High Shear Stresses under Exercise Condition Destroy Circulating Tumor Cells in a Microfluidic System

Post-diagnosis physical activity and sedentary behaviour and colorectal cancer prognosis: A Global Cancer Update Programme (CUP Global) systematic literature review and meta-analysis

Low physical activity and high sedentary behaviour have been clearly linked with colorectal cancer development, yet data on their potential role in colorectal cancer survival is limited. Better characterisation of these relationships is needed for the development of post-diagnosis physical activity and sedentary behaviour guidance for colorectal cancer survivors. We searched PubMed and Embase through 28 February 2022 for studies assessing post-diagnosis physical activity, and/or sedentary behaviour in relation to all-cause and cause-specific mortality and recurrence after colorectal cancer diagnosis. Total and recreational physical activity were assessed overall and by frequency, duration, intensity, and volume using categorical, linear, and non-linear dose-response random-effects meta-analyses. The Global Cancer Update Programme (CUP Global) independent Expert Committee on Cancer Survivorship and Expert Panel interpreted and graded the likelihood of causality. We identified 16 observational studies on 82,220 non-overlapping patients from six countries. Physical activity was consistently inversely associated with colorectal cancer morbidity and mortality outcomes, with 13%-60% estimated reductions in risk. Sedentary behaviour was positively associated with all-cause mortality. The evidence had methodological limitations including potential confounding, selection bias and reverse causation, coupled with a limited number of studies for most associations. The CUP Global Expert panel concluded limited-suggestive evidence for recreational physical activity with all-cause mortality and cancer recurrence. Total physical activity and its specific domains and dimensions, and sedentary behaviour were all graded as limited-no conclusion for all outcomes. Future research should focus on randomised trials, while observational studies should obtain objective and repeated physical activity measures and better adjustment for confounders.

Suppressive effects of exercise-conditioned serum on cancer cells: A narrative review of the influence of exercise mode, volume, and intensity

Cancer is a major cause of morbidity and mortality worldwide, and the incidence is increasing, highlighting the need for effective strategies to treat this disease. Exercise has emerged as fundamental therapeutic medicine in the management of cancer, associated with a lower risk of recurrence and increased survival. Several avenues of research demonstrate reduction in growth, proliferation, and increased apoptosis of cancer cells, including breast, prostate, colorectal, and lung cancer, when cultured by serum collected after exercise in vitro (i.e., the cultivation of cancer cell lines in an experimental setting, which simplifies the biological system and provides mechanistic insight into cell responses). The underlying mechanisms of exercise-induced cancer suppressive effects may be attributed to the alteration in circulating factors, such as skeletal muscle-induced cytokines (i.e., myokines) and hormones. However, exercise-induced tumor suppressive effects and detailed information about training interventions are not well investigated, constraining more precise application of exercise medicine within clinical oncology. To date, it remains unclear what role different training modes (i.e., resistance and aerobic training) as well as volume and intensity have on exercise-conditioned serum and its effects on cancer cells. Nevertheless, the available evidence is that a single bout of aerobic training at moderate to vigorous intensity has cancer suppressive effects, while for chronic training interventions, exercise volume appears to be an influential candidate driving cancer inhibitory effects regardless of training mode. Insights for future research investigating training modes, volume and intensity are provided to further our understanding of the effects of exercise-conditioned serum on cancer cells.

Distinguishing high-metastasis-potential circulating tumor cells through fluidic shear stress in a bloodstream-like microfluidic circulatory system

Circulating tumor cells (CTCs) play a critical role as initiators in tumor metastasis, which unlocks an irreversible process of cancer progression. Regarding the fluid environment of intravascular CTCs, a comprehensive understanding of the impact of hemodynamic shear stress on CTCs is of profound significance but remains vague. Here, we report a microfluidic circulatory system that can emulate the CTC microenvironment to research the responses of typical liver cancer cells to varying levels of fluid shear stress (FSS). We observe that HepG2 cells surviving FSS exhibit a marked overexpression of TLR4 and TPPP3, which are shown to be associated with the colony formation, migration, and anti-apoptosis abilities of HepG2. Furthermore, overexpression of these two genes in another liver cancer cell line with normally low TLR4 and TPPP3 expression, SK-Hep-1 cells, by lentivirus-mediated transfection also confirms the critical role of TLR4 and TPPP3 in improving colony formation, migration, and survival capability under a fluid environment. Interestingly, in vivo experiments show SK-Hep-1 cells, overexpressed with these genes, have enhanced metastatic potential to the liver and lungs in mouse models via tail vein injection. Mechanistically, TLR4 and TPPP3 upregulated by FSS may increase FSS-mediated cell survival and metastasis through the p53-Bax signaling pathway. Moreover, elevated levels of these genes correlate with poorer overall survival in liver cancer patients, suggesting that our findings could offer new therapeutic strategies for early cancer diagnosis and targeted treatment development.

Mesenchymal Stromal Cells Increase the Natural Killer Resistance of Circulating Tumor Cells via Intercellular Signaling of cGAS-STING-IFNβ-HLA

Circulating tumor cells (CTCs) shed from primary tumors must overcome the cytotoxicity of immune cells, particularly natural killer (NK) cells, to cause metastasis. The tumor microenvironment (TME) protects tumor cells from the cytotoxicity of immune cells, which is partially executed by cancer-associated mesenchymal stromal cells (MSCs). However, the mechanisms by which MSCs influence the NK resistance of CTCs remain poorly understood. This study demonstrates that MSCs enhance the NK resistance of cancer cells in a gap junction-dependent manner, thereby promoting the survival and metastatic seeding of CTCs in immunocompromised mice. Tumor cells crosstalk with MSCs through an intercellular cGAS-cGAMP-STING signaling loop, leading to increased production of interferon-β (IFNβ) by MSCs. IFNβ reversely enhances the type I IFN (IFN-I) signaling in tumor cells and hence the expression of human leukocyte antigen class I (HLA-I) on the cell surface, protecting the tumor cells from NK cytotoxicity. Disruption of this loop reverses NK sensitivity in tumor cells and decreases tumor metastasis. Moreover, there are positive correlations between IFN-I signaling, HLA-I expression, and NK tolerance in human tumor samples. Thus, the NK-resistant signaling loop between tumor cells and MSCs may serve as a novel therapeutic target.

The impact of tumor microenvironment: unraveling the role of physical cues in breast cancer progression

Metastasis accounts for the vast majority of breast cancer-related fatalities. Although the contribution of genetic and epigenetic modifications to breast cancer progression has been widely acknowledged, emerging evidence underscores the pivotal role of physical stimuli in driving breast cancer metastasis. In this review, we summarize the changes in the mechanics of the breast cancer microenvironment and describe the various forces that impact migrating and circulating tumor cells throughout the metastatic process. We also discuss the mechanosensing and mechanotransducing molecules responsible for promoting the malignant phenotype in breast cancer cells. Gaining a comprehensive understanding of the mechanobiology of breast cancer carries substantial potential to propel progress in prognosis, diagnosis, and patient treatment.

Multiplex, high-throughput method to study cancer and immune cell mechanotransduction

Studying cellular mechanoresponses during cancer metastasis is limited by sample variation or complex protocols that current techniques require. Metastasis is governed by mechanotransduction, whereby cells translate external stimuli, such as circulatory fluid shear stress (FSS), into biochemical cues. We present high-throughput, semi-automated methods to expose cells to FSS using the VIAFLO96 multichannel pipetting device custom-fitted with 22 G needles, increasing the maximum FSS 94-fold from the unmodified tips. Specifically, we develop protocols to semi-automatically stain live samples and to fix, permeabilize, and intracellularly process cells for flow cytometry analysis. Our first model system confirmed that the pro-apoptotic effects of TRAIL therapeutics in prostate cancer cells can be enhanced via FSS-induced Piezo1 activation. Our second system implements this multiplex methodology to show that FSS exposure (290 dyn cm-2) increases activation of murine bone marrow-derived dendritic cells. These methodologies greatly improve the mechanobiology workflow, offering a high-throughput, multiplex approach.

Insights into the mechanobiology of cancer metastasis via microfluidic technologies

During cancer metastasis, cancer cells will encounter various microenvironments with diverse physical characteristics. Changes in these physical characteristics such as tension, stiffness, viscosity, compression, and fluid shear can generate biomechanical cues that affect cancer cells, dynamically influencing numerous pathophysiological mechanisms. For example, a dense extracellular matrix drives cancer cells to reorganize their cytoskeleton structures, facilitating confined migration, while this dense and restricted space also acts as a physical barrier that potentially results in nuclear rupture. Identifying these pathophysiological processes and understanding their underlying mechanobiological mechanisms can aid in the development of more effective therapeutics targeted to cancer metastasis. In this review, we outline the advances of engineering microfluidic devices in vitro and their role in replicating tumor microenvironment to mimic in vivo settings. We highlight the potential cellular mechanisms that mediate their ability to adapt to different microenvironments. Meanwhile, we also discuss some important mechanical cues that still remain challenging to replicate in current microfluidic devices in future direction. While much remains to be explored about cancer mechanobiology, we believe the developments of microfluidic devices will reveal how these physical cues impact the behaviors of cancer cells. It will be crucial in the understanding of cancer metastasis, and potentially contributing to better drug development and cancer therapy.

Circulating tumor cells with metastasis-initiating competence survive fluid shear stress during hematogenous dissemination through CXCR4-PI3K/AKT signaling

To seed lethal secondary lesions, circulating tumor cells (CTCs) must survive all rate-limiting factors during hematogenous dissemination, including fluid shear stress (FSS) that poses a grand challenge to their survival. We thus hypothesized that CTCs with the ability to survive FSS in vasculature might hold metastasis-initiating competence. This study reported that FSS of physiologic magnitude selected a small subpopulation of suspended tumor cells in vitro with the traits of metastasis-initiating cells, including stemness, migration/invasion potential, cellular plasticity, and biophysical properties. These shear-selected cells generated local and metastatic tumors at the primary and distal sites efficiently, implicating their metastasis competence. Mechanistically, FSS activated the mechanosensitive protein CXCR4 and the downstream PI3K/AKT signaling, which were essential in shear-mediated selection of metastasis-competent CTCs. In summary, these findings conclude that CTCs with metastasis-initiating competence survive FSS during hematogenous dissemination through CXCR4-PI3K/AKT signaling, which may provide new therapeutic targets for the early prevention of tumor metastasis.

Computational analysis of cancer cell adhesion in curved vessels affected by wall shear stress for prediction of metastatic spreading

Introduction: The dynamics of circulating tumor cells (CTCs) within blood vessels play a pivotal role in predicting metastatic spreading of cancer within the body. However, the limited understanding and method to quantitatively investigate the influence of vascular architecture on CTC dynamics hinders our ability to predict metastatic process effectively. To address this limitation, the present study was conducted to investigate the influence of blood vessel tortuosity on the behaviour of CTCs, focusing specifically on establishing methods and examining the role of shear stress in CTC-vessel wall interactions and its subsequent impact on metastasis. Methods: We computationally simulated CTC behaviour under various shear stress conditions induced by vessel tortuosity. Our computational model, based on the lattice Boltzmann method (LBM) and a coarse-grained spectrin-link membrane model, efficiently simulates blood plasma dynamics and CTC deformability. The model incorporates fluid-structure interactions and receptor-ligand interactions crucial for CTC adhesion using the immersed boundary method (IBM). Results: Our findings reveal that uniform shear stress in straight vessels leads to predictable CTC-vessel interactions, whereas in curved vessels, asymmetrical flow patterns and altered shear stress create distinct adhesion dynamics, potentially influencing CTC extravasation. Quantitative analysis shows a 25% decrease in the wall shear stress in low-shear regions and a 58.5% increase in the high-shear region. We observed high-shear regions in curved vessels to be potential sites for increased CTC adhesion and extravasation, facilitated by elevated endothelial expression of adhesion molecules. This phenomenon correlates with the increased number of adhesion bonds, which rises to approximately 40 in high-shear regions, compared to around 12 for straight vessels and approximately 5-6 in low-shear regions. The findings also indicate an optimal cellular stiffness necessary for successful CTC extravasation in curved vessels. Discussion: By the quantitative assessment of the risk of CTC extravasation as a function of vessel tortuosity, our study offers a novel tool for the prediction of metastasis risk to support the development of personalized therapeutic interventions based on individual vascular characteristics and tumor cell properties.

Low-Frequency Ultrasound Sensitive Piezo1 Channels Regulate Keloid-Related Characteristics of Fibroblasts

Keloids are benign fibroproliferative tumors that severely diminish the quality of life due to discomfort, dysfunction, and disfigurement. Recently, ultrasound technology as a noninvasive adjuvant therapy is developed to optimize treatment protocols. However, the biophysical mechanisms have not yet been fully elucidated. Here, it is proposed that piezo-type mechanosensitive ion channel component 1 (Piezo1) plays an important role in low-frequency sonophoresis (LFS) induced mechanical transduction pathways that trigger downstream cellular signaling processes. It is demonstrated that patient-derived primary keloid fibroblasts (PKF), NIH 3T3, and HFF-1 cell migration are inhibited, and PKF apoptosis is significantly increased by LFS stimulation. And the effects of LFS is diminished by the application of GsMTx-4, the selective inhibitor of Piezo1, and the knockdown of Piezo1. More importantly, the effects of LFS can be imitated by Yoda1, an agonist of Piezo1 channels. Establishing a patient-derived xenograft keloid implantation mouse model further verified these results, as LFS significantly decreased the volume and weight of the keloids. Moreover, blocking the Piezo1 channel impaired the effectiveness of LFS treatment. These results suggest that LFS inhibits the malignant characteristics of keloids by activating the Piezo1 channel, thus providing a theoretical basis for improving the clinical treatment of keloids.

Survival mechanisms of circulating tumor cells and their implications for cancer treatment

Metastasis remains the principal trigger for relapse and mortality across diverse cancer types. Circulating tumor cells (CTCs), which originate from the primary tumor or its metastatic sites, traverse the vascular system, serving as precursors in cancer recurrence and metastasis. Nevertheless, before CTCs can establish themselves in the distant parenchyma, they must overcome significant challenges present within the circulatory system, including hydrodynamic shear stress (HSS), oxidative damage, anoikis, and immune surveillance. Recently, there has been a growing body of compelling evidence suggesting that a specific subset of CTCs can persist within the bloodstream, but the precise mechanisms of their survival remain largely elusive. This review aims to present an outline of the survival challenges encountered by CTCs and to summarize the recent advancements in understanding the underlying survival mechanisms, suggesting their implications for cancer treatment.

Evidence and therapeutic implications of biomechanically regulated immunosurveillance in cancer and other diseases

Disease progression is usually accompanied by changes in the biochemical composition of cells and tissues and their biophysical properties. For instance, hallmarks of cancer include the stiffening of tissues caused by extracellular matrix remodelling and the softening of individual cancer cells. In this context, accumulating evidence has shown that immune cells sense and respond to mechanical signals from the environment. However, the mechanisms regulating these mechanical aspects of immune surveillance remain partially understood. The growing appreciation for the 'mechano-immunology' field has urged researchers to investigate how immune cells sense and respond to mechanical cues in various disease settings, paving the way for the development of novel engineering strategies that aim at mechanically modulating and potentiating immune cells for enhanced immunotherapies. Recent pioneer developments in this direction have laid the foundations for leveraging 'mechanical immunoengineering' strategies to treat various diseases. This Review first outlines the mechanical changes occurring during pathological progression in several diseases, including cancer, fibrosis and infection. We next highlight the mechanosensitive nature of immune cells and how mechanical forces govern the immune responses in different diseases. Finally, we discuss how targeting the biomechanical features of the disease milieu and immune cells is a promising strategy for manipulating therapeutic outcomes.

Stress in the metastatic journey - the role of cell communication and clustering in breast cancer progression and treatment resistance

Breast cancer stands as the most prevalent malignancy afflicting women. Despite significant advancements in its diagnosis and treatment, breast cancer metastasis continues to be a leading cause of mortality among women. To metastasize, cancer cells face numerous challenges: breaking away from the primary tumor, surviving in the circulation, establishing in a distant location, evading immune detection and, finally, thriving to initiate a new tumor. Each of these sequential steps requires cancer cells to adapt to a myriad of stressors and develop survival mechanisms. In addition, most patients with breast cancer undergo surgical removal of their primary tumor and have various therapeutic interventions designed to eradicate cancer cells. Despite this plethora of attacks and stresses, certain cancer cells not only manage to persist but also proliferate robustly, giving rise to substantial tumors that frequently culminate in the patient's demise. To enhance patient outcomes, there is an imperative need for a deeper understanding of the molecular and cellular mechanisms that empower cancer cells to not only survive but also expand. Herein, we delve into the intrinsic stresses that cancer cells encounter throughout the metastatic journey and the additional stresses induced by therapeutic interventions. We focus on elucidating the remarkable strategies adopted by cancer cells, such as cell-cell clustering and intricate cell-cell communication mechanisms, to ensure their survival.

Hydrodynamic shear stress' impact on mammalian cell properties and its applications in 3D bioprinting

As an effective cell assembly method, three-dimensional bioprinting has been widely used in building organ models and tissue repair over the past decade. However, different shear stresses induced throughout the entire printing process can cause complex impacts on cell integrity, including reducing cell viability, provoking morphological changes and altering cellular functionalities. The potential effects that may occur and the conditions under which these effects manifest are not clearly understood. Here, we review systematically how different mammalian cells respond under shear stress. We enumerate available experimental apparatus, and we categorise properties that can be affected under disparate stress patterns. We also summarise cell damaging mathematical models as a predicting reference for the design of bioprinting systems. We concluded that it is essential to quantify specific cell resistance to shear stress for the optimisation of bioprinting systems. Besides, as substantial positive impacts, including inducing cell alignment and promoting cell motility, can be generated by shear stress, we suggest that we find the proper range of shear stress and actively utilise its positive influences in the development of future systems.

Cancer Metastasis-on-a-Chip for Modeling Metastatic Cascade and Drug Screening

Microfluidic chips are valuable tools for studying intricate cellular and cell-microenvironment interactions. Traditional in vitro cancer models lack accuracy in mimicking the complexities of in vivo tumor microenvironment. However, cancer-metastasis-on-a-chip (CMoC) models combine the advantages of 3D cultures and microfluidic technology, serving as powerful platforms for exploring cancer mechanisms and facilitating drug screening. These chips are able to compartmentalize the metastatic cascade, deepening the understanding of its underlying mechanisms. This article provides an overview of current CMoC models, focusing on distinctive models that simulate invasion, intravasation, circulation, extravasation, and colonization, and their applications in drug screening. Furthermore, challenges faced by CMoC and microfluidic technologies are discussed, while exploring promising future directions in cancer research. The ongoing development and integration of these models into cancer studies are expected to drive transformative advancements in the field.

Characterization of Cancer Cell Mechanics by Measuring Active Deformation Behavior

Active deformation behavior reflects cell structural dynamics adapting to varying environmental constraints during malignancy progression. In most cases, cell mechanics is characterized by modeling using static equilibrium systems, which fails to comprehend cell deformation behavior leading to inaccuracies in distinguishing cancer cells from normal cells. Here, a method is introduced to measure the active deformation behavior of cancer cells using atomic force microscopy (AFM) and the newly developed deformation behavior cytometry (DBC). During the measurement, cells are deformed and allows a long timescale relaxation (≈5 s). Two parameters are derived to represent deformation behavior: apparent Poisson's ratio for adherent cells, which is measured with AFM and refers to the ratio of the lateral strain to the longitudinal strain of the cell, and shape recovery for suspended cells, which is measured with DBC. Active deformation behavior defines cancer cell mechanics better than traditional mechanical parameters (e.g., stiffness, diffusion, and viscosity). Additionally, aquaporins are essential for promoting the deformation behavior, while the actin cytoskeleton acts as a downstream effector. Therefore, the potential application of the cancer cell active deformation behavior as a biomechanical marker or therapeutic target in cancer treatment should be evaluated.

A Balance between Inter- and Intra-Microgel Mechanics Governs Stem Cell Viability in Injectable Dynamic Granular Hydrogels

Injectable hydrogels are increasingly explored for the delivery of cells to tissue. These materials exhibit both liquid-like properties, protecting cells from mechanical stress during injection, and solid-like properties, providing a stable 3D engraftment niche. Many strategies for modulating injectable hydrogels tune liquid- and solid-like material properties simultaneously, such that formulation changes designed to improve injectability can reduce stability at the delivery site. The ability to independently tune liquid- and solid-like properties would greatly facilitate formulation development. Here, such a strategy is presented in which cells are ensconced in the pores between microscopic granular hyaluronic acid (HA) hydrogels (microgels), where elasticity is tuned with static covalent intra-microgel crosslinks and flowability with mechanosensitive adamantane-cyclodextrin (AC) inter-microgel crosslinks. Using the same AC-free microgels as a 3D printing support bath, the location of each cell is preserved as it exits the needle, allowing identification of the mechanism driving mechanical trauma-induced cell death. The microgel AC concentration is varied to find the threshold from microgel yielding- to AC interaction-dominated injectability, and this threshold is exploited to fabricate a microgel with better injection-protecting performance. This delivery strategy, and the balance between intra- and inter-microgel properties it reveals, may facilitate the development of new cell injection formulations.

Biophysics in tumor growth and progression: from single mechano-sensitive molecules to mechanomedicine

Evidence from physical sciences in oncology increasingly suggests that the interplay between the biophysical tumor microenvironment and genetic regulation has significant impact on tumor progression. Especially, tumor cells and the associated stromal cells not only alter their own cytoskeleton and physical properties but also remodel the microenvironment with anomalous physical properties. Together, these altered mechano-omics of tumor tissues and their constituents fundamentally shift the mechanotransduction paradigms in tumorous and stromal cells and activate oncogenic signaling within the neoplastic niche to facilitate tumor progression. However, current findings on tumor biophysics are limited, scattered, and often contradictory in multiple contexts. Systematic understanding of how biophysical cues influence tumor pathophysiology is still lacking. This review discusses recent different schools of findings in tumor biophysics that have arisen from multi-scale mechanobiology and the cutting-edge technologies. These findings range from the molecular and cellular to the whole tissue level and feature functional crosstalk between mechanotransduction and oncogenic signaling. We highlight the potential of these anomalous physical alterations as new therapeutic targets for cancer mechanomedicine. This framework reconciles opposing opinions in the field, proposes new directions for future cancer research, and conceptualizes novel mechanomedicine landscape to overcome the inherent shortcomings of conventional cancer diagnosis and therapies.

Travelling under pressure - hypoxia and shear stress in the metastatic journey

Cancer cell invasion, intravasation and survival in the bloodstream are early steps of the metastatic process, pivotal to enabling the spread of cancer to distant tissues. Circulating tumor cells (CTCs) represent a highly selected subpopulation of cancer cells that tamed these critical steps, and a better understanding of their biology and driving molecular principles may facilitate the development of novel tools to prevent metastasis. Here, we describe key research advances in this field, aiming at describing early metastasis-related processes such as collective invasion, shedding, and survival of CTCs in the bloodstream, paying particular attention to microenvironmental factors like hypoxia and mechanical stress, considered as important influencers of the metastatic journey.

Mechanotransduction: Forcing a change in metabolism

Epithelial and endothelial cells experience numerous mechanical cues throughout their lifetimes. Cells resist these forces by fortifying their cytoskeletal networks and adhesions. This reinforcement is energetically costly. Here we describe how these energetic demands are met. We focus on the response of epithelial and endothelial cells to mechanical cues, describe the energetic needs of epithelia and endothelia, and identify the mechanisms these cells employ to increase glycolysis, oxidative phosphorylation, and fatty acid metabolism. We discuss the similarities and differences in the responses of the two cell types.

Pathological and Therapeutic Significance of Tumor-Derived Extracellular Vesicles in Cancer Cell Migration and Metastasis

The infiltration of primary tumors and metastasis formation at distant sites strongly impact the prognosis and the quality of life of cancer patients. Current therapies including surgery, radiotherapy, and chemotherapy are limited in targeting the complex cell migration mechanisms responsible for cancer cell invasiveness and metastasis. A better understanding of these mechanisms and the development of new therapies are urgently needed. Extracellular vesicles (EVs) are lipid-enveloped particles involved in inter-tissue and inter-cell communication. This review article focuses on the impact of EVs released by tumor cells, specifically on cancer cell migration and metastasis. We first introduce cell migration processes and EV subtypes, and we give an overview of how tumor-derived EVs (TDEVs) may impact cancer cell migration. Then, we discuss ongoing EV-based cancer therapeutic approaches, including the inhibition of general EV-related mechanisms as well as the use of EVs for anti-cancer drug delivery, focusing on the harnessing of TDEVs. We propose a protein-EV shuttle as a route alternative to secretion or cell membrane binding, influencing downstream signaling and the final effect on target cells, with strong implications in tumorigenesis. Finally, we highlight the pitfalls and limitations of therapeutic EV exploitation that must be overcome to realize the promise of EVs for cancer therapy.

Shear Stress Drives the Cleavage Activation of Protease-Activated Receptor 2 by PRSS3/Mesotrypsin to Promote Invasion and Metastasis of Circulating Lung Cancer Cells

When circulating tumor cells (CTCs) travel in circulation, they can be killed by detachment-induced anoikis and fluidic shear stress (SS)-mediated apoptosis. Circulatory treatment, which can make CTCs detached but also generate SS, can increase metastasis of cancer cells. To identify SS-specific mechanosensors without detachment impacts, a microfluidic circulatory system is used to generate arteriosus SS and compare transcriptome profiles of circulating lung cancer cells with suspended cells. Half of the cancer cells can survive SS damage and show higher invasion ability. Mesotrypsin (PRSS3), protease-activated receptor 2 (PAR2), and the subunit of activating protein 1, Fos-related antigen 1 (FOSL1), are upregulated by SS, and their high expression is responsible for promoting invasion and metastasis. SS triggers PRSS3 to cleave the N-terminal inhibitory domain of PAR2 within 2 h. As a G protein-coupled receptor, PAR2 further activates the Gαi protein to turn on the Src-ERK/p38/JNK-FRA1/cJUN axis to promote the expression of epithelial-mesenchymal transition markers, and also PRSS3, which facilitates metastasis. Enriched PRSS3, PAR2, and FOSL1 in human tumor samples and their correlations with worse outcomes reveal their clinical significance. PAR2 may serve as an SS-specific mechanosensor cleavable by PRSS3 in circulation, which provides new insights for targeting metastasis-initiating CTCs.

Advanced in vitro models for renal cell carcinoma therapy design

Renal cell carcinoma (RCC) and its principal subtype, clear cell RCC, are the most diagnosed kidney cancer. Despite substantial improvement over the last decades, current pharmacological intervention still fails to achieve long-term therapeutic success. RCC is characterized by a high intra- and inter-tumoral heterogeneity and is heavily influenced by the crosstalk of the cells composing the tumor microenvironment, such as cancer-associated fibroblasts, endothelial cells and immune cells. Moreover, multiple physicochemical properties such as pH, interstitial pressure or oxygenation may also play an important role. These elements are often poorly recapitulated in in vitro models used for drug development. This inadequate recapitulation of the tumor is partially responsible for the current lack of an effective and curative treatment. Therefore, there are needs for more complex in vitro or ex vivo drug screening models. In this review, we discuss the current state-of-the-art of RCC models and suggest strategies for their further development.

Flourishing tumor organoids: History, emerging technology, and application

Malignant tumors are one of the leading causes of death which impose an increasingly heavy burden on all countries. Therefore, the establishment of research models that closely resemble original tumor characteristics is crucial to further understanding the mechanisms of malignant tumor development, developing safer and more effective drugs, and formulating personalized treatment plans. Recently, organoids have been widely used in tumor research owing to their advantages including preserving the structure, heterogeneity, and cellular functions of the original tumor, together with the ease of manipulation. This review describes the history and characteristics of tumor organoids and the synergistic combination of three-dimensional (3D) culture approaches for tumor organoids with emerging technologies, including tissue-engineered cell scaffolds, microfluidic devices, 3D bioprinting, rotating wall vessels, and clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR-Cas9). Additionally, the progress in research and the applications in basic and clinical research of tumor organoid models are summarized. This includes studies of the mechanism of tumor development, drug development and screening, precision medicine, immunotherapy, and simulation of the tumor microenvironment. Finally, the existing shortcomings of tumor organoids and possible future directions are discussed.

Fluid shear stress enhances natural killer cell's cytotoxicity toward circulating tumor cells through NKG2D-mediated mechanosensing

Tumor cells metastasize to distant organs mainly via hematogenous dissemination, in which circulating tumor cells (CTCs) are relatively vulnerable, and eliminating these cells has great potential to prevent metastasis. In vasculature, natural killer (NK) cells are the major effector lymphocytes for efficient killing of CTCs under fluid shear stress (FSS), which is an important mechanical cue in tumor metastasis. However, the influence of FSS on the cytotoxicity of NK cells against CTCs remains elusive. We report that the death rate of CTCs under both NK cells and FSS is much higher than the combined death induced by either NK cells or FSS, suggesting that FSS may enhance NK cell's cytotoxicity. This death increment is elicited by shear-induced NK activation and granzyme B entry into target cells rather than the death ligand TRAIL or secreted cytokines TNF-α and IFN-γ. When NK cells form conjugates with CTCs or adhere to MICA-coated substrates, NK cell activating receptor NKG2D can directly sense FSS to induce NK activation and degranulation. These findings reveal the promotive effect of FSS on NK cell's cytotoxicity toward CTCs, thus providing new insight into immune surveillance of CTCs within circulation.

Coculture of cancer cells with platelets increases their survival and metastasis by activating the TGFβ/Smad/PAI-1 and PI3K/AKT pathways

When cancer cells enter the bloodstream, they can interact with platelets to acquire stronger survival and metastatic abilities. To elucidate the underlying mechanisms, we cocultured metastatic melanoma and triple-negative breast cancer cells with species-homologous platelets. We found that cocultured cancer cells displayed higher viabilities in circulation, stronger capacities for cell migration, invasion, and colony formation in vitro, and more tumorigenesis and metastasis in mice. RNA sequencing analysis revealed that the level of serpin family E member 1 (SERPINE1) was significantly upregulated in cocultured cancer cells. Knockdown of SERPINE1 reversed the coculture-elevated survival and metastatic phenotypes of cancer cells. Mechanistic studies indicated that coculture with platelets activated the TGFβ/Smad pathway to induce SERPINE1 expression in cancer cells, which encodes plasminogen activator inhibitor 1 (PAI-1). PAI-1 then activated PI3K to increase the phosphorylation of AKTThr308 and Bad to elevate Bcl-2, which enhanced cell survival in circulation. Moreover, higher levels of PAI-1 were detected in metastatic tumors from melanoma and triple-negative breast cancer patients than in normal tissues, and high levels of PAI-1 were associated with a shorter overall survival time and worse disease progression in breast cancer. PAI-1 may act as a potential biomarker for detecting and treating metastatic tumor cells.

Receptor-Ligand Binding: Effect of Mechanical Factors

Gaining insight into the in situ receptor-ligand binding is pivotal for revealing the molecular mechanisms underlying the physiological and pathological processes and will contribute to drug discovery and biomedical application. An important issue involved is how the receptor-ligand binding responds to mechanical stimuli. This review aims to provide an overview of the current understanding of the effect of several representative mechanical factors, such as tension, shear stress, stretch, compression, and substrate stiffness on receptor-ligand binding, wherein the biomedical implications are focused. In addition, we highlight the importance of synergistic development of experimental and computational methods for fully understanding the in situ receptor-ligand binding, and further studies should focus on the coupling effects of these mechanical factors.

Mechanobiology and survival strategies of circulating tumor cells: a process towards the invasive and metastatic phenotype

Metastatic progression is the deadliest feature of cancer. Cancer cell growth, invasion, intravasation, circulation, arrest/adhesion and extravasation require specific mechanical properties to allow cell survival and the completion of the metastatic cascade. Circulating tumor cells (CTCs) come into contact with the capillary bed during extravasation/intravasation at the beginning of the metastatic cascade. However, CTC mechanobiology and survival strategies in the bloodstream, and specifically in the microcirculation, are not well known. A fraction of CTCs can extravasate and colonize distant areas despite the biomechanical constriction forces that are exerted by the microcirculation and that strongly decrease tumor cell survival. Furthermore, accumulating evidence shows that several CTC adaptations, via molecular factors and interactions with blood components (e.g., immune cells and platelets inside capillaries), may promote metastasis formation. To better understand CTC journey in the microcirculation as part of the metastatic cascade, we reviewed how CTC mechanobiology and interaction with other cell types in the bloodstream help them to survive the harsh conditions in the circulatory system and to metastasize in distant organs.

Metabolic reprogramming in response to cell mechanics

Much attention has been dedicated to understanding how cells sense and respond to mechanical forces. The types of forces cells experience as well as the repertoire of cell surface receptors that sense these forces have been identified. Key mechanisms for transmitting that force to the cell interior have also emerged. Yet, how cells process mechanical information and integrate it with other cellular events remains largely unexplored. Here we review the mechanisms underlying mechanotransduction at cell-cell and cell-matrix adhesions, and we summarize the current understanding of how cells integrate information from the distinct adhesion complexes with cell metabolism.

Mechanotherapy in oncology: Targeting nuclear mechanics and mechanotransduction

Mechanotherapy is proposed as a new option for cancer treatment. Increasing evidence suggests that characteristic differences are present in the nuclear mechanics and mechanotransduction of cancer cells compared with those of normal cells. Recent advances in understanding nuclear mechanics and mechanotransduction provide not only further insights into the process of malignant transformation but also useful references for developing new therapeutic approaches. Herein, we present an overview of the alterations of nuclear mechanics and mechanotransduction in cancer cells and highlight their implications in cancer mechanotherapy.

Elevation of Cytoplasmic Calcium Suppresses Microtentacle Formation and Function in Breast Tumor Cells

Cytoskeletal remodeling in circulating tumor cells (CTCs) facilitates metastatic spread. Previous oncology studies examine sustained aberrant calcium (Ca²⁺) signaling and cytoskeletal remodeling scrutinizing long-term phenotypes such as tumorigenesis and metastasis. The significance of acute Ca²⁺ signaling in tumor cells that occur within seconds to minutes is overlooked. This study investigates rapid cytoplasmic Ca²⁺ elevation in suspended cells on actin and tubulin cytoskeletal rearrangements and the metastatic microtentacle (McTN) phenotype. The compounds Ionomycin and Thapsigargin acutely increase cytoplasmic Ca²⁺, suppressing McTNs in the metastatic breast cancer cell lines MDA-MB-231 and MDA-MB-436. Functional decreases in McTN-mediated reattachment and cell clustering during the first 24 h of treatment are not attributed to cytotoxicity. Rapid cytoplasmic Ca²⁺ elevation was correlated to Ca²⁺-induced actin cortex contraction and rearrangement via myosin light chain 2 and cofilin activity, while the inhibition of actin polymerization with Latrunculin A reversed Ca²⁺-mediated McTN suppression. Preclinical and phase 1 and 2 clinical trial data have established Thapsigargin derivatives as cytotoxic anticancer agents. The results from this study suggest an alternative molecular mechanism by which these compounds act, and proof-of-principle Ca²⁺-modulating compounds can rapidly induce morphological changes in free-floating tumor cells to reduce metastatic phenotypes.

Designing, analyzing, and interpreting observational studies of physical activity and cancer outcomes from a clinical oncology perspective

Observational studies may play an important role in evaluating physical activity (PA) as a cancer treatment; however, few studies have been designed, analyzed, or interpreted from a clinical oncology perspective. The purpose of the present paper is to apply the Exercise as Cancer Treatment (EXACT) Framework to assess current observational studies of PA and cancer outcomes from a clinical oncology perspective and provide recommendations to improve their clinical utility. Recent systematic reviews and meta-analyses of over 130 observational studies have concluded that higher prediagnosis and postdiagnosis PA are associated with lower risks of cancer-specific and all-cause mortality. Most of these studies, however, have: (a) included cancer patients receiving heterogeneous treatment protocols, (b) provided minimal details about those cancer treatments, (c) assessed PA prediagnosis and/or postdiagnosis without reference to those cancer treatments, (d) reported mainly mortality outcomes, and (e) examined subgroups based on demographic and disease variables but not cancer treatments. As a result, current observational studies on PA and cancer outcomes have played a modest role in informing clinical exercise trials and clinical oncology practice. To improve their clinical utility, we recommend that future observational studies of PA and cancer outcomes: (a) recruit cancer patients receiving the same or similar first-line treatment protocols, (b) collect detailed data on all planned and unplanned cancer treatments beyond whether or not cancer treatments were received, (c) assess PA in relation to cancer treatments (i.e., before, during, between, after) rather than in relation to the cancer diagnosis (i.e., various time periods before and after diagnosis), (d) collect data on cancer-specific outcomes (e.g., disease response, progression, recurrence) in addition to mortality, (e) conduct subgroup analyses based on cancer treatments received in addition to demographic and disease variables, and (f) interpret mechanisms for any associations between PA and cancer-specific outcomes based on the clinical oncology scenario that is recapitulated rather than referencing generic mechanisms or discordant preclinical models. In conclusion, observational studies are well-suited to contribute important knowledge regarding the role of PA as a cancer treatment; however, modifications to study design and analysis are necessary if they are to inform clinical research and practice.

Effect of capillary fluid flow on single cancer cell cycle dynamics, motility, volume and morphology

From primary tumours and disseminating to secondary organs, cancer cells experience a wide variety of fluid flow profiles when passing through blood vessels or the lymphatic system before extravasation. Sinusoidal capillaries are a common site for extravasation. Therefore, we aim to investigate how metastatic cancer cells react to a biophysical cue such as capillary fluid flow by quantifying its effect on metastatic cell cycle progression, motility, cell and nuclear volume, and morphology. We use MDA-MB-231 breast cancer cells genetically modified with fluorescent ubiquitination-based cell cycle indicator 2 (FUCCI2) as a model system. Single cells are trapped using a microfluidic device and exposed to different laminar flows. Quantitative time-lapse imaging in both 2D epifluorescence and 3D confocal microscopy is performed using in-house software FUCCItrack. In addition, 3D time-lapse with cell and nuclear segmentation is performed with a deep learning approach to streamline the image processing of big datasets. We show that at a single cell level, faster fluid flow leads to a shorter S/G2/M phase and an overall shorter cell cycle, as well as increase in cell motility irrespective of the flow direction. 3D time-lapse confocal imaging of MDA-FUCCI2 single cells reveals the evolution of cell and nuclear volume and morphology as a function of a specific cell cycle phase. Both cell and nuclear volume increase linearly over time. Cell morphology elongates more strongly during the S/G2/M phase, whereas the nuclear shape remains constant. Under the highest flow conditions, only during the S/G2/M phase can we observe a more elongated nucleus, while the cell sphericity remains similar to the control. Collectively, this data, together with the deep learning approach, provides new insights into the potential impact of fluid flow at a single cell level.

Focusing on the hypoxia-inducible factor pathway: role, regulation, and therapy for osteoarthritis

Osteoarthritis (OA) is a common chronic disabling disease that affects hundreds of millions of people around the world. The most important pathological feature is the rupture and loss of articular cartilage, and the characteristics of avascular joint tissues lead to limited repair ability. Currently, there is no effective treatment to prevent cartilage degeneration. Studies on the mechanism of cartilage metabolism revealed that hypoxia-inducible factors (HIFs) are key regulatory genes that maintain the balance of cartilage catabolism-matrix anabolism and are considered to be the major OA regulator and promising OA treatment target. Although the exact mechanism of HIFs in OA needs to be further clarified, many drugs that directly or indirectly act on HIF signaling pathways have been confirmed by animal experiments and regarded as promising treatments for OA. Targeting HIFs will provide a promising strategy for the development of new OA drugs. This article reviews the regulation of HIFs on intra-articular cartilage homeostasis and its influence on the progression of osteoarthritis and summarizes the recent advances in OA therapies targeting the HIF system.

Drug susceptibility testing of circulating lung cancer cells for personalized treatment

The presence of Circulating tumor cells (CTCs) has been proven to be correlated with disease progression and the patient's response to treatment. However, the culture of CTCs for clinical utility is still a big challenge. We have developed a short-term method that enables CTCs culture and provides an opportunity to monitor drug susceptibility testing in individual patients. In a proof-of-concept study, we established a unique method using Matrigel® coated in 96 well plate to enable cancer cell clusters to attach and proliferate. The culture method using Matrigel® provides in vitro conditions and improves the attachment and differentiation of anchorage-dependent epithelial cells proliferation and mimics the tumor microenvironment. We further treated the cells attached to Matrigel® with the same drug regimen as the patient has undergone. Around 30.7% of the CTCs were viable after the drug treatment. We also correlated the decrease in cell viability after drug treatment with the reduction in the pleural effusion of the patient as seen by the images obtained from CT scans pre-and post-treatment. Moreover, as per the RECIST criterion, the patient had exhibited a positive response to the treatment. The short-term culturing of CTC along with the drug susceptibility testing offers a novel method to predict patient response to the treatment and could be utilized for screening suitable drug combinations for personalized treatment.

Physical activity prevents tumor metastasis through modulation of immune function

Metastasis is responsible for 90% of deaths in cancer patients. Most patients diagnosed with metastatic cancer will die within 5 years. PA is good for health and has become an emerging adjuvant therapy for cancer survivors. Regular moderate exercise substantially lowers the incidence and recurrence of several cancers, alleviates cancer-related adverse events, enhances the efficacy of anti-cancer treatments, and improves the quality of life of cancer patients. Revealing the mechanisms of PA inhibiting tumor metastasis could upgrade our understanding of cancer biology and help researchers explore new therapeutic strategies to improve survival in cancer patients. However, it remains poorly understood how physical activity prevents metastasis by modulating tumor behavior. The immune system is involved in each step of tumor metastasis. From invasion to colonization, immune cells interact with tumor cells to secret cytokines and proteases to remodel the tumor microenvironment. Substantial studies demonstrated the ability of physical activity to induce antitumor effects of immune cells. This provides the possibility that physical activity can modulate immune cells behavior to attenuate tumor metastasis. The purpose of this review is to discuss and summarize the critical link between immune function and exercise in metastasis prevention.

Cancer cells can be killed mechanically or with combinations of cytoskeletal inhibitors

For over two centuries, clinicians have hypothesized that cancer developed preferentially at the sites of repeated damage, indicating that cancer is basically “continued healing.” Tumor cells can develop over time into other more malignant types in different environments. Interestingly, indefinite growth correlates with the depletion of a modular, early rigidity sensor, whereas restoring these sensors in tumor cells blocks tumor growth on soft surfaces and metastases. Importantly, normal and tumor cells from many different tissues exhibit transformed growth without the early rigidity sensor. When sensors are restored in tumor cells by replenishing depleted mechanosensory proteins that are often cytoskeletal, cells revert to normal rigidity-dependent growth. Surprisingly, transformed growth cells are sensitive to mechanical stretching or ultrasound which will cause apoptosis of transformed growth cells (Mechanoptosis). Mechanoptosis is driven by calcium entry through mechanosensitive Piezo1 channels that activate a calcium-induced calpain response commonly found in tumor cells. Since tumor cells from many different tissues are in a transformed growth state that is, characterized by increased growth, an altered cytoskeleton and mechanoptosis, it is possible to inhibit growth of many different tumors by mechanical activity and potentially by cytoskeletal inhibitors.

Amiri H, Mas-hafi S, Banerjee B, Vesey G, Miansari M, Ebrahimi Warkiani M. Rapid and Continuous Cryopreservation of Stem Cells with a 3D Micromixer

Cryopreservation is the final step of stem cell production before the cryostorage of the product. Conventional methods of adding cryoprotecting agents (CPA) into the cells can be manual or automated with robotic arms. However, challenging issues with these methods at industrial-scale production are the insufficient mixing of cells and CPA, leading to damage of cells, discontinuous feeding, the batch-to-batch difference in products, and, occasionally, cross-contamination. Therefore, the current study proposes an alternative way to overcome the abovementioned challenges; a highly efficient micromixer for low-cost, continuous, labour-free, and automated mixing of stem cells with CPA solutions. Our results show that our micromixer provides a more homogenous mixing of cells and CPA compared to the manual mixing method, while the cell properties, including surface markers, differentiation potential, proliferation, morphology, and therapeutic potential, are well preserved.

Neutrophil extracellular traps facilitate cancer metastasis: cellular mechanisms and therapeutic strategies

Background

The formation of neutrophil extracellular traps (NETs) was initially discovered as a novel immune response against pathogens. Recent studies have also suggested that NETs play an important role in tumor progression. This review summarizes the cellular mechanisms by which NETs promote distant metastasis and discusses the possible clinical applications targeting NETs.

Method

The relevant literature from PubMed and Google Scholar (2001–2021) have been reviewed for this article.

Results

The presence of NETs has been detected in various primary tumors and metastatic sites. NET-associated interactions have been observed throughout the different stages of metastasis, including initial tumor cell detachment, intravasation and extravasation, the survival of circulating tumor cells, the settlement and the growth of metastatic tumor cells. Several in vitro and in vivo studies proved that inhibiting NET formation resulted in anti-cancer effects. The biosafety and efficacy of some NET inhibitors have also been demonstrated in early phase clinical trials.

Conclusions

Considering the role of NETs in tumor progression, NETs could be a promising diagnostic and therapeutic target for cancer management. However, current evidence is mostly derived from experimental models and as such more clinical studies are still needed to verify the clinical significance of NETs in oncological settings.

Mechanosensitive Channel PIEZO1 Senses Shear Force to Induce KLF2/4 Expression via CaMKII/MEKK3/ERK5 Axis in Endothelial Cells

Shear stress exerted by the blood stream modulates endothelial functions through altering gene expression. KLF2 and KLF4, the mechanosensitive transcription factors, are promoted by laminar flow to maintain endothelial homeostasis. However, how the expression of KLF2/4 is regulated by shear stress is poorly understood. Here, we showed that the activation of PIEZO1 upregulates the expression of KLF2/4 in endothelial cells. Mice with endothelial-specific deletion of Piezo1 exhibit reduced KLF2/4 expression in thoracic aorta and pulmonary vascular endothelial cells. Mechanistically, shear stress activates PIEZO1, which results in a calcium influx and subsequently activation of CaMKII. CaMKII interacts with and activates MEKK3 to promote MEKK3/MEK5/ERK5 signaling and ultimately induce the transcription of KLF2/4. Our data provide the molecular insight into how endothelial cells sense and convert mechanical stimuli into a biological response to promote KLF2/4 expression for the maintenance of endothelial function and homeostasis.

Applications of Microfluidics and Organ-on-a-Chip in Cancer Research

Taking the life of nearly 10 million people annually, cancer has become one of the major causes of mortality worldwide and a hot topic for researchers to find innovative approaches to demystify the disease and drug development. Having its root lying in microelectronics, microfluidics seems to hold great potential to explore our limited knowledge in the field of oncology. It offers numerous advantages such as a low sample volume, minimal cost, parallelization, and portability and has been advanced in the field of molecular biology and chemical synthesis. The platform has been proved to be valuable in cancer research, especially for diagnostics and prognosis purposes and has been successfully employed in recent years. Organ-on-a-chip, a biomimetic microfluidic platform, simulating the complexity of a human organ, has emerged as a breakthrough in cancer research as it provides a dynamic platform to simulate tumor growth and progression in a chip. This paper aims at giving an overview of microfluidics and organ-on-a-chip technology incorporating their historical development, physics of fluid flow and application in oncology. The current applications of microfluidics and organ-on-a-chip in the field of cancer research have been copiously discussed integrating the major application areas such as the isolation of CTCs, studying the cancer cell phenotype as well as metastasis, replicating TME in organ-on-a-chip and drug development. This technology’s significance and limitations are also addressed, giving readers a comprehensive picture of the ability of the microfluidic platform to advance the field of oncology.

Fluid shear stress in a logarithmic microfluidic device enhances cancer cell stemness marker expression

Fluid shear stress (FSS) is crucial in cancer cell survival and tumor development. Noteworthily, cancer cells are exposed to several degrees of FSS in the tumor microenvironment and during metastasis. Consequently, the stemness marker expression in cancer cells changes with the FSS signal, although it is unclear how it varies with different magnitudes and during metastasis. The current work explores the stemness and drug resistance characteristics of the cervical cancer cell line HeLa in a microfluidic device with a wide range of physiological FSS. Hence, the microfluidic device was designed to achieve a logarithmic flow distribution in four culture chambers, realizing four orders of biological shear stress on a single chip. The cell cycle analysis demonstrated altered cell proliferation and mitotic arrest after FSS treatment. In addition, EdU staining revealed increased cell proliferation with medium to low FSS, whereas high shear had a suppressing effect. FSS increased competence to withstand higher intracellular ROS and mitochondrial membrane potential in HeLa. Furthermore, stemness-related gene (Sox2, N-cadherin) and cell surface marker (CD44, CD33, CD117) expressions were enhanced by FSS mechanotransduction in a magnitude-dependent manner. In summary, these stemness-like properties were concurrent with the drug resistance capability of HeLa towards doxorubicin. Overall, our microfluidic device elucidates cancer cell survival and drug resistance mechanisms during metastasis and in cancer relapse patients.

Fluid shear stress regulates the survival of circulating tumor cells via nuclear expansion

Distant metastasis mainly occurs through hematogenous dissemination, where suspended circulating tumor cells (CTCs) experience a considerable level of fluid shear stress. We recently reported that shear flow induced substantial apoptosis of CTCs, although a small subpopulation could still persist. However, how suspended tumor cells survive in shear flow remains poorly understood. This study finds that fluid shear stress eliminates the majority of suspended CTCs and increases nuclear size, whereas it has no effect on the viability of adherent tumor cells and decreases their nuclear size. Shear flow promotes histone acetylation in suspended tumor cells, the inhibition of which using one drug suppresses shear-induced nuclear expansion, suggesting that shear stress might increase nuclear size through histone acetylation. Suppressing histone acetylation-mediated nuclear expansion enhances shear-induced apoptosis of CTCs. These findings suggest that suspended tumor cells respond to shear stress through histone acetylation-mediated nuclear expansion, which protects CTCs from shear-induced destruction. Our study elucidates a unique mechanism underlying the mechanotransduction of suspended CTCs to shear flow, which might hold therapeutic promise for CTC eradication.

Experimental determination of shear stresses on an artificial transcoelomic metastasis model using optical tweezers: A comparison with numerical simulation

BACKGROUND

One of the reported pathways of cancer spread is the transcoelomic pathway, which is understood as the spread of cancer cells in the abdominal and thoracic cavities through interstitial fluid. It has been proven that the shear stresses caused by microfluidic currents on cancer tumors in the abdominal and thoracic cavities cause the detachment of cancer cells triggering transcoelomic metastasis; however, the magnitude of shear stresses has not yet been measured experimentally.

OBJECTIVES

The objective of this study is to develop an experimental methodology using optical tweezers to approximate the shear stresses suffered by a nonporous, rigid artificial cancerous nodule model.

METHODS

Artificial cancerous nodule model was made by the agglomeration of 2 μm diameter polystyrene particles in a microfluidic platform. Optical tweezers were used as a velocimetry tool and shear stresses on the surface of the nodule model were approximated with the viscous shear stress equation. The results were verified with a numerical simulation performed in Ansys Fluent.

RESULTS

Shear stress originated by microflow over artificial cancerous nodule model were quantified both experimentally and numerically, showing good agreement between both methods. Such stress on the nodules' surface was much greater than that suffered by the wall on which the nodule model was located and dependent of the nodule model geometry. Although the experiment and simulation of this study were performed using a rigid and nonporous nodule model, the conclusion obtained about the increase of shear stresses applies to permeable, porous, and soft nodules as well, because the shear stresses are associated to the acceleration of the fluid originated by the reduction of the cross-sectional area.

CONCLUSIONS

Shear stress over artificial nodule model were successfully quantified using optical tweezer-based velocimetry technique and verified through numerical calculation. Advantages of experimental technique are: (1) it allows to control the position in a three-dimensional plane, allowing measurements in the vicinity of the analyzed surfaces, and (2) it is applicable for very low Reynolds number (R_e  « 1). On the other hand, as disadvantages: (1) it tends to be complicated to perform velocity measurements over obstacles and (2) it is limited in trapping distance.

Unraveling Cancer Metastatic Cascade Using Microfluidics-based Technologies

Cancer has long been a leading cause of death. The primary tumor, however, is not the main cause of death in more than 90% of cases. It is the complex process of metastasis that makes cancer deadly. The invasion metastasis cascade is the multi-step biological process of cancer cell dissemination to distant organ sites and adaptation to the new microenvironment site. Unraveling the metastasis process can provide great insight into cancer death prevention or even treatment. Microfluidics is a promising platform, that provides a wide range of applications in metastasis-related investigations. Cell culture microfluidic technologies for in vitro modeling of cancer tissues with fluid flow and the presence of mechanical factors have led to the organ-on-a-chip platforms. Moreover, microfluidic systems have also been exploited for capturing and characterization of circulating tumor cells (CTCs) that provide crucial information on the metastatic behavior of a tumor. We present a comprehensive review of the recent developments in the application of microfluidics-based systems for analysis and understanding of the metastasis cascade from a wider perspective.

Tumor-resident intracellular microbiota promotes metastatic colonization in breast cancer

Tumor-resident intracellular microbiota is an emerging tumor component that has been documented for a variety of cancer types with unclear biological functions. Here, we explored the functional significance of these intratumor bacteria, primarily using a murine spontaneous breast-tumor model MMTV-PyMT. We found that depletion of intratumor bacteria significantly reduced lung metastasis without affecting primary tumor growth. During metastatic colonization, intratumor bacteria carried by circulating tumor cells promoted host-cell survival by enhancing resistance to fluid shear stress by reorganizing actin cytoskeleton. We further showed that intratumor administration of selected bacteria strains isolated from tumor-resident microbiota promoted metastasis in two murine tumor models with significantly different levels of metastasis potential. Our findings suggest that tumor-resident microbiota, albeit at low biomass, play an important role in promoting cancer metastasis, intervention of which might therefore be worth exploring for advancing oncology care.

Recent advances in microfluidic devices for single-cell cultivation: methods and applications

Single-cell analysis is essential to improve our understanding of cell functionality from cellular and subcellular aspects for diagnosis and therapy. Single-cell cultivation is one of the most important processes in single-cell analysis, which allows the monitoring of actual information of individual cells and provides sufficient single-cell clones and cell-derived products for further analysis. The microfluidic device is a fast-rising system that offers efficient, effective, and sensitive single-cell cultivation and real-time single-cell analysis conducted either on-chip or off-chip. Here, we introduce the importance of single-cell cultivation from the aspects of cellular and subcellular studies. We highlight the materials and structures utilized in microfluidic devices for single-cell cultivation. We further discuss biological applications utilizing single-cell cultivation-based microfluidics, such as cellular phenotyping, cell-cell interactions, and omics profiling. Finally, present limitations and future prospects of microfluidics for single-cell cultivation are also discussed.

Circulating tumor cells: Towards mechanical phenotyping of metastasis

During cancer progression, metastatic dissemination accounts for ∼90% of death in patients. Metastasis occurs upon dissemination of circulating tumor cells (CTC) through body fluids, in particular the bloodstream, and several key steps remain elusive. Although the majority of CTCs travel as single cells, they can form clusters either with themselves (homoclusters) or with other circulating cells (heteroclusters) and thereby increase their metastatic potential. In addition, cancer cell mechanics and mechanical cues from the microenvironment are important factors during metastatic progression. Recent progress in intravital imaging technologies, biophysical methods, and microfluidic-based isolation of CTCs allow now to probe mechanics at single cell resolution while shedding light on key steps of the hematogenous metastatic cascade. In this review, we discuss the importance of CTC mechanics and their correlation with metastatic success and how such development could lead to the identification of therapeutically relevant targets.