Angiogenesis promoted by vascular endothelial growth factor: regulation through alpha1beta1 and alpha2beta1 integrins

Aggretin Venom Polypeptide as a Novel Anti-angiogenesis Agent by Targeting Integrin alpha2beta1

VEGF and VEGFR antibodies have been used as a therapeutic strategy to inhibit angiogenesis in many diseases; however, frequent and repeated administration of these antibodies to patients induces immunogenicity. In previous studies, we demonstrated that aggretin, a heterodimeric snake venom C-type lectin, exhibits pro-angiogenic activities via integrin α2β1 ligation. We hypothesised that small-mass aggretin fragments may bind integrin α2β1 and act as antagonists of angiogenesis. In this study, the anti-angiogenic efficacy of a synthesised aggretin α-chain C-terminus (AACT, residue 106–136) was evaluated in both in vitro and in vivo angiogenesis models. The AACT demonstrated inhibitory effects on collagen-induced platelet aggregation and HUVEC adhesion to immobilised collagen. These results indicated that AACT may block integrin α2β1−collagen interaction. AACT also inhibited HUVEC migration and tube formation. Aortic ring sprouting and Matrigel implant models demonstrated that AACT markedly inhibited VEGF-induced neovascularisation. In addition, induction of FAK/PI3K/ERK1/2 tyrosine phosphorylation and talin 1/2 associated with integrin β1 which are induced by VEGF were blocked by AACT. Similarly, tyrosine phosphorylation of VEFGR2 and ERK1/2 induced by VEGF was diminished in integrin α2-silenced endothelial cells. Our results demonstrate that AACT is a potential therapeutic candidate for angiogenesis related-diseases via integrin α2β1 blockade.

Annexin A8 promotes VEGF-A driven endothelial cell sprouting

The physiological and pathological process of angiogenesis relies on orchestrated endothelial cell (EC) adhesion, migration and formation of new vessels. Here we report that human umbilical vein endothelial cells (HUVECs) deficient in Annexin A8 (AnxA8), a member of the annexin family of Ca²⁺- and membrane binding proteins, are strongly deficient in their ability to sprout in response to vascular endothelial growth factor (VEGF)-A, and are strongly impaired in their ability to migrate and adhere to β1 integrin-binding extracellular matrix (ECM) proteins. We find that these cells are defective in the formation of complexes containing the tetraspanin CD63, the main VEGF-A receptor VEGFR2, and the β1 integrin subunit, on the cell surface. We observe that upon VEGF-A activation of AnxA8-depleted HUVECs, VEGFR2 internalization is reduced, phosphorylation of VEGFR2 is increased, and the spatial distribution of Tyr577-phosphorylated focal adhesion kinase (pFAK577) is altered. We conclude that AnxA8 affects CD63/VEGFR2/β1 integrin complex formation, leading to hyperactivation of the VEGF-A signal transduction pathway, and severely disturbed VEGF-A-driven angiogenic sprouting.

Breast cancer cells alter the dynamics of stromal fibronectin-collagen interactions

Breast cancer cells recruit surrounding stromal cells, such as cancer-associated fibroblasts (CAFs), to remodel their extracellular matrix (ECM) and promote invasive tumor growth. Two major ECM components, fibronectin (Fn) and collagen I (Col I), are known to interact with each other to regulate cellular behavior. In this study, we seek to understand how Fn and Col I interplay and promote a dysregulated signaling pathway to facilitate tumor progression. Specifically, we investigated the evolution of tumor-conditioned stromal ECM composition, structure, and relaxation. Furthermore, we assessed how evolving Fn-Col I interactions gradually affected pro-angiogenic signaling. Our data first indicate that CAFs initially assembled a strained, viscous, and unfolded Fn matrix. This early altered Fn matrix was later remodeled into a thick Col I-rich matrix that was characteristic of a dense tumor mass. Next, our results suggest that this ECM remodeling was primarily mediated by matrix metalloproteinases (MMPs). This MMP activity caused profound structural and mechanical changes in the developing ECM, which then modified vascular endothelial growth factor (VEGF) secretion by CAFs and matrix sequestration. Collectively, these findings enhance our understanding of the mechanisms by which Fn and Col I synergistically interplay in promoting a sustained altered signaling cascade to remodel the breast tumor stroma for invasive breast tumor growth.

Integrins as Therapeutic Targets for Respiratory Diseases

Integrins are a large family of transmembrane heterodimeric proteins that constitute the main receptors for extracellular matrix components. Integrins were initially thought to be primarily involved in the maintenance of cell adhesion and tissue integrity. However, it is now appreciated that integrins play important roles in many other biological processes such as cell survival, proliferation, differentiation, migration, cell shape and polarity. Lung cells express numerous combinations and permutations of integrin heterodimers. The complexity and diversity of different integrin heterodimers being implicated in different lung diseases present a major challenge for drug development. Here we provide a comprehensive overview of the current knowledge of integrins from studies in cell culture to integrin knockout mouse models and provide an update of results from clinical trials for which integrins are therapeutic targets with a focus on respiratory diseases (asthma, emphysema, pneumonia, lung cancer, pulmonary fibrosis and sarcoidosis).

An Overview of VEGF-Mediated Signal Transduction

Vascular endothelial growth factor (VEGF) plays a fundamental role in angiogenesis and endothelial cell biology, and has been the subject of intense study as a result. VEGF acts via a diverse and complex range of signaling pathways, with new targets constantly being discovered. This review attempts to summarize the current state of knowledge regarding VEGF cell signaling in endothelial and cardiovascular biology, with a particular emphasis on its role in angiogenesis.

Stable engineered vascular networks from human induced pluripotent stem cell-derived endothelial cells cultured in synthetic hydrogels

Here, we describe an in vitro strategy to model vascular morphogenesis where human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) are encapsulated in peptide-functionalized poly(ethylene glycol) (PEG) hydrogels, either on standard well plates or within a passive pumping polydimethylsiloxane (PDMS) tri-channel microfluidic device. PEG hydrogels permissive towards cellular remodeling were fabricated using thiol-ene photopolymerization to incorporate matrix metalloproteinase (MMP)-degradable crosslinks and CRGDS cell adhesion peptide. Time lapse microscopy, immunofluorescence imaging, and RNA sequencing (RNA-Seq) demonstrated that iPSC-ECs formed vascular networks through mechanisms that were consistent with in vivo vasculogenesis and angiogenesis when cultured in PEG hydrogels. Migrating iPSC-ECs condensed into clusters, elongated into tubules, and formed polygonal networks through sprouting. Genes upregulated for iPSC-ECs cultured in PEG hydrogels relative to control cells on tissue culture polystyrene (TCP) surfaces included adhesion, matrix remodeling, and Notch signaling pathway genes relevant to in vivo vascular development. Vascular networks with lumens were stable for at least 14days when iPSC-ECs were encapsulated in PEG hydrogels that were polymerized within the central channel of the microfluidic device. Therefore, iPSC-ECs cultured in peptide-functionalized PEG hydrogels offer a defined platform for investigating vascular morphogenesis in vitro using both standard and microfluidic formats.

STATEMENT OF SIGNIFICANCE

Human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) cultured in synthetic hydrogels self-assemble into capillary networks through mechanisms consistent with in vivo vascular morphogenesis.

Disorders of Vascular Permeability

The endothelial barrier maintains vascular and tissue homeostasis and modulates many physiological processes, such as angiogenesis. Vascular barrier integrity can be disrupted by a variety of soluble permeability factors, and changes in barrier function can exacerbate tissue damage during disease progression. Understanding endothelial barrier function is critical for vascular homeostasis. Many of the signaling pathways promoting vascular permeability can also be triggered during disease, resulting in prolonged or uncontrolled vascular leak. It is believed that recovery of the normal vasculature requires diminishing this hyperpermeable state. Although the molecular mechanisms governing vascular leak have been studied over the last few decades, recent advances have identified new therapeutic targets that have begun to show preclinical and clinical promise. These approaches have been successfully applied to an increasing number of disease conditions. New perspectives regarding how vascular leak impacts the progression of various diseases are highlighted in this review.

Integrin-specific hydrogels functionalized with VEGF for vascularization and bone regeneration of critical-size bone defects

Vascularization of bone defects is considered a crucial component to the successful regeneration of large bone defects. Although vascular endothelial growth factor (VEGF) has been delivered to critical-size bone defect models to augment blood vessel infiltration into the defect area, its potential to increase bone repair remains ambiguous. In this study, we investigated whether integrin-specific biomaterials modulate the effects of VEGF on bone regeneration. We engineered protease-degradable, VEGF-loaded poly(ethylene glycol) (PEG) hydrogels functionalized with either a triple-helical, α2 β1 integrin-specific peptide GGYGGGP(GPP)5 GFOGER(GPP)5 GPC (GFOGER) or an αv β3 integrin-targeting peptide GRGDSPC (RGD). Covalent incorporation of VEGF into the PEG hydrogel allowed for protease degradation-dependent release of the protein while maintaining VEGF bioactivity. When applied to critical-size segmental defects in the murine radius, GFOGER-functionalized VEGF-free hydrogels exhibited significantly increased vascular volume and density and resulted in a larger number of thicker blood vessels compared to RGD-functionalized VEGF-free hydrogels. VEGF-loaded RGD hydrogels increased vascularization compared to VEGF-free RGD hydrogels, but the levels of vascularization for these VEGF-containing RGD hydrogels were similar to those of VEGF-free GFOGER hydrogels. VEGF transiently increased bone regeneration in RGD hydrogels but had no effect at later time points. In GFOGER hydrogels, VEGF did not show an effect on bone regeneration. However, VEGF-free GFOGER hydrogels resulted in increased bone regeneration compared to VEGF-free RGD hydrogels. These findings demonstrate the importance of integrin-specificity in engineering constructs for vascularization and associated bone regeneration.

Cellular recognition and macropinocytosis-like internalization of nanoparticles targeted to integrin α2β1

Targeting nanoparticles to desired intracellular compartments is a major challenge. Integrin-type adhesion receptors are connected to different endocytosis routes in a receptor-specific manner. According to our previous observations, the internalization of an α2β1-integrin-echovirus-1 complex takes place via a macropinocytosis-like mechanism, suggesting that the receptor could be used to target nanoparticles to this specific entry route. Here, silica-based nanoparticles, carrying monoclonal antibodies against the α2β1 integrin as address labels, were synthesized. Studies with flow cytometry, atomic force microscopy and confocal microscopy showed the particles to attach to the cell surface via the α2β1 integrin. Furthermore, quantitative analysis of nanoparticle trafficking inside the cell performed with the BioImageXD software indicated that the particles enter cells via a macropinocytosis-like process and end up in caveolin-1 positive structures. Thus, we suggest that different integrins can guide particles to distinct endocytosis routes and, subsequently, also to specific intracellular compartments. In addition, we show that with the BioImageXD software it is possible to conduct sensitive and complex analyses of the behavior of small fluorescent particles inside cells, using basic confocal microscopy images.

Endothelial cell response to chemical, biological, and physical cues in bioactive hydrogels

The highly tunable biological, chemical, and physical properties of bioactive hydrogels enable their use in an array of tissue engineering and drug delivery applications. Systematic modulation of these properties can be used to elucidate key cell-material interactions to improve therapeutic effects. For example, the rate and extent of endothelialization are critical to the long-term success of many blood-contacting devices. To this end, we have developed a bioactive hydrogel that could be used as coating on cardiovascular devices to enhance endothelial cell (EC) adhesion and migration. The current work investigates the relative impact of hydrogel variables on key endothelialization processes. The bioactive hydrogel is based on poly(ethylene glycol) (PEG) and a streptococcal collagen-like (Scl2-2) protein that has been modified with integrin α1β1 and α2β1 binding sites. The use of PEG hydrogels allows for incorporation of specific bioactive cues and independent manipulation of scaffold properties. The selective integrin binding of Scl2-2 was compared to more traditional collagen-modified PEG hydrogels to determine the effect of integrin binding on cell behavior. Protein functionalization density, protein concentration, and substrate modulus were independently tuned with both Scl2-2 and collagen to determine the effect of each variable on EC adhesion, spreading, and migration. The findings here demonstrate that increasing substrate modulus, decreasing functionalization density, and increasing protein concentration can be utilized to increase EC adhesion and migration. Additionally, PEG-Scl2-2 hydrogels had higher migration speeds and proliferation over 1 week compared with PEG-collagen gels, demonstrating that selective integrin binding can be used to enhance cell-material interactions. Overall, these studies contribute to the understanding of the effects of matrix cues on EC interactions and demonstrate the strong potential of PEG-Scl2-2 hydrogels to promote endothelialization of blood-contacting devices.

Alpha2beta1 integrin in cancer development and chemoresistance

Extracellular matrix, via its receptors the integrins, has emerged as a crucial factor in cancer development. The α2β1 integrin is a major collagen receptor that is widely expressed and known to promote cell migration and control tissue homeostasis. Growing evidence suggests that it can be a key pathway in cancer. Recent studies have shown that α2β1 integrin is a regulator of cancer metastasis either by promoting or inhibiting the dissemination process of cancer cells. The α2β1 integrin signaling can also enhance tumor angiogenesis. Emerging evidence supports a role for α2β1 integrin in cancer chemoresistance especially in hematological malignancies originating from the T cell lineage. In addition, α2β1 integrin has been associated with cancer stem cells. In this review, we will discuss the complex role of α2β1 integrin in these processes. Collagen is a major matrix protein of the tumor microenvironment and thus, understanding how α2β1 integrin regulates cancer pathogenesis is likely to lead to new therapeutic approaches and agents for cancer treatment.

Effect of therapeutic ultrasound on brain angiogenesis following intracerebral hemorrhage in rats

Intracerebral hemorrhage (ICH) can produce severe neurological deficits in stroke survivors. However, few effective approaches are available to improve the recovery from ICH. Given that therapeutic ultrasound exposure can enhance on angiogenesis in peripheral tissues, the present study was designed to examine the effects of therapeutic ultrasound exposure on the brain angiogenesis following ICH. To this end, we applied once daily therapeutic ultrasound treatment to rats for 7 consecutive days after intracranial infusion of vehicle (Sham control) or collagenase (ICH). Repeated exposure to the low intensity of therapeutic ultrasound decreased behavioral scores in ICH rats, but not in sham control rats. Such an effect was correlated with an increased number of vessel-like structures and microvessels and PCNA positive cells in vWF-positive blood vessels in perihematomal brain tissues at post-ICH day 7. Furthermore, immunohistochemistry and western blotting results showed that ICH trigged the expression of extracellular matrix (ECM)-related molecules, including collagen Is, III, and IV, as well as integrins αvβ3 and α5β1, and exposure to therapeutic ultrasound increased the expression of these molecules. Therefore, our results indicated that repeated exposure to a low intensity of therapeutic ultrasound can increase the expression of collagen and integrins of ECM-related molecules, promote the formation of a large number of vessel-like structure and capillaries around the hematoma, and accelerate the recovery of neurological function impaired by ICH.

Low-Energy Ultrasound Treatment Improves Regional Tumor Vessel Infarction by Retargeted Tissue Factor

OBJECTIVES

To enhance the regional antitumor activity of the vascular-targeting agent truncated tissue factor (tTF)-NGR by combining the therapy with low-energy ultrasound (US) treatment.

METHODS

For the in vitro US exposure of human umbilical vein endothelial cells (HUVECs), cells were put in the focus of a US transducer. For analysis of the US-induced phosphatidylserine (PS) surface concentration on HUVECs, flow cytometry was used. To demonstrate the differences in the procoagulatory efficacy of TF-derivative tTF-NGR on binding to HUVECs with a low versus high surface concentration of PS, we performed factor X activation assays. For low-energy US pretreatment, HT1080 fibrosarcoma xenotransplant-bearing nude mice were treated by tumor-regional US-mediated stimulation (ie, destruction) of microbubbles. The therapy cohorts received the tumor vessel-infarcting tTF-NGR protein with or without US pretreatment (5 minutes after US stimulation via intraperitoneal injection on 3 consecutive days).

RESULTS

Combination therapy experiments with xenotransplant-bearing nude mice significantly increased the antitumor activity of tTF-NGR by regional low-energy US destruction of vascular microbubbles in tumor vessels shortly before application of tTF-NGR (P < .05). Mechanistic studies proved the upregulation of anionic PS on the outer leaflet of the lipid bilayer of endothelial cell membranes by low-energy US and a consecutive higher potential of these preapoptotic endothelial cells to activate coagulation via tTF-NGR and coagulation factor X as being a basis for this synergistic activity.

CONCLUSIONS

Combining retargeted tTF to tumor vessels with proapoptotic stimuli for the tumor vascular endothelium increases the antitumor effects of tumor vascular infarction. Ultrasound treatment may thus be useful in this respect for regional tumor therapy.

Astrocytic β1-integrin affects cellular composition of murine blood brain barrier in the cerebral cortex

The blood brain barrier (BBB) is composed of endothelial cells, astrocytes, and pericytes and maintains functional homeostasis by regulating transport of ions, fluid and cells between blood and neural tissue. The cellular and molecular pathways that contribute to the formation of the BBB in the developing brain have not been fully deciphered. β1-integrin (β1-itg) within endothelial cells is known to play a critical role in vasculogenesis. However, the role of astrocytic β1-itg in BBB development is not known. Our study used a mouse glial fibrillary acidic protein (GFAP)-cre transgenic line to selectively ablate β1-itg within astrocytes. We found that deletion of astrocytic β1-itg had a striking effect on the different cell types that form the BBB. Mutant mice had a decreased density of aquaporin-4 immunoreactivity within the perivascular astrocytic end-feet. We also found decreases in immunoreactivity for vimentin and CD-31 within endothelial cells. These changes were not accompanied by functional changes in BBB under physiological conditions as assessed by extravasation of large and small molecular weight molecules. However, mutant mice had an increased incidence of severe cystic injury in response to neonatal hypoxia. Our findings show that astrocytic β1-itg has an important role in defining cellular properties of the blood brain barrier in the cerebral cortex.

Sulfonamide inhibitors of α2β1 integrin reveal the essential role of collagen receptors in in vivo models of inflammation

Small molecule inhibitors of α2β1 integrin, a major cellular collagen receptor, have been reported to inhibit platelet function, kidney injury, and angiogenesis. Since α2β1 integrin is abundantly expressed on various inflammation-associated cells, we tested whether recently developed α2β1 blocking sulfonamides have anti-inflammatory properties. Integrin α2β1 inhibitors were shown to reduce the signs of inflammation in arachidonic acid-induced ear edema, PAF stimulated air pouch, ovalbumin-induced skin hypersensitivity, adjuvant arthritis, and collagen-induced arthritis. Thus, these sulfonamides are potential drugs for acute and allergic inflammation, hypersensitivity, and arthritis. One sulfonamide with potent anti-inflammatory activity has previously been reported to be selective for activated integrins, but not to inhibit platelet function. Thus, the experiments also revealed fundamental differences in the action of nonactivated and activated α2β1 integrins in inflammation when compared to thrombosis.

Molecular mechanism of local drug delivery with Paclitaxel-eluting membranes in biliary and pancreatic cancer: new application for an old drug

Implantation of self-expanding metal stents (SEMS) is palliation for patients suffering from inoperable malignant obstructions associated with biliary and pancreatic cancers. Chemotherapeutic agent-eluting stents have been developed because SEMS are susceptible to occlusion by tumor in-growth. We reported recently that paclitaxel-eluting SEMS provide enhanced local drug delivery in an animal model. However, little is known about the molecular mechanisms by which paclitaxel-eluting stents attenuate tumor growth. We investigated the signal transduction pathways underlying the antiproliferative effects of a paclitaxel-eluting membrane (PEM) implanted in pancreatic/cholangiocarcinoma tumor bearing nude mice. Molecular and cellular alterations were analyzed in the PEM-implanted pancreatic/cholangiocarcinoma xenograft tumors by Western blot, immunoprecipitation, and immunofluorescence. The quantities of paclitaxel released into the tumor and plasma were determined by liquid chromatography-tandem mass spectroscopy. Paclitaxel from the PEM and its diffusion into the tumor inhibited angiogenesis, which involved suppression of mammalian target of rapamycin (mTOR) through regulation of hypoxia inducible factor (HIF-1) and increased apoptosis. Moreover, implantation of the PEM inhibited tumor-stromal interaction-related expression of proteins such as CD44, SPARC, matrix metalloproteinase-2, and vimentin. Local delivery of paclitaxel from a PEM inhibited growth of pancreatic/cholangiocarcinoma tumors in nude mice by suppressing angiogenesis via the mTOR and inducing apoptosis signal pathway.

Proteoglycan form and function: A comprehensive nomenclature of proteoglycans

We provide a comprehensive classification of the proteoglycan gene families and respective protein cores. This updated nomenclature is based on three criteria: Cellular and subcellular location, overall gene/protein homology, and the utilization of specific protein modules within their respective protein cores. These three signatures were utilized to design four major classes of proteoglycans with distinct forms and functions: the intracellular, cell-surface, pericellular and extracellular proteoglycans. The proposed nomenclature encompasses forty-three distinct proteoglycan-encoding genes and many alternatively-spliced variants. The biological functions of these four proteoglycan families are critically assessed in development, cancer and angiogenesis, and in various acquired and genetic diseases where their expression is aberrant.

The role of perlecan and endorepellin in the control of tumor angiogenesis and endothelial cell autophagy

During tumor growth and angiogenesis there is a dynamic remodeling of tissue architecture often accompanied by the release of extracellular matrix constituents full of biological activity. One of the key constituents of the tumor microenvironment is the large heparan sulfate proteoglycan perlecan. This proteoglycan, strategically located at cell surfaces and within basement membranes, is a well-defined pro-angiogenic molecule when intact. However, when partially processed by proteases released during cancer remodeling and invasion, the C-terminal fragment of perlecan, known as endorepellin, has opposite effects than its parent molecule. Endorepellin is a potent inhibitor of angiogenesis by exerting a dual receptor antagonism by simultaneously engaging VEGFR2 and α2β1 integrin. Signaling through the α2β1 integrin leads to actin disassembly and block of endothelial cell migration, necessary for capillary morphogenesis. Signaling through the VEGFR2 induces dephosphorylation of the receptor via activation of SHP-1 and suppression of downstream proangiogenic effectors, especially attenuating VEGFA expression. A novel and emerging role of endorepellin is its ability to evoke autophagy by activating Peg3 and various canonical autophagic markers. This effect is specific for endothelial cells as these are the primary cells expressing both VEGFR2 and α2β1 integrin. Thus, an endogenous fragment of a ubiquitous proteoglycan can regulate both angiogenesis and autophagy through a dual receptor antagonism. The biological properties of this natural endogenous protein place endorepellin as a potential therapeutic agent against cancer or diseases where angiogenesis is prominent.

Disintegrins from snake venoms and their applications in cancer research and therapy

Integrins regulate diverse functions in cancer pathology and in tumor cell development and contribute to important processes such as cell shape, survival, proliferation, transcription, angiogenesis, migration, and invasion. A number of snake venom proteins have the ability to interact with integrins. Among these are the disintegrins, a family of small, non-enzymatic, and cysteine-rich proteins found in the venom of numerous snake families. The venom proteins may have a potential role in terms of novel therapeutic leads for cancer treatment. Disintegrin can target specific integrins and as such it is conceivable that they could interfere in important processes involved in carcinogenesis, tumor growth, invasion and migration. Herein we present a survey of studies involving the use of snake venom disintegrins for cancer detection and treatment. The aim of this review is to highlight the relationship of integrins with cancer and to present examples as to how certain disintegrins can detect and affect biological processes related to cancer. This in turn will illustrate the great potential of these molecules for cancer research. Furthermore, we also outline several new approaches being created to address problems commonly associated with the clinical application of peptide-based drugs such as instability, immunogenicity, and availability.

A topical aqueous oxygen emulsion stimulates granulation tissue formation in a porcine second-degree burn wound

BACKGROUND

Oxygen is an essential substance for wound healing. Limited studies have shown that topical oxygen can influence healing. This study evaluated the effects of a Topical Oxygen Emulsion (TOE) on burn wound healing.

METHODS

A porcine second-degree burn wound model was used in the study. Burn wounds were randomly assigned to TOE, vehicle control, and no-treatment (air) groups. Effects of TOE on the granulation tissue formation and angiogenesis were studied using hematoxylin and eosin histological analysis. Protein production and gene expression of types I and III collagen and vascular endothelial growth factor (VEGF) were determined using immunofluorescent staining and Reverse Transcription and Polymerase Chain Reaction (RT-PCR), respectively.

RESULTS

The TOE treated wounds exhibited better angiogenesis and granulation tissue formation by histology examination. The immunofluorescence staining and RT-PCR analysis demonstrated that protein production and mRNA expression of VEGF and collagen III were significantly higher in TOE treatment group than vehicle alone and air control groups, while there was no significant difference in the level of collagen I.

CONCLUSIONS

Our data demonstrate that TOE enhances burn wound healing via stimulating the expression of VEGF and type III collagen and strongly indicates the potential use of TOE in wounds.

Induction of integrin α2 in a highly bone metastatic human prostate cancer cell line: roles of RANKL and AR under three-dimensional suspension culture

Background

Prostate cancer (PCa) bone metastasis can be markedly enhanced by increased receptor activator of NF kappa-B ligand (RANKL) expression in PCa cells. Molecular mechanisms that account for the increased predilection of PCa for bone include increased bone turnover, promotion of PCa cell growth and survival in the bone environment, and recruitment of bystander dormant cells to participate in bone metastasis. The current study tests the hypothesis that PCa cells acquire high adhesion to bone matrix proteins, which controls PCa bone colonization, under the RANKL/RANK and AR axes.

Methods

We used a highly bone metastatic RANKL-overexpressing LNCaP PCa cell line, LNCaP^RANKL, as a model to pursue the molecular mechanisms underlying the increased adhesion of PCa cells to collagens. A three-dimensional (3-D) suspension PCa organoid model was developed. The functions of integrin α₂ in cell adhesion and survival were evaluated by flow cytometry and western blot. AR expression and functionality were compared in 2-D monolayer versus 3-D suspension cultures using AR promoter- and PSA promoter-luciferase activity. AR role in cell adhesion was assessed using an adhesion assay.

Results

LNCaP^RANKL cells were shown to adhere tightly to ColI matrix through increased α₂ integrin expression. This increased adhesion, concomitant with activation of the FAK and Akt pathways, was further enhanced by culturing LNCaP^RANKL cells in 3-D suspension. Under the influence of 3-D suspension culture, AR was restored in LNCaP^RANKL cells via downregulation of AP-4 transcription factor, and supported increased α₂ integrin expression and adhesion to ColI.

Conclusion

3-D suspension culture and in vivo PCa tumor growth restore AR through downregulation of AP-4, enhancing integrin α₂ expression and adhesion to ColI which is rich in bone matrices. The interactions of PCa with ColI, mediated by integrin α₂ and AR expression, could be a key molecular event accounting for PCa bone metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-208) contains supplementary material, which is available to authorized users.

Effects of integrins and integrin αvβ3 inhibitor on angiogenesis in cerebral ischemic stroke

Integrins such as αvβ3, α5β1 play a key role in angiogenesis regulation, invasion and metastasis, inflammation, wound healing, etc. The up-regulation of integrin αvβ3 after cerebral ischemic stroke can promote angiogenesis, which in turn improves functional recovery. In addition, the integrin αvβ3 inhibitor can block the blood-brain barrier (BBB) leakage induced by vascular endothelial growth factor (VEGF) and also can reduce inflammatory reaction, decrease the deposition of fibrinogen. Other studies showed that integrin αvβ3 is not essential in revascularization. Therefore, the effect of integrin αvβ3 in the whole process of brain function recovery merits further study.

Extracellular matrix modulates angiogenesis in physiological and pathological conditions

Angiogenesis is a multistep process driven by a wide range of positive and negative regulatory factors. Extracellular matrix (ECM) plays a crucial role in the regulation of this process. The degradation of ECM, occurring in response to an angiogenic stimulus, leads to degradation or partial modification of matrix molecules, release of soluble factors, and exposure of cryptic sites with pro- and/or antiangiogenic activity. ECM molecules and fragments, resulting from proteolysis, can also act directly as inflammatory stimuli, and this can explain the exacerbated angiogenesis that drives and maintains several inflammatory diseases. In this review we have summarized some of the more recent literature data concerning the molecular control of ECM in angiogenesis in both physiological and pathological conditions.

Endorepellin evokes autophagy in endothelial cells

Endorepellin, the C-terminal fragment of the heparan sulfate proteoglycan perlecan, possesses angiostatic activity via dual receptor antagonism, through concurrent binding to the α2β1 integrin and vascular endothelial growth factor receptor 2 (VEGFR2). Here, we discovered that soluble endorepellin induced autophagy in endothelial cells by modulating the expression of Beclin 1, LC3, and p62, three established autophagic markers. Moreover, endorepellin evoked expression of the imprinted tumor suppressor gene Peg3 and its co-localization with Beclin 1 and LC3 in autophagosomes, suggesting a major role for this gene in endothelial cell autophagy. Mechanistically, endorepellin induced autophagy by down-regulating VEGFR2 via the two LG1/2 domains, whereas the C-terminal LG3 domain, the portion responsible for binding the α2β1 integrin, was ineffective. Endorepellin also induced transcriptional activity of the BECN1 promoter in endothelial cells, and the VEGFR2-specific tyrosine kinase inhibitor, SU5416, blocked this effect. Finally, we found a correlation between endorepellin-evoked inhibition of capillary morphogenesis and enhanced autophagy. Thus, we have identified a new role for this endogenous angiostatic fragment in inducing autophagy through a VEGFR2-dependent but α2β1 integrin-independent pathway. This novel mechanism specifically targets endothelial cells and could represent a promising new strategy to potentiate the angiostatic effect of endorepellin and perhaps other angiostatic matrix proteins.

Redox signaling as a therapeutic target to inhibit myofibroblast activation in degenerative fibrotic disease

Degenerative fibrotic diseases encompass numerous systemic and organ-specific disorders. Despite their associated significant morbidity and mortality, there is currently no effective antifibrotic treatment. Fibrosis is characterized by the development and persistence of myofibroblasts, whose unregulated deposition of extracellular matrix components disrupts signaling cascades and normal tissue architecture leading to organ failure and death. The profibrotic cytokine transforming growth factor beta (TGFβ) is considered the foremost inducer of fibrosis, driving myofibroblast differentiation in diverse tissues. This review summarizes recent in vitro and in vivo data demonstrating that TGF β-induced myofibroblast differentiation is driven by a prooxidant shift in redox homeostasis. Elevated NADPH oxidase 4 (NOX4)-derived hydrogen peroxide (H2O2) supported by concomitant decreases in nitric oxide (NO) signaling and reactive oxygen species scavengers are central factors in the molecular pathogenesis of fibrosis in numerous tissues and organs. Moreover, complex interplay between NOX4-derived H2O2 and NO signaling regulates myofibroblast differentiation. Restoring redox homeostasis via antioxidants or NOX4 inactivation as well as by enhancing NO signaling via activation of soluble guanylyl cyclases or inhibition of phosphodiesterases can inhibit and reverse myofibroblast differentiation. Thus, dysregulated redox signaling represents a potential therapeutic target for the treatment of wide variety of different degenerative fibrotic disorders.

Inhibitory effects of recombinant RTS-jerdostatin on integrin α1β1 function during adhesion, migration and proliferation of rat aortic smooth muscle cells and angiogenesis

Jerdostatin, a short RTS-disintegrin cloned from venom gland mRNA of Protobothrops jerdonii, selectively blocks the adhesion of α1β1 integrin to collagen IV. Integrin α1β1 is highly expressed in smooth muscle cells (SMC) surrounding small blood vessels and vascular endothelial cells. Vascular SMC adhesion, migration and proliferation are important processes during normal vascular development. Using recombinant jerdostatin we have investigated the role of the α1β1 integrin on the adhesion of vascular SMC to collagen IV, and the potential relevance of blocking this crucial component of focal adhesions as an anti-angiogenic strategy. Our results show that jerdostatin does not interact with canonical collagen-binding site on the isolated A-domain of the α1 integrin subunit. r-Jerdostatin inhibited the adhesion of RASMCs to immobilized CB3 fragment in a dose-dependent manner, triggering to round-up, retraction, and finally detachment of the cells. r-Jerdostatin did not affect the adhesion of human SMCs to CB3, presumably because the high expression of α2β1 integrin compensated for α1β1 integrin blockage by jerdostatin. r-Jerdostatin dose-dependently inhibited α1β1 integrin-dependent HUVEC tube formation. However, VEGF-driven tube formation in the matrigel assay was only completely abolished when binding of integrin α2β1 to collagen was also inhibited by the C-type lectin-like rhodocetin. As a whole, our work emphasizes the relevance of using specific inhibitors for dissecting the role of α1β1 integrin in physiological and pathological conditions.

Integrin α1β1

Integrin α1β1 is widely expressed in mesenchyme and the immune system, as well as a minority of epithelial tissues. Signaling through α1 contributes to the regulation of extracellular matrix composition, in addition to supplying in some tissues a proliferative and survival signal that appears to be unique among the collagen binding integrins. α1 provides a tissue retention function for cells of the immune system including monocytes and T cells, where it also contributes to their long-term survival, providing for peripheral T cell memory, and contributing to diseases of autoimmunity. The viability of α1 null mice, as well as the generation of therapeutic monoclonal antibodies against this molecule, have enabled studies of the role of α1 in a wide range of pathophysiological circumstances. The immune functions of α1 make it a rational therapeutic target.

α2β1 Integrin

The α2β1 integrin, also known as VLA-2, GPIa-IIa, CD49b, was first identified as an extracellular matrix receptor for collagens and/or laminins [55, 56]. It is now recognized that the α2β1 integrin serves as a receptor for many matrix and nonmatrix molecules [35, 79, 128]. Extensive analyses have clearly elucidated the α2 I domain structural motifs required for ligand binding, and also defined distinct conformations that lead to inactive, partially active or highly active ligand binding [3, 37, 66, 123, 136, 137, 140]. The mechanisms by which the α2β1 integrin plays a critical role in platelet function and homeostasis have been carefully defined via in vitro and in vivo experiments [76, 104, 117, 125]. Genetic and epidemiologic studies have confirmed human physiology and disease states mediated by this receptor in immunity, cancer, and development [6, 20, 21, 32, 43, 90]. The role of the α2β1 integrin in these multiple complex biologic processes will be discussed in the chapter.

Current understanding of molecular and cellular mechanisms in fibroplasia and angiogenesis during acute wound healing

Cutaneous wound healing ultimately functions to facilitate barrier restoration following injury-induced loss of skin integrity. It is an evolutionarily conserved, multi-cellular, multi-molecular process involving co-ordinated inter-play between complex signalling networks. Cellular proliferation is recognised as the third stage of this sequence. Within this phase, fibroplasia and angiogenesis are co-dependent processes which must be successfully completed in order to form an evolving extracellular matrix and granulation tissue. The resultant structures guide cellular infiltration, differentiation and secretory profile within the wound environment and consequently have major influence on the success or failure of wound healing. This review integrates in vitro, animal and human in vivo studies, to provide up to date descriptions of molecular and cellular interactions involved in fibroplasia and angiogenesis. Significant molecular networks include adhesion molecules, proteinases, cytokines and chemokines as well as a plethora of growth factors. These signals are produced by, and affect behaviour of, cells including fibroblasts, fibrocytes, keratinocytes, endothelial cells and inflammatory cells resulting in significant cellular phenotypic and functional plasticity, as well as controlling composition and remodelling of structural proteins including collagen and fibronectin. The interdependent relationship between angiogenesis and fibroplasia relies on dynamic reciprocity between cellular components, matrix proteins and bioactive molecules. Unbalanced regulation of any one component can have significant consequences resulting in delayed healing, chronic wounds or abnormal scar formation. Greater understanding of angiogenic and fibroplastic mechanisms underlying chronic wound pathogenesis has identified novel therapeutic targets and enabled development of improved treatment strategies including topical growth factors and skin substitutes.

Glycated collagen and altered glucose increase endothelial cell adhesion strength

Cell adhesion strength is important to cell survival, proliferation, migration, and mechanotransduction, yet changes in endothelial cell adhesion strength have not yet been examined in diseases such as diabetes with high rates of cardiovascular complications. We therefore investigated porcine aortic endothelial cell adhesion strength on native and glycated collagen-coated substrates and in low, normal, and high glucose culture using a spinning disc apparatus. Adhesion strength increased by 30 dynes/cm(2) in cells on glycated collagen as compared to native collagen. Attachment studies revealed that cells use higher adhesion strength αv β3 integrins to bind to glycated collagen instead of the typical α2 β1 integrins used to bind to native collagen. Similarly, endothelial cells cultured in low and high glucose had 15 dynes/cm(2) higher adhesion strength than cells in normal glucose after 2 days. Increased adhesion strength was due to elevated VEGF release and intracellular PKC in low and high glucose cells, respectively. Thus glucose increased endothelial cell adhesion strength via different underlying mechanisms. These adhesion strength changes could contribute to diabetic vascular disease, including accelerated atherosclerosis and disordered angiogenesis.

Fibrin and collagen differentially but synergistically regulate sprout angiogenesis of human dermal microvascular endothelial cells in 3-dimensional matrix

Angiogenesis is a highly regulated event involving complex, dynamic interactions between microvascular endothelial cells and extracellular matrix (ECM) proteins. Alteration of ECM composition and architecture is a hallmark feature of wound clot and tumor stroma. We previously reported that during angiogenesis, endothelial cell responses to growth factors are modulated by the compositional and mechanical properties of a surrounding three-dimensional (3D) extracellular matrix (ECM) that is dominated by either cross-linked fibrin or type I collagen. However, the role of 3D ECM in the regulation of angiogenesis associated with wound healing and tumor growth is not well defined. This study investigates the correlation of sprout angiogenesis and ECM microenvironment using in vivo and in vitro 3D angiogenesis models. It demonstrates that fibrin and type I collagen 3D matrices differentially but synergistically regulate sprout angiogenesis. Thus blocking both integrin alpha v beta 3 and integrin alpha 2 beta 1 might be a novel strategy to synergistically block sprout angiogenesis in solid tumors.

Vascular endothelial growth factor promotes anatomical and functional recovery of injured peripheral nerves in the avascular cornea

Peripheral nerve injury is a major neurological disorder that can cause severe motor and sensory dysfunction. Neurogenic effects of vascular endothelial growth factor (VEGF) have been found in the central nervous system, and we examined whether VEGF could promote anatomical and functional recovery of peripheral nerves after injury using an avascular corneal nerve injury model. We found that VEGF enhanced neurite elongation in isolated trigeminal ganglion neurons in a dose-dependent manner. This effect was suppressed by neutralizing antibodies for VEGF receptor (VEGFR) 1 and 2 or neuropilin receptor 1 or by VEGFR2 inhibitors (SU 1498 and Ki 8751). In vivo, mice receiving sustained VEGF via implanted pellets showed increased corneal nerve regeneration after superficial injury compared with those receiving vehicle. VEGF injected subconjunctivally at the time of injury accelerated reinnervation, the recovery of mechanosensation, and epithelial wound healing. Endogenous VEGF expression was up-regulated in the corneal epithelium and stroma after wounding. Thus, VEGF can mediate peripheral neuron growth but requires the activation of multiple VEGF receptor types. In addition, VEGF can accelerate the return of sensory and trophic functions of damaged peripheral nerves. Wounding induces the expression of VEFG, which may modulate physiological nerve repair.

Anticancer therapy by tumor vessel infarction with polyethylene glycol conjugated retargeted tissue factor

tTF-NGR consists of the extracellular domain of tissue factor and the peptide GNGRAHA, a ligand of the surface protein aminopeptidase N and of integrin αvβ3. Both surface proteins are upregulated on endothelial cells of tumor vessels. tTF-NGR shows antitumor activity in xenografts and inhibition of tumor blood flow in cancer patients. We performed random TMS(PEG)12 PEGylation of tTF-NGR to improve the antitumor profile of the molecule. PEGylation resulted in an approximately 2-log step decreased procoagulatory activity of the molecule. Pharmacokinetic studies in mice showed a more than 1-log step higher mean area under the curve. Comparison of the LD10 values for both compounds and their lowest effective antitumor dose against human tumor xenografts showed an improved therapeutic range (active/toxic dose in mg/kg body weight) of 1/5 mg/kg for tTF-NGR and 3/>160 mg/kg for TMS(PEG)12 tTF-NGR. Results demonstrate that PEGylation can significantly improve the therapeutic range of tTF-NGR.

Identification of inhibitors of α2β1 integrin, members of C-lectin type proteins, in Echis sochureki venom

Snake venom antagonists of α2β1 integrin have been identified as members of a C-lectin type family of proteins (CLP). In the present study, we characterized three new CLPs isolated from Echis sochureki venom, which interact with this integrin. These proteins were purified using a combination of gel filtration, ion exchange chromatography and reverse phase HPLC. Sochicetin-A and sochicetin-B potently inhibited adhesion of cells expressing α2β1 integrin and binding of isolated α2β1 ectodomain to collagen I, as well as bound to recombinant GST-α2A domain in ELISA, whereas activity of sochicetin-C in these assays was approximately two orders of magnitude lower. Structurally, sochicetin-B and sochicetin-C are typical heterodimeric αβ CLPs, whereas sochicetin-A exhibits a trimer of its subunits (αβ)₃ in the quaternary structure. Immobilized sochicetins supported adhesion of glioma cell lines, LN18 and LBC3, whereas in a soluble form they partially inhibited adhesion of these cells to collagen I. Glioma cells spread very poorly on sochicetin-A, showing no cytoskeleton rearrangement typical for adhesion to collagen I or fibronectin. Adhesion on CLP does not involve focal adhesion elements, such as vinculin. Sochicetin-A also inhibited collagen-induced platelet aggregation, similar to other CLPs' action on the blood coagulation system.

Endorepellin laminin-like globular 1/2 domains bind Ig3-5 of vascular endothelial growth factor (VEGF) receptor 2 and block pro-angiogenic signaling by VEGFA in endothelial cells

Endorepellin, a processed fragment of perlecan protein core, possesses anti-angiogenic activity by antagonizing endothelial cells. Endorepellin contains three laminin G-like (LG) domains and binds simultaneously to vascular endothelial growth factor receptor 2 (VEGFR2) and α2β1 integrin, resulting in dual receptor antagonism. Treatment of endothelial cells with endorepellin inhibits transcription of VEGFA, the natural ligand for VEGFR2, attenuating the pro-survival and migratory activities of VEGFA/VEGFR2 signaling cascade. Here, we investigated the specific binding site of endorepellin within the ectodomain of VEGFR2. Full-length endorepellin was not capable of displacing VEGFA binding from VEGFR2 and LG3 domain alone did not bind VEGFR2. This suggested different binding mechanisms of the extracellular Ig domains of VEGFR2. Therefore, we hypothesized that endorepellin would bind through its proximal LG1/2 domains to VEGFR2 in a different region than VEGFA. Indeed, we found that LG1/2 did not bind Ig1-3, but did bind with high affinity to Ig3-5, distal to the known VEGFA binding site, i.e. Ig2-3. These results support a role for endorepellin as an allosteric inhibitor of VEGFR2. Moreover, we found that LG1/2 blocked the rapid VEGFA activation of VEGFR2 at Tyr1175 in endothelial cells. In contrast, LG1/2 did not result in actin cytoskeletal disassembly in endothelial cells whereas LG3 alone did induce cytoskeletal collapse. However, LG1/2 did inhibit VEGFA-dependent endothelial migration through fibrillar collagen I. These studies provide a mechanistic understanding of how the different LG domains of endorepellin signal in endothelial cells while serving as a template for protein design of receptor tyrosine kinase antagonists.

Targeting receptor-mediated endocytotic pathways with nanoparticles: rationale and advances

Targeting of drugs and their carrier systems by using receptor-mediated endocytotic pathways was in its nascent stages 25 years ago. In the intervening years, an explosion of knowledge focused on design and synthesis of nanoparticulate delivery systems as well as elucidation of the cellular complexity of what was previously-termed receptor-mediated endocytosis has now created a situation when it has become possible to design and test the feasibility of delivery of highly specific nanoparticle drug carriers to specific cells and tissue. This review outlines the mechanisms governing the major modes of receptor-mediated endocytosis used in drug delivery and highlights recent approaches using these as targets for in vivo drug delivery of nanoparticles. The review also discusses some of the inherent complexity associated with the simple shift from a ligand-drug conjugate versus a ligand-nanoparticle conjugate, in terms of ligand valency and its relationship to the mode of receptor-mediated internalization.

Acute and impaired wound healing: pathophysiology and current methods for drug delivery, part 2: role of growth factors in normal and pathological wound healing: therapeutic potential and methods of delivery

This is the second of 2 articles that discuss the biology and pathophysiology of wound healing, reviewing the role that growth factors play in this process and describing the current methods for growth factor delivery into the wound bed.

OmpA-mediated rickettsial adherence to and invasion of human endothelial cells is dependent upon interaction with α2β1 integrin

Rickettsia conorii, a member of the spotted fever group (SFG) of the genus Rickettsia and causative agent of Mediterranean spotted fever, is an obligate intracellular pathogen capable of infecting various mammalian cell types. SFG rickettsiae express two major immunodominant surface cell antigen (Sca) proteins, OmpB (Sca5) and OmpA (Sca0). While OmpB-mediated entry has been characterized, the contribution of OmpA has not been well defined. Here we show OmpA expression in Escherichia coli is sufficient to mediate adherence to and invasion of non-phagocytic human endothelial cells. A recombinant soluble C-terminal OmpA protein domain (954-1735) with predicted structural homology to the Bordetella pertussis pertactin protein binds mammalian cells and perturbs R. conorii invasion by interacting with several mammalian proteins including β1 integrin. Using functional blocking antibodies, small interfering RNA transfection, and mouse embryonic fibroblast cell lines, we illustrate the contribution of α2β1 integrin as a mammalian ligand involved in R. conorii invasion of primary endothelial cells. We further demonstrate that OmpA-mediated attachment to mammalian cells is in part dependent on a conserved non-continuous RGD motif present in a predicted C-terminal 'pertactin' domain in OmpA.Our results demonstrate that multiple adhesin-receptor pairs are sufficient in mediating efficient bacterial invasion of R. conorii.

Hypoxia and hypoxia signaling in tissue repair and fibrosis

Following injury, vascular damage results in the loss of perfusion and consequent low oxygen tension (hypoxia) which may be exacerbated by a rapid influx of inflammatory and mesenchymal cells with high metabolic demands for oxygen. Changes in systemic and cellular oxygen concentrations induce tightly regulated response pathways that attempt to restore oxygen supply to cells and modulate cell function in hypoxic conditions. Most of these responses occur through the induction of the transcription factor hypoxia-inducible factor-1 (HIF-1) which regulates many processes needed for tissue repair during ischemia in the damaged tissue. HIF-1 transcriptionally upregulates expression of metabolic proteins (GLUT-1), adhesion proteins (integrins), soluble growth factors (TGF-β and VEGF), and extracellular matrix components (type I collagen and fibronectin), which enhance the repair process. For these reasons, HIF-1 is viewed as a positive regulator of wound healing and a potential regulator of organ repair and tissue fibrosis. Understanding the complex role of hypoxia in the loss of function in scarring tissues and biology of chronic wound, and organ repair will aid in the development of pharmaceutical agents that can redress the detrimental outcomes often seen in repair and scarring.

Therapeutic targeting of redox signaling in myofibroblast differentiation and age-related fibrotic disease

Myofibroblast activation plays a central role during normal wound healing. Whereas insufficient myofibroblast activation impairs wound healing, excessive myofibroblast activation promotes fibrosis in diverse tissues (including benign prostatic hyperplasia, BPH) leading to organ dysfunction and also promotes a stromal response that supports tumor progression. The incidence of impaired wound healing, tissue fibrosis, BPH, and certain cancers strongly increases with age. This paper summarizes findings from in vitro fibroblast-to-myofibroblast differentiation systems that serve as cellular models to study fibrogenesis of diverse tissues. Supported by substantial in vivo data, a large body of evidence indicates that myofibroblast differentiation induced by the profibrotic cytokine transforming growth factor beta is driven by a prooxidant shift in redox homeostasis due to elevated production of NADPH oxidase 4 (NOX4)-derived hydrogen peroxide and supported by concomitant decreases in nitric oxide/cGMP signaling and reactive oxygen species (ROS) scavenging enzymes. Fibroblast-to-myofibroblast differentiation can be inhibited and reversed by restoring redox homeostasis using antioxidants or NOX4 inactivation as well as enhancing nitric oxide/cGMP signaling via activation of soluble guanylyl cyclases or inhibition of phosphodiesterases. Current evidence indicates the therapeutic potential of targeting the prooxidant shift in redox homeostasis for the treatment of age-related diseases associated with myofibroblast dysregulation.

Vixapatin (VP12), a c-type lectin-protein from Vipera xantina palestinae venom: characterization as a novel anti-angiogenic compound

A C-type lectin-like protein (CTL), originally identified as VP12 and lately named Vixapatin, was isolated and characterized from Israeli viper Vipera xantina palestinae snake venom. This CTL was characterized as a selective α2β1 integrin inhibitor with anti-melanoma metastatic activity. The major aim of the present study was to prove the possibility that this protein is also a potent novel anti-angiogenic compound. Using an adhesion assay, we demonstrated that Vixapatin selectively and potently inhibited the α2 mediated adhesion of K562 over-expressing cells, with IC(50) of 3 nM. 3 nM Vixapatin blocked proliferation of human dermal microvascular endothelial cells (HDMEC); 25 nM inhibited collagen I induced migration of human fibrosarcoma HT-1080 cells; and 50 nM rat C6 glioma and human breast carcinoma MDA-MB-231 cells. 1 µM Vixapatin reduced HDMEC tube formation by 75% in a Matrigel assay. Furthermore, 1 µM Vixapatin decreased by 70% bFGF-induced physiological angiogenesis, and by 94% C6 glioma-induced pathological angiogenesis, in shell-less embryonic quail chorioallantoic membrane assay. Vixapatin's ability to inhibit all steps of the angiogenesis process suggest that it is a novel pharmacological tool for studying α2β1 integrin mediated angiogenesis and a lead compound for the development of a novel anti-angiogenic/angiostatic/anti-cancer drug.

Hydrogel macroporosity and the prolongation of transgene expression and the enhancement of angiogenesis

The utility of hydrogels for regenerative medicine can be improved through localized gene delivery to enhance their bioactivity. However, current systems typically lead to low-level transgene expression located in host tissue surrounding the implant. Herein, we investigated the inclusion of macropores into hydrogels to facilitate cell ingrowth and enhance gene delivery within the macropores in vivo. Macropores were created within PEG hydrogels by gelation around gelatin microspheres, with gelatin subsequently dissolved by incubation at 37 °C. The macropores were interconnected, as evidenced by homogeneous cell seeding in vitro and complete cell infiltration in vivo. Lentivirus loaded within hydrogels following gelation retained its activity relative to the unencapsulated control virus. In vivo, macroporous PEG demonstrated sustained, elevated levels of transgene expression for 6 weeks, while hydrogels without macropores had transient expression. Transduced cells were located throughout the macroporous structure, while non-macroporous PEG hydrogels had transduction only in the adjacent host tissue. Delivery of lentivirus encoding for VEGF increased vascularization relative to the control, with vessels throughout the macropores of the hydrogel. The inclusion of macropores within the hydrogel to enhance cell infiltration enhances transduction and influences tissue development, which has implications for multiple regenerative medicine applications.

Role of vascular endothelial growth factor (VEGF) and VEGF-R genotyping in guiding the metastatic process in pT4a resected gastric cancer patients

In radically resected gastric cancer the possibility to predict the site of relapse could be clinically relevant for the selection of post-surgical management. We previously showed that specific tumour integrins genotypes are independently associated with either peritoneal or hematogenous metastases (ITGA and ITGV). Recently VEGF and VEGF-R polymorphisms have been demonstrated to potentially affect tumour angiogenesis and the metastatic process in gastric cancer. We then investigated the role of VEGFs and VEGF-R genotyping in determining either peritoneal carcinosis or hematogenous metastases in radically resected gastric cancer patients. Tumour genotyping for integrins (ITGA and ITGV) was also performed according to our previous findings. Genotyping for VEGF-A, VEGF-C, VEGFR-1,2,3 and ITGA and ITGV was carried out on pT4a radically resected gastric tumours recurring with either peritoneal-only carcinosis or hematogenous metastases. 101 patients fulfilled the inclusion criteria: 57 with peritoneal carcinomatosis only and 44 with hematogenous spread only. At multivariate analysis, intestinal histology and the AC genotype of rs699947 (VEGFA) showed to independently correlate with hematogenous metastases (p = 0.0008 and 0.008 respectively), whereas diffuse histology and the AA genotype of rs2269772 (ITGA) independently correlated with peritoneal-only diffusion (p = <0.0001 and 0.03 respectively). Our results seem to indicate that combining information from genotyping of rs699947 (VEGFA, AC), rs2269772 (ITGA, AA) and tumour histology could allow clinicians to individuate gastric cancer at high risk for recurrence either with peritoneal or hematogenous metastases. The selection tool deriving from this analysis may allow an optimal use of the available treatment strategies in these patients.