Single and combined effects of alphavbeta3- and alpha5beta1-integrins on capillary tube formation in a human fibrinous matrix

Calcium Phosphates: A Key to Next-Generation In Vitro Bone Modeling

The replication of bone physiology under laboratory conditions is a prime target behind the development of in vitro bone models. The model should be robust enough to elicit an unbiased response when stimulated experimentally, giving reproducible outcomes. In vitro bone tissue generation majorly requires the availability of cellular components, the presence of factors promoting cellular proliferation and differentiation, efficient nutrient supply, and a supporting matrix for the cells to anchor - gaining predefined topology. Calcium phosphates (CaP) are difficult to ignore while considering the above requirements of a bone model. Therefore, the current review focuses on the role of CaP in developing an in vitro bone model addressing the prerequisites of bone tissue generation. Special emphasis is given to the physico-chemical properties of CaP that promote osteogenesis, angiogenesis and provide sufficient mechanical strength for load-bearing applications. Finally, the future course of action is discussed to ensure efficient utilization of CaP in the in vitro bone model development field.

Scaffold Chemical Model Based on Collagen-Methyl Methacrylate Graft Copolymers

Polymerization of methyl methacrylate (MMA) in aqueous collagen (Col) dispersion was studied in the presence of tributylborane (TBB) and p-quinone: 2,5-di-tert-butyl-p-benzoquinone (2,5-DTBQ), p-benzoquinone (BQ), duroquinone (DQ), and p-naphthoquinone (NQ). It was found that this system leads to the formation of a grafted cross-linked copolymer. The inhibitory effect of p-quinone determines the amount of unreacted monomer, homopolymer, and percentage of grafted poly(methyl methacrylate) (PMMA). The synthesis combines two approaches to form a grafted copolymer with a cross-linked structure-"grafting to" and "grafting from". The resulting products exhibit biodegradation under the action of enzymes, do not have toxicity, and demonstrate a stimulating effect on cell growth. At the same time, the denaturation of collagen occurring at elevated temperatures does not impair the characteristics of copolymers. These results allow us to present the research as a scaffold chemical model. Comparison of the properties of the obtained copolymers helps to determine the optimal method for the synthesis of scaffold precursors-synthesis of a collagen and poly(methyl methacrylate) copolymer at 60 °C in a 1% acetic acid dispersion of fish collagen with a mass ratio of the components collagen:MMA:TBB:2,5-DTBQ equal to 1:1:0.015:0.25.

PAX5/ITGAX Contributed to the Progression of Atherosclerosis by Regulation of B Differentiation via TNF-α Signaling Pathway

To investigate the effect of paired box protein 5 (PAX5)/integrin subunit alpha X (ITGAX) in atherosclerosis (AS). AS model was established using ApoE-/- mice (C57BL/6). Human vascular smooth muscle cells (HVSMCs) were stimulated with ox-LDL. Quantitative reverse transcription polymerase chain reaction and Western blotting were used to detect the expression levels of genes and proteins. Reporter constructs and luciferase assays were used to investigate the role of ITGAX and PAX5. Cells proliferation and inflammation factors were detected. The results presented that aortic plaque area, lipid content, serum triglyceride, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol levels were significantly increased in the high-fat diet group (p < 0.05). ITGAX was upregulated in atherosclerotic tissues. In addition, ox-LDL treatment induced HVSMCs proliferation, migration, and invasion. Reporter constructs and luciferase assays indicated ITGAX interaction with PAX5. Furthermore, siITGAX and siPAX5 cotransfection restored the rate of HVSMCs in G1 and S and G2/M phases, decreased the content of tumor necrosis factor-alpha (TNF-ɑ), interleukin (IL)-6, and IL-8 (p < 0.05). Interestingly, siITGAX and siPAX5 cotransfection also decreased the expression levels of TNF-α, TNF-R1, TNF-R2, CD19, and CD86 (p < 0.05). Our results suggest that ITGAX may be a potential therapeutic target for AS.

Dysregulation of integrin αvβ3 and α5β1 impedes migration of placental endothelial cells in fetal growth restriction

Placentas from pregnancies complicated by severe early-onset fetal growth restriction (FGR) exhibit diminished vascular development mediated by impaired angiogenesis, but underlying mechanisms remain unknown. In this study, we show that FGR endothelial cells demonstrate inherently reduced migratory capacity despite the presence of fibronectin, a matrix protein abundant in placental stroma that displays abnormal organization in FGR placentas. Thus, we hypothesized that aberrant endothelial-fibronectin interactions in FGR are a key mechanism underlying impaired FGR endothelial migration. Using human fetoplacental endothelial cells isolated from uncomplicated term control and FGR pregnancies, we assessed integrin α5β1 and αvβ3 regulation during cell migration. We show that endothelial integrin α5β1 and αvβ3 interactions with fibronectin are required for migration and that FGR endothelial cells responded differentially to integrin inhibition, indicating integrin dysregulation in FGR. Whole-cell expression was not different between groups. However, there were significantly more integrins in focal adhesions and reduced intracellular trafficking in FGR. These newly identified changes in FGR endothelial cellular processes represent previously unidentified mechanisms contributing to persistent angiogenic deficiencies in FGR.

Biofabrication of vasculature in microphysiological models of bone

Bone contains a dense network of blood vessels that are essential to its homoeostasis, endocrine function, mineral metabolism and regenerative functions. In addition, bone vasculature is implicated in a number of prominent skeletal diseases, and bone has high affinity for metastatic cancers. Despite vasculature being an integral part of bone physiology and pathophysiology, it is often ignored or oversimplified inin vitrobone models. However, 3D physiologically relevant vasculature can now be engineeredin vitro, with microphysiological systems (MPS) increasingly being used as platforms for engineering this physiologically relevant vasculature. In recent years, vascularised models of bone in MPSs systems have been reported in the literature, representing the beginning of a possible technological step change in how bone is modelledin vitro. Vascularised bone MPSs is a subfield of bone research in its nascency, however given the impact of MPSs has had inin vitroorgan modelling, and the crucial role of vasculature to bone physiology, these systems stand to have a substantial impact on bone research. However, engineering vasculature within the specific design restraints of the bone niche is significantly challenging given the different requirements for engineering bone and vasculature. With this in mind, this paper aims to serve as technical guidance for the biofabrication of vascularised bone tissue within MPS devices. We first discuss the key engineering and biological considerations for engineering more physiologically relevant vasculaturein vitrowithin the specific design constraints of the bone niche. We next explore emerging applications of vascularised bone MPSs, and conclude with a discussion on the current status of vascularised bone MPS biofabrication and suggest directions for development of next generation vascularised bone MPSs.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

Dermal mesenchymal stem cells promoted adhesion and migration of endothelial cells by integrin in psoriasis

The unusual dilatation of dermal capillaries and angiogenesis played important roles in psoriasis. Some genes and proteins of dermal mesenchymal stem cells (DMSCs) from psoriasis are abnormal and related to the function of endothelial cells (ECs). The present study was aimed to evaluate whether psoriatic DMSCs could affect adhesion and migration of ECs through neovascularization-related integrins in psoriasis. Human DMSCs, collected from psoriasis lesions and healthy skin, respectively, were cocultured with human umbilical vein endothelial cells (HUVECs). The expression levels of three integrins, that is, αvβ3, αvβ5, and α5β1 in HUVECs were tested by quantitative real-time polymerase chain reaction and Western blot analysis. The adhesion and migration of HUVECs were detected by adhesion assay and migration assay. The results showed that in psoriasis group, the expression of αVβ3 and α5β1 of HUVECs markedly increased 2.50- and 3.71-fold in messenger RNA levels, and significantly increased 1.63- and 1.92-fold in protein levels, comparing to healthy control group (all p < .05). But β5 was not significantly different between the two groups (p > .05). In addition, compared with control, psoriatic DMSCs promoted HUVECs adhesion by 1.62-fold and migration by 2.91-fold (all p < .05). In conclusion, psoriatic DMSCs impact HUVECs adhesion and migration by upregulating the expression of integrins αVβ3 and α5β1.

Biopolymer Hydrogel Scaffold as an Artificial Cell Niche for Mesenchymal Stem Cells

The activity of stem cell processes is regulated by internal and external signals of the cell "niche". In general, the niche of stem cells can be represented as the microenvironment of the cells, providing a signal complex, determining the properties of the cells. At the same time, the "niche" concept implies feedback. Cells can modify their microenvironment, supporting homeostasis or remodeling the composition and structure of the extracellular matrix. To ensure the regenerative potential of tissue engineering products the "niche" concept should be taken into account. To investigate interactions in an experimental niche, an original hydrogel biopolymer scaffold with encapsulated mesenchymal adipose-derived stem cells (ASCs) was used in this study. The scaffold provides for cell adhesion, active cell growth, and proliferative activity. Cells cultured within a scaffold are distinguished by the presence of a developed cytoskeleton and they form a cellular network. ASCs cultured within a scaffold change their microenvironment by secreting VEGF-A and remodeling the scaffold structure. Scaffold biodegradation processes were evaluated after previous culturing of the ASCs in the scaffolds for periods of either 24 h or six days. The revealed differences confirmed that changes had occurred in the properties of scaffolds remodeled by cells during cultivation. The mechanisms of the identified changes and the possibility of considering the presented scaffold as an appropriate artificial niche for ASCs are discussed.

Enzymatic Hydrolysis of Marine Collagen and Fibrinogen Proteins in the Presence of Thrombin

: Enzymatic hydrolysis of native collagen and fibrinogen was carried out under comparable conditions at room temperature. The molecular weight parameters of proteins before and after hydrolysis by thrombin were monitored by gel-penetrating chromatography (GPC). An analysis of the experiment results shows that the molecular weight parameters of the initial fibrinogen (Fn) and cod collagen (CC) are very similar. High molecular CC decays within the first minute, forming two low molecular fractions. The main part (~80%) falls on the fraction with a value of Mw less than 10 kDa. The initial high molecular fraction of Fn with Mw ~320-340 kDa is not completely hydrolyzed even after three days of control. The presence of low molecular fractions with Mw ~17 and Mw ~10 kDa in the solution slightly increases within an hour and noticeably increases for three days. The destruction of macromolecules of high molecular collagen to hydrolysis products appears almost completely within the first minute mainly to the polymer with Mw ~10 kDa, and enzymatic hydrolysis of fibrinogen proceeds slower than that of collagen, but also mainly to the polymer with Mw ~10 kDa. Comparative photos of the surfaces of native collagen, fibrinogen and the scaffold based on them were obtained.

Hydrogel scaffolds based on blood plasma cryoprecipitate and collagen derived from various sources: Structural, mechanical and biological characteristics

At present there is a growing need for tissue engineering products, including the products of scaffold-technologies. Biopolymer hydrogel scaffolds have a number of advantages and are increasingly being used to provide means of cell transfer for therapeutic treatments and for inducing tissue regeneration. This work presents original hydrogel biopolymer scaffolds based on a blood plasma cryoprecipitate and collagen and formed under conditions of enzymatic hydrolysis. Two differently originated collagens were used for the scaffold formation. During this work the structural and mechanical characteristics of the scaffold were studied. It was found that, depending on the origin of collagen, scaffolds possess differences in their structural and mechanical characteristics. Both types of hydrogel scaffolds have good biocompatibility and provide conditions that maintain the three-dimensional growth of adipose tissue stem cells. Hence, scaffolds based on such a blood plasma cryoprecipitate and collagen have good prospects as cell carriers and can be widely used in regenerative medicine.

Integrin alpha x stimulates cancer angiogenesis through PI3K/Akt signaling-mediated VEGFR2/VEGF-A overexpression in blood vessel endothelial cells

Integrin alpha x (ITGAX), a member of the integrin family, usually serves as a receptor of the extracellular matrix. Recently, accumulating evidence suggests that ITGAX may be involved in angiogenesis in dendritic cells. Herein, we report a direct role of ITGAX in angiogenesis during tumor development. Overexpression of ITGAX in human umbilical vein endothelial cells (HUVECs) enhanced their proliferation, migration, and tube formation and promoted xenograft ovarian tumor angiogenesis and growth. Further study showed that overexpression of ITGAX activated the PI3k/Akt pathway, leading to the enhanced expression of c-Myc, vascular endothelial growth factor-A (VEGF-A), and VEGF receptor 2 (VEGFR2), whereas, the treatment of cells with PI3K inhibitor diminished these effects. Besides, c-Myc was observed to bind to the VEGF-A promoter. By Co-Immunoprecipitation (Co-IP) assay, we manifested the interaction between ITGAX and VEGFR2 or the phosphorylated VEGFR2. Immunostaining of human ovarian cancer specimens suggested that endothelial cells of micro-blood vessels displayed strong expression of VEGF-A, c-Myc, VEGFR2, and the PI3K signaling molecules. Also, overexpression of ITGAX in HUVECs could stimulate the spheroid formation of ovarian cancer cells. Our study uncovered that ITGAX stimulates angiogenesis through the PI3K/Akt signaling-mediated VEGFR2/VEGF-A overexpression during cancer development.

Comparative in vitro/theoretical studies on the anti-angiogenic activity of date pollen hydro-alcoholic extract: Highlighting the important roles of its hot polyphenols

Introduction: Date palm pollen (DPP) is the male reproductive soft powder from date flowers widely used as the valuable dietary supplement to fortify the size of testis and ovarian to increase the power of sex. This part of date palm significantly exhibited anti-diabetic, anti-inflammation and protective effects against male and female infertility. Though the anticancer activity of date fruits was previously reported, the DPP anti-angiogenic effects were not reported, and as the first study, its inhibitory effects were examined in the current study.

Methods: The DPP soft powder was collected to prepare its hydro-alcoholic extract to examine its anti-angiogenic activity in an in vitro model. At different concentrations, the cytotoxicity of the prepared extract was examined on human umbilical vein endothelial cells (HUVECs) using lactate dehydrogenase method. Cell proliferation was determined using the MTT assay and cytodex-3D model in collagen gel was used to assay its possible anti-angiogenic activity. The expression of VEGF, MMP-2 and MMP-9 genes was measured using real-time polymerase chain reaction (PCR). Finally, molecular docking simulation was used to highlight the possible role of DPP polyphenols to interact with the associated receptors.

Results: The prepared hydro-alcoholic extract exhibited significant anti-angiogenic activity in a dose-dependent manner and decreased the endothelial cell proliferation. The calculated IC₅₀ value for the examined extract in angiogenesis model was 260 µg·mL, respectively. Also, the expression of VEGF, MMP-2 and MMP-9 genes were significantly decreased. Docking simulation results unveiled that the isolated DPP polyphenols have the affinity to interact with ctDNA, VEGF and its receptors.

Conclusion: The DPP is the new source of non-toxic anti-cancer agents to use as a dietary supplement in the pre-treatment of cancer.

Mechanoreciprocity in cell migration

Cell migration is an adaptive process that depends on and responds to physical and molecular triggers. Moving cells sense and respond to tissue mechanics and induce transient or permanent tissue modifications, including extracellular matrix stiffening, compression and deformation, protein unfolding, proteolytic remodelling and jamming transitions. Here we discuss how the bi-directional relationship of cell-tissue interactions (mechanoreciprocity) allows cells to change position and contributes to single-cell and collective movement, structural and molecular tissue organization, and cell fate decisions.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Beyond adhesion: emerging roles for integrins in control of the tumor microenvironment

While integrins were originally discovered as cell adhesion receptors, recent studies have reinforced the concept that integrins have central roles in cancer that extend far beyond controlling cell adhesion and migration. Indeed, as transmembrane cell surface receptors that occupy a critical position at the interface of cellular and extracellular interactions and are capable of both "inside-out" and "outside-in" signaling, integrins are uniquely poised to regulate the cell's ability to promote, sense, and react to changes in the tumor microenvironment. Moreover, integrins are present on all cell types in the tumor microenvironment, and they have important roles in regulating intercellular communication. Decades of promising pre-clinical studies have implicated certain integrins as attractive therapeutic targets in the cancer clinic. Nevertheless, results of the few clinical trials that target integrins in cancer have thus far been disappointing. Importantly, these clinical failures likely reflect the emerging complexity of individual and combinatorial integrin function within both tumor cells and other cell types of the tumor microenvironment, together with a need to explore integrin-targeting agents not just as monotherapies but also as adjuvants to more conventional radiotherapies or chemotherapies. In this review, we will examine recent advances toward understanding how integrins regulate cancer progression, including their roles in intercellular communication and modulation of the tumor microenvironment. Additionally, we will discuss factors that underlie the limited efficacy of current efforts to target integrins in the cancer clinic as well as potential strategies to overcome these challenges.

Transformed MDCK cells secrete elevated MMP1 that generates LAMA5 fragments promoting endothelial cell angiogenesis

Epithelial-mesenchymal transition (EMT) enhances the migration and invasion of cancer cells, and is regulated by various molecular mechanisms including extracellular matrix metalloproteinase (MMP) activity. Previously, we reported transformation of epithelial Madin-Darby canine kidney (MDCK) cells with oncogenic H-Ras (21D1 cells) induces EMT, and significantly elevates MMP1 expression. To explore the biological significance, in this study we characterized 21D1 cells with knocked-down MMP1 expression (21D1^−MMP1). MMP1 silencing diminished 21D1 cell migration, invasion and anchorage-independent growth in vitro. Additionally, 21D1^−MMP1 cells displayed reduced tumour volume when grown as in vivo subcutaneous xenografts in mice. Depletion of MMP1 lowered the ability of the cellular secretome (extracellular culture medium) to influence recipient cell behaviour. For example, supplementation with 21D1 secretome elevated cell migration of recipient fibroblasts, and enhanced endothelial cell angiogenesis (vessel length and branching). By contrast, 21D1^−MMP1 secretome was less potent in both functional assays. We reveal laminin subunit alpha-5 (LAMA5) as a novel biological substrate of MMP1, that generates internal and C-terminal proteolytic fragments in 21D1 secretome. Furthermore, antibody-based inhibition of integrin αvβ3 on endothelial cells nullified the angiogenic capability of 21D1 secretome. Therefore, we report this as a new VEGF-independent mechanism that oncogenic cells may employ to promote tumour angiogenesis.

IFN-β affects the angiogenic potential of circulating angiogenic cells by activating calpain 1

Circulating angiogenic cells (CACs) are monocyte-derived cells with endothelial characteristics, which contribute to both angiogenesis and arteriogenesis in a paracrine way. Interferon-β (IFN-β) is known to inhibit these divergent processes in animals and patients. We hypothesized that IFN-β might act by affecting the differentiation and function of CACs. CACs were cultured from peripheral blood mononuclear cells and phenotypically characterized by surface expression of monocytic and endothelial markers. IFN-β significantly reduced the number of CACs by 18–64%. Apoptosis was not induced by IFN-β, neither in mononuclear cells during differentiation, nor after maturation to CACs. Rather, IFN-β impaired adhesion to, and spreading on, fibronectin, which was dependent on α5β1 (VLA-5)-integrin. IFN-β affected the function of VLA-5 in mature CACs, leading to rounding and detachment of cells, by induction of calpain 1 activity. Cell rounding and detachment was completely reversed by inhibition of calpain 1 activity in mature CACs. During in vitro capillary formation, CAC addition and calpain 1 inhibition enhanced sprouting of endothelial cells to a comparable extent, but were not sufficient to rescue tube formation in the presence of IFN-β. We show that the IFN-β-induced reduction of the numbers of in vitro differentiated CACs is based on activation of calpain 1, resulting in an attenuated adhesion to extracellular matrix proteins via VLA-5. In vivo, this could lead to inhibition of vessel formation due to reduction of the locally recruited CAC numbers and their paracrine angiogenic factors.

Fibrin-based 3D matrices induce angiogenic behavior of adipose-derived stem cells

Engineered three-dimensional biomaterials are known to affect the regenerative capacity of stem cells. The extent to which these materials can modify cellular activities is still poorly understood, particularly for adipose-derived stem cells (ASCs). This study evaluates PEGylated fibrin (P-fibrin) gels as an ASC-carrying scaffold for encouraging local angiogenesis by comparing with two commonly used hydrogels (i.e., collagen and fibrin) in the tissue-engineering field. Human ASCs in P-fibrin were compared to cultures in collagen and fibrin under basic growth media without any additional soluble factors. ASCs proliferated similarly in all gel scaffolds but showed significantly elongated morphologies in the P-fibrin gels relative to other gels. P-fibrin elicited higher von Willebrand factor expression in ASCs than either collagen or fibrin while cells in collagen expressed more smooth muscle alpha actin than in other gels. VEGF was secreted more at 7 days in fibrin and P-fibrin than in collagen and several other angiogenic and immunomodulatory cytokines were similarly enhanced. Fibrin-based matrices appear to activate angiogenic signaling in ASCs while P-fibrin matrices are uniquely able to also drive a vessel-like ASC phenotype. Collectively, these results suggest that P-fibrin promotes the angiogenic potential of ASC-based therapeutic applications.

Strategies to inhibit tumor associated integrin receptors: rationale for dual and multi-antagonists

The integrins are a family of 24 heterodimeric transmembrane cell surface receptors. Involvement in cell attachment to the extracellular matrix, motility, and proliferation identifies integrins as therapeutic targets in cancer and associated conditions: thrombosis, angiogenesis, and osteoporosis. The most reported strategy for drug development is synthesis of an agent that is highly selective for a single integrin receptor. However, the ability of cancer cells to change their integrin repertoire in response to drug treatment renders this approach vulnerable to the development of resistance and paradoxical promotion of tumor growth. Here, we review progress toward development of antagonists targeting two or more members of the Arg-Gly-Asp (RGD) binding integrins, notably αvβ3, αvβ5, αvβ6, αvβ8, α5β1, and αIIbβ3, as anticancer therapeutics.

In Vitro Microvessel Growth and Remodeling within a Three-dimensional Microfluidic Environment

This paper presents in vitro microvascular network formation within 3D gel scaffolds made from different concentrations of type-I collagen, fibrin, or a mixture of collagen and fibrin, using a simple microfluidic platform. Initially, microvascular network formation of human umbilical vein endothelial cells was examined using live time-lapse confocal microscopy every 90 min from 3 h to 12 h after seeding within three different concentrations of collagen gel scaffolds. Among the three conditions of collagen gel scaffolds (2.0 mg/ml, 2.5 mg/ml, and 3.0 mg/ml), the number of skeleton within collagen gel scaffolds was consistently the highest (3.0 mg/ml), followed by those of collagen gel scaffolds (2.5 mg/ml and 2.0 mg/ml). Results demonstrated that concentration of collagen gel scaffolds, which influences matrix stiffness and ligand density, may affect microvascular network formation during the early stages of vasculogenesis. In addition, the maturation of microvascular networks in monoculture under different gel compositions within gel scaffolds (2.5 mg/ml) was examined for 7 d using live confocal microscopy. It was confirmed that pure fibrin gel scaffolds are preferable to collagen gel or collagen/fibrin combinations, significantly reducing matrix retractions during maturation of microvascular networks for 7 d. Finally, early steps in the maturation process of microvascular networks for 14 d were characterized by demonstrating sequential steps of branching, expanding, remodeling, pruning, and clear delineation of lumens within fibrin gel scaffolds. Our findings demonstrate an in vitro model for generating mature microvascular networks within 3D microfluidic fibrin gel scaffolds (2.5 mg/ml), and furthermore suggest the importance of gel concentration and composition in promoting the maturation of microvascular networks.

A practical synthesis of [(18) F]FtRGD: an angiogenesis biomarker for PET

Integrins have become increasingly attractive targets for molecular imaging of angiogenesis with positron emission tomography or single-photon emission computed tomography, but the reliable production of radiopharmaceuticals remains challenging. A strategy for chemoselective labeling of the integrin ligand-c(RGDyK) peptide-has been developed on the basis of the Cu(I)-catalyzed conjugation reaction. Recently, we reported a nucleophilic detagging and fluorous solid-phase extraction method providing an easy way to implement an approach for obtaining 2-[(18) F]fluoroethyl azide. In this work, we report the practical use of this method for the preparation of the 2-[(18) F]fluoroethyl-triazolyl conjugated c(RGDyK) peptide: [(18) F]FtRGD. The two-step, two-pot synthesis, HPLC purification, and reformulation could be readily performed with a standard nucleophilic radiofluorination synthesizer (GE TRACERlab FXFN ), with minimal modifications. [(18) F]FtRGD was obtained in a solution for injection (>500 MBq/mL) in 10-30% nondecay-corrected radiochemical yield, excellent radiochemical purity (>98%), and 28 ± 13 GBq/µmol specific activity. [(18) F]FtRGD (Ki  = 54 ± 14 nM for αV β3 and 1.7 ± 0.2 nM for αV β5 ) was evaluated in mice and showed good stability in vivo, good tumor-to-background ratio (1.6 ± 0.3 %ID/g at 1.5 h post-injection in U87-MG tumors), and rapid urinary excretion. Therefore, [(18) F]FtRGD proved valuable for preclinical positron emission tomography imaging of integrin expression.

RGD-Binding Integrins in Prostate Cancer: Expression Patterns and Therapeutic Prospects against Bone Metastasis

Prostate cancer is the third leading cause of male cancer deaths in the developed world. The current lack of highly specific detection methods and efficient therapeutic agents for advanced disease have been identified as problems requiring further research. The integrins play a vital role in the cross-talk between the cell and extracellular matrix, enhancing the growth, migration, invasion and metastasis of cancer cells. Progression and metastasis of prostate adenocarcinoma is strongly associated with changes in integrin expression, notably abnormal expression and activation of the β₃ integrins in tumour cells, which promotes haematogenous spread and tumour growth in bone. As such, influencing integrin cell expression and function using targeted therapeutics represents a potential treatment for bone metastasis, the most common and debilitating complication of advanced prostate cancer. In this review, we highlight the multiple ways in which RGD-binding integrins contribute to prostate cancer progression and metastasis, and identify the rationale for development of multi-integrin antagonists targeting the RGD-binding subfamily as molecularly targeted agents for its treatment.

Opticin exerts its anti-angiogenic activity by regulating extracellular matrix adhesiveness

Opticin is an extracellular matrix glycoprotein that we identified associated with the collagen network of the vitreous humor of the eye. Recently, we discovered that opticin possesses anti-angiogenic activity using a murine oxygen-induced retinopathy model: here, we investigate the underlying mechanism. Using an ex vivo chick chorioallantoic membrane assay, we show that opticin inhibits angiogenesis when stimulated by a range of growth factors. We show that it suppresses capillary morphogenesis, inhibits endothelial invasion, and promotes capillary network regression in three-dimensional matrices of collagen and Matrigel(TM). We then show that opticin binds to collagen and thereby competitively inhibits endothelial cell interactions with collagen via α(1)β(1) and α(2)β(1) integrins, thereby preventing the strong adhesion that is required for proangiogenic signaling via these integrins.

Semaphorin 5A, an axon guidance molecule, enhances the invasion and metastasis of human gastric cancer through activation of MMP9

Semaphorin 5A, a member of semaphorin family, was originally identified as axonal guidance factor functioning during neuronal development. Previously, we showed that the expression of semaphorin 5A might contribute to the metastasis of gastric cancer. However, its functional roles and mechanism(s) in invasion and metastasis of gastric cancer remain unclear. By using human gastric caner cell lines Parental SGC7901, SGC7901-siScrambled and SGC7901-siSema 5A, we found that semaphorin 5A significantly promoted the invasive and metastatic abilities of gastric cancer cell in vitro. Semaphorin 5A increased the expression of MMP9 by activating phosphorylated ErK1/2 in gastric cancer cell. Furthermore, MEK inhibitor PD98059 and MMP9 antibody (Ab) significantly inhibited in vitro invasive and metastatic abilities induced by semaphorin 5A. Taken together, the present work revealed a novel function of semaphorin 5A that the existence of semaphorin 5A could promote invasion and metastasis of gastric cancer by regulating MMP9 expression, at least partially, via the MEK/ERKs signal transduction pathway. Semaphorin 5A and its regulated molecules could be the potential targets for cancer therapy.

¹²⁵I-radiolabeled morpholine-containing arginine-glycine-aspartate (RGD) ligand of αvβ₃ integrin as a molecular imaging probe for angiogenesis

In this paper, using a hybrid small-animal Micro SPECT/CT imaging system, we report that a new (125)I-Cilengitide-like RGD-cyclopentapeptide, containing d-morpholine-3-carboxylic acid, interacts in vivo with α(v)β(3) integrin expressed by melanoma cells. Images clearly show that the (125)I-compound has the capacity to monitor the growth of a melanoma xenograft. Indeed, retention of the labeled ligand in the tumor mass has a good tumor/background ratio, and a significant reduction of its uptake was observed after injection of unlabeled ligand. These results suggest that the use of (125)I-labeled morpholine-based RGD-cyclopentapeptides targeting α(v)β(3) positive tumors may play a role in future therapeutic strategies.

RAM, an RGDS analog, exerts potent anti-melanoma effects in vitro and in vivo

Peptides containing the RGD sequence are under continuous investigation given their ability to control cell adhesion and apoptosis. Since small peptides are quickly metabolized and degraded in vivo, developing analogs resistant to serum-induced degradation is a challenging task. RGD analogs developed so far are known as molecules mostly inhibiting cell adhesion; this feature may reduce cell proliferation and tumor development but may not induce regression of tumors or metastases already formed. In the current study, carried out in melanoma in vitro and in vivo models, we show that RAM, an RGD-non-peptide Analog-Molecule, strongly inhibits cells adhesion onto plastic, vitronectin, fibronectin, laminin and von Willebrand Factor while it does not inhibit cell adhesion onto collagen IV, similarly to the RGDS template peptide. It also strongly inhibits in vitro cell proliferation, migration and DNA-synthesis, increases melanoma cells apoptosis and reduces survivin expression. All such effects were observed in collagen IV seeded cells, therefore are most likely independent from the anti adhesive properties. Further, RAM is more stable than the template RGDS; in fact it maintains its anti-proliferation and anti-adhesion effects after long serum exposure while RGDS almost completely loses its effects upon serum exposure. In a mouse metastatic melanoma in vivo model, increasing doses of RAM significantly reduce up to about 80% lung metastases development, while comparable doses of RGDS are less potent. In conclusion these data show that RAM is a potent inhibitor of melanoma growth in vitro, strongly reduces melanoma metastases development in vivo and represents a novel candidate for further in vivo investigations in the cancer treatment field.

Fibronectin-hyaluronic acid composite hydrogels for three-dimensional endothelial cell culture

Biomaterials that actively promote both wound healing and angiogenesis are of critical importance for many biomedical applications, including tissue engineering. In particular, hyaluronic acid (HA) is an important player that has multiple roles throughout the angiogenic process in the body. Previously, our laboratory has developed photocrosslinkable HA-based scaffolds that promote angiogenesis when implanted in vivo. This paper reports the incorporation of a photocrosslinkable fibronectin (FN) conjugate into three-dimensional (3-D) HA hydrogel networks to enhance endothelial cell adhesion and angiogenesis. The results demonstrate significantly better retention of FN that was photocrosslinked within HA hydrogels compared to FN that was physically adsorbed within HA hydrogels. Increased viability of endothelial cells cultured in 3-D HA hydrogels with photoimmobilized FN, compared to adsorbed FN, was also observed. Endothelial cells were cultured within hydrogels for up to 6 days, a period over which cell proliferation, migration and an angiogenic phenotype were influenced by varying the concentration of incorporated FN. The results demonstrate the potential of these composite hydrogels as biomaterial scaffolds capable of promoting wound healing and angiogenesis.

Role of fibrin structure in thrombosis and vascular disease

Fibrin clot formation is a key event in the development of thrombotic disease and is the final step in a multifactor coagulation cascade. Fibrinogen is a large glycoprotein that forms the basis of a fibrin clot. Each fibrinogen molecule is comprised of two sets of Aα, Bβ, and γ polypeptide chains that form a protein containing two distal D regions connected to a central E region by a coiled-coil segment. Fibrin is produced upon cleavage of the fibrinopeptides by thrombin, which can then form double-stranded half staggered oligomers that lengthen into protofibrils. The protofibrils then aggregate and branch, yielding a three-dimensional clot network. Factor XIII, a transglutaminase, cross-links the fibrin stabilizing the clot protecting it from mechanical stress and proteolytic attack. The mechanical properties of the fibrin clot are essential for its function as it must prevent bleeding but still allow the penetration of cells. This viscoelastic property is generated at the level of each individual fiber up to the complete clot. Fibrinolysis is the mechanism of clot removal, and involves a cascade of interacting zymogens and enzymes that act in concert with clot formation to maintain blood flow. Clots vary significantly in structure between individuals due to both genetic and environmental factors and this has an effect on clot stability and susceptibility to lysis. There is increasing evidence that clot structure is a determinant for the development of disease and this review will discuss the determinants for clot structure and the association with thrombosis and vascular disease.

Molecular weight fibrinogen variants alter gene expression and functional characteristics of human endothelial cells

BACKGROUND

Fibrin is a temporary matrix that not only seals a wound, but also provides a temporary matrix structure for invading cells during wound healing. Two naturally occurring fibrinogen variants, high molecular weight (HMW) and low molecular weight (LMW) fibrinogen, display different properties in supporting angiogenesis in vivo and in vitro.

OBJECTIVES

This study was aimed at investigating the functional characteristics and molecular mechanisms of human microvascular endothelial cells (HMVECs) cultured on HMW and LMW fibrin matrices.

METHODS AND RESULTS

HMVECs on HMW fibrin matrices showed increased proliferation and tube formation as compared with their counterparts on unfractionated and LMW fibrin. Degradation of HMW fibrin was markedly enhanced by the presence of HMVECs, that of LMW fibrin was enhanced only slightly. However, the expression levels of fibrinolysis-regulating proteins and integrins were similar. Subsequent microarray analysis revealed that the expression of 377 genes differed significantly between HMVECs cultured on HMW fibrin and those cultured on LMW fibrin. Among these genes, UNC5B, DLL4 and the DLL4-Notch downstream targets Hey1, Hey2 and Hes1 showed increased expression in HMVECs on LMW fibrin. However, pharmacologic and genetic (DLL4 small interfering RNA) inhibition of DLL4-Notch signaling blunted rather than enhanced proliferation and tube formation by HMVECs on both fibrin variants.

CONCLUSIONS

Heterogeneity in naturally occurring fibrinogen strongly influences endothelial cell proliferation and tube formation, and causes alterations in gene expression, including that of DLL4-Notch. The higher fibrinolytic sensitivity of HMW fibrin in the presence of HMVECs contributes to increased tube formation. Although the expression of DLL4-Notch was altered, it did not explain the enhanced tube formation in HMW fibrin. This study provides new perspectives for biological and tissue engineering applications.

Integrins as therapeutic targets: lessons and opportunities

The integrins are a large family of cell adhesion molecules that are essential for the regulation of cell growth and function. The identification of key roles for integrins in a diverse range of diseases, including cancer, infection, thrombosis and autoimmune disorders, has revealed their substantial potential as therapeutic targets. However, so far, pharmacological inhibitors for only three integrins have received marketing approval. This article discusses the structure and function of integrins, their roles in disease and the chequered history of the approved integrin antagonists. Recent advances in the understanding of integrin function, ligand interaction and signalling pathways suggest novel strategies for inhibiting integrin function that could help harness their full potential as therapeutic targets.

Stromal cells and integrins: conforming to the needs of the tumor microenvironment

The microenvironment of a tumor is constituted of a heterogenous population of stromal cells, extracellular matrix components, and secreted factors, all of which make the tumor microenvironment distinct from that of normal tissue. Unlike healthy cells, tumor cells require these unique surroundings to metastasize, spread, and form a secondary tumor at a distant site. In this review, we discuss that stromal cells such as fibroblasts and immune cells including macrophages, their secreted factors, such as vascular endothelial growth factor, transforming growth factor beta, and various chemokines, and the integrins that connect the various cell types play a particularly vital role in the survival of a growing tumor mass. Macrophages and fibroblasts are uniquely plastic cells because they are not only able to switch from tumor suppressing to tumor supporting phenotypes but also able to adopt various tumor-supporting functions based on their location within the microenvironment. Integrins serve as the backbone for all of these prometastatic operations because their function as cell-cell and cell-matrix signal transducers are important for the heterogenous components of the microenvironment to communicate.