VEGF and angiopoietin signaling in tumor angiogenesis and metastasis

Angiopoietin signaling in the vasculature

The angiopoietin (Ang) growth factors and the endothelial Tie receptors regulate blood and lymphatic vessel development, and vascular permeability, inflammation, angiogenic remodeling and tumor vascularization in adult tissues. The angiopoietins activate the Tie receptors in unique in trans complexes at endothelial cell-cell and cell-matrix contacts. In addition, integrins have been implicated in the regulation of Ang-Tie signaling. Recent interest has focused on the function of angiopoietin-2 and its inhibition in the tumor vasculature and also in other pathological conditions associated with endothelial dysfunction. Here we review the current understanding of the signaling functions of the Ang-Tie pathway and its potential for future development of targeted vascular therapeutics.

Calorie restriction and cancer prevention: a mechanistic perspective

Calorie restriction (CR) is one of the most potent broadly acting dietary interventions for inducing weight loss and for inhibiting cancer in experimental models. Translation of the mechanistic lessons learned from research on CR to cancer prevention strategies in human beings is important given the high prevalence of excess energy intake, obesity, and metabolic syndrome in many parts of the world and the established links between obesity-associated metabolic perturbations and increased risk or progression of many types of cancer. This review synthesizes findings on the biological mechanisms underlying many of the anticancer effects of CR, with emphasis on the impact of CR on growth factor signaling pathways, inflammation, cellular and systemic energy homeostasis pathways, vascular perturbations, and the tumor microenvironment. These CR-responsive pathways and processes represent targets for translating CR research into effective cancer prevention strategies in human beings.

Interleukin-6, vascular endothelial growth factor and transforming growth factor beta 1 in canine steroid responsive meningitis-arteritis

Background

Steroid Responsive Meningitis-Arteritis (SRMA) is a common cause of inflammation of the canine central nervous system (CNS). To investigate if transforming growth factor beta 1 (TGF-β₁), interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) are involved in the production of excessive immunoglobulin A (IgA), the induction of acute phase proteins and in the development of a systemic necrotizing vasculitis, characteristic of SRMA, these three signalling proteins were evaluated.

Results

Cerebrospinal fluid (CSF) and serum samples of dogs during the acute phase of SRMA (SRMA) were tested for IL-6, VEGF and TGF- β₁. Results were compared to those of dogs affected with SRMA during treatment (SRMA Th) and during relapse (SRMA R), to dogs with other meningoencephalomyelitides (ME), with miscellaneous non-inflammatory diseases of the CNS (CNS-Mix), with idiopathic epilepsy (IE), with systemic inflammatory diseases (Syst. Infl.) and with healthy dogs (Healthy). Concentrations of IL-6 and VEGF in CSF were significantly elevated in the SRMA group compared to the other disease categories (p < 0.05). The CSF concentrations of TGF-β₁ were increased in SRMA group, but statistically significant differences were found only in comparison with Healthy and CNS-Mix groups. No differences were detected in the serum concentrations of TGF-β₁ between the different groups. In untreated SRMA patients, a positive correlation (r_Spear = 0.3549; P = 0.0337) between concentrations of TGF-β₁ and IgA concentration was found in CSF, while concentrations of IL-6 and VEGF in CSF positively correlated with the degree of pleocytosis (r_Spear = 0.8323; P < 0.0001 and r_Spear = 0.5711; P = 0.0166, respectively).

Conclusions

Our results suggest that these three signalling proteins are biomarkers of disease activity in SRMA. VEGF might play an important role in the development of a systemic arteritis. TGF-β₁ is considered to be involved in the excessive IgA production, while IL-6 in the pleocytosis. The combined intrathecal increase of TGF-β₁ and IL-6 detected in SRMA could possibly force CD4 progenitors to differentiate towards the newly described Th17 lymphocyte subset and enhance the autoimmune response.

Evaluating tumor angiogenesis

The evaluation of tumor angiogenesis in pancreatic cancers involves determining the status of tumor vasculature and hypoxia in the tumor. Describing the nature and extent of tumor angiogenesis involves evaluating the expression of endothelial and perivascular cells within the tumor, and the expression of angiogenesis-related genes in tumor vasculature. Here we describe the methodology for assessment of tumor vasculature in murine mouse models of cancer. Specifically, we provide methodology for the evaluation of tumor hypoxia, tumor vessel perfusion, and chromogenic and fluorescent immunohistochemistry applied to tumor vascular analysis.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

The role of the VEGF-C/VEGFRs axis in tumor progression and therapy

Vascular endothelial growth factor C (VEGF-C) has been identified as a multifaceted factor participating in the regulation of tumor angiogenesis and lymphangiogenesis. VEGF-C is not only expressed in endothelial cells, but also in tumor cells. VEGF-C signaling is important for progression of various cancer types through both VEGF receptor-2 (VEGFR-2) and VEGF receptor-3 (VEGFR-3). Likewise, both receptors are expressed mainly on endothelial cells, but also expressed in tumor cells. The dimeric VEGF-C undergoes a series of proteolytic cleavage steps that increase the protein binding affinity to VEGFR-3; however, only complete processing, removing both the N- and C-terminal propeptides, yields mature VEGF-C that can bind to VEGFR-2. The processed VEGF-C can bind and activate VEGFR-3 homodimers and VEGFR-2/VEGFR-3 heterodimers to elicit biological responses. High levels of VEGF-C expression and VEGF-C/VEGFRs signaling correlate significantly with poorer prognosis in a variety of malignancies. Therefore, the development of new drugs that selectively target the VEGF-C/VEGFRs axis seems to be an effective means to potentiate anti-tumor therapies in the future.

Sox17 promotes tumor angiogenesis and destabilizes tumor vessels in mice

Little is known about the transcriptional regulation of tumor angiogenesis, and tumor ECs (tECs) remain poorly characterized. Here, we studied the expression pattern of the transcription factor Sox17 in the vasculature of murine and human tumors and investigated the function of Sox17 during tumor angiogenesis using Sox17 genetic mouse models. Sox17 was specifically expressed in tECs in a heterogeneous pattern; in particular, strong Sox17 expression distinguished tECs with high VEGFR2 expression. Whereas overexpression of Sox17 in tECs promoted tumor angiogenesis and vascular abnormalities, Sox17 deletion in tECs reduced tumor angiogenesis and normalized tumor vessels, inhibiting tumor growth. Tumor vessel normalization by Sox17 deletion was long lasting, improved anticancer drug delivery into tumors, and inhibited tumor metastasis. Sox17 promoted endothelial sprouting behavior and upregulated VEGFR2 expression in a cell-intrinsic manner. Moreover, Sox17 increased the percentage of tumor-associated CD11b+Gr-1+ myeloid cells within tumors. The vascular effects of Sox17 persisted throughout tumor growth. Interestingly, Sox17 expression specific to tECs was also observed in highly vascularized human glioblastoma samples. Our findings establish Sox17 as a key regulator of tumor angiogenesis and tumor progression.

sVEGF R1 and Tie-2 levels during chemotherapy of lung cancer patients

Angiogenesis plays important role in tumor growth and development. Protein ligands and their receptor tyrosine kinases are crucial in tumor related angiogenesis. Ligand/receptor systems such as vascular endothelial growth factor (VEGF), and tyrosine kinase with immunoglobulin-like and epidermal growth factor homology domains (Tie) family play important role in this phenomenon. The aim of this study was to evaluate the concentration of soluble receptor of VEGF (sVEGF R1) and Tie-2 domain in plasma of lung cancer patients before and after chemotherapy. Forty four lung cancer patients, 11 with small lung cancer (SCLC), 5 females and 6 males (mean age 60.2, range 39-72 years), and 33 patients with non-small cell lung cancer (N-SCLC), 6 females and 27 males (mean age 61.9, range 42-78 years) received four courses of chemotherapy. Control group consisted of 44 patients with COPD, 4 females and 40 males (mean age 37.1, 18-60 years). In all cases clinical partial response was achieved. Both sVEGF R1 and Tie-2 concentrations were elevated in cancer group before treatment compared with control: sVEGF (pg/ml): 60.7 and 66.2 vs. 48.8 and Tie-2 (ng/ml): 37.3 and 37.5 vs. 30.7 in SCLC and N-SCLC vs. C, respectively. Treatment decreased sVEGF R1 (pg/ml): 66.7 vs. 11.6 (p < 0.05) and 66.2 vs. 14.39 (p < 0.001), and Tie-2 (ng/ml): 37.3 vs. 26.3 (p < 0.05) and 37.5 vs. 25.7 (p < 0.001) in SCLC and N-SCLC, respectively. We conclude that VEGF R1and Tie-2 receptors may play important role in lung cancer development and their receptor concentrations may reflect the patients' response to treatment.

Circadian clock disruptions and the risk of cancer

Disrupted circadian rhythms may lead to failures in the control of the cell division cycle and the subsequent malignant cell growth. In order to understand the pathogenesis of cancer more in detail, it is crucial to identify those mechanisms of action which contribute to the loss of control of the cell division cycle. This mini-review focuses on the recent findings concerning the links between the human circadian clock and cancer. Clinical implications concern not only feasible methods for the assessment of the circadian time of an individual or for the determination of the best time for administration of a drug of treatment, but also in the future genetic tests for screening and for planning treatment.

Altered local and systemic immune profiles underlie lymph node metastasis in breast cancer patients

Cancer-mediated immune dysfunction contributes to tumor progression and correlates with patient outcome. Metastasis to tumor draining lymph nodes (TDLNs) is an important step in breast cancer progression and is used to predict patient outcome and survival. Although lymph nodes are important immune organs, the role of immune cells in TDLNs has not been thoroughly investigated. We hypothesized that the host immune response in node negative (NN) patients is more intact and thereby can resist tumor invasion compared to node positive (NP) patients. As such, lymph node metastasis requires breakdown of the host immune response in addition to escape of cancer cells from the tumor. To investigate the immunological differences between NN and NP breast cancer patients, we purified and profiled immune cells from the three major compartments where cancer and immune cells interact: tumor, TDLNs and peripheral blood. Significant down-regulation of genes associated with immune-related pathways and up-regulation of genes associated with tumor-promoting pathways was consistently observed in NP patients' TDLNs compared to NN patients. Importantly, these signatures were seen even in NP patients' tumor-free TDLNs, suggesting that such immune changes are not driven solely by local tumor invasion. Furthermore, similar patterns were also observed in NP patients' tumor and blood immune cells, suggesting that immunological differences between NN and NP patients are systemic. Together, these findings suggest that alterations in overall immune function may underlie risk for LN metastasis in breast cancer patients.

Tumor angiogenesis and anti-angiogenic therapy

Anti-angiogenic therapy is an anti-cancer strategy that targets the new vessels that grow to provide oxygen and nutrients to actively proliferating tumor cells. Most of the current anti-cancer reagents used in the clinical setting indiscriminately target all rapidly dividing cells, resulting in severe adverse effects such as immunosuppression, intestinal problems and hair loss. In comparison, anti-angiogenic reagents theoretically have fewer side effects because, except in the uterine endometrium, neoangiogenesis rarely occurs in healthy adults. Currently, the most established approach for limiting tumor angiogenesis is blockade of the vascular endothelial growth factor (VEGF) pathway. In line with the results of preclinical studies, significant therapeutic effects of VEGF blockers have been reported in various types of human cancers, even in patients with progressive/recurrent cancer who could not otherwise be treated. However, some patients are refractory to this treatment or acquire resistance to VEGF inhibitors. Moreover, several studies have shown that VEGF blockade damages healthy vessels and results in adverse effects such as hemorrhagic and thrombotic events. In recent research that indicated possible ways to overcome these problems, several VEGF-independent and tumor-selective pro-angiogenic mechanisms were discovered that could be targeted in combination with or without conventional VEGF blockade. These findings offer opportunities to greatly improve current anti-angiogenic treatment for cancer.

Complex role of γδ T-cell-derived cytokines and growth factors in cancer

γδ T cells are innate lymphocytes that recognize and kill a range of tumor cells and are currently being explored as a target for tumor immunotherapy. However, γδ T cells play a complex role in cancer and can promote, as well as inhibit, tumor growth. In addition to tumor cell killing, γδ T cells express a number of cytokines and other soluble factors in response to tumors. Soluble factors expressed by γδ T cells in these settings include interferon-γ, tumor necrosis factor-α, interleukin (IL)-4, IL-10, transforming growth factor-β, IL-17, and a number of growth factors. These factors have differing and sometimes opposing effects on antitumor immunity and tumor angiogenesis, and likely contribute to the complex role of these cells in cancer. Here, we review studies in both mice and humans that examine differential cytokine secretion by γδ T cells in response to tumors and tumor immunotherapy, and discuss the influence of these γδ T-cell-derived factors on tumor growth.

Controlling escape from angiogenesis inhibitors

Selective inhibition of vascular endothelial growth factor (VEGF) increases the efficacy of chemotherapy and has beneficial effects on multiple advanced cancers, but response is often limited and the disease eventually progresses. Changes in the tumour microenvironment--hypoxia among them--that result from vascular pruning, suppressed angiogenesis and other consequences of VEGF inhibition can promote escape and tumour progression. New therapeutic approaches that target pathways that are involved in the escape mechanisms add the benefits of blocking tumour progression to those of slowing tumour growth by inhibiting angiogenesis.

Quantification of plasma and bone marrow VEGF and angiopoietin-2 levels in pediatric malignancies

INTRODUCTION

Data on angiogenesis in pediatric patients with malignancy are scarce. Our aim was to study angiogenic growth factors vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang2) in pediatric oncological patients at diagnosis and a few months after the beginning of the therapy.

PATIENTS AND METHODS

Eighty-four consecutive patients with malignancy were included in this study. The levels of plasma and bone marrow VEGF and Ang2 were analyzed by enzyme-linked immunosorbent assay.

RESULTS

The levels of VEGF were higher in patients with solid tumors than in patients with leukemias (P=0.003), whereas Ang2 concentrations showed the opposite (P=0.003). Interestingly, the plasma concentrations of both VEGF and Ang2 correlated with concentrations in the bone marrow (P<0.05). Leukemia patients with lower VEGF level and patients with higher Ang2 level at follow-up had longer event-free survival than other patients (P=0.032 and 0.053, respectively).

DISCUSSION

The results of our study enlighten the behavior of 2 different angiogenic factors in pediatric patients with malignancy. An interesting finding was the connection between survival of pediatric leukemia patients and angiogenic factor levels a few months after the beginning of therapy. Pathophysiology and clinical applications of these findings need further studies.

Grape seed proanthocyanidins inhibit colon cancer-induced angiogenesis through suppressing the expression of VEGF and Ang1

Tumor cells trigger angiogenesis through overexpression of various angiogenic factors including vascular endothelial growth factor (VEGF) and angiopoietin 1 (Ang1). Therefore, inhibition of the expression of both VEGF and Ang1, the initial step of tumor angiogenesis, is a promising strategy for cancer chemoprevention and therapy. Grape seed proanthocyanidins (GSPs) are widely consumed dietary supplements that have antitumor activity. Due to their polymeric structure, GSPs are poorly absorbed along the gastrointestinal tract and can reach the colon at high concentrations, allowing these chemicals to act as chemopreventive agents for colon cancer. In the present study, we found that GSPs inhibited colon tumor-induced angiogenesis and, thus, the growth of colon tumor xenografts on the chick chorioallantoic membranes. The mechanisms of their action were related to inhibiting the expression of both VEGF and Ang1 through scavenging reactive oxygen species. Previous studies have demonstrated that the chemopreventive effects of GSPs on colon cancer are associated with their growth inhibitory and apoptosis-inducing effects. Our results demonstrate another mechanism by which GSPs inhibit colon tumor growth, which will be helpful for developing GSPs as a pharmacologically safe angiopreventive agent against colorectal cancer.

Prognostic value of vascular endothelial growth factor in patients with head and neck cancer: A meta-analysis

BACKGROUND

The correlation between vascular endothelial growth factor (VEGF) overexpression and the clinical outcome of head and neck cancer remains inconclusive. This meta-analysis aimed to evaluate the prognostic value of VEGF in patients with head and neck cancer.

METHODS

We searched Ovid MEDLINE, EMBASE and 2 Chinese science databases in order to enroll all eligible articles. Forty-seven studies were included in this meta-analysis. All results were evaluated by the random-effects model.

RESULTS

VEGF overexpression is significantly associated with worse overall survival (OS; hazard ratio [HR], 1.89; 95% confidence interval [CI], 1.61-2.22) and progression-free survival (PFS; HR, 1.68; 95% CI, 1.33-2.12). Subgroup analysis reveals that VEGF overexpression is a significant poor predictor for nasopharyngeal cancer (HR, 1.66; 95% CI, 1.30-2.12) and salivary gland cancer (HR, 3.32; 95% CI, 1.61-6.84).

CONCLUSION

Our meta-analysis supports that VEGF overexpression is an available poor predictor for patients with head and neck cancer.

Angiopoietins in angiogenesis

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

Endothelial Wnt/β-catenin signaling inhibits glioma angiogenesis and normalizes tumor blood vessels by inducing PDGF-B expression

Wnt modulates glioma vascularization by regulating PDGF-B expression.

Endothelial Wnt/β-catenin signaling is necessary for angiogenesis of the central nervous system and blood–brain barrier (BBB) differentiation, but its relevance for glioma vascularization is unknown. In this study, we show that doxycycline-dependent Wnt1 expression in subcutaneous and intracranial mouse glioma models induced endothelial Wnt/β-catenin signaling and led to diminished tumor growth, reduced vascular density, and normalized vessels with increased mural cell attachment. These findings were corroborated in GL261 glioma cells intracranially transplanted in mice expressing dominant-active β-catenin specifically in the endothelium. Enforced endothelial β-catenin signaling restored BBB characteristics, whereas inhibition by Dkk1 (Dickkopf-1) had opposing effects. By overactivating the Wnt pathway, we induced the Wnt/β-catenin–Dll4/Notch signaling cascade in tumor endothelia, blocking an angiogenic and favoring a quiescent vascular phenotype, indicated by induction of stalk cell genes. We show that β-catenin transcriptional activity directly regulated endothelial expression of platelet-derived growth factor B (PDGF-B), leading to mural cell recruitment thereby contributing to vascular quiescence and barrier function. We propose that reinforced Wnt/β-catenin signaling leads to inhibition of angiogenesis with normalized and less permeable vessels, which might prove to be a valuable therapeutic target for antiangiogenic and edema glioma therapy.

Novel targets against retinal angiogenesis in diabetic retinopathy

Proliferative diabetic retinopathy (PDR), characterized by pathologic retinal angiogenesis, is a major cause of blindness in the USA and globally. Treatments targeting vascular endothelial growth factor (VEGF) have emerged as a beneficial part of the therapeutic armamentarium for this condition, highlighting the utility of identifying and targeting specific pathogenic molecules. There continues to be active research into the molecular players regulating retinal angiogenesis, including pro-angiogenic factors, anti-angiogenic factors, and integrins and matrix proteinases. New insights have been especially prominent regarding molecules which regulate specialized endothelial cells called tip cells, which play a lead role in endothelial sprouting. Together, these research efforts are uncovering new, important molecular regulators of retinal angiogenesis, which provide fertile areas for therapeutic exploration. This review discusses potential molecular targets, with an emphasis towards newer targets.

Progressive increase of matrix metalloprotease-9 and interleukin-8 serum levels during carcinogenic process in human colorectal tract

BACKGROUND

Inflammatory reactions, known to promote tumor growth and invasion, have been found associated with colorectal carcinoma (CRC). Macrophages are the chief component of the inflammatory infiltration that occurs early in the progression from non-invasive to malignant tumor, with a switch from the pro-inflammatory phenotype to the tumor-promoting phenotype. Tumor and stroma are additional sources of inflammation-related molecules. The study aimed to evaluate, during colorectal carcinogenesis from benign to malignant phases: i) the trend of serum levels of IL-8, IL-6, TGFβ1, VEGF and MMPs; ii) the parallel trend of CRP serum levels; iii) derangement of the principal TGFβ1 receptors (TGFβ1RI/RII) in tumor tissues.

METHODOLOGY/PRINCIPAL FINDINGS

96 patients with colon adenomas or CRC at different stages of progression, and 17 controls, were recruited. Serum IL-8, IL-6, TGFβ1, VEGF, MMPs and CRP levels were analyzed before endoscopy or surgery. TGFβ1 receptors were evaluated in adenoma biopsies and surgically-removed colorectal adenocarcinomas. Serum levels of IL-8 in adenocarcinoma patients were increased from stage II, when also the enzymatic activity of MMP-9 increased. Of note, the increasing trend of the two serum markers was found significantly correlated. Trend of serum CRP was also very similar to that of IL-8 and MMP-9, but just below statistical significance. TGFβ1 levels were lower at stage III CRC, while IL-6 and VEGF levels had no significant variations. In tissue specimens, TGFβ1 receptors were already absent in about 50% of adenomas, and this percentage of missing receptors markedly increased in CRC stages III and IV.

CONCLUSIONS

Combined quantification of serum IL-8, MMP-9 and CRP, appears a reliable and advanced index of inflammation-related processes during malignant phase of colorectal carcinogenesis, since these molecules remain within normal range in colorectal adenoma bearing patients, while consistently increase in the blood of CRC patients, even if from stage II only.

ADAMTS5: A New Player in the Vascular Field

This Commentary highlights the article by Kumar et al, showing that ADAMTS5 suppresses tumor growth by down-regulating other angiogenesis-inducing factors in addition to VEGF and that the central TSR1 domain of ADAMTS5 is required in this function.

Pathological neoangiogenesis depends on oxidative stress regulation by ATM

The ataxia telangiectasia mutated (ATM) kinase, a master regulator of the DNA damage response (DDR), acts as a barrier to cellular senescence and tumorigenesis. Aside from DDR signaling, ATM also functions in oxidative defense. Here we show that Atm in mice is activated specifically in immature vessels in response to the accumulation of reactive oxygen species (ROS). Global or endothelial-specific Atm deficiency in mice blocked pathological neoangiogenesis in the retina. This block resulted from increased amounts of ROS and excessive activation of the mitogen activated kinase p38α rather than from defects in the canonical DDR pathway. Atm deficiency also lowered tumor angiogenesis and enhanced the antiangiogenic action of vascular endothelial growth factor (Vegf) blockade. These data suggest that pathological neoangiogenesis requires ATM-mediated oxidative defense and that agents that promote excessive ROS generation may have beneficial effects in the treatment of neovascular disease.

Grape seed proanthocyanidins inhibit angiogenesis via the downregulation of both vascular endothelial growth factor and angiopoietin signaling

Vascular endothelial growth factor (VEGF)/VEGF receptor 2 and angiopoietin 1/tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 2 signaling pathways regulate different, but complementary, aspects of blood vessel growth in tumors. Simultaneous inhibition of both pathways not only exhibits additive antiangiogenic effects but also overcomes the resistance to anti-VEGF therapy. Grape seed proanthocyanidins (GSPs) are widely consumed dietary supplements with antiangiogenic activity. However, the molecular mechanisms underlying their antiangiogenic action have not been fully understood. We hypothesized that GSPs modulate multiple signaling pathways to exhibit antiangiogenic effects. In the present study, we aimed to test this hypothesis by examining the effects of GSPs on human microvascular endothelial cell-1 and chick chorioallantoic membrane. Our results showed that GSPs inhibited the migration, matrix metalloproteinase-2 and -9 secretion, and tube formation of human microvascular endothelial cell-1 in vitro in a dose-dependent manner. In addition, chick chorioallantoic membrane angiogenesis assay showed that GSPs inhibited neovascularization in a dose-dependent manner. Furthermore, we demonstrated that GSPs inhibited the phosphorylation of VEGF receptor 2 and tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 2 as well as downstream signaling component extracellular signal-regulated kinase 1/2. In summary, these data suggest that GSPs inhibit both VEGF and angiopoietin 1 signaling to execute the antiangiogenic effects and indicate that GSPs could be developed as a pharmacologically safe chemopreventive agent against cancer.

Methylseleninic acid restricts tumor growth in nude mice model of metastatic breast cancer probably via inhibiting angiopoietin-2

BACKGROUND

Angiopoietin-2 (Ang-2) plays critical roles in vascular morphogenesis and its upregulation is frequently associated with various tumors. Previous studies showed that certain selenium compounds possess anti-tumor effects. However, the underlining mechanism has not been elucidated in detail. Plus, results of research on the anti-tumor effects of selenium compounds remain controversial.

METHODS

We investigated levels of Ang-2 and vascular endothelial growth factor (VEGF) on the estrogen-independent bone metastatic mammary cancer (MDA-MB-231) cells in response to treatment by methylseleninic acid (MSeA), and further examined the effects of MSeA oral administration on xenograft mammary tumors of athymic nude mice by RT-PCR, Western, radioimmuno assay, and Immunohistochemistry.

RESULTS

Treatment of MDA-MB-231 cells with MSeA caused significant reduction of Ang-2 mRNA transcripts and secretion of Ang-2 proteins by the cells. Level of VEGF protein was accordingly decreased following the treatment. Compared with the controls, oral administration of MSeA (3 mg/kg/day for 18 days) to the nude mice carrying MDA-MB-231 induced tumors resulted in significant reduction in xenograft tumor volume and weights, significant decrease in microvascular density, and promotion of vascular normalization by increasing pericytes coverage. As expected, level of VEGF was also decreased in MSeA treated tumors.

CONCLUSIONS

Our results point out that MSeA exerts its anti-tumor effects, at least in part, by inhibiting the Ang-2/Tie2 pathway, probably via inhibiting VEGF.

Integrating genetic and gene expression evidence into genome-wide association analysis of gene sets

Single variant or single gene analyses generally account for only a small proportion of the phenotypic variation in complex traits. Alternatively, gene set or pathway association analyses are playing an increasingly important role in uncovering genetic architectures of complex traits through the identification of systematic genetic interactions. Two dominant paradigms for gene set analyses are association analyses based on SNP genotypes and those based on gene expression profiles. However, gene-disease association can manifest in many ways, such as alterations of gene expression, genotype, and copy number; thus, an integrative approach combining multiple forms of evidence can more accurately and comprehensively capture pathway associations. We have developed a single statistical framework, Gene Set Association Analysis (GSAA), that simultaneously measures genome-wide patterns of genetic variation and gene expression variation to identify sets of genes enriched for differential expression and/or trait-associated genetic markers. Simulation studies illustrate that joint analyses of genomic data increase the power to detect real associations when compared with gene set methods that use only one genomic data type. The analysis of two human diseases, glioblastoma and Crohn's disease, detected abnormalities in previously identified disease-associated pathways, such as pathways related to PI3K signaling, DNA damage response, and the activation of NFKB. In addition, GSAA predicted novel pathway associations, for example, differential genetic and expression characteristics in genes from the ABC transporter family in glioblastoma and from the HLA system in Crohn's disease. These demonstrate that GSAA can help uncover biological pathways underlying human diseases and complex traits.

Filopodia and adhesion in cancer cell motility

Slender bundled actin containing plasma membrane protrusions, called filopodia, are important for many essential cellular processes like cell adhesion, migration, angiogenesis and the formation of cell-cell contacts. In migrating cells, filopodia are the pioneers at the leading edge which probe the environment for cues. Integrins are cell surface adhesion receptors critically implicated in cell migration and they are transported actively to filopodia tips by an unconventional myosin, myosin-X. Integrin mediated adhesion stabilizes filopodia and promotes cell migration even though integrins are not essential for filopodia initiation. Myosin-X binds also PIP3 and this regulates its activation and localization to filopodia. Filopodia stimulate cell migration in many cell types and increased filopodia density has been described in cancer. Furthermore, several proteins implicated in filopodia formation, like fascin, are also relevant for cancer progression. To investigate this further, we performed a meta-analysis of the expression profiles of 10 filopodia-linked genes in human breast cancer. These data implicated that several different filopodia inducing genes may contribute in a collective manner to cancer progression and the high metastasis rates associated with basal-type breast carcinomas.

Ginsenoside Rg3 inhibits endothelial progenitor cell differentiation through attenuation of VEGF-dependent Akt/eNOS signaling

Endothelial progenitor cells (EPCs) play a critical role both in vascular repair after cell transplantation for ischemic diseases and in the growth of early tumors by intervening with the angiogenic switch during tumor progression. This paper reports on the effect of ginsenoside Rg3 in EPCs as a candidate angiogenesis inhibitor for in vitro functional assays. CD34⁺ cells were isolated from human cord blood and the study investigated whether or not ginsenoside Rg3 regulated EPC bioactivities including cell proliferation, differentiation, migration and tube formation. Although ginsenoside Rg3 did not affect the ex vivo expansion of CD34 and/or KDR (VEGFR2) stem/progenitor cells, treatment with ginsenoside Rg3 led to a significant decrease in CD34-expressing cells, specifically the absolute number of expanded CD34⁺ cells. Importantly, a significantly decreased number of EPC colony-forming units among human cord blood-derived CD34⁺ cells was observed, implying that ginsenoside Rg3 inhibited EPC differentiation, in particular, the commitment to primitive EPC colonies (the early stage of EPC differentiation). Moreover, treatment of CD34-derived EPCs with ginsenoside Rg3 resulted in the attenuation of VEGF-dependent Akt/eNOS signaling as well as the inhibition of migration and tube formation. In conclusion, this study provides in vitro evidence for ginsenoside Rg3 as a potential therapeutic molecule, specifically as an angiogenesis inhibitor that functions by attenuating EPC bioactivities.

Cancer stem cells, tumor dormancy, and metastasis

Tumor cells can persist undetectably for an extended period of time in primary tumors and in disseminated cancer cells. Very little is known about why and how these tumors persist for extended periods of time and then evolve to malignancy. The discovery of cancer stem cells (CSCs) in human tumors challenges our current understanding of tumor recurrence, drug resistance, and metastasis, and opens up new research directions on how cancer cells are capable of switching from dormancy to malignancy. Although overlapping molecules and pathways have been reported to regulate the stem-like phenotype of CSCs and metastasis, accumulated evidence has suggested additional clonal diversity within the stem-like cancer cell subpopulation. This review will describe the current hypothesis linking CSCs and metastasis and summarize mechanisms important for metastatic CSCs to re-initiate tumors in the secondary sites. A better understanding of CSCs' contribution to clinical tumor dormancy and metastasis will provide new therapeutic revenues to eradicate metastatic tumors and significantly reduce the mortality of cancer patients.