Cell stiffness determined by atomic force microscopy and its correlation with cell motility

How do cells stiffen?

Cell stiffness is an important characteristic of cells and their response to external stimuli. In this review, we survey methods used to measure cell stiffness, summarize stimuli that alter cell stiffness, and discuss signaling pathways and mechanisms that control cell stiffness. Several pathological states are characterized by changes in cell stiffness, suggesting this property can serve as a potential diagnostic marker or therapeutic target. Therefore, we consider the effect of cell stiffness on signaling and growth processes required for homeostasis and dysfunction in healthy and pathological states. Specifically, the composition and structure of the cell membrane and cytoskeleton are major determinants of cell stiffness, and studies have identified signaling pathways that affect cytoskeletal dynamics both directly and by altered gene expression. We present the results of studies interrogating the effects of biophysical and biochemical stimuli on the cytoskeleton and other cellular components and how these factors determine the stiffness of both individual cells and multicellular structures. Overall, these studies represent an intersection of the fields of polymer physics, protein biochemistry, and mechanics, and identify specific mechanisms involved in mediating cell stiffness that can serve as therapeutic targets.

Platelets’ Nanomechanics and Morphology in Neurodegenerative Pathologies

The imaging and force–distance curve modes of atomic force microscopy (AFM) are explored to compare the morphological and mechanical signatures of platelets from patients diagnosed with classical neurodegenerative diseases (NDDs) and healthy individuals. Our data demonstrate the potential of AFM to distinguish between the three NDDs—Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), and normal healthy platelets. The common features of platelets in the three pathologies are reduced membrane surface roughness, area and height, and enhanced nanomechanics in comparison with healthy cells. These changes might be related to general phenomena associated with reorganization in the platelet membrane morphology and cytoskeleton, a key factor for all platelets’ functions. Importantly, the platelets’ signatures are modified to a different extent in the three pathologies, most significant in ALS, less pronounced in PD and the least in AD platelets, which shows the specificity associated with each pathology. Moreover, different degree of activation, distinct pseudopodia and nanocluster formation characterize ALS, PD and AD platelets. The strongest alterations in the biophysical properties correlate with the highest activation of ALS platelets, which reflect the most significant changes in their nanoarchitecture. The specific platelet signatures that mark each of the studied pathologies can be added as novel biomarkers to the currently used diagnostic tools.

Triple negative breast cancer-derived small extracellular vesicles as modulator of biomechanics in target cells

Extracellular vesicle (EV) mediated communication has recently been proposed as one of the pivotal routes in the development of cancer metastasis. EVs are nano-sized vesicles swapped between cells, carrying a biologically active content that can promote tumor-induced immune suppression, metastasis and angiogenesis. Thus, EVs constitute a potential target in cancer therapy. However, their role in triggering the premetastatic niche and in tumor spreading is still unclear. Here, we focused on the EV ability to modulate the biomechanical properties of target cells, known to play a crucial role in metastatic spreading. To this purpose, we isolated and thoroughly characterized triple-negative breast cancer (TNBC)-derived small EVs. We then evaluated variations in the mechanical properties (cell stiffness, cytoskeleton/nuclear/morphology and Yap activity rearrangements) of non-metastatic breast cancer MCF7 cells upon EV treatment. Our results suggest that TNBC-derived small EVs are able to directly modify MCF7 cells by inducing a decrease in cell stiffness, rearrangements in cytoskeleton, focal adhesions and nuclear/cellular morphology, and an increase in Yap downstream gene expression. Testing the biomechanical response of cells after EV addition might represent a new functional assay in metastatic cancer framework that can be exploited for future application both in diagnosis and in therapy.

Impact of Polypyridyl Ru Complexes on Angiogenesis-Contribution to Their Antimetastatic Activity

The use of polypyridyl Ru complexes to inhibit metastasis is a novel approach, and recent studies have shown promising results. We have reported recently that Ru (II) complexes gathering two 4,7-diphenyl-1,10-phenanthroline (dip) ligands and the one being 2,2'-bipyridine (bpy) or its derivative with a 4-[3-(2-nitro-1H-imidazol-1-yl)propyl (bpy-NitroIm) or 5-(4-{4'-methyl-[2,2'-bipyridine]-4-yl}but-1-yn-1-yl)pyridine-2-carbaldehyde semicarbazone (bpy-SC) moieties can alter the metastatic cascade, among others, by modulating cell adhesion properties. In this work, we show further studies of this group of complexes by evaluating their effect on HMEC-1 endothelial cells. While all the tested complexes significantly inhibited the endothelial cell migration, Ru-bpy additionally interrupted the pseudovessels formation. Functional changes in endothelial cells might arise from the impact of the studied compounds on cell elasticity and expression of proteins (vinculin and paxillin) involved in focal adhesions. Furthermore, molecular studies showed that complexes modulate the expression of cell adhesion molecules, which has been suggested to be one of the factors that mediate the activation of angiogenesis. Based on the performed studies, we can conclude that the investigated polypyridyl Ru (II) complexes can deregulate the functionality of endothelial cells which may lead to the inhibition of angiogenesis.

Mechanical Forces Govern Interactions of Host Cells with Intracellular Bacterial Pathogens

To combat infectious diseases, it is important to understand how host cells interact with bacterial pathogens. Signals conveyed from pathogen to host, and vice versa, may be either chemical or mechanical. While the molecular and biochemical basis of host-pathogen interactions has been extensively explored, relatively less is known about mechanical signals and responses in the context of those interactions. Nevertheless, a wide variety of bacterial pathogens appear to have developed mechanisms to alter the cellular biomechanics of their hosts in order to promote their survival and dissemination, and in turn many host responses to infection rely on mechanical alterations in host cells and tissues to limit the spread of infection. In this review, we present recent findings on how mechanical forces generated by host cells can promote or obstruct the dissemination of intracellular bacterial pathogens. In addition, we discuss how in vivo extracellular mechanical signals influence interactions between host cells and intracellular bacterial pathogens. Examples of such signals include shear stresses caused by fluid flow over the surface of cells and variable stiffness of the extracellular matrix on which cells are anchored. We highlight bioengineering-inspired tools and techniques that can be used to measure host cell mechanics during infection. These allow for the interrogation of how mechanical signals can modulate infection alongside biochemical signals. We hope that this review will inspire the microbiology community to embrace those tools in future studies so that host cell biomechanics can be more readily explored in the context of infection studies.

Manipulation and Mechanical Deformation of Leukemia Cells by High-Frequency Ultrasound Single Beam

Ultrasound single-beam acoustic tweezer system has attracted increasing attention in the field of biomechanics. Cell biomechanics play a pivotal role in leukemia cell functions. To better understand and compare the cell mechanics of the leukemia cells, herein, we fabricated an acoustic tweezer system in-house connected with a 50-MHz high-frequency cylinder ultrasound transducer. Selected leukemia cells (Jurkat, K562, and MV-411 cells) were cultured, trapped, and manipulated by high-frequency ultrasound single beam, which was transmitted from the ultrasound transducer without contacting any cells. The relative deformability of each leukemia cell was measured, characterized, and compared, and the leukemia cell (Jurkat cell) gaining the highest deformability was highlighted. Our results demonstrate that the high-frequency ultrasound single beam can be utilized to manipulate and characterize leukemia cells, which can be applied to study potential mechanisms in the immune system and cell biomechanics in other cell types.

Bidirectional Regulation of Cell Mechanical Motion via a Gold Nanorods-Acoustic Streaming System

Cell mechanical motion is a key physiological process that relies on the dynamics of actin filaments. Herein, a localized shear-force system based on gigahertz acoustic streaming (AS) is proposed, which can simultaneously realize intracellular delivery and cellular mechanical regulation. The results demonstrate that gold nanorods (AuNRs) can be delivered into the cytoplasm and even the nuclei of cancer and normal cells within a few minutes by AS stimulation. The delivery efficiency of AS stimulation is four times higher than that of endocytosis. Moreover, AS can effectively promote cytoskeleton assembly, regulate cell stiffness and change cell morphology. Since the inhibitory effect of AuNRs on cytoskeleton assembly, this AuNRs-AS system is able to inhibit or promote cell mechanical motion in a controlled manner by regulating the mechanical properties of cells. The bidirectional regulation of cell motion is further verified via scratch experiments, in which AuNRs-treated cells recover their motion ability through AS stimulation. In particular, the results of AuNRs-AS mechanical regulation on cell are related to the intrinsic properties of cell lines, revealing to more obvious effects on the cells with higher motor capacities. In summary, this acoustic technology has shown superiorities in controllable cell-motion manipulation, indicating its potential in building a multifunctional, integrated cytomechanics regulation platform.

Lipidomic and Membrane Mechanical Signatures in Triple-Negative Breast Cancer: Scope for Membrane-Based Theranostics

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer associated with poor prognosis, higher grade, and a high rate of metastatic occurrence. Limited therapeutic interventions and the compounding issue of drug resistance in triple-negative breast cancer warrants the discovery of novel therapeutic targets and diagnostic modules. To this view, in addition to proteins, lipids also regulate cellular functions via the formation of membranes that modulate membrane protein function, diffusion, and their localization; thus, orchestrating signaling hot spots enriched in specific lipids/proteins on cell membranes. Lipid deregulation in cancer leads to reprogramming of the membrane dynamics and functions impacting cell proliferation, metabolism, and metastasis, providing exciting starting points for developing lipid-based approaches for treating TNBC. In this review, we provide a detailed account of specific lipidic changes in breast cancer, link the altered lipidome with membrane structure and mechanical properties, and describe how these are linked to subsequent downstream functions implicit in cancer progression, metastasis, and chemoresistance. At the fundamental level, we discuss how the lipid-centric findings in TNBC are providing cues for developing lipid-inspired theranostic strategies while bridging existing gaps in our understanding of the functional involvement of lipid membranes in cancer.

A JAM-A-tetraspanin-αvβ5 integrin complex regulates contact inhibition of locomotion

Contact inhibition of locomotion (CIL) is a process that regulates cell motility upon collision with other cells. Improper regulation of CIL has been implicated in cancer cell dissemination. Here, we identify the cell adhesion molecule JAM-A as a central regulator of CIL in tumor cells. JAM-A is part of a multimolecular signaling complex in which tetraspanins CD9 and CD81 link JAM-A to αvβ5 integrin. JAM-A binds Csk and inhibits the activity of αvβ5 integrin-associated Src. Loss of JAM-A results in increased activities of downstream effectors of Src, including Erk1/2, Abi1, and paxillin, as well as increased activity of Rac1 at cell-cell contact sites. As a consequence, JAM-A-depleted cells show increased motility, have a higher cell-matrix turnover, and fail to halt migration when colliding with other cells. We also find that proper regulation of CIL depends on αvβ5 integrin engagement. Our findings identify a molecular mechanism that regulates CIL in tumor cells and have implications on tumor cell dissemination.

Cancer cell mechanobiology: a new frontier for cancer research

The study of physical and mechanical features of cancer cells, or cancer cell mechanobiology, is a new frontier in cancer research. Such studies may enhance our understanding of the disease process, especially mechanisms associated with cancer cell invasion and metastasis, and may help the effort of developing diagnostic biomarkers and therapeutic drug targets. Cancer cell mechanobiological changes are associated with the complex interplay of activation/inactivation of multiple signaling pathways, which can occur at both the genetic and epigenetic levels, and the interactions with the cancer microenvironment. It has been shown that metastatic tumor cells are more compliant than morphologically similar benign cells in actual human samples. Subsequent studies from us and others further demonstrated that cell mechanical properties are strongly associated with cancer cell invasive and metastatic potential, and thus may serve as a diagnostic marker of detecting cancer cells in human body fluid samples. In this review, we provide a brief narrative of the molecular mechanisms underlying cancer cell mechanobiology, the technological platforms utilized to study cancer cell mechanobiology, the status of cancer cell mechanobiological studies in various cancer types, and the potential clinical applications of cancer cell mechanobiological study in cancer early detection, diagnosis, and treatment.

Epithelial plasticity in COPD results in cellular unjamming due to an increase in polymerized actin

The airway epithelium is subjected to insults such as cigarette smoke (CS), a primary cause of chronic obstructive pulmonary disease (COPD) and serves as an excellent model to study cell plasticity. Here, we show that both CS-exposed and COPD-patient derived epithelia (CHBE) display quantitative evidence of cellular plasticity, with loss of specialized apical features and a transcriptional profile suggestive of partial epithelial-to-mesenchymal transition (pEMT), albeit with distinct cell motion indicative of cellular unjamming. These injured/diseased cells have an increased fraction of polymerized actin, due to loss of the actin-severing protein cofilin-1. We observed that decreasing polymerized actin restores the jammed state in both CHBE and CS-exposed epithelia, indicating that the fraction of polymerized actin is critical in unjamming the epithelia. Our kinetic energy spectral analysis suggests that loss of cofilin-1 results in unjamming, similar to that seen with both CS exposure and in CHBE cells. The findings suggest that in response to chronic injury, although epithelial cells display evidence of pEMT, their movement is more consistent with cellular unjamming. Inhibitors of actin polymerization rectify the unjamming features of the monolayer. This article has an associated First Person interview with the first author of the paper.

Bidirectional Modulation of Neuronal Cells Electrical and Mechanical Properties Through Pristine and Functionalized Graphene Substrates

In recent years, the quest for surface modifications to promote neuronal cell interfacing and modulation has risen. This course is justified by the requirements of emerging technological and medical approaches attempting to effectively interact with central nervous system cells, as in the case of brain-machine interfaces or neuroprosthetic. In that regard, the remarkable cytocompatibility and ease of chemical functionalization characterizing surface-immobilized graphene-based nanomaterials (GBNs) make them increasingly appealing for these purposes. Here, we compared the (morpho)mechanical and functional adaptation of rat primary hippocampal neurons when interfaced with surfaces covered with pristine single-layer graphene (pSLG) and phenylacetic acid-functionalized single-layer graphene (fSLG). Our results confirmed the intrinsic ability of glass-supported single-layer graphene to boost neuronal activity highlighting, conversely, the downturn inducible by the surface insertion of phenylacetic acid moieties. fSLG-interfaced neurons showed a significant reduction in spontaneous postsynaptic currents (PSCs), coupled to reduced cell stiffness and altered focal adhesion organization compared to control samples. Overall, we have here demonstrated that graphene substrates, both pristine and functionalized, could be alternatively used to intrinsically promote or depress neuronal activity in primary hippocampal cultures.

SARS-CoV-2 nucleocapsid protein adheres to replication organelles before viral assembly at the Golgi/ERGIC and lysosome-mediated egress

Despite being the target of extensive research efforts due to the COVID-19 (coronavirus disease 2019) pandemic, relatively little is known about the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication within cells. We investigate and characterize the tightly orchestrated virus assembly by visualizing the spatiotemporal dynamics of the four structural SARS-CoV-2 proteins at high resolution. The nucleoprotein is expressed first and accumulates around folded endoplasmic reticulum (ER) membranes in convoluted layers that contain viral RNA replication foci. We find that, of the three transmembrane proteins, the membrane protein appears at the Golgi apparatus/ER-to-Golgi intermediate compartment before the spike and envelope proteins. Relocation of a lysosome marker toward the assembly compartment and its detection in transport vesicles of viral proteins confirm an important role of lysosomes in SARS-CoV-2 egress. These data provide insights into the spatiotemporal regulation of SARS-CoV-2 assembly and refine the current understanding of SARS-CoV-2 replication.

Combating amyloid-induced cellular toxicity and stiffness by designer peptidomimetics

Amyloid beta (Aβ) aggregation species-associated cellular stress instigates cytotoxicity and adverse cellular stiffness in neuronal cells. The study and modulation of these adverse effects demand immediate attention to tackle Alzheimer's disease (AD). We present a de novo design, synthesis and evaluation of Aβ14-23 peptidomimetics with cyclic dipeptide (CDP) units at defined positions. Our study identified Akd^NMC with CDP units at the middle, N- and C-termini as a potent candidate to understand and ameliorate Aβ aggregation-induced cellular toxicity and adverse stiffness.

Aβ14-23 peptidomimetics incorporated with cyclic dipeptide-based unnatural amino acid at defined positions serve as potential candidates to understand and ameliorate amyloid-induced cellular toxicity and physio-mechanical anomalies.

Subcellular elements responsive to the biomechanical activity of triple-negative breast cancer-derived small extracellular vesicles

Triple-negative breast cancer (TNBC) stands out for its aggressive, fast spread, and highly metastatic behavior and for being unresponsive to the classical hormonal therapy. It is considered a disease with a poor prognosis and limited treatment options. Among the mechanisms that contribute to TNBC spreading, attention has been recently paid to small extracellular vesicles (sEVs), nano-sized vesicles that by transferring bioactive molecules to recipient cells play a crucial role in the intercellular communication among cancer, healthy cells, and tumor microenvironment. In particular, TNBC-derived sEVs have been shown to alter proliferation, metastasis, drug resistance, and biomechanical properties of target cells. To shed light on the molecular mechanisms involved in sEVs mediation of cell biomechanics, we investigated the effects of sEVs on the main subcellular players, i.e., cell membrane, cytoskeleton, and nuclear chromatin organization. Our results unveiled that TNBC-derived sEVs are able to promote the formation and elongation of cellular protrusions, soften the cell body, and induce chromatin decondensation in recipient cells. In particular, our data suggest that chromatin decondensation is the main cause of the global cell softening. The present study added new details and unveiled a novel mechanism of activity of the TNBC-derived sEVs, providing information for the efficient translation of sEVs to cancer theranostics.

Cancer-cell stiffening via cholesterol depletion enhances adoptive T-cell immunotherapy

Malignant transformation and tumour progression are associated with cancer-cell softening. Yet how the biomechanics of cancer cells affects T-cell-mediated cytotoxicity and thus the outcomes of adoptive T-cell immunotherapies is unknown. Here we show that T-cell-mediated cancer-cell killing is hampered for cortically soft cancer cells, which have plasma membranes enriched in cholesterol, and that cancer-cell stiffening via cholesterol depletion augments T-cell cytotoxicity and enhances the efficacy of adoptive T-cell therapy against solid tumours in mice. We also show that the enhanced cytotoxicity against stiffened cancer cells is mediated by augmented T-cell forces arising from an increased accumulation of filamentous actin at the immunological synapse, and that cancer-cell stiffening has negligible influence on: T-cell-receptor signalling, production of cytolytic proteins such as granzyme B, secretion of interferon gamma and tumour necrosis factor alpha, and Fas-receptor-Fas-ligand interactions. Our findings reveal a mechanical immune checkpoint that could be targeted therapeutically to improve the effectiveness of cancer immunotherapies.

Mechanical activation of spike fosters SARS-CoV-2 viral infection

The outbreak of SARS-CoV-2 (SARS2) has caused a global COVID-19 pandemic. The spike protein of SARS2 (SARS2-S) recognizes host receptors, including ACE2, to initiate viral entry in a complex biomechanical environment. Here, we reveal that tensile force, generated by bending of the host cell membrane, strengthens spike recognition of ACE2 and accelerates the detachment of spike's S1 subunit from the S2 subunit to rapidly prime the viral fusion machinery. Mechanistically, such mechano-activation is fulfilled by force-induced opening and rotation of spike's receptor-binding domain to prolong the bond lifetime of spike/ACE2 binding, up to 4 times longer than that of SARS-S binding with ACE2 under 10 pN force application, and subsequently by force-accelerated S1/S2 detachment which is up to ~10³ times faster than that in the no-force condition. Interestingly, the SARS2-S D614G mutant, a more infectious variant, shows 3-time stronger force-dependent ACE2 binding and 35-time faster force-induced S1/S2 detachment. We also reveal that an anti-S1/S2 non-RBD-blocking antibody that was derived from convalescent COVID-19 patients with potent neutralizing capability can reduce S1/S2 detachment by 3 × 10⁶ times under force. Our study sheds light on the mechano-chemistry of spike activation and on developing a non-RBD-blocking but S1/S2-locking therapeutic strategy to prevent SARS2 invasion.

Cytoskeletal Actin Structure in Osteosarcoma Cells Determines Metastatic Phenotype via Regulating Cell Stiffness, Migration, and Transmigration

Osteosarcoma is the most common primary malignant bone tumor. The cause of death due to osteosarcoma is typically a consequence of metastasis to the lung. Controlling metastasis leads to improved prognosis for osteosarcoma patients. The cell stiffness of several tumor types is involved in metastatic potential; however, it is unclear whether the metastatic potential of osteosarcoma depends on cell stiffness. In this study, we analyzed the cell stiffness of the low metastatic Dunn cell line and its highly metastatic LM8 subline, and compared actin organization, cell proliferation, and metastasis. Actin cytoskeleton, polymerization, stiffness, and other cellular properties were analyzed. The organization of the actin cytoskeleton was evaluated by staining F-actin with Alexa Fluor 488 phalloidin. Cell stiffness was measured using Atomic Force Microscopy (AFM). Cell proliferation, migration, invasion, and adhesion were also evaluated. All experiments were performed using mouse osteosarcoma cell lines cultured in the absence and presence of cytochalasin. In LM8 cells, actin polymerization was strongly suppressed and actin levels were significantly lower than in Dunn cells. Stiffness evaluation revealed that LM8 cells were significantly softer than Dunn. Young’s modulus images showed more rigid fibrillar structures were present in Dunn cells than in LM8 cells. LM8 cells also exhibited a significantly higher proliferation. The migration and invasion potential were also higher in LM8 cells, whereas the adhesion potential was higher in Dunn cells. The administration of cytochalasin resulted in actin filament fragmentation and decreased actin staining intensity and cell stiffness in both LM8 and Dunn cells. Cells with high metastatic potential exhibited lower actin levels and cell stiffness than cells with low metastatic potential. The metastatic phenotype is highly correlated to actin status and cell stiffness in osteosarcoma cells. These results suggest that evaluation of actin dynamics and cell stiffness is an important quantitative diagnostic parameter for predicting metastatic potential. We believe that these parameters represent new reliable quantitative indicators that can facilitate the development of new drugs against metastasis.

Mechanical Studies of the Third Dimension in Cancer: From 2D to 3D Model

From the development of self-aggregating, scaffold-free multicellular spheroids to the inclusion of scaffold systems, 3D models have progressively increased in complexity to better mimic native tissues. The inclusion of a third dimension in cancer models allows researchers to zoom out from a significant but limited cancer cell research approach to a wider investigation of the tumor microenvironment. This model can include multiple cell types and many elements from the extracellular matrix (ECM), which provides mechanical support for the tissue, mediates cell-microenvironment interactions, and plays a key role in cancer cell invasion. Both biochemical and biophysical signals from the extracellular space strongly influence cell fate, the epigenetic landscape, and gene expression. Specifically, a detailed mechanistic understanding of tumor cell-ECM interactions, especially during cancer invasion, is lacking. In this review, we focus on the latest achievements in the study of ECM biomechanics and mechanosensing in cancer on 3D scaffold-based and scaffold-free models, focusing on each platform's level of complexity, up-to-date mechanical tests performed, limitations, and potential for further improvements.

Extracellular Calcium Ion Concentration Regulates Chondrocyte Elastic Modulus and Adhesion Behavior

Extracellular calcium ion concentration levels increase in human osteoarthritic (OA) joints and contribute to OA pathogenesis. Given the fact that OA is a mechanical problem, the effect of the extracellular calcium level ([Ca²⁺]) on the mechanical behavior of primary human OA chondrocytes remains to be elucidated. Here, we measured the elastic modulus and cell–ECM adhesion forces of human primary chondrocytes with atomic force microscopy (AFM) at different extracellular calcium ion concentration ([Ca²⁺]) levels. With the [Ca²⁺] level increasing from the normal baseline level, the elastic modulus of chondrocytes showed a trend of an increase and a subsequent decrease at the level of [Ca²⁺], reaching 2.75 mM. The maximum increment of the elastic modulus of chondrocytes is a 37% increase at the peak point. The maximum unbinding force of cell-ECM adhesion increased by up to 72% at the peak point relative to the baseline level. qPCR and immunofluorescence also indicated that dose-dependent changes in the expression of myosin and integrin β1 due to the elevated [Ca²⁺] may be responsible for the variations in cell stiffness and cell-ECM adhesion. Scratch assay showed that the chondrocyte migration ability was modulated by cell stiffness and cell-ECM adhesion: as chondrocyte’s elastic modulus and cell-ECM adhesion force increased, the migration speed of chondrocytes decreased. Taken together, our results showed that [Ca²⁺] could regulate chondrocytes stiffness and cell-ECM adhesion, and consequently, influence cell migration, which is critical in cartilage repair.

Integrin α5 mediates intrinsic cisplatin resistance in three-dimensional nasopharyngeal carcinoma spheroids via the inhibition of phosphorylated ERK /caspase-3 induced apoptosis

Nasopharyngeal carcinoma (NPC) originates in the nasopharynx epithelium. Although concurrent chemoradiation therapy followed by chemotherapy is considered as an effective treatment, there is substantial drug resistance in locally advanced NPC patients. One major contributor to the chemoresistance includes aberrant expression of cell adhesion molecules, such as integrin α and β subunits, giving rise to cell adhesion-mediated drug resistance. Thus, the aim of this study was to investigate the effect of integrin α5 on the development of intrinsic cisplatin resistance in NPC and the associated underlying mechanisms using in vitro three-dimensional (3D) spheroid models, as well as induced cisplatin-resistant NPC (NPCcisR). We demonstrated that established 3D highly- (5-8F) and lowly- (6-10B) metastatic NPC spheroids overexpressed integrin α5 and aggravated their resistance to cisplatin. Besides, enhanced integrin α5 resulted in substantially reduced growth, corresponding to G₀/G₁ and G₂/M cell cycle arrest. In addition, 5-8FcisR and 6-10BcisR cells in 3D forms synergistically strengthened endurance of their spheroids to cisplatin treatment as observed by increased resistance index (RI) and decreased apoptosis. Mechanistically, the aberrantly expressed integrin α5 decreased drug susceptibility in NPC spheroids by inactivating ERK and inhibition of caspase-3 inducing apoptosis. Furthermore, the effect of integrin α5 inducing intrinsic resistance was verified via treatment with ATN-161, a peptide inhibitor for integrin α5β1. The results showed dramatic reduction in integrin α5 expression, reversal of ERK phosphorylation and caspase-3 cleavage, together with elevated cisplatin sensitivity, indicating regulation of innate drug resistance via integrin α5. Taken together, our findings suggest that integrin α5 could act as a promising target to enhance the chemotherapeutic sensitivity in NPC.

Hierarchical micro-/nanotopography for tuning structures and mechanics of cells probed by atomic force microscopy

Extracellular matrix plays an important role in regulating the behaviors of cells, and utilizing matrix physics to control cell fate has been a promising way for cell and tissue engineering. However, the nanoscale situations taking place during the topography-regulated cell-matrix interactions are still not fully understood to the best of our knowledge. The invention of atomic force microscopy (AFM) provides a powerful tool to characterize the structures and properties of living biological systems under aqueous conditions with unprecedented spatial resolution. In this work, with the use of AFM, structural and mechanical dynamics of individual cells grown on micro-/nanotopographical surface were revealed. First, the microgroove patterned silicon substrates were fabricated by photolithography. Next, nanogranular topography was formed on microgroove substrates by cell culture medium protein deposition, which was visualized by in situ AFM imaging. The micro-/nanotopographical substrates were then used to grow two types of cells (3T3 cell or MCF-7 cell). AFM morphological imaging and mechanical measurements were applied to characterize the changes of cells grown on the micro-/nanotopographical substrates. The experimental results showed the significant alterations in cellular structures and cellular mechanics caused by micro-/nanotopography. The study provides a novel way based on AFM to unveil the native nanostructures and mechanical properties of cell-matrix interfaces with high spatial resolution in liquids, which will have potential impacts on the studies of topography-tuned cell behaviors.

Stiffening of Cancer Cell Membranes Is a Key Biophysical Mechanism of Primary and Tertiary Cancer Prevention with Green Tea Polyphenols

Over the past 30 years, research of green tea polyphenols, especially (-)-epigallocatechin gallate (EGCG), has revealed that consumption of green tea is a practical and effective primary cancer prevention method for the general population. More recently, we believe that green tea polyphenols are beneficial for tertiary cancer prevention using green tea alone or combined with anticancer drugs because EGCG has the potential to inhibit metastatic progression and stemness, and enhance antitumor immunity. In an effort to identify a common underlying mechanism responsible for EGCG's multifunctional effects on various molecular targets, we studied the biophysical effects of EGCG on cell stiffness using atomic force microscopy. We found that EGCG acts to stiffen the membranes of cancer cells, leading to inhibition of signaling pathways of various receptors. Stiffening of membranes with EGCG inhibited AXL receptor tyrosine kinase, a stimulator of cell softening, motility and stemness, and expression of programmed cell death-ligand 1. This review covers the following: i) primary cancer prevention using EGCG or green tea, ii) tertiary cancer prevention by combining EGCG and anticancer drugs, iii) inhibition of metastasis with EGCG by stiffening the cell membrane, iv) inhibition of AXL receptor tyrosine kinase, a stimulator of cell softening and motility, with EGCG, v) inhibition of stemness properties with EGCG, and vi) EGCG as an alternative chemical immune checkpoint inhibitor. Development of new drugs that enhance stiffening of cancer cell membranes may be an effective strategy for tertiary cancer prevention and treatment.

Contractility, focal adhesion orientation, and stress fiber orientation drive cancer cell polarity and migration along wavy ECM substrates

Contact guidance is a powerful topographical cue that induces persistent directional cell migration. Healthy tissue stroma is characterized by a meshwork of wavy extracellular matrix (ECM) fiber bundles, whereas metastasis-prone stroma exhibit less wavy, more linear fibers. The latter topography correlates with poor prognosis, whereas more wavy bundles correlate with benign tumors. We designed nanotopographic ECM-coated substrates that mimic collagen fibril waveforms seen in tumors and healthy tissues to determine how these nanotopographies may regulate cancer cell polarization and migration machineries. Cell polarization and directional migration were inhibited by fibril-like wave substrates above a threshold amplitude. Although polarity signals and actin nucleation factors were required for polarization and migration on low-amplitude wave substrates, they did not localize to cell leading edges. Instead, these factors localized to wave peaks, creating multiple "cryptic leading edges" within cells. On high-amplitude wave substrates, retrograde flow from large cryptic leading edges depolarized stress fibers and focal adhesions and inhibited cell migration. On low-amplitude wave substrates, actomyosin contractility overrode the small cryptic leading edges and drove stress fiber and focal adhesion orientation along the wave axis to mediate directional migration. Cancer cells of different intrinsic contractility depolarized at different wave amplitudes, and cell polarization response to wavy substrates could be tuned by manipulating contractility. We propose that ECM fibril waveforms with sufficiently high amplitude around tumors may serve as "cell polarization barriers," decreasing directional migration of tumor cells, which could be overcome by up-regulation of tumor cell contractility.

Pulling the springs of a cell by single-molecule force spectroscopy

The fundamental unit of the human body comprises of the cells which remain embedded in a fibrillar network of extracellular matrix proteins which in turn provides necessary anchorage the cells. Tissue repair, regeneration and reprogramming predominantly involve a traction force mediated signalling originating in the ECM and travelling deep into the cell including the nucleus via circuitry of spring-like filamentous proteins like microfilaments or actin, intermediate filaments and microtubules to elicit a response in the form of mechanical movement as well as biochemical changes. The 'springiness' of these proteins is highlighted in their extension-contraction behaviour which is manifested as an effect of differential traction force. Atomic force microscope (AFM) provides the magic eye to visualize and quantify such force-extension/indentation events in these filamentous proteins as well as in whole cells. In this review, we have presented a summary of the current understanding and advancement of such measurements by AFM based single-molecule force spectroscopy in the context of cytoskeletal and nucleoskeletal proteins which act in tandem to facilitate mechanotransduction.

Microfluidic Assessment of Drug Effects on Physical Properties of Androgen Sensitive and Non-Sensitive Prostate Cancer Cells

The identification and treatment of androgen-independent prostate cancer are both challenging and significant. In this work, high-throughput deformability cytometry was employed to assess the effects of two anti-cancer drugs, docetaxel and enzalutamide, on androgen-sensitive prostate cancer cells (LNCaP) and androgen-independent prostate cancer cells (PC-3), respectively. The quantified results show that PC-3 and LNCaP present not only different intrinsic physical properties but also different physical responses to the same anti-cancer drug. PC-3 cells possess greater stiffness and a smaller size than LNCaP cells. As the docetaxel concentration increases, PC-3 cells present an increase in stiffness and size, but LNCaP cells only present an increase in stiffness. As the enzalutamide concentration increases, PC-3 cells present no physical changes but LNCaP cells present changes in both cell size and deformation. These results demonstrated that cellular physical properties quantified by the deformability cytometry are effective indicators for identifying the androgen-independent prostate cancer cells from androgen-sensitive prostate cancer cells and evaluating drug effects on these two types of prostate cancer.

Cell Cytoskeleton and Stiffness Are Mechanical Indicators of Organotropism in Breast Cancer

Simple Summary

Cancer cell dissemination exhibits organ preference or organotropism. Although the influence of intrinsic biochemical factors on organotropism has been intensely studied, little is known about the roles of mechanical properties of metastatic cancer cells. Our study suggests that there may be a correlation between cell cytoskeleton/stiffness and organotropism. We find that the cytoskeleton and stiffness of breast cancer cell subpopulations with different metastatic preference match the mechanics of the metastasized organs. The modification of cell cytoskeleton significantly influences the organotropism-related gene expression pattern and mechanoresponses on soft substrates which mimic brain tissue stiffness. These findings highlight the key role of cell cytoskeleton in specific organ metastasis, which may not only reflect but also impact the metastatic organ preference.

Abstract

Tumor metastasis involves the dissemination of tumor cells from the primary lesion to other organs and the subsequent formation of secondary tumors, which leads to the majority of cancer-related deaths. Clinical findings show that cancer cell dissemination is not random but exhibits organ preference or organotropism. While intrinsic biochemical factors of cancer cells have been extensively studied in organotropism, much less is known about the role of cell cytoskeleton and mechanics. Herein, we demonstrate that cell cytoskeleton and mechanics are correlated with organotropism. The result of cell stiffness measurements shows that breast cancer cells with bone tropism are much stiffer with enhanced F-actin, while tumor cells with brain tropism are softer with lower F-actin than their parental cells. The difference in cellular stiffness matches the difference in the rigidity of their metastasized organs. Further, disrupting the cytoskeleton of breast cancer cells with bone tropism not only elevates the expressions of brain metastasis-related genes but also increases cell spreading and proliferation on soft substrates mimicking the stiffness of brain tissue. Stabilizing the cytoskeleton of cancer cells with brain tropism upregulates bone metastasis-related genes while reduces the mechanoadaptation ability on soft substrates. Taken together, these findings demonstrate that cell cytoskeleton and biophysical properties of breast cancer subpopulations correlate with their metastatic preference in terms of gene expression pattern and mechanoadaptation ability, implying the potential role of cell cytoskeleton in organotropism.

Piezo1 Channels Contribute to the Regulation of Human Atrial Fibroblast Mechanical Properties and Matrix Stiffness Sensing

The mechanical environment of cardiac cells changes continuously and undergoes major alterations during diseases. Most cardiac diseases, including atrial fibrillation, are accompanied by fibrosis which can impair both electrical and mechanical function of the heart. A key characteristic of fibrotic tissue is excessive accumulation of extracellular matrix, leading to increased tissue stiffness. Cells are known to respond to changes in their mechanical environment, but the molecular mechanisms underlying this ability are incompletely understood. We used cell culture systems and hydrogels with tunable stiffness, combined with advanced biophysical and imaging techniques, to elucidate the roles of the stretch-activated channel Piezo1 in human atrial fibroblast mechano-sensing. Changing the expression level of Piezo1 revealed that this mechano-sensor contributes to the organization of the cytoskeleton, affecting mechanical properties of human embryonic kidney cells and human atrial fibroblasts. Our results suggest that this response is independent of Piezo1-mediated ion conduction at the plasma membrane, and mediated in part by components of the integrin pathway. Further, we show that Piezo1 is instrumental for fibroblast adaptation to changes in matrix stiffness, and that Piezo1-induced cell stiffening is transmitted in a paracrine manner to other cells by a signaling mechanism requiring interleukin-6. Piezo1 may be a new candidate for targeted interference with cardiac fibroblast function.

The distribution of liver cancer stem cells correlates with the mechanical heterogeneity of liver cancer tissue

The survival of cancer stem cells is usually limited to a specific tumor microenvironment, and this microenvironment plays a vital role in the development of tumors. The mechanical properties of the microenvironment differ in different regions of solid tumors. However, in solid tumors, whether the distribution of cancer stem cells relates to the mechanical microenvironment of different regions is still unclear. In this study, we undertook a biophysical and biochemical assessment of the changes in the mechanical properties of liver tissue during the progression of liver cancer and explored the distribution of liver cancer stem cells in liver cancer tissues. Our analysis confirmed previous observations that the stiffness of liver tissue gradually increased with the progress of fibrosis. In liver cancer tissues, we found obvious mechanical heterogeneity: the core of the tumor was soft, the invasive front tissue was the hardest, and the para-cancer tissue was in an intermediate state. Interestingly, the greatest number of liver cancer stem cells was found in the invasive front part of the tumor. We finally established that stroma stiffness correlated with the number of liver cancer stem cells. These findings indicate that the distribution of liver cancer stem cells correlates with the mechanical heterogeneity of liver cancer tissue. This result provides a theoretical basis for the development of targeted therapies against the mechanical microenvironment of liver cancer stem cells.

Modulated Start-Up Mode of Cancer Cell Migration Through Spinophilin-Tubular Networks

Spinophilin (SPL) is a multifunctional actin-binding scaffolding protein. Although increased research on SPL in cancer biology has revealed a tumor suppressive role, its modulation in cancer biology, and oncological relevance remains elusive. Thus, we determined the role of SPL in the modulation of the junctional network and cellular migration in A549 lung cancer cell line. Knockdown of SPL promoted cancer cell invasion in agarose spot and scratch wound assays. Attenuation of SPL expression also enhanced invadopodia, as revealed by enhanced vinculin spots, and enhanced sodium bicarbonate cotransporter NBC activity without enhancing membranous expression of NBCn1. Disruption of the tubular structure with nocodazole treatment revealed enhanced SPL expression and reduced NBC activity and A549 migration. SPL-mediated junctional modulation and tubular stability affected bicarbonate transporter activity in A549 cells. The junctional modulatory function of SPL in start-up migration, such as remodeling of tight junctions, enhanced invadopodia, and increased NBC activity, revealed here would support fundamental research and the development of an initial target against lung cancer cell migration.

Human mammary epithelial cells in a mature, stratified epithelial layer flatten and stiffen compared to single and confluent cells

BACKGROUND

The epithelium forms a protective barrier against external biological, chemical and physical insults. So far, AFM-based, micro-mechanical measurements have only been performed on single cells and confluent cells, but not yet on cells in mature layers.

METHODS

Using a combination of atomic force, fluorescence and confocal microscopy, we determined the changes in stiffness, morphology and actin distribution of human mammary epithelial cells (HMECs) as they transition from single cells to confluency to a mature layer.

RESULTS

Single HMECs have a tall, round (planoconvex) morphology, have actin stress fibers at the base, have diffuse cortical actin, and have a stiffness of 1 kPa. Confluent HMECs start to become flatter, basal actin stress fibers start to disappear, and actin accumulates laterally where cells abut. Overall stiffness is still 1 kPa with two-fold higher stiffness in the abutting regions. As HMECs mature and form multilayered structures, cells on apical surfaces become flatter (apically more level), wider, and seven times stiffer (mean, 7 kPa) than single and confluent cells. The main drivers of these changes are actin filaments, as cells show strong actin accumulation in the regions where cells adjoin, and in the apical regions.

CONCLUSIONS

HMECs stiffen, flatten and redistribute actin upon transiting from single cells to mature, confluent layers.

GENERAL SIGNIFICANCE

Our findings advance the understanding of breast ductal morphogenesis and mechanical homeostasis.

Effects of green light photobiomodulation on Dental Pulp Stem Cells: enhanced proliferation and improved wound healing by cytoskeleton reorganization and cell softening

Photobiomodulation (PBM) has been shown to improve cell proliferation and cell migration. Many cell types have been investigated, with most studies using deep penetrating red light irradiation. Considering the interest of surface biostimulation of oral mesenchymal cells after surgical wound, the present study aimed to assess green light irradiation effects on Dental Pulp Stem Cells' (DPSC) proliferation and migration. To understand the mechanisms underlying these effects, we investigated cytoskeleton organization and subsequent cell shape and stiffness. A 532-nm wavelength Nd:YAG laser (30 mW) was applied between 30 and 600 s on DPSC in vitro. Cell proliferation was analyzed at 24, 48, and 72 h after irradiation, by cell counting and enzymatic activity quantification (paranitrophenylphosphate phosphatase (pNPP) test). A wound healing assay was used to study cell migration after irradiation. Effects of PBM on cytoskeleton organization and cell shape were assessed by actin filaments staining. Elasticity changes after irradiation were quantified in terms of Young's modulus measured using Atomic Force Microscopy (AFM) force spectroscopy. Green light significantly improved DPSC proliferation with a maximal effect obtained after 300-s irradiation (energy fluence 5 J/cm2). This irradiation had a significant impact on cell migration, improving wound healing after 24 h. These results were concomitant with a decrease of cells' Young's modulus after irradiation. This cell softening was explained by actin cytoskeleton reorganization, with diminution of cell circularity and more abundant pseudopodia. This study highlights the interest of green laser PMB for the proliferation and migration of mesenchymal stem cells, with encouraging results for clinical application, especially for surgical wound healing procedures.

Methods for Studying Endometrial Pathology and the Potential of Atomic Force Microscopy in the Research of Endometrium

The endometrium lines the uterine cavity, enables implantation of the embryo, and provides an environment for its development and growth. Numerous methods, including microscopic and immunoenzymatic techniques, have been used to study the properties of the cells and tissue of the endometrium to understand changes during, e.g., the menstrual cycle or implantation. Taking into account the existing state of knowledge on the endometrium and the research carried out using other tissues, it can be concluded that the mechanical properties of the tissue and its cells are crucial for their proper functioning. This review intends to emphasize the potential of atomic force microscopy (AFM) in the research of endometrium properties. AFM enables imaging of tissues or single cells, roughness analysis, and determination of the mechanical properties (Young’s modulus) of single cells or tissues, or their adhesion. AFM has been previously shown to be useful to derive force maps. Combining the information regarding cell mechanics with the alternations of cell morphology or gene/protein expression provides deeper insight into the uterine pathology. The determination of the elastic modulus of cells in pathological states, such as cancer, has been proved to be useful in diagnostics.

Enhancement of Podocyte Attachment on Polyacrylamide Hydrogels with Gelatin-Based Polymers

Biological activities of cells such as survival and differentiation processes are mainly maintained by a specific extracellular matrix (ECM). Hydrogels have recently been employed successfully in tissue engineering applications. In particular, scaffolds made of gelatin methacrylate-based hydrogels (GelMA) showed great potential due to their biocompatibility, biofunctionality, and low mechanical strength. The development of a hydrogel having tunable and appropriate mechanical properties as well as chemical and biological cues was the aim of this work. A synthetic and biological hybrid hydrogel was developed to mimic the biological and mechanical properties of native ECM. A combination of gelatin methacrylate and acrylamide (GelMA-AAm)-based hydrogels was studied, and it showed tunable mechanical properties upon changing the polymer concentrations. Different GelMA-AAm samples were prepared and studied by varying the concentrations of GelMA and AAm (AAm_2.5% + GelMA_3%, AAm_5% + GelMA_3%, and AAm_5% + GelMA_5%). The swelling behavior, biodegradability, physicochemical and mechanical properties of GelMA-AAm were also characterized. The results showed a variation of swelling capability and a tunable elasticity ranging from 4.03 to 24.98 kPa depending on polymer concentrations. Moreover, the podocyte cell morphology, cytoskeleton reorganization and differentiation were evaluated as a function of GelMA-AAm mechanical properties. We concluded that the AAm_2.5% + GelMA_3% hydrogel sample having an elasticity of 4.03 kPa can mimic the native kidney glomerular basement membrane (GBM) elasticity and allow podocyte cell attachment without the functionalization of the gel surface with adhesion proteins compared to synthetic hydrogels (PAAm). This work will further enhance the knowledge of the behavior of podocyte cells to understand their biological properties in both healthy and diseased states.

Effect of Substrate Stiffness on Physicochemical Properties of Normal and Fibrotic Lung Fibroblasts

The presented research aims to verify whether physicochemical properties of lung fibroblasts, modified by substrate stiffness, can be used to discriminate between normal and fibrotic cells from idiopathic pulmonary fibrosis (IPF). The impact of polydimethylsiloxane (PDMS) substrate stiffness on the physicochemical properties of normal (LL24) and IPF-derived lung fibroblasts (LL97A) was examined in detail. The growth and elasticity of cells were assessed using fluorescence microscopy and atomic force microscopy working in force spectroscopy mode, respectively. The number of fibroblasts, as well as their shape and the arrangement, strongly depends on the mechanical properties of the substrate. Moreover, normal fibroblasts remain more rigid as compared to their fibrotic counterparts, which may indicate the impairments of IPF-derived fibroblasts induced by the fibrosis process. The chemical properties of normal and IPF-derived lung fibroblasts inspected using time-of-flight secondary ion mass spectrometry, and analyzed complexly with principal component analysis (PCA), show a significant difference in the distribution of cholesterol and phospholipids. Based on the observed distinctions between healthy and fibrotic cells, the mechanical properties of cells may serve as prospective diagnostic biomarkers enabling fast and reliable identification of idiopathic pulmonary fibrosis (IPF).

Application of atomic force microscope in diagnosis of single cancer cells

Changes in mechanical properties of cells are closely related to a variety of diseases. As an advanced technology on the micro/nano scale, atomic force microscopy is the most suitable tool for information acquisition of living cells in human body fluids. AFMs are able to measure and characterize the mechanical properties of cells which can be used as effective markers to distinguish between different cell types and cells in different states (benign or cancerous). Therefore, they can be employed to obtain additional information to that obtained via the traditional biochemistry methods for better identifying and diagnosing cancer cells for humans, proposing better treatment methods and prognosis, and unravelling the pathogenesis of the disease. In this report, we review the use of AFMs in cancerous tissues, organs, and cancer cells cultured in vitro to obtain cellular mechanical properties, demonstrate and summarize the results of AFMs in cancer biology, and look forward to possible future applications and the direction of development.

Recent Advances on the Model, Measurement Technique, and Application of Single Cell Mechanics

Since the cell was discovered by humans, it has been an important research subject for researchers. The mechanical response of cells to external stimuli and the biomechanical response inside cells are of great significance for maintaining the life activities of cells. These biomechanical behaviors have wide applications in the fields of disease research and micromanipulation. In order to study the mechanical behavior of single cells, various cell mechanics models have been proposed. In addition, the measurement technologies of single cells have been greatly developed. These models, combined with experimental techniques, can effectively explain the biomechanical behavior and reaction mechanism of cells. In this review, we first introduce the basic concept and biomechanical background of cells, then summarize the research progress of internal force models and experimental techniques in the field of cell mechanics and discuss the latest mechanical models and experimental methods. We summarize the application directions of cell mechanics and put forward the future perspectives of a cell mechanics model.

Potential antitumor activity of digitoxin and user-designed analog administered to human lung cancer cells

BACKGROUND

Cardiac glycosides (CGs), such as digitoxin, are traditionally used for treatment of congestive heart failure; recently they also gained attention for their anticancer properties. Previous studies showed that digitoxin and a synthetic L-sugar monosaccharide analog treatment decreases cancer cell proliferation, increases apoptosis, and pro-adhesion abilities; however, no reports are available on their potential to alter lung cancer cell cytoskeleton structure and reduce migratory ability. Herein, we investigated the anticancer effects of digitoxin and its analog, digitoxigenin-α-L-rhamnoside (D6MA), to establish whether cytoskeleton reorganization and reduced motility are drug-induced cellular outcomes.

METHODS

We treated non-small cell lung carcinoma cells (NSCLCs) with sub-therapeutic, therapeutic, and toxic concentrations of digitoxin and D6MA respectively, followed by both single point and real-time assays to evaluate changes in cellular gene and protein expression, adhesion, elasticity, and migration.

RESULTS

Digitoxin and D6MA induced a decrease in matrix metalloproteinases expression via altered focal adhesion signaling and a suppression of the phosphoinositide 3-kinases / protein kinase B pathway which lead to enhanced adhesion, altered elasticity, and reduced motility of NSCLCs. Global gene expression analysis identified dose-dependent changes to nuclear factor kappa-light-chain-enhancer, epithelial tumor, and microtubule dynamics signaling.

CONCLUSIONS

Our study demonstrates that digitoxin and D6MA can target antitumor signaling pathways to alter NSCLC cytoskeleton and migratory ability to thus potentially reduce their tumorigenicity.

SIGNIFICANCE

Discovering signaling pathways that control cancer's cell phenotype and how such pathways are affected by CG treatment will potentially allow for active usage of synthetic CG analogs as therapeutic agents in advanced lung conditions.

Physical Constraints and Forces Involved in Phagocytosis

Phagocytosis is a specialized process that enables cellular ingestion and clearance of microbes, dead cells and tissue debris that are too large for other endocytic routes. As such, it is an essential component of tissue homeostasis and the innate immune response, and also provides a link to the adaptive immune response. However, ingestion of large particulate materials represents a monumental task for phagocytic cells. It requires profound reorganization of the cell morphology around the target in a controlled manner, which is limited by biophysical constraints. Experimental and theoretical studies have identified critical aspects associated with the interconnected biophysical properties of the receptors, the membrane, and the actin cytoskeleton that can determine the success of large particle internalization. In this review, we will discuss the major physical constraints involved in the formation of a phagosome. Focusing on two of the most-studied types of phagocytic receptors, the Fcγ receptors and the complement receptor 3 (αMβ2 integrin), we will describe the complex molecular mechanisms employed by phagocytes to overcome these physical constraints.

Unexpected therapeutic effects of cisplatin

Cisplatin is a widely used chemotherapeutic agent that is clinically approved to fight both carcinomas and sarcomas. It has relatively high efficiency in treating ovarian cancers and metastatic testicular cancers. It is generally accepted that the major mechanism of cisplatin anti-cancer action is DNA damage. However, cisplatin is also effective in metastatic cancers and should, therefore, affect slow-cycling cancer stem cells in some way. In this review, we focused on the alternative effects of cisplatin that can support a good therapeutic response. First, attention was paid to the effects of cisplatin at the cellular level such as changes in intracellular pH and cellular mechanical properties. Alternative cellular targets of cisplatin, and the effects of cisplatin on cancer cell metabolism and ER stress were also discussed. Furthermore, the impacts of cisplatin on the tumor microenvironment and in the whole organism context were reviewed. In this review, we try to reveal possible causes of the unexpected effectiveness of this anti-cancer drug.

Mechanical Properties of Human Bronchial Epithelial Cells Expressing Wt- and Mutant CFTR

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). A single recessive mutation, the deletion of phenylalanine 508 (F508del), causes severe CF and resides on 70% of mutant chromosomes. Disorganization of the actin cytoskeleton has been previously reported in relation to the CF phenotype. In this work, we aimed to understand this alteration by means of Atomic Force Microscopy and Force Feedback Microscopy investigation of mechanical properties of cystic fibrosis bronchial epithelial (CFBE) cells stably transduced with either wild type (wt-) or F508del-CFTR. We show here that the expression of mutant CFTR causes a decrease in the cell’s apparent Young modulus as compared to the expression of the wt protein.

Flow-induced Shear Stress Confers Resistance to Carboplatin in an Adherent Three-Dimensional Model for Ovarian Cancer: A Role for EGFR-Targeted Photoimmunotherapy Informed by Physical Stress

A key reason for the persistently grim statistics associated with metastatic ovarian cancer is resistance to conventional agents, including platinum-based chemotherapies. A major source of treatment failure is the high degree of genetic and molecular heterogeneity, which results from significant underlying genomic instability, as well as stromal and physical cues in the microenvironment. Ovarian cancer commonly disseminates via transcoelomic routes to distant sites, which is associated with the frequent production of malignant ascites, as well as the poorest prognosis. In addition to providing a cell and protein-rich environment for cancer growth and progression, ascitic fluid also confers physical stress on tumors. An understudied area in ovarian cancer research is the impact of fluid shear stress on treatment failure. Here, we investigate the effect of fluid shear stress on response to platinum-based chemotherapy and the modulation of molecular pathways associated with aggressive disease in a perfusion model for adherent 3D ovarian cancer nodules. Resistance to carboplatin is observed under flow with a concomitant increase in the expression and activation of the epidermal growth factor receptor (EGFR) as well as downstream signaling members mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) and extracellular signal-regulated kinase (ERK). The uptake of platinum by the 3D ovarian cancer nodules was significantly higher in flow cultures compared to static cultures. A downregulation of phospho-focal adhesion kinase (p-FAK), vinculin, and phospho-paxillin was observed following carboplatin treatment in both flow and static cultures. Interestingly, low-dose anti-EGFR photoimmunotherapy (PIT), a targeted photochemical modality, was found to be equally effective in ovarian tumors grown under flow and static conditions. These findings highlight the need to further develop PIT-based combinations that target the EGFR, and sensitize ovarian cancers to chemotherapy in the context of flow-induced shear stress.

Heavy Metal Exposure Leads to Rapid Changes in Cellular Biophysical Properties

Biophysical properties of cells, such as cell mechanics, cell shape, and cell migration, are emerging hallmarks for characterizing various cell functions. Conversely, disruptions to these biophysical properties may be used as reliable indicators of disruptions to cell homeostasis, such as in the case of chemical-induced toxicity. In this study, we demonstrate that treatment of lead(II) nitrate and cadmium nitrate leads to dosage-dependent changes in a collection of biophysical properties, including cellular traction forces, focal adhesions, mechanical stiffness, cell shape, migration speed, permeability, and wound-healing efficacy in mammalian cells. As those changes appear within a few hours after the treatment with a trace amount of lead/cadmium, our results highlight the promise of using biophysical properties to screen environmental chemicals to identify potential toxicants and establish dose response curves. Our systematic and quantitative characterization of the rapid changes in cytoskeletal structure and cell functions upon heavy metal treatment may inspire new research on the mechanisms of toxicity.

A Soft Mechanical Phenotype of SH-SY5Y Neuroblastoma and Primary Human Neurons Is Resilient to Oligomeric Aβ(1-42) Injury

Aggregated amyloid beta (Aβ) is widely reported to cause neuronal dystrophy and toxicity through multiple pathways: oxidative stress, disrupting calcium homeostasis, and cytoskeletal dysregulation. The neuro-cytoskeleton is a dynamic structure that reorganizes to maintain cell homeostasis in response to varying soluble and physical cues presented from the extracellular matrix (ECM). Due this relationship between cell health and the ECM, we hypothesize that amyloid toxicity may be directly influenced by physical changes to the ECM (stiffness and dimensionality) through mechanosensitive pathways, and while previous studies demonstrated that Aβ can distort focal adhesion signaling with pathological consequences, these studies do not address the physical contribution from a physiologically relevant matrix. To test our hypothesis that physical cues can adjust Aβ toxicity, SH-SY5Y human neuroblastoma and primary human cortical neurons were plated on soft and stiff, 2D polyacrylamide matrices or suspended in 3D collagen gels. Each cell culture was exposed to escalating concentrations of oligomeric or fibrillated Aβ(1-42) with MTS viability and lactate dehydrogenase toxicity assessed. Actin restructuring was further monitored in live cells by atomic force microscopy nanoindentation, and our results demonstrate that increasing either matrix stiffness or exposure to oligomeric Aβ promotes F-actin polymerization and cell stiffening, while mature Aβ fibrils yielded no apparent cell stiffening and minor toxicity. Moreover, the rounded, softer mechanical phenotype displayed by cells plated onto a compliant matrix also demonstrated a resilience to oligomeric Aβ as noted by a significant recovery of viability when compared to same-dosed cells plated on traditional tissue culture plastic. This recovery was reproduced pharmacologically through inhibiting actin polymerization with cytochalasin D prior to Aβ exposure. These studies indicate that the cell-ECM interface can modify amyloid toxicity in neurons and the matrix-mediated pathways that promote this protection may offer unique targets in amyloid pathologies like Alzheimer's disease.

Biophysical changes caused by altered MUC13 expression in pancreatic cancer cells

BACKGROUND

Pancreatic cancer is one of the most lethal cancers in the United States. This is partly due to the difficulty in early detection of this disease as well as poor therapeutic responses to currently available regimens. Our previous reports suggest that mucin 13 (MUC13, a transmembrane mucin common to gastrointestinal cells) is aberrantly expressed in this disease state, and has been implicated with a worsened prognosis and an enhanced metastatic potential in PanCa. However, virtually no information currently exists to describe the biophysical ramifications of this protein.

METHODS

To demonstrate the biophysical effect of MUC13 in PanCa, we generated overexpressing and knockdown model cell lines for PanCa and subsequently subjected them to various biophysical experiments using atomic force microscopy (AFM) and cellular aggregation studies.

RESULTS

AFM-based nanoindentation data showed significant biophysical effects with MUC13 modulation in PanCa cells. The overexpression of MUC13 in Panc-1 cells led to an expected decrease in modulus, and a corresponding decrease in adhesion. With MUC13 knockdown, HPAF-II cells exhibited an increased modulus and adhesion. These results were confirmed with altered cell-cell adhesion as seen with aggregation assays.

CONCLUSIONS

MUC13 led to significant biophysical changes in PanCa cells and which exhibited characteristic phenotypic changes in cells demonstrated in previous work from our lab. This work gives insight into the use of biophysical measurements that could be used to help diagnose or monitor cancers as well as determine the effects of genetic alterations at a mechanical level.

Physical Constraints and Forces Involved in Phagocytosis

Phagocytosis is a specialized process that enables cellular ingestion and clearance of microbes, dead cells and tissue debris that are too large for other endocytic routes. As such, it is an essential component of tissue homeostasis and the innate immune response, and also provides a link to the adaptive immune response. However, ingestion of large particulate materials represents a monumental task for phagocytic cells. It requires profound reorganization of the cell morphology around the target in a controlled manner, which is limited by biophysical constraints. Experimental and theoretical studies have identified critical aspects associated with the interconnected biophysical properties of the receptors, the membrane, and the actin cytoskeleton that can determine the success of large particle internalization. In this review, we will discuss the major physical constraints involved in the formation of a phagosome. Focusing on two of the most-studied types of phagocytic receptors, the Fcγ receptors and the complement receptor 3 (αMβ2 integrin), we will describe the complex molecular mechanisms employed by phagocytes to overcome these physical constraints.

Mechanical Property Changes in Breast Cancer Cells Induced by Stimulation with Macrophage Secretions in Vitro

The contribution of secretions from tumor-associated macrophage (TAM)-like cells to the stimulation of mechanical property changes in murine breast cancer cells was studied using an in vitro model system. A murine breast cancer cell line (FP10SC2) was stimulated by adding macrophage (J774.2) cultivation medium containing stimulation molecules secreted from the macrophages, and changes in mechanical properties were compared before and after stimulation. As a result, cell elasticity decreased, degradation ability of the extracellular matrix increased, and the expression of plakoglobin was upregulated. These results indicate that cancer cell malignancy is upregulated by this stimulation. Moreover, changes in intercellular adhesion strengths between pairs of cancer cells were measured before and after stimulation using atomic force microscopy (AFM). The maximum force required to separate cells was increased by stimulation with the secreted factors. These results indicate the possibility that TAMs cause changes in the mechanical properties of cancer cells in tumor microenvironments, and in vitro measurements of mechanical property changes in cancer cells will be useful to study interactions between cells in tumor microenvironments.