Angiopoietin-2 functions as a Tie2 agonist in tumor models, where it limits the effects of VEGF inhibition

Opposing actions of angiopoietin-2 on Tie2 signaling and FOXO1 activation

Angiopoietin-2 (ANG2) regulates blood vessel remodeling in many pathological conditions through differential effects on Tie2 signaling. While ANG2 competes with ANG1 to inhibit Tie2, it can paradoxically also promote Tie2 phosphorylation (p-Tie2). A related paradox is that both inactivation and overactivation of Tie2 can result in vascular remodeling. Here, we reconciled these opposing actions of ANG2 by manipulating conditions that govern its actions in the vasculature. ANG2 drove vascular remodeling during Mycoplasma pulmonis infection by acting as a Tie2 antagonist, which led to p-Tie2 suppression, forkhead box O1 (FOXO1) activation, increased ANG2 expression, and vessel leakiness. These changes were exaggerated by anti-Tie2 antibody, inhibition of PI3K signaling, or ANG2 overexpression and were reduced by anti-ANG2 antibody or exogenous ANG1. In contrast, under pathogen-free conditions, ANG2 drove vascular remodeling by acting as an agonist, promoting high p-Tie2, low FOXO1 activation, and no leakage. Tie1 activation was strong under pathogen-free conditions, but infection or TNF-α led to Tie1 inactivation by ectodomain cleavage and promoted the Tie2 antagonist action of ANG2. Together, these data indicate that ANG2 activation of Tie2 supports stable enlargement of normal nonleaky vessels, but reduction of Tie1 in inflammation leads to ANG2 antagonism of Tie2 and initiates a positive feedback loop wherein FOXO1-driven ANG2 expression promotes vascular remodeling and leakage.

Systematic analysis of circulating soluble angiogenesis-associated proteins in ICON7 identifies Tie2 as a biomarker of vascular progression on bevacizumab

BACKGROUND

There is a critical need for predictive/resistance biomarkers for VEGF inhibitors to optimise their use.

METHODS

Blood samples were collected during and following treatment and, where appropriate, upon progression from ovarian cancer patients in ICON7, a randomised phase III trial of carboplatin and paclitaxel with or without bevacizumab. Plasma concentrations of 15 circulating angio-biomarkers were measured using a validated multiplex ELISA, analysed through a novel network analysis and their relevance to the PFS then determined.

RESULTS

Samples (n=650) were analysed from 92 patients. Bevacizumab induced correlative relationships between Ang1 and Tie2 plasma concentrations, which reduced after initiation of treatment and remained decreased until progressive disease occurred. A 50% increase from the nadir in the concentration of circulating Tie2 (or the product of circulating Ang1 and Tie2) predicted tumour progression. Combining Tie2 with GCIG-defined Ca125 data yielded a significant improvement in the prediction of progressive disease in patients receiving bevacizumab in comparison with Ca125 alone (74.1% vs 47.3%, P<1 × 10(-9)).

CONCLUSIONS

Tie2 is a vascular progression marker for bevacizumab-treated ovarian cancer patients. Tie2 in combination with Ca125 provides superior information to clinicians on progressive disease in patients with VEGFi-treated ovarian cancers.

Tumor-associated macrophages and anti-tumor therapies: complex links

Myeloid cells infiltrating the tumor microenvironment, especially tumor-associated macrophages (TAMs), are essential providers of cancer-related inflammation, a condition known to accelerate tumor progression and limit the response to anti-tumor therapies. As a matter of fact, TAMs may have a dual role while interfering with cancer treatments, as they can either promote or impair their functionality. Here we review the connection between macrophages and anticancer therapies; moreover, we provide an overview of the different strategies to target or re-program TAMs for therapeutic purposes.

Suppression of KSHV-induced angiopoietin-2 inhibits angiogenesis, infiltration of inflammatory cells, and tumor growth

Kaposi's sarcoma (KS) is a highly angiogenic and inflammatory neoplasia. The angiogenic and inflammatory cytokine angiopoietin-2 (Ang-2) is strongly expressed in KS due to Kaposi's sarcoma-associated herpesvirus (KSHV) infection. In the present study, we determined how Ang-2 contributes to development of KS by using telomerase-immortalized human umbilical vein endothelial cells (TIVE) as a model, which become malignantly transformed and express increased levels of Ang-2 following KSHV infection. Ang-2 released from TIVE-KSHV cells induces tyrosine phosphorylation of Tie-2 receptor from both human and mouse endothelial cells and promotes angiogenesis in nude mice. Functional inhibition or expressional "knock-down" of Ang-2 in these cells blocks angiogenesis and inhibits tumor growth. Ang-2 suppression also reduces the numbers of infiltrating monocytes/macrophages in tumors. In transwell-based cell migration assays, Ang-2 indeed enhances migration of human monocytes in a dose-dependent manner. These results underscore a pivotal role of KSHV-induced Ang-2 in KS tumor development by promoting both angiogenesis and inflammation. Our data also suggest that selective drug targeting of Ang-2 may be used for treatment of KS.

Single-cell RNA-seq reveals cell type-specific transcriptional signatures at the maternal-foetal interface during pregnancy

Growth and survival of the mammalian embryo within the uterine environment depends on the placenta, a highly complex vascularized organ comprised of both maternal and foetal tissues. Recent experiments demonstrate that the zinc finger transcriptional repressor Prdm1/Blimp1 is essential for specification of spiral artery trophoblast giant cells (SpA-TGCs) that invade and remodel maternal blood vessels. To learn more about functional contributions made by Blimp1+ cell lineages here we perform the first single-cell RNA-seq analysis of the placenta. Cell types of both foetal and maternal origin are profiled. Comparisons with microarray datasets from mutant placenta and in vitro differentiated trophoblast stem cells allow us to identify Blimp1-dependent transcripts enriched in SpA-TGCs. Our experiments provide new insights into the functionally distinct cell types present at the maternal–foetal interface and advance our knowledge of dynamic gene expression patterns controlling placental morphogenesis and vascular mimicry.

The zinc finger transcriptional repressor Prdm1/Blimp1 is essential for remodelling maternal blood vessels in a subset of trophoblast cells. Here, the authors perform single-cell RNA-seq analysis on this Blimp1+ lineage, identifying functionally distinct cell types present at the maternal–foetal interface.

Association of Angiopoietin-2 and Ki-67 Expression with Vascular Density and Sunitinib Response in Metastatic Renal Cell Carcinoma

The Angiopoietin-2 (Ang2, Angpt2) growth factor is a context-dependent antagonist/agonist ligand of the endothelial Tie2 receptor tyrosine kinase and known to promote tumour angiogenesis and metastasis. Angiopoietin antagonists have been tested in clinical cancer trials in combination with VEGF-based anti-angiogenic therapy, including sunitinib, which is widely used as a first-line therapy for metastatic renal cell carcinoma (mRCC). However, little is known about Ang2 protein expression in human tumours and the correlation of tumour Ang2 expression with tumour vascularization, tumour cell proliferation and response to anti-angiogenic therapies. Here, we evaluated, using immunohistochemistry, the expression of Ang2, CD31 and the cell proliferation marker Ki-67 in the primary kidney cancer from 136 mRCC patients, who received first-line sunitinib after nephrectomy. Ang2 protein expression was restrained to RCC tumour vessels, and correlated with tumour vascularization and response to sunitinib. High pre-therapeutic Ang2 expression, and more strongly, combined high expression of both Ang2 and CD31, were associated with a high clinical benefit rate (CBR). Low cancer Ki-67 expression, but not Ang2 or CD31 expression, was associated with favourable progression-free (PFS) and overall survival (OS) as compared to patients with high Ki-67 expression (PFS 6.5 vs. 10.6 months, P = 0.009; OS, 15.7 vs. 28.5 months, P = 0.015). In summary, in this study to investigate endothelial Ang2 in mRCC patients treated with first-line sunitinib, high cancer Ang2 expression was associated with the CBR, but not PFS or OS, whereas low Ki-67 expression was significantly associated with long PFS and OS.

Ang-2/VEGF bispecific antibody reprograms macrophages and resident microglia to anti-tumor phenotype and prolongs glioblastoma survival

Inhibition of the vascular endothelial growth factor (VEGF) pathway has failed to improve overall survival of patients with glioblastoma (GBM). We previously showed that angiopoietin-2 (Ang-2) overexpression compromised the benefit from anti-VEGF therapy in a preclinical GBM model. Here we investigated whether dual Ang-2/VEGF inhibition could overcome resistance to anti-VEGF treatment. We treated mice bearing orthotopic syngeneic (Gl261) GBMs or human (MGG8) GBM xenografts with antibodies inhibiting VEGF (B20), or Ang-2/VEGF (CrossMab, A2V). We examined the effects of treatment on the tumor vasculature, immune cell populations, tumor growth, and survival in both the Gl261 and MGG8 tumor models. We found that in the Gl261 model, which displays a highly abnormal tumor vasculature, A2V decreased vessel density, delayed tumor growth, and prolonged survival compared with B20. In the MGG8 model, which displays a low degree of vessel abnormality, A2V induced no significant changes in the tumor vasculature but still prolonged survival. In both the Gl261 and MGG8 models A2V reprogrammed protumor M2 macrophages toward the antitumor M1 phenotype. Our findings indicate that A2V may prolong survival in mice with GBM by reprogramming the tumor immune microenvironment and delaying tumor growth.

Dual inhibition of Ang-2 and VEGF receptors normalizes tumor vasculature and prolongs survival in glioblastoma by altering macrophages

Glioblastomas (GBMs) rapidly become refractory to anti-VEGF therapies. We previously demonstrated that ectopic overexpression of angiopoietin-2 (Ang-2) compromises the benefits of anti-VEGF receptor (VEGFR) treatment in murine GBM models and that circulating Ang-2 levels in GBM patients rebound after an initial decrease following cediranib (a pan-VEGFR tyrosine kinase inhibitor) administration. Here we tested whether dual inhibition of VEGFR/Ang-2 could improve survival in two orthotopic models of GBM, Gl261 and U87. Dual therapy using cediranib and MEDI3617 (an anti-Ang-2-neutralizing antibody) improved survival over each therapy alone by delaying Gl261 growth and increasing U87 necrosis, effectively reducing viable tumor burden. Consistent with their vascular-modulating function, the dual therapies enhanced morphological normalization of vessels. Dual therapy also led to changes in tumor-associated macrophages (TAMs). Inhibition of TAM recruitment using an anti-colony-stimulating factor-1 antibody compromised the survival benefit of dual therapy. Thus, dual inhibition of VEGFR/Ang-2 prolongs survival in preclinical GBM models by reducing tumor burden, improving normalization, and altering TAMs. This approach may represent a potential therapeutic strategy to overcome the limitations of anti-VEGFR monotherapy in GBM patients by integrating the complementary effects of anti-Ang2 treatment on vessels and immune cells.

Evaluation of Angiopoietin-2 as a biomarker in gastric cancer: results from the randomised phase III AVAGAST trial

Background:

In the phase III AVAGAST trial, the addition of bevacizumab to chemotherapy improved progression-free survival (PFS) but not overall survival (OS) in patients with advanced gastric cancer. We studied the role of Angiopoietin-2 (Ang-2), a key driver of tumour angiogenesis, metastasis and resistance to antiangiogenic treatment, as a biomarker.

Methods:

Previously untreated, advanced gastric cancer patients were randomly assigned to receive bevacizumab (n=387) or placebo (n=387) in combination with chemotherapy. Plasma collected at baseline and at progression was analysed by ELISA. The role of Ang-2 as a prognostic and a predictive biomarker of bevacizumab efficacy was studied using a Cox proportional hazards model. Logistic regression analysis was applied for correlations with metastasis.

Results:

Median baseline plasma Ang-2 levels were lower in Asian (2143 pg ml⁻¹) vs non-Asian patients (3193 pg ml⁻¹), P<0.0001. Baseline plasma Ang-2 was identified as an independent prognostic marker for OS but did not predict bevacizumab efficacy alone or in combination with baseline VEGF. Baseline plasma Ang-2 correlated with the frequency of liver metastasis (LM) at any time: Odds ratio per 1000 pg ml⁻¹ increase: 1.19; 95% CI 1.10–1.29; P<0.0001 (non-Asians) and 1.37; 95% CI 1.13–1.64; P=0.0010 (Asians).

Conclusions:

Baseline plasma Ang-2 is a novel prognostic biomarker for OS in advanced gastric cancer strongly associated with LM. Differences in Ang-2 mediated vascular response may, in part, account for outcome differences between Asian and non-Asian patients; however, data have to be further validated. Ang-2 is a promising drug target in gastric cancer.

Gastrointestinal angiodysplasia is associated with significant gastrointestinal bleeding in patients with continuous left ventricular assist devices

BACKGROUND AND STUDY AIMS

Patients with a continuous-flow left ventricular assist device (LVAD) have a 65 % incidence of bleeding events within the first year. The majority of gastrointestinal bleeding (GIB) is from gastrointestinal angiodyplasia (GIAD). The primary aim of the study was to determine whether GIAD was associated with a higher rate of significant bleeding, an increased number of bleeding events per year, and a higher rate of transfusion compared to non-GIAD sources.

PATIENTS AND METHODS

This retrospective cohort study included 118 individuals who received a LVAD at a tertiary medical center from 2006 through 2014. Patients were subdivided into GIB and non-GIB for comparison of patient demographics, comorbid conditions, and laboratory data. GIB was further divided into sources of GIB, GIAD, obscure, or non-GIAD to establish severity of bleeding, rate of re-bleeding, and transfusion rate.

RESULTS

GIAD is associated with an increased number of bleeding events compared to non-GIAD sources of GIB (2.07 vs 1.23, P = 0.01) and a higher number of bleeding events per year (0.806 vs. 0.455 P = 0.001). GIAD compared to non-GIAD sources of GIB was associated with an increased incidence of major bleeding (100 % vs 60 %, P = 0.006) and increased rates of transfusion (8.8 vs 2.95 units, P = 0.0004). Cox Regression analysis between non-GIB and GIAD demonstrated increased risk with age (P = 0.001), history of chronic kidney disease (P = 0.005), and length of stay after LVAD implantation of more than 45 days (P = 0.04). History of hypertension (P = 0.045), diabetes mellitus (P = 0.016), and male gender was associated with decreased risk (P = 0.04).

CONCLUSION

Patients with a continuous-flow LVAD who develop a GIB secondary to GIAD have a higher rate of major bleeding, multiple bleeding events, and require more transfusions to achieve stabilization compared to patients who do not have GIAD.

Angiogenesis in malignant melanoma

Despite the development of novel therapies, the therapy of malignant melanoma remains challenging. Various studies have shown the vascular system to be pivotal for metastasis in melanoma. Consequently, the effect of various antiangiogenic therapies has been and is being investigated in preclinical and clinical trials. While most studies focus on inhibition of vascular endothelial growth factor (VEGF) signaling, others are aimed at determining the effect of multikinase inhibitors or the inhibition of angiogenic integrin activity. However, overall survival rates have not significantly improved in clinical trials with antiangiogenic agents. Resistance to anti-VEGF monotherapy has been observed in several studies, especially in malignant melanoma. Angiopoietin-2 (Ang-2) represents a promising candidate molecule for antiangiogenic therapy and the effect of Ang-2 inhibitors is currently being explored in first trials. In melanoma, Ang-2 has been shown to be a marker for metastasis formation and represents an interesting therapeutic target molecule. Future studies are required to analyze the effect of a combined approach, using anti-VEGF and anti-Ang-2, as therapy for malignant melanoma.

Vasculotide reduces endothelial permeability and tumor cell extravasation in the absence of binding to or agonistic activation of Tie2

Angiopoietin-1 (Ang1) activation of Tie2 receptors on endothelial cells (ECs) reduces adhesion by tumor cells (TCs) and limits junctional permeability to TC diapedesis. We hypothesized that systemic therapy with Vasculotide (VT)—a purported Ang1 mimetic, Tie2 agonist—can reduce the extravasation of potentially metastatic circulating TCs by similarly stabilizing the host vasculature. In vitro, VT and Ang1 treatments impeded endothelial hypermeability and the transendothelial migration of MDA-MB-231•LM2-4 (breast), HT29 (colon), or SN12 (renal) cancer cells to varying degrees. In mice, VT treatment inhibited the transit of TCs through the pulmonary endothelium, but not the hepatic or lymphatic endothelium. In the in vivo LM2-4 model, VT monotherapy had no effect on primary tumors, but significantly delayed distant metastatic dissemination to the lungs. In the post-surgical adjuvant treatment setting, VT therapeutically complemented sunitinib therapy, an anti-angiogenic tyrosine kinase inhibitor which limited the local growth of residual disease. Unexpectedly, detailed investigations into the putative mechanism of action of VT revealed no evidence of Tie2 agonism or Tie2 binding; alternative mechanisms have yet to be determined.

Angiogenesis- and Hypoxia-Associated Proteins as Early Indicators of the Outcome in Patients with Metastatic Breast Cancer Given First-Line Bevacizumab-Based Therapy

PURPOSE

We examined whether pretreatment levels of angiogenesis- or hypoxia-related proteins and their changes after one cycle of first-line bevacizumab-based therapy were associated with response, PFS, or OS in patients with metastatic breast cancer.

EXPERIMENTAL DESIGN

We included 181 patients enrolled in the phase II ATX trial evaluating first-line paclitaxel and bevacizumab without or with capecitabine (NTR1348). Plasma samples were analyzed for VEGF-A, soluble VEGFR2 (sVEGFR2), angiopoietin 2 (ANG2), soluble TIE2 (sTIE2), IL6, IL8, and carbonic anhydrase 9 (CA9). Baseline serum CA15-3 was documented. HR was adjusted for confounding factors. Where appropriate, an optimal cut-off value defining a high and a low group was determined with Martingale residuals.

RESULTS

At baseline, multiple proteins were significantly associated with PFS (ANG2, IL6, IL8, CA9, CA15-3) and OS (ANG2, sTIE2, IL6, IL8, CA9, CA15-3). After one cycle, VEGF-A, ANG2, sTIE2, and IL8 significantly decreased, while sVEGFR2 and CA9 significantly increased. The relative change in sVEGFR2 (P= 0.01) and IL8 (P= 0.001) was associated with response. Defining optimal cut-off, patients with a high CA9 rise (>2.9%) had better PFS (HR 0.45) and OS (HR 0.54) than those with low/no rise.

CONCLUSIONS

Multiple angiogenesis- or hypoxia-related proteins were prognostic for PFS and OS. Molecular agents targeting these proteins might be beneficial in patients with high levels. Changes in IL8 or sVEGFR2 levels at second cycle appear predictive for response. Changes in CA9 levels during bevacizumab-based therapy for prediction of PFS and OS merit further study.

Circulating angiopoietin-1 and -2 in patients with stable and exacerbated asthma

BACKGROUND

Angiopoietin (Ang)-1 and -2 are involved in the pathogenesis of asthma and have been identified as markers of asthma severity.

OBJECTIVE

To determine the relation between circulating angiopoietins and clinical variables of patients with asthma.

METHODS

Fifty patients with bronchial asthma and 25 healthy controls were enrolled. Ang1 and Ang2 plasma levels were analyzed in patients with stable and exacerbated asthma.

RESULTS

Plasma Ang1 levels were 28.4 ± 4.01 pg/mg in patients with bronchial asthma and 21.2 ± 5.21 pg/mg in healthy controls. Plasma Ang2 levels were 23.96 ± 1.38 pg/mg in patients with bronchial asthma compared with 36.8 ± 4.46 pg/mg in healthy controls (P = .010). The ratio of Ang2 to Ang1 was lower in patients with asthma than in control subjects. Plasma Ang1 concentrations were correlated with the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC), and plasma Ang2 levels were correlated with FEV1 percentage of predicted, FEV1/FVC, and total immunoglobulin E values. The ratio of Ang2 to Ang1 was correlated with FEV1 percentage of predicted and FEV1/FVC. Although plasma Ang1 levels tended to be lower in the exacerbated state than in the stable state in patients with asthma, Ang2 levels were higher in the exacerbated state than in the stable state in patients with asthma (P = .001). Plasma Ang2 levels were correlated with initial eosinophil proportions and initial neutrophil proportions. Plasma Ang2 levels and the ratio of Ang2 to Ang1 were correlated with blood eosinophil proportions in the exacerbated state.

CONCLUSION

These results indicate that circulating angiopoietins could be a useful marker of asthma exacerbation.

Angiopoietin-2 May Be Involved in the Resistance to Bevacizumab in Recurrent Glioblastoma

Despite encouraging response rate of bevacizumab (BVZ) in recurrent glioblastoma, many patients do not respond to this schedule and most of the responders develop an early relapse. Plasma concentrations of VEGF, PlGF, Ang2, and sTie2 were assessed by ELISA before and during BVZ treatment in seventy patients. Baseline levels of VEGF-A, and PlGF were higher in patients than in healthy volunteers, whereas no difference was found for Ang2, and sTie2. No biomarker at baseline was associated with response, PFS or OS. At recurrence, the authors observed an increase of Ang2 suggesting that Ang2/sTie2 could be involved in the resistance to BVZ.

Anti-angiogenic alternatives to VEGF blockade

Angiogenesis is a major requirement for tumour formation and development. Anti-angiogenic treatments aim to starve the tumour of nutrients and oxygen and also guard against metastasis. The main anti-angiogenic agents to date have focused on blocking the pro-angiogenic vascular endothelial growth factors (VEGFs). While this approach has seen some success and has provided a proof of principle that such anti-angiogenic agents can be used as treatment, the overall outcome of VEGF blockade has been somewhat disappointing. There is a current need for new strategies in inhibiting tumour angiogenesis; this article will review current and historical examples in blocking various membrane receptors and components of the extracellular matrix important in angiogenesis. Targeting these newly discovered pro-angiogenic proteins could provide novel strategies for cancer therapy.

Combined Ang-2 and VEGF serum levels: holding hands as a new integral biomarker in non-small-cell lung cancers

AIM

Evaluate if serum levels of VEGF and Ang-2 are correlated in non-small-cell lung cancers (NSCLCs) and its implications in the diagnostic and prognostic of the disease.

PATIENTS & METHODS

Unselected cohort of 145 NSCLC patients and 30 control individuals. The serum levels of Ang-2 and VEGF of each patient were measured by ELISA prior to treatment.

RESULTS & CONCLUSIONS

Serum levels of Ang-2 and VEGF are correlated (p < 0.0001). High serum levels of Ang-2 and VEGF isolated and both combined (high(Ang-2/VEGF)) correlate with likelihood of presenting NSCLC (p = 0.016; p = 0.003; p < 0.0001, respectively). Serum levels of Ang-2 and high(Ang-2/VEGF) but not VEGF alone are independent prognostic factors (p = 0.001; p = 0.619; p = 0.005). High(Ang-2/VEGF) serum levels could be exploited as a new valuable integral biomarker in NSCLC.

Cancer anti-angiogenesis vaccines: Is the tumor vasculature antigenically unique?

Angiogenesis is essential for the growth and metastasis of solid tumors. The tumor endothelium exists in a state of chronic activation and proliferation, fueled by the tumor milieu where angiogenic mediators are aberrantly over-expressed. Uncontrolled tumor growth, immune evasion, and therapeutic resistance are all driven by the dysregulated and constitutive angiogenesis occurring in the vasculature. Accordingly, great efforts have been dedicated toward identifying molecular signatures of this pathological angiogenesis in order to devise selective tumor endothelium targeting therapies while minimizing potential autoimmunity against physiologically normal endothelium. Vaccination with angiogenic antigens to generate cellular and/or humoral immunity against the tumor endothelium has proven to be a promising strategy for inhibiting or normalizing tumor angiogenesis and reducing cancer growth. Here we review tumor endothelium vaccines developed to date including active immunization strategies using specific tumor endothelium-associated antigens and whole endothelial cell-based vaccines designed to elicit immune responses against diverse target antigens. Among the novel therapeutic options, we describe a placenta-derived endothelial cell vaccine, ValloVax™, a polyvalent vaccine that is antigenically similar to proliferating tumor endothelium and is supported by pre-clinical studies to be safe and efficacious against several tumor types.

A Phase I First-in-Human Study of Nesvacumab (REGN910), a Fully Human Anti-Angiopoietin-2 (Ang2) Monoclonal Antibody, in Patients with Advanced Solid Tumors

PURPOSE

Nesvacumab (REGN910) is a fully human immunoglobulin G1 (IgG1) monoclonal antibody that specifically binds and inactivates the Tie2 receptor ligand Ang2 with high affinity, but shows no binding to Ang1. The main objectives of this trial were to determine the safety, tolerability, dose-limiting toxicities (DLT), and recommended phase II dose (RP2D) of nesvacumab.

EXPERIMENTAL DESIGN

Nesvacumab was administered intravenously every two weeks with dose escalations from 1 to 20 mg/kg in patients with advanced solid tumors.

RESULTS

A total of 47 patients were treated with nesvacumab. No patients in the dose escalation phase experienced DLTs, therefore a maximum tolerated dose (MTD) was not reached. The most common nesvacumab-related adverse events were fatigue (23.4%), peripheral edema (21.3%), decreased appetite, and diarrhea (each 10.6%; all grade ≤ 2). Nesvacumab was characterized by linear kinetics and had a terminal half-life of 6.35 to 9.66 days in a dose-independent manner. Best response by RECIST 1.1 in 43 evaluable patients included 1 partial response (adrenocortical carcinoma) of 24 weeks duration. Two patients with hepatocellular carcinoma had stable disease (SD) > 16 weeks, with tumor regression and >50% decrease in α-fetoprotein. Analyses of putative angiogenesis biomarkers in serum and tumor biopsies were uninformative for treatment duration.

CONCLUSIONS

Nesvacumab safety profile was acceptable at all dose levels tested. Preliminary antitumor activity was observed in patients with treatment-refractory advanced solid tumors. On the basis of cumulative safety, antitumor activity, pharmacokinetic and pharmacodynamic data, the 20 mg/kg dose was determined to be the RP2D.

The pathogenic role of angiogenesis in rheumatoid arthritis

Angiogenesis is the formation of new capillaries from pre-existing vasculature, which plays a critical role in the pathogenesis of several inflammatory autoimmune diseases such as rheumatoid arthritis (RA), spondyloarthropathies, psoriasis, systemic lupus erythematosus, systemic sclerosis, and atherosclerosis. In RA, excessive migration of circulating leukocytes into the inflamed joint necessitates formation of new blood vessels to provide nutrients and oxygen to the hypertrophic joint. The dominance of the pro-angiogenic factors over the endogenous angiostatic mediators triggers angiogenesis. In this review article, we highlight the underlying mechanisms by which cells present in the RA synovial tissue are modulated to secrete pro-angiogenic factors. We focus on the significance of pro-angiogenic factors such as growth factors, hypoxia-inducible factors, cytokines, chemokines, matrix metalloproteinases, and adhesion molecules on RA pathogenesis. As pro-angiogenic factors are primarily produced from RA synovial tissue macrophages and fibroblasts, we emphasize the key role of RA synovial tissue lining layer in maintaining synovitis through neovascularization. Lastly, we summarize the specific approaches utilized to target angiogenesis. We conclude that the formation of new blood vessels plays an indispensable role in RA progression. However, since the function of several pro-angiogenic mediators is cross regulated, discovering novel approaches to target multiple cascades or selecting an upstream cascade that impairs the activity of a number of pro-angiogenic factors may provide a promising strategy for RA therapy.

Mechanisms of Vessel Pruning and Regression

The field of angiogenesis research has primarily focused on the mechanisms of sprouting angiogenesis. Yet vascular networks formed by vessel sprouting subsequently undergo extensive vascular remodeling to form a functional and mature vasculature. This "trimming" includes distinct processes of vascular pruning, the regression of selected vascular branches. In some situations complete vascular networks may undergo physiological regression. Vessel regression is an understudied yet emerging field of research. This review summarizes the state-of-the-art of vessel pruning and regression with a focus on the cellular processes and the molecular regulators of vessel maintenance and regression.

Evaluation of efficacy and safety markers in a phase II study of metastatic colorectal cancer treated with aflibercept in the first-line setting

Background:

Aflibercept (ziv-aflibercept) is an anti-angiogenic agent recently approved in combination with FOLFIRI for the treatment of metastatic colorectal cancer (mCRC) patients previously treated with oxaliplatin. Despite heterogeneity in response to aflibercept, no biomarkers for efficacy or adverse effects have been identified. Here we present biomarker data from the randomised phase II AFFIRM trial assessing aflibercept in combination with mFOLFOX6 first line in mCRC.

Methods:

Ninety-six somatic mutations in key oncogenic drivers of mCRC and 133 common single-nucleotide polymorphisms (SNPs) in vascular endothelial growth factor (VEGF) pathway genes were analysed, and 27 plasma markers measured at baseline, during and after treatment. We assessed correlations of these three classes of biomarkers with progression-free survival (PFS) and adverse events (AEs).

Results:

Somatic mutations identified in KRAS, BRAF, NRAS, PIK3CA and PIK3R1 did not significantly correlate with PFS (multiple testing-adjusted false discovery rate (FDR) or multiple testing-adjusted FDR>0.3). None of the individual SNPs correlated with PFS (multiple testing-adjusted FDR>0.22), but at the gene level variability in VEGFB significantly correlated with PFS (multiple testing-adjusted FDR=0.0423). Although none of the plasma markers measured at baseline significantly correlated with PFS, high levels of circulating IL8 at baseline together with increased levels of IL8 during treatment were significantly associated with reduced PFS (multiple testing-adjusted FDR=0.0478). No association was found between biomarkers and AEs.

Conclusions:

This represents the first biomarker study in mCRC treated with aflibercept. High IL8 plasma levels at baseline and subsequent increases in IL8 were associated with worse PFS, suggesting that IL8 may act as a potentially predictive biomarker of aflibercept treatment outcome.

The Orphan Receptor Tie1 Controls Angiogenesis and Vascular Remodeling by Differentially Regulating Tie2 in Tip and Stalk Cells

Tie1 is a mechanistically poorly characterized endothelial cell (EC)-specific orphan receptor. Yet, Tie1 deletion is embryonic lethal and Tie1 has been implicated in critical vascular pathologies, including atherosclerosis and tumor angiogenesis. Here, we show that Tie1 does not function independently but exerts context-dependent effects on the related receptor Tie2. Tie1 was identified as an EC activation marker that is expressed during angiogenesis by a subset of angiogenic tip and remodeling stalk cells and downregulated in the adult quiescent vasculature. Functionally, Tie1 expression by angiogenic EC contributes to shaping the tip cell phenotype by negatively regulating Tie2 surface presentation. In contrast, Tie1 acts in remodeling stalk cells cooperatively to sustain Tie2 signaling. Collectively, our data support an interactive model of Tie1 and Tie2 function, in which dynamically regulated Tie1 versus Tie2 expression determines the net positive or negative effect of Tie1 on Tie2 signaling.

Photoacoustic Tomography Detects Early Vessel Regression and Normalization During Ovarian Tumor Response to the Antiangiogenic Therapy Trebananib

The primary aim of this study was to assess the potential of in vivo photoacoustic tomography for direct functional measurement of ovarian tumor response to antiangiogenic therapy.

METHODS

In vivo studies were performed with institutional animal care and use committee approval. We used an orthotopic mouse model of ovarian cancer treated with trebananib (n = 9) or vehicle (n = 9). Tumor-bearing mice were randomized into trebananib or vehicle groups at day 10 and dosed on days 12, 15, and 18 after implantation. Photoacoustic tomography and blood draws were performed at day 10 and then 24 h after each drug dose. Tumors were excised for histopathology after the final studies on day 19. Data analysis to test for statistical significance was performed blinded.

RESULTS

Blockade of angiopoietin signaling using trebananib resulted in reduced total hemoglobin-weighted photoacoustic signal (n = 9, P = 0.01) and increased oxyhemoglobin-weighted photoacoustic signal (n = 9, P < 0.01). The latter observation indicated normalization of the residual tumor vessels, which was also implied by low levels of angiopoietin 1 in serum biomarker profiling (0.76 ± 0.12 ng/mL). These noninvasive measures reflected a 30% reduction in microvessel density and increased vessel maturation in ex vivo sections.

CONCLUSION

Photoacoustic tomography is able to evaluate both vessel regression and normalization in response to trebananib. Noninvasive imaging data were supported by modulation of serum markers in vitro and ex vivo histopathology.

Classical and non-classical proangiogenic factors as a target of antiangiogenic therapy in tumor microenvironment

Angiogenesis is sustained by classical and non-classical proangiogenic factors (PFs) acting in tumor microenvironment and these factors are also potential targets of antiangiogenic therapies. All PFs induce the overexpression of several signaling pathways that lead to migration and proliferation of endothelial cells contributing to tumor angiogenesis and survival of cancer cells. In this review, we have analyzed each PF with its specific receptor/s and we have summarized the available antiangiogenic drugs (e.g. monoclonal antibodies) targeting these PFs, some of these agents have already been approved, others are currently in development for the treatment of several human malignancies.

Effect of Ang-2-VEGF-A Bispecific Antibody in Renal Cell Carcinoma

The blockade of VEGF pathway has been clinically validated as an initial treatment for renal cell carcinoma (RCC). Angiopoietin-2 (Ang-2) has been indicated as a key regulator for angiogenesis escape. The effect of a novel bispecific antibody (A2V CrossMab) against both Ang-2 and VEGF was investigated in comparison with either factor. A2V CrossMab significantly reduced tumor volume, vessel density, and interstitial fluid pressure compared to either monotherapy of anti-VEGF or anti-Ang-2. Host-derived angiogenesis-related genes have been significantly down-regulated in A2V CrossMab group. These data demonstrate that A2V CrossMab has additive anti-tumor effect for the treatment of RCC.

Control of the blood-brain barrier function in cancer cell metastasis

Cerebral metastases are the most common brain neoplasms seen clinically in the adults and comprise more than half of all brain tumours. Actual treatment options for brain metastases that include surgical resection, radiotherapy and chemotherapy are rarely curative, although palliative treatment improves survival and life quality of patients carrying brain-metastatic tumours. Chemotherapy in particular has also shown limited or no activity in brain metastasis of most tumour types. Many chemotherapeutic agents used systemically do not cross the blood-brain barrier (BBB), whereas others may transiently weaken the BBB and allow extravasation of tumour cells from the circulation into the brain parenchyma. Increasing evidence points out that the interaction between the BBB and tumour cells plays a key role for implantation and growth of brain metastases in the central nervous system. The BBB, as the tightest endothelial barrier, prevents both early detection and treatment by creating a privileged microenvironment. Therefore, as observed in several in vivo studies, precise targetting the BBB by a specific transient opening of the structure making it permeable for therapeutic compounds, might potentially help to overcome this difficult clinical problem. Moreover, a better understanding of the molecular features of the BBB, its interrelation with metastatic tumour cells and the elucidation of cellular mechanisms responsible for establishing cerebral metastasis must be clearly outlined in order to promote treatment modalities that particularly involve chemotherapy. This in turn would substantially expand the survival and quality of life of patients with brain metastasis, and potentially increase the remission rate. Therefore, the focus of this review is to summarise the current knowledge on the role and function of the BBB in cancer metastasis.

Macrophages are recruited to hypoxic tumor areas and acquire a pro-angiogenic M2-polarized phenotype via hypoxic cancer cell derived cytokines Oncostatin M and Eotaxin

TAMs, a unique and distinct M2-skewed myeloid population of tumor stroma, exhibiting pro-tumor functions is fast emerging as a potential target for anti-cancer immunotherapy. Macrophage-recruitment and M2-polarization represent key TAMs-related phenomenon that are amenable to therapeutic intervention. However successful translation of these approaches into effective therapeutic regimen requires better characterization of tumor-microenvironment derived signals that regulate macrophage recruitment and their polarization. Owing to hypoxic milieu being a persistent feature of tumor-microenvironment and a major contributor to malignancy and treatment resistance, the current study was planned with an aim to decipher tumor cell responses to hypoxia vis-a-vis macrophage homing and phenotype switching. Here, we show that hypoxia-primed cancer cells chemoattract and polarize macrophages to pro-angiogenic M2-polarized subtype via Eotaxin and Oncostatin M. Concordantly, hypoxic regions of human breast-cancer specimen exhibited elevated Eotaxin and Oncostatin M levels with concurrently elevated M2-macrophage content. Blockade of Eotaxin/Oncostatin M not only prevented hypoxic breast-cancer cells from recruiting and polarizing macrophages towards an M2-polarized phenotype and retarded tumor progression in 4T1/BALB/c-syngenic-mice-model of breast-cancer but also enhanced the efficacy of anti-angiogenic Bevacizumab. The findings established these two cytokines as novel targets for devising effective anticancer therapy particularly for tumors that are refractory or develop resistance to anti-angiogenic therapeutics.

Aggressive primary cutaneous B-cell lymphomas show increased Angiopoietin-2-induced angiogenesis

Primary cutaneous large B-cell lymphomas, leg type (PCLBCL/LT) are primary cutaneous B-cell lymphoma (PCBCL) with an intermediate prognosis. Therefore, antracycline-based polychemotherapy combined with rituximab has been recommended as first-line treatment. Yet, despite this regimen, the 5-year survival rate remains 50-66% only. Angiogenesis, the formation of a vascular network, is essential for the pathogenesis of nodal lymphomas. So far, no study has analysed angiogenesis and its key factors in PCLBCL/LT. The present study was aimed at characterizing angiogenesis in PCLBCL/LT to identify the angiogenic molecules as potential therapeutic targets. The intra-tumoral microvessel density (MVD) was assessed by immunohistochemical studies of CD20 and CD31. The MVD was higher in PCLBCL/LT compared with indolent PCBCL. Analyses of open-source microarray data showed correlation between the angiogenic molecule angiopoietin-2 (Ang-2) and pan-endothelial cell markers. ELISA studies determined a shift between Ang-2 and Ang-1 towards Ang-2 in the peripheral blood of PCLBCL/LT patients. Immunofluorescence costainings against the Ang receptor Tie2/angiogenic integrins/CD34 revealed that the vasculature in both aggressive and indolent PCBCL tumors harbours an endothelial cell subpopulation with reduced expression of Tie2. In contrast, the alternative Ang-2 binding partners, angiogenic integrins, are strongly expressed in PCBCL. In line with these findings, downstream targets of Ang-2-integrin signalling, that is phosphorylation of focal adhesion kinase at Tyr397, and sprouting angiogenesis are enhanced in PCLBCL/LT. Our data present Ang-2 as a promising therapeutic target and anti-angiogenic therapy as a new line in treatment of PCLBCL/LT as a hitherto intractable disease.

Overexpression of angiopoietin-2 in rats and patients with liver fibrosis. Therapeutic consequences of its inhibition

BACKGROUND & AIMS

Studies in experimental models of cirrhosis showed that anti-angiogenic treatments may be effective for the treatment of liver fibrosis. In this context, angiopoietins are potential therapeutic targets as they are involved in the maintenance and stabilization of newly formed blood vessels. In addition, angiopoietin-2 is expressed in fibrotic livers and its inhibition in tumours results in vessel stability. Therefore, our study was aimed to assess the therapeutic utility of inhibiting angiopoietin-2.

METHODS

Circulating levels of angiopoietin-1 and angiopoietin-2 were quantified by ELISA in CCl4 -treated rats and in patients with cirrhosis. In vivo blockade of angiopoietin-2 in rats with liver fibrosis was performed with a chemically programmed antibody, CVX-060.

RESULTS

High levels of angiopoietin-2 were found in the systemic and suprahepatic circulation of cirrhotic patients and the ratio angiopoietin-1/angiopoietin-2 inversely correlated with prognostic models for alcoholic liver disease. Chronic treatment of CCl4 -treated rats with CVX-060 was associated with a significant decrease in inflammatory infiltrate, normalization of the hepatic microvasculature and reduction in VCAM-1 vascular expression. The anti-angiopoietin-2 treatment was also associated with less liver fibrosis and with lower levels of circulating transaminases. CVX-060 treatment was not associated with either vascular pruning in healthy tissue or compensatory overexpression of VEGF.

CONCLUSIONS

Inhibition of angiopoietin-2 is an effective and safe treatment for liver fibrosis in CCl4 -treated rats, acting mainly through the induction of vessel normalization and the attenuation of hepatic inflammatory infiltrate. Therefore, inhibition of angiopoietin-2 offers a therapeutic alternative for liver fibrosis.

The TIE Receptor Family

The endothelial TIE1 and TIE2 receptor tyrosine kinases form a distinct subfamily characterized by their unique extracellular domains. Together with the angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG), the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietins exist in multimeric forms that activate the TIE receptors via unique mechanism. In endothelial cell–cell contacts, angiopoietins induce the formation of homomeric in trans TIE receptor complexes extending across the cell junctions, whereas matrix-bound angiopoietin-1 (ANG1) activates the TIE receptors in a cis configuration. In comparison to the vascular endothelial growth factor receptors, the TIE receptors undergo little ubiquitin-mediated degradation after activation, whereas TIE2 signaling is negatively regulated by the vascular endothelial protein tyrosine phosphatase, VE-PTP. ANG1 activation of TIE2 supports vascular stabilization, whereas angiopoietin-2 (ANG2), a context-dependent weak TIE2 agonist/antagonist, promotes pathological tumor angiogenesis, vascular permeability, and inflammation. Recently, ANG2 has been found to mediate some of its vascular destabilizing and angiogenic functions via integrin signalling. The circulating levels of ANG2 are increased in cancer, and in several human diseases associated with inflammation and vascular leak, for example, in sepsis. Blocking of ANG2 has emerged as a potential novel therapeutic strategy for these diseases. In addition, preclinical results demonstrate that genetic TIE1 deletion in mice inhibits the vascularization and growth of tumor isografts and protects from atherosclerosis, with little effect on normal vascular homeostasis in adult mice. The ability of the ANG-TIE pathway to control vessel stability and angiogenesis makes it an interesting vascular target for the treatment of the various diseases.

mTOR inhibition improves fibroblast growth factor receptor targeting in hepatocellular carcinoma

BACKGROUND

Systemic therapy has proven only marginal effects in hepatocellular carcinoma (HCC) so far. The aim of this study was to evaluate the effect of targeting fibroblast growth factor receptor (FGFR) on tumour and stromal cells in HCC models.

METHODS

Human and murine HCC cells, endothelial cells (ECs), vascular smooth muscle cells (VSMCs), hepatic stellate cells (HSCs), human HCC samples, FGFR inhibitor BGJ398 and mammalian target of rapamycin (mTOR) inhibitor rapamycin were used. Effects on growth, motility, signalling and angiogenic markers were determined. In vivo subcutaneous and syngeneic orthotopic tumour models were used.

RESULTS

In tumour cells and ECs, targeting FGFR showed significant inhibitory effects on signalling and motility. Minor effects of FGFR inhibition were observed on VSMCs and HSCs, which were significantly enhanced by combining FGFR and mTOR blockade. In vivo daily (5 mg kg(-1)) treatment with BGJ398 led to a significant growth inhibition in subcutaneous tumour models, but only a combination of FGFR and mTOR blockade impaired tumour growth in the orthotopic model. This was paralleled by reduced tumour cell proliferation, vascularisation, pericytes and increased apoptosis.

CONCLUSIONS

Targeting FGFR with BGJ398 affects tumour cells and ECs, whereas only a combination with mTOR inhibition impairs recruitment of VSMCs and HSCs. Therefore, this study provides evidence for combined FGFR/mTOR inhibition in HCC.

Host age is a systemic regulator of gene expression impacting cancer progression

Aging is the major determinant of cancer incidence, which, in turn, is likely dictated in large part by processes that influence the progression of early subclinical (occult) cancers. However, there is little understanding of how aging informs changes in aggregate host signaling that favor cancer progression. In this study, we provide direct evidence that aging can serve as an organizing axis to define cancer progression-modulating processes. As a model system to explore this concept, we employed adolescent (68 days), young adult (143 days), middle-aged (551 days), and old (736 days) C57BL/6 mice as syngeneic hosts for engraftment of Lewis lung cancer to identify signaling and functional processes varying with host age. Older hosts exhibited dysregulated angiogenesis, metabolism, and apoptosis, all of which are associated with cancer progression. TGFβ1, a central player in these systemic processes, was downregulated consistently in older hosts. Our findings directly supported the conclusion of a strong host age dependence in determining the host tumor control dynamic. Furthermore, our results offer initial mechanism-based insights into how aging modulates tumor progression in ways that may be actionable for therapy or prevention.

Role of the angiopoietin/Tie system in pregnancy (Review)

Angiopoietin-1 and -2 are endogenous ligands for the vascular endothelium-specific receptor tyrosine kinase Tie-2. The angiopoietin/Tie system plays a critical role in the regulation of endothelial cell survival and vascular maturation and stability. Apart from its well-established role in vascular morphogenesis, emerging data support the involvement of angiopoietins in inflammation and various malignancies. Previous studies have underlined the significance of several angiogenic factors in normal placental development. In addition, angiogenic imbalance is observed in pregnancy complications related to impaired placentation, such as preeclampsia (PE) and intrauterine growth restriction (IUGR). However, there is only limited information available on the role of the angiopoietin/Tie system in the establishment of a competent feto-maternal vascular system. In this review, we present the current knowledge regarding the role of angiopoietins in normal pregnancy and pregnancy complications.

Multitargeting strategy using lenvatinib and golvatinib: maximizing anti-angiogenesis activity in a preclinical cancer model

Almost all cancers show intrinsic and/or evasive resistance to vascular endothelial growth factor (VEGF) inhibitors by multiple mechanisms. Serum angiopoietin-2 (Ang2) level has been proposed as a potential biomarker of VEGF inhibitor response in several cancers. From these clinical observations, the Ang2 and Tie2 (its receptor) axis has been focused on as a promising target. Here, we show a novel strategy to circumvent the resistance by combining multi-tyrosine kinase inhibitors lenvatinib (VEGF receptor, fibroblast growth factor receptor, and RET inhibitor) and golvatinib (E7050; c-Met, Tie2, and EphB4 inhibitor). Tie2 identifies a highly pro-angiogenic macrophage subset, Tie2-expressing macrophages (TEM). Angi-Tie2 and EphB4-EphrinB2 signaling plays critical roles in pericyte-mediated vessel stabilization. In vitro analyses suggested that golvatinib combined with lenvatinib inhibited pericyte-mediated vessel stabilization and TEM differentiation. In thyroid and endometrial cancer models, golvatinib and lenvatinib inhibited pericyte network development and TEM infiltration, resulting in severe perfusion disorder and massive apoptosis. Body weight loss was tolerable, and no macroscopic change was observed. These preclinical studies suggest that modulation of the tumor microenvironment by a strategic and well-tolerated combination of multi-targeting tyrosine kinase inhibitors may sensitize cancer to VEGF inhibitors.

Endothelial destabilization by angiopoietin-2 via integrin β1 activation

Angiopoietins regulate vascular homeostasis via the endothelial Tie receptor tyrosine kinases. Angiopoietin-1 (Ang1) supports endothelial stabilization via Tie2 activation. Angiopoietin-2 (Ang2) functions as a context-dependent Tie2 agonist/antagonist promoting pathological angiogenesis, vascular permeability and inflammation. Elucidating Ang2-dependent mechanisms of vascular destablization is critical for rational design of angiopoietin antagonists that have demonstrated therapeutic efficacy in cancer trials. Here, we report that Ang2, but not Ang1, activates β1-integrin, leading to endothelial destablization. Autocrine Ang2 signalling upon Tie2 silencing, or in Ang2 transgenic mice, promotes β1-integrin-positive elongated matrix adhesions and actin stress fibres, regulating vascular endothelial-cadherin-containing cell–cell junctions. The Tie2-silenced monolayer integrity is rescued by β1-integrin, phosphoinositide-3 kinase or Rho kinase inhibition, and by re-expression of a membrane-bound Tie2 ectodomain. Furthermore, Tie2 silencing increases, whereas Ang2 blocking inhibits transendothelial tumour cell migration in vitro. These results establish Ang2-mediated β1-integrin activation as a promoter of endothelial destablization, explaining the controversial vascular functions of Ang1 and Ang2.

Angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) have opposing effects on vascular stability through their receptor Tie2, but there is evidence for Tie2-independent functions of Ang2. Here, Hakanpaa et al. show that Ang2 directly activates β1-integrin, leading to rearrangement of the actin cytoskeleton and decreased VE-cadherin in cell–cell junctions.

Postsurgical adjuvant tumor therapy by combining anti-angiopoietin-2 and metronomic chemotherapy limits metastatic growth

Antiangiogenic tumor therapy has failed in the adjuvant setting. Here we show that inhibition of the Tie2 ligand angiopoietin-2 (Ang2) effectively blocks metastatic growth in preclinical mouse models of postsurgical adjuvant therapy. Ang2 antibody treatment combines well with low-dose metronomic chemotherapy (LDMC) in settings in which maximum-dose chemotherapy does not prove effective. Mechanistically, Ang2 blockade could be linked to quenching the inflammatory and angiogenic response of endothelial cells (ECs) in the metastatic niche. Reduced EC adhesion molecule and chemokine expression inhibits the recruitment of tumor-promoting CCR2(+)Tie2(-) metastasis-associated macrophages. Moreover, LDMC contributes to therapeutic efficacy by inhibiting the recruitment of protumorigenic bone marrow-derived myeloid cells. Collectively, these data provide a rationale for mechanism-guided adjuvant tumor therapies.

Serum angiopoietin-2 and soluble VEGFR-2 levels predict malignancy of ovarian neoplasm and poor prognosis in epithelial ovarian cancer

Background

The aim of the study was to explore the serum levels of eight angiogenesis biomarkers in patients with benign, borderline or malignant epithelial ovarian neoplasms and to compare them to those of healthy controls. In addition, we aimed to study how those biomarkers predict the clinical course and survival of patients with epithelial ovarian cancer.

Methods

We enrolled 132 patients with ovarian neoplasms and 32 unaffected women in this study. Serum samples were collected preoperatively at the time of diagnosis and the levels of angiogenesis biomarkers were measured with an ELISA.

Results

Levels of Ang-1, Ang-2, VEGF, VEGF-D, VEGF/sVEGFR-2 and Ang-2/ sVEGFR-2 ratios were elevated whereas sVEGFR-2 was lower in patients with ovarian carcinoma than in women with normal ovaries, benign and/or borderline ovarian neoplasms. In ROC analysis, the area under the curve for serum Ang-2/sVEGFR-2 ratio (0.76) was greater than Ang-2 (0.75) and VEGF (0.65) but lower than for CA 125 (0.90) to differentiate ovarian cancer from benign or borderline ovarian tumors. In ovarian cancer high Ang-2/sVEGFR-2 ratio was associated with the presence of ascites, high stage and grade of ovarian cancer, with the size of primary residual tumor >1 cm and with recurrence of disease. Elevated Ang-2, VEGF, VEGF/sVEGFR-2, Ang-2/VEGF and Ang-2/sVEGFR-2 ratios and low level of sVEGFR-2 were significant predictors of poor overall survival (OS) and recurrence free survival (RFS) in univariate survival analyses.

Conclusions

Ovarian cancer patients had elevated levels of angiogenesis related growth factors in circulation reflecting increased angiogenesis and poor prognosis. The serum level of Ang-2 predicted most accurately poor OS and Ang-2/sVEGFR-2 ratio malignancy of ovarian neoplasms and short RFS.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-696) contains supplementary material, which is available to authorized users.

Gln-362 of angiopoietin-2 mediates migration of tumor and endothelial cells through association with α5β1 integrin

Angiopoietin-2 (Ang-2) not only regulates angiogenesis by binding to its well known receptor Tie2 on endothelial cells but also controls sprouting of Tie2-negative angiogenic endothelial cells and invasion of Tie2-negative non-endothelial cells by binding to integrins. However, the molecular mechanism of the Ang-2/integrin association has been unclear. In this study, we found that the Gln-362 residue of Ang-2 was essential for binding to α5β1 integrin. A Q362E Ang-2 mutant, which still bound to Tie2, failed to associate with α5β1 integrin and was unable to activate the integrin downstream signaling of focal adhesion kinase. In addition, unlike wild-type Ang-2, the Q362E Ang-2 mutant was defective in mediating invasion of Tie2-negative glioma or Tie2-positive endothelial cells. Furthermore, the tailpiece domain of the α5 subunit in α5β1 integrin was critical for binding to Ang-2. Taken together, these results provide a novel insight into the mechanism of integrin regulation by Ang-2, which contributes to tumor invasion and endothelial cell migration in a Tie2-independent manner.

An in vitro cord formation assay identifies unique vascular phenotypes associated with angiogenic growth factors

Vascular endothelial growth factor (VEGF) plays a dominant role in angiogenesis. While inhibitors of the VEGF pathway are approved for the treatment of a number of tumor types, the effectiveness is limited and evasive resistance is common. One mechanism of evasive resistance to inhibition of the VEGF pathway is upregulation of other pro-angiogenic factors such as fibroblast growth factor (FGF) and epidermal growth factor (EGF). Numerous in vitro assays examine angiogenesis, but many of these assays are performed in media or matrix with multiple growth factors or are driven by VEGF. In order to study angiogenesis driven by other growth factors, we developed a basal medium to use on a co-culture cord formation system of adipose derived stem cells (ADSCs) and endothelial colony forming cells (ECFCs). We found that cord formation driven by different angiogenic factors led to unique phenotypes that could be differentiated and combination studies indicate dominant phenotypes elicited by some growth factors. VEGF-driven cords were highly covered by smooth muscle actin, and bFGF-driven cords had thicker nodes, while EGF-driven cords were highly branched. Multiparametric analysis indicated that when combined EGF has a dominant phenotype. In addition, because this assay system is run in minimal medium, potential proangiogenic molecules can be screened. Using this assay we identified an inhibitor that promoted cord formation, which was translated into in vivo tumor models. Together this study illustrates the unique roles of multiple anti-angiogenic agents, which may lead to improvements in therapeutic angiogenesis efforts and better rational for anti-angiogenic therapy.

Role of angiopoietin-2 in adaptive tumor resistance to VEGF signaling blockade

Angiopoietin-2 (ANG2/ANGPT2) is a context-dependent TIE2 receptor agonist/antagonist and proangiogenic factor. Although ANG2 neutralization improves tumor angiogenesis and growth inhibition by vascular endothelial growth factor (VEGF)-A signaling blockade, the mechanistic underpinnings of such therapeutic benefits remain poorly explored. We employed late-stage RIP1-Tag2 pancreatic neuroendocrine tumors (PNETs) and MMTV-PyMT mammary adenocarcinomas, which develop resistance to VEGF receptor 2 (VEGFR2) blockade. We found that VEGFR2 inhibition upregulated ANG2 and vascular TIE2 and enhanced infiltration by TIE2-expressing macrophages in the PNETs. Dual ANG2/VEGFR2 blockade suppressed revascularization and progression in most of the PNETs, whereas it had only minor additive effects in the mammary tumors, which did not upregulate ANG2 upon VEGFR2 inhibition. ANG2/VEGFR2 blockade did not elicit increased PNET invasion and metastasis, although it exacerbated tumor hypoxia and hematopoietic cell infiltration. These findings suggest that evasive tumor resistance to anti-VEGFA therapy may involve the adaptive enforcement of ANG2-TIE2 signaling, which can be reversed by ANG2 neutralization.

Understanding the mechanisms of action of antiangiogenic agents in metastatic colorectal cancer: a clinician's perspective

Multiple clinical trials using bevacizumab, ziv-aflibercept, and regorafenib have recently demonstrated efficacy for patients with metastatic colorectal cancer. While the net clinical benefit of each of these therapies in the second-line and refractory disease setting appears to be similar, important distinctions exist between the agents at the pharmacodynamic, tumor microenvironment, and clinical levels. The purpose of this review is to survey the preclinical evidence regarding the mechanisms of action of these novel antiangiogenic agents and provide an overview of their respective clinical activity, while highlighting distinctions between therapies. Fundamental understanding of these distinctions may aid in clinical decisions and choice of antiangiogenic therapies.

Statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, potentiate the anti-angiogenic effects of bevacizumab by suppressing angiopoietin2, BiP, and Hsp90α in human colorectal cancer

Background:

Statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, are commonly prescribed because of their therapeutic and preventive effects on cardiovascular diseases. Even though they have been occasionally reported to have antitumour activity, it is unknown whether statins have anti-angiogenic effect in human colorectal cancer (CRC).

Methods:

A total of 11 human CRC cell lines were used to test the effects of bevacizumab, statins, and bevacizumab plus statins on human umbilical vein endothelial cell (HUVEC) viability and invasion in vitro. To determine the molecular mechanism of statins as anti-angiogenic agents, we performed an angiogenesis antibody array and proteomics analysis and confirmed the results using immunoblot assay, HUVEC invasion rescue assay, and siRNA assay. The antitumoural effects of bevacizumab and statins were evaluated in xenograft models.

Results:

A conventional dose of statins (simvastatin 0.2 μM, lovastatin 0.4 μM, atorvastatin 0.1 μM, and pravastatin 0.4 μM) in combination with bevacizumab directly reduced the cell viability, migration, invasion, and tube formation of HUVECs. The culture media of the CRC cells treated with bevacizumab or statins were also found to inhibit HUVEC invasion by suppressing angiogenic mediators, such as angiopoietin2, binding immunoglobulin protein (BiP), and Hsp90α. The combined treatment with bevacizumab and simvastatin significantly reduced the growth and metastases of xenograft tumours compared with treatment with bevacizumab alone.

Conclusions:

The addition of simvastatin at a dose used in patients with cardiovascular diseases (40–80 mg once daily) may potentiate the anti-angiogenic effects of bevacizumab on CRC by suppressing angiopoietin2, BiP, and Hsp90α in cancer cells. A clinical trial of simvastatin in combination with bevacizumab in patients with CRC is needed.