CXCR2-Dependent Endothelial Progenitor Cell Mobilization in Pancreatic Cancer Growth

Neovascularization is essential for tumor growth. We have previously reported that the chemokine receptor CXCR2 is an important regulator in tumor angiogenesis. Here we report that the mobilization of bone marrow (BM)-derived endothelial progenitor cells (EPCs) is impaired in CXCR2 knockout mice harboring pancreatic cancers. The circulating levels of EPCs (positive for CD34, CD117, CD133, or CD146) are decreased in the bone marrow and/or blood of tumor-bearing CXCR2 knockout mice. CXCR2 gene knockout reduced BM-derived EPC proliferation, differentiation, and vasculogenesis in vitro. EPCs double positive for CD34 and CD133 increased tumor angiogenesis and pancreatic cancer growth in vivo. In addition, CD133(+) and CD146(+) EPCs in human pancreatic cancer are increased compared with normal pancreas tissue. These findings indicate a role of BM-derived EPC in pancreatic cancer growth and provide a cellular mechanism for CXCR2 mediated tumor neovascularization.     

The involvement of endothelial progenitor cells in tumor angiogenesis

Endothelial progenitor cells (EPCs) have been isolated from peripheral blood CD34, VEGFR-2, or AC 133 (CD133) antigen-positive cells, which may home to site of neovascularization and differentiate into endothelial cells in situ. Endothelial cells contribute to tumor angiogenesis, and can originate from sprouting or co-option of neighbouring pre-existing vessels. Emerging evidence indicate that bone marrow-derived circulating EPCs can contribute to tumor angiogenesis and growth of certain tumors. This review article will summarize the literature data concerning this new role played by EPCs in tumor angiogenesis.     

Increased circulating AC133+ CD34+ endothelial progenitor cells in children with hemangioma

Hemangioma is the most common soft-tissue tumor of infancy. Despite the frequency of these vascular tumors, the origin of hemangioma-endothelial cells is unknown. Circulating endothelial progenitor cells (EPCs) have recently been identified as vascular stem cells with the capacity to contribute to postnatal vascular development. We have attempted to determine whether circulating EPCs are increased in hemangioma patients and thereby provide insight into the role of EPCs in hemangioma growth. METHODS AND RESULTS: Peripheral blood mononuclear cells (PBMCs) were isolated from hemangioma patients undergoing surgical resection (N = 5) and from age-matched controls (N = 5) undergoing strabismus correction surgery. PBMCs were stained with fluorescent-labeled antibodies for AC133, CD34, and VEGFR2/KDR. Fluorescent-labeled isotype antibodies served as negative controls. Histologic sections of surgical specimens were stained with the specific hemangioma markers Glut1, CD32, and merosin, to confirm the diagnosis of common hemangioma of infancy. EPCs harvested from healthy adult volunteers were stained with Glut1, CD32, and merosin, to assess whether cultured EPCs express known hemangioma markers. Hemangioma patients had a 15-fold increase in the number of circulating CD34 AC133 dual-staining cells relative to controls (0.78+/-0.14% vs.0.052+/-0.017%, respectively). Similarly, the number of PBMCs that stained positively for both CD34 and KDR was also increased in hemangioma patients (0.49+/-0.074% vs. 0.19+/-0.041% in controls). Cultured EPCs stained positively for the known hemangioma markers Glut1, CD32, merosin. CONCLUSIONS: This is the first study to suggest a role for EPCs in the pathogenesis of hemangioma. Our results imply that increased levels of circulating EPCs may contribute to the formation of this vascular tumor.     

Intralesional injection of adenovirus encoding CC chemokine ligand 16 inhibits mammary tumor growth and prevents metastatic-induced death after surgical removal of the treated primary tumor

The CC chemokine ligand (CCL)16 exerts chemotactic activity on human monocytes and lymphocytes. Although no murine homologous has been defined, the TSA mouse adenocarcinoma cells engineered to express human CCL16 are rapidly rejected by syngenic mice. An adenovirus encoding CCL16 (AdCCL16) was generated using a Cre-Lox-based system and was used to determine whether this chemokine might also block pre-existing tumors. Both recombinant and viral CCL16 showed in vitro chemotactic activity for murine CD4(+) and CD8(+) lymphocytes and dendritic cells (DC). AdCCL16, but not the control empty vector, when injected in established nodules significantly delayed tumor growth. Immunohistochemistry revealed accumulation of CD4(+) and CD8(+) T cells and DC in the treated tumors as well as in draining lymph nodes. DC from such lymph nodes stimulated IFN-gamma by a T cell clone specific for the known TSA tumor-associated Ag (TAA), suggesting the tumor origin of these cells. Lymphocytes from the same nodes showed specific CTL activity against TSA tumor cells and their immunodominant TAA peptide. Antitumor activity required CD4, CD8, and IFN-gamma production, as shown using subset-depleted and knockout mice. Despite the robust and rapid immune response triggered by intratumoral injection of AdCCL16, the lesions were not completely rejected; however, the same treatment given before surgical excision of primary lesions prevented metastatic spread and cured 63% of mice bearing the 4T1 mammary adenocarcinoma, which is perhaps the most compelling model of spontaneous metastasis.     

Intratumoral,not circulating,endothelial progenitor cells share genetic aberrations with glial tumor cells

Literature data indicate that glioma stem cells may give rise to both tumor cells and endothelial progenitor cells (EPCs). Malignant glioma patients usually have increased levels of circulating (EPCs) and these cells are known to contribute to the glioma neovasculature. In this study we compared the intratumoral and circulating EPCs of glioma patients for a set of common glioma genotypical aberrations (amplification of EGFR; deletion of PTEN and aneusomy of chromosomes 7 and 10). We found that the EPCs present in the tumor tissues, not the circulating EPCs, share genetic aberrations with the tumor cells. EPCs with EGFR amplification were found in 46% and with PTEN deletion in 36% of the cases. EPCs with polysomy 7 and monosomy 10 were detected in 56% and 38% of the cases while centrosomal abnormalities in EPCs were found in 68% of the cases. The presence of genetic aberrations of glioma cells in intratumoral EPCs may point to transdifferentiation of glioma stem cells into EPCs. However, the tissue specific CD133 splice variant of blood EPCs was detected in the glioma tissues but not in control brains, suggestive of a blood origin of at least part of the intratumoral EPCs. The findings highlight the complexity of the cellular constituents of glioma neovascularization which should be taken into account when developing anti‐angiogenic strategies for gliomas. J. Cell. Physiol. 228: 1383–1390, 2013. © 2012 Wiley Periodicals, Inc.     

Comparison between total endothelial progenitor cell isolation versus enriched Cd133+ culture

Endothelial progenitor cells (EPCs) play a role in endogenous neovascularization of ischaemic tissues. Isolation and characterization of EPCs from circulating mononuclear cells are important for developing targeted cellular therapies and reproducibility of data are the major scientific goals. Here we compared two currently employed isolation methods, i.e. from total peripheral blood mononuclear cells (PBMCs) and from enriched CD133(+) cells, by defining the cell morphology and functional activities. We show that EPCs from cultured PBMCs resulted in an adherent population of 23% +/- 4% merged cells positive for Dil-Ac-LDL and lectin, whereas the percentage of double positive cells in cultured CD133(+) enriched cells was 50% +/- 7% (P < 0.01). These data were obtained through a novel and a more complete method of analysis of cell calculations (specifically by dividing each microscope field into 120 subfields). When stimulated with tumour necrosis factor alpha (TNF)-alpha and glucose, cell number was reduced in EPCs from total PBMCs and, more consistently, in CD133(+) enriched cells. However, both cultured total PBMCs and CD133(+) enriched cells respond similarly to TNF-alpha or glucose-induced p38-phosphorylation. EPCs from both procedures show similar results in terms of phenotype and response to modulators of their functional activities. However, when the cell phenotype of CD133(+) enrichment-derived cells was compared with that of cells from the total PBMC, a significant increase in CD133(+) expression was observed (P < 0.01) This may have relevance during intervention studies using cultured EPCs.     

Alloimmunity to human endothelial cells derived from cord blood progenitors

There is considerable interest in exploiting circulating endothelial progenitor cells (EPCs) for therapeutic organ repair. Such cells may be differentiated into endothelial cells (ECs) in vitro and then expanded for use in tissue engineering. Vessel-derived ECs are variably immunogenic, depending upon tissue source, and it is unknown whether ECs derived from cord blood EPCs are able to initiate an allogeneic response. In this study, we compare the phenotype and alloantigenicity of human cord blood progenitor cell-derived ECs with HUVECs isolated from the same donors. Human cord blood progenitor cell-derived ECs are very similar to HUVECs in the expression of proteins relevant for alloimmunity, including MHC molecules, costimulators, adhesion molecules, cytokines, chemokines, and IDO, and in their ability to initiate allogeneic CD4(+) and CD8(+) memory T cell responses in vitro and in vivo. These findings have significant implications for the use of cord blood EPCs in regenerative medicine or tissue engineering.     

Id1 restrains p21 expression to control endothelial progenitor cell formation

Loss of Id1 in the bone marrow (BM) severely impairs tumor angiogenesis resulting in significant inhibition of tumor growth. This phenotype has been associated with the absence of circulating endothelial progenitor cells (EPCs) in the peripheral blood of Id1 mutant mice. However, the manner in which Id1 loss in the BM controls EPC generation or mobilization is largely unknown. Using genetically modified mouse models we demonstrate here that the generation of EPCs in the BM depends on the ability of Id1 to restrain the expression of its target gene p21. Through a series of cellular and functional studies we show that the increased myeloid commitment of BM stem cells and the absence of EPCs in Id1 knockout mice are associated with elevated p21 expression. Genetic ablation of p21 rescues the EPC population in the Id1 null animals, re-establishing functional BM-derived angiogenesis and restoring normal tumor growth. These results demonstrate that the restraint of p21 expression by Id1 is one key element of its activity in facilitating the generation of EPCs in the BM and highlight the critical role these cells play in tumor angiogenesis.     

血管再生中的内皮祖细胞

循环血液里存在一种被称为内皮祖细胞(endothelial progenitor cells,EPCs)的祖细胞亚群,具有在体内外分化为成熟内皮细胞的能力。根据内皮祖细胞与其他血液细胞的粘附能力的差异和内皮祖细胞的抗原特异性,内皮祖细胞可通过贴壁培养和免疫磁珠筛选而分离获得。内皮祖细胞可特异性表达三种祖细胞分子标志：CD133、CD34和血管内皮生长因子受体-2。当内皮祖细胞分化为成熟内皮细胞后,血小板内皮细胞粘附分子-1(CD31)、血管内皮粘附素(VE-cadherin,又称CD144)和Ⅷ因子(vWF)表达将上调。越来越多的证据显示,内皮祖细胞有利于体内内皮损伤后修复和血管再生。我们的研究发现,内皮祖细胞可修复apoE-缺陷小鼠血管移植物中的损伤内皮并且在动脉血管外膜中存在大量的血管祖细胞。然而,在机体的血管再生和动脉硬化的形成进程中,这些内皮祖细胞的作用和机制还不太明确。另外,有关机体内相应心血管疾病危险因素是如何影响内皮祖细胞功能的机制也不清楚。因此,对内皮祖细胞的归巢、释放和粘附机制的进一步深入研究将有助于人们探索内皮祖细胞的基础理论和临床应用价值。     

Endothelial progenitor cells: identity defined?

In the past decade, researchers have gained important insights on the role of bone marrow (BM)-derived cells in adult neovascularization. A subset of BM-derived cells, called endothelial progenitor cells (EPCs), has been of particular interest, as these cells were suggested to home to sites of neovascularization and neoendothelialization and differentiate into endothelial cells (ECs) in situ , a process referred to as postnatal vasculogenesis. Therefore, EPCs were proposed as a potential regenerative tool for treating human vascular disease and a possible target to restrict vessel growth in tumour pathology. However, conflicting results have been reported in the field, and the identification, characterization, and exact role of EPCs in vascular biology is still a subject of much discussion. The focus of this review is on the controversial issues in the field of EPCs which are related to the lack of a unique EPC marker, identification challenges related to the paucity of EPCs in the circulation, and the important phenotypical and functional overlap between EPCs, haematopoietic cells and mature ECs. We also discuss our recent findings on the origin of endothelial outgrowth cells (EOCs), showing that this in vitro defined EC population does not originate from circulating CD133⁺ cells or CD45⁺ haematopoietic cells.     

The Neural Stem/Progenitor Cell Marker Nestin Is Expressed in Proliferative Endothelial Cells,but Not in Mature Vasculature

Nestin is an intermediate filament protein that is known as a neural stem/progenitor cell marker. It is expressed in undifferentiated central nervous system (CNS) cells during development, but also in normal adult CNS and in CNS tumor cells. Additionally, nestin is expressed in endothelial cells (ECs) of CNS tumor tissues and of adult tissues that replenish by angiogenesis. However, the regulation of nestin expression in vascular endothelium has not been analyzed in detail. This study showed that nestin expression was observed in proliferating endothelial progenitor cells (EPCs), but not in mature ECs. In adherent cultured cells derived from bone marrow cells, EPCs that highly expressed nestin also expressed the endothelial marker CD31 and the proliferation marker Ki67. ECs cultured without growth factors showed attenuated nestin immunoreactivity as they matured. Transgenic mice that carried the enhanced green fluorescent protein under the control of the CNS-specific second intronic enhancer of the nestin gene showed no reporter gene expression in EPCs. This indicated that the mechanisms of nestin gene expression were different in EPCs and CNS cells. Immunohistochemistry showed nestin expression in neovascular cells from two distinct murine models. Our results demonstrate that nestin can be used as a marker protein for neovascularization. (J Histochem Cytochem 58:721–730, 2010)     

On the role of endothelial progenitor cells in tumor neovascularization

The exact role that bone marrow (BM)-derived endothelial progenitor cells (EPCs) play in tumor neovascularization is heavily debated. We develop a quantitative three-compartment model with predictive power regarding the dynamics of tumorigenesis. There are two distinct processes by which tumor neovasculature can be built: angiogenesis is the formation of new blood vessels from preexisting vessels; vasculogenesis is the formation of new vessels by recruiting circulating EPCs. We show that vasculogenesis-driven and angiogenesis-driven tumors grow in different ways. (i) If angiogenesis is the prevailing process, then the tumor mass (and volume) will grow as a cubic power of time, and BM-derived EPCs will stay at a constant level. (ii) If vasculogenesis is the dominant process, then the tumor mass will be characterized by a linear growth in time, and the number of circulating EPCs (after possibly increasing to a maximum) will decrease to low levels. With this information, one can identify the "signature" of each of the processes in the observations of tumor growth and the dynamics of the relevant characteristics, such as the level of BM-derived EPCs. We show how our results can help explain some apparently contradictory experimental data. We also propose ways to couple this study with directed experiments to identify the exact role of vasculogenesis in tumor progression.     

Decursin inhibits vasculogenesis in early tumor progression by suppression of endothelial progenitor cell differentiation and function

Endothelial progenitor cells (EPCs) contribute to the tumor vasculature during tumor progression. Decursin isolated from the herb Angelica gigas is known to possess potent anti‐inflammatory activities. Recently, we reported that decursin is a novel candidate for an angiogenesis inhibitor [Jung et al., 2009 ]. In this study, we investigated whether decursin regulates EPC differentiation and function to inhibit tumor vasculogenesis. We isolated AC133+ cells from human cord blood and decursin significantly decreased the number of EPC colony forming units of human cord blood‐derived AC133+ cells that produce functional EPC progenies. Decursin dose‐dependently decreased the cell number of EPC committing cells as demonstrated by EPC expansion studies. Decursin inhibited EPC differentiation from progenitor cells into spindle‐shaped EPC colonies. Additionally, decursin inhibited proliferation and migration of early EPCs isolated from mouse bone marrow. Furthermore, decursin suppressed expression of angiopoietin‐2, angiopoietin receptor Tie‐2, Flk‐1 (vascular endothelial growth factor receptor‐2), and endothelial nitric oxide synthase in mouse BM derived EPCs in a dose‐dependent manner. Decursin suppressed tube formation ability of EPCs in collaboration with HUVEC. Decursin (4 mg/kg) inhibited tumor‐induced mobilization of circulating EPCs (CD34 + /VEGFR‐2+ cells) from bone marrow and early incorporation of Dil‐Ac‐LDL‐labeled or green fluorescent protein (GFP)+ EPCs into neovessels of xenograft Lewis lung carcinoma tumors in wild‐type‐ or bone‐marrow‐transplanted mice. Accordingly, decursin attenuated EPC‐derived endothelial cells in neovessels of Lewis lung carcinoma tumor masses grown in mice. Together, decursin likely affects EPC differentiation and function, thereby inhibiting tumor vasculogenesis in early tumorigenesis. J. Cell. Biochem. 113: 1478–1487, 2012. © 2012 Wiley Periodicals, Inc.     

Nitric oxide-mediated tumoricidal activity of murine microglial cells

Experimental metastases in the brain of mice are infiltrated by microglia, and parabiosis experiments of green fluorescent protein (GFP(+)) and GFP(-) mice revealed that these microglia are derived from circulating monocytes (GFP(+), F4/80(+), and CD68(+)). These findings raised the question as to whether microglia (specialized macrophages) possess tumoricidal activity. C8-B4 murine microglia cells were incubated in vitro in medium (control) or in medium containing both lipopolysaccharide and interferon-γ. Control microglia were not tumoricidal against a number of murine and human tumor cells, whereas lipopolysaccharide/interferon-γ-activated microglia lysed murine and human tumor cells by release of nitric oxide. Parallel experiments with murine peritoneal macrophages produced identical results. Neither activated microglia nor activated macrophages lysed nontumorigenic murine or human cells. Collectively, these data demonstrate that brain metastasis-associated microglia are derived from circulating mononuclear cells and exhibit selective and specific tumoricidal activity.     

IFN-gamma-dependent inhibition of tumor angiogenesis by tumor-infiltrating CD4+ T cells requires tumor responsiveness to IFN-gamma

The importance of CD4(+) T cells in the induction of an optimal antitumor immune response has largely been attributed to their ability to provide costimulatory signals for the priming of MHC class I-restricted CD8(+) CTL. However, many reports have demonstrated a requirement for CD4(+) T cells in the effector phase of tumor rejection indicating a greater responsibility for CD4(+) T cells in controlling tumor outgrowth. We demonstrate here a critical role for CD4(+) T cells in restraining initial tumor development through the inhibition of tumor angiogenesis. Using a tumor variant that is unresponsive to IFN-gamma, we show that tumor responsiveness to IFN-gamma is necessary for IFN-gamma-dependent inhibition of tumor angiogenesis by CD4(+) T cells. These studies reveal a pivotal role for CD4(+) T cells in controlling early tumor development through inhibition of tumor angiogenesis.     

Recruitment of human cord blood-derived endothelial colony-forming cells to sites of tumor angiogenesis

Background aimsEndothelial progenitor cells (EPCs) specifically home to sites of malignant growth, rendering them attractive for anti-cancer therapies. Data are conflicting on the phenotype and quantitative contribution toward tumor angiogenesis based on differing culture assays to outgrow EPCs. To evaluate the origin and early phenotype of EPCs and to define a population with enhanced tumor-targeting capacity, we evaluated a hierarchy of cord blood-derived EPCs modeling the multi-step nature of tumor homing.MethodsCD34⁺ mononuclear cells were isolated from fresh cord blood and cultured to derive endothelial colony-forming cells (ECFCs). Human umbilical vein endothelial cells (HUVECs) served as control. Using intra-vital microscopy, the recruitment was analyzed in mice bearing C6 xenografts. Adhesion, migration, transmigration and differentiation were further addressed.ResultsWithin the primary passage, ECFCs underwent a rapid maturation from a CD45⁺ and CD31⁺ phenotype to a CD45^? and endothelial marker positive phenotype. Assessing in vivo tumor recruitment, ECFCs had the highest activity in all steps analyzed. In vitro, ECFCs demonstrated significantly higher adhesion under static and flow conditions. Similarly, ECFCs exhibited highest migratory and trans-migratory activity toward tumor-conditioned medium. On subcutaneous implantation, only ECFCs formed blood vessels covered with perivascular cells, similar to HUVECs.ConclusionsOur study indicates that ECFCs emerge from a CD45⁺ and CD31⁺ progenitor and rapidly mature in culture. ECFCs have a significantly higher potential for tumor targeting than non-cultured CD34⁺ cells and HUVECs. They are ideal candidates for future cell-based anti-cancer therapies.     

Cyclosporine increases ischemia-induced endothelial progenitor cell mobilization through manipulation of the CD26 system

Cyclosporin A (CsA) improves the success rate of transplantation. The CD26/dipeptidylpeptidase IV (DPP IV) system plays a critical role in mobilizing endothelial progenitor cells (EPCs) from bone marrow. This study investigated whether CsA manipulates CD26/DPP IV activity and increases EPC mobilization. C57BL/6 mice were divided into control and CsA-treated groups. Before and after hindlimb ischemia was induced, circulating EPC number and serum levels of different cytokines were measured. Compared with the controls, CsA treatment significantly increased the blood levels of stroma-derived factor-1alpha and stem cell factor after ischemic stress (P < 0.001). The CsA group displayed a significant increase in the number of circulating EPCs (sca-1+KDR+ and c-kit+CD31+ EPCs, both P < 0.05). In vivo, CsA caused a significant increase in the numbers of EPCs incorporated into the Matrigel and ischemic limbs (P < 0.05). In the peripheral blood, CsA significantly decreased CD26+ cell numbers and attenuated the plasma CD26/DPP IV activity (P < 0.001). Furthermore, short-term CsA treatment significantly improved the perfusion of ischemic limbs and decreased the spontaneous digital amputation rate. In summary, CsA manipulates the mobilization of EPCs into the circulation via the CD26/DPP IV system. Short-term CsA treatment has beneficial effects on angiogenesis of ischemic tissues.     

Phloroglucinol inhibits the bioactivities of endothelial progenitor cells and suppresses tumor angiogenesis in LLC-tumor-bearing mice

Background

There is increasing evidence that phloroglucinol, a compound from Ecklonia cava, induces the apoptosis of cancer cells, eventually suppressing tumor angiogenesis.

Methodology/Principal Findings

This is the first report on phloroglucinol''s ability to potentially inhibit the functional bioactivities of endothelial progenitor cells (EPCs) and thereby attenuate tumor growth and angiogenesis in the Lewis lung carcinoma (LLC)-tumor-bearing mouse model. Although Phloroglucinol did not affect their cell toxicity, it specifically inhibited vascular endothelial growth factor (VEGF) dependent migration and capillary-like tube formation of EPCs. Our matrigel plug assay clearly indicated that orally injected phloroglucinol effectively disrupts VEGF-induced neovessel formation. Moreover, we demonstrated that when phloroglucinol is orally administered, it significantly inhibits tumor growth and angiogenesis as well as CD45⁻/CD34⁺ progenitor mobilization into peripheral blood in vivo in the LLC-tumor-bearing mouse model.

Conclusions/Significance

These results suggest a novel role for phloroglucinol: Phloroglucinol might be a modulator of circulating EPC bioactivities, eventually suppressing tumorigenesis. Therefore, phloroglucinol might be a candidate compound for biosafe drugs that target tumor angiogenesis.     

FTY720 suppresses liver tumor metastasis by reducing the population of circulating endothelial progenitor cells

Background

Surgical procedures such as liver resection and liver transplantation are the first-line treatments for hepatocellular carcinoma (HCC) patients. However, the high incidence of tumor recurrence and metastasis after liver surgery remains a major problem. Recent studies have shown that hepatic ischemia-reperfusion (I/R) injury and endothelial progenitor cells (EPCs) contribute to tumor growth and metastasis. We aim to investigate the mechanism of FTY720, which was originally applied as an immunomodulator, on suppression of liver tumor metastasis after liver resection and partial hepatic I/R injury.

Methodology/Principal Findings

An orthotopic liver tumor model in Buffalo rat was established using the hepatocellular carcinoma cell line McA-RH7777. Two weeks after orthotopic liver tumor implantation, the rats underwent liver resection for tumor-bearing lobe and partial hepatic I/R injury. FTY720 (2 mg/kg) was administered through the inferior caval vein before and after I/R injury. Blood samples were taken at days 0, 1, 3, 7, 14, 21 and 28 for detection of circulating EPCs (CD133+CD34+). Our results showed that intrahepatic and lung metastases were significantly inhibited together with less tumor angiogenesis by FTY720 treatment. The number of circulating EPCs was also significantly decreased by FTY720 treatment from day 7 to day 28. Hepatic gene expressions of CXCL10, VEGF, CXCR3, CXCR4 induced by hepatic I/R injury were down-regulated in the treatment group.

Conclusions/Significance

FTY720 suppressed liver tumor metastasis after liver resection marred by hepatic I/R injury in a rat liver tumor model by attenuating hepatic I/R injury and reducing circulating EPCs.