Integrin α5β1 facilitates cancer cell invasion through enhanced contractile forces

Antibody therapy in pancreatic cancer: mAb-ye we're onto something?

Pancreatic cancer remains an extremely deadly disease, with little improvement seen in treatment or outcomes over the last 40 years. Targeted monoclonal antibody therapy is one area that has been explored in attempts to tackle this disease. This review examines antibodies that have undergone clinical evaluation in pancreatic cancer. These antibodies target a wide variety of molecules, including tumour cell surface, stromal, immune and embryonic pathway targets. We discuss the therapeutic utility of these therapies both as monotherapeutics and in combination with other treatments such as chemotherapy. While antibody therapy for pancreatic cancer has yet to yield significant success, lessons learned from research thus far highlights future directions that may help overcome observed hurdles to yield clinically efficacious results.

Artocarpin Targets Focal Adhesion Kinase-Dependent Epithelial to Mesenchymal Transition and Suppresses Migratory-Associated Integrins in Lung Cancer Cells

Focal adhesion kinase (FAK) controls several cancer aggressive potentials of cell movement and dissemination. As epithelial–mesenchymal transition (EMT) and the migratory-associated integrins, known influencers of metastasis, have been found to be linked with FAK activity, this study unraveled the potential pharmacological effect of artocarpin in targeting FAK resulting in the suppression of EMT and migratory behaviors of lung cancer cells. Treatment with artocarpin was applied at concentrations of 0–10 μM, and the results showed non-cytotoxicity in lung cancer cell lines (A549 and H460), normal lung (BEAS-2B) cells and primary metastatic lung cancer cells (ELC12, ELC16, and ELC20). We also found that artocarpin (0–10 µM) had no effect on cell viability, proliferation, and migration in BEAS-2B cells. For metastasis-related approaches, artocarpin significantly inhibited cell migration, invasion, and filopodia formation. Artocarpin also dramatically suppressed anchorage-independent growth, cancer stem cell (CSC) spheroid formation, and viability of CSC-rich spheroids. For molecular targets of artocarpin action, computational molecular docking revealed that artocarpin had the best binding affinity of −8.0 kcal/mol with FAK protein. Consistently, FAK-downstream proteins, namely active Akt (phosphorylated Akt), active mTOR (phosphorylated mTOR), and Cdc42, and EMT marker and transcription factor (N-cadherin, Vimentin, and Slug), were found to be significantly depleted in response to artocarpin treatment. Furthermore, we found the decrease of Caveolin-1 (Cav-1) accompanied by the reduction of integrin-αν and integrin-β3. Taken together, these findings support the anti-metastasis potentials of the compound to be further developed for cancer therapy.

RGD-Binding Integrins Revisited: How Recently Discovered Functions and Novel Synthetic Ligands (Re-)Shape an Ever-Evolving Field

Integrins have been extensively investigated as therapeutic targets over the last decades, which has been inspired by their multiple functions in cancer progression, metastasis, and angiogenesis as well as a continuously expanding number of other diseases, e.g., sepsis, fibrosis, and viral infections, possibly also Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2). Although integrin-targeted (cancer) therapy trials did not meet the high expectations yet, integrins are still valid and promising targets due to their elevated expression and surface accessibility on diseased cells. Thus, for the future successful clinical translation of integrin-targeted compounds, revisited and innovative treatment strategies have to be explored based on accumulated knowledge of integrin biology. For this, refined approaches are demanded aiming at alternative and improved preclinical models, optimized selectivity and pharmacological properties of integrin ligands, as well as more sophisticated treatment protocols considering dose fine-tuning of compounds. Moreover, integrin ligands exert high accuracy in disease monitoring as diagnostic molecular imaging tools, enabling patient selection for individualized integrin-targeted therapy. The present review comprehensively analyzes the state-of-the-art knowledge on the roles of RGD-binding integrin subtypes in cancer and non-cancerous diseases and outlines the latest achievements in the design and development of synthetic ligands and their application in biomedical, translational, and molecular imaging approaches. Indeed, substantial progress has already been made, including advanced ligand designs, numerous elaborated pre-clinical and first-in-human studies, while the discovery of novel applications for integrin ligands remains to be explored.

Self-reinforcing directionality generates truncated Lévy walks without the power-law assumption

We introduce a persistent random walk model with finite velocity and self-reinforcing directionality, which explains how exponentially distributed runs self-organize into truncated Lévy walks observed in active intracellular transport by Chen et al. [Nature Mater., 14, 589 (2015)10.1038/nmat4239]. We derive the nonhomogeneous in space and time, hyperbolic partial differential equation for the probability density function (PDF) of particle position. This PDF exhibits a bimodal density (aggregation phenomena) in the superdiffusive regime, which is not observed in classical linear hyperbolic and Lévy walk models. We find the exact solutions for the first and second moments and criteria for the transition to superdiffusion.

A crossroad between placental and tumor biology: What have we learnt?

Placenta in certain species including the human has evolved as a highly invasive tumor-like organ invading the uterus aned its vasculature to derive oxygen and nutrients for the fetus and exchange waste products. While several excellent reviews have been written comparing hemochorial placentation with tumors, no comprehensive review is available dealing with mechanistic insights into what makes them different, and what tumor biologists can learn from placental biologists, and vice versa. In this review, we analyze the structure-function relationship of the human placenta, emphasizing the functional need of the spatio-temporally orchestrated trophoblast invasiveness for fetal development and growth, and pathological consequences of aberrant invasiveness for fetal and maternal health. We then analyze similarities and differences between the placenta and invasive tumors in terms of hallmarks of cancer, some key molecules regulating their invasive functions, and how placental cancers (choriocarcinomas) or other cancers become refractory or even addicted to these invasion-restraining molecules. We cite in vitro models of human trophoblast and choriocarcinoma cell lines utilized to study mechanisms in normal placental development as well as those responsible for tumor progression. We discuss the pathobiology of hyper-invasive placentas and show thattrophoblastic neoplasias are a unique and heterogeneous class of tumors. We delve into the questions as to why metastasis from other organs rarely occurs at the placental site and whether pregnancy makes the mother more or less vulnerable to cancer-related morbidity/mortality. We attempt to compare trophoblast stem cells and cancer stem cells. Finally, we leave the readers with some thoughts as foods of future investigations.

Tissue engineered platforms for studying primary and metastatic neoplasm behavior in bone

Cancer is the second leading cause of death in the United States, claiming more than 560,000 lives each year. Osteosarcoma (OS) is the most common primary malignant tumor of bone in children and young adults, while bone is a common site of metastasis for tumors initiating from other tissues. The heterogeneity, continual evolution, and complexity of this disease at different stages of tumor progression drives a critical need for physiologically relevant models that capture the dynamic cancer microenvironment and advance chemotherapy techniques. Monolayer cultures have been favored for cell-based research for decades due to their simplicity and scalability. However, the nature of these models makes it impossible to fully describe the biomechanical and biochemical cues present in 3-dimensional (3D) microenvironments, such as ECM stiffness, degradability, surface topography, and adhesivity. Biomaterials have emerged as valuable tools to model the behavior of various cancers by creating highly tunable 3D systems for studying neoplasm behavior, screening chemotherapeutic drugs, and developing novel treatment delivery techniques. This review highlights the recent application of biomaterials toward the development of tumor models, details methods for their tunability, and discusses the clinical and therapeutic applications of these systems.

The Roles of Integrin α5β1 in Human Cancer

Cell adhesion to the extracellular matrix has important roles in tissue integrity and human health. Integrins are heterodimeric cell surface receptors that are composed by two non-covalently linked alpha and beta subunits that mainly participate in the interaction of cell-cell adhesion and cell-extracellular matrix and regulate cell motility, adhesion, differentiation, migration, proliferation, etc. In mammals, there have been eighteen α subunits and 8 β subunits and so far 24 distinct types of αβ integrin heterodimers have been identified in humans. Integrin α5β1, also known as the fibronectin receptor, is a heterodimer with α5 and β1 subunits and has emerged as an essential mediator in many human carcinomas. Integrin α5β1 alteration is closely linked to the progression of several types of human cancers, including cell proliferation, angiogenesis, tumor metastasis, and cancerogenesis. In this review, we will introduce the functions of integrin α5β1 in cancer progression and also explore its regulatory mechanisms. Additionally, the potential clinical applications as a target for cancer imaging and therapy are discussed. Collectively, the information reviewed here may increase the understanding of integrin α5β1 as a potential therapeutic target for cancer.

Nanoscale Molecular Quantification of Stem Cell-Hydrogel Interactions

A common approach to tailoring synthetic hydrogels for regenerative medicine applications involves incorporating RGD cell adhesion peptides, yet assessing the cellular response to engineered microenvironments at the nanoscale remains challenging. To date, no study has demonstrated how RGD concentration in hydrogels affects the presentation of individual cell surface receptors. Here we studied the interaction between human mesenchymal stem cells (hMSCs) and RGD-functionalized poly(ethylene glycol) hydrogels, by correlating macro- and nanoscale single-cell interfacial quantification techniques. We quantified RGD unbinding forces on a synthetic hydrogel using single cell atomic force spectroscopy, revealing that short-term binding of hMSCs was sensitive to RGD concentration. We also performed direct stochastic optical reconstruction microscopy (dSTORM) to quantify the molecular interactions between integrin α5β1 and a biomaterial, unexpectedly revealing that increased integrin clustering at the hydrogel-cell interface correlated with fewer available RGD binding sites. Our complementary, quantitative approach uncovered mechanistic insights into specific stem cell-hydrogel interactions, where dSTORM provides nanoscale sensitivity to RGD-dependent differences in cell surface localization of integrin α5β1. Our findings reveal that it is possible to precisely determine how peptide-functionalized hydrogels interact with cells at the molecular scale, thus providing a basis to fine-tune the spatial presentation of bioactive ligands.

New Actors Driving the Epithelial-Mesenchymal Transition in Cancer: The Role of Leptin

Leptin is a hormone secreted mainly by adipocytes; physiologically, it participates in the control of appetite and energy expenditure. However, it has also been linked to tumor progression in different epithelial cancers. In this review, we describe the effect of leptin on epithelial-mesenchymal transition (EMT) markers in different study models, including in vitro, in vivo, and patient studies and in various types of cancer, including breast, prostate, lung, and ovarian cancer. The different studies report that leptin promotes the expression of mesenchymal markers and a decrease in epithelial markers, in addition to promoting EMT-related processes such as cell migration and invasion and poor prognosis in patients with cancer. Finally, we report that leptin has the greatest biological relevance in EMT and tumor progression in breast, lung, prostate, esophageal, and ovarian cancer. This relationship could be due to the key role played by the enriched tumor microenvironment in adipose tissue. Together, these findings demonstrate that leptin is a key biomolecule that drives EMT and metastasis in cancer.

Collective cancer cell invasion in contact with fibroblasts through integrin-α5β1/fibronectin interaction in collagen matrix

Interaction of cancer cells with cancer-associated fibroblasts (CAFs) plays critical roles in tumor progression. Recently we proposed a new tumor invasion mechanism in which invasive cancer cells individually migrate on elongate protrusions of CAFs (CAF fibers) in 3-D collagen matrix. In this mechanism, cancer cells interact with fibronectin fibrils assembled on CAFs mainly through integrin-α5β1. Here we tested whether this mechanism is applicable to the collective invasion of cancer cells, using two E-cadherin-expressing adenocarcinoma cell lines, DLD-1 (colon) and MCF-7 (breast). When hybrid spheroids of DLD-1 cells with CAFs were embedded into collagen gel, DLD-1 cells collectively but very slowly migrated through the collagen matrix in contact with CAFs. Epidermal growth factor and tumor necrosis factor-α promoted the collective invasion, possibly by reducing the E-cadherin junction, as did the transforming growth factor-β inhibitor SB431542 by stimulating the outgrowth of CAFs. Transforming growth factor-β itself inhibited the cancer cell invasion. Efficient collective invasion of DLD-1 cells required large CAF fibers or their assembly as stable adhesion substrates. Experiments with function-blocking Abs and siRNAs confirmed that DLD-1 cells adhered to fibronectin fibrils on CAFs mainly through integrin-α5β1. Anti-E-cadherin Ab promoted the single cell invasion of DLD-1 cells by dissociating the E-cadherin junction. Although the binding affinity of MCF-7 cells to CAFs was lower than DLD-1, they also collectively invaded the collagen matrix in a similar fashion to DLD-1 cells. Our results suggest that the direct interaction with CAFs, as well as environmental cytokines, contributes to the collective invasion of cancers.

Advancing Cell-Instructive Biomaterials Through Increased Understanding of Cell Receptor Spacing and Material Surface Functionalization

Abstract

Regenerative medicine is aimed at restoring normal tissue function and can benefit from the application of tissue engineering and nano-therapeutics. In order for regenerative therapies to be effective, the spatiotemporal integration of tissue-engineered scaffolds by the native tissue, and the binding/release of therapeutic payloads by nano-materials, must be tightly controlled at the nanoscale in order to direct cell fate. However, due to a lack of insight regarding cell–material interactions at the nanoscale and subsequent downstream signaling, the clinical translation of regenerative therapies is limited due to poor material integration, rapid clearance, and complications such as graft-versus-host disease. This review paper is intended to outline our current understanding of cell–material interactions with the aim of highlighting potential areas for knowledge advancement or application in the field of regenerative medicine. This is achieved by reviewing the nanoscale organization of key cell surface receptors, the current techniques used to control the presentation of cell-interactive molecules on material surfaces, and the most advanced techniques for characterizing the interactions that occur between cell surface receptors and materials intended for use in regenerative medicine.

Lay Summary

The combination of biology, chemistry, materials science, and imaging technology affords exciting opportunities to better diagnose and treat a wide range of diseases. Recent advances in imaging technologies have enabled better understanding of the specific interactions that occur between human cells and their immediate surroundings in both health and disease. This biological understanding can be used to design smart therapies and tissue replacements that better mimic native tissue. Here, we discuss the advances in molecular biology and technologies that can be employed to functionalize materials and characterize their interaction with biological entities to facilitate the design of more sophisticated medical therapies.

Actin as a Target to Reduce Cell Invasiveness in Initial Stages of Metastasis

We demonstrate the relative roles of the cell cytoskeleton, and specific importance of actin in facilitating mechanical aspects of metastatic invasion. A crucial step in metastasis, the typically lethal spread of cancer to distant body-sites, is cell invasion through dense tissues composed of extracellular matrix and various non-cancerous cells. Cell invasion requires cell-cytoskeleton remodeling to facilitate dynamic morphological changes and force application. We have previously shown invasive cell subsets in heterogeneous samples can rapidly (2 h) and forcefully indent non-degradable, impenetrable, synthetic gels to cell-scale depths. The amounts of indenting cells and their attained depths provide the mechanical invasiveness of the sample, which as we have shown agrees with the in vitro metastatic potential and the in vivo metastatic risk in humans. To identify invasive force-application mechanisms, we evaluated changes in mechanical invasiveness following chemical perturbations targeting the structure and function of cytoskeleton elements and associated proteins. We evaluate effects on short-term (2-hr) indentations of single, well-spaced or closely situated cells as compared to long-time-scale Boyden chamber migration. We show that actomyosin inhibition may be used to reduce (mechanical) invasiveness of single or collectively invading cells, while actin-disruption may induce escape-response of treated single-cells, which may promote metastasis.

Exposure of the cryptic de-adhesive site FNIII14 in fibronectin molecule and its binding to membrane-type eEF1A induce migration and invasion of cancer cells via β1-integrin inactivation

Cell migration is a highly coordinated process that involves not only integrin-mediated adhesion but also de-adhesion. We previously found that a cryptic de-adhesive site within fibronectin molecule, termed FNIII14, weakens cell adhesion to the extracellular matrix by inactivating β1-integrins. Surprisingly, eukaryotic translation elongation factor-1A (eEF1A), an essential factor during protein biosynthesis, was identified as a membrane receptor that mediates the de-adhesive effect of FNIII14. Here, we demonstrate that FNIII14-mediated de-adhesion causes enhanced migration and invasion in two types of highly invasive/metastatic cancer cells, resulting in the initiation of metastasis. Both in vitro migration and invasion of highly invasive human melanoma cell line, Mum2B, were inhibited by a matrix metalloproteinase (MMP)-2/9 inhibitor or a function-blocking antibody against FNIII14 (anti-FNIII14 Ab), suggesting that MMP-mediated exposure of the cryptic de-adhesive site FNIII14 was responsible for Mum2B cell migration and invasion. The MMP-induced FNIII14 exposure was also shown to be functional in the migration and invasion of highly metastatic mouse breast cancer cell line 4T1. Overexpression and knockdown experiments of eEF1A in Mum2B cells revealed that the migration and invasion were dependent on the membrane levels of eEF1A. In vivo experiments using tumor xenograft mouse models derived from Mum2B and 4T1 cell lines showed that the anti-FNIII14 Ab has a significant anti-metastatic effect. Thus, these results provide novel insights into the regulation of cancer cell migration and invasion and suggest promising targets for anti-metastasis strategies.

Expression of PDGF-A, PDGFRA, integrin subunit alpha V and selectin E is increased in canine cutaneous fibrosarcomas

We investigated the expression of platelet derived growth factor alpha (PDGFA); its receptor, PDGFRA; integrin subunit alpha V; and selectin E in cutaneous fibrosarcomas in dogs. Ten cases of canine fibrosarcomas were obtained from the archive of the Department of Pathology, Ondokuz Mayis University, Samsun. Tissue sections were cut and stained with hematoxylin and eosin, Alcian blue-periodic acid Schiff, Masson's trichrome, and also immunostained. Eight tumors classified as spontaneous fibrosarcomas exhibited interwoven bundles of spindle shaped cells with oval to plump nuclei and scant cytoplasm, while two tumors exhibited features of injection site fibrosarcoma with peripheral infiltration of mononuclear cells and intratumor necrosis. We found that neoplastic cells from all cases exhibited cytoplasmic expression of PDGFA, and cytoplasmic and nuclear staining for PDGFRA. Integrin subunit alpha V immunostaining was observed in all cases, while selectin E expression was observed in vascular endothelial cells and neoplastic cells. A significant positive correlation was found between the expression of PDGFA and integrin subunit alpha V. Our findings indicate that PDGFA, PDGFRA, integrin subunit alpha V and selectin E are expressed strongly in canine cutaneous fibrosarcomas and may contribute to tumor progression.

Mechanical Cues Affect Migration and Invasion of Cells From Three Different Directions

Cell migration and invasion is a key driving factor for providing essential cellular functions under physiological conditions or the malignant progression of tumors following downward the metastatic cascade. Although there has been plentiful of molecules identified to support the migration and invasion of cells, the mechanical aspects have not yet been explored in a combined and systematic manner. In addition, the cellular environment has been classically and frequently assumed to be homogeneous for reasons of simplicity. However, motility assays have led to various models for migration covering only some aspects and supporting factors that in some cases also include mechanical factors. Instead of specific models, in this review, a more or less holistic model for cell motility in 3D is envisioned covering all these different aspects with a special emphasis on the mechanical cues from a biophysical perspective. After introducing the mechanical aspects of cell migration and invasion and presenting the heterogeneity of extracellular matrices, the three distinct directions of cell motility focusing on the mechanical aspects are presented. These three different directions are as follows: firstly, the commonly used invasion tests using structural and structure-based mechanical environmental signals; secondly, the mechano-invasion assay, in which cells are studied by mechanical forces to migrate and invade; and thirdly, cell mechanics, including cytoskeletal and nuclear mechanics, to influence cell migration and invasion. Since the interaction between the cell and the microenvironment is bi-directional in these assays, these should be accounted in migration and invasion approaches focusing on the mechanical aspects. Beyond this, there is also the interaction between the cytoskeleton of the cell and its other compartments, such as the cell nucleus. In specific, a three-element approach is presented for addressing the effect of mechanics on cell migration and invasion by including the effect of the mechano-phenotype of the cytoskeleton, nucleus and the cell's microenvironment into the analysis. In precise terms, the combination of these three research approaches including experimental techniques seems to be promising for revealing bi-directional impacts of mechanical alterations of the cellular microenvironment on cells and internal mechanical fluctuations or changes of cells on the surroundings. Finally, different approaches are discussed and thereby a model for the broad impact of mechanics on cell migration and invasion is evolved.

Environmentally controlled magnetic nano-tweezer for living cells and extracellular matrices

The magnetic tweezer technique has become a versatile tool for unfolding or folding of individual molecules, mainly DNA. In addition to single molecule analysis, the magnetic tweezer can be used to analyze the mechanical properties of cells and extracellular matrices. We have established a magnetic tweezer that is capable of measuring the linear and non-linear viscoelastic behavior of a wide range of soft matter in precisely controlled environmental conditions, such as temperature, CO₂ and humidity. The magnetic tweezer presented in this study is suitable to detect specific differences in the mechanical properties of different cell lines, such as human breast cancer cells and mouse embryonic fibroblasts, as well as collagen matrices of distinct concentrations in the presence and absence of fibronectin crosslinks. The precise calibration and control mechanism employed in the presented magnetic tweezer setup provides the ability to apply physiological force up to 5 nN on 4.5 µm superparamagnetic beads coated with fibronectin and coupled to the cells or collagen matrices. These measurements reveal specific local linear and non-linear viscoelastic behavior of the investigated samples. The viscoelastic response of cells and collagen matrices to the force application is best described by a weak power law behavior. Our results demonstrate that the stress stiffening response and the fluidization of cells is cell type specific and varies largely between differently invasive and aggressive cancer cells. Finally, we showed that the viscoelastic behavior of collagen matrices with and without fibronectin crosslinks measured by the magnetic tweezer can be related to the microstructure of these matrices.

S100A9 promotes prostate cancer cell invasion by activating TLR4/NF-κB/integrin β1/FAK signaling

Background

S100A9, which is expressed in prostate cancer, has been reported in association with prostate cancer progression. However, the role of S100A9 in prostate cancer metastasis is largely unknown. The aim of this study was to investigate the effect of S100A9 on prostate cancer cell invasion and the involved mechanisms.

Materials and methods

Integrin β1 expression in PC-3 and DU-145 cells was determined by quantitative real-time polymerase chain reaction (PCR) (qRT-PCR) and Western blot. Cellular invasion was measured by transwell invasion assay. Western blot was used to determine protein expression. Concentrations of S100A9 and fibronectin were analyzed by enzyme-linked immunosorbent assay. The protein interaction was detected by immunoprecipitation. The NF-κB activity was measured by luciferase reporter assay. The DU-145 cells metastasis in vivo was determined in mice xenograft models after S100A9 overexpression.

Results

S100A9 promoted prostate cancer cells invasion, integrin β1 expression and fibronectin secretion. Further investigation evidenced that S100A9 interacted with Toll-like receptor 4 (TLR4) and activated NF-κB, which was responsible for tumor cell invasion, integrin β1 up-regulation and focal adhesion kinase (FAK) phosphorylation. Furthermore, integrin β1 inhibition led to decreased FAK phosphorylation and reduced tumor cell invasion. Overexpression of S100A9 increased xenograft tumor micro-metastases, integrin β1 expression and induced NF-κB and FAK activation in vivo.

Conclusion

Our study demonstrated that S100A9 promotes prostate cancer cell invasion, and one of the underlying molecular mechanisms is that S100A9 activates integrin β1/FAK through TLR4/NF-κB signaling leading to metastasis of prostate cancer cell.

A Multiscale Model to Predict Neuronal Cell Deformation with Varying Extracellular Matrix Stiffness and Topography

INTRODUCTION

Neuronal cells are sensitive to mechanical properties of extracellular matrix (ECM) such as stiffness and topography. Cells contract and exert a force on ECM to detect the microenvironment, which activates the signaling pathway to influence the cell functions such as differentiation, migration, and proliferation. There are numerous transmembrane proteins that transmit signals; however, integrin and neural cellular adhesion molecules (NCAM) play an important role in sensing the ECM mechanical properties. Mechanotransduction of cell-ECM is the key to understand the influence of ECM stiffness and topography; therefore, in this study, we develop a multiscale computational model to investigate these properties.

METHODS

This model couples the molecular behavior of integrin and NCAM to microscale interactions of neuronal cell and the ECM. We analyze the atomistic/molecular behavior of integrin and NCAM due to mechanical stimuli using steered molecular dynamics. The microscale properties of the neuronal cell and the ECM are simulated using non-linear finite element analysis by applying cell contractility.

RESULTS

We predict that by increasing the ECM stiffness, a neuronal cell exerts greater stress on the ECM. However, this stress reaches a saturation value for a threshold stiffness of ECM, and the saturation value is affected by the ECM thickness, topography, and clustering of integrin and NCAMs. Further, the ECM topography leads to asymmetric stress and deformation in the neuronal cell. Predicted stress distribution in neuronal cell and ECM are consistent with experimental results from the literature.

CONCLUSION

The multiscale computational model will guide in selecting the optimal ECM stiffness and topography range for in vitro studies.

Probing the recognition specificity of αVβ1 integrin and syndecan-4 using force spectroscopy

The knowledge on how cells interact with microenvironment is particularly important in understanding the interaction of cancer cells with surrounding stroma, which affects cell migration, adhesion, and metastasis. The main cell surface receptors responsible for the interaction with extracellular matrix (ECM) are integrins, however, they are not the only ones. Integrins are accompanied to other molecules such as syndecans. The role of the latter has not yet been fully established. In our study, we would like to answer the question of whether integrins and syndecans, possessing similar functions, share also similar unbinding properties. By using single molecule force spectroscopy (SMFS), we conducted measurements of the unbinding properties of α_Vβ₁ and syndecan-4 in the interaction with vitronectin (VN), which, as each ECM protein, possesses two binding sites specific to integrins and syndecans. The unbinding force and the kinetic off rate constant derived from SMFS describe the stability of single molecular complex. Obtained data show one barrier transition for each complex. The proposed model shows that the unbinding of α_Vβ₁ from VN proceeds before the unbinding of SDC-4. However, despite different unbinding kinetics, the access to both receptors is needed for cell growth and proliferation.

Effect of Nuclear Stiffness on Cell Mechanics and Migration of Human Breast Cancer Cells

The migration and invasion of cancer cells through 3D confined extracellular matrices is coupled to cell mechanics and the mechanics of the extracellular matrix. Cell mechanics is mainly determined by both the mechanics of the largest organelle in the cell, the nucleus, and the cytoskeletal architecture of the cell. Hence, cytoskeletal and nuclear mechanics are the major contributors to cell mechanics. Among other factors, steric hindrances of the extracellular matrix confinement are supposed to affect nuclear mechanics and thus also influence cell mechanics. Therefore, we propose that the percentage of invasive cells and their invasion depths into loose and dense 3D extracellular matrices is regulated by both nuclear and cytoskeletal mechanics. In order to investigate the effect of both nuclear and cytoskeletal mechanics on the overall cell mechanics, we firstly altered nuclear mechanics by the chromatin de-condensing reagent Trichostatin A (TSA) and secondly altered cytoskeletal mechanics by addition of actin polymerization inhibitor Latrunculin A and the myosin inhibitor Blebbistatin. In fact, we found that TSA-treated MDA-MB-231 human breast cancer cells increased their invasion depth in dense 3D extracellular matrices, whereas the invasion depths in loose matrices were decreased. Similarly, the invasion depths of TSA-treated MCF-7 human breast cancer cells in dense matrices were significantly increased compared to loose matrices, where the invasion depths were decreased. These results are also valid in the presence of a matrix-metalloproteinase inhibitor GM6001. Using atomic force microscopy (AFM), we found that the nuclear stiffnesses of both MDA-MB-231 and MCF-7 breast cancer cells were pronouncedly higher than their cytoskeletal stiffness, whereas the stiffness of the nucleus of human mammary epithelial cells was decreased compared to their cytoskeleton. TSA treatment reduced cytoskeletal and nuclear stiffness of MCF-7 cells, as expected. However, a softening of the nucleus by TSA treatment may induce a stiffening of the cytoskeleton of MDA-MB-231 cells and subsequently an apparent stiffening of the nucleus. Inhibiting actin polymerization using Latrunculin A revealed a softer nucleus of MDA-MB-231 cells under TSA treatment. This indicates that the actin-dependent cytoskeletal stiffness seems to be influenced by the TSA-induced nuclear stiffness changes. Finally, the combined treatment with TSA and Latrunculin A further justifies the hypothesis of apparent nuclear stiffening, indicating that cytoskeletal mechanics seem to be regulated by nuclear mechanics.

The SHCA adapter protein cooperates with lipoma-preferred partner in the regulation of adhesion dynamics and invadopodia formation

SHC adaptor protein (SHCA) and lipoma-preferred partner (LPP) mediate transforming growth factor β (TGFβ)-induced breast cancer cell migration and invasion. Reduced expression of either protein diminishes breast cancer lung metastasis, but the reason for this effect is unclear. Here, using total internal reflection fluorescence (TIRF) microscopy, we found that TGFβ enhanced the assembly and disassembly rates of paxillin-containing adhesions in an SHCA-dependent manner through the phosphorylation of the specific SHCA tyrosine residues Tyr-239, Tyr-240, and Tyr-313. Using a BioID proximity labeling approach, we show that SHCA exists in a complex with a variety of actin cytoskeletal proteins, including paxillin and LPP. Consistent with a functional interaction between SHCA and LPP, TGFβ-induced LPP localization to cellular adhesions depended on SHCA. Once localized to the adhesions, LPP was required for TGFβ-induced increases in cell migration and adhesion dynamics. Mutations that impaired LPP localization to adhesions (mLIM1) or impeded interactions with the actin cytoskeleton via α-actinin (ΔABD) abrogated migratory responses to TGFβ. Live-cell TIRF microscopy revealed that SHCA clustering at the cell membrane preceded LPP recruitment. We therefore hypothesize that, in the presence of TGFβ, SHCA promotes the formation of small, dynamic adhesions by acting as a nucleator of focal complex formation. Finally, we defined a previously unknown function for SHCA in the formation of invadopodia, a process that also required LPP. Our results reveal that SHCA controls the formation and function of adhesions and invadopodia, two key cellular structures required for breast cancer metastasis.

Qualitative analysis of contribution of intracellular skeletal changes to cellular elasticity

Cells are dynamic structures that continually generate and sustain mechanical forces within their environments. Cells respond to mechanical forces by changing their shape, moving, and differentiating. These reactions are caused by intracellular skeletal changes, which induce changes in cellular mechanical properties such as stiffness, elasticity, viscoelasticity, and adhesiveness. Interdisciplinary research combining molecular biology with physics and mechanical engineering has been conducted to characterize cellular mechanical properties and understand the fundamental mechanisms of mechanotransduction. In this review, we focus on the role of cytoskeletal proteins in cellular mechanics. The specific role of each cytoskeletal protein, including actin, intermediate filaments, and microtubules, on cellular elasticity is summarized along with the effects of interactions between the fibers.

Integrin Subtypes and Nanoscale Ligand Presentation Influence Drug Sensitivity in Cancer Cells

Cancer cell-matrix interactions have been shown to enhance cancer cell survival via the activation of pro-survival signaling pathways. These pathways are initiated at the site of interaction, i.e., integrins, and thus, their inhibition has been the target of therapeutic strategies. Individual roles for fibronectin-binding integrin subtypes α_vβ₃ and α₅β₁ have been shown for various cellular processes; however, a systematic comparison of their function in adhesion-dependent chemoresistance is lacking. Here, we utilize integrin subtype-specific peptidomimetics for α_vβ₃ and α₅β₁, both as blocking agents on fibronectin-coated surfaces and as surface-immobilized adhesion sites, in order to parse out their role in breast cancer cell survival. Block copolymer micelle nanolithography is utilized to immobilize peptidomimetics onto highly ordered gold nanoparticle arrays with biologically relevant interparticle spacings (35, 50, or 70 nm), thereby providing a platform for ascertaining the dependence of ligand spacing in chemoprotection. We show that several cellular properties-morphology, focal adhesion formation, and migration-are intricately linked to both the integrin subtype and their nanospacing. Importantly, we show that chemotherapeutic drug sensitivity is highly dependent on both parameters, with smaller ligand spacing generally hindering survival. Furthermore, we identify ligand type-specific patterns of drug sensitivity, with enhanced chemosurvival when cells engage α_vβ₃ vs α₅β₁ on fibronectin; however, this is heavily reliant on nanoscale spacing, as the opposite is observed when ligands are spaced at 70 nm. These data imply that even nanoscale alterations in extracellular matrix properties have profound effects on cancer cell survival and can thus inform future therapies and drug testing platforms.

The Extracellular Matrix: An Accomplice in Gastric Cancer Development and Progression

The extracellular matrix (ECM) is a dynamic and highly organized tissue structure, providing support and maintaining normal epithelial architecture. In the last decade, increasing evidence has emerged demonstrating that alterations in ECM composition and assembly strongly affect cellular function and behavior. Even though the detailed mechanisms underlying cell-ECM crosstalk are yet to unravel, it is well established that ECM deregulation accompanies the development of many pathological conditions, such as gastric cancer. Notably, gastric cancer remains a worldwide concern, representing the third most frequent cause of cancer-associated deaths. Despite increased surveillance protocols, patients are usually diagnosed at advanced disease stages, urging the identification of novel diagnostic biomarkers and efficient therapeutic strategies. In this review, we provide a comprehensive overview regarding expression patterns of ECM components and cognate receptors described in normal gastric epithelium, pre-malignant lesions, and gastric carcinomas. Important insights are also discussed for the use of ECM-associated molecules as predictive biomarkers of the disease or as potential targets in gastric cancer.

Protease-activated receptor signalling initiates α5β1-integrin-mediated adhesion in non-haematopoietic cells

Haematopoietic cells and platelets employ G-protein-coupled receptors (GPCRs) to sense extracellular information and respond by initiating integrin-mediated adhesion. So far, such processes have not been demonstrated in non-haematopoietic cells. Here, we report that the activation of protease-activated receptors PAR1 and PAR2 induce multiple signalling pathways to establish α₅β₁-integrin-mediated adhesion. First, PARs signal via Gβγ and PI3K to α₅β₁-integrins to adopt a talin- and kindlin-dependent high-affinity conformation, which triggers fibronectin binding and initiates cell adhesion. Then, within 60 s, PARs signal via Gα₁₃, Gα_i, ROCK and Src to strengthen the α₅β₁-integrin-mediated adhesion. Furthermore, PAR signalling changes the abundance of numerous proteins in the adhesome assembled by α₅β₁-integrins, including Gα₁₃, vacuolar protein-sorting-associated protein 36, and band 4.1-like protein 4B or 5, and accelerates cell adhesion maturation, spreading and migration. The mechanistic insights describe how agonist binding to PAR employs GPCR and integrin-signalling pathways to initiate and regulate adhesion and to guide physiological responses of non-haematopoietic cells.

Stopping transformed cancer cell growth by rigidity sensing

A common feature of cancer cells is the alteration of kinases and biochemical signalling pathways enabling transformed growth on soft matrices, whereas cytoskeletal protein alterations are thought to be a secondary issue. However, we report here that cancer cells from different tissues can be toggled between transformed and rigidity-dependent growth states by the absence or presence of mechanosensory modules, respectively. In various cancer lines from different tissues, cells had over tenfold fewer rigidity-sensing contractions compared with normal cells from the same tissues. Restoring normal levels of cytoskeletal proteins, including tropomyosins, restored rigidity sensing and rigidity-dependent growth. Further depletion of other rigidity sensor proteins, including myosin IIA, restored transformed growth and blocked sensing. In addition, restoration of rigidity sensing to cancer cells inhibited tumour formation and changed expression patterns. Thus, the depletion of rigidity-sensing modules through alterations in cytoskeletal protein levels enables cancer cell growth on soft surfaces, which is an enabling factor for cancer progression.

Low Dosed Curcumin Combined with Visible Light Exposure Inhibits Renal Cell Carcinoma Metastatic Behavior In Vitro

Recent documentation shows that a curcumin-induced growth arrest of renal cell carcinoma (RCC) cells can be amplified by visible light. This study was designed to investigate whether this strategy may also contribute to blocking metastatic progression of RCC. Low dosed curcumin (0.2 µg/mL; 0.54 µM) was applied to A498, Caki1, or KTCTL-26 cells for 1 h, followed by exposure to visible light for 5 min (400–550 nm, 5500 lx). Adhesion to human vascular endothelial cells or immobilized collagen was then evaluated. The influence of curcumin on chemotaxis and migration was also investigated, as well as curcumin induced alterations of α and β integrin expression. Curcumin without light exposure or light exposure without curcumin induced no alterations, whereas curcumin plus light significantly inhibited RCC adhesion, migration, and chemotaxis. This was associated with a distinct reduction of α3, α5, β1, and β3 integrins in all cell lines. Separate blocking of each of these integrin subtypes led to significant modification of tumor cell adhesion and chemotactic behavior. Combining low dosed curcumin with light considerably suppressed RCC binding activity and chemotactic movement and was associated with lowered integrin α and β subtypes. Therefore, curcumin combined with visible light holds promise for inhibiting metastatic processes in RCC.

Inhibition of TPA‑induced metastatic potential by morin hydrate in MCF‑7 human breast cancer cells via the Akt/GSK‑3β/c‑Fos signaling pathway

Plant flavonoid 2',3,4',5,7‑pentahydroxyflavone (morin hydrate), isolated from the family Moraceae (Morus alba L.), is known to have anti‑inflammatory and anticancer effects. However, its pharmaceutical effects on metastasis have not been fully elucidated to date. Therefore, the current study investigated the effects of morin hydrate on cancer metastasis in MCF‑7 human breast cancer cells. The results showed that morin hydrate suppressed 12‑O‑tetradecanoylphorbol‑13‑acetate (TPA)‑induced cell migration and invasion via the inhibition of matrix metalloproteinase (MMP)‑9 activity. Furthermore, gene expression level of MMP‑9, MMP‑7, urokinase plasminogen activator (uPA), uPA receptor (uPAR) and fibronectin were significantly decreased by morin hydrate treatment. Morin hydrate inhibited the phosphorylation of Akt and glycogen synthase kinase (GSK)‑3β, and downregulated the expression of an activator protein‑1 subunit c‑Fos. In addition, the GSK‑3β phosphorylation and c‑Fos expression were suppressed by PI3K/Akt pathway inhibitors, LY294002 and wortmannin. Taken together, these results demonstrated that morin hydrate reduced the metastatic potential in TPA‑treated MCF‑7 human breast cancer cells via the inhibition of MMPs, uPA and uPAR, and the underlying Akt/GSK‑3β/c‑Fos pathway. Therefore, the present investigation suggested that morin hydrate may be a natural substance with a preventive potential for metastasis in breast cancer cells.

The Tumor Microenvironment: Focus on Extracellular Matrix

The extracellular matrix (ECM) regulates the development and maintains tissue homeostasis. The ECM is composed of a complex network of molecules presenting distinct biochemical properties to regulate cell growth, survival, motility, and differentiation. Among their components, proteoglycans (PGs) are considered one of the main components of ECM. Its composition, biomechanics, and anisotropy are exquisitely tuned to reflect the physiological state of the tissue. The loss of ECM's homeostasis is seen as one of the hallmarks of cancer and, typically, defines transitional events in tumor progression and metastasis. In this chapter, we discuss the types of proteoglycans and their roles in cancer. It has been observed that the amount of some ECM components is increased, while others are decreased, depending on the type of tumor. However, both conditions corroborate with tumor progression and malignancy. Therefore, ECM components have an increasingly important role in carcinogenesis and this leads us to believe that their understanding may be a key in the discovery of new anti-tumor therapies. In this book, the main ECM components will be discussed in more detail in each chapter.

Intensity-based registration of bright-field and second-harmonic generation images of histopathology tissue sections

The use of second-harmonic generation (SHG) microscopy in biomedical research is rapidly increasing. This is due in large part to the wide spread interest of using this imaging technique to examine the role of fibrillar collagen organization in diseases such as cancer. The co-examination of SHG images and traditional bright-field (BF) images of hematoxylin and eosin (H&E) stained tissue as a gold standard clinical validation is usually required. However, image registration of these two modalities has been mostly done by manually selecting corresponding landmarks which is labor intensive and error prone. We designed, implemented, and validated the first image intensity-based registration method capable of automatically aligning SHG images and BF images. In our algorithmic approach, a feature extractor is used to pre-process the BF image to block the content features not visible in SHG images and the output image is then aligned with the SHG image by maximizing the common image features. An alignment matrix maximizing the image mutual information is found by evolutionary optimization and the optimization is facilitated using a hierarchical multiresolution framework. The automatic registration results were compared to traditional manual registration to assess the performance of the algorithm. The proposed algorithm has been successfully used in several biomedical studies such as pancreatic and kidney cancer studies and shown great efficacy.

Targeting Integrins in Cancer Nanomedicine: Applications in Cancer Diagnosis and Therapy

Due to advancements in nanotechnology, the application of nanosized materials (nanomaterials) in cancer diagnostics and therapeutics has become a leading area in cancer research. The decoration of nanomaterial surfaces with biological ligands is a major strategy for directing the actions of nanomaterials specifically to cancer cells. These ligands can bind to specific receptors on the cell surface and enable nanomaterials to actively target cancer cells. Integrins are one of the cell surface receptors that regulate the communication between cells and their microenvironment. Several integrins are overexpressed in many types of cancer cells and the tumor microvasculature and function in the mediation of various cellular events. Therefore, the surface modification of nanomaterials with integrin-specific ligands not only increases their binding affinity to cancer cells but also enhances the cellular uptake of nanomaterials through the intracellular trafficking of integrins. Moreover, the integrin-specific ligands themselves interfere with cancer migration and invasion by interacting with integrins, and this finding provides a novel direction for new treatment approaches in cancer nanomedicine. This article reviews the integrin-specific ligands that have been used in cancer nanomedicine and provides an overview of the recent progress in cancer diagnostics and therapeutic strategies involving the use of integrin-targeted nanomaterials.

G0/G1 Switch 2 Induces Cell Survival and Metastasis through Integrin-Mediated Signal Transduction in Human Invasive Breast Cancer Cells

Human breast cancer cell line, MDA-MB-231, is highly invasive and aggressive, compared to less invasive cell line, MCF-7. To explore the genes that might influence the malignancy of MDA-MB-231, DNA microarray analysis was performed. The results showed that G0/G1 switch 2 (G0S2) was one of the most highly expressed genes among the genes upregulated in MDA-MB-231. Although G0S2 acts as a direct inhibitor of adipose triglyceride lipase, action of G0S2 in cancer progression is not yet understood. To investigate whether G0S2 affects invasiveness of MDA-MB-231 cells, G0S2 expression was inhibited using siRNA, which led to decreased cell proliferation, migration, and invasion of MDA-MB-231 cells. Consequently, G0S2 inhibition inactivated integrinregulated FAK-Src signaling, which promoted Hippo signaling and inactivated ERK1/2 signaling. In addition, G0S2 downregulation decreased β-catenin expression, while E-cadherin expression was increased. It was demonstrated for the first time that G0S2 mediates the Hippo pathway and induces epithelial to mesenchymal transition (EMT). Taken together, our results suggest that G0S2 is a major factor contributing to cell survival and metastasis of MDA-MB-231 cells.

Weighted Gene Co-Expression Network Analysis Identifies Hub Genes Associated with Occurrence and Prognosis of Oral Squamous Cell Carcinoma

Background

The aim of this study was to identify biomarkers closely related to the pathogenesis and prognosis of oral squamous cell carcinoma (OSCC) by using weighted gene co-expression network analysis (WGCNA) based on integrative transcriptome datasets.

Material/Methods

Gene expression profiles of OSCC were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were obtained and we then performed with Gene ontology (GO) and pathway enrichment analysis as well as protein–protein interactions (PPI) network analysis. WGCNA was used to construct the co-expression network. Multipart results were intersected to acquire the candidate genes, and survival analysis was used to identify the hub genes.

Results

A total of 568 DEGs, including 272 upregulated genes and 296 downregulated genes, were identified. GO and pathway analyses revealed that these DEGs were mainly enriched in extracellular matrix (ECM), ECM organization, structural constituent of muscle, and ECM-receptor interaction. The PPI network of DEGs was established, comprising 428 nodes and 1944 edges. In the co-expression network, pink module was the key module, in which 34 genes with high connectivity were identified. After the intersection of multipart results, 24 common genes were chosen as the candidate genes, among which 7 hub genes (PLAU, SERPINE1, LAMC2, ITGA5, TGFBI, FSCN1, and HLF) were identified using survival analysis.

Conclusions

Seven potential biomarkers were identified as being closely related with the initiation and prognosis of OSCC and might serve as potential targets for early diagnosis and personalized therapy of OSCC.

Therapy with multi-epitope virus-like particles of B19 parvovirus reduce tumor growth and lung metastasis in an aggressive breast cancer mouse model

Triple-negative breast cancer is a major health problem that lacks molecular targets for therapy. Neoepitopes represent a viable option to induce antitumor immune responses, but they have limitations, such as low immunogenicity and tolerance induction. Parvovirus B19 virus-like particles may be used to deliver neoepitopes to prime cellular immunity. We designed and evaluated the therapeutic effect of VP2 B19-virus-like particles, with multi-neoepitopes, in a 4T1 breast cancer model. Balb/c mice received four therapeutic immunizations with multi-neoepitopes-virus-like, wild type-virus-like, vehicle, or virus-like plus Cry1Ac adjuvant particles, intraperitoneally and peritumorally. Tumor growth, lung macro-metastasis, and specific immune responses were evaluated. Therapeutic administration of multi-epitopes virus-like particles significantly delayed tumor growth and decreased the lung macro-metastasis number, in comparison to treatment with wild type-virus-like particles, which surprisingly also elicited antitumoral effects that were improved with the adjuvant. Only treatments with multi-epitope virus-like particles induced specific proliferative responses of CD8 and CD4 T lymphocytes and Granzyme-B production in lymphatic nodes local to the tumor. Treatment with recombinant multiple neoepitopes-virus-like particles induced specific cellular responses, inhibited tumor growth and macro-metastasis, thus B19-virus-like particles may function as an effective delivery system for neoepitopes for personalized immunotherapy.

The transmembrane protein fibrocystin/polyductin regulates cell mechanics and cell motility

Polycystic kidney disease is a disorder that leads to fluid filled cysts that replace normal renal tubes. During the process of cellular development and in the progression of the diseases, fibrocystin can lead to impaired organ formation and even cause organ defects. Besides cellular polarity, mechanical properties play major roles in providing the optimal apical-basal or anterior-posterior symmetry within epithelial cells. A breakdown of the cell symmetry that is usually associated with mechanical property changes and it is known to be essential in many biological processes such as cell migration, polarity and pattern formation especially during development and diseases such as the autosomal recessive cystic kidney disease. Since the breakdown of the cell symmetry can be evoked by several proteins including fibrocystin, we hypothesized that cell mechanics are altered by fibrocystin. However, the effect of fibrocystin on cell migration and cellular mechanical properties is still unclear. In order to explore the function of fibrocystin on cell migration and mechanics, we analyzed fibrocystin knockdown epithelial cells in comparison to fibrocystin control cells. We found that invasiveness of fibrocystin knockdown cells into dense 3D matrices was increased and more efficient compared to control cells. Using optical cell stretching and atomic force microscopy, fibrocystin knockdown cells were more deformable and exhibited weaker cell-matrix as well as cell-cell adhesion forces, respectively. In summary, these findings show that fibrocystin knockdown cells displayed increased 3D matrix invasion through providing increased cellular deformability, decreased cell-matrix and reduced cell-cell adhesion forces.

The Role of the Optical Stretcher Is Crucial in the Investigation of Cell Mechanics Regulating Cell Adhesion and Motility

The mechanical properties of cells, tissues, and the surrounding extracellular matrix environment play important roles in the process of cell adhesion and migration. In physiological and pathological processes of the cells, such as wound healing and cancer, the capacity to migrate through the extracellular matrix is crucial. Hence biophysical techniques were used to determine the mechanical properties of cells that facilitate the various migratory capacities. Since the field of mechanobiology is rapidly growing, the reliable and reproducible characterization of cell mechanics is required that facilitates the adhesion and migration of cells. One of these cell mechanical techniques is the optical stretching device, which was originally developed to investigate the mechanical properties of cells, such as the deformation of single cells in suspension. After discussing the strengths and weaknesses of the technology, the latest findings in optical stretching-based cell mechanics are presented in this review. Finally, the mechanical properties of cells are correlated with their migratory potential and it is pointed out how the inhibition of biomolecules that contribute to the to the maintenance of cytoskeletal structures in cells affect their mechanical deformability.

Targeting integrins for cancer management using nanotherapeutic approaches: Recent advances and challenges

Integrins are the main cell surface receptors and execute multifaceted functions such as the bidirectional transmission of signals (i.e., inside-out and outside-in) and provide communication between cells and their microenvironments. Integrins are the key regulators of critical biological functions and contribute significantly to the promotion of cancer at almost every stage of disease progression from initial tumor formation to metastasis. Integrin expressions are frequently altered in different cancers, and consequently, several therapeutic strategies targeting integrins have been developed. Furthermore, nanotechnology-based approaches have been devised to overcome the intrinsic limitations of conventional therapies for cancer management, and have been shown to more precise, safer, and highly effective therapeutic tools. Although nanotechnology-based approaches have achieved substantial success for the management of cancer, certain obstacles remain such as inadequate knowledge of nano-bio interactions and the challenges associated with the three stages of clinical trials. This review highlights the different roles of integrins and of integrin-dependent signaling in various cancers and describes the applications of nanotherapeutics targeting integrins. In addition, we discuss RGD-based approaches and challenges posed to cancer management.

High-Affinity α5β1-Integrin-Selective Bicyclic RGD Peptides Identified via Screening of Designed Random Libraries

We report the identification of high-affinity and selectivity integrin α₅β₁-binding bicyclic peptides via "designed random libraries", that is, the screening of libraries comprising the universal integrin-binding sequence Arg-Gly-Asp (RGD) in the first loop in combination with a randomized sequence (XXX) in the second loop. Screening of first-generation libraries for α₅β₁-binding peptides yielded a triple-digit nanomolar bicyclic α₅β₁-binder (C_T3RGDc_T3AYGC_T3, IC₅₀ = 406 nM). Next-generation libraries were designed by partially varying the structure of the strongest first-generation lead inhibitor and screened for improved affinities and selectivities for this receptor. In this way, we identified three high-affinity α₅β₁-binders (C_T3RGDc_T3AYJC_T3, J = d-Leu, IC₅₀ = 90 nM; C_T3RGDc_T3AYaC_T3, IC₅₀ = 156 nM; C_T3RGDc_T3AWGC_T3, IC₅₀ = 173 nM), of which one even showed a higher α₅β₁-affinity than the 32 amino acid benchmark peptide knottin-RGD (IC₅₀ = 114 nM). Affinity for α₅β₁-integrin was confirmed by SPFS analysis showing a K_d of 4.1 nM for Cy5-labeled RGD-bicycle C_T3RGDc_T3AYJC_T3 (J = d-Leu) and a somewhat higher K_d (9.0 nM) for Cy5-labeled knottin-RGD. The α₅β₁-bicycles, for example, C_T3RGDc_T3AYJC_T3 (J = d-Leu), showed excellent selectivities over α_vβ₅ (IC₅₀ ratio α₅β₁/α_vβ₅ between <0.009 and 0.039) and acceptable selectivities over α_vβ₃ (IC₅₀ ratios α₅β₁/α_vβ₃ between 0.090 and 0.157). In vitro staining of adipose-derived stem cells with Cy5-labeled peptides using confocal microscopy revealed strong binding of the α₅β₁-selective bicycle C_T3RGDc_T3AWGC_T3 to integrins in their natural environment, illustrating the high potential of these RGD bicycles as markers for α₅β₁-integrin expression.

CKAP4 Regulates Cell Migration via the Interaction with and Recycling of Integrin

Cytoskeleton-associated protein 4 (CKAP4) is an endoplasmic reticulum protein that is also present in the cell surface membrane, where it acts as a receptor for Dickkopf1 (DKK1). In this study, we found that CKAP4 interacts with β1 integrin and controls the recycling of α5β1 integrin independently of DKK1. In S2-CP8 cells, knockdown of CKAP4 but not DKK1 enlarged the size of cell adhesion sites and enhanced cell adhesion to fibronectin, resulting in decreased cell migration. When CKAP4 was depleted, the levels of α5 but not β1 integrin were increased in the cell surface membrane. A similar phenotype was observed in other cells expressing low levels of DKK1. In S2-CP8 cells, α5 integrin was trafficked with β1 integrin and CKAP4 to the lysosome or recycled with β1 integrin. In CKAP4-depleted cells, the internalization of α5β1 integrin was unchanged, but its recycling was upregulated. Knockdown of sorting nexin 17 (SNX17), a mediator of integrin recycling, abrogated the increased α5 integrin levels caused by CKAP4 knockdown. CKAP4 bound to SNX17, and its knockdown enhanced the recruitment of α5β1 integrin to SNX17. These results suggest that CKAP4 suppresses the recycling of α5β1 integrin and coordinates cell adhesion sites and migration independently of DKK1.

Studying Normal Tissue Radiation Effects using Extracellular Matrix Hydrogels

Radiation is a therapy for patients with triple negative breast cancer. The effect of radiation on the extracellular matrix (ECM) of healthy breast tissue and its role in local recurrence at the primary tumor site are unknown. Here we present a method for the decellularization, lyophilization, and fabrication of ECM hydrogels derived from murine mammary fat pads. Results are presented on the effectiveness of the decellularization process, and rheological parameters were assessed. GFP- and luciferase-labeled breast cancer cells encapsulated in the hydrogels demonstrated an increase in proliferation in irradiated hydrogels. Finally, phalloidin conjugate staining was employed to visualize cytoskeleton organization of encapsulated tumor cells. Our goal is to present a method for fabricating hydrogels for in vitro study that mimic the in vivo breast tissue environment and its response to radiation in order to study tumor cell behavior.

Mechanochemical Signaling of the Extracellular Matrix in Epithelial-Mesenchymal Transition

Epithelial-Mesenchymal Transition (EMT) is a critical process in embryonic development in which epithelial cells undergo a transdifferentiation into mesenchymal cells. This process is essential for tissue patterning and organization, and it has also been implicated in a wide array of pathologies. While the intracellular signaling pathways that regulate EMT are well-understood, there is increasing evidence that the mechanical properties and composition of the extracellular matrix (ECM) also play a key role in regulating EMT. In turn, EMT drives changes in the mechanics and composition of the ECM, creating a feedback loop that is tightly regulated in healthy tissues, but is often dysregulated in disease. Here we present a review that summarizes our understanding of how ECM mechanics and composition regulate EMT, and how in turn EMT alters ECM mechanics and composition.

New Insights Into the Golgi Stacking Proteins

The Golgi stacking proteins, GRASP55 and GRASP65, are best known for their roles in Golgi structure formation. These peripheral Golgi proteins form trans-oligomers that hold the flat cisternal membranes into stacks. Depletion of both GRASP proteins in cells disrupts the Golgi stack structure, increases protein trafficking, but impairs accurate glycosylation, and sorting. Golgi unstacking by GRASPs depletion also reduces cell adhesion and migration in an integrin-dependent manner. In addition to Golgi structure formation and regulation of cellular activities, GRASPs, in particular GRASP55, have recently drawn attention in their roles in autophagy, and unconventional secretion. In autophagy, GRASP55 senses the energy level by O-GlcNAcylation, which regulates GRASP55 translocation from the Golgi to the autophagosome-lysosome interface, where it interacts with LC3 and LAMP2 to facilitate autophagosome-lysosome fusion. This newly discovered function of GRASP55 in autophagy may help explain its role in the stress-induced, autophagosome-dependent unconventional secretion. In this review, we summarize the emerging functions of the GRASP proteins, focusing on their roles in cell adhesion and migration, autophagy, unconventional secretion, as well as on novel GRASP-interacting proteins.

Fast and reliable advanced two-step pore-size analysis of biomimetic 3D extracellular matrix scaffolds

The tissue microenvironment is a major contributor to cellular functions, such as cell adhesion, migration and invasion. A critical physical parameter for determining the effect of the microenvironment on cellular functions is the average pore-size of filamentous scaffolds, such as 3D collagen fiber matrices, which are assembled by the polymerization of biopolymers. The scaffolds of these matrices can be analyzed easily by using state-of-the-art laser scanning confocal imaging. However, the generation of a quantitative estimate of the pore-size in a 3D microenvironment is not trivial. In this study, we present a reliable and fast analytical method, which relies on a two-step 3D pore-size analysis utilizing several state-of-the-art image analysis methods, such as total variation (TV) denoising and adaptive local thresholds, and another crucial parameter, such as pore-coverage. We propose an iterative approach of pore-size analysis to determine even the smallest and obscure pores in a collagen scaffold. Additionally, we propose a novel parameter, the pseudo-pore-size, which describes a virtual scaffold porosity. In order to validate the advanced two-step pore-size analysis different types of artificial collagens, such as a rat and bovine mixture with two different collagen concentrations have been utilized. Additionally, we compare a traditional approach with our method using an artificially generated network with predefined pore-size distributions. Indeed, our analytical method provides a precise, fast and parameter-free, user-independent and automatic analysis of 3D pore topology, such as pore-sizes and pore-coverage. Additionally, we are able to determine non-physiological network topologies by taking the pore-coverage as a goodness-of-fit parameter.

The matrix environmental and cell mechanical properties regulate cell migration and contribute to the invasive phenotype of cancer cells

The minimal structural unit of a solid tumor is a single cell or a cellular compartment such as the nucleus. A closer look inside the cells reveals that there are functional compartments or even structural domains determining the overall properties of a cell such as the mechanical phenotype. The mechanical interaction of these living cells leads to the complex organization such as compartments, tissues and organs of organisms including mammals. In contrast to passive non-living materials, living cells actively respond to the mechanical perturbations occurring in their microenvironment during diseases such as fibrosis and cancer. The transformation of single cancer cells in highly aggressive and hence malignant cancer cells during malignant cancer progression encompasses the basement membrane crossing, the invasion of connective tissue, the stroma microenvironments and transbarrier migration, which all require the immediate interaction of the aggressive and invasive cancer cells with the surrounding extracellular matrix environment including normal embedded neighboring cells. All these steps of the metastatic pathway seem to involve mechanical interactions between cancer cells and their microenvironment. The pathology of cancer due to a broad heterogeneity of cancer types is still not fully understood. Hence it is necessary to reveal the signaling pathways such as mechanotransduction pathways that seem to be commonly involved in the development and establishment of the metastatic and mechanical phenotype in several carcinoma cells. We still do not know whether there exist distinct metastatic genes regulating the progression of tumors. These metastatic genes may then be activated either during the progression of cancer by themselves on their migration path or in earlier stages of oncogenesis through activated oncogenes or inactivated tumor suppressor genes, both of which promote the metastatic phenotype. In more detail, the adhesion of cancer cells to their surrounding stroma induces the generation of intracellular contraction forces that deform their microenvironments by alignment of fibers. The amplitude of these forces can adapt to the mechanical properties of the microenvironment. Moreover, the adhesion strength of cancer cells seems to determine whether a cancer cell is able to migrate through connective tissue or across barriers such as the basement membrane or endothelial cell linings of blood or lymph vessels in order to metastasize. In turn, exposure of adherent cancer cells to physical forces, such as shear flow in vessels or compression forces around tumors, reinforces cell adhesion, regulates cell contractility and restructures the ordering of the local stroma matrix that leads subsequently to secretion of crosslinking proteins or matrix degrading enzymes. Hence invasive cancer cells alter the mechanical properties of their microenvironment. From a mechanobiological point-of-view, the recognized physical signals are transduced into biochemical signaling events that guide cellular responses such as cancer progression after the malignant transition of cancer cells from an epithelial and non-motile phenotype to a mesenchymal and motile (invasive) phenotype providing cellular motility. This transition can also be described as the physical attempt to relate this cancer cell transitional behavior to a T1 phase transition such as the jamming to unjamming transition. During the invasion of cancer cells, cell adaptation occurs to mechanical alterations of the local stroma, such as enhanced stroma upon fibrosis, and therefore we need to uncover underlying mechano-coupling and mechano-regulating functional processes that reinforce the invasion of cancer cells. Moreover, these mechanisms may also be responsible for the awakening of dormant residual cancer cells within the microenvironment. Physicists were initially tempted to consider the steps of the cancer metastasis cascade as single events caused by a single mechanical alteration of the overall properties of the cancer cell. However, this general and simple view has been challenged by the finding that several mechanical properties of cancer cells and their microenvironment influence each other and continuously contribute to tumor growth and cancer progression. In addition, basement membrane crossing, cell invasion and transbarrier migration during cancer progression is explained in physical terms by applying physical principles on living cells regardless of their complexity and individual differences of cancer types. As a novel approach, the impact of the individual microenvironment surrounding cancer cells is also included. Moreover, new theories and models are still needed to understand why certain cancers are malignant and aggressive, while others stay still benign. However, due to the broad variety of cancer types, there may be various pathways solely suitable for specific cancer types and distinct steps in the process of cancer progression. In this review, physical concepts and hypotheses of cancer initiation and progression including cancer cell basement membrane crossing, invasion and transbarrier migration are presented and discussed from a biophysical point-of-view. In addition, the crosstalk between cancer cells and a chronically altered microenvironment, such as fibrosis, is discussed including the basic physical concepts of fibrosis and the cellular responses to mechanical stress caused by the mechanically altered microenvironment. Here, is highlighted how biophysical approaches, both experimentally and theoretically, have an impact on classical hallmarks of cancer and fibrosis and how they contribute to the understanding of the regulation of cancer and its progression by sensing and responding to the physical environmental properties through mechanotransduction processes. Finally, this review discusses various physical models of cell migration such as blebbing, nuclear piston, protrusive force and unjamming transition migration modes and how they contribute to cancer progression. Moreover, these cellular migration modes are influenced by microenvironmental perturbances such as fibrosis that can induce mechanical alterations in cancer cells, which in turn may impact the environment. Hence, the classical hallmarks of cancer need to be refined by including biomechanical properties of cells, cell clusters and tissues and their microenvironment to understand mechano-regulatory processes within cancer cells and the entire organism.

The Small GTPase Rac1 Increases Cell Surface Stiffness and Enhances 3D Migration Into Extracellular Matrices

Membrane ruffling and lamellipodia formation promote the motility of adherent cells in two-dimensional motility assays by mechano-sensing of the microenvironment and initiation of focal adhesions towards their surroundings. Lamellipodium formation is stimulated by small Rho GTPases of the Rac subfamily, since genetic removal of these GTPases abolishes lamellipodium assembly. The relevance of lamellipodial or invadopodial structures for facilitating cellular mechanics and 3D cell motility is still unclear. Here, we hypothesized that Rac1 affects cell mechanics and facilitates 3D invasion. Thus, we explored whether fibroblasts that are genetically deficient for Rac1 (lacking Rac2 and Rac3) harbor altered mechanical properties, such as cellular deformability, intercellular adhesion forces and force exertion, and exhibit alterations in 3D motility. Rac1 knockout and control cells were analyzed for changes in deformability by applying an external force using an optical stretcher. Five Rac1 knockout cell lines were pronouncedly more deformable than Rac1 control cells upon stress application. Using AFM, we found that cell-cell adhesion forces are increased in Rac1 knockout compared to Rac1-expressing fibroblasts. Since mechanical deformability, cell-cell adhesion strength and 3D motility may be functionally connected, we investigated whether increased deformability of Rac1 knockout cells correlates with changes in 3D motility. All five Rac1 knockout clones displayed much lower 3D motility than Rac1-expressing controls. Moreover, force exertion was reduced in Rac1 knockout cells, as assessed by 3D fiber displacement analysis. Interference with cellular stiffness through blocking of actin polymerization by Latrunculin A could not further reduce invasion of Rac1 knockout cells. In contrast, Rac1-expressing controls treated with Latrunculin A were again more deformable and less invasive, suggesting actin polymerization is a major determinant of observed Rac1-dependent effects. Together, we propose that regulation of 3D motility by Rac1 partly involves cellular mechanics such as deformability and exertion of forces.

Breast Cancer Cells Adapt Contractile Forces to Overcome Steric Hindrance

Cell migration through the extracellular matrix is governed by the interplay between cell-generated propulsion forces, adhesion forces, and resisting forces arising from the steric hindrance of the matrix. Steric hindrance in turn depends on matrix porosity, matrix deformability, cell size, and cell deformability. In this study, we investigate how cells respond to changes in steric hindrance that arise from altered cell mechanical properties. Specifically, we measure traction forces, cell morphology, and invasiveness of MDA-MB 231 breast cancer cells in three-dimensional collagen gels. To modulate cell mechanical properties, we either decrease nuclear deformability by twofold overexpression of the nuclear protein lamin A or we introduce into the cells stiff polystyrene beads with a diameter larger than the average matrix pore size. Despite this increase of steric hindrance, we find that cell invasion is only marginally inhibited, as measured by the fraction of motile cells and the mean invasion depth. To compensate for increased steric hindrance, cells employ two alternative strategies. Cells with higher nuclear stiffness increase their force polarity, whereas cells with large beads increase their net contractility. Under both conditions, the collagen matrix surrounding the cells stiffens dramatically and carries increased strain energy, suggesting that increased force polarity and increased net contractility are functionally equivalent strategies for overcoming an increased steric hindrance.

Placenta-conditioned extracellular matrix (ECM) activates breast cancer cell survival mechanisms: A key for future distant metastases

The extracellular matrix (ECM) affects cancer cell characteristics. Inability of normal epithelial cells to attach to the ECM induces apoptosis (anoikis). Cancer cells are often anoikis resistant, a prerequisite for their metastatic spread. Previously we demonstrated that the placenta manipulates its surrounding ECM in a way that prevents breast cancer cells (BCCL) attachment and induces their motility and aggregation. This fits with the fact that although breast cancer during pregnancy is often advanced, metastasis to the placenta is rarely observed. Placental intervillous space provides suitable conditions for cancer cell arrival. Yet, the outcome of the short communication between the placental ECM to the BCCL and its effect on BCCL malignant potential are unknown, and are the focus of our study. In the current study we analyzed the effect of placental ECM on BCCL survival pathways and drug resistance. Microarray analysis suggested activation of the NF-κB and stress response pathways. Indeed, the placenta-conditioned ECM induced autophagy in ERα + BCCL, inactivated the NF-κB inhibitor (IκB) and increased integrin α5 in the BCCL. The autophagy mediated MCF-7 and T47D migration and the placental ECM-BCCL interactions reduced the BCCL sensitivity to Taxol. We also demonstrated by using siRNA that integrin α5 was responsible for the MCF-7 autophagy and suggest this molecule as a suitable target for therapy.

GRASP depletion-mediated Golgi destruction decreases cell adhesion and migration via the reduction of α5β1 integrin

The Golgi apparatus is a membrane-bound organelle that serves as the center for trafficking and processing of proteins and lipids. To perform these functions, the Golgi forms a multilayer stacked structure held by GRASP55 and GRASP65 trans-oligomers and perhaps their binding partners. Depletion of GRASP proteins disrupts Golgi stack formation and impairs critical functions of the Golgi, such as accurate protein glycosylation and sorting. However, how Golgi destruction affects other cellular activities is so far unknown. Here, we report that depletion of GRASP proteins reduces cell attachment and migration. Interestingly, GRASP depletion reduces the protein level of α5β1 integrin, the major cell adhesion molecule at the surface of HeLa and MDA-MB-231 cells, due to decreased integrin protein synthesis. GRASP depletion also increases cell growth and total protein synthesis. These new findings enrich our understanding on the role of the Golgi in cell physiology and provide a potential target for treating protein-trafficking disorders.

Cancer cell migration on elongate protrusions of fibroblasts in collagen matrix

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