Angiopoietin: a TIE(d) balance in tumor angiogenesis

Development of a biosensor-based immunogenicity assay capable of blocking soluble drug target interference

As with other protein therapeutics, trebananib (AMG 386), an investigational peptide Fc-fusion protein ("peptibody") that inhibits angiogenesis by neutralizing the interaction of angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) with the Tie2 receptor, has the potential to trigger an immune response in cancer patients treated with the therapeutic. An electrochemiluminescence bridging anti-drug antibody (ADA) assay that was utilized to support early-phase clinical trials in the development of trebananib was found to lack adequate sensitivity and drug tolerance in later-phase clinical studies when higher doses of trebananib were administered. Therefore, we developed a surface plasmon resonance (SPR) immunoassay method utilizing a secondary confirmatory detector antibody (goat anti-human IgG F[ab']2) known to cross-react with human IgG and IgM to better assess the potential impact of immunogenicity on the pharmacokinetics, pharmacodynamics, and toxicity of trebananib. The SPR method was more sensitive than the electrochemiluminescence bridging assay because of signal amplification from the confirmatory binding of the detector antibody; drug tolerance was improved since antibody binding avidity does not affect detection on this platform. Despite the inability of the confirmatory detector antibody to bind angiopoietins in protein-free buffer, false-positive ADA results were generated from patient serum samples containing Ang1 and Ang2 through an apparently specific binding between the angiopoietins and the confirmatory detector antibody, likely mediated by the interaction of the angiopoietins with serum immunoglobulins. Addition to the sample diluent of a human antibody that specifically binds to Ang1 and Ang2 with high affinity resulted in a complete block of angiopoietin interference without affecting ADA detection. This biosensor-based assay provides a reliable method for assessing immunogenicity in phase 3 clinical trials.

Angiopoietin-2 Serum Levels Improve Noninvasive Fibrosis Staging in Chronic Hepatitis C: A Fibrogenic-Angiogenic Link

AIMS

Accurate liver fibrosis staging is crucial for the management of chronic hepatitis C (CHC). The invasiveness and cost burden of liver biopsy have driven the search for new noninvasive biomarkers of fibrosis. Based on the link between serum angiopoietin-1 and 2 levels and CHC progression, we aimed to determine the value of these angiogenic factors as noninvasive biomarkers of liver fibrosis.

METHODS

Serum levels of angiopoietin-1 and -2 were measured by ELISA in 108 CHC patients who underwent pretreatment liver biopsy. The correlation between angiopoietins and clinical and demographic variables with liver fibrosis was analyzed by univariate regression. Significant factors were then subjected to multivariate analysis, from which we constructed a novel noninvasive liver fibrosis index (AngioScore), whose performance was validated in an independent series of 71 CHC patients. The accuracy of this model was compared with other documented fibrosis algorithms by De Long test.

RESULTS

Angiopoietins correlated significantly with hepatic fibrosis; however, only angiopoietin-2 was retained in the final model, which also included age, platelets, AST, INR, and GGT. The model was validated and behaved considerably better than other fibrosis indices in discriminating all, significant, moderate and severe liver fibrosis (0.886, 0.920, 0.923). Using clinically relevant cutoffs, we classified CHC patients by discarding significant fibrosis and diagnosing moderate and severe fibrosis with greater accuracy, sensitivity, and specificity.

CONCLUSIONS

Our novel noninvasive liver fibrosis model, based on serum angiopoietin-2 levels, outperforms other indices and should help substantially in managing CHC and monitoring long-term follow-up prognosis.

Angiopoietin-2 expression is correlated with angiogenesis and overall survival in oral squamous cell carcinoma

This study sought to determine the expression of angiopoietin-2 (Ang-2) and vascular endothelial cell growth factor (VEGF) in oral squamous cell carcinoma (OSCC) and assess their correlations with tumor progression, angiogenesis, vessel maturation, and clinical survival. Tumor tissue from 102 OSCC patients, adjacent noncancerous oral tissue from 79 OSCC patients, and normal oral mucosa from 35 control patients were examined for Ang-2 and VEGF expression using conventional immunohistochemistry. Microvessel density (MVD) and vessel maturation index (VMI) were assessed by double-label immunohistochemistry staining using anti-CD34 and anti-alpha-smooth muscle actin, respectively. Although the proportion of OSCC samples positive for Ang-2 or VEGF expression was significantly higher than that observed in the adjacent noncancerous tissue and normal oral mucosa (P < 0.001), neither Ang-2 nor VEGF expression was associated with the clinicopathological parameters analyzed in OSCC patients. However, MVD and VMI were significantly associated with the expression of Ang-2 (P = 0.001 and P = 0.014, respectively); VEGF expression was associated MVD (P = 0.004). The MVD of OSCC tissues expressing both Ang-2 and VEGF was significantly higher than observed in the double-negative samples (P < 0.05). Multivariate regression and Kaplan-Meier analyses revealed that Ang-2 was negatively associated with the overall survival of OSCC patients. Expression of Ang-2 was associated with angiogenesis and vessel maturation in OSCC. Further studies will evaluate the prognostic value of determining Ang-2 expression in OSCC.

Endothelins reciprocally regulate VEGF-A and angiopoietin-1 production in cultured rat astrocytes: implications on astrocytic proliferation

Vascular endothelial growth factors (VEGFs) and angiopoietins (ANGs) are involved in pathophysiological responses in damaged nerve tissues. Astrocytes produce VEGFs and ANGs upon brain ischemia and traumatic injury. To clarify the extracellular signals regulating VEGF and ANG production, effects of endothelins (ETs), a family of endothelium-derived peptides, were examined in cultured rat astrocytes. ET-1 (100 nM) and Ala(1,3,11,15)-ET-1 (100 nM), an ET(B) receptor agonist, increased VEGF-A mRNA levels in cultured astrocytes, while ANG-1 mRNA was decreased by ETs. ET-1 did not affect astrocytic VEGF-B, placental growth factor (PLGF), and ANG-2 mRNA levels. The effects of ET-1 on VEGF-A and ANG-1 mRNAs were inhibited by BQ788, an ET(B) antagonist. Release of VEGF-A proteins from cultured astrocytes was increased by ET-1. In contrast, ET-1 reduced release of astrocytic ANG-1. Exogenous ET-1 (100 nM) and VEGF(165) (100 ng/mL), an isopeptide of VEGF-A, stimulated bromodeoxyuridine (BrdU) incorporation into cultured astrocytes. Treatment with ET-1 and VEGF(165) increased the numbers of cyclin D1-positive astrocytes. Exogenous ANG-1 (250 ng/mL) did not stimulate the BrdU incorporation. Increases in BrdU incorporation by ET-1 and VEGF(165) were not affected by ANG-1. In 60-70% confluent cultures, SU4312 (10 μM), a VEGF receptor tyrosine kinase inhibitor, partially reduced the effects of ET-1 on BrdU incorporation and cyclin D1 expression. ET-induced BrdU incorporation and cyclin D1 expression were reduced by a neutralizing antibody against VEGF-A. Our findings suggest that ET-1 is a factor regulating astrocytic VEGF-A and ANG-1, and that increased VEGF-A production potentiates ET-induced astrocytic proliferation by an autocrine mechanism.

Angiopoietins in angiogenesis

Tie-1 and Tie-2 tyrosine kinase receptors are expressed specifically on vascular endothelial cells and on a certain subtype of macrophages implicated in angiogenesis, thus, they have been a major focus of angiogenesis research. Tie-1 and Tie-2 are essential for vascular maturation during developmental, physiological and pathological angiogenesis. Angiopoietin 1-4 (Ang-1-4) have been identified as bona fide ligands of the Tie-2 receptor, while Tie-1 remains an orphan receptor which is able to heterodimerize with Tie-2 and to modulate Tie-2 signal transduction. The most exhaustively studied angiopoietins are Ang-1 and Ang-2. Ang-1 is a critical player in vessel maturation and it mediates migration, adhesion and survival of endothelial cells. Ang-2 disrupts the connections between the endothelium and perivascular cells and promotes cell death and vascular regression. Yet, in conjunction with VEGF, Ang-2 promotes neo-vascularization. Hence, angiopoietins exert crucial roles in the angiogenic switch during tumor progression, and increased expression of Ang-2 relative to Ang-1 in tumors correlates with poor prognosis. Its central role in the regulation of physiological and pathological angiogenesis makes the angiopoietin/Tie signaling pathway a therapeutically attractive target for the treatment of vascular disease and cancer.

Genetic polymorphism in a VEGF-independent angiogenesis gene ANGPT1 and overall survival of colorectal cancer patients after surgical resection

Background

The VEGF-independent angiogenic signaling plays an important role in the development of colorectal cancer (CRC). However, its implication in the clinical outcome of CRC has not been reported. This study aimed to investigate the association between genetic variations in several major VEGF-independent signaling pathway genes and the overall survival of CRC patients.

Methods

Seven single nucleotide polymorphisms (SNPs) in four important VEGF-independent angiogenic genes (ANGPT1, AMOT, DLL4 and ENG) were genotyped in a Chinese population with 408 CRC patients.

Results

One SNP, rs1954727 in ANGPT1, was significantly associated with CRC overall survival. Compared to patients with the homozygous wild-type genotype of rs1954727, those with heterozygous and homozygous variant genotypes exhibited a favorable overall survival with a hazard ratio (HR) of 0.89 (95% confidence interval [CI] 0.55–1.43, P = 0.623), and 0.32 (95% CI 0.15–0.71, P = 0.005), respectively (P trend = 0.008). In stratified analysis, this association remained significant in patients receiving chemotherapy (P trend = 0.012), but not in those without chemotherapy. We further evaluated the effects of chemotherapy on CRC survival that was stratified by rs1954727 genotypes. We found that chemotherapy resulted in a significantly better overall survival in the CRC patients (HR = 0.44, 95% CI 0.26–0.75, P = 0.002), which was especially prominent in those patients with the heterozygous genotype of rs1954727 (HR = 0.45, 95%CI 0.22–0.92, P = 0.028).

Conclusion

Our data suggest that rs1954727 in ANGPT1 gene might be a prognostic biomarker for the overall survival of CRC patients, especially in those receiving chemotherapy, a finding that warrants validation in larger independent populations.

Meat Science and Muscle Biology Symposium: stem cell niche and postnatal muscle growth

Stem cell niche plays a critical role in regulating the behavior and function of adult stem cells that underlie tissue growth, maintenance, and regeneration. In the skeletal muscle, stem cells, called satellite cells, contribute to postnatal muscle growth and hypertrophy, and thus, meat production in agricultural animals. Satellite cells are located adjacent to mature muscle fibers underneath a sheath of basal lamina. Microenvironmental signals from extracellular matrix mediated by the basal lamina and from the host myofiber both impinge on satellite cells to regulate their activity. Furthermore, several types of muscle interstitial cells, including intramuscular preadipocytes and connective tissue fibroblasts, have recently been shown to interact with satellite cells and actively regulate the growth and regeneration of postnatal skeletal muscles. From this regard, interstitial adipogenic cells are not only important for marbling and meat quality, but also represent an additional cellular component of the satellite cell niche. At the molecular level, these interstitial cells may interact with satellite cells through cell surface ligands, such as delta-like 1 homolog (Dlk1) protein whose overexpression is thought to be responsible for muscle hypertrophy in callipyge sheep. In fact, extracellular Dlk1 protein has been shown to promote the myogenic differentiation of satellite cells. Understanding the cellular and molecular mechanisms within the stem cell niche that regulate satellite cell differentiation and maintain muscle homeostasis may lead to promising approaches to optimizing muscle growth and composition, thus improving meat production and quality.

Tumor-targeted drug delivery with aptamers

Cancer is one of the leading causes of death around the world. Tumor-targeted drug delivery is one of the major areas in cancer research. Aptamers exhibit many desirable properties for tumor-targeted drug delivery, such as ease of selection and synthesis, high binding affinity and specificity, low immunogenicity, and versatile synthetic accessibility. Over the last several years, aptamers have quickly become a new class of targeting ligands for drug delivery applications. In this review, we will discuss in detail about aptamer-based delivery of chemotherapy drugs (e.g. doxorubicin, docetaxel, daunorubicin, and cisplatin), toxins (e.g. gelonin and various photodynamic therapy agents), and a variety of small interfering RNAs. Although the results are promising which warrants enthusiasm for aptamer-based drug delivery, tumor homing of aptamer-based conjugates after systemic injection has only been achieved in one report. Much remains to be done before aptamer-based drug delivery can reach clinical trials and eventually the day-to-day management of cancer patients. Therefore, future directions and challenges in aptamer-based drug delivery are also discussed.

Expression of the vascular endothelial growth factor and angiopoietins in mucoepidermoid carcinoma of salivary gland

Disrupted coordination of angiogenesis regulating signals, among them the vascular endothelial growth factor (VEGF) and angiopoietins (Angs), has been associated with abnormal angiogenesis and tumor progression. While VEGF induces endothelial cell proliferation, thereby initiating vessel formation, Angs are subsequently required for mural cell attachment, thus influencing remodeling and maturation of this vasculature. In addition to tumor cell, endothelial and mural cells, as well as myofibroblasts may also contribute to the secretion of these factors. In this study, we have analyzed by immunohistochemistry the expression of VEGF, Ang-1, Ang-2 and the Angs receptor Tie2 in both the stroma and tumor cells of mucoepidermoid carcinoma (MEC) of salivary gland. We have demonstrated that when myofibroblasts were detected adjacent to the cancer cells, they were frequently associated with intense positive staining for Ang-1 and Ang-2, and no reactivity to VEGF and Tie2. These myofibroblast-rich Ang-1 and Ang-2-stained areas were more commonly found in high-grade MEC cases than in low-grade ones. As for the malignant cells, they frequently expressed all proteins studied, but Ang-2 and VEGF were detected at higher levels compared to Ang-1 and Tie2. Our results indicate that the MEC environment favors cooperative activity between Angs and VEGF in modulating vascular growth and tumor aggressiveness.

5'-(N-ethylcarboxamido) adenosine improves angiogenesis in transplanted human ovarian tissue

To investigate the effect of 5'-(N-ethylcarboxamido) adenosine (NECA), an adenosine agonist, on triggering angiogenesis in transplanted human ovarian tissue, the expression of angiopoietin-1 (Ang1), Ang2, vascular endothelial growth factor 121 (VEGF-121) and VEGF-189 at both gene and protein levels as well as the density of vasculature were studied in tissue fragments grafted to NECA-treated and control groups of nude mice. The results showed that NECA treatment triggered down-regulation of Ang1, induced VEGF-189 expression, and stimulated neovascularization, highlighting the beneficial effect of NECA on the process of angiogenesis.

Brain pericytes: emerging concepts and functional roles in brain homeostasis

Brain pericytes are an important constituent of neurovascular unit. They encircle endothelial cells and contribute to the maturation and stabilization of the capillaries in the brain. Recent studies have revealed that brain pericytes play pivotal roles in a variety of brain functions, such as regulation of capillary flow, angiogenesis, blood brain barrier, immune responses, and hemostasis. In addition, brain pericytes are pluripotent and can differentiate into different lineages similar to mesenchymal stem cells. The brain pericytes are revisited as a key player to maintain brain function and repair brain damage.

Angiopoietins-1 and -2 play opposing roles in endothelial sprouting of embryoid bodies in 3D culture and their receptor Tie-2 associates with the cell-cell adhesion molecule PECAM1

Angiopoietins 1 and 2, ligands for the receptor kinase Tie-2, have been proposed to play critical but opposing roles in vascular development. Since signaling by Tie-2 is likely affected by other endothelial cell receptors such as Flk-1, the receptor for VEGF, and cell-cell adhesion receptors PECAM1 and VE-cad, we explored their interactions in a 3D model of vasculogenesis. When murine embryoid bodies (EBs) were treated with VEGF in Matrigel in the presence or absence of Ang-1 or Ang-2 for eight days, Ang-1 abrogated vascular sprouting for treatments started at days 0 or 3. In contrast, Ang-2 greatly accelerated vascular sprouting compared to untreated EBs. These results were confirmed in a second model system where VEGF treated HUVECs were grown in Matrigel in the presence or absence of Ang-1 or Ang-2. Since vascular sprouting must be precisely controlled in the developing embryo, it is likely that cell-cell adhesion molecules play a role in sensing the density of vascular sprouts. In this respect, we have shown that PECAM1 and CEACAM1 play essential roles in vascular sprouting. We now show that PECAM1 is associated with Tie-2, becomes phosphorylated on its ITIMs, and recruits the inhibitory phosphatases SHP-1 and SHP-2. In addition, PECAM1 is associated with VE-cad and may similarly regulate its signaling via recruitment of SHP-1/2.

Angiopoietin-2 drives lymphatic metastasis of pancreatic cancer

Lymphatic metastasis constitutes a critical route of disease dissemination, which limits the prognosis of patients with pancreatic ductal adenocarcinoma (PDAC). As lymphangiogenesis has been implicated in stimulation of lymphatic metastasis by vascular endothelial growth factor-C (VEGF-C) and VEGF-D, we studied the effect of the angioregulatory growth factor angiopoietin-2 (Ang-2) on PDAC progression. Ang-2 was found to be expressed in transformed cells of human PDAC specimens, with corresponding Tie-2 receptors present on blood and lymphatic endothelium. In vitro in PDAC cells, Ang-2 was subject to autocrine/paracrine TGF-β stimulation (2-fold induction, P=0.0106) acting on the -61- to +476-bp element of the human Ang-2 promoter. In turn, Ang-2 regulated the expression of genes involved in cell motility and tumor suppression. Orthotopic PDAC xenografts with forced expression of Ang-2, but not Ang-1, displayed increased blood and lymphatic vessel density, and an enhanced rate of lymphatic metastasis (6.7- to 9.1-fold, P<0.01), which was prevented by sequestration of Ang-2 via coexpression of soluble Tie-2. Notably, elevated circulating Ang-2 in patients with PDAC correlated with the extent of lymphatic metastasis. Furthermore, median survival was reduced from 28.4 to 7.7 mo in patients with circulating Ang-2 ≥ 75th percentile (P=0.0005). These findings indicate that Ang-2 participates in the control of lymphatic metastasis, constitutes a noninvasive prognostic biomarker, and may provide an accessible therapeutic target in PDAC.

Novel targeted agents for the treatment of bladder cancer: translating laboratory advances into clinical application

Bladder cancer is a common and frequently lethal cancer. Natural history studies indicate two distinct clinical and molecular entities corresponding to invasive and non-muscle invasive disease. The high frequency of recurrence of noninvasive bladder cancer and poor survival rate of invasive bladder cancer emphasizes the need for novel therapeutic approaches. These mechanisms of tumor development and promotion in bladder cancer are strongly associated with several growth factor pathways including the fibroblast, epidermal, and the vascular endothelial growth factor pathways. In this review, efforts to translate the growing body of basic science research of novel treatments into clinical applications will be explored.

Corticosteroids modulate angiogenic soluble factors in ulcerative colitis patients

AIMS

The aim of this study was to compare angiogenic factors in serum levels of active ulcerative colitis (UC) patients and in healthy controls, and to analyze these angiogenic levels depending on the achievement of remission after oral corticosteroid treatment throughout treatment, and according to the Truelove-Witts activity index.

METHODS

Blood samples were collected from 13 patients receiving oral corticosteroids for treatment of UC flares at three different intervals--baseline, during, and after treatment--and from 26 healthy controls. Vascular endothelial growth factor (VEGF), placental growth factor (PlGF), VEGF receptor 1 (VEGFR1), angiopoietins (Ang) 1 and 2, and its receptor Tie2 were assayed by ELISA.

RESULTS

While VEGF and Ang2 levels in UC patients were higher than in healthy controls (P < 0.05), UC patients showed lower levels of Ang1 than healthy individuals (P < 0.05). In UC patients who achieved clinical remission after corticosteroid treatment, a statistically significant higher baseline serum level of PlGF was observed (22 ± 5 vs. 18 ± 2; P < 0.05). Angiogenic factor levels varied during treatment; however, they did not show a statistically significant correlation to the activity of the disease.

CONCLUSIONS

VEGF, Ang1, and Ang2 levels showed statistically significant differences between UC patients and healthy controls. Although determination of PlGF serum levels before corticosteroid treatment might be helpful to anticipate the response by UC patients, no angiogenic pattern that could accurately predict "a priori" this response to corticosteroid treatment was observed. Corticosteroids altered temporarily circulating levels of VEGF, angiopoietins and Tie2. No correlation was found between systemic levels of angiogenic factors and the clinical activity of UC.

Blood vessels and the satellite cell niche

The fate of stem cell is regulated by cues received from the surrounding area. Recently, the concept of "stem cell zone"--rather than a predefined niche--introduced the notion of dynamic and permanent interactions between stem cells and their microenvironment. In adult skeletal muscle, satellite cells are considered as the main stem cells responsible for muscle repair and maintenance. They are localized close to vessels regardless their state of activation and differentiation. Moreover, the number of satellite cells is positively correlated to the capillarization of the myofiber. Angiogenesis has been known for a long time to be essential for muscle repair. However, relationships between vessel cells and satellite/myogenic cells that govern myogenic cell expansion, myogenesis, and angiogenesis have been only recently investigated. In this chapter, we discuss the possible existence of a vascular amplifying/differentiating niche, in an attempt to reconciliate several recent observations showing that satellite/myogenic cells interact with various cell types during the time course of muscle regeneration. Indeed, endothelial cells (ECs) stimulate myogenic cell growth and, inversely, differentiating myogenic cells promote angiogenesis. However, stromal cells may also provide some proliferating or differentiating cues to satellite/myogenic cells in this vascular area. Although some molecular effectors have been identified, including growth factors and cytokines, molecular regulations that occur within this vascular amplifying/differentiating niche requires further investigation. At the end of muscle repair, maturation of newly formed vessels takes place. In this context, we discuss the potential quiescence niche of satellite cells and the specific role of periendothelial cells. Indeed, periendothelial cells promote the return to quiescence of a subset of satellite/myogenic cells and maintain their quiescence (through Angiopoietin-1/Tie-2 signaling). We ask to what extent the environment may control the fate choice of satellite/myogenic cells and we also question the "hypoxic niche" in skeletal muscle, such a quiescence niche having being observed in the bone marrow.

Pheochromocytomas: the (pseudo)-hypoxia hypothesis

Hypoxia and pheochromocytoma/paraganglioma have a long common history. Since the description, almost 40 years ago, of an increased incidence of head and neck paragangliomas in chronic hypoxia, discoveries on oxygen-sensing and on hereditary paraganglioma in the beginning of years 2000 provided the proof of concept of a strong link between these neuroendocrine tumors and the hypoxic pathway. It was demonstrated that both SDH and VHL genes mutations lead to the abnormal stabilization and activation of hypoxia-inducible factors, and to the subsequent regulation of multiple target genes, the products of which are implicated in proliferation, apoptosis, angiogenesis, energy metabolism or invasiveness and metastases. Altogether, physiological, genetic, cellular and molecular data collected over years all point to a central role of the hypoxic or pseudohypoxic pathway in pheochromocytoma and paraganglioma tumorigenesis.

Pilot study to relate clinical outcome in pancreatic carcinoma and angiogenic plasma factors/circulating mature/progenitor endothelial cells: Preliminary results

Circulating endothelial cells (CEC) and bone marrow-derived endothelial progenitors (ECP) play important roles in tumor growth and have been proposed as non-invasive markers of angiogenesis. However, CEC and ECP levels have not been investigated in pancreatic carcinoma patients. Using four-color flow cytometry procedures, we evaluated the count of resting (rCEC) and activated (aCEC) endothelial cells and ECP in the peripheral blood of pancreatic carcinoma patients before and after chemotherapy, consisting of gemcitabine (GEM) alone or in combination with oxaliplatin (OX), or with 5-fluorouracil (5-FU). We also correlated CEC and ECP levels with plasma levels of relevant angiogenic factors, such as vascular endothelial growth factor (VEGF)-A, VEGF-D, angiopoietin (Angio)-1, and chemokine C-X-C motif ligand (CXCL)12, measured by ELISA, and with clinical features of pancreatic cancer. The aCEC, rCEC, ECP, and VEGF-A plasma levels were significantly higher in locally-advanced and metastatic patients than controls. Both ECP and VEGF-A levels correlated positively with disease stage and inversely with patient's overall survival. Measurements after the treatment course showed that VEGF-A plasma concentrations and ECP counts had decreased significantly. In particular, VEGF-A and rCEC were significantly down after treatment with GEM alone or in combination with OX. No significant differences in terms of circulating angiogenic factor or endothelial cell subtype levels were found between responders (patients entering partial remission or with stable disease) and non-responders (patients with progressive disease). The study provides insights into angiogenesis mechanisms in pancreatic carcinoma, for which anti-angiogenic targeting of VEGF-A and ECP could be of interest.

Impact of tumor microenvironment on oncolytic viral therapy

Interactions between tumor cells and their microenvironment have been shown to play a very significant role in the initiation, progression, and invasiveness of cancer. These tumor-stromal interactions are capable of altering the delivery and effectiveness of therapeutics into the tumor and are also known to influence future resistance and re-growth after treatment. Here we review recent advances in the understanding of the tumor microenvironment and its response to oncolytic viral therapy. The multifaceted environmental response to viral therapy can influence viral infection, replication, and propagation within the tumor. Recent studies have unveiled the complicated temporal changes in the tumor vasculature post-oncolytic virus (OV) treatment, and their impact on tumor biology. Similarly, the secreted extracellular matrix in solid tumors can affect both infection and spread of the therapeutic virus. Together, these complex changes in the tumor microenvironment also modulate the activation of the innate antiviral host immune response, leading to quick and efficient viral clearance. In order to combat these detrimental responses, viruses have been combined with pharmacological adjuvants and "armed" with therapeutic genes in order to suppress the pernicious environmental conditions following therapy. In this review we will discuss the impact of the tumor environment on viral therapy and examine some of the recent literature investigating methods of modulating this environment to enhance oncolysis.

Blood vessels, a potential therapeutic target in rheumatoid arthritis?

New micro-vessels formation within synovium and macro-vessels endothelial damage with atheroma are two major features of rheumatoid arthritis, the former related to the articular involvement of the disease, the latter to its main systemic complication. The similarities between pannus development and solid tumors growth, and the efficacy of anti-angiogenic treatments in oncology, opened the perspective of directly targeting angiogenesis in arthritis. Nevertheless, despite the success of different anti-angiogenic therapeutic strategies in many arthritis experimental models, the application in human disease is still lacking. Recent data suggest that synovial neoangiogenesis and macro-vessels endothelial damage might be two linked phenomena. While synovial angiogenesis seems to be detrimental to endothelial damage repair, even anti-angiogenic treatments might paradoxically aggravate macro-vascular disease, especially in the context of uncontrolled inflammation. These elements induce to further explore the interconnections between inflammation and angiogenesis on one side and between micro- and macro-vascular diseases on the other, in order to establish the proper way to therapeutically target blood vessels in rheumatoid arthritis.

Angiopoietin-4 promotes glioblastoma progression by enhancing tumor cell viability and angiogenesis

Glioblastoma multiforme (GBM) is a highly invasive and vascularized aggressive brain tumor. Less than 10% of GBM patients survive >5 years after diagnosis. Angiogenesis plays an important role in GBM growth, and antiangiogenesis-based therapies have shown clinical efficacy for GBM patients. Unfortunately, therapeutic resistance often develops in these patients, suggesting that GBM cells are capable of switching their dependency on one proangiogenic signaling pathway to an alternative one. Therefore, it is important to identify novel angiogenic factors that play essential roles in tumor angiogenesis and GBM progression. Angiopoietins (Ang-1, Ang-2, and Ang-4) are the ligands of the Tie-2 receptor tyrosine kinase (RTK). The roles of Ang-1 and Ang-2 in tumor angiogenesis have been established. However, little is known about how Ang-4 affects tumor angiogenesis and GBM progression and the mechanism underlying its effects. In our current study, we establish that Ang-4 is upregulated in human GBM tissues and cells. We show that, like endothelial cells, human GBM cells express Tie-2 RTK. We first establish that Ang-4 promotes in vivo growth of human GBM cells by promoting tumor angiogenesis and directly activating extracellular signal-regulated kinase 1/2 (Erk1/2) in GBM cells. Our results establish the novel effects of Ang-4 on tumor angiogenesis and GBM progression and suggest that this pro-GBM effect of Ang-4 is mediated by promoting tumor angiogenesis and activating Erk1/2 kinase in GBM cells. Together, our results suggest that the Ang-4-Tie-2 functional axis is an attractive therapeutic target for GBM.

Double antiangiogenic protein, DAAP, targeting VEGF-A and angiopoietins in tumor angiogenesis, metastasis, and vascular leakage

Two vascular growth factor families, VEGF and the angiopoietins, play critical and coordinate roles in tumor progression and metastasis. A single inhibitor targeting both VEGF and angiopoietins is not available. Here, we developed a chimeric decoy receptor, namely double anti-angiogenic protein (DAAP), which can simultaneously bind VEGF-A and angiopoietins, blocking their actions. Compared to VEGF-Trap or Tie2-Fc, which block either VEGF-A or angiopoietins alone, we believe DAAP is a highly effective molecule for regressing tumor angiogenesis and metastasis in implanted and spontaneous solid tumors; it can also effectively reduce ascites formation and vascular leakage in an ovarian carcinoma model. Thus, simultaneous blockade of VEGF-A and angiopoietins with DAAP is an effective therapeutic strategy for blocking tumor angiogenesis, metastasis, and vascular leakage.

Molecular characterization of the vascular features of focal nodular hyperplasia and hepatocellular adenoma: a role for angiopoietin-1

Focal nodular hyperplasia (FNH) and hepatocellular adenoma (HCA) are two hepatic nodular lesions of different etiologies. FNH, a polyclonal lesion, is assumed to be a regenerative reaction following a vascular injury, whereas HCA is a monoclonal, benign neoplastic lesion. In addition to features that are predominantly found in either FNH or HCA (e.g., dystrophic vessels in FNH and single arteries in HCA), FNH and HCA share morphological vascular abnormalities such as dilated sinusoids. We hypothesized that these anomalous vascular features are associated with altered expression of growth factors involved in vascular remodeling. This was based on reports of morphologically abnormal hepatic vasculature and nodular lesions in transgenic models of hepatocytic overexpression of angiopoietin-1 (Ang-1), a member of the angiopoietin family, which is crucially involved in vascular morphogenesis and homeostasis. We investigated gene and protein expression of members of the angiopoietin system and vascular endothelial growth factor A (VEGF-A) and its receptors in 9 FNH samples, 13 HCA samples, and 9 histologically normal livers. In comparison with normal samples, a significant increase in Ang-1 was found in FNH (P < 0.01) and HCA (P < 0.05), whereas no significant changes in Ang-2, receptor tyrosine kinase with immunoglobulin-like and EGF-like domains 2, VEGF-A, or vascular endothelial growth factor receptor 2 (VEGFR-2) were observed.

CONCLUSION

Because of the different etiological contexts of a preceding vascular injury in FNH and a neoplastic growth in HCA, Ang-1 might exert different effects on the vasculature in these lesions. In FNH, it could predominantly stimulate recruitment of myofibroblasts and result in dystrophic vessels, whereas in HCA, it may drive vascular remodeling that produces enlarged vessels and arterial sprouting that generates single arteries.

Angiogenesis inhibitors: current strategies and future prospects

Angiogenesis has become an attractive target for drug therapy because of its key role in tumor growth. An extensive array of compounds is currently in preclinical development, with many now entering the clinic and/or achieving approval from the US Food and Drug Administration. Several regulatory and signaling molecules governing angiogenesis are of interest, including growth factors (eg, vascular endothelial growth factor, platelet-derived growth factor, fibroblast growth factor, and epidermal growth factor), receptor tyrosine kinases, and transcription factors such as hypoxia inducible factor, as well as molecules involved in mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signaling. Pharmacologic agents have been identified that target these pathways, yet for some agents (notably thalidomide), an understanding of the specific mechanisms of antitumor action has proved elusive. The following review describes key molecular mechanisms and novel therapies that are on the horizon for antiangiogenic tumor therapy.

Role of secreted frizzled-related protein 3 in human renal cell carcinoma

The secreted frizzled-related protein (sFRP) family plays an important role in the inhibition of the Wnt signaling pathway in various cancers. The functional significance of Wnt antagonist sFRP3 has not been investigated in renal cancer. We performed tissue microarray and found that the level of sFRP3 protein was high in normal kidney, low in primary renal cancer tissues, and high in metastatic renal cancer tissues. Therefore, we hypothesized that sFRP3 may play an important role in metastatic renal cancer. To test this hypothesis, we performed a series of experiments to determine the role of sFRP3 using primary and metastatic renal cancer cell lines. Functional analysis showed increased numbers of viable and invaded cells and tube formation and decreased numbers of apoptotic cells in the sFRP3-transfected renal cancer cell line A498. Promotion of tumor growth was also observed in nude mice injected with sFRP3-transfected A498 cells. In contrast, the number of viable cells and invasive cells was decreased in sFRP3 mRNA knockdown metastatic cells (ACHN and Hs891.T). To investigate the mechanism of sFRP3 function, we performed microarray analysis to see which genes were upregulated or downregulated by sFRP3 expression. Among these genes, MMP-3 and ANGPT1 were significantly upregulated in sFRP3-transfected cells. In conclusion, this is the first report to show that sFRP3 expression promotes cell growth, invasion, and inhibition of apoptosis in renal cancer cells.

COUP-TFII regulates tumor growth and metastasis by modulating tumor angiogenesis

Tumor growth depends on nutrients and oxygen supplied by the vasculature through angiogenesis. Here, we show that the chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), a member of the nuclear receptor family, is a major angiogenesis regulator within the tumor microenvironment. Conditional ablation of COUP-TFII in adults severely compromised neoangiogenesis and suppressed tumor growth in xenograft mouse models. In addition, tumor growth and tumor metastasis were also impaired in a spontaneous mammary-gland tumor model in the absence of COUP-TFII. We showed that COUP-TFII directly regulates the transcription of Angiopoietin-1 in pericytes to enhance neoangiogenesis. Importantly, provision of Angiopoietin-1 partially restores the angiogenic defects exhibited by the COUP-TFII-deficient mice, which supports the notion that COUP-TFII controls Angiopoietin-1/Tie2 signaling to regulate tumor angiogenesis. Because COUP-TFII has little impact on normal adult physiological function, our results raise an interesting possibility that inhibition of COUP-TFII may offer a therapeutic approach for anticancer intervention.

Imaging angiogenesis of genitourinary tumors

Angiogenesis is a key process in the growth and metastasis of cancer, and genitourinary tumors are no exception. The evolution of angiogenesis as an important target for novel anticancer therapeutics has brought with it new challenges for in vivo imaging. Most imaging techniques quantify physiological parameters, such as blood volume and capillary endothelial permeability. Although CT, PET and ultrasonography have shown promise, MRI is the most common method used to evaluate angiogenesis in clinical trials of genitourinary tumors. Pilot studies of MRI, CT and ultrasonography in patients with renal cancer have produced promising results; reductions in vascular permeability and blood flow have been correlated with progression-free survival. The vascular characteristics of prostate cancer have been evaluated by MRI, and this has been suggested as a means of assessing tumor response to hormone deprivation therapy. Current evidence highlights the potential of angiogenesis imaging in the diagnosis, staging and possibly response monitoring of bladder cancer. In the future, assessment of the angiogenic process at the structural, functional and molecular levels, before, during and after antiangiogenic therapy will undoubtedly be integrated into wider clinical practice.

Angiopoietin-2 promotes disease progression of neuroendocrine tumors

PURPOSE

Inhibition of angiogenesis represents a promising therapeutic strategy in neuroendocrine tumors. Angiopoietin-2 (Ang-2), a ligand of the endothelial tyrosine kinase Tie-2, is emerging as a key regulator of vascular remodeling during tumor angiogenesis. We therefore addressed the expression and biological significance of Ang-2 in human neuroendocrine tumors.

EXPERIMENTAL DESIGN

Surgical specimens and serum from neuroendocrine tumor patients were used to determine Ang-2 expression by in situ hybridization or ELISA (circulating Ang-2). Ang-2 biological effects were evaluated following stable transfection into BON human pancreatic neuroendocrine tumor cells. BON clones were grown as orthotopic xenografts in nude mice to determine tumor growth and abdominal metastatic spread. Further analyses included microvessel density, lymphatic vessel density, and nodal invasion.

RESULTS

Specimens from pancreatic neuroendocrine tumors and nontransformed pancreatic tissue revealed uniform expression of Ang-2 mRNA in endothelial cells. In contrast, epithelial expression of Ang-2 mRNA occurred exclusively in neuroendocrine tumors. Overexpression of Ang-2 in BON orthotopic xenografts did not affect primary tumor growth, although successful Ang-2 induction was confirmed from elevated serum levels. However, increased microvessel density and enhanced lymphatic metastasis were evident in Ang-2-expressing tumors, indicating a functional role of Ang-2 in experimental neuroendocrine tumors. Consistent with this notion, circulating Ang-2 was significantly elevated in neuroendocrine tumor patients compared with healthy controls. Circulating Ang-2 furthermore correlated with metastatic versus localized disease. The highest Ang-2 concentrations occurred in patients with liver metastasis, and concentrations >or=75th percentile predicted shorter survival (P = 0.0003).

CONCLUSION

Induction of Ang-2 in neuroendocrine tumors represents a clinically relevant pathomechanism of disease progression and constitutes an adverse prognostic marker.

A human monoclonal anti-ANG2 antibody leads to broad antitumor activity in combination with VEGF inhibitors and chemotherapy agents in preclinical models

Localized angiopoietin-2 (Ang2) expression has been shown to function as a key regulator of blood vessel remodeling and tumor angiogenesis, making it an attractive candidate for antiangiogenic therapy. A fully human monoclonal antibody (3.19.3) was developed, which may have significant pharmaceutical advantages over synthetic peptide-based approaches in terms of reduced immunogenicity and increased half-life to block Ang2 function. The 3.19.3 antibody potently binds Ang2 with an equilibrium dissociation constant of 86 pmol/L, leading to inhibition of Tie2 receptor phosphorylation in cell-based assays. In preclinical models, 3.19.3 treatment blocked blood vessel formation in Matrigel plug assays and in human tumor xenografts. In vivo studies with 3.19.3 consistently showed broad antitumor activity as a single agent across a panel of diverse subcutaneous and orthotopic xenograft models. Combination studies of 3.19.3 with cytotoxic drugs or anti-vascular endothelial growth factor agents showed significant improvements in antitumor activity over single-agent treatments alone with no apparent evidence of increased toxicity. Initial pharmacokinetic profiling studies in mice and nonhuman primates suggested that 3.19.3 has a predicted human half-life of 10 to 14 days. These studies provide preclinical data for 3.19.3 as a potential new antiangiogenic therapy as a single agent or in combination with chemotherapy or vascular endothelial growth factor inhibitors for the treatment of cancer.

Autocrine and paracrine angiopoietin 1/Tie-2 signaling promotes muscle satellite cell self-renewal

Mechanisms governing muscle satellite cell withdrawal from cell cycle to enter into quiescence remain poorly understood. We studied the role of angiopoietin 1 (Ang1) and its receptor Tie-2 in the regulation of myogenic precursor cell (mpc) fate. In human and mouse, Tie-2 was preferentially expressed by quiescent satellite cells in vivo and reserve cells (RCs) in vitro. Ang1/Tie-2 signaling, through ERK1/2 pathway, decreased mpc proliferation and differentiation, increased the number of cells in G0, increased expression of RC-associated markers (p130, Pax7, Myf-5, M-cadherin), and downregulated expression of differentiation-associated markers. Silencing Tie-2 had opposite effects. Cells located in the satellite cell neighborhood (smooth muscle cells, fibroblasts) upregulated RC-associated markers by secreting Ang1 in vitro. In vivo, Tie-2 blockade and Ang1 overexpression increased the number of cycling and quiescent satellite cells, respectively. We propose that Ang1/Tie-2 signaling regulates mpc self-renewal by controlling the return to quiescence of a subset of satellite cells.

Contrasting actions of selective inhibitors of angiopoietin-1 and angiopoietin-2 on the normalization of tumor blood vessels

Angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) have complex actions in angiogenesis and vascular remodeling due to their effects on Tie2 receptor signaling. Ang2 blocks Ang1-mediated activation of Tie2 in endothelial cells under certain conditions but is a Tie2 receptor agonist in others. We examined the effects of selective inhibitors of Ang1 (mL4-3) or Ang2 (L1-7[N]), alone or in combination, on the vasculature of human Colo205 tumors in mice. The Ang2 inhibitor decreased the overall abundance of tumor blood vessels by reducing tumor growth and keeping vascular density constant. After inhibition of Ang2, tumor vessels had many features of normal blood vessels (normalization), as evidenced by junctional accumulation of vascular endothelial-cadherin, junctional adhesion molecule-A, and platelet/endothelial cell adhesion molecule-1 in endothelial cells, increased pericyte coverage, reduced endothelial sprouting, and remodeling into smaller, more uniform vessels. The Ang1 inhibitor by itself had little noticeable effect on the tumor vasculature. However, when administered with the Ang2 inhibitor, the Ang1 inhibitor prevented tumor vessel normalization, but not the reduction in tumor vascularity produced by the Ang2 inhibitor. These findings are consistent with a model whereby inhibition of Ang2 leads to normalization of tumor blood vessels by permitting the unopposed action of Ang1, but decreases tumor vascularity primarily by blocking Ang2 actions.

Vascular characterization of clear cell sarcoma of the kidney in a child: a case report and review

Clear cell sarcoma of the kidney (CCSK) is uncommon pediatric renal tumor and can present a significant therapeutic challenge in those patients whose tumors spread beyond the kidney. Thus, identifying potential novel targets for treatment may be clinically important. Clear cell sarcoma of the kidney is characterized by a unique vascular pattern, in which nests of tumor cells are separated by regularly-spaced, fine fibrovascular septa. This distinctive histopathology raises the possibility that understanding the factors which drive angiogenesis in CCSK tumors may suggest new therapeutic targets. Here, we describe a case of CCSK and present immunohistochemical studies of its vasculature.

Angiogenesis and lymphangiogenesis are downregulated in primary breast cancer

BACKGROUND

Angiogenesis and lymphangiogenesis are considered to play key roles in tumour growth, progression and metastasis. However, targeting tumour angiogenesis in clinical trials showed only modest efficacy. We therefore scrutinised the concept of tumour angiogenesis and lymphangiogenesis by analysing the expression of crucial markers involved in these processes in primary breast cancer.

METHODS

We analysed the expression of angiogenic, lymphangiogenic or antiangiogenic factors, their respective receptors and specific markers for endothelial and lymphendothelial cells by quantitative real-time RT-PCR in primary breast cancer and compared the expression profiles to non-cancerous, tumour-adjacent tissues and breast tissues from healthy women.

RESULTS

We found decreased mRNA amounts of major angiogenic and lymphangiogenic factors in tumour compared to healthy tissues, whereas antiangiogenic factors were upregulated. Concomitantly, angiogenic and lymphangiogenic receptors were downregulated in breast tumours. This antiangiogenic, antilymphangiogenic microenvironment was even more pronounced in aggressive tumours and accompanied by reduced amounts of endothelial and lymphatic endothelial cell markers.

CONCLUSION

Primary breast tumours are not a site of highly active angiogenesis and lymphangiogenesis. Selection for tumour cells that survive with minimal vascular supply may account for this observation in clinical apparent tumours.

Targeting tumor angiogenesis

Our understanding of the process of tumor angiogenesis has changed significantly since the late 1970s, when vascular endothelial growth factor (VEGF) was first identified as vascular permeability factor and later found to be the major mediator of physiologic and pathologic angiogenesis. Since then, several additional VEGF-related ligands, VEGF receptors (VEGFRs), and complementary/alternative pathways that regulate tumor angiogenesis have been identified. Over the last decade, several antiangiogenic agents have been developed with the aim to inhibit new blood vessel growth, and we have learned that VEGF inhibition does far more than simply block new blood vessel growth. Clinical studies have demonstrated an improvement of progression-free and overall survivals with anti-VEGF therapy (with or without chemotherapy) in patients with advanced-stage malignancies. Unfortunately, even when anti-VEGF therapy is effective, the benefit of therapy is short-lived, with the development of tumor growth. We now recognize the presence of numerous complementary and redundant pathways that regulate tumor vasculature. For example, VEGF/VEGFR and angiopoietin/Tie-2 axes are two redundant, complementary components regulating tumor angiogenesis and vascular maintenance. The current clinical challenge is to identify: (1) factors that predict efficacy, and (2) markers of tumor response to anti-VEGF therapy, which can be achieved only by developing a thorough understanding of the biology of the VEGF system and the role of complementary pathways that may mediate resistance to anti-VEGF therapy.

VE-PTP controls blood vessel development by balancing Tie-2 activity

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is an endothelial-specific receptor-type tyrosine phosphatase that associates with Tie-2 and VE-cadherin. VE-PTP gene disruption leads to embryonic lethality, vascular remodeling defects, and enlargement of vascular structures in extraembryonic tissues. We show here that antibodies against the extracellular part of VE-PTP mimic the effects of VE-PTP gene disruption exemplified by vessel enlargement in allantois explants. These effects require the presence of the angiopoietin receptor Tie-2. Analyzing the mechanism we found that anti-VE-PTP antibodies trigger endocytosis and selectively affect Tie-2-associated, but not VE-cadherin-associated VE-PTP. Dissociation of VE-PTP triggers the activation of Tie-2, leading to enhanced endothelial cell proliferation and enlargement of vascular structures through activation of Erk1/2. Importantly, the antibody effect on vessel enlargement is also observed in newborn mice. We conclude that VE-PTP is required to balance Tie-2 activity and endothelial cell proliferation, thereby controlling blood vessel development and vessel size.