Crosstalk between angiogenesis and lymphangiogenesis in tumor progression.

Extensive studies have identified reliable markers of lymphatic endothelial cells, and mechanisms and molecules that regulate development and growth of the lymphatic vessels. Vascular endothelial growth factors (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. By binding to its endothelial cell surface receptors VEGFR-1 and VEGFR-2, VEGF-A mediates vascular leakage, endothelial proliferation and migration. Angiopoietin-2 (Ang-2) is expressed at sites of blood vessel remodeling and invasion, and factors that induce angiogenesis in vivo, such as VEGF-A, upregulate Ang-2 in endothelial cells. In this review, we summarize the literature concerning the crosstalk between angiogenesis and lymphangiogenesis in tumor progression, that is, involvement of VEGF-C, VEGF-D and VEGFR-3 in angiogenesis, and the role played by VEGF-A and Ang-2 in lymphangiogenesis, respectively.     

Over expression of vascular endothelial growth factor and its receptor during the development of estrogen-induced rat pituitary tumors may mediate estrogen-initiated tumor angiogenesis

Estrogens, which have been associated with several types of human and animal cancers, can induce tumor angiogenesis in the pituitary of Fischer 344 rats. The mechanistic details of tumor angiogenesis induction, during estrogen carcinogenesis, are still unknown. To elucidate the role of estrogen in the regulation of tumor angiogenesis in the pituitary of female rats, the density of blood vessels was analysed using factor VIII related antigen (FVIIIRAg) immunohistochemistry and the expression of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) was examined by Western blot and immunohistochemical analysis. The expression of VEGF receptor (VEGFR-2/Flk-1/KDR) was also examined by immunohistochemistry. The results demonstrated that 17beta-estradiol (E2) induces neovascularization, as well as the growth and enlargement of blood vessels after 7 days of exposure. The high tumor angiogenic potential was associated with an elevated VEGF/VPF protein expression in the E2 exposed pituitary of ovariectomized (OVEX) rats. VEGF/VPF and FVIIIRAg immunohistochemistry and endothelial specific lectin (UEA1) binding studies, indicate that the elevation of VEGF protein expression initially occurred in both blood vessels and non-endothelial cells. After 15 days of E2 exposure, VEGF/VPF protein expression, in the non- endothelial cell population, sharply declined and was restricted to the blood vessels. The function of non-endothelial-derived VEGF is not clear. Furthermore, immunohistochemical studies demonstrated that VEGFR- 2 (flk-1/KDR), expression was elevated significantly in the endothelial cells of microblood vessels after 7 days of E2 exposure. These findings suggest that over expression of VEGF and its receptor (VEGFR-2) may play an important role in the initial step of the regulation of estrogen induced tumor angiogenesis in the rat pituitary.      

The tyrosine kinase inhibitor cediranib blocks ligand-induced vascular endothelial growth factor receptor-3 activity and lymphangiogenesis

Solid tumors express a range of factors required to sustain their growth and promote their dissemination. Among these are vascular endothelial growth factor-A (VEGF-A), the key angiogenic stimulant, and VEGF-C, a primary mediator of lymphangiogenesis. Small molecule tyrosine kinase inhibitors offer the potential to inhibit more than one kinase and impede tumor growth by multiple mechanisms. However, their potency toward individual targets can vary. Cediranib (RECENTIN; AZD2171) is an inhibitor of VEGF signaling that has been shown in experimental models to prevent VEGF-A-induced angiogenesis and primary tumor growth, yet the effects of cediranib on VEGF receptor (VEGFR)-3-mediated endothelial cell function and lymphangiogenesis are unknown. To better understand the activity of cediranib against VEGFR-3 and its associated signaling events compared with its activity against VEGFR-2, we used the receptor-specific ligands VEGF-E and VEGF-C156S. In human endothelial cells, cediranib inhibited VEGF-E-induced phosphorylation of VEGFR-2 and VEGF-C156S-induced phosphorylation of VEGFR-3 at concentrations of 相似文献   

Vascular endothelial growth factor receptor-2: its unique signaling and specific ligand,VEGF-E

Vascular endothelial growth factor receptor-2 (VEGFR-2/KDR/Flk-1) is a high-affinity receptor for vascular endothelial growth factor-A (VEGF-A), and mediates most of the endothelial growth and survival signals from VEGF-A. VEGFR-2 has a typical tyrosine kinase receptor structure with seven immunoglobulin (Ig)-like domains in the extracellular region, as well as a long kinase insert in the tyrosine kinase domain. It utilizes a unique signaling system for DNA synthesis in vascular endothelial cells, i.e. a phospholipase Cγ-protein kinaseC-Raf-MAP kinase pathway. Although VEGF-A binds two receptors, VEGFR-1 and -2, a newly isolated ligand VEGF-E (Orf-virus-derived VEGF) binds and activates only VEGFR-2. Transgenic mice expressing VEGF-E_NZ-7 showed a dramatic increase in angiogenesis with very few side effects (such as edema and hemorrhagic spots), suggesting strong angiogenic signaling and a potential clinical utility of VEGF-E. VEGF family members bear three loops produced via three intramolecular disulfide bonds, and cooperation between loop-1 and loop-3 is necessary for the specific binding and activation of VEGFR-2 for angiogenesis. As it directly upregulates tumor angiogenesis, VEGFR-2 is an appropriate target for suppression of solid tumor growth using exogenous antibodies, small inhibitory molecules and in vivo stimulation of the immune system.     

Targeting Angiogenesis in Cancer Therapy: Moving Beyond Vascular Endothelial Growth Factor

Angiogenesis, or the formation of new capillary blood vessels, occurs primarily during human development and reproduction; however, aberrant regulation of angiogenesis is also a fundamental process found in several pathologic conditions, including cancer. As a process required for invasion and metastasis, tumor angiogenesis constitutes an important point of control of cancer progression. Although not yet completely understood, the complex process of tumor angiogenesis involves highly regulated orchestration of multiple signaling pathways. The proangiogenic signaling molecule vascular endothelial growth factor (VEGF) and its cognate receptor (VEGF receptor 2 [VEGFR-2]) play a central role in angiogenesis and often are highly expressed in human cancers, and initial clinical efforts to develop antiangiogenic treatments focused largely on inhibiting VEGF/VEGFR signaling. Such approaches, however, often lead to transient responses and further disease progression because angiogenesis is regulated by multiple pathways that are able to compensate for each other when single pathways are inhibited. The platelet-derived growth factor (PDGF) and PDGF receptor (PDGFR) and fibroblast growth factor (FGF) and FGF receptor (FGFR) pathways, for example, provide potential escape mechanisms from anti-VEGF/VEGFR therapy that could facilitate resumption of tumor growth. Accordingly, more recent treatments have focused on inhibiting multiple signaling pathways simultaneously. This comprehensive review discusses the limitations of inhibiting VEGF signaling alone as an antiangiogenic strategy, the importance of other angiogenic pathways including PDGF/PDGFR and FGF/FGFR, and the novel current and emerging agents that target multiple angiogenic pathways for the treatment of advanced solid tumors.

Implications for Practice:

Significant advances in cancer treatment have been achieved with the development of antiangiogenic agents, the majority of which have focused on inhibition of the vascular endothelial growth factor (VEGF) pathway. VEGF targeting alone, however, has not proven to be as efficacious as originally hoped, and it is increasingly clear that there are many interconnected and compensatory pathways that can overcome VEGF-targeted inhibition of angiogenesis. Maximizing the potential of antiangiogenic therapy is likely to require a broader therapeutic approach using a new generation of multitargeted antiangiogenic agents.     

Differential effects of VEGFR-1 and VEGFR-2 inhibition on tumor metastases based on host organ environment

Tumors induce new blood vessel growth primarily from host organ microvascular endothelial cells (EC), and microvasculature differs significantly between the lung and liver. Vascular endothelial growth factor (VEGF or VEGF-A) promotion of tumor angiogenesis is thought to be mediated primarily by VEGF receptor-2 (VEGFR-2). In this study, VEGFR-2 antibody (DC101) inhibited growth of RenCa renal cell carcinoma lung metastases by 26%, whereas VEGFR-1 antibody (MF-1) had no effect. However, VEGFR-2 neutralization had no effect on RenCa liver metastases, whereas VEGFR-1 neutralization decreased RenCa liver metastases by 31%. For CT26 colon carcinoma liver metastases, inhibition of both VEGFR-1 and VEGFR-2 was required to induce growth delay. VEGFR-1 or VEGFR-2 inhibition decreased tumor burden not by preventing the establishment of micrometastases but rather by preventing vascularization and growth of micrometastases by 55% and 43%, respectively. VEGF induced greater phosphorylation of VEGFR-2 in lung ECs and of VEGFR-1 in liver ECs. EC proliferation, migration, and capillary tube formation in vitro were suppressed more by VEGFR-2 inhibition for lung EC and more by VEGFR-1 inhibition for liver EC. Collectively, our results indicate that liver metastases are more reliant on VEGFR-1 than lung metastases to mediate angiogenesis due to differential activity of VEGFRs on liver EC versus lung EC. Thus, therapies inhibiting specific VEGFRs should consider the targeted sites of metastatic disease.     

抗肿瘤血管生成靶向治疗进展

血管生成是肿瘤生长和转移的关键。抗血管生成是一种癌策略,其目标是抗为活跃增殖的肿瘤细胞提供氧气和营养的新生血管。通过阻断新血管的生成抑制癌症的生长和转移。目前,最确定的抑制肿瘤血管生成的方法是阻断血管内皮生长因子（vascular endothelial growth factor,VEGF）通路。但最近,一些非VEGF因子如血小板衍生因子（platelet-derived growth factor,PDGF）、成纤维细胞生长因子（fibroblast growth factor,FGF）、肝细胞生长因子（hepatocyte growth factor,HGF）及血管生成素（angiogenin,Ang）等也参与肿瘤血管生成,强调有必要发展药物针对多种促血管生成途径。     

E7050: A dual c-Met and VEGFR-2 tyrosine kinase inhibitor promotes tumor regression and prolongs survival in mouse xenograft models

c-Met is the cellular receptor for hepatocyte growth factor (HGF) and is known to be dysregulated in various types of human cancers. Activation of the HGF/c-Met pathway causes tumor progression, invasion, and metastasis. Vascular endothelial growth factor (VEGF) is also known as a key molecule in tumor progression through the induction of tumor angiogenesis. Because of their key roles in tumor progression, these pathways provide attractive targets for therapeutic intervention. We have generated a novel, orally active, small molecule compound, E7050, which inhibits both c-Met and vascular endothelial growth factor receptor (VEGFR)-2. In vitro studies indicate that E7050 potently inhibits phosphorylation of both c-Met and VEGFR-2. E7050 also potently represses the growth of both c- met amplified tumor cells and endothelial cells stimulated with either HGF or VEGF. In vivo studies using E7050 showed inhibition of the phosphorylation of c-Met and VEGFR-2 in tumors, and strong inhibition of tumor growth and tumor angiogenesis in xenograft models. Treatment of some tumor lines containing c- met amplifications with high doses of E7050 (50–200 mg/kg) induced tumor regression and disappearance. In a peritoneal dissemination model, E7050 showed an antitumor effect against peritoneal tumors as well as a significant prolongation of lifespan in treated mice. Our results indicate that E7050 is a potent inhibitor of c-Met and VEGFR-2 and has therapeutic potential for the treatment of cancer. ( Cancer Sci 2009)     

Novel therapeutic approaches for targeting tumor angiogenesis

Current attempts to disrupt the complex process of tumor blood vessel formation are predominantly focused on targeting the vascular endothelial growth factor (VEGF)-VEGFR signaling pathway. Although clinically proven to inhibit VEGF and its receptors, these pharmacologic agents are selective, but not specific. Consequently, many of the approved inhibitors also impair other molecular targets leading to increased toxicity. Current efforts to unravel the complexity of tumor angiogenesis have identified several new candidates for antivascular therapy. In this review article, we identify well-established and novel angiogenic molecules and discuss benefits of the therapeutic approaches based on targeting of such factors.     

VEGF receptor signaling in tumor angiogenesis

The growth of human tumors and development of metastases depend on the de novo formation of blood vessels. The formation of new blood vessels is tightly regulated by specific growth factors that target receptor tyrosine kinases (RTKs). Vascular endothelial growth factor (VEGF) and the Flk-1/KDR RTK have been implicated as the key endothelial cell-specific factor signaling pathway required for pathological angiogenesis, including tumor neovascularization. Inhibition of the VEGF tyrosine kinase signaling pathway blocks new blood vessel formation in growing tumors, leading to stasis or regression of tumor growth. Advances in understanding the biology of angiogenesis have led to the development of several therapeutic modalities for the inhibition of the VEGF tyrosine kinase signaling pathway. A number of these modalities are under investigation in clinical studies to evaluate their potential to treat human cancers.     

Different cascades in the signaling pathway of two vascular endothelial growth factor (VEGF) receptors for the VEGF-mediated murine hepatocellular carcinoma development

It has been shown that the interaction between the potent angiogenic factor; the vascular endothelial growth factor (VEGF) and its receptors (VEGFR-1 and VEGFR-2), plays a pivotal role in tumor development, including hepatocellular carcinoma (HCC). However, the properties of the respective VEGF receptor in the signaling transduction pathway of VEGF-mediated effects in HCC have not been elucidated yet. The aim of this study was to examine the respective signaling pathway of two VEGFRs in the VEGF-mediated murine HCC development and angiogenesis. We examined the signaling cascades of VEGFR-1 and VEGFR-2 in the VEGF-mediated HCC development in combination with a retroviral tetracycline (tet)-regulated (Retro-Tet) gene expression system, which can manipulate the gene expression in vivo by providing tet in the drinking water, as well as VEGFR-1 and VEGFR-2 specific neutralizing monoclonal antibodies (R-1mAb and R-2mAb, respectively). Both R-1mAb and R-2mAb significantly suppressed the VEGF-mediated tumor growth associated with reduction of the tumoral neovascularization, and the combination treatment with both mAbs almost completely attenuated the tumor development and angiogenesis. The protein kinase-C (PKC) and MEK1/2 activities in the tumor were markedly attenuated by treatment with R-2mAb, whereas R-1mAb did not alter these activities. These results suggested that both VEGFR-1 and VEGFR-2 play important roles, and lie in the different signaling cascades by which VEGF augments HCC development and angiogenesis.     

Cannabinoids inhibit the vascular endothelial growth factor pathway in gliomas

Cannabinoids inhibit tumor angiogenesis in mice, but the mechanism of their antiangiogenic action is still unknown. Because the vascular endothelial growth factor (VEGF) pathway plays a critical role in tumor angiogenesis, here we studied whether cannabinoids affect it. As a first approach, cDNA array analysis showed that cannabinoid administration to mice bearing s.c. gliomas lowered the expression of various VEGF pathway-related genes. The use of other methods (ELISA, Western blotting, and confocal microscopy) provided additional evidence that cannabinoids depressed the VEGF pathway by decreasing the production of VEGF and the activation of VEGF receptor (VEGFR)-2, the most prominent VEGF receptor, in cultured glioma cells and in mouse gliomas. Cannabinoid-induced inhibition of VEGF production and VEGFR-2 activation was abrogated both in vitro and in vivo by pharmacological blockade of ceramide biosynthesis. These changes in the VEGF pathway were paralleled by changes in tumor size. Moreover, intratumoral administration of the cannabinoid Delta9-tetrahydrocannabinol to two patients with glioblastoma multiforme (grade IV astrocytoma) decreased VEGF levels and VEGFR-2 activation in the tumors. Because blockade of the VEGF pathway constitutes one of the most promising antitumoral approaches currently available, the present findings provide a novel pharmacological target for cannabinoid-based therapies.     

Angiogenesis in patients with craniopharyngiomas: correlation with treatment and outcome

BACKGROUND: Craniopharyngiomas are histologically benign epithelial neoplasms of the sellar region that often exhibit aggressive and invasive growth. The authors hypothesized that tumor proliferation, spread, and recurrence are angiogenesis dependent and investigated the significance of vascularization relative to biologic behavior. To the authors' knowledge, angiogenesis for patients with craniopharyngiomas has not been examined to date. METHODS: The authors measured microvessel densities in resected, histologically proven craniopharyngiomas using immunostains for CD-34, a monoclonal antibody that selectively recognizes endothelial cells. Both histologic types of craniopharyngiomas, adamantinomatous and papillary, were included in the study. In addition, the cellular distribution of vascular endothelial growth factor (VEGF), a strong stimulator of new vessel formation, was assessed by both immunohistochemistry and in situ hybridization for VEGF receptor 2 (VEGFR-2) mRNA expression. RESULTS: Histologically, small numbers of capillaries were identified in temporal stroma but not in their epithelial components. Immunohistochemistry revealed strong, conclusive cytoplasmic immunoreactivity for VEGF in the epithelial cells of both adamantinomatous craniopharyngiomas and papillary craniopharyngiomas. In situ hybridization showed that VEGFR-2 mRNA was expressed widely, not only in neoplastic epithelium but also in capillary endothelium. CONCLUSIONS: Tumors with greater microvessel density regrow more frequently compared with tumors that have lower microvessel density, suggesting that the extent of angiogenesis is of prognostic value in patients with craniopharyngioma. VEGFR-2 may act as a key modulator of VEGF activity in endothelial cells and nonendothelial cells, indicating that VEGF plays an important role in the behavior of craniopharyngiomas.     

Role of the vascular endothelial growth factor pathway in tumor growth and angiogenesis.

New blood vessel formation (angiogenesis) is a fundamental event in the process of tumor growth and metastatic dissemination. Hence, the molecular basis of tumor angiogenesis has been of keen interest in the field of cancer research. The vascular endothelial growth factor (VEGF) pathway is well established as one of the key regulators of this process. The VEGF/VEGF-receptor axis is composed of multiple ligands and receptors with overlapping and distinct ligand-receptor binding specificities, cell-type expression, and function. Activation of the VEGF-receptor pathway triggers a network of signaling processes that promote endothelial cell growth, migration, and survival from pre-existing vasculature. In addition, VEGF mediates vessel permeability, and has been associated with malignant effusions. More recently, an important role for VEGF has emerged in mobilization of endothelial progenitor cells from the bone marrow to distant sites of neovascularization. The well-established role of VEGF in promoting tumor angiogenesis and the pathogenesis of human cancers has led to the rational design and development of agents that selectively target this pathway. Studies with various anti-VEGF/VEGF-receptor therapies have shown that these agents can potently inhibit angiogenesis and tumor growth in preclinical models. Recently, an anti-VEGF antibody (bevacizumab), when used in combination with chemotherapy, was shown to significantly improve survival and response rates in patients with metastatic colorectal cancer and thus, validate VEGF pathway inhibitors as an important new treatment modality in cancer therapy.     

Vascular endothelial growth factor is an in vivo survival factor for tumor endothelium in a murine model of colorectal carcinoma liver metastases

BACKGROUND: Recent studies have suggested that vascular endothelial growth factor (VEGF), in addition to its proangiogenic properties, also functions as a survival factor for endothelial cells. The authors hypothesized that inhibition of VEGF activity by blockade of VEGF receptor-2 (R-2) function prevents angiogenesis and decreases tumor growth in colon carcinoma liver metastases. METHODS: Spleens of mice were injected with human colon carcinoma cells producing liver metastases. After 7 days of tumor growth, groups of mice received either antibody to VEGFR-2 (DC101) or phosphate-buffered saline (control). In a follow-up experiment, a similar treatment regimen was followed except that mice were sacrificed at 1-week intervals to assess the time course of endothelial cell and tumor cell apoptosis. RESULTS: After 21 days of therapy, the authors observed a significant decrease in vessel counts in liver metastases from human colon carcinoma in nude mice after therapy with VEGFR-2 antibody. Tumor cell apoptosis was increased significantly in the tumors of mice receiving DC101. Temporal studies with immunofluorescent double staining for the microvasculature and apoptotic cells revealed an increase in endothelial cell apoptosis that preceded an increase in tumor cell apoptosis. In vitro, treatment of human umbilical vein endothelial cells with antibody to VEGFR-2 produced a > 2.5-fold increase in endothelial cell apoptosis. CONCLUSIONS: Therapy targeting the VEGFR-2 inhibited tumor growth in a murine model of colon carcinoma liver metastasis. Surprisingly, this therapy did not only inhibit angiogenesis but also led to endothelial cell death. These findings suggest that VEGF, via VEGFR-2 signaling, functions as a survival factor for tumor endothelial cells in liver metastases from colon carcinoma.     

Angiogenesis inhibitors in the treatment of non-small cell lung cancer

A therapeutic plateau seems to have been reached with the standard treatment of cytotoxic chemotherapy alone for advanced stage non-small cell lung cancer (NSCLC) and new treatment options are urgently needed. Recent insight into the molecular biology of cancer has identified angiogenesis as one of the key biological processes. The major player in tumor angiogenesis is the vascular endothelial growth factor (VEGF) pathway. VEGF is expressed in the majority of NSCLC and overexpression is associated with a poor prognosis. The VEGF pathway can be inhibited in two main ways: targeting VEGF directly or inhibiting the VEGF receptors. The development of angiogenesis inhibitors has shown great promise in the treatment of NSCLC. Bevacizumab, an anti-VEGF antibody, has been approved for the treatment of advanced NSCLC and other drugs are undergoing phase III investigation. However, a number of unresolved issues remain. In this review, we discuss the main angiogenesis inhibitors in development for the treatment of NSCLC focusing on the VEGF pathway.     

Bee venom inhibits tumor angiogenesis and metastasis by inhibiting tyrosine phosphorylation of VEGFR-2 in LLC-tumor-bearing mice

Bee venom (BV) treatment is the therapeutic application of honeybee venom (HBV) for treating various diseases in Oriental medicine. In the present work, the authors investigated the functional specificity of BV as an angiogenesis inhibitor using in vitro models and in vivo mouse angiogenesis and lung metastasis models. BV significantly inhibited the viability of Lewis lung carcinoma (LLC) cells but did not affect peripheral blood mononuclear lymphocytes (PBML) cells. BV also inhibited vascular endothelial growth factor (VEGF)-induced proliferation, migration and capillary-like tube formation of human umbilical vein endothelial cells (HUVECs). Western blotting analysis showed that BV inhibited AKT and MAPK phosphorylation in LLC cells and HUVECs and down regulated expression of VEGF and VEGFR-2 of LLC cells and HUVECs. Also, BV effectively disrupted VEGF-induced neovascularization in Matrigel plugs in our in vivo angiogenesis assay. When given subcutaneously, BV also significantly suppressed tumor angiogenesis through inhibition of VEGF and VEGFR-2 in LLC model. Mice bearing subcutaneous LLC tumors were treated with 1 μg/ml or 10 μg/ml of BV. They showed reductions ranging between 49% and 62% in primary tumor volume and reduction of spontaneous pulmonary metastasis occurrences. Furthermore, BV treatment in the spontaneous lung metastases model after primary tumor excision prolonged their median survival time from 27 to 58 days. These results suggest that the tumor-specific anti-angiogenic activity of BV takes effect during different stages of tumor progression by blocking the tyrosine phosphorylation of VEGFR-2, and validate the application of BV in lung cancer treatment.