A catalytic role for proangiogenic marrow-derived cells in tumor neovascularization

Angiogenesis after ischemic stroke

Owing to its high disability and mortality rates, stroke has been the second leading cause of death worldwide. Since the pathological mechanisms of stroke are not fully understood, there are few clinical treatment strategies available with an exception of tissue plasminogen activator (tPA), the only FDA-approved drug for the treatment of ischemic stroke. Angiogenesis is an important protective mechanism that promotes neural regeneration and functional recovery during the pathophysiological process of stroke. Thus, inducing angiogenesis in the peri-infarct area could effectively improve hemodynamics, and promote vascular remodeling and recovery of neurovascular function after ischemic stroke. In this review, we summarize the cellular and molecular mechanisms affecting angiogenesis after cerebral ischemia registered in PubMed, and provide pro-angiogenic strategies for exploring the treatment of ischemic stroke, including endothelial progenitor cells, mesenchymal stem cells, growth factors, cytokines, non-coding RNAs, etc.

Clinical progress of anti-angiogenic targeted therapy and combination therapy for gastric cancer

The incidence of gastric cancer is increasing year by year. Most gastric cancers are already in the advanced stage with poor prognosis when diagnosed, which means the current treatment is not satisfactory. Angiogenesis is an important link in the occurrence and development of tumors, and there are multiple anti-angiogenesis targeted therapies. To comprehensively evaluate the efficacy and safety of anti-angiogenic targeted drugs alone and in combination against gastric cancer, we systematically searched and sorted out relevant literature. In this review, we summarized the efficacy and safety of Ramucirumab, Bevacizumab, Apatinib, Fruquintinib, Sorafenib, Sunitinib, Pazopanib on gastric cancer when used alone or in combination based on prospective clinical trials reported in the literature, and sorted response biomarkers. We also summarized the challenges faced by anti-angiogenesis therapy for gastric cancer and available solutions. Finally, the characteristics of the current clinical research are summarized and suggestions and prospects are raised. This review will serve as a good reference for the clinical research of anti-angiogenic targeted drugs in the treatment of gastric cancer.

The Impact of Obesity, Adipose Tissue, and Tumor Microenvironment on Macrophage Polarization and Metastasis

Tumor metastasis is a major cause of death in cancer patients. It involves not only the intrinsic alterations within tumor cells, but also crosstalk between these cells and components of the tumor microenvironment (TME). Tumorigenesis is a complex and dynamic process, involving the following three main stages: initiation, progression, and metastasis. The transition between these stages depends on the changes within the extracellular matrix (ECM), in which tumor and stromal cells reside. This matrix, under the effect of growth factors, cytokines, and adipokines, can be morphologically altered, degraded, or reorganized. Many cancers evolve to form an immunosuppressive TME locally and create a pre-metastatic niche in other tissue sites. TME and pre-metastatic niches include myofibroblasts, immuno-inflammatory cells (macrophages), adipocytes, blood, and lymphatic vascular networks. Several studies have highlighted the adipocyte-macrophage interaction as a key driver of cancer progression and dissemination. The following two main classes of macrophages are distinguished: M1 (pro-inflammatory/anti-tumor) and M2 (anti-inflammatory/pro-tumor). These cells exhibit distinct microenvironment-dependent phenotypes that can promote or inhibit metastasis. On the other hand, obesity in cancer patients has been linked to a poor prognosis. In this regard, tumor-associated adipocytes modulate TME through the secretion of inflammatory mediators, which modulate and recruit tumor-associated macrophages (TAM). Hereby, this review describes the cellular and molecular mechanisms that link inflammation, obesity, and cancer. It provides a comprehensive overview of adipocytes and macrophages in the ECM as they control cancer initiation, progression, and invasion. In addition, it addresses the mechanisms of tumor anchoring and recruitment for M1, M2, and TAM macrophages, specifically highlighting their origin, classification, polarization, and regulatory networks, as well as their roles in the regulation of angiogenesis, invasion, metastasis, and immunosuppression, specifically highlighting the role of adipocytes in this process.

CARD11 is a prognostic biomarker and correlated with immune infiltrates in uveal melanoma

Uveal melanoma (UVM), the most common primary intraocular malignancy, has a high mortality because of a high propensity to metastasize. Our study analyzed prognostic value and immune-related characteristics of CARD11 in UVM, hoping to provide a potential management and research direction. The RNA-sequence data of 80 UVM patients were downloaded from The Cancer Genome Atlas database and divided them into high- and low-expression groups. We analyzed the differentially expressed genes, enrichment analyses and the infiltration of immune cells using the R package and Gene-Set Enrichment Analysis. A clinical prediction nomogram and protein-protein interaction network were constructed and the first 8 genes were considered as the hub-genes. Finally, we constructed a competing endogenous RNA (ceRNA) network by Cytoscape and analyzed the statistical data via the R software. Here we found that CARD11 expression had notable correlation with UVM clinicopathological features, which was also an independent predictor for overall survival (OS). Intriguingly, CARD11 had a positively correlation to autophagy, cellular senescence and apoptosis. Infiltration of monocytes was significantly higher in low CARD11 expression group, and infiltration of T cells regulatory was lower in the same group. Functional enrichment analyses revealed that CARD11 was positively related to T cell activation pathways and cell adhesion molecules. The expressions of hub-genes were all increased in the high CARD11 expression group and the ceRNA network showed the interaction among mRNA, miRNA and lncRNA. These findings show that high CARD11 expression in UVM is associated with poor OS, indicating that CARD11 may serve as a potential biomarker for the diagnosis and prognosis of the UVM.

The role of vascular niche and endothelial cells in organogenesis and regeneration

The term vascular niche indicate the physical and biochemical microenvironment around blood vessel where endothelial cells, pericytes, and smooth muscle cells organize themselves to form blood vessels and release molecules involved in the recruitment of hematopoietic stem cells, endothelial progenitor cells and mesenchymal stem cells. The vascular niche creates a permissive environment that enables different cell types to realize their developmental or regenerative programs. In this context, the proximity between the endothelium and the new-forming cellular components of organs suggests an essential role of endothelial cells in the organs maturation. Dynamic interactions between specific organ endothelial cells and different cellular conponents are crucial for different organ morphogenesis and function. Conversely, organs provide cues shaping vascular network structure.

Molecular insights and novel approaches for targeting tumor metastasis

In recent years, due to the effective drug delivery and preciseness of tumor sites or microenvironment, the targeted drug delivery approaches have gained ample attention for tumor metastasis therapy. The conventional treatment approaches for metastasis therapy have reported with immense adverse effects because they exhibited maximum probability of killing the carcinogenic cells along with healthy cells. The tumor vasculature, comprising of vasculogenic impressions and angiogenesis, greatly depends upon the growth and metastasis in the tumors. Therefore, various nanocarriers-based delivery approaches for targeting to tumor vasculature have been attempted as efficient and potential approaches for the treatment of tumor metastasis and the associated lesions. Furthermore, the targeted drug delivery approaches have found to be most apt way to overcome from all the limitations and adverse effects associated with the conventional therapies. In this review, various approaches for efficient targeting of pharmacologically active chemotherapeutics against tumor metastasis with the cohesive objectives of prognosis, tracking and therapy are summarized.

Eosinophil and lymphocyte counts predict bevacizumab response and survival in recurrent glioblastoma

Background

There is a lack of biomarkers to identify glioblastoma (GBM) patients who may benefit from specific salvage therapies, such as the anti-angiogenic agent bevacizumab. We hypothesized that circulating blood counts may serve as biomarkers for treatment response and clinical outcomes.

Methods

Complete blood counts, clinical data, and radiographic information were collected retrospectively from 84 recurrent GBM patients receiving bevacizumab (10 mg/kg every 2 weeks). Significant biomarkers were categorized into quartiles and the association with clinical outcomes was assessed using the Kaplan–Meier method.

Results

The median treatment duration and survival on bevacizumab (OS-A) was 88 and 192 days, respectively. On multivariate analysis, MGMT promoter methylation (hazard ratio [HR] 0.504, P = .031), increases in red blood cells (HR 0.496, P = .035), and increases in eosinophils (HR 0.048, P = .054) during treatment predicted improved OS-A. Patients in the first and fourth quartiles of eosinophil changes had a 12-month survival probability of 5.6% and 41.2% (P < .0001), respectively. Treatment response was associated with increases in eosinophil counts (P = .009) and improved progression-free survival (P = .013). On multivariate analysis, increases in lymphocyte counts among responders predicted improved OS-A (HR 0.389, P = .044). Responders in the first and fourth quartiles of lymphocyte changes had a 12-month survival probability of 0% and 44.4% (P = .019), respectively. Changes in platelet counts differed before and after radiographic response (P = .014).

Conclusions

Changes in circulating eosinophil, lymphocyte, and platelet counts may predict treatment response and clinical outcomes in patients with recurrent GBM receiving bevacizumab.

[Science, truth and beliefs]

This article aims at discussing some aspects of the relationship between science, truth and belief. I will primarily focus on the scientific activity in the biological and medical sciences and how it relates to the notion of truth and belief and not discuss the relationship with specific religions. Science has specific methodologies to obtain knowledge. Philosophers have analyzed how scientific knowledge is acquired and have tried to identify its characteristics and to establish some general rules of how knowledge through science is gained. Radical theorists have disputed the value of the scientific method despite science's indisputable successes. If science is a rational activity, it is not free from belief. Belief can have a positive and negative impact on the acquisition of scientific knowledge and the idea of human nature. These different issues will be discussed in depth in this article.

Tanshinone IIA inhibits angiogenesis in human endothelial progenitor cells in vitro and in vivo

Accumulating evidence reports that bone marrow-derived endothelial progenitor cells (EPCs) regulate angiogenesis, postnatal neovascularization and tumor metastasis. It has been suggested that understanding the molecular targets and pharmacological functions of natural products is important for novel drug discovery. Tanshinone IIA is a major diterpene quinone compound isolated from Danshen (Salvia miltiorrhiza) and is widely used in traditional Chinese medicine (TCM). Evidence indicates that tanshinone IIA modulates angiogenic functions in human umbilical vein endothelial cells. However, the anti-angiogenic activity of tanshinone IIA in human EPCs has not been addressed. Here, we report that tanshinone IIA dramatically suppresses vascular endothelial growth factor (VEGF)-promoted migration and tube formation of human EPCs, without cytotoxic effects. We also show that tanshinone IIA markedly inhibits VEGF-induced angiogenesis in the chick embryo chorioallantoic membrane (CAM) model. Importantly, tanshinone IIA significantly attenuated microvessel formation and the expression of EPC-specific markers in the in vivo Matrigel plug assay in mice. Further, we found that tanshinone IIA inhibits EPC angiogenesis through the PLC, Akt and JNK signaling pathways. Our report is the first to reveal that tanshinone IIA reduces EPC angiogenesis both in vitro and in vivo. Tanshinone IIA is a promising natural product worthy of further development for the treatment of cancer and other angiogenesis-related pathologies.

Bone Niches, Hematopoietic Stem Cells, and Vessel Formation

Bone marrow (BM) is a source of hematopoietic stem cells (HSCs). HSCs are localized in both the endosteum, in the so-called endosteal niche, and close to thin-walled and fenestrated sinusoidal vessel in the center of BM, in the so-called vascular niche. HSCs give rise to all types of mature blood cells through a process finely controlled by numerous signals emerging from the bone marrow niches where HSCs reside. This review will focus on the description of the role of BM niches in the control of the fate of HSCs and will also highlight the role of the BM niches in the regulation of vasculogenesis and angiogenesis. Moreover, alterations of the signals in niche microenvironment are involved in many aspects of tumor progression and vascularization and further knowledge could provide the basis for the development of new therapeutic strategies.

Chimeric Mouse model to track the migration of bone marrow derived cells in glioblastoma following anti-angiogenic treatments

Bone marrow derived cells (BMDCs) have been shown to contribute in the tumor development. In vivo animal models to investigate the role of BMDCs in tumor development are poorly explored. We established a novel chimeric mouse model using as low as 5 × 10(6) GFP+ BM cells in athymic nude mice, which resulted in >70% engraftment within 14 d. In addition, chimera was established in NOD-SCID mice, which displayed >70% with in 28 d. Since anti-angiogenic therapies (AAT) were used as an adjuvant against VEGF-VEGFR pathway to normalize blood vessels in glioblastoma (GBM), which resulted into marked hypoxia and recruited BMDCs to the tumor microenvironment (TME). We exploited chimeric mice in athymic nude background to develop orthotopic U251 tumor and tested receptor tyrosine kinase inhibitors and CXCR4 antagonist against GBM. We were able to track GFP+ BMDCs in the tumor brain using highly sensitive multispectral optical imaging instrument. Increased tumor growth associated with the infiltration of GFP+ BMDCs acquiring suppressive myeloid and endothelial phenotypes was seen in TME following treatments. Immunofluorescence study showed GFP+ cells accumulated at the site of VEGF, SDF1 and PDGF expression, and at the periphery of the tumors following treatments. In conclusion, we developed a preclinical chimeric model of GBM and phenotypes of tumor infiltrated BMDCs were investigated in context of AATs. Chimeric mouse model could be used to study detailed cellular and molecular mechanisms of interaction of BMDCs and TME in cancer.

Bone marrow derived myeloid cells orchestrate antiangiogenic resistance in glioblastoma through coordinated molecular networks

Glioblastoma (GBM) is a hypervascular and malignant form of brain tumors. Anti-angiogenic therapies (AAT) were used as an adjuvant against VEGF-VEGFR pathway to normalize blood vessels in clinical and preclinical studies, which resulted into marked hypoxia and recruited bone marrow derived cells (BMDCs) to the tumor microenvironment (TME). In vivo animal models to track BMDCs and investigate molecular mechanisms in AAT resistance are rare. We exploited recently established chimeric mouse to develop orthotopic U251 tumor, which uses as low as 5 × 10(6) GFP+ BM cells in athymic nude mice and engrafted >70% GFP+ cells within 14 days. Our unpublished data and published studies have indicated the involvement of immunosuppressive myeloid cells in therapeutic resistance in glioma. Similarly, in the present study, vatalanib significantly increased CD68+ myeloid cells, and CD133+, CD34+ and Tie2+ endothelial cell signatures. Therefore, we tested inhibition of CSF1R+ myeloid cells using GW2580 that reduced tumor growth by decreasing myeloid (Gr1+ CD11b+ and F4/80+) and angiogenic (CD202b+ and VEGFR2+) cell signatures in TME. CSF1R blockade significantly decreased inflammatory, proangiogenic and immunosuppressive molecular signatures compared to vehicle, vatalanib or combination. TCK1 or CXCL7, a potent chemoattractant and activator of neutrophils, was observed as most significantly decreased cytokine in CSF1R blockade. ERK MAPK pathway was involved in cytokine network regulation. In conclusion, present study confirmed the contribution of myeloid cells in GBM development and therapeutic resistance using chimeric mouse model. We identified novel molecular networks including CXCL7 chemokine as a promising target for future studies. Nonetheless, survival studies are required to assess the beneficial effect of CSF1R blockade.

Bone marrow-derived vascular modulatory cells in pulmonary arterial hypertension

Hematopoiesis and vascular homeostasis are closely linked to each other via subsets of circulating bone marrow-derived cells with potent activity to repair endothelial injury and promote angiogenesis. As a consequence, abnormalities in hematopoiesis will eventually affect vascular health. Pulmonary arterial hypertension (PAH) is a vascular disease characterized by severe remodeling of the pulmonary artery wall. Over the past decade, circulating hematopoietic cells have been assigned an increasing role in the remodeling, such that these cells have been used in new therapeutic strategies. More recently, research has been extended to the bone marrow where these cells originate to identify abnormalities in hematopoiesis that may underlie PAH. Here, we review the current literature and identify gaps in knowledge of the myeloid effects on PAH.

Myeloid Derived Suppressor Cells: Fuel the Fire

Low oxygen tension, hypoxia, is a characteristic of many tumors and associated with the poor prognosis. Hypoxia invites bone marrow derived cells (BMDCs) from bone marrow to the site of tumor. These recruited CXCR4+ BMDCs provide favorable environment for the tumor growth by acquiring pro-angiogenic phenotype such as CD45+VEGFR2+ Endothelial Progenitor Cells (EPC), or CD45+Tie2+ myeloid cells. CD11b+CD13+ myeloid population of the BMDCs modulate tumor progression. These myeloid populations retain immunosuppressive characteristics, for example, myeloid derived suppressor cells (MDSCs), and regulates immune- suppression by inhibiting cytotoxic T cell function. In addition, MDSCs were observed at the premetastatic niche of the distant organs in other tumors. Protumorigenic and prometastatic role of the myeloid cells provides a basis for therapeutic targeting of immunosuppression and thus inhibiting tumor development and metastasis.

Human endothelial progenitor cells

Human endothelial progenitor cells (EPCs) have been generally defined as circulating cells that express a variety of cell surface markers similar to those expressed by vascular endothelial cells, adhere to endothelium at sites of hypoxia/ischemia, and participate in new vessel formation. Although no specific marker for an EPC has been identified, a panel of markers has been consistently used as a surrogate marker for cells displaying the vascular regenerative properties of the putative EPC. However, it is now clear that a host of hematopoietic and vascular endothelial subsets display the same panel of antigens and can only be discriminated by an extensive gene expression analysis or use of a variety of functional assays that are not often applied. This article reviews our current understanding of the many cell subsets that constitute the term EPC and provides a concluding perspective as to the various roles played by these circulating or resident cells in vessel repair and regeneration in human subjects.

Butein Inhibits Angiogenesis of Human Endothelial Progenitor Cells via the Translation Dependent Signaling Pathway

Compelling evidence indicates that bone marrow-derived endothelial progenitor cells (EPCs) can contribute to postnatal neovascularization and tumor angiogenesis. EPCs have been shown to play a "catalytic" role in metastatic progression by mediating the angiogenic switch. Understanding the pharmacological functions and molecular targets of natural products is critical for drug development. Butein, a natural chalcone derivative, has been reported to exert potent anticancer activity. However, the antiangiogenic activity of butein has not been addressed. In this study, we found that butein inhibited serum- and vascular endothelial growth factor- (VEGF-) induced cell proliferation, migration, and tube formation of human EPCs in a concentration dependent manner without cytotoxic effect. Furthermore, butein markedly abrogated VEGF-induced vessels sprouting from aortic rings and suppressed microvessel formation in the Matrigel implant assay in vivo. In addition, butein concentration-dependently repressed the phosphorylation of Akt, mTOR, and the major downstream effectors, p70S6K, 4E-BP1, and eIF4E in EPCs. Taken together, our results demonstrate for the first time that butein exhibits the antiangiogenic effect both in vitro and in vivo by targeting the translational machinery. Butein is a promising angiogenesis inhibitor with the potential for treatment of cancer and other angiogenesis-related diseases.

TIMP-2 targets tumor-associated myeloid suppressor cells with effects in cancer immune dysfunction and angiogenesis

Angiogenesis and inflammation are important therapeutic targets in non-small cell lung cancer (NSCLC). It is well known that proteolysis mediated by matrix metalloproteinases (MMPs) promotes angiogenesis and inflammation in the tumor microenvironment. Here, the effects of the MMP inhibitor TIMP-2 on NSCLC inflammation and angiogenesis were evaluated in TIMP-2-deficient (timp2-/-) mice injected subcutaneously (SC) with Lewis lung carcinoma cells and compared with the effects on tumors in wild-type mice. TIMP-2-deficient mice demonstrated increased tumor growth, enhanced expression of angiogenic marker αvβ3 in tumor and endothelial cells, and significantly higher serum vascular endothelial growth factor-A levels. Tumor-bearing timp2-/- mice showed a significant number of inflammatory cells in their tumors, upregulation of inflammation mediators, nuclear factor-kappaB, and Annexin A1, as well as higher levels of serum interleukin (IL)-6. Phenotypic analysis revealed an increase in myeloid-derived suppressor cell (MDSC) cells (CD11b+ and Gr-1+) that coexpressed vascular-endothelial-growth factor receptor 1 (VEGF-R1) and elevated MMP activation present in tumors and spleens from timp2-/- mice. Furthermore, TIMP-2-deficient tumors upregulated expression of the immunosuppressing genes controlling MDSC growth, IL-10, IL-13, IL-11, and chemokine ligand (CCL-5/RANTES), and decreased interferon-γ and increased CD40L. Moreover, forced TIMP-2 expression in human lung adenocarcinoma A-549 resulted in a significant reduction of MDSCs recruited into tumors, as well as suppression of angiogenesis and tumor growth. The increase in MDSCs has been linked to cancer immunosuppression and angiogenesis. Therefore, this study supports TIMP-2 as a negative regulator of MDSCs with important implications for the immunotherapy and/or antiangiogenic treatment of NSCLC.

Cyclophosphamide creates a receptive microenvironment for prostate cancer skeletal metastasis

A number of cancers predominantly metastasize to bone, due to its complex microenvironment and multiple types of constitutive cells. Prostate cancer especially has been shown to localize preferentially to bones with higher marrow cellularity. Using an experimental prostate cancer metastasis model, we investigated the effects of cyclophosphamide, a bone marrow-suppressive chemotherapeutic drug, on the development and growth of metastatic tumors in bone. Priming the murine host with cyclophosphamide before intracardiac tumor cell inoculation was found to significantly promote tumor localization and subsequent growth in bone. Shortly after cyclophosphamide treatment, there was an abrupt expansion of myeloid lineage cells in the bone marrow and the peripheral blood, associated with increases in cytokines with myelogenic potential such as C-C chemokine ligand (CCL)2, interleukin (IL)-6, and VEGF-A. More importantly, neutralizing host-derived murine CCL2, but not IL-6, in the premetastatic murine host significantly reduced the prometastatic effects of cyclophosphamide. Together, our findings suggest that bone marrow perturbation by cytotoxic chemotherapy can contribute to bone metastasis via a transient increase in bone marrow myeloid cells and myelogenic cytokines. These changes can be reversed by inhibition of CCL2.

Issues to be considered when studying cancer in vitro

Various cancer treatment approaches have shown promising results when tested preclinically. The results of clinical trials, however, are often disappointing. While searching for the reasons responsible for their failures, the relevance of experimental and preclinical models has to be taken into account. Possible factors that should be considered, including cell modifications during in vitro cultivation, lack of both the relevant interactions and the structural context in vitro have been summarized in the present review.

Reversing resistance to vascular-disrupting agents by blocking late mobilization of circulating endothelial progenitor cells

The prevailing concept is that immediate mobilization of bone marrow-derived circulating endothelial progenitor cells (CEP) is a key mechanism mediating tumor resistance to vascular-disrupting agents (VDA). Here, we show that administration of VDA to tumor-bearing mice induces 2 distinct peaks in CEPs: an early, unspecific CEP efflux followed by a late yet more dramatic tumor-specific CEP burst that infiltrates tumors and is recruited to vessels. Combination with antiangiogenic drugs could not disrupt the early peak but completely abrogated the late VDA-induced CEP burst, blunted bone marrow-derived cell recruitment to tumors, and resulted in striking antitumor efficacy, indicating that the late CEP burst might be crucial to tumor recovery after VDA therapy. CEP and circulating endothelial cell kinetics in VDA-treated patients with cancer were remarkably consistent with our preclinical data. These findings expand the current understanding of vasculogenic "rebounds" that may be targeted to improve VDA-based strategies.

SIGNIFICANCE

Our findings suggest that resistance to VDA therapy may be strongly mediated by late, rather than early, tumor-specific recruitment of CEPs, the suppression of which resulted in increased VDA-mediated antitumor efficacy. VDA-based therapy might thus be significantly enhanced by combination strategies targeting late CEP mobilization.

Prognostic value of circulating VEGFR2+ bone marrow-derived progenitor cells in patients with advanced cancer

We hypothesised that host-related markers, possibly reflecting tumour aggressiveness, such as circulating endothelial cells (CEC) and circulating VEGFR2(+) bone marrow-derived (BMD) progenitor cells, could have prognostic value in patients with advanced cancer enrolled in early anticancer drug development trials. Baseline CECs (CD45(-)CD31(+)CD146(+)7AAD(-) cells) and circulating VEGFR2(+)-BMD progenitor cells (defined as CD45(dim)CD34(+)VEGFR2(+)7AAD(-) cells) were measured by flow-cytometry in 71 and 58 patients included in phase 1 trials testing novel anti-vascular or anti-angiogenic agents. Correlations between levels of CECs, circulating VEGFR2(+)-BMD progenitor cells, clinical and biological prognostic factors (i.e. the Royal Marsden Hospital (RMH) score), and overall survival (OS) were studied. The median value of CECs was 12 CEC/ml (range 0-154/ml). The median level of VEGFR2(+)-BMD progenitor cells was 1.3% (range 0-32.5%) of circulating BMD-CD34(+) progenitors. While OS was not correlated with CEC levels, it was significantly worse in patients with high VEGFR2(+)-BMD progenitor levels (>1%) (median OS 9.0 versus 17.0 months), and with a RMH prognostic score >0 (median OS 9.0 versus 24.2 months). The prognostic value of VEGFR2(+)-BMD progenitor levels remained significant (hazard ratio (HR) = 2.3, 95% confidence interval (CI), 1.1-4.6, p = 0.02) after multivariate analysis. A composite VEGFR2(+)-BMD progenitor level/RHM score ≥ 2 was significantly associated with an increased risk of death compared to scores of 0 or 1 (median OS 9.0 versus 18.4 months, HR = 2.6 (95%CI, 1.2-5.8, p = 0.02)). High circulating VEGFR2(+)-BMD progenitor levels are associated with poor prognostics and when combined to classical clinical and biological parameters could provide a new tool for patient selection in early anticancer drug trials.

The white adipose tissue used in lipotransfer procedures is a rich reservoir of CD34+ progenitors able to promote cancer progression

Previous studies have suggested a "catalytic role" in neoplastic angiogenesis and cancer progression for bone marrow-derived endothelial progenitor cells (EPC). However, preclinical and clinical studies have shown that the quantitative role of marrow-derived EPCs in cancer vascularization is extremely variable. We have found that human and murine white adipose tissue (WAT) is a very rich reservoir of CD45-CD34(+) EPCs with endothelial differentiation potential, containing a mean of 263 times more CD45-CD34(+) cells/mL than bone marrow. Compared with marrow-derived CD34(+) cells mobilized in blood by granulocyte colony-stimulating factor, purified WAT-CD34(+) cells expressed similar levels of stemness-related genes, significantly increased levels of angiogenesis-related genes, and increased levels of FAP-α, a crucial suppressor of antitumor immunity. In vitro, WAT-CD34(+) cells generated mature endothelial cells and capillary tubes as efficiently as mature mesenchymal cells. The coinjection of human WAT-CD34(+) cells from lipotransfer procedures contributed to tumor vascularization and significantly increased tumor growth and metastases in several orthotopic models of human breast cancer in immunodeficient mice. Endothelial cells derived from human WAT-CD34(+) cells lined the lumen of cancer vessels. These data indicate that CD34(+) WAT cells can promote cancer progression and metastases. Our results highlight the importance of gaining a better understanding of the role of different WAT-derived cells used in lipotransfer for breast reconstruction in patients with breast cancer.

New facets of matrix metalloproteinases MMP-2 and MMP-9 as cell surface transducers: outside-in signaling and relationship to tumor progression

This review focuses on matrix metalloproteinases (MMPs)-2 (gelatinase A) and -9 (gelatinase B), both of which are cancer-associated, secreted, zinc-dependent endopeptidases. Gelatinases cleave many different targets (extracellular matrix, cytokines, growth factors, chemokines and cytokine/growth factor receptors) that in turn regulate key signaling pathways in cell growth, migration, invasion, inflammation and angiogenesis. Interactions with cell surface integral membrane proteins (CD44, αVβ/αβ1/αβ2 integrins and Ku protein) can occur through the gelatinases' active site or hemopexin-like C-terminal domain. This review evaluates the recent literature on the non-enzymatic, signal transduction roles of surface-bound gelatinases and their subsequent effects on cell survival, migration and angiogenesis. Gelatinases have long been drug targets. The current status of gelatinase inhibitors as anticancer agents and their failure in the clinic is discussed in light of these new data on the gelatinases' roles as cell surface transducers - data that may lead to the design and development of novel, gelatinase-targeting inhibitors.

Proangiogenic Factor PlGF Programs CD11b+ Myelomonocytes in Breast Cancer during Differentiation of Their Hematopoietic Progenitors

Tumor-mobilized bone marrow–derived CD11b+ myeloid cells promote tumor angiogenesis, but how and when these cells acquire proangiogenic properties is not fully elucidated. Here, we show that CD11b+ myelomonocytic cells develop proangiogenic properties during their differentiation from CD34+ hematopoietic progenitors and that placenta growth factor (PlGF) is critical in promoting this education. Cultures of human CD34+ progenitors supplemented with conditioned medium from breast cancer cell lines or PlGF, but not from nontumorigenic breast epithelial lines, generate CD11b+ cells capable of inducing endothelial cell sprouting in vitro and angiogenesis in vivo. An anti–Flt-1 mAb or soluble Flt-1 abolished the generation of proangiogenic activity during differentiation from progenitor cells. Moreover, inhibition of metalloproteinase activity, but not VEGF, during the endothelial sprouting assay blocked sprouting induced by these proangiogenic CD11b+ myelomonocytes. In a mouse model of breast cancer, circulating CD11b+ cells were proangiogenic in the sprouting assays. Silencing of PlGF in tumor cells prevented the generation of proangiogenic activity in circulating CD11b+ cells, inhibited tumor blood flow, and slowed tumor growth. Peripheral blood of breast cancer patients at diagnosis, but not of healthy individuals, contained elevated levels of PlGF and circulating proangiogenic CD11b+ myelomonocytes. Taken together, our results show that cancer cells can program proangiogenic activity in CD11b+ myelomonocytes during differentiation of their progenitor cells in a PlGF-dependent manner. These findings impact breast cancer biology, detection, and treatment. Cancer Res; 71(11); 3781–91. ©2011 AACR.

CEACAM1 creates a pro-angiogenic tumor microenvironment that supports tumor vessel maturation

We have studied the effects of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) on tumor angiogenesis in murine ductal mammary adenocarcinomas. We crossed transgenic mice with whey acidic protein promoter-driven large T-antigen expression (WAP-T mice) with oncogene-induced mammary carcinogenesis with CEACAM1null mice, and with Tie2-Ceacam1 transgenics, in which the Tie2 promoter drives endothelial overexpression of CEACAM1 (WAP-T × CEACAM1(endo+) mice), and analyzed tumor vascularization, angiogenesis and vessel maturation in these mice. Using flat-panel volume computed tomography (fpVCT) and histology, we found that WAP-T × CEACAM1(endo+) mice exhibited enhanced tumoral vascularization owing to CEACAM1(+) vessels in the tumor periphery, and increased intratumoral angiogenesis compared with controls. In contrast, vascularization of CEACAM1null/WAP-T-derived tumors was poor, and tumor vessels were dilated, leaky and showed poor pericyte coverage. Consequently, the tumoral vasculature could not be visualized in CEACAM1null/WAP-T mice by fpVCT, and we observed poor organization of the perivascular extracellular matrix (ECM), accompanied by the accumulation of collagen IV-degrading matrix metalloproteinase 9(+) (MMP9(+)) leukocytes and stromal cells. Vascular instability and alterations in ECM structure were accompanied by a significant increase in pulmonary metastases in CEACAM1null/WAP-T mice, whereas only occasional metastases were observed in CEACAM1(+) hosts. In CEACAM1(+) hosts, intratumoral vessels did not express CEACAM1, but they were intact, extensively covered with pericytes and framed by a well-organized perivascular ECM. MMP9(+) accessory cells were largely absent. Orthotopic transplantation of primary WAP-T- and CEACAM1null/WAP-T tumors into all three mouse lines confirmed that a CEACAM1(+) host environment is a prerequisite for productive angiogenic remodeling of the tumor microenvironment. Hence, CEACAM1 expression in the tumor periphery determines the vascular phenotype in a tumor, whereas systemic absence of CEACAM1 interferes with the formation of an organized tumor matrix and intratumoral vessel maturation.

Up-regulated myeloid-derived suppressor cell contributes to hepatocellular carcinoma development by impairing dendritic cell function

OBJECTIVE

Defective immune function is an important cause of tumor development. Accumulation of myeloid-derived suppressor cell (MDSC) associated with inhibition of dendritic cell (DC) function is one of the major immunological abnormalities in cancer. However, the molecular mechanism of the phenomenon remains unclear.

MATERIAL AND METHODS

We evaluated T cell stimulatory activity and interleukin (IL)-12 production of DC in a mouse model of liver cancer (hepatocellular carcinoma [HCC] mice). Then we detected the frequency of MDSC in spleen, peripheral blood (PB), lymph node (LN) and tumor tissue of HCC mice and its potential mechanisms. We also evaluated IL-10 production of MDSC and mechanism by which MDSC inhibit DC function.

RESULTS

Toll-like receptor (TLR)-ligand (LPS, CpG, poly(I:C))-induced IL-12 production of DC was decreased in HCC mice compared with control. The T cell stimulatory activity of DC was lower in HCC mice than in controls. Meanwhile, an increase in the frequency of MDSC in tumor development was detected in spleen, PB, LN and tumor, and the IL-10 levels were higher in HCC mice derived MDSC than in control. Furthermore, the MDSC inhibited TLR-ligand-induced IL-12 production of DC by IL-10 production and suppressed T cell stimulatory activity of DC. Finally, we demonstrated that the increase in the frequency of MDSC was mediated by MyD88-NF-kB pathway.

CONCLUSIONS

Our study suggests a new role for MDSCs in HCC development by suppressing host immune responses, and these findings have important implications when designing immunotherapy protocols.

Circulating endothelial and endothelial progenitor cells in non-small-cell lung cancer

New treatments have recently been introduced for treating non-small-cell lung cancer. Chemotherapeutic agents, such as pemetrexed, and targeted therapies, such as bevacizumab, erlotinib or gefitinib, have extended treatment options for selected histological subgroups. Antiangiogenic treatments, either associated with conventional chemotherapeutic drugs or given alone as maintenance therapy, constitute an active clinical research field. However, not all lung cancer patients benefit from antiangiogenic compounds. Moreover, tumour response assessment is often difficult when using these drugs, since targeted therapies generally do not cause rapid and measurable tumour shrinkage but, rather, long stabilisations and slight density changes on imaging tests. The finding of clinical or biological factors that might identify patients who will better benefit from these treatments, as well as identifying surrogate markers of tumour response and prognosis, is an issue of great interest. In that sense, different research lines have investigated the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor receptor (VEGFR) pathways. Circulating endothelial (CECs) and endothelial progenitor cells (CEPCs) are of prognostic value in different types of cancers, and relevant data are published about their potential usefulness as predictors of response to chemotherapy and antiangiogenic treatments. In this review, we discuss the data available on the role of CECs and CEPCs as prognostic factors and as surrogate markers of treatment response in non-small-cell lung cancer.

Roles of sphingosine-1-phosphate signaling in angiogenesis

Sphingosine-1-phosphate (S1P) is a blood-borne lipid mediator with pleiotropic biological activities. S1P acts via the specific cell surface G-protein-coupled receptors, S1P_1-5. S1P₁ and S1P₂ were originally identified from vascular endothelial cells (ECs) and smooth muscle cells, respectively. Emerging evidence shows that S1P plays crucial roles in the regulation of vascular functions, including vascular formation, barrier protection and vascular tone via S1P₁, S1P₂ and S1P₃. In particular, S1P regulates vascular formation through multiple mechanisms; S1P exerts both positive and negative effects on angiogenesis and vascular maturation. The positive and negative effects of S1P are mediated by S1P₁ and S1P₂, respectively. These effects of S1P₁ and S1P₂ are probably mediated by the S1P receptors expressed in multiple cell types including ECs and bone-marrow-derived cells. The receptor-subtype-specific, distinct effects of S1P favor the development of novel therapeutic tactics for antitumor angiogenesis in cancer and therapeutic angiogenesis in ischemic diseases.

Hsp90 as a gatekeeper of tumor angiogenesis: clinical promise and potential pitfalls

Tumor vascularization is an essential modulator of early tumor growth, progression, and therapeutic outcome. Although antiangiogenic treatments appear promising, intrinsic and acquired tumor resistance contributes to treatment failure. Clinical inhibition of the molecular chaperone heat shock protein 90 (Hsp90) provides an opportunity to target multiple aspects of this signaling resiliency, which may elicit more robust and enduring tumor repression relative to effects elicited by specifically targeted agents. This review highlights several primary effectors of angiogenesis modulated by Hsp90 and describes the clinical challenges posed by the redundant circuitry of these pathways. The four main topics addressed include (1) Hsp90-mediated regulation of HIF/VEGF signaling, (2) chaperone-dependent regulation of HIF-independent VEGF-mediated angiogenesis, (3) Hsp90-dependent targeting of key proangiogenic receptor tyrosine kinases and modulation of drug resistance, and (4) consideration of factors such as tumor microenvironment that pose several challenges for the clinical efficacy of anti-angiogenic therapy and Hsp90-targeted strategies.

Cellular and soluble markers of tumor angiogenesis: from patient selection to the identification of the most appropriate postresistance therapy

Antiangiogenic drugs are now intensively used in clinical oncology, but some drawbacks still hamper their development. First, it is frequently unclear what patient subpopulation is likely to gain clinical benefit from these expensive therapies; second, there is evidence of (sometimes rapid) development of drug resistance in many patients; third, the results of some preclinical and clinical studies have suggested acceleration of malignant cell aggressiveness when some antiangiogenic therapies are terminated. Here we discuss the role of soluble molecules and cellular markers of neoplastic angiogenesis for patient selection and follow-up during treatment. These markers should help clinicians to decide the right therapy, advise them of the generation of mechanisms of drug resistance during antiangiogenic treatment, and finally suggest the most appropriate next line of therapy according to the new patterns of cancer vascularization induced by antiangiogenic therapies.

Molecular pathways and targets in cancer-related inflammation

Selected inflammatory conditions increase the risk of cancer. An inflammatory component is present also in the micro-environment of tumours epidemiologically unrelated to inflammation. An intrinsic (driven by genetic events that cause neoplasia) and an extrinsic (driven by inflammatory conditions which predispose to cancer) pathway link inflammation and cancer. Smouldering inflammation in the tumour microenvironment contributes to proliferation and survival of malignant cells, angiogenesis, metastasis, subversion of adaptive immunity, response to hormones, and chemotherapeutic agents. Emerging evidence also suggests that cancer-related inflammation promotes genetic instability. Thus, cancer-related inflammation represents a target for innovative diagnostic and therapeutic strategies.

Endothelial dysfunction in diabetes: potential application of circulating markers as advanced diagnostic and prognostic tools

Endothelial dysfunction is a predisposing factor for vascular disease in diabetes, which contributes significantly to the mortality of diabetic patients. The currently utilized assessment methods of endothelial function/dysfunction in humans are associated with various limitations. Circulating endothelial-derived/associated markers have been proposed as potential alternatives for evaluation of the endothelium in condition of vascular disorders. These indicators include von Willebrand factor, soluble thrombomodulin, soluble E-selectin, asymmetric dimethylarginine, tissue plasminogen activator, endothelial microparticles, circulating endothelial cells and circulating endothelial progenitor cells. While tentative evidence is available for most of these biomarkers to serve as reliable sources of information, their usefulness for routine clinical applications has not yet been established. Thus, circulating endothelial markers are currently the subject of intense research interest and it is anticipated that as more information becomes available their improved quantification will provide a suitable diagnostic and prognostic tool for vascular events in diabetes and related diseases.

Phosphatidylinositol 3,4,5-triphosphate-dependent Rac exchanger 1 (P-Rex-1), a guanine nucleotide exchange factor for Rac, mediates angiogenic responses to stromal cell-derived factor-1/chemokine stromal cell derived factor-1 (SDF-1/CXCL-12) linked to Rac activation, endothelial cell migration, and in vitro angiogenesis

Stromal cell-derived factor-1 (SDF-1/CXCL-12) and vascular endothelial growth factor (VEGF), which can be secreted by hypoxic tumors, promote the generation of new blood vessels. These potent angiogenic factors stimulate endothelial cell migration via the activation of Rho GTPases and the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway. Thus, characterization of guanine nucleotide exchange factors critical in the angiogenic signaling cascades offers the possibility of identifying novel molecular targets. We demonstrated previously that mammalian target of rapamycin, an important effector and regulator of PI3K/AKT, activates phosphatidylinositol 3,4,5-triphosphate-dependent Rac exchanger 1 (P-Rex1), a Rac guanine nucleotide exchange factor identified as a target of G betagamma and PI3K, via direct interactions. In this study, we tested the hypothesis that P-Rex1 is involved in the angiogenic responses elicited by SDF-1 and VEGF. Using a knockdown approach, we demonstrate that P-Rex1 is indeed required for SDF-1 promoted signaling pathway, because there is decreased Rac activation, cell migration, and in vitro angiogenesis in P-Rex1 knockdown cells stimulated with SDF-1. In contrast, P-Rex1 knockdown does not affect responses to VEGF, and signaling to extracellular signal-regulated kinase in response to either angiogenic factor is not sensitive to P-Rex1 knockdown. We also demonstrate that in endothelial cells, VEGF promotes an increase in the expression of endogenous P-Rex1 and the SDF-1 receptor CXCR4, In addition, VEGF-pretreated cells show an increased migratory and angiogenic response to SDF-1, suggesting that VEGF stimulation can complement SDF-1/CXCR4 signaling to induce angiogenesis. We conclude that P-Rex1 is a key element in SDF-1-induced angiogenic responses and a potential target for therapeutic intervention.

Circulating endothelial cells as biomarkers in clinical oncology

Circulating endothelial cells (CECs) and circulating endothelial progenitors (CEPs) play a different role in cancer development, acting as possible markers of vascular turnover/damage (CECs) and vasculogenesis (CEPs). Preclinical and clinical data suggest that CEC enumeration might be useful to define the best treatment option for patients who are candidate to anti-angiogenic therapy, while CEPs seem to have a "catalytic" role in different steps of cancer progression and recurrence after therapy. The definition of CEC and CEP phenotype and the standardization of CEC and CEP enumeration procedures are highly warranted to use these cells as biomarkers in clinical trials in oncology, and to compare results from different studies.

Instructive role of the vascular niche in promoting tumour growth and tissue repair by angiocrine factors

The precise mechanisms whereby anti-angiogenesis therapy blocks tumour growth or causes vascular toxicity are unknown. We propose that endothelial cells establish a vascular niche that promotes tumour growth and tissue repair not only by delivering nutrients and O2 but also through an 'angiocrine' mechanism by producing stem and progenitor cell-active trophogens. Identification of endothelial-derived instructive angiocrine factors will allow direct tumour targeting, while diminishing the unwanted side effects associated with the use of anti-angiogenic agents.

COX-2 and prostaglandin EP3/EP4 signaling regulate the tumor stromal proangiogenic microenvironment via CXCL12-CXCR4 chemokine systems

Bone marrow (BM)-derived hematopoietic cells, which are major components of tumor stroma, determine the tumor microenvironment and regulate tumor phenotypes. Cyclooxygenase (COX)-2 and endogenous prostaglandins are important determinants for tumor growth and tumor-associated angiogenesis; however, their contributions to stromal formation and angiogenesis remain unclear. In this study, we observed that Lewis lung carcinoma cells implanted in wild-type mice formed a tumor mass with extensive stromal formation that was markedly suppressed by COX-2 inhibition, which reduced the recruitment of BM cells. Notably, COX-2 inhibition attenuated CXCL12/CXCR4 expression as well as expression of several other chemokines. Indeed, in a Matrigel model, prostaglandin (PG) E2 enhanced stromal formation and CXCL12/CXCR4 expression. In addition, a COX-2 inhibitor suppressed stromal formation and reduced expression of CXCL12/CXCR4 and a fibroblast marker (S100A4) in a micropore chamber model. Moreover, stromal formation after tumor implantation was suppressed in EP3-/- mice and EP4-/- mice, in which stromal expression of CXCL12/CXCR4 and S100A4 was reduced. The EP3 or EP4 knockout suppressed S100A4+ fibroblasts, CXCL12+, and/or CXCR4+ stromal cells as well. Immunofluorescent analyses revealed that CXCL12+CXCR4+S100A4+ fibroblasts mainly comprised stromal cells and most of these were recruited from the BM. Additionally, either EP3- or EP4-specific agonists stimulated CXCL12 expression by fibroblasts in vitro. The present results address the novel activities of COX-2/PGE2-EP3/EP4 signaling that modulate tumor biology and show that CXCL12/CXCR4 axis may play a crucial role in tumor stromal formation and angiogenesis under the control of prostaglandins.

S1P(2), the G protein-coupled receptor for sphingosine-1-phosphate, negatively regulates tumor angiogenesis and tumor growth in vivo in mice

Sphingosine-1-phosphate (S1P) has been implicated in tumor angiogenesis by acting through the G(i)-coupled chemotactic receptor S1P(1). Here, we report that the distinct receptor S1P(2) is responsible for mediating the G(12/13)/Rho-dependent inhibitory effects of S1P on Akt, Rac, and cell migration, thereby negatively regulating tumor angiogenesis and tumor growth. By using S1P(2)(LacZ/+) mice, we found that S1P(2) was expressed in both tumor and normal blood vessels in many organs, in both endothelial cells (EC) and vascular smooth muscle cells, as well as in tumor-associated, CD11b-positive bone marrow-derived cells (BMDC). Lewis lung carcinoma or B16 melanoma cells implanted in S1P(2)-deficient (S1P(2)(-/-)) mice displayed accelerated tumor growth and angiogenesis with enhanced association of vascular smooth muscle cells and pericytes. S1P(2)(-/-) ECs exhibited enhanced Rac activity, Akt phosphorylation, cell migration, proliferation, and tube formation in vitro. Coinjection of S1P(2)(-/-) ECs and tumor cells into wild-type mice also produced a relative enhancement of tumor growth and angiogenesis in vivo. S1P(2)(-/-) mice were also more efficient at recruiting CD11b-positive BMDCs into tumors compared with wild-type siblings. Bone marrow chimera experiments revealed that S1P(2) acted in BMDCs to promote tumor growth and angiogenesis. Our results indicate that, in contrast to endothelial S1P(1), which stimulates tumor angiogenesis, S1P(2) on ECs and BMDCs mediates a potent inhibition of tumor angiogenesis, suggesting a novel therapeutic tactic for anticancer treatment.

Myeloid-derived suppressor cells in mammary tumor progression in FVB Neu transgenic mice

Female mice transgenic for the rat proto-oncogene c-erb-B2, under control of the mouse mammary tumor virus (MMTV) promoter (neuN), spontaneously develop metastatic mammary carcinomas. The development of these mammary tumors is associated with increased number of GR-1(+)CD11b(+) myeloid derived suppressor cells (MDSCs) in the peripheral blood (PB), spleen and tumor. We report a complex relationship between tumor growth, MDSCs and immune regulatory molecules in non-mutated neu transgenic mice on a FVB background (FVB-neuN). The first and second tumors in FVB-neuN mice develop at a median of 265 (147-579) and 329 (161-523) days, respectively, resulting in a median survival time (MST) of 432 (201 to >500) days. During tumor growth, significantly increased number of MDSCs is observed in the PB and spleen, as well as, in infiltrating the mammary tumors. Our results demonstrate a direct correlation between tumor size and the number of MDSCs infiltrating the tumor and an inverse relationship between the frequency of CD4(+) T-cells and MDSCs in the spleen. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assessment of enzyme and cytokine transcript levels in the spleen, tumor, tumor-infiltrating non-parenchymal cells (NPCs) and mammary glands revealed a significant increase in transcript levels from grossly normal mammary glands and tumor-infiltrating NPCs during tumor progression. Tumor NPCs, as compared to spleen cells from wild-type (w/t) mice, expressed significantly higher levels of arginase-1 (ARG-1), nitric oxide synthase (NOS-2), vascular endothelial growth factor (VEGF-A) and significantly lower levels of interferon (IFN)-gamma, interleukin (IL)-2 and fms-like tyrosine kinase-3 ligand (Flt3L) transcript levels. Transcript levels in the spleens of tumor-bearing (TB) mice also differed from normal mice, although to a lesser extent than transcript levels from tumor-infiltrating NPCs. Furthermore, both spleen cells and NPCs from TB mice, but not control mice, suppressed alloantigen responses by syngeneic control spleen cells. Correlative studies revealed that the number of MDSCs in the spleen was directly associated with granulocyte colony stimulating factor (G-CSF) transcript levels in the spleen; while the number of MDSCs in the tumors was directly correlated with splenic granulocyte macrophage stimulating factor (GM-CSF) transcript levels, tumor volume and tumor cell number. Together our results support a role for MDSCs in tumor initiation and progressive, T-cell depression and loss of function provide evidence which support multiple mechanisms of MDSC expansion in a site-dependent manner.

Human inflammatory synovial fibroblasts induce enhanced myeloid cell recruitment and angiogenesis through a hypoxia-inducible transcription factor 1alpha/vascular endothelial growth factor-mediated pathway in immunodeficient mice

OBJECTIVE

Hyperplasia and phenotypic changes in fibroblasts are often observed in chronic inflammatory lesions, and yet the autonomous pathogenic contribution of these changes is uncertain. The purpose of this study was to analyze the intrinsic ability of fibroblasts from chronically inflamed synovial tissue to drive cell recruitment and angiogenesis.

METHODS

Fibroblasts from patients with rheumatoid arthritis (RA) or osteoarthritis (OA), as well as fibroblasts from healthy synovial tissue and healthy skin, were cultured and subcutaneously engrafted into immunodeficient mice. Cell infiltration and angiogenesis were analyzed in the grafts by immunohistochemical studies. The role of vascular endothelial growth factor (VEGF), CXCL12, and hypoxia-inducible transcription factor 1alpha (HIF-1alpha) in these processes was investigated using specific antagonists or small interfering RNA (siRNA)-mediated down-regulation of HIF-1alpha in fibroblasts.

RESULTS

Inflammatory (OA and RA) synovial fibroblasts, compared with healthy dermal or synovial tissue fibroblasts, induced a significant enhancement in myeloid cell infiltration and angiogenesis in immunodeficient mice. These activities were associated with increased constitutive and hypoxia-induced expression of VEGF, but not CXCL12, in inflammatory fibroblasts compared with healthy fibroblasts. VEGF and CXCL12 antagonists significantly reduced myeloid cell infiltration and angiogenesis. Furthermore, targeting of HIF-1alpha expression by siRNA or of HIF-1alpha transcriptional activity by the small molecule chetomin in RA fibroblasts significantly reduced both responses.

CONCLUSION

These results demonstrate that chronic synovial inflammation is associated with stable fibroblast changes that, under hypoxic conditions, are sufficient to induce inflammatory cell recruitment and angiogenesis, both of which are processes relevant to the perpetuation of chronic inflammation.

Pleiotropic roles of matrix metalloproteinases in tumor angiogenesis: contrasting, overlapping and compensatory functions

A number of extensive reviews are available discussing the roles of MMPs in various aspects of cancer progression from benign tumor formation to overt cancer present with deadly metastases. This review will focus specifically on the evidence functionally linking the MMPs and tumor-induced angiogenesis in various in vivo models. Emphasis has been placed on the cellular origin of the MMPs in tumor tissue, the requirement of proMMP activation and the resulting proteolytic activity for the induction and progression of tumor angiogenesis, and the pleiotropic roles for some of the MMPs. The functional mechanisms of the angiogenic MMPs are discussed as well as their catalytic detection in complex biological systems. In addition, the contribution of active MMPs to metastatic spread and establishment of secondary metastasis will be discussed in view of the findings indicating that MMPs are involved in the preparation of pre-metastatic niches. Finally, the most recent evidence, indicating the pro-metastatic consequences of anti-angiogenic therapies employing MMP inhibitors will be presented as examples highlighting possible outcomes of interfering with the pleiotropic nature of the MMP functionality.

Suppression of tumor angiogenesis by Galpha(13) haploinsufficiency

Heterotrimeric G proteins are critical transducers of cellular signaling. Of the four families of G proteins, the physiological function of Galpha(13) is less well understood. Galpha(13) gene-deleted mice die at embryonic day approximately 9.5. Here, we show that heterozygous Galpha(13)(+/-) mice display defects in adult angiogenesis. Female Galpha(13)(+/-) mice showed a higher number of immature follicles and a lower density of blood vessels in the mature corpus luteum compared with Galpha(13)(+/+) mice. Furthermore, implanted tumors grew slower in Galpha(13)(+/-) host mice. These tumor tissues had many fewer blood vessels compared with those from Galpha(13)(+/+) host mice. Moreover, bone marrow-derived progenitor cells from Galpha(13)(+/+) mice rescued the failed growth of allografted tumors when reconstituted into irradiated Galpha(13)(+/-) mice. Hence, Galpha(13) is haploinsufficient for adult angiogenesis in both the female reproductive system and tumor angiogenesis.

PAKing up to the endothelium

Angiogenesis recapitulates the growth of blood vessels that progressively expand and remodel into a highly organized and stereotyped vascular network. During adulthood, endothelial cells that formed the vascular wall retain their plasticity and can be engaged in neo-vascularization in response to physiological stimuli, such as hypoxia, wound healing and tissue repair, ovarian cycle and pregnancy. In addition, numerous human diseases and pathological conditions are characterized by an excessive, uncontrolled and aberrant angiogenesis. The signalling pathways involving the small Rho GTPase, Rac and its downstream effector the p21-activated serine/threonine kinase (PAK) had recently emerged as pleiotropic modulators in these processes. Indeed, Rac and PAK were found to modulate endothelial cell biology, such as sprouting, migration, polarity, proliferation, lumen formation, and maturation. Elucidating the Rac/PAK molecular circuitry will provide essential information for the development of new therapeutic agents designed to normalize the blood vasculature in human diseases.

The role of bone-marrow-derived cells in tumor growth, metastasis initiation and progression

Emerging evidence from murine models suggests that tumor-specific endocrine factors systemically stimulate the quiescent bone marrow (BM) compartment, resulting in the expansion, mobilization and recruitment of BM progenitor cells. Discrete subsets of tumor-instigated BM-derived progenitor cells support tumor progression and metastasis by regulating angiogenesis, inflammation and immune suppression. Notably, clinical studies have begun to reveal that increased BM recruitment in tumors is associated with poor prognosis. Thus, the BM-derived tumor microenvironment is an attractive therapeutic target, and drugs targeting the components of the microenvironment are currently in clinical trials. Here, we focus on recent advances and emerging concepts regarding the intriguing role of BM-derived cells in tumor growth, metastasis initiation and progression, and we discuss future directions in the context of novel diagnostic and therapeutic opportunities.

The definition of EPCs and other bone marrow cells contributing to neoangiogenesis and tumor growth: is there common ground for understanding the roles of numerous marrow-derived cells in the neoangiogenic process?

Interest in the regulation of blood vessel formation as a mechanism to permit unregulated tumor cell growth was a prescient hypothesis of Dr. Judah Folkman nearly 3 decades ago. Understanding the cellular and molecular mechanisms that affect the recruitment, expansion, and turnover of the tumor microvasculature continues to evolve. While the fundamental paradigms for improving blood flow to growing, injured, diseased, or tumor infiltrated tissues are well known, the potential role of bone marrow derived circulating endothelial progenitor cells (EPCs) to function as postnatal vasculogenic precursors for tumor microvasculature has become a controversial premise. We will briefly review some recently published high profile papers that appear to derive polar interpretations for the role of EPCs in the angiogenic switch and discuss possible reasons for the disparate views in work conducted in both mouse and man.