Switching of vascular phenotypes within a murine breast cancer model induced by angiopoietin-2

Exploring the Anti-Leukemic Effect of the Synthetic Retinoid ST1926 on Malignant T Cells: A Comprehensive Proteomics Approach

T-cell malignancies represent a group of complex cancers arising from T cells and include aggressive subtypes such as Adult T-cell Leukemia/Lymphoma (ATL) and T-cell Acute Lymphoblastic Leukemia (T-ALL). Patients with these aggressive subtypes still represent an unmet medical condition. The synthetic adamantyl retinoid ST1926, a potent DNA polymerase-α inhibitor, proved a promising potency in preclinical models of ATL and peripheral T-cell lymphoma. Using advanced liquid chromatography-mass spectrometry (LC-MS/MS) techniques, we explored the effects of ST1926 on global protein expression in ATL (HuT-102) and T-ALL (MOLT-4) cells. We demonstrate that ST1926 triggers differentiation and apoptosis in malignant T-cells while halting tumor progression. Evidence at the proteomics level reveals the impact of ST1926 on crucial DNA replication enzymes and cell cycle regulation, highlighting its potential to reduce leukemogenesis and promote apoptosis. Our findings underscore the potential of ST1926 as an innovative therapeutic approach to address these aggressive T-cell malignancies, providing valuable insights into developing new targeted therapies and improving the outcomes and prognosis of patients with these challenging diseases.

Extracellular vesicles in the HCC microenvironment: Implications for therapy and biomarkers

Hepatocellular carcinoma (HCC) stands as the sixth most prevalent cancer and the third leading cause of cancer mortality globally. Despite surgical resection being the preferred approach for early-stage HCC, most patients are diagnosed at intermediate to advanced stages, limiting treatment options to chemotherapy and immunotherapy, which often yield poor outcomes. Extracellular vesicles (EVs), minute lipid-bilayered particles released by diverse cells under various physiological and pathological conditions, are crucial for mediating communication between cells. Mounting evidence indicates that EVs sourced from different cells can profoundly influence the HCC tumor microenvironment (TME), thereby affecting the progression of HCC. Given their immunogenicity and liver-targeting properties, these EVs not only hold promise for HCC treatment but also provide avenues for advancing early diagnostic methods and assessing prognosis. This review not only describes the function of EVs within the HCC tumor microenvironment but also analyzes their therapeutic advantages and explores their significance in various therapeutic approaches for HCC, including chemotherapy, immunotherapy, combination therapy, and their role as innovative drug delivery carriers. Furthermore, it highlights the potential of EVs as biomarkers for the diagnosis and prognosis of HCC.

Role of Angiogenesis and Its Biomarkers in Development of Targeted Tumor Therapies

Angiogenesis plays a significant role in the human body, from wound healing to tumor progression. "Angiogenic switch" indicates a time-restricted event where the imbalance between pro- and antiangiogenic factors results in the transition from prevascular hyperplasia to outgrowing vascularized tumor, which eventually leads to the malignant cancer progression. In the last decade, molecular players, i.e., angiogenic biomarkers and underlying molecular pathways involved in tumorigenesis, have been intensely investigated. Disrupting the initiation and halting the progression of angiogenesis by targeting these biomarkers and molecular pathways has been considered as a potential treatment approach for tumor angiogenesis. This review discusses the currently known biomarkers and available antiangiogenic therapies in cancer, i.e., monoclonal antibodies, aptamers, small molecular inhibitors, miRNAs, siRNAs, angiostatin, endostatin, and melatonin analogues, either approved by the U.S. Food and Drug Administration or currently under clinical and preclinical investigations.

Enhancement of immune surveillance in breast cancer by targeting hypoxic tumor endothelium: Can it be an immunological switch point?

Breast cancer ranks second among the causes of cancer-related deaths in women. In spite of the recent advances achieved in the diagnosis and treatment of breast cancer, further study is required to overcome the risk of cancer resistance to treatment and thereby improve the prognosis of individuals with advanced-stage breast cancer. The existence of a hypoxic microenvironment is a well-known event in the development of mutagenesis and rapid proliferation of cancer cells. Tumor cells, purposefully cause local hypoxia in order to induce angiogenesis and growth factors that promote tumor growth and metastatic characteristics, while healthy tissue surrounding the tumor suffers damage or mutate. It has been found that these settings with low oxygen levels cause immunosuppression and a lack of immune surveillance by reducing the activation and recruitment of tumor infiltrating leukocytes (TILs). The immune system is further suppressed by hypoxic tumor endothelium through a variety of ways, which creates an immunosuppressive milieu in the tumor microenvironment. Non responsiveness of tumor endothelium to inflammatory signals or endothelial anergy exclude effector T cells from the tumor milieu. Expression of endothelial specific antigens and immunoinhibitory molecules like Programmed death ligand 1,2 (PDL-1, 2) and T cell immunoglobulin and mucin-domain containing-3 (TIM-3) by tumor endothelium adds fuel to the fire by inhibiting T lymphocytes while promoting regulatory T cells. The hypoxic microenvironment in turn recruits Myeloid Derived Suppressor Cells (MDSCs), Tumor Associated Macrophages (TAMs) and T regulatory cells (Treg). The structure and function of newly generated blood vessels within tumors, on the other hand, are aberrant, lacking the specific organization of normal tissue vasculature. Vascular normalisation may work for a variety of tumour types and show to be an advantageous complement to immunotherapy for improving tumour access. By enhancing immune response in the hypoxic tumor microenvironment, via immune-herbal therapeutic and immune-nutraceuticals based approaches that leverage immunological evasion of tumor, will be briefly reviewed in this article. Whether these tactics may be the game changer for emerging immunological switch point to attenuate the breast cancer growth and prevent metastatic cell division, is the key concern of the current study.

Anti-angiogenic therapy in ovarian cancer: Current understandings and prospects of precision medicine

Ovarian cancer (OC) remains the most fatal disease of gynecologic malignant tumors. Angiogenesis refers to the development of new vessels from pre-existing ones, which is responsible for supplying nutrients and removing metabolic waste. Although not yet completely understood, tumor vascularization is orchestrated by multiple secreted factors and signaling pathways. The most central proangiogenic signal, vascular endothelial growth factor (VEGF)/VEGFR signaling, is also the primary target of initial clinical anti-angiogenic effort. However, the efficiency of therapy has so far been modest due to the low response rate and rapidly emerging acquiring resistance. This review focused on the current understanding of the in-depth mechanisms of tumor angiogenesis, together with the newest reports of clinical trial outcomes and resistance mechanism of anti-angiogenic agents in OC. We also emphatically summarized and analyzed previously reported biomarkers and predictive models to describe the prospect of precision therapy of anti-angiogenic drugs in OC.

JunB is a key regulator of multiple myeloma bone marrow angiogenesis

Bone marrow (BM) angiogenesis significantly influences disease progression in multiple myeloma (MM) patients and correlates with adverse prognosis. The present study shows a statistically significant correlation of the AP-1 family member JunB with VEGF, VEGFB, and IGF1 expression levels in MM. In contrast to the angiogenic master regulator Hif-1α, JunB protein levels were independent of hypoxia. Results in tumor-cell models that allow the induction of JunB knockdown or JunB activation, respectively, corroborated the functional role of JunB in the production and secretion of these angiogenic factors (AFs). Consequently, conditioned media derived from MM cells after JunB knockdown or JunB activation either inhibited or stimulated in vitro angiogenesis. The impact of JunB on MM BM angiogenesis was finally confirmed in a dynamic 3D model of the BM microenvironment, a xenograft mouse model as well as in patient-derived BM sections. In summary, in continuation of our previous study (Fan et al., 2017), the present report reveals for the first time that JunB is not only a mediator of MM cell survival, proliferation, and drug resistance, but also a promoter of AF transcription and consequently of MM BM angiogenesis. Our results thereby underscore worldwide efforts to target AP-1 transcription factors such as JunB as a promising strategy in MM therapy.

The Amino-Terminal Oligomerization Domain of Angiopoietin-2 Affects Vascular Remodeling, Mammary Gland Tumor Growth, and Lung Metastasis in Mice

Angiopoietin-2 (ANGPT2) is a context-dependent TIE2 agonistic or antagonistic ligand that induces diverse responses in cancer. Blocking ANGPT2 provides a promising strategy for inhibiting tumor growth and metastasis, yet variable effects of targeting ANGPT2 have complicated drug development. ANGPT2₄₄₃ is a naturally occurring, lower oligomeric protein isoform whose expression is increased in cancer. Here, we use a knock-in mouse line (mice expressing Angpt2₄₄₃), a genetic model for breast cancer and metastasis (MMTV-PyMT), a syngeneic melanoma lung colonization model (B16F10), and orthotopic injection of E0771 breast cancer cells to show that alternative forms increase the diversity of Angpt2 function. In a mouse retina model of angiogenesis, expression of Angpt2₄₄₃ caused impaired venous development, suggesting enhanced function as a competitive antagonist for Tie2. In mammary gland tumor models, Angpt2₄₄₃ differentially affected primary tumor growth and vascularization; these varying effects were associated with Angpt2 protein localization in the endothelium or in the stromal extracellular matrix as well as the frequency of Tie2-positive tumor blood vessels. In the presence of metastatic cells, Angpt2₄₄₃ promoted destabilization of pulmonary vasculature and lung metastasis. In vitro, ANGPT2₄₄₃ was susceptible to proteolytical cleavage, resulting in a monomeric ligand (ANGPT2_DAP) that inhibited ANGPT1- or ANGPT4-induced TIE2 activation but did not bind to alternative ANGPT2 receptor α5β1 integrin. Collectively, these data reveal novel roles for the ANGPT2 N-terminal domain in blood vessel remodeling, tumor growth, metastasis, integrin binding, and proteolytic regulation. SIGNIFICANCE: This study identifies the role of the N-terminal oligomerization domain of angiopoietin-2 in vascular remodeling and lung metastasis and provides new insights into mechanisms underlying the versatile functions of angiopoietin-2 in cancer.See related commentary by Kamiyama and Augustin, p. 35.

Molecular description of ANGPT2 associated colorectal carcinoma

Angiopoietin-2 (ANGPT2) is a prognostic factor in metastatic colorectal cancer (CRC). Nevertheless, it remains to be elucidated which molecular characteristics make up the ANGPT2-related poor-prognosis CRC subset. Public transcriptomic datasets were collected from Gene Expression Omnibus GEO and with the TCGAbiolinks R-package for the TCGA. After appropriate normalization, differential expression analysis was performed using Benjamini and Hochberg method for false discovery rate. Plasma from two prospective clinical trials were used to investigate the clinical impact of ANGPT2-related biomarkers. In the 935 samples included in four annotated platforms (GPL) and derived from localized CRC, ANGPT2^hi expression conferred a worst overall survival (HR = 1.20; p = 0.02). CRC stage, ANGPT2^hi expression but not Consortium Molecular Subtype (CMS) predict overall survival in multivariate analysis. ANGPT2 expression was not correlated with a specific CMS nor to RAS, RAF, MSI, p53, CIN, CIMP genomic alterations. Gene expression analysis revealed that ANGPT2^hi CRC subset is characterized by angiogenesis-related gene expression, presence of myeloid cells, stromal organization and resistance to chemotherapy. A prognostic model was proposed using seric levels of ANGPT2, STC1 and CD138 in 97 mCRC patients. Our results provide evidence that ANGPT2 is a prognostic factor in localized CRC and defined a specific CRC subset with potential clinical implementation.

Tumor angiogenesis: causes, consequences, challenges and opportunities

Tumor vascularization occurs through several distinct biological processes, which not only vary between tumor type and anatomic location, but also occur simultaneously within the same cancer tissue. These processes are orchestrated by a range of secreted factors and signaling pathways and can involve participation of non-endothelial cells, such as progenitors or cancer stem cells. Anti-angiogenic therapies using either antibodies or tyrosine kinase inhibitors have been approved to treat several types of cancer. However, the benefit of treatment has so far been modest, some patients not responding at all and others acquiring resistance. It is becoming increasingly clear that blocking tumors from accessing the circulation is not an easy task to accomplish. Tumor vessel functionality and gene expression often differ vastly when comparing different cancer subtypes, and vessel phenotype can be markedly heterogeneous within a single tumor. Here, we summarize the current understanding of cellular and molecular mechanisms involved in tumor angiogenesis and discuss challenges and opportunities associated with vascular targeting.

Hypoxia as a signal for prison breakout in cancer

PURPOSE OF REVIEW

We discuss recent discoveries in hypoxic cellular pathophysiology and explore the interplay between hypoxic malignant cells and other stromal elements. This review will provide an update on the effects of hypoxia on cancer outcomes and therapeutic resistance.

RECENT FINDINGS

Hypoxia has been discovered to be a key driver for tumor progression, both because of impacts on tumor cells and separately on the wider tumor microenvironment. The latter effects occur via epithelial mesenchymal transition, autophagy and metabolic switching. Through epithelial mesenchymal transition, hypoxia both drives metastasis and renders key target tissues receptive to metastasis. Autophagy is a double-edged sword which requires greater understanding to ascertain when it is a threat. Metabolic switching allows tumor cells to access hypoxic survival mechanisms even under normoxic conditions.Every element of the malignant stroma contributes to hypoxia-driven progression. Exosomal transfer of molecules from hypoxic tumor cells to target stromal cell types and the importance of microRNAs in intercellular communication have emerged as key themes.Antiangiogenic resistance can be caused by hypoxia-driven vasculogenic mimicry. Beyond this, hypoxia contributes to resistance to virtually all oncological treatment modalities.

SUMMARY

Recent advances have moved us closer to being able to exploit hypoxic mechanisms to overcome hypoxia-driven progression and therapy failure.

Experimental and computational analyses reveal dynamics of tumor vessel cooption and optimal treatment strategies

Cooption of the host vasculature is a strategy that some cancers use to sustain tumor progression without-or before-angiogenesis or in response to antiangiogenic therapy. Facilitated by certain growth factors, cooption can mediate tumor infiltration and confer resistance to antiangiogenic drugs. Unfortunately, this mode of tumor progression is difficult to target because the underlying mechanisms are not fully understood. Here, we analyzed the dynamics of vessel cooption during tumor progression and in response to antiangiogenic treatment in gliomas and brain metastases. We followed tumor evolution during escape from antiangiogenic treatment as cancer cells coopted, and apparently mechanically compressed, host vessels. To gain deeper understanding, we developed a mathematical model, which incorporated compression of coopted vessels, resulting in hypoxia and formation of new vessels by angiogenesis. Even if antiangiogenic therapy can block such secondary angiogenesis, the tumor can sustain itself by coopting existing vessels. Hence, tumor progression can only be stopped by combination therapies that judiciously block both angiogenesis and cooption. Furthermore, the model suggests that sequential blockade is likely to be more beneficial than simultaneous blockade.

Anti-angiogenic Targets: Angiopoietin and Angiopoietin Receptors

Tumor blood vessel formation (angiogenesis) is essential for tumor growth and metastasis. Two main endothelial ligand–receptor pathways regulating angiogenesis are vascular endothelial growth factor (VEGF) receptor and angiopoietin-TIE receptor pathways. The angiopoietin-TIE pathway is required for the remodeling and maturation of the blood and lymphatic vessels during embryonic development after VEGF and VEGF-C mediated development of the primary vascular plexus. Angiopoietin-1 (ANGPT1) stabilizes the vasculature after angiogenic processes, via tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (TIE2) activation. In contrast, ANGPT2 is upregulated at sites of vascular remodeling. ANGPT2 is secreted by activated endothelial cells in inflammation, promoting vascular destabilization. ANGPT2 has been found to be expressed in many human cancers. Intriguingly, in preclinical models inhibition of ANGPT2 has provided promising results in preventing tumor angiogenesis, tumor growth, and metastasis, making it an attractive candidate to target in tumors. However, until now the first ANGPT2 targeting therapies have been less effective in clinical trials than in experimental models. Additionally, in preclinical models combined therapy against ANGPT2 and VEGF or immune checkpoint inhibitors has been superior to monotherapies, and these pathways are also targeted in early clinical trials. In order to improve current anti-angiogenic therapies and successfully exploit ANGPT2 as a target for cancer treatment, the biology of the angiopoietin-TIE pathway needs to be profoundly clarified.

Model of vascular desmoplastic multispecies tumor growth

We present a three-dimensional nonlinear tumor growth model composed of heterogeneous cell types in a multicomponent-multispecies system, including viable, dead, healthy host, and extra-cellular matrix (ECM) tissue species. The model includes the capability for abnormal ECM dynamics noted in tumor development, as exemplified by pancreatic ductal adenocarcinoma, including dense desmoplasia typically characterized by a significant increase of interstitial connective tissue. An elastic energy is implemented to provide elasticity to the connective tissue. Cancer-associated fibroblasts (myofibroblasts) are modeled as key contributors to this ECM remodeling. The tumor growth is driven by growth factors released by these stromal cells as well as by oxygen and glucose provided by blood vasculature which along with lymphatics are stimulated to proliferate in and around the tumor based on pro-angiogenic factors released by hypoxic tissue regions. Cellular metabolic processes are simulated, including respiration and glycolysis with lactate fermentation. The bicarbonate buffering system is included for cellular pH regulation. This model system may be of use to simulate the complex interactions between tumor and stromal cells as well as the associated ECM and vascular remodeling that typically characterize malignant cancers notorious for poor therapeutic response.

Angiopoietin-2 promotes ER+ breast cancer cell survival in bone marrow niche

In estrogen receptor-positive (ER+) breast cancer, it is recognized that metastases may develop after a long period of dormancy. Bone marrow (BM) vascular niche is where the dormant tumor cells are most likely to reside. So far, it is not fully understood why the dormant tumor cells become proliferative and eventually generate tumor. We hypothesized that therapeutic or menopause-related estrogen depletion may be the switch behind dormant ER+ tumor cell awakening in BM. We utilized an existing experimental model of BM endothelial niche that can simulate ER+ tumor cell dormancy to test our hypothesis. In results, estrogen depletion paradoxically promoted ER+ tumor cell proliferation in the BM endothelial niche, and their molecular phenotype shifted from dormant to awaken. Following estrogen depletion, the BM niche cells produced angiopoietin-2 (ANGPT2), which destabilized niche endothelium by interfering ANGPT1/Tie2 signaling, and promoted ER+ tumor cell survival under estrogen deficiency via cell surface integrin &1. Knockdown of ANGPT2 completely negated ER+ tumor cell awakening in the niche. Furthermore, ANGPT2 expression in ER+ tumor human samples was associated with increased risk of distant metastasis only in those who underwent adjuvant estrogen depletion therapy, not in those who did not undergo adjuvant therapy. In conclusion, we demonstrate that ANGPT2 signaling activated after estrogen depletion paradoxically triggers ER+ tumor cell awakening from dormancy in their BM niche, partly indirectly via endothelial Tie2 receptor and partly directly via tumor cell surface integrin &1.

Total and not bevacizumab-bound vascular endothelial growth factor as potential predictive factors to bevacizumab-based chemotherapy in colorectal cancer

AIM: To identify suitable biomarkers of response to bevacizumab (BV) - it remains an open question. The measurement of serum vascular endothelial growth factor (VEGF) has been proposed as a predictive factor for this drug, even if literature data are contradictory.

METHODS: We prospectively evaluated the role of BV, total and not BV-bound VEGF and angiopoietin-2 (Ang-2) serum levels as potential predictive factors of response for BV in combination with an oxaliplatin-based chemotherapy. BV, Ang-2, total and not BV-bound VEGF levels were measured at baseline, before 2^nd and 5^th cycle of oxaliplatin-based chemotherapy in 20 consecutive metastatic colorectal cancer patients.

RESULTS: Results were correlated to response to treatment. Variability in BV levels have been found, with decreased level in less responding patients. In particular, the concentration of BV increased of 3.96 ± 0.69 folds in serum of responsive patients after 3 more cycles of therapy compared to those with stable or progressive disease with a 0.72 ± 0.25 and 2.10 ± 0.13 fold increase, respectively. The determination of free and total VEGF demonstrated that the ratio between the two values, evaluated immediately before the 2^nd and the 5^th cycle of therapy, decreased from 26.65% ± 1.33% to 15.50% ± 3.47% in responsive patients and from 53.41% ± 4.75 to 34.95% ± 2.88% in those with stable disease. Conversely, in those with progression of disease, the ratio showed the opposite behavior coming up from 25.99% ± 5.23% to 51.71% ± 5.28%. The Ang-2 levels did not show any relationship.

CONCLUSION: Our data show that the ratio of not BV-bound VEGF to total VEGF serum and BV plasma concentrations for predicting the response to BV plus oxaliplatin-based chemotherapy could be a promising biomarker of response to BV.

Elevated Angiopoietin-2 Level in Patients With Continuous-Flow Left Ventricular Assist Devices Leads to Altered Angiogenesis and Is Associated With Higher Nonsurgical Bleeding

BACKGROUND

Nonsurgical bleeding is the most common adverse event in patients with continuous-flow left ventricular assist devices (LVADs) and is caused by arteriovenous malformations. We hypothesized that deregulation of an angiogenic factor, angiopoietin-2 (Ang-2), in patients with LVADs leads to increased angiogenesis and higher nonsurgical bleeding.

METHODS

Ang-2 and thrombin levels were measured by ELISA and Western blotting, respectively, in blood samples from 101 patients with heart failure, LVAD, or orthotopic heart transplantation. Ang-2 expression in endothelial biopsy was quantified by immunofluorescence. Angiogenesis was determined by in vitro tube formation from serum from each patient with or without Ang-2-blocking antibody. Ang-2 gene expression was measured by reverse transcription-polymerase chain reaction in endothelial cells incubated with plasma from each patient with or without the thrombin receptor blocker vorapaxar.

RESULTS

Compared with patients with heart failure or those with orthotopic heart transplantation, serum levels and endothelial expression of Ang-2 were higher in LVAD patients (P=0.001 and P<0.001, respectively). This corresponded to an increased angiogenic potential of serum from patients with LVADs (P<0.001), which was normalized with Ang-2 blockade. Furthermore, plasma from LVAD patients contained higher amounts of thrombin (P=0.003), which was associated with activation of the contact coagulation system. Plasma from LVAD patients induced more Ang-2 gene expression in endothelial cells (P<0.001), which was reduced with thrombin receptor blockade (P=0.013). LVAD patients with Ang-2 levels above the mean (12.32 ng/mL) had more nonsurgical bleeding events compared with patients with Ang-2 levels below the mean (P=0.003).

CONCLUSIONS

Our findings indicate that thrombin-induced Ang-2 expression in LVAD patients leads to increased angiogenesis in vitro and may be associated with higher nonsurgical bleeding events. Ang-2 therefore may contribute to arteriovenous malformation formation and subsequent bleeding in LVAD patients.

Tumor suppressor control of the cancer stem cell niche

Mammary stem cells (MSCs) expansion is associated with aggressive human breast cancer. The nuclear receptor peroxisome proliferator activated receptor γ (PPARγ) is a breast cancer tumor suppressor, but the mechanisms of this suppression are not completely characterized. To determine whether PPARγ regulates MSC expansion in mammary cancer, we deleted PPARγ expression in the mammary epithelium of an in vivo model of basal breast cancer. Loss of PPARγ expression reduced tumor latency, and expanded the CD24+/CD49f(hi) MSC population. PPARγ-null mammary tumors exhibited increased angiogenesis, which was detected in human breast cancer. In vivo inhibition of a PPARγ-regulated miR-15a/angiopoietin-1 pathway blocked increased angiogenesis and MSC expansion. PPARγ bound and activated a canonical response element in the miR-15a gene. PPARγ-null tumors were sensitive to the targeted anti-angiogenic drug sunitinib but resistant to cytotoxic chemotherapy. Normalization of tumor vasculature with sunitinib resulted in objective response to cytotoxic chemotherapy. Chemotherapy-treated PPARγ-null mammary tumors exhibited luminal phenotype and expansion of unipotent CD61+ luminal progenitor cells. Transplantation of chemotherapy-treated luminal progenitor cells recapitulated the luminal phenotype. These results have important implications for anti-angiogenic therapy in breast cancer patients.

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.

Prognostic value of angiopoietin-2 for death risk stratification in patients with metastatic colorectal carcinoma

BACKGROUND

Baseline prognostic biomarkers stratifying treatment strategies in first-line metastatic colorectal cancer (mCRC) are lacking. Angiopoietin-2 (Ang-2) is proposed as a potential biomarker in several cancers. We therefore decided to establish the additional prognostic value of Ang-2 for overall survival (OS) in patients with first-line mCRC.

METHODS

We enrolled 177 patients treated with a bevacizumab containing chemotherapy in two prospective phase II clinical trials. Patient plasma samples were collected at baseline. ELISAs were used to measure Ang-2.

RESULTS

The multivariable Cox model identified increased lactate dehydrogenase [HR, 1.60; 95% confidence interval (CI), 1.04-2.45; P = 0.03] and Ang-2 log-transformation level (HR, 1.59; 95% CI, 1.14-2.21; P = 0.0065) as two significant independent OS prognostic factors. It exhibited good calibration (P = 0.8) and discrimination (C-index: 0.64; 95% CI, 0.58-0.68). Ang-2 parameter inclusion in the GERCOR reference model significantly and strongly improved its discriminative ability because the C-statistic increased significantly from 0.61 to 0.63 (bootstrap mean difference = 0.07; 95% CI, 0.069-0.077). Interestingly, the addition of Ang-2 binary information with a 5 ng/mL cutoff value to the GERCOR model allowed the reclassification of intermediate-risk profile patients (41%) into two subsets of low and high risks.

CONCLUSIONS

Our study provides robust evidence in favor of baseline Ang-2 prognostic value for OS adding to the conventional factors. Its assessment appears to be useful for the improvement in risk stratification for patients with intermediate-risk profile.

IMPACT

Ang-2 ability to predict OS at diagnosis could be of interest in the selection of patients eligible for intermittent or sequential therapeutic strategies dedicated to the optimization of patients' quality of life and chemotherapy cost-effectiveness. Cancer Epidemiol Biomarkers Prev; 24(3); 603-12. ©2015 AACR.

Angiogenesis in spontaneous tumors and implications for comparative tumor biology

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

Receptor tyrosine kinase-mediated angiogenesis

The endothelial cell is the essential cell type forming the inner layer of the vasculature. Two families of receptor tyrosine kinases (RTKs) are almost completely endothelial cell specific: the vascular endothelial growth factor (VEGF) receptors (VEGFR1-3) and the Tie receptors (Tie1 and Tie2). Both are key players governing the generation of blood and lymphatic vessels during embryonic development. Because the growth of new blood and lymphatic vessels (or the lack thereof) is a central element in many diseases, the VEGF and the Tie receptors provide attractive therapeutic targets in various diseases. Indeed, several drugs directed to these RTK signaling pathways are already on the market, whereas many are in clinical trials. Here we review the VEGFR and Tie families, their involvement in developmental and pathological angiogenesis, and the different possibilities for targeting them to either block or enhance angiogenesis and lymphangiogenesis.

Vessel co-option in primary human tumors and metastases: an obstacle to effective anti-angiogenic treatment?

Angiogenesis has been regarded as essential for tumor growth and progression. Studies of many human tumors, however, suggest that their microcirculation may be provided by nonsprouting vessels and that a variety of tumors can grow and metastasize without angiogenesis. Vessel co-option, where tumor cells migrate along the preexisting vessels of the host organ, is regarded as an alternative tumor blood supply. Vessel co-option may occur in many malignancies, but so far mostly reported in highly vascularized tissues such as brain, lung, and liver. In primary and metastatic lung cancer and liver metastasis from different primary origins, as much as 10–30% of the tumors are reported to use this alternative blood supply. In addition, vessel co-option is introduced as a potential explanation of antiangiogenic drug resistance, although the impact of vessel co-option in this clinical setting is still to be further explored. In this review we discuss tumor vessel co-option with specific examples of vessel co-option in primary and secondary tumors and a consideration of the clinical implications of this alternative tumor blood supply.

Both primary and metastatic tumors use preexisting host tissue vessels as their blood supply. Tumors may grow to a clinically detectable size without angiogenesis and makes them less likely to respond to drugs designed to target the abnormal vasculature produced by angiogenesis, but further studies to explore the biological and clinical implication of these co-opted vessels is needed.

Isolation and characterization of endothelial cells from intramuscular hemangioma

BACKGROUND

Intramuscular hemangiomas (IMHs) are benign vascular tumors of deep soft tissue characterized by endothelial cell (EC) proliferation. The purpose of this study was to isolate ECs from IMH, characterize their angiogenic phenotype and functional characteristics, and search for a possible signaling pathway related to IMH development.

METHODS

EC Isolation from IMH was performed by digestion, filtration, washing, incubation, and purification in sequence. Tie2 expression was compared between ECs from IMH and controls using reverse transcriptase polymerase chain reaction (RT-PCR). Cell invasion and proliferation assays were used to analyze functional responses of ECs to angiopoietin 1 (Ang1) and vascular endothelial growth factor (VEGF). Expression of downstream targets was analyzed using Western blot analysis.

RESULTS

Isolated ECs showed typical cobblestone appearance under light microscopy and formed capillary-like tubular structures using Matrigel tube-forming assay. RT-PCR of isolated ECs from six patients showed increased expression of Tie2 and VEGF receptor 1 (VEGFR1) compared with control ECs. Tie2 activation by Ang1 compared with VEGFR1 by VEGF resulted in increased EC migration and proliferation. Western blot analysis showed increased Tie2 expression in hemangioma samples compared with normal ECs. Phosphorylated Akt and phosphorylated forkhead box O1 (FOXO1) expression was observed in hemangioma samples only.

CONCLUSION

EC isolation from IMH could be a useful tool for further research. These results suggest that increased Tie2 expression, via Akt-FOXO1 pathway activation, may play an important role in IMH pathogenesis.

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

The angiopoietins Ang1 (ANGPT1) and Ang2 (ANGPT2) are secreted factors that bind to the endothelial cell-specific receptor tyrosine kinase Tie2 (TEK) and regulate angiogenesis. Ang1 activates Tie2 to promote blood vessel maturation and stabilization. In contrast, Ang2, which is highly expressed by tumor endothelial cells, is thought to inhibit Tie2 activity and destabilize blood vessels, thereby facilitating VEGF-dependent vessel growth. Here, we show that the inhibition of tumor xenograft growth caused by an Ang2-specific antibody (REGN910) is reversed by systemic administration of the Tie2 agonist Ang1. These results indicate that Ang2 blockade inhibits tumor growth by decreasing Tie2 activity, showing that Ang2 is a Tie2 activator. REGN910 treatment of tumors resulted in increased expression of genes that are repressed by Tie2 activation, providing further evidence that REGN910 inhibits Tie2 signaling. Combination treatment with REGN910 plus the VEGF blocker aflibercept reduced tumor vascularity and tumor perfusion more dramatically than either single agent, resulting in more extensive tumor cell death and more potent inhibition of tumor growth. Challenging the prevailing model of Ang2 as a destabilizing factor, our findings indicate that Ang2 plays a protective role in tumor endothelial cells by activating Tie2, thereby limiting the antivascular effects of VEGF inhibition. Thus, blockade of Ang2 might enhance the clinical benefits currently provided by anti-VEGF agents. .

CD31 angiogenesis and combined expression of HIF-1α and HIF-2α are prognostic in primary clear-cell renal cell carcinoma (CC-RCC), but HIFα transcriptional products are not: implications for antiangiogenic trials and HIFα biomarker studies in primary CC-RCC

Hypoxia-inducible factors, HIF-1α and HIF-2α, are expressed in the majority of clear-cell renal cell carcinoma (CC-RCC). In vitro, HIFα isoforms regulate a differential set of genes, and their effects in vivo within CC-RCC tumours may affect outcome. The role of angiogenesis and HIFα transcriptional products, including those involved in cell metabolism and morphological dedifferentiation have not been extensively investigated and might have relevance to the development of antiangiogenic or anti-HIFα trials in primary CC-RCC, either before or after radical nephrectomy. We analysed 168 consecutive clear-cell renal tumours from 1983 to 1999 within tissue microarrays and assessed expression of HIF-1α and HIF-2α together with the protein expression of seven of their target genes (BNIP3, CA9, Cyclin D1, GLUT-1, LDH5, Oct-4 and VEGF). The expression of these factors was compared with patient overall survival and CD31 angiogenesis. We found that HIFα antigenicity deteriorated with the age of the paraffin block (P < 0.0001) and in tumours from 1983 to 1992 was deemed not to be reliable. Similar findings were found in aged archival osteosarcoma samples. This might have important implications for retrospective biomarker studies that rely on archival tissue material. HIF-1α(HIGH)/HIF-2α(LOW) tumours had a worse overall survival compared with HIF-1α(LOW)/HIF-2α(LOW) tumours (P = 0.04). Surprisingly, on multivariate analysis, high levels of CD31(+) angiogenesis was shown to be an independent prognostic marker of increased overall survival (P = 0.003). We propose that better differentiation of vascular endothelium may be a reflection of a greater production of vessel stabilization factors versus pro-angiogenic factors, and therefore a less aggressive phenotype.

Effects of angiopoietin-2-blocking antibody on endothelial cell-cell junctions and lung metastasis

Background

Angiopoietin-2 (Ang2), a ligand for endothelial TEK (Tie2) tyrosine kinase receptor, is induced in hypoxic endothelial cells of tumors, where it promotes tumor angiogenesis and growth. However, the effects of Ang2 on tumor lymphangiogenesis and metastasis are poorly characterized.

Methods

We addressed the effect of Ang2 on tumor progression and metastasis using systemic Ang2 overexpression in mice carrying tumor xenografts, endothelium-specific overexpression of Ang2 in VEC-tTA/Tet-OS-Ang2 transgenic mice implanted with isogenic tumors, and administration of Ang2-blocking antibodies to tumor-bearing immunodeficient mice. Fisher's exact test was used for analysis of metastasis occurrence, and repeated measures one-way analysis of variance was used for the analysis of primary tumor growth curves. Unpaired t test was used for all other analyses. All statistical tests were two-sided.

Results

Adenoviral expression of Ang2 increased lymph node and lung metastasis in tumor xenografts. The metastatic burden in the lungs was increased in transgenic mice in which Ang2 expression was induced specifically in the vascular endothelium (tumor burden per grid, VEC-tTA/Tet-OS-Ang2 mice [n = 5] vs control mice [n = 4]: 45.23 vs 12.26 mm², difference = 32.67 mm², 95% confidence interval = 31.87 to 34.07, P < .001). Ang2-blocking antibodies reduced lymph node and lung metastasis, as well as tumor lymphangiogenesis, and decreased tumor cell homing to the lungs after intravenous injection. In the lung metastases, Ang2 overexpression decreased endothelial integrity, whereas the Ang2-blocking antibodies improved endothelial cell–cell junctions and basement membrane contacts of metastasis-associated lung capillaries. At the cellular level, the Ang2-blocking antibodies induced the internalization of Ang2-Tie2 receptor complexes from endothelial cell–cell junctions in endothelial–tumor cell cocultures.

Conclusion

Our results indicate that blocking Ang2 inhibits metastatic dissemination in part by enhancing the integrity of endothelial cell–cell junctions.

Overexpression of angiopoietin-2 impairs myocardial angiogenesis and exacerbates cardiac fibrosis in the diabetic db/db mouse model

The angiopoietins/Tie-2 system is essential for the maintenance of vascular integrity and angiogenesis. The functional role of angiopoietin-2 (Ang-2) in the regulation of angiogenesis is dependent on other growth factors such as VEGF and a given physiopathological conditions. This study investigates the potential role of Ang-2 in myocardial angiogenesis and fibrosis formation in the diabetic db/db mouse. Diabetic db/db mice received intramyocardial administration of either adenovirus Ang-2 (Ad-CMV-Ang-2) or Ad-β-gal. The levels of Tie-2, VEGF, caspase-3, Wnt7b, fibroblast-specific protein-1 (FSP-1), and adhesion molecules (ICAM-1 and VCAM-1) expression were measured. Apoptosis, capillary density, and cardiac fibrosis were also analyzed in the db/db mouse hearts. Overexpression of Ang-2 suppressed Tie-2 and VEGF expression in db/db mouse hearts together with significant upregulation of Wnt7b expression. Overexpression of Ang-2 also sensitizes ICAM-1 and VCAM-1 expression in db/db mouse hearts. Immunohistochemical analysis revealed that overexpression of Ang-2 resulted in a gradual apoptosis as well as interstitial fibrosis formation, these leading to a significant loss of capillary density. Data from these studies were confirmed in cultured mouse heart microvascular endothelial cells (MHMEC) exposed to excessive Ang-2. Exposure of MHMEC to Ang-2 resulted in increased caspase-3 activity and endothelial apoptosis. Knockdown of Ang-2 attenuated high glucose-induced endothelial cell apoptosis. Further, counterbalance of Ang-2 by overexpression of Ang-1 reversed loss of capillary density and fibrosis formation in db/db mouse hearts. Our data demonstrate that Ang-2 increases endothelial apoptosis, sensitizes myocardial microvascular inflammation, and promotes cardiac fibrosis and thus contributes to loss of capillary density in diabetic diseases.

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.

VEGF and angiopoietin signaling in tumor angiogenesis and metastasis

Solid tumors require blood vessels for growth and dissemination, and lymphatic vessels as additional conduits for metastatic spread. The identification of growth factor receptor pathways regulating angiogenesis has led to the clinical approval of the first antiangiogenic molecules targeted against the vascular endothelial growth factor (VEGF)-VEGF receptor (VEGFR)-2 pathway. However, in many cases resistance to anti-VEGF-VEGFR therapy occurs, and thus far the clinical benefit has been limited to only modest improvements in overall survival. Therefore, novel treatment modalities are required. Here, we discuss the members of the VEGF-VEGFR family as well as the angiopoietin growth factors and their Tie receptors as potential novel targets for antiangiogenic and antilymphangiogenic therapies.

Heterogeneity of vascular and progenitor cell compartments in tumours from MMTV-PyVmT transgenic mice during mammary cancer progression

Transgenic mice are important tools for our study of breast cancer pathobiology. In order to evaluate changes in cell phenotype with breast cancer progression, we examined vascular and progenitor cell characteristics in tumours derived from MMTV-PyVmT mice. We performed dual-immunofluorescence staining for Tie2, pTie2Y1100, VEGFR2 and PDGFR-β and the pan-endothelial marker PECAM-1 (CD31) in 39 tumours from MMTV-PyVmT transgenic mice grouped by nuclear grade and tumour morphology. Immunohistochemical staining for Aldh1a1 was performed in MMTV-PyVmT-derived tumours and in non-transgenic mouse mammary glands. Tumour blood vessels were heterogeneous in all samples analysed, with the proportion of Tie2-, pTie2 (Y1100)-, VEGFR2- and PDGFR-β-positive tumour blood vessels ranging from 18-98%, 7-40%, 19-86% and 16-94% respectively. We observed a statistically significant difference in vascular pTie2Y1100 levels between low-nuclear-grade tumours and intermediate-/high-nuclear-grade tumours (P=0.03) and an increase in the proportion of PDGFR-β-positive tumour blood vessels in tumours with high vs. Intermediate-nuclear grade tumours (P<0.01). Aldh1a1-positive mammary epithelial cells were observed in the terminal end buds of non-transgenic mammary glands and Aldh1a1-positive mammary tumour cells were observed in tumours from MMTV-PyVmT transgenic mice. We observed a decrease in the average number of Aldh1a1-positive cells in tumours with a non-invasive vs. solid morphology (P=0.03), and in the average number of Aldh1a1-positive mammary tumour cells in low vs. intermediate and low vs. High-nuclear grade tumours (P<0.001). Our findings suggest heterogeneous expression of several molecules important for tumour angiogenesis and tumour progression that are currently under investigation as therapeutic targets for metastatic breast cancer.

Identification of serum angiopoietin-2 as a biomarker for clinical outcome of colorectal cancer patients treated with bevacizumab-containing therapy

Background:

The combination of chemotherapy with the vascular endothelial growth factor (VEGF) antibody bevacizumab is a standard of care in advanced colorectal cancer (CRC). However, biomarkers predicting outcome of bevacizumab-containing treatment are lacking. As angiopoietin-2 (Ang-2) is a key regulator of vascular remodelling in concert with VEGF, we investigated its role as a biomarker in metastatic CRC.

Methods:

Serum Ang-2 levels were measured in 33 healthy volunteers and 90 patients with CRC. Of these, 34 had metastatic disease and received bevacizumab-containing therapy. To determine the tissue of origin of Ang-2, quantitative real-time PCR was performed on microdissected cryosections of human CRC and in a murine xenograft model of CRC using species-specific amplification.

Results:

Ang-2 originated from the stromal compartment of CRC tissues. Serum Ang-2 levels were significantly elevated in patients with metastatic CRC compared with healthy controls. Amongst patients receiving bevacizumab-containing treatment, low pre-therapeutic serum Ang-2 levels were associated with a significant better response rate (82 vs 31% P<0.01), a prolonged median progression-free survival (14.1 vs 8.5 months; P<0.01) and a reduction of 91% in the hazard of death (P<0.05).

Conclusion:

Serum Ang-2 is a candidate biomarker for outcome of patients with metastatic CRC treated with bevacizumab-containing therapy, and it should be further validated to customise combined chemotherapeutic and anti-angiogenic treatment.

Integration of transcript expression, copy number and LOH analysis of infiltrating ductal carcinoma of the breast

Background

A major challenge in the interpretation of genomic profiling data generated from breast cancer samples is the identification of driver genes as distinct from bystander genes which do not impact tumorigenesis. One way to assess the relative importance of alterations in the transcriptome profile is to combine parallel analyses that assess changes in the copy number alterations (CNAs). This integrated analysis permits the identification of genes with altered expression that map within specific chromosomal regions which demonstrate copy number alterations, providing a mechanistic approach to identify the 'driver genes'.

Methods

We have performed whole genome analysis of CNAs using the Affymetrix 250K Mapping array on 22 infiltrating ductal carcinoma samples (IDCs). Analysis of transcript expression alterations was performed using the Affymetrix U133 Plus2.0 array on 16 IDC samples. Fourteen IDC samples were analyzed using both platforms and the data integrated. We also incorporated data from loss of heterozygosity (LOH) analysis to identify genes showing altered expression in LOH regions.

Results

Common chromosome gains and amplifications were identified at 1q21.3, 6p21.3, 7p11.2-p12.1, 8q21.11 and 8q24.3. A novel amplicon was identified at 5p15.33. Frequent losses were found at 1p36.22, 8q23.3, 11p13, 11q23, and 22q13. Over 130 genes were identified with concurrent increases or decreases in expression that mapped to these regions of copy number alterations. LOH analysis revealed three tumors with whole chromosome or p arm allelic loss of chromosome 17. Genes were identified that mapped to copy neutral LOH regions. LOH with accompanying copy loss was detected on Xp24 and Xp25 and genes mapping to these regions with decreased expression were identified. Gene expression data highlighted the PPARα/RXRα Activation Pathway as down-regulated in the tumor samples.

Conclusion

We have demonstrated the utility of the application of integrated analysis using high resolution CGH and whole genome transcript analysis for detecting driver genes in IDC. The high resolution platform allowed a refined demarcation of CNAs and gene expression profiling provided a mechanism to detect genes directly impacted by the CNA. This is the first report of LOH integrated with gene expression in IDC using a high resolution platform.

Angiopoietin-2 regulates gene expression in TIE2-expressing monocytes and augments their inherent proangiogenic functions

TIE2-expressing monocytes/macrophages (TEM) are a highly proangiogenic subset of myeloid cells in tumors. Here, we show that circulating human TEMs are already preprogrammed in the circulation to be more angiogenic and express higher levels of such proangiogenic genes as matrix metalloproteinase-9 (MMP-9), VEGFA, COX-2, and WNT5A than TIE2(-) monocytes. Additionally, angiopoietin-2 (ANG-2) markedly enhanced the proangiogenic activity of TEMs and increased their expression of two proangiogenic enzymes: thymidine phosphorylase (TP) and cathepsin B (CTSB). Three "alternatively activated" (or M2-like) macrophage markers were also upregulated by ANG-2 in TEMs: interleukin-10, mannose receptor (MRC1), and CCL17. To investigate the effects of ANG-2 on the phenotype and function of TEMs in tumors, we used a double-transgenic (DT) mouse model in which ANG-2 was specifically overexpressed by endothelial cells. Syngeneic tumors grown in these ANG-2 DT mice were more vascularized and contained greater numbers of TEMs than those in wild-type (WT) mice. In both tumor types, expression of MMP-9 and MRC1 was mainly restricted to tumor TEMs rather than TIE2(-) macrophages. Furthermore, tumor TEMs expressed higher levels of MRC1, TP, and CTSB in ANG-2 DT tumors than WT tumors. Taken together, our data show that although circulating TEMs are innately proangiogenic, exposure to tumor-derived ANG-2 stimulates these cells to exhibit a broader, tumor-promoting phenotype. As such, the ANG-2-TEM axis may represent a new target for antiangiogenic cancer therapies.

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.

Angiopoietins

The formation of new blood vessels plays an important role during the development and progression of a disease. In recent years, there has been a tremendous effort to uncover the molecular mechanisms that drive blood vessel growth in adult tissues. Angiopoietins belong to a family of growth factors that are critically involved in blood vessel formation during developmental and pathological angiogenesis. The importance of Angiopoietin signaling has been recognized in transgenic mouse models as the genetic ablation of Ang-1, and its primary receptor Tie2 has led to early embryonic lethality. Interesting and unusual for a family of ligands, Ang-2 has been identified as an antagonist of Ang-1 in endothelial cells as evidenced by a similar embryonic phenotype when Ang-2 was overexpressed in transgenic mice. In this review, we focus on the functional consequences of autocrine Angiopoietin signaling in endothelial cells.

Simulation-based comparison of two approaches frequently used for dynamic contrast-enhanced MRI

PURPOSE

The purpose was to compare two approaches for the acquisition and analysis of dynamic-contrast-enhanced MRI data with respect to differences in the modelling of the arterial input-function (AIF), the dependency of the model parameters on physiological parameters and their numerical stability. Eight hundred tissue concentration curves were simulated for different combinations of perfusion, permeability, interstitial volume and plasma volume based on two measured AIFs and analysed according to the two commonly used approaches. The transfer constants (Approach 1) K (trans) and (Approach 2) k (ep) were correlated with all tissue parameters. K (trans) showed a stronger dependency on perfusion, and k (ep) on permeability. The volume parameters (Approach 1) v (e) and (Approach 2) A were mainly influenced by the interstitial and plasma volume. Both approaches allow only rough characterisation of tissue microcirculation and microvasculature. Approach 2 seems to be somewhat more robust than 1, mainly due to the different methods of CA administration.