Showing papers on "Angiogenesis published in 2011"

Molecular mechanisms and clinical applications of angiogenesis

Abstract: Blood vessels deliver oxygen and nutrients to every part of the body, but also nourish diseases such as cancer. Over the past decade, our understanding of the molecular mechanisms of angiogenesis (blood vessel growth) has increased at an explosive rate and has led to the approval of anti-angiogenic drugs for cancer and eye diseases. So far, hundreds of thousands of patients have benefited from blockers of the angiogenic protein vascular endothelial growth factor, but limited efficacy and resistance remain outstanding problems. Recent preclinical and clinical studies have shown new molecular targets and principles, which may provide avenues for improving the therapeutic benefit from anti-angiogenic strategies.

Tumor angiogenesis: molecular pathways and therapeutic targets

Abstract: As angiogenesis is essential for tumor growth and metastasis, controlling tumor-associated angiogenesis is a promising tactic in limiting cancer progression. The tumor microenvironment comprises numerous signaling molecules and pathways that influence the angiogenic response. Understanding how these components functionally interact as angiogenic stimuli or as repressors and how mechanisms of resistance arise is required for the identification of new therapeutic strategies. Achieving a durable and efficient antiangiogenic response will require approaches to simultaneously or sequentially target multiple aspects of the tumor microenvironment.

Normalization of the vasculature for treatment of cancer and other diseases

Abstract: New vessel formation (angiogenesis) is an essential physiological process for embryologic development, normal growth, and tissue repair. Angiogenesis is tightly regulated at the molecular level. Dy...

Tumour vascularization via endothelial differentiation of glioblastoma stem-like cells

Abstract: Glioblastoma is a highly angiogenetic malignancy, the neoformed vessels of which are thought to arise by sprouting of pre-existing brain capillaries. The recent demonstration that a population of glioblastoma stem-like cells (GSCs) maintains glioblastomas indicates that the progeny of these cells may not be confined to the neural lineage. Normal neural stem cells are able to differentiate into functional endothelial cells. The connection between neural stem cells and the endothelial compartment seems to be critical in glioblastoma, where cancer stem cells closely interact with the vascular niche and promote angiogenesis through the release of vascular endothelial growth factor (VEGF) and stromal-derived factor 1 (refs 5-9). Here we show that a variable number (range 20-90%, mean 60.7%) of endothelial cells in glioblastoma carry the same genomic alteration as tumour cells, indicating that a significant portion of the vascular endothelium has a neoplastic origin. The vascular endothelium contained a subset of tumorigenic cells that produced highly vascularized anaplastic tumours with areas of vasculogenic mimicry in immunocompromised mice. In vitro culture of GSCs in endothelial conditions generated progeny with phenotypic and functional features of endothelial cells. Likewise, orthotopic or subcutaneous injection of GSCs in immunocompromised mice produced tumour xenografts, the vessels of which were primarily composed of human endothelial cells. Selective targeting of endothelial cells generated by GSCs in mouse xenografts resulted in tumour reduction and degeneration, indicating the functional relevance of the GSC-derived endothelial vessels. These findings describe a new mechanism for tumour vasculogenesis and may explain the presence of cancer-derived endothelial-like cells in several malignancies.

Regorafenib (BAY 73-4506): a new oral multikinase inhibitor of angiogenic, stromal and oncogenic receptor tyrosine kinases with potent preclinical antitumor activity

Abstract: Angiogenesis, a critical driver of tumor development, is controlled by interconnected signaling pathways. Vascular endothelial growth factor receptor (VEGFR) 2 and tyrosine kinase with immunoglobulin and epidermal growth factor homology domain 2 play crucial roles in the biology of normal and tumor vasculature. Regorafenib (BAY 73-4506), a novel oral multikinase inhibitor, potently inhibits these endothelial cell kinases in biochemical and cellular kinase phosphorylation assays. Furthermore, regorafenib inhibits additional angiogenic kinases (VEGFR1/3, platelet-derived growth factor receptor-β and fibroblast growth factor receptor 1) and the mutant oncogenic kinases KIT, RET and B-RAF. The antiangiogenic effect of regorafenib was demonstrated in vivo by dynamic contrast-enhanced magnetic resonance imaging. Regorafenib administered once orally at 10 mg/kg significantly decreased the extravasation of Gadomer in the vasculature of rat GS9L glioblastoma tumor xenografts. In a daily (qd)×4 dosing study, the pharmacodynamic effects persisted for 48 hr after the last dosing and correlated with tumor growth inhibition (TGI). A significant reduction in tumor microvessel area was observed in a human colorectal xenograft after qd×5 dosing at 10 and 30 mg/kg. Regorafenib exhibited potent dose-dependent TGI in various preclinical human xenograft models in mice, with tumor shrinkages observed in breast MDA-MB-231 and renal 786-O carcinoma models. Pharmacodynamic analyses of the breast model revealed strong reduction in staining of proliferation marker Ki-67 and phosphorylated extracellular regulated kinases 1/2. These data demonstrate that regorafenib is a well-tolerated, orally active multikinase inhibitor with a distinct target profile that may have therapeutic benefit in human malignancies.

Tumour hypoxia promotes tolerance and angiogenesis via CCL28 and T reg cells

Abstract: Although immune mechanisms can suppress tumour growth, tumours establish potent, overlapping mechanisms that mediate immune evasion. Emerging evidence suggests a link between angiogenesis and the tolerance of tumours to immune mechanisms. Hypoxia, a condition that is known to drive angiogenesis in tumours, results in the release of damage-associated pattern molecules, which can trigger the rejection of tumours by the immune system. Thus, the counter-activation of tolerance mechanisms at the site of tumour hypoxia would be a crucial condition for maintaining the immunological escape of tumours. However, a direct link between tumour hypoxia and tolerance through the recruitment of regulatory cells has not been established. We proposed that tumour hypoxia induces the expression of chemotactic factors that promote tolerance. Here we show that tumour hypoxia promotes the recruitment of regulatory T (T(reg)) cells through induction of expression of the chemokine CC-chemokine ligand 28 (CCL28), which, in turn, promotes tumour tolerance and angiogenesis. Thus, peripheral immune tolerance and angiogenesis programs are closely connected and cooperate to sustain tumour growth.

Cabozantinib (XL184), a Novel MET and VEGFR2 Inhibitor, Simultaneously Suppresses Metastasis, Angiogenesis, and Tumor Growth

Abstract: The signaling pathway of the receptor tyrosine kinase MET and its ligand hepatocyte growth factor (HGF) is important for cell growth, survival, and motility and is functionally linked to the signaling pathway of VEGF, which is widely recognized as a key effector in angiogenesis and cancer progression. Dysregulation of the MET/VEGF axis is found in a number of human malignancies and has been associated with tumorigenesis. Cabozantinib (XL184) is a small-molecule kinase inhibitor with potent activity toward MET and VEGF receptor 2 (VEGFR2), as well as a number of other receptor tyrosine kinases that have also been implicated in tumor pathobiology, including RET, KIT, AXL, and FLT3. Treatment with cabozantinib inhibited MET and VEGFR2 phosphorylation in vitro and in tumor models in vivo and led to significant reductions in cell invasion in vitro . In mouse models, cabozantinib dramatically altered tumor pathology, resulting in decreased tumor and endothelial cell proliferation coupled with increased apoptosis and dose-dependent inhibition of tumor growth in breast, lung, and glioma tumor models. Importantly, treatment with cabozantinib did not increase lung tumor burden in an experimental model of metastasis, which has been observed with inhibitors of VEGF signaling that do not target MET. Collectively, these data suggest that cabozantinib is a promising agent for inhibiting tumor angiogenesis and metastasis in cancers with dysregulated MET and VEGFR signaling. Mol Cancer Ther; 10(12); 2298–308. ©2011 AACR .

Vascular Endothelial Growth Factor (VEGF) and Its Receptor (VEGFR) Signaling in Angiogenesis: A Crucial Target for Anti- and Pro-Angiogenic Therapies

Abstract: The vascular endothelial growth factor (VEGF) and its receptor (VEGFR) have been shown to play major roles not only in physiological but also in most pathological angiogenesis, such as cancer. VEGF belongs to the PDGF supergene family characterized by 8 conserved cysteines and functions as a homodimer structure. VEGF-A regulates angiogenesis and vascular permeability by activating 2 receptors, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk1 in mice). On the other hand, VEGF-C/VEGF-D and their receptor, VEGFR-3 (Flt-4), mainly regulate lymphangiogenesis. The VEGF family includes other interesting variants, one of which is the virally encoded VEGF-E and another is specifically expressed in the venom of the habu snake (Trimeresurus flavoviridis). VEGFRs are distantly related to the PDGFR family; however, they are unique with respect to their structure and signaling system. Unlike members of the PDGFR family that strongly stimulate the PI3K-Akt pathway toward cell proliferation, VEGFR-2, the major signal transducer for angiogenesis, preferentially utilizes the PLCγ-PKC-MAPK pathway for signaling. The VEGF-VEGFR system is an important target for anti-angiogenic therapy in cancer and is also an attractive system for pro-angiogenic therapy in the treatment of neuronal degeneration and ischemic diseases.

PI3K/AKT/mTOR Pathway in Angiogenesis

Abstract: The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway is activated in the majority of human cancers. This pathway is known to play a key role in numerous cellular functions including proliferation, adhesion, migration, invasion, metabolism, and survival, but in the current review we focus on its role in angiogenesis. PI3K activation may occur via RAS mutation, loss of phosphatase and tensin homolog (PTEN), or by increased expression of growth factor receptors such as epidermal growth factor receptor. There is a connection between the PI3K pathway and angiogenesis. Hypoxia leads to HIF-1α stabilization and is a major stimulus for increased vascular endothelial growth factor (VEGF) production by tumor cells. However, activation of the PI3K/AKT pathway in tumor cells can also increase VEGF secretion, both by hypoxia-inducible factor 1 (HIF-1) dependent and independent mechanisms. The PI3K/AKT pathway also modulates the expression of other angiogenic factors such as nitric oxide and angiopoietins. Numerous inhibitors targeting the PI3K/AKT/mTOR pathway have been developed, and these agents have been shown to decrease VEGF secretion and angiogenesis. The effect of these inhibitors on tumor vasculature can be difficult to predict. The vasculature of tumors is aberrant, leading to sluggish bloodflow and elevated interstitial blood pressure, which can be perpetuated by the high levels of VEGF. Hence, decreasing VEGF expression can paradoxically lead to vascular normalization and improved bloodflow in some tumors. In addition to its importance in cancer, the PI3K pathway also plays an essential role in the formation of normal blood vessels during development. Embryos with kinase-dead p110α catalytic subunit of PI3K develop vascular defects. Stimulation of endothelial cells by VEGF leads to activation of the PI3K pathway within these cells, which is important for cell migration. Sustained endothelial activation of AKT1 has been shown to induce the formation of structurally abnormal blood vessels that recapitulate the aberrations of tumor vessels. Hence, the PI3K pathway plays an important role in regulating angiogenesis both in normal tissues and in cancers.

Hypoxia-Induced Angiogenesis Good and Evil

Abstract: The vascular network delivers oxygen (O(2)) and nutrients to all cells within the body. It is therefore not surprising that O(2) availability serves as a primary regulator of this complex organ. Most transcriptional responses to low O(2) are mediated by hypoxia-inducible factors (HIFs), highly conserved transcription factors that control the expression of numerous angiogenic, metabolic, and cell cycle genes. Accordingly, the HIF pathway is currently viewed as a master regulator of angiogenesis. HIF modulation could provide therapeutic benefit for a wide array of pathologies, including cancer, ischemic heart disease, peripheral artery disease, wound healing, and neovascular eye diseases. Hypoxia promotes vessel growth by upregulating multiple pro-angiogenic pathways that mediate key aspects of endothelial, stromal, and vascular support cell biology. Interestingly, recent studies show that hypoxia influences additional aspects of angiogenesis, including vessel patterning, maturation, and function. Through extensive research, the integral role of hypoxia and HIF signaling in human disease is becoming increasingly clear. Consequently, a thorough understanding of how hypoxia regulates angiogenesis through an ever-expanding number of pathways in multiple cell types will be essential for the identification of new therapeutic targets and modalities.

Molecular control of endothelial cell behaviour during blood vessel morphogenesis

Abstract: The vertebrate vasculature forms an extensive branched network of blood vessels that supplies tissues with nutrients and oxygen. During vascular development, coordinated control of endothelial cell behaviour at the levels of cell migration, proliferation, polarity, differentiation and cell-cell communication is critical for functional blood vessel morphogenesis. Recent data uncover elaborate transcriptional, post-transcriptional and post-translational mechanisms that fine-tune key signalling pathways (such as the vascular endothelial growth factor and Notch pathways) to control endothelial cell behaviour during blood vessel sprouting (angiogenesis). These emerging frameworks controlling angiogenesis provide unique insights into fundamental biological processes common to other systems, such as tissue branching morphogenesis, mechanotransduction and tubulogenesis.

Signal transduction by vascular endothelial growth factor receptors.

Abstract: VEGFs (vascular endothelial growth factors) control vascular development during embryogenesis and the function of blood vessels and lymphatic vessels in the adult. There are five related mammalian ligands, which act through three receptor tyrosine kinases. Signalling is modulated through neuropilins, which act as VEGF co-receptors. Heparan sulfate and integrins are also important modulators of VEGF signalling. Therapeutic agents that interfere with VEGF signalling have been developed with the aim of decreasing angiogenesis in diseases that involve tissue growth and inflammation, such as cancer. The present review will outline the current understanding and consequent biology of VEGF receptor signalling.

Microvesicles Released from Human Renal Cancer Stem Cells Stimulate Angiogenesis and Formation of Lung Premetastatic Niche

Abstract: Recent studies suggest that tumor-derived microvesicles (MV) act as a vehicle for exchange of genetic information between tumor and stromal cells, engendering a favorable microenvironment for cancer development. Within the tumor mass, all cell types may contribute to MV shedding, but specific contributions to tumor progression have yet to be established. Here we report that a subset of tumor-initiating cells expressing the mesenchymal stem cell marker CD105 in human renal cell carcinoma releases MVs that trigger angiogenesis and promote the formation of a premetastatic niche. MVs derived only from CD105-positive cancer stem cells conferred an activated angiogenic phenotype to normal human endothelial cells, stimulating their growth and vessel formation after in vivo implantation in immunocompromised severe combined immunodeficient (SCID) mice. Furthermore, treating SCID mice with MVs shed from CD105-positive cells greatly enhanced lung metastases induced by i.v. injection of renal carcinoma cells. Molecular characterization of CD105-positive MVs defines a set of proangiogenic mRNAs and microRNAs implicated in tumor progression and metastases. Our results define a specific source of cancer stem cell-derived MVs that contribute to triggering the angiogenic switch and coordinating metastatic diffusion during tumor progression.

Lactate influx through the endothelial cell monocarboxylate transporter MCT1 supports an NF-κB/IL-8 pathway that drives tumor angiogenesis.

Abstract: Lactate generated from pyruvate fuels production of intracellular NAD(+) as an end result of the glycolytic process in tumors. Elevated lactate concentration represents a good indicator of the metabolic adaptation of tumors and is actually correlated to clinical outcome in a variety of human cancers. In this study, we investigated whether lactate could directly modulate the endothelial phenotype and thereby tumor vascular morphogenesis and perfusion. We found that lactate could enter endothelial cells through the monocarboxylate transporter MCT-1, trigger the phosphorylation/degradation of IκBα, and then stimulate an autocrine NF-κB/IL-8 (CXCL8) pathway driving cell migration and tube formation. These effects were prevented by 2-oxoglutarate and reactive oxygen species (ROS) inhibitors, pointing to a role for prolyl-hydroxylase and ROS in the integration of lactate signaling in endothelial cells. PHD2 silencing in endothelial cells recapitulated the proangiogenic effects of lactate, whereas a blocking IL-8 antibody or IL-8-targeting siRNA prevented them. Finally, we documented in mouse xenograft models of human colorectal and breast cancer that lactate release from tumor cells through the MCT4 (and not MCT1) transporter is sufficient to stimulate IL-8-dependent angiogenesis and tumor growth. In conclusion, our findings establish a signaling role for lactate in endothelial cells and they identify the lactate/NF-κB/IL-8 pathway as an important link between tumor metabolism and angiogenesis.

Hexokinase 2 is a key mediator of aerobic glycolysis and promotes tumor growth in human glioblastoma multiforme

Abstract: Proliferating embryonic and cancer cells preferentially use aerobic glycolysis to support growth, a metabolic alteration commonly referred to as the “Warburg effect.” Here, we show that the glycolytic enzyme hexokinase 2 (HK2) is crucial for the Warburg effect in human glioblastoma multiforme (GBM), the most common malignant brain tumor. In contrast to normal brain and low-grade gliomas, which express predominantly HK1, GBMs show increased HK2 expression. HK2 expression correlates with worse overall survival of GBM patients. Depletion of HK2, but neither HK1 nor pyruvate kinase M2, in GBM cells restored oxidative glucose metabolism and increased sensitivity to cell death inducers such as radiation and temozolomide. Intracranial xenografts of HK2-depleted GBM cells showed decreased proliferation and angiogenesis, but increased invasion, as well as diminished expression of hypoxia inducible factor 1α and vascular endothelial growth factor. In contrast, exogenous HK2 expression in GBM cells led to increased proliferation, therapeutic resistance, and intracranial growth. Growth was dependent on both glucose phosphorylation and mitochondrial translocation mediated by AKT signaling, which is often aberrantly activated in GBMs. Collectively, these findings suggest that therapeutic strategies to modulate the Warburg effect, such as targeting of HK2, may interfere with growth and therapeutic sensitivity of some GBMs.

Bone marrow angiogenesis and progression in multiple myeloma

Abstract: Multiple myeloma plasma cells home and expand in the bone marrow where cause an unbalanced bone remodelling with increased bone resorption and low bone formation that represent the typical feature in the majority of patients. A clinically relevant aspect of the interactions of multiple myeloma plasma cells in the bone marrow microenvironment is neovascularization, a constant hallmark of disease progression. This process is only partially supported by factors such as vascular endothelial growth factor, fibroblast growth factor-2 and metalloproteinases, which are directly secreted by the tumor cells. In fact, the presence in the bone marrow microenvironment of cytokines, in particular interleukin-6, as a consequence of plasma cell-stromal cell interactions, induces the production and secretion of angiogenic factors by other cells present in the bone microenvironment, thus contributing to the angiogenic switch during the progression of the disease. Near angiogenesis vasculogenesis occur in the bone marrow of myeloma patients and contribute to the vascular three formation. In the bone marrow of myeloma patients haematopoietic stem cells are recruited and induced to differentiate into endothelial cells by the angiogenic cytokines present in the microenvironment. Myeloma plasma cells also induce angiogenesis indirectly via recruitment and activation of stromal inflammatory cells (i.e.: macrophages and mast cells) to secrete their own angiogenic factors. They are recruited and activated by tumor plasma cells through the secretion of fibroblast growth factor-2, interleukin-8, and other chemokines, such as ITAC, Mig, IP-10. When macrophages and mast cells are activated they secrete their angiogenic factors: fibroblast growth factor-2, vascular endothelial growth factor, granulocyte-colony stimulating factor, granulocyte macrophage-colony stimulating factor, which contribute to enhance the tumor neovascularization. Finally, myeloma macrophages when exposed to vascular endothelial growth factor and fibroblast growth factor-2 secreted by plasma cells shows vasculogenic ability and acquire endothelial cell markers and transform into cells functionally and phenotypically similar to paired bone marrow endothelial cells. So they participate to the formation of the bone marrow capillary network (vasculogenic mimicry).

Anti-VEGF treatment reduces blood supply and increases tumor cell invasion in glioblastoma

Abstract: Bevacizumab, an antibody against vascular endothelial growth factor (VEGF), is a promising, yet controversial, drug in human glioblastoma treatment (GBM). Its effects on tumor burden, recurrence, and vascular physiology are unclear. We therefore determined the tumor response to bevacizumab at the phenotypic, physiological, and molecular level in a clinically relevant intracranial GBM xenograft model derived from patient tumor spheroids. Using anatomical and physiological magnetic resonance imaging (MRI), we show that bevacizumab causes a strong decrease in contrast enhancement while having only a marginal effect on tumor growth. Interestingly, dynamic contrast-enhanced MRI revealed a significant reduction of the vascular supply, as evidenced by a decrease in intratumoral blood flow and volume and, at the morphological level, by a strong reduction of large- and medium-sized blood vessels. Electron microscopy revealed fewer mitochondria in the treated tumor cells. Importantly, this was accompanied by a 68% increase in infiltrating tumor cells in the brain parenchyma. At the molecular level we observed an increase in lactate and alanine metabolites, together with an induction of hypoxia-inducible factor 1α and an activation of the phosphatidyl-inositol-3-kinase pathway. These data strongly suggest that vascular remodeling induced by anti-VEGF treatment leads to a more hypoxic tumor microenvironment. This favors a metabolic change in the tumor cells toward glycolysis, which leads to enhanced tumor cell invasion into the normal brain. The present work underlines the need to combine anti-angiogenic treatment in GBMs with drugs targeting specific signaling or metabolic pathways linked to the glycolytic phenotype.

The Many Faces of Endothelial Microparticles

Abstract: Endothelial microparticles (EMP) are complex vesicular structures shed from activated or apoptotic endothelial cells. They play a remarkable role in coagulation, inflammation, endothelial function, and angiogenesis and thus disturb the vascular homeostasis, contributing to the progression of vascular diseases. As a cause or a consequence, elevated levels of EMP were found in plasma from patients with vascular diseases, where they serve as a surrogate marker of endothelial function. More recent data challenged the presumed deleterious role of EMP because they could promote cell survival, exert antiinflammatory effects, counteract coagulation processes, or induce endothelial regeneration. This review focuses on the ambivalent role of EMP in vascular homeostasis.

Exosomes From Human CD34+ Stem Cells Mediate Their Proangiogenic Paracrine Activity

Abstract: Rationale: Transplantation of human CD34+ stem cells to ischemic tissues has been associated with reduced angina, improved exercise time, and reduced amputation rates in phase 2 clinical trials and has been shown to induce neovascularization in preclinical models. Previous studies have suggested that paracrine factors secreted by these proangiogenic cells are responsible, at least in part, for the angiogenic effects induced by CD34+ cell transplantation. Objective: Our objective was to investigate the mechanism of CD34+ stem cell–induced proangiogenic paracrine effects and to examine if exosomes, a component of paracrine secretion, are involved. Methods and Results: Exosomes collected from the conditioned media of mobilized human CD34+ cells had the characteristic size (40 to 90 nm; determined by dynamic light scattering), cup-shaped morphology (electron microscopy), expressed exosome-marker proteins CD63, phosphatidylserine (flow cytometry) and TSG101 (immunoblotting), besides expressing CD34+ cell lineage marker protein, CD34. In vitro, CD34+ exosomes replicated the angiogenic activity of CD34+ cells by increasing endothelial cell viability, proliferation, and tube formation on Matrigel. In vivo, the CD34+ exosomes stimulated angiogenesis in Matrigel plug and corneal assays. Interestingly, exosomes from CD34+ cells but not from CD34+ cell–depleted mononuclear cells had angiogenic activity. Conclusions: Our data demonstrate that human CD34+ cells secrete exosomes that have independent angiogenic activity both in vitro and in vivo. CD34+ exosomes may represent a significant component of the paracrine effect of progenitor cell transplantation for therapeutic angiogenesis. # Novelty and Significance {#article-title-11}

Transdifferentiation of glioblastoma cells into vascular endothelial cells

Abstract: Glioblastoma (GBM) is the most malignant brain tumor and is highly resistant to intensive combination therapies and anti-VEGF therapies. To assess the resistance mechanism to anti-VEGF therapy, we examined the vessels of GBMs in tumors that were induced by the transduction of p53+/− heterozygous mice with lentiviral vectors containing oncogenes and the marker GFP in the hippocampus of GFAP-Cre recombinase (Cre) mice. We were surprised to observe GFP+ vascular endothelial cells (ECs). Transplantation of mouse GBM cells revealed that the tumor-derived endothelial cells (TDECs) originated from tumor-initiating cells and did not result from cell fusion of ECs and tumor cells. An in vitro differentiation assay suggested that hypoxia is an important factor in the differentiation of tumor cells to ECs and is independent of VEGF. TDEC formation was not only resistant to an anti-VEGF receptor inhibitor in mouse GBMs but it led to an increase in their frequency. A xenograft model of human GBM spheres from clinical specimens and direct clinical samples from patients with GBM also showed the presence of TDECs. We suggest that the TDEC is an important player in the resistance to anti-VEGF therapy, and hence a potential target for GBM therapy.

MiR-21 induced angiogenesis through AKT and ERK activation and HIF-1α expression.

Abstract: MicroRNAs (miRNAs) are endogenous, small noncoding RNAs that play important roles in various cellular functions and tumor development. Recent studies have indicated that miR-21 is one of the important miRNAs associated with tumor growth and metastasis, but the role and molecular mechanism of miR-21 in regulating tumor angiogenesis remain to be elucidated. In this study, miR-21 was overexpressed by transfecting pre-miR-21 into human prostate cancer cells and tumor angiogenesis was assayed using chicken chorioallantoic membrane (CAM). We found that overexpression of miR-21 in DU145 cells increased the expression of HIF-1α and VEGF, and induced tumor angiogenesis. AKT and extracellular regulated kinases (ERK) 1/2 are activated by miR-21. Inhibition of miR-21 by the antigomir blocked this process. Overexpression of the miR-21 target, PTEN, also inhibited tumor angiogenesis by partially inactivating AKT and ERK and decreasing the expression of HIF-1 and VEGF. The AKT and ERK inhibitors, LY294002 and U0126, suppressed HIF-1α and VEGF expression and angiogenesis. Moreover, inhibition of HIF-1α expression alone abolished miR-21-inducing tumor angiogenesis, indicating that HIF-1α is required for miR-21-upregulated angiogenesis. Therefore, we demonstrate that miR-21 induces tumor angiogenesis through targeting PTEN, leading to activate AKT and ERK1/2 signaling pathways, and thereby enhancing HIF-1α and VEGF expression; HIF-1α is a key downstream target of miR-21 in regulating tumor angiogenesis.

NF-κB addiction and its role in cancer: ‘one size does not fit all’

Abstract: Activation of nuclear factor (NF)-κB, one of the most investigated transcription factors, has been found to control multiple cellular processes in cancer including inflammation, transformation, proliferation, angiogenesis, invasion, metastasis, chemoresistance and radioresistance. NF-κB is constitutively active in most tumor cells, and its suppression inhibits the growth of tumor cells, leading to the concept of 'NF-κB addiction' in cancer cells. Why NF-κB is constitutively and persistently active in cancer cells is not fully understood, but multiple mechanisms have been delineated including agents that activate NF-κB (such as viruses, viral proteins, bacteria and cytokines), signaling intermediates (such as mutant receptors, overexpression of kinases, mutant oncoproteins, degradation of IκBα, histone deacetylase, overexpression of transglutaminase and iNOS) and cross talk between NF-κB and other transcription factors (such as STAT3, HIF-1α, AP1, SP, p53, PPARγ, β-catenin, AR, GR and ER). As NF-κB is 'pre-active' in cancer cells through unrelated mechanisms, classic inhibitors of NF-κB (for example, bortezomib) are unlikely to mediate their anticancer effects through suppression of NF-κB. This review discusses multiple mechanisms of NF-κB activation and their regulation by multitargeted agents in contrast to monotargeted agents, thus 'one size does not fit all' cancers.

A vascular niche and a VEGF–Nrp1 loop regulate the initiation and stemness of skin tumours

Abstract: Angiogenesis is critical during tumour initiation and malignant progression. Different strategies aimed at blocking vascular endothelial growth factor (VEGF) and its receptors have been developed to inhibit angiogenesis in cancer patients. It has become increasingly clear that in addition to its effect on angiogenesis, other mechanisms including a direct effect of VEGF on tumour cells may account for the efficiency of VEGF-blockade therapies. Cancer stem cells (CSCs) have been described in various cancers including squamous tumours of the skin. Here we use a mouse model of skin tumours to investigate the impact of the vascular niche and VEGF signalling on controlling the stemness (the ability to self renew and differentiate) of squamous skin tumours during the early stages of tumour progression. We show that CSCs of skin papillomas are localized in a perivascular niche, in the immediate vicinity of endothelial cells. Furthermore, blocking VEGFR2 caused tumour regression not only by decreasing the microvascular density, but also by reducing CSC pool size and impairing CSC renewal properties. Conditional deletion of Vegfa in tumour epithelial cells caused tumours to regress, whereas VEGF overexpression by tumour epithelial cells accelerated tumour growth. In addition to its well-known effect on angiogenesis, VEGF affected skin tumour growth by promoting cancer stemness and symmetric CSC division, leading to CSC expansion. Moreover, deletion of neuropilin-1 (Nrp1), a VEGF co-receptor expressed in cutaneous CSCs, blocked VEGF's ability to promote cancer stemness and renewal. Our results identify a dual role for tumour-cell-derived VEGF in promoting cancer stemness: by stimulating angiogenesis in a paracrine manner, VEGF creates a perivascular niche for CSCs, and by directly affecting CSCs through Nrp1 in an autocrine loop, VEGF stimulates cancer stemness and renewal. Finally, deletion of Nrp1 in normal epidermis prevents skin tumour initiation. These results may have important implications for the prevention and treatment of skin cancers.

YN968D1 is a novel and selective inhibitor of vascular endothelial growth factor receptor-2 tyrosine kinase with potent activity in vitro and in vivo

Abstract: Angiogenesis is an important process in cell development, especially in cancer. Vascular endothelial growth factor (VEGF) signaling is an important regulator of angiogenesis. Several therapies that act against VEGF signal transduction have been developed, including YN968D1, which is a potent inhibitor of the VEGF signaling pathway. This study investigated the antitumor activity of YN968D1 (apatinib mesylate) in vitro and in vivo. YN968D1 potently suppressed the kinase activities of VEGFR-2, c-kit and c-src, and inhibited cellular phosphorylation of VEGFR-2, c-kit and PDGFRβ. YN968D1 effectively inhibited proliferation, migration and tube formation of human umbilical vein endothelial cells induced by FBS, and blocked the budding of rat aortic ring. In vivo, YN968D1 alone and in combination with chemotherapeutic agents effectively inhibited the growth of several established human tumor xenograft models with little toxicity. A phase I study of YN968D1 has shown encouraging antitumor activity and a manageable toxicity profile. These findings suggest that YN968D1 has promise as an antitumor drug and might have clinical benefits.