Molecular regulation of lymphangiogenesis in development and tumor microenvironment

Lymphangiogenesis orchestrating tumor microenvironment: Face changing in immunotherapy

In the era of immunotherapy, the lymphatic system has garnered significant attention from researchers. Increasing evidence highlights the complex regulation of lymphatic vessels (LVs) within the tumor microenvironment, unveiling a paradox in tumor progression: while LVs enhance immune surveillance, they simultaneously foster immune suppression. This review summarizes the regulatory factors of lymphangiogenesis, discusses the intricate effects of LVs on immunotherapy, and emphasizes the potential connection between lymphangiogenesis and tertiary lymphoid structure. Additionally, current therapeutic strategies targeting lymphangiogenesis are critically evaluated, with a forward-looking perspective on future research directions and regulatory approaches to achieve precise targeting and optimize immunotherapy paradigms.

Proliferative diabetic retinopathy transcriptomes reveal angiogenesis, anti-angiogenic therapy escape mechanisms, fibrosis and lymphatic involvement

Proliferative diabetic retinopathy (PDR) is a sight-threatening diabetic complication in urgent need of new therapies. In this study we identify potential molecular mechanisms and target candidates in the pathogenesis of PDR fibrovascular tissue formation. We performed mRNA sequencing of RNA isolated from eleven excised fibrovascular membranes of type 1 diabetic PDR patients and two non-diabetic patients with rhegmatogenous retinal detachment with proliferative vitreoretinopathy. We determined differentially expressed genes between these groups and performed pathway and gene ontology term enrichment analyses to identify potential underlying mechanisms, pathways, and regulators. Multiple pro-angiogenic processes, including VEGFA-dependent and -independent pathways, as well as processes related to lymphatic development, epithelial to mesenchymal transition (EMT), wound healing, inflammation, fibrosis, and extracellular matrix (ECM) composition, were overrepresented in PDR. Overrepresentation of different angiogenic processes may help to explain the transient nature of the benefits that many patients receive from current intravitreal anti-angiogenic therapies, highlighting the importance of combinatorial treatments. Enrichment of genes and pathways related to lymphatic development indicates that targeting lymphatic involvement in PDR progression could have therapeutic relevance. Together with overrepresentation of EMT and fibrosis as well as differential ECM composition, these findings demonstrate the complexity of PDR fibrovascular tissue formation and provide avenues for the development of novel treatments.

Novel Concepts: Langerhans Cells in the Tumour Microenvironment

Langerhans cells (LCs) are immune cells that reside in the stratified epithelium of the skin and mucosal membranes. They play a range of roles in the skin, including antigen presentation and maintenance of peripheral tolerance. Reports of LC numbers have been variable in different cancer types, with the majority of studies indicating a reduction in their number. Changes in the cytokine profile and other secreted molecules, downregulation of surface molecules on cells and hypoxia all contribute to the regulation of LCs in the tumour microenvironment. Functionally, LCs have been reported to regulate immunity and carcinogenesis in different cancer types. An improved understanding of the function and biology of LCs in tumours is essential knowledge that underpins the development of new cancer immunotherapies.

Decomposing the subclonal structure of tumors with two-way mixture models on copy number aberrations

Multistage tumorigenesis is a dynamic process characterized by the accumulation of mutations. Thus, a tumor mass is composed of genetically divergent cell subclones. With the advancement of next-generation sequencing (NGS), mathematical models have been recently developed to decompose tumor subclonal architecture from a collective genome sequencing data. Most of the methods focused on single-nucleotide variants (SNVs). However, somatic copy number aberrations (CNAs) also play critical roles in carcinogenesis. Therefore, further modeling subclonal CNAs composition would hold the promise to improve the analysis of tumor heterogeneity and cancer evolution. To address this issue, we developed a two-way mixture Poisson model, named CloneDeMix for the deconvolution of read-depth information. It can infer the subclonal copy number, mutational cellular prevalence (MCP), subclone composition, and the order in which mutations occurred in the evolutionary hierarchy. The performance of CloneDeMix was systematically assessed in simulations. As a result, the accuracy of CNA inference was nearly 93% and the MCP was also accurately restored. Furthermore, we also demonstrated its applicability using head and neck cancer samples from TCGA. Our results inform about the extent of subclonal CNA diversity, and a group of candidate genes that probably initiate lymph node metastasis during tumor evolution was also discovered. Most importantly, these driver genes are located at 11q13.3 which is highly susceptible to copy number change in head and neck cancer genomes. This study successfully estimates subclonal CNAs and exhibit the evolutionary relationships of mutation events. By doing so, we can track tumor heterogeneity and identify crucial mutations during evolution process. Hence, it facilitates not only understanding the cancer development but finding potential therapeutic targets. Briefly, this framework has implications for improved modeling of tumor evolution and the importance of inclusion of subclonal CNAs.

Lymphangiogenesis in Oral Squamous Cell Carcinoma: Correlation with VEGF-C Expression and Lymph Node Metastasis

Background

Oral squamous cell carcinoma (OSCC) is the most common oral malignancy that preferentially spreads to the cervical lymph node which, when involved, complicates the anticancer therapy and threatens the patient life. It was suggested that lymph node metastasis may be facilitated by lymphangiogenesis. VEGF-C is one of the most important lymphangiogenic inducers that promotes the lymphatic vessels growth and supports the survival of adult lymphatic endothelial cells.

Methods

Lymphatic vessels density (LVD) and LV morphometry were digitally evaluated using D2-40. The expression of VEGF-C was also assessed using immunohistochemistry and real-time polymerase chain reaction in 6 normal oral mucosa cases and 72 cases of OSCC. The correlation between LVD and LV morphometry, VEGF-C, and lymph node metastasis was statistically assessed.

Results

A positive cytoplasmic expression of VEGF-C was detected in both epithelial and connective tissue cells in 97% of OSCC, while all normal tissues reacted negatively. A greater expression of VEGF-C was associated with larger and more dilated LV and lymph node metastasis but not with LVD.

Conclusion

VEGF-C is actively involved in the invasion and metastasis of OSCC via inducing morphological changes in LV. VEGF-C may be a promising target for anticancer therapy.

The role of lymphangiogenesis and angiogenesis in tumor metastasis

BACKGROUND

Metastasis is the main cause of mortality in cancer patients. Two major routes of cancer cell spread are currently being recognized: dissemination via blood vessels (hematogenous spread) and dissemination via the lymphatic system (lymphogenous spread). Here, our current knowledge on the role of both blood and lymphatic vessels in cancer cell metastasis is summarized. In addition, I will discuss why cancer cells select one or both of the two routes to disseminate and I will provide a short description of the passive and active models of intravasation. Finally, lymphatic vessel density (LVD), blood vessel density (BVD), interstitial fluid pressure (IFP) and tumor hypoxia, as well as regional lymph node metastasis and the recently discovered primo vascular system (PVS) will be highlighted as important factors influencing tumor cell motility and spread and, ultimately, clinical outcome.

CONCLUSIONS

Lymphangiogenesis and angiogenesis are important phenomena involved in the spread of cancer cells and they are associated with a poor prognosis. It is anticipated that new discoveries and advancing knowledge on these phenomena will allow an improvement in the treatment of cancer patients.

Analysis of gene expression of secreted factors associated with breast cancer metastases in breast cancer subtypes

Breast cancer is a heterogeneous disease, having multiple subtypes with different malignant phenotypes. The triple-negative breast cancer, or basal breast cancer, is highly aggressive, metastatic, and difficult to treat. Previously, we identified that key molecules (IL6, CSF2, CCL5, VEGFA, and VEGFC) secreted by tumor cells and stromal cells in basal breast cancer can promote metastasis. It remains to assess whether these molecules function similarly in other subtypes of breast cancer. Here, we characterize the relative gene expression of the five secreted molecules and their associated receptors (GP130, GMRA, GMRB, CCR5, VEGFR2, NRP1, VEGFR3, NRP2) in the basal, HER2 (human epidermal growth factor receptor 2) positive, luminal A, and luminal B subtypes using high throughput data from tumor samples in The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC). IL6 and CCL5 gene expression are basal breast cancer specific, whereas high gene expression of GP130 was observed in luminal A/B. VEGFA/C and CSF2 mRNA are overexpressed in HER2 positive breast cancer, with VEGFA and CSF2 also overexpressed in basal breast cancer. Further study of the specific protein function of these factors within their associated cancer subtypes may yield personalized biomarkers and treatment modalities.

Itraconazole can inhibit malignant pleural effusion by suppressing lymphangiogenesis in mice

BACKGROUND

The presence of malignant pleural effusion (MPE) indicates a poor prognosis in patients with non-small cell lung cancer (NSCLC). Itraconazole has been identified as a potent inhibitor of endothelial cell proliferation that suppresses angiogenesis; however, its role in the suppression of lymphangiogenesis is still unclear. The aim of this study was to investigate the efficacy of itraconazole for MPE and the mechanism of lymphangiogenesis suppression.

METHODS

Lewis lung carcinoma (LLC) cells were injected into the mouse pleural cavity to establish the MPE mouse model, followed by randomization of the mice into three groups. Each mice was injected with either a high dose of itraconazole (25 mg/kg, H-ITCZ), a low dose of itraconazole (8 mg/kg, L-ITCZ), or 50 μL of hydroxypropyl-β-cyclodextrin (130 mg/mL, H-β-C) into the pleural cavity four times every 3 days. The MPE of the mice was collected and measured with a 1 mL syringe. The vascular endothelial growth factor-C (VEGF-C) expression level in the MPE was detected by enzyme-linked immunosorbent assay (ELISA), while the VEGF-C expression and lymphatic micro vessel density (LMVD) in the tumor tissue was observed by immunohistochemistry (IHC) staining.

RESULTS

The number of pleural tumor foci, the volume of pleural effusion, the LMVD and the VEGF-C expression levels in the tumor tissue were significantly reduced in the H-ITCZ-treated group.

CONCLUSIONS

Our results revealed that itraconazole may play an important role in the MPE mice by suppressing lymphangiogenesis, which demonstrated the usefulness of itraconazole in the treatment of MPE.

Crosstalk between cancer cells and blood endothelial and lymphatic endothelial cells in tumour and organ microenvironment

Tumour and organ microenvironments are crucial for cancer progression and metastasis. Crosstalk between multiple non-malignant cell types in the microenvironments and cancer cells promotes tumour growth and metastasis. Blood and lymphatic endothelial cells (BEC and LEC) are two of the components in the microenvironments. Tumour blood vessels (BV), comprising BEC, serve as conduits for blood supply into the tumour, and are important for tumour growth as well as haematogenous tumour dissemination. Lymphatic vessels (LV), comprising LEC, which are relatively leaky compared with BV, are essential for lymphogenous tumour dissemination. In addition to describing the conventional roles of the BV and LV, we also discuss newly emerging roles of these endothelial cells: their crosstalk with cancer cells via molecules secreted by the BEC and LEC (also called angiocrine and lymphangiocrine factors). This review suggests that BEC and LEC in various microenvironments can be orchestrators of tumour progression and proposes new mechanism-based strategies to discover new therapies to supplement conventional anti-angiogenic and anti-lymphangiogenic therapies.

Cancer stem cells, lymphangiogenesis, and lymphatic metastasis

Although current opinion indicates that tumor-induced lymphangiogenesis plays a key role in promoting the initial spread of malignant tumors, the mechanism that underlies lymphatic spread is not clear. The recent discovery of cancer stem cells (CSCs) in human tumors has challenged our current understanding of tumor recurrence, drug resistance, and metastasis, and opens up new research directions on how cancer cells are capable of switching from dormancy to malignancy. CSCs can be directly and indirectly involved in tumor-induced lymphangiogenesis and ultimately promote lymphatic metastasis. However, the details and the possible relationship between CSCs, lymphangiogenesis, and lymphatic metastasis remain ambiguous, and the origin of tumor lymphatic endothelial cells is controversial. Elucidation of these factors may provide useful information for future research and cancer treatment. In this article, we summarize current knowledge of CSCs, tumor-induced lymphangiogenesis, and lymphatic metastasis and attempt to find an association between key molecular and cellular mechanisms. We provide an overview of CSCs and lymphatic vasculature as potential therapeutic targets. CSC- and lymphatic vasculature-targeted therapy may bring new hope for cancer treatment.

Genetic Dissection of Tie Pathway in Mouse Lymphatic Maturation and Valve Development

Objective—

The genetic program underlying lymphatic development is still incompletely understood. This study aims to dissect the role of receptor tyrosine kinase with immunoglobulin-like and EGF (epidermal growth factor)-like domains 1 (Tie1) and Tie2 in lymphatic formation using genetically modified mouse models.

Approach and Results—

We generated conditional knockout mouse models targeting Tie1, Tie2, and angiopoietin-2 in this study. Tie1 Δ ICD /Δ ICD mice, with its intracellular domain targeted, appeared normal at E10.5 but displayed subcutaneous edema by E13.5. Lymph sac formation occurred in Tie1 Δ ICD /Δ ICD mice, but they had defects with the remodeling of primary lymphatic network to form collecting vessels and valvulogenesis. Consistently, induced deletion of Tie1-ICD postnatally using a ubiquitous Cre deleter led to abnormal lymphangiogenesis and valve formation in Tie1-ICD iUCKO/ − mice. In comparison with the lymphatic phenotype of Tie1 mutants, we found that the diameter of lymphatic capillaries was significantly less in mice deficient of angiopoietin-2, besides the disruption of collecting lymphatic vessel formation as previously reported. There was also no lymphedema observed in Ang2 −/− mice during embryonic development, which differs from that of Tie1 Δ ICD /Δ ICD mice. We further investigated whether Tie1 exerted its function via Tie2 during lymphatic development. To our surprise, genetic deletion of Tie2 ( Tie2 iUCKO/ − ) in neonate mice did not affect lymphatic vessel growth and maturation.

Conclusions—

In contrast to the important role of Tie2 in the regulation of blood vascular development, Tie1 is crucial in the process of lymphatic remodeling and maturation, which is independent of Tie2.

[Lymphatic vascular system, development and lymph formation. Review]

The lymphatic vascular system is widely developed among vertebrates. Lymphatic vessels provide the interstitial fluid (20% of the body weight) drainage through interstitial prelymphatic channels, capillaries, precollectors and collectors flowing into the venous blood. Endothelial cells of capillaries are overlapped and fixed to interstitial collagen and elastic fibres by anchoring filaments facilitating the fluid transfer. Precollectors and collectors have valves controlling the lymph flux direction. In addition to external mechanisms, the lymphangions of collectors have contracting muscle cells driving the flow. Lymphatic endothelial cells are routinely identified by the expression of podoplanin, LYVE-1 and VEGFR3. In the embryo, prelymphatic endothelial cells emerge from the cardinal veins and migrate into the mesenchyma forming embryonic lymphatic sacs. Prox1, Sox18 and COUP-TFII play a major role in the endothelial speciation, VEGFC as VEGFD combined to VEGFR3 in cell migration and proliferation and FoxC2 in valves development. In cancer or inflammation, various factors secreted by cancer cells and/or inflammatory cells induce a neolymphangiogenesis. Recently it has been shown that cells from the bone marrow could be potential precursors for lymphatic endothelial cells.

Lymphatic biomarkers in primary melanomas as predictors of regional lymph node metastasis and patient outcomes

Recently developed lymphatic-specific immunohistochemical markers can now be utilized to assess intratumoral and/or peritumoral lymphatic vessel density (LVD), to detect lymphatic vessel invasion (LVI) by melanoma cells and to identify lymphatic marker expression in melanoma cells themselves. We systematically reviewed the available evidence for the expression of lymphatic markers as predictors of regional node metastasis and survival in melanoma patients. The currently available evidence suggests that LVD (particularly in a peritumoral location) and LVI are predictors of sentinel node metastasis and poorer survival. Nevertheless, adherence to international guidelines in the conduct and reporting of the studies was generally poor, with wide methodologic variations and heterogeneous findings. Larger, carefully conducted and well-reported studies that confirm these preliminary findings are required before it would be appropriate to recommend the routine application of costly and time-consuming immunohistochemistry for lymphatic markers in the routine clinical assessment of primary cutaneous melanomas.