Induced lymphatic sinus hyperplasia in sentinel lymph nodes by VEGF-C as the earliest premetastatic indicator

Research on tumor-induced lymphangiogenesis has predominantly focused on alterations and abnormal growth of peritumoral and intratumoral lymphatic vessels. However, recent evidence indicates that lymphangiogenesis of sentinel lymph nodes might also contribute to cancer progression. In clinical oncology, the sentinel lymph nodes play an important role in diagnosis, staging and management of disease. The prognostic value that may be placed in the analysis of various parameters in tumor-free lymph nodes is still under debate. We, therefore, chose to investigate genetically fluorescent MDA-MB-435/green fluorescent protein human cancer cells transfected to overexpress VEGF-C in a nude mouse model and investigated metastasis, lymph node lymphangiogenesis, lymph node angiogenesis and size of sentinel lymph nodes. The nature of MDA-MB-435, identified as a breast cancer cell line for several decades, has recently been reidentified as being from melanoma origin. Vascular endothelial growth factor-C overexpression induced early metastasis and significantly increased the lymphatic vessel area in sentinel lymph nodes even before the tumor metastasis. At early time-points, expansion of the lymphatic network was observed even though no difference of blood vessel area and lymph node size was detected. These results suggest that primary tumors -via secretion of VEGF-C- can induce hyperplasia of the sentinel lymph node lymphatic vessel network and thereby promote their further spread. In cases of tumor-free lymph nodes the increased lymphatic network of sentinel lymph nodes is a very early premetastatic sign and may provide a new prognostic indicator and target for aggressive diseases.

Lymphangiogenesis and cancer

Historically, lymphatic vessels were considered passive participants in tumor metastasis by simply providing channels for tumor cells to transit to draining lymph nodes. The discovery of several key lymphatic-specific molecular markers and an increased availability of in vitro and in vivo experimental systems to study lymphatic biology have however highlighted a much more complex, active role for the lymphatic vasculature in metastatic tumor spread. This review will briefly describe the lymphatic system and lymphangiogenesis and then focus on the role of the lymphatic system in cancer metastasis. The progression of our understanding from the lymphatic system as a somewhat passive conduit for metastasis to an active participant in metastatic tumor dissemination, regulated by a complex array of lymphangiogenic factors, chemokines, and immune cell subsets, will be described.

Identification of UV-protective activators of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) by combining a chemical library screen with computer-based virtual screening

Nuclear factor erythroid-derived 2-related factor 2 (Nrf2) is a master regulator of cellular antioxidant defense systems, and activation of this transcription factor is a promising strategy for protection of skin and other organs from environmental insults. To identify efficient Nrf2 activators in keratinocytes, we combined a chemical library screen with computer-based virtual screening. Among 14 novel Nrf2 activators, the most potent compound, a nitrophenyl derivative of 2-chloro-5-nitro-N-phenyl-benzamide, was characterized with regard to its molecular mechanism of action. This compound induced the expression of cytoprotective genes in keratinocytes isolated from wild-type but not from Nrf2-deficient mice. Most importantly, it showed low toxicity and protected primary human keratinocytes from UVB-induced cell death. Therefore, it represents a potential lead compound for the development of drugs for skin protection under stress conditions. Our study demonstrates that chemical library screening combined with advanced computational similarity searching is a powerful strategy for identification of bioactive compounds, and it points toward an innovative therapeutic approach against UVB-induced skin damage.

Analysis of a novel highly metastatic melanoma cell line identifies osteopontin as a new lymphangiogenic factor

Tumor cell invasion and metastasis are hallmarks of malignancy. Despite recent advances in the understanding of lymphatic spread, the mechanisms by which tumors metastasize to sentinel/distant lymph nodes and beyond are poorly understood. To gain new insights into this complex process, we established highly metastatic melanoma cell lines by in vivo passaging the B16 parental cell line through the lymphatic system. In this study we characterized morphology, rate of cell proliferation, colony formation, migration, tumorigenicity, lymph flow, and capacities to induce tumor- and sentinel lymph node-lymphangiogenesis. Furthermore, microarray-based comparative analysis between parental and passaged cell lines was performed to identify specific gene expression profiles. The most differentially expressed gene was SPP (osteopontin), a secreted glycophosphoprotein which is known to be involved in cancer metastasis. Overexpression of osteopontin in B16 F1-variant was confirmed by western blot analysis and quantitative RT-PCR. Treatment of cultured lymphatic endothelial cells (LECs) with osteopontin promoted cell migration mediated by the integrin α9 pathway. Our results identify osteopontin as a novel lymphangiogenic factor.

An unexpected role of semaphorin3a-neuropilin-1 signaling in lymphatic vessel maturation and valve formation

RATIONALE

Lymphatic vasculature plays important roles in tissue fluid homeostasis maintenance and in the pathology of human diseases. Yet, the molecular mechanisms that control lymphatic vessel maturation remain largely unknown.

OBJECTIVE

We analyzed the gene expression profiles of ex vivo isolated lymphatic endothelial cells to identify novel lymphatic vessel expressed genes and we investigated the role of semaphorin 3A (Sema3A) and neuropilin-1 (Nrp-1) in lymphatic vessel maturation and function.

METHODS AND RESULTS

Lymphatic and blood vascular endothelial cells from mouse intestine were isolated using fluorescence-activated cell sorting, and transcriptional profiling was performed. We found that the axonal guidance molecules Sema3A and Sema3D were highly expressed by lymphatic vessels. Importantly, we found that the semaphorin receptor Nrp-1 is expressed on the perivascular cells of the collecting lymphatic vessels. Treatment of mice in utero (E12.5-E16.5) with an antibody that blocks Sema3A binding to Nrp-1 but not with an antibody that blocks VEGF-A binding to Nrp-1 resulted in a complex phenotype of impaired lymphatic vessel function, enhanced perivascular cell coverage, and abnormal lymphatic vessel and valve morphology.

CONCLUSIONS

Together, these results reveal an unanticipated role of Sema3A-Nrp-1 signaling in the maturation of the lymphatic vascular network likely via regulating the perivascular cell coverage of the vessels thus affecting lymphatic vessel function and lymphatic valve development.

Interaction of tumor cells and lymphatic vessels in cancer progression

Metastatic spread of cancer through the lymphatic system affects hundreds of thousands of patients yearly. Growth of new lymphatic vessels, lymphangiogenesis, is activated in cancer and inflammation, but is largely inactive in normal physiology, and therefore offers therapeutic potential. Key mediators of lymphangiogenesis have been identified in developmental studies. During embryonic development, lymphatic endothelial cells derive from the blood vascular endothelium and differentiate under the guidance of lymphatic-specific regulators, such as the prospero homeobox 1 transcription factor. Vascular endothelial growth factor-C (VEGF-C) and VEGF receptor 3 signaling are essential for the further development of lymphatic vessels and therefore they provide a promising target for inhibition of tumor lymphangiogenesis. Lymphangiogenesis is important for the progression of solid tumors as shown for melanoma and breast cancer. Tumor cells may use chemokine gradients as guidance cues and enter lymphatic vessels through intercellular openings between endothelial cell junctions or, possibly, by inducing larger discontinuities in the endothelial cell layer. Tumor-draining sentinel lymph nodes show enhanced lymphangiogenesis even before cancer metastasis and they may function as a permissive 'lymphovascular niche' for the survival of metastatic cells. Although our current knowledge indicates that the development of anti-lymphangiogenic therapies may be beneficial for the treatment of cancer patients, several open questions remain with regard to the frequency, mechanisms and biological importance of lymphatic metastases.

Down-regulation of microRNA-34a* in rheumatoid arthritis synovial fibroblasts promotes apoptosis resistance

OBJECTIVE

To investigate the expression and effect of the microRNA-34 (miR-34) family on apoptosis in rheumatoid arthritis synovial fibroblasts (RASFs).

METHODS

Expression of the miR-34 family in synovial fibroblasts with or without stimulation with Toll-like receptor (TLR) ligands, tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), hypoxia, or 5-azacytidine was analyzed by real-time polymerase chain reaction (PCR). Promoter methylation was studied by combined bisulfite restriction analysis. The effects of overexpression and silencing of miR-34a and miR-34a* on apoptosis were analyzed by annexin V/propidium iodide staining. Production of X-linked inhibitor of apoptosis protein (XIAP) was assessed by real-time PCR and immunohistochemistry analysis. Reporter gene assay was used to study the signaling pathways of miR-34a*.

RESULTS

Basal expression levels of miR-34a* were found to be reduced in synovial fibroblasts from RA patients compared to osteoarthritis patients, whereas levels of miR-34a, miR-34b/b*, and miR-34c/c* did not differ. Neither TNFα, IL-1β, TLR ligands, nor hypoxia altered miR-34a* expression. However, we demonstrated that the promoter of miR-34a/34a* was methylated and showed that transcription of the miR-34a duplex was induced upon treatment with demethylating agents. Enforced expression of miR-34a* led to an increased rate of FasL- and TRAIL-mediated apoptosis in RASFs. Moreover, levels of miR-34a* were highly correlated with expression of XIAP, which was found to be up-regulated in RA synovial cells. Finally, we identified XIAP as a direct target of miR-34a*.

CONCLUSION

Our data provide evidence of a methylation-specific down-regulation of proapoptotic miR-34a* in RASFs. Decreased expression of miR- 34a* results in up-regulation of its direct target XIAP, thereby contributing to resistance of RASFs to apoptosis.

Polyphyllin D, a steroidal saponin from Paris polyphylla, inhibits endothelial cell functions in vitro and angiogenesis in zebrafish embryos in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Angiogenesis, the process of blood vessel formation, is critical to tumour growth. The importance of angiogenesis in tumour development has lead to the development of anti-angiogenic strategies to inhibit tumour growth. In this study, polyphyllin D (PD), an active component in Chinese herb, Paris polyphylla, was evaluated for its potential anti-angiogenic effects.

MATERIALS AND METHODS

The inhibitory effects of PD on three important processes involved in angiogenesis, i.e. proliferation, migration and differentiation were examined using human microvascular endothelial cell line HMEC-1 by MTT assay, scratch assay and tube formation assay, respectively. Using zebrafish embryos as an animal model of angiogenesis, the anti-angiogenic effect of PD was further verified in vivo.

RESULTS

PD suppressed the growth of HMEC-1 cells at 0.1-0.4 μM without toxic effects. At 0.3 μM and 0.4 μM, PD significantly inhibited endothelial cell migration and capillary tube formation. About 70% of the zebrafish embryos showed defects in intersegmental vessel formation upon treatment with PD at concentrations of 0.156 μM and 0.313 μM.

CONCLUSION

The anti-angiogenic effects of PD have been explored in the study which implied a potential therapeutic development of PD in cancer treatment.

SIRT1 overexpression in the rheumatoid arthritis synovium contributes to proinflammatory cytokine production and apoptosis resistance

OBJECTIVE

To analyse the expression of SIRT1 in synovial tissues and cells of patients with rheumatoid arthritis (RA) and to study the function of SIRT1 in inflammation and apoptosis in RA.

METHODS

Levels of SIRT1 expression were analysed in synovial tissues and cells from patients with RA by real-time PCR and western blotting before and after stimulation with toll-like receptor ligands, tumour necrosis factor α (TNFα) and interleukin 1β (IL-1β). Immunohistochemistry was used to study the localisation of SIRT1. Fluorescence activated cell sorting analysis was performed to investigate the effect of SIRT1 on apoptosis. Peripheral blood monocytes and rheumatoid arthritis synovial fibroblasts (RASFs) were transfected with wild-type or enzymatically inactive SIRT1 expression vectors or with siRNA targeting SIRT1. Cytokine analysis of IL-6, IL-8 and TNFα were performed by ELISA to study the role of SIRT1 on proinflammatory mediators of RA.

RESULTS

SIRT1 was found to be constitutively upregulated in synovial tissues and cells from patients with RA compared to osteoarthritis. TNFα stimulation of RASFs and monocytes resulted in further induced expression levels of SIRT1. Silencing of SIRT1 promoted apoptosis in RASFs, whereas SIRT1 overexpression protected cells from apoptosis. Inhibition of SIRT1 enzymatic activity by inhibitors, siRNA and overexpression of an enzymatically inactive form of SIRT1 reduced lipopolysaccharide-induced levels of TNFα in monocytes. Similarly, knockdown of SIRT1 resulted in a reduction of proinflammatory IL-6 and IL-8 in RASFs.

CONCLUSION

The TNFα-induced overexpression of SIRT1 in RA synovial cells contributes to chronic inflammation by promoting proinflammatory cytokine production and inhibiting apoptosis.

Lipoxygenase mediates invasion of intrametastatic lymphatic vessels and propagates lymph node metastasis of human mammary carcinoma xenografts in mouse

In individuals with mammary carcinoma, the most relevant prognostic predictor of distant organ metastasis and clinical outcome is the status of axillary lymph node metastasis. Metastases form initially in axillary sentinel lymph nodes and progress via connecting lymphatic vessels into postsentinel lymph nodes. However, the mechanisms of consecutive lymph node colonization are unknown. Through the analysis of human mammary carcinomas and their matching axillary lymph nodes, we show here that intrametastatic lymphatic vessels and bulk tumor cell invasion into these vessels highly correlate with formation of postsentinel metastasis. In an in vitro model of tumor bulk invasion, human mammary carcinoma cells caused circular defects in lymphatic endothelial monolayers. These circular defects were highly reminiscent of defects of the lymphovascular walls at sites of tumor invasion in vivo and were primarily generated by the tumor-derived arachidonic acid metabolite 12S-HETE following 15-lipoxygenase-1 (ALOX15) catalysis. Accordingly, pharmacological inhibition and shRNA knockdown of ALOX15 each repressed formation of circular defects in vitro. Importantly, ALOX15 knockdown antagonized formation of lymph node metastasis in xenografted tumors. Furthermore, expression of lipoxygenase in human sentinel lymph node metastases correlated inversely with metastasis-free survival. These results provide evidence that lipoxygenase serves as a mediator of tumor cell invasion into lymphatic vessels and formation of lymph node metastasis in ductal mammary carcinomas.

A role for all-trans-retinoic acid in the early steps of lymphatic vasculature development

The molecular mechanisms that regulate the earliest steps of lymphatic vascular system development are unknown. To identify regulators of lymphatic competence and commitment, we used an in vitro vascular assay with mouse embryonic stem cell-derived embryoid bodies (EBs). We found that incubation with retinoic acid (RA) and, more potently, with RA in combination with cAMP, induced the expression of the lymphatic competence marker LYVE-1 in the vascular structures of the EBs. This effect was dependent on RA receptor (RAR)-α and protein kinase A signaling. RA-cAMP incubation also promoted the development of CD31+/LYVE-1+/Prox1+ cell clusters. In situ studies revealed that RAR-α is expressed by endothelial cells of the cardinal vein in ED 9.5-11.5 mouse embryos. Timed exposure of mouse and Xenopus embryos to excess of RA upregulated LYVE-1 and VEGFR-3 on embryonic veins and increased formation of Prox1-positive lymphatic progenitors. These findings indicate that RA signaling mediates the earliest steps of lymphatic vasculature development.

In vivo imaging of inflammation- and tumor-induced lymph node lymphangiogenesis by immuno-positron emission tomography

Metastasis to regional lymph nodes (LN) is a prognostic indicator for cancer progression. There is a great demand for sensitive and noninvasive methods to detect metastasis to LNs. Whereas conventional in vivo imaging approaches have focused on the detection of cancer cells, lymphangiogenesis within tumor-draining LNs might be the earliest sign of metastasis. In mouse models of LN lymphangiogenesis, we found that systemically injected antibodies to lymphatic epitopes accumulated in the lymphatic vasculature in tissues and LNs. Using a (124)I-labeled antibody against the lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), we imaged, for the first time, inflammation- and tumor-draining LNs with expanded lymphatic networks in vivo by positron emission tomography (PET). Anti-LYVE-1 immuno-PET enabled visualization of lymphatic vessel expansion in LNs bearing metastases that were not detected by [(18)F]fluorodeoxyglucose-PET, which is clinically applied to detect cancer metastases. Immuno-PET with lymphatic-specific antibodies may open up new avenues for the early detection of metastasis, and the images obtained might be used as biomarkers for the progression of diseases associated with lymphangiogenesis.

Stimulation of lymphangiogenesis via VEGFR-3 inhibits chronic skin inflammation

The role of lymphangiogenesis in inflammation has remained unclear. To investigate the role of lymphatic versus blood vasculature in chronic skin inflammation, we inhibited vascular endothelial growth factor (VEGF) receptor (VEGFR) signaling by function-blocking antibodies in the established keratin 14 (K14)–VEGF-A transgenic (Tg) mouse model of chronic cutaneous inflammation. Although treatment with an anti–VEGFR-2 antibody inhibited skin inflammation, epidermal hyperplasia, inflammatory infiltration, and angiogenesis, systemic inhibition of VEGFR-3, surprisingly, increased inflammatory edema formation and inflammatory cell accumulation despite inhibition of lymphangiogenesis. Importantly, chronic Tg delivery of the lymphangiogenic factor VEGF-C to the skin of K14-VEGF-A mice completely inhibited development of chronic skin inflammation, epidermal hyperplasia and abnormal differentiation, and accumulation of CD8 T cells. Similar results were found after Tg delivery of mouse VEGF-D that only activates VEGFR-3 but not VEGFR-2. Moreover, intracutaneous injection of recombinant VEGF-C156S, which only activates VEGFR-3, significantly reduced inflammation. Although lymphatic drainage was inhibited in chronic skin inflammation, it was enhanced by Tg VEGF-C delivery. Together, these results reveal an unanticipated active role of lymphatic vessels in controlling chronic inflammation. Stimulation of functional lymphangiogenesis via VEGFR-3, in addition to antiangiogenic therapy, might therefore serve as a novel strategy to treat chronic inflammatory disorders of the skin and possibly also other organs.

Quantitative imaging of lymphatic function with liposomal indocyanine green

Lymphatic vessels play a major role in cancer progression and in postsurgical lymphedema, and several new therapeutic approaches targeting lymphatics are currently being developed. Thus, there is a critical need for quantitative imaging methods to measure lymphatic flow. Indocyanine green (ICG) has been used for optical imaging of the lymphatic system, but it is unstable in solution and may rapidly enter venous capillaries after local injection. We developed a novel liposomal formulation of ICG (LP-ICG), resulting in vastly improved stability in solution and an increased fluorescence signal with a shift toward longer wavelength absorption and emission. When injected intradermally to mice, LP-ICG was specifically taken up by lymphatic vessels and allowed improved visualization of deep lymph nodes. In a genetic mouse model of lymphatic dysfunction, injection of LP-ICG showed no enhancement of draining lymph nodes and slower clearance from the injection site. In mice bearing B16 luciferase-expressing melanomas expressing vascular endothelial growth factor-C (VEGF-C), sequential near-IR imaging of intradermally injected LP-ICG enabled quantification of lymphatic flow. Increased flow through draining lymph nodes was observed in mice bearing VEGF-C-expressing tumors without metastases, whereas a decreased flow pattern was seen in mice with a higher lymph node tumor burden. This new method will likely facilitate quantitative studies of lymphatic function in preclinical investigations and may also have potential for imaging of lymphedema or improved sentinel lymph detection in cancer.

Tumor lymphangiogenesis and metastasis to lymph nodes induced by cancer cell expression of podoplanin

The membrane glycoprotein podoplanin is expressed by several types of human cancers and might be associated with their malignant progression. Its exact biological function and molecular targets are unclear, however. Here, we assessed the relevance of tumor cell expression of podoplanin in cancer metastasis to lymph nodes, using a human MCF7 breast carcinoma xenograft model. We found that podoplanin expression promoted tumor cell motility in vitro and, unexpectedly, increased tumor lymphangiogenesis and metastasis to regional lymph nodes in vivo, without promoting primary tumor growth. Importantly, high cancer cell expression levels of podoplanin correlated with lymph node metastasis and reduced survival times in a large cohort of 252 oral squamous cell carcinoma patients. Based on comparative transcriptional profiling of tumor xenografts, we identified endothelin-1, villin-1, and tenascin-C as potential mediators of podoplanin-induced tumor lymphangiogenesis and metastasis. These unexpected findings identify a novel mechanism of tumor lymphangiogenesis and metastasis induced by cancer cell expression of podoplanin, suggesting that reagents designed to interfere with podoplanin function might be developed as therapeutics for patients with advanced cancer.

Abstract LB-362: PlGF inhibition phenocopies PlGF deficiency in cancer

To overcome the resistance to VEGF-inhibitor treatment, additional anti-angiogenic agents need to be valorized. Placental growth factor (PlGF), a VEGF homologue, stimulates endothelial, tumor and inflammatory cells. Studies in independently generated PlGF−/− mice by us and Regeneron identified a role for PlGF in inflammatory, ischemic and malignant disease, while the anti-PlGF mAb 5D11D4 blocks growth of implanted tumors. Several clinical studies also show that PlGF levels correlate with poor prognosis in diverse types of cancer, while the humanized anti-human PlGF mAb TB403 has been succesfully tested in a phase I trial in out-treated cancer patients. However, genetic evidence for a disease-candidate role of PlGF or an effect of the anti-PlGF mAb 5D11D4 in spontaneous cancer models has been lacking so far. Here, we show that loss of PlGF inhibited a carcinogen-induced skin tumor model papilloma formation and angiogenesis. Furthermore, silencing of PlGF in a transgenic hepatocellular carcinoma (HCC) model reduced tumor size and incidence. In a carcinogen-induced HCC model, most WT but only a minority of PlGF−/− mice died, while fewer tumor nodules developed in PlGF−/− mice. When WT mice with established HCC were treated with 5D11D4, more control IgG than 5D11D4 treated mice died. PlGF blockage inhibited the characteristic arterialization response in these tumors and blocked vessel abnormalization in HCC leading to reduced levels of hypoxia, known to stimulate HCC growth, however, without affecting microvascular density. These findings indicate that the anti-cancer activity of PlGF-blockage is not reflected by a change in vessel density alone. In the Rip1Tag2 model, no differences between WT and PlGF−/− mice or 5D11D4-treated mice in tumor burden or incidence were found, indicating that 5D11D4 does not have off-target effects. Resistance of this model is likely due to the lack of infiltration by Gr1+ neutrophils by PlGF blockage. These findings and previously published results of a Phase I trial with TB403 warrant furter analysis of anti-PlGF strategies for (non)-oncology indications.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-362.

Abstract 3386: In vivo imaging of inflammation- and tumor-induced lymph node lymphangiogenesis by immuno-positron emission tomography

Metastasis to regional lymph nodes is a prognostic indicator for cancer progression. There is a great demand for sensitive and non-invasive methods to detect metastasis to the lymph nodes. While conventional in vivo imaging approaches have focused on the detection of cancer cells, lymphangiogenesis within tumor draining lymph nodes might be the earliest sign of metastasis. In mouse models of lymph node lymphangiogenesis, we found that systemically injected antibodies to lymphatic epitopes accumulated in the lymphatic vasculature in tissues and lymph nodes. Using a 124I-labeled antibody against the lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), we imaged, for the first time, inflammation-and tumor-draining lymph nodes with expanded lymphatic networks in vivo by positron emission tomography. This method might open up new avenues for the early detection of metastases and the images obtained might be used as biomarkers for the progression of diseases associated with lymphangiogenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3386.

Nodal lymphangiogenesis and metastasis: Role of tumor-induced lymphatic vessel activation in extramammary Paget's disease

Nodal lymphangiogenesis promotes distant lymph node (LN) metastasis in experimental cancer models. However, the role of nodal lymphangiogenesis in distant metastasis and in the overall survival of cancer patients remains unknown. Therefore, we investigated mechanisms that might facilitate regional and distant LN metastasis in extramammary Paget's disease (EMPD). We retrospectively analyzed the impact of tumor-induced lymphatic vessel activation on the survival of 116 patients, the largest cohort with EMPD studied to date. Nodal lymphangiogenesis was significantly increased in metastatic, compared with tumor-free, LNs (P = 0.022). Increased lymphatic invasion within regional LNs was significantly associated with distant metastasis in LN (P = 0.047) and organs (P = 0.003). Thus, invasion within regional LNs is a powerful indicator of systemic tumor spread and reduced patient survival in EMPD (P = 0.0004). Lymphatic vessels associated with tumors expressed stromal cell-derived factor-1 (SDF-1), whereas CXCR4 was expressed on invasive Paget cells undergoing epithelial-mesenchymal transition (EMT)-like process. A431 cells overexpressing Snail expressed increased levels of CXCR4 in the presence of transforming growth factor-beta1. Haptotactic migration assays confirmed that Snail-induced EMT-like process promotes tumor cell motility via the CXCR4-SDF-1 axis. Sinusoidal lymphatic endothelial cells and macrophages expressed SDF-1 in subcapsular sinuses of lymph nodes before Paget cell arrival. Our findings reveal that EMT-related features likely promote lymphatic metastasis of EMPD by activating the CXCR4-SDF-1 axis.

TScratch: a novel and simple software tool for automated analysis of monolayer wound healing assays

Cell migration plays a major role in development, physiology, and disease, and is frequently evaluated in vitro by the monolayer wound healing assay. The assay analysis, however, is a time-consuming task that is often performed manually. In order to accelerate this analysis, we have developed TScratch, a new, freely available image analysis technique and associated software tool that uses the fast discrete curvelet transform to automate the measurement of the area occupied by cells in the images. This tool helps to significantly reduce the time needed for analysis and enables objective and reproducible quantification of assays. The software also offers a graphical user interface which allows easy inspection of analysis results and, if desired, manual modification of analysis parameters. The automated analysis was validated by comparing its results with manual-analysis results for a range of different cell lines. The comparisons demonstrate a close agreement for the vast majority of images that were examined and indicate that the present computational tool can reproduce statistically significant results in experiments with well-known cell migration inhibitors and enhancers.

Lymphangiogenesis and cancer metastasis

Metastasis is a characteristic trait of most tumour types and the cause for the majority of cancer deaths. Many tumour types, including melanoma and breast and prostate cancers, first metastasize via lymphatic vessels to their regional lymph nodes. Although the connection between lymph node metastases and shorter survival times of patients was made decades ago, the active involvement of the lymphatic system in cancer, metastasis has been unravelled only recently, after molecular markers of lymphatic vessels were identified. A growing body of evidence indicates that tumour-induced lymphangiogenesis is a predictive indicator of metastasis to lymph nodes and might also be a target for prevention of metastasis. This article reviews the current understanding of lymphangiogenesis in cancer anti-lymphangiogenic strategies for prevention and therapy of metastatic disease, quantification of lymphangiogenesis for the prognosis and diagnosis of metastasis and in vivo imaging technologies for the assessment of lymphatic vessels, drainage and lymph nodes.

The lymphatic system in health and disease

The lymphatic vascular system has an important role in the regulation of tissue pressure, immune surveillance and the absorption of dietary fat in the intestine. There is growing evidence that the lymphatic system also contributes to a number of diseases, such as lymphedema, cancer metastasis and different inflammatory disorders. The discovery of various molecular markers allowing the distinction of blood and lymphatic vessels, together with the availability of a increasing number of in vitro and in vivo models to study various aspects of lymphatic biology, has enabled tremendous progress in research into the development and function of the lymphatic system. This review discusses recent advances in our understanding of the embryonic development of the lymphatic vasculature, the molecular mechanisms mediating lymphangiogenesis in the adult, the role of lymphangiogenesis in chronic inflammation and lymphatic cancer metastasis, and the emerging importance of the lymphatic vasculature as a therapeutic target.

Galectin-8 interacts with podoplanin and modulates lymphatic endothelial cell functions

Podoplanin is a small, mucin-like membrane glycoprotein highly expressed by lymphatic but not by blood vascular endothelial cells. Although it was shown to be indispensable for the correct formation and function of the lymphatic vasculature, its precise molecular function has remained unknown. In the present study, we identified the mammalian lectin galectin-8 as a novel, glycosylation-dependent interaction partner of podoplanin. Galectin-8 is a tandem-repeat type galectin, which interacts with cell surface glycoproteins, including certain integrins, as well as with extracellular matrix molecules such as fibronectin. Here we show that, similar to podoplanin, galectin-8 is more highly expressed by lymphatic than by blood vascular endothelial cells, and that it promotes lymphatic endothelial cell adhesion as well as haptotactic migration when immobilized onto a surface, while inhibiting the formation of tube-like structures by lymphatic endothelial cells in a collagen matrix when incorporated into the matrix. Importantly, functions of blood vascular endothelial cells, which lack podoplanin expression, are not affected by galectin-8. These data suggest a role for galectin-8 and podoplanin in supporting the connection of the lymphatic endothelium to the surrounding extracellular matrix, most likely in cooperation with other glycoproteins on the surface of lymphatic endothelial cells.

The angiogenesis inhibitor thrombospondin-1 inhibits acute cutaneous hypersensitivity reactions

There is increasing evidence that vascular remodeling and endothelial cell activation promote acute and chronic inflammation. Thrombospondin 1 (TSP-1) is a potent endogenous angiogenesis inhibitor thought to play an important role in maintaining cutaneous vascular quiescence. We first investigated TSP-1 expression in human and contact hypersensitivity (CHS) reactions and found that TSP-1 was upregulated in the inflamed skin of patients and in mice. To elucidate the function of TSP-1 in cutaneous inflammation, we induced CHS reactions in the skin of mice with targeted epidermal TSP-1 overexpression in TSP-1-deficient mice and in wild-type mice. We found decreased edema formation, angiogenesis, and inflammatory infiltrate in the inflamed skin of TSP-1 transgenic mice. Conversely, TSP-1-deficient mice exhibited an enhanced and prolonged inflammation, characterized by increased edema formation, enhanced vascular remodeling, and increased neutrophilic infiltrate, when compared with wild-type mice. Moreover, we found strong upregulation of the proinflammatory cytokines IL-1beta, macrophage inflammatory protein 2, and tumor necrosis factor-alpha in the inflamed skin of TSP-1-deficient mice. Our results indicate that TSP-1 downregulates cutaneous delayed-type hypersensitivity reactions by acting on several distinct pathways mediating skin inflammation.

Lymphatic invasion in cutaneous melanoma is associated with sentinel lymph node metastasis

BACKGROUND

Sentinel lymph node (SLN) metastasis is a major determinant for staging, prognostication and clinical management of patients with cutaneous melanoma. However, the role of lymphatic vs. vascular invasion (VI) for SLN spread remains unclear.

METHODS

We compared the frequency of lymphatic invasion (LI) vs. VI in melanoma sections from 94 patients with a mean three-year clinical follow up using immunostains for the lymphatic endothelial markers D2-40 (podoplanin) and LYVE-1 and the panvascular marker CD31.

RESULTS

LI occurred more frequently than VI (16 vs. 3%, respectively, p = 0.001) and correlated with higher American Joint Committee on Cancer stage at diagnosis (p = 0.0004). In a univariate analysis, LI was strongly associated with SLN metastasis (p = 0.008), independent of tumor thickness. In a multivariate analysis, LI was not a significant risk factor for SLN metastasis. The presence of intratumoral lymphatics (ITLs) was associated with distant metastasis, whereas VI was rare and did not correlate with SLN or distant metastasis. A combination of LI and ITL had higher positive and negative predictive values for the risk of developing SLN metastasis compared with routine histology and VI.

CONCLUSION

Detection of LI in the primary tumor may aid in identifying melanoma patients with the propensity to develop SLN metastasis.

Coxsackie- and adenovirus receptor (CAR) is expressed in lymphatic vessels in human skin and affects lymphatic endothelial cell function in vitro

Lymphatic vessels play an important role in tissue fluid homeostasis, intestinal fat absorption and immunosurveillance. Furthermore, they are involved in pathologic conditions, such as tumor cell metastasis and chronic inflammation. In comparison to blood vessels, the molecular phenotype of lymphatic vessels is less well characterized. Performing comparative gene expression analysis we have recently found that coxsackie- and adenovirus receptor (CAR) is significantly more highly expressed in cultured human, skin-derived lymphatic endothelial cells (LECs), as compared to blood vascular endothelial cells. Here, we have confirmed these results at the protein level, using Western blot and FACS analysis. Immunofluorescence performed on human skin confirmed that CAR is expressed at detectable levels in lymphatic vessels, but not in blood vessels. To address the functional significance of CAR expression, we modulated CAR expression levels in cultured LECs in vitro by siRNA- and vector-based transfection approaches. Functional assays performed with the transfected cells revealed that CAR is involved in distinct cellular processes in LECs, such as cell adhesion, migration, tube formation and the control of vascular permeability. In contrast, no effect of CAR on LEC proliferation was observed. Overall, our data suggest that CAR stabilizes LEC-LEC interactions in the skin and may contribute to lymphatic vessel integrity.

Lymphatic-specific expression of dipeptidyl peptidase IV and its dual role in lymphatic endothelial function

Lymphatic vessels play an important role in the maintenance of tissue fluid homeostasis and in the transport of immune cells to lymph nodes, but they also serve as the major conduit for cancer metastasis to regional lymph nodes. However, the molecular mechanisms regulating these functions are poorly understood. Based on transcriptional profiling studies of cultured human dermal lymphatic (LEC) versus blood vascular endothelial cells (BEC), we found that dipeptidyl peptidase IV (DPPIV) mRNA and protein are much more strongly expressed by cultured lymphatic endothelium than by blood vascular endothelium that only expressed low levels of DPPIV in culture. The enzymatic cleavage activity of DPPIV was significantly higher in cultured LEC than in BEC. Differential immunofluorescence analyses of human organ tissue microarrays for DPPIV and several vascular lineage-specific markers revealed that DPPIV is also specifically expressed in situ by lymphatic vessels of the skin, esophagus, small intestine, breast and ovary. Moreover, siRNA-mediated DPPIV knockdown inhibited LEC adhesion to collagen type I and to fibronectin, and also reduced cell migration and formation of tube-like structures. These results identify DPPIV as a novel lymphatic marker and mediator of lymphatic endothelial cell functions.

Tumor lymphangiogenesis and melanoma metastasis

Malignant melanomas of the skin primarily metastasize to lymph nodes, and the detection of sentinel lymph node metastases serves as an important prognostic parameter. There is now compelling evidence that melanomas can induce lymphangiogenesis (growth of lymphatic vessels), mainly at the tumor-stroma interface, and that the level of tumor lymphangiogenesis is correlated with the incidence of sentinel lymph node metastases and with disease-free survival. Thus, tumor lymphangiogenesis can serve as a novel prognostic predictor in melanoma. Vascular endothelial growth factor (VEGF)-C, released by melanoma cells and by tumor-associated macrophages, likely represents the major lymphangiogenic factor in melanoma, although other members of the VEGF family might also be involved. The recent discovery that tumors can induce a premetastatic niche, by inducing lymphatic vessel growth in sentinel lymph nodes even before metastasis, and that lymph node lymphangiogenesis enhances metastatic spread, indicates that activated lymphatic vessels represent novel targets for the detection and/or therapy of melanoma metastases.

Growth hormone promotes lymphangiogenesis

The lymphatic system plays an important role in inflammation and cancer progression, although the molecular mechanisms involved are poorly understood. As determined using comparative transcriptional profiling studies of cultured lymphatic endothelial cells versus blood vascular endothelial cells, growth hormone receptor was expressed at much higher levels in lymphatic endothelial cells than in blood vascular endothelial cells. These findings were confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction and Western blot analyses. Growth hormone induced in vitro proliferation, sprouting, tube formation, and migration of lymphatic endothelial cells, and the mitogenic effect was independent of vascular endothelial growth factor receptor-2 or -3 activation. Growth hormone also inhibited serum starvation-induced lymphatic endothelial cell apoptosis. No major alterations of lymphatic vessels were detected in the normal skin of bovine growth hormone-transgenic mice. However, transgenic delivery of growth hormone accelerated lymphatic vessel ingrowth into the granulation tissue of full-thickness skin wounds, and intradermal delivery of growth hormone resulted in enlargement and enhanced proliferation of cutaneous lymphatic vessels in wild-type mice. These results identify growth hormone as a novel lymphangiogenic factor.

Inhibition of chronic and acute skin inflammation by treatment with a vascular endothelial growth factor receptor tyrosine kinase inhibitor

Although vascular remodeling is a hallmark of many chronic inflammatory disorders, antivascular strategies to treat these conditions have received little attention to date. We investigated the effects of a newly identified vascular endothelial growth factor (VEGF) receptor tyrosine-kinase inhibitor, NVP-BAW2881, on endothelial cell function in vitro and its anti-inflammatory activity in different animal models. NVP-BAW2881 inhibited proliferation, migration, and tube formation by human umbilical vein endothelial cells and lymphatic endothelial cells in vitro. In a transgenic mouse model of psoriasis, NVP-BAW2881 reduced the number of blood and lymphatic vessels and infiltrating leukocytes in the skin, and normalized the epidermal architecture. NVP-BAW2881 also displayed strong anti-inflammatory effects in models of acute inflammation; pretreatment with topical NVP-BAW2881 significantly inhibited VEGF-A-induced vascular permeability in the skin of pigs and mice. Furthermore, topical application of NVP-BAW2881 reduced the inflammatory response elicited in pig skin by UV-B irradiation or by contact hypersensitivity reactions. These results demonstrate for the first time that VEGF receptor tyrosine-kinase inhibitors might be used to treat patients with inflammatory skin disorders such as psoriasis.

Altered expression of MicroRNA in synovial fibroblasts and synovial tissue in rheumatoid arthritis

OBJECTIVE

MicroRNAs (miRNA) have recently emerged as a new class of modulators of gene expression. In this study we investigated the expression, regulation, and function of miR-155 and miR-146a in rheumatoid arthritis (RA) synovial fibroblasts (RASFs) and RA synovial tissue.

METHODS

Locked nucleic acid microarray was used to screen for differentially expressed miRNA in RASFs treated with tumor necrosis factor alpha (TNFalpha). TaqMan-based real-time polymerase chain reaction was applied to measure the levels of miR-155 and miR-146a. Enforced overexpression of miR-155 was used to investigate the function of miR-155 in RASFs.

RESULTS

Microarray analysis of miRNA expressed in RASFs treated with TNFalpha revealed a prominent up-regulation of miR-155. Constitutive expression of both miR-155 and miR-146a was higher in RASFs than in those from patients with osteoarthritis (OA), and expression of miR-155 could be further induced by TNFalpha, interleukin-1beta, lipopolysaccharide, poly(I-C), and bacterial lipoprotein. The expression of miR-155 in RA synovial tissue was higher than in OA synovial tissue. Enforced expression of miR-155 in RASFs was found to repress the levels of matrix metalloproteinase 3 (MMP-3) and reduce the induction of MMPs 3 and 1 by Toll-like receptor ligands and cytokines. Moreover, compared with monocytes from RA peripheral blood, RA synovial fluid monocytes displayed higher levels of miR-155.

CONCLUSION

This study provides the first description of increased expression of miRNA miR-155 and miR-146a in RA. Based on these findings, we postulate that the inflammatory milieu may alter miRNA expression profiles in resident cells of the rheumatoid joints. Considering the repressive effect of miR-155 on the expression of MMPs 3 and 1 in RASFs, we hypothesize that miR-155 may be involved in modulation of the destructive properties of RASFs.

Identification of the surface-accessible, lineage-specific vascular proteome by two-dimensional peptide mapping

The formation of blood vessels (angiogenesis) and of lymphatic vessels (lymphangiogenesis) actively contributes to cancer progression and inflammation. Thus, there has been a quest for identifying the molecular mechanisms that control lymphatic and blood vessel formation and function. Membrane and extracellular matrix proteins can serve as suitable targets for imaging and/or therapeutic targeting; however, conventional proteomic technologies often fail to identify them systematically due to insolubility in water and low abundance of membrane proteins. To circumvent this problem, we applied a gel-free proteomics methodology termed two-dimensional peptide mapping (2D-PM) to cultured blood vascular (BECs) and lymphatic (LECs) endothelial cells. 2D-PM comprises biotinylation of surface-accessible proteins, their selective enrichment, separation by HPLC, and analysis by mass spectrometry. We identified 184 proteins that were specifically or predominantly expressed by LECs and 185 proteins specifically expressed by BECs, whereas 377 additional proteins were equally detected in both cell types. For representative proteins, the differential, lineage-specific expression was confirmed by Western analyses of cultured cells and by differential immunofluorescence analyses of tissue samples. Our results identify the surface-accessible, vascular lineage-specific proteome, and they also reveal 2D-PM as a powerful technology for the large-scale screening of lineage-specific protein expression.

Pathways targeting tumor lymphangiogenesis

Tumor metastasis to sentinel lymph nodes represents the first step of tumor dissemination in most human cancers and serves as a major prognostic indicator for disease progression. Recent studies have revealed that tumors can actively induce the formation of lymphatic vessels, and that tumor lymphangiogenesis is correlated with lymph node metastasis in experimental cancer models and in several types of human cancers. Metastatic tumor cells may continue to promote lymphatic vessel growth even after their metastasis to sentinel lymph nodes, likely promoting further cancer spread. Vascular endothelial growth factor-C (VEGF-C) and VEGF-D were the first specific lymphangiogenesis factors identified, acting predominantly via VEGF receptor-3 (VEGFR-3) that is expressed by lymphatic endothelial cells, and a large number of clinical studies have shown a correlation between tumor expression of VEGF-C or VEGF-D and lymph node metastasis. VEGFR-3 activation promotes lymphatic endothelial cell proliferation, migration, and survival via the extracellular signal-regulated kinase 1/2, the phosphatidylinositol 3-kinase/AKT, and the c-Jun NH(2)-terminal kinase 1/2 pathways. Additional tumor lymphangiogenesis factors have been recently identified, including VEGF-A. Importantly, blockade of the VEGFR-3 pathway by specific antibodies, by soluble receptor constructs, and by small molecule kinase inhibitors efficiently inhibits experimental tumor lymphangiogenesis and metastasis and might also represent a novel therapeutic avenue for the treatment of human cancers.

Nitric oxide mediates lymphatic vessel activation via soluble guanylate cyclase alpha1beta1-impact on inflammation

The lymphatic vascular system regulates tissue fluid homeostasis and the afferent phase of the immune response, and it is also involved in tumor metastasis. There is increasing evidence that lymphatic vessels also mediate acute and chronic inflammation. However, the mechanisms and functional consequences of lymphangiogenesis under inflammatory conditions are largely unknown. Here, we show that lymphatic endothelial cells (LECs) specifically express the alpha1beta1 isoform of soluble guanylate cyclase (sGC), that vascular endothelial growth factor-A potently induces sGCalpha1beta1, and that nitric oxide (NO) -induced LEC proliferation, migration, and cGMP production in LECs are specifically dependent on sGCalpha1beta1. Moreover, the specific sGC inhibitor NS-2028 completely prevents ultraviolet B-irradiation-induced lymphatic vessel enlargement, edema formation, and skin inflammation in vivo. These findings identify a crucial role of the NO/sGCalpha1beta1/cGMP pathway in modulating lymphatic vessel function. The blockade of sGCalpha1beta1 signaling might serve as a novel therapeutic strategy for inhibiting lymphangiogenesis and inflammation, in addition to its effects on the blood vasculature.

Lymphangiogenesis in development and disease

The lymphatic vascular system plays an important role in the maintenance of fluid homeostasis, in the afferent immune response, in the intestinal lipid uptake and in the metastatic spread of malignant cells. The recent discovery of specific markers and growth factors for lymphatic endothelium and the establishment of genetic mouse models with impairment of lymphatic function have provided novel insights into the molecular control of the lymphatic system in physiology and in embryonic development. They have also identified molecular pathways whose mutational inactivation leads to human diseases associated with lymphedema. Moreover, the lymphatic system plays a major role in chronic inflammatory diseases and in transplant rejection. Importantly, malignant tumors can directly promote lymphangiogenesis within the primary tumor and in draining lymph nodes, leading to enhanced cancer metastasis to lymph nodes and beyond. Based upon these findings, novel therapeutic strategies are currently being developed that aim at inhibiting or promoting the formation and function of lymphatic vessels in disease.

VEGF-A produced by chronically inflamed tissue induces lymphangiogenesis in draining lymph nodes

Lymphangiogenesis is involved in tumor cell metastasis and plays a major role in chronic inflammatory disorders. To investigate the role of lymphangiogenesis in inflammation, we induced and maintained delayed-type hypersensitivity (DTH) reactions in the ears of mice and then analyzed the resulting lymphangiogenesis in the inflamed tissue and draining lymph nodes (LNs) by quantitative fluorescence-activated cell sorting (FACS) and by immunofluorescence. Long-lasting inflammation induced a significant increase in the number of lymphatic endothelial cells, not only in the inflamed ears but also in the ear-draining auricular LNs. Inflammation-induced lymphangiogenesis was potently blocked by systemic administration of a vascular endothelial growth factor (VEGF)-A neutralizing antibody. Surprisingly, tissue inflammation specifically induced LN lymphangiogenesis but not LN angiogenesis. These findings were explained by analysis of both VEGF-A protein and mRNA levels, which revealed that VEGF-A was expressed at high mRNA and protein levels in inflamed ears but that expression was increased only at the protein level in activated LNs. Inflammation-induced lymphangiogenesis in LNs was independent of the presence of nodal B lymphocytes, as shown in B cell-deficient mice. Our data reveal that chronic inflammation actively induces lymphangiogenesis in LNs, which is controlled remotely, by lymphangiogenic factors produced at the site of inflammation.

A human mAb specific to oncofetal fibronectin selectively targets chronic skin inflammation in vivo

The antibody-based targeted delivery of bioactive agents to sites of angiogenesis is an attractive therapeutic strategy for cancer treatment, but is largely unexplored for chronic inflammatory diseases. In this article, we show that the extra domain B (EDB) domain of fibronectin, a marker of angiogenesis, is expressed in psoriatic lesions, and that the anti-EDB human antibody L19 can selectively localize to chronically inflamed skin in vivo. The L19-based delivery of the cytokines IL10 and IL12 did not improve or worsen inflammation in a mouse model of chronic skin inflammation, which overexpressed vascular endothelial growth factor under the control of the keratin-14 promoter. By contrast, the L19-based targeted delivery of the proinflammatory cytokine IL2 or of the photosensitizer Sn(IV) chlorin e6 resulted in an increased swelling and reddening of inflamed skin. These results indicate that antibodies specific to components of the modified extracellular matrix can selectively accumulate at chronically inflamed sites in vivo. This observation now stimulates the search for bioactive molecules which can be fused to antibodies and which may confer a therapeutic benefit as a result of their preferential accumulation in psoriatic lesions and other sites of inflammation.

Vascular endothelial growth factor-A mediates ultraviolet B-induced impairment of lymphatic vessel function

UVB irradiation of the skin induces erythema, epidermal hyperplasia, vascular hyperpermeability, and edema formation. Previous studies have revealed that the cutaneous blood vasculature plays a critical role in the mediation of photodamage. In contrast, the role of lymphatic vessels, which play an essential role in the maintenance of tissue fluid balance, in the response to UVB irradiation has remained unknown. We report here that both acute and chronic UVB irradiation of murine skin results in prominent enlargement of lymphatic vessels. Surprisingly, these enlarged lymphatic vessels were functionally impaired and hyperpermeable, as detected by intravital lymphangiography. The expression levels of vascular endothelial growth factor (VEGF)-A but not of the known lymphangiogenesis factors VEGF-C or VEGF-D, were enhanced in UVB-irradiated epidermis. Targeted overexpression of VEGF-A in the epidermis of transgenic mice led to increased enlargement and leakage of lymphatic vessels after acute UVB irradiation, whereas systemic blockade of VEGF-A signaling largely prevented lymphatic vessel abnormalities and photodamage induced by UVB. Together, these findings identify lymphatic vessels as novel targets for UVB-induced cutaneous photodamage and suggest that VEGF-A mediates impairment of lymphatic vessel function, thereby contributing to the adverse effects of UVB irradiation on the skin.

VEGF-C-induced lymphangiogenesis in sentinel lymph nodes promotes tumor metastasis to distant sites

The mechanisms by which tumors metastasize to sentinel and distant lymph nodes, and beyond, are poorly understood. We developed transgenic mice that overexpress vascular endothelial growth factor-C (VEGF-C) and green fluorescent protein specifically in the skin and studied the effects of chemically-induced skin carcinogenesis in this model. We found that in contrast to VEGF-A, VEGF-C does not increase the growth of primary tumors, but instead induces expansion of lymphatic networks within sentinel lymph nodes, even before the onset of metastasis. Once the metastatic cells arrived at the sentinel lymph nodes, the extent of lymphangiogenesis at these sites increased. Of importance, in mice with metastasis-containing sentinel lymph nodes, tumors that expressed VEGF-C were more likely to metastasize to additional organs, such as distal lymph nodes and lungs. No metastases were observed in distant organs in the absence of lymph node metastases. These findings indicate an important role of VEGF-C-induced lymph node lymphangiogenesis in the promotion of cancer metastasis beyond the sentinel lymph nodes. VEGF-C is therefore a good target to slow or even prevent the onset of metastasis.