Feeling Stress: The Mechanics of Cancer Progression and Aggression

Advances on colorectal cancer 3D models: The needed translational technology for nanomedicine screening

Colorectal cancer (CRC) is a heterogeneous and molecularly complex disease, associated with high mortality worldwide, exposing the urgent need for novel therapeutic approaches. Their development and translation to the clinic have been hampered, partially due to the absence of reliable cellular models that resemble key features of the human disease. While traditional 2D models are not able to provide consistent and predictive responses about the in vivo efficiency of the formulation, animal models frequently fail to recapitulate cancer progression and to reproduce adverse effects. On its turn, multicellular 3D systems, by mimicking key genetic, physical and mechanical cues of the tumor microenvironment, constitute a promising tool in cancer research. In addition, they constitute more physiological and relevant environment for anticancer drugs screening and for predicting patient's response towards personalized approaches, bridging the gap between simplified 2D models and unrepresentative animal models. In this review, we provide an overview of CRC 3D models for translational research, with focus on their potential for nanomedicines screening.

Cell biology: How cancer cells coerce normal cells into tumorigenesis

The role of altered tissue mechanics in early cancer development is not well understood. A new study reveals how oncogene activation generates force within a tissue to impact cell division in surrounding normal cells, which then contribute to tumour formation.

Molecular cancer cell responses to solid compressive stress and interstitial fluid pressure

Alterations to the mechanical properties of the microenvironment are a hallmark of cancer. Elevated mechanical stresses exist in many solid tumors and elicit responses from cancer cells. Uncontrolled growth in confined environments gives rise to elevated solid compressive stress on cancer cells. Recruitment of leaky blood vessels and an absence of functioning lymphatic vessels causes a rise in the interstitial fluid pressure. Here we review the role of the cancer cell cytoskeleton and the nucleus in mediating both the initial and adaptive cancer cell response to these two types of mechanical stresses. We review how these mechanical stresses alter cancer cell functions such as proliferation, apoptosis, and migration.

Effects of miR-224-5p-enhanced downregulation of pannexin-1 on docetaxel-induced apoptosis in amoeboid-like CD44high oral cancer cells

We previously found that microRNAs play major roles in the maintenance of amoeboid-like oral squamous cell carcinoma (OSCC) cells with high expression of CD44 (CD44^high ). However, the roles of microRNAs in chemotherapeutic resistance exhibited by CD44^high amoeboid-like OSCC cells are unclear. Here, docetaxel-induced apoptosis was examined in CD44^high OSCC cells (CD44^high OM-1 cells) cultured on laminin-coated silicone gel. Amoeboid-like CD44^high OSCC cells exhibited robust resistance to docetaxel-induced apoptosis and significant upregulation of miR-224-5p expression compared with epithelial-like CD44^high OSCC cells and mesenchymal-like CD44^high OSCC cells. The expression of pannexin-1 (PANX1), a channel-forming protein that regulates the release of ATP, was significantly upregulated following transfection of amoeboid-like CD44^high OSCC cells with an miR-224-5p inhibitor. These results suggest that miR-224-5p inhibits PANX1 expression. Furthermore, miR-224-5p inhibitor-transfected amoeboid-like CD44^high OSCC cells exhibited significant enhancement of the proportion of apoptotic cells; however, this effect was significantly inhibited by knockdown of PANX1 with PANX1 small interfering RNA. Additionally, the miR-224-5p inhibitor-enhanced extracellular ATP levels were significantly reduced by PANX1 knockdown. These findings imply that miR-224-5p plays a vital role in the resistance to docetaxel-induced apoptosis by attenuating PANX1-induced ATP discharge. Moreover, amoeboid-like CD44^high OSCC cells may be involved in chemotherapeutic resistance of OSCC.

Adhesion-mediated mechanosignaling forces mitohormesis

Mitochondria control eukaryotic cell fate by producing the energy needed to support life and the signals required to execute programed cell death. The biochemical milieu is known to affect mitochondrial function and contribute to the dysfunctional mitochondrial phenotypes implicated in cancer and the morbidities of aging. However, the physical characteristics of the extracellular matrix are also altered in cancerous and aging tissues. Here, we demonstrate that cells sense the physical properties of the extracellular matrix and activate a mitochondrial stress response that adaptively tunes mitochondrial function via solute carrier family 9 member A1-dependent ion exchange and heat shock factor 1-dependent transcription. Overall, our data indicate that adhesion-mediated mechanosignaling may play an unappreciated role in the altered mitochondrial functions observed in aging and cancer.

Matrix Stiffness Modulates Metabolic Interaction between Human Stromal and Breast Cancer Cells to Stimulate Epithelial Motility

Breast tumors belong to the type of desmoplastic lesion in which a stiffer tissue structure is a determinant of breast cancer progression and constitutes a risk factor for breast cancer development. It has been proposed that cancer-associated stromal cells (responsible for this fibrotic phenomenon) are able to metabolize glucose via lactate production, which supports the catabolic metabolism of cancer cells. The aim of this work was to investigate the possible functional link between these two processes. To measure the effect of matrix rigidity on metabolic determinations, we used compliant elastic polyacrylamide gels as a substrate material, to which matrix molecules were covalently linked. We evaluated metabolite transport in stromal cells using two different FRET (Fluorescence Resonance Energy Transfer) nanosensors specific for glucose and lactate. Cell migration/invasion was evaluated using Transwell devices. We show that increased stiffness stimulates lactate production and glucose uptake by mammary fibroblasts. This response was correlated with the expression of stromal glucose transporter Glut1 and monocarboxylate transporters MCT4. Moreover, mammary stromal cells cultured on stiff matrices generated soluble factors that stimulated epithelial breast migration in a stiffness-dependent manner. Using a normal breast stromal cell line, we found that a stiffer extracellular matrix favors the acquisition mechanistical properties that promote metabolic reprograming and also constitute a stimulus for epithelial motility. This new knowledge will help us to better understand the complex relationship between fibrosis, metabolic reprogramming, and cancer malignancy.

A Nomogram Based on a Collagen Feature Support Vector Machine for Predicting the Treatment Response to Neoadjuvant Chemoradiotherapy in Rectal Cancer Patients

BACKGROUND

The relationship between collagen features (CFs) in the tumor microenvironment and the treatment response to neoadjuvant chemoradiotherapy (nCRT) is still unknown. This study aimed to develop and validate a perdition model based on the CFs and clinicopathological characteristics to predict the treatment response to nCRT among locally advanced rectal cancer (LARC) patients.

METHODS

In this multicenter, retrospective analysis, 428 patients were included and randomly divided into a training cohort (299 patients) and validation cohort (129 patients) [7:3 ratio]. A total of 11 CFs were extracted from a multiphoton image of pretreatment biopsy, and a support vector machine (SVM) was then used to construct a CFs-SVM classifier. A prediction model was developed and presented with a nomogram using multivariable analysis. Further validation of the nomogram was performed in the validation cohort.

RESULTS

The CFs-SVM classifier, which integrated collagen area, straightness, and crosslink density, was significantly associated with treatment response. Predictors contained in the nomogram included the CFs-SVM classifier and clinicopathological characteristics by multivariable analysis. The CFs nomogram demonstrated good discrimination, with area under the receiver operating characteristic curves (AUROCs) of 0.834 in the training cohort and 0.854 in the validation cohort. Decision curve analysis indicated that the CFs nomogram was clinically useful. Moreover, compared with the traditional clinicopathological model, the CFs nomogram showed more powerful discrimination in determining the response to nCRT.

CONCLUSIONS

The CFs-SVM classifier based on CFs in the tumor microenvironment is associated with treatment response, and the CFs nomogram integrating the CFs-SVM classifier and clinicopathological characteristics is useful for individualized prediction of the treatment response to nCRT among LARC patients.

Mechanical Control of Cell Migration by the Metastasis Suppressor Tetraspanin CD82/KAI1

The plasma membrane is a key actor of cell migration. For instance, its tension controls persistent cell migration and cell surface caveolae integrity. Then, caveolae constituents such as caveolin-1 can initiate a mechanotransduction loop that involves actin- and focal adhesion-dependent control of the mechanosensor YAP to finely tune cell migration. Tetraspanin CD82 (also named KAI-1) is an integral membrane protein and a metastasis suppressor. Its expression is lost in many cancers including breast cancer. It is a strong inhibitor of cell migration by a little-known mechanism. We demonstrated here that CD82 controls persistent 2D migration of EGF-induced single cells, stress fibers and focal adhesion sizes and dynamics. Mechanistically, we found that CD82 regulates membrane tension, cell surface caveolae abundance and YAP nuclear translocation in a caveolin-1-dependent manner. Altogether, our data show that CD82 controls 2D cell migration using membrane-driven mechanics involving caveolin and the YAP pathway.

Interactions between Cancer-Associated Fibroblasts and T Cells in the Pancreatic Tumor Microenvironment and the Role of Chemokines

Less than 10% of patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) survive 5 years or more, making it one of the most fatal cancers. Accumulation of T cells in pancreatic tumors is associated with better prognosis, but immunotherapies to enhance the anti-tumor activity of infiltrating T cells are failing in this devastating disease. Pancreatic tumors are characterized by a desmoplastic stroma, which mainly consists of activated cancer-associated fibroblasts (CAFs). Pancreatic CAFs have emerged as important regulators of the tumor microenvironment by contributing to immune evasion through the release of chemokines, cytokines, and growth factors, which alters T-cell migration, differentiation and cytotoxic activity. However, recent discoveries have also revealed that subsets of CAFs with diverse functions can either restrain or promote tumor progression. Here, we discuss our current knowledge about the interactions between CAFs and T cells in PDAC and summarize different therapy strategies targeting the CAF-T cell axis with focus on CAF-derived soluble immunosuppressive factors and chemokines. Identifying the functions of different CAF subsets and understanding their roles in T-cell trafficking within the tumor may be fundamental for the development of an effective combinational treatment for PDAC.

Advanced mechanotherapy: Biotensegrity for governing metastatic tumor cell fate via modulating the extracellular matrix

Mechano-transduction is the procedure of mechanical stimulus translation via cells, among substrate shear flow, topography, and stiffness into a biochemical answer. TAZ and YAP are transcriptional coactivators which are recognized as relay proteins that promote mechano-transduction within the Hippo pathway. With regard to healthy cells in homeostasis, mechano-transduction regularly restricts proliferation, and TAZ and YAP are totally inactive. During cancer development a YAP/TAZ - stimulating positive response loop is formed between the growing tumor and the stiffening ECM. As tumor developments, local stromal and cancerous cells take advantage of mechanotransduction to enhance proliferation, induce their migratory into remote tissues, and promote chemotherapeutic resistance. As a newly progresses paradigm, nanoparticle-conjunctions (such as magnetic nanoparticles, and graphene derivatives nanoparticles) hold significant promises for remote regulation of cells and their relevant events at molecular scale. Despite outstanding developments in employing nanoparticles for drug targeting studies, the role of nanoparticles on cellular behaviors (proliferation, migration, and differentiation) has still required more evaluations in the field of mechanotherapy. In this paper, the in-depth contribution of mechano-transduction is discussed during tumor progression, and how these consequences can be evaluated in vitro.

PI3K functions as a hub in mechanotransduction

Mammalian cells integrate different types of stimuli that govern their fate. These stimuli encompass biochemical as well as biomechanical cues (shear, tensile, and compressive stresses) that are usually studied separately. The phosphatidylinositol 3-kinase (PI3K) enzymes, producing signaling phosphoinositides at plasma and intracellular membranes, are key in intracellular signaling and vesicular trafficking pathways. Recent evidence in cancer research demonstrates that these enzymes are essential in mechanotransduction. Despite this, the importance of the integration of biomechanical cues and PI3K-driven biochemical signals is underestimated. In this opinion article, we make the hypothesis that modeling of biomechanical cues is critical to understand PI3K oncogenicity. We also identify known/missing knowledge in terms of isoform specificity and molecular pathways of activation, knowledge that is needed for clinical applications.

Biophysical interactions between components of the tumor microenvironment promote metastasis

During metastasis, tumor cells need to adapt to their dynamic microenvironment and modify their mechanical properties in response to both chemical and mechanical stimulation. Physical interactions occur between cancer cells and the surrounding matrix including cell movements and cell shape alterations through the process of mechanotransduction. The latter describes the translation of external mechanical cues into intracellular biochemical signaling. Reorganization of both the cytoskeleton and the extracellular matrix (ECM) plays a critical role in these spreading steps. Migrating tumor cells show increased motility in order to cross the tumor microenvironment, migrate through ECM and reach the bloodstream to the metastatic site. There are specific factors affecting these processes, as well as the survival of circulating tumor cells (CTC) in the blood flow until they finally invade the secondary tissue to form metastasis. This review aims to study the mechanisms of metastasis from a biomechanical perspective and investigate cell migration, with a focus on the alterations in the cytoskeleton through this journey and the effect of biologic fluids on metastasis. Understanding of the biophysical mechanisms that promote tumor metastasis may contribute successful therapeutic approaches in the fight against cancer.

Mechanical Regulation of Transcription: Recent Advances

Mechanotransduction is the ability of a cell to sense mechanical cues from its microenvironment and convert them into biochemical signals to elicit adaptive transcriptional and other cellular responses. Here, we describe recent advances in the field of mechanical regulation of transcription, highlight mechanical regulation of the epigenome as a key novel aspect of mechanotransduction, and describe recent technological advances that could further elucidate the link between mechanical stimuli and gene expression. In this review, we emphasize the importance of mechanotransduction as one of the governing principles of cancer progression, underscoring the need to conduct further studies of the molecular mechanisms involved in sensing mechanical cues and coordinating transcriptional responses.

Tumor Extracellular Matrix Stiffness Promptly Modulates the Phenotype and Gene Expression of Infiltrating T Lymphocytes

The immune system is a fine modulator of the tumor biology supporting or inhibiting its progression, growth, invasion and conveys the pharmacological treatment effect. Tumors, on their side, have developed escaping mechanisms from the immune system action ranging from the direct secretion of biochemical signals to an indirect reaction, in which the cellular actors of the tumor microenvironment (TME) collaborate to mechanically condition the extracellular matrix (ECM) making it inhospitable to immune cells. TME is composed of several cell lines besides cancer cells, including tumor-associated macrophages, cancer-associated fibroblasts, CD4+ and CD8+ lymphocytes, and innate immunity cells. These populations interface with each other to prepare a conservative response, capable of evading the defense mechanisms implemented by the host's immune system. The presence or absence, in particular, of cytotoxic CD8+ cells in the vicinity of the main tumor mass, is able to predict, respectively, the success or failure of drug therapy. Among various mechanisms of immunescaping, in this study, we characterized the modulation of the phenotypic profile of CD4+ and CD8+ cells in resting and activated states, in response to the mechanical pressure exerted by a three-dimensional in vitro system, able to recapitulate the rheological and stiffness properties of the tumor ECM.

Aspects of the Tumor Microenvironment Involved in Immune Resistance and Drug Resistance

The tumor microenvironment (TME) is a complex and ever-changing "rogue organ" composed of its own blood supply, lymphatic and nervous systems, stroma, immune cells and extracellular matrix (ECM). These complex components, utilizing both benign and malignant cells, nurture the harsh, immunosuppressive and nutrient-deficient environment necessary for tumor cell growth, proliferation and phenotypic flexibility and variation. An important aspect of the TME is cellular crosstalk and cell-to-ECM communication. This interaction induces the release of soluble factors responsible for immune evasion and ECM remodeling, which further contribute to therapy resistance. Other aspects are the presence of exosomes contributed by both malignant and benign cells, circulating deregulated microRNAs and TME-specific metabolic patterns which further potentiate the progression and/or resistance to therapy. In addition to biochemical signaling, specific TME characteristics such as the hypoxic environment, metabolic derangements, and abnormal mechanical forces have been implicated in the development of treatment resistance. In this review, we will provide an overview of tumor microenvironmental composition, structure, and features that influence immune suppression and contribute to treatment resistance.

The Individual Effects of Cyclin-Dependent Kinase Inhibitors on Head and Neck Cancer Cells-A Systematic Analysis

Cyclin-dependent kinase inhibitors (CDKi´s) display cytotoxic activity against different malignancies, including head and neck squamous cell carcinomas (HNSCC). By coordinating the DNA damage response, these substances may be combined with cytostatics to enhance cytotoxicity. Here, we investigated the influence of different CDKi´s (palbociclib, dinaciclib, THZ1) on two HNSCC cell lines in monotherapy and combination therapy with clinically-approved drugs (5-FU, Cisplatin, cetuximab). Apoptosis/necrosis, cell cycle, invasiveness, senescence, radiation-induced γ-H2AX DNA double-strand breaks, and effects on the actin filament were studied. Furthermore, the potential to increase tumor immunogenicity was assessed by analyzing Calreticulin translocation and immune relevant surface markers. Finally, an in vivo mouse model was used to analyze the effect of dinaciclib and Cisplatin combination therapy. Dinaciclib, palbociclib, and THZ1 displayed anti-neoplastic activity after low-dose treatment, while the two latter substances slightly enhanced radiosensitivity. Dinaciclib decelerated wound healing, decreased invasiveness, and induced MHC-I, accompanied by high amounts of surface-bound Calreticulin. Numbers of early and late apoptotic cells increased initially (24 h), while necrosis dominated afterward. Antitumoral effects of the selective CDKi palbociclib were weaker, but combinations with 5-FU potentiated effects of the monotherapy. Additionally, CDKi and CDKi/chemotherapy combinations induced MHC I, indicative of enhanced immunogenicity. The in vivo studies revealed a cell line-specific response with best tumor growth control in the combination approach. Global acting CDKi's should be further investigated as targeting agents for HNSCC, either individually or in combination with selected drugs. The ability of dinaciclib to increase the immunogenicity of tumor cells renders this substance a particularly interesting candidate for immune-based oncological treatment regimens.

Contributions of the distinct biophysical phenotype of polyploidal giant cancer cells to cancer progression

Polyploid giant cancer cells (PGCCs) are a commonly observed histological feature of human tumors and are particularly prominent in late stage and drug resistant cancers. The chromosomal duplication conferred by their aneuploidy gives rise to DNA damage resistance and complex tumor cell karyotypes, a driving factor in chemotherapy resistance and disease relapse. Furthermore, PGCCs also exhibit key cytoskeletal features that give rise to a distinct biophysical phenotype, including increased density of polymerized actin and vimentin intermediate filaments, nuclear and cytoskeletal stiffening, increased traction force, and migratory persistence. Despite recent research highlighting the role PGCCs play in cancer progression, this population of tumor cells remains poorly characterized in terms of their biophysical properties. In this review, we will discuss the various aspects of their biomolecular phenotype, such as increased stemness as well as a mixed EMT signature. These features have been extensively associated with tumorigenesis and recurrence, and aggressive cancers. Additionally, we will also examine the distinct PGCC cytoskeletal features of actin and filamentous vimentin. Specifically, how the differential organization of these networks serve to support their increased size and drive migratory persistence. These findings could shed light on potential therapeutic strategies that allow for specific elimination or mitigation of the invasive potential of these polyploid cancer cells. Lastly, we will examine how the biophysical and molecular phenotype of PGCCs combine to tip the scale in favor of promoting cancer progression, presenting an important target in the clinical treatment of cancer.

3D Spheroids Versus 3D Tumor-Like Microcapsules: Confinement and Mechanical Stress May Lead to the Expression of Malignant Responses in Cancer Cells

As 2D surfaces fail to resemble the tumoral milieu, current discussions are focused on which 3D cell culture strategy may better lead the cells to express in vitro most of the malignant hints described in vivo. In this study, this question is assessed by analyzing the full genetic profile of MCF7 cells cultured either as 3D spheroids-considered as "gold standard" for in vitro cancer research- or immobilized in 3D tumor-like microcapsules, by RNA-Seq and transcriptomic methods, allowing to discriminate at big-data scale, which in vitro strategy can better resemble most of the malignant features described in neoplastic diseases. The results clearly show that mechanical stress, rather than 3D morphology only, stimulates most of the biological processes involved in cancer pathogenicity, such as cytoskeletal organization, migration, and stemness. Furthermore, cells entrapped in hydrogel-based scaffolds are likely expressing other physiological hints described in malignancy, such as the upregulated expression of metalloproteinases or the resistance to anticancer drugs, among others. According to the knowledge, this study represents the first attempt to answer which 3D experimental system can better mimic the neoplastic architecture in vitro, emphasizing the relevance of confinement in cancer pathogenicity, which can be easily achieved by using hydrogel-based matrices.

Matrix-driven changes in metabolism support cytoskeletal activity to promote cell migration

The microenvironment provides both active and passive mechanical cues that regulate cell morphology, adhesion, migration, and metabolism. Although the cellular response to those mechanical cues often requires energy-intensive actin cytoskeletal remodeling and actomyosin contractility, it remains unclear how cells dynamically adapt their metabolic activity to altered mechanical cues to support migration. Here, we investigated the changes in cellular metabolic activity in response to different two-dimensional and three-dimensional microenvironmental conditions and how these changes relate to cytoskeletal activity and migration. Utilizing collagen micropatterning on polyacrylamide gels, intracellular energy levels and oxidative phosphorylation were found to be correlated with cell elongation and spreading and necessary for membrane ruffling. To determine whether this relationship holds in more physiological three-dimensional matrices, collagen matrices were used to show that intracellular energy state was also correlated with protrusive activity and increased with matrix density. Pharmacological inhibition of oxidative phosphorylation revealed that cancer cells rely on oxidative phosphorylation to meet the elevated energy requirements for protrusive activity and migration in denser matrices. Together, these findings suggest that mechanical regulation of cytoskeletal activity during spreading and migration by the physical microenvironment is driven by an altered metabolic profile.

Oxygen gradient and tumor heterogeneity: The chronicle of a toxic relationship

The commencement of cancer is attributed to one or a few cells that become rogue and attain the property of immortality. The inception of distinct cancer cell clones during the hyperplastic and dysplastic stages of cancer progression is the utimate consequence of the dysregulated cellular pathways and the proliferative potential itself. Furthermore, a critical factor that adds a layer of complexity to this pre-existent intra-tumoral heterogeneity (ITH) is the foundation of an oxygen gradient, that is established due to the improper architecture of the tumor vasculature. Therefore, as a resultant effect, the poorly oxygenated regions thus formed and characterized as hypoxic, promote the emergence of aggressive and treatment-resistant cancer cell clones. The extraordinary property of the hypoxic cancer cells to exist harmoniously with cancerous and non-cancerous cells in the tumor microenvironment (TME) further increases the intricacies of ITH. Here in this review, the pivotal influence of differential oxygen concentrations in shaping the ITH is thoroughly discussed. We also emphasize on the vitality of the interacting networks that govern the overall fate of oxygen gradient-dependent origin of tumor heterogeneity. Additionally, the implications of less-appreciated reverse Warburg effect, a symbiotic metabolic coupling, and the associated epigenetic regulation of rewiring of cancer metabolism in response to oxygen gradients, have been highlighted as critical influencers of ITH.

Fabrication of Adhesive Substrate for Incorporating Hydrogels to Investigate the Influence of Stiffness on Cancer Cell Behavior

Stiffness control of cell culture platforms provides researchers in cell biology with the ability to study different experimental models in conditions of mimicking physiological or pathological microenvironments. Nevertheless, the signal transduction pathways and drug sensibility of cancer cells have been poorly characterized widely using biomimetic platforms because the limited experience of cancer cell biology groups about handling substrates with specific mechanical properties. The protein cross-linking and stiffening control are crucial checkpoints that could strongly affect cell adhesion and spreading, misrepresenting the data acquired, and also generating inaccurate cellular models. Here, we introduce a simple method to adhere to polyacrylamide (PAA) hydrogels on glass coverslips without any special treatment for mechanics studies in cancer cell biology. By using a commercial photosensitive glue, Loctite 3525, it is possible to polymerize PAA hydrogels directly on glass surfaces. Furthermore, we describe a cross-linking reaction method to attach proteins to PAA as an alternative method to Sulfo-SANPAH cross-linking, which is sometimes difficult to implement and reproduce. In this chapter, we describe a reliable procedure to fabricate ECM protein-cross-linked PAA hydrogels for mechanotransduction studies on cancer cells.

Type I collagen deletion in αSMA+ myofibroblasts augments immune suppression and accelerates progression of pancreatic cancer

Stromal desmoplastic reaction in pancreatic ductal adenocarcinoma (PDAC) involves significant accumulation of type I collagen (Col1). However, the precise molecular and mechanistic contribution of Col1 in PDAC progression remains unknown. Activated pancreatic stellate cells/αSMA+ myofibroblasts are major contributors of Col1 in the PDAC stroma. We use a dual-recombinase genetic mouse model of spontaneous PDAC to delete Col1 specifically in myofibroblasts. This results in significant reduction of total stromal Col1 content and accelerates the emergence of PanINs and PDAC, decreasing overall survival. Col1 deletion leads to Cxcl5 upregulation in cancer cells via SOX9. Increase in Cxcl5 is associated with recruitment of myeloid-derived suppressor cells and suppression of CD8+ T cells, which can be attenuated with combined targeting of CXCR2 and CCR2 to restrain accelerated PDAC progression in the setting of stromal Col1 deletion. Our results unravel the fundamental role of myofibroblast-derived Co1l in regulating tumor immunity and restraining PDAC progression.

Can mechanical forces attune heterotypic cell-cell communications?

Heterotypic cell lineages relentlessly exchange biomechanical signals among themselves in metazoan organs. Hence, cell-cell communications are pivotal for organ physiology and pathogenesis. Every cell lineage of an organ responds differently to a specific signal due to its unique receptibility and signal interpretation capacity. These distinct cellular responses generate a system-scale signaling network that helps in generating a specific organ phenotype. Although the reciprocal biochemical signal exchange between non-identical neighboring cells is known to be an essential factor for organ functioning, if, then how, mechanical cues incite these signals is not yet quite explored. Cells within organ tissues experience multiple mechanical forces, such as stretching, bending, compression, and shear stress. Forms and magnitudes of mechanical forces influence biochemical signaling in a cell-specific manner. Additionally, the biophysical state of acellular extracellular matrix (ECM) can transmit exclusive mechanical cues to specific cells of an organ. As it scaffolds heterotypic cells and tissues in close proximities, therefore, ECM can easily be contemplated as a mechanical conduit for signal exchange among them. However, force-stimulated signal transduction is not always physiological, aberrant force sensing by tissue-resident cells can transduce anomalous signals to each other, and potentially can promote pathological phenotypes. Herein, I attempt to put forward a perspective on how mechanical forces may influence signal transductions among heterotypic cell populations and how they feedback each other to achieve a transient or perpetual alteration in metazoan organs. A mechanistic insight of organ scale mechanotransduction can emanate the possibility of finding potential biomarkers and novel therapeutic strategies to deal with pathogenesis and organ regeneration.

Location, location, location: how the tissue microenvironment affects inflammation in RA

Current treatments for rheumatoid arthritis (RA) do not work well for a large proportion of patients, or at all in some individuals, and cannot cure or prevent this disease. One major obstacle to developing better drugs is a lack of complete understanding of how inflammatory joint disease arises and progresses. Emerging evidence indicates an important role for the tissue microenvironment in the pathogenesis of RA. Each tissue is made up of cells surrounded and supported by a unique extracellular matrix (ECM). These complex molecular networks define tissue architecture and provide environmental signals that programme site-specific cell behaviour. In the synovium, a main site of disease activity in RA, positional and disease stage-specific cellular diversity exist. Improved understanding of the architecture of the synovium from gross anatomy to the single-cell level, in parallel with evidence demonstrating how the synovial ECM is vital for synovial homeostasis and how dysregulated signals from the ECM promote chronic inflammation and tissue destruction in the RA joint, has opened up new ways of thinking about the pathogenesis of RA. These new ideas provide novel therapeutic approaches for patients with difficult-to-treat disease and could also be used in disease prevention.

Interfacial Curvature in Confined Coculture Directs Stromal Cell Activity with Spatial Corralling of Pancreatic Cancer Cells

Interfacial cues in the tumor microenvironment direct the activity and assembly of multiple cell types. Pancreatic cancer, along with breast and prostate cancers, is enriched with cancer-associated fibroblasts (CAFs) that activate to coordinate the deposition of the extracellular matrix, which can comprise over 90% of the tumor mass. While it is clear that matrix underlies the severity of the disease, the relationship between stromal-tumor cell assembly and cell-matrix dynamics remains elusive. Micropatterned hydrogels deconstruct the interplay between matrix stiffness and geometric confinement, guiding heterotypic cell populations and matrix assembly in pancreatic cancer. Interfacial cues at the perimeter of microislands guide CAF migration and direct cancer cell assembly. Computational modeling shows curvature-stress dependent cellular localization for cancer and CAFs in coculture. Regions of convex curvature enhance edge stress that activates a myofibroblast phenotype in the CAFs with migration and increased collagen I deposition, ultimately leading to a central "corralling" of cancer cells. Inhibiting mechanotransduction pathways decreases CAF activation and the associated corralling phenotype. Together, this work reveals how interfacial biophysical cues underpin aspects of stromal desmoplasia, a hallmark of disease severity and chemoresistance in the pancreatic, breast, and prostate cancers, thereby providing a tool to expand stroma-targeting therapeutic strategies.

Cytotoxic lymphocytes target characteristic biophysical vulnerabilities in cancer

Immune cells identify and destroy tumors by recognizing cellular traits indicative of oncogenic transformation. In this study, we found that myocardin-related transcription factors (MRTFs), which promote migration and metastatic invasion, also sensitize cancer cells to the immune system. Melanoma and breast cancer cells with high MRTF expression were selectively eliminated by cytotoxic lymphocytes in mouse models of metastasis. This immunosurveillance phenotype was further enhanced by treatment with immune checkpoint blockade (ICB) antibodies. We also observed that high MRTF signaling in human melanoma is associated with ICB efficacy in patients. Using biophysical and functional assays, we showed that MRTF overexpression rigidified the filamentous actin cytoskeleton and that this mechanical change rendered mouse and human cancer cells more vulnerable to cytotoxic T lymphocytes and natural killer cells. Collectively, these results suggest that immunosurveillance has a mechanical dimension, which we call mechanosurveillance, that is particularly relevant for the targeting of metastatic disease.

Architectural control of metabolic plasticity in epithelial cancer cells

Metabolic plasticity enables cancer cells to switch between glycolysis and oxidative phosphorylation to adapt to changing conditions during cancer progression, whereas metabolic dependencies limit plasticity. To understand a role for the architectural environment in these processes we examined metabolic dependencies of cancer cells cultured in flat (2D) and organotypic (3D) environments. Here we show that cancer cells in flat cultures exist in a high energy state (oxidative phosphorylation), are glycolytic, and depend on glucose and glutamine for growth. In contrast, cells in organotypic culture exhibit lower energy and glycolysis, with extensive metabolic plasticity to maintain growth during glucose or amino acid deprivation. Expression of KRAS^G12V in organotypic cells drives glucose dependence, however cells retain metabolic plasticity to glutamine deprivation. Finally, our data reveal that mechanical properties control metabolic plasticity, which correlates with canonical Wnt signaling. In summary, our work highlights that the architectural and mechanical properties influence cells to permit or restrict metabolic plasticity.

Understanding the influence of substrate when growing tumorspheres

Background

Cancer stem cells are important for the development of many solid tumors. These cells receive promoting and inhibitory signals that depend on the nature of their environment (their niche) and determine cell dynamics. Mechanical stresses are crucial to the initiation and interpretation of these signals.

Methods

A two-population mathematical model of tumorsphere growth is used to interpret the results of a series of experiments recently carried out in Tianjin, China, and extract information about the intraspecific and interspecific interactions between cancer stem cell and differentiated cancer cell populations.

Results

The model allows us to reconstruct the time evolution of the cancer stem cell fraction, which was not directly measured. We find that, in the presence of stem cell growth factors, the interspecific cooperation between cancer stem cells and differentiated cancer cells induces a positive feedback loop that determines growth, independently of substrate hardness. In a frustrated attempt to reconstitute the stem cell niche, the number of cancer stem cells increases continuously with a reproduction rate that is enhanced by a hard substrate. For growth on soft agar, intraspecific interactions are always inhibitory, but on hard agar the interactions between stem cells are collaborative while those between differentiated cells are strongly inhibitory. Evidence also suggests that a hard substrate brings about a large fraction of asymmetric stem cell divisions. In the absence of stem cell growth factors, the barrier to differentiation is broken and overall growth is faster, even if the stem cell number is conserved.

Conclusions

Our interpretation of the experimental results validates the centrality of the concept of stem cell niche when tumor growth is fueled by cancer stem cells. Niche memory is found to be responsible for the characteristic population dynamics observed in tumorspheres. The model also shows why substratum stiffness has a deep influence on the behavior of cancer stem cells, stiffer substrates leading to a larger proportion of asymmetric doublings. A specific condition for the growth of the cancer stem cell number is also obtained

Supplementary Information

The online version contains supplementary material available at (10.1186/s12885-021-07918-1).

Advanced Spheroid, Tumouroid and 3D Bioprinted In-Vitro Models of Adult and Paediatric Glioblastoma

The life expectancy of patients with high-grade glioma (HGG) has not improved in decades. One of the crucial tools to enable future improvement is advanced models that faithfully recapitulate the tumour microenvironment; they can be used for high-throughput screening that in future may enable accurate personalised drug screens. Currently, advanced models are crucial for identifying and understanding potential new targets, assessing new chemotherapeutic compounds or other treatment modalities. Recently, various methodologies have come into use that have allowed the validation of complex models—namely, spheroids, tumouroids, hydrogel-embedded cultures (matrix-supported) and advanced bioengineered cultures assembled with bioprinting and microfluidics. This review is designed to present the state of advanced models of HGG, whilst focusing as much as is possible on the paediatric form of the disease. The reality remains, however, that paediatric HGG (pHGG) models are years behind those of adult HGG. Our goal is to bring this to light in the hope that pGBM models can be improved upon.

A constriction channel analysis of astrocytoma stiffness and disease progression

Studies have demonstrated that cancer cells tend to have reduced stiffness (Young's modulus) compared to their healthy counterparts. The mechanical properties of primary brain cancer cells, however, have remained largely unstudied. To investigate whether the stiffness of primary brain cancer cells decreases as malignancy increases, we used a microfluidic constriction channel device to deform healthy astrocytes and astrocytoma cells of grade II, III, and IV and measured the entry time, transit time, and elongation. Calculating cell stiffness directly from the experimental measurements is not possible. To overcome this challenge, finite element simulations of the cell entry into the constriction channel were used to train a neural network to calculate the stiffness of the analyzed cells based on their experimentally measured diameter, entry time, and elongation in the channel. Our study provides the first calculation of stiffness for grades II and III astrocytoma and is the first to apply a neural network analysis to determine cell mechanical properties from a constriction channel device. Our results suggest that the stiffness of astrocytoma cells is not well-correlated with the cell grade. Furthermore, while other non-central-nervous-system cell types typically show reduced stiffness of malignant cells, we found that most astrocytoma cell lines had increased stiffness compared to healthy astrocytes, with lower-grade astrocytoma having higher stiffness values than grade IV glioblastoma. Differences in nucleus-to-cytoplasm ratio only partly explain differences in stiffness values. Although our study does have limitations, our results do not show a strong correlation of stiffness with cell grade, suggesting that other factors may play important roles in determining the invasive capability of astrocytoma. Future studies are warranted to further elucidate the mechanical properties of astrocytoma across various pathological grades.

Mechanobiology of Autophagy: The Unexplored Side of Cancer

Proper execution of cellular function, maintenance of cellular homeostasis and cell survival depend on functional integration of cellular processes and correct orchestration of cellular responses to stresses. Cancer transformation is a common negative consequence of mismanagement of coordinated response by the cell. In this scenario, by maintaining the balance among synthesis, degradation, and recycling of cytosolic components including proteins, lipids, and organelles the process of autophagy plays a central role. Several environmental stresses activate autophagy, among those hypoxia, DNA damage, inflammation, and metabolic challenges such as starvation. In addition to these chemical challenges, there is a requirement for cells to cope with mechanical stresses stemming from their microenvironment. Cells accomplish this task by activating an intrinsic mechanical response mediated by cytoskeleton active processes and through mechanosensitive protein complexes which interface the cells with their mechano-environment. Despite autophagy and cell mechanics being known to play crucial transforming roles during oncogenesis and malignant progression their interplay is largely overlooked. In this review, we highlight the role of physical forces in autophagy regulation and their potential implications in both physiological as well as pathological conditions. By taking a mechanical perspective, we wish to stimulate novel questions to further the investigation of the mechanical requirements of autophagy and appreciate the extent to which mechanical signals affect this process.

Piezo 1 activation facilitates cholangiocarcinoma metastasis via Hippo/YAP signaling axis

Tumor metastasis is one of the major factors for the high mortality in cholangiocarcinoma (CCA), but its underlying mechanisms are not fully understood. Here, we report that Piezo-type mechanosensitive ion channel component 1 (Piezo 1) is detected to be significantly upregulated in CCA tissues, which is linked to a poor prognosis in patients, suggesting that Piezo 1 may act in a pro-metastatic role in CCA development. Piezo 1 is activated through 20% simulated physiological stretch, and deleting Piezo 1 impedes epithelial-to-mesenchymal transition (EMT) of CCA cells, as well as impairing their metastatic capacity in vitro and in vivo. Mechanistically, the activation of Piezo 1 results in large amounts of Yes-associated protein 1 (YAP) translocated into the nucleus from the cytoplasm, and thus the motility of CCA cells is significantly increased. These findings indicate that mechanical stimulation induces Piezo 1 activation, which might be involved in CCA metastasis via the Hippo/YAP signaling axis. Therefore, Piezo 1 and its downstream effectors may be a novel therapeutic target for CCA treatment.

Stiffness increases with myofibroblast content and collagen density in mesenchymal high grade serous ovarian cancer

Women diagnosed with high-grade serous ovarian cancers (HGSOC) are still likely to exhibit a bad prognosis, particularly when suffering from HGSOC of the Mesenchymal molecular subtype (50% cases). These tumors show a desmoplastic reaction with accumulation of extracellular matrix proteins and high content of cancer-associated fibroblasts. Using patient-derived xenograft mouse models of Mesenchymal and Non-Mesenchymal HGSOC, we show here that HGSOC exhibit distinct stiffness depending on their molecular subtype. Indeed, tumor stiffness strongly correlates with tumor growth in Mesenchymal HGSOC, while Non-Mesenchymal tumors remain soft. Moreover, we observe that tumor stiffening is associated with high stromal content, collagen network remodeling, and MAPK/MEK pathway activation. Furthermore, tumor stiffness accompanies a glycolytic metabolic switch in the epithelial compartment, as expected based on Warburg's effect, but also in stromal cells. This effect is restricted to the central part of stiff Mesenchymal tumors. Indeed, stiff Mesenchymal tumors remain softer at the periphery than at the core, with stromal cells secreting high levels of collagens and showing an OXPHOS metabolism. Thus, our study suggests that tumor stiffness could be at the crossroad of three major processes, i.e. matrix remodeling, MEK activation and stromal metabolic switch that might explain at least in part Mesenchymal HGSOC aggressiveness.

Advances in biofabrication techniques for collagen-based 3D in vitro culture models for breast cancer research

Collagen is the most abundant component of the extracellular matrix (ECM), therefore it represents an ideal biomaterial for the culture of a variety of cell types. Recently, collagen-based scaffolds have shown promise as 3D culture platforms for breast cancer-based research. Two-dimensional (2D) in vitro culture models, while useful for gaining preliminary insights, are ultimately flawed as they do not adequately replicate the tumour microenvironment. As a result, they do not facilitate proper 3D cell-cell/cell-matrix interactions and often an exaggerated response to therapeutic agents occurs. The ECM plays a crucial role in the development and spread of cancer. Alterations within the ECM have a significant impact on the pathogenesis of cancer, the initiation of metastasis and ultimate progression of the disease. 3D in vitro culture models that aim to replicate the tumour microenvironment have the potential to offer a new frontier for cancer research with cell growth, morphology and genetic properties that more closely match in vivo cancers. While initial 3D in vitro culture models used in breast cancer research consisted of simple hydrogel platforms, recent advances in biofabrication techniques, including freeze-drying, electrospinning and 3D bioprinting, have enabled the fabrication of biomimetic collagen-based platforms that more closely replicate the breast cancer ECM. This review highlights the current application of collagen-based scaffolds as 3D in vitro culture models for breast cancer research, specifically for adherence-based scaffolds (i.e. matrix-assisted). Finally, the future perspectives of 3D in vitro breast cancer models and their potential to lead to an improved understanding of breast cancer diagnosis and treatment are discussed.

Growth of tumor emboli within a vessel model reveals dependence on the magnitude of mechanical constraint

Tumor emboli-aggregates of tumor cells within vessels-pose a clinical challenge as they are associated with increased metastasis and tumor recurrence. When growing within a vessel, tumor emboli are subject to a unique mechanical constraint provided by the tubular geometry of the vessel. Current models of tumor emboli use unconstrained multicellular tumor spheroids, which neglect this mechanical interplay. Here, we modeled a lymphatic vessel as a 200 μm-diameter channel in either a stiff or soft, bioinert agarose matrix to create a vessel-like constraint model (VLCM), and we modeled colon or breast cancer tumor emboli with aggregates of HCT116 or SUM149PT cells, respectively. The stiff matrix VLCM constrained the tumor emboli to the cylindrical channel, which led to continuous growth of the emboli, in contrast to the growth rate reduction that unconstrained spheroids exhibit. Emboli morphology in the soft matrix VLCM, however, was dependent on the magnitude of mechanical mismatch between the matrix and the cell aggregates. In general, when the elastic modulus of the matrix of the VLCM was greater than the emboli (EVLCM/Eemb > 1), the emboli were constrained to grow within the channel, and when the elastic modulus of the matrix was less than the emboli (0 < EVLCM/Eemb < 1), the emboli bulged into the matrix. Due to a large difference in myosin II expression between the cell lines, we hypothesized that tumor cell aggregate stiffness is an indicator of cellular force-generating capability. Inhibitors of myosin-related force generation decreased the elastic modulus and/or increased the stress relaxation of the tumor cell aggregates, effectively increasing the mechanical mismatch. The increased mechanical mismatch after drug treatment was correlated with increased confinement of tumor emboli growth along the channel, which may translate to increased tumor burden due to the increased tumor volume within the diffusion distance of nutrients and oxygen.

Proteinaceous Hydrogels for Bioengineering Advanced 3D Tumor Models

The establishment of tumor microenvironment using biomimetic in vitro models that recapitulate key tumor hallmarks including the tumor supporting extracellular matrix (ECM) is in high demand for accelerating the discovery and preclinical validation of more effective anticancer therapeutics. To date, ECM-mimetic hydrogels have been widely explored for 3D in vitro disease modeling owing to their bioactive properties that can be further adapted to the biochemical and biophysical properties of native tumors. Gathering on this momentum, herein the current landscape of intrinsically bioactive protein and peptide hydrogels that have been employed for 3D tumor modeling are discussed. Initially, the importance of recreating such microenvironment and the main considerations for generating ECM-mimetic 3D hydrogel in vitro tumor models are showcased. A comprehensive discussion focusing protein, peptide, or hybrid ECM-mimetic platforms employed for modeling cancer cells/stroma cross-talk and for the preclinical evaluation of candidate anticancer therapies is also provided. Further development of tumor-tunable, proteinaceous or peptide 3D microtesting platforms with microenvironment-specific biophysical and biomolecular cues will contribute to better mimic the in vivo scenario, and improve the predictability of preclinical screening of generalized or personalized therapeutics.

Membrane tension buffering by caveolae: a role in cancer?

Caveolae are bulb-like invaginations made up of two essential structural proteins, caveolin-1 and cavins, which are abundantly present at the plasma membrane of vertebrate cells. Since their discovery more than 60 years ago, the function of caveolae has been mired in controversy. The last decade has seen the characterization of new caveolae components and regulators together with the discovery of additional cellular functions that have shed new light on these enigmatic structures. Early on, caveolae and/or caveolin-1 have been involved in the regulation of several parameters associated with cancer progression such as cell migration, metastasis, angiogenesis, or cell growth. These studies have revealed that caveolin-1 and more recently cavin-1 have a dual role with either a negative or a positive effect on most of these parameters. The recent discovery that caveolae can act as mechanosensors has sparked an array of new studies that have addressed the mechanobiology of caveolae in various cellular functions. This review summarizes the current knowledge on caveolae and their role in cancer development through their activity in membrane tension buffering. We propose that the role of caveolae in cancer has to be revisited through their response to the mechanical forces encountered by cancer cells during tumor mass development.

Tumor-stroma biomechanical crosstalk: a perspective on the role of caveolin-1 in tumor progression

Tumor stiffening is a hallmark of malignancy that actively drives tumor progression and aggressiveness. Recent research has shed light onto several molecular underpinnings of this biomechanical process, which has a reciprocal crosstalk between tumor cells, stromal fibroblasts, and extracellular matrix remodeling at its core. This dynamic communication shapes the tumor microenvironment; significantly determines disease features including therapeutic resistance, relapse, or metastasis; and potentially holds the key for novel antitumor strategies. Caveolae and their components emerge as integrators of different aspects of cell function, mechanotransduction, and ECM-cell interaction. Here, we review our current knowledge on the several pivotal roles of the essential caveolar component caveolin-1 in this multidirectional biomechanical crosstalk and highlight standing questions in the field.

Micropatterned Surfaces Expose the Coupling between Actin Cytoskeleton-Lamin/Nesprin and Nuclear Deformability of Breast Cancer Cells with Different Malignancies

Mechanotransduction proteins transfer mechanical stimuli through nucleo-cytoskeletal coupling and affect the nuclear morphology of cancer cells. However, the contribution of actin filament integrity has never been studied directly. It is hypothesized that differences in nuclear deformability of cancer cells are influenced by the integrity of actin filaments. In this study, transparent micropatterned surfaces as simple tools to screen cytoskeletal and nuclear distortions are presented. Surfaces decorated with micropillars are used to culture and image breast cancer cells and quantify their deformation using shape descriptors (circularity, area, perimeter). Using two drugs (cytochalasin D and jasplakinolide), actin filaments are disrupted. Deformation of cells on micropillars is decreased upon drug treatment as shown by increased circularity. However, the effect is much smaller on benign MCF10A than on malignant MCF7 and MDAMB231 cells. On micropatterned surfaces, molecular analysis shows that Lamin A/C and Nesprin-2 expressions decreased but, after drug treatment, increased in malignant cells but not in benign cells. These findings suggest that Lamin A/C, Nesprin-2 and actin filaments are critical in mechanotransduction of cancer cells. Consequently, transparent micropatterned surfaces can be used as image analysis platforms to provide robust, high throughput measurements of nuclear deformability of cancer cells, including the effect of cytoskeletal elements.

The Extracellular Matrix-Derived Biomarkers for Diagnosis, Prognosis, and Personalized Therapy of Malignant Tumors

The tumor biomarkers already have proven clinical value and have become an integral part in cancer management and modern translational oncology. The tumor tissue microenvironment (TME), which includes extracellular matrix (ECM), signaling molecules, immune and stromal cells, and adjacent non-tumorous tissue, contributes to cancer pathogenesis. Thus, TME-derived biomarkers have many clinical applications. This review is predominately based on the most recent publications (manuscripts published in a last 5 years, or seminal publications published earlier) and fills a gap in the current literature on the cancer biomarkers derived from the TME, with particular attention given to the ECM and products of its processing and degradation, ECM-associated extracellular vesicles (EVs), biomechanical characteristics of ECM, and ECM-derived biomarkers predicting response to the immunotherapy. We discuss the clinical utility of the TME-incorporating three-dimensional in vitro and ex vivo cell culture models for personalized therapy. We conclude that ECM is a critical driver of malignancies and ECM-derived biomarkers should be included in diagnostics and prognostics panels of markers in the clinic.

Modulating the Crosstalk between the Tumor and the Microenvironment Using SiRNA: A Flexible Strategy for Breast Cancer Treatment

Simple Summary

With this review we aimed to collect the most relevant scientific findings regarding siRNA therapeutic tools against breast cancer microenvironment. Remarkably, breast cancer treatments have been redirected towards the tumor microenvironment components, mainly involved in patients’ relapse and pharmacological resistance. Therefore, siRNAs represent a promising strategy to jeopardize the tumor microenvironment interplay thanks to their non-toxic and specific effects.

Abstract

Tumorigenesis is a complex and multistep process in which sequential mutations in oncogenes and tumor-suppressor genes result in enhanced proliferation and apoptosis escape. Over the past decades, several studies have provided evidence that tumors are more than merely a mass of malignant cancer cells, with the tumor microenvironment (TME) also contributing to cancer progression. For this reason, the focus of cancer research in recent years has shifted from the malignant cancer cell itself to the TME and its interactions. Since the TME actively participates in tumor progression, therapeutic strategies targeting it have created great interest. In this context, much attention has been paid to the potential application of small interfering RNA (siRNA), a class of non-coding RNA that has the ability to downregulate the expression of target genes in a sequence-specific way. This is paving the way for a novel therapeutic approach for the treatment of several diseases, including cancer. In this review, we describe recent efforts in developing siRNA therapeutics for the treatment of breast cancer, with particular emphasis on TME regulation. We focus on studies that adapt siRNA design to reprogram/re-educate the TME and eradicate the interplay between cancer cells and TME.

Mechanical strain induces phenotypic changes in breast cancer cells and promotes immunosuppression in the tumor microenvironment

Breast cancer (BCa) proliferates within a complex, three-dimensional microenvironment amid heterogeneous biochemical and biophysical cues. Understanding how mechanical forces within the tumor microenvironment (TME) regulate BCa phenotype is of great interest. We demonstrate that mechanical strain enhanced the proliferation and migration of both estrogen receptor⁺ and triple-negative (TNBC) human and mouse BCa cells. Furthermore, a critical role for exosomes derived from cells subjected to mechanical strain in these pro-tumorigenic effects was identified. Exosome production by TNBC cells increased upon exposure to oscillatory strain (OS), which correlated with elevated cell proliferation. Using a syngeneic, orthotopic mouse model of TNBC, we identified that preconditioning BCa cells with OS significantly increased tumor growth and myeloid-derived suppressor cells (MDSCs) and M2 macrophages in the TME. This pro-tumorigenic myeloid cell enrichment also correlated with a decrease in CD8⁺ T cells. An increase in PD-L1⁺ exosome release from BCa cells following OS supported additive T cell inhibitory functions in the TME. The role of exosomes in MDSC and M2 macrophage was confirmed in vivo by cytotracking fluorescent exosomes, derived from labeled 4T1.2 cells, preconditioned with OS. In addition, in vivo internalization and intratumoral localization of tumor-cell derived exosomes was observed within MDSCs, M2 macrophages, and CD45-negative cell populations following direct injection of fluorescently-labeled exosomes. Our data demonstrate that exposure to mechanical strain promotes invasive and pro-tumorigenic phenotypes in BCa cells, indicating that mechanical strain can impact the growth and proliferation of cancer cell, alter exosome production by BCa, and induce immunosuppression in the TME by dampening anti-tumor immunity.

Actin dynamics during tumor cell dissemination

The actin cytoskeleton is a dynamic network that regulates cellular behavior from development to disease. By rearranging the actin cytoskeleton, cells are capable of migrating and invading during developmental processes; however, many of these cellular properties are hijacked by cancer cells to escape primary tumors and disseminate to distant organs in the body. In this review article, we highlight recent work describing how cancer cells regulate the actin cytoskeleton to achieve efficient invasion and metastatic colonization. We also review new imaging technologies that are capable of revealing the complex architecture and regulation of the actin cytoskeleton during motility and invasion of tumor cells.

Genomic Amplification and Functional Dependency of the Gamma Actin Gene ACTG1 in Uterine Cancer

Sarcomere and cytoskeleton genes, or actomyosin genes, regulate cell biology including mechanical stress, cell motility, and cell division. While actomyosin genes are recurrently dysregulated in cancers, their oncogenic roles have not been examined in a lineage-specific fashion. In this report, we investigated dysregulation of nine sarcomeric and cytoskeletal genes across 20 cancer lineages. We found that uterine cancers harbored the highest frequencies of amplification and overexpression of the gamma actin gene, ACTG1. Each of the four subtypes of uterine cancers, mixed endometrial carcinomas, serous carcinomas, endometroid carcinomas, and carcinosarcomas harbored between 5~20% of ACTG1 gene amplification or overexpression. Clinically, patients with ACTG1 gains had a poor prognosis. ACTG1 gains showed transcriptional patterns that reflect activation of oncogenic signals, repressed response to innate immunity, or immunotherapy. Functionally, the CRISPR-CAS9 gene deletion of ACTG1 had the most robust and consistent effects in uterine cancer cells relative to 20 other lineages. Overall, we propose that ACTG1 regulates the fitness of uterine cancer cells by modulating cell-intrinsic properties and the tumor microenvironment. In summary, the ACTG1 functions relative to other actomyosin genes support the notion that it is a potential biomarker and a target gene in uterine cancer precision therapies.

Breast Cancer Cells in Microgravity: New Aspects for Cancer Research

Breast cancer is the leading cause of cancer death in females. The incidence has risen dramatically during recent decades. Dismissed as an "unsolved problem of the last century", breast cancer still represents a health burden with no effective solution identified so far. Microgravity (µg) research might be an unusual method to combat the disease, but cancer biologists decided to harness the power of µg as an exceptional method to increase efficacy and precision of future breast cancer therapies. Numerous studies have indicated that µg has a great impact on cancer cells; by influencing proliferation, survival, and migration, it shifts breast cancer cells toward a less aggressive phenotype. In addition, through the de novo generation of tumor spheroids, µg research provides a reliable in vitro 3D tumor model for preclinical cancer drug development and to study various processes of cancer progression. In summary, µg has become an important tool in understanding and influencing breast cancer biology.

Microenvironmental Determinants of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) belongs to the most lethal solid tumors in humans. A histological hallmark feature of PDAC is the pronounced tumor microenvironment (TME) that dynamically evolves during tumor progression. The TME consists of different non-neoplastic cells such as cancer-associated fibroblasts, immune cells, endothelial cells, and neurons. Furthermore, abundant extracellular matrix components such as collagen and hyaluronic acid as well as matricellular proteins create a highly dynamic and hypovascular TME with multiple biochemical and physical interactions among the various cellular and acellular components that promote tumor progression and therapeutic resistance. In recent years, intensive research efforts have resulted in a significantly improved understanding of the biology and pathophysiology of the TME in PDAC, and novel stroma-targeted approaches are emerging that may help to improve the devastating prognosis of PDAC patients. However, none of anti-stromal therapies has been approved in patients so far, and there is still a large discrepancy between multiple successful preclinical results and subsequent failure in clinical trials. Furthermore, recent findings suggest that parts of the TME may also possess tumor-restraining properties rendering tailored therapies even more challenging.

Viscoelastic properties of biopolymer hydrogels determined by Brillouin spectroscopy: A probe of tissue micromechanics

Many problems in mechanobiology urgently require characterization of the micromechanical properties of cells and tissues. Brillouin light scattering has been proposed as an emerging optical elastography technique to meet this need. However, the information contained in the Brillouin spectrum is still a matter of debate because of fundamental problems in understanding the role of water in biomechanics and in relating the Brillouin data to low-frequency macroscopic mechanical parameters. Here, we investigate this question using gelatin as a model system in which the macroscopic physical properties can be manipulated to mimic all the relevant biological states of matter, ranging from the liquid to the gel and the glassy phase. We demonstrate that Brillouin spectroscopy is able to reveal both the elastic and viscous properties of biopolymers that are central to the structure and function of biological tissues.