Three-dimensional collagen matrix induces a mechanosensitive invasive epithelial phenotype

Regulation of p65 nuclear localization and chromatin states by compressive force

The tumor microenvironment (TME) is a dynamic ecosystem, that evolves with the developing tumor to support its growth and metastasis. A key aspect of TME evolution is the recruitment of stromal fibroblasts, carried out via the release of various tumor signals including tumor necrosis factor (TNFα). These tumor signals in turn alter the mechanical properties of the TME as the tumor grows. Because of the important role of stromal cells in supporting tumor progression, new therapies aim to target stromal fibroblasts. However, these therapies have been unsuccessful in part due to the limited understanding of cross-talk between chemical and altered mechanical signaling within stromal fibroblasts. To investigate this, we designed a coculture assay with YFP-TNFα releasing spheroids embedded within collagen gels alongside fibroblasts to mimic the stromal response within the TME. This resulted in the nuclear translocation of p65 in the stromal fibroblasts which was further intensified by the addition of compressive stress. The combination of mechanical and chemical signals led to cytoskeletal disruption and induced a distinct chromatin state in the stromal fibroblasts. These results highlight the important cross-talk between cytokine signaling and mechanical forces on stromal cells within the TME and facilitate the development of a better spheroid model for therapeutic interventions.

Global versus local matrix remodeling drives rotational versus invasive collective migration of epithelial cells

The coordinated movement of cell collectives is essential for normal epithelial tissue development, maintenance, and cancer progression. Here, we report on a minimal 3D extracellular matrix (ECM) system wherein both invasive collective migration (ICM) and rotational collective migration (RCM) arise spontaneously from individually seeded epithelial cells of mammary and hepatic origin, regardless of whether they express adherens junctions, and lead to ductal-like and acinar-like structures, respectively. Quantitative microscopy and cellular Potts modeling reveal that initial differences in cell protrusion dynamics and matrix-remodeling localization generate RCM and ICM behavior in confining 3D ECM. Matrix-remodeling activity by matrix metalloproteinases (MMPs) is localized to the base of protrusions in cells that initiate ICM, whereas RCM does not require MMPs and is associated with ITGβ1-mediated remodeling localized globally around the cell body. Further analysis in vitro and in vivo supports the concept that distinct matrix-remodeling strategies encode collective migration behaviors and tissue structure.

Sp1 mechanotransduction regulates breast cancer cell invasion in response to multiple tumor-mimicking extracellular matrix cues

Breast cancer progression is marked by extracellular matrix (ECM) remodeling, including increased stiffness, faster stress relaxation, and elevated collagen levels. In vitro experiments have revealed a role for each of these factors to individually promote malignant behavior, but their combined effects remain unclear. To address this, we developed alginate-collagen hydrogels with independently tunable stiffness, stress relaxation, and collagen density. We show that these combined tumor-mimicking ECM cues reinforced invasive morphologies and promoted spheroid invasion in breast cancer and mammary epithelial cells. High stiffness and low collagen density in slow-relaxing matrices led to the greatest cell migration speed and displacement. RNA-seq revealed Sp1 target gene enrichment in response to both individual and combined ECM cues, with a greater enrichment observed under multiple cues. Notably, high expression of Sp1 target genes upregulated by fast stress relaxation correlated with poor patient survival. Mechanistically, we found that phosphorylated-Sp1 (T453) was increasingly located in the nucleus in stiff and/or fast relaxing matrices, which was regulated by PI3K and ERK1/2 signaling, as well as actomyosin contractility. This study emphasizes how multiple ECM cues in complex microenvironments reinforce malignant traits and supports an emerging role for Sp1 as a mechanoresponsive transcription factor.

Fibrotic extracellular matrix preferentially induces a partial Epithelial-Mesenchymal Transition phenotype in a 3-D agent based model of fibrosis

One of the main drivers of fibrotic diseases is epithelial-mesenchymal transition (EMT): a transdifferentiation process in which cells undergo a phenotypic change from an epithelial state to a pro-migratory state. The cytokine transforming growth factor-β1 (TGF-β1) has been previously shown to regulate EMT. TGF-β1 binds to fibronectin (FN) fibrils, which are the primary extracellular matrix (ECM) component in renal fibrosis. We have previously demonstrated experimentally that inhibition of FN fibrillogenesis and/or TGF-β1 tethering to FN inhibits EMT. However, these studies have only been conducted on 2-D cell monolayers, and the role of TGF-β1-FN tethering in 3-D cellular environments is not clear. As such, we sought to develop a 3-D computational model of epithelial spheroids that captured both EMT signaling dynamics and TGF-β1-FN tethering dynamics. We have incorporated the bi-stable EMT switch model developed by Tian et al. (2013) into a 3-D multicellular model to capture both temporal and spatial TGF-β1 signaling dynamics. We showed that the addition of increasing concentrations of exogeneous TGF-β1 led to faster EMT progression, indicated by increased expression of mesenchymal markers, decreased cell proliferation and increased migration. We then incorporated TGF-β1-FN fibril tethering by locally reducing the TGF-β1 diffusion coefficient as a function of EMT to simulate the reduced movement of TGF-β1 when tethered to FN fibrils during fibrosis. We showed that incorporation of TGF-β1 tethering to FN fibrils promoted a partial EMT state, independent of exogenous TGF-β1 concentration, indicating a mechanism by which fibrotic ECM can promote a partial EMT state.

Tumor-associated macrophages restrict CD8+ T cell function through collagen deposition and metabolic reprogramming of the breast cancer microenvironment

Tumor progression is accompanied by fibrosis, a condition of excessive extracellular matrix accumulation, which is associated with diminished antitumor immune infiltration. Here we demonstrate that tumor-associated macrophages (TAMs) respond to the stiffened fibrotic tumor microenvironment (TME) by initiating a collagen biosynthesis program directed by transforming growth factor-β. A collateral effect of this programming is an untenable metabolic milieu for productive CD8+ T cell antitumor responses, as collagen-synthesizing macrophages consume environmental arginine, synthesize proline and secrete ornithine that compromises CD8+ T cell function in female breast cancer. Thus, a stiff and fibrotic TME may impede antitumor immunity not only by direct physical exclusion of CD8+ T cells but also through secondary effects of a mechano-metabolic programming of TAMs, which creates an inhospitable metabolic milieu for CD8+ T cells to respond to anticancer immunotherapies.

Intracellular pH dynamics respond to microenvironment stiffening and mediate vasculogenic mimicry through β-catenin

Dysregulated intracellular pH (pHi) dynamics and an altered tumor microenvironment have emerged as drivers of cancer cell phenotypes. However, the molecular integration between the physical properties of the microenvironment and dynamic intracellular signaling responses remains unclear. Here, we use two metastatic cell models, one breast and one lung, to assess pHi response to varying extracellular matrix (ECM) stiffness. To experimentally model ECM stiffening, we use two tunable-stiffness hydrogel systems: Matrigel and hyaluronic acid (HA) gels, which mimic the increased protein secretion and crosslinking associated with ECM stiffening. We find that single-cell pHi decreases with increased ECM stiffness in both hydrogel systems and both metastatic cell types. We also observed that stiff ECM promotes vasculogenic mimicry (VM), a phenotype associated with metastasis and resistance. Importantly, we show that decreased pHi is both a necessary and sufficient mediator of VM, as raising pHi on stiff ECM reduces VM phenotypes and lowering pHi on soft ECM drives VM. We characterize β-catenin as a pH-dependent molecular mediator of pH-dependent VM, where stiffness-driven changes in β-catenin abundance can be overridden by increased pHi. We uncover a dynamic relationship between matrix stiffness and pHi, thus suggesting pHi dynamics can override mechanosensitive cell responses to the extracellular microenvironment.

Comparison of three-dimensional cell culture techniques of dedifferentiated liposarcoma and their integration with future research

Background: Dedifferentiated liposarcoma is a formidable sarcoma subtype due to its high local recurrence rate and resistance to medical treatment. While 2D cell cultures are still commonly used, 3D cell culture systems have emerged as a promising alternative, particularly scaffold-based techniques that enable the creation of 3D models with more accurate cell-stroma interactions. Objective: To investigate how 3D structures with or without the scaffold existence would affect liposarcoma cell lines growth morphologically and biologically. Methods: Lipo246 and Lipo863 cell lines were cultured in 3D using four different methods; Matrigel® ECM scaffold method, Collagen ECM scaffold method, ULA plate method and Hanging drop method, in addition to conventional 2D cell culture methods. All samples were processed for histopathological analysis (HE, IHC and DNAscope™), Western blot, and qPCR; moreover, 3D collagen-based models were treated with different doses of SAR405838, a well-known inhibitor of MDM2, and cell viability was assessed in comparison to 2D model drug response. Results: Regarding morphology, cell lines behaved differently comparing the scaffold-based and scaffold-free methods. Lipo863 formed spheroids in Matrigel® but not in collagen, while Lipo246 did not form spheroids in either collagen or Matrigel®. On the other hand, both cell lines formed spheroids using scaffold-free methods. All samples retained liposarcoma characteristic, such as high level of MDM2 protein expression and MDM2 DNA amplification after being cultivated in 3D. 3D collagen samples showed higher cell viability after SAR40538 treatment than 2D models, while cells sensitive to the drug died by apoptosis or necrosis. Conclusion: Our results prompt us to extend our investigation by applying our 3D models to further oncological relevant applications, which may help address unresolved questions about dedifferentiated liposarcoma biology.

A Decision Tree to Guide Human and Mouse Mammary Organoid Model Selection

Over the past 50 years, researchers from the mammary gland field have launched a collection of distinctive 3D cell culture systems to study multiple aspects of mammary gland physiology and disease. As our knowledge about the mammary gland evolves, more sophisticated 3D cell culture systems are required to answer more and more complex questions. Nowadays, morphologically complex mammary organoids can be generated in distinct 3D settings, along with reproduction of multiple aspects of the gland microenvironment. Yet, each 3D culture protocol comes with its advantages and limitations, where some culture systems are best suited to study stemness potential, whereas others are tailored towards the study of mammary gland morphogenesis. Therefore, prior to starting a 3D mammary culture experiment, it is important to consider and select the ideal culture model to address the biological question of interest. The number and technical requirements of novel 3D cell culture methods vastly increased over the past decades, making it currently challenging and time consuming to identify the best experimental testing. In this chapter, we provide a summary of the most promising murine and human 3D organoid models that are currently used in mammary gland biology research. For each model, we will provide a brief description of the protocol and an overview of the expected morphological outcome, the advantages of the model, and the potential pitfalls, to guide the reader to the best model of choice for specific applications.

In Vitro Organoid-Based Assays Reveal SMAD4 Tumor-Suppressive Mechanisms for Serrated Colorectal Cancer Invasion

Colon cancer is the third most prominent cancer and second leading cause of cancer-related deaths in the United States. Up to 20% of colon cancers follow the serrated tumor pathway driven by mutations in the MAPK pathway. Loss of SMAD4 function occurs in the majority of late-stage colon cancers and is associated with aggressive cancer progression. Therefore, it is important to develop technology to accurately model and better understand the genetic mechanisms behind cancer invasion. Organoids derived from tumors found in the Smad4KO BRAFV600E/+ mouse model present multiple phenotypes characteristic of invasion both in ex vivo and in vivo systems. Smad4KO BRAFV600E/+ tumor organoids can migrate through 3D culture and infiltrate through transwell membranes. This invasive behavior can be suppressed when SMAD4 is re-expressed in the tumor organoids. RNA-Seq analysis reveals that SMAD4 expression in organoids rapidly regulates transcripts associated with extracellular matrix and secreted proteins, suggesting that the mechanisms employed by SMAD4 to inhibit invasion are associated with regulation of extracellular matrix and secretory pathways. These findings indicate new models to study SMAD4 regulation of tumor invasion and an additional layer of complexity in the tumor-suppressive function of the SMAD4/Tgfβ pathway.

An engineered glioblastoma model yields novel macrophage-secreted drivers of invasion

Glioblastomas (GBMs) are highly invasive brain tumors replete with brain- and blood-derived macrophages, collectively known as tumor-associated macrophages (TAMs). Targeting TAMs has been proposed as a therapeutic strategy but has thus far yielded limited clinical success in slowing GBM progression, due in part to an incomplete understanding of TAM function in GBM. Here, by using an engineered hyaluronic acid-based 3D invasion platform, patient-derived GBM cells, and multi-omics analysis of GBM tumor microenvironments, we show that M2-polarized macrophages stimulate GBM stem cell (GSC) mesenchymal transition and invasion. We identify TAM-derived transforming growth factor beta induced (TGFβI/BIGH3) as a pro-tumorigenic factor in the GBM microenvironment. In GBM patients, BIGH3 mRNA expression correlates with poor patient prognosis and is highest in the most aggressive GBM molecular subtype. Inhibiting TAM-derived BIGH3 signaling with a blocking antibody or small molecule inhibitor suppresses GSC invasion. Our work highlights the utility of 3D in vitro tumor microenvironment platforms to investigate TAM-cancer cell crosstalk and offers new insights into TAM function to guide novel TAM-targeting therapies.

Embedded Bioprinting of Breast Tumor Cells and Organoids Using Low-Concentration Collagen-Based Bioinks

Bioinks for 3D bioprinting of tumor models should not only meet printability requirements but also accurately maintain and support phenotypes of tumor surrounding cells to recapitulate key tumor hallmarks. Collagen is a major extracellular matrix protein for solid tumors, but low viscosity of collagen solution has made 3D bioprinted cancer models challenging. This work produces embedded, bioprinted breast cancer cells and tumor organoid models using low-concentration collagen I based bioinks. The biocompatible and physically crosslinked silk fibroin hydrogel is used to generate the support bath for the embedded 3D printing. The composition of the collagen I based bioink is optimized with a thermoresponsive hyaluronic acid-based polymer to maintain the phenotypes of both the noninvasive epithelial and invasive breast cancer cells, as well as cancer-associated fibroblasts. Mouse breast tumor organoids are bioprinted using optimized collagen bioink to mimic in vivo tumor morphology. A vascularized tumor model is also created using a similar strategy, with significantly enhanced vasculature formation under hypoxia. This study shows the great potential of embedded bioprinted breast tumor models utilizing a low-concentration collagen-based bioink for advancing the understanding of tumor cell biology and facilitating drug discovery research.

Collective directional migration drives the formation of heteroclonal cancer cell clusters

Metastasisation occurs through the acquisition of invasive and survival capabilities that allow tumour cells to colonise distant sites. While the role of multicellular aggregates in cancer dissemination is acknowledged, the mechanisms that drive the formation of multiclonal cell aggregates are not fully elucidated. Here, we show that cancer cells of different tissue of origins can perform collective directional migration and can actively form heteroclonal aggregates in 3D, through a proliferation-independent mechanism. Coalescence of distant cell clusters is mediated by subcellular actin-rich protrusions and multicellular outgrowths that extend towards neighbouring aggregates. Coherently, perturbation of cytoskeletal dynamics impairs collective migration while myosin II activation is necessary for multicellular movements. We put forward the hypothesis that cluster attraction is mediated by secreted soluble factors. Such a hypothesis is consistent with the abrogation of aggregation by inhibition of PI3K/AKT/mTOR and MEK/ERK, the chemoattracting activity of conditioned culture media and with a wide screening of secreted proteins. Our results present a novel collective migration model and shed light on the mechanisms of formation of heteroclonal aggregates in cancer.

Modelling adult stem cells and their niche in health and disease with epithelial organoids

Adult stem cells are responsible for homoeostasis and regeneration of epithelial tissues. Stem cell function is regulated by both cell autonomous mechanisms as well as the niche. Deregulated stem cell function contributes to diseases such as cancer. Epithelial organoid cultures generated from tissue-resident adult stem cells have allowed unprecedented insights into the biology of epithelial tissues. The subsequent adaptation of organoid technology enabled the modelling of the communication of stem cells with their cellular and non-cellular niche as well as diseases. Starting from its first model described in 2009, the murine small intestinal organoid, we discuss here how epithelial organoid cultures have been become a prime in vitro research tool for cell and developmental biology, bioengineering, and biomedicine in the last decade.

The effect of matrices on the gene expression profile of patient-derived head and neck carcinoma cells for in vitro therapy testing

OBJECTIVE

Head and neck squamous cell carcinoma (HNSCC) is a highly aggressive tumor with a 5-year mortality rate of ~ 50%. New in vitro methods are needed for testing patients' cancer cell response to anti-cancer treatments. We aimed to investigate how the gene expression of fresh carcinoma tissue samples and freshly digested single cancer cells change after short-term cell culturing on plastic, Matrigel or Myogel. Additionally, we studied the effect of these changes on the cancer cells' response to anti-cancer treatments.

MATERIALS/METHODS

Fresh tissue samples from HNSCC patients were obtained perioperatively and single cells were enzymatically isolated and cultured on either plastic, Matrigel or Myogel. We treated the cultured cells with cisplatin, cetuximab, and irradiation; and performed cell viability measurement. RNA was isolated from fresh tissue samples, freshly isolated single cells and cultured cells, and RNA sequencing transcriptome profiling and gene set enrichment analysis were performed.

RESULTS

Cancer cells obtained from fresh tissue samples changed their gene expression regardless of the culturing conditions, which may be due to the enzymatic digestion of the tissue. Myogel was more effective than Matrigel at supporting the upregulation of pathways related to cancer cell proliferation and invasion. The impacts of anti-cancer treatments varied between culturing conditions.

CONCLUSIONS

Our study showed the challenge of in vitro cancer drug testing using enzymatic cell digestion. The upregulation of many targeted pathways in the cultured cells may partially explain the common clinical failure of the targeted cancer drugs that pass the in vitro testing.

The Growing Importance of Three-Dimensional Models and Microphysiological Systems in the Assessment of Mycotoxin Toxicity

Current investigations in the field of toxicology mostly rely on 2D cell cultures and animal models. Although well-accepted, the traditional 2D cell-culture approach has evident drawbacks and is distant from the in vivo microenvironment. To overcome these limitations, increasing efforts have been made in the development of alternative models that can better recapitulate the in vivo architecture of tissues and organs. Even though the use of 3D cultures is gaining popularity, there are still open questions on their robustness and standardization. In this review, we discuss the current spheroid culture and organ-on-a-chip techniques as well as the main conceptual and technical considerations for the correct establishment of such models. For each system, the toxicological functional assays are then discussed, highlighting their major advantages, disadvantages, and limitations. Finally, a focus on the applications of 3D cell culture for mycotoxin toxicity assessments is provided. Given the known difficulties in defining the safety ranges of exposure for regulatory agency policies, we are confident that the application of alternative methods may greatly improve the overall risk assessment.

Fiber density and matrix stiffness modulate distinct cell migration modes in a 3D stroma mimetic composite hydrogel

The peritumoral stroma is a complex 3D tissue that provides cells with myriad biophysical and biochemical cues. Histologic observations suggest that during metastatic spread of carcinomas, these cues influence transformed epithelial cells, prompting a diversity of migration modes spanning single cell and multicellular phenotypes. Purported consequences of these variations in tumor escape strategies include differential metastatic capability and therapy resistance. Therefore, understanding how cues from the peritumoral stromal microenvironment regulate migration mode has both prognostic and therapeutic value. Here, we utilize a synthetic stromal mimetic in which matrix fiber density and bulk hydrogel mechanics can be orthogonally tuned to investigate the contribution of these two key matrix attributes on MCF10A migration mode phenotypes, epithelial-mesenchymal transition (EMT), and invasive potential. We develop an automated computational image analysis framework to extract migratory phenotypes from fluorescent images and determine 3D migration metrics relevant to metastatic spread. Using this analysis, we find that matrix fiber density and bulk hydrogel mechanics distinctly contribute to a variety of MCF10A migration modes including amoeboid, single mesenchymal, clusters, and strands. We identify combinations of physical and soluble cues that induce a variety of migration modes originating from the same MCF10A spheroid and use these settings to examine a functional consequence of migration mode -resistance to apoptosis. We find that cells migrating as strands are more resistant to staurosporine-induced apoptosis than either disconnected clusters or individual invading cells. Improved models of the peritumoral stromal microenvironment and understanding of the relationships between matrix attributes and cell migration mode can aid ongoing efforts to identify effective cancer therapeutics that address cell plasticity-based therapy resistances. STATEMENT OF SIGNIFICANCE: Stromal extracellular matrix structure dictates both cell homeostasis and activation towards migratory phenotypes. However decoupling the effects of myriad biophysical cues has been difficult to achieve. Here, we encapsulate electrospun fiber segments within an amorphous hydrogel to create a fiber-reinforced hydrogel composite in which fiber density and hydrogel stiffness can be orthogonally tuned. Quantification of 3D cell migration reveal these two parameters uniquely contribute to a diversity of migration phenotypes spanning amoeboid, single mesenchymal, multicellular cluster, and collective strand. By tuning biophysical and biochemical cues to elicit heterogeneous migration phenotypes, we find that collective strands best resist apoptosis. This work establishes a composite approach to modulate fibrous topography and bulk hydrogel mechanics and identified biomaterial parameters to direct distinct 3D cell migration phenotypes.

An In Vitro Approach to Model EMT in Breast Cancer

During the progression from ductal carcinoma in situ (DCIS) to invasive breast cancer (IBC), cells must overcome the physically restraining basement membrane (BM), which compartmentalizes the epithelium from the stroma. Since the extracellular matrix (ECM) of the epithelial and stromal compartments are biochemically and physically distinct from one another, the progression demands a certain degree of cellular plasticity for a primary tumor to become invasive. The epithelial-to-mesenchymal transition (EMT) depicts such a cell program, equipping cancer cells with features allowing for dissemination from the epithelial entity and stromal invasion at the single-cell level. Here, the reciprocal interference between an altering tumor microenvironment and the EMT phenotype was investigated in vitro. BM-typical collagen IV and stroma-typical collagen I coatings were applied as provisional 2D matrices. Pro-inflammatory growth factors were introduced to improve tissue mimicry. Whereas the growth on coated surfaces only slightly affected the EMT phenotype, the combinatorial action of collagen with growth factor TGF-β1 induced prominent phenotypic changes. However, EMT induction was independent of collagen type, and cellular accessibility for EMT-like changes was strongly cell-line dependent. Summarizing the entire body of data, an EMT-phenotyping model was used to determine cellular EMT status and estimate EMT-like changes. The miR200c-mediated reversion of mesenchymal MDA-MB-231 cells is reflected by our EMT-phenotype model, thus emphasizing its potential to predict the therapeutic efficacy of EMT-targeting drugs in the future.

The role of glycans in the mechanobiology of cancer

Although cancer is a genetic disease, physical changes such as stiffening of the extracellular matrix also commonly occur in cancer. Cancer cells sense and respond to extracellular matrix stiffening through the process of mechanotransduction. Cancer cell mechanotransduction can enhance cancer-promoting cell behaviors such as survival signaling, proliferation, and migration. Glycans, carbohydrate-based polymers, have recently emerged as important mediators and/or modulators of cancer cell mechanotransduction. Stiffer tumors are characterized by increased glycan content on cancer cells and their associated extracellular matrix. Here we review the role of cancer-associated glycans in coupled mechanical and biochemical alterations during cancer progression. We discuss the recent evidence on how increased expression of different glycans, in the form of glycoproteins and proteoglycans, contributes to both mechanical changes in tumors and corresponding cancer cell responses. We conclude with a summary of emerging tools that can be used to modify glycans for future studies in cancer mechanobiology.

Spatio-Temporal Changes of Extracellular Matrix (ECM) Stiffness in the Development of the Leech Hirudo verbana

The invertebrate leech Hirudo verbana represents a powerful experimental animal model for improving the knowledge about the functional interaction between the extracellular matrix (ECM) and cells within the tissue microenvironment (TME), and the key role played by ECM stiffness during development and growth. Indeed, the medicinal leech is characterized by a simple anatomical organization reproducing many aspects of the basic biological processes of vertebrates and in which a rapid spatiotemporal development is well established and easily assessed. Our results show that ECM structural organization, as well as the amount of fibrillar and non-fibrillar collagen are deeply different from hatching leeches to adult ones. In addition, the changes in ECM remodelling occurring during the different leech developmental stages, leads to a gradient of stiffness regulating both the path of migratory cells and their fates. The ability of cells to perceive and respond to changes in ECM composition and mechanics strictly depend on nuclear or cytoplasmic expression of Yes-Associated Protein 1 (YAP1), a key mediator converting mechanical signals into transcriptional outputs, expression, and activation.

Pre-glycation impairs gelation of high concentration collagen solutions

There remains a need for stiffer collagen hydrogels for tissue engineering and disease modeling applications. Pre-glycation, or glycation of collagen in solution prior to gelation, has been shown to increase the mechanics of collagen hydrogels while maintaining high viability of encapsulated cells. The stiffness of glycated collagen gels can be increased by increasing the collagen concentration, sugar concentration, and glycation time. However, previous studies on pre-glycation of collagen have used low collagen concentrations and/or low sugar concentrations and have not investigated the effect of glycation time. Therefore, the objective of this study was to determine the effects of pre-glycation with high sugar concentrations (up to 500 mM) and extended glycation times (up to 21 days) on high concentration collagen (8 mg/ml). The addition of sugar to the collagen and the formation of advanced glycation end products (AGEs) were quantified. The ability to gel successfully and rheological properties were determined and correlated with biochemical characterizations. Successful collagen gelation and rheological properties of pre-glycated collagen were found to be strongly dependent on the ratio of added sugars to added AGEs with high ratios impairing gelation and low ratios resulting in optimal storage moduli. There is likely a competing effect during pre-glycation of the formation of AGEs resulting in crosslinking of collagen and the formation of Amadori intermediates acting to increase collagen solubility. Overall, this study shows that collagen glycation can be optimized by increasing the formation of AGEs while maintaining a low ratio of added sugar to added AGEs.

Biomaterials and bioengineering to guide tissue morphogenesis in epithelial organoids

Organoids are self-organized and miniatured in vitro models of organs and recapitulate key aspects of organ architecture and function, leading to rapid progress in understanding tissue development and disease. However, current organoid culture systems lack accurate spatiotemporal control over biochemical and physical cues that occur during in vivo organogenesis and fail to recapitulate the complexity of organ development, causing the generation of immature organoids partially resembling tissues in vivo. Recent advances in biomaterials and microengineering technologies paved the way for better recapitulation of organ morphogenesis and the generation of anatomically-relevant organoids. For this, understanding the native ECM components and organization of a target organ is essential in providing rational design of extracellular scaffolds that support organoid growth and maturation similarly to the in vivo microenvironment. In this review, we focus on epithelial organoids that resemble the spatial distinct structure and function of organs lined with epithelial cells including intestine, skin, lung, liver, and kidney. We first discuss the ECM diversity and organization found in epithelial organs and provide an overview of developing hydrogel systems for epithelial organoid culture emphasizing their key parameters to determine cell fates. Finally, we review the recent advances in tissue engineering and microfabrication technologies including bioprinting and microfluidics to overcome the limitations of traditional organoid cultures. The integration of engineering methodologies with the organoid systems provides a novel approach for instructing organoid morphogenesis via precise spatiotemporal modulation of bioactive cues and the establishment of high-throughput screening platforms.

AGE-breaker ALT711 reverses glycation-mediated cancer cell migration

Diabetes is associated with increased risk of breast cancer and worse prognoses for cancer patients. Hyperglycemia can result in increased glycation, the process wherein crosslinkages are formed between sugars and extracellular matrix (ECM) proteins through the formation of advanced glycation endproducts (AGEs). Although accumulation of AGEs occurs naturally in vivo over time, it is greatly accelerated by the hyperglycemic environment of diabetic patients. AGE accumulation has been linked to stiffening-related diseases such as hypertension, cancer metastasis, and neurodegenerative disorders. In response, several AGE-inhibiting and AGE-breaking drugs have received significant attention for their ability to reduce AGE accumulation. The resulting effects of these drugs on cell behavior is not well understood. In this study, we measured cancer cell migration in glycated collagen with and without the AGE-breaking drug alagebrium chloride (ALT711) to investigate the drug's ability to disrupt ECM crosslinks and reduce tumor cell spreading, contractility, and migration. The mechanical properties and chemical composition of collagen glycated with increasing concentrations of glucose with and without ALT711 treatment were measured. Increasing glucose concentration resulted in increased AGE accumulation and matrix stiffness as well as increased cancer cell contractility, elongation, and migration. Treatment with ALT711 significantly lowered AGE accumulation within the collagen, decreased collagen stiffness, and reduced cell migration. These findings suggest that while hyperglycemia can increase collagen matrix stiffness, resulting in increased breast cancer cell migration, an AGE-breaker can reverse this phenotype and may be a viable treatment option for reducing cancer cell migration due to glycation.

Polarized NHE1 and SWELL1 regulate migration direction, efficiency and metastasis

Cell migration regulates diverse (patho)physiological processes, including cancer metastasis. According to the Osmotic Engine Model, polarization of NHE1 at the leading edge of confined cells facilitates water uptake, cell protrusion and motility. The physiological relevance of the Osmotic Engine Model and the identity of molecules mediating cell rear shrinkage remain elusive. Here, we demonstrate that NHE1 and SWELL1 preferentially polarize at the cell leading and trailing edges, respectively, mediate cell volume regulation, cell dissemination from spheroids and confined migration. SWELL1 polarization confers migration direction and efficiency, as predicted mathematically and determined experimentally via optogenetic spatiotemporal regulation. Optogenetic RhoA activation at the cell front triggers SWELL1 re-distribution and migration direction reversal in SWELL1-expressing, but not SWELL1-knockdown, cells. Efficient cell reversal also requires Cdc42, which controls NHE1 repolarization. Dual NHE1/SWELL1 knockdown inhibits breast cancer cell extravasation and metastasis in vivo, thereby illustrating the physiological significance of the Osmotic Engine Model.

Interplay of the transcription factor MRTF-A and matrix stiffness controls mammary acinar structure and protrusion formation

Background

Ongoing differentiation processes characterize the mammary gland during sexual development and reproduction. In contrast, defective remodelling is assumed to be causal for breast tumorigenesis. We have shown recently that the myocardin-related transcription factor A (MRTF-A) is essential for forming regular hollow acinar structures. Moreover, MRTF-A activity is known to depend on the biochemical and physical properties of the surrounding extracellular matrix. In this study we analysed the mutual interaction of different matrix stiffnesses and MRTF-A activities on formation and maintenance of mammary acini.

Methods

Human MCF10A acini and primary mature organoids isolated from murine mammary glands were cultivated in 3D on soft and stiff matrices (200–4000 Pa) in conjunction with the Rho/MRTF/SRF pathway inhibitor CCG-203971 and genetic activation of MRTF-A.

Results

Three-dimensional growth on stiff collagen matrices (> 3000 Pa) was accompanied by increased MRTF-A activity and formation of invasive protrusions in acini cultures of human mammary MCF10A cells. Differential coating and synthetic hydrogels indicated that protrusion formation was attributable to stiffness but not the biochemical constitution of the matrix. Stiffness-induced protrusion formation was also observed in preformed acini isolated from murine mammary glands. Acinar outgrowth in both the MCF10A acini and the primary organoids was partially reverted by treatment with the Rho/MRTF/SRF pathway inhibitor CCG-203971. However, genetic activation of MRTF-A in the mature primary acini also reduced protrusion formation on stiff matrices, whilst it strongly promoted luminal filling matrix-independently.

Conclusion

Our results suggest an intricate crosstalk between matrix stiffness and MRTF-A, whose activity is required for protrusion formation and sufficient for luminal filling of mammary acini.

Real-Time Fluorescence Visualization and Quantitation of Cell Growth and Death in Response to Treatment in 3D Collagen-Based Tumor Model

The use of 3D in vitro tumor models has become a common trend in cancer biology studies as well as drug screening and preclinical testing of drug candidates. The transition from 2D to 3D matrix-based cell cultures requires modification of methods for assessing tumor growth. We propose the method for assessing the growth of tumor cells in a collagen hydrogel using macro-scale registration and quantification of the gel epi-fluorescence. The technique does not require gel destruction, can be used for real-time observation of fast (in seconds) cellular responses and demonstrates high agreement with cell counting approaches or measuring total DNA content. The potency of the method was proven in experiments aimed at testing cytotoxic activity of chemotherapeutic drug (cisplatin) and recombinant targeted toxin (DARPin-LoPE) against two different tumor cell lines genetically labelled with fluorescent proteins. Moreover, using fluorescent proteins with sensor properties allows registration of dynamic changes in cells’ metabolism, which was shown for the case of sensor of caspase 3 activity.

Silk fibers assisted long-term 3D culture of human primary urinary stem cells via inhibition of senescence-associated genes: Potential use in the assessment of chronic mitochondrial toxicity

Despite being widely applied in drug development, existing in vitro 2D cell-based models are not suitable to assess chronic mitochondrial toxicity. A novel in vitro assay system mimicking in vivo microenvironment for this purpose is urgently needed. The goal of this study is to establish a 3D cell platform as a reliable, sensitive, cost-efficient, and high-throughput assay to predict drug-induced mitochondrial toxicity. We evaluated a long-term culture of human primary urine-derived stem cells (USC) seeded in 3D silk fiber matrix (3D USC-SFM) and further tested chronic mitochondrial toxicity induced by Zalcitabine (ddC, a nucleoside reverse transcriptase inhibitor) as a test drug, compared to USC grown in spheroids. The numbers of USC remain steady in 3D spheroids for 4 weeks and 3D SFM for 6 weeks. However, the majority (95%) of USC survived in 3D SFM, while cell numbers significantly declined in 3D spheroids at 6 weeks. Highly porous SFM provides large-scale numbers of cells by increasing the yield of USC 125-fold/well, which enables the carrying of sufficient cells for multiple experiments with less labor and lower cost, compared to 3D spheroids. The levels of mtDNA content and mitochondrial superoxide dismutase₂ [SOD2] as an oxidative stress biomarker and cell senescence genes (RB and P16, p21) of USC were all stably retained in 3D USC-SFM, while those were significantly increased in spheroids. mtDNA content and mitochondrial mass in both 3D culture models significantly decreased six weeks after treatment of ddC (0.2, 2, and 10 μM), compared to 0.1% DMSO control. Levels of complexes I, II, and III significantly decreased in 3D SFM-USC treated with ddC, compared to only complex I level which declined in spheroids. A dose- and time-dependent chronic MtT displayed in the 3D USC-SFM model, but not in spheroids. Thus, a long-term 3D culture model of human primary USC provides a cost-effective and sensitive approach potential for the assessment of drug-induced chronic mitochondrial toxicity.

Investigation of Host-Microbe-Parasite Interactions in an In Vitro 3D Model of the Vertebrate Gut

In vitro models of the gut-microbiome axis are in high demand. Conventionally, intestinal monolayers grown on Transwell setups are used to test the effects of commensals/pathogens on the barrier integrity, both under homeostatic and pathophysiological conditions. While such models remain valuable for deepening the understanding of host-microbe interactions, often, they lack key biological components that mediate this intricate crosstalk. Here, a 3D in vitro model of the vertebrate intestinal epithelium, interfaced with immune cells surviving in culture for over 3 weeks, is developed and applied to proof-of-concept studies of host-microbe interactions. More specifically, the establishment of stable host-microbe cocultures is described and functional and morphological changes in the intestinal barrier induced by the presence of commensal bacteria are shown. Finally, evidence is provided that the 3D vertebrate gut models can be used as platforms to test host-microbe-parasite interactions. Exposure of gut-immune-bacteria cocultures to helminth "excretory/secretory products" induces in vivo-like up-/down-regulation of certain cytokines. These findings support the robustness of the modular in vitro cell systems for investigating the dynamics of host-microbe crosstalk and pave the way toward new approaches for systems biology studies of pathogens that cannot be maintained in vitro, including parasitic helminths.

A mechanistic protrusive-based model for 3D cell migration

Cell migration is essential for a variety of biological processes, such as embryogenesis, wound healing, and the immune response. After more than a century of research-mainly on flat surfaces-, there are still many unknowns about cell motility. In particular, regarding how cells migrate within 3D matrices, which more accurately replicate in vivo conditions. We present a novel in silico model of 3D mesenchymal cell migration regulated by the chemical and mechanical profile of the surrounding environment. This in silico model considers cell's adhesive and nuclear phenotypes, the effects of the steric hindrance of the matrix, and cells ability to degradate the ECM. These factors are crucial when investigating the increasing difficulty that migrating cells find to squeeze their nuclei through dense matrices, which may act as physical barriers. Our results agree with previous in vitro observations where fibroblasts cultured in collagen-based hydrogels did not durotax toward regions with higher collagen concentrations. Instead, they exhibited an adurotactic behavior, following a more random trajectory. Overall, cell's migratory response in 3D domains depends on its phenotype, and the properties of the surrounding environment, that is, 3D cell motion is strongly dependent on the context.

Novel Brain-Stiffness-Mimicking Matrix Gel Enables Comprehensive Invasion Analysis of 3D Cultured GBM Cells

Glioblastoma (GBM) is the most common malignant primary brain tumor in adults, which is fast growing and tends to invade surrounding normal brain tissues. Uncovering the molecular and cellular mechanisms of GBM high invasion potential is of great importance for the treatment and prognostic prediction. However, the commonly used two-dimensional (2D) cell culture and analysis system suffers from lack of the heterogeneity and in vivo property of brain tissues. Here, we established a three-dimensional (3D) cell culture-based analysis system that could better recapitulate the heterogeneity of GBM and mimic the in vivo conditions in the brain. The GBM cell lines, DBTRG and U251, were cultured by hanging drop culture into the GBM multicellular spheroids, which were embedded in the optimized 3D brain-stiffness-mimicking matrix gel (0.5 mg/ml Collagen Ⅰ + 3 mg/ml Matrigel+ 3.3 mg/ml Hyaluronic Acid (HA)). The biochemical composition of the optimized matrix gel is similar to that of the brain microenvironment, and the elastic modulus is close to that of the brain tissue. The dynamics of the GBM spheroids was examined using high-content imaging for 60 h, and four metrics including invasion distance, invasion area, single-cell invasion velocity, and directionality were employed to quantify the invasion capacity. The result showed that DBTRG cells possess higher invasion capacity than U251 cells, which was consistent with the results of the classic transwell test. Transcriptome analysis of both cell lines was performed to explore the underlying molecular mechanisms. Our novel brain-stiffness-mimicking matrix gel enables comprehensive invasion analysis of the 3D cultured GBM cells and provides a model basis for in-depth exploration of the mechanisms regulating GBM invasion including the interaction between GBM cells and brain stroma.

Comparing the Secretomes of Chemorefractory and Chemoresistant Ovarian Cancer Cell Populations

High-grade serous ovarian cancer (HGSOC) constitutes the majority of all ovarian cancer cases and has staggering rates of both refractory and recurrent disease. While most patients respond to the initial treatment with paclitaxel and platinum-based drugs, up to 25% do not, and of the remaining that do, 75% experience disease recurrence within the subsequent two years. Intrinsic resistance in refractory cases is driven by environmental stressors like tumor hypoxia which alter the tumor microenvironment to promote cancer progression and resistance to anticancer drugs. Recurrent disease describes the acquisition of chemoresistance whereby cancer cells survive the initial exposure to chemotherapy and develop adaptations to enhance their chances of surviving subsequent treatments. Of the environmental stressors cancer cells endure, exposure to hypoxia has been identified as a potent trigger and priming agent for the development of chemoresistance. Both in the presence of the stress of hypoxia or the therapeutic stress of chemotherapy, cancer cells manage to cope and develop adaptations which prime populations to survive in future stress. One adaptation is the modification in the secretome. Chemoresistance is associated with translational reprogramming for increased protein synthesis, ribosome biogenesis, and vesicle trafficking. This leads to increased production of soluble proteins and extracellular vesicles (EVs) involved in autocrine and paracrine signaling processes. Numerous studies have demonstrated that these factors are largely altered between the secretomes of chemosensitive and chemoresistant patients. Such factors include cytokines, growth factors, EVs, and EV-encapsulated microRNAs (miRNAs), which serve to induce invasive molecular, biophysical, and chemoresistant phenotypes in neighboring normal and cancer cells. This review examines the modifications in the secretome of distinct chemoresistant ovarian cancer cell populations and specific secreted factors, which may serve as candidate biomarkers for aggressive and chemoresistant cancers.

Biocompatible micro tweezers for 3D hydrogel organoid array mechanical characterization

This study presents novel biocompatible Polydimethylsiloxane (PDMS)-based micromechanical tweezers (μTweezers) capable of the stiffness characterization and manipulation of hydrogel-based organoids. The system showed great potential for complementing established mechanical characterization methods such as Atomic Force Microscopy (AFM), parallel plate compression (PPC), and nanoindentation, while significantly reducing the volume of valuable hydrogels used for testing. We achieved a volume reduction of ~0.22 μl/sample using the μTweezers vs. ~157 μl/sample using the PPC, while targeting high-throughput measurement of widely adopted micro-mesoscale (a few hundred μm-1500 μm) 3D cell cultures. The μTweezers applied and measured nano-millinewton forces through cantilever' deflection with high linearity and tunability for different applications; the assembly is compatible with typical inverted optical microscopes and fit on standard tissue culture Petri dishes, allowing mechanical compression characterization of arrayed 3D hydrogel-based organoids in a high throughput manner. The average achievable output per group was 40 tests per hour, where 20 organoids and 20 reference images in one 35 mm petri dish were tested, illustrating efficient productivity to match the increasing demand on 3D organoids' applications. The changes in stiffness of collagen I hydrogel organoids in four conditions were measured, with ovarian cancer cells (SKOV3) or without (control). The Young's modulus of the control group (Control-day 0, E = 407± 146, n = 4) measured by PPC was used as a reference modulus, where the relative elastic compressive modulus of the other groups based on the stiffness measurements was also calculated (control-day 0, E = 407 Pa), (SKOV3-day 0, E = 318 Pa), (control-day 5, E = 528 Pa), and (SKOV3-day 5, E = 376 Pa). The SKOV3-embedded hydrogel-based organoids had more shrinkage and lowered moduli on day 0 and day 5 than controls, consistently, while SKOV3 embedded organoids increased in stiffness in a similar trend to the collagen I control from day 0 to day 5. The proposed method can contribute to the biomedical, biochemical, and regenerative engineering fields, where bulk mechanical characterization is of interest. The μTweezers will also provide attractive design and application concepts to soft membrane-micro 3D robotics, sensors, and actuators.

Cell-extracellular matrix dynamics

The sites of interaction between a cell and its surrounding microenvironment serve as dynamic signaling hubs that regulate cellular adaptations during developmental processes, immune functions, wound healing, cell migration, cancer invasion and metastasis, as well as in many other disease states. For most cell types, these interactions are established by integrin receptors binding directly to extracellular matrix proteins, such as the numerous collagens or fibronectin. For the cell, these points of contact provide vital cues by sampling environmental conditions, both chemical and physical. The overall regulation of this dynamic interaction involves both extracellular and intracellular components and can be highly variable. In this review, we highlight recent advances and hypotheses about the mechanisms and regulation of cell-ECM interactions, from the molecular to the tissue level, with a particular focus on cell migration. We then explore how cancer cell invasion and metastasis are deeply rooted in altered regulation of this vital interaction.

Intratumoral Heterogeneity Promotes Collective Cancer Invasion through NOTCH1 Variation

Cellular and molecular heterogeneity within tumors has long been associated with the progression of cancer to an aggressive phenotype and a poor prognosis. However, how such intratumoral heterogeneity contributes to the invasiveness of cancer is largely unknown. Here, using a tumor bioengineering approach, we investigate the interaction between molecular subtypes within bladder microtumors and the corresponding effects on their invasiveness. Our results reveal heterogeneous microtumors formed by multiple molecular subtypes possess enhanced invasiveness compared to individual cells, even when both cells are not invasive individually. To examine the molecular mechanism of intratumoral heterogeneity mediated invasiveness, live single cell biosensing, RNA interference, and CRISPR-Cas9 gene editing approaches were applied to investigate and control the composition of the microtumors. An agent-based computational model was also developed to evaluate the influence of NOTCH1 variation on DLL4 expression within a microtumor. The data indicate that intratumoral variation in NOTCH1 expression can lead to upregulation of DLL4 expression within the microtumor and enhancement of microtumor invasiveness. Overall, our results reveal a novel mechanism of heterogeneity mediated invasiveness through intratumoral variation of gene expression.

Aged Breast Extracellular Matrix Drives Mammary Epithelial Cells to an Invasive and Cancer-Like Phenotype

Age is a major risk factor for cancer. While the importance of age related genetic alterations in cells on cancer progression is well documented, the effect of aging extracellular matrix (ECM) has been overlooked. This study shows that the aging breast ECM alone is sufficient to drive normal human mammary epithelial cells (KTB21) to a more invasive and cancer-like phenotype, while promoting motility and invasiveness in MDA-MB-231 cells. Decellularized breast matrix from aged mice leads to loss of E-cadherin membrane localization in KTB21 cells, increased cell motility and invasion, and increased production of inflammatory cytokines and cancer-related proteins. The aged matrix upregulates cancer-related genes in KTB21 cells and enriches a cell subpopulation highly expressing epithelial-mesenchymal transition-related genes. Lysyl oxidase knockdown reverts the aged matrix-induced changes to the young levels; it relocalizes E-cadherin to cell membrane, and reduces cell motility, invasion, and cytokine production. These results show for the first time that the aging ECM harbors key biochemical, physical, and mechanical cues contributing to invasive and cancer-like behavior in healthy and cancer mammary cells. Differential response of cells to young and aged ECMs can lead to identification of new targets for cancer treatment and prevention.

Exploiting differential effects of actomyosin contractility to control cell sorting among breast cancer cells

In order to gain a greater understanding of the factors that drive spatial organization in multicellular aggregates of cancer cells, we investigate the segregation patterns of 6 breast cell lines of varying degree of mesenchymal character during formation of mixed aggregates. Cell sorting is considered in the context of available adhesion proteins and cellular contractility. It is found that the primary compaction mediator (cadherins or integrins) for a given cell type in isolation plays an important role in compaction speed, which in turn is the major factor dictating preference for interior or exterior position within mixed aggregates. In particular, cadherin-deficient, invasion-competent cells tend to position towards the outside of aggregates, facilitating access to extracellular matrix. Reducing actomyosin contractility is found to have a differential effect on spheroid formation depending on compaction mechanism. Inhibition of contractility has a significant stabilizing effect on cell-cell adhesions in integrin-driven aggregation and a mildly destabilizing effect in cadherin-based aggregation. This differential response is exploited to statically control aggregate organization and dynamically rearrange cells in pre-formed aggregates. Sequestration of invasive cells in the interior of spheroids provides a physical barrier that reduces invasion in three-dimensional culture, revealing a potential strategy for containment of invasive cell types.

Aligned forces: Origins and mechanisms of cancer dissemination guided by extracellular matrix architecture

Organized extracellular matrix (ECM), in the form of aligned architectures, is a critical mediator of directed cancer cell migration by contact guidance, leading to metastasis in solid tumors. Current models suggest anisotropic force generation through the engagement of key adhesion and cytoskeletal complexes drives contact-guided migration. Likewise, disrupting the balance between cell-cell and cell-ECM forces, driven by ECM engagement for cells at the tumor-stromal interface, initiates and drives local invasion. Furthermore, processes such as traction forces exerted by cancer and stromal cells, spontaneous reorientation of matrix-producing fibroblasts, and direct binding of ECM modifying proteins lead to the emergence of collagen alignment in tumors. Thus, as we obtain a deeper understanding of the origins of ECM alignment and the mechanisms by which it is maintained to direct invasion, we are poised to use the new paradigm of stroma-targeted therapies to disrupt this vital axis of disease progression in solid tumors.

Biomaterials for intestinal organoid technology and personalized disease modeling

Recent advances in intestinal organoid technologies have paved the way for in vitro recapitulation of the homeostatic renewal of adult tissues, tissue or organ morphogenesis during development, and pathogenesis of many disorders. In vitro modelling of individual patient diseases using organoid systems have been considered key in establishing rational design of personalized treatment strategies and in improving therapeutic outcomes. In addition, the transplantation of organoids into diseased tissues represents a novel approach to treat currently incurable diseases. Emerging evidence from intensive studies suggests that organoid systems' development and functional maturation depends on the presence of an extracellular matrix with suitable biophysical properties, where advanced synthetic hydrogels open new avenues for theoretical control of organoid phenotypes and potential applications of organoids in therapeutic purposes. In this review, we discuss the status, applications, challenges and perspectives of intestinal organoid systems emphasising on hydrogels and their properties suitable for intestinal organoid culture. We provide an overview of hydrogels used for intestinal organoid culture and key factors regulating their biological activity. The comparison of different hydrogels would be a theoretical basis for establishing design principles of synthetic niches directing intestinal cell fates and functions. STATEMENT OF SIGNIFICANCE: Intestinal organoid is an in vitro recapitulation of the gut, which self-organizes from intestinal stem cells and maintains many features of the native tissue. Since the development of this technology, intestinal organoid systems have made significant contribution to rapid progress in intestinal biology. Prevailing methodology for organoid culture, however, depends on animal-derived matrices and suffers from variability and potential risk for contamination of pathogens, limiting their therapeutic application. Synthetic scaffold matrices, hydrogels, might provide solutions to these issues and deepen our understanding on how intestinal cells sense and respond to key biophysical properties of the surrounding matrices. This review provides an overview of developing intestinal models and biomaterials, thereby leading to better understanding of current intestinal organoid systems for both biologists and materials scientists.

Embracing Mechanobiology in Next Generation Organ-On-A-Chip Models of Bone Metastasis

Bone metastasis in breast cancer is associated with high mortality. Biomechanical cues presented by the extracellular matrix play a vital role in driving cancer metastasis. The lack of in vitro models that recapitulate the mechanical aspects of the in vivo microenvironment hinders the development of novel targeted therapies. Organ-on-a-chip (OOAC) platforms have recently emerged as a new generation of in vitro models that can mimic cell-cell interactions, enable control over fluid flow and allow the introduction of mechanical cues. Biomaterials used within OOAC platforms can determine the physical microenvironment that cells reside in and affect their behavior, adhesion, and localization. Refining the design of OOAC platforms to recreate microenvironmental regulation of metastasis and probe cell-matrix interactions will advance our understanding of breast cancer metastasis and support the development of next-generation metastasis-on-a-chip platforms. In this mini-review, we discuss the role of mechanobiology on the behavior of breast cancer and bone-residing cells, summarize the current capabilities of OOAC platforms for modeling breast cancer metastasis to bone, and highlight design opportunities offered by the incorporation of mechanobiological cues in these platforms.

Generation of ductal organoids from normal mammary luminal cells reveals invasive potential

Here we present an experimental model for human luminal progenitor cells that enables single, primary cells isolated from normal tissue to generate complex branched structures resembling the ductal morphology of low-grade carcinoma of no special type. Thereby, we find that ductal structures are generated through invasive branching morphogenesis via matrix remodeling and identify reduced actomyosin contractility as a prerequisite for invasion. In addition, we show that knockout of E-cadherin causes a dissolution of duct formation as observed in invasive lobular carcinoma, a subtype of invasive carcinomas where E-cadherin function is frequently lost. Thus, our model shows that invasive capacity can be elicited from normal luminal cells in specific environments, which results in low-grade no special type morphology. This assay offers a platform to investigate the dynamics of luminal cell invasion and unravel the impact of genetic and non-genetic aberrations on invasive morphology. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Microenvironmental control of cell fate decisions in mammary gland development and cancer

Cell fate decisions are critical for adequate tissue development, maintenance and regeneration. In the mammary gland, epithelial cell fates are tightly controlled by the microenvironment. Here, we review how cell fate decisions are regulated by components of the microenvironment during mammary gland development and how pathological changes in the microenvironment can alter cell fates, leading to malignancy. Specifically, we describe the current understanding of how mammary cell fate is controlled and directed by three elements: the extracellular matrix, the immune microenvironment, and hormones-and how these elements can converge to create microenvironments that promote a fourth element: DNA damage.

Generation of 3D Tumor Spheroids with Encapsulating Basement Membranes for Invasion Studies

In the past, in vitro studies of invasion and tumor progression were performed primarily using cancer cells cultured on a flat, two‐dimensional (2D) surface in a monolayer. In recent years, however, many studies have demonstrated differences in cell signaling and cell migration between 2D and 3D cell cultures. Traditional 2D monolayer cancer cell invasion models do not fully recapitulate 3D cell‐to‐cell and cell−to−extracellular matrix interactions that in vivo models can provide. Moreover, although in vivo animal models are irreplaceable for studying tumor biology and metastasis, they are costly, time‐consuming, and impractical for answering preliminary questions. Thus, emergent and evolving 3D spheroid cell culture models have changed the way we study tumors and their interactions with their surrounding extracellular matrix. In the case of breast cancer, metastasis of breast cancer tumors results in high mortality rates, and thus development of robust cell culture models that are reproducible and practical for studying breast cancer progression is important for ultimately developing preventatives for cancer metastasis. This article provides a set of protocols for generating uniform spheroids with a thin sheet of basement membrane for studying the initial invasion of mammary epithelial cells into a surrounding collagen‐rich extracellular matrix. Details are provided for generating 3D spheroids with a basement membrane, polymerizing collagen I, embedding the spheroids in the 3D collagen gel, and immunostaining the spheroids for invasion studies. Published 2020. U.S. Government.

Basic Protocol 1: Growth of uniformly sized tumor spheroids with an encapsulating basement membrane

Basic Protocol 2: Polymerization and embedding of tumor spheroids in a 3D type I collagen gel

Alternate Protocol: Embedding of tumor spheroids in collagen gels using a sandwich method

Basic Protocol 3: Fixing and immunostaining of tumor spheroids embedded in 3D collagen gels

3D In Vitro Models for Investigating the Role of Stiffness in Cancer Invasion

BACKGROUND

Tumorigenesis is attributed to the interactions of cancer cells with the tumor microenvironment through both biochemical cues and physical stimuli. Increased matrix deposition and realignment of the collagen fibers are detected by cancer cells, inducing epithelial-to-mesenchymal transition, which in turn stimulates cell motility and invasiveness.

METHODS

This review provides an overview of current research on the role of the physical microenvironment in cancer invasion. This was achieved by using a systematic approach and providing meta-analyses. Particular focus was placed on in vitro three-dimensional models of epithelial cancers. We investigated questions such as the effect of matrix stiffening, activation of stromal cells, and identified potential advances in mechano-based therapies.

RESULTS

Meta-analysis revealed that 64% of studies report cancer invasion promotion as stiffness increases, while 36% report the opposite. Experimental approaches and data interpretations were varied, each affecting the invasion of cancer differently. Examples are the experimental timeframes used (24 h to 21 days), the type of polymer used (24 types), and choice of cell line (33 cell lines). The stiffness of the 3D matrices varied from 0.5 to 300 kPa and 19% of these matrices' stiffness were outside commonly accepted physiological range. 100% of the studies outside biological stiffness range (above 20 kPa) report that stiffness does not promote cancer invasion.

CONCLUSIONS

Taking this analysis into account, we inform on the type of experimental approaches that could be the most relevant and provide what would be a standardized protocol and reporting strategy.

The role of nonlinear mechanical properties of biomimetic hydrogels for organoid growth

Cell-driven plastic remodeling of the extracellular matrix (ECM) is a key regulator driving cell invasion and organoid morphogenesis in 3D. While, mostly, the linear properties are reported, the nonlinear and plastic property of the used matrix is required for these processes to occur. Here, we report on the nonlinear and plastic mechanical properties of networks derived from collagen I, Matrigel, and related hybrid gels and link their mechanical response to the underlying collagen structure. We reveal the predominantly linear behavior of Matrigel over a wide range of strains and contrast this to the highly nonlinear and plastic response of collagen upon mechanical load. We show that the mechanical nonlinear response of collagen can be gradually diminished by enriching the network stepwise with Matrigel. This tunability results from the suppression of collagen polymerization in the presence of Matrigel, resulting in a collagen network structure with significant smaller mesh size and consequent contribution to the mechanical response. Thus, the nonlinear plastic properties and structure of the ECM is not simply the addition of two independent network types but depends on the exact polymerization conditions. The understanding of this interplay is key toward an understanding of the dependencies of cellular interactions with their ECM and sheds light on the nonlinear cell-ECM interaction during organogenesis.

Associated anisotropy of intrinsic NAD(P)H for monitoring changes in the metabolic activities of breast cancer cells (4T1) in three-dimensional collagen matrix

The majority of in vitro studies of living cells are routinely conducted in a two-dimensional (2D) monolayer culture. Recent studies, however, suggest that 2D cell culture promotes specific types of aberrant cell behaviors due to the growth on non-physiologically stiff surfaces and the lack of the tissue-based extracellular matrix. Here, we investigate the sensitivity of the two-photon (2P) rotational dynamics of the intrinsic reduced nicotinamide adenine dinucleotide (phosphate), NAD(P)H, to changes in the metabolic state of the metastatic murine breast cancer cells (4T1) in 2D monolayer and three-dimensional (3D) collagen matrix cultures. Time-resolved 2P-associated anisotropy measurements reveal that the rotational dynamics of free and enzyme-bound NAD(P)H in 4T1 cells are correlated to changes in the metabolic state of 2D and 3D cell cultures. In addition to the type of cell culture, we also investigated the metabolic response of 4T1 cells to treatment with two metabolic inhibitors (MD1 and TPPBr). The statistical analyses of our results enabled us to identify which of the fitting parameters of the observed time-resolved associate anisotropy of cellular NAD(P)H were significantly sensitive to changes in the metabolic state of 4T1 cells. Using a black-box model, the population fractions of free and bound NAD(P)H were used to estimate the corresponding equilibrium constant and the standard Gibbs free energy changes that are associated with underlying metabolic pathways of 4T1 cells in 2D and 3D cultures. These rotational dynamics analyses are in agreement with the standard 2P-fluorescence lifetime imaging microscopy (FLIM) measurements on the same cell line, cell cultures, and metabolic inhibition. These studies represent an important step towards the development of a noninvasive, time-resolved associated anisotropy to complement 2P-FLIM in order to elucidate the underlying cellular metabolism and metabolic plasticity in more complex in vivo, tumor-like models using intrinsic NADH autofluorescence.

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.

The epithelial-mesenchymal transition and the cytoskeleton in bioengineered systems

The epithelial-mesenchymal transition (EMT) is intrinsically linked to alterations of the intracellular cytoskeleton and the extracellular matrix. After EMT, cells acquire an elongated morphology with front/back polarity, which can be attributed to actin-driven protrusion formation as well as the gain of vimentin expression. Consequently, cells can deform and remodel the surrounding matrix in order to facilitate local invasion. In this review, we highlight recent bioengineering approaches to elucidate EMT and functional changes in the cytoskeleton. First, we review transitions between multicellular clusters and dispersed individuals on planar surfaces, which often exhibit coordinated behaviors driven by leader cells and EMT. Second, we consider the functional role of vimentin, which can be probed at subcellular length scales and within confined spaces. Third, we discuss the role of topographical patterning and EMT via a contact guidance like mechanism. Finally, we address how multicellular clusters disorganize and disseminate in 3D matrix. These new technologies enable controlled physical microenvironments and higher-resolution spatiotemporal measurements of EMT at the single cell level. In closing, we consider future directions for the field and outstanding questions regarding EMT and the cytoskeleton for human cancer progression. Video Abstract.

Dynamic light scattering microrheology for soft and living materials

We present a method for using dynamic light scattering in the single-scattering limit to measure the viscoelastic moduli of soft materials. This microrheology technique only requires a small sample volume of 12 μL to measure up to six decades in time of rheological behavior. We demonstrate the use of dynamic light scattering microrheology (DLSμR) on a variety of soft materials, including dilute polymer solutions, covalently-crosslinked polymer gels, and active, biological fluids. In this work, we detail the procedure for applying the technique to new materials and discuss the critical considerations for implementing the technique, including a custom analysis script for analyzing data output. We focus on the advantages of applying DLSμR to biologically relevant materials: breast cancer cells encapsulated in a collagen gel and cystic fibrosis sputum. DLSμR is an easy, efficient, and economical rheological technique that can guide the design of new polymeric materials and facilitate the understanding of the underlying physics governing behavior of naturally derived materials.

Collagen I triggers directional migration, invasion and matrix remodeling of stroma cells in a 3D spheroid model of endometriosis

Endometriosis is a painful gynecological condition characterized by ectopic growth of endometrial cells. Little is known about its pathogenesis, which is partially due to a lack of suitable experimental models. Here, we use endometrial stromal (St-T1b), primary endometriotic stromal, epithelial endometriotic (12Z) and co-culture (1:1 St-T1b:12Z) spheroids to mimic the architecture of endometrium, and either collagen I or Matrigel to model ectopic locations. Stromal spheroids, but not single cells, assumed coordinated directional migration followed by matrix remodeling of collagen I on day 5 or 7, resembling ectopic lesions. While generally a higher area fold increase of spheroids occurred on collagen I compared to Matrigel, directional migration was not observed in co-culture or in 12Z cells. The fold increase in area on collagen I was significantly reduced by MMP inhibition in stromal but not 12Z cells. Inhibiting ROCK signalling responsible for actomyosin contraction increased the fold increase of area and metabolic activity compared to untreated controls on Matrigel. The number of protrusions emanating from 12Z spheroids on Matrigel was decreased by microRNA miR-200b and increased by miR-145. This study demonstrates that spheroid assay is a promising pre-clinical tool that can be used to evaluate small molecule drugs and microRNA-based therapeutics for endometriosis.

The Role of Microenvironmental Cues and Mechanical Loading Milieus in Breast Cancer Cell Progression and Metastasis

Cancer can disrupt the microenvironments and mechanical homeostatic actions in multiple scales from large tissue modification to altered cellular signaling pathway in mechanotransduction. In this review, we highlight recent progresses in breast cancer cell mechanobiology focusing on cell-microenvironment interaction and mechanical loading regulation of cells. First, the effects of microenvironmental cues on breast cancer cell progression and metastasis will be reviewed with respect to substrate stiffness, chemical/topographic substrate patterning, and 2D vs. 3D cultures. Then, the role of mechanical loading situations such as tensile stretch, compression, and flow-induced shear will be discussed in relation to breast cancer cell mechanobiology and metastasis prevention. Ultimately, the substrate microenvironment and mechanical signal will work together to control cancer cell progression and metastasis. The discussions on breast cancer cell responsiveness to mechanical signals, from static substrate and dynamic loading, and the mechanotransduction pathways involved will facilitate interdisciplinary knowledge transfer, enabling further insights into prognostic markers, mechanically mediated metastasis pathways for therapeutic targets, and model systems required to advance cancer mechanobiology.

Microrheology reveals simultaneous cell-mediated matrix stiffening and fluidization that underlie breast cancer invasion

Living tissues embody a unique class of hybrid materials in which active and thermal forces are inextricably linked. Mechanical characterization of tissues demands descriptors that respect this hybrid nature. In this work, we develop a microrheology-based force spectrum analysis (FSA) technique to dissect the active and passive fluctuations of the extracellular matrix (ECM) in three-dimensional (3D) cell culture models. In two different stromal models and a 3D breast cancer spheroid model, our FSA reveals emergent hybrid dynamics that involve both high-frequency stress stiffening and low-frequency fluidization of the ECM. We show that this is a general consequence of nonlinear coupling between active forces and the frequency-dependent viscoelasticity of stress-stiffening networks. In 3D breast cancer spheroids, this dual active stiffening and fluidization is tightly connected with invasion. Our results suggest a mechanism whereby breast cancer cells reconcile the seemingly contradictory requirements for both tension and malleability in the ECM during invasion.