VEGFA, APP, and NUMB may regulate the development of CRC, and represent new targets for its diagnosis, prognosis, and treatment.

VEGF-A isoform-specific regulation of calcium ion flux, transcriptional activation and endothelial cell migration

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology such as cell migration, proliferation, tubulogenesis and cell-cell interactions. Numerous isoforms of VEGF-A exist but their physiological significance is unclear. Here we evaluated two different VEGF-A isoforms and discovered differential regulation of cytosolic calcium ion flux, transcription factor localisation and endothelial cell response. Analysis of VEGF-A isoform-specific stimulation of VEGFR2-dependent signal transduction revealed differential capabilities for isoform activation of multiple signal transduction pathways. VEGF-A₁₆₅ treatment promoted increased phospholipase Cγ1 phosphorylation, which was proportional to the subsequent rise in cytosolic calcium ions, in comparison to cells treated with VEGF-A₁₂₁. A major consequence of this VEGF-A isoform-specific calcium ion flux in endothelial cells is differential dephosphorylation and subsequent nuclear translocation of the transcription factor NFATc2. Using reverse genetics, we discovered that NFATc2 is functionally required for VEGF-A-stimulated endothelial cell migration but not tubulogenesis. This work presents a new mechanism for understanding how VEGF-A isoforms program complex cellular outputs by converting signal transduction pathways into transcription factor redistribution to the nucleus, as well as defining a novel role for NFATc2 in regulating the endothelial cell response.

Overexpression of VEGF183 promotes murine breast cancer cell proliferation in vitro and induces dilated intratumoral microvessels

Vascular endothelial growth factor (VEGF) was considered as a critical growth factor for tumor expansion. The roles of VEGF121, VEGF165, and VEGF189 in tumor growth have been intensely investigated; however, involvements of another extracellular matrix (ECM)-binding VEGF isoform, namely VEGF183 (six amino acids shorter than VEGF189 in exon 6a), in physiological or pathological processes are still unclear although the wide tissue distribution. To investigate the role of VEGF183 in carcinogenesis, we generated murine breast cancer cell (EMT-6) clones stably overexpressing VEGF183, VEGF121, VEGF165, and VEGF189 shortened as V183, V121, V165, and V189, respectively. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) results showed that VEGF183, like all other VEGF-overexpressing isoforms except for VEGF121, could enhance the proliferation of mouse breast cancer EMT-6 cells. Immunochemistry results displayed that overexpressing VEGF183 and VEGF189 in EMT-6 cells induced larger proportional dilated microvessels. On the other hand, results from cell wound healing experiments demonstrated that all of the VEGF-overexpressing isoforms could increase the chemotaxis of EMT-6 cells in vitro. In conclusion, our results supported the idea that overexpression of VEGF183 promotes murine breast cancer cell proliferation in vitro and induces dilated intratumoral microvessels, and it plays a dissimilar role in comparison with that of VEGF189.

VEGF Splicing and the Role of VEGF Splice Variants: From Physiological-Pathological Conditions to Specific Pre-mRNA Splicing

During this past decade, the vascular endothelial growth factor (VEGF) pathway has been extensively studied. VEGF is a paradigm of molecular regulation since its expression is controlled at all possible steps including transcription, mRNA stability, translation, and pre-mRNA splicing. The latter form of molecular regulation is probably the least studied. This field has been neglected; yet different forms of VEGF with different sizes and different physiological properties issued from alternative splicing have been described a long time ago. Recently a new level of complexity was added to the field of splicing of VEGF pre-mRNA. Whereas thousands of publications have described VEGF as a pro-angiogenic factor, an alternative splicing event generates specific anti-angiogenic forms of VEGF that only differ from the others by a modification in the last six amino acids of the protein. According to the scientists who discovered these isoforms, which are indistinguishable from the pro-angiogenic ones with pan VEGF antibodies, some of the literature on VEGF is at least inexact if not completely false. Moreover, the presence of anti-angiogenic forms of VEGF may explain the disappointing efficacy of anti-VEGF therapies on the overall survival of patients with different forms of cancers and with wet age-related macular degeneration. This review focuses on the existence of the different alternative splice variants of VEGF and the molecular mechanisms associated with their expression and function.

Identification by high-throughput imaging of the histone methyltransferase EHMT2 as an epigenetic regulator of VEGFA alternative splicing

Recent evidence points to a role of chromatin in regulation of alternative pre-mRNA splicing (AS). In order to identify novel chromatin regulators of AS, we screened an RNAi library of chromatin proteins using a cell-based high-throughput in vivo assay. We identified a set of chromatin proteins that regulate AS. Using simultaneous genome-wide expression and AS analysis, we demonstrate distinct and non-overlapping functions of these chromatin modifiers on transcription and AS. Detailed mechanistic characterization of one dual function chromatin modifier, the H3K9 methyltransferase EHMT2 (G9a), identified VEGFA as a major chromatin-mediated AS target. Silencing of EHMT2, or its heterodimer partner EHMT1, affects AS by promoting exclusion of VEGFA exon 6a, but does not alter total VEGFA mRNA levels. The epigenetic regulatory mechanism of AS by EHMT2 involves an adaptor system consisting of the chromatin modulator HP1γ, which binds methylated H3K9 and recruits splicing regulator SRSF1. The epigenetic regulation of VEGFA is physiologically relevant since EHMT2 is transcriptionally induced in response to hypoxia and triggers concomitant changes in AS of VEGFA. These results characterize a novel epigenetic regulatory mechanism of AS and they demonstrate separate roles of epigenetic modifiers in transcription and alternative splicing.

Vascular endothelial growth factor: therapeutic possibilities and challenges for the treatment of ischemia. Cytokine. 2015;71:385-393. [PMID: 25240960 DOI: 10.1016/j.cyto.2014.08.005]

Vascular endothelial growth factor (VEGF) is a notable chemokine that plays critical roles in angiogenesis and vasculogenesis. The contemporary body of literature contains a substantial amount of information regarding its chemical properties as well as its fundamental role in vascular development. Studies strongly indicate its potential use as a therapeutic agent, especially in the vascular restoration of injured and ischemic tissues. VEGF therapy could be most beneficial for diseases whose pathologies revolve around tissue inflammation and necrosis, such as myocardial infarction and stroke, as well as ischemic bowel diseases such as acute mesenteric ischemia and necrotizing enterocolitis. However, a delicate balance exists between the therapeutic benefits of VEGF and the hazards of tumor growth and neo-angiogenesis. Effective future research surrounding VEGF may allow for the development of effective therapies for ischemia which simultaneously limit its more deleterious side effects. This review will: (1) summarize the current understanding of the molecular aspects and function of VEGF, (2) review potential benefits of its use in medical therapy, (3) denote its role in tumorigenesis and inflammation when overexpressed, and (4) elucidate the qualities which make it a viable compound of study for diagnostic and therapeutic applications.

Tumour cells expressing single VEGF isoforms display distinct growth, survival and migration characteristics

Vascular endothelial growth factor-A (VEGF) is produced by most cancer cells as multiple isoforms, which display distinct biological activities. VEGF plays an undisputed role in tumour growth, vascularisation and metastasis; nevertheless the functions of individual isoforms in these processes remain poorly understood. We investigated the effects of three main murine isoforms (VEGF188, 164 and 120) on tumour cell behaviour, using a panel of fibrosarcoma cells we developed that express them individually under endogenous promoter control. Fibrosarcomas expressing only VEGF188 (fs188) or wild type controls (fswt) were typically mesenchymal, formed ruffles and displayed strong matrix-binding activity. VEGF164- and VEGF120-producing cells (fs164 and fs120 respectively) were less typically mesenchymal, lacked ruffles but formed abundant cell-cell contacts. On 3D collagen, fs188 cells remained mesenchymal while fs164 and fs120 cells adopted rounded/amoeboid and a mix of rounded and elongated morphologies respectively. Consistent with their mesenchymal characteristics, fs188 cells migrated significantly faster than fs164 or fs120 cells on 2D surfaces while contractility inhibitors accelerated fs164 and fs120 cell migration. VEGF164/VEGF120 expression correlated with faster proliferation rates and lower levels of spontaneous apoptosis than VEGF188 expression. Nevertheless, VEGF188 was associated with constitutively active/phosphorylated AKT, ERK1/2 and Stat3 proteins. Differences in proliferation rates and apoptosis could be explained by defective signalling downstream of pAKT to FOXO and GSK3 in fs188 and fswt cells, which also correlated with p27/p21 cyclin-dependent kinase inhibitor over-expression. All cells expressed tyrosine kinase VEGF receptors, but these were not active/activatable suggesting that inherent differences between the cell lines are governed by endogenous VEGF isoform expression through complex interactions that are independent of tyrosine kinase receptor activation. VEGF isoforms are emerging as potential biomarkers for anti-VEGF therapies. Our results reveal novel roles of individual isoforms associated with cancer growth and metastasis and highlight the importance of understanding their diverse actions.

VEGF-A isoforms differentially regulate ATF-2-dependent VCAM-1 gene expression and endothelial-leukocyte interactions

VEGF-A isoforms differentially stimulate endothelial VCAM-1 gene expression via an ERK1/2 protein kinase and ATF-2 transcription factor–dependent mechanism. Such signal transduction enables VEGF-A isoform–specific stimulation of leukocyte binding to endothelial cells, explaining how inflammation could be differentially regulated.

Vascular endothelial growth factor A (VEGF-A) regulates many aspects of vascular physiology. VEGF-A stimulates signal transduction pathways that modulate endothelial outputs such as cell migration, proliferation, tubulogenesis, and cell–cell interactions. Multiple VEGF-A isoforms exist, but the biological significance of this is unclear. Here we analyzed VEGF-A isoform–specific stimulation of VCAM-1 gene expression, which controls endothelial–leukocyte interactions, and show that this is dependent on both ERK1/2 and activating transcription factor-2 (ATF-2). VEGF-A isoforms showed differential ERK1/2 and p38 MAPK phosphorylation kinetics. A key feature of VEGF-A isoform–specific ERK1/2 activation and nuclear translocation was increased phosphorylation of ATF-2 on threonine residue 71 (T71). Using reverse genetics, we showed ATF-2 to be functionally required for VEGF-A–stimulated endothelial VCAM-1 gene expression. ATF-2 knockdown blocked VEGF-A–stimulated VCAM-1 expression and endothelial–leukocyte interactions. ATF-2 was also required for other endothelial cell outputs, such as cell migration and tubulogenesis. In contrast, VCAM-1 was essential only for promoting endothelial–leukocyte interactions. This work presents a new paradigm for understanding how soluble growth factor isoforms program complex cellular outputs and responses by modulating signal transduction pathways.

Regulation of tumor growth and metastasis: the role of tumor microenvironment

The presence of abnormal cells with malignant potential or neoplastic characteristics is a relatively common phenomenon. The interaction of these abnormal cells with their microenvironment is essential for tumor development, protection from the body's immune or defence mechanisms, later progression and the development of life-threatening or metastatic disease. The tumor microenvironment is a collective term that includes the tumor's surrounding and supportive stroma, the different effectors of the immune system, blood platelets, hormones and other humoral factors. A better understanding of the interplay between the tumor cells and its microenvironment can provide efficient tools for cancer management, as well as better prevention, screening and risk assessment protocols.

Is there a pAkt between VEGF and oral cancer cell migration?

The PI3K-Akt signalling pathway is a well-established driver of cancer progression. One key process promoted by Akt phosphorylation is tumour cell motility; however the mechanism of VEGF-induced Akt phosphorylation leading to motility remains poorly understood. Previously, we have shown that Akt phosphorylation induced by different factors causes both stimulation and inhibition of motility in different cell types. However, differential phosphorylation of Akt at T308 and S473 residues by VEGF and its role in head and neck cancer cell motility and progression is unknown. The cell lines investigated in this study exhibited a change in phosphorylation of Akt in response to VEGF. However, in terms of motility, VEGF stimulated oral cancer and its associated cell lines, but not normal keratinocytes or oral mucosal fibroblasts. The addition of a PI3 kinase and mTOR inhibitor, inhibited the phosphorylation of Akt and also effectively blocked VEGF-induced oral cancer cell motility, whereas only the PI3 kinase inhibitor blocked oral cancer associated fibroblast cell motility. This study therefore discloses that two different mechanisms of Akt phosphorylation control the motility potential of different cell lines. Akt phosphorylated at both residues controls oral cancer cell motility. Furthermore, immunohistochemical analysis of VEGF positive human head and neck tumour tissues showed a significant increase in Akt phosphorylation at the T308 residue, suggesting that pAkt T308 may be associated with tumour progression in vivo.

Promise of multiphoton detection in discovery and diagnostic proteomics

Proteomics has lacked adequate methods for handling the complexity (hundreds of thousands of different proteins) and range of protein concentrations (> or =10(6)) of eukaryotic proteomes. New multiphoton-detection methods for ultrasensitive detection of proteins produce 10,000-fold gains in sensitivity and allow highly quantitative, linear detection of 50 zmol (30,000 molecules) to 500 fmol of proteins in complex samples. The potential of multiphoton detection in top-down proteomics analyses is illustrated with applications in monitoring proteomes in very small numbers of cells, in identifying and monitoring complex functional isoforms of cancer-related proteins, and in super-sensitive immunoassays of serum proteins for high-performance detection of cancer.

Extracellular regulation of VEGF: isoforms, proteolysis, and vascular patterning

The regulation of vascular endothelial growth factor A (VEGF) is critical to neovascularization in numerous tissues under physiological and pathological conditions. VEGF has multiple isoforms, created by alternative splicing or proteolytic cleavage, and characterized by different receptor-binding and matrix-binding properties. These isoforms are known to give rise to a spectrum of angiogenesis patterns marked by differences in branching, which has functional implications for tissues. In this review, we detail the extensive extracellular regulation of VEGF and the ability of VEGF to dictate the vascular phenotype. We explore the role of VEGF-releasing proteases and soluble carrier molecules on VEGF activity. While proteases such as MMP9 can 'release' matrix-bound VEGF and promote angiogenesis, for example as a key step in carcinogenesis, proteases can also suppress VEGF's angiogenic effects. We explore what dictates pro- or anti-angiogenic behavior. We also seek to understand the phenomenon of VEGF gradient formation. Strong VEGF gradients are thought to be due to decreased rates of diffusion from reversible matrix binding, however theoretical studies show that this scenario cannot give rise to lasting VEGF gradients in vivo. We propose that gradients are formed through degradation of sequestered VEGF. Finally, we review how different aspects of the VEGF signal, such as its concentration, gradient, matrix-binding, and NRP1-binding can differentially affect angiogenesis. We explore how this allows VEGF to regulate the formation of vascular networks across a spectrum of high to low branching densities, and from normal to pathological angiogenesis. A better understanding of the control of angiogenesis is necessary to improve upon limitations of current angiogenic therapies.

Differential expression of capillary VEGF isoforms following traumatic brain injury

OBJECTIVES

While it is known that angiogenesis occurs after trauma, we sought to characterize the expression of vascular endothelial growth factor (VEGF) subtypes, vascular endothelial growth factor receptor 2 (VEGFR2) and angiopoietin within capillaries of animals subjected to traumatic brain injury (TBI). Further, we sought to characterize pericyte cell death in isolated capillaries.

METHODS

We used Marmarou's acceleration impact model to induce head trauma and measured VEGF, VEGFR2 and angiopoietin levels in isolated capillaries. TUNEL was used to determine pericyte cell death.

RESULTS

The VEGF response was restricted to the VEGF120 isoform. No increase in transcripts for VEGF164 and VEGF188 was observed. VEGFR2 was marginally increased and angiopoietin was increased. A subset of pericytes were TUNEL-positive.

DISCUSSION

These results show a distinct expression pattern of angiogenic factors following injury and suggest that pericyte involvement in adaptive angiogenesis may be altered following TBI.

Genetic and pharmacologic inhibition of complement impairs endothelial cell function and ablates ovarian cancer neovascularization. Neoplasia. 2012;14:994-1004. [PMID: 23226093 DOI: 10.1593/neo.121262]

Complement activation plays a critical role in controlling inflammatory responses. To assess the role of complement during ovarian cancer progression, we crossed two strains of mice with genetic complement deficiencies with transgenic mice that develop epithelial ovarian cancer (TgMISIIR-TAg). TgMISIIR-TAg mice fully or partially deficient for complement factor 3 (C3) (Tg(+)C3(KO) and Tg(+)C3(HET), respectively) or fully deficient for complement factor C5a receptor (C5aR) (Tg(+)C5aR(KO)) develop either no ovarian tumors or tumors that were small and poorly vascularized compared to wild-type littermates (Tg(+)C3(WT), Tg(+)C5aR(WT)). The percentage of tumor infiltrating immune cells in Tg(+)C3(HET) tumors compared to Tg(+)C3(WT) controls was either similar (macrophages, B cells, myeloid-derived suppressor cells), elevated (effector T cells), or decreased (regulatory T cells). Regardless of these ratios, cytokine production by immune cells taken from Tg(+)C3(HET) tumors was reduced on stimulation compared to Tg(+)C3(WT) controls. Interestingly, CD31(+) endothelial cell (EC) function in angiogenesis was significantly impaired in both C3(KO) and C5aR(KO) mice. Further, using the C5aR antagonist PMX53, tube formation of ECs was shown to be C5a-dependent, possibly through interactions with the VEGF(165) but not VEGF(121) isoform. Finally, the mouse VEGF(164) transcript was underexpressed in C3(KO) livers compare to C3(WT) livers. Thus, we conclude that complement inhibition blocks tumor outgrowth by altering EC function and VEGF(165) expression.

In vivo characterization of 68Ga-NOTA-VEGF 121 for the imaging of VEGF receptor expression in U87MG tumor xenograft models

PURPOSE

Vascular endothelial growth factor receptors (VEGFRs) are associated with tumor growth and induction of tumor angiogenesis and are known to be overexpressed in various human tumors. In the present study, we prepared and evaluated (68)Ga-1,4,7-triazacyclononane-1,4,7-triacetic acid-benzyl (NOTA)-VEGF(121) as a positron emission tomography (PET) radioligand for the in vivo imaging of VEGFR expression.

METHODS

(68)Ga-NOTA-VEGF(121) was prepared by conjugation of VEGF(121) and p-SCN-NOTA, followed by radiolabeling with (68)GaCl(3) and then purification using a PD-10 column. Human aortic endothelial cell (HAEC) binding of (68)Ga-NOTA-VEGF(121) was measured as a function of time. MicroPET and biodistribution studies of U87MG tumor xenografted mice were performed at 1, 2, and 4 h after injection of (68)Ga-NOTA-VEGF(121). The tumor tissues were then sectioned and subjected to immunostaining.

RESULTS

The decay-corrected radiochemical yield of (68)Ga-NOTA-VEGF(121) was 40 ± 4.5 % and specific activity was 243.1 ± 104.6 GBq/μmol (8.6 ± 3.7 GBq/mg). (68)Ga-NOTA-VEGF(121) was avidly taken up by HAECs in a time-dependent manner, and the uptake was blocked either by 32 % with VEGF(121) or by 49 % with VEGFR2 antibody at 4 h post-incubation. In microPET images of U87MG tumor xenografted mice, radioactivity was accumulated in tumors (2.73±0.32 %ID/g at 2 h), and the uptake was blocked by 40 % in the presence of VEGF(121). In biodistribution studies, tumor uptake (1.84±0.14 %ID/g at 2 h) was blocked with VEGF(121) at a similar level (52 %) to that of microPET images. Immunostaining analysis of U87MG tumor tissues obtained after the microPET imaging showed high levels of VEGFR2 expression.

CONCLUSION

These results demonstrate that (68)Ga-NOTA-VEGF(121) has potential for the in vivo imaging of VEGFR expression. In addition, our results also suggest that the in vivo characteristics of radiolabeled VEGF depend on the properties of the radioisotope and the chelator used.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

Predicting the effects of anti-angiogenic agents targeting specific VEGF isoforms

Vascular endothelial growth factor (VEGF) is a key mediator of angiogenesis, whose effect on cancer growth and development is well characterized. Alternative splicing of VEGF leads to several different isoforms, which are differentially expressed in various tumor types and have distinct functions in tumor blood vessel formation. Many cancer therapies aim to inhibit angiogenesis by targeting VEGF and preventing intracellular signaling leading to tumor vascularization; however, the effects of targeting specific VEGF isoforms have received little attention in the clinical setting. In this work, we investigate the effects of selectively targeting a single VEGF isoform, as compared with inhibiting all isoforms. We utilize a molecular-detailed whole-body compartment model of VEGF transport and kinetics in the presence of breast tumor. The model includes two major VEGF isoforms, VEGF(121) and VEGF(165), receptors VEGFR1 and VEGFR2, and co-receptors Neuropilin-1 and Neuropilin-2. We utilize the model to predict the concentrations of free VEGF, the number of VEGF/VEGFR2 complexes (considered to be pro-angiogenic), and the receptor occupancy profiles following inhibition of VEGF using isoform-specific anti-VEGF agents. We predict that targeting VEGF(121) leads to a 54% and 84% reduction in free VEGF in tumors that secrete both VEGF isoforms or tumors that overexpress VEGF(121), respectively. Additionally, 21% of the VEGFR2 molecules in the blood are ligated following inhibition of VEGF(121), compared with 88% when both isoforms are targeted. Targeting VEGF(121) reduces tumor free VEGF and is an effective treatment strategy. Our results provide a basis for clinical investigation of isoform-specific anti-VEGF agents.

Evaluation of the angiogenesis inhibitor KR-31831 in SKOV-3 tumor-bearing mice using (64)Cu-DOTA-VEGF(121) and microPET

KR-31831 ((2R,3R,4S)-6-amino-4-[N-(4-chloropheyl)-N-(1H-imidazol-2ylmethyl)amino]-3-hydroxyl-2-methyl-2-dimethoxymethyl-3,4-dihydro-2H-1-benzopyran), an angiogenesis inhibitor, was evaluated in tumor-bearing mice using molecular imaging technology. Pre-treatment microPET images were acquired on SKOV-3 cell-implanted nude mice after injection with (64)Cu-DOTA-VEGF(121). KR-31831 (50 mg/kg) was then injected intraperitoneally into the treatment group (n=3), while injection vehicle was injected into the control (n=4) and blocking (n=3) groups. After injections occurred daily for 28 days, all groups of mice underwent post-treatment microPET imaging after injection with (64)Cu-DOTA-VEGF(121). The post-treatment images showed high tumor uptake in the control group and reduced tumor uptake in both the blocking and treatment groups. ROI analysis of the tumor images revealed 6.25%±1.18% ID/g at 1 h, 6.55%±0.69% ID/g at 2 h, and 4.68%±0.63% ID/g at 16 h in the control group; 3.87%±0.45% ID/g at 1 h, 4.50%±0.44% ID/g at 2 h, and 3.63%±0.25% ID/g at 16 h in the blocking group; and 4.03%±0.74% ID/g at 1 h, 4.37%±0.67% ID/g at 2 h, and 3.83%±0.90% ID/g at 16 h in the treatment group. Biodistribution obtained after the post-treatment microPET imaging also demonstrated high tumor uptake (3.74%±0.27% ID/g) in the control group and reduced uptakes in both the blocking group (2.69%±0.73% ID/g, P<.05) and the treatment group (3.11%±0.25% ID/g, P<.05), which correlated well with microPET imaging data. Immunofluorescence analysis showed higher levels of VEGFR2 and CD31 expressions in tumor tissues of the control and blocking groups than in tumor tissues of the treatment group. These results suggest that the antiangiogenic activity of KR-31831 is mediated through VEGFR2 and microPET serves as a useful molecular imaging tool for evaluation of a newly developed angiogenesis inhibitor, KR-31831.

Identification of colorectal cancer metastasis markers by an angiogenesis-related cytokine-antibody array

AIM: To investigate the angiogenesis-related protein expression profile characterizing metastatic colorectal cancer (mCRC) with the aim of identifying prognostic markers.

METHODS: The expression of 44 angiogenesis-secreted factors was measured by a novel cytokine antibody array methodology. The study evaluated vascular endothelial growth factor (VEGF) and its soluble vascular endothelial growth factor receptor (sVEGFR)-1 protein levels by enzyme immunoassay (EIA) in a panel of 16 CRC cell lines. mRNA VEGF and VEGF-A isoforms were quantified by quantitative reverse-transcription polymerase chain reaction (Q-RT-PCR) and vascular endothelial growth factor receptor (VEGFR)-2 expression was analyzed by flow cytometry.

RESULTS: Metastasis-derived CRC cell lines expressed a distinctive molecular profile as compared with those isolated from a primary tumor site. Metastatic CRC cell lines were characterized by higher expression of angiopoietin-2 (Ang-2), macrophage chemoattractant proteins-3/4 (MCP-3/4), matrix metalloproteinase-1 (MMP-1), and the chemokines interferon γ inducible T cell α chemoattractant protein (I-TAC), monocyte chemoattractant protein I-309, and interleukins interleukin (IL)-2 and IL-1α, as compared to primary tumor cell lines. In contrast, primary CRC cell lines expressed higher levels of interferon γ (IFN-γ), insulin-like growth factor-1 (IGF-1), IL-6, leptin, epidermal growth factor (EGF), placental growth factor (PlGF), thrombopoietin, transforming growth factor β1 (TGF-β1) and VEGF-D, as compared with the metastatic cell lines. VEGF expression does not significantly differ according to the CRC cellular origin in normoxia. Severe hypoxia induced VEGF expression up-regulation but contrary to expectations, metastatic CRC cell lines did not respond as much as primary cell lines to the hypoxic stimulus. In CRC primary-derived cell lines, we observed a two-fold increase in VEGF expression between normoxia and hypoxia as compared to metastatic cell lines. CRC cell lines express a similar pattern of VEGF isoforms (VEGF₁₂₁, VEGF₁₆₅ and VEGF₁₈₉) despite variability in VEGF expression, where the major transcript was VEGF₁₂₁. No relevant expression of VEGFR-2 was found in CRC cell lines, as compared to that of human umbilical vein endothelial cells and sVEGFR-1 expression did not depend on the CRC cellular origin.

CONCLUSION: A distinct angiogenesis-related expression pattern characterizes metastatic CRC cell lines. Factors other than VEGF appear as prognostic markers and intervention targets in the metastatic CRC setting.

Overexpression of VEGF189 in breast cancer cells induces apoptosis via NRP1 under stress conditions

The existence of multiple VEGF-A isoforms raised the possibility that they may have distinct functions in tumor growth. We have previously published that VEGF189 and VEGF165 contribute to breast cancer progression and angiogenesis, but VEGF165 induced the most rapid tumor uptake. Since VEGF165 has been described as a survival factor for breast tumor cells, we questioned here the effects of VEGF189 on the survival/apoptosis of MDA-MB-231 cells. We used clones which overexpress VEGF189 (V189) or VEGF165 (V165) isoforms and compared them to a control one (cV). Overexpression of VEGF189 resulted in increased cell apoptosis, as determined by Annexin-V apoptosis assay, under serum starvation and doxorubicin treatment, while VEGF 165 was confirmed to be a survival factor. Since MDA-MB-231 highly express NRP1 (a co-receptor for VEGF-A), we used short hairpin RNA (shRNA) to knockdown NRP1 expression. V189shNRP1 clones were characterized by reduced apoptosis and higher necrosis, as compared to V189shCtl, under stress conditions. Unexpectedly, NRP1 knock-down had no effect on the survival or apoptosis of V165 cells. VEGF189 showed greater affinity towards NRP1 than VEGF165 using a BIAcore binding assay. Finally, since endogenously produced urokinase-type plasminogen (uPA) has been found to prevent apoptosis in breast cancers, we analyzed the level of uPA activity in our clones. An inhibition of uPA activity was observed in V189shNRP1 clones. Altogether, these results suggest a major role of NRP1 in apoptosis induced by VEGF189 in stress conditions and confirm VEGF165 as a survival factor.

The role of different VEGF isoforms in scar formation after glaucoma filtration surgery

Vascular endothelial growth factor (VEGF) plays an important role in both physiological and pathological angiogenesis. Our previous studies showed a differential role of VEGF isoforms in retinal physiological angiogenesis. We also demonstrated that non-selective inhibition of VEGF by bevacizumab had a beneficial effect on surgical outcome after glaucoma filtration surgery by reducing angiogenesis as well as fibrosis. However, the function of the VEGF isoforms in pathological angiogenesis and wound healing in the eye still remains unidentified. This study was designed to elucidate the differential roles of VEGF isoforms in scar formation after trabeculectomy. Furthermore, we also investigated whether pegaptanib (Macugen™, Pfizer), an aptamer which specifically blocks VEGF(165), could improve surgical outcome by reducing postoperative scarring. VEGF-R2 and neuropilin-1 (NRP-1) expression was analyzed in vitro by RT-PCR, and were found to be expressed at higher levels in human umbilical vein endothelial cells (HUVEC) as compared to Tenon fibroblasts (TF). The effect of the different VEGF isoforms (VEGF(121), VEGF(165) and VEGF(189)) and pegaptanib on cell proliferation was determined via WST-1 assay. Endothelial cell proliferation was stimulated after addition of VEGF(121) and VEGF(165), whereas VEGF(121) and VEGF(189) increased fibroblast growth. These effects on proliferation were associated with an activation of the ERK pathway, as revealed using the TransAM c-Myc assay. Inhibition of the ERK pathway, by PD98059 administration, significantly reduced VEGF isoform induced cell growth. A dose-dependent reduction of endothelial cell proliferation was observed after pegaptanib administration, while only the highest dose was able to inhibit fibroblast growth. Next, the in vivo effect of pegaptanib was investigated in a rabbit model of trabeculectomy. The surgical outcome was evaluated by performing clinical investigations (IOP, bleb area, height and survival), as well as histomorphometric analyses of angiogenesis (CD31), inflammation (CD45) and fibrosis (Sirius Red). A single postoperative application of pegaptanib had a beneficial impact on surgical outcome, mainly by reducing angiogenesis, but not inflammation or collagen deposition. Repeated injections slightly improved surgical outcome, but again solely by reducing angiogenesis. In summary, our results revealed that the VEGF isoforms play a differential role in ocular wound healing: VEGF(165) and VEGF(121) predominantly affect blood vessel growth, whereas VEGF(189) is rather involved in fibrosis, an important process in wound healing.

Formation of VEGF isoform-specific spatial distributions governing angiogenesis: computational analysis

BACKGROUND

The spatial distribution of vascular endothelial growth factor A (VEGF) is an important mediator of vascular patterning. Previous experimental studies in the mouse hindbrain and retina have suggested that VEGF alternative splicing, which controls the ability of VEGF to bind to heparan sulfate proteoglycans (HSPGs) in the extracellular matrix (ECM), plays a key role in controlling VEGF diffusion and gradients in tissues. Conversely, proteolysis notably by matrix metalloproteinases (MMPs), plays a critical role in pathological situations by releasing matrix-sequestered VEGF and modulating angiogenesis. However, computational models have predicted that HSPG binding alone does not affect VEGF localization or gradients at steady state.

RESULTS

Using a 3D molecular-detailed reaction-diffusion model of VEGF ligand-receptor kinetics and transport, we test alternate models of VEGF transport in the extracellular environment surrounding an endothelial sprout. We show that differences in localization between VEGF isoforms, as observed experimentally in the mouse hindbrain, as well as the ability of proteases to redistribute VEGF in pathological situations, are consistent with a model where VEGF is endogenously cleared or degraded in an isoform-specific manner. We use our predictions of the VEGF distribution to quantify a tip cell's receptor binding and gradient sensing capacity. A novel prediction is that neuropilin-1, despite functioning as a coreceptor to VEGF₁₆₅-VEGFR2 binding, reduces the ability of a cell to gauge the relative steepness of the VEGF distribution. Comparing our model to available in vivo vascular patterning data suggests that vascular phenotypes are most consistently predicted at short range by the soluble fraction of the VEGF distributions, or at longer range by matrix-bound VEGF detected in a filopodia-dependent manner.

CONCLUSIONS

Isoform-specific VEGF degradation provides a possible explanation for numerous examples of isoform specificity in VEGF patterning and examples of proteases relocation of VEGF upon release.

Vascular Endothelial Growth Factor A isoform mRNA expression in pediatric acute myeloid leukemia

In AML high VEGFA protein expression correlates with poor overall and relapse-free survival (OS/RFS). To date, the relevance of the various VEGFA isoforms is unclear. We determined VEGF121, VEGF145, VEGF148, VEGF165, VEGF183, and VEGF189 mRNA expression in pediatric AML samples and investigated the relation between VEGFA isoform expression and clinicopatholologic characteristics and outcome. A significant co-expression of VEGF121, VEGF165, VEGF183, and VEGF189 isoforms was apparent (mean rho = 0.716, P < 0.0001). This co-expression justifies measuring a single VEGFA isoform (e.g., 121, 165, 183, and 189) as representative expression of all VEGFA isoforms in future studies designed to determine the prognostic importance of VEGFA isoforms.

Novel aspects of corneal angiogenic and lymphangiogenic privilege

In this article, we provide the results of experimental studies demonstrating that corneal avascularity is an active process involving the production of anti-angiogenic factors, which counterbalance the pro-angiogenic/lymphangiogenic factors that are upregulated during wound healing. We also summarize pertinent published reports regarding corneal neovascularization (NV), corneal lymphangiogenesis and corneal angiogenic/lymphangiogenic privilege. We outline the clinical causes of corneal NV, and discuss the angiogenic proteins (VEGF and bFGF) and angiogenesis regulatory proteins. We also describe the role of matrix metalloproteinases MMP-2, -7, and MT1-MMP, anti-angiogenic factors, and lymphangiogenic regulatory proteins during corneal wound healing. Established and potential new therapies for the treatment of corneal neovascularization are also discussed.

The importance of -460 C/T and +405 G/C single nucleotide polymorphisms to the function of vascular endothelial growth factor A in colorectal cancer

PURPOSE

The present study investigated the functional influence of the single nucleotide polymorphisms (SNPs) -460 C/T and +405 G/C at vascular endothelial growth factor A (VEGF-A), mRNA and protein levels in colorectal cancer (CRC) and normal colorectal tissue.

METHODS

Blood and tissue were collected from 113 patients surgically resected for colorectal cancer. SNPs were analysed from genomic DNA by PCR, the VEGF-A gene expression analysis was performed by RT-PCR and protein analysis by ELISA.

RESULTS

The T-allele in the -460 C/T SNP and the C-allele in the +405 G/C SNP were associated with significantly lower VEGF-A protein levels in normal colorectal tissue. There were no differences in protein levels in the malignant tissue according to genotypes. No differences were observed at the gene expression levels either.

CONCLUSION

The results indicate that the two SNPs have a functional influence on the VEGF-A protein levels in normal colorectal tissue. The possible clinical implications of the findings need further investigation.

Molecular diversity of VEGF-A as a regulator of its biological activity

The vascular endothelial growth factor (VEGF) family of proteins regulates blood flow, growth, and function in both normal physiology and disease processes. VEGF-A is alternatively spliced to form multiple isoforms, in two subfamilies, that have specific, novel functions. Alternative splicing of exons 5-7 of the VEGF gene generates forms with differing bioavailability and activities, whereas alternative splice-site selection in exon 8 generates proangiogenic, termed VEGF(xxx), or antiangiogenic proteins, termed VEGF(xxx)b. Despite its name, emerging roles for VEGF isoforms on cell types other than endothelium have now been identified. Although VEGF-A has conventionally been considered to be a family of proangiogenic, propermeability vasodilators, the identification of effects on nonendothelial cells, and the discovery of the antiangiogenic subfamily of splice isoforms, has added further complexity to their regulation of microvascular function. The distally spliced antiangiogenic isoforms are expressed in normal human tissue, but downregulated in angiogenic diseases, such as cancer and proliferative retinopathy, and in developmental pathologies, such as Denys Drash syndrome and preeclampsia. Here, we examine the molecular diversity of VEGF-A as a regulator of its biological activity and compare the role of the pro- and antiangiogenic VEGF-A splice isoforms in both normal and pathophysiological processes.

VEGF(121)b, a new member of the VEGF(xxx)b family of VEGF-A splice isoforms, inhibits neovascularisation and tumour growth in vivo

Background:

The key mediator of new vessel formation in cancer and other diseases is VEGF-A. VEGF-A exists as alternatively spliced isoforms - the pro-angiogenic VEGF_xxx family generated by exon 8 proximal splicing, and a sister family, termed VEGF_xxxb, exemplified by VEGF₁₆₅b, generated by distal splicing of exon 8. However, it is unknown whether this anti-angiogenic property of VEGF₁₆₅b is a general property of the VEGF_xxxb family of isoforms.

Methods:

The mRNA and protein expression of VEGF₁₂₁b was studied in human tissue. The effect of VEGF₁₂₁b was analysed by saturation binding to VEGF receptors, endothelial migration, apoptosis, xenograft tumour growth, pre-retinal neovascularisation and imaging of biodistribution in tumour-bearing mice with radioactive VEGF₁₂₁b.

Results:

The existence of VEGF₁₂₁b was confirmed in normal human tissues. VEGF₁₂₁b binds both VEGF receptors with similar affinity as other VEGF isoforms, but inhibits endothelial cell migration and is cytoprotective to endothelial cells through VEGFR-2 activation. Administration of VEGF₁₂₁b normalised retinal vasculature by reducing both angiogenesis and ischaemia. VEGF₁₂₁b reduced the growth of xenografted human colon tumours in association with reduced microvascular density, and an intravenous bolus of VEGF₁₂₁b is taken up into colon tumour xenografts.

Conclusion:

Here we identify a second member of the family, VEGF₁₂₁b, with similar properties to those of VEGF₁₆₅b, and underline the importance of the six amino acids of exon 8b in the anti-angiogenic activity of the VEGF_xxxb isoforms.

Effect of raloxifene on vascular endothelial growth factor expression in breast carcinomas of postmenopausal women

OBJECTIVE

This study aimed to evaluate the effect of raloxifene on vascular endothelial growth factor (VEGF) expression in breast carcinomas of postmenopausal women.

MATERIALS AND METHODS

Sixteen postmenopausal patients with operable stage II, oestrogen receptor-positive, infiltrating ductal breast carcinoma were treated with raloxifene at a dose of 60 mg/day, for a period of 28 days prior to definitive surgery. Tumour size varied from 3 to 5 cm (mean 3.7 cm) and mean age of patients was 61.8 years (range 49-72 years). Tumour samples were obtained by incisional biopsy at the time of diagnosis and again at the time of surgery. Immunohistochemical evaluation of VEGF expression was assessed semiquantitatively based on fraction of stained tumour cells and on intensity of staining. McNemar's test of symmetry was used to evaluate agreement between positive or negative classification of VEGF expression prior to and following raloxifene treatment (P < 0.05).

RESULTS

Fourteen of the 16 patients (88%) were classified as positive for VEGF expression prior to raloxifene treatment, while only 5 (31%) were classified as positive following treatment (P < 0.007).

CONCLUSION

Raloxifene significantly reduced VEGF expression in these oestrogen receptor-positive breast carcinomas of postmenopausal women.

Antivascular endothelial growth factor therapy for neovascular age-related macular degeneration

PURPOSE OF REVIEW

The most important recent advance in the treatment of neovascular age-related macular degeneration (AMD) is the development of antivascular endothelial growth factor (anti-VEGF) therapeutic agents that preserve and improve visual acuity by arresting choroidal neovascular growth and reducing vascular permeability. This review describes the current literature on the use of this therapeutic approach in the management of neovascular AMD.

RECENT FINDINGS

Two anti-VEGF agents, pegaptanib sodium and ranibizumab, are currently approved by the United States Food and Drug Administration for the treatment of neovascular AMD. In addition, off-label use of a third anti-VEGF agent, bevacizumab, as a treatment option for neovascular AMD has become common worldwide. Other anti-VEGF agent strategies that have shown efficacy include small interfering RNA agents to silence the VEGF gene and receptor and the fusion protein VEGF trap.

SUMMARY

The accumulation of preclinical and clinical evidence implicating VEGF-A in the pathogenesis of neovascular AMD has provided a strong rationale for the development of anti-VEGF agents for this disease. Anti-VEGF therapies have been used successfully in the clinic, encouraging their use in the treatment of other neovascular eye diseases.

Atrial fibrillation is associated with cardiac hypoxia

BACKGROUND

Atrial fibrillation (AF), the most common human arrhythmia, is responsible for substantial morbidity and mortality and may be promoted by selective atrial ischemia and atrial fibrosis. Consequently, we investigated markers for hypoxia and angiogenesis in AF.

METHODS

Right atrial appendages (n=158) were grouped according to heart rhythm [sinus rhythm (SR) or AF]. The degree of fibrosis and microvessel density of all patients were determined morphometrically using Sirius-Red- and CD34/CD105-stained sections, respectively. Next, sections (n=77) underwent immunostaining to detect hypoxia- and angiogenesis-related proteins [hypoxia-inducible factor (HIF)1 alpha, HIF2 alpha, vascular endothelial growth factor (VEGF), VEGF receptor 2 (KDR), phosphorylated KDR (pKDR), carboanhydrase IX, platelet-derived growth factor] and the apoptosis-related B-cell lymphoma 2 protein.

RESULTS

Fibrosis progressed significantly from 14.7+/-0.8% (SR) to 22.3+/-1.4% (AF). While the positive cytoplasmic staining of HIF1 alpha, HIF2 alpha, VEGF, KDR, and pKDR rose significantly from SR to AF, their nuclear fractions fell (only pKDR significantly). The median CD34/CD105-positive microvessel size increased significantly from SR to AF.

CONCLUSIONS

AF is closely associated with an atrial up-regulation of hypoxic and angiogenic markers. Whether this is cause, effect, or co-phenomenon of fibrosis remains to be investigated. It is conceivable that fibrosis might lead to an increased O(2) diffusion distance and thus induce ischemic signaling, which, in turn, leads to angiogenesis.

Catalyser-21(TM), a mineral water derived from leaf soil, inhibits tumor cell invasion and angiogenesis

Catalyser-21(TM) is a mineral water derived from natural leaf soil containing various organic and inorganic substances. Previous reports suggested a possibility that Catalyser-21(TM) has antioxidative potential and could inhibit angiogenesis and cancer cell invasiveness. Angiogenesis is a prerequisite for cancer cells to spread to surrounding tissues. Vascular endothelial growth factor (VEGF) is a major angiogenic factor in the formation of blood capillaries by cancer cells to supply nutrients and oxygen for their sustained growth. Matrix metalloproteinase-2 (MMP-2) is another key enzyme for cancer cell metastasis. To assess the anti-angiogenic activity of Catalyser-21(TM), we first examined cell viability using a human cervical cancer cell line, HeLa, and a fibrosarcoma cell line, HT1080. The results showed that Catalyser-21(TM) decreased the viability of both cell types in a dose-dependent manner. Flow cytometric analysis proved that Catalyser-21(TM) scavenges intracellular H(2)O(2) in both cell types. RT-PCR demonstrated that both VEGF and MMP-2 gene transcription was suppressed after Catalyser-21(TM) treatment. Both Matrigel and tubule formation experiments showed an effect of Catalyser-21(TM). These results suggest that Catalyser-21(TM) has potential as an anti-tumor agent.

Microenvironment changes (in pH) affect VEGF alternative splicing. Cancer Microenviron. 2008;1:131-139. [PMID: 19308691 DOI: 10.1007/s12307-008-0013-4]

Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors. Although the relative contribution of the VEGF isoforms has been studied in tumor angiogenesis, little is known about the mechanisms that regulate the alternative splicing process. Here, we tested microenvironment cues that might regulate VEGF alternative splicing. To test this, we used endometrial cancer cells that produce all VEGF isoforms as a model, and exposed them to varying pH levels, hormones, glucose and CoCl₂ (to mimic hypoxia). Low pH had the most consistent effects in inducing variations in VEGF splicing pattern (VEGF121 increased significantly, p < 0.001, when compared to VEGF145, 165 or 189). This was accompanied by activation of the p38 stress pathway and SR proteins (splicing factors) expression and phosphorylation. SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production. Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

Distinct signaling pathways confer different vascular responses to VEGF 121 and VEGF 165

Vascular endothelial growth factor (VEGF) is a pleiotropic factor that regulates embryonal vasculogenesis, tumor angiogenesis and vascular permeability. Among eight differential isoforms, VEGF 121 mainly regulates vascular permeability, while VEGF 165 induces angiogenesis. Our previous studies have suggested that VEGF 121 and VEGF 165 are mainly detected in the lesions of psoriasis and atopic dermatitis, especially VEGF 121. VEGF 121 is the most predominant isoform, which plays a major role in the increased vascular permeability in the aforementioned skin lesions. Thus, the differential expression of VEGF isoforms may be critical in determining either an angiogenic or a hyper-permeable state. However, the distinct VEGF signaling pathways that induce angiogenesis and vascular hyper-permeability in endothelial cells have never been demonstrated. To clarify the differential effects elicited by VEGF 121 and VEGF 165, we compared the biological responses and the signaling pathways activated by VEGF 121 and VEGF 165 in human umbilical vein endothelial cells (HUVEC). VEGF 165 significantly increased the level of phosphorylation in the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, whereas VEGF 121 had little to no effect. In contrast, VEGF 121 induced rapid activation of the Src pathway, while VEGF 165 showed a less pronounced and delayed activation of the Src pathway. Furthermore, the VEGF-induced hyper-permeability and cell proliferation of HUVEC were inhibited by a Src inhibitor (PP2) and a MEK inhibitor (PD98059), respectively. These results indicate that distinct signaling pathways confer different vascular responses to VEGF 121 and VEGF 165.