Targeting the ANG2/TIE2 axis inhibits tumor growth and metastasis by impairing angiogenesis and disabling rebounds of proangiogenic myeloid cells

Tumor-infiltrating myeloid cells convey proangiogenic programs that counteract the efficacy of antiangiogenic therapy. Here, we show that blocking angiopoietin-2 (ANG2), a TIE2 ligand and angiogenic factor expressed by activated endothelial cells (ECs), regresses the tumor vasculature and inhibits progression of late-stage, metastatic MMTV-PyMT mammary carcinomas and RIP1-Tag2 pancreatic insulinomas. ANG2 blockade did not inhibit recruitment of MRC1(+) TIE2-expressing macrophages (TEMs) but impeded their upregulation of Tie2, association with blood vessels, and ability to restore angiogenesis in tumors. Conditional Tie2 gene knockdown in TEMs was sufficient to decrease tumor angiogenesis. Our findings support a model wherein the ANG2-TIE2 axis mediates cell-to-cell interactions between TEMs and ECs that are important for tumor angiogenesis and can be targeted to induce effective antitumor responses.     

人类肿瘤中Tie2阳性单核巨噬细胞研究进展

Tie2阳性单核巨噬细胞（TEMs）是一类表达酪氨酸激酶受体Tie2的单核细胞或巨噬细胞,在人类和鼠类中均有发现,可存在于外周血和组织中,参与肿瘤血管生成、淋巴管生成和免疫抑制等肿瘤微环境的形成。现有研究发现TEMs对于多种肿瘤具有潜在的临床诊断及预后指导意义,有望为肿瘤治疗提供新的靶向策略,本文就TEMs在肿瘤中的研究进展作一综述     

Tie2 identifies a hematopoietic lineage of proangiogenic monocytes required for tumor vessel formation and a mesenchymal population of pericyte progenitors

Bone marrow-derived cells contribute to tumor angiogenesis. Here, we demonstrate that monocytes expressing the Tie2 receptor (Tie2-expressing monocytes [TEMs]) (1) are a distinct hematopoietic lineage of proangiogenic cells, (2) are selectively recruited to spontaneous and orthotopic tumors, (3) promote angiogenesis in a paracrine manner, and (4) account for most of the proangiogenic activity of myeloid cells in tumors. Remarkably, TEM knockout completely prevented human glioma neovascularization in the mouse brain and induced substantial tumor regression. Besides TEMs and endothelial cells (ECs), Tie2 expression distinguished a rare population of tumor stroma-derived mesenchymal progenitors representing a primary source of tumor pericytes. Therefore, Tie2 expression characterizes three distinct cell types required for tumor neovascularization: ECs, proangiogenic cells of hematopoietic origin, and pericyte precursors of mesenchymal origin.     

表达Tie2的单核细胞在肿瘤研究中的进展

表达Tie2的单核细胞(TEM)仅存在于外周血及肿瘤组织中,在肿瘤血管生成中发挥重要作用.TEM能够被血管生成素2(Ang2)及缺氧化学信号募集进入肿瘤组织,分化成表达Tie2的巨噬细胞,通过旁分泌作用参与肿瘤血管生成.肝癌、结肠癌、乳腺癌、恶性胶质瘤等肿瘤中检测到TEM水平升高,这对于肿瘤的诊断及预后判断有一定的提示作用.近年研究发现,TEM可用于抗肿瘤药物的靶向递送,能有效抑制肿瘤的生长和转移,同时TEM也是抗肿瘤治疗的潜在靶点.然而TEM在肿瘤微血管密度、临床分级及预后判断中的作用并不明确,目前针对TEM具体功能的探究引起了学者的广泛关注.     

乳腺癌组织中Ang-2和受体Tie2的表达及与血管生成的关系

目的：探讨Ang-2和Tie2的表达与乳腺癌浸润和转移的关系。方法：选用42例乳腺癌标本、16例乳腺纤维腺瘤及13例正常乳腺组织,以SP法进行Ang-2、Tie2及CD34标记的微血管密度（MVD）的检测,并分析其与临床病理特征的关系。结果：在乳腺癌组织中,Ang-2、Tie2阳性表达率分别为95．2％和92．9％;明显高于正常乳腺组织（15．4％、12．5％）和乳腺纤维腺瘤组织（15．4％,15．4％）,P=0．001。CD34标记的MVD与Ang-2、Tie2密切相关。结论：人乳腺癌中血管生成增加,Ang-2和Tie2在乳腺癌血管生成和进展中可能起重要作用。     

Angiopoietin-1 and myeloma-induced angiogenesis

Multiple myeloma (MM) is a plasma cell malignancy characterized by an increase of the bone marrow angiogenesis. Angiopoietin-1 (Ang-1) is a critical factor in the regulation of physiological and pathological vessel formation that acts by binding to a specific receptor Tie2 expressed on endothelial cells. Recent evidences indicate that human MM cells produce Ang-1 and up-regulate its receptor Tie2 in bone marrow endothelial cells. An overexpression of Ang-1 has been also found in MM cells as compared to normal plasma cells. The correlation between Ang-1 expression and BM angiogenesis, demonstrated in MM patients, and the inhibitory effect of Tie2 blocking on MM-induced vessel formation suggest that Ang-1 production by MM cells is critically involved in the angiogenic process in MM. In this review we focalize our attention on Ang-1/Tie2 system and its role in MM-induced angiogenesis.     

Tumor-targeted interferon-alpha delivery by Tie2-expressing monocytes inhibits tumor growth and metastasis

The use of type I interferons (IFNs) in cancer therapy has been limited by ineffective dosing and significant toxicity. Here, we exploited the tumor-homing ability of proangiogenic Tie2-expressing monocytes (TEMs) to deliver IFN-alpha to tumors. By transplanting hematopoietic progenitors transduced with a Tie2 promoter/enhancer-driven Ifna1 gene, we turned TEMs into IFN-alpha cell vehicles that efficiently targeted the IFN response to orthotopic human gliomas and spontaneous mouse mammary carcinomas and obtained significant antitumor responses and near complete abrogation of metastasis. TEM-mediated IFN-alpha delivery inhibited tumor angiogenesis and activated innate and adaptive immune cells but did not impair myelopoiesis and wound healing detectably. These results illustrate the therapeutic potential of gene- and cell-based IFN-alpha delivery and should allow the development of IFN treatments that more effectively treat cancer.     

Macrophage-derived SHP-2 inhibits the metastasis of colorectal cancer via Tie2-PI3K signals

This research aimed to explore the influence of Src homology-2 containing protein tyrosine phosphatase (SHP- 2) on the functions of tyrosine kinase receptors with immunoglobulin and EGF homology domains 2 (Tie2)-expressing monocyte/macrophages (TEMs) and the influence of the angiopoietin(Ang)/Tie2-phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) (Ang/Tie2-PI3K/Akt/mTOR) signaling pathway on the tumor microvascular remodeling in an immunosuppressive microenvironment. In vivo, SHP-2- deficient mice were used to construct colorectal cancer (CRC) liver metastasis models. SHP-2-deficient mice had significantly more metastatic cancer and inhibited nodules on the liver surface than wild-type mice, and the high-level expression of p-Tie2 was found in the liver tissue of the macrophages’ specific SHP-2-deficient mice (SHP-2MACKO) + planted tumor mice. Compared with the SHP-2 wild type mice (SHP-2WT) + planted tumor group, the SHP-2MAC-KO + planted tumor group experienced increased expression of p-Tie2, p-PI3K, p-Akt, p-mTOR, vascular endothelial growth factor (VEGF), cyclooxygenase-2 (COX-2), matrix metalloproteinase 2 (MMP2), and MMP9 in the liver tissue. TEMs selected by in vitro experiments were co-cultured with remodeling endothelial cells and tumor cells as carriers. It was found that when Angpt1/2 was used for stimulation, the SHP-2MAC-KO + Angpt1/2 group displayed evident increases in the expression of the Ang/Tie2-PI3K/Akt/mTOR pathway. The number of cells passing through the lower chamber and the basement membrane and the number of blood vessels formed by cells compared with the SHP-2WT + Angpt1/2 group, while these indexes were subjected to no changes under the simultaneous stimulation of Angpt1/2 + Neamine. To sum up, the conditional knockout of SHP-2 can activate the Ang/Tie2-PI3K/Akt/mTOR pathway in TEMs, thereby strengthening tumor micro angiogenesis in the microenvironment and facilitating CRC liver metastasis.     

The dynamic roles of angiopoietins in tumor angiogenesis

Angiopoietin (Ang)-1 and -2, and mouse Ang-3/human Ang-4 are ligands of the receptor tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Tie)-2. It is well established that the Ang-Tie-2 pathway is involved in tumor angiogenesis. However, the exact effects of angiopoietins on tumor angiogenesis are under debate. Experimental and clinical studies have demonstrated that increased expression of Ang-1 and -2 promotes or inhibits tumor angiogenesis, and correlates with a reduced or extended survival time of patients, and with a declined or improved clinical outcome. In general, these studies suggest that Ang-1 is a proangiogenic factor that promotes endothelial cell survival and tumor angiogenesis, especially in the presence of vascular endothelial growth factor; whereas Ang-2 destabilizes vasculature that leads to the initiation of angiogenesis or apoptosis of endothelial cells/vessel regression in the presence or absence of vascular endothelial growth factor, respectively, and that the cell-surface tethered Ang-3 displays antiangiogenic activity. Together, these results suggest that the Ang-Tie-2 functional axis is an attractive target for antiangiogenesis-based cancer therapy.     

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.     

Serum Levels of Angiogenic Factors and their Prognostic Relevance in Bladder Cancer

Angiogenesis plays a critical role in tumor growth. VEGF, angiopoietins (Ang-1, Ang-2) and their tyrosine kinase receptor Tie2 are major regulators of angiogenesis. The aim of this study was to evaluate the prognostic value of the serum levels of these factors in bladder cancer. We analyzed the serum samples of 117 bladder cancer patients and 64 healthy volunteers by enzyme linked immunosorbent assay (ELISA) for Ang-1, Ang-2, VEGF and the extracellular domain of Tie2. The statistical evaluation of the obtained data was performed via Kaplan–Meier log-rank test, univariate Cox analyses as well as Cox proportional hazards regression model. Serum Ang-1 levels of bladder cancer patients were significantly higher (p < 0.001), while soluble Ang-2 and Tie2 levels were significantly lower (p = 0.016 and p = 0.001 respectively) in patients than those in controls. Cox univariate analysis revealed high sTie2 serum level as a risk factor for metastasis and as a borderline significant risk factor for disease related death (p = 0.022 and p = 0.081 respectively). These correlations were independent from tumor stage and grade in a Cox multivariate model (p = 0.016 and p = 0.069). These data indicate that the serum levels of analyzed angiogenic factors do change characteristically in bladder cancer. The soluble extracellular serum level of Tie2 may provide a stage and grade independent diagnostic tool to select a high risk group of bladder cancer patients.     

Expression of angiopoietins and vascular endothelial growth factors and their clinical significance in acute myeloid leukemia

Angiogenic factors play an essential role in normal and pathologic angiogenesis, but their clinical role in acute myeloid leukemia (AML) remains unclear. We investigated the expression of Ang-1, Ang-2, Tie2, VEGF-A, and VEGF-C genes in bone marrow (BM) mononuclear cells by real-time quantitative PCR (RQ-PCR) in a cohort of 126 patients with newly diagnosed de novo AML and normal marrow donors. Here we show that high pre-treatment levels of Ang-2 in the BM indicate an unfavorable prognosis in AML. Only karyotype (hazard ratio 2.19, 95% CI 1.25-3.42, P=0.005) and expression of Ang-2 (hazard ratio 2.05, 95% CI 1.20-3.52, P=0.009), but not other angiogenic factors, were independent prognostic factors for overall survival by multivariate analysis. The prognostic significance of Ang-2 expression was more obvious in the subgroup of patients with intermediate-risk cytogenetics. Subgroup analysis showed that Ang-2 expression had prognostic impact on patients with low (but not high) Ang-1 or Tie2 levels, and on patients with high (but not low) VEGF-A or VEGF-C levels.     

促血管生成素及其受体的异常表达与胃癌血管生成的关系

Objective： To explore angiopoietins （Ang-1, Ang-2）/Tie-2 expression and angiogenesis in stomach carcinomas. Methods： RT-PCR and immunohistochemistry were used to detect angiopoietins/Tie- 2 mRNA and protein expression in stomach carcinomas and their adjacent normal mucosa. Microvessel density （MVD） was counted according to CD34 immunohistochemical staining. Results： There was positive expression of Angiopoietins/Tie-2 mRNA and protein in stomach carcinomas and their paired adjacent normal mucosa. It was found that correlation between Ang-1 protein, Tie-2 mRNA expression and MVD was negative （F=-0.440, F=-0.267; P〈0.05）, while the correlation between Ang-2 mRNA and its protein, Ang-2/Ang-1 protein ratio and MVD was positive （F=0.319, F=-729, F=739; P〈0.05）. Moreover, MVD in groups with Ang-2 mRNAT/N ratio over 1.2 （the ratio of Ang-2 mRNA in stomach carcinoma to its adjacent normal mucosa） was higher than those with the ratio under 1.2. Conclusion： It was suggested that Ang-1 and Ang-2 antagonizes in the angiogenesis and the anglogenesis in tumor ultimately depended on Ang-2/Ang-1 ratio, once the expression of Ang-2 is higher than Ang-1 in some degree, the angiogenesis in tumors was promoted, otherwise oppositely. In other words, Ang-2 plays dominant role in the action of angiogenesis in tumors.     

Human epidermal growth factor receptor 2 regulates angiopoietin-2 expression in breast cancer via AKT and mitogen-activated protein kinase pathways

Abnormal activation of human epidermal growth factor receptor 2 (HER2; ErbB-2) in breast tumors results in increased metastasis and angiogenesis, as well as reduced survival. Here, we show that angiopoietin-2 (Ang-2) expression correlates with HER2 activity in human breast cancer cell lines. Inhibiting HER2 activity with anti-HER2 monoclonal antibody trastuzumab (Herceptin) or HER2 short interfering RNA in tumor cells down-regulates Ang-2 expression. Consistent with the important roles of AKT and mitogen-activated protein kinase in the HER2 signaling pathway, AKT and ERK mitogen-activated protein kinase (MAPK) kinase activity is necessary for Ang-2 up-regulation by HER2. Moreover, overexpression of HER2 protein up-regulates Ang-2 expression. Heregulin-beta1-induced Ang-2 up-regulation is abrogated when AKT and ERK kinase activity are blocked. Immunohistochemical analysis of HER2 and Ang-2 proteins in human breast carcinomas shows that Ang-2 expression in breast cancer correlates with HER2 expression. These studies provide evidence that the Ang-2 gene is regulated by HER2 activity in breast cancer, and propose an additional mechanism for HER2 contributing to tumor angiogenesis and metastasis.     

胃癌组织中Ａｎｇ ２和ＶＥＧＦ的表达与血管生成的关系

目的：研究胃癌组织中血管生成素-２（Ａｎｇ-２）和血管内皮生长因子（ＶＥＧＦ）的表达与临床病理学特征和肿瘤血管生成的关系。方法：应用免疫组织化学方法检测５５例胃癌组织以及１２例胃癌癌旁组织和正常胃组织中Ａｎｇ-２、ＶＥＧＦ表达及微血管密度（ＭＶＤ）。结果：Ａｎｇ-２、ＶＥＧＦ表达及ＭＶＤ在胃癌组织中均显著高于癌旁组织及正常胃组织（Ｐ＜０.０５）;胃癌组织Ａｎｇ-２、ＶＥＧＦ表达与浸润深度、淋巴结转移、病理分期、肿瘤分化程度密切相关（Ｐ＜０.０５）;Ａｎｇ-２与ＶＥＧＦ表达呈正相关性（Ｐ＜０.０５）。结论：Ａｎｇ-２、ＶＥＧＦ在胃癌组织中高表达,两者在胃癌的肿瘤血管生成和进展中起重要作用。     

血管生成素-2与肿瘤血管生成的研究进展

 肿瘤血管生成是恶性肿瘤快速增殖和转移的重要途径,多种细胞及分子因素参与肿瘤血管生成过程。血管生成素-2（Ang-2）是重要的血管内皮生长因子之一,主要通过松解血管结构、破坏血管稳定性而影响肿瘤血管生成。近年来研究证实Ang-2在肿瘤血管生成中与其他血管生长因子相互作用共同调节新生血管形成。随着研究的新进展,Ang-2不仅会成为抗肿瘤血管生成治疗的重要靶点,而且联合其他信号通路作为共同靶点将进一步提高临床抗肿瘤疗效。     

Angiopoietin-3 inhibits pulmonary metastasis by inhibiting tumor angiogenesis

Angiopoietins (Ang-1, Ang-2, and Ang-3) are the ligands of Tie-2 receptor tyrosine kinase. The essential roles of Ang-1 and Tie-2 in embryonic angiogenesis have been established, and studies have demonstrated the involvement of Ang-1 and Ang-2 in tumor angiogenesis. However, the role of Ang-3 in tumor angiogenesis and metastasis and the mechanism underlying its function are totally unknown. We have shown recently that Ang-3 is tethered on cell surface via heparan sulfate proteoglycans. In our current study, we have demonstrated that overexpression of Ang-3 inhibits pulmonary metastasis of Lewis lung carcinoma and TA3 mammary carcinoma (TA3) cells by inhibiting tumor angiogenesis and promoting apoptosis of the tumor cells. In addition, we have demonstrated that the binding of Ang-3 to the cell surface is required for the effective inhibition of Ang-3 on tumor metastasis and that Ang-3 inhibits endothelial cell proliferation and survival and blocks Ang-1- and vascular endothelial growth factor-induced activation of extracellular signal-regulated kinase 1/2 and Akt kinases, which likely underlie the Ang-3-mediated inhibition on tumor angiogenesis and metastasis.     

The effects of angiopoietin-1 and -2 on tumor growth and angiogenesis in human colon cancer

Angiopoietin (Ang) 1 and Ang-2 are important regulators of endothelial cell survival. Current models suggest that an increase in Ang-2 expression in endothelial cells leads to initiation of angiogenesis. We stably transfected HT29 colon cancer cells with cDNA constructs for Ang-1 or -2 or with vector alone, injected the cells s.c. into nude mice, and assessed tumor growth. Immunohistochemical analyses confirmed sustained increases of Ang-1 and -2 in the tumors. The tumors produced by the Ang-2-transfected cells were larger than the tumors produced in the other groups; those tumors also had higher vessel counts and proliferative indices than tumors in the other groups. Tumors produced by the Ang-1 transfectants had fewer vessels and lower tumor cell proliferative indices than tumors in the other groups. These data suggest that imbalances between Ang-1 and -2 that result in a net gain of Ang-2 activity lead to enhanced tumor angiogenesis and growth.