An epigenetically distinct breast cancer cell subpopulation promotes collective invasion

Development of betabodies: the next generation of phosphatidylserine targeting agents

Externalized phosphatidylserine (PS) is a phospholipid and a selective marker of the tumor microenvironment (TME). It is exposed on the outer leaflet of the plasma membrane of tumor-associated endothelial cells, apoptotic tumor cells, and some viable tumor cells, where it functions in part to suppress immune responses by binding to PS receptors expressed on tumor-infiltrating myeloid cells. PS has been targeted with antibodies, such as bavituximab, that bind the phospholipid via a cofactor, β2-glycoprotein 1 (β2GP1); these antibodies showed excellent specificity for tumor vasculature and induce an immune stimulatory environment. We have advanced this concept by developing the next generation of PS targeting agent, a fusion protein (betabody) constructed by linking PS-binding domain V of β2GP1 to the Fc of an IgG2a. Betabodies bind to externalized PS with high affinity (∼1 nM), without the requirement of a co-factor and localize robustly to the TME. We demonstrate that betabodies are a direct PS-targeting agent that have the potential to be used as anti-tumor therapy, drug delivery vehicles, and tools for imaging the TME.

The molecular crosstalk of the hippo cascade in breast cancer: A potential central susceptibility

The incidence of breast cancer is perpetually growing globally, and it remains a major public health problem and the leading cause of mortality in women. Though the aberrant activities of the Hippo pathway have been reported to be associated with cancer, constructive knowledge of the pathway connecting the various elements of breast cancer remains to be elucidated. The Hippo transducers, yes-associated protein (YAP) and transcriptional co-activator with PDZ binding motif (TAZ), are reported to be either tumor suppressors, oncogenes, or independent prognostic markers in breast cancer. Thus, there is further need for an explicative evaluation of the dilemma with this molecular contribution of Hippo transducers in modulating breast malignancy. In this review, we summarize the intricate crosstalk of the Hippo pathway in different aspects of breast malignancy, including stem-likeness, cellular signaling, metabolic adaptations, tumor microenvironment, and immune responses. The collective data shows that Hippo transducers play an indispensable role in mammary tumor formation, progression, and dissemination. However, the cellular functions of YAP/TAZ in tumorigenesis might be largely dependent on the mechanical and biophysical cues they interact with, as well as on the cell phenotype. This review provides a glimpse into the plausible biological contributions of the cascade to the inward progression of breast carcinoma and suggests potential therapeutic prospects.

Photoactivatable substrates show diverse phenotypes of leader cells in collective migration when moving along different extracellular matrix proteins

In cancer metastasis, collectively migrating clusters are discriminated into leader and follower cells that move through extracellular matrices (ECMs) with different characteristics. The impact of changes in ECM protein types on leader cells and migrating clusters is unknown. To address this, we investigated the response of leader cells and migrating clusters upon moving from one ECM protein to another using a photoactivatable substrate bearing photocleavable PEG (PCP), whose surface changes from protein-repellent to protein-adhesive in response to light. We chose laminin and collagen I for our study since they are abundant in two distinct regions in living tissues, namely basement membrane and connective tissue. Using the photoactivatable substrates, the precise deposition of the first ECM protein in the irradiated areas was achieved, followed by creating well-defined cellular confinements. Secondary irradiation enabled the deposition of the second ECM protein in the new irradiated regions, resulting in region-selective heterogeneous and homogenous ECM protein-coated surfaces. Different tendencies in leader cell formation from laminin into laminin compared to those migrating from laminin into collagen were observed. The formation of focal adhesion and actin structures for cells within the same cluster in the ECM proteins responded according to the underlying ECM protein type. Finally, integrin β1 was crucial for the appearance of leader cells for clusters migrating from laminin into collagen. However, when it came to laminin into laminin, integrin β1 was not responsible. This highlights the correlation between leader cells in collective migration and the biochemical signals that arise from underlying extracellular matrix proteins.

Identification of Neural Crest and Neural Crest-Derived Cancer Cell Invasion and Migration Genes Using High-throughput Screening and Deep Attention Networks

Background

Cell migration and invasion are well-coordinated processes in development and disease but remain poorly understood. We previously showed that highly migratory neural crest (NC) cells share a 45-gene panel with other cell invasion phenomena, including cancer. To identify critical genes of the 45-gene panel, we performed a high-throughput siRNA screen and used statistical and deep learning methods to compare NC- versus non-NC-derived human cell lines.

Results

We find 14 out of 45 genes significantly reduces c8161 melanoma cell migration; only 4 are shared with HT1080 fibrosarcoma cells (BMP4, ITGB1, KCNE3, RASGRP1). Deep learning attention network analysis identified distinct cell-cell interaction patterns and significant alterations after BMP4 or RASGRP1 knockdown in c8161 cells. Addition of recombinant proteins to the culture media identified 5 out of the 10 known secreted molecules stimulate c8161 cell migration, including BMP4. BMP4 siRNA knockdown inhibited c8161 cell invasion in vivo and in vitro ; however, its addition to the culture media rescued c8161 cell invasion.

Conclusion

A high-throughput screen and deep learning rapidly distilled a 45-gene panel to a small subset of genes that appear critical to melanoma cell invasion and warrant deeper in vivo functional analysis for their role in driving the neural crest.

How important is EMT for cancer metastasis?

Epithelial-to-mesenchymal transition (EMT), a biological phenomenon of cellular plasticity initially reported in embryonic development, has been increasingly recognized for its importance in cancer progression and metastasis. Despite tremendous progress being made in the past 2 decades in our understanding of the molecular mechanism and functional importance of EMT in cancer, there are several mysteries around EMT that remain unresolved. In this Unsolved Mystery, we focus on the variety of EMT types in metastasis, cooperative and collective EMT behaviors, spatiotemporal characterization of EMT, and strategies of therapeutically targeting EMT. We also highlight new technical advances that will facilitate the efforts to elucidate the unsolved mysteries of EMT in metastasis.

u-track3D: Measuring, navigating, and validating dense particle trajectories in three dimensions

We describe u-track3D, a software package that extends the versatile u-track framework established in 2D to address the specific challenges of 3D particle tracking. First, we present the performance of the new package in quantifying a variety of intracellular dynamics imaged by multiple 3D microcopy platforms and on the standard 3D test dataset of the particle tracking challenge. These analyses indicate that u-track3D presents a tracking solution that is competitive to both conventional and deep-learning-based approaches. We then present the concept of dynamic region of interest (dynROI), which allows an experimenter to interact with dynamic 3D processes in 2D views amenable to visual inspection. Third, we present an estimator of trackability that automatically defines a score for every trajectory, thereby overcoming the challenges of trajectory validation by visual inspection. With these combined strategies, u-track3D provides a complete framework for unbiased studies of molecular processes in complex volumetric sequences.

In Vitro Organoid-Based Assays Reveal SMAD4 Tumor-Suppressive Mechanisms for Serrated Colorectal Cancer Invasion

Colon cancer is the third most prominent cancer and second leading cause of cancer-related deaths in the United States. Up to 20% of colon cancers follow the serrated tumor pathway driven by mutations in the MAPK pathway. Loss of SMAD4 function occurs in the majority of late-stage colon cancers and is associated with aggressive cancer progression. Therefore, it is important to develop technology to accurately model and better understand the genetic mechanisms behind cancer invasion. Organoids derived from tumors found in the Smad4KO BRAFV600E/+ mouse model present multiple phenotypes characteristic of invasion both in ex vivo and in vivo systems. Smad4KO BRAFV600E/+ tumor organoids can migrate through 3D culture and infiltrate through transwell membranes. This invasive behavior can be suppressed when SMAD4 is re-expressed in the tumor organoids. RNA-Seq analysis reveals that SMAD4 expression in organoids rapidly regulates transcripts associated with extracellular matrix and secreted proteins, suggesting that the mechanisms employed by SMAD4 to inhibit invasion are associated with regulation of extracellular matrix and secretory pathways. These findings indicate new models to study SMAD4 regulation of tumor invasion and an additional layer of complexity in the tumor-suppressive function of the SMAD4/Tgfβ pathway.

Unexpected Differences in the Speed of Non-Malignant versus Malignant Cell Migration Reveal Differential Basal Intracellular ATP Levels

Cellular locomotion is required for survival, fertility, proper embryonic development, regeneration, and wound healing. Cell migration is a major component of metastasis, which accounts for two-thirds of all solid tumor deaths. While many studies have demonstrated increased energy requirements, metabolic rates, and migration of cancer cells compared with normal cells, few have systematically compared normal and cancer cell migration as well as energy requirements side by side. Thus, we investigated how non-malignant and malignant cells migrate, utilizing several cell lines from the breast and lung. Initial screening was performed in an unbiased high-throughput manner for the ability to migrate/invade on collagen and/or Matrigel. We unexpectedly observed that all the non-malignant lung cells moved significantly faster than cells derived from lung tumors regardless of the growth media used. Given the paradigm-shifting nature of our discovery, we pursued the mechanisms that could be responsible. Neither mass, cell doubling, nor volume accounted for the individual speed and track length of the normal cells. Non-malignant cells had higher levels of intracellular ATP at premigratory-wound induction stages. Meanwhile, cancer cells also increased intracellular ATP at premigratory-wound induction, but not to the levels of the normal cells, indicating the possibility for further therapeutic investigation.

Tumour follower cells: A novel driver of leader cells in collective invasion (Review)

Collective cellular invasion in malignant tumours is typically characterized by the cooperative migration of multiple cells in close proximity to each other. Follower cells are led away from the tumour by specialized leader cells, and both cell populations play a crucial role in collective invasion. Follower cells form the main body of the migration system and depend on intercellular contact for migration, whereas leader cells indicate the direction for the entire cell population. Although collective invasion can occur in epithelial and non‑epithelial malignant neoplasms, such as medulloblastoma and rhabdomyosarcoma, the present review mainly provided an extensive analysis of epithelial tumours. In the present review, the cooperative mechanisms of contact inhibition locomotion between follower and leader cells, where follower cells coordinate and direct collective movement through physical (mechanical) and chemical (signalling) interactions, is summarised. In addition, the molecular mechanisms of follower cell invasion and metastasis during remodelling and degradation of the extracellular matrix and how chemotaxis and lateral inhibition mediate follower cell behaviour were analysed. It was also demonstrated that follower cells exhibit genetic and metabolic heterogeneity during invasion, unlike leader cells.

Phenotypically sorted highly and weakly migratory triple negative breast cancer cells exhibit migratory and metastatic commensalism

BACKGROUND

Intratumor heterogeneity is a well-established hallmark of cancer that impedes cancer research, diagnosis, and treatment. Previously, we phenotypically sorted human breast cancer cells based on migratory potential. When injected into mice, highly migratory cells were weakly metastatic and weakly migratory cells were highly metastatic. The purpose of this study was to determine whether these weakly and highly migratory cells interact with each other in vitro or in vivo.

METHODS

To assess the relationship between heterogeneity in cancer cell migration and metastatic fitness, MDA-MB-231 and SUM159PT triple negative breast cancer cells were phenotypically sorted into highly migratory and weakly migratory subpopulations and assayed separately and in a 1:1 mixture in vitro and in vivo for metastatic behaviors. Unpaired, two-tailed Student's t-tests, Mann-Whitney tests, ordinary, one-way ANOVAs, and Kruskal-Wallis H tests were performed as appropriate with p < 0.05 as the cutoff for statistical significance.

RESULTS

When highly and weakly migratory cells are co-seeded in mixed spheroids, the weakly migratory cells migrated farther than weakly migratory only spheroids. In mixed spheroids, leader-follower behavior occurred with highly migratory cells leading the weakly migratory cells in migration strands. When cell suspensions of highly migratory, weakly migratory, or a 1:1 mixture of both subpopulations were injected orthotopically into mice, both the mixed cell suspensions and weakly migratory cells showed significant distal metastasis, but the highly migratory cells did not metastasize significantly to any location. Notably, significantly more distal metastasis was observed in mice injected with the 1:1 mixture compared to either subpopulation alone.

CONCLUSIONS

This study suggests that weakly migratory cells interact with highly migratory cells in a commensal fashion resulting in increased migration and metastasis. Together, these findings indicate that cancer cell subpopulation migration ability does not correlate with metastatic potential and that cooperation between highly migratory and weakly migratory subpopulations can enhance overall metastatic fitness.

Long noncoding RNA MALAT1 is dynamically regulated in leader cells during collective cancer invasion

Cancer cells collectively invade using a leader-follower organization, but the regulation of leader cells during this dynamic process is poorly understood. Using a dual double-stranded locked nucleic acid (LNA) nanobiosensor that tracks long noncoding RNA (lncRNA) dynamics in live single cells, we monitored the spatiotemporal distribution of lncRNA during collective cancer invasion. We show that the lncRNA MALAT1 (metastasis-associated lung adenocarcinoma transcript 1) is dynamically regulated in the invading fronts of cancer cells and patient-derived spheroids. MALAT1 transcripts exhibit distinct abundance, diffusivity, and distribution between leader and follower cells. MALAT1 expression increases when a cancer cell becomes a leader and decreases when the collective migration process stops. Transient knockdown of MALAT1 prevents the formation of leader cells and abolishes the invasion of cancer cells. Taken together, our single-cell analysis suggests that MALAT1 is dynamically regulated in leader cells during collective cancer invasion.

Unraveling the Role of Epithelial-Mesenchymal Transition in Adenoid Cystic Carcinoma of the Salivary Glands: A Comprehensive Review

Salivary adenoid cystic carcinoma (SACC) is considered a challenging malignancy; it is characterized by a slow-growing nature, yet a high risk of recurrence and distant metastasis, presenting significant hurdles in its treatment and management. At present, there are no approved targeted agents available for the management of SACC and systemic chemotherapy protocols that have demonstrated efficacy remain to be elucidated. Epithelial-mesenchymal transition (EMT) is a complex process that is closely associated with tumor progression and metastasis, enabling epithelial cells to acquire mesenchymal properties, including increased mobility and invasiveness. Several molecular signaling pathways have been implicated in the regulation of EMT in SACC, and understanding these mechanisms is crucial to identifying new therapeutic targets and developing more effective treatment approaches. This manuscript aims to provide a comprehensive overview of the latest research on the role of EMT in SACC, including the molecular pathways and biomarkers involved in EMT regulation. By highlighting the most recent findings, this review offers insights into potential new therapeutic strategies that could improve the management of SACC patients, especially those with recurrent or metastatic disease.

Cadherins and catenins in cancer: connecting cancer pathways and tumor microenvironment

Cadherin-catenin complexes are integral components of the adherens junctions crucial for cell-cell adhesion and tissue homeostasis. Dysregulation of these complexes is linked to cancer development via alteration of cell-autonomous oncogenic signaling pathways and extrinsic tumor microenvironment. Advances in multiomics have uncovered key signaling events in multiple cancer types, creating a need for a better understanding of the crosstalk between cadherin-catenin complexes and oncogenic pathways. In this review, we focus on the biological functions of classical cadherins and associated catenins, describe how their dysregulation influences major cancer pathways, and discuss feedback regulation mechanisms between cadherin complexes and cellular signaling. We discuss evidence of cross regulation in the following contexts: Hippo-Yap/Taz and receptor tyrosine kinase signaling, key pathways involved in cell proliferation and growth; Wnt, Notch, and hedgehog signaling, key developmental pathways involved in human cancer; as well as TGFβ and the epithelial-to-mesenchymal transition program, an important process for cancer cell plasticity. Moreover, we briefly explore the role of cadherins and catenins in mechanotransduction and the immune tumor microenvironment.

Triple negative breast tumors contain heterogeneous cancer cells expressing distinct KRAS-dependent collective and disseminative invasion programs

Inter-patient and intra-tumoral heterogeneity complicate the identification of predictive biomarkers and effective treatments for basal triple negative breast cancer (b-TNBC). Invasion is the initiating event in metastasis and can occur by both collective and single-cell mechanisms. We cultured primary organoids from a b-TNBC genetically engineered mouse model in 3D collagen gels to characterize their invasive behavior. We observed that organoids from the same tumor presented different phenotypes that we classified as non-invasive, collective and disseminative. To identify molecular regulators driving these invasive phenotypes, we developed a workflow to isolate individual organoids from the collagen gels based on invasive morphology and perform RNA sequencing. We next tested the requirement of differentially regulated genes for invasion using shRNA knock-down. Strikingly, KRAS was required for both collective and disseminative phenotypes. We then performed a drug screen targeting signaling nodes upstream and downstream of KRAS. We found that inhibition of EGFR, MAPK/ERK, or PI3K/AKT signaling reduced invasion. Of these, ERK inhibition was striking for its ability to potently inhibit collective invasion and dissemination. We conclude that different cancer cells in the same b-TNBC tumor can express different metastatic molecular programs and identified KRAS and ERK as essential regulators of collective and single cell dissemination.

Lysyl hydroxylase LH1 promotes confined migration and metastasis of cancer cells by stabilizing Septin2 to enhance actin network

BACKGROUND

Excessive extracellular matrix deposition and increased stiffness are typical features of solid tumors such as hepatocellular carcinoma (HCC) and pancreatic ductal adenocarcinoma (PDAC). These conditions create confined spaces for tumor cell migration and metastasis. The regulatory mechanism of confined migration remains unclear.

METHODS

LC-MS was applied to determine the differentially expressed proteins between HCC tissues and corresponding adjacent tissue. Collective migration and single cell migration microfluidic devices with 6 μm-high confined channels were designed and fabricated to mimic the in vivo confined space. 3D invasion assay was created by Matrigel and Collagen I mixture treat to adherent cells. 3D spheroid formation under various stiffness environment was developed by different substitution percentage GelMA. Immunoprecipitation was performed to pull down the LH1-binding proteins, which were identified by LC-MS. Immunofluorescent staining, FRET, RT-PCR, Western blotting, FRAP, CCK-8, transwell cell migration, wound healing, orthotopic liver injection mouse model and in vivo imaging were used to evaluate the target expression and cellular phenotype.

RESULTS

Lysyl hydroxylase 1 (LH1) promoted the confined migration of cancer cells at both collective and single cell levels. In addition, LH1 enhanced cell invasion in a 3D biomimetic model and spheroid formation in stiffer environments. High LH1 expression correlated with poor prognosis of both HCC and PDAC patients, while it also promoted in vivo metastasis. Mechanistically, LH1 bound and stabilized Septin2 (SEPT2) to enhance actin polymerization, depending on the hydroxylase domain. Finally, the subpopulation with high expression of both LH1 and SEPT2 had the poorest prognosis.

CONCLUSIONS

LH1 promotes the confined migration and metastasis of cancer cells by stabilizing SEPT2 and thus facilitating actin polymerization.

Orchestration of Collective Migration and Metastasis by Tumor Cell Clusters

Metastatic dissemination has lethal consequences for cancer patients. Accruing evidence supports the hypothesis that tumor cells can migrate and metastasize as clusters of cells while maintaining contacts with one another. Collective metastasis enables tumor cells to colonize secondary sites more efficiently, resist cell death, and evade the immune system. On the other hand, tumor cell clusters face unique challenges for dissemination particularly during systemic dissemination. Here, we review recent progress toward understanding how tumor cell clusters overcome these disadvantages as well as mechanisms they utilize to gain advantages throughout the metastatic process. We consider useful models for studying collective metastasis and reflect on how the study of collective metastasis suggests new opportunities for eradicating and preventing metastatic disease.

Invadopodia enable cooperative invasion and metastasis of breast cancer cells

Invasive and non-invasive cancer cells can invade together during cooperative invasion. However, the events leading to it, role of the epithelial-mesenchymal transition and the consequences this may have on metastasis are unknown. In this study, we demonstrate that the isogenic 4T1 and 67NR breast cancer cells sort from each other in 3D spheroids, followed by cooperative invasion. By time-lapse microscopy, we show that the invasive 4T1 cells move more persistently compared to non-invasive 67NR, sorting and accumulating at the spheroid-matrix interface, a process dependent on cell-matrix adhesions and independent from E-cadherin cell-cell adhesions. Elimination of invadopodia in 4T1 cells blocks invasion, demonstrating that invadopodia requirement is limited to leader cells. Importantly, we demonstrate that cells with and without invadopodia can also engage in cooperative metastasis in preclinical mouse models. Altogether, our results suggest that a small number of cells with invadopodia can drive the metastasis of heterogeneous cell clusters.

Cooperative invasion requires the formation of invadopodia in the leader cells, and a small number of leader cells may be enough to facilitate cooperative invasion and metastasis, including non-invadopodia forming cancer cells.

Integrin α11β1 in tumor fibrosis: more than just another cancer-associated fibroblast biomarker?

There is currently an increased interest in understanding the role of the tumor microenvironment (TME) in tumor growth and progression. In this context the role of integrins in cancer-associated fibroblasts (CAFs) will need to be carefully re-evaluated. Fibroblast-derived cells are not only in the focus in tumors, but also in tissue fibrosis as well as in inflammatory conditions. The recent transcriptional profiling of what has been called "the pan-fibroblast cell lineage" in mouse and human tissues has identified novel transcriptional biomarker mRNAs encoding the secreted ECM proteins dermatopontin and collagen XV as well as the phosphatidylinositol-anchored membrane protein Pi16. Some of the genes identified in these fibroblasts scRNA-seq datasets will be useful for rigorous comparative characterizations of fibroblast-derived cell subpopulations. At the same time, it will be a challenge in the coming years to validate these transcriptional mRNA datasets at the protein-(expression) and at tissue-(distribution) levels and to find useful protein biomarker reagents that will facilitate fibroblast profiling at the cell level. In the current review we will focus on the role of the collagen-binding integrin α11β1 in CAFs, summarizing our own work as well as published datasets with information on α11 mRNA expression in selected tumors. Our experimental data suggest that α11β1 is more than just another biomarker and that it as a functional collagen receptor in the TME is playing a central role in regulating collagen assembly and matrix remodeling, which in turn impact tumor growth and metastasis.

Proteolytic and mechanical remodeling of the extracellular matrix by invadopodia in cancer

Cancer invasion and metastasis require remodeling of the adjacent extracellular matrix (ECM). In this mini review, we will cover the mechanisms of proteolytic degradation and the mechanical remodeling of the ECM by cancer cells, with a focus on invadopodia. Invadopodia are membrane protrusions unique to cancer cells, characterized by an actin core and by the focal degradation of ECM via matrix metalloproteases (MMPs). While ECM can also be remodeled, at lower levels, by focal adhesions, or internal collagen digestion, invadopodia are now recognized as the major mechanism for MMP-dependent pericellular ECM degradation by cancer cells. Recent evidence suggests that the completion of epithelial-mesenchymal transition may be dispensable for invadopodia and metastasis, and that invadopodia are required not only for mesenchymal, single cell invasion, but also for collective invasion. During collective invasion, invadopodia was then shown to be located in leader cells, allowing follower cells to move via cooperation. Collectively, this suggests that invadopodia function may be a requirement not only for later steps of metastasis, but also for early invasion of epithelial cells into the stromal tissue. Over the last decade, invadopodia studies have transitioned into in 3D andin vivosettings, leading to the confirmation of their essential role in metastasis in preclinical animal models. In summary, invadopodia may hold a great potential for individual risk assessment as a prognostic marker for metastasis, as well as a therapeutic target.

Autocrine pro-legumain promotes breast cancer metastasis via binding to integrin αvβ3

Tumor metastasis is the leading cause of cancer-associated mortality. Unfortunately, the underlying mechanism of metastasis is poorly understood. Expression of legumain (LGMN), an endo-lysosomal cysteine protease, positively correlates with breast cancer metastatic progression and poor prognosis. Here, we report that LGMN is secreted in the zymogen form by motile breast cancer cells. Through binding to cell surface integrin αvβ3 via an RGD motif, the autocrine pro-LGMN activates FAK-Src-RhoA signaling in cancer cells and promotes cancer cell migration and invasion independent of LGMN protease activity. Either silencing LGMN expression or mutationally abolishing pro-LGMN‒αvβ3 interaction significantly inhibits cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Finally, we developed a monoclonal antibody against LGMN RGD motif, which blocks pro-LGMN‒αvβ3 binding, and effectively suppresses cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Thus, disruption of pro-LGMN‒integrin αvβ3 interaction may be a potentially promising strategy for treating breast cancer metastasis.

Tumour invasion and dissemination

Activating invasion and metastasis are one of the primary hallmarks of cancer, the latter representing the leading cause of death in cancer patients. Whilst many advances in this area have been made in recent years, the process of cancer dissemination and the underlying mechanisms governing invasion are still poorly understood. Cancer cells exhibit multiple invasion strategies, including switching between modes of invasion and plasticity in response to therapies, surgical interventions and environmental stimuli. The ability of cancer cells to switch migratory modes and their inherent plasticity highlights the critical challenge preventing the successful design of cancer and anti-metastatic therapies. This mini-review presents current knowledge on the critical models of tumour invasion and dissemination. We also discuss the current issues surrounding current treatments and arising therapeutic opportunities. We propose that the establishment of novel approaches to study the key biological mechanisms underlying the metastatic cascade is critical in finding novel targets that could ultimately lead to complete inhibition of cancer cell invasion and dissemination.

Identifying drivers of breast cancer metastasis in progressively invasive subpopulations of zebrafish-xenografted MDA-MB-231

Cancer metastasis is the primary cause of the high mortality rate among human cancers. Efforts to identify therapeutic agents targeting cancer metastasis frequently fail to demonstrate efficacy in clinical trials despite strong preclinical evidence. Until recently, most preclinical studies used mouse models to evaluate anti-metastatic agents. Mouse models are time-consuming and expensive. In addition, an important drawback is that mouse models inadequately model the early stages of metastasis which plausibly leads to the poor correlation with clinical outcomes.

Here, we report an in vivo model based on xenografted zebrafish embryos where we select for progressively invasive subpopulations of MDA-MB-231 breast cancer cells. A subpopulation analogous to circulating tumor cells found in human cancers was selected by injection of MDA-MB-231 cells into the yolk sacs of 2 days post-fertilized zebrafish embryos and selecting cells that migrated to the tail. The selected subpopulation derived from MDA-MB-231 cells were increasingly invasive in zebrafish. Isolation of these subpopulations and propagation in vitro revealed morphological changes consistent with activation of an epithelial-mesenchymal transition program. Differential gene analysis and knockdown of genes identified gene-candidates (DDIT4, MT1X, CTSD, and SERPINE1) as potential targets for anti-metastasis therapeutics. Furthermore, RNA-splicing analysis reinforced the importance of BIRC5 splice variants in breast cancer metastasis. This is the first report using zebrafish to isolate and expand progressively invasive populations of human cancer cells. The model has potential applications in understanding the metastatic process, identification and/or development of therapeutics that specifically target metastatic cells and formulating personalized treatment strategies for individual cancer patients.

XRN2 Is Required for Cell Motility and Invasion in Glioblastomas

One of the major obstacles in treating brain cancers, particularly glioblastoma multiforme, is the occurrence of secondary tumor lesions that arise in areas of the brain and are inoperable while obtaining resistance to current therapeutic agents. Thus, gaining a better understanding of the cellular factors that regulate glioblastoma multiforme cellular movement is imperative. In our study, we demonstrate that the 5'-3' exoribonuclease XRN2 is important to the invasive nature of glioblastoma. A loss of XRN2 decreases cellular speed, displacement, and movement through a matrix of established glioblastoma multiforme cell lines. Additionally, a loss of XRN2 abolishes tumor formation in orthotopic mouse xenograft implanted with G55 glioblastoma multiforme cells. One reason for these observations is that loss of XRN2 disrupts the expression profile of several cellular factors that are important for tumor invasion in glioblastoma multiforme cells. Importantly, XRN2 mRNA and protein levels are elevated in glioblastoma multiforme patient samples. Elevation in XRN2 mRNA also correlates with poor overall patient survival. These data demonstrate that XRN2 is an important cellular factor regulating one of the major obstacles in treating glioblastomas and is a potential molecular target that can greatly enhance patient survival.

The changing role of natural killer cells in cancer metastasis

Natural killer (NK) cells are innate immune cells that are critical to the body's antitumor and antimetastatic defense. As such, novel therapies are being developed to utilize NK cells as part of a next generation of immunotherapies to treat patients with metastatic disease. Therefore, it is essential for us to examine how metastatic cancer cells and NK cells interact with each other throughout the metastatic cascade. In this Review, we highlight the recent body of work that has begun to answer these questions. We explore how the unique biology of cancer cells at each stage of metastasis alters fundamental NK cell biology, including how cancer cells can evade immunosurveillance and co-opt NK cells into cells that promote metastasis. We also discuss the translational potential of this knowledge.

Insights into the Steps of Breast Cancer-Brain Metastases Development: Tumor Cell Interactions with the Blood-Brain Barrier

Brain metastases (BM) represent a growing problem for breast cancer (BC) patients. Recent studies have demonstrated a strong impact of the BC molecular subtype on the incidence of BM development. This study explores the interaction between BC cells of different molecular subtypes and the blood–brain barrier (BBB). We compared the ability of BC cells of different molecular subtypes to overcome several steps (adhesion to the brain endothelium, disruption of the BBB, and invasion through the endothelial layer) during cerebral metastases formation, in vitro as well as in vivo. Further, the impact of these cells on the BBB was deciphered at the molecular level by transcriptome analysis of the triple-negative (TNBC) cells themselves as well as of hBMECs after cocultivation with BC cell secretomes. Compared to luminal BC cells, TNBC cells have a greater ability to influence the BBB in vitro and consequently develop BM in vivo. The brain-seeking subline and parental TNBC cells behaved similarly in terms of adhesion, whereas the first showed a stronger impact on the brain endothelium integrity and increased invasive ability. The comparative transcriptome revealed potential brain-metastatic-specific key regulators involved in the aforementioned processes, e.g., the angiogenesis-related factors TNXIP and CXCL1. In addition, the transcriptomes of the two TNBC cell lines strongly differed in certain angiogenesis-associated factors and in several genes related to cell migration and invasion. Based on the present study, we hypothesize that the tumor cell’s ability to disrupt the BBB via angiogenesis activation, together with increased cellular motility, is required for BC cells to overcome the BBB and develop brain metastases.

The Expression Pattern of Hypoxia-Related Genes Predicts the Prognosis and Mediates Drug Resistance in Colorectal Cancer

Background: Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths worldwide. However, due to the heterogeneity of CRC, the clinical therapy outcomes differ among patients. There is a need to identify predictive biomarkers to efficiently facilitate CRC treatment and prognosis.

Methods: The expression profiles from Gene Expression Omnibus (GEO) database were used to identify cancer hallmarks associated with CRC outcomes. An accurate gene signature based on the prognosis related cancer hallmarks was further constructed.

Results: Hypoxia was identified to be the primary factor that could influence CRC outcomes. Sixteen hypoxia-related genes were selected to construct a risk gene signature (HGS) associated with individuals’ prognosis, which was validated in three independent cohorts. Further, stromal and immune cells in tumor microenvironment (TME) were found to be associated with hypoxia. Finally, among the 16 hypoxia-related genes, six genes (DCBLD2, PLEC, S100A11, PLAT, PPAP2B and LAMC2) were identified as the most attributable ones to drug resistance.

Conclusion: HGS can accurately predict CRC prognosis. The expression of the drug resistance-related genes is critical in CRC treatment decision-making.

The biophysics of cancer: emerging insights from micro- and nanoscale tools

Cancer is a complex and dynamic disease that is aberrant both biologically and physically. There is growing appreciation that physical abnormalities with both cancer cells and their microenvironment that span multiple length scales are important drivers for cancer growth and metastasis. The scope of this review is to highlight the key advancements in micro- and nano-scale tools for delineating the cause and consequences of the aberrant physical properties of tumors. We focus our review on three important physical aspects of cancer: 1) solid mechanical properties, 2) fluid mechanical properties, and 3) mechanical alterations to cancer cells. Beyond posing physical barriers to the delivery of cancer therapeutics, these properties are also known to influence numerous biological processes, including cancer cell invasion and migration leading to metastasis, and response and resistance to therapy. We comment on how micro- and nanoscale tools have transformed our fundamental understanding of the physical dynamics of cancer progression and their potential for bridging towards future applications at the interface of oncology and physical sciences.

Epithelial to Mesenchymal Transition: Key Regulator of Pancreatic Ductal Adenocarcinoma Progression and Chemoresistance

Simple Summary

Pancreatic ductal adenocarcinoma’s (PDAC) dismal prognosis is associated with its aggressive biological behavior and resistance to chemotherapy. Epithelial to mesenchymal transition (EMT) has been recognized as a key driver of PDAC progression and development of drug resistance. EMT is a transient and reversible process leading to transdifferentiation of epithelial cells into a more mesenchymal phenotype. It is regulated by multiple signaling pathways that control the activity of a transcription factors network. Activation of EMT in pre-invasive stages of PDAC has been accused for early dissemination. Furthermore, it contributes to the development of intratumoral heterogeneity and drug resistance. This review summarizes the available data regarding signaling networks regulating EMT and describes the integral role of EMT in different aspects of PDAC pathogenesis.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignancies, characterized by aggressive biological behavior and a lack of response to currently available chemotherapy. Emerging evidence has identified epithelial to mesenchymal transition (EMT) as a key driver of PDAC progression and a central regulator in the development of drug resistance. EMT is a reversible transdifferentiation process controlled by complex interactions between multiple signaling pathways such as TGFb, Wnt, and Notch, which converge to a network of specific transcription factors. Activation of EMT transcriptional reprogramming converts cancer cells of epithelial differentiation into a more mesenchymal phenotypic state. EMT occurrence in pre-invasive pancreatic lesions has been implicated in early PDAC dissemination. Moreover, cancer cell phenotypic plasticity driven by EMT contributes to intratumoral heterogeneity and drug tolerance and is mechanistically associated with the emergence of cells exhibiting cancer stem cells (CSCs) phenotype. In this review we summarize the available data on the signaling cascades regulating EMT and the molecular isnteractions between pancreatic cancer and stromal cells that activate them. In addition, we provide a link between EMT, tumor progression, and chemoresistance in PDAC.

Integration of Epigenetic Mechanisms into Non-Genotoxic Carcinogenicity Hazard Assessment: Focus on DNA Methylation and Histone Modifications

Epigenetics involves a series of mechanisms that entail histone and DNA covalent modifications and non-coding RNAs, and that collectively contribute to programing cell functions and differentiation. Epigenetic anomalies and DNA mutations are co-drivers of cellular dysfunctions, including carcinogenesis. Alterations of the epigenetic system occur in cancers whether the initial carcinogenic events are from genotoxic (GTxC) or non-genotoxic (NGTxC) carcinogens. NGTxC are not inherently DNA reactive, they do not have a unifying mode of action and as yet there are no regulatory test guidelines addressing mechanisms of NGTxC. To fil this gap, the Test Guideline Programme of the Organisation for Economic Cooperation and Development is developing a framework for an integrated approach for the testing and assessment (IATA) of NGTxC and is considering assays that address key events of cancer hallmarks. Here, with the intent of better understanding the applicability of epigenetic assays in chemical carcinogenicity assessment, we focus on DNA methylation and histone modifications and review: (1) epigenetic mechanisms contributing to carcinogenesis, (2) epigenetic mechanisms altered following exposure to arsenic, nickel, or phenobarbital in order to identify common carcinogen-specific mechanisms, (3) characteristics of a series of epigenetic assay types, and (4) epigenetic assay validation needs in the context of chemical hazard assessment. As a key component of numerous NGTxC mechanisms of action, epigenetic assays included in IATA assay combinations can contribute to improved chemical carcinogen identification for the better protection of public health.

Decoding leader cells in collective cancer invasion

Collective cancer invasion with leader-follower organization is increasingly recognized as a predominant mechanism in the metastatic cascade. Leader cells support cancer invasion by creating invasion tracks, sensing environmental cues and coordinating with follower cells biochemically and biomechanically. With the latest developments in experimental and computational models and analysis techniques, the range of specific traits and features of leader cells reported in the literature is rapidly expanding. Yet, despite their importance, there is no consensus on how leader cells arise or their essential characteristics. In this Perspective, we propose a framework for defining the essential aspects of leader cells and provide a unifying perspective on the varying cellular and molecular programmes that are adopted by each leader cell subtype to accomplish their functions. This Perspective can lead to more effective strategies to interdict a major contributor to metastatic capability.

Epithelial plasticity, epithelial-mesenchymal transition, and the TGF-β family

Epithelial cells repress epithelial characteristics and elaborate mesenchymal characteristics to migrate to other locations and acquire new properties. Epithelial plasticity responses are directed through cooperation of signaling pathways, with TGF-β and TGF-β-related proteins playing prominent instructive roles. Epithelial-mesenchymal transitions (EMTs) directed by activin-like molecules, bone morphogenetic proteins, or TGF-β regulate metazoan development and wound healing and drive fibrosis and cancer progression. In carcinomas, diverse EMTs enable stem cell generation, anti-cancer drug resistance, genomic instability, and localized immunosuppression. This review discusses roles of TGF-β and TGF-β-related proteins, and underlying molecular mechanisms, in epithelial plasticity in development and wound healing, fibrosis, and cancer.

Context-Dependent Roles of Claudins in Tumorigenesis

The barrier and fence functions of the claudin protein family are fundamental to tissue integrity and human health. Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation. Studies have uncovered that claudins engage in nearly all aspects of tumor biology and steps of tumor development, suggesting their promise as targets for treatment or biomarkers for diagnosis and prognosis. However, claudins can be either tumor promoters or tumor suppressors depending on the context, which emphasizes the importance of taking various factors, including organ type, environmental context and genetic confounders, into account when studying the biological functions and targeting of claudins in cancer. This review discusses the complicated roles and intrinsic and extrinsic determinants of the context-specific effects of claudins in cancer.

Chemokines orchestrate tumor cells and the microenvironment to achieve metastatic heterogeneity

Chemokines, a subfamily of the cell cytokines, are low molecular weight proteins known to induce chemotaxis in leukocytes in response to inflammatory and pathogenic signals. A plethora of literature demonstrates that chemokines and their receptors regulate tumor progression and metastasis. With these diverse functionalities, chemokines act as a fundamental link between the tumor cells and their microenvironment. Recent studies demonstrate that the biology of chemokines and their receptor in metastasis is complex as numerous chemokines are involved in regulating site-specific tumor growth and metastasis. Successful treatment of disseminated cancer is a significant challenge. The most crucial problem for treating metastatic cancer is developing therapy regimes capable of overcoming heterogeneity problems within primary tumors and among metastases and within metastases (intralesional). This heterogeneity of malignant tumor cells can be related to metastatic potential, response to chemotherapy or specific immunotherapy, and many other factors. In this review, we have emphasized the role of chemokines in the process of metastasis and metastatic heterogeneity. Individual chemokines may not express the full potential to address metastatic heterogeneity, but chemokine networks need exploration. Understanding the interplay between chemokine-chemokine receptor networks between the tumor cells and their microenvironment is a novel approach to overcome the problem of metastatic heterogeneity. Recent advances in the understanding of chemokine networks pave the way for developing a potential targeted therapeutic strategy to treat metastatic cancer.

A Pipeline for Integrated Theory and Data-Driven Modeling of Biomedical Data

Genome sequencing technologies have the potential to transform clinical decision making and biomedical research by enabling high-throughput measurements of the genome at a granular level. However, to truly understand mechanisms of disease and predict the effects of medical interventions, high-throughput data must be integrated with demographic, phenotypic, environmental, and behavioral data from individuals. Further, effective knowledge discovery methods must infer relationships between these data types. We recently proposed a pipeline (CausalMGM) to achieve this. CausalMGM uses probabilistic graphical models to infer the relationships between variables in the data; however, CausalMGM's graphical structure learning algorithm can only handle small datasets efficiently. We propose a new methodology (piPref-Div) that selects the most informative variables for CausalMGM, enabling it to scale. We validate the efficacy of piPref-Div against other feature selection methods and demonstrate how the use of the full pipeline improves breast cancer outcome prediction and provides biologically interpretable views of gene expression data.

AXL Is a Key Factor for Cell Plasticity and Promotes Metastasis in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA), a leading cause of cancer-related death in the United States, has a high metastatic rate, and is associated with persistent immune suppression. AXL, a member of the TAM (TYRO3, AXL, MERTK) receptor tyrosine kinase family, is a driver of metastasis and immune suppression in multiple cancer types. Here we use single-cell RNA-sequencing to reveal that AXL is expressed highly in tumor cells that have a mesenchymal-like phenotype and that AXL expression correlates with classic markers of epithelial-to-mesenchymal transition. We demonstrate that AXL deficiency extends survival, reduces primary and metastatic burden, and enhances sensitivity to gemcitabine in an autochthonous model of PDA. PDA in AXL-deficient mice displayed a more differentiated histology, higher nucleoside transporter expression, and a more active immune microenvironment compared with PDA in wild-type mice. Finally, we demonstrate that AXL-positive poorly differentiated tumor cells are critical for PDA progression and metastasis, emphasizing the potential of AXL as a therapeutic target in PDA. IMPLICATIONS: These studies implicate AXL as a marker of undifferentiated PDA cells and a target for therapy.

Molecular features and gene expression signature of metastatic colorectal cancer (Review)

Uncontrollable metastatic outgrowth process is the leading cause of mortality worldwide, even in the case of colorectal cancer. Colorectal cancer (CRC) accounts for approximately 10% of all annually diagnosed cancers and 50% of CRC patients will develop metastases in the course of disease. Most patients with metastatic CRC have incurable disease. Even if patients undergo resection of liver metastases, the 5‑year survival rate ranges from 25 to 58%. Next‑generation sequencing of tumour specimens from large colorectal cancer patient cohorts has led to major advances in elucidating the genomic landscape of these tumours and paired metastases. The expression profiles of primary CRC and their metastatic lesions at both the gene and pathway levels were compared and led to the selection of early driver genes responsible for carcinogenesis and metastasis‑specific genes that increased the metastatic process. The genetic, transcriptional and epigenetic alteration encoded by these genes and their combination influence many pivotal signalling pathways, enabling the dissemination and outgrowth in distant organs. Therapeutic regimens affecting several different active pathways may have important implications for therapeutic efficacy.

Targeting PVT1 Exon 9 Re-Expresses Claudin 4 Protein and Inhibits Migration by Claudin-Low Triple Negative Breast Cancer Cells

PVT1 is a long non-coding RNA transcribed from a gene located at the 8q24 chromosomal region that has been implicated in multiple cancers including breast cancer (BC). Amplification of the 8q24 chromosomal region is a common event in BC and is associated with poor clinical outcomes. Claudin-low (CL) triple negative breast cancer (TNBC) is a subtype of BC with a particularly dismal outcome. We assessed PVT1 exon 9 expression in the T47D estrogen receptor positive BC cell line, and in the MDA MB 468 and MDA MB 231 TNBC cell lines, followed by the assessment of the expression of claudins 1, 3, 4 and 7, in MDA MB 468 and MDA MB 231 (TNBC) cells. We found that MDA MB 231 TNBC cells significantly express less claudin 1, 3, 4, and 7 than MDA MB 468 TNBC cells. PVT1 exon 9 is significantly upregulated in MDA MB 231 CL TNBC cells, and significantly downregulated in MDA MB 468 claudin high (CH) TNBC cells, in comparison to T47D estrogen receptor positive BC cells. We then analyzed the functional consequences of siRNA targeting of PVT1 exon 9 expression in the MDA MB 231 CL TNBC cells. Notably, siRNA targeting of PVT1 exon 9 expression in the MDA MB 231 CL TNBC cells led to a significant reduction in migration and the re-expression of claudin 4. Taken together, our data indicate that PVT1 exon 9 regulates claudin 4 expression and migration in CL TNBC cells, and may have clinical implications in CL TNBC.

Modelling Cell Invasion: A Review of What JD Murray and the Embryo Can Teach Us

Cell invasion and cell plasticity are critical to human development but are also striking features of cancer metastasis. By distributing a multipotent cell type from a place of birth to distal locations, the vertebrate embryo builds organs. In comparison, metastatic tumor cells often acquire a de-differentiated phenotype and migrate away from a primary site to inhabit new microenvironments, disrupting normal organ function. Countless observations of both embryonic cell migration and tumor metastasis have demonstrated complex cell signaling and interactive behaviors that have long confounded scientist and clinician alike. James D. Murray realized the important role of mathematics in biology and developed a unique strategy to address complex biological questions such as these. His work offers a practical template for constructing clear, logical, direct and verifiable models that help to explain complex cell behaviors and direct new experiments. His pioneering work at the interface of development and cancer made significant contributions to glioblastoma cancer and embryonic pattern formation using often simple models with tremendous predictive potential. Here, we provide a brief overview of advances in cell invasion and cell plasticity using the embryonic neural crest and its ancestral relationship to aggressive cancers that put into current context the timeless aspects of his work.

Dll4/Notch1 signalling pathway is required in collective invasion of salivary adenoid cystic carcinoma

High expression of δ‑like ligand 4 (Dll4) is reportedly related to the invasion, metastasis, and clinical prognosis of various malignant tumours. Our previous study revealed that collective cell invasion was a common pattern in salivary adenoid cystic carcinoma (SACC). However, the roles of the Dll4/Notch1 signalling pathway in the collective invasion of SACC remain unclear. The present study revealed that Dll4 expression was higher at the invasive front of SACC, and that this upregulation was associated with solid tumour type, high TNM grade, and high rates of metastasis and recurrence. Furthermore, the expression levels of Notch1 and Dll4 were positively correlated at the invasive front, and a three‑dimensional (3D) culture model revealed that leader cells showed high expression of Dll4, while follower cells showed high expression of Notch1. Moreover, silencing of Dll4 expression using small interfering RNA reduced the migration, invasion, and collective invasion of SACC cells, and these abilities were rescued by Notch1 overexpression. Finally, SACC collective invasion was increased via the Dll4/Notch1 signalling pathway in experiments that involved a stiff 3D gel, hypoxia and co‑culture with human endothelial cells. These findings indicated that the Dll4/Notch1 signalling pathway may be involved in the collective invasion of SACC, which may help to provide possible targets for the treatment of SACC.

Metastasis: crosstalk between tissue mechanics and tumour cell plasticity

Despite the fact that different genetic programmes drive metastasis of solid tumours, the ultimate outcome is the same: tumour cells are empowered to pass a series of physical hurdles to escape the primary tumour and disseminate to other organs. Epithelial-to-mesenchymal transition (EMT) has been proposed to drive the detachment of individual cells from primary tumour masses and facilitate the subsequent establishment of metastases in distant organs. However, this concept has been challenged by observations from pathologists and from studies in animal models, in which partial and transient acquisition of mesenchymal traits is seen but tumour cells travel collectively rather than as individuals. In this review, we discuss how crosstalk between a hybrid E/M state and variations in the mechanical aspects of the tumour microenvironment can provide tumour cells with the plasticity required for strategies to navigate surrounding tissues en route to dissemination. Targeting such plasticity provides therapeutic opportunities to combat metastasis.

Transitional dynamics of cancer stem cells in invasion and metastasis

At the onset, few cancer cells amidst the tumor bulk, identified as cancer stem cells (CSCs) or early disseminated cancer cells (eDCCs) are capable of survival post conventional therapy and persist as minimal residual disease (MRD). Metastatic subclones emerge both early and late in the life of primary tumor ensuing an ongoing regional clonal evolution of progenitor cells in metastatic and primary tumors. In the last decade, multiple studies proposed various identities of stem-like cells that undergo transitions to adapt to the changing microenvironment as the disease progresses. This review advocates with substantial evidence the dynamic model of tumor propagation by exploring the specific cell types, reversible phenotypic plasticity between the tumorigenic leader seeds and the supporting follower cancer cells both in circulation and in solid tissue to accurately decipher tumor promoting clones and its role in metastatic dissemination and tumor re-growth. (142 words).

miR614 Expression Enhances Breast Cancer Cell Motility

Using a data driven analysis of a high-content screen, we have uncovered new regulators of epithelial-to-mesenchymal transition (EMT) induced cell migration. Our results suggest that increased expression of miR614 can alter cell intrinsic gene expression to enhance single cell and collective migration in multiple contexts. Interestingly, miR614 specifically increased the expression of the EMT transcription factor Slug while not altering existing epithelial character or inducing other canonical EMT regulatory factors. Analysis of two different cell lines identified a set of genes whose expression is altered by the miR614 through direct and indirect mechanisms. Prioritization driven by functional testing of 25 of the miR614 suppressed genes uncovered the mitochondrial small GTPase Miro1 and the transmembrane protein TAPT1 as miR614 suppressed genes that inhibit migration. Notably, the suppression of either Miro1 or TAPT1 was sufficient to increase Slug expression and the rate of cell migration. Importantly, reduced TAPT1 expression correlated with an increased risk of relapse in breast cancer patients. Together, our results reveal how increased miR614 expression and the suppression of TAPT1 and Miro1 modulate the EMT state and migratory properties of breast cancer cells.

Tactics of cancer invasion: solitary and collective invasion

Much attention has been paid on the mechanism of cancer invasion from the viewpoint of the behaviour of individual cancer cells. On the other hand, histopathological analyses of specimens from cancer patients and of cancer invasion model animals have revealed that cancer cells often exhibit collective invasion, characterized by sustained cell-to-cell adhesion and polarized invasion as cell clusters. Interestingly, it has recently become evident that during collective invasion of cancer cells, the cells localized at invasion front (leader cells) and the cells following them (follower cells) exhibit distinct cellular characteristics, and that there exist the cells expressing representative proteins related to both epithelial and mesenchymal properties simultaneously, designated as hybrid epithelial-to-mesenchymal transition (EMT)-induced cells, in cancer tissue. Furthermore, the findings that cells adopted in hybrid EMT state form clusters and show collective invasion in vitro emphasize an importance of hybrid EMT-induced cells in collective cancer invasion. In this article, we overview recent findings of the mechanism underlying collective invasion of cancer cells and discuss the possibility of controlling cancer invasion and metastasis by targeting this process.

A novel prognostic two-gene signature for triple negative breast cancer

The absence of a robust risk stratification tool for triple negative breast cancer (TNBC) underlies imprecise and nonselective treatment of these patients with cytotoxic chemotherapy. This study aimed to interrogate transcriptomes of TNBC resected samples using next generation sequencing to identify novel biomarkers associated with disease outcomes. A subset of cases (n = 112) from a large, well-characterized cohort of primary TNBC (n = 333) were subjected to RNA-sequencing. Reads were aligned to the human reference genome (GRCH38.83) using the STAR aligner and gene expression quantified using HTSEQ. We identified genes associated with distant metastasis-free survival and breast cancer-specific survival by applying supervised artificial neural network analysis with gene selection to the RNA-sequencing data. The prognostic ability of these genes was validated using the Breast Cancer Gene-Expression Miner v4. 0 and Genotype 2 outcome datasets. Multivariate Cox regression analysis identified a prognostic gene signature that was independently associated with poor prognosis. Finally, we corroborated our results from the two-gene prognostic signature by their protein expression using immunohistochemistry. Artificial neural network identified two gene panels that strongly predicted distant metastasis-free survival and breast cancer-specific survival. Univariate Cox regression analysis of 21 genes common to both panels revealed that the expression level of eight genes was independently associated with poor prognosis (p < 0.05). Adjusting for clinicopathological factors including patient's age, grade, nodal stage, tumor size, and lymphovascular invasion using multivariate Cox regression analysis yielded a two-gene prognostic signature (ACSM4 and SPDYC), which was associated with poor prognosis (p < 0.05) independent of other prognostic variables. We validated the protein expression of these two genes, and it was significantly associated with patient outcome in both independent and combined manner (p < 0.05). Our study identifies a prognostic gene signature that can predict prognosis in TNBC patients and could potentially be used to guide the clinical management of TNBC patients.

Coexpression Module Construction by Weighted Gene Coexpression Network Analysis and Identify Potential Prognostic Markers of Breast Cancer

Background: Breast cancer (BC) is a malignant tumor with the highest morbidity among women, disrupting millions of their lives worldwide each year. However, the molecular mechanisms underlying remain unclear. Methods: The RNA-Sequencing and clinical data of BC patients from The Cancer Genome Atlas (TCGA) database were analyzed by weighted gene coexpression network analysis (WGCNA). Additionally, coexpressed modules were used to detect their correlation with the clinical traits of BC. Next, nodes of the most significant coexpression modules were used for Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, mRNA-lncRNA coexpression network and survival analyses. Results: In total, 2056 differentially expressed mRNAs (DEmRNAs) and 297 differentially expressed lncRNAs (DElncRNAs) were identified and subjected to WGCNA analysis, and 12 coexpression modules were generated. The top five significant modules (turquoise, green, red, brown, and blue modules) were related to one or more clinical traits of BC. In particular, the turquoise and green modules were chosen for further analysis. Next, by lncRNA-mRNA coexpression analysis of the turquoise and green modules, 12 DEmRNAs and 2 DElncRNAs were identified as hub nodes. The lncRNA-associated mRNAs of the networks were commonly related to several cancer-related pathways. Moreover, these networks also revealed central roles for RP11-389C8.2 and TGFBR2 in the turquoise module and MYLK, KIT, and RP11-394O4.5 in the green module. Furthermore, 16 DEmRNAs and 3 DElncRNAs in these two modules were significantly correlated with the overall survival of BC patients. Conclusions: The authors' study identified some prognostic biomarkers that might play important roles in the development and treatment of BC. In particular, lncRNAs AC016995.3, RP1-193H18.2, and RP11-166D19.1 were novel biomarkers for BC.

Pancreatic Adenocarcinoma Invasiveness and the Tumor Microenvironment: From Biology to Clinical Trials

Pancreatic adenocarcinoma (PDAC) originates in the glandular compartment of the exocrine pancreas. Histologically, PDAC tumors are characterized by a parenchyma that is embedded in a particularly prominent stromal component or desmoplastic stroma. The unique characteristics of the desmoplastic stroma shape the microenvironment of PDAC and modulate the reciprocal interactions between cancer and stromal cells in ways that have profound effects in the pathophysiology and treatment of this disease. Here, we review some of the most recent findings regarding the regulation of PDAC cell invasion by the unique microenvironment of this tumor, and how new knowledge is being translated into novel therapeutic approaches.

Collective invasion induced by an autocrine purinergic loop through connexin-43 hemichannels

Progression of epithelial cancers predominantly proceeds by collective invasion of cell groups with coordinated cell-cell junctions and multicellular cytoskeletal activity. Collectively invading breast cancer cells express the gap junction protein connexin-43 (Cx43), yet whether Cx43 regulates collective invasion remains unclear. We here show that Cx43 mediates gap-junctional coupling between collectively invading breast cancer cells and, via hemichannels, adenosine nucleotide/nucleoside release into the extracellular space. Using molecular interference and rescue strategies, we identify that Cx43 hemichannel function, but not intercellular communication, induces leader cell activity and collective migration through the engagement of the adenosine receptor 1 (ADORA1) and AKT signaling. Accordingly, pharmacological inhibition of ADORA1 or AKT signaling caused leader cell collapse and halted collective invasion. ADORA1 inhibition further reduced local invasion of orthotopic mammary tumors in vivo, and joint up-regulation of Cx43 and ADORA1 in breast cancer patients correlated with decreased relapse-free survival. This identifies autocrine purinergic signaling, through Cx43 hemichannels, as a critical pathway in leader cell function and collective invasion.

A systems biology approach to discovering pathway signaling dysregulation in metastasis

Total metastatic burden is the primary cause of death for many cancer patients. While the process of metastasis has been studied widely, much remains to be understood. Moreover, few agents have been developed that specifically target the major steps of the metastatic cascade. Many individual genes and pathways have been implicated in metastasis but a holistic view of how these interact and cooperate to regulate and execute the process remains somewhat rudimentary. It is unclear whether all of the signaling features that regulate and execute metastasis are yet fully understood. Novel features of a complex system such as metastasis can often be discovered by taking a systems-based approach. We introduce the concepts of systems modeling and define some of the central challenges facing the application of a multidisciplinary systems-based approach to understanding metastasis and finding actionable targets therein. These challenges include appreciating the unique properties of the high-dimensional omics data often used for modeling, limitations in knowledge of the system (metastasis), tumor heterogeneity and sampling bias, and some of the issues key to understanding critical features of molecular signaling in the context of metastasis. We also provide a brief introduction to integrative modeling that focuses on both the nodes and edges of molecular signaling networks. Finally, we offer some observations on future directions as they relate to developing a systems-based model of the metastatic cascade.

CD147 promotes collective invasion through cathepsin B in hepatocellular carcinoma

Background

Mounting evidence suggests that solid tumors display the features of collective invasion, however, the molecular mechanisms are far from clear. This study aims to verify the role and the underlying mechanisms of CD147 in collective invasion in hepatocellular carcinoma.

Methods

Immunostaining was used to analyze human hepatocellular carcinoma specimens and three-dimensional cultures. Three-dimensional invasion model was established to mimic in vivo invasion. RNA-sequencing was used to identify downstream effectors.

Results

Human hepatocellular carcinoma underwent collective invasion and CD147 was observed to be upregulated at the invasive front of tumor cell groups. CD147 was demonstrated to promote collective invasion using the modified three-dimensional invasion model, which recapitulated the main features of collective invasion. Through transcriptome analysis and enzyme activity assay, we found that CD147 enhanced cathepsin B expression and activity. Upregulated cathepsin B in hepatocellular carcinoma cells facilitated migration and invasion, which mediated CD147-induced invasive phenotype in hepatocellular carcinoma. In terms of mechanism, we found that CD147 promoted cathepsin B transcription by activating β-catenin signaling as a result of reduced GSK-3β expression. Furthermore, we found that elevated expression of CD147 as well as cathepsin B were correlated with poor prognosis in patients with hepatocellular carcinoma.

Conclusions

CD147 promotes hepatocellular carcinoma cells collective invasion via upregulating cathepsin B expression and targeting CD147 would be valuable for the development of novel therapeutic modalities against invasion and metastasis of cancer.