Angiopellosis as an Alternative Mechanism of Cell Extravasation

The Role of Circulating Tumor Cells as a Liquid Biopsy for Cancer: Advances, Biology, Technical Challenges, and Clinical Relevance

Cancer remains a leading cause of mortality worldwide, with metastasis significantly contributing to its lethality. The metastatic spread of tumor cells, primarily through the bloodstream, underscores the importance of circulating tumor cells (CTCs) in oncological research. As a critical component of liquid biopsies, CTCs offer a non-invasive and dynamic window into tumor biology, providing invaluable insights into cancer dissemination, disease progression, and response to treatment. This review article delves into the recent advancements in CTC research, highlighting their emerging role as a biomarker in various cancer types. We explore the latest technologies and methods for CTC isolation and detection, alongside novel approaches to characterizing their biology through genomics, transcriptomics, proteomics, and epigenetic profiling. Additionally, we examine the clinical implementation of these findings, assessing how CTCs are transforming the landscape of cancer diagnosis, prognosis, and management. By offering a comprehensive overview of current developments and potential future directions, this review underscores the significance of CTCs in enhancing our understanding of cancer and in shaping personalized therapeutic strategies, particularly for patients with metastatic disease.

A model for the dissemination of circulating tumour cell clusters involving platelet recruitment and a plastic switch between cooperative and individual behaviours

BACKGROUND

In spite of extensive research, cancer remains a major health problem worldwide. As cancer progresses, cells acquire traits that allow them to disperse and disseminate to distant locations in the body - a process known as metastasis. While in the vasculature, these cells are referred to as circulating tumour cells (CTCs) and can manifest either as single cells or clusters of cells (i.e., CTC clusters), with the latter being the most aggressive. The increased metastatic potential of CTC clusters is generally associated with cooperative group benefits in terms of survival, including increased resistance to shear stress, anoikis, immune attacks and drugs. However, the adoption of a group phenotype poses a challenge when exiting the vasculature (extravasation) as the large size can hinder the passage through vessel walls. Despite their significant role in the metastatic process, the mechanisms through which CTC clusters extravasate remain largely unknown. Based on the observed in vivo association between CTC clusters and platelets, we hypothesized that cancer cells take advantage of the platelet-derived Transforming Growth Factor Beta 1 (TGF-β1) - a signalling factor that has been widely implicated in many aspects of cancer, to facilitate their own dissemination. To address this possibility, we evaluated the effect of exogenous TGF-β1 on an experimentally evolved non-small cell lung cancer cell line that we previously developed and used to investigate the biology of CTC clusters.

RESULTS

We found that exogenous TGF-β1 induced the dissociation of clusters in suspension into adherent single cells. Once adhered, cells released their own TGF-β1 and were able to individually migrate and invade in the absence of exogenous TGF-β1. Based on these findings we developed a model that involves a TGF-β1-mediated plastic switch between a cooperative phenotype and a single-celled stage that enables the extravasation of CTC clusters.

CONCLUSIONS

This model allows for the possibility that therapies can be developed against TGF-β1 signalling components and/or TGF-β1 target genes to suppress the metastatic potential of CTC clusters. Considering the negative impact that metastasis has on cancer prognosis and the lack of therapies against this process, interfering with the ability of CTC clusters to switch between cooperative and individual behaviours could provide new strategies to improve patient survival.

Mechanisms of Cardiac Repair in Cell Therapy

Heart failure is an important cause of morbidity and mortality. More than 20 years ago, special interest was drawn to cell therapy as a means of restoring damaged hearts to working condition. But progress has not been straightforward as many of our initial assumptions turned out to be wrong. In this review, we critically examine the last 20 years of progress in cardiac cell therapy and focus on several of the popular beliefs surrounding cell therapy to illustrate the mechanisms involved in restoring heart function after cardiac injury. Are they true or false?

Metastasis prevention: How to catch metastatic seeds

Despite considerable advances in the evolution of anticancer therapies, metastasis still remains the main cause of cancer mortality. Therefore, current strategies for cancer cure should be redirected towards prevention of metastasis. Targeting metastatic pathways represents a promising therapeutic opportunity aimed at obstructing tumor cell dissemination and metastatic colonization. In this review, we focus on preclinical studies and clinical trials over the last five years that showed high efficacy in suppressing metastasis through targeting lymph node dissemination, tumor cell extravasation, reactive oxygen species, pre-metastatic niche, exosome machinery, and dormancy.

Oncolytic viruses as emerging therapy against cancers including Oncovirus-induced cancers

There are several human viruses with known potential for causing cancers including, Hepatitis B virus, Hepatitis C virus, Epstein-Barr virus, Kaposi's sarcoma herpesvirus, Human T-cell lymphotropic virus, Human papillomavirus, and Merkel cell polyomavirus. Cancer is the second leading cause of death that affects humans worldwide, especially in developing countries. Surgery, chemotherapy, and radiotherapy can cure about 60% of humans with cancer but recurrent and metastatic diseases remain a major reason for death. In recent years, understanding the molecular characteristics of cancer cells has led to the improvement of therapeutic strategies using novel emerging therapies. Oncolytic viruses with the potential of lysing cancer cells defined the field of oncolytic virology, hence becoming a biotechnology tool rather than just a cause of disease. This study mainly focused on targeting cell proliferation and death pathways in human tumor-inducing viruses by developing innovative therapies for cancer patients based on the natural oncolytic properties of reovirus. To kill tumor cells efficiently and reduce the chance of recurrence both the direct ability of reovirus infection to lyse the tumor cells and the stimulation of a potent host immune response are applied. Hence, bioengineered stem cells can be used as smart carriers to improve the efficacy of oncolytic reovirus and safety profiles.

Intracoronary transplantation of pluripotent stem cell-derived cardiomyocytes: Inefficient procedure for cardiac regeneration

Advances in stem cell biology have facilitated cardiac regeneration, and many animal studies and several initial clinical trials have been conducted using human pluripotent stem cell-derived cardiomyocytes (PSC-CMs). Most preclinical and clinical studies have typically transplanted PSC-CMs via the following two distinct approaches: direct intramyocardial injection or epicardial delivery of engineered heart tissue. Both approaches present common disadvantages, including a mandatory thoracotomy and poor engraftment. Furthermore, a standard transplantation approach has yet to be established. In this study, we tested the feasibility of performing intracoronary administration of PSC-CMs based on a commonly used method of transplanting somatic stem cells. Six male cynomolgus monkeys underwent intracoronary administration of dispersed human PSC-CMs or PSC-CM aggregates, which are called cardiac spheroids, with multiple cell dosages. The recipient animals were sacrificed at 4 weeks post-transplantation for histological analysis. Intracoronary administration of dispersed human PSC-CMs in the cynomolgus monkeys did not lead to coronary embolism or graft survival. Although the transplanted cardiac spheroids became partially engrafted, they also induced scar formation due to cardiac ischemic injury. Cardiac engraftment and scar formation were reasonably consistent with the spheroid size or cell dosage. These findings indicate that intracoronary transplantation of PSC-CMs is an inefficient therapeutic approach.

Mild cold stress specifically disturbs clustering movement of DFCs and sequential organ left-right patterning in zebrafish

In poikilothermic animals, the distinct acclimatization ability of different organs has been previously addressed, while the tissue-specific role of cold stress in early development is largely unknown. In this study, we discovered that despite its role in delaying embryonic development, mild cold stress (22°C) does not disturb multiple-organ progenitor specification, but does give rise to organ left-right (LR) patterning defects. Regarding the mechanism, the data showed that mild cold stress downregulated the expression of cell-adhesion genes cdh1 and cdh2 during gastrulation, especially in dorsal forerunner cells (DFCs), which partially disturbed the clustering movement of DFCs, Kupffer’s vesicle (KV) morphogenesis, and ciliogenesis. As a result, the defects of KV/cilia disrupted asymmetric nodal signaling and subsequent heart and liver LR patterning. In conclusion, our data novelly identified that, in early development, DFCs are more sensitive to mild cold stress, and mild cold stress repressed the expression of cell adhesion-related gene cdh1 and cdh2. This role partially disturbed the clustering movement of DFCs, which resulted in defective KV/cilia development and sequential organ LR patterning defects.

Adaptable Microfluidic Vessel-on-a-Chip Platform for Investigating Tumor Metastatic Transport in Bloodstream

Cancer metastasis counts for 90% of cancer fatalities, and its development process is still a mystery. The dynamic process of tumor metastatic transport in the blood vessel is not well understood, in which some biomechanical factors, such as shear stress and various flow patterns, may have significant impacts. Here, we report a microfluidic vessel-on-a-chip platform for recapitulating several key metastatic steps of tumor cells in blood vessels on the same chip, including intravasation, circulating tumor cell (CTC) vascular adhesion, and extravasation. Due to its excellent adaptability, our system can reproduce various microenvironments to investigate the specific interactions between CTCs and blood vessels. On the basis of this platform, effects of important biomechanical factors on CTC adhesion such as vascular surface properties and vessel geometry-dependent hemodynamics were specifically inspected. We demonstrated that CTC adhesion is more likely to occur under certain mechano-physiological situations, such as vessels with vascular glycocalyx (VGCX) shedding and hemodynamic disturbances. Finally, computational models of both the fluidic dynamics in vessels and CTC adhesion were established based on the confocal scanned 3D images. The modeling results are believed to provide insights into exploring tumor metastasis progression and inspire new ideas for anticancer therapy development.

Cell-Cell Interactions Drive Metastasis of Circulating Tumor Microemboli

Circulating tumor cells are the cellular mediators of distant metastasis in solid malignancies. Their metastatic potential can be augmented by clustering with other tumor cells or nonmalignant cells, forming circulating tumor microemboli (CTM). Cell-cell interactions are key regulators within CTM that convey enhanced metastatic properties, including improved cell survival, immune evasion, and effective extravasation into distant organs. However, the cellular and molecular mechanism of CTM formation, as well as the biology of interactions between tumor cells and immune cells, platelets, and stromal cells in the circulation, remains to be determined. Here, we review the current literature on cell-cell interactions in homotypic and heterotypic CTM and provide perspectives on therapeutic strategies to attenuate CTM-mediated metastasis by targeting cell-cell interactions.

A Zebrafish Model of Metastatic Colonization Pinpoints Cellular Mechanisms of Circulating Tumor Cell Extravasation

Metastasis is a multistep process in which cells must detach, migrate/invade local structures, intravasate, circulate, extravasate, and colonize. A full understanding of the complexity of this process has been limited by the lack of ability to study these steps in isolation with detailed molecular analyses. Leveraging a comparative oncology approach, we injected canine osteosarcoma cells into the circulation of transgenic zebrafish with fluorescent blood vessels in a biologically dynamic metastasis extravasation model. Circulating tumor cell clusters that successfully extravasated the vasculature as multicellular units were isolated under intravital imaging (n = 6). These extravasation-positive tumor cell clusters sublines were then molecularly profiled by RNA-Seq. Using a systems-level analysis, we pinpointed the downregulation of KRAS signaling, immune pathways, and extracellular matrix (ECM) organization as enriched in extravasated cells (p < 0.05). Within the extracellular matrix remodeling pathway, we identified versican (VCAN) as consistently upregulated and central to the ECM gene regulatory network (p < 0.05). Versican expression is prognostic for a poorer metastasis-free and overall survival in patients with osteosarcoma. Together, our results provide a novel experimental framework to study discrete steps in the metastatic process. Using this system, we identify the versican/ECM network dysregulation as a potential contributor to osteosarcoma circulating tumor cell metastasis.

Collective metastasis: coordinating the multicellular voyage

The metastatic process is arduous. Cancer cells must escape the confines of the primary tumor, make their way into and travel through the circulation, then survive and proliferate in unfavorable microenvironments. A key question is how cancer cells overcome these multiple barriers to orchestrate distant organ colonization. Accumulating evidence in human patients and animal models supports the hypothesis that clusters of tumor cells can complete the entire metastatic journey in a process referred to as collective metastasis. Here we highlight recent studies unraveling how multicellular coordination, via both physical and biochemical coupling of cells, induces cooperative properties advantageous for the completion of metastasis. We discuss conceptual challenges and unique mechanisms arising from collective dissemination that are distinct from single cell-based metastasis. Finally, we consider how the dissection of molecular transitions regulating collective metastasis could offer potential insight into cancer therapy.

Impairing flow-mediated endothelial remodeling reduces extravasation of tumor cells

Tumor progression and metastatic dissemination are driven by cell-intrinsic and biomechanical cues that favor the growth of life-threatening secondary tumors. We recently identified pro-metastatic vascular regions with blood flow profiles that are permissive for the arrest of circulating tumor cells. We have further established that such flow profiles also control endothelial remodeling, which favors extravasation of arrested CTCs. Yet, how shear forces control endothelial remodeling is unknown. In the present work, we aimed at dissecting the cellular and molecular mechanisms driving blood flow-dependent endothelial remodeling. Transcriptomic analysis of endothelial cells revealed that blood flow enhanced VEGFR signaling, among others. Using a combination of in vitro microfluidics and intravital imaging in zebrafish embryos, we now demonstrate that the early flow-driven endothelial response can be prevented upon specific inhibition of VEGFR tyrosine kinase and subsequent signaling. Inhibitory targeting of VEGFRs reduced endothelial remodeling and subsequent metastatic extravasation. These results confirm the importance of VEGFR-dependent endothelial remodeling as a driving force of CTC extravasation and metastatic dissemination. Furthermore, the present work suggests that therapies targeting endothelial remodeling might be a relevant clinical strategy in order to impede metastatic progression.

Three-Dimensional Imaging in Stem Cell-Based Researches

Stem cells have an important role in regenerative therapies, developmental biology studies and drug screening. Basic and translational research in stem cell technology needs more detailed imaging techniques. The possibility of cell-based therapeutic strategies has been validated in the stem cell field over recent years, a more detailed characterization of the properties of stem cells is needed for connectomics of large assemblies and structural analyses of these cells. The aim of stem cell imaging is the characterization of differentiation state, cellular function, purity and cell location. Recent progress in stem cell imaging field has included ultrasound-based technique to study living stem cells and florescence microscopy-based technique to investigate stem cell three-dimensional (3D) structures. Here, we summarized the fundamental characteristics of stem cells via 3D imaging methods and also discussed the emerging literatures on 3D imaging in stem cell research and the applications of both classical 2D imaging techniques and 3D methods on stem cells biology.

Mesenchymal Stem Cells for Neurological Disorders

Neurological disorders are becoming a growing burden as society ages, and there is a compelling need to address this spiraling problem. Stem cell-based regenerative medicine is becoming an increasingly attractive approach to designing therapies for such disorders. The unique characteristics of mesenchymal stem cells (MSCs) make them among the most sought after cell sources. Researchers have extensively studied the modulatory properties of MSCs and their engineering, labeling, and delivery methods to the brain. The first part of this review provides an overview of studies on the application of MSCs to various neurological diseases, including stroke, traumatic brain injury, spinal cord injury, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease, Parkinson's disease, and other less frequently studied clinical entities. In the second part, stem cell delivery to the brain is focused. This fundamental but still understudied problem needs to be overcome to apply stem cells to brain diseases successfully. Here the value of cell engineering is also emphasized to facilitate MSC diapedesis, migration, and homing to brain areas affected by the disease to implement precision medicine paradigms into stem cell-based therapies.

Visualizing cancer extravasation: from mechanistic studies to drug development

Metastasis is a multistep process that accounts for the majority of cancer-related death. By the end of metastasize dissemination, circulating tumor cells (CTC) need to extravasate the blood vessels at metastatic sites to form new colonization. Although cancer cell extravasation is a crucial step in cancer metastasis, it has not been successfully targeted by current anti-metastasis strategies due to the lack of a thorough understanding of the molecular mechanisms that regulate this process. This review focuses on recent progress in cancer extravasation visualization techniques, including the development of both in vitro and in vivo cancer extravasation models, that shed light on the underlying mechanisms. Specifically, multiple cancer extravasation stages, such as the adhesion to the endothelium and transendothelial migration, are successfully probed using these technologies. Moreover, the roles of different cell adhesive molecules, chemokines, and growth factors, as well as the mechanical factors in these stages are well illustrated. Deeper understandings of cancer extravasation mechanisms offer us new opportunities to escalate the discovery of anti-extravasation drugs and therapies and improve the prognosis of cancer patients.

Mechanical Adaptability of Tumor Cells in Metastasis

The most dangerous aspect of cancer lies in metastatic progression. Tumor cells will successfully form life-threatening metastases when they undergo sequential steps along a journey from the primary tumor to distant organs. From a biomechanics standpoint, growth, invasion, intravasation, circulation, arrest/adhesion, and extravasation of tumor cells demand particular cell-mechanical properties in order to survive and complete the metastatic cascade. With metastatic cells usually being softer than their non-malignant counterparts, high deformability for both the cell and its nucleus is thought to offer a significant advantage for metastatic potential. However, it is still unclear whether there is a finely tuned but fixed mechanical state that accommodates all mechanical features required for survival throughout the cascade or whether tumor cells need to dynamically refine their properties and intracellular components at each new step encountered. Here, we review the various mechanical requirements successful cancer cells might need to fulfill along their journey and speculate on the possibility that they dynamically adapt their properties accordingly. The mechanical signature of a successful cancer cell might actually be its ability to adapt to the successive microenvironmental constraints along the different steps of the journey.

Cellular dynamics of myogenic cell migration: molecular mechanisms and implications for skeletal muscle cell therapies

Directional cell migration is a critical process underlying morphogenesis and post-natal tissue regeneration. During embryonic myogenesis, migration of skeletal myogenic progenitors is essential to generate the anlagen of limbs, diaphragm and tongue, whereas in post-natal skeletal muscles, migration of muscle satellite (stem) cells towards regions of injury is necessary for repair and regeneration of muscle fibres. Additionally, safe and efficient migration of transplanted cells is critical in cell therapies, both allogeneic and autologous. Although various myogenic cell types have been administered intramuscularly or intravascularly, functional restoration has not been achieved yet in patients with degenerative diseases affecting multiple large muscles. One of the key reasons for this negative outcome is the limited migration of donor cells, which hinders the overall cell engraftment potential. Here, we review mechanisms of myogenic stem/progenitor cell migration during skeletal muscle development and post-natal regeneration. Furthermore, strategies utilised to improve migratory capacity of myogenic cells are examined in order to identify potential treatments that may be applied to future transplantation protocols.

Circulating tumor cells as Trojan Horse for understanding, preventing, and treating cancer: a critical appraisal

Circulating tumor cells (CTCs) are regarded as harbingers of metastases. Their ability to predict response to therapy, relapse, and resistance to treatment has proposed their value as putative diagnostic and prognostic indicators. CTCs represent one of the zeniths of cancer evolution in terms of cell survival; however, the triggers of CTC generation, the identification of potentially metastatic CTCs, and the mechanisms contributing to their heterogeneity and aggressiveness represent issues not yet fully deciphered. Thus, prior to enabling liquid biopsy applications to reach clinical prime time, understanding how the above mechanistic information can be applied to improve treatment decisions is a key challenge. Here, we provide our perspective on how CTCs can provide mechanistic insights into tumor pathogenesis, as well as on CTC clinical value. In doing so, we aim to (a) describe how CTCs disseminate from the primary tumor, and their link to epithelial-mesenchymal transition (EMT); (b) trace the route of CTCs through the circulation, focusing on tumor self-seeding and the possibility of tertiary metastasis; (c) describe possible mechanisms underlying the enhanced metastatic potential of CTCs; (d) discuss how CTC could provide further information on the tissue of origin, especially in cancer of unknown primary origin. We also provide a comprehensive review of meta-analyses assessing the prognostic significance of CTCs, to highlight the emerging role of CTCs in clinical oncology. We also explore how cell-free circulating tumor DNA (ctDNA) analysis, using a combination of genomic and phylogenetic analysis, can offer insights into CTC biology, including our understanding of CTC heterogeneity and tumor evolution. Last, we discuss emerging technologies, such as high-throughput quantitative imaging, radiogenomics, machine learning approaches, and the emerging breath biopsy. These technologies could compliment CTC and ctDNA analyses, and they collectively represent major future steps in cancer detection, monitoring, and management.

Neutrophils: Accomplices in metastasis

Metastasis is a critical cause of treatment failure and death in patients with advanced malignancies. Tumor cells can leave the primary site and enter the bloodstream; these circulating tumor cells then colonize target organs by overcoming blood shear stress, evading immune surveillance, and silencing the offensive capabilities of immune cells, eventually forming metastatic foci. From leaving the primary focus to the completion of distant metastasis, malignant tumor cells are supported and/or antagonized by certain immune cells. In particular, it has been found that myeloid granulocytes play an important role in this process. This review therefore aims to comprehensively describe the significance of neutrophils in solid tumor metastasis in terms of their supporting role in initiating the invasion and migration of tumor cells and assisting the colonization of circulating tumor cells in distant target organs, with the hope of providing insight into and ideas for anti-tumor metastasis treatment of tumor patients.

Mesenchymal stem cells injected into carotid artery to target focal brain injury home to perivascular space

Rationale: The groundbreaking discovery of mesenchymal stem cells (MSCs) with their multifaceted benefits led to their widespread application in experimental medicine, including neurology. Efficient delivery of MSCs to damaged regions of the central nervous system may be a critical factor in determining outcome. Integrin VLA-4 (α4β1) coded by ITGA4 and ITGB1 genes is an adhesion molecule expressed by leukocytes, which is responsible for initiation of their diapedesis through cell docking to the inflamed vessel wall expressing VCAM1 receptor. This function of VLA-4 has been recapitulated in neural stem cells and glial progenitors. Thus, it was prudent to investigate this tool as a vehicle driving extravasation of MSCs. Since MSCs naturally express ITGB1 subunit, we decided to supplement them with ITGA4 only. The purpose of our current study is to investigate the eventual fate of IA delivered ITGA4 engineered and naive MSCs.

Methods: mRNA-ITGA4 transfected and naive MSCs were injected to right internal carotid artery of rats with focal brain injury. Through next three days MSC presence in animals' brain was navigated by magnetic resonance imaging. Transplanted cell location relative to the brain blood vessels and host immunological reaction were analyzed post-mortem by immunohistochemistry. The chemotaxis of modified and naive MSCs was additionally examined in in vitro transwell migration assay.

Results: Both naïve and ITGA4-overexpressing cells remained inside the vascular lumen over the first two days after IA infusion. On the third day, 39% of mRNA-ITGA4 modified and 51% naïve MSCs homed to perivascular space in the injury region (p=NS). The gradual decrease of both naive and mRNA-ITGA4 transfected hBM-MSCs in the rat brain was observed. mRNA-ITGA4 transfected MSCs appeared to be more vulnerable to phagocytosis than naïve cells. Moreover, in vitro study revealed that homogenate from the injured brain repels migration of MSCs, corroborating the incomplete extravasation observed in vivo.

Conclusions: In summary, IA transplanted MSCs are capable of homing to the perivascular space, an integral part of neurovascular unit, which might contribute to the replacement of injured pericytes, a critical element facilitating restoration of CNS function. The mRNA-ITGA4 transfection improves cell docking to vessel but this net benefit vanishes over the next two days due to fast clearance from cerebral vessels of the majority of transplanted cells, regardless of their engineering status. The drawbacks of mRNA-ITGA4 transfection become apparent on day 3 post transplantation due to the lower survival and higher vulnerability to host immune attack.

Epithelial-Mesenchymal Transition Induces Podocalyxin to Promote Extravasation via Ezrin Signaling

The epithelial-mesenchymal transition (EMT) endows carcinoma cells with traits needed to complete many of the steps leading to metastasis formation, but its contributions specifically to the late step of extravasation remain understudied. We find that breast cancer cells that have undergone an EMT extravasate more efficiently from blood vessels both in vitro and in vivo. Analysis of gene expression changes associated with the EMT program led to the identification of an EMT-induced cell-surface protein, podocalyxin (PODXL), as a key mediator of extravasation in mesenchymal breast and pancreatic carcinoma cells. PODXL promotes extravasation through direct interaction of its intracellular domain with the cytoskeletal linker protein ezrin. Ezrin proceeds to establish dorsal cortical polarity, enabling the transition of cancer cells from a non-polarized, rounded cell morphology to an invasive extravasation-competent shape. Hence, the EMT program can directly enhance the efficiency of extravasation and subsequent metastasis formation through a PODXL-ezrin signaling axis.

Circulating tumor cells exit circulation while maintaining multicellularity, augmenting metastatic potential

Metastasis accounts for the majority of all cancer deaths, yet the process remains poorly understood. A pivotal step in the metastasis process is the exiting of tumor cells from the circulation, a process known as extravasation. However, it is unclear how tumor cells extravasate and whether multicellular clusters of tumor cells possess the ability to exit as a whole or must first disassociate. In this study, we use in vivo zebrafish and mouse models to elucidate the mechanism tumor cells use to extravasate. We found that circulating tumor cells exit the circulation using the recently identified extravasation mechanism, angiopellosis, and do so as both clusters and individual cells. We further show that when melanoma and cervical cancer cells utilize this extravasation method to exit as clusters, they exhibit an increased ability to form tumors at distant sites through the expression of unique genetic profiles. Collectively, we present a new model for tumor cell extravasation of both individual and multicellular circulating tumor cells.This article has an associated First Person interview with the first author of the paper.

Metastatic Niches and the Modulatory Contribution of Mesenchymal Stem Cells and Its Exosomes

Mesenchymal stem cells (MSCs) represent an interesting population due to their capacity to release a variety of cytokines, chemokines, and growth factors, and due to their motile nature and homing ability. MSCs can be isolated from different sources, like adipose tissue or bone marrow, and have the capacity to differentiate, both in vivo and in vitro, into adipocytes, chondrocytes, and osteoblasts, making them even more interesting in the regenerative medicine field. Tumor associated stroma has been recognized as a key element in tumor progression, necessary for the biological success of the tumor, and MSCs represent a functionally fundamental part of this associated stroma. Exosomes represent one of the dominant signaling pathways within the tumor microenvironment. Their biology raises high interest, with implications in different biological processes involved in cancer progression, such as the formation of the pre-metastatic niche. This is critical during the metastatic cascade, given that it is the formation of a permissive context that would allow metastatic tumor cells survival within the new environment. In this context, we explored the role of exosomes, particularly MSCs-derived exosomes as direct or indirect modulators. All this points out a possible new tool useful for designing better treatment and detection strategies for metastatic progression, including the management of chemoresistance.

A platform for artificial intelligence based identification of the extravasation potential of cancer cells into the brain metastatic niche

Brain metastases are the most lethal complication of advanced cancer; therefore, it is critical to identify when a tumor has the potential to metastasize to the brain. There are currently no interventions that shed light on the potential of primary tumors to metastasize to the brain. We constructed and tested a platform to quantitatively profile the dynamic phenotypes of cancer cells from aggressive triple negative breast cancer cell lines and patient derived xenografts (PDXs), generated from a primary tumor and brain metastases from tumors of diverse organs of origin. Combining an advanced live cell imaging algorithm and artificial intelligence, we profile cancer cell extravasation within a microfluidic blood-brain niche (μBBN) chip, to detect the minute differences between cells with brain metastatic potential and those without with a PPV of 0.91 in the context of this study. The results show remarkably sharp and reproducible distinction between cells that do and those which do not metastasize inside of the device.

A New Era of Cardiac Cell Therapy: Opportunities and Challenges

Myocardial infarction (MI), caused by coronary heart disease (CHD), remains one of the most common causes of death in the United States. Over the last few decades, scientists have invested considerable resources on the study and development of cell therapies for myocardial regeneration after MI. However, due to a number of limitations, they are not yet readily available for clinical applications. Mounting evidence supports the theory that paracrine products are the main contributors to the regenerative effects attributed to these cell therapies. The next generation of cell-based MI therapies will identify and isolate cell products and derivatives, integrate them with biocompatible materials and technologies, and use them for the regeneration of damaged myocardial tissue. This review discusses the progress made thus far in pursuit of this new generation of cell therapies. Their fundamental regenerative mechanisms, their potential to combine with other therapeutic products, and their role in shaping new clinical approaches for heart tissue engineering, are addressed.

Myths, reality and future of mesenchymal stem cell therapy

Mesenchymal stem cell (MSC) therapy represents an alternative approach for tissue regeneration and inflammation control. In spite of a huge amount of preclinical data that has been accumulated on the therapeutic properties of MSCs, there are many conflicting results, possibly due to differences in the properties of MSCs obtained from different sources or underestimated mechanisms of MSC in vivo behavior. This review consolidates the in vivo effects of MSC therapy, discusses the fate of MSCs after intravascular and local delivery and proposes possible trends in MSC therapy.

Transfer and Integration of Breast Milk Stem Cells to the Brain of Suckling Pups

Beside its unique nutritional content breast milk also contains live cells from the mother. Fate of these cells in the offspring has not been adequately described. In this study, we aimed to detect and identify maternal cells in the suckling’s blood and the brain. Green fluorescent protein expressing transgenic female mice (GFP+) were used as foster mothers to breastfeed wildtype newborn pups. One week and two months after the birth, blood samples and brains of the sucklings were analyzed to detect presence of GFP+ cells by fluorescence activated cell sorting, polymerase chain reaction and immunohistochemistry on the brain sections and optically cleared brains. The tests confirmed that maternal cells were detectable in the blood and the brain of the pups and that they differentiated into both neuronal and glial cell types in the brain. This phenomenon represents breastfeeding – induced microchimerism in the brain with functional implications remain to be understood.

Programming Cell-Cell Interactions through Non-genetic Membrane Engineering

The ability to direct targeted intercellular interactions has the potential to enable and expand the use of cell-based therapies for regenerative medicine, tissue engineering, and immunotherapy. While genetic engineering approaches have proven effective, these techniques are not amenable to all cell types and often yield permanent modifications with potentially long-lasting adverse effects, restricting their application. To circumvent these limitations, there is intense interest in developing non-genetic methods to modify cell membranes with functional groups that will enable the recognition of target cells. While many such techniques have been developed, relatively few have been applied to directing specific cell-cell interactions. This review details these non-genetic membrane engineering approaches-namely, hydrophobic membrane insertion, chemical modification, liposome fusion, metabolic engineering, and enzymatic remodeling-and summarizes their major applications. Based on this analysis, perspective is provided on the ideal features of these systems with an emphasis on the potential for clinical translation.

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.

Acellular Mouse Kidney ECM can be Used as a Three-Dimensional Substrate to Test the Differentiation Potential of Embryonic Stem Cell Derived Renal Progenitors

The development of strategies for tissue regeneration and bio-artificial organ development is based on our understanding of embryogenesis. Differentiation protocols attempt to recapitulate the signaling modalities of gastrulation and organogenesis, coupled with cell selection regimens to isolate the cells of choice. This strategy is impeded by the lack of optimal in vitro culture systems since traditional culture systems do not allow for the three-dimensional interaction between cells and the extracellular matrix. While artificial three-dimensional scaffolds are available, using the natural extracellular matrix scaffold is advantageous because it has a distinct architecture that is difficult to replicate. The adult extracellular matrix is predicted to mediate signaling related to tissue repair not embryogenesis but existing similarities between the two argues that the extracellular matrix will influence the differentiation of stem and progenitor cells. Previous studies using undifferentiated embryonic stem cells grown directly on acellular kidney ECM demonstrated that the acellular kidney supported cell growth but limited differentiation occurred. Using mouse kidney extracellular matrix and mouse embryonic stem cells we report that the extracellular matrix can support the development of kidney structures if the stem cells are first differentiated to kidney progenitor cells before being applied to the acellular organ.

Concise Review: Is Cardiac Cell Therapy Dead? Embarrassing Trial Outcomes and New Directions for the Future

Stem cell therapy is a promising strategy for tissue regeneration. The therapeutic benefits of cell therapy are mediated by both direct and indirect mechanisms. However, the application of stem cell therapy in the clinic is hampered by several limitations. This concise review provides a brief introduction into stem cell therapies for ischemic heart disease. It summarizes cell‐based and cell‐free paradigms, their limitations, and the benefits of using them to target disease. stemcellstranslationalmedicine2018;7:354–359

Beyond the Matrix: The Many Non-ECM Ligands for Integrins

The traditional view of integrins portrays these highly conserved cell surface receptors as mediators of cellular attachment to the extracellular matrix (ECM), and to a lesser degree, as coordinators of leukocyte adhesion to the endothelium. These canonical activities are indispensable; however, there is also a wide variety of integrin functions mediated by non-ECM ligands that transcend the traditional roles of integrins. Some of these unorthodox roles involve cell-cell interactions and are engaged to support immune functions such as leukocyte transmigration, recognition of opsonization factors, and stimulation of neutrophil extracellular traps. Other cell-cell interactions mediated by integrins include hematopoietic stem cell and tumor cell homing to target tissues. Integrins also serve as cell-surface receptors for various growth factors, hormones, and small molecules. Interestingly, integrins have also been exploited by a wide variety of organisms including viruses and bacteria to support infectious activities such as cellular adhesion and/or cellular internalization. Additionally, the disruption of integrin function through the use of soluble integrin ligands is a common strategy adopted by several parasites in order to inhibit blood clotting during hematophagy, or by venomous snakes to kill prey. In this review, we strive to go beyond the matrix and summarize non-ECM ligands that interact with integrins in order to highlight these non-traditional functions of integrins.

Targeted repair of heart injury by stem cells fused with platelet nanovesicles

Stem cell transplantation, as used clinically, suffers from low retention and engraftment of the transplanted cells. Inspired by the ability of platelets to recruit stem cells to sites of injury on blood vessels, we hypothesized that platelets might enhance the vascular delivery of cardiac stem cells (CSCs) to sites of myocardial infarction injury. Here, we show that CSCs with platelet nanovesicles fused onto their surface membranes express platelet surface markers that are associated with platelet adhesion to injury sites. We also find that the modified CSCs selectively bind collagen-coated surfaces and endothelium-denuded rat aortas, and that in rat and porcine models of acute myocardial infarction the modified CSCs increase retention in the heart and reduce infarct size. Platelet-nanovesicle-fused CSCs thus possess the natural targeting and repairing ability of their parental cell types. This stem cell manipulation approach is fast, straightforward and safe, does not require genetic alteration of the cells, and should be generalizable to multiple cell types.

Methodological aspects of MRI of transplanted superparamagnetic iron oxide-labeled mesenchymal stem cells in live rat brain

In vivo tracking of transplanted mesenchymal stem cells (MSCs) migration and homing is vital for understanding the mechanisms of beneficial effects of MSCs transplantation in animal models of diseases and in clinical trials. Transplanted cells can be labeled with superparamagnetic iron oxide (SPIO) particles and visualized in vivo using a number of iron sensitive MRI techniques. However, the applicability of those techniques for SPIO-labeled MSCs tracking in live brain has not been sufficiently investigated. The goal of this study was to estimate the efficiency of various MRI techniques of SPIO-labeled cell tracing in the brain. To achieve that goal, the precision and specificity of T2WI, T2*WI and SWI (Susceptibility-Weighted Imaging) techniques of SPIO-labeled MSCs tracing in vitro and in live rat brain were for the first time compared in the same experiment. We have shown that SWI presents the most sensitive pulse sequence for SPIO-labeled MSCs MR visualization. After intracerebral administration due to limitations caused by local micro-hemorrhages the visualization threshold was 10² cells, while after intra-arterial transplantation SWI permitted detection of several cells or even single cells. There is just one publication claiming detection of individual SPIO-labeled MSCs in live brain, while the other state much lower sensitivity, describe detection of different cell types or high resolution tracing of MSCs in other tissues. This study confirms the possibility of single cell tracing in live brain and outlines the necessary conditions. SWI is a method convenient for the detection of single SPIO labeled MSCs and small groups of SPIO labeled MSCs in brain tissue and can be appropriate for monitoring migration and homing of transplanted cells in basic and translational neuroscience.

Cellular mechanisms underlying cardiac engraftment of stem cells

INTRODUCTION

Over the past decade, it has become clear that long-term engraftment of any ex vivo expanded cell product transplanted into injured myocardium is modest and all therapeutic regeneration is mediated by stimulation of endogenous repair rather than differentiation of transplanted cells into working myocardium. Given that increasing the retention of transplanted cells boosts myocardial function, focus on the fundamental mechanisms limiting retention and survival of transplanted cells may enable strategies to help to restore normal cardiac function. Areas covered: This review outlines the challenges confronting cardiac engraftment of ex vivo expanded cells and explores means of enhancing cell-mediated repair of injured myocardium. Expert opinion: Stem cell therapy has already come a long way in terms of regenerating damaged hearts though the poor retention of transplanted cells limits the full potential of truly cardiotrophic cell products. Multifaceted strategies directed towards fundamental mechanisms limiting the long-term survival of transplanted cells will be needed to enhance transplanted cell retention and cell-mediated repair of damaged myocardium for cardiac cell therapy to reach its full potential.

Mesenchymal Stromal Cells as Anti-Inflammatory and Regenerative Mediators for Donor Kidneys During Normothermic Machine Perfusion

There is great demand for transplant kidneys for the treatment of end-stage kidney disease patients. To expand the donor pool, organs from older and comorbid brain death donors, so-called expanded criteria donors (ECD), as well as donation after circulatory death donors, are considered for transplantation. However, the quality of these organs may be inferior to standard donor organs. A major issue affecting graft function and survival is ischemia/reperfusion injury, which particularly affects kidneys from deceased donors. The development of hypothermic machine perfusion has been introduced in kidney transplantation as a preservation technique and has improved outcomes in ECD and marginal organs compared to static cold storage. Normothermic machine perfusion (NMP) is the most recent evolution of perfusion technology and allows assessment of the donor organ before transplantation. The possibility to control the content of the perfusion fluid offers opportunities for damage control and reparative therapies during machine perfusion. Mesenchymal stromal cells (MSC) have been demonstrated to possess potent regenerative properties via the release of paracrine effectors. The combination of NMP and MSC administration at the same time is a promising procedure in the field of transplantation. Therefore, the MePEP consortium has been created to study this novel modality of treatment in preparation for human trials. MePEP aims to assess the therapeutic effects of MSC administered ex vivo by NMP in the mechanisms of injury and repair in a porcine kidney autotransplantation model.

Mitochondrial transplantation: From animal models to clinical use in humans

Mitochondrial transplantation is a novel therapeutic intervention to treat ischemia/reperfusion related disorders. The method for mitochondrial transplantation is simple and rapid and can be delivered to the end organ either by direct injection or vascular infusion. In this review, we provide mechanistic and histological studies in large animal models and present data to show clinical efficacy in human patients.

Therapeutic microparticles functionalized with biomimetic cardiac stem cell membranes and secretome

Stem cell therapy represents a promising strategy in regenerative medicine. However, cells need to be carefully preserved and processed before usage. In addition, cell transplantation carries immunogenicity and/or tumourigenicity risks. Mounting lines of evidence indicate that stem cells exert their beneficial effects mainly through secretion (of regenerative factors) and membrane-based cell–cell interaction with the injured cells. Here, we fabricate a synthetic cell-mimicking microparticle (CMMP) that recapitulates stem cell functions in tissue repair. CMMPs carry similar secreted proteins and membranes as genuine cardiac stem cells do. In a mouse model of myocardial infarction, injection of CMMPs leads to the preservation of viable myocardium and augmentation of cardiac functions similar to cardiac stem cell therapy. CMMPs (derived from human cells) do not stimulate T-cell infiltration in immuno-competent mice. In conclusion, CMMPs act as ‘synthetic stem cells’ which mimic the paracrine and biointerfacing activities of natural stem cells in therapeutic cardiac regeneration.

Stem cells exert their beneficial effects through secretion of regenerative factors. Here, the authors take the membranes and secreted factors from cardiac stem cells and generate a synthetic cell-mimicking microparticle, which, on injection in a mouse model of myocardial infarction, improves cardiac function.