Role of bone marrow-derived cells in angiogenesis: focus on macrophages and pericytes

Endocannabinoids and their receptors modulate endometriosis pathogenesis and immune response

Endometriosis (EM), characterized by the presence of endometrial-like tissue outside the uterus, is the leading cause of chronic pelvic pain and infertility in females of reproductive age. Despite its high prevalence, the molecular mechanisms underlying EM pathogenesis remain poorly understood. The endocannabinoid system (ECS) is known to influence several cardinal features of this complex disease including pain, vascularization, and overall lesion survival, but the exact mechanisms are not known. Utilizing CNR1 knockout (k/o), CNR2 k/o, and wild-type (WT) mouse models of EM, we reveal contributions of ECS and these receptors in disease initiation, progression, and immune modulation. Particularly, we identified EM-specific T cell dysfunction in the CNR2 k/o mouse model of EM. We also demonstrate the impact of decidualization-induced changes on ECS components, and the unique disease-associated transcriptional landscape of ECS components in EM. Imaging mass cytometry (IMC) analysis revealed distinct features of the microenvironment between CNR1, CNR2, and WT genotypes in the presence or absence of decidualization. This study, for the first time, provides an in-depth analysis of the involvement of the ECS in EM pathogenesis and lays the foundation for the development of novel therapeutic interventions to alleviate the burden of this debilitating condition.

Notoginsenoside R1 decreases intraplaque neovascularization by governing pericyte-endothelial cell communication via Ang1/Tie2 axis in atherosclerosis

Atherosclerosis represents the major cause of mortality worldwide and triggers higher risk of acute cardiovascular events. Pericytes-endothelial cells (ECs) communication is orchestrated by ligand-receptor interaction generating a microenvironment which results in intraplaque neovascularization, that is closely associated with atherosclerotic plaque instability. Notoginsenoside R1 (R1) exhibits anti-atherosclerotic bioactivity, but its effect on angiogenesis in atherosclerotic plaque remains elusive. The aim of our study is to explore the therapeutic effect of R1 on vulnerable plaque and investigate its potential mechanism against intraplaque neovascularization. The impacts of R1 on plaque stability and intraplaque neovascularization were assessed in ApoE-/- mice induced by high-fat diet. Pericytes-ECs direct or non-direct contact co-cultured with VEGF-A stimulation were used as the in vitro angiogenesis models. Overexpressing Ang1 in pericytes was performed to investigate the underlying mechanism. In vivo experiments, R1 treatment reversed atherosclerotic plaque vulnerability and decreased the presence of neovessels in ApoE-/- mice. Additionally, R1 reduced the expression of Ang1 in pericytes. In vitro experiments demonstrated that R1 suppressed pro-angiogenic behavior of ECs induced by pericytes cultured with VEGF-A. Mechanistic studies revealed that the anti-angiogenic effect of R1 was dependent on the inhibition of Ang1 and Tie2 expression, as the effects were partially reversed after Ang1 overexpressing in pericytes. Our study demonstrated that R1 treatment inhibited intraplaque neovascularization by governing pericyte-EC association via suppressing Ang1-Tie2/PI3K-AKT paracrine signaling pathway. R1 represents a novel therapeutic strategy for atherosclerotic vulnerable plaques in clinical application.

In vitro microvascular engineering approaches and strategies for interstitial tissue integration

The increasing gap between clinical demand for tissue or organ transplants and the availability of donated tissue highlights the emerging opportunities for lab-grown or synthetically engineered tissue. While the field of tissue engineering has existed for nearly half a century, its clinical translation remains unrealised, in part, due to a limited ability to engineer sufficient vascular supply into fabricated tissue, which is necessary to enable nutrient and waste exchange, prevent cellular necrosis, and support tissue proliferation. Techniques to develop anatomically relevant, functional vascular networks in vitro have made significant progress in the last decade, however, the challenge now remains as to how best incorporate these throughout dense parenchymal tissue-like structures to address diffusion-limited development and allow for the fabrication of large-scale vascularised tissue. This review explores advances made in the laboratory engineering of vasculature structures and summarises recent attempts to integrate vascular networks together with sophisticated in vitro avascular tissue and organ-like structures. STATEMENT OF SIGNIFICANCE: The ability to grow full scale, functional tissue and organs in vitro is primarily limited by an inability to adequately diffuse oxygen and nutrients throughout developing cellularised structures, which generally results from the absence of perfusable vessel networks. Techniques to engineering both perfusable vascular networks and avascular miniaturised organ-like structures have recently increased in complexity, sophistication, and physiological relevance. However, integrating these two essential elements into a single functioning vascularised tissue structure represents a significant spatial and temporal engineering challenge which is yet to be surmounted. Here, we explore a range of vessel morphogenic phenomena essential for tissue-vascular co-development, as well as evaluate a range of recent noteworthy approaches for generating vascularised tissue products in vitro.

Peanut sprout tea extract inhibits lung metastasis of 4T1 murine mammary carcinoma cells by suppressing the crosstalk between cancer cells and macrophages in BALB/c mice

BACKGROUND/OBJECTIVES

As peanuts germinate, the content of the components beneficial to health, such as resveratrol, increases within the peanut sprout. This study examined whether the ethanol extract of peanut sprout tea (PSTE) inhibits breast cancer growth and metastasis.

MATERIALS/METHODS

After orthotopically injecting 4T1 cells into BALB/c mice to induce breast cancer, 0, 30, or 60 mg/kg body weight/day of PSTE was administered orally. Angiogenesis-related protein expression in the tumors and the degree of metastasis were analyzed. 4T1 and RAW 264.7 cells were co-cultured, and reverse transcription polymerase chain reaction was performed to measure the crosstalk between breast cancer cells and macrophages.

RESULTS

PSTE reduced tumor growth and lung metastasis. In particular, PSTE decreased matrix metalloproteinase-9, platelet endothelial cell adhesion molecule-1, vascular endothelial growth factor-A, F4/80, CD11c, macrophage mannose receptor, macrophage colony-stimulating factor, and monocyte chemoattractant protein 1 expression in the tumors. Moreover, PSTE prevented 4T1 cell migration, invasion, and macrophage activity in RAW 264.7 cells. PSTE inhibited the crosstalk between 4T1 cells and RAW 264.7 cells and promoted the macrophage M1 subtype while inhibiting the M2 subtype.

CONCLUSIONS

These results suggest that PSTE blocks breast cancer growth and metastasis to the lungs. This may be because the PSTE treatment inhibits the crosstalk between mammary cancer cells and macrophages and inhibits the differentiation of macrophages into the M2 subtype.

Pericyte-Glioblastoma Cell Interaction: A Key Target to Prevent Glioblastoma Progression

Multiple biological processes rely on direct intercellular interactions to regulate cell proliferation and migration in embryonic development and cancer processes. Tumor development and growth depends on close interactions between cancer cells and cells in the tumor microenvironment. During embryonic development, morphogenetic signals and direct cell contacts control cell proliferation, polarity, and morphogenesis. Cancer cells communicate with cells in the tumor niche through molecular signals and intercellular contacts, thereby modifying the vascular architecture and antitumor surveillance processes and consequently enabling tumor growth and survival. While looking for cell-to-cell signaling mechanisms that are common to both brain development and cancer progression, we have studied the infiltration process in glioblastoma multiforme (GBM), which is the most malignant primary brain tumor and with the worst prognosis. Cell-to-cell contacts, by means of filopodia-like structures, between GBM cells and brain pericytes (PCs) are necessary for adequate cell signaling during cancer infiltration; similarly, contacts between embryonic regions, via cytonemes, are required for embryo regionalization and development. This GBM-PC interaction provokes two important changes in the physiological function of these perivascular cells, namely, (i) vascular co-option with changes in cell contractility and vascular malformation, and (ii) changes in the PC transcriptome, modifying the microvesicles and protein secretome, which leads to the development of an immunosuppressive phenotype that promotes tumor immune tolerance. Moreover, the GTPase Cdc42 regulates cell polarity across organisms, from yeast to humans, playing a central role in GBM cell-PC interaction and maintaining vascular co-option. As such, a review of the molecular and cellular mechanisms underlying the development and maintenance of the physical interactions between cancer cells and PCs is of particular interest.

The Characteristics and Survival Potential Under Sub-lethal Stress of Mesenchymal Stromal/Stem Cells Isolated from the Human Vascular Wall

Mesenchymal stromal/stem cells (MSCs) have been identified in multiple human tissues, including the vascular wall. High proliferative potential, multilineage, and immunomodulatory properties make vascular MSCs promising candidates for regenerative medicine. Indeed, their location is strategic for controlling vascular and extra-vascular tissue homeostasis. However, the clinical application of MSCs, and in particular vascular MSCs, is still challenging. Current studies are focused on developing strategies to improve MSC therapeutic applications, like priming MSCs with stress conditions (hypoxia, nutrient deprivation) to achieve a higher therapeutic potential. The goal of the present study is to review the main findings regarding the MSCs isolated from the human vascular wall. Further, the main priming strategies tested on MSCs from different sources are reported, together with the experience on vascular MSCs isolated from healthy cryopreserved and pathological arteries. Stress induction can be a priming approach able to improve MSC effectiveness through several mechanisms that are discussed in this review. Nevertheless, these issues have not been completely explored in vascular MSCs and potential side effects need to be investigated.

Contribution of Bone Marrow-derived Cells to Reparative Dentinogenesis Using Bone Marrow Transplantation Model

INTRODUCTION

The aim of this study was to analyze the contribution of bone marrow-derived cells (BMDCs) to reparative dentinogenesis using bone marrow transplantation (BMT) and pulp capping as an in vivo model.

METHODS

A chimeric mouse model was created through the injection of BMDCs expressing green fluorescent protein (GFP+ BMDCs) from C57BL/6 GFP+ transgenic donor mice into irradiated C57BL/6 wild-type recipient mice (GFP- mice). These GFP- chimeric mice (containing transplanted GFP+ BMDCs) were subjected to microscopic pulp exposure and capping with white mineral trioxide aggregate (n = 18) or Biodentine (Septodont, St Maur-des-Fossés, France) (n = 18) in the maxillary first molar. Maxillary arches from GFP- chimeric mice (with the capped tooth) were isolated and histologically processed 5 (n = 9) and 7 (n = 9) weeks after BMT. Confocal laser microscopy and immunohistochemical analysis were performed to assess the presence of GFP+ BMDCs and the expression of dentin sialoprotein, an odontoblast marker, for those cells contributing to reparative dentinogenesis in the dental pulp.

RESULTS

Confocal laser microscopic analyses evidenced the presence of GFP+ BMDCs in close association with reparative dentin synthesized at the site of pulp exposure in GFP- mice 5 and 7 weeks after BMT. Immunohistochemical analysis revealed that GFP+ BMDCs in close association with reparative dentin expressed DSP, suggesting the contribution of nonresident GFP+ BMDCs to reparative dentinogenesis.

CONCLUSIONS

These data suggest the presence of nonresident BMDCs in reparative dentinogenesis and its contribution to dental pulp regeneration in the pulp healing process.

Alternative Strategies to Inhibit Tumor Vascularization

Endothelial cells present in tumors show different origin, phenotype, and genotype with respect to the normal counterpart. Various mechanisms of intra-tumor vasculogenesis sustain the complexity of tumor vasculature, which can be further modified by signals deriving from the tumor microenvironment. As a result, resistance to anti-VEGF therapy and activation of compensatory pathways remain a challenge in the treatment of cancer patients, revealing the need to explore alternative strategies to the classical anti-angiogenic drugs. In this review, we will describe some alternative strategies to inhibit tumor vascularization, including targeting of antigens and signaling pathways overexpressed by tumor endothelial cells, the development of endothelial vaccinations, and the use of extracellular vesicles. In addition, anti-angiogenic drugs with normalizing effects on tumor vessels will be discussed. Finally, we will present the concept of endothelial demesenchymalization as an alternative approach to restore normal endothelial cell phenotype.

Fibrocytes: A Novel Stromal Cells to Regulate Resistance to Anti-Angiogenic Therapy and Cancer Progression

An adequate blood supply is essential for cancer cells to survive and grow; thus, the concept of inhibiting tumor angiogenesis has been applied to cancer therapy, and several drugs are already in clinical use. It has been shown that treatment with those anti-angiogenic drugs improved the response rate and prolonged the survival of patients with various types of cancer; however, it is also true that the effect was mostly limited. Currently, the disappointing clinical results are explained by the existence of intrinsic or acquired resistance to the therapy mediated by both tumor cells and stromal cells. This article reviews the mechanisms of resistance mediated by stromal cells such as endothelial cells, pericytes, fibroblasts and myeloid cells, with an emphasis on fibrocytes, which were recently identified as the cell type responsible for regulating acquired resistance to anti-angiogenic therapy. In addition, the other emerging role of fibrocytes as mediator-producing cells in tumor progression is discussed.

Identification of different macrophage subpopulations with distinct activities in a mouse model of oxygen-induced retinopathy

The aim of the present study was to characterize the phenotypic shift, quantity and role changes in different subgroups of retinal macrophages in a mouse model of oxygen-induced retinopathy (OIR). The mRNA expression levels of macrophage M1 and M2 subgroup marker genes and polarization-associated genes were analyzed by RT-qPCR. The number of M1 and M2 macrophages in our mouse model of OIR was analyzed by flow cytometry at different time points during the progression of OIR. Immunofluorescence whole mount staining of the retinas of mice with OIR was performed at different time points to examine the influx of macrophages, as well as the morphological characteristics and roles of M1 and M2 macrophages. An increased number of macrophages was recruited during the progression of angiogenesis in the retinas of mice with OIR due to the pro-inflammatory microenvironment containing high levels of cell adhesion and leukocyte transendothelial migration molecules. RT-qPCR and flow cytometric analysis at different time points revealed a decline in the number of M1 cells from a significantly high level at post-natal day (P)13 to a relatively normal level at P21, as well as an increase in the number of M2 cells from P13 to P21 in the mice with OIR, implicating a shift of macrophage polarization towards the M2 subtype. Immunofluorescence staining suggested that the M1 cells interacted with endothelial tip cells at the vascular front, while M2 cells embraced the emerging vessels and bridged the neighboring vessel sprouts. Thus, our data indicate that macrophages play an active role in OIR by contributing to the different steps of neovascularization. Our findings indicate that tissue macrophages may be considered as a potential target for the anti-angiogenic therapy of ocular neovascularization disease.

Antiangiogenic and Antitumor Activities of Aflibercept, a Soluble VEGF Receptor-1 and -2, in a Mouse Model of Hepatocellular Carcinoma

BACKGROUND & AIM: Aflibercept known as ziv-aflibercept in the United States is a soluble decoy receptor of both vascular endothelial growth factor (VEGF) receptor-1 and -2 known to inhibit the binding of VEGF and placental growth factor (PlGF) to VEGF receptor-1 and -2. Here, we analyzed the mechanisms of the antitumor effects of aflibercept in mouse hepatoma models. METHODS: In in vitro studies, we determined the effects of aflibercept on human umbilical vein cell (HUVEC) proliferation and bone marrow (BM) cell differentiation to endothelial progenitor cells (EPCs). In in vivo experiments, aflibercept was injected intraperitoneally in hepatoma cell tumor-bearing mice, and its inhibitory effects on tumor growth and BM cell migration to tumor tissues were evaluated. RESULTS: Aflibercept suppressed phosphorylation of VEGF receptor-1 and -2 in HUVEC and dose-dependently inhibited VEGF-induced HUVEC proliferation. It suppressed the differentiation of BM cells to EPCs and migration of BM cells to tumor tissues. It also suppressed tumor growth and prolonged survival time of tumor-bearing mice without side effects. In tumor tissues, aflibercept upregulated the expression of hypoxia inducible factor1-α, VEGF, PlGF, fibroblast growth factor-2, platelet derived growth factor-BB, and transforming growth factor-α and reduced microvascular density. It also reduced sinusoidal density in noncancerous liver tissues. CONCLUSIONS: Our results demonstrated potent antitumor activity for aflibercept in a mouse model of hepatocellular carcinoma. These effects were mediated through inhibition of neovascularization, caused by inhibition of endothelial cell proliferation, EPC differentiation, and BM cell migration to tumor tissues.

Arginase inhibition suppresses lung metastasis in the 4T1 breast cancer model independently of the immunomodulatory and anti-metastatic effects of VEGFR-2 blockade

Tumor angiogenesis promotes tumor growth and metastasis. Anti-angiogenic therapy in combination with chemotherapy is used for the treatment of metastatic cancers, including breast cancer but therapeutic benefits are limited. Mobilization and accumulation of myeloid-derived suppressor cells (MDSC) during tumor progression and therapy have been implicated in metastasis formation and resistance to anti-angiogenic treatments. Here, we used the 4T1 orthotopic syngenic mouse model of mammary adenocarcinoma to investigate the effect of VEGF/VEGFR-2 axis inhibition on lung metastasis, MDSC and regulatory T cells (Tregs). We show that treatment with the anti-VEGFR-2 blocking antibody DC101 inhibits primary tumor growth, angiogenesis and lung metastasis. DC101 treatment had no effect on MDSC mobilization, but partially attenuated the inhibitory effect of mMDSC on T cell proliferation and decreased the frequency of Tregs in primary tumors and lung metastases. Strikingly, DC101 treatment induced the expression of the immune-suppressive molecule arginase I in mMDSC. Treatment with the arginase inhibitor N^ω-hydroxy-nor-Arginine (Nor-NOHA) reduced the inhibitory effect of MDSC on T cell proliferation and inhibited number and size of lung metastasis but had little or no additional effects in combination with DC101. In conclusion, DC101 treatment suppresses 4T1 tumor growth and metastasis, partially reverses the inhibitory effect of mMDSC on T cell proliferation, decreases Tregs in tumors and increases arginase I expression in mMDSC. Arginase inhibition suppresses lung metastasis independently of DC101 effects. These observations contribute to the further characterization of the immunomodulatory effect of anti-VEGF/VEGFR2 therapy and provide a rationale to pursue arginase inhibition as potential anti-metastatic therapy.

Endostatin inhibits the growth and migration of 4T1 mouse breast cancer cells by skewing macrophage polarity toward the M1 phenotype

The phenotypic diversity of tumor-associated macrophages (TAMs) increases with tumor development. One of the hallmarks of malignancy is the polarization of TAMs from a pro-immune (M1) phenotype to an immunosuppressive (M2) phenotype. However, the molecular basis of this process is still unclear. Endostatin is a powerful inhibitor of angiogenesis capable of suppressing tumor growth and metastasis. Here, we demonstrate that endostatin induces RAW264.7 cell polarization toward the M1 phenotype in vitro. Endostatin has no effect on TAM numbers in vivo, but results in an increased proportion of F4/80(+)Nos2(+) cells and a decreased proportion of F4/80(+)CD206(+) cells. Overexpression of endostatin in RAW264.7 cells resulted in a decrease in the phosphorylation of STAT3, an increase in expression of vascular endothelial growth factor A and placental growth factor, and an increase in the phosphorylation of STAT1, IκBα and p65 proteins compared with controls. These results indicate that endostatin regulates macrophage polarization, promoting the M1 phenotype by targeting NF-κB and STAT signaling.

Effect of methacrylic acid beads on the sonic hedgehog signaling pathway and macrophage polarization in a subcutaneous injection mouse model

Poly(methacrylic acid-co-methyl methacrylate) (MAA) beads promote a vascular regenerative response when used in diabetic wound healing. Previous studies reported that MAA beads modulated the expression of sonic hedgehog (Shh) and inflammation related genes in diabetic wounds. The aim of this work was to follow up on these observations in a subcutaneous injection model to study the host response in the absence of the confounding factors of diabetic wound healing. In this model, MAA beads improved vascularization in healthy mice of both sexes compared to control poly(methyl methacrylate) (MM) beads, with a stronger effect seen in males than females. MAA-induced vessels were perfusable, as evidenced from the CLARITY-processed images. In Shh-Cre-eGFP/Ptch1-LacZ non-diabetic transgenic mice, the increased vessel formation was accompanied by a higher density of cells expressing GFP (Shh) and β-Gal (patched 1, Ptch1) suggesting MAA enhanced the activation of the Shh pathway. Ptch1 is the Shh receptor and a target of the pathway. MAA beads also modulated the inflammatory cell infiltrate in CD1 mice: more neutrophils and more macrophages were noted with MAA relative to MM beads at days 1 and 7, respectively. In addition, MAA beads biased macrophages towards a MHCII-CD206+ ("M2") polarization state. This study suggests that the Shh pathway and an altered inflammatory response are two elements of the complex mechanism whereby MAA-based biomaterials effect vascular regeneration.

Macrophages: An Inflammatory Link Between Angiogenesis and Lymphangiogenesis

Angiogenesis and lymphangiogenesis often occur in response to tissue injury or in the presence of pathology (e.g., cancer), and it is these types of environments in which macrophages are activated and increased in number. Moreover, the blood vascular microcirculation and the lymphatic circulation serve as the conduits for entry and exit for monocyte-derived macrophages in nearly every tissue and organ. Macrophages both affect and are affected by the vessels through which they travel. Therefore, it is not surprising that examination of macrophage behaviors in both angiogenesis and lymphangiogenesis has yielded interesting observations that suggest macrophages may be key regulators of these complex growth and remodeling processes. In this review, we will take a closer look at macrophages through the lens of angiogenesis and lymphangiogenesis, examining how their dynamic behaviors may regulate vessel sprouting and function. We present macrophages as a cellular link that spatially and temporally connects angiogenesis with lymphangiogenesis, in both physiological growth and in pathological adaptations, such as tumorigenesis. As such, attempts to therapeutically target macrophages in order to affect these processes may be particularly effective, and studying macrophages in both settings will accelerate the field's understanding of this important cell type in health and disease.

Cellular Model of Atherogenesis Based on Pluripotent Vascular Wall Pericytes

Pericytes are pluripotent cells that can be found in the vascular wall of both microvessels and large arteries and veins. They have distinct morphology with long branching processes and form numerous contacts with each other and with endothelial cells, organizing the vascular wall cells into a three-dimensional network. Accumulating evidence demonstrates that pericytes may play a key role in the pathogenesis of vascular disorders, including atherosclerosis. Macrovascular pericytes are able to accumulate lipids and contribute to growth and vascularization of the atherosclerotic plaque. Moreover, they participate in the local inflammatory process and thrombosis, which can lead to fatal consequences. At the same time, pericytes can represent a useful model for studying the atherosclerotic process and for the development of novel therapeutic approaches. In particular, they are suitable for testing various substances' potential for decreasing lipid accumulation induced by the incubation of cells with atherogenic low-density lipoprotein. In this review we will discuss the application of cellular models for studying atherosclerosis and provide several examples of successful application of these models to drug research.

Mycobacterium tuberculosis H37Rv infected THP-1 cells induce epithelial mesenchymal transition (EMT) in lung adenocarcinoma epithelial cell line (A549)

Chronic infections of Mycobacterium tuberculosis (MTB) cause oxidative stress, TLR activation and production of inflammatory cytokines and thus can create an environment reinforcing tumorigenesis, progression and metastasis. Epidemiological studies have established a relation between lung cancer and tuberculosis but cellular mechanism is still poorly understood. In present study, we have shown for the first time that MTB infection in human monocytic cell line (THP-1) enhances invasion and induces EMT characteristics in lung adenocarcinoma cell line (A549) during co-culture. After co-culture with MTB infected THP-1 cells A549 cells exhibited morphological and molecular signatures of EMT. During co-culture, expression of inflammatory cytokines like TNF-α, IL-1β and IL-6 was enhanced in the microenvironment of A549 cells in comparison to single culture of A549 cells. Using pharmacological inhibitors of JNK (SP-600125) and p38 MAPK (SB-203580), we demonstrated the involvement of JNK and p38 MAPK in MTB induced EMT induction in A549 cells. To the best of our knowledge this is the first report demonstrating the role of MTB infection in induction of metastasis associated EMT in lung cancer.

The glioblastoma vasculature as a target for cancer therapy

Glioblastoma is characterized by microvascular proliferation and a highly abnormal dysfunctional vasculature. The glioblastoma vessels differ significantly from normal brain vessels morphologically, functionally and molecularly. The present review provides a brief overview of the current understanding of the formation, functional abnormalities and specific gene expression of glioblastoma vessels and the consequences of vascular abnormalization for the tumour microenvironment.

Compensatory angiogenesis and tumor refractoriness

Since the establishment of tumor angiogenesis as a therapeutic target, an excitement in developing the anti-angiogenic agents was resulted in tailoring a humanized monoclonal antibody (Bevacizumab) against vascular endothelial growth factor (VEGF): a key factor in recruiting angiogenesis. The past three decades' research in the area of angiogenesis also invented a series of novel and effective anti-angiogenic agents targeting the VEGF signaling axis. Despite the demonstrable clinical benefits of anti-angiogenic therapy, the preclinical and clinical data of the current therapeutic settings clearly indicate the transient efficacy, restoration of tumor progression and aggressive recurrence of tumor invasion after the withdrawal of anti-angiogenic therapy. Therefore, the impact of this therapeutic regime on improving overall survival of patients has been disappointing in clinic. The recent advances in pathophysiology of tumor angiogenesis and related molecular and cellular underpinnings attributed the conspiracy of compensatory angiogenic pathways in conferring evasive and intrinsic tumor resistance to anti-angiogenic agents. The understandings of how these pathways functionally cross-talk for sustaining tumor angiogenesis during VEGF blockade is essential and perhaps may act as a basic prerequisite for designing novel therapeutic strategies to combat the growing arrogance of tumors toward anti-angiogenic agents. The present review offers a discourse on major compensatory angiogenic pathways operating at cellular and molecular levels and their attributes with resistance to anti-angiogenic agents along with strategic opinions on future setting in targeting tumor angiogenesis.

Glioblastoma: a pathogenic crosstalk between tumor cells and pericytes

Cancers likely originate in progenitor zones containing stem cells and perivascular stromal cells. Much evidence suggests stromal cells play a central role in tumor initiation and progression. Brain perivascular cells (pericytes) are contractile and function normally to regulate vessel tone and morphology, have stem cell properties, are interconvertible with macrophages and are involved in new vessel formation during angiogenesis. Nevertheless, how pericytes contribute to brain tumor infiltration is not known. In this study we have investigated the underlying mechanism by which the most lethal brain cancer, Glioblastoma Multiforme (GBM) interacts with pre-existing blood vessels (co-option) to promote tumor initiation and progression. Here, using mouse xenografts and laminin-coated silicone substrates, we show that GBM malignancy proceeds via specific and previously unknown interactions of tumor cells with brain pericytes. Two-photon and confocal live imaging revealed that GBM cells employ novel, Cdc42-dependent and actin-based cytoplasmic extensions, that we call flectopodia, to modify the normal contractile activity of pericytes. This results in the co-option of modified pre-existing blood vessels that support the expansion of the tumor margin. Furthermore, our data provide evidence for GBM cell/pericyte fusion-hybrids, some of which are located on abnormally constricted vessels ahead of the tumor and linked to tumor-promoting hypoxia. Remarkably, inhibiting Cdc42 function impairs vessel co-option and converts pericytes to a phagocytic/macrophage-like phenotype, thus favoring an innate immune response against the tumor. Our work, therefore, identifies for the first time a key GBM contact-dependent interaction that switches pericyte function from tumor-suppressor to tumor-promoter, indicating that GBM may harbor the seeds of its own destruction. These data support the development of therapeutic strategies directed against co-option (preventing incorporation and modification of pre-existing blood vessels), possibly in combination with anti-angiogenesis (blocking new vessel formation), which could lead to improved vascular targeting not only in Glioblastoma but also for other cancers.

The complexity of cell composition of the intima of large arteries: focus on pericyte-like cells

Pericytes, which are also known as Rouget cells or perivascular cells, are considered to represent a likely distinct pool of vascular cells that are extremely branched and located mostly in the periphery of the vascular system. The family of pericytes is a heterogeneous cell population that includes pericytes and pericyte-like cells. Accumulated data indicate that networks of pericyte-like cells exist in normal non-atherosclerotic intima, and that pericyte-like cells can be involved in the development of atherosclerotic lesions from the very early stages of disease. The pathogenic role of arterial pericytes and pericyte-like cells also might be important in advanced and complicated atherosclerotic lesions via realizing mechanisms of vascular remodelling, ectopic ossification, intraplaque neovascularization, and probably thrombosis.

Eribulin mesylate exerts specific gene expression changes in pericytes and shortens pericyte-driven capillary network in vitro

Background

Eribulin mesylate is a synthetic macrocyclic ketone analog of the marine sponge natural product halichondrin B. Eribulin is a tubulin-binding drug and approved in many countries worldwide for treatment of certain patients with advanced breast cancer. Here we investigated antiproliferative and antiangiogenic effects of eribulin on vascular cells, human umbilical vein endothelial cells (HUVECs) and human brain vascular pericytes (HBVPs), in vitro in comparison with another tubulin-binding drug, paclitaxel.

Methods

HUVECs and HBVPs were treated with either eribulin or paclitaxel and their antiproliferative effects were evaluated. Global gene expression profiling changes caused by drug treatments were studied using Affymetrix microarray platform and custom TaqMan Low Density Cards. To examine effects of the drugs on pericyte-driven in vitro angiogenesis, we compared lengths of capillary networks in co-cultures of HUVECs with HBVPs.

Results

Both eribulin and paclitaxel showed potent activities in in vitro proliferation of HUVECs and HBVPs, with the half-maximal inhibitory concentrations (IC₅₀) in low- to sub-nmol/L concentrations. When gene expression changes were assessed in HUVECs, the majority of affected genes overlapped for both treatments (59%), while in HBVPs, altered gene signatures were drug-dependent and the overlap was limited to just 12%. In HBVPs, eribulin selectively affected 11 pathways (p < 0.01) such as Cell Cycle Control of Chromosomal Replication. In contrast, paclitaxel was tended to regulate 27 pathways such as PI3K/AKT. Only 5 pathways were commonly affected by both treatments. In in vitro pericyte-driven angiogenesis model, paclitaxel showed limited activity while eribulin shortened the formed capillary networks of HUVECs driven by HBVPs at low nmol/L concentrations starting at day 3 after treatments.

Conclusions

Our findings suggest that pericytes, but not endothelial cells, responded differently, to two mechanistically-distinct tubulin-binding drugs, eribulin and paclitaxel. While eribulin and paclitaxel induced similar changes in gene expression in endothelial cells, in pericytes their altered gene expression was unique and drug-specific. In the functional endothelial-pericyte co-culture assay, eribulin, but not paclitaxel showed strong efficacy not only as a cytotoxic drug but also as a potent antivascular agent that affected pericyte-driven in vitro angiogenesis.

Angiogenesis in spontaneous tumors and implications for comparative tumor biology

Blood supply is essential for development and growth of tumors and angiogenesis is the fundamental process of new blood vessel formation from preexisting ones. Angiogenesis is a prognostic indicator for a variety of tumors, and it coincides with increased shedding of neoplastic cells into the circulation and metastasis. Several molecules such as cell surface receptors, growth factors, and enzymes are involved in this process. While antiangiogenic therapy for cancer has been proposed over 20 years ago, it has garnered much controversy in recent years within the scientific community. The complex relationships between the angiogenic signaling cascade and antiangiogenic substances have indicated the angiogenic pathway as a valid target for anticancer drug development and VEGF has become the primary antiangiogenic drug target. This review discusses the basic and clinical perspectives of angiogenesis highlighting the importance of comparative biology in understanding tumor angiogenesis and the integration of these model systems for future drug development.

Obesity promotes breast cancer by CCL2-mediated macrophage recruitment and angiogenesis

Obesity is one of the most important preventable causes of cancer and the most significant risk factor for breast cancer in postmenopausal women. Compared with lean women, obese women are more likely to be diagnosed with a larger, higher grade tumor, an increased incidence of lymph node metastases, and elevated risk of distant recurrence. However, the mechanisms connecting obesity to the pathogenesis of breast cancer are poorly defined. Here, we show that during obesity, adipocytes within human and mouse breast tissues recruit and activate macrophages through a previously uncharacterized CCL2/IL-1β/CXCL12 signaling pathway. Activated macrophages in turn promote stromal vascularization and angiogenesis even before the formation of cancer. Recapitulating these changes using a novel humanized breast cancer model was sufficient to promote angiogenesis and prime the microenvironment prior to neoplastic transformation for accelerated breast oncogenesis. These findings provide a mechanistic role for adipocytes and macrophages before carcinogenesis that may be critical for prevention and treatment of obesity-related cancer.

Rheumatoid arthritis with deficiency pattern in traditional chinese medicine shows correlation with cold and hot patterns in gene expression profiles

In our precious study, the correlation between cold and hot patterns in traditional Chinese medicine (TCM) and gene expression profiles in rheumatoid arthritis (RA) has been explored. Based on TCM theory, deficiency pattern is another key pattern diagnosis among RA patients, which leads to a specific treatment principle in clinical management. Therefore, a further analysis was performed aiming at exploring the characteristic gene expression profile of deficiency pattern and its correlation with cold and hot patterns in RA patients by bioinformatics analysis approach based on gene expression profiles data detected with microarray technology. The TCM deficiency pattern-related genes network comprises 7 significantly, highly connected regions which are mainly involved in protein transcription processes, protein ubiquitination, toll-like receptor activated NF- κ B regulated gene transcription and apoptosis, RNA clipping, NF- κ B signal, nucleotide metabolism-related apoptosis, and immune response processes. Toll-like receptor activated NF- κ B regulated gene transcription and apoptosis pathways are potential specific pathways related to TCM deficiency patterns in RA patients; TCM deficiency pattern is probably related to immune response. Network analysis can be used as a powerful tool for detecting the characteristic mechanism related to specific TCM pattern and the correlations between different patterns.

Distribution of bone-marrow-derived endothelial and immune cells in a murine colitis-associated colorectal cancer model

Inflammatory bowel disease (IBD) can lead to an increased risk of developing colorectal cancer (CRC). The aim of this study was to establish a model for combined bone marrow transplantation (BMT) and colitis-associated colorectal cancer (CAC) and to define the contribution of BM-derived cells during the inflammation associated with carcinogenesis. We established a model for BMT using green fluorescent protein (GFP) transgenic mice, followed by AOM/DSS-induced CAC, and performed confocal microscopy analysis on in vivo living tissue and frozen tumor sections. Our imaging analyses showed that GFP-positive cells extensively infiltrated the tumor stroma and that some WGA and GFP or CD31 and GFP double-positive cells were observed in the lining of tumor vessels. Flow cytometry analysis of the tumor-infiltrating cells showed that the GFP-positive CD11c+ DCs cells were one-third of the GFP+/CD11C- cells, and that half of these DCs (0.96% vs 1.02%) were GFP-positive BM-derived cells. The majority of CD4⁺ T cells were GFP-negative (12.02% vs 1.9%), and we discovered a novel CD4⁺ CD11c⁺ DC subset (0.34% vs 1.64%). In conclusion, we defined the distribution of BM-derived endothelial cells, CD11c⁺ DCs and CD4⁺ T cells in tumors. This model might be useful for elucidating the diverse BM-derived cell types and functions during the progression of colitis-associated colorectal cancer.

The many facets of PEDF in drug discovery and disease: a diamond in the rough or split personality disorder?

INTRODUCTION

Pigment epithelium-derived factor (PEDF) was discovered as a neurotrophic factor secreted by retinal pigment epithelial cells. A decade later, it re-emerged as a powerful angiogenesis inhibitor guarding ocular function. Since then, significant advances were made identifying PEDF's mechanisms, targets and biomedical applications.

AREAS COVERED

The authors review several methodologies that have generated significant new information about the potential of PEDF as a drug. Furthermore, the authors review and discuss mechanistic and structure-function analyses combined with the functional mapping of active fragments, which have yielded several short bioactive PEDF peptides. Additionally, the authors present functional studies in knockout animals and human correlates that have provided important information about conditions amenable to PEDF-based therapies.

EXPERT OPINION

Through its four known receptors, PEDF causes a wide range of cellular events vitally important for the organism, which include survival and differentiation, migration and invasion, lipid metabolism and stem cell maintenance. These processes are deregulated in multiple pathological conditions, including cancer, metabolic and cardiovascular disease. PEDF has been successfully used in countless preclinical models of these conditions and human correlates suggest a wide utility of PEDF-based drugs. The most significant clinical application of PEDF, to date, is its potential therapeutic use for age-related macular degeneration. Moreover, PEDF-based gene therapy has advanced to early stage clinical trials. PEDF active fragments have been mapped and used to design short peptide mimetics conferring distinct functions of PEDF, which may address specific clinical problems and become prototype drugs.

MSC and Tumors: Homing, Differentiation, and Secretion Influence Therapeutic Potential

: Mesenchymal stromal/stem cells (MSC) are adult multipotent progenitors with fibroblast-like morphology able to differentiate into adipocytic, osteogenic, chondrogenic, and myogenic lineages. Due to these properties, MSC have been studied and introduced as therapeutics in regenerative medicine. Preliminary studies have also shown a possible involvement of MSC as precursors of cellular elements within tumor microenvironments, in particular tumor-associated fibroblasts (TAF). Among a number of different possible origins, TAF may originate from a pool of circulating progenitors from bone marrow or adipose tissue-derived MSC. There is growing evidence to corroborate that cells immunophenotypically defined as MSC are able to reside as TAF influencing the tumor microenvironment in a potentially bi-phasic and obscure manner: either promoting or inhibiting growth depending on tumor context and MSC sources. Here we focus on relationships between the tumor microenvironment, cancer cells, and MSC, analyzing their diverse ability to influence neoplastic development. Associated activities include MSC homing driven by the secretion of various mediators, differentiation towards TAF phenotypes, and reciprocal interactions with the tumor cells. These are reviewed here with the aim of understanding the biological functions of MSC that can be exploited for innovative cancer therapy.