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Showing papers on "Angiogenesis published in 2008"


Journal ArticleDOI
TL;DR: Emerging data support a proposition that two modes of unconventional resistance underlieAngiogenesis inhibitors targeting the vascular endothelial growth factor signalling pathways are affording demonstrable therapeutic efficacy in mouse models of cancer and in an increasing number of human cancers.
Abstract: In both preclinical and clinical settings, the benefits of angiogenesis inhibitors targeting the vascular endothelial growth factor signalling pathways are at best transitory and followed by restoration of tumour growth and progression. Emerging data support a proposition that two modes of unconventional resistance underlie such results.

2,670 citations


Journal ArticleDOI
TL;DR: Basic aspects of the PDGF ligands and receptors, their developmental and pathological functions, principles of their pharmacological inhibition, and results using PDGF pathway-inhibitory or stimulatory drugs in preclinical and clinical contexts are reviewed.
Abstract: Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) have served as prototypes for growth factor and receptor tyrosine kinase function for more than 25 years. Studies of PDGFs and PDGFRs in animal development have revealed roles for PDGFR-alpha signaling in gastrulation and in the development of the cranial and cardiac neural crest, gonads, lung, intestine, skin, CNS, and skeleton. Similarly, roles for PDGFR-beta signaling have been established in blood vessel formation and early hematopoiesis. PDGF signaling is implicated in a range of diseases. Autocrine activation of PDGF signaling pathways is involved in certain gliomas, sarcomas, and leukemias. Paracrine PDGF signaling is commonly observed in epithelial cancers, where it triggers stromal recruitment and may be involved in epithelial-mesenchymal transition, thereby affecting tumor growth, angiogenesis, invasion, and metastasis. PDGFs drive pathological mesenchymal responses in vascular disorders such as atherosclerosis, restenosis, pulmonary hypertension, and retinal diseases, as well as in fibrotic diseases, including pulmonary fibrosis, liver cirrhosis, scleroderma, glomerulosclerosis, and cardiac fibrosis. We review basic aspects of the PDGF ligands and receptors, their developmental and pathological functions, principles of their pharmacological inhibition, and results using PDGF pathway-inhibitory or stimulatory drugs in preclinical and clinical contexts.

2,074 citations


Journal ArticleDOI
TL;DR: Limiting the effects of IL-8 signaling may be a significant therapeutic intervention in targeting the tumor microenvironment because of its role in regulating the transcriptional activity of the androgen receptor.
Abstract: Interleukin-8 (IL-8) is a proinflammatory CXC chemokine associated with the promotion of neutrophil chemotaxis and degranulation. This chemokine activates multiple intracellular signaling pathways downstream of two cell-surface, G protein-coupled receptors (CXCR1 and CXCR2). Increased expression of IL-8 and/or its receptors has been characterized in cancer cells, endothelial cells, infiltrating neutrophils, and tumor-associated macrophages, suggesting that IL-8 may function as a significant regulatory factor within the tumor microenvironment. The induction of IL-8 signaling activates multiple upstream signaling pathways that (a) impinge on gene expression via regulation of numerous transcription factor activities, (b) modulate the cellular proteome at the level of translation, and/or (c) effect the organization of the cell cytoskeleton through posttranslational regulation of regulatory proteins. As a consequence of the diversity of effectors and downstream targets, IL-8 signaling promotes angiogenic responses in endothelial cells, increases proliferation and survival of endothelial and cancer cells, and potentiates the migration of cancer cells, endothelial cells, and infiltrating neutrophils at the tumor site. Accordingly, IL-8 expression correlates with the angiogenesis, tumorigenicity, and metastasis of tumors in numerous xenograft and orthotopic in vivo models. Recently, IL-8 signaling has been implicated in regulating the transcriptional activity of the androgen receptor, underpinning the transition to an androgen-independent proliferation of prostate cancer cells. In addition, stress and drug-induced IL-8 signaling has been shown to confer chemotherapeutic resistance in cancer cells. Therefore, inhibiting the effects of IL-8 signaling may be a significant therapeutic intervention in targeting the tumor microenvironment.

1,852 citations


Journal ArticleDOI
TL;DR: It is shown that an endothelial cell-restricted microRNA (miR-126) mediates developmental angiogenesis in vivo and enhances the proangiogenic actions of VEGF and FGF and promotes blood vessel formation by repressing the expression of Spred-1, an intracellular inhibitor of angiogenic signaling.

1,682 citations


Journal ArticleDOI
TL;DR: It is found that miR-126 regulated the response of endothelial cells to VEGF, providing a new target for modulating vascular formation and function and illustrating that a single miRNA can regulate vascular integrity and angiogenesis.

1,528 citations


Journal ArticleDOI
TL;DR: It is demonstrated that HIF1alpha, the direct effector of hypoxia, partly through increases in SDF1 alpha, induces recruitment of bone marrow-derived CD45+ myeloid cells containing Tie2+, VEGFR1+, CD11b+, and F4/80+ subpopulations, as well as endothelial and pericyte progenitor cells to promote neovascularization in glioblastoma.

1,083 citations


Journal ArticleDOI
TL;DR: Curcumin has been found to inhibit the proliferation of various tumor cells in culture, prevents carcinogen-induced cancers in rodents, and inhibits the growth of human tumors in xenotransplant or orthOTransplant animal models either alone or in combination with chemotherapeutic agents or radiation.

1,006 citations


Journal ArticleDOI
21 Feb 2008-Nature
TL;DR: PGC-1α and ERR-α, major regulators of mitochondrial function in response to exercise and other stimuli, also control a novel angiogenic pathway that delivers needed oxygen and substrates, and may provide a novel therapeutic target for treating ischaemic diseases.
Abstract: Ischaemia of the heart, brain and limbs is a leading cause of morbidity and mortality worldwide. Hypoxia stimulates the secretion of vascular endothelial growth factor (VEGF) and other angiogenic factors, leading to neovascularization and protection against ischaemic injury. Here we show that the transcriptional coactivator PGC-1alpha (peroxisome-proliferator-activated receptor-gamma coactivator-1alpha), a potent metabolic sensor and regulator, is induced by a lack of nutrients and oxygen, and PGC-1alpha powerfully regulates VEGF expression and angiogenesis in cultured muscle cells and skeletal muscle in vivo. PGC-1alpha-/- mice show a striking failure to reconstitute blood flow in a normal manner to the limb after an ischaemic insult, whereas transgenic expression of PGC-1alpha in skeletal muscle is protective. Surprisingly, the induction of VEGF by PGC-1alpha does not involve the canonical hypoxia response pathway and hypoxia inducible factor (HIF). Instead, PGC-1alpha coactivates the orphan nuclear receptor ERR-alpha (oestrogen-related receptor-alpha) on conserved binding sites found in the promoter and in a cluster within the first intron of the VEGF gene. Thus, PGC-1alpha and ERR-alpha, major regulators of mitochondrial function in response to exercise and other stimuli, also control a novel angiogenic pathway that delivers needed oxygen and substrates. PGC-1alpha may provide a novel therapeutic target for treating ischaemic diseases.

995 citations


Journal ArticleDOI
TL;DR: The evidence implicating integrins as a family of fundamental regulators of angiogenesis and lymphangiogenesis is reviewed, and several integrin-targeted therapeutic agents are currently in clinical trials for cancer therapy.
Abstract: Blood vessels promote tumour growth, and both blood and lymphatic vessels facilitate tumour metastasis by serving as conduits for the transport of tumour cells to new sites. Angiogenesis and lymphangiogenesis are regulated by integrins, which are members of a family of cell surface receptors whose ligands are extracellular matrix proteins and immunoglobulin superfamily molecules. Select integrins promote endothelial cell migration and survival during angiogenesis and lymphangiogenesis, whereas other integrins promote pro-angiogenic macrophage trafficking to tumours. Several integrin-targeted therapeutic agents are currently in clinical trials for cancer therapy. Here, we review the evidence implicating integrins as a family of fundamental regulators of angiogenesis and lymphangiogenesis.

969 citations


Journal ArticleDOI
TL;DR: The role of TAM in the inflammatory micro-environment of solid tumors is discussed and a potential target for future therapeutic approaches is identified.
Abstract: The link between inflammation and cancer proposed more than a century ago by Rudolf Virchow, who noticed the infiltration of leukocytes in malignant tissues, has recently found a number of genetic and molecular confirmations. Experimental, clinical and epidemiological studies have revealed that chronic inflammation contributes to cancer progression and even predisposes to different types of cancer. Cancer-associated inflammation includes: the presence of leukocyte infiltration; the expression of cytokines such as tumor necrosis factor (TNF) or interleukin (IL)-1; chemokines such as CCL2 and CXCL8; active tissue remodelling and neo-angiogenesis. Tumor-associated macrophages (TAM) are key regulators of the link between inflammation and cancer. Many observations indicate that, in the tumor micro-environment, TAM have several protumoral functions, including expression of growth factors, matrix proteases, promotion of angiogenesis and suppression of adaptive immunity. In this review we will discuss the role of TAM in the inflammatory micro-environment of solid tumors and will try to identify potential target for future therapeutic approaches.

914 citations


Journal ArticleDOI
TL;DR: Although BIBF 1120 is rapidly metabolized in vivo by methylester cleavage, resulting in a short mean residence time, once daily oral dosing is fully efficacious in xenograft models, preclinical findings suggest that long-term clinical outcomes may improve with blockade of additional proangiogenic receptor tyrosine kinases.
Abstract: Inhibition of tumor angiogenesis through blockade of the vascular endothelial growth factor (VEGF) signaling pathway is a novel treatment modality in oncology. Preclinical findings suggest that long-term clinical outcomes may improve with blockade of additional proangiogenic receptor tyrosine kinases: platelet-derived growth factor receptors (PDGFR) and fibroblast growth factor receptors (FGFR). BIBF 1120 is an indolinone derivative potently blocking VEGF receptor (VEGFR), PDGFR and FGFR kinase activity in enzymatic assays (IC50, 20–100 nmol/L). BIBF 1120 inhibits mitogen-activated protein kinase and Akt signaling pathways in three cell types contributing to angiogenesis, endothelial cells, pericytes, and smooth muscle cells, resulting in inhibition of cell proliferation (EC50, 10–80 nmol/L) and apoptosis. In all tumor models tested thus far, including human tumor xenografts growing in nude mice and a syngeneic rat tumor model, BIBF 1120 is highly active at well-tolerated doses (25–100 mg/kg daily p.o.), as measured by magnetic resonance imaging of tumor perfusion after 3 days, reducing vessel density and vessel integrity after 5 days, and inducing profound growth inhibition. A distinct pharmacodynamic feature of BIBF 1120 in cell culture is sustained pathway inhibition (up to 32 hours after 1-hour treatment), suggesting slow receptor off-kinetics. Although BIBF 1120 is rapidly metabolized in vivo by methylester cleavage, resulting in a short mean residence time, once daily oral dosing is fully efficacious in xenograft models. These distinctive pharmacokinetic and pharmacodynamic properties may help explain clinical observations with BIBF 1120, currently entering phase III clinical development. [Cancer Res 2008;68(12):4774–82]

Journal ArticleDOI
03 Apr 2008-Nature
TL;DR: It is shown that generic siRNAs might treat angiogenic disorders that affect 8% of the world’s population, and that si RNAs might induce unanticipated vascular or immune effects.
Abstract: Clinical trials of small interfering RNA (siRNA) targeting vascular endothelial growth factor-A (VEGFA) or its receptor VEGFR1 (also called FLT1), in patients with blinding choroidal neovascularization (CNV) from age-related macular degeneration, are premised on gene silencing by means of intracellular RNA interference (RNAi). We show instead that CNV inhibition is a siRNA-class effect: 21-nucleotide or longer siRNAs targeting non-mammalian genes, non-expressed genes, non-genomic sequences, pro- and anti-angiogenic genes, and RNAi-incompetent siRNAs all suppressed CNV in mice comparably to siRNAs targeting Vegfa or Vegfr1 without off-target RNAi or interferon-α/β activation. Non-targeted (against non-mammalian genes) and targeted (against Vegfa or Vegfr1) siRNA suppressed CNV via cell-surface toll-like receptor 3 (TLR3), its adaptor TRIF, and induction of interferon-γ and interleukin-12. Non-targeted siRNA suppressed dermal neovascularization in mice as effectively as Vegfa siRNA. siRNA-induced inhibition of neovascularization required a minimum length of 21 nucleotides, a bridging necessity in a modelled 2:1 TLR3–RNA complex. Choroidal endothelial cells from people expressing the TLR3 coding variant 412FF were refractory to extracellular siRNA-induced cytotoxicity, facilitating individualized pharmacogenetic therapy. Multiple human endothelial cell types expressed surface TLR3, indicating that generic siRNAs might treat angiogenic disorders that affect 8% of the world’s population, and that siRNAs might induce unanticipated vascular or immune effects.

Journal ArticleDOI
TL;DR: The identification of miRNAs and their respective targets may offer new therapeutic strategies to treat vascular diseases such as atherosclerosis, to improve neovascularization after ischaemia, or to prevent tumour progression.
Abstract: The integrity of the endothelial monolayer is fundamental for the homoeostasis of the vascular system. Functional endothelial cells are also required for the growth of new blood vessels during neovascularization. Although multiple growth factors have been shown to regulate angiogenesis and vascular development, little is known about the complex upstream regulation of gene expression and translation. MicroRNAs (miRNAs) are an emerging class of highly conserved, non-coding small RNAs that regulate gene expression on the post-transcriptional level by inhibiting the translation of protein from mRNA or by promoting the degradation of mRNA. More than 500 human miRNAs have been identified so far, and increasing evidence indicates that miRNAs have distinct expression profiles and play crucial roles in various physiological and pathological processes such as cardiogenesis, haematopoietic lineage differentiation, and oncogenesis. Meanwhile, a few specific miRNAs that regulate endothelial cell functions and angiogenesis have been described. Let7-f, miR-27b, and mir-130a were identified as pro-angiogenic miRNAs. In contrast, miR-221 and miR-222 inhibit endothelial cell migration, proliferation, and angiogenesis in vitro by targeting the stem cell factor receptor c-kit and indirectly regulating endothelial nitric oxide synthase expression. Moreover, some miRNAs are involved in tumour angiogenesis such as the miR-17-92 cluster and miR-378. Early studies also indicate the contribution of specific miRNAs (e.g. miR-155, miR-21, and miR-126) to vascular inflammation and diseases. Thus, the identification of miRNAs and their respective targets may offer new therapeutic strategies to treat vascular diseases such as atherosclerosis, to improve neovascularization after ischaemia, or to prevent tumour progression.

Journal ArticleDOI
01 Feb 2008-Blood
TL;DR: Using double immunofluorescence and immunoelectron microscopy, it is shown that pro- and antiangiogenic proteins are separated in distinct subpopulations of alpha-granules in platelets and megakaryocytes, which may provide a mechanism by which platelets can locally stimulate or inhibit angiogenesis.

Journal ArticleDOI
TL;DR: It is shown that human bone marrow-derived mesenchymal stem cells exposed to tumor-conditioned medium (TCM) over a prolonged period of time assume a CAF-like myofibroblastic phenotype, which suggests that hMSCs are a source of CAFs and can be used in the modeling of tumor-stroma interactions.
Abstract: Carcinoma-associated fibroblasts (CAF) have recently been implicated in important aspects of epithelial solid tumor biology, such as neoplastic progression, tumor growth, angiogenesis, and metastasis. However, neither the source of CAFs nor the differences between CAFs and fibroblasts from nonneoplastic tissue have been well defined. In this study, we show that human bone marrow–derived mesenchymal stem cells (hMSCs) exposed to tumor-conditioned medium (TCM) over a prolonged period of time assume a CAF-like myofibroblastic phenotype. More importantly, these cells exhibit functional properties of CAFs, including sustained expression of stromal-derived factor-1 (SDF-1) and the ability to promote tumor cell growth both in vitro and in an in vivo coimplantation model, and expression of myofibroblast markers, including α-smooth muscle actin and fibroblast surface protein. hMSCs induced to differentiate to a myofibroblast-like phenotype using 5-azacytidine do not promote tumor cell growth as efficiently as hMSCs cultured in TCM nor do they show increased SDF-1 expression. Furthermore, gene expression profiling revealed similarities between TCM-exposed hMSCs and CAFs. Taken together, these data suggest that hMSCs are a source of CAFs and can be used in the modeling of tumor-stroma interactions. To our knowledge, this is the first report showing that hMSCs become activated and resemble carcinoma-associated myofibroblasts on prolonged exposure to conditioned medium from MDAMB231 human breast cancer cells. [Cancer Res 2008;68(11):4331–9]

Journal ArticleDOI
31 Jul 2008-Nature
TL;DR: It is demonstrated that VEGFR-3 is highly expressed in angiogenic sprouts, and genetic targeting or blocking of VEG FR-3 signalling with monoclonal antibodies results in decreased sprouting, vascular density, vessel branching and endothelial cell proliferation in mouse angiogenesis models, implicate VEGfr-3 as a regulator of vascular network formation.
Abstract: Angiogenesis, the growth of new blood vessels from pre-existing vasculature, is a key process in several pathological conditions, including tumour growth and age-related macular degeneration. Vascular endothelial growth factors (VEGFs) stimulate angiogenesis and lymphangiogenesis by activating VEGF receptor (VEGFR) tyrosine kinases in endothelial cells. VEGFR-3 (also known as FLT-4) is present in all endothelia during development, and in the adult it becomes restricted to the lymphatic endothelium. However, VEGFR-3 is upregulated in the microvasculature of tumours and wounds. Here we demonstrate that VEGFR-3 is highly expressed in angiogenic sprouts, and genetic targeting of VEGFR-3 or blocking of VEGFR-3 signalling with monoclonal antibodies results in decreased sprouting, vascular density, vessel branching and endothelial cell proliferation in mouse angiogenesis models. Stimulation of VEGFR-3 augmented VEGF-induced angiogenesis and sustained angiogenesis even in the presence of VEGFR-2 (also known as KDR or FLK-1) inhibitors, whereas antibodies against VEGFR-3 and VEGFR-2 in combination resulted in additive inhibition of angiogenesis and tumour growth. Furthermore, genetic or pharmacological disruption of the Notch signalling pathway led to widespread endothelial VEGFR-3 expression and excessive sprouting, which was inhibited by blocking VEGFR-3 signals. Our results implicate VEGFR-3 as a regulator of vascular network formation. Targeting VEGFR-3 may provide additional efficacy for anti-angiogenic therapies, especially towards vessels that are resistant to VEGF or VEGFR-2 inhibitors.

Journal ArticleDOI
TL;DR: The present article highlights the role of various proinflammatory mediators in carcinogenesis and their promise as potential targets for chemoprevention of inflammation-associated carcinogenesis.
Abstract: Chronic inflammation plays a multifaceted role in carcinogenesis. Mounting evidence from preclinical and clinical studies suggests that persistent inflammation functions as a driving force in the journey to cancer. The possible mechanisms by which inflammation can contribute to carcinogenesis include induction of genomic instability, alterations in epigenetic events and subsequent inappropriate gene expression, enhanced proliferation of initiated cells, resistance to apoptosis, aggressive tumor neovascularization, invasion through tumor-associated basement membrane and metastasis, etc. Inflammation-induced reactive oxygen and nitrogen species cause damage to important cellular components (e.g., DNA, proteins and lipids), which can directly or indirectly contribute to malignant cell transformation. Overexpression, elevated secretion, or abnormal activation of proinflammatory mediators, such as cytokines, chemokines, cyclooxygenase-2, prostaglandins, inducible nitric oxide synthase, and nitric oxide, and a distinct network of intracellular signaling molecules including upstream kinases and transcription factors facilitate tumor promotion and progression. While inflammation promotes development of cancer, components of the tumor microenvironment, such as tumor cells, stromal cells in surrounding tissue and infiltrated inflammatory/immune cells generate an intratumoral inflammatory state by aberrant expression or activation of some proinflammatory molecules. Many of proinflammatory mediators, especially cytokines, chemokines and prostaglandins, turn on the angiogenic switches mainly controlled by vascular endothelial growth factor, thereby inducing inflammatory angiogenesis and tumor cell-stroma communication. This will end up with tumor angiogenesis, metastasis and invasion. Moreover, cellular microRNAs are emerging as a potential link between inflammation and cancer. The present article highlights the role of various proinflammatory mediators in carcinogenesis and their promise as potential targets for chemoprevention of inflammation-associated carcinogenesis.

Journal ArticleDOI
TL;DR: HIF regulates multiple aspects of tumorigenesis, including angiogenesis, proliferation, metabolism, metastasis, differentiation, and response to radiation therapy, making it a critical regulator of the malignant phenotype.
Abstract: Hypoxia-inducible factors (HIFs) are essential mediators of the cellular oxygen-signaling pathway. They are heterodimeric transcription factors consisting of an oxygen-sensitive alpha subunit (HIF-α) and a constitutive beta subunit (HIF-β) that facilitate both oxygen delivery and adaptation to oxygen deprivation by regulating the expression of genes that control glucose uptake, metabolism, angiogenesis, erythropoiesis, cell proliferation, and apoptosis. In most experimental models, the HIF pathway is a positive regulator of tumor growth as its inhibition often results in tumor suppression. In clinical samples, HIF is found elevated and correlates with poor patient prognosis in a variety of cancers. In summary, HIF regulates multiple aspects of tumorigenesis, including angiogenesis, proliferation, metabolism, metastasis, differentiation, and response to radiation therapy, making it a critical regulator of the malignant phenotype.

Journal ArticleDOI
TL;DR: Results from the laboratory and others support a role for CSCs in the angiogenic drive as well as the mechanism of antiangiogenic agents, which are also becoming integrated in the treatment paradigm of an increasing number of cancers.
Abstract: In an increasing number of cancers, tumor populations called cancer stem cells (CSCs), or tumor-initiating cells, have been defined in functional assays of self-renewal and tumor initiation. Moreov...

Journal ArticleDOI
11 Jan 2008-Science
TL;DR: It is shown that tumors induce expression of the transcription factor Id1 in the EPCs and that suppression of Id1 after metastatic colonization blocked EPC mobilization, caused angiogenesis inhibition, impaired pulmonary macrometastases, and increased survival of tumor-bearing animals.
Abstract: Angiogenesis-mediated progression of micrometastasis to lethal macrometastasis is the major cause of death in cancer patients. Here, using mouse models of pulmonary metastasis, we identify bone marrow (BM)-derived endothelial progenitor cells (EPCs) as critical regulators of this angiogenic switch. We show that tumors induce expression of the transcription factor Id1 in the EPCs and that suppression of Id1 after metastatic colonization blocked EPC mobilization, caused angiogenesis inhibition, impaired pulmonary macrometastases, and increased survival of tumor-bearing animals. These findings establish the role of EPCs in metastatic progression in preclinical models and suggest that selective targeting of EPCs may merit investigation as a therapy for cancer patients with lung metastases.

Journal ArticleDOI
TL;DR: Targeting inflammatory pathways following infarction may reduce cardiomyocyte injury and attenuate adverse remodeling, and understanding the role of the immune system in cardiac repair is necessary in order to design optimal strategies for cardiac regeneration.

Journal ArticleDOI
TL;DR: The roles played by VEGF in the pathogenesis of retinopathy of prematurity, diabetic Retinopathy and age-related macular degeneration are described and the potential disadvantages of inhibiting VEGf will be discussed, as will the rationales for targeting other V EGF-related modulators of angiogenesis.

Journal ArticleDOI
TL;DR: The aim of this review is to provide an overview of the recent progress on role of ROS derived from NADPH oxidase and redox signaling events involved in angiogenesis, and to provide insight into the NADPH oxidation andRedox signaling components as potential therapeutic targets for tumorAngiogenesis.

Journal ArticleDOI
TL;DR: It is shown that CD133 negative glioma cells are tumorgenic in nude rats, and thatCD133 positive cells can be obtained from these tumors, suggesting that it may be involved during brain tumor progression.
Abstract: CD133 is a cell surface marker expressed on progenitors of haematopoietic and endothelial cell lineages. Moreover, several studies have identified CD133 as a marker of brain tumor-initiating cells. In this study, human glioblastoma multiforme biopsies were engrafted intracerebrally into nude rats. The resulting tumors were serially passaged in vivo, and monitored by magnetic resonance imaging. CD133 expression was analyzed at various passages. Tumors initiated directly from the biopsies expressed little or no CD133, and showed no contrast enhancement suggesting an intact blood-brain barrier. During passaging, the tumors gradually displayed more contrast enhancement, increased angiogenesis and a shorter survival. Real-time qPCR and immunoblots showed that this was accompanied by increased CD133 expression. Primary biopsy spheroids and xenograft tumors were subsequently dissociated and flow sorted into CD133 negative and CD133 positive cell populations. Both populations incorporated BrdU in cell culture, and expressed the neural precursor marker nestin. Notably, CD133 negative cells derived from 6 different patients were tumorgenic when implanted into the rat brains. For 3 of these patients, analysis showed that the resulting tumors contained CD133 positive cells. In conclusion, we show that CD133 negative glioma cells are tumorgenic in nude rats, and that CD133 positive cells can be obtained from these tumors. Upon passaging of the tumors in vivo, CD133 expression is upregulated, coinciding with the onset of angiogenesis and a shorter survival. Thus, our findings do not suggest that CD133 expression is required for brain tumor initiation, but that it may be involved during brain tumor progression.

Journal ArticleDOI
11 Dec 2008-Nature
TL;DR: A role is defined for VEGF as an inhibitor of neovascularization on the basis of its capacity to disrupt VSMC function and reveals a dichotomous role for V EGF and VEGf-R2 signalling as both a promoter of endothelial cell function and a negative regulator of VSMCs and vessel maturation.
Abstract: Angiogenesis does not only depend on endothelial cell invasion and proliferation: it also requires pericyte coverage of vascular sprouts for vessel stabilization. These processes are coordinated by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) through their cognate receptors on endothelial cells and vascular smooth muscle cells (VSMCs), respectively. PDGF induces neovascularization by priming VSMCs/pericytes to release pro-angiogenic mediators. Although VEGF directly stimulates endothelial cell proliferation and migration, its role in pericyte biology is less clear. Here we define a role for VEGF as an inhibitor of neovascularization on the basis of its capacity to disrupt VSMC function. Specifically, under conditions of PDGF-mediated angiogenesis, VEGF ablates pericyte coverage of nascent vascular sprouts, leading to vessel destabilization. At the molecular level, VEGF-mediated activation of VEGF-R2 suppresses PDGF-Rbeta signalling in VSMCs through the assembly of a previously undescribed receptor complex consisting of PDGF-Rbeta and VEGF-R2. Inhibition of VEGF-R2 not only prevents assembly of this receptor complex but also restores angiogenesis in tissues exposed to both VEGF and PDGF. Finally, genetic deletion of tumour cell VEGF disrupts PDGF-Rbeta/VEGF-R2 complex formation and increases tumour vessel maturation. These findings underscore the importance of VSMCs/pericytes in neovascularization and reveal a dichotomous role for VEGF and VEGF-R2 signalling as both a promoter of endothelial cell function and a negative regulator of VSMCs and vessel maturation.

Journal ArticleDOI
03 Nov 2008-PLOS ONE
TL;DR: Results indicate an important role for endogenous VEGF in the maintenance and function of adult retina neuronal cells and indicate that anti-VEGF therapies should be administered with caution.
Abstract: Background: Vascular endothelial growth factor (VEGF) is well known for its role in normal and pathologic neovascularization. However, a growing body of evidence indicates that VEGF also acts on non-vascular cells, both developmentally as well as in the adult. In light of the widespread use of systemic and intraocular anti-VEGF therapies for the treatment of angiogenesis associated with tumor growth and wet macular degeneration, systematic investigation of the role of VEGF in the adult retina is critical. Methods and Findings: Using immunohistochemistry and Lac-Z reporter mouse lines, we report that VEGF is produced by various cells in the adult mouse retina and that VEGFR2, the primary signaling receptor, is also widely expressed, with strong

Journal ArticleDOI
TL;DR: Although axitinib inhibits platelet-derived growth factor receptors and KIT with nanomolar in vitro potencies, based on pharmacokinetic/pharmacodynamic analysis, axitine acts primarily as a VEGFR tyrosine kinase inhibitor at the current clinical exposure.
Abstract: Purpose: Axitinib (AG-013736) is a potent and selective inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases 1 to 3 that is in clinical development for the treatment of solid tumors. We provide a comprehensive description of its in vitro characteristics and activities, in vivo antiangiogenesis, and antitumor efficacy and translational pharmacology data. Experimental Design: The potency, kinase selectivity, pharmacologic activity, and antitumor efficacy of axitinib were assessed in various nonclinical models. Results: Axitinib inhibits cellular autophosphorylation of VEGF receptors (VEGFR) with picomolar IC 50 values. Counterscreening across multiple kinase and protein panels shows it is selective for VEGFRs. Axitinib blocks VEGF-mediated endothelial cell survival, tube formation, and downstream signaling through endothelial nitric oxide synthase, Akt and extracellular signal-regulated kinase. Following twice daily oral administration, axitinib produces consistent and dose-dependent antitumor efficacy that is associated with blocking VEGFR-2 phosphorylation, vascular permeability, angiogenesis, and concomitant induction of tumor cell apoptosis. Axitinib in combination with chemotherapeutic or targeted agents enhances antitumor efficacy in many tumor models compared with single agent alone. Dose scheduling studies in a human pancreatic tumor xenograft model show that simultaneous administration of axitinib and gemcitabine without prolonged dose interruption or truncation of axitinib produces the greatest antitumor efficacy. The efficacious drug concentrations predicted in nonclinical studies are consistent with the range achieved in the clinic. Although axitinib inhibits platelet-derived growth factor receptors and KIT with nanomolar in vitro potencies, based on pharmacokinetic/pharmacodynamic analysis, axitinib acts primarily as a VEGFR tyrosine kinase inhibitor at the current clinical exposure. Conclusions: The selectivity, potency for VEGFRs, and robust nonclinical activity may afford broad opportunities for axitinib to improve cancer therapy.

Journal ArticleDOI
15 May 2008-Nature
TL;DR: This is the first demonstration, to the authors' knowledge, of reduced tumour angiogenesis and improved immune therapeutic outcome on loss of a vascular gene function and establishes a previously unrecognized role of G-protein signalling in tumourAngiogenesis.
Abstract: The vasculature of solid tumours is morphologically aberrant and characterized by dilated and fragile vessels, intensive vessel sprouting and loss of hierarchical architecture. Constant vessel remodelling leads to spontaneous haemorrhages and increased interstitial fluid pressure in the tumour environment. Tumour-related angiogenesis supports tumour growth and is also a major obstacle for successful immune therapy as it prevents migration of immune effector cells into established tumour parenchyma. The molecular mechanisms for these angiogenic alterations are largely unknown. Here we identify regulator of G-protein signalling 5 (Rgs5) as a master gene responsible for the abnormal tumour vascular morphology in mice. Loss of Rgs5 results in pericyte maturation, vascular normalization and consequent marked reductions in tumour hypoxia and vessel leakiness. These vascular and intratumoral changes enhance influx of immune effector cells into tumour parenchyma and markedly prolong survival of tumour-bearing mice. This is the first demonstration, to our knowledge, of reduced tumour angiogenesis and improved immune therapeutic outcome on loss of a vascular gene function and establishes a previously unrecognized role of G-protein signalling in tumour angiogenesis.

Journal ArticleDOI
29 May 2008-Nature
TL;DR: It is shown that only p110α activity is essential for vascular development and the first in vivo evidence for p110-isoform selectivity in endothelial PI3K signalling during angiogenesis is provided.
Abstract: The p110α isoform of phosphoinositide 3-kinase is shown to play a critical role in normal and pathological angiogenesis. In particular, it is needed to mediate the migration of endothelial cells downstream of VEGF receptor activation, acting upstream of RhoA. This finding suggests that p110a-selective inhibitors, in addition to their direct effects in inhibiting cancer cell proliferation, will also impact on pathological angiogenesis in tumours. The p110α isoform of phosphoinositide 3-kinase has a critical role in angiogenesis. In particular, it is needed to mediate the migration of endothelial cells downstream of VEGF receptor activation, acting upstream of RhoA. The results suggest that pharmacological inhibition of the p110α isoform may be useful in anti-angiogenesis therapy of cancer. Phosphoinositide 3-kinases (PI3Ks) signal downstream of multiple cell-surface receptor types. Class IA PI3K isoforms1 couple to tyrosine kinases and consist of a p110 catalytic subunit (p110α, p110β or p110δ), constitutively bound to one of five distinct p85 regulatory subunits. PI3Ks have been implicated in angiogenesis2,3,4,5, but little is known about potential selectivity among the PI3K isoforms and their mechanism of action in endothelial cells during angiogenesis in vivo. Here we show that only p110α activity is essential for vascular development. Ubiquitous or endothelial cell-specific inactivation of p110α led to embryonic lethality at mid-gestation because of severe defects in angiogenic sprouting and vascular remodelling. p110α exerts this critical endothelial cell-autonomous function by regulating endothelial cell migration through the small GTPase RhoA. p110α activity is particularly high in endothelial cells and preferentially induced by tyrosine kinase ligands (such as vascular endothelial growth factor (VEGF)-A). In contrast, p110β in endothelial cells signals downstream of G-protein-coupled receptor (GPCR) ligands such as SDF-1α, whereas p110δ is expressed at low level and contributes only minimally to PI3K activity in endothelial cells. These results provide the first in vivo evidence for p110-isoform selectivity in endothelial PI3K signalling during angiogenesis.

Journal ArticleDOI
19 Sep 2008-Immunity
TL;DR: The considerations for generating promising therapeutic antitumor vaccines that use DCs are discussed, and chemotherapies, causing DC activation, enhanced crosspresentation, lymphodepletion, and reduction of immunosuppressive leukocytes, act synergistically with vaccines or adoptive T cell transfer.