Blockade of vascular endothelial growth factor receptor-3 signaling inhibits fibroblast growth factor-2-induced lymphangiogenesis in mouse cornea

Suppression of VEGFR-3 signaling inhibits lymph node metastasis in gastric cancer

In gastric cancer, lymph node metastasis is one of the major prognostic factors and forms the basis for surgical removal of local lymph nodes. Recently, several studies have demonstrated that overexpression of lymphangiogenic growth factor VEGF-C or VEGF-D induces tumor lymphangiogenesis and promotes lymphatic metastasis in mouse tumor models. We examined whether these processes could be inhibited in naturally metastatic tumors by blocking of their cognate receptor VEGFR-3 signaling pathway. Using a mouse orthotopic gastric cancer model which has a high frequency of lymph node metastasis, we estimated lymphatic vessels in gastric cancers by immunostaining for VEGFR-3 and other specific lymphatic markers, LYVE-1 and prox-1. Then we systemically administered anti-VEGFR-3 blocking antibodies. This treatment resulted in the inhibition of regional lymph node metastasis and reduction of lymphatic vessel density in the primary tumors. In addition, increased density of LYVE-1-positive lymphatic vessels of primary tumors was closely correlated with lymph node metastasis in human samples of gastric cancer. Antilymphangiogenesis by inhibiting VEGFR-3 signaling could provide a potential strategy for the prevention of lymph node metastasis in gastric cancer.

Expression of vascular endothelial growth factor (VEGF)-C and VEGF-D, and their receptor VEGFR-3, during different stages of cervical carcinogenesis

Cervical carcinogenesis has well-defined stages of disease progression including three grades of pre-invasive lesions--cervical intraepithelial neoplasia grades 1-3 (CIN 1-3)--and invasive cervical cancer. However, the biological properties of CIN lesions prone to develop invasive disease are not well defined. Recent observations suggest that early invasive disease spreads to regional lymph nodes in several tumour types and that growth factors (VEGF-C and VEGF-D) involved in new lymphatic vessel formation may play a crucial role in this process. The present study has assessed the expression of VEGF-C and VEGF-D, and their receptor VEGFR-3, in 152 cervical lesions (33 CIN 1, 33 CIN 2, 37 CIN 3, and 49 squamous cell carcinomas) to determine whether expression of lymphangiogenic factors occurs prior to invasion. The presence of lymphatic vessels was determined using LYVE-1 and podoplanin staining, as well as double immunostaining for LYVE-1/CD34 and podoplanin/CD34. In situ hybridization was performed to determine VEGFR-3 mRNA expression. A significant positive correlation was found between VEGF-C, VEGF-D, and VEGFR-3 expression through the different stages of cervical carcinogenesis. Significant differences in protein expression for VEGF-C, VEGF-D, and VEGFR-3 were found between CIN 1-2 and CIN 3 (p<0.001 for all), but not between CIN 3 and cervical cancer. More than 50% of the CIN 3 lesions showed moderate to strong staining for VEGF-C and VEGF-D, whereas most of the early pre-cancerous lesions (CIN 1 and 2) were negative. In cervical cancer, similar observations to those in CIN 3 were found. VEGFR-3 mRNA expression was found in the cytoplasm of epithelial neoplastic cells and VEGFR3 protein expression was found in more than 50% of CIN 3 lesions and cervical cancers, compared with 15% in CIN 1 and 2. These findings suggest an autocrine growth stimulation pattern via VEGFR-3. Adjacent CIN 3 was present in nine cervical cancers and displayed strong expression for VEGF-C, VEGF-D, and VEGFR-3. These results suggest that in cervical carcinogenesis a switch to the lymphangiogenic phenotype may occur at the stage of CIN 3.

Expression and significance of VEGF-C and FLT-4 in gastric cancer

AIM: To investigate the expression of pathological factors of VEGF-C and its receptor FLT-4 in primary gastric cancer and adjacent normal tissues.

METHODS: The expression of VEGF-C and FLT-4 was studied in 80 primary gastric cancers and adjacent normal tissues from the same patients by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immumohistochemistry.

RESULTS: Both primary gastric cancer and adjacent normal tissue could express VEGF-C and FLT-4, and FLT-4 expression was also detected in endothelial cells of stromal blood vessels and lymphatic vessels. There was a significant difference in expression of VEGF-C between primary tumor and adjacent normal tissue samples (P = 0.01), and a statistical correlation between VEGF-C and FLT-4 expression in tumors (P = 0.00886). With regard to VEGF-C expression, there was a significant difference between moderate-poor differential type and high differential type (P = 0.032), and a significant difference between positive and negative lymph node metastases (P = 0.024). However, there was no significant difference between positive and negative serosal invasions (P = 0.219).

CONCLUSION: VEGF-C and its receptor FLT-4 play a role in the development of gastric cancer, and the tumors with expression of VEGF-C and FLT-4 are more likely to have lymph node metastasis.

B lymphocyte-specific c-Myc expression stimulates early and functional expansion of the vasculature and lymphatics during lymphomagenesis

Expression of the c-myc proto-oncogene is deregulated in many human cancers. We examined the role of c-Myc in stimulating angiogenesis and lymphangiogenesis in a highly metastatic murine model of Burkitt's lymphoma (E micro -c-myc), where c-Myc is expressed exclusively in B lymphocytes. Immunohistochemical analysis of bone marrow and lymph nodes from young (preneoplastic) E micro -c-myc transgenic mice revealed increased growth of blood vessels, which are functional by dye flow assay. Lymphatic sinuses also increased in size and number within the lymph nodes, as demonstrated by immunostaining for with a lymphatic endothelial marker 10.1.1. The 10.1.1 antibody recognizes VEGFR-2- and VEGFR-3-positive lymphatic sinuses and vessels within lymph nodes, and also recognizes lymphatic vessels in other tissues. Subcutaneously injected dye traveled more efficiently through draining lymph nodes in E micro -c-myc mice, indicating that these hypertrophic lymphatic sinuses increase lymph flow. Purified B lymphocytes and lymphoid tissues from E micro -c-myc mice expressed increased levels of vascular endothelial growth factor (VEGF) by immunohistochemical or immunoblot assays, which could promote blood and lymphatic vessel growth through interaction with VEGFR-2, which is expressed on the endothelium of both vessel types. These results indicate that constitutive c-Myc expression stimulates angiogenesis and lymphangiogenesis, which may promote the rapid growth and metastasis of c-Myc-expressing cancer cells, respectively.

Gene Transfer for Therapeutic Vascular Growth in Myocardial and Peripheral Ischemia

Therapeutic vascular growth in the treatment of peripheral and myocardial ischemia has not yet fulfilled its expectations in clinical trials. Randomized, double-blinded placebo-controlled trials have predominantly shown the safety and feasibility but not the clear-cut clinically relevant efficacy of angiogenic gene or recombinant growth factor therapy. It is likely that growth factor levels achieved with single injections of recombinant protein or naked plasmid DNA are too low to induce any relevant angiogenic effects. Also, the route of administration of gene transfer vectors has not been optimal in many cases leading to low gene-transfer efficacy. Animal experiments using intramuscular or intramyocardial injections of adenovirus encoding vascular endothelial growth factor (VEGF, VEGF-A), the mature form of VEGF-D, and fibroblast growth factors (FGF-1, -2, and -4) have shown high angiogenic efficacy. Adenoviral overexpression of VEGF receptor-2 ligands, VEGF-A and the mature form of VEGF-D, enlarge the preexisting capillaries in skeletal muscle and myocardium via nitric oxide(NO)-mediated mechanisms and via proliferation of both endothelial cells and pericytes, resulting in markedly increased tissue perfusion. VEGF also enhances collateral growth, which is probably secondary to increased peripheral capillary blood flow and shear stress. As a side effect of VEGF overexpression and rapid microvessel enlargement, vascular permeability increases and may result in substantial tissue edema and pericardial effusion in the heart. Because of the transient adenoviral gene expression, the majority of angiogenic effects and side effects return to baseline by 2 weeks after the gene transfer. In contrast, VEGF overexpression lasting over 4 weeks has been shown to induce the growth of a persistent vascular network in preclinical models. To improve efficacy, the choice of the vascular growth factor, gene transfer vector, and route of administration should be optimized in future clinical trials. This review is focused on these issues.

Extracellular matrix regulates endothelial functions through interaction of VEGFR-3 and integrin ?5?1

Endothelium extracellular matrix (ECM) interactions can provide distinct spatial and molecular signals which control cellular proliferation, migration, and differentiation. Here, we investigated the role of fibronectin (FN), a major ECM protein, on the functions of lymphatic endothelial cells (LEC). We observed that FN, the ligand for integrin alpha5beta1, selectively promoted the growth of LEC as compared with vitronectin (VN) in the presence of the ligand for vascular endothelial growth factor receptor 3 [VEGFR-3 (VEGF-C156S)]. Upon investigating the mechanisms whereby ECM components regulate VEGFR-3 signaling, we found that FN transactivated VEGFR-3 and significantly enhanced the phosphorylation of VEGFR-3 induced by VEGF-C156S as compared to VN. An enhanced association of the integrin subunit alpha5 or beta1 with VEGFR-3, after stimulation with VEGF-C156S, was observed by co-immunoprecipitation. While blockade of integrin alpha5beta1 inhibited the VEGF-C156S-induced phosphorylation of VEGFR-3, no similar effect was obtained by blocking integrin alphavbeta3. FN also protected the endothelial cells from serum deprivation-induced apoptosis. Moreover, while the specific PI3 kinase inhibitor, LY294002, abolished this FN-mediated cell survival, the MAPK kinase inhibitor, PD98059, had no significant effect. Furthermore, a dominant-negative mutant of VEGFR-3 (G857R) reduced VEGF-C156S or FN-mediated cell survival, as well as the activities of PI3 kinase/Akt. Our results indicate that integrin alpha5beta1 participates in the activation of both VEGFR-3 and its downstream PI3 kinase/Akt signaling pathway, which is essential for FN-mediated lymphatic endothelial cell survival and proliferation.

Fibroblast growth factor-2-mediated capillary morphogenesis of endothelial cells requires signals via Flt-1/vascular endothelial growth factor receptor-1: possible involvement of c-Akt

Capillary morphogenesis is a crucial angiogenic response of endothelial cells. Although fibroblast growth factor-2 (FGF-2) potently induces capillary morphogenesis, the contribution of vascular endothelial growth factor-A (VEGF-A) in this response has not been clarified well. Here we examined the role of VEGF signaling in FGF-2-induced capillary morphogenesis by murine brain capillary endothelial cells (IBE cells) and human umbilical vein endothelial cells. FGF-2-treated IBE cells rapidly extended on Matrigel in association with actin reorganization. Chimeric protein, of which the extracellular domain of VEGF receptor-1 (VEGFR-1) fused to immunoglobulin Fc, inhibited FGF-2-induced cell extension, resulting in decreased capillary morphogenesis. Blocking antibody against VEGFR-1 inhibited FGF-2-induced capillary formation. Also, anti-VEGF-A antibody inhibited FGF-2-induced capillary morphogenesis, which was restored by the addition of placental growth factor-1. Similar results were obtained by the experiments with human umbilical vein endothelial cells. Expression of kinase-inactive c-Akt in IBE cells showed impaired capillary morphogenesis promoted by FGF-2. Conversely, stable cell lines expressing activated c-Akt demonstrated ligand-independent capillaries, which were resistant to the treatment with anti-VEGFR-1 blocking antibody. Upstream of c-Akt, calmodulin-dependent signals seemed to be involved. Taken together, signals via VEGFR-1 were required for FGF-2-induced capillary morphogenesis by endothelial cells, and c-Akt activity seemed to be involved in this process.

Novel expression of vascular endothelial growth factor receptor (VEGFR)-3 and VEGF-C on corneal dendritic cells

Vascular endothelial growth factor-3 (VEGFR-3) plays a critical role in embryonic cardiovascular development and is thought to be expressed exclusively on the lymphatic endothelium, high endothelial venules, and rarely on adult vascular endothelium. Recent evidence also suggests expression of VEGFR-3 on some tumor-associated macrophages. We have studied the expression of VEGFR-3, its ligand VEGF-C and the co-receptor neuropilin-2, in normal and inflamed corneas and characterized the phenotype and distribution of VEGFR-3(+) cells. Our data demonstrate, for the first time, the expression of VEGFR-3 on corneal dendritic cells (DC) and its up-regulation in inflammation. VEGFR-3(+) DC are CD11c(+)CD45(+)CD11b(+), and are mostly major histocompatibility (MHC) class II(-)CD80(-)CD86(-), indicating immature DC of a monocytic lineage. During inflammation, there is rapid increase in the number of VEGFR-3(+) DC in the cornea associated with heightened membranous expression as compared to a mostly intracellular expression in uninflamed tissue. VEGFR-3(+) DC in normal corneas are VEGF-C(-)neuropilin-2(-), but express VEGF-C in inflammation. Interestingly, similar cells are absent both in the normal and inflamed skin. These data demonstrate, for the first time, the expression of VEGFR-3 and VEGF-C on tissue DC, which implicate a novel potential relationship between lymphangiogenesis and leukocyte trafficking in the eye.

The secretory proprotein convertases furin, PC5, and PC7 activate VEGF-C to induce tumorigenesis

The secretory factor VEGF-C has been directly implicated in various physiological processes during embryogenesis and human cancers. However, the importance of the conversion of its precursor proVEGF-C to mature VEGF-C in tumorigenesis, and vessel formation and the identity of the protease(s) that regulate these processes is/are not known. The intracellular processing of proVEGF-C that occurs within the dibasic motif HSIIRR(227)SL suggests the involvement of the proprotein convertases (PCs) in this process. In addition, furin and VEGF-C were found to be coordinately expressed in adult mouse tissues. Cotransfection of the furin-deficient colon carcinoma cell line LoVo with proVEGF-C and different PC members revealed that furin, PC5, and PC7 are candidate VEGF-C convertases. This finding is consistent with the in vitro digestions of an internally quenched synthetic fluorogenic peptide mimicking the cleavage site of proVEGF-C ((220)Q-VHSIIRR downward arrow SLP(230)). The processing of proVEGF-C is blocked by the inhibitory prosegments of furin, PC5, and PACE4, as well as by furin-motif variants of alpha2-macroglobulin and alpha1-antitrypsin. Subcutaneous injection of CHO cells stably expressing VEGF-C into nude mice enhanced angiogenesis and lymphangiogenesis, but not tumor growth. In contrast, expression of proVEGF-C obtained following mutation of the cleavage site (HSIIRR(227)SL to HSIISS(227)SL) inhibits angiogenesis and lymphangiogenesis as well as tumor growth. Our findings demonstrate the processing of proVEGF-C by PCs and highlight the potential use of PC inhibitors as agents for inhibiting malignancies induced by VEGF-C.

Tumor lymphangiogenesis: a novel prognostic indicator for cutaneous melanoma metastasis and survival

Malignant melanomas of the skin are distinguished by their propensity for early metastatic spread via lymphatic vessels to regional lymph nodes, and lymph node metastasis is a major determinant for the staging and clinical management of melanoma. However, the importance of tumor-induced lymphangiogenesis for lymphatic melanoma spread has remained unclear. We investigated whether tumor lymphangiogenesis occurs in human malignant melanomas of the skin and whether the extent of tumor lymphangiogenesis may be related to the risk for lymph node metastasis and to patient survival, using double immunostains for the novel lymphatic endothelial marker LYVE-1 and for the panvascular marker CD31. Tumor samples were obtained from clinically and histologically closely matched cases of primary melanomas with early lymph node metastasis (n = 18) and from nonmetastatic melanomas (n = 19). Hot spots of proliferating intratumoral and peritumoral lymphatic vessels were detected in a large number of melanomas. The incidence of intratumoral lymphatics was significantly higher in metastatic melanomas and correlated with poor disease-free survival. Metastatic melanomas had significantly more and larger tumor-associated lymphatic vessels, and a relative lymphatic vessel area of >1.5% was significantly associated with poor disease-free and overall survival. In contrast, no differences in the density of tumor-associated blood vessels were found. Vascular endothelial growth factor and vascular endothelial growth factor-C expression was equally detected in a minority of cases in both groups. Our results reveal tumor lymphangiogenesis as a novel prognostic indicator for the risk of lymph node metastasis in cutaneous melanoma.

Gene transfer as a tool to induce therapeutic vascular growth

Therapeutic induction of vascular growth may provide a treatment option for those patients with myocardial or peripheral ischemia who are not suited to conventional revascularization therapies. Some lymphatic vascular disorders may also be amenable to this therapy. However, clear evidence of efficacy must be obtained from phase 2 and 3 clinical trials before these new treatments can be entered into clinical practice. Apart from the clinical applications, gene transfer aimed at stimulating or blocking vascular growth with various growth factors, cytokines, transcription factors and receptors or their antagonists is useful for analyzing the effects of those molecules on the vasculature, especially when gene targeting results in lethality or when large animal models are required.

Corneal lymphangiogenesis: evidence, mechanisms, and implications for corneal transplant immunology

PURPOSE

The normal cornea is devoid of blood and lymphatic vessels but can become vascularized secondary to a variety of corneal diseases and surgical manipulations. Whereas corneal (hem)angiogenesis, i.e., the outgrowth of new blood vessels from preexisting limbal vessels, is obvious both clinically and histologically, proof of associated corneal lymphangiogenesis has long been hampered by invisibility and lack of specific markers. This has changed with the recent discovery of the lymphatic endothelial markers vascular endothelial growth factor receptor 3, LYVE-1 (a lymphatic endothelium-specific hyaluronan receptor), Prox 1, and Podoplanin.

METHODS

We herein summarize the current evidence for lymphangiogenesis in the cornea and describe its molecular markers and mediators. Furthermore, the pathophysiologic implications of corneal lymphangiogenesis for corneal transplant immunology are discussed.

RESULTS

Whereas corneal angiogenesis in vascularized high-risk beds provides a route of entry for immune effector cells to the graft, lymphangiogenesis enables the exit of antigen-presenting cells and antigenic material from the graft to regional lymph nodes, thus inducing alloimmunization and subsequent graft rejection.

CONCLUSIONS

Antilymphangiogenic strategies may improve transplant survival both in the high- and low-risk setting of corneal transplantation.

Tumour-Induced Angiogenesis: A Review

Angiogenesis, the formation of new blood vessels, has become a broad subject and is a very active area for current research. This paper describes the main biological events involved in angiogenesis and their importance in cancer progression. In the first section, a fundamental overview of tumour biology is presented. In the second section, the biology of healthy blood vessels is described and, in the third section, the mechanisms of cell migration and proliferation, which are crucial to angiogenesis, are discussed. In the fourth section, a detailed account of tumour-induced angiogenesis is given, whilst the pro- and anti-angiogenic factors involved are reviewed in the fifth section. Finally, the processes of tumour invasion and metastasis are examined in the sixth section.

Human Schlemm's canal cells express the endothelial adherens proteins, VE-cadherin and PECAM-1

Purpose. The majority of resistance to outflow of aqueous humor resides at or near the inner wall of Schlemm's canal (SC). Transmembrane proteins that contribute to the generation of resistance to aqueous outflow likely participate in junctional complexes between SC cells. The purpose of the present study was to examine the expression of cadherins in SC cells that play a significant role in adherens junction complexes that control permeability of vascular endothelia. Methods. Identification of cadherin subtype mRNAs was examined by hybridization screening of three different SC cDNA libraries and by polymerase chain reaction analysis with degenerate primers. Expression of endothelial adherens proteins, vascular endothelial (VE)-cadherin and platelet endothelial cell adhesion molecule-1 (PECAM-1), was examined by western blot analyses of whole cell lysates prepared from SC and trabecular meshwork cells and by immunofluorescence microscopy of frozen sections of human anterior chambers. As controls, bovine retinal, bovine aortic, human umbilical vein and human iliac vein endothelial cells were examined for VE-cadherin expression. Results. Screens of SC cDNAs revealed abundant expression of N-cadherin and VE-cadherin. Expression of VE-cadherin protein was identified in both inner and outer wall SC cells, appropriately localized to SC intercellular borders and appeared as a single band of approximately 130 kDa by western blot analysis. Specific labeling of PECAM-1 was similar to VE-cadherin and appeared as a single band of approximately 130 kDa by western blot analysis. Conclusions. VE-cadherin and PECAM-1 expression in SC suggests that SC cells are vascular in origin and contain adherens protein likely involved in restricting fluid flow across the inner wall of SC.

The role of fibroblast growth factors in vascular development

Fibroblast growth factors (FGFs) are considered angiogenic factors, yet the exact relationship between FGF and vascular development in normal and pathological tissue has long remained elusive. However, recent results from gene inactivation and transgenic studies in mice and in culture systems have demonstrated the role of FGFs in vessel assembly and sprouting. FGFs also promote blood-vessel branching and induce lymphangiogenesis. Novel players in FGF-mediated angiogenesis have been identified, such as p38 mitogen-activated protein kinase. Tumour angiogenesis is regulated by FGFs directly or indirectly via secondary angiogenesis factors, such as vascular endothelial growth factor. The newly established angiogenic role of FGFs makes FGF or molecules targeting FGF and its receptor promising candidates for the development of novel therapeutics.

Lymphangiogenesis and cancer metastasis

Lymphatic vessels are important for the spread of solid tumours, but the mechanisms that underlie lymphatic spread and the role of lymphangiogenesis (the growth of lymphatics) in tumour metastasis has been less clear. This article reviews recent experimental and clinico-pathological data indicating that growth factors that stimulate lymphangiogenesis in tumours are associated with an enhanced metastatic process.