Vascular endothelial growth factor-a promotes peritumoral lymphangiogenesis and lymphatic metastasis

Small molecule anticancer drugs approved during 2021-2022: Synthesis and clinical applications

Drugs have structural homology across similar biological targets. Small molecule drugs have the efficacy to target specific molecular targets within the cancer cells with enhanced cell membrane permeability, oral administration, selectivity, and specific affinity. The objective of this review is to highlight the clinical importance and synthetic routes of new small molecule oncology drugs approved by the FDA during the period 2021-2022. These marketed drugs are listed based on the month and year of approval in chronological order. We believed that an in-depth insight into the synthetic approaches for the construction of these chemical entities would enhance the ability to develop new drugs more efficiently.

Advances in lymphatic metastasis of non-small cell lung cancer

Lung cancer is a deeply malignant tumor with high incidence and mortality. Despite the rapid development of diagnosis and treatment technology, abundant patients with lung cancer are still inevitably faced with recurrence and metastasis, contributing to death. Lymphatic metastasis is the first step of distant metastasis and an important prognostic indicator of non-small cell lung cancer. Tumor-induced lymphangiogenesis is involved in the construction of the tumor microenvironment, except promoting malignant proliferation and metastasis of tumor cells, it also plays a crucial role in individual response to treatment, especially immunotherapy. Thus, this article reviews the current research status of lymphatic metastasis in non-small cell lung cancer, in order to provide some insights for the basic research and clinical and translational application in this field.

VE-cadherin junction dynamics in initial lymphatic vessels promotes lymph node metastasis

The endothelial junction component vascular endothelial (VE)-cadherin governs junctional dynamics in the blood and lymphatic vasculature. Here, we explored how lymphatic junction stability is modulated by elevated VEGFA signaling to facilitate metastasis to sentinel lymph nodes. Zippering of VE-cadherin junctions was established in dermal initial lymphatic vessels after VEGFA injection and in tumor-proximal lymphatics in mice. Shape analysis of pan-cellular VE-cadherin fragments revealed that junctional zippering was accompanied by accumulation of small round-shaped VE-cadherin fragments in the lymphatic endothelium. In mice expressing a mutant VEGFR2 lacking the Y949 phosphosite (Vegfr2 Y949F/Y949F ) required for activation of Src family kinases, zippering of lymphatic junctions persisted, whereas accumulation of small VE-cadherin fragments was suppressed. Moreover, tumor cell entry into initial lymphatic vessels and subsequent metastatic spread to lymph nodes was reduced in mutant mice compared with WT, after challenge with B16F10 melanoma or EO771 breast cancer. We conclude that VEGFA mediates zippering of VE-cadherin junctions in initial lymphatics. Zippering is accompanied by increased VE-cadherin fragmentation through VEGFA-induced Src kinase activation, correlating with tumor dissemination to sentinel lymph nodes.

Lymph node metastases in breast cancer: Mechanisms and molecular imaging

Breast cancer is the most common malignant disease of women in the world. Breast cancer often metastasizes to axillary lymph nodes. Accurate assessment of the status of axillary lymph nodes is crucial to the staging and treatment of breast cancer. None of the methods used clinically for preoperative noninvasive examination of axillary lymph nodes can accurately identify cancer cells from a molecular level. In recent years, with the in-depth study of lymph node metastases, the mechanisms and molecular imaging of lymph node metastases in breast cancer have been reported. In this review, we highlight the new progress in the study of the main mechanisms of lymph node metastases in breast cancer. In addition, we analyze the advantages and disadvantages of traditional preoperative axillary lymph node imaging methods for breast cancer, and list molecular imaging methods that can accurately identify breast cancer cells in lymph nodes.

Regulating mitochondrial metabolism by targeting pyruvate dehydrogenase with dichloroacetate, a metabolic messenger

Dichloroacetate (DCA) is a naturally occurring xenobiotic that has been used as an investigational drug for over 50 years. Originally found to lower blood glucose levels and alter fat metabolism in diabetic rats, this small molecule was found to serve primarily as a pyruvate dehydrogenase kinase inhibitor. Pyruvate dehydrogenase kinase inhibits pyruvate dehydrogenase complex, the catalyst for oxidative decarboxylation of pyruvate to produce acetyl coenzyme A. Several congenital and acquired disease states share a similar pathobiology with respect to glucose homeostasis under distress that leads to a preferential shift from the more efficient oxidative phosphorylation to glycolysis. By reversing this process, DCA can increase available energy and reduce lactic acidosis. The purpose of this review is to examine the literature surrounding this metabolic messenger as it presents exciting opportunities for future investigation and clinical application in therapy including cancer, metabolic disorders, cerebral ischemia, trauma, and sepsis.

Lymph node metastasis and tumor-educated immune tolerance: Potential therapeutic targets against distant metastasis

Lymph node metastasis has been shown to positively associated with the prognosis of many cancers. However, in clinical treatment, lymphadenectomy is not always successful, suggesting that immune cells in the tumor and sentinel lymph nodes still play a pivotal role in tumor immunosuppression. Recent studies had shown that tumors can tolerate immune cells through multiple strategies, including tumor-induced macrophage reprogramming, T cells inactivation, production of B cells pathogenic antibodies and activation of regulatory T cells to promote tumor colonization, growth, and metastasis in lymph nodes. We reviewed the bidirectional effect of immune cells on anti-tumor or promotion of cancer cell metastasis during lymph node metastasis, and the mechanisms by which malignant cancer cells modify immune cells to create a more favorable environment for the growth and survival of cancer cells. Research and treatment strategies focusing on the immune system in lymph nodes and potential immune targets in lymph node metastasis were also be discussed.

The Lymphatic Endothelium in the Context of Radioimmuno-Oncology

The study of lymphatic tumor vasculature has been gaining interest in the context of cancer immunotherapy. These vessels constitute conduits for immune cells' transit toward the lymph nodes, and they endow tumors with routes to metastasize to the lymph nodes and, from them, toward distant sites. In addition, this vasculature participates in the modulation of the immune response directly through the interaction with tumor-infiltrating leukocytes and indirectly through the secretion of cytokines and chemokines that attract leukocytes and tumor cells. Radiotherapy constitutes the therapeutic option for more than 50% of solid tumors. Besides impacting transformed cells, RT affects stromal cells such as endothelial and immune cells. Mature lymphatic endothelial cells are resistant to RT, but we do not know to what extent RT may affect tumor-aberrant lymphatics. RT compromises lymphatic integrity and functionality, and it is a risk factor to the onset of lymphedema, a condition characterized by deficient lymphatic drainage and compromised tissue homeostasis. This review aims to provide evidence of RT's effects on tumor vessels, particularly on lymphatic endothelial cell physiology and immune properties. We will also explore the therapeutic options available so far to modulate signaling through lymphatic endothelial cell receptors and their repercussions on tumor immune cells in the context of cancer. There is a need for careful consideration of the RT dosage to come to terms with the participation of the lymphatic vasculature in anti-tumor response. Here, we provide new approaches to enhance the contribution of the lymphatic endothelium to radioimmuno-oncology.

Reprogramming of sentinel lymph node microenvironment during tumor metastasis

Metastasis is a major cause of death in patients with cancer. The two main routes for cancer cell dissemination are the blood and lymphatic systems. The underlying mechanism of hematogenous metastasis has been well characterized in the past few decades. However, our understanding of the molecular basis of lymphatic metastasis remains at a premature stage. Conceptually, cancer cells invade into lymphatic capillary, passively move to collecting lymphatic vessels, migrate into sentinel lymph node (SLN;, the first lymph node to which cancer cells spread from the primary tumor), and enter the blood circulatory system via the subclavian vein. Before arriving, cancer cells release specific soluble factors to modulate the microenvironment in SLN to establish a beachhead for successful colonization. After colonization, cancer cells inhibit anti-tumor immunity by inducing the recruitment of regulatory T cell and myeloid-derived suppressor cells, suppressing the function of dendritic cell and CD8⁺ T cell, and promoting the release of immunosuppressive cytokines. The development of novel strategies to reverse cancer cell-triggered SLN remodeling may re-activate immunity to reduce beachhead buildup and distant metastasis. In addition to being a microanatomic location for metastasis, the SLN is also an important site for immune modulation. Nanotechnology-based approaches to deliver lymph node-tropic antibodies or drug-conjugated nanoparticles to kill cancer cells on site are a new direction for cancer treatment. Conversely, the induction of stronger immunity by promoting antigen presentation in lymph nodes provides an alternate way to enhance the efficacy of immune checkpoint therapy and cancer vaccine. In this review article, we summarize recent findings on the reprogramming of SLN during lymphatic invasion and discuss the possibility of inhibiting tumor metastasis and eliciting anti-tumor immunity by targeting SLN.

Efficient Radiomics-Based Classification of Multi-Parametric MR Images to Identify Volumetric Habitats and Signatures in Glioblastoma: A Machine Learning Approach

Simple Summary

Glioblastomas carry a poor prognosis and usually presents with heterogeneous regions in the brain tumor. Multi-parametric MR images can show morphological characteristics. Radiomics features refer to the extraction of a large number of quantitative measurements that describe the geometry, intensity, and texture which were extracted from contrast-enhanced T1-weighted images from anatomical MRI and metabolic features from PET. It also provides a qualitative image interpretation as well as cellular, molecular, and tumor properties. Thus, it derives additional information about the entire tumor volume which is generally of irregular shape and size from routinely evaluated “non-invasive” imaging biomarkers techniques. We demonstrated volumetric habitats and signatures in necrosis, solid tumor, peritumoral tissue, and edema with key biological processes and phenotype features. This provides physicians with key information on how the disease is progressing in the brain and can also give an indication of how well treatment is working.

Abstract

Glioblastoma (GBM) is a fast-growing and aggressive brain tumor of the central nervous system. It encroaches on brain tissue with heterogeneous regions of a necrotic core, solid part, peritumoral tissue, and edema. This study provided qualitative image interpretation in GBM subregions and radiomics features in quantitative usage of image analysis, as well as ratios of these tumor components. The aim of this study was to assess the potential of multi-parametric MR fingerprinting with volumetric tumor phenotype and radiomic features to underlie biological process and prognostic status of patients with cerebral gliomas. Based on efficiently classified and retrieved cerebral multi-parametric MRI, all data were analyzed to derive volume-based data of the entire tumor from local cohorts and The Cancer Imaging Archive (TCIA) cohorts with GBM. Edema was mainly enriched for homeostasis whereas necrosis was associated with texture features. The proportional volume size of the edema was about 1.5 times larger than the size of the solid part tumor. The volume size of the solid part was approximately 0.7 times in the necrosis area. Therefore, the multi-parametric MRI-based radiomics model reveals efficiently classified tumor subregions of GBM and suggests that prognostic radiomic features from routine MRI examination may also be significantly associated with key biological processes as a practical imaging biomarker.

Acetone Extract of Cornus officinalis Leaves Exerts Anti-Melanoma Effects via Inhibiting STAT3 Signaling

Purpose

This research aims to investigate the intervention and mechanism of 50% acetone extract of C. officinalis leaves (SZYY) on melanoma xenografts.

Patients and Methods

Tumor size and cardiac function were measured via ultrasound. The accumulation of 2-deoxy-D-glucose (2-DG) in tumor tissue was examined with near-infrared in vivo imaging. Flow cytometry was performed to assess apoptosis and reactive oxygen species (ROS) levels in tumor and immune cells in spleen. The levels of inflammatory cytokines in serum were detected by cytometric bead array. The expression of proliferation-, apoptosis-, and angiogenesis-related proteins in tumor cells was measured to evaluate the underlying mechanisms. Subsequently, the effects of four compounds separated from SZYY on the proliferation and migration of A375 cells and STAT3 signaling were examined. The peak identification and contents of the four components were performed via high-performance liquid chromatography (HPLC). Finally, we evaluated the inhibitory effects of STAT3 overexpression on the cytotoxic activity of four constituents in A375 cells.

Results

SZYY inhibited the growth and glycolysis of melanoma xenograft in mice, improved cardiac function, increased the percentages of macrophages, neutrophils, and lymphocytes in spleen, reduced the levels of IL-6, IL-17A, TNF-α, and IFN-γ in serum, promoted apoptosis and oxidative stress in tumor tissues, and inhibited STAT3 phosphorylation and expression of angiogenic factors. Chemical analysis showed that SZYY is rich in loganin, rutin, triohimas C, and triohimas D, which all could restrain the proliferation and migration of A375 cells and inhibit the phosphorylation and nuclear translocation of STAT3. Moreover, STAT3 overexpression could diminish the cytotoxic activity of four compounds on A375 cells.

Conclusion

SZYY could exert anti-melanoma effects via inhibiting STAT3 signaling to induce apoptosis and inhibit tumor angiogenesis. Its active ingredients might be loganin, rutin, triohimas C, and triohimas D.

PEDF inhibits lymphatic metastasis of nasopharyngeal carcinoma as a new lymphangiogenesis inhibitor

Nasopharyngeal carcinoma (NPC) is one of the most malignant tumors in southern China and Asia, and lymph node metastasis is an important cause for treatment failure. Lymphangiogenesis is a crucial step in lymphatic metastasis of NPC, while little is known about lymphangiogenesis in NPC. Similar to angiogenesis, lymphangitic neovascularization is a process of balance between pro-lymphangiogenesis and anti-lymphangiogenesis factors, but there are few studies on endogenous lymphangiogenesis inhibitors. Pigment epithelium-derived factor (PEDF) is a well-known effective endogenous angiogenesis inhibitor. However, the relationship between PEDF and lymphangiogenesis remains unknown. Our present study reveals that PEDF is lowly expressed in human NPC tissues with poor prognosis and is negatively correlated with lymphatic vessel density (LVD). Consistently, PEDF inhibits lymphangiogenesis and lymphatic metastasis of NPC in vivo experiments. Mechanistically, PEDF inhibits the proliferation, migration, and tube formation of lymphatic endothelial cells and promotes cell apoptosis. On the other hand, PEDF reduces the expression and secretion of vascular endothelial growth factor C (VEGF-C) of NPC cells through the nuclear factor-κB (NF-κB) signaling pathway. Our findings indicate that PEDF plays a vital role in lymphatic metastasis by targeting both lymphatic endothelial cells and NPC cells, and PEDF may represent a novel therapeutic target for NPC.

Prostaglandin E2 Receptor 4 (EP4) as a Therapeutic Target to Impede Breast Cancer-Associated Angiogenesis and Lymphangiogenesis

The formation of new blood (angiogenesis) and lymphatic (lymphangiogenesis) vessels are major events associated with most epithelial malignancies, including breast cancer. Angiogenesis is essential for cancer cell survival. Lymphangiogenesis is critical in maintaining tumoral interstitial fluid balance and importing tumor-facilitatory immune cells. Both vascular routes also serve as conduits for cancer metastasis. Intratumoral hypoxia promotes both events by stimulating multiple angiogenic/lymphangiogenic growth factors. Studies on tumor-associated lymphangiogenesis and its exploitation for therapy have received less attention from the research community than those on angiogenesis. Inflammation is a key mediator of both processes, hijacked by many cancers by the aberrant expression of the inflammation-associated enzyme cyclo-oxygenase (COX)-2. In this review, we focus on breast cancer and showed that COX-2 is a major promoter of both events, primarily resulting from the activation of prostaglandin (PG) E receptor EP4 on tumor cells, tumor-infiltrating immune cells, and endothelial cells; and the induction of oncogenic microRNAs. The COX-2/EP4 pathway also promotes additional events in breast cancer progression, such as cancer cell migration, invasion, and the stimulation of stem-like cells. Based on a combination of studies using multiple breast cancer models, we show that EP4 antagonists hold a major promise in breast cancer therapy in combination with other modalities including immune check-point inhibitors.

Control of Gene Expression by Exosome-Derived Non-Coding RNAs in Cancer Angiogenesis and Lymphangiogenesis

Abstract: Tumour angiogenesis and lymphangiogenesis are hallmarks of cancer and have been associated with tumour progression, tumour metastasis and poor patient prognosis. Many factors regulate angiogenesis and lymphangiogenesis in cancer including non-coding RNAs which are a category of RNAs that do not encode proteins and have important regulatory functions at transcriptional and post-transcriptional levels. Non-coding RNAs can be encapsulated in extracellular vesicles called exosomes which are secreted by tumour cells or other cells in the tumour microenvironment and can then be taken up by the endothelial cells of blood vessels and lymphatic vessels. The "delivery" of these non-coding RNAs to endothelial cells in tumours can facilitate tumour angiogenesis and lymphangiogenesis. Here we review recent findings about exosomal non-coding RNAs, specifically microRNAs and long non-coding RNAs, which regulate tumour angiogenesis and lymphangiogenesis in cancer. We then focus on the potential use of these molecules as cancer biomarkers and opportunities for exploiting ncRNAs for the treatment of cancer.

A multi-omics study on cutaneous and uveal melanoma

AIM

To present the multi-omics landscape of cutaneous melanoma (CM) and uveal melanoma (UM) from The Cancer Genome Atlas (TCGA).

METHODS

The differentially expressed genes (DEGs) between CM and UM were found and integrated into a gene ontology enrichment analysis. Besides, the differentially expressed miRNAs were also identified. We also compared the methylation level of CM with UM and identified the differentially methylated regions to integrate with the DEGs to display the relationship between the gene expression and DNA methylation. The differentially expressed transcription factors (TFs) were identified.

RESULTS

Though CM had more mutational burden than UM, they shared several similarities such as the same rankings in diverse variant types. Except GNAQ and GNA11, the other top 18 mutated genes of the combined group were mostly detected in CM instead of UM. On the transcriptomic level, 4610 DEGs were found and integrated into a gene ontology enrichment analysis. We also identified 485 differentially expressed miRNAs. The methylation analysis showed that UM had a significantly higher methylation level than CM. The integration of differentially methylated regions and DEGs demonstrated that most DEGs were downregulated in UM and the hypo- and hypermethylation presented no obvious difference within these DEGs. Finally, 116 hypermethylated TFs and 114 hypomethylated TFs were identified as differentially expressed TFs in CM when compared with UM.

CONCLUSION

This multi-omics study on comparing CM with UM confirms that they differ in all analyzed levels. Of notice, the results also offer new insights with implications for elucidating certain unclear problems such as the distinct role of epithelial mesenchymal transition in two melanomas, the different metastatic routes of CM and UM and the liver tropism of metastatic UM.

The Roles of Non-Coding RNAs in Tumor-Associated Lymphangiogenesis

Simple Summary

The lymphatic system plays key roles in the bodies’ defence against disease, including cancer. The expansion of this system is termed lymphangiogenesis and it is orchestrated by factors and conditions within the microenvironment. One approach to prevent cancer progression is by interfering with these microenvironment factors that promote this process and that facilitate the spread of cancer cells to distant organs. One of these factors are non-coding RNAs. This review will summarize recent findings of the distinct roles played by non-coding RNAs in the lymphatic system within normal tissues and tumours. Understanding the mechanisms involved in this process can provide new avenues for therapeutic intervention for inhibiting the spread of cancer.

Abstract

Lymphatic vessels are regarded as the ”forgotten” circulation. Despite this, growing evidence has shown significant roles for the lymphatic circulation in normal and pathological conditions in humans, including cancers. The dissemination of tumor cells to other organs is often mediated by lymphatic vessels that serve as a conduit and is often referred to as tumor-associated lymphangiogenesis. Some of the most well-studied lymphangiogenic factors that govern tumor lymphangiogenesis are the vascular endothelial growth factor (VEGF-C/D and VEGFR-2/3), neuroplilin-2 (NRP2), fibroblast growth factor (FGF), and hepatocyte growth factor (HGF), to name a few. However, recent findings have illustrated that non-coding RNAs are significantly involved in regulating gene expression in most biological processes, including lymphangiogenesis. In this review, we focus on the regulation of growth factors and non-coding RNAs (ncRNAs) in the lymphatic development in normal and cancer physiology. Then, we discuss the lymphangiogenic factors that necessitate tumor-associated lymphangiogenesis, with regards to ncRNAs in various types of cancer. Understanding the different roles of ncRNAs in regulating lymphatic vasculature in normal and cancer conditions may pave the way towards the development of ncRNA-based anti-lymphangiogenic therapy.

Tivozanib in renal cell carcinoma: a new approach to previously treated disease

Targeted therapies have been a mainstay of the renal cell carcinoma (RCC) treatment paradigm for the better part of two decades. Multikinase inhibitors of the vascular endothelial growth factor receptor tyrosine kinases (VEGF-TKIs) comprise nearly all targeted therapies in RCC, having been prospectively tested through large, multi-institutional phase III trials. Tivozanib is a VEGF-TKI with high selectivity for VEGF receptors 1–3. Tivozanib has been under investigation for nearly 15 years, with a robust portfolio of preclinical and clinical data. This review seeks to characterize tivozanib within the context of RCC by highlighting preclinical and early clinical trials alongside the phase III trials in RCC, TIVO-1, and TIVO-3. We also aim to explore further trials of tivozanib, whether in combination with other agents and/or in differing disease settings, while providing insight into the utility of tivozanib as a clinical tool for the management of RCC.

Lymphatic Endothelial Cell Progenitors in the Tumor Microenvironment

Tumor lymphatics play a key role in cancer progression as they are solely responsible for transporting malignant cells to regional lymph nodes (LNs), a process that precedes and promotes systemic lethal spread. It is broadly accepted that tumor lymphatic sprouting is induced mainly by soluble factors derived from tumor-associated macrophages (TAMs) and malignant cells. However, emerging evidence strongly suggests that a subset of TAMs, myeloid-lymphatic endothelial cell progenitors (M-LECP), also contribute to the expansion of lymphatics through both secretion of paracrine factors and a self-autonomous mode. M-LECP are derived from bone marrow (BM) precursors of the monocyte-macrophage lineage and characterized by unique co-expression of markers identifying lymphatic endothelial cells (LEC), stem cells, M2-type macrophages, and myeloid-derived immunosuppressive cells. This review describes current evidence for the origin of M-LECP in the bone marrow, their recruitment tumors and intratumoral trafficking, similarities to other TAM subsets, and mechanisms promoting tumor lymphatics. We also describe M-LECP integration into preexisting lymphatic vessels and discuss potential mechanisms and significance of this event. We conclude that improved mechanistic understanding of M-LECP functions within the tumor environment may lead to new therapeutic approaches to suppress tumor lymphangiogenesis and metastasis to lymph nodes.

Hypoxia: Overview on Hypoxia-Mediated Mechanisms with a Focus on the Role of HIF Genes

Hypoxia represents a frequent player in a number of malignancies, contributing to the development of the neoplastic disease. This review will discuss the means by which hypoxia powers the mechanisms behind cancer progression, with a majority of examples from lung cancer, the leading malignancy in terms of incidence and mortality rates (the frequent reference toward lung cancer is also for simplification purposes and follow up of the global mechanism in the context of a disease). The effects induced by low oxygen levels are orchestrated by hypoxia-inducible factors (HIFs) which regulate the expression of numerous genes involved in cancer progression. Hypoxia induces epithelial-to-mesenchymal transition (EMT) and metastasis through a complex machinery, by mediating various pathways such as TGF-β, PI3k/Akt, Wnt, and Jagged/Notch. Concomitantly, hypoxic environment has a vast implication in angiogenesis by stimulating vessel growth through the HIF-1α/VEGF axis. Low levels of oxygen can also promote the process through several other secondary factors, including ANGPT2, FGF, and HGF. Metabolic adaptations caused by hypoxia include the Warburg effect-a metabolic switch to glycolysis-and GLUT1 overexpression. The switch is achieved by directly increasing the expression of numerous glycolytic enzymes that are isoforms of those found in non-malignant cells.

Current understanding of lymphatic vessels in the central nervous system

Lymphangiogenesis is associated with some pathological conditions such as inflammation, tissue repair, and tumor growth. Recently, a paradigm shift occurred following the discovery of meningeal lymphatic structures in the human central nervous system (CNS); these structures may be a key drainage route for cerebrospinal fluid (CSF) into the peripheral blood and may also contribute to inflammatory reaction and immune surveillance of the CNS. Lymphatic vessels located along the dural sinuses absorb CSF from the adjacent subarachnoid space and brain interstitial fluid via the glymphatic system, which is composed of aquaporin-4 water channels expressed on perivascular astrocytic end-feet membranes. Magnetic resonance imaging (MRI) clearly visualized these lymphatic vessels in the human dura mater. The conception of some neurological disorders, such as multiple sclerosis and Alzheimer's disease, has been changed by this paradigm shift. Meningeal lymphatic vessels could be a promising therapeutic target for the prevention of neurological disorders. However, the involvement of meningeal lymphatic vessels in the pathophysiology has not been fully elucidated and is the subject of future investigations. In this article, to understand the involvement of meningeal lymphatic vessels in neurological disorders, we review the differences between lymphangiogenesis in the CNS and in other tissues during both developmental and adulthood stages, and pathological conditions that may be associated with meningeal lymphatic vessels in the CNS.

Roles of prostaglandins in tumor-associated lymphangiogenesis with special reference to breast cancer

Lymphangiogenesis (formation of new lymphatic vessels), unlike angiogenesis, has been a lesser-focused field in cancer biology, because of earlier controversy regarding whether lymphatic metastasis occurs via pre-existing or newly formed lymphatics. Recent evidence reveals that peri-tumoral or intra-tumoral lymphangiogenesis is a precursor for lymphatic metastasis in most carcinomas and melanomas. Two major lymphangiogenic factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, are produced by cancer cells or immune cells such as macrophages in the tumor-stroma to promote sprouting of lymphatics from lymphatic endothelial cells (LEC) or LEC precursors (LECP) by binding to their primary (high affinity) receptor VEGF-R3 or secondary receptors VEGF-R2, neuropilin (NRP)2 and α9/β1 integrin. Many other growth factors/receptors such as VEGF-A/VEGF-R2, fibroblast growth factor (FGF)2/FGF-R, platelet-derived growth factor (PDGF)/PDGF-R, hepatocyte growth factor (HGF)/C-Met, angiopoietins (Ang)1, 2/Tie2, and chemokines/ chemokine receptors (CCL21/CCR7, CCL12/CCR4) can also stimulate LEC sprouting directly or indirectly. This review deals with the roles of prostaglandins (PG), in particular PGE2, in cancer-associated lymphangiogenesis, with special emphasis on breast cancer. We show that cyclooxygenase (COX)-2 expression by breast cancer cells or tumor stroma leading to high PGE2 levels in the tumor milieu promotes lymphangiogenesis and lymphatic metastases, resulting from binding of PGE2 to PGE receptors (EP, in particular EP4) on multiple cell types: tumor cells, tumor-infiltrating immune cells, and LEC. EP4 activation on cancer cells and macrophages upregulated VEGF-C/D production to stimulate LEC sprouting. Furthermore, ligation of EP4 with PGE2 on cancer or host cells can initiate a new cascade of molecular events leading to cross-talk between cancer cells and LEC, facilitating lymphangiogenesis and lympho-vascular transport of cancer cells. We make a case for EP4 as a potential therapeutic target for breast cancer.

Tumor-associated lymphangiogenesis predicts unfavorable prognosis of intrahepatic cholangiocarcinoma

Background

Tumor-associated lymphangiogenesis is considered significant in number of solid malignancies. However, its impact on prognosis of intrahepatic cholangiocarcinoma (ICC) after resection remains further confirmation. Herein, we conducted this study to evaluate prognostic impact of tumor-associated lymphangiogenesis in patients with ICC.

Methods

Extent of tumor-associated lymphangiogenesis of ICC was evaluated by quantifying microlymphatic vessel density (MLVD) from immunohistochemical staining of a lymphatic endothelial-specific antibody (podoplanin). Clinicopathological characteristics were comprehensively analyzed to identify MLVD-associated factors. The patients were stratified into high and low MLVD groups according to the distinctive correlation between the MLVD and overall survival using the Spearman’s correlation test. Kaplan-Meier estimation was performed to confirm prognostic impact of MLVD in patients with ICC. Univariate and multivariate analyses were performed using the Cox proportional hazard model.

Results

The MLVD between 4 to 12 counts showed inverse proportion to the overall survival (Spearman’s r = − 0.66; 95% confidence interval [CI], − 0.82 to − 0.39; p <  0.0001), which was set as a cut-off for the high MLVD group, whereas the MLVD between 13 to 25 showed no correlation to the overall survival (r = − 0.11; 95% CI, − 0.38 to 0.19; p = 0.4791). The high MLVD group showed more frequent lymph node metastasis (p <  0.001) and were more likely to suffer from recurrence of the tumor compared to the low MLVD group (p <  0.001). The high MLVD was found to be independently associated with reduced overall and recurrence-free survival. The 5-year overall survival of the patients with high MLVD was significantly lower compared to those with low MLVD (0% vs 48%).

Conclusions

Our study reveals that tumor-associated lymphangiogenesis is significantly associated with increased lymphatic metastasis, recurrence of the tumor, and reduced overall survival in patients with ICC, thus providing guidance when estimating postresection prognosis.

Regulation of Blood and Lymphatic Vessels by Immune Cells in Tumors and Metastasis

Research over the last decades has provided strong evidence for the pivotal role of the tumor-associated blood and lymphatic vasculature in supporting immunoevasion and in subverting T cell-mediated immunosurveillance. Conversely, tumor blood and lymphatic vessel growth is in part regulated by the immune system, with infiltrating innate as well as adaptive immune cells providing both immunosuppressive and various angiogenic signals. Thus, tumor angiogenesis and escape of immunosurveillance are two cancer hallmarks that are tightly linked and interregulated by cell constituents from compartments secreting both chemokines and cytokines. In this review, we discuss the implication and regulation of innate and adaptive immune cells in regulating blood and lymphatic angiogenesis in tumor progression and metastases. Moreover, we also highlight novel therapeutic approaches that target the tumor vasculature as well as the immune compartment to sustain and improve therapeutic efficacy in cancer.

Hypoxia-Dependent Angiogenesis and Lymphangiogenesis in Cancer

Hypoxia (low O₂) is a ubiquitous feature of solid cancers, arising as a mismatch between cellular O₂ supply and consumption. Hypoxia is associated to metastatic disease and mortality owing to its ability to stimulate the formation of blood (angiogenesis) and lymphatic vessels (lymphangiogenesis), thereby allowing cancer cells to escape the unfavorable tumor microenvironment and disseminate into secondary sites. This review outlines molecular mechanisms by which intratumoral hypoxia regulates the expression of motogenic and mitogenic factors that induce angiogenesis and lymphangiogenesis, whilst discussing their implications for metastatic cancers.

Dihydroartemisinin enhances VEGFR1 expression through up-regulation of ETS-1 transcription factor

Angiogenesis is required for tumor growth. Dihydroartemisinin (DHA), a the effective anti-malarial derivative of artemisinin, demonstrated potent anti-angiogenic activities that closely related to the regulation of vascular endothelial growth factor (VEGF) signaling cascade. VEGF receptor 1 (VEGFR1), a receptor in endothelial cells (ECs), coordinately regulate angiogenic activity triggered by ligand-receptor binding. Here we aimed to explore the effects of DHA on VEGFR1 expression in ECs. We found that DHA significantly increases VEGFR1 expression in human umbilical vein endothelial cells (HUVECs). In addition, DHA significantly upregulates the level of V-Ets Avian Erythroblastosis Virus E26 Oncogene Homolog 1 (ETS-1), a transcriptional factor which binds to the human VEGFR1 promoter. ChIP assay showed that DHA increases ETS-1 binding to the -52 ETS motif on the VEGFR1 promoter. Knockdown of ETS-1 by RNA interference abolished DHA-induced increase of VEGFR1 expression. Taken together, we demonstrated that DHA elevates VEGFR1 expression via up-regulation of ETS-1 transcription in HUVECs.

Preclinical models for precision oncology

Precision medicine approaches have revolutionized oncology. Personalized treatments require not only identification of the driving molecular alterations, but also development of targeted therapies and diagnostic tests to identify the appropriate patient populations for clinical trials and subsequent therapeutic implementation. Preclinical in vitro and in vivo models are widely used to predict efficacy of newly developed treatments. Here we discuss whether, and to what extent, preclinical models including cell lines, organoids and tumorgrafts recapitulate key features of human tumors. The potential of preclinical models to anticipate treatment efficacy and clinical benefit is also presented, using examples in different tumor types.

Simultaneous blockade of IL-6 and CCL5 signaling for synergistic inhibition of triple-negative breast cancer growth and metastasis

Background

Metastatic triple-negative breast cancer (TNBC) is a heterogeneous and incurable disease. Numerous studies have been conducted to seek molecular targets to treat TNBC effectively, but chemotherapy is still the main choice for patients with TNBC. We have previously presented evidence of the important roles of interleukin-6 (IL-6) and chemokine (C-C motif) ligand 5 (CCL5) in TNBC tumor growth and metastasis. These experiments highlighted the importance of the crosstalk between cancer cells and stromal lymphatic endothelial cells (LECs) in tumor growth and metastasis.

Methods

We examined the viability and migration of MDA-MB-231-LN, SUM149, and SUM159 cells co-cultured with LECs when treated with maraviroc (CCR5 inhibitor) and tocilizumab (anti-IL-6 receptor antibody). To assess the anti-tumor effects of the combination of these two drugs in an athymic nude mouse model, MDA-MB-231-LN cells were implanted in the mammary fat pad and maraviroc (8 mg/kg, orally daily) and cMR16-1 (murine surrogate of the anti-IL-6R antibody, 10 mg/kg, IP, 3 days a week) were administrated for 5 weeks and effects on tumor growth and thoracic metastasis were measured.

Results

In this study, we used maraviroc and tocilizumab to confirm that IL-6 and CCL5 signaling are key pathways promoting TNBC cell proliferation and migration. Further, in a xenograft mouse model, we showed that tumor growth was dramatically inhibited by cMR16-1, the mouse version of the anti-IL6R antibody. The combination of maraviroc and cMR16-1 caused significant reduction of TNBC tumor growth compared to the single agents. Significantly, the combination of maraviroc and cMR16-1 abrogated thoracic metastasis.

Conclusion

Taken together, these findings show that IL-6 and CCL5 signaling, which promote crosstalk between TNBC and lymphatic vessels, are key enhancers of TNBC tumor growth and metastasis. Furthermore, these results demonstrate that a drug combination inhibiting these pathways may be a promising therapy for TNBC patients.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0981-3) contains supplementary material, which is available to authorized users.

Dual roles of endothelial FGF-2-FGFR1-PDGF-BB and perivascular FGF-2-FGFR2-PDGFRβ signaling pathways in tumor vascular remodeling

Perivascular cells are important cellular components in the tumor microenvironment (TME) and they modulate vascular integrity, remodeling, stability, and functions. Here we show using mice models that FGF-2 is a potent pericyte-stimulating factor in tumors. Mechanistically, FGF-2 binds to FGFR2 to stimulate pericyte proliferation and orchestrates the PDGFRβ signaling for vascular recruitment. FGF-2 sensitizes the PDGFRβ signaling through increasing PDGFRβ levels in pericytes. To ensure activation of PDGFRβ, the FGF-2-FGFR1-siganling induces PDGF-BB and PDGF-DD, two ligands for PDGFRβ, in angiogenic endothelial cells. Thus, FGF-2 directly and indirectly stimulates pericyte proliferation and recruitment by modulating the PDGF-PDGFRβ signaling. Our study identifies a novel mechanism by which the FGF-2 and PDGF-BB collaboratively modulate perivascular cell coverage in tumor vessels, thus providing mechanistic insights of pericyte-endothelial cell interactions in TME and conceptual implications for treatment of cancers and other diseases by targeting the FGF-2-FGFR-pericyte axis.

PD-1/PD-L1 and VEGF-A/VEGF-C expression in lymph node microenvironment and association with melanoma metastasis and survival

Regional lymph nodes are affected frequently by melanoma metastasis. Its microenvironment may be associated with tumor progression. We investigated sentinel nodes with and without tumor and negative nodes surrounding positive nodes, looking for patterns related to tumor immune interaction and lymphovascular progression. We quantified programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1, vascular endothelial growth factor (VEGF)-A/VEGF-C expressions in lymph nodes of 103 patients who underwent sentinel lymph node biopsy. Two groups were studied: negative sentinel lymph nodes and positive ones. Negative lymph nodes of sequential lymphadenectomy from positive cases were also studied. Markers were assessed by immunohistochemistry. Results were related to clinical/histological outcomes. VEGF-A/VEGF-C analysis showed higher positivity in metastatic nodes and higher positivity in the surrounding negative nodes from positive cases in comparison with nonmetastatic patients. Programmed cell death-ligand 1, studied only in metastasis, presented high positivity, not associated with prognosis. PD-1 expressions were similar in the groups with a 1% cutoff and higher in the metastasis with a 5% cutoff. Higher VEGF-A expression was related to higher pathological stages. PD-1 expression in the lymph node was associated with higher survival. Other clinical and histopatological variables were not associated with marker expression patterns. VEGF-A and VEGF-C expressions in lymph nodes were associated with the presence of lymph node metastasis. PD-1 expression in the lymph node was related to higher survival rates and this should be explored in the context of adjuvant immunotherapy.

Common mechanism of pathogenesis in various types of metastatic osteosarcoma

The present study aimed to investigate the common metastatic mechanism in various types of metastatic osteosarcoma (OS). Gene expression profiles generated from the metastatic OS KHOS and KRIB cell lines and the non-metastatic OS HOS cell line were compared. Two groups of differentially expressed genes (DEGs) between KHOS or KRIB and HOS were screened (P<0.01 and |fold change| ≥2) and then underwent Gene Ontology (GO) and pathway enrichment analyses. Subsequently, the protein-protein interaction (PPI) network was constructed and the subnetwork was mined. Furthermore, overlapping DEGs of these two groups were identified and pathway enrichment and regulatory network analyses were performed. A total of 1,552 and 1,330 DEGs from KHOS vs. HOS and KRIB vs. HOS were obtained, respectively. GO and pathway enrichment analyses of DEGs between KRIB and HOS, including anatomical structure morphogenesis and focal adhesion, were similar to those between KHOS and HOS. Vascular endothelial growth factor A and epidermal growth factor receptor were hub nodes in the PPI network for KHOS and KRIB. Subnetworks of these two groups were similar. In addition, 421 upregulated and 595 downregulated overlapping genes were enriched in the mitogen-activated protein kinase and transforming growth factor-β signaling pathways. Furthermore, seven vital transcription factors, including hes-related family bHLH transcription factor with YRPW motif 1 (HEY1), were obtained. Overall, different types of metastatic OS were shown to exhibit a similar mechanism of pathogenesis. With the exception of cell adhesion and angiogenesis, recapitulation of the morphogenetic processes facilitates OS tumor formation and metastasis. Genes such as HEY1 are important for metastatic OS. Further studies are required in order to confirm these results.

Blockade of MMP-2 and MMP-9 inhibits corneal lymphangiogenesis

PURPOSE

To investigate the roles of a selective MMP-2 and -9 inhibitor (SB-3CT) in corneal inflammatory lymphangiogenesis.

METHODS

The expression of MMP-2 and -9 in the cornea after suture inplacement, treated with SB-3CT or negative control, was detected by real-time polymerase chain reaction (PCR). Inflammatory corneal neovascularization (NV) was induced by corneal suture placement. Mice were treated with SB-3CT eye drops (twice daily for 1 week, 5 μL per drop; 50, 100, or 200 μM). The outgrowth of blood and lymphatic vessels, and macrophage recruitment were analyzed by immunofluorescence assay. The expressions of vascular endothelial growth factor-C (VEGF-C) and its receptor VEGFR-3 were tested by real-time PCR.

RESULTS

MMP-2 and -9 expression were suppressed significantly by treatment with SB-3CT. The data demonstrated, for the first time, that SB-3CT strongly reduced corneal lymphangiogenesis and macrophage infiltration during inflammation. Furthermore, expressions of VEGF-C and its receptor VEGFR-3 were significantly inhibited by SB-3CT during corneal lymphangiogenesis.

CONCLUSIONS

These novel findings indicated that blockade of MMP-2 and -9 could inhibit lymphangiogenesis. Further investigation of this factor may provide novel therapies for transplant rejection and other lymphatic disorders.

Salt Sensitivity of Angiogenesis Inhibition-Induced Blood Pressure Rise: Role of Interstitial Sodium Accumulation?

In response to salt loading, Na⁺ and Cl^- accumulate in the skin in excess of water, stimulating skin lymphangiogenesis via activation of the mononuclear phagocyte system cell-derived vascular endothelial growth factor-C-vascular endothelial growth factor type 3 receptor signaling pathway. Inhibition of this pathway results in salt-sensitive hypertension. Sunitinib is an antiangiogenic, anticancer agent that blocks all 3 vascular endothelial growth factor receptors and increases blood pressure. We explored the salt dependency of sunitinib-induced hypertension and whether impairment of skin lymphangiogenesis is an underlying mechanism. Normotensive Wistar-Kyoto rats were exposed to a normal or high salt with or without sunitinib administration. Sunitinib induced a 15 mm Hg rise in telemetrically measured blood pressure, which was aggravated by a high-salt diet (HSD), resulting in a decline of the slope of the pressure-natriuresis curve. Without affecting body weight, plasma Na⁺ concentration or renal function, Na⁺ and Cl^- skin content increased by 31% and 32% with the high salt and by 49% and 50% with the HSD plus sunitinib, whereas skin water increased by 17% and 24%, respectively. Skin mononuclear phagocyte system cell density increased both during sunitinib and a HSD, but no further increment was seen when HSD and sunitinib were combined. HSD increased skin lymphangiogenesis, while sunitinib tended to decrease lymphangiogenesis, both during a normal-salt diet and HSD. We conclude that sunitinib induces hypertension that is aggravated by high salt intake and not accompanied by impaired skin lymphangiogenesis.

Experimental animal modeling for immuno-oncology

Immuno-oncology (I/O) research has intensified significantly in recent years due to the breakthrough development and the regulatory approval of several immune checkpoint inhibitors, leading to the rapid expansion of the new discovery of novel I/O therapies, new checkpoint inhibitors and beyond. However, many I/O questions remain unanswered, including why only certain subsets of patients respond to these treatments, who the responders would be, and how to expand patient response (the conversion of non-responders or maximizing response in partial responders). All of these require relevant I/O experimental systems, particularly relevant preclinical animal models. Compared to other oncology drug discovery, e.g. cytotoxic and targeted drugs, a lack of relevant animal models is a major obstacle in I/O drug discovery, and an urgent and unmet need. Despite the obvious importance, and the fact that much I/O research has been performed using many different animal models, there are few comprehensive and introductory reviews on this topic. This article attempts to review the efforts in development of a variety of such models, as well as their applications and limitations for readers new to the field, particularly those in the pharmaceutical industry.

Deciphering Pro-Lymphangiogenic Programs during Mammary Involution and Postpartum Breast Cancer

Postpartum breast cancers are a highly metastatic subset of young women’s breast cancers defined as breast cancers diagnosed in the postpartum period or within 5 years of last child birth. Women diagnosed with postpartum breast cancer are nearly twice as likely to develop metastasis and to die from breast cancer when compared with nulliparous women. Additionally, epidemiological studies utilizing multiple cohorts also suggest that nearly half of all breast cancers in women aged <45 qualify as postpartum cases. Understanding the biology that underlies this increased risk for metastasis and death may lead to identification of targeted interventions that will benefit the large number of young women with breast cancer who fall into this subset. Preclinical mouse models of postpartum breast cancer have revealed that breast tumor cells become more aggressive if they are present during the normal physiologic process of postpartum mammary gland involution in mice. As involution appears to be a period of lymphatic growth and remodeling, and human postpartum breast cancers have high peritumor lymphatic vessel density (LVD) and increased incidence of lymph node metastasis (1, 2), we propose that novel insight into is to be gained through the study of the biological mechanisms driving normal postpartum mammary lymphangiogenesis as well as in the microenvironment of postpartum tumors.

Association between VEGF-A, C and D expression and lymph node involvement in breast cancer: a meta-analysis

BACKGROUND

Metastasis is the primary cause of death in patients with breast cancer. Although VEGF-A, C and D are considered to be prime factors in lymph node metastasis in breast cancer, the published studies have conflicting conclusions.

METHODS

To resolve this conflict, we conducted a meta-analysis of 37 studies (n = 5,001 patients) evaluating the correlation between VEGF-A, C and D immunohistochemical expression and lymph node metastasis (LNM). The meta-analysis included 22 studies of VEGF-A, 17 of VEGF-C, and 6 of VEGF-D. The relationships between VEGF-A, C and D and clinicopathological parameters were also examined.

RESULTS

The results showed a significant association between VEGF-A or VEGF-C overexpression and LNM (risk ratio [RR] = 1.28 [95% CI 1.04-1.58], p = 0.02; and RR = 1.36 [95% CI 1.07-1.72], p = 0.01, respectively). Subgroup evaluation showed a significant association between VEGF-A, C and D overexpression and LNM when analyses were limited to Asian patients (RR = 1.78 [95% CI 1.28-2.46], p = 0.0005; RR = 1.38 [95% CI 1.04-1.84], p = 0.03, and RR = 2.62 [95% CI 1.35-5.09], p = 0.004, respectively). VEGF-A overexpression was significantly associated with lymph vessel invasion (RR = 1.86 [95% CI 1.33-2.60], p = 0.0003). Overexpression of VEGF-C or VEGF-D was significantly associated with HER-2 positivity (RR = 1.30 [95% CI 1.06-1.59], p = 0.01; and RR = 1.75 [95% CI 1.01-3.03], p = 0.05, respectively).

CONCLUSIONS

With some limitations, our meta-analysis indicated that VEGF-A and C could predict LNM in patients with breast cancer, particularly Asian patients.

Tumor lymphangiogenesis and new drug development

Traditionally, tumor-associated lymphatic vessels have been regarded as passive by-standers, serving simply as a drainage system for interstitial fluid generated within the tumor. However, with growing evidence that tumors actively induce lymphangiogenesis, and that the number of lymphatic vessels closely correlates with metastasis and clinical outcome in various types of cancer, this picture has changed dramatically in recent years. Tumor-associated lymphatic vessels have now emerged as a valid therapeutic target to control metastatic disease, and the first specific anti-lymphangiogenic drugs have recently entered clinical testing. Furthermore, we are just beginning to understand the whole functional spectrum of tumor-associated lymphatic vessels, which not only concerns transport of fluid and metastatic cells, but also includes the regulation of cancer stemness and specific inhibition of immune responses, opening new venues for therapeutic applications. Therefore, we predict that specific targeting of lymphatic vessels and their function will become an important tool for future cancer treatment.

The lymphatic system and pancreatic cancer

This review summarizes current knowledge of the biology, pathology and clinical understanding of lymphatic invasion and metastasis in pancreatic cancer. We discuss the clinical and biological consequences of lymphatic invasion and metastasis, including paraneoplastic effects on immune responses and consider the possible benefit of therapies to treat tumors that are localized to lymphatics. A review of current techniques and methods to study interactions between tumors and lymphatics is presented.

Non-caveolar caveolin-1 expression in prostate cancer cells promotes lymphangiogenesis

Lymphangiogenesis allows prostate cancer (PCa) lymphatic metastasis, which is associated with poor prognosis and short survival rates. Caveolin-1 (Cav-1) is a membrane protein localized in caveolae, but also exists in non-caveolar, cellular or extracellular forms. Cav-1 is overexpressed in PCa, promotes prostate tumour progression and metastasis. We investigated the effect of caveolar and non-caveolar Cav-1 on PCa lymphangiogenic potential. Cav-1 was down-regulated in PC3 and DU145, and ectopically expressed in LNCaP cells. The effect of PCa cell conditioned media on lymphatic endothelial cell (LEC) viability, chemotaxis, chemokinesis and differentiation was assessed. The effect of Cav-1 on PCa cell expression of lymphangiogenesis-modulators VEGF-A and VEGF-C was assessed using qPCR and ELISA of the conditioned medium. Non-caveolar Cav-1, whether exogenous or endogenous (in LNCaP and PC3 cells, respectively) enhanced LEC proliferation, migration and differentiation. In contrast, caveolar Cav-1 (in DU145 cells) did not significantly affect PCa cell lymphangiogenic potential. The effect of non-caveolar Cav-1 on LECs was mediated by increased expression of VEGF-A as demonstrated by neutralization by anti-VEGF-A antibody. This study unveils for the first time a crucial role for non-caveolar Cav-1 in modulating PCa cell expression of VEGF-A and subsequent LEC proliferation, migration and tube formation.

Th2 cytokines inhibit lymphangiogenesis

Lymphangiogenesis is the process by which new lymphatic vessels grow in response to pathologic stimuli such as wound healing, inflammation, and tumor metastasis. It is well-recognized that growth factors and cytokines regulate lymphangiogenesis by promoting or inhibiting lymphatic endothelial cell (LEC) proliferation, migration and differentiation. Our group has shown that the expression of T-helper 2 (Th2) cytokines is markedly increased in lymphedema, and that these cytokines inhibit lymphatic function by increasing fibrosis and promoting changes in the extracellular matrix. However, while the evidence supporting a role for T cells and Th2 cytokines as negative regulators of lymphatic function is clear, the direct effects of Th2 cytokines on isolated LECs remains poorly understood. Using in vitro and in vivo studies, we show that physiologic doses of interleukin-4 (IL-4) and interleukin-13 (IL-13) have profound anti-lymphangiogenic effects and potently impair LEC survival, proliferation, migration, and tubule formation. Inhibition of these cytokines with targeted monoclonal antibodies in the cornea suture model specifically increases inflammatory lymphangiogenesis without concomitant changes in angiogenesis. These findings suggest that manipulation of anti-lymphangiogenic pathways may represent a novel and potent means of improving lymphangiogenesis.

The circadian clock and hypoxia in tumor cell de-differentiation and metastasis

BACKGROUND

Cancer is considered to develop due to disruptions in the tissue microenvironment in addition to genetic disruptions in the tumor cells themselves. The two most important microenvironmental disruptions in cancer are arguably tissue hypoxia and disrupted circadian rhythmicity. Endothelial cells, which line the luminal side of all blood vessels transport oxygen or endocrine circadian regulators to the tissue and are therefore of key importance for circadian disruption and hypoxia in tumors.

SCOPE OF REVIEW

Here I review recent findings on the role of circadian rhythms and hypoxia in cancer and metastasis, with particular emphasis on how these pathways link tumor metastasis to pathological functions of blood vessels. The involvement of disrupted cell metabolism and redox homeostasis in this context and the use of novel zebrafish models for such studies will be discussed.

MAJOR CONCLUSIONS

Circadian rhythms and hypoxia are involved in tumor metastasis on all levels from pathological deregulation of the cell to the tissue and the whole organism. Pathological tumor blood vessels cause hypoxia and disruption in circadian rhythmicity which in turn drives tumor metastasis. Zebrafish models may be used to increase our understanding of the mechanisms behind hypoxia and circadian regulation of metastasis.

GENERAL SIGNIFICANCE

Disrupted blood flow in tumors is currently seen as a therapeutic goal in cancer treatment, but may drive invasion and metastasis via pathological hypoxia and circadian clock signaling. Understanding the molecular details behind such regulation is important to optimize treatment for patients with solid tumors in the future. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Bone marrow-derived mesenchymal stem cells drive lymphangiogenesis

It is now well accepted that multipotent Bone-Marrow Mesenchymal Stem Cells (BM-MSC) contribute to cancer progression through several mechanisms including angiogenesis. However, their involvement during the lymphangiogenic process is poorly described. Using BM-MSC isolated from mice of two different backgrounds, we demonstrate a paracrine lymphangiogenic action of BM-MSC both in vivo and in vitro. Co-injection of BM-MSC and tumor cells in mice increased the in vivo tumor growth and intratumoral lymphatic vessel density. In addition, BM-MSC or their conditioned medium stimulated the recruitment of lymphatic vessels in vivo in an ear sponge assay, and ex vivo in the lymphatic ring assay (LRA). In vitro, MSC conditioned medium also increased the proliferation rate and the migration of both primary lymphatic endothelial cells (LEC) and an immortalized lymphatic endothelial cell line. Mechanistically, these pro-lymphangiogenic effects relied on the secretion of Vascular Endothelial Growth Factor (VEGF)-A by BM-MSC that activates VEGF Receptor (VEGFR)-2 pathway on LEC. Indeed, the trapping of VEGF-A in MSC conditioned medium by soluble VEGF Receptors (sVEGFR)-1, -2 or the inhibition of VEGFR-2 activity by a specific inhibitor (ZM 323881) both decreased LEC proliferation, migration and the phosphorylation of their main downstream target ERK1/2. This study provides direct unprecedented evidence for a paracrine lymphangiogenic action of BM-MSC via the production of VEGF-A which acts on LEC VEGFR-2.

Prognostic value of vascular endothelial growth factors A and C in oral squamous cell carcinoma

BACKGROUND

Vascular endothelial growth factor (VEGF) family members play a major role in angiogenesis and vascularization. VEGF-A promotes tumor angiogenesis by stimulating the growth of tumor vascular endothelial cells. In addition, VEGF-C has been identified as a potent inducer of lymphangiogenesis in tumor and lymph node metastasis. Previous studies have investigated the association between clinicopathological factors and the expression of VEGF-A and VEGF-C in oral squamous cell carcinoma cancer (OSCC), but the results are contradictory. In this study, we investigated the relationship between VEGF-A and VEGF-C expression and OSCC clinicopathological factors and prognosis.

METHODS

Expression of VEGF-A and VEGF-C was evaluated in surgical specimens from 61 patients with OSCC and three human oral cancer cell lines (OSC-19, OSC-20 and HOC313) by immunohistochemical staining and enzyme-linked immunosorbent assay, respectively. We also determined the relationship between the 5-year survival rate and clinicopathological factors, such as TNM classification (Union for International Cancer Control, UICC), lymph node metastasis, recurrence, histological differentiation, location, and mode of invasion.

RESULTS

VEGF-A expression correlated significantly with lymph node metastasis. VEGF-C expression was associated with lymph node metastasis, recurrence, and a poorer 5-year survival rate. A multivariate analysis demonstrated that VEGF-C is an independent prognostic factor for patients with OSCC. VEGF-C expression was significantly up-regulated in HOC313 cells compared to OSC-19 and OSC-20 cells.

CONCLUSIONS

These results indicate that VEGF-C may be a predictive factor for OSCC outcome, lymph node metastasis, and recurrence. Moreover, VEGF-C may be an important factor in the development of new therapies for OSCC patients.

Role of tumor associated macrophages in tumor angiogenesis and lymphangiogenesis

Tumor angiogenesis is an essential process for supplying rapidly growing malignant tissues with essential nutrients and oxygen. An angiogenic switch allows tumor cells to survive and grow, and provides them access to vasculature resulting in metastatic disease. Monocyte-derived macrophages recruited and reprogrammed by tumor cells serve as a major source of angiogenic factors boosting the angiogenic switch. Tumor endothelium releases angiopoietin-2 and further facilitates recruitment of TIE2 receptor expressing monocytes (TEM) into tumor sites. Tumor-associated macrophages (TAM) sense hypoxia in avascular areas of tumors, and react by production of angiogenic factors such as VEGFA. VEGFA stimulates chemotaxis of endothelial cells (EC) and macrophages. In some tumors, TAM appeared to be a major source of MMP9. Elevated expression of MMP9 by TAM mediates extracellular matrix (ECM) degradation and the release of bioactive VEGFA. Other angiogenic factors released by TAM include basic fibroblast growth factor (bFGF), thymidine phosphorylase (TP), urokinase-type plasminogen activator (uPA), and adrenomedullin (ADM). The same factors used by macrophages for the induction of angiogenesis [like vascular endothelial growth factor A (VEGF-A) and MMP9] support lymphangiogenesis. TAM can express LYVE-1, one of the established markers of lymphatic endothelium. TAM support tumor lymphangiogenesis not only by secretion of pro-lymphangiogenic factors but also by trans-differentiation into lymphatic EC. New pro-angiogenic factor YKL-40 belongs to a family of mammalian chitinase-like proteins (CLP) that act as cytokines or growth factors. Human CLP family comprises YKL-40, YKL-39, and SI-CLP. Production of all three CLP in macrophages is antagonistically regulated by cytokines. It was recently established that YKL-40 induces angiogenesis in vitro and in animal tumor models. YKL-40-neutralizing monoclonal antibody blocks tumor angiogenesis and progression. The role of YKL-39 and SI-CLP in tumor angiogenesis and lymphangiogenesis remains to be investigated.

Lymphangiogenic factors, mechanisms, and applications

Lymphangiogenesis, the growth of lymphatic vessels, is essential in embryonic development. In adults, it is involved in many pathological processes such as lymphedema, inflammatory diseases, and tumor metastasis. Advances during the past decade have dramatically increased the knowledge of the mechanisms of lymphangiogenesis, including the roles of transcription factors, lymphangiogenic growth factors and their receptors, and intercellular and intracellular signaling cascades. Strategies based on these mechanisms are being tested in the treatment of various human diseases such as cancer, lymphedema, and tissue allograft rejection. This Review summarizes the recent progress on lymphangiogenic mechanisms and their applications in disease treatment.

Lymphangiogenesis and lymphatic vessel remodelling in cancer

The generation of new lymphatic vessels through lymphangiogenesis and the remodelling of existing lymphatics are thought to be important steps in cancer metastasis. The past decade has been exciting in terms of research into the molecular and cellular biology of lymphatic vessels in cancer, and it has been shown that the molecular control of tumour lymphangiogenesis has similarities to that of tumour angiogenesis. Nevertheless, there are significant mechanistic differences between these biological processes. We are now developing a greater understanding of the specific roles of distinct lymphatic vessel subtypes in cancer, and this provides opportunities to improve diagnostic and therapeutic approaches that aim to restrict the progression of cancer.

AIP1 mediates vascular endothelial cell growth factor receptor-3-dependent angiogenic and lymphangiogenic responses

OBJECTIVE

To investigate the novel function of ASK1-interacting protein-1 (AIP1) in vascular endothelial cell growth factor receptor (VEGFR)-3 signaling, and VEGFR-3-dependent angiogenesis and lymphangiogenesis.

APPROACH AND RESULTS

AIP1, a signaling scaffold protein, is highly expressed in the vascular endothelium. We have previously reported that AIP1 functions as an endogenous inhibitor in pathological angiogenesis by blocking VEGFR-2 activity. Surprisingly, here we observe that mice with a global deletion of AIP1-knockout mice (AIP1-KO) exhibit reduced retinal angiogenesis with less sprouting and fewer branches. Vascular endothelial cell (but not neuronal)-specific deletion of AIP1 causes similar defects in retinal angiogenesis. The reduced retinal angiogenesis correlates with reduced expression in VEGFR-3 despite increased VEGFR-2 levels in AIP1-KO retinas. Consistent with the reduced expression of VEGFR-3, AIP1-KO show delayed developmental lymphangiogenesis in neonatal skin and mesentery, and mount weaker VEGF-C-induced cornea lymphangiogenesis. In vitro, human lymphatic endothelial cells with AIP1 small interfering RNA knockdown, retinal endothelial cells, and lymphatic endothelial cells isolated from AIP1-KO all show attenuated VEGF-C-induced VEGFR-3 signaling. Mechanistically, we demonstrate that AIP1 via vegfr-3-specific miR-1236 increases VEGFR-3 protein expression and that, by directly binding to VEGFR-3, it enhances VEGFR-3 endocytosis and stability.

CONCLUSION

Our in vivo and in vitro results provide the first insight into the mechanism by which AIP1 mediates VEGFR-3-dependent angiogenic and lymphangiogenic signaling.

Vascular endothelial growth factor receptor-2 promotes the development of the lymphatic vasculature

Vascular endothelial growth factor receptor 2 (VEGFR2) is highly expressed by lymphatic endothelial cells and has been shown to stimulate lymphangiogenesis in adult mice. However, the role VEGFR2 serves in the development of the lymphatic vascular system has not been defined. Here we use the Cre-lox system to show that the proper development of the lymphatic vasculature requires VEGFR2 expression by lymphatic endothelium. We show that Lyve-1^wt/Cre;Vegfr2^flox/flox mice possess significantly fewer dermal lymphatic vessels than Vegfr2^flox/flox mice. Although Lyve-1^wt/Cre;Vegfr2^flox/flox mice exhibit lymphatic hypoplasia, the lymphatic network is functional and contains all of the key features of a normal lymphatic network (initial lymphatic vessels and valved collecting vessels surrounded by smooth muscle cells (SMCs)). We also show that Lyve-1^Cre mice display robust Cre activity in macrophages and in blood vessels in the yolk sac, liver and lung. This activity dramatically impairs the development of blood vessels in these tissues in Lyve-1^wt/Cre;Vegfr2^flox/flox embryos, most of which die after embryonic day14.5. Lastly, we show that inactivation of Vegfr2 in the myeloid lineage does not affect the development of the lymphatic vasculature. Therefore, the abnormal lymphatic phenotype of Lyve-1^wt/Cre;Vegfr2^flox/flox mice is due to the deletion of Vegfr2 in the lymphatic vasculature not macrophages. Together, this work demonstrates that VEGFR2 directly promotes the expansion of the lymphatic network and further defines the molecular mechanisms controlling the development of the lymphatic vascular system.

Activation of the epidermal growth factor receptor promotes lymphangiogenesis in the skin

BACKGROUND

The lymphatic vascular system regulates tissue fluid homeostasis and plays important roles in immune surveillance, inflammation and cancer metastasis. However, the molecular mechanisms involved in the regulation of lymphangiogenesis remain incompletely characterized.

OBJECTIVE

We aimed to identify new pathways involved in the promotion of skin lymphangiogenesis.

METHODS

We used a mouse embryonic stem cell-derived embryoid body vascular differentiation assay to investigate the effects of a selection of pharmacological agents with the potential to inhibit blood and/or lymphatic vessel formation. We also used a subcutaneous Matrigel assay to study candidate lymphangiogenesis factors as well as skin-specific transgenic mice.

RESULTS

We found that compounds inhibiting the epidermal growth factor (EGF) receptor (EGFR) led to an impaired formation of lymphatic vessel-like structures. In vitro studies with human dermal lymphatic endothelial cells (LECs), that were found to express EGFR, revealed that EGF promotes lymphatic vessel formation. This effect was inhibited by EGFR-blocking antibodies and by low molecular weight inhibitors of the EGFR associated tyrosine kinase. Incorporation of EGF into a mouse matrigel plug assay showed that EGF promotes enlargement of lymphatic vessels in the skin in vivo. Moreover, transgenic mice with skin-specific overexpression of amphiregulin, another agonistic ligand of the EGFR, displayed an enhanced size and density of lymphatic vessels in the skin.

CONCLUSION

These findings reveal that EGFR activation is involved in lymphatic remodeling and suggest that specific EGFR antagonists might be used to inhibit pathological lymphangiogenesis.