Semaphorin 3A overcomes cancer hypoxia and metastatic dissemination induced by antiangiogenic treatment in mice

Semaphorins in tumor microenvironment: Biological mechanisms and therapeutic progress

Hallmark features of the tumor microenvironment include immune cells, stromal cells, blood vessels, and extracellular matrix (ECM), providing a conducive environment for the growth and survival of tumors. Recent advances in the understanding of cancer biology have highlighted the functional role of semaphorins (SEMAs). SEMAs are a large and diverse family of widely expressed secreted and membrane-binding proteins, which were initially implicated in axon guidance and neural development. However, it is now clear that they are widely expressed beyond the nervous system and participate in regulating immune responses and cancer progression. In fact, accumulating evidence disclosed that different SEMAs can either stimulate or restrict tumor progression, some of which act as important regulators of tumor angiogenesis. Conversely, limited information is known about the functional relevance of SEMA signals in TME. In this setting, we systematically elaborate the role SEMAs and their major receptors played in characterized components of TME. Furthermore, we provide a convergent view of current SEMAs pharmacological progress in clinical treatment and also put forward their potential application value and clinical prospects in the future.

Semmaphorin 3 A causes immune suppression by inducing cytoskeletal paralysis in tumour-specific CD8+ T cells

Semaphorin-3A (SEMA3A) functions as a chemorepulsive signal during development and can affect T cells by altering their filamentous actin (F-actin) cytoskeleton. The exact extent of these effects on tumour-specific T cells are not completely understood. Here we demonstrate that Neuropilin-1 (NRP1) and Plexin-A1 and Plexin-A4 are upregulated on stimulated CD8+ T cells, allowing tumour-derived SEMA3A to inhibit T cell migration and assembly of the immunological synapse. Deletion of NRP1 in both CD4+ and CD8+ T cells enhance CD8+ T-cell infiltration into tumours and restricted tumour growth in animal models. Conversely, over-expression of SEMA3A inhibit CD8+ T-cell infiltration. We further show that SEMA3A affects CD8+ T cell F-actin, leading to inhibition of immune synapse formation and motility. Examining a clear cell renal cell carcinoma patient cohort, we find that SEMA3A expression is associated with reduced survival, and that T-cells appear trapped in SEMA3A rich regions. Our study establishes SEMA3A as an inhibitor of effector CD8+ T cell tumour infiltration, suggesting that blocking NRP1 could improve T cell function in tumours.

The Inhibition of Vessel Co-Option as an Emerging Strategy for Cancer Therapy

Vessel co-option (VCO) is a non-angiogenic mechanism of vascularization that has been associated to anti-angiogenic therapy. In VCO, cancer cells hijack the pre-existing blood vessels and use them to obtain oxygen and nutrients and invade adjacent tissue. Multiple primary tumors and metastases undergo VCO in highly vascularized tissues such as the lungs, liver or brain. VCO has been associated with a worse prognosis. The cellular and molecular mechanisms that undergo VCO are poorly understood. Recent studies have demonstrated that co-opted vessels show a quiescent phenotype in contrast to angiogenic tumor blood vessels. On the other hand, it is believed that during VCO, cancer cells are adhered to basement membrane from pre-existing blood vessels by using integrins, show enhanced motility and a mesenchymal phenotype. Other components of the tumor microenvironment (TME) such as extracellular matrix, immune cells or extracellular vesicles play important roles in vessel co-option maintenance. There are no strategies to inhibit VCO, and thus, to eliminate resistance to anti-angiogenic therapy. This review summarizes all the molecular mechanisms involved in vessel co-option analyzing the possible therapeutic strategies to inhibit this process.

The role of semaphorins in allergic diseases

Semaphorins were originally identified as guidance molecules in neural development. However, accumulating evidence indicates that 'immune semaphorins' are critically involved in regulating immune cell activation, differentiation, mobility and migration. Semaphorins are also intimately associated with the pathogenesis of allergic diseases including asthma, allergic rhinitis, atopic dermatitis, allergic conjunctivitis, and eosinophilic chronic rhinosinusitis. Interestingly, reflecting their function in positive or negative regulation of immune cells, levels of some semaphorins are increased while others are decreased in patients with allergic diseases. This review presents the pathogenic functions of immune semaphorins in allergic inflammation and discusses the potential use of these molecules as therapeutic targets for allergic diseases.

Alleviating hypoxia to improve cancer immunotherapy

Tumor hypoxia resulting from abnormal and dysfunctional tumor vascular network poses a substantial obstacle to immunotherapy. In fact, hypoxia creates an immunosuppressive tumor microenvironment (TME) through promoting angiogenesis, metabolic reprogramming, extracellular matrix remodeling, epithelial-mesenchymal transition (EMT), p53 inactivation, and immune evasion. Vascular normalization, a strategy aimed at restoring the structure and function of tumor blood vessels, has been shown to improve oxygen delivery and reverse hypoxia-induced signaling pathways, thus alleviates hypoxia and potentiates cancer immunotherapy. In this review, we discuss the mechanisms of tumor tissue hypoxia and its impacts on immune cells and cancer immunotherapy, as well as the approaches to induce tumor vascular normalization. We also summarize the evidence supporting the use of vascular normalization in combination with cancer immunotherapy, and highlight the challenges and future directions of this overlooked important field. By targeting the fundamental problem of tumor hypoxia, vascular normalization proposes a promising strategy to enhance the efficacy of cancer immunotherapy and improve clinical outcomes for cancer patients.

Evodiamine impairs HIF1A histone lactylation to inhibit Sema3A-mediated angiogenesis and PD-L1 by inducing ferroptosis in prostate cancer

Prostate cancer (PCa) is among the most commonly diagnosed solid cancers in male adults. However, most anti-angiogenic therapies and immunotherapies fail to achieve durable remission in advanced PCa. Integrative analysis indicated that Sema3A was negatively correlated with the pathological malignancy and was involved in angiogenesis, cell adhesion, and immune infiltrates in PCa. Sema3A significantly inhibited vascular endothelial growth factor (VEGFA)-induced colony formation, cell proliferation, and PD-L1 expression in PCa cells. Network pharmacological analysis demonstrated that evodiamine, a natural alkaloid compound derived from Evodiae fructus fruits, might regulate Sema3A, lipid metabolism, and monocarboxylic acid transport signaling of PCa. Evodiamine evidently inhibited PCa cell viability in a time-dose-dependent manner. Furthermore, evodiamine impaired angiogenesis by increasing Sema3A expression, and induced ferroptosis by reducing glutathione peroxidase 4 (GPX4) expression, which could be reversed by the ferroptosis blocker ferrostatin-1. Lactate treatment increased hypoxia-inducible factor (HIF)-1α and PD-L1 expressions while restricting Sema3A expression in PCa cells, which could be reversed by silencing monocarboxylate transporter 4 (MCT4) expression. Moreover, evodiamine markedly blocked lactate-induced angiogenesis by restricting histone lactylation and expression of HIF1A in PCa cells, further enhancing Sema3A transcription while inhibiting that of PD-L1. In vivo, evodiamine remarkably inhibited PCa xenograft growth in nude mice, repressing expressions of HIF1α, H3K18la, GPX4, PD-L1, and proliferation, while hindering angiogenesis by increasing Sema3A expression. Therefore, Sema3A represents an essential antineoplastic biomarker, while evodiamine may act as a metabolic-epigenetic modulator, as well as a promising agent in either PCa anti-angiogenic therapy or immunotherapy.

Mind the (guidance) signals! Translational relevance of semaphorins, plexins, and neuropilins in pancreatic cancer

Pancreatic cancer is a major cause of demise worldwide. Although key associated genetic changes have been discovered, disease progression is sustained by pathogenic mechanisms that are poorly understood at the molecular level. In particular, the tissue microenvironment of pancreatic adenocarcinoma (PDAC) is usually characterized by high stromal content, scarce recruitment of immune cells, and the presence of neuronal fibers. Semaphorins and their receptors, plexins and neuropilins, comprise a wide family of regulatory signals that control neurons, endothelial and immune cells, embryo development, and normal tissue homeostasis, as well as the microenvironment of human tumors. We focus on the role of these molecular signals in pancreatic cancer progression, as revealed by experimental research and clinical studies, including novel approaches for cancer treatment.

Semaphorins and Their Roles in Breast Cancer: Implications for Therapy Resistance

Breast cancer is the most common cancer worldwide and a leading cause of cancer-related deaths in women. The clinical management of breast cancer is further complicated by the heterogeneous nature of the disease, which results in varying prognoses and treatment responses in patients. The semaphorins are a family of proteins with varied roles in development and homoeostasis. They are also expressed in a wide range of human cancers and are implicated as regulators of tumour growth, angiogenesis, metastasis and immune evasion. More recently, semaphorins have been implicated in drug resistance across a range of malignancies. In breast cancer, semaphorins are associated with resistance to endocrine therapy as well as breast cancer chemotherapeutic agents such as taxanes and anthracyclines. This review will focus on the semaphorins involved in breast cancer progression and their association with drug resistance.

Pancreatic cancer cell-derived semaphorin 3A promotes neuron recruitment to accelerate tumor growth and dissemination

Perineural invasion and neurogenesis are frequently observed in pancreatic ductal adenocarcinoma (PDAC), and they are associated with a poor prognosis. Axon guidance factor semaphorin 3A (SEMA3A) is upregulated in PDAC. However, it remains unclear whether cancer-derived SEMA3A influences nerve innervation and pancreatic tumorigenesis. In silico analyses were performed using PROGgene and NetworkAnalyst to clarify the importance of SEMA3A and its receptors, plexin A1 (PLXNA1) and neuropilin 2 (NRP2), in pancreatic cancer. In vitro assays, including migration, neurite outgrowth, and 3D recruitment, were performed to study the effects of SEMA3A on neuronal behaviors. Additionally, an orthotopic animal study using C57BL/6 mice was performed to validate the in vitro findings. Expression of SEMA3A and its receptors predicted worse prognosis for PDAC. Cancer-derived SEMA3A promoted neural migration, neurite outgrowth, and neural recruitment. Furthermore, SEMA3A-induced effects depended on PLXNA1, NRP2, and MAPK activation. Trametinib, an approved MAPK kinase (MEK) inhibitor, counteracted SEMA3A-enhanced neuronal activity in vitro. Inhibition of SEMA3A by shRNA in pancreatic cancer cells resulted in decreased neural recruitment, tumor growth, and dissemination in vivo. Our results suggested that cancer-secreted SEMA3A plays an important role in promoting neo-neurogenesis and progression of PDAC.

Plexin-B3 expression stimulates MET signaling, breast cancer stem cell specification, and lung metastasis

Intratumoral hypoxia is a microenvironmental feature that promotes breast cancer progression and is associated with cancer mortality. Plexin B3 (PLXNB3) is highly expressed in estrogen receptor-negative breast cancer, but the underlying mechanisms and consequences have not been thoroughly investigated. Here, we report that PLXNB3 expression is increased in response to hypoxia and that PLXNB3 is a direct target gene of hypoxia-inducible factor 1 (HIF-1) in human breast cancer cells. PLXNB3 expression is correlated with HIF-1α immunohistochemistry, breast cancer grade and stage, and patient mortality. Mechanistically, PLXNB3 is required for hypoxia-induced MET/SRC/focal adhesion kinase (FAK) and MET/SRC/STAT3/NANOG signaling as well as hypoxia-induced breast cancer cell migration, invasion, and cancer stem cell specification. PLXNB3 knockdown impairs tumor formation and lung metastasis in orthotopic breast cancer mouse models.

Angiogenesis in NENs, with a focus on gastroenteropancreatic NENs: from biology to current and future therapeutic implications

Neuroendocrine neoplasms (NENs) are highly vascularized malignancies arising from cells of the diffuse neuroendocrine system. An intricated cross-talk exists between NEN cells and the tumor microenvironment, and three main molecular circuits (VEGF/VEGFR pathway, FGF-dependent signaling and PDGF/PDGFR axis) have been shown to regulate angiogenesis in these neoplasms. Multiple randomized trials have investigated antiangiogenic agents over the past two decades, and sunitinib is currently approved for the treatment of advanced, progressive, G1/G2 pancreatic NENs. In recent years, two phase III clinical trials have demonstrated the efficacy and safety of surufatinib, a multi-tyrosine kinase angioimmune inhibitor, in patients with well-differentiated pancreatic and extrapancreatic NENs, and two studies of this agent are currently underway in Europe and US. The HIF-2α inhibitor belzutifan has recently received regulatory approval for the treatment of tumors arising in the context of Von-Hippel Lindau syndrome including pancreatic NENs, and a study of this drug in patients with sporadic tumors is presently ongoing. Combinations of antiangiogenic agents with chemotherapeutics and targeted drugs have been tested, with accumulating toxicities being a matter of concern. The potential of antiangiogenic agents in fine-tuning the immune microenvironment of NENs to enhance the activity of immune checkpoint inhibitors has been only partially elucidated, and further research should be carried out at this regard. Here, we review the current understanding of the biology of angiogenesis in NENs and provide a summary of the latest clinical investigations on antiangiogenic drugs in this malignancy.

miR-181b targets semaphorin 3A to mediate TGF-β-induced endothelial-mesenchymal transition related to atrial fibrillation

Atrial fibrosis is an essential contributor to atrial fibrillation (AF). It remains unclear whether atrial endocardial endothelial cells (AEECs) that undergo endothelial-mesenchymal transition (EndMT) are among the sources of atrial fibroblasts. We studied human atria, TGF-β-treated human AEECs, cardiac-specific TGF-β-transgenic mice, and heart failure rabbits to identify the underlying mechanism of EndMT in atrial fibrosis. Using isolated AEECs, we found that miR-181b was induced in TGF-β-treated AEECs, which decreased semaphorin 3A (Sema3A) and increased EndMT markers, and these effects could be reversed by a miR-181b antagomir. Experiments in which Sema3A was increased by a peptide or decreased by a siRNA in AEECs revealed a mechanistic link between Sema3A and LIM-kinase 1/phosphorylated cofilin (LIMK/p-cofilin) signaling and suggested that Sema3A is upstream of LIMK in regulating actin remodeling through p-cofilin. Administration of the miR-181b antagomir or recombinant Sema3A to TGF-β-transgenic mice evoked increased Sema3A, reduced EndMT markers, and significantly decreased atrial fibrosis and AF vulnerability. Our study provides a mechanistic link between the induction of EndMT by TGF-β via miR-181b/Sema3A/LIMK/p-cofilin signaling to atrial fibrosis. Blocking miR-181b and increasing Sema3A are potential strategies for AF therapeutic intervention.

Cancer combination therapies by angiogenesis inhibitors; a comprehensive review

Abnormal vasculature is one of the most conspicuous traits of tumor tissue, largely contributing to tumor immune evasion. The deregulation mainly arises from the potentiated pro-angiogenic factors secretion and can also target immune cells' biological events, such as migration and activation. Owing to this fact, angiogenesis blockade therapy was established to fight cancer by eliminating the nutrient and oxygen supply to the malignant cells by impairing the vascular network. Given the dominant role of vascular-endothelium growth factor (VEGF) in the angiogenesis process, the well-known anti-angiogenic agents mainly depend on the targeting of its actions. However, cancer cells mainly show resistance to anti-angiogenic agents by several mechanisms, and also potentiated local invasiveness and also distant metastasis have been observed following their administration. Herein, we will focus on clinical developments of angiogenesis blockade therapy, more particular, in combination with other conventional treatments, such as immunotherapy, chemoradiotherapy, targeted therapy, and also cancer vaccines. Video abstract.

Cancer Cells Promote Phenotypic Alterations in Hepatocytes at the Edge of Cancer Cell Nests to Facilitate Vessel Co-Option Establishment in Colorectal Cancer Liver Metastases

Simple Summary

Tumour cells in colorectal cancer liver metastases (CRCLM) obtain their blood supply via two major mechanisms: (i) sprouting angiogenesis, through the generation of new vessels; (ii) vessel co-option, where the cancer cells hijack the pre-existing vasculature. The current treatment for CRCLM targets angiogenesis; however, these treatments are ineffective on cancer cells utilizing vessel co-option to gain their blood supply. Our study suggests that cancer cells stimulate phenotypic alterations in the cells of surrounding liver tissue (hepatocytes) in vessel co-opting lesions. These modifications facilitate cancer cells to infiltrate through the liver tissue and hijack the pre-existing vasculature to obtain oxygen and nutrients.

Abstract

Vessel co-option is correlated with resistance against anti-angiogenic therapy in colorectal cancer liver metastases (CRCLM). Vessel co-opting lesions are characterized by highly motile cancer cells that move toward and along the pre-existing vessels in the surrounding nonmalignant tissue and co-opt them to gain access to nutrients. To access the sinusoidal vessels, the cancer cells in vessel co-opting lesions must displace the hepatocytes and occupy their space. However, the mechanisms underlying this displacement are unknown. Herein, we examined the involvement of apoptosis, autophagy, motility, and epithelial–mesenchymal transition (EMT) pathways in hepatocyte displacement by cancer cells. We demonstrate that cancer cells induce the expression of the proteins that are associated with the upregulation of apoptosis, motility, and EMT in adjacent hepatocytes in vitro and in vivo. Accordingly, we observe the upregulation of cleaved caspase-3, cleaved poly (ADP-ribose) polymerase-1 (PARP-1) and actin-related protein 2/3 (ARP2/3) in adjacent hepatocytes to cancer cell nests, while we notice a downregulation of E-cadherin. Importantly, the knockdown of runt-related transcription factor 1 (RUNX1) in cancer cells attenuates the function of cancer cells in hepatocytes alterations in vitro and in vivo. Altogether, our data suggest that cancer cells exploit various mechanisms to displace hepatocytes and access the sinusoidal vessels to establish vessel co-option.

Semaphorin 3A attenuates the hypoxia suppression of osteogenesis in periodontal ligament stem cells

OBJECTIVE AND BACKGROUND

The occurrence and development of periodontitis are closely related to hypoxia of the periodontal microenvironment. Periodontal ligament stem cells (PDLSCs) are considered to have potential to regenerate periodontal tissues. Semaphorin 3A (Sema3A) plays an essential role in promoting osteogenesis. However, the effect of Sema3A on osteogenesis of PDLSCs under hypoxia remains unclear. The aim of this study was to investigate the effect of Sema3A on osteogenesis of PDLSCs under hypoxia.

METHODS

Isolated PDLSCs were identified using flow cytometry. Adipogenic differentiation potential was identified by oil red O staining. Osteogenesis was measured using Alizarin Red S staining and ALP staining. Intracellular hypoxia was induced using cobalt chloride (CoCl₂ ). The expression level of hypoxia-inducible factor-1α (HIF-1α) was detected via ELISA. Expression of osteogenic markers and Sema3A was analyzed using western blot and real-time PCR.

RESULTS

The proliferation and osteogenesis of PDLSCs were markedly inhibited with increased concentrations of CoCl₂ . Under the treatment with a low concentration of CoCl₂ , expression of related osteogenic markers and Sema3A decreased in a time-dependent manner. ARS and ALP staining results also showed that osteogenic calcification decreased under hypoxia. Apigenin, an inhibitor of HIF-1α, effectively up-regulated expression of Sema3A and osteogenic markers with CoCl₂ treatment. Moreover, exogenous Sema3A significantly increased the expression of osteogenesis-related markers and mineralization of PDLSCs according to ALP and ARS staining with CoCl₂ treatment.

CONCLUSIONS

Hypoxia markedly inhibited osteogenesis of PDLSCs. Sema3A explicitly attenuated the hypoxia suppression of osteogenesis in PDLSCs.

The Aflibercept-Induced MicroRNA Profile in the Vitreous of Proliferative Diabetic Retinopathy Patients Detected by Next-Generation Sequencing

Purpose: Vascular endothelial growth factor-A (VEGF-A) is an important pathogenic factor in proliferative diabetic retinopathy (PDR), and aflibercept (Eylea) is one of the widely used anti-VEGF agents. This study investigated the microRNA (miRNA) profiles in the vitreous of 5 idiopathic macular hole patients (non-diabetic controls), 5 untreated PDR patients (no-treatment group), and 5 PDR patients treated with intravitreal aflibercept injection (treatment group).

Methods: Next-generation sequencing was performed to determine the miRNA profiles. Deregulated miRNAs were validated with quantitative real-time PCR (qRT-PCR) in another cohort. The mRNA profile data (GSE160310) of PDR patients were retrieved from the Gene Expression Omnibus (GEO) database. The function of differentially expressed miRNAs and mRNAs was annotated by bioinformatic analysis and literature study.

Results: Twenty-nine miRNAs were significantly dysregulated in the three groups, of which 19,984 target mRNAs were predicted. Hsa-miR-3184-3p, hsa-miR-24-3p, and hsa-miR-197-3p were validated to be remarkably upregulated in no-treatment group versus controls, and significantly downregulated in treatment group versus no-treatment group. In the GSE160310 profile, 204 deregulated protein-coding mRNAs were identified, and finally 179 overlapped mRNAs between the 19,984 target mRNAs and 204 deregulated mRNAs were included for further analysis. Function analysis provided several roles of aflibercept-induced miRNAs, promoting the alternation of drug sensitivity or resistance-related mRNAs, and regulating critical mRNAs involved in angiogenesis and retinal fibrosis.

Conclusion: Hsa-miR-3184-3p, hsa-miR-24-3p, and hsa-miR-197-3p were highly expressed in PDR patients, and intravitreal aflibercept injection could reverse this alteration. Intravitreal aflibercept injection may involve in regulating cell sensitivity or resistance to drug, angiogenesis, and retinal fibrosis.

Establishment of a 3D model of tumor-driven angiogenesis to study the effects of anti-angiogenic drugs on pericyte recruitment

Hepatocellular carcinoma (HCC), as a well-vascularized tumor, has attracted increasing attention in antiangiogenic therapies. Notably, emerging studies reveal that the long-term administration of antiangiogenic drugs induces hypoxia in tumors. Pericytes, which play a vital role in vascular stabilization and maturation, have been documented to be associated with antiangiogenic drug-induced tumor hypoxia. However, the role of antiangiogenic agents in regulating pericyte behavior still remains elusive. In this study, by using immunostaining analysis, we first demonstrated that tumors obtained from HCC patients were highly angiogenic, in which vessels were irregularly covered by pericytes. Therefore, we established a new 3D model of tumor-driven angiogenesis by culturing endothelial cells, pericytes, cancer stem cells (CSCs) and mesenchymal stem cells (MSCs) with microcarriers in order to investigate the effects and mechanisms exerted by antiangiogenic agents on pericyte recruitment during tumor angiogenesis. Interestingly, microcarriers, as supporting matrices, enhanced the interactions between tumor cells and the extracellular matrix (ECM), promoted malignancy of tumor cells and increased tumor angiogenesis within the 3D model, as determined by qRT-PCR and immunostaining. More importantly, we showed that zoledronic acid (ZA) reversed the inhibited pericyte recruitment, which was induced by sorafenib (Sora) treatment, through fostering the expression and activation of ErbB1/ErbB2 and PDGFR-β in pericytes, in both an in vitro 3D model and an in vivo xenograft HCC mouse model. Hence, our model provides a more pathophysiologically relevant platform for the assessment of therapeutic effects of antiangiogenic compounds and identification of novel pharmacological targets, which might efficiently improve the benefits of antiangiogenic treatment for HCC patients.

HGF/MET Axis Induces Tumor Secretion of Tenascin-C and Promotes Stromal Rewiring in Pancreatic Cancer

Simple Summary

It has been previously shown that activation of the MET receptor by its ligand, the hepatocyte growth factor (HGF), modulates the tumor-stroma cross-talk in models of pancreatic cancer. We now wish to cast light on the molecular mechanisms by which this ligand/receptor pair sustains the interaction between cancer cells and the tumor microenviroment. To this end, we compared data obtained by large-scale analysis of gene expression in pancreatic cancer cells grown in the presence of HGF versus cells grown in the presence of HGF and treated with specific inhibitors of HGF/MET signaling. By clustering differentially expressed genes according to functional groups, we identified candidate genes involved in the process. Among these, tenascin C was selected due to its activity in sustaining the malignant phenotype. Our results highlight a new role for tenascin C, which could represent the operative arm through which MET promotes activation of the stromal compartment in pancreatic cancer.

Abstract

Pancreatic ductal adenocarcinoma is an aggressive tumor characterized by the presence of an abundant stromal compartment contributing significantly to the malignant phenotype. Pancreatic stellate cells are peculiar fibroblasts present in the stroma and represent the predominant source of extracellular matrix proteins, pro-inflammatory cytokines, and growth factors, including hepatocyte growth factor (HGF). Exploiting a co-culture system of human pancreatic stellate cells and cancer cells, we demonstrated that fibroblast activation was reduced upon HGF/MET axis inhibition. To unveil the signaling pathways sustaining stroma modulation orchestrated by MET activation in the tumor, we analyzed the gene expression profile in pancreatic cancer cells stimulated with HGF and treated with HGF/MET inhibitors. Transcriptome analysis showed that, among all the genes modulated by HGF, a subset of 125 genes was restored to the basal level following treatment with the inhibitors. By examining these genes via ingenuity pathway analysis, tenascin C emerged as a promising candidate linking MET signaling and tumor microenvironment. MET-dependent tenascin C modulation in pancreatic cancer cells was validated at RNA and protein levels both in vitro and in vivo. In conclusion, this work identifies tenascin C as a gene modulated by MET activation, suggesting a role in MET-mediated tumor-stroma interplay occurring during pancreatic tumor progression.

Interactions between semaphorins and plexin-neuropilin receptor complexes in the membranes of live cells

Signaling of semaphorin ligands via their plexin–neuropilin receptors is involved in tissue patterning in the developing embryo. These proteins play roles in cell migration and adhesion but are also important in disease etiology, including in cancer angiogenesis and metastasis. While some structures of the soluble domains of these receptors have been determined, the conformations of the full-length receptor complexes are just beginning to be elucidated, especially within the context of the plasma membrane. Pulsed-interleaved excitation fluorescence cross-correlation spectroscopy allows direct insight into the formation of protein–protein interactions in the membranes of live cells. Here, we investigated the homodimerization of neuropilin-1 (Nrp1), plexin A2, plexin A4, and plexin D1 using pulsed-interleaved excitation fluorescence cross-correlation spectroscopy. Consistent with previous studies, we found that Nrp1, plexin A2, and plexin A4 are present as dimers in the absence of exogenous ligand. Plexin D1, on the other hand, was monomeric under similar conditions, which had not been previously reported. We also found that plexin A2 and A4 assemble into a heteromeric complex. Stimulation with semaphorin 3A or semaphorin 3C neither disrupts nor enhances the dimerization of the receptors when expressed alone, suggesting that activation involves a conformational change rather than a shift in the monomer–dimer equilibrium. However, upon stimulation with semaphorin 3C, plexin D1 and Nrp1 form a heteromeric complex. This analysis of interactions provides a complementary approach to the existing structural and biochemical data that will aid in the development of new therapeutic strategies to target these receptors in cancer.

The Role of Semaphorins and Their Receptors in Innate Immune Responses and Clinical Diseases of Acute Inflammation

Semaphorins are a group of proteins that have been studied extensively for their critical function in neuronal development. They have been shown to regulate airway development, tumorigenesis, autoimmune diseases, and the adaptive immune response. Notably, emerging literature describes the role of immunoregulatory semaphorins and their receptors, plexins and neuropilins, as modulators of innate immunity and diseases defined by acute injury to the kidneys, abdomen, heart and lungs. In this review we discuss the pathogenic functions of semaphorins in clinical conditions of acute inflammation, including sepsis and acute lung injury, with a focus on regulation of the innate immune response as well as potential future therapeutic targeting.

SEMAPHORINS and their receptors: focus on the crosstalk between melanoma and hypoxia

Hypoxia, a condition of oxygen deprivation, is considered a hallmark of tumor microenvironment regulating several pathways and promoting cancer progression and resistance to therapy. Semaphorins, a family of about 20 secreted, transmembrane and GPI-linked glycoproteins, and their cognate receptors (plexins and neuropilins) play a pivotal role in the crosstalk between cancer and stromal cells present in the tumor microenvironment. Many studies reported that some semaphorins are involved in the development of a permissive tumor niche, guiding cell-cell communication and, consequently, the development and progression, as well as the response to therapy, of different cancer histotypes, including melanoma.

In this review we will summarize the state of art of semaphorins regulation by hypoxic condition in cancer with different origin. We will also describe evidence about the ability of semaphorins to affect the expression and activity of transcription factors activated by hypoxia, such as hypoxia-inducible factor-1. Finally, we will focus our attention on findings reporting the role of semaphorins in melanocytes transformation, melanoma progression and response to therapy. Further studies are necessary to understand the mechanisms through which semaphorins induce their effect and to shed light on the possibility to use semaphorins or their cognate receptors as prognostic markers and/or therapeutic targets in melanoma or other malignancies.

Abnormal Crosstalk between Endothelial Cells and Podocytes Mediates Tyrosine Kinase Inhibitor (TKI)-Induced Nephrotoxicity

Vascular endothelial growth factor A (VEGFA) and its receptor VEGFR2 are the main targets of antiangiogenic therapies, and proteinuria is one of the common adverse events associated with the inhibition of the VEGFA/VEGFR2 pathway. The proteinuric kidney damage induced by VEGFR2 tyrosine kinase inhibitors (TKIs) is characterized by podocyte foot process effacement. TKI therapy promotes the formation of abnormal endothelial‒podocyte crosstalk, which plays a key role in TKI-induced podocyte injury and proteinuric nephropathy. This review article summarizes the underlying mechanism by which the abnormal endothelial‒podocyte crosstalk mediates podocyte injury and discusses the possible molecules and signal pathways involved in abnormal endothelial‒podocyte crosstalk. What is more, we highlight the molecules involved in podocyte injury and determine the essential roles of Rac1 and Cdc42; this provides evidence for exploring the abnormal endothelial‒podocyte crosstalk in TKI-induced nephrotoxicity.

The Tumour Vasculature as a Target to Modulate Leucocyte Trafficking

Simple Summary

Tumour blood vessels, characterised by abnormal morphology and function, create an immunosuppressive tumour microenvironment via restricting the appropriate leucocyte subsets trafficking. Strategies to trigger phenotypic alteration in tumour vascular system to resemble normal vascular system, named vascular normalisation, promote effective trafficking of leucocytes into tumours through enhancing the interactions between leucocytes and endothelial cells. This review specifically demonstrates how targeting tumour blood vessels modulates the critical steps of leucocyte trafficking. Furthermore, selective regulation of leucocyte subsets trafficking in tumours can be achieved by vasculature-targeting strategies, contributing to improved immunotherapy and thereby delayed tumour progression.

Abstract

The effectiveness of immunotherapy against solid tumours is dependent on the appropriate leucocyte subsets trafficking and accumulating in the tumour microenvironment (TME) with recruitment occurring at the endothelium. Such recruitment involves interactions between the leucocytes and the endothelial cells (ECs) of the vessel and occurs through a series of steps including leucocyte capture, their rolling, adhesion, and intraluminal crawling, and finally leucocyte transendothelial migration across the endothelium. The tumour vasculature can curb the trafficking of leucocytes through influencing each step of the leucocyte recruitment process, ultimately producing an immunoresistant microenvironment. Modulation of the tumour vasculature by strategies such as vascular normalisation have proven to be efficient in facilitating leucocyte trafficking into tumours and enhancing immunotherapy. In this review, we discuss the underlying mechanisms of abnormal tumour vasculature and its impact on leucocyte trafficking, and potential strategies for overcoming the tumour vascular abnormalities to boost immunotherapy via increasing leucocyte recruitment.

Hypoxia-Driven Effects in Cancer: Characterization, Mechanisms, and Therapeutic Implications

Hypoxia, a common feature of solid tumors, greatly hinders the efficacy of conventional cancer treatments such as chemo-, radio-, and immunotherapy. The depletion of oxygen in proliferating and advanced tumors causes an array of genetic, transcriptional, and metabolic adaptations that promote survival, metastasis, and a clinically malignant phenotype. At the nexus of these interconnected pathways are hypoxia-inducible factors (HIFs) which orchestrate transcriptional responses under hypoxia. The following review summarizes current literature regarding effects of hypoxia on DNA repair, metastasis, epithelial-to-mesenchymal transition, the cancer stem cell phenotype, and therapy resistance. We also discuss mechanisms and pathways, such as HIF signaling, mitochondrial dynamics, exosomes, and the unfolded protein response, that contribute to hypoxia-induced phenotypic changes. Finally, novel therapeutics that target the hypoxic tumor microenvironment or interfere with hypoxia-induced pathways are reviewed.

Class-3 semaphorins: Potent multifunctional modulators for angiogenesis-associated diseases

Semaphorins, the neuronal guidance cues, were shown to have broad influences on pathophysiological processes such as bone remodeling, immune responses, and angiogenesis. In particular, Class-3 Semaphorins (SEMA3) is considered a vital regulator involved in angiogenesis. Scientific evidence has pointed to the role of angiogenesis in many diseases, and numerous efforts have been made to explore the possibilities of curing those diseases by targeting angiogenesis. Nevertheless, the efficacies are limited owing to the complex mechanisms of angiogenesis. Hence, investigating the mechanisms of SEMA3 in angiogenesis may contribute to novel therapeutics for diseases. Previous reviews mainly focused on the various functions of semaphorins in one particular disease, and the specific angiogenesis mechanism of SEMA3 in diverse diseases has not been well elucidated. Additionally, the role of SEMA3 in angiogenesis remains elusive, as contradicting results have been found in different disease types. Some evidence from recent studies implies that, while most SEMA3 molecules inhibit pathological angiogenesis in different diseases, occasionally SEMA3 may also promote angiogenesis. This review summarizes the specific role of SEMA3 in a variety of angiogenesis-associated diseases, and documents SEMA3 may be a promising therapeutic target for treating angiogenesis-associated diseases.

B7 immune-checkpoints as targets for the treatment of neuroendocrine tumors

The B7 family, and their receptors, the CD28 family, are major immune checkpoints that regulate T-cell activation and function. In the present study, we explore the role of two B7 immune-checkpoints: HERV-H LTR-Associating Protein 2 (HHLA2) and B7 Family Member, H4 (B7x), in the progression of gastrointestinal and pancreatic neuroendocrine tumors (GINETs and PNETs). We demonstrated that both HHLA2 and B7x were expressed to a high degree in human GINETs and PNETs. We determined that the expression of B7x and HHLA2 correlates with higher grade and higher incidence of nodal and distant spread. Furthermore, we confirmed that HIF-1α overexpression is associated with the upregulation of B7x both in our in vivo (animal model) and in vitro (cell culture) models. When grown in vitro, islet tumor β-cells lack B7x expression, unless cultured under hypoxic conditions, which results in both hypoxia-inducible factor 1 subunit alpha (HIF-1α) and B7x upregulation. In vivo, we demonstrated that Men1/B7x double knockout (KO) mice (with loss of B7x expression) exhibited decreased islet β-cell proliferation and tumor transformation accompanied by increased T-cell infiltration compared with Men1 single knockout mice. We have also shown that systemic administration of a B7x mAb to our Men1 KO mice with PNETs promotes an antitumor response mediated by increased T-cell infiltration. These findings suggest that B7x may be a critical mediator of tumor immunity in the tumor microenvironment of NETs. Therefore, targeting B7x offers an attractive strategy for the immunotherapy of patients suffering from NETs.

Semaphorins as emerging clinical biomarkers and therapeutic targets in cancer

Semaphorins are a large family of developmental regulatory signals, characterized by aberrant expression in human cancers. These molecules crucially control cell-cell communication, cell migration, invasion and metastasis, tumor angiogenesis, inflammatory and anti-cancer immune responses. Semaphorins comprise secreted and cell surface-exposed molecules and their receptors are mainly found in the Plexin and Neuropilin families, which are further implicated in a signaling network controlling the tumor microenvironment. Accumulating evidence indicates that semaphorins may be considered as novel clinical biomarkers for cancer, especially for the prediction of patient survival and responsiveness to therapy. Moreover, preclinical experimental studies have demonstrated that targeting semaphorin signaling can interfere with tumor growth and/or metastatic dissemination, suggesting their relevance as novel therapeutic targets in cancer; this has also prompted the development of semaphorin-interfering molecules for application in the clinic. Here we will survey, in diverse human cancers, the current knowledge about the relevance of semaphorin family members, and conceptualize potential lines of future research development in this field.

HIV Protease Inhibitors Block HPV16-Induced Murine Cervical Carcinoma and Promote Vessel Normalization in Association with MMP-9 Inhibition and TIMP-3 Induction

Antiretrovirals belonging to the human immunodeficiency virus (HIV) protease inhibitor (HIV-PI) class exert inhibitory effects across several cancer types by targeting tumor cells and its microenvironment. Cervical carcinoma represents a leading cause of morbidity and mortality, particularly in women doubly infected with high-risk human papillomaviruses (HR-HPV) and HIV; of note, combined antiretroviral therapy has reduced cervical carcinoma onset and progression in HIV-infected women. We evaluated the effectiveness and mechanism(s) of action of HIV-PI against cervical carcinoma using a transgenic model of HR-HPV-induced estrogen-promoted cervical carcinoma (HPV16/E2) and found that treatment of mice with ritonavir-boosted HIV-PI, including indinavir, saquinavir, and lopinavir, blocked the growth and promoted the regression of murine cervical carcinoma. This was associated with inhibition of tumor angiogenesis, coupled to downregulation of matrix metalloproteinase (MMP)-9, reduction of VEGF/VEGFR2 complex, and concomitant upregulation of tissue inhibitor of metalloproteinase-3 (TIMP-3). HIV-PI also promoted deposition of collagen IV at the epithelial and vascular basement membrane and normalization of both vessel architecture and functionality. In agreement with this, HIV-PI reduced tumor hypoxia and enhanced the delivery and antitumor activity of conventional chemotherapy. Remarkably, TIMP-3 expression gradually decreased during progression of human dysplastic lesions into cervical carcinoma. This study identified the MMP-9/VEGF proangiogenic axis and its modulation by TIMP-3 as novel HIV-PI targets for the blockade of cervical intraepithelial neoplasia/cervical carcinoma development and invasiveness and the normalization of tumor vessel functions. These findings may lead to new therapeutic indications of HIV-PI to treat cervical carcinoma and other tumors in either HIV-infected or uninfected patients.

Tumor microenvironment conditions that favor vessel co-option in colorectal cancer liver metastases: A theoretical model

Vessel co-option is an alternative strategy by which tumour cells vascularize and gain access to nutrients to support tumour growth, survival and metastasis. In vessel co-option, the cancer cells move towards the pre-existing vasculature and hijack them. Vessel co-option is adopted by a wide range of human tumours including colorectal cancer liver metastases (CRCLM) and is responsible for the effectiveness of treatment in CRCLM. Furthermore, vessel co-option is an intrinsic feature and an acquired mechanism of resistance to anti-angiogenic treatment. In this review, we describe the microenvironment, the molecular players, discovered thus far of co-opting CRCLM lesions and propose a theoretical model. We also highlight key unanswered questions that are critical to improving our understanding of CRCLM vessel co-option and for the development of effective approaches for the treatment of co-opting tumours.

Influences of Semaphorin 3A Expression on Clinicopathological Features, Human Papillomavirus Status, and Prognosis in Oropharyngeal Carcinoma

Human papillomavirus (HPV) infection is now identified as a major etiologic factor for oropharyngeal cancer (OPC), and HPV positivity is well established better prognostic marker in OPC. Now, predictable markers for the prognosis of the patients who are stratified by HPV has been investigated in. Semaphorin 3A (SEMA3A) is a well-known axon guidance molecule in the nervous system. It is also known as a tumor suppressor in various cancers. In the present study, we examined the relationships between SEMA3A and clinicopathologic features, especially HPV status, and neoangiogenesis, and its prognostic significance for OPC patients. Thirty-two OPC patients and 17 normal patients were analyzed for SEMA3A expression by immunohistochemical analysis. We also analyzed 22 OPC specimens for CD34 expression as a marker of neoangiogenesis. SEMA3A was significantly downregulated in OPC compared with chronic tonsillitis tissues (p = 0.005). SEMA3A expression was negatively correlated with CD34 expression (r = −0.466, p = 0.033). Moreover, the higher SEMA3A expression cohort showed better survival than the lower SEMA3A expression cohort regardless of HPV status (p = 0.035). These results suggest that SEMA3A expression is a prognostic marker for survival regardless of HPV status and is associated with anti-angiogenesis in OPC.

Resistance to Anti-angiogenic Therapies: A Mechanism Depending on the Time of Exposure to the Drugs

Angiogenesis, the formation of new blood vessels from preexisting one, represents a critical process for oxygen and nutrient supply to proliferating cells, therefore promoting tumor growth and metastasis. The Vascular Endothelial Growth Factor (VEGF) pathway is one of the key mediators of angiogenesis in cancer. Therefore, several therapies including monoclonal antibodies or tyrosine kinase inhibitors target this axis. Although preclinical studies demonstrated strong antitumor activity, clinical studies were disappointing. Antiangiogenic drugs, used to treat metastatic patients suffering of different types of cancers, prolonged survival to different extents but are not curative. In this review, we focused on different mechanisms involved in resistance to antiangiogenic therapies from early stage resistance involving mainly tumor cells to late stages related to the adaptation of the microenvironment.

Characterization of Class-3 Semaphorin Receptors, Neuropilins and Plexins, as Therapeutic Targets in a Pan-Cancer Study

Class-3 semaphorins (SEMA3s), initially characterized as axon guidance cues, have been recognized as key regulators for immune responses, angiogenesis, tumorigenesis and drug responses. The functions of SEMA3s are attributed to the activation of downstream signaling cascades mainly mediated by cell surface receptors neuropilins (NRPs) and plexins (PLXNs), yet their roles in human cancers are not completely understood. Here, we provided a detailed pan-cancer analysis of NRPs and PLXNs in their expression, and association with key signal transducers, patient survival, tumor microenvironment (TME), and drug responses. The expression of NRPs and PLXNs were dysregulated in many cancer types, and the majority of them were further dysregulated in metastatic tumors, indicating a role in metastatic progression. Importantly, the expression of these genes was frequently associated with key transducers, patient survival, TME, and drug responses; however, the direction of the association varied for the particular gene queried and the specific cancer type/subtype tested. Specifically, NRP1, NRP2, PLXNA1, PLXNA3, PLXNB3, PLXNC1, and PLXND1 were primarily associated with aggressive phenotypes, whereas the rest were more associated with favorable prognosis. These data highlighted the need to study each as a separate entity in a cancer type- and subtype-dependent manner.

Normalizing Function of Tumor Vessels: Progress, Opportunities, and Challenges

Abnormal blood and lymphatic vessels create a hostile tumor microenvironment characterized by hypoxia, low pH, and elevated interstitial fluid pressure. These abnormalities fuel tumor progression, immunosuppression, and treatment resistance. In 2001, we proposed a novel hypothesis that the judicious use of antiangiogenesis agents-originally developed to starve tumors-could transiently normalize tumor vessels and improve the outcome of anticancer drugs administered during the window of normalization. In addition to providing preclinical and clinical evidence in support of this hypothesis, we also revealed the underlying molecular mechanisms. In parallel, we demonstrated that desmoplasia could also impair vascular function by compressing vessels, and that normalizing the extracellular matrix could improve vascular function and treatment outcome in both preclinical and clinical settings. Here, we summarize the progress made in understanding and applying the normalization concept to cancer and outline opportunities and challenges ahead to improve patient outcomes using various normalizing strategies.

A pan-cancer study of class-3 semaphorins as therapeutic targets in cancer

BACKGROUND

Initially characterized as axon guidance factors, semaphorins also have been implicated to have critical roles in multiple physiological and developmental functions, including the regulation of immune responses, angiogenesis, organ formation, and the etiology of multiple forms of cancer. Moreover, their contribution in immunity and the regulation of tumour microenvironment is becoming increasingly recognized. Here, we provide a comprehensive analysis of class-3 semaphorins, the only secreted family of genes among veterbrate semaphorins, in terms of their expression profiles and their association with patient survival. We also relate their role with immune subtypes, tumour microenvironment, and drug sensitivity using a pan-cancer study.

RESULTS

Expression profiles of class-3 semaphorins (SEMA3s) and their association with patient survival and tumour microenvironment were studied in 31 cancer types using the TCGA pan-cancer data. The expression of SEMA3 family varies in different cancer types with striking inter- and intra- cancer heterogeneity. In general, our results show that SEMA3A, SEMA3C, and SEMA3F are primarily upregulated in cancer cells, while the rest of SEMA3s are mainly down-regulated in the tested tumours. The expression of SEMA3 family members was frequently associated with patient overall survival. However, the direction of the association varied with regards to the particular SEMA3 isoform queried and the specific cancer type tested. More specifically, SEMA3A and SEMA3E primarily associate with a poor prognosis of survival, while SEMA3G typically associates with survival advantage. The rest of SEMA3s show either survival advantage or disadvantage dependent on cancer type. In addition, all SEMA3 genes show significant association with immune infiltrate subtypes, and they also correlate with level of stromal cell infiltration and tumour cell stemness with various degrees. Finally, our study revealed that SEMA3 genes, especially SEMA3C and SEMA3F may contribute to drug induced cancer cell resistance.

CONCLUSIONS

Our systematic analysis of class-3 semaphorin gene expression and their association with immune infiltrates, tumour microenvironment and cancer patient outcomes highlights the need to study each SEMA3 member as a separate entity within each specific cancer type. Also our study validated the identification of class-3 semaphorin signals as promising therapeutic targets in cancer although further laboratory validation still needed.

Overexpression of Semaphorin 3A is a Marker Associated with Poor Prognosis in Patients with Nasopharyngeal Carcinoma

Semaphorins were discovered as guidance signals that mediate neural development. Recent studies suggest that semaphorin 3A (Sema3A), a member of the semaphorin family, is involved in the development of several cancers. This study aimed to analyze the association of Sema3A with the clinical features of nasopharyngeal carcinoma (NPC), an Epstein–Barr virus-associated carcinoma, and the Epstein–Barr virus primary oncogene latent membrane protein 1 (LMP1). The expression of Sema3A and LMP1 was immunohistochemically examined in the 35 NPC specimens. The mean expression scores for Sema3A and LMP1 were 20.8% ± 14.5% and 13.9% ± 14.8%, respectively. The expression of Sema3A significantly correlated with that of LMP1 (r = 0.41, p = 0.014). In addition, the Sema3A high cohort showed significantly poorer prognosis than the Sema3A low cohort. Sema3A expression was higher in the LMP1-positive KH-1 and KR-4 cell lines compared to the LMP1-negative HeLa cells. Overexpression of LMP1 in the LMP1-negative AdAH cell line upregulated Sema3A expression, both at the transcriptional and translational level. Finally, Sema3A expression was associated with poor prognosis in patients with NPC. Our data suggest that LMP1 induces the expression of Sema3A, which may promote tumor progression in NPC.

Resistance Mechanisms to Anti-angiogenic Therapies in Cancer

Tumor growth and metastasis rely on tumor vascular network for the adequate supply of oxygen and nutrients. Tumor angiogenesis relies on a highly complex program of growth factor signaling, endothelial cell (EC) proliferation, extracellular matrix (ECM) remodeling, and stromal cell interactions. Numerous pro-angiogenic drivers have been identified, the most important of which is the vascular endothelial growth factor (VEGF). The importance of pro-angiogenic inducers in tumor growth, invasion and extravasation make them an excellent therapeutic target in several types of cancers. Hence, the number of anti-angiogenic agents developed for cancer treatment has risen over the past decade, with at least eighty drugs being investigated in preclinical studies and phase I-III clinical trials. To date, the most common approaches to the inhibition of the VEGF axis include the blockade of VEGF receptors (VEGFRs) or ligands by neutralizing antibodies, as well as the inhibition of receptor tyrosine kinase (RTK) enzymes. Despite promising preclinical results, anti-angiogenic monotherapies led only to mild clinical benefits. The minimal benefits could be secondary to primary or acquired resistance, through the activation of alternative mechanisms that sustain tumor vascularization and growth. Mechanisms of resistance are categorized into VEGF-dependent alterations, non-VEGF pathways and stromal cell interactions. Thus, complementary approaches such as the combination of these inhibitors with agents targeting alternative mechanisms of blood vessel formation are urgently needed. This review provides an updated overview on the pathophysiology of angiogenesis during tumor growth. It also sheds light on the different pro-angiogenic and anti-angiogenic agents that have been developed to date. Finally, it highlights the preclinical evidence for mechanisms of angiogenic resistance and suggests novel therapeutic approaches that might be exploited with the ultimate aim of overcoming resistance and improving clinical outcomes for patients with cancer.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

Potential Therapeutic Strategies for Lung and Breast Cancers through Understanding the Anti-Angiogenesis Resistance Mechanisms

Breast and lung cancers are among the top cancer types in terms of incidence and mortality burden worldwide. One of the challenges in the treatment of breast and lung cancers is their resistance to administered drugs, as observed with angiogenesis inhibitors. Based on clinical and pre-clinical findings, these two types of cancers have gained the ability to resist angiogenesis inhibitors through several mechanisms that rely on cellular and extracellular factors. This resistance is mediated through angiogenesis-independent vascularization, and it is related to cancer cells and their microenvironment. The mechanisms that cancer cells utilize include metabolic symbiosis and invasion, and they also take advantage of neighboring cells like macrophages, endothelial cells, myeloid and adipose cells. Overcoming resistance is of great interest, and researchers are investigating possible strategies to enhance sensitivity towards angiogenesis inhibitors. These strategies involved targeting multiple players in angiogenesis, epigenetics, hypoxia, cellular metabolism and the immune system. This review aims to discuss the mechanisms of resistance to angiogenesis inhibitors and to highlight recently developed approaches to overcome this resistance.

Heterogeneity of Vascular Endothelial Cells, De Novo Arteriogenesis and Therapeutic Implications in Pancreatic Neuroendocrine Tumors

Arteriogenesis supplies oxygen and nutrients in the tumor microenvironment (TME), which may play an important role in tumor growth and metastasis. Pancreatic neuroendocrine tumors (pNETs) are the second most common pancreatic malignancy and are frequently metastatic on presentation. Nearly a third of pNETs secrete bioactive substances causing debilitating symptoms. Current treatment options for metastatic pNETs are limited. Importantly, these tumors are highly vascularized and heterogeneous neoplasms, in which the heterogeneity of vascular endothelial cells (ECs) and de novo arteriogenesis may be critical for their progression. Current anti-angiogenetic targeted treatments have not shown substantial clinical benefits, and they are poorly tolerated. This review article describes EC heterogeneity and heterogeneous tumor-associated ECs (TAECs) in the TME and emphasizes the concept of de novo arteriogenesis in the TME. The authors also emphasize the challenges of current antiangiogenic therapy in pNETs and discuss the potential of tumor arteriogenesis as a novel therapeutic target. Finally, the authors prospect the clinical potential of targeting the FoxO1-CD36-Notch pathway that is associated with both pNET progression and arteriogenesis and provide insights into the clinical implications of targeting plasticity of cancer stem cells (CSCs) and vascular niche, particularly the arteriolar niche within the TME in pNETs, which will also provide insights into other types of cancer, including breast cancer, lung cancer, and malignant melanoma.

Targeting Angiogenesis in Pancreatic Neuroendocrine Tumors: Resistance Mechanisms

Despite being infrequent tumors, the incidence and prevalence of pancreatic neuroendocrine tumors (P-NETs) has been rising over the past few decades. In recent years, rigorous phase III clinical trials have been conducted, allowing the approval of several drugs that have become the standard of care in these patients. Although various treatments are used in clinical practice, including somatostatin analogues (SSAs), biological therapies like sunitinib or everolimus, peptide receptor radionuclide therapy (PRRT) or even chemotherapy, a consensus regarding the optimal sequence of treatment has not yet been reached. Notwithstanding, sunitinib is largely used in these patients after the promising results shown in SUN111 phase III clinical trial. However, both prompt progression as well as tumor recurrence after initial response have been reported, suggesting the existence of primary and acquired resistances to this antiangiogenic drug. In this review, we aim to summarize the most relevant mechanisms of angiogenesis resistance that are key contributors of tumor progression and dissemination. Furthermore, several targeted molecules acting selectively against these pathways have shown promising results in preclinical models, and preliminary results from ongoing clinical trials are awaited.

A rationally designed NRP1-independent superagonist SEMA3A mutant is an effective anticancer agent

Vascular normalizing strategies, aimed at ameliorating blood vessel perfusion and lessening tissue hypoxia, are treatments that may improve the outcome of cancer patients. Secreted class 3 semaphorins (SEMA3), which are thought to directly bind neuropilin (NRP) co-receptors that, in turn, associate with and elicit plexin (PLXN) receptor signaling, are effective normalizing agents of the cancer vasculature. Yet, SEMA3A was also reported to trigger adverse side effects via NRP1. We rationally designed and generated a safe, parenterally deliverable, and NRP1-independent SEMA3A point mutant isoform that, unlike its wild-type counterpart, binds PLXNA4 with nanomolar affinity and has much greater biochemical and biological activities in cultured endothelial cells. In vivo, when parenterally administered in mouse models of pancreatic cancer, the NRP1-independent SEMA3A point mutant successfully normalized the vasculature, inhibited tumor growth, curbed metastatic dissemination, and effectively improved the supply and anticancer activity of chemotherapy. Mutant SEMA3A also inhibited retinal neovascularization in a mouse model of age-related macular degeneration. In summary, mutant SEMA3A is a vascular normalizing agent that can be exploited to treat cancer and, potentially, other diseases characterized by pathological angiogenesis.

Weibel-Palade Bodies Orchestrate Pericytes During Angiogenesis

Objective Weibel-Palade bodies (WPBs) are endothelial cell (EC)-specific organelles formed by vWF (von Willebrand factor) polymerization and that contain the proangiogenic factor Ang-2 (angiopoietin-2). WPB exocytosis has been shown to be implicated for vascular repair and inflammatory responses. Here, we investigate the role of WPBs during angiogenesis and vessel stabilization. Approach and Results WPB density in ECs decreased at the angiogenic front of retinal vascular network during development and neovascularization compared with stable vessels. In vitro, VEGF (vascular endothelial growth factor) induced a VEGFR-2 (vascular endothelial growth factor receptor-2)-dependent exocytosis of WPBs that contain Ang-2 and consequently the secretion of vWF and Ang-2. Blocking VEGF-dependant WPB exocytosis and Ang-2 secretion promoted pericyte migration toward ECs. Pericyte migration was inhibited by adding recombinant Ang-2 or by silencing Ang-1 (angiopoietin-1) or Tie2 (angiopoietin-1 receptor) in pericytes. Consistently, in vivo anti-VEGF treatment induced accumulation of WPBs in retinal vessels because of the inhibition of WPB exocytosis and promoted the increase of pericyte coverage of retinal vessels during angiogenesis. In tumor angiogenesis, depletion of WPBs in vWF knockout tumor-bearing mice promoted an increase of tumor angiogenesis and a decrease of pericyte coverage of tumor vessels. By another approach, normalized tumor vessels had higher WPB density. Conclusions We demonstrate that WPB exocytosis and Ang-2 secretion are regulated during angiogenesis to limit pericyte coverage of remodeling vessels by disrupting Ang-1/Tie2 autocrine signaling in pericytes.

The Prognostic Value of Serum Semaphorin3A and VEGF Levels in Patients with Metastatic Colorectal Cancer

PURPOSE

Despite new treatment options in metastatic colorectal cancer (mCRC), new prognostic markers are still needed to determine optimal chemoregimen especially for anti-angiogenesis drugs. In this study, we evaluated the serum semaphorin and VEGF-A levels as prognostic factors in patients with mCRC.

METHODS

Patients with diagnosed mCRC who were treated with first-line bevacizumab plus chemotherapy were included in the study. Venous blood samples of 37 patients with metastatic colon cancer were taken, and serum semaphorin 3A and VEGF-A levels were studied in pre-treatment and the 1st and third months after the treatment was initiated.

RESULTS

Totally, 37 patients were enrolled in the study. The patients' mean age was 62 years. Twenty-eight (49%) of the patients were male, and 19 (51%) were female. Serum semaphorin3A (sema3A) levels of the patients were 5.4 ± 7.4 ng/ml before the treatment, 3.5 ± 3.3 ng/ml at the first month, and 3.5 ± 3.7 ng/ml at the third month. Serum VEGF-A levels were 27.7 ± 32.9 ng/l before the treatment, 23.1 ± 28.1 ng/l at the first month, and 28.9 ± 30.2 ng/l at the third month. There was no significant correlation between the survival and pre-treatment VEGF-A level (p = 0.064). Overall survival (OS) was statistically significantly higher in patients with pre-treatment semaphorin 3A levels below 5.4 ng/ml than higher than 5.4 ng/ml (10.5 months vs 4.5 months, respectively, HR 0.23, 95% CI 19.635-11,391, p = 0.012).

CONCLUSION

Pre-treatment semaphorin 3A level can be a prognostic marker for the mCRC patients who were treated with bevacizumab in patients with metastatic colorectal cancer.

NR4A3 fusion proteins trigger an axon guidance switch that marks the difference between EWSR1 and TAF15 translocated extraskeletal myxoid chondrosarcomas

Extraskeletal myxoid chondrosarcoma (EMC) is a rare sarcoma histotype with uncertain differentiation. EMC is hallmarked by the rearrangement of the NR4A3 gene, which in most cases fuses with EWSR1 or TAF15. TAF15‐translocated EMC seem to feature a more aggressive course compared to EWSR1‐positive EMCs, but whether the type of NR4A3 chimera impinges upon EMC biology is still largely undefined. To gain insights on this issue, a series of EMC samples (7 EWSR1‐NR4A3 and 5 TAF15‐NR4A3) were transcriptionally profiled. Our study unveiled that the two EMC variants display a distinct transcriptional profile and that the axon guidance pathway is a major discriminant. In particular, class 4–6 semaphorins and axonal guidance cues endowed with pro‐tumorigenic activity were more expressed in TAF15‐NR4A3 tumors; vice versa, class 3 semaphorins, considered to convey growth inhibitory signals, were more abundant in EWSR1‐NR4A3 EMC. Intriguingly, the dichotomy in axon guidance signaling observed in the two tumor variants was recapitulated in in vitro cell models engineered to ectopically express EWSR1‐NR4A3 or TAF15‐NR4A3. Moreover, TAF15‐NR4A3 cells displayed a more pronounced tumorigenic potential, as assessed by anchorage‐independent growth. Overall, our results indicate that the type of NR4A3 chimera dictates an axon guidance switch and impacts on tumor cell biology. These findings may provide a framework for interpretation of the different clinical–pathological features of the two EMC variants and lay down the bases for the development of novel patient stratification criteria and therapeutic approaches. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Semaphorins and Their Receptors in Hematological Malignancies

While semaphorins were initially identified as axonal guidance cues for wiring the neural network, it was then recognized their wide relevance in tissue development and homeostasis. Notably, semaphorin activities were also extensively studied in many types of solid tumors; however, their relevance in hematological malignancies is far from understood. In this mini-review, we surveyed the current knowledge about semaphorins and their receptors in leukemias, lymphomas, and multiple myeloma. Noteworthy, current data support a promoting role for Semaphorin 4D and Neuropilin-1 in these tumors, while Semaphorin 3A seems to consistently act as oncosuppressor in leukemias and multiple myeloma. The expression levels and functional activities of SEMA3B, SEMA3F, and Neuropilin-2 have furthermore been investigated in leukemias and lymphoma cells. Herein, we reviewed the state of the art and highlighted some of the open questions to be addressed in the field.

Semaphorin-3A inhibits multiple myeloma progression in a mouse model

Previous studies revealed that progression of multiple myeloma (MM) is associated with downregulation of semaphorin-3A (sema3A) expression in bone marrow endothelial cells. We therefore determined if serum sema3A concentrations are correlated with MM progression and if sema3A can affect MM progression. We find that the concentration of sema3A in sera of MM patients is strongly reduced and that the decrease is correlated with disease progression. A similar depletion is found in patients having acute myeloid leukemia and acute lymphoblastic leukemia but not in cancer forms that do not involve the bone marrow such as in colon cancer. Expression of a modified sema3A [furin-resistant sema3A (FR-sema3A)] stabilized against cleavage by furin-like proprotein convertases in CAG MM cells did not affect their behavior in-vitro. CAG cells injected into the tail vein of severe combined immunodeficient (SCID) mice home to the bone marrow and proliferate, mimicking MM disease progression. Disease progression in mice injected with CAG cells expressing FR-sema3A was inhibited, resulting in prolonged survival and a lower incidence of bone lesions. Histological examination and fluorescence-activated cell sorting analysis revealed that FR-sema3A expression reduced the infiltration of the CAG cells into the bone marrow, reduced bone marrow necrosis and reduced angiogenesis induced by the MM cells in the bone marrow. Our results suggest that measurement of sema3A serum concentrations may be of use for the diagnosis and for the monitoring of malignancies of the bone marrow such as MM. Furthermore, our results suggest that FR-sema3A may perhaps find use as an inhibitor of MM disease progression.

Modulation of pericytes by a fusion protein comprising of a PDGFRβ-antagonistic affibody and TNFα induces tumor vessel normalization and improves chemotherapy

The delivery of anticancer drugs is hampered by tumor vessels with abnormal structure and function, which requires that vessel normalization be mediated by pharmaceutics. The current strategies for vessel normalization focus on direct modulation of endothelial cells (ECs), which frequently affect vessels in normal tissues. Modulating EC-supporting cells, such as pericytes (PCs), is a new direction. Here, we produced a fusion protein, Z-TNFα, by fusing the platelet-derived growth factor receptor β (PDGFRβ)- antagonistic affibody Z_PDGFRβ to tumor necrosis factor α (TNFα). Owing to the affinity of fused Z_PDGFRβ for PDGFRβ, Z-TNFα binds PDGFRβ⁺ PCs but not PDGFRβ^- ECs. Low-dose (1 μg/mouse) Z-TNFα treatment remodeled the tumor vessels, thus reducing vessel permeability and increasing vessel perfusion. As a result, the Z-TNFα treatment improved the delivery of doxorubicin (DOX) and enhanced its antitumor effect, indicating that Z-TNFα induced normalization of tumor vessels. Mechanically, the tumor vessel normalization mediated by Z-TNFα might be attributed to the reduction of vascular endothelial growth factor (VEGF) secretion by PCs and the elevated expression of intercellular cell adhesion molecule-1 (ICAM-1) in PCs, which might suppress the proliferation and migration of ECs and simultaneously trigger interaction between perivascular macrophages and PCs. These results demonstrated that tumor-associated PCs could be considered novel target cells for vessel normalization, and Z-TNFα might be developed as a potential tool for antitumor combination therapy.

Resistance to targeted treatment of gastroenteropancreatic neuroendocrine tumors

The mammalian target of rapamycin (mTOR) is part of the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt)/mTOR signaling. The PI3K/Akt/mTOR pathway has a pivotal role in the oncogenesis of neuroendocrine tumors (NETs). In addition, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) drive angiogenesis in NETs and therefore contributes to neuroendocrine tumor development. Hence, mTOR and angiogenesis inhibitors have been developed. Everolimus, a first-generation mTOR inhibitor, has shown significant survival benefit in advanced gastroenteropancreatic NETs. Sunitinib, a pan-tyrosine kinase inhibitor that targets the VEGF receptor, has proven to increase progression-free survival in advanced pancreatic NETs. Nevertheless, primary and acquired resistance to rapalogs and sunitinib has limited the clinical benefit for NET patients. Despite the identification of multiple molecular mechanisms of resistance, no predictive biomarker has made it to the clinic. This review is focused on the mTOR signaling and angiogenesis in NET, the molecular mechanisms of primary and acquired resistance to everolimus and sunitinib and how to overcome this resistance by alternative drug compounds.