Alphastatin, a 24-amino acid fragment of human fibrinogen, is a potent new inhibitor of activated endothelial cells in vitro and in vivo

Fibrinogen and tumors

Elevated plasma fibrinogen (Fg) levels consistently correlate with an unfavorable prognosis in various tumor patient cohorts. Within the tumor microenvironment, aberrant deposition and expression of Fg have been consistently observed, interacting with multiple cellular receptors and thereby accentuating its role as a regulator of inflammatory processes. Specifically, Fg serves to stimulate and recruit immune cells and pro-inflammatory cytokines, thereby contributing to the promotion of tumor progression. Additionally, Fg and its fragments exhibit dichotomous effects on tumor angiogenesis. Notably, Fg also facilitates tumor migration through both platelet-dependent and platelet-independent mechanisms. Recent studies have illuminated several tumor-related signaling pathways influenced by Fg. This review provides a comprehensive summary of the intricate involvement of Fg in tumor biology, elucidating its multifaceted role and the underlying mechanisms.

The Role of Fibrin(ogen) in Wound Healing and Infection Control

Fibrinogen, one of the most abundant plasma proteins playing a key role in hemostasis, is an important modulator of wound healing and host defense against microbes. In the current review, we address the role of fibrin(ogen) throughout the process of wound healing and subsequent tissue repair. Initially fibrin(ogen) acts as a provisional matrix supporting incoming leukocytes and acting as reservoir for growth factors. It later goes on to support re-epithelialization, angiogenesis, and fibroplasia. Importantly, removal of fibrin(ogen) from the wound is essential for wound healing to progress. We also discuss how fibrin(ogen) functions through several mechanisms to protect the host against bacterial infection by providing a physical barrier, entrapment of bacteria in fibrin(ogen) networks, and by directing immune cell function. The central role of fibrin(ogen) in defense against bacterial infection has made it a target of bacterial proteins, evolved to interact with fibrin(ogen) to manipulate clot formation and degradation for the purpose of promoting microbial virulence and survival. Further understanding of the dual roles of fibrin(ogen) in wound healing and infection could provide novel means of therapy to improve recovery from surgical or chronic wounds and help to prevent infection from highly virulent bacterial strains, including those resistant to antibiotics.

Alphastatin-Loaded Chitosan Nanoparticle Preparation and Its Antiangiogenic Effect on Lung Carcinoma

Alphastatin is a 24-amino acid peptide and can suppress tumor angiogenesis by inhibiting both the migration and tubule formation of vascular endothelial cells. However, the anticancer effect of Alphastatin is limited due to the short half-life and degradation in the body. In this study, Alphastatin-loaded chitosan nanoparticles (AsCs NPs) were prepared with an initial concentration of 2 mg/ml for chitosan and 1 mg/ml for Alphastatin. AsCs NPs presented the encapsulation efficiency of 32.4%, the mean particle size of 387.4 nm, the polydispersity index of 0.223, and the zeta potential of +28.1 mV. AsCs NPs have a sustained release for 6 days and were stable in serum for at least 24 hours. And the NPs could preserve the integrity of encapsulated Alphastatin and released Alphastatin for 24 hours. In a subcutaneous LA975 lung carcinoma xenograft T739 mouse model, AsCs NPs significantly inhibited the tumor growth, tumor volume, and microvessel density (MVD), and the antitumor effect was even stronger than that of Alphastatin. In addition, the VEGF-induced tube formation of HUVEC could be inhibited by AsCs NPs in vitro and the serum containing AsCs NPs, and the protein level of SphK1 in HUVEC was also decreased by AsCs NPs, suggesting an inhibitory effect of AsCs NPs on the SphK1-S1P signaling pathway. Furthermore, hemolysis assay showed a safety on blood compatibility of AsCs NPs. Our study indicated that AsCs NPs inhibited the SphK1-S1P signaling pathway and enhanced the antiangiogenic effect of Alphastatin both in vitro and in vivo.

Markers and Biomarkers of Endothelium: When Something Is Rotten in the State

Endothelium is a community of endothelial cells (ECs), which line the blood and lymphatic vessels, thus forming an interface between the tissues and the blood or lympha. This strategic position of endothelium infers its indispensable functional role in controlling vasoregulation, haemostasis, and inflammation. The state of endothelium is simultaneously the cause and effect of many diseases, and this is coupled with modifications of endothelial phenotype represented by markers and with biochemical profile of blood represented by biomarkers. In this paper, we briefly review data on the functional role of endothelium, give definitions of endothelial markers and biomarkers, touch on the methodological approaches for revealing biomarkers, present an implicit role of endothelium in some toxicological mechanistic studies, and survey the role of reactive oxygen species (ROS) in modulation of endothelial status.

Peptides derived from plasma proteins released by bothropasin, a metalloprotease present in the Bothrops jararaca venom

Viperid snake venoms contain proteases that affect hemostasis by degrading important proteins such as those that participate in the coagulation cascade. The Bothrops jararaca venom presents as its main components metallo and serine proteases, which comprise around 65% of the venom composition. Bothropasin is a hemorrhagic metalloprotease from the B. jararaca venom which causes disruption of the basement membrane of the vascular endothelium, resulting in bleeding. Although the bothropasin ability to degrade plasmatic and extracellular matrix proteins in vitro has been described, the primary sequence of the released peptides is unknown. This research study presents the peptide identification from both fibrinogen and fibronectin, generated by bothropasin proteolytic activity. Among the fibrinogen derived peptides identified by mass spectrometry, analogous of endogenous products like the fibrinopeptides A and B were found, as well as other sequences described in the literature with vasoactive or antiangiogenic properties. A series of peptides derived from fibronectin by the action of bothropasin were described, and for most of them no biological activity has been described. However, exceptionally a peptide that is known as a bond site for B cells was found. This study indicates that, beyond to the degradation of human proteins, bothropasin can generate bioactive peptides, which may participate in the envenoming process by Bothrops snakes. Also important, the knowledge of the formed peptides, based on the cleavage sites of the hydrolyzed proteins, provided the opportunity to study the primary specificity of bothropasin.

Fibrinogen-derived fibrinostatin inhibits tumor growth through anti-angiogenesis

Angiogenesis is a prerequisite of tumor growth and metastasis and, thus, anti‐angiogenesis treatment has become an important part of cancer therapy. A 15‐amino acid peptide of the fibrinogen α chain, fibrinostatin, was previously found in serum samples of gastric cancer patients. Herein we demonstrated that fibrinostatin has anti‐angiogenesis activity in several angiogenesis models and it reduces tumor growth in mouse xenografts and allografts. Increased tumor necrosis and reduced microvessel density in tumors were observed in mouse xenograft models. Fibrinostatin inhibited proliferation and induced apoptosis in HUVEC, but not in cancer cells. In addition, fibrinostatin specifically entered HUVEC. Fibrinostatin also prevented migration, adhesion and tubule formation of HUVEC in vitro. A single‐dose acute toxicity testing and a repeated‐dose chronic toxicity study in the mouse, rat and monkey indicated that fibrinostatin had a wide margin of safety. Taken together, fibrinostatin shows promise as a potential anti‐angiogenesis therapeutic agent.

A thin layer angiogenesis assay: a modified basement matrix assay for assessment of endothelial cell differentiation

Background

Basement matrices such as Matrigel™ and Geltrex™ are used in a variety of cell culture assays of anchorage-dependent differentiation including endothelial cell tube formation assays. The volumes of matrix recommended for these assays (approximately 150 μl/cm²) are costly, limit working distances for microscopy, and require cell detachment for subsequent molecular analysis. Here we describe the development and validation of a thin-layer angiogenesis (TLA) assay for assessing the angiogenic potential of endothelial cells that overcomes these limitations.

Results

Geltrex™ basement matrix at 5 μl/cm² in 24-well (10 μl) or 96-well (2 μl) plates supports endothelial cell differentiation into tube-like structures in a comparable manner to the standard larger volumes of matrix. Since working distances are reduced, high-resolution single cell microscopy, including DIC and confocal imaging, can be used readily. Using MitoTracker dye we now demonstrate, for the first time, live mitochondrial dynamics and visualise the 3-dimensional network of mitochondria present in differentiated endothelial cells. Using a standard commercial total RNA extraction kit (Qiagen) we also show direct RNA extraction and RT-qPCR from differentiated endothelial cells without the need to initially detach cells from their supporting matrix.

Conclusions

We present here a new thin-layer assay (TLA) for measuring the anchorage-dependent differentiation of endothelial cells into tube-like structures which retains all the characteristics of the traditional approach but with the added benefit of a greatly lowered cost and better compatibility with other techniques, including RT-qPCR and high-resolution microscopy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-014-0041-5) contains supplementary material, which is available to authorized users.

Inhibition of xenograft human glioma tumor growth by lentivirus-mediated gene transfer of alphastatin

Angiogenesis is crucial for the development and metastasis of human brain glioma. Based on our previous successful construction of a lentivirus-mediated alphastatin (an endogenous angiogenesis inhibitor) gene transfer system and our findings that alphastatin exhibited potent inhibitory effects on the migration and differentiation of human umbilical vein endothelial cell lines (HUVECs) induced by vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) in vitro, here, we investigated the effect of using lentiviral vectors to overexpress alphastatin in human glioma cells to show whether sustained long-term expression of alphastatin diminishes tumor growth in a xenograft glioma model. We found that the transduced glioma cells sustainedly secreted alphastatin, which did not affect the proliferative ability of the glioma cells. Furthermore, tumor xenografts treated with the recombinant lentivirus were significantly smaller compared to the control xenografts and vascularity within the treated tumors was evidently decreased. Our data suggest that stable expression of alphastatin inhibits human glioma growth by inhibiting angiogenesis, with a probable mechanism of suppressing the turnover of VE-cadherin membrane molecules.

Macrophages in malignant pleural effusions - alternatively activated tumor associated macrophages

Pleural macrophages are involved in local defense mechanisms against environmental pollution, bacteria and cancer. Their main function encompasses phagocytosis of degenerated mesothelial cells. In human pleural effusions macrophages represent more than half of all cells. A model of polarized macrophage activation (M1 and M2) was proposed, which defines a functionally different macrophage populations generated in response to various factors present in the inflamed environment. Tumor associated macrophages are a major component of the inflammatory infiltrate of most cancers. They can promote the proliferation and spread of cancer cells in the early stages of carcinogenesis and during metastasis. Macrophages isolated from malignant pleural effusions as well as tumor associated macrophages exhibit weak cytotoxic activity against tumor cells, increase their proliferative activity and may protect tumor cells from apoptosis. Defining biology of macrophages present in specific environment of the pleural effusion could allow the introduction of innovative diagnostic and therapeutic strategies.

Advances in research of antiangiogenic drugs for gastric cancer

Gastric cancer is the most common cancer of the digestive system and the first leading cause of cancer deaths in China. Conventional surgery and chemotherapeutic regimens can not significantly improve the poor prognosis of gastric cancer. In recent years, molecular targeted therapy has become a hot topic in the treatment of cancers, and many antiangiogenic drugs for treatment of gastric cancer have been developed, including monoclonal antibodies or soluble receptors that bind and neutralize vascular endothelial growth factor (VEGF), tyrosine kinase receptor inhibitors, and antibodies against VEGF receptors (VEGFRs).

Anti-tumor effect of lentivirus-mediated gene transfer of alphastatin on human glioma

Alphastatin, an endogenous angiogenesis inhibitor, has recently been used as an anticancer agent in several tumor models. This study was to investigate whether local sustained long-term expression of alphastatin could serve to diminish tumor growth of a human xenograft glioma model. We found that the recombinant alphastatin lentiviruses were able to stably infect HUVECs, and infected HUVECs could sustainably secrete alphastatin, which exhibited potent inhibitory effects on HUVECs migration, differentiation but not proliferation induced by vascular endothelial growth factor (VEGF) or basic fibroblast growth factor(bFGF). And the expression of secreted protein alphastatin markedly decreased tumor vascularization and inhibited tumor growth. Additionally, alphastatin inhibited VEGF- or bFGF-induced initial stage of angiogenesis by reducing JNk and ERK phosphorylation in vitro. Taken together, these data demonstrate that secreted protein alphastatin inhibits VEGF- or bFGF-induced angiogenesis by suppressing JNK and ERK kinases activation pathways in HUVECs, and markedly inhibits tumor angiogenesis in vivo. Consequently lentivirus-mediated gene transfer might represent an effective strategy for expression of alphastatin to achieve inhibition of human malignant glioma proliferation and tumor progression.

Novel aspects of fibrin(ogen) fragments during inflammation

Coagulation is fundamental for the confinement of infection and/or the inflammatory response to a limited area. Under pathological inflammatory conditions such as arthritis, multiple sclerosis or sepsis, an uncontrolled activation of the coagulation system contributes to inflammation, microvascular failure and organ dysfunction. Coagulation is initiated by the activation of thrombin, which, in turn, triggers fibrin formation by the release of fibrinopeptides. Fibrin is cleaved by plasmin, resulting in clot lysis and an accompanied generation of fibrin fragments such as D and E fragments. Various coagulation factors, including fibrinogen and/or fibrin [fibrin(ogen)] and also fibrin degradation products, modulate the inflammatory response by affecting leukocyte migration and cytokine production. Fibrin fragments are mostly proinflammatory, however, Bβ15-42 in particular possesses potential antiinflammatory effects. Bβ15-42 inhibits Rho-kinase activation by dissociating Fyn from Rho and, hence prevents stress-induced loss of endothelial barrier function and also leukocyte migration. This article summarizes the state-of-the-art in inflammatory modulation by fibrin(ogen) and fibrin fragments. However, further research is required to gain better understanding of the entire role fibrin fragments play during inflammation and, possibly, disease development.

Targeting the anthrax receptors, TEM-8 and CMG-2, for anti-angiogenic therapy

The anthrax toxin receptors tumor endothelial marker-8 (TEM-8) and capillary morphogenesis gene-2 (CMG-2) are responsible for allowing entry of anthrax toxin into host cells. These receptors were first discovered due to their enhanced expression on endothelial cells undergoing blood vessel growth or angiogenesis in model systems. Inhibition of angiogenesis is an important strategy for current anti-cancer therapies and treatment of retinal diseases. Functional roles for TEM-8 and CMG-2 in angiogenesis have recently emerged. TEM-8 appears to regulate endothelial cell migration and tubule formation whereas a role for CMG-2 in endothelial proliferation has been documented. TEM-8 and CMG-2 bind differentially to extracellular matrix proteins including collagen I, collagen IV and laminin and these properties may be responsible for their apparent roles in regulating endothelial cell behavior during angiogenesis. TEM-8-binding moieties have also been suggested to be useful in selectively targeting anti-angiogenic and anti-tumorigenic therapies to tumor endothelium. Additionally, studies of modified forms of lethal toxin (LeTx) have demonstrated that targeted inhibition of MAPKs within tumor vessels may represent an efficacious anti-angiogenic strategy.

Anti-tissue factor short hairpin RNA inhibits breast cancer growth in vivo

In breast cancer, there is a correlation between tissue factor (TF) expression, angiogenesis and disease progression. TF stimulates tumour angiogenesis, in part, through up-regulation of vascular endothelial growth factor (VEGF). Therefore, this study aimed to establish whether TF stimulates angiogenesis and tumour progression directly and independent of VEGF up-regulation. Initially, the effects of TF and VEGF were assessed on endothelial cell migration (Boyden chamber) and differentiation (tubule formation on Matrigel). Subsequently, MDA-MB-436 breast cancer cells, which produce high levels of both TF and VEGF (western blot analysis), were established in vivo, following which tumours were treated three times per week for 3 weeks with intra-tumoural injections of either anti-VEGF siRNA, anti-TF shRNA, the two treatments combined, or relevant controls. Both VEGF and TF significantly stimulated endothelial cell migration and tubule formation (P < 0.02). Breast cancer xenografts (MDA-MB-436) treated with TF or VEGF-specific agents demonstrated significant inhibition in tumour growth (VEGFsiRNA 61%; final volume: 236.2 ± 23.2 mm(3) vs TFshRNA 89%; 161.9 ± 17.4 mm(3) vs combination 93%; 136.3 ± 9.2 mm(3) vs control 400.4 ± 32.7 mm(3); P < 0.005). Microvessel density (MVD), a measure of angiogenesis, was also significantly inhibited in all groups (MVD in control = 29 ± 2.9; TFshRNA = 18 ± 1.1; VEGFsiRNA = 16.7 ± 1.5; both = 12 ± 2.1; P < 0.004), whereas the proliferative index of the tumours was only reduced in the TFshRNA-treated groups (control = 0.51 ± 0.011; TFshRNA = 0.41 ± 0.014; VEGFsiRNA = 0.49 ± 0.013; both = 0.41 ± 0.004; P < 0.008). These data suggest that TF has a direct effect on primary breast cancer growth and angiogenesis, and that specific inhibition of the TF-signalling pathway has potential for the treatment of primary breast cancer.

Angiopoietin-2 regulates gene expression in TIE2-expressing monocytes and augments their inherent proangiogenic functions

TIE2-expressing monocytes/macrophages (TEM) are a highly proangiogenic subset of myeloid cells in tumors. Here, we show that circulating human TEMs are already preprogrammed in the circulation to be more angiogenic and express higher levels of such proangiogenic genes as matrix metalloproteinase-9 (MMP-9), VEGFA, COX-2, and WNT5A than TIE2(-) monocytes. Additionally, angiopoietin-2 (ANG-2) markedly enhanced the proangiogenic activity of TEMs and increased their expression of two proangiogenic enzymes: thymidine phosphorylase (TP) and cathepsin B (CTSB). Three "alternatively activated" (or M2-like) macrophage markers were also upregulated by ANG-2 in TEMs: interleukin-10, mannose receptor (MRC1), and CCL17. To investigate the effects of ANG-2 on the phenotype and function of TEMs in tumors, we used a double-transgenic (DT) mouse model in which ANG-2 was specifically overexpressed by endothelial cells. Syngeneic tumors grown in these ANG-2 DT mice were more vascularized and contained greater numbers of TEMs than those in wild-type (WT) mice. In both tumor types, expression of MMP-9 and MRC1 was mainly restricted to tumor TEMs rather than TIE2(-) macrophages. Furthermore, tumor TEMs expressed higher levels of MRC1, TP, and CTSB in ANG-2 DT tumors than WT tumors. Taken together, our data show that although circulating TEMs are innately proangiogenic, exposure to tumor-derived ANG-2 stimulates these cells to exhibit a broader, tumor-promoting phenotype. As such, the ANG-2-TEM axis may represent a new target for antiangiogenic cancer therapies.

Thrombospondin-1 as a Paradigm for the Development of Antiangiogenic Agents Endowed with Multiple Mechanisms of Action

Uncontrolled neovascularization occurs in several angiogenesis-dependent diseases, including cancer. Neovascularization is tightly controlled by the balance between angiogenic growth factors and antiangiogenic agents. The various natural angiogenesis inhibitors identified so far affect neovascularization by different mechanisms of action. Thrombospondin-1 (TSP-1) is a matricellular modular glycoprotein that acts as a powerful endogenous inhibitor of angiogenesis. It acts both indirectly, by sequestering angiogenic growth factors and effectors in the extracellular environment, and directly, by inducing an antiangiogenic program in endothelial cells following engagement of specific receptors including CD36, CD47, integrins and proteoglycans (all involved in angiogenesis ). In view of its central, multifaceted role in angiogenesis, TSP-1 has served as a source of antiangiogenic tools, including TSP-1 fragments, synthetic peptides and peptidomimetics, gene therapy strategies, and agents that up-regulate TSP-1 expression. This review discusses TSP-1-based inhibitors of angiogenesis, their mechanisms of action and therapeutic potential, drawing our experience with angiogenic growth factor-interacting TSP-1 peptides, and the possibility of exploiting them to design novel antiangiogenic agents.

A novel fragment derived from the beta chain of human fibrinogen, beta43-63, is a potent inhibitor of activated endothelial cells in vitro and in vivo

BACKGROUND

Angiogenesis and haemostasis are closely linked within tumours with many haemostatic proteins regulating tumour angiogenesis. Indeed we previously identified a fragment of human fibrinogen, fibrinogen E-fragment (FgnE) with potent anti-angiogenic properties in vitro and cytotoxic effects on tumour vessels in vivo. We therefore investigated which region of FgnE was mediating vessel cytotoxicity.

METHODS

Human dermal microvascular endothelial cells (ECs) were used to test the efficacy of peptides derived from FgnE on proliferation, migration, differentiation, apoptosis and adhesion before testing the efficacy of an active peptide on tumour vasculature in vivo.

RESULTS

We identified a 20-amino-acid peptide derived from the beta chain of FgnE, beta43-63, which had no effect on EC proliferation or migration but markedly inhibited the ability of activated ECs to form tubules or to adhere to various constituents of the extracellular matrix - collagen IV, fibronectin and vitronectin. Furthermore, our data show that beta43-63 interacts with ECs, in part, by binding to alpha(v)beta(3), so soluble alpha(v)beta(3) abrogated beta43-63 inhibition of tubule formation by activated ECs. Finally, when injected into mice bearing tumour xenografts, beta43-63 inhibited tumour vascularisation and induced formation of significant tumour necrosis.

CONCLUSIONS

Taken together, these data suggest that beta43-63 is a novel anti-tumour peptide whose anti-angiogenic effects are mediated by alpha(v)beta(3).

A critical analysis of current in vitro and in vivo angiogenesis assays

The study of angiogenesis has grown exponentially over the past 40 years with the recognition that angiogenesis is essential for numerous pathologies and, more recently, with the advent of successful drugs to inhibit angiogenesis in tumours. The main problem with angiogenesis research remains the choice of appropriate assays to evaluate the efficacy of potential new drugs and to identify potential targets within the angiogenic process. This selection is made more complex by the recognition that heterogeneity occurs, not only within the endothelial cells themselves, but also within the specific microenvironment to be studied. Thus, it is essential to choose the assay conditions and cell types that most closely resemble the angiogenic disease being studied. This is especially important when aiming to translate data from in vitro to in vivo and from preclinical to the clinic. Here we critically review and highlight recent advances in the principle assays in common use including those for endothelial cell proliferation, migration, differentiation and co-culture with fibroblasts and mural cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as chick chorioallantoic membrane (CAM), zebrafish, sponge implantation, corneal, dorsal air sac, chamber and tumour angiogenesis models. Finally, we briefly discuss the direction likely to be taken in future studies, which include the use of increasingly sophisticated imaging analysis systems for data acquisition.

Expression of a protease-resistant insulin-like growth factor-binding protein-4 inhibits tumour growth in a murine model of breast cancer

Background:

Insulin-like growth factor 1 (IGF1) promotes breast cancer and disease progression. Bioavailability of IGF1 is modulated by IGF-binding proteins (IGFBPs). IGFBP4 inhibits IGF1 activity but cleavage by pregnancy-associated plasma protein-A (PAPP-A) protease releases active IGF1.

Methods:

Expression of IGF pathway components and PAPP-A was assessed by western blot or RT–PCR. IGFBP4 (dBP4) resistant to PAPP-A cleavage, but retaining IGF-binding capacity, was used to block IGF activity in vivo. 4T1.2 mouse mammary adenocarcinoma cells transfected with empty vector, vector expressing wild-type IGFBP4 or vector expressing dBP4 were implanted in the mammary fat pad of BALB/c mice and tumour growth was assessed. Tumour angiogenesis and endothelial cell apoptosis were assessed by immunohistochemistry.

Results:

4T1.2 cells expressed the IGF1R receptor and IGFBP4. PAPP-A was expressed within mammary tumours but not by 4T1.2 cells. Proliferation and vascular endothelial growth factor (VEGF) production by 4T1.2 cells was increased by IGF1(E3R) (recombinant IGF1 resistant to binding by IGFBPs) but not by wild-type IGF1. IGF1-stimulated microvascular endothelial cell proliferation was blocked by recombinant IGFBP4. 4T1.2 tumours expressing dBP4 grew significantly more slowly than controls or tumours expressing wild-type IGFBP4. Inhibition of tumour growth by dBP4 was accompanied by the increased endothelial cell apoptosis.

Conclusion:

Protease-resistant IGFBP4 blocks IGF activity, tumour growth and angiogenesis .

Molecular imaging of vessels in mouse models of disease

Vascular imaging of angiogenesis in mouse models of disease requires multi modal imaging hardware capable of targeting both structure and function at different physical scales. The three dimensional (3D) structure and function vascular information allows for accurate differentiation between biological processes. For example, image analysis of vessel development in angiogenesis vs. arteriogenesis enables more accurate detection of biological variation between subjects and more robust and reliable diagnosis of disease. In the recent years a number of micro imaging modalities have emerged in the field as preferred means for this purpose. They provide 3D volumetric data suitable for analysis, quantification, validation, and visualization of results in animal models. This review highlights the capabilities of microCT, ultrasound and microPET for multimodal imaging of angiogenesis and molecular vascular targets in a mouse model of tumor angiogenesis. The basic principles of the imaging modalities are described and experimental results are presented.

C-terminal ADAMTS-18 fragment induces oxidative platelet fragmentation, dissolves platelet aggregates, and protects against carotid artery occlusion and cerebral stroke

Anti-platelet integrin GPIIIa49-66 antibody (Ab) induces complement-independent platelet oxidative fragmentation and death by generation of platelet peroxide following NADPH oxidase activation. A C-terminal 385-amino acid fragment of ADAMTS-18 (a disintegrin metalloproteinase with thrombospondin motifs produced in endothelial cells) induces oxidative platelet fragmentation in an identical kinetic fashion as anti-GPIIIa49-66 Ab. Endothelial cell ADAMTS-18 secretion is enhanced by thrombin and activated by thrombin cleavage to fragment platelets. Platelet aggregates produced ex vivo with ADP or collagen and fibrinogen are destroyed by the C-terminal ADAMTS-18 fragment. Anti-ADAMTS-18 Ab shortens the tail vein bleeding time. The C-terminal fragment protects against FeCI3-induced carotid artery thrombosis as well as cerebral infarction in a postischemic stroke model. Thus, a new mechanism is proposed for platelet thrombus clearance, via platelet oxidative fragmentation induced by thrombin cleavage of ADAMTS-18.

Human-derived nanoparticles and vascular response to injury in rabbit carotid arteries: proof of principle

Self-calcifying, self-replicating nanoparticles have been isolated from calcified human tissues. However, it is unclear if these nanoparticles participate in disease processes. Therefore, this study was designed to preliminarily test the hypothesis that human-derived nanoparticles are causal to arterial disease processes. One carotid artery of 3 kg male rabbits was denuded of endothelium; the contralateral artery remained unoperated as a control. Each rabbit was injected intravenously with either saline, calcified, or decalcified nanoparticles cultured from calcified human arteries or kidney stones. After 35 days, both injured and control arteries were removed for histological examination. Injured arteries from rabbits injected with saline showed minimal, eccentric intimal hyperplasia. Injured arteries from rabbits injected with calcified kidney stone- and arterial-derived nanoparticles occluded, sometimes with canalization. The calcified kidney stone-derived nanoparticles caused calcifications within the occlusion. Responses to injury in rabbits injected with decalcified kidney stone-derived nanoparticles were similar to those observed in saline-injected animals. However, decalcified arterial-derived nanoparticles produced intimal hyperplasia that varied from moderate to occlusion with canalization and calcification. This study offers the first evidence that there may be a causal relationship between human-derived nanoparticles and response to injury including calcification in arteries with damaged endothelium.

Matrix metalloproteinase control of capillary morphogenesis

Matrix metalloproteinases (MMPs) play crucial roles in a variety of normal (e.g., blood vessel formation, bone development) and pathophysiological (e.g., wound healing, cancer) processes. This is not only due to their ability to degrade the surrounding extracellular matrix (ECM), but also because MMPs function to reveal cryptic matrix binding sites, release matrix-bound growth factors inherent to these processes, and activate a variety of cell surface molecules. The process of blood vessel formation, in particular, is regulated by what is widely classified as the angiogenic switch: a mixture of both pro- and antiangiogenic factors that function to counteract each other unless the stimuli from one side exceeds the other to disrupt the quiescent state. Although it was initially thought that MMPs were strictly proangiogenic, new functions for this proteolytic family, such as mediating vascular regression and generating matrix fragments with antiangiogenic capacities, have been discovered in the last decade. These findings cast MMPs as multifaceted pro- and antiangiogenic effectors. The purpose of this review is to introduce the reader to the general structure and characterization of the MMP family and to discuss the temporal and spatial regulation of their gene expression and enzymatic activity in the following crucial steps associated with angiogenesis: degradation of the vascular basement membrane, proliferation and invasion of endothelial cells within the subjacent ECM, organization into immature tubules, maturation of these nascent vessels, and the pruning and regression of the vascular network.

Vascular disease in scleroderma: angiogenesis and vascular repair

Vascular abnormalities are one of the primary pathologic components of scleroderma. An early vascular indicator is aberrant nail fold capillaries that appear to undergo a switch from a pro- to anti-angiogenic process. Later in the disease process, ineffective and aberrant wound healing becomes apparent with frequent and widespread fibrosis. Pulmonary hypertension, largely due to the loss of pulmonary arterial vasculature, is frequently observed in late stages of the disease. The common theme of all these processes is abnormal regeneration of the vasculature and ongoing vascular losses due to defective maintenance of the vasculature. Although most aspects of vascular injury in scleroderma are poorly understood, certain biologic themes are beginning to emerge that are important in understanding scleroderma-related vascular disease.

Targeting tumors with peptides from natural sources

Peptide-based therapies offer the potential for non-genotoxic, genotype-specific alternatives, or adjuvants, to the current range of traditional cancer treatments. Such a patient-tailored cancer-cell-directed therapeutic approach should have fewer side effects and could well be more effective than the current drug- or combination-based regimens. Here, we review the potential of novel natural anticancer peptides such as necrotic peptides, apoptotic peptides, function-blocking peptides, antiangiogenic peptides and immunostimulatory peptides in the context of their ability to induce tumor regression. We focus on the therapeutic prospects of anticancer peptides and their possible application in tumor therapy.

Impact of the non-cellular tumor microenvironment on metastasis: potential therapeutic and imaging opportunities

Evidence is accumulating that the malignant phenotype of a given tumor is dependent not only on the intrinsic characteristics of tumor cells, but also on the cooperative interactions of non-neoplastic cells, soluble secreted factors and the non-cellular solid-state ECM network that comprise the tumor microenvironment. Given the ability of the tumor microenvironment to regulate the cellular phenotype, recent efforts have focused on understanding the molecular mechanisms by which cells sense, assimilate, interpret, and ultimately respond to their immediate surroundings. Exciting new studies are beginning to unravel the complex interactions between the numerous cell types and regulatory factors within the tumor microenvironment that function cooperatively to control tumor cell invasion and metastasis. Here, we will focus on studies concerning a common theme, which is the central importance of the non-cellular solid-state compartment as a master regulator of the malignant phenotype. We will highlight the non-cellular solid-state compartment as a relatively untapped source of therapeutic and imaging targets and how cellular interactions with these targets may regulate tumor metastasis.

Sphingolipid metabolizing enzymes as novel therapeutic targets

Pharmacological interference with sphingolipid metabolizing enzymes promises to provide novel ways to modulate cellular pathways relevant in multiple diseases. In this review, we focus on two sphingolipid signaling molecules, sphingosine-1-phosphate (S1P) and ceramide, as they are involved in cell fate decisions (survival vs. apoptosis) and in a wide range of pathophysiological processes. For S1P, we will discuss sphingosine kinases and S1P lyase as the enzymes which are crucial for its production and degradation, respectively, emphasizing the potential therapeutic usefulness of inhibitors of these enzymes. For ceramide, we will concentrate on acid sphingomyelinase, and critically review the substantial literature which implicates this enzyme as a worthwhile target for pharmacological inhibitors. It will become clear that the task to validate these enzymes as drug targets is not finished and many questions regarding the therapeutic usefulness of their inhibitors remain unanswered. Still this approach holds promise for a number of totally new therapies, and, on the way, detailed insight into sphingolipid signaling pathways can be gained.

Current concepts in normal and defective angiogenesis: implications for systemic sclerosis

Vascular abnormalities are a major component of systemic sclerosis, but little is known about the events or mechanisms that initiate vascular injury and prevent its repair. Early stages of systemic sclerosis are characterized by an exaggerated angiogenic response later replaced by defective wound healing and fibrosis. In this review, we summarize the current knowledge of the angiogenic imbalance in systemic sclerosis.

Identification of key residues involved in mediating the in vivo anti-tumor/anti-endothelial activity of Alphastatin

BACKGROUND

We have recently shown that Alphastatin, a 24-amino-acid peptide (ADSGEGDFLAEGGGVRGPRVVERH) derived from human fibrinogen has anti-endothelial properties in vitro and in vivo.

OBJECTIVES

The aim of this study was to determine the activity of a terminally modified (stabilized) form of Alphastatin in vitro and in vivo and to identify the key residues required for this activity.

METHODS

The in vitro activity of modified Alphastatin, truncates and mutants was determined by endothelial cell (HuDMEC) tubule formation and migration. Active peptides were then assessed in vivo using syngeneic murine subcutaneous 4T1 mammary carcinomas.

RESULTS

Modified Alphastatin-inhibited HuDMEC migration and tubule formation in response to multiple growth factors and caused a 45% inhibition in tumor growth when administered intravenously at 0.25 mg kg(-1) (three times per week). Intravenous (i.v.) administration proved non-toxic at all doses investigated, whereas oral and intraperitoneal (i.p.) administration demonstrated neither anti-tumor activity nor toxicity. Truncations of Alphastatin revealed an 11-amino-acid peptide (DFLAEGGGVRG), termed AHN419, which inhibited endothelial cell activity in vitro; however, intravenous AHN419 caused a non-significant growth inhibition in vivo. Single amino acid substitutions to alanine along the entire length of Alphastatin indicated that additional residues outside the AHN419 sequence were required for full activity.

CONCLUSIONS

Terminal modification of Alphastatin altered the in vivo efficacy and these studies suggest that a hydrophobic cluster (Phe8, Leu9, Ala10 and Val15) is essential for the biological activity, but additional residues, including Ser3-Gly14, Pro18-Val20 and Arg23 are required for full inhibitory activity of Alphastatin.

Treatment of solid tumors and metastases by fibrinogen-targeted anticancer drug therapy

The accumulation of fibrin/fibrinogen and other coagulation factors in and around solid tumors and metastatic foci has been recognized for a century as an aspect of cancer pathology. On this basis, anticoagulants and fibrinolytic agents have been deployed as adjuvant anticancer therapies, but they have proved clinically useful for only a small proportion of tumors and they only control the functions of the coagulant components. Overuse or long-term application of anticoagulants and fibrinolytic agents often lead to undesirable side-effects. Here, we propose that anticancer drugs that act by different mechanisms can inhibit tumor-associated coagulation, and it may be possible to develop drugs that specifically targeting tumor-related coagulation, have specific cytotoxic effects on tumor and metastatic cells. We provide laboratory and clinical evidence supporting the hypothesis and offer proposals for future applications.

Human ovarian cancer ascites fluid contains a mixture of incompletely degraded soluble products of fibrin that collectively possess an antiangiogenic property

Ovarian cancer ascites fluid (OCAF) displayed an antiangiogenic property in a chick chorioallantoic membrane (CAM) assay. This property was attributed in part to angiostatin although angiostatin-free OCAF retained a net antiangiogenic property. Recently, immunopurified fibrin(ogen) degradation products (FDPs) from malignant effusions of VX2 tumor-burdened rabbits exhibited antiangiogenic activity on the CAM. We questioned whether the FDPs of OCAF were also antiangiogenic. FDPs were immunopurified from individual OCAF samples, characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis /western blots, enzyme-linked immunosorbent assays, and CAM assays. FDPs of OCAFs consisted of soluble high molecular weight (MW) fragments (>200 kd; approximately 40% of total FDPs), D-dimer (approximately 180 kd; approximately 37%), fragment D (approximately 90 kd; approximately 15%), and fragment E (approximately 50 kd; approximately 8%); intact fibrinogen was absent. When applied to CAM surfaces (0.5-1.6 mg/10 mL), purified FDPs significantly reduced the area of chorionic capillaries from 90% (in controls) to 47% over a 48-h period; from CAM sections, capillary density was reduced from 60% (controls) to 26%. FDPs prepared from fibrinogen displayed a similar antiangiogenic effect. Further digestion of OCAF FDPs by human plasmin caused degradation of high MW fragments, releasing additional D-dimer, fragment D, and fragment E. Of the fibrinogen-related components, OCAF contained only soluble FDPs (including incompletely digested fibrin fragments). Collectively, these FDPs contributed to the net antiangiogenic property of ascites fluid.

Alphastatin downregulates vascular endothelial cells sphingosine kinase activity and suppresses tumor growth in nude mice bearing human gastric cancer xenografts

AIM: To investigate whether alphastatin could inhibit human gastric cancer growth and furthermore whether sphingosine kinase (SPK) activity is involved in this process.

METHODS: Using migration assay, MTT assay and Matrigel assay, the effect of alphastatin on vascular endothelial cells (ECs) was evaluated in vitro. SPK and endothelial differentiation gene (EDG)-1, -3, -5 mRNAs were detected by reverse transcription-polymerase chain reaction (RT-PCR). SPK activity assay was used to evaluate the effect of alphastatin on ECs. Matrigel plug assay in nude mice was used to investigate the effect of alphastatin on angiogenesis in vivo. Female nude mice were subcutaneously implanted with human gastric cancer cells (BGC823) for the tumor xenografts studies. Micro vessel density was analyzed in Factor VIII-stained tumor sections by the immunohistochemical SP method.

RESULTS: In vitro, alphastatin inhibited the migration and tube formation of ECs, but had no effect on proliferation of ECs. RT-PCR analysis demonstrated that ECs expressed SPK and EDG-1, -3, -5 mRNAs. In vivo, alphastatin sufficiently suppressed neovascularization of the tumor in the nude mice. Daily administration of alphastatin produced significant tumor growth suppression. Immunohistochemical studies of tumor tissues revealed decreased micro vessel density in alphastatin-treated animals as compared with controls.

CONCLUSION: Downregulating ECs SPK activity may be one of the mechanisms that alphastatin inhibits gastric cancer angiogenesis. Alphastatin might be a useful and relatively nontoxic adjuvant therapy in the treatment of gastric cancer.

Fibrin structure and wound healing

Fibrinogen and fibrin play an important role in blood clotting, fibrinolysis, cellular and matrix interactions, inflammation, wound healing, angiogenesis, and neoplasia. The contribution of fibrin(ogen) to these processes largely depends not only on the characteristics of the fibrin(ogen) itself, but also on interactions between specific-binding sites on fibrin(ogen), pro-enzymes, clotting factors, enzyme inhibitors, and cell receptors. In this review, the molecular and cellular biology of fibrin(ogen) is reviewed in the context of cutaneous wound repair. The outcome of wound healing depends largely on the fibrin structure, such as the thickness of the fibers, the number of branch points, the porosity, and the permeability. The binding of fibrin(ogen) to hemostasis proteins and platelets as well as to several different cells such as endothelial cells, smooth muscle cells, fibroblasts, leukocytes, and keratinocytes is indispensable during the process of wound repair. High-molecular-weight and low-molecular-weight fibrinogen, two naturally occurring variants of fibrin, are important determinants of angiogenesis and differ in their cell growth stimulation, clotting rate, and fibrin polymerization characteristics. Fibrin sealants have been investigated as matrices to promote wound healing. These sealants may also be an ideal delivery vehicle to deliver extra cells for the treatment of chronic wounds.

The angiogenic function of nucleolin is mediated by vascular endothelial growth factor and nonmuscle myosin

Nucleolin, originally described as a nuclear protein, was recently found to be expressed on the surface of endothelial cells during angiogenic. However, the functions of cell-surface nucleolin in angiogenic remain mysterious. Here we report that upon endothelial cells adhering to extracellular matrix components, vascular endothelial growth factor (VEGF) mobilizes nucleolin from nucleus to cell surface. Functional blockage or down-regulation of the expression of cell-surface nucleolin in endothelial cells significantly inhibits the migration of endothelial cells and prevents capillary-tubule formation. Moreover, nonmuscle myosin heavy chain 9 (MyH9), an actin-based motor protein, is identified as a nucleolin-binding protein. Subsequent studies reveal that MyH9 serves as a physical linker between nucleolin and cytoskeleton, thus modulating the translocation of nucleolin. Knocking down endogenous MyH9, specifically inhibiting myosin activity, or overexpressing functional deficient MyH9 disrupts the organization of cell-surface nucleolin and inhibits its angiogenic function. These studies indicate that VEGF, extracellular matrix, and intracellular motor protein MyH9 are all essential for the novel function of nucleolin in angiogenic.

Pericellular proteases in angiogenesis and vasculogenesis

Pericellular proteases play an important role in angiogenesis and vasculogenesis. They comprise (membrane-type) matrix metalloproteinases [(MT-)MMPs], serine proteases, cysteine cathepsins, and membrane-bound aminopeptidases. Specific inhibitors regulate them. Major roles in initiating angiogenesis have been attributed to MT1-matrix metalloproteinase (MMP), MMP-2, and MMP-9. Whereas MT-MMPs are membrane-bound by nature, MMP-2 and MMP-9 can localize to the membrane by binding to alphavbeta3-integrin and CD44, respectively. Proteases switch on neovascularization by activation, liberation, and modification of angiogenic growth factors and degradation of the endothelial and interstitial matrix. They also modify the properties of angiogenic growth factors and cytokines. Neovascularization requires cell migration, which depends on the assembly of protease-protein complexes at the migrating cell front. MT1-MMP and urokinase (u-PA) form multiprotein complexes in the lamellipodia and focal adhesions of migrating cells, facilitating proteolysis and sufficient support for endothelial cell migration and survival. Excessive proteolysis causes loss of endothelial cell-matrix interaction and impairs angiogenesis. MMP-9 and cathepsin L stimulate the recruitment and action of blood- or bone-marrow-derived accessory cells that enhance angiogenesis. Proteases also generate fragments of extracellular matrix and hemostasis factors that have anti-angiogenic properties. Understanding the complexity of protease activities in angiogenesis contributes to recognizing new targets for stimulation or inhibition of neovascularization in disease.

Macrophage responses to hypoxia: implications for tumor progression and anti-cancer therapies

The presence of multiple areas of hypoxia (low oxygen tension) is a hallmark feature of human and experimental tumors. Monocytes are continually recruited into tumors, differentiate into tumor-associated macrophages (TAMs), and then accumulate in these hypoxic areas. A number of recent studies have shown that macrophages respond to the levels of hypoxia found in tumors by up-regulating such transcription factors as hypoxia-inducible factors 1 and 2, which in turn activate a broad array of mitogenic, pro-invasive, pro-angiogenic, and pro-metastatic genes. This could explain why high numbers of TAMs correlate with poor prognosis in various forms of cancer. In this review, we assess the evidence for hypoxia activating a distinct, pro-tumor phenotype in macrophages and the possible effect of this on the growth, invasion, angiogenesis, and immune evasion of tumors. We also discuss current attempts to selectively target TAMs for destruction or to use them to deliver gene therapy specifically to hypoxic tumor sites.

Angiogenesis inhibitors found within the haemostasis pathway

Angiogenesis, the development of new blood vessels from the existing vasculature, and haemostasis, the coagulation cascade leading to formation of a clot, are among the most consistent host responses associated with cancer. Importantly, these two pathways interrelate, with blood coagulation and fibrinolysis influencing tumor angiogenesis directly, thereby contributing to tumor growth. Moreover, many endogenous inhibitors of angiogenesis are found within platelets or harboured as cryptic fragments of haemostatic proteins. In this review we outline ways in which angiogenesis is coordinated and regulated by haemostasis in human cancer. Then we detail the experimental and pre-clinical evidence for the ability of many of these endogenous proteins to inhibit tumor angiogenesis and thus their potential to be anti-cancer agents, with particular reference to any clinical trials.

Endogenous angiogenesis inhibitors

When the FDA commissioner announced in February 2004 the approval of Avastin for the treatment of patients with colon cancer, he called angiogenesis inhibitors a fourth modality of anti-cancer therapy. Because angiogenesis inhibitors are relatively less toxic than conventional chemotherapy and have a lower risk of drug resistance, they may also represent a new class of anti-cancer agents, some of which have sufficiently reduced toxicity that they may be safely used long term. These include immunotherapy, vaccines, telomerase inhibitors, apoptosis inducers, low dose metronomic chemotherapy, novel hormonal therapies, gene therapy and others. However, at least 16 endogenous angiogenesis inhibitors have been discovered in the circulation, and/or in the extracellular matrix. These may become the safest and least toxic of anti-cancer therapies. Four are already being administered by injection in clinical trials for cancer. Recently, it has been reported that at least two endogenous angiogenesis inhibitors can be significantly increased in humans (endostatin), and in mice (thrombospondin), by oral administration of small molecules which themselves are already FDA approved for other uses. This finding suggests several new clinical applications for the future, including the possibility of guiding the use of angiogenesis inhibitors by blood or urinary biomarkers, currently being developed, that may detect the presence of cancer before it is symptomatic, or before it can be located by conventional methods.

Current methods for assaying angiogenesis in vitro and in vivo

Angiogenesis, the development of new blood vessels from an existing vasculature, is essential in normal developmental processes and in numerous pathologies, including diabetic retinopathy, psoriasis and tumour growth and metastases. One of the problems faced by angiogenesis researchers has been the difficulty of finding suitable methods for assessing the effects of regulators of the angiogenic response. The ideal assay would be reliable, technically straightforward, easily quantifiable and, most importantly, physiologically relevant. Here, we review the advantages and limitations of the principal assays in use, including those for the proliferation, migration and differentiation of endothelial cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as sponge implantation, corneal, chamber, zebrafish, chick chorioallantoic membrane (CAM) and tumour angiogenesis models.