High affinity interaction of integrin alpha4beta1 (VLA-4) and vascular cell adhesion molecule 1 (VCAM-1) enhances migration of human melanoma cells across activated endothelial cell layers

Acid-sensing receptor GPR4 plays a crucial role in lymphatic cancer metastasis

Cancer tissues exhibit an acidic microenvironment owing to the accumulation of protons and lactic acid produced by cancer and inflammatory cells. To examine the role of an acidic microenvironment in lymphatic cancer metastasis, gene expression profiling was conducted using human dermal lymphatic endothelial cells (HDLECs) treated with a low pH medium. Microarray and gene set enrichment analysis revealed that acid treatment induced the expression of inflammation-related genes in HDLECs, including genes encoding chemokines and adhesion molecules. Acid treatment-induced chemokines C-X3-C motif chemokine ligand 1 (CX3CL1) and C-X-C motif chemokine ligand 6 (CXCL6) autocrinally promoted the growth and tube formation of HDLECs. The expression of vascular cell adhesion molecule 1 (VCAM-1) increased in HDLECs after acid treatment in a time-dependent manner, which, in turn, enhanced their adhesion to melanoma cells. Among various acid-sensing receptors, HDLECs basally expressed G protein-coupled receptor 4 (GPR4), which was augmented under the acidic microenvironment. The induction of chemokines or VCAM-1 under acidic conditions was attenuated by GPR4 knockdown in HDLECs. In addition, lymph node metastases in a mouse melanoma model were suppressed by administering an anti-VCAM-1 antibody or a GPR4 antagonist. These results suggest that an acidic microenvironment modifies the function of lymphatic endothelial cells via GPR4, thereby promoting lymphatic cancer metastasis. Acid-sensing receptors and their downstream molecules might serve as preventive or therapeutic targets in cancer.

Age-dependent loss of HAPLN1 erodes vascular integrity via indirect upregulation of endothelial ICAM1 in melanoma

Melanoma, the most lethal form of skin cancer, often has worse outcomes in older patients. We previously demonstrated that an age-related decrease in the secreted extracellular matrix (ECM) protein HAPLN1 has a role in slowing melanoma progression. Here we show that HAPLN1 in the dermal ECM is sufficient to maintain the integrity of melanoma-associated blood vessels, as indicated by increased collagen and VE-cadherin expression. Specifically, we show that HAPLN1 in the ECM increases hyaluronic acid and decreases endothelial cell expression of ICAM1. ICAM1 phosphorylates and internalizes VE-cadherin, a critical determinant of vascular integrity, resulting in permeable blood vessels. We found that blocking ICAM1 reduces tumor size and metastasis in older mice. These results suggest that HAPLN1 alters endothelial ICAM1expression in an indirect, matrix-dependent manner. Targeting ICAM1 could be a potential treatment strategy for older patients with melanoma, emphasizing the role of aging in tumorigenesis.

Marques I, Frenz M, Joyce JA, Lyck R. Compromised Blood-Brain Barrier Junctions Enhance Melanoma Cell Intercalation and Extravasation

Melanoma frequently metastasises to the brain, and a detailed understanding of the molecular and cellular mechanisms underlying melanoma cell extravasation across the blood-brain barrier (BBB) is important for preventing brain metastasis formation. Making use of primary mouse brain microvascular endothelial cells (pMBMECs) as an in vitro BBB model, we imaged the interaction of melanoma cells into pMBMEC monolayers. We observed exclusive junctional intercalation of melanoma cells and confirmed that melanoma-induced pMBMEC barrier disruption can be rescued by protease inhibition. Interleukin (IL)-1β stimulated pMBMECs or PECAM-1-knockout (-ko) pMBMECs were employed to model compromised BBB barrier properties in vitro and to determine increased melanoma cell intercalation compared to pMBMECs with intact junctions. The newly generated brain-homing melanoma cell line YUMM1.1-BrM4 was used to reveal increased in vivo extravasation of melanoma cells across the BBB of barrier-compromised PECAM-1-deficient mice compared to controls. Taken together, our data indicate that preserving BBB integrity is an important measure to limit the formation of melanoma-brain metastasis.

Integrins and the Metastasis-like Dissemination of Acute Lymphoblastic Leukemia to the Central Nervous System

Acute lymphoblastic leukemia (ALL) disseminates with high prevalence to the central nervous system (CNS) in a process resembling aspects of the CNS surveillance of normal immune cells as well as aspects of brain metastasis from solid cancers. Importantly, inside the CNS, the ALL blasts are typically confined within the cerebrospinal fluid (CSF)-filled cavities of the subarachnoid space, which they use as a sanctuary protected from both chemotherapy and immune cells. At present, high cumulative doses of intrathecal chemotherapy are administered to patients, but this is associated with neurotoxicity and CNS relapse still occurs. Thus, it is imperative to identify markers and novel therapy targets specific to CNS ALL. Integrins represent a family of adhesion molecules involved in cell-cell and cell-matrix interactions, implicated in the adhesion and migration of metastatic cancer cells, normal immune cells, and leukemic blasts. The ability of integrins to also facilitate cell-adhesion mediated drug resistance, combined with recent discoveries of integrin-dependent routes of leukemic cells into the CNS, have sparked a renewed interest in integrins as markers and therapeutic targets in CNS leukemia. Here, we review the roles of integrins in CNS surveillance by normal lymphocytes, dissemination to the CNS by ALL cells, and brain metastasis from solid cancers. Furthermore, we discuss whether ALL dissemination to the CNS abides by known hallmarks of metastasis, and the potential roles of integrins in this context.

Cell-adhesion Molecules as Key Mechanisms of Tumor Invasion: The Case of Breast Cancer

Cancer is a major health problem worldwide and the second leading cause of death following cardiovascular diseases. Breast cancer is the leading cause of mortality and morbidity among women and one of the most common malignant neoplasms prompt to metastatic disease. In the present review, the mechanisms of the major cell adhesion molecules involved in tumor invasion are discussed, focusing on the case of breast cancer. A non-systematic updated revision of the literature was performed in order to assemble information regarding the expression of the adhesion cell molecules associated with metastasis.

Conversation before crossing: dissecting metastatic tumor-vascular interactions in microphysiological systems

Tumor metastasis via the circulation requires crossing the vascular barrier twice: first, during intravasation when tumor cells disseminate from the primary site through proximal vasculature, and second, during extravasation, when tumor cells exit the circulation to form distant metastatic seeds. During these key metastatic events, chemomechanical signaling between tumor cells and endothelial cells elicits reciprocal changes in cell morphology and behavior that are necessary to breach the vessel wall. Existing experimental systems have provided a limited understanding of the diverse mechanisms underlying tumor-endothelial interactions during intravasation and extravasation. Recent advances in microphysiological systems have revolutionized the ability to generate miniaturized human tissues with tailored three-dimensional architectures, physiological cell interfaces, and precise chemical and physical microenvironments. By doing so, microphysiological systems enable experimental access to complex morphogenic processes associated with human tumor progression with unprecedented resolution and biological control. Here, we discuss recent examples in which microphysiological systems have been leveraged to reveal new mechanistic insight into cellular and molecular control systems operating at the tumor-endothelial interface during intravasation and extravasation.

The pleiotropic role of galectin-3 in melanoma progression: Unraveling the enigma

Melanoma is a highly aggressive skin cancer with poor outcomes associated with distant metastasis. Intrinsic properties of melanoma cells alongside the crosstalk between melanoma cells and surrounding microenvironment determine the tumor behavior. Galectin-3 (Gal-3), a ß-galactoside-binding lectin, has emerged as a major effector in cancer progression, including melanoma behavior. Data from melanoma models and patient studies reveal that Gal-3 expression is dysregulated, both intracellularly and extracellularly, throughout the stages of melanoma progression. This review summarizes the most recent data and hypotheses on Gal-3 and its tumor-modulating functions, highlighting its role in driving melanoma growth, invasion, and metastatic colonization. It also provides insight into potential Gal-3-targeted strategies for melanoma diagnosis and treatment.

Hydrocephalus in Nfix−/− Mice Is Underpinned by Changes in Ependymal Cell Physiology

Nuclear factor one X (NFIX) is a transcription factor required for normal ependymal development. Constitutive loss of Nfix in mice (Nfix−/−) is associated with hydrocephalus and sloughing of the dorsal ependyma within the lateral ventricles. Previous studies have implicated NFIX in the transcriptional regulation of genes encoding for factors essential to ependymal development. However, the cellular and molecular mechanisms underpinning hydrocephalus in Nfix−/− mice are unknown. To investigate the role of NFIX in hydrocephalus, we examined ependymal cells in brains from postnatal Nfix−/− and control (Nfix+/+) mice using a combination of confocal and electron microscopy. This revealed that the ependymal cells in Nfix−/− mice exhibited abnormal cilia structure and disrupted localisation of adhesion proteins. Furthermore, we modelled ependymal cell adhesion using epithelial cell culture and revealed changes in extracellular matrix and adherens junction gene expression following knockdown of NFIX. Finally, the ablation of Nfix from ependymal cells in the adult brain using a conditional approach culminated in enlarged ventricles, sloughing of ependymal cells from the lateral ventricles and abnormal localisation of adhesion proteins, which are phenotypes observed during development. Collectively, these data demonstrate a pivotal role for NFIX in the regulation of cell adhesion within ependymal cells of the lateral ventricles.

Integrin Signaling Shaping BTK-Inhibitor Resistance

Integrins are adhesion molecules that function as anchors in retaining tumor cells in supportive tissues and facilitating metastasis. Beta1 integrins are known to contribute to cell adhesion-mediated drug resistance in cancer. Very late antigen-4 (VLA-4), a CD49d/CD29 heterodimer, is a beta1 integrin implicated in therapy resistance in both solid tumors and haematological malignancies such as chronic lymphocytic leukemia (CLL). A complex inside-out signaling mechanism activates VLA-4, which might include several therapeutic targets for CLL. Treatment regimens for this disease have recently shifted towards novel agents targeting BCR signaling. Bruton’s tyrosine kinase (BTK) is a component of B cell receptor signaling and BTK inhibitors such as ibrutinib are highly successful; however, their limitations include indefinite drug administration, the development of therapy resistance, and toxicities. VLA-4 might be activated independently of BTK, resulting in an ongoing interaction of CD49d-expressing leukemic cells with their surrounding tissue, which may reduce the success of therapy with BTK inhibitors and increases the need for alternative therapies. In this context, we discuss the inside-out signaling cascade culminating in VLA-4 activation, consider the advantages and disadvantages of BTK inhibitors in CLL and elucidate the mechanisms behind cell adhesion-mediated drug resistance.

The blockage of downstream P2Y2 receptor signaling inhibits the prostate cancer cell adhesion to endothelial cells

AIMS

Prostate cancer is the second most frequently malignancy in men worldwide. Most deaths are caused by metastasis, and tumor cell dissemination involves the interaction with endothelial cells. However, the endothelial cell signaling involved in such interaction is not entirely understood. The tumor microenvironment contains extracellular ATP, an endogenous agonist of the purinergic P2Y₂ receptor (P2Y₂R). P2Y₂R signaling changes endothelial cell phenotype, which may be relevant to cancer pathophysiology. Therefore, we hypothesized that P2Y₂R activation could favor the metastatic prostate cancer cells adhesion to endothelial cells.

MAIN METHODS

For adhesion assays, confluent endothelial cells EA.hy926 were treated with P2Y₂R agonists before adding and imaging stained DU-145 cells. Alternatively, fluorescent probes and antibodies were used to determine intracellular endothelial Ca²⁺, nitric oxide (NO), and flow cytometry assays.

KEY FINDINGS

Endothelial P2Y₂R activation with ATP, UTP, or the selective agonist 2-thio-UTP increased DU-145 cell adhesion to EA.hy926 cells. This effect required endothelial cell Ca²⁺ mobilization and relied on the endothelial expression of VCAM-1 and ICAM-1. Conversely, inhibiting this proadhesive endothelial phenotype could impair DU-145 cell adhesion. To evaluate this, we chose atorvastatin based on its notable improvement of endothelial cell dysfunction. Atorvastatin blocked UTP-induced DU-145 cell adhesion to endothelial cell monolayer in a NO-dependent manner, unveiling a P2Y₂R and NO signaling crosstalk.

SIGNIFICANCE

Endothelial P2Y₂R signaling contributes to the adhesion of metastatic prostate cancer cells suggesting that the downstream signaling blockade by statins could be a putative mechanism to reduce prostate cancer metastasis.

PET Imaging of VLA-4 in a New BRAFV600E Mouse Model of Melanoma

PURPOSE

Despite unprecedented responses to immune checkpoint inhibitors and targeted therapy in melanoma, a major subset of patients progresses and have few effective salvage options. We have previously demonstrated robust, selective uptake of the peptidomimetic LLP2A labeled with Cu-64 ([64Cu]-LLP2A) for positron emission tomography (PET) imaging in subcutaneous and metastatic models of B16F10 murine melanoma. LLP2A binds with high affinity to very late antigen-4 (VLA-4, integrin α4β1), a transmembrane protein overexpressed in melanoma and other cancers that facilitates tumor growth and metastasis. Yet B16F10 fails to faithfully reflect human melanoma biology, as it lacks certain oncogenic driver mutations, including BRAF mutations found in ≥ 50 % of clinical specimens. Here, we evaluated the PET tracer [64Cu]-CB-TE1A1P-PEG4-LLP2A ([64Cu]-LLP2A) in novel, translational BRAFV600E mutant melanoma models differing in VLA-4 expression-BPR (VLA-4-) and BPRα (VLA-4+).

PROCEDURES

BPR cells were transduced with α4 (CD49d) to overexpress intact cell surface VLA-4 (BPRα). The binding affinity of [64Cu]-LLP2A to BPR and BPRα cells was determined by saturation binding assays. [64Cu]-LLP2A internalization into B16F10, BPR, and BPRα cells was quantified via a plate-based assay. Tracer biodistribution and PET/CT imaging were evaluated in mice bearing subcutaneous BPR and BPRα tumors.

RESULTS

[64Cu]-LLP2A demonstrated high binding affinity to BPRα (Kd = 1.4 nM) but indeterminate binding to BPR cells. VLA-4+ BPRα and B16F10 displayed comparable time-dependent [64Cu]-LLP2A internalization, whereas BPR internalization was undetectable. PET/CT showed increased tracer uptake in BPRα tumors vs. BPR tumors in vivo, which was validated by significantly greater (p < 0.0001) BPRα tumor uptake in biodistribution analyses.

CONCLUSIONS

[64Cu]-LLP2A discriminates BPRα (VLA-4+) vs. BPR (VLA-4-) melanomas in vivo, supporting translation of these BRAF-mutated melanoma models via prospective imaging and theranostic studies. These results extend the utility of LLP2A to selectively target clinically relevant and therapy-resistant tumor variants toward its use for therapeutic patient care.

Extracellular ATP promotes angiogenesis and adhesion of TNBC cells to endothelial cells via up-regulation of CTGF

Our previous works have indicated that extracellular ATP is an important prometastasis factor. However, the molecular mechanism involved needs to be further studied. We demonstrated that extracellular ATP treatment could upregulate the expression of connective tissue growth factor (CTGF) in both triple‐negative breast cancer (TNBC) cells and endothelial cells (ECs). Extracellular ATP stimulated the migration of TNBC cells and ECs, and angiogenesis of ECs via the P2Y2––YAP‐CTGF axis. Furthermore, we demonstrated that adenosine triphosphate (ATP) stimulated TNBC cell adhesion to ECs and transmigration through the EC layer via CTGF by upregulation of integrin β1 on TNBC cells and VCAM‐1 on ECs. Both apyrase (ATP‐diphosphohydrolase) and CTGF shRNA treatments could inhibit the metastasis of inoculated tumors to lung and liver in a mouse model, and these treated tumors had fewer blood vessels. Collectively, our data indicated that extracellular ATP promotes tumor angiogenesis and the interactions between TNBC cells and ECs through upregulation of CTGF, thereby stimulating TNBC metastasis. The pleiotropic effects of ATP in angiogenesis and cell adhesion suggest that extracellular ATP or CTGF could be an effective target for TNBC therapy.

Tumor-Derived Exosomes Modulate Primary Site Tumor Metastasis

Tumor-derived exosomes (TDEs) are actively produced and released by tumor cells and carry messages from tumor cells to healthy cells or abnormal cells, and they participate in tumor metastasis. In this review, we explore the underlying mechanism of action of TDEs in tumor metastasis. TDEs transport tumor-derived proteins and non-coding RNA to tumor cells and promote migration. Transport to normal cells, such as vascular endothelial cells and immune cells, promotes angiogenesis, inhibits immune cell activation, and improves chances of tumor implantation. Thus, TDEs contribute to tumor metastasis. We summarize the function of TDEs and their components in tumor metastasis and illuminate shortcomings for advancing research on TDEs in tumor metastasis.

The microenvironment of brain metastases from solid tumors

Brain metastasis (BrM) is an area of unmet medical need that poses unique therapeutic challenges and heralds a dismal prognosis. The intracranial tumor microenvironment (TME) presents several challenges, including the therapy-resistant blood-brain barrier, a unique immune milieu, distinct intercellular interactions, and specific metabolic conditions, that are responsible for treatment failures and poor clinical outcomes. There is a complex interplay between malignant cells that metastasize to the central nervous system (CNS) and the native TME. Cancer cells take advantage of vascular, neuronal, immune, and anatomical vulnerabilities to proliferate with mechanisms specific to the CNS. In this review, we discuss unique aspects of the TME in the context of brain metastases and pathways through which the TME may hold the key to the discovery of new and effective therapies for patients with BrM.

Rho GTPase signalling networks in cancer cell transendothelial migration

Rho GTPases are small signalling G-proteins that are central regulators of cytoskeleton dynamics, and thereby regulate many cellular processes, including the shape, adhesion and migration of cells. As such, Rho GTPases are also essential for the invasive behaviour of cancer cells, and thus involved in several steps of the metastatic cascade, including the extravasation of cancer cells. Extravasation, the process by which cancer cells leave the circulation by transmigrating through the endothelium that lines capillary walls, is an essential step for metastasis towards distant organs. During extravasation, Rho GTPase signalling networks not only regulate the transmigration of cancer cells but also regulate the interactions between cancer and endothelial cells and are involved in the disruption of the endothelial barrier function, ultimately allowing cancer cells to extravasate into the underlying tissue and potentially form metastases. Thus, targeting Rho GTPase signalling networks in cancer may be an effective approach to inhibit extravasation and metastasis. In this review, the complex process of cancer cell extravasation will be discussed in detail. Additionally, the roles and regulation of Rho GTPase signalling networks during cancer cell extravasation will be discussed, both from a cancer cell and endothelial cell point of view.

New 4-Aminoproline-Based Small Molecule Cyclopeptidomimetics as Potential Modulators of α4β1 Integrin

Integrin α₄β₁ belongs to the leukocyte integrin family and represents a therapeutic target of relevant interest given its primary role in mediating inflammation, autoimmune pathologies and cancer-related diseases. The focus of the present work is the design, synthesis and characterization of new peptidomimetic compounds that are potentially able to recognize α₄β₁ integrin and interfere with its function. To this aim, a collection of seven new cyclic peptidomimetics possessing both a 4-aminoproline (Amp) core scaffold grafted onto key α₄β₁-recognizing sequences and the (2-methylphenyl)ureido-phenylacetyl (MPUPA) appendage, was designed, with the support of molecular modeling studies. The new compounds were synthesized through SPPS procedures followed by in-solution cyclization maneuvers. The biological evaluation of the new cyclic ligands in cell adhesion assays on Jurkat cells revealed promising submicromolar agonist activity in one compound, namely, the c[Amp(MPUPA)Val-Asp-Leu] cyclopeptide. Further investigations will be necessary to complete the characterization of this class of compounds.

Exosomes and organ-specific metastasis

The transmission of information between tumor cells and other cell types in the tumor microenvironment plays an important role in tumor metastasis and is critically modulated by exosomes and other mediators. Tumor-derived exosomes can promote epithelial-mesenchymal transition, angiogenesis, immune escape, formation of the pre-metastatic microenvironment, and transmission of drug-resistant molecules, thereby promoting tumor growth, invasion, and metastasis. Integrins are important regulatory molecules on exosomes that can locate metastatic cells at the initial stage of metastasis and show good organotropism. This fact suggests that a clear understanding of the roles of exosomal integrins will be beneficial for future clinical applications. Follow-up studies on exosomes using continuously updated purification techniques and identification methods are extremely important. In addition to their potential as cancer biomarkers, exosomes also provide new research directions for precision medicine. Currently, exosomes have potential value in disease treatment and provide clinicians with more meaningful judgment standards.

Abiotrophia defectiva DnaK Promotes Fibronectin-Mediated Adherence to HUVECs and Induces a Proinflammatory Response

Abiotrophia defectiva is a nutritionally variant streptococci that is found in the oral cavity, and it is an etiologic agent of infective endocarditis. We have previously reported the binding activity of A. defectiva to fibronectin and to human umbilical vein endothelial cells (HUVECs). However, the contribution of some adhesion factors on the binding properties has not been well delineated. In this study, we identified DnaK, a chaperon protein, as being one of the binding molecules of A. defectiva to fibronectin. Recombinant DnaK (rDnaK) bound immobilized fibronectin in a concentration-dependent manner, and anti-DnaK antiserum reduced the binding activity of A. defectiva with both fibronectin and HUVECs. Furthermore, DnaK were observed on the cell surfaces via immune-electroscopic analysis with anti-DnaK antiserum. Expression of IL-8, CCL2, ICAM-1, and VCAM-1 was upregulated with the A. defectiva rDnaK treatment in HUVECs. Furthermore, TNF-α secretion of THP-1 macrophages was also upregulated with the rDnaK. We observed these upregulations in rDnaK treated with polymyxin B, but not in the heat-treated rDnaK. The findings show that A. defectiva DnaK functions not only as an adhesin to HUVECs via the binding to fibronectin but also as a proinflammatory agent in the pathogenicity to cause infective endocarditis.

Inhibitory Effects of Bilirubin on Colonization and Migration of A431 and SK-MEL-3 Skin Cancer Cells Compared with Human Dermal Fibroblasts (HDF)

This study evaluated the inhibitory effects of bilirubin on colony formation and cell migration of melanoma and non-melanoma skin cancer cell lines SK-MEL-3 and A431, compared with normal human dermal fibroblasts (HDF). The IC₅₀ obtained from the MTT assay was 125, 100, and 75 μM bilirubin for HDF, A431, and SK-MEL-3 cells, respectively. The colony formation and cell migration of cancer cells, treated with 100 μM bilirubin, were reduced significantly (p < 0.05). Bilirubin decreased cell adhesion and inhibited cell colonization via inducing apoptosis and cell death. Also by interaction with migration main factors, bilirubin caused inhibition the cell migration.

Chimeric Antigen Receptor (CAR) T Cell Therapy for Metastatic Melanoma: Challenges and Road Ahead

Metastatic melanoma is the most aggressive and difficult to treat type of skin cancer, with a survival rate of less than 10%. Metastatic melanoma has conventionally been considered very difficult to treat; however, recent progress in understanding the cellular and molecular mechanisms involved in the tumorigenesis, metastasis and immune escape have led to the introduction of new therapies. These include targeted molecular therapy and novel immune-based approaches such as immune checkpoint blockade (ICB), tumor-infiltrating lymphocytes (TILs), and genetically engineered T-lymphocytes such as chimeric antigen receptor (CAR) T cells. Among these, CAR T cell therapy has recently made promising strides towards the treatment of advanced hematological and solid cancers. Although CAR T cell therapy might offer new hope for melanoma patients, it is not without its shortcomings, which include off-target toxicity, and the emergence of resistance to therapy (e.g., due to antigen loss), leading to eventual relapse. The present review will not only describe the basic steps of melanoma metastasis, but also discuss how CAR T cells could treat metastatic melanoma. We will outline specific strategies including combination approaches that could be used to overcome some limitations of CAR T cell therapy for metastatic melanoma.

Control of Tumor Progression by Angiocrine Factors

Tumor progression, therapy resistance and metastasis are profoundly controlled by the tumor microenvironment. The contribution of endothelial cells to tumor progression was initially only attributed to the formation of new blood vessels (angiogenesis). Research in the last decade has revealed however that endothelial cells control their microenvironment through the expression of membrane-bound and secreted factors. Such angiocrine functions are frequently hijacked by cancer cells, which deregulate the signaling pathways controlling the expression of angiocrine factors. Here, we review the crosstalk between cancer cells and endothelial cells and how this contributes to the cancer stem cell phenotype, epithelial to mesenchymal transition, immunosuppression, remodeling of the extracellular matrix and intravasation of cancer cells into the bloodstream. We also address the long-distance crosstalk of a primary tumor with endothelial cells at the pre-metastatic niche and how this contributes to metastasis.

MultiVERSE: a multiplex and multiplex-heterogeneous network embedding approach

Network embedding approaches are gaining momentum to analyse a large variety of networks. Indeed, these approaches have demonstrated their effectiveness in tasks such as community detection, node classification, and link prediction. However, very few network embedding methods have been specifically designed to handle multiplex networks, i.e. networks composed of different layers sharing the same set of nodes but having different types of edges. Moreover, to our knowledge, existing approaches cannot embed multiple nodes from multiplex-heterogeneous networks, i.e. networks composed of several multiplex networks containing both different types of nodes and edges. In this study, we propose MultiVERSE, an extension of the VERSE framework using Random Walks with Restart on Multiplex (RWR-M) and Multiplex-Heterogeneous (RWR-MH) networks. MultiVERSE is a fast and scalable method to learn node embeddings from multiplex and multiplex-heterogeneous networks. We evaluate MultiVERSE on several biological and social networks and demonstrate its performance. MultiVERSE indeed outperforms most of the other methods in the tasks of link prediction and network reconstruction for multiplex network embedding, and is also efficient in link prediction for multiplex-heterogeneous network embedding. Finally, we apply MultiVERSE to study rare disease-gene associations using link prediction and clustering. MultiVERSE is freely available on github at https://github.com/Lpiol/MultiVERSE .

Influence of Immune Microenvironment on Diagnosis and Prognosis of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is an immunosuppressive malignancy accompanied by noted alterations in various immune cells and cytokines. Recognition of the immune system's role in contributing to cancer development is an important advancement in our original understanding of carcinoma. We obtained HNSCC gene expression and clinical data from The Cancer Genome Atlas (TCGA) database. We assessed the relative proportion of 22 Infiltrating immune cell types in both HNSCC and adjacent non-cancer tissues using Cell-type Identification By Estimating Relative Subsets Of RNA Transcripts (CIBERSORT) method, identifying the influence of the immune cells content in tumor staging and survival prediction. We further predicted the tumor purity, and the presence of infiltrating stromal/immune cells in HNSCC tissues using Estimation of STromal and Immune cells in Malignant Tumor tissues using Expression data (ESTIMATE) algorithm, identifying its potential correlation with patient survival. Stromal and immune score-associated differentially expressed genes (DEGs) were subsequently verified and their roles in immune response were displayed by functional enrichment analysis and protein-protein interaction (PPI) network. Our research demonstrated the underlying association between the immune microenvironment and HNSCC, and the results were intended to serve as valuable terms for HNSCC diagnosis, prognosis, and targeted immune therapy.

Abnormal promoter DNA hypermethylation of the integrin, nidogen, and dystroglycan genes in breast cancer

Cell transmembrane receptors and extracellular matrix components play a pivotal role in regulating cell activity and providing for the concerted integration of cells in the tissue structures. We have assessed DNA methylation in the promoter regions of eight integrin genes, two nidogen genes, and the dystroglycan gene in normal breast tissues and breast carcinomas (BC). The protein products of these genes interact with the basement membrane proteins LAMA1, LAMA2, and LAMB1; abnormal hypermethylation of the LAMA1, LAMA2, and LAMB1 promoters in BC has been described in our previous publications. In the present study, the frequencies of abnormal promoter hypermethylation in BC were 13% for ITGA1, 31% for ITGA4, 4% for ITGA7, 39% for ITGA9, 38% for NID1, and 41% for NID2. ITGA2, ITGA3, ITGA6, ITGB1, and DAG1 promoters were nonmethylated in normal and BC samples. ITGA4, ITGA9, and NID1 promoter hypermethylation was associated with the HER2 positive tumors, and promoter hypermethylation of ITGA1, ITGA9, NID1 and NID2 was associated with a genome-wide CpG island hypermethylated BC subtype. Given that ITGA4 is not expressed in normal breast, one might suggest that its abnormal promoter hypermethylation in cancer is non-functional and is thus merely a passenger epimutation. Yet, this assumption is not supported by our finding that it is not associated with a hypermethylated BC subtype. ITGA4 acquires expression in a subset of breast carcinomas, and methylation of its promoter may be preventive against expression in some tumors. Strong association of abnormal ITGA4 hypermethylation with the HER2 positive tumors (p = 0.0025) suggests that simultaneous presence of both HER2 and integrin α4 receptors is not beneficial for tumor cells. This may imply HER2 and integrin α4 signaling pathways interactions that are yet to be discovered.

Probing Intravascular Adhesion and Extravasation of Tumor Cells with Microfluidics

Cancer metastasis is a multistep process during which tumor cells leave the primary tumor mass and form distant secondary colonies that are lethal. Circulating tumor cells (CTCs) are transported by body fluids to reach distant organs, where they will extravasate and either remain dormant or form new tumor foci. Development of methods to study the behavior of CTCs at the late stages of the intravascular journey is thus required to dissect the molecular mechanisms at play. Using recently developed microfluidics approaches, we have demonstrated that CTCs arrest intravascularly, through a two-step process: (a) CTCs stop using low energy and rapidly activated adhesion receptors to form transient metastable adhesions and (b) CTCs stabilize their adhesions to the endothelial layer with high energy and slowly activated adhesion receptors. In this methods chapter, we describe these easy-to-implement quantitative methods using commercially available microfluidic channels. We detail the use of fast live imaging combined to fine-tuned perfusion to measure the adhesion potential of CTC depending on flow velocities. We document how rapidly engaged early metastable adhesion can be discriminated from slower activated stable adhesion using microfluidics. Finally, CTC extravasation potential can be assessed within this setup using long-term cell culture under flow. Altogether, this experimental pipeline can be adapted to probe the adhesion (to the endothelial layer) and extravasation potential of any circulating cell.

Bladder cancer-derived interleukin-1 converts the vascular endothelium into a pro-inflammatory and pro-coagulatory surface

Background

Bladder cancer cells orchestrate tumour progression by pro-inflammatory cytokines. Cytokines modulate the local tumour microenvironment and increase the susceptibility of tumour distant tissues for metastasis. Here, we investigated the impact of human bladder cancer cell derived factors on the ability to modulate and activate human vascular endothelial cells.

Methods

The pro-inflammatory and pro-coagulatory potential of four different bladder cancer cell lines was accessed by qRT-PCR arrays and ELISA. Modulation and activation of endothelial cells was studied in microfluidic devices. Clinical relevance of our findings was confirmed by immune histology in tissue samples of bladder cancer patients and public transcriptome data.

Results

The unbalanced ratio between interleukin (IL)-1 and IL-1 receptor antagonist (IL-1ra) in the secretome of bladder cancer cells converted the quiescent vascular endothelium into a pro-adhesive, pro-inflammatory, and pro-coagulatory surface. Microfluidic experiments showed that tumour cell induced endothelial cell activation promoted leukocyte recruitment and platelet adhesion. Human bladder cancer tissue analysis confirmed that loss of IL-1ra and elevated IL-1 expression was associated with enhanced cancer progression.

Conclusions

Our data indicate that IL-1 and IL-1ra were dysregulated in bladder cancer and could facilitate tumour dissemination through endothelial cell activation. Targeting the IL-1/IL-1ra axis might attenuate tumour-mediated inflammation and metastasis formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-020-07548-z.

Cutaneous melanoma dissemination is dependent on the malignant cell properties and factors of intercellular crosstalk in the cancer microenvironment (Review)

The incidence of cutaneous malignant melanoma has been steadily increasing worldwide for several decades. This phenomenon seems to follow the trend observed in many types of malignancies caused by multiple significant factors, including ageing. Despite the progress in cutaneous malignant melanoma therapeutic options, the curability of advanced disease after metastasis represents a serious challenge for further research. In this review, we summarise data on the microenvironment of cutaneous malignant melanoma with emphasis on intercellular signalling during the disease progression. Malignant melanocytes with features of neural crest stem cells interact with non‑malignant populations within this microenvironment. We focus on representative bioactive factors regulating this intercellular crosstalk. We describe the possible key factors and signalling cascades responsible for the high complexity of the melanoma microenvironment and its premetastatic niches. Furthermore, we present the concept of melanoma early becoming a systemic disease. This systemic effect is presented as a background for the new horizons in the therapy of cutaneous melanoma.

ADAM28: Another ambivalent protease in cancer

Emergence of novel therapeutic options in a perspective of personalized therapy of cancer relies on the discovery of precise molecular mechanisms involved in the switch from a localized tumor to invasive metastasis spread. Pro-tumor functions have been mostly ascribed to proteolytic enzymes from the metalloproteinase family including A Disintegrin And Metalloproteinases (ADAMs). Particularly, when expressed by cancer cells, ADAM28 protease supports cancer cell proliferation, survival and migration as well as metastatic progression. In sharp contrast, ADAM28 derived from the tumor microenvironment has shown to exert strong protective effects against deleterious metastasis dissemination. Indeed, depletion of host-derived ADAM28 (ADAM28 KO mice) accelerates colonization lung tissues, increases tumor foci implantation, and impairs T cell immune response. In this review, we outline specific ADAM28 functions when specifically expressed by carcinoma cells or by tumor microenvironment. Finally, we discuss about future research strategies that could be pursued to highlight new functions of this protease in cancer.

Evaluation of [225Ac]Ac-DOTA-anti-VLA-4 for targeted alpha therapy of metastatic melanoma

Very late antigen 4 (VLA-4; also called integrin α4β1) is overexpressed in melanoma tumor cells with an active role in tumor growth, angiogenesis, and metastasis, making VLA-4 a potential target for targeted alpha therapy (TAT).

METHODS

An anti-VLA-4 antibody was conjugated to DOTA for [²²⁵Ac]Ac-labeling and DTPA for [¹¹¹In]In-labeling. The resulting agents, [²²⁵Ac]Ac- or [¹¹¹In]In-labeled anti-VLA-4 were evaluated in vitro, including binding affinity, internalization, and colony formation assays as well as in vivo biodistribution studies. In addition, the therapeutic efficacy of [²²⁵Ac]Ac-DOTA-anti-VLA-4 was evaluated in a disseminated disease mouse model of melanoma.

RESULTS

[¹¹¹In]In-DTPA-anti-VLA-4 demonstrated high affinity for VLA-4 (K_d = 5.2 ± 1.6 nM). [²²⁵Ac]Ac-DOTA-anti-VLA-4 was labeled with an apparent molar activity of 3.5 MBq/nmol and > 95% radiochemical purity. Colony formation assays demonstrated a decrease in the surviving fraction of B16F10 cells treated with [²²⁵Ac]Ac-DOTA-anti-VLA-4 compared to control. Biodistribution studies demonstrated accumulation in the VLA-4-positive tumor and VLA-4 rich organs. Therapeutic efficacy studies demonstrated a significant increase in survival in mice treated with [²²⁵Ac]Ac-DOTA-anti-VLA-4 as compared to controls.

CONCLUSION

The work presented here demonstrated that [²²⁵Ac]Ac-DOTA-anti-VLA-4 was effective as a treatment in mice with disseminated disease, but potentially has dose limiting hematopoietic toxicity. Preliminary studies presented here also supported the potential to overcome this limitation by exploring a pre-loading or blocking dose strategy, to optimize the targeting vector to help minimize the absorbed dose to VLA-4 rich organs while maximizing the dose delivered to VLA-4-positive melanoma tumor cells.

Melanoma in the liver: Oxidative stress and the mechanisms of metastatic cell survival

Metastatic melanoma is a fatal disease with a rapid systemic dissemination. The most frequent target sites are the liver, bone, and brain. Melanoma metastases represent a heterogeneous cell population, which associates with genomic instability and resistance to therapy. Interaction of melanoma cells with the hepatic sinusoidal endothelium initiates a signaling cascade involving cytokines, growth factors, bioactive lipids, and reactive oxygen and nitrogen species produced by the cancer cell, the endothelium, and also by different immune cells. Endothelial cell-derived NO and H₂O₂ and the action of immune cells cause the death of most melanoma cells that reach the hepatic microvascularization. Surviving melanoma cells attached to the endothelium of pre-capillary arterioles or sinusoids may follow two mechanisms of extravasation: a) migration through vessel fenestrae or b) intravascular proliferation followed by vessel rupture and microinflammation. Invading melanoma cells first form micrometastases within the normal lobular hepatic architecture via a mechanism regulated by cross-talk with the stroma and multiple microenvironment-related molecular signals. In this review special emphasis is placed on neuroendocrine (systemic) mechanisms as potential promoters of liver metastatic growth. Growing metastatic cells undergo functional and metabolic changes that increase their capacity to withstand oxidative/nitrosative stress, which favors their survival. This adaptive process also involves upregulation of Bcl-2-related antideath mechanisms, which seems to lead to the generation of more resistant cell subclones.

Cerebrovascular inflammation promotes the formation of brain metastases

Brain metastases are the most prevalent intracranial malignancy. Patient outcome is poor and treatment options are limited. Hence, new avenues must be explored to identify potential therapeutic targets. Inflammation is a known critical component of cancer progression. Intratumoral inflammation drives progression and leads to the release of circulating tumor cells (CTCs). Inflammation at distant sites promotes adhesion of CTCs to the activated endothelium and then initiates the formation of metastases. These interactions mostly involve cell adhesion molecules expressed by activated endothelial cells. For example, the vascular cell adhesion molecule-1 (VCAM-1) is known to promote transendothelial migration of cancer cells in different organs. However, it is unclear whether a similar mechanism occurs within the specialized environment of the brain. Our objective was therefore to use molecular imaging to assess the potential role of VCAM-1 in promoting the entry of CTCs into the brain. First, magnetic resonance imaging (MRI) and histological analyses revealed that cerebrovascular inflammation induced by intracranial injection of lipopolysaccharide significantly increased the expression of VCAM-1 in the Balb/c mouse brain. Next, intracardiac injection of 4T1 mammary carcinoma cancer cells in animals with cerebrovascular inflammation yielded a higher brain metastasis burden than in the control animals. Finally, blocking VCAM-1 prior to 4T1 cells injection prevented this increased metastatic burden. Here, we demonstrated that by contributing to CTCs adhesion to the activated cerebrovascular endothelium, VCAM-1 improves the capacity of CTCs to form metastatic foci in the brain.

Melanoma in the Eyes of Mechanobiology

Skin is the largest organ of the human body with several important functions that can be impaired by injury, genetic or chronic diseases. Among all skin diseases, melanoma is one of the most severe, which can lead to death, due to metastization. Mechanotransduction has a crucial role for motility, invasion, adhesion and metastization processes, since it deals with the response of cells to physical forces. Signaling pathways are important to understand how physical cues produced or mediated by the Extracellular Matrix (ECM), affect healthy and tumor cells. During these processes, several molecules in the nucleus and cytoplasm are activated. Melanocytes, keratinocytes, fibroblasts and the ECM, play a crucial role in melanoma formation. This manuscript will address the synergy among melanocytes, keratinocytes, fibroblasts cells and the ECM considering their mechanical contribution and relevance in this disease. Mechanical properties of melanoma cells can also be influenced by pigmentation, which can be associated with changes in stiffness. Mechanical changes can be related with the adhesion, migration, or invasiveness potential of melanoma cells promoting a high metastization capacity of this cancer. Mechanosensing, mechanotransduction, and mechanoresponse will be highlighted with respect to the motility, invasion, adhesion and metastization in melanoma cancer.

Role of CyPA in cardiac hypertrophy and remodeling

Pathological cardiac hypertrophy is a complex process and eventually develops into heart failure, in which the heart responds to various intrinsic or external stress, involving increased interstitial fibrosis, cell death and cardiac dysfunction. Studies have shown that oxidative stress is an important mechanism for this maladaptation. Cyclophilin A (CyPA) is a member of the cyclophilin (CyPs) family. Many cells secrete CyPA to the outside of the cells in response to oxidative stress. CyPA from blood vessels and the heart itself participate in a variety of signaling pathways to regulate the production of reactive oxygen species (ROS) and mediate inflammation, promote cardiomyocyte hypertrophy and proliferation of cardiac fibroblasts, stimulate endothelial injury and vascular smooth muscle hyperplasia, and promote the dissolution of extracellular matrix (ECM) by activating matrix metalloproteinases (MMPs). The events triggered by CyPA cause a decline of diastolic and systolic function and finally lead to the occurrence of heart failure. This article aims to introduce the role and mechanism of CyPA in cardiac hypertrophy and remodeling, and highlights its potential role as a disease biomarker and therapeutic target.

VLA-4 mediated adhesion of melanoma cells on the blood-brain barrier is the critical cue for melanoma cell intercalation and barrier disruption

Melanoma is the most aggressive skin cancer in humans. One severe complication is the formation of brain metastasis, which requires extravasation of melanoma cells across the tight blood-brain barrier (BBB). Previously, VLA-4 has been assigned a role for the adhesive interaction of melanoma cells with non-BBB endothelial cells. However, the role of melanoma VLA-4 for breaching the BBB remained unknown. In this study, we used a mouse in vitro BBB model and imaged the shear resistant arrest of melanoma cells on the BBB. Similar to effector T cells, inflammatory conditions of the BBB increased the arrest of melanoma cells followed by a unique post-arrest behavior lacking immediate crawling. However, over time, melanoma cells intercalated into the BBB and compromised its barrier properties. Most importantly, antibody ablation of VLA-4 abrogated melanoma shear resistant arrest on and intercalation into the BBB and protected the BBB from barrier breakdown. A tissue microarray established from human brain metastasis revealed that indeed a majority of 92% of all human melanoma brain metastases stained VLA-4 positive. We propose VLA-4 as a target for the inhibition of brain metastasis formation in the context of personalized medicine identifying metastasizing VLA-4 positive melanoma.

Innovative Therapeutic Strategies for Effective Treatment of Brain Metastases

Brain metastases are the most prevalent of intracranial malignancies. They are associated with a very poor prognosis and near 100% mortality. This has been the case for decades, largely because we lack effective therapeutics to augment surgery and radiotherapy. Notwithstanding improvements in the precision and efficacy of these life-prolonging treatments, with no reliable options for adjunct systemic therapy, brain recurrences are virtually inevitable. The factors limiting intracranial efficacy of existing agents are both physiological and molecular in nature. For example, heterogeneous permeability, abnormal perfusion and high interstitial pressure oppose the conventional convective delivery of circulating drugs, thus new delivery strategies are needed to achieve uniform drug uptake at therapeutic concentrations. Brain metastases are also highly adapted to their microenvironment, with complex cross-talk between the tumor, the stroma and the neural compartments driving speciation and drug resistance. New strategies must account for resistance mechanisms that are frequently engaged in this milieu, such as HER3 and other receptor tyrosine kinases that become induced and activated in the brain microenvironment. Here, we discuss molecular and physiological factors that contribute to the recalcitrance of these tumors, and review emerging therapeutic strategies, including agents targeting the PI3K axis, immunotherapies, nanomedicines and MRI-guided focused ultrasound for externally controlling drug delivery.

Regulation of cell migration by α4 and α9 integrins

Integrins are heterodimeric transmembrane receptors that play an essential role in enabling cells to sense and bind to extracellular ligands. Activation and clustering of integrins leads to the formation of focal adhesions at the plasma membrane that subsequently initiate signalling pathways to control a broad range of functional endpoints including cell migration, proliferation and survival. The α4 and α9 integrins form a small sub-family of receptors that share some specific ligands and binding partners. Although relatively poorly studied compared with other integrin family members, emerging evidence suggests that despite restricted cell and tissue expression profiles, these integrins play a key role in the regulation of signalling pathways controlling cytoskeletal remodelling and migration in both adherent and non-adherent cell types. This review summarises the known shared and specific roles for α4 and α9 integrins and highlights the importance of these receptors in controlling cell migration within both homeostatic and disease settings.

Cancer cell migration on elongate protrusions of fibroblasts in collagen matrix

Cancer-associated fibroblasts (CAFs) play critical roles in the tumor progression. However, it remains unclear how cancer cells migrate in the three-dimensional (3D) matrix of cancer tissues and how CAFs support the cancer invasion. Here we propose a novel mechanism of fibroblast-dependent cancer cell invasion in the 3D collagen matrix. Human cancer cell lines from the pancreas (Panc-1), lung (A549) and some other organs actively adhered to normal fibroblasts and primary lung CAFs in cultures. To show its significance in tumor invasion, we designed a new invasion assay in which homogeneous microspheroids consisting of cancer cells and fibroblasts were embedded into collagen gel. Time-lapse experiments showed that cancer cells adhered to and quickly migrated on the long protrusions of fibroblasts in the 3D collagen matrix. Fibroblast-free cancer cells poorly invaded the matrix. Experiments with function-blocking antibodies, siRNAs, and immunocytochemistry demonstrated that cancer cells adhered to fibroblasts through integrin α5β1-mediated binding to fibronectin on the surface of fibroblasts. Immunochemical analyses of the co-cultures and lung cancers suggested that cancer cells could acquire the migratory force by the fibronectin/integrin signaling. Our results also revealed that the fibroblast-bound fibronectin was a preferential substrate for cancer cells to migrate in the collagen matrix.

The functional role of integrins during intra- and extravasation within the metastatic cascade

Formation of distant metastases is by far the most common cause of cancer-related deaths. The process of metastasis formation is complex, and within this complex process the formation of migratory cells, the so called epithelial mesenchymal transition (EMT), which enables cancer cells to break loose from the primary tumor mass and to enter the bloodstream, is of particular importance. To break loose from the primary cancer, cancer cells have to down-regulate the cell-to-cell adhesion molecuIes (CAMs) which keep them attached to neighboring cancer cells. In contrast to this downregulation of CAMS in the primary tumor, cancer cells up-regulate other types of CAMs, that enable them to attach to the endothelium in the organ of the future metastasis. During EMT, the expression of cell-to-cell and cell-to-matrix adhesion molecules and their down- and upregulation is therefore critical for metastasis formation. Tumor cells mimic leukocytes to enable transmigration of the endothelial barrier at the metastatic site. The attachment of leukocytes/cancer cells to the endothelium are mediated by several CAMs different from those at the site of the primary tumor. These CAMs and their ligands are organized in a sequential row, the leukocyte adhesion cascade. In this adhesion process, integrins and their ligands are centrally involved in the molecular interactions governing the transmigration. This review discusses the integrin expression patterns found on primary tumor cells and studies whether their expression correlates with tumor progression, metastatic capacity and prognosis. Simultaneously, further possible, but so far unclearly characterized, alternative adhesion molecules and/or ligands, will be considered and emerging therapeutic possibilities reviewed.

FAK inhibition reduces metastasis of α4 integrin-expressing melanoma to lymph nodes by targeting lymphatic VCAM-1 expression

Malignant melanoma typically metastasizes to lymph nodes (LNs) as a primary or in-transit lesion before secondary metastasis occurs, and LN biopsy is a common procedure to diagnose melanoma progression. Since cancer metastasis is a complex process where various interactions between tumor cells and the stroma play key roles in establishing metastatic lesions, the exact mechanisms underlying melanoma metastasis to LNs remains unknown. It has been known that focal adhesion kinase (FAK) activity promotes the expression of proinflammatory vascular cell adhesion molecule-1 (VCAM-1). As VCAM-1 is a major receptor for α4 integrin and plays a key role in leukocyte recruitment, we reasoned that inhibition of FAK activity may reduce VCAM-1 expression within LNs and thus reduce metastasis of α4 integrin-expressing melanoma to LNs. First, we found that a pharmacological FAK inhibitor, PF-271, blocked tumor necrosis factor-α (TNF-α)-mediated VCAM-1 expression on human dermal lymphatic endothelial cells (HDLECs). In vitro, PF-271 significantly decreased B16F10 melanoma adhesion to and transmigration through HDLECs compared to TNF-α treated cells. Furthermore, in vivo FAK inhibition by oral PF-271 administration reduced VCAM-1 expression in inguinal, cervical, and popliteal LNs compared to vehicle treated mice. Finally, in a footpad metastasis model, B16F10 melanoma cells were injected into the right footpad of C57BL/6 mice, and PF-271 (50 mg/kg, twice daily for 6 days) was orally administrated after 1 week of tumor transplantation. While untreated mice exhibited significant metastatic melanoma lesions in popliteal LNs, PF-271 treated mice showed only marginal melanoma metastasis. These results support the possibility that FAK inhibitors may be a novel preventative option in melanoma metastasis by blocking VCAM-1 expression in LNs.

Connective tissue growth factor stimulates osteosarcoma cell migration and induces osteosarcoma metastasis by upregulating VCAM-1 expression

Osteosarcoma is the most common bone malignancy that occurs in the young population. After osteosarcoma cells metastasize to the lung, prognosis is very poor owing to difficulties in early diagnosis and effective treatment. Recently, connective tissue growth factor (CTGF) was reported to be a critical contributor to osteosarcoma metastasis. However, the detailed mechanism associated with CTGF-directed migration in bone neoplasms is still mostly unknown. Through the in vivo and in vitro examination of osteosarcoma cells, this study suggests that VCAM-1 up-regulation and increased osteosarcoma cell migration are involved in this process. Antagonizing αvβ3 integrin inhibited cell migration. Moreover, FAK, PI3K, Akt and NF-κB activation were also shown to be involved in CTGF-mediated osteosarcoma metastasis. Taken together, CTGF promotes VCAM-1 production and further induces osteosarcoma metastasis via the αvβ3 integrin/FAK/PI3K/Akt/NF-κB signaling pathway, which could represent a promising clinical target to improve patient outcome.

Functional interplay between secreted ligands and receptors in melanoma

Melanoma, the most aggressive form of skin cancer, results from the malignant transformation of melanocytes located in the basement membrane separating the epidermal and dermal skin compartments. Cutaneous melanoma is often initiated by solar ultraviolet radiation (UVR)-induced mutations. Melanocytes intimately interact with keratinocytes, which provide growth factors and melanocortin peptides acting as paracrine regulators of proliferation and differentiation. Keratinocyte-derived melanocortins activate melanocortin-1 receptor (MC1R) to protect melanocytes from the carcinogenic effect of UVR. Accordingly, MC1R is a major determinant of susceptibility to melanoma. Despite extensive phenotypic heterogeneity and high mutation loads, the molecular basis of melanomagenesis and the molecules mediating the crosstalk between melanoma and stromal cells are relatively well understood. Mutations of intracellular effectors of receptor tyrosine kinase (RTK) signalling, notably NRAS and BRAF, are major driver events more frequent than mutations in RTKs. Nevertheless, melanomas often display aberrant signalling from RTKs such as KIT, ERRB1-4, FGFR, MET and PDGFR, which contribute to disease progression and resistance to targeted therapies. Progress has also been made to unravel the role of the tumour secretome in preparing the metastatic niche. However, key aspects of the melanoma-stroma interplay, such as the molecular determinants of dormancy, remain poorly understood.

Hemodynamic Forces Tune the Arrest, Adhesion, and Extravasation of Circulating Tumor Cells

Metastatic seeding is driven by cell-intrinsic and environmental cues, yet the contribution of biomechanics is poorly known. We aim to elucidate the impact of blood flow on the arrest and the extravasation of circulating tumor cells (CTCs) in vivo. Using the zebrafish embryo, we show that arrest of CTCs occurs in vessels with favorable flow profiles where flow forces control the adhesion efficacy of CTCs to the endothelium. We biophysically identified the threshold values of flow and adhesion forces allowing successful arrest of CTCs. In addition, flow forces fine-tune tumor cell extravasation by impairing the remodeling properties of the endothelium. Importantly, we also observe endothelial remodeling at arrest sites of CTCs in mouse brain capillaries. Finally, we observed that human supratentorial brain metastases preferably develop in areas with low perfusion. These results demonstrate that hemodynamic profiles at metastatic sites regulate key steps of extravasation preceding metastatic outgrowth.

Overexpression of VLA-4 in glial-restricted precursors enhances their endothelial docking and induces diapedesis in a mouse stroke model

The loss of oligodendrocytes after stroke is one of the major causes of secondary injury. Glial-restricted progenitors (GRPs) have remylenating potential after intraparenchymal cerebral transplantation. The intraarterial (IA) injection route is an attractive gateway for global brain delivery, but, after IA infusion, naive GRPs fail to bind to the cerebral vasculature. The aim of this study was to test whether overexpression of Very Late Antigen-4 (VLA-4) increases endothelial docking and cerebral homing of GRPs in a stroke model. Mouse GRPs were co-transfected with DNA plasmids encoding VLA-4 subunits (α4, β1). The adhesion capacity and migration were assessed using a microfluidic assay. In vivo imaging of the docking and homing of IA-infused cells was performed using two-photon microscopy in a mouse middle cerebral artery occlusion (MCAO) model. Compared to naïve GRPs, transfection of GRPs with VLA-4 resulted in >60% higher adhesion (p < 0.05) to both purified Vascular Cell Adhesion Molecule-11 (VCAM-11) and TNFα-induced endothelial VCAM-1. VLA-4⁺GRPs displayed a higher migration in response to a chemoattractant gradient. Following IA infusion, VLA-4⁺GRPs adhered to the vasculature at three-fold greater numbers than naïve GRPs. Multi-photon imaging confirmed that VLA-4 overexpression increases the efficiency of GRP docking and leads to diapedesis after IA transplantation. This strategy may be further exploited to increase the efficacy of cellular therapeutics.

Integrins as therapeutic targets in the organ-specific metastasis of human malignant melanoma

Integrins are a large family of adhesion molecules that mediate cell-cell and cell-extracellular matrix interactions. Among the 24 integrin isoforms, many have been found to be associated with tumor angiogenesis, tumor cell migration and proliferation, and metastasis. Integrins, especially αvβ3, αvβ5 and α5β1, participate in mediating tumor angiogenesis by interacting with the vascular endothelial growth factor and angiopoietin-Tie signaling pathways. Melanoma patients have a poor prognosis when the primary tumor has generated distant metastases, and the melanoma metastatic site is an independent predictor of the survival of these patients. Different integrins on the melanoma cell surface preferentially direct circulating melanoma cells to different organs and promote the development of metastases at specific organ sites. For instance, melanoma cells expressing integrin β3 tend to metastasize to the lungs, whereas those expressing integrin β1 preferentially generate lymph node metastases. Moreover, tumor cell-derived exosomes which contain different integrins may prepare a pre-metastatic niche in specific organs and promote organ-specific metastases. Because of the important role that integrins play in tumor angiogenesis and metastasis, they have become promising targets for the treatment of advanced cancer. In this paper, we review the integrin isoforms responsible for angiogenesis and organ-specific metastasis in malignant melanoma and the inhibitors that have been considered for the future treatment of metastatic disease.

Kindlin-1 Promotes Pulmonary Breast Cancer Metastasis

In breast cancer, increased expression of the cytoskeletal adaptor protein Kindlin-1 has been linked to increased risks of lung metastasis, but the functional basis is unknown. Here, we show that in a mouse model of polyomavirus middle T antigen-induced mammary tumorigenesis, loss of Kindlin-1 reduced early pulmonary arrest and later development of lung metastasis. This phenotype relied on the ability of Kindlin-1 to bind and activate β integrin heterodimers. Kindlin-1 loss reduced α4 integrin-mediated adhesion of mammary tumor cells to the adhesion molecule VCAM-1 on endothelial cells. Treating mice with an anti-VCAM-1 blocking antibody prevented early pulmonary arrest. Kindlin-1 loss also resulted in reduced secretion of several factors linked to metastatic spread, including the lung metastasis regulator tenascin-C, showing that Kindlin-1 regulated metastatic dissemination by an additional mechanism in the tumor microenvironment. Overall, our results show that Kindlin-1 contributes functionally to early pulmonary metastasis of breast cancer.Significance: These findings provide a mechanistic proof in mice that Kindin-1, an integrin-binding adaptor protein, is a critical mediator of early lung metastasis of breast cancer. Cancer Res; 78(6); 1484-96. ©2018 AACR.

Preliminary evaluation of 18F-labeled LLP2A-trifluoroborate conjugates as VLA-4 (α4β1 integrin) specific radiotracers for PET imaging of melanoma

INTRODUCTION

The transmembrane α₄β₁ integrin receptor, or very-late antigen 4 (VLA-4), is associated with tumor metastasis and angiogenesis, the development of chemotherapeutic drug resistance, and is overexpressed in multiple myelomas, osteosarcomas, lymphomas, leukemias, and melanomas. The peptidomimetic, LLP2A, is a high-affinity ligand with specificity for the extracellular portion of VLA-4 and several conjugates have been evaluated in vivo by NIR-fluorescence, ¹¹¹In-SPECT and ⁶⁸Ga- and ⁶⁴Cu-PET imaging, but to date, not with ¹⁸F-PET.

METHODS

Using two highly stable organotrifluoroborate prosthetic groups: ammoniumdimethyl-trifluoroborate (AMBF₃) and a new N-pyridinyl-para-trifluoroborate (N-Pyr-p-BF₃), both capable of facile aqueous ¹⁸F-labeling by isotope exchange (IEX), we present the first PET imaging evaluations of two [¹⁸F]R-BF₃^--PEG₂-LLP2A tracers using VLA-4 overexpressing B16-F10 murine melanoma tumor mouse models.

RESULTS

Here, we demonstrate successful one-step ¹⁸F-labeling of both conjugates with wet NCA [¹⁸F]F^- in radiochemical yields of up to 11.6% within 75 min at molar activities of 40-100 GBq/μmol. Average tumor uptake values based on ex vivo biodistribution values were 4.4%ID/g (11) and 2.8%ID/g (12) using ¹⁸F-labeled LLP2A-conjugates with the two prosthetic groups: N-Pyr-p-BF₃ (5) and alkyl-N,N-dimethylammonio-BF₃ (AMBF₃) (7), respectively, and was found to be target-specific as evidenced by in vivo blocking controls. Dynamic PET scanning and biodistribution studies revealed slow clearance of the [¹⁸F]R-BF₃^--PEG₂-LLP2A tracers from the tumors, and also substantial uptake in the intestines, gall bladder, liver and bladder. Observed bone uptake was blockable, consistent with known VLA-4 expression in hematopoietic stem cells found in bone marrow.

CONCLUSIONS

These studies show that these [¹⁸F]R-BF₃^--PEG₂-LLP2A conjugates (11 and 12) are promising VLA-4 targeting radiotracers, yet, further optimization will be required to reduce uptake in the gastro-intestinal tract.

Altered integrin expression patterns shown by microarray in human cutaneous melanoma

A large variety of molecular pathways in melanoma progression suggests that no individual molecular alteration is crucial in itself. Our aim was to define the molecular alterations underlying metastasis formation. Gene expression profiling was performed using microarray and qRT-PCR to define alterations between matched primary and metastatic melanoma cell lines. These data were integrated with publicly available unmatched tissue data. The invasiveness of cell lines was determined by Matrigel invasion assays and invasive clones from primary melanoma-derived cell lines were also selected. Two metastatic cell line models were created: the regional lymph node WM983A-WM983A-WM983B and the distant lung WM793B-WM793B-1205Lu metastatic models. The majority of metastasis genes were downregulated and enriched in adhesion and ITGA6-B4 pathways. Upregulation of immune pathways was characteristic of distant metastases, whereas increased Rap1 signaling was specific for regional (sub)cutaneous metastases. qRT-PCR analysis of selected integrins (A2, A3, A4, A9, B5, B8, A6, B1, and B3) highlighted the possible importance of ITGA3/4 and B8 in the metastatic process, distinguishing regional and distant metastases. We identified functionally relevant gene clusters that influenced metastasis formation. Our data provide further evidence that integrin expression patterns may be important in distant metastasis formation.

Clinical relevance of integrin alpha 4 in gastrointestinal stromal tumours

The molecular mechanisms for the dissemination and metastasis of gastrointestinal stromal tumours (GIST) are incompletely understood. The purpose of the study was to investigate the clinical relevance of integrin alpha 4 (ITGA4) expression in GIST. GIST transcriptomes were first compared with transcriptomes of other types of cancer and histologically normal gastrointestinal tract tissue in the MediSapiens in silico database. ITGA4 was identified as an unusually highly expressed gene in GIST. Therefore, the effects of ITGA4 knock‐down and selective integrin alpha 4 beta 1 (VLA‐4) inhibitors on tumour cell proliferation and invasion were investigated in three GIST cell lines. In addition, the prognostic role of ITGA4 expression in cancer cells was investigated in a series of 147 GIST patients with immunohistochemistry. Inhibition of ITGA4‐related signalling decreased GIST cell invasion in all investigated GIST cell lines. ITGA4 protein was expressed in 62 (42.2%) of the 147 GISTs examined, and expression was significantly associated with distant metastases during the course of the disease and several adverse prognostic features. Patients whose GIST expressed strongly ITGA4 had unfavourable GIST‐specific survival and overall survival compared to patients with low or no ITGA4 expression. Taken together, ITGA4 is an important integrin in the molecular pathogenesis of GIST and may influence their clinical behaviour.