Engineering three-dimensional collagen matrices to provide contact guidance during 3D cell migration

A survey of physical methods for studying nuclear mechanics and mechanobiology

It is increasingly appreciated that the cell nucleus is not only a home for DNA but also a complex material that resists physical deformations and dynamically responds to external mechanical cues. The molecules that confer mechanical properties to nuclei certainly contribute to laminopathies and possibly contribute to cellular mechanotransduction and physical processes in cancer such as metastasis. Studying nuclear mechanics and the downstream biochemical consequences or their modulation requires a suite of complex assays for applying, measuring, and visualizing mechanical forces across diverse length, time, and force scales. Here, we review the current methods in nuclear mechanics and mechanobiology, placing specific emphasis on each of their unique advantages and limitations. Furthermore, we explore important considerations in selecting a new methodology as are demonstrated by recent examples from the literature. We conclude by providing an outlook on the development of new methods and the judicious use of the current techniques for continued exploration into the role of nuclear mechanobiology.

The Role of Rho GTPases During Fibroblast Spreading, Migration, and Myofibroblast Differentiation in 3D Synthetic Fibrous Matrices

INTRODUCTION

Connective tissue repair and mechanosensing are tightly entwined in vivo and occur within a complex three-dimensional (3D), fibrous extracellular matrix (ECM). Typically driven by activated fibroblasts, wound repair involves well-defined steps of cell spreading, migration, proliferation, and fibrous ECM deposition. While the role of Rho GTPases in regulating these processes has been explored extensively in two-dimensional cell culture models, much less is known about their role in more physiologic, 3D environments.

METHODS

We employed a 3D, fibrous and protease-sensitive hydrogel model of interstitial ECM to study the interplay between Rho GTPases and fibrous matrix cues in fibroblasts during wound healing.

RESULTS

Modulating fiber density within protease-sensitive hydrogels, we confirmed previous findings that heightened fiber density promotes fibroblast spreading and proliferation. The presence of matrix fibers furthermore corresponded to increased cell migration speeds and macroscopic hydrogel contraction arising from fibroblast generated forces. During fibroblast spreading, Rac1 and RhoA GTPase activity proved crucial for fiber-mediated cell spreading and contact guidance along matrix fibers, while Cdc42 was dispensable. In contrast, interplay between RhoA, Rac1, and Cdc42 contributed to fiber-mediated myofibroblast differentiation and matrix contraction over longer time scales.

CONCLUSION

These observations may provide insights into tissue repair processes in vivo and motivate the incorporation of cell-adhesive fibers within synthetic hydrogels for material-guided wound repair strategies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12195-021-00698-5.

Distinct roles of nonmuscle myosin II isoforms for establishing tension and elasticity during cell morphodynamics

Nonmuscle myosin II (NM II) is an integral part of essential cellular processes, including adhesion and migration. Mammalian cells express up to three isoforms termed NM IIA, B, and C. We used U2OS cells to create CRISPR/Cas9-based knockouts of all three isoforms and analyzed the phenotypes on homogenously coated surfaces, in collagen gels, and on micropatterned substrates. In contrast to homogenously coated surfaces, a structured environment supports a cellular phenotype with invaginated actin arcs even in the absence of NM IIA-induced contractility. A quantitative shape analysis of cells on micropatterns combined with a scale-bridging mathematical model reveals that NM IIA is essential to build up cellular tension during initial stages of force generation, while NM IIB is necessary to elastically stabilize NM IIA-generated tension. A dynamic cell stretch/release experiment in a three-dimensional scaffold confirms these conclusions and in addition reveals a novel role for NM IIC, namely the ability to establish tensional homeostasis.

Cell contact guidance via sensing anisotropy of network mechanical resistance

Despite the ubiquitous importance of cell contact guidance, the signal-inducing contact guidance of mammalian cells in an aligned fibril network has defied elucidation. This is due to multiple interdependent signals that an aligned fibril network presents to cells, including, at least, anisotropy of adhesion, porosity, and mechanical resistance. By forming aligned fibrin gels with the same alignment strength, but cross-linked to different extents, the anisotropic mechanical resistance hypothesis of contact guidance was tested for human dermal fibroblasts. The cross-linking was shown to increase the mechanical resistance anisotropy, without detectable change in network microstructure and without change in cell adhesion to the cross-linked fibrin gel. This methodology thus isolated anisotropic mechanical resistance as a variable for fixed anisotropy of adhesion and porosity. The mechanical resistance anisotropy |Y*| ^-1 - |X*| ^-1 increased over fourfold in terms of the Fourier magnitudes of microbead displacement |X*| and |Y*| at the drive frequency with respect to alignment direction Y obtained by optical forces in active microrheology. Cells were found to exhibit stronger contact guidance in the cross-linked gels possessing greater mechanical resistance anisotropy: the cell anisotropy index based on the tensor of cell orientation, which has a range 0 to 1, increased by 18% with the fourfold increase in mechanical resistance anisotropy. We also show that modulation of adhesion via function-blocking antibodies can modulate the guidance response, suggesting a concomitant role of cell adhesion. These results indicate that fibroblasts can exhibit contact guidance in aligned fibril networks by sensing anisotropy of network mechanical resistance.

Engineering fiber anisotropy within natural collagen hydrogels

It is well known that biophysical properties of the extracellular matrix (ECM), including stiffness, porosity, composition, and fiber alignment (anisotropy), play a crucial role in controlling cell behavior in vivo. Type I collagen (collagen I) is a ubiquitous structural component in the ECM and has become a popular hydrogel material that can be tuned to replicate the mechanical properties found in vivo. In this review article, we describe popular methods to create 2-D and 3-D collagen I hydrogels with anisotropic fiber architectures. We focus on methods that can be readily translated from engineering and materials science laboratories to the life-science community with the overall goal of helping to increase the physiological relevance of cell culture assays.

Collagen-based biomaterials for biomedical applications

Collagen is an insoluble fibrous protein that composes the extracellular matrix in animals. Although collagen has been used as a biomaterial since 1881, the properties and the complex structure of collagen are still extensive study subjects worldwide. In this article, several topics of importance for understanding collagen research are reviewed starting from its historical milestones, followed by the description of the collagen superfamily and its complex structures, with a focus on type I collagen. Subsequently, some of the superior properties of collagen-based biomaterials, such as biocompatibility, biodegradability, mechanical properties, and cell activities, are pinpointed. These properties make collagen applicable in biomedicine, such as wound healing, tissue engineering, surface coating of medical devices, and skin supplementation. Moreover, some antimicrobial strategies and the general host tissue responses regarding collagen as a biomaterial are presented. Finally, the current status and clinical application of the three-dimensional (3D) printing techniques for the fabrication of collagen-based scaffolds and the reconstruction of the human heart's constituents, such as capillary structures or even the entire organ, are discussed. Besides, an overall outlook for the future of this unique biomaterial is provided.

Microengineered 3D Collagen Gels with Independently Tunable Fiber Anisotropy and Directionality

Cellular processes, including differentiation, proliferation, and migration, have been linked to the alignment (anisotropy) and orientation (directionality) of collagen fibers in the native extracellular matrix (ECM). Given the critical role that biophysical cell-matrix interactions play in regulating biological functions, several microfluidic-based methods have been used to establish 3D collagen gels with defined fiber properties; these gels have helped to establish quantitative relationships between structural ECM cues and observed cell responses. Although existing microfluidic fabrication methods provide excellent definition over collagen fiber anisotropy, they have not demonstrated the independent control over fiber anisotropy and directionality necessary to replicate in vivo collagen architecture. Therefore, to advance collagen microengineering capabilities, we present a user-friendly technology platform that uses controlled fluid flows within a non-uniform microfluidic channel network to create collagen landscapes that can be tuned as a function of extensional strain rate. Herein, we demonstrate capabilities to i) control the degree of fiber anisotropy, ii) create spatial gradients in fiber anisotropy, iii) independently define fiber directionality, and iv) generate multi-material interfaces within a 3D environment. We then address the practical issue of integrating cells into microfluidic systems by using a peel-off template technique to provide direct access to microengineered collagen gels, and demonstrate that cells respond to the defined properties of the landscape. Finally, the platform's modular capability is highlighted by integrating a sub-micrometer thick porous parylene membrane onto the microengineered collagen as a method to define cell-substrate interactions.

Second Harmonic Generation Imaging of Collagen in Chronically Implantable Electrodes in Brain Tissue

Advances in neural engineering have brought about a number of implantable devices for improved brain stimulation and recording. Unfortunately, many of these micro-implants have not been adopted due to issues of signal loss, deterioration, and host response to the device. While glial scar characterization is critical to better understand the mechanisms that affect device functionality or tissue viability, analysis is frequently hindered by immunohistochemical tissue processing methods that result in device shattering and tissue tearing artifacts. Devices are commonly removed prior to sectioning, which can itself disturb the quality of the study. In this methods implementation study, we use the label free, optical sectioning method of second harmonic generation (SHG) to examine brain slices of various implanted intracortical electrodes and demonstrate collagen fiber distribution not found in normal brain tissue. SHG can easily be used in conjunction with multiphoton microscopy to allow direct intrinsic visualization of collagen-containing glial scars on the surface of cortically implanted electrode probes without imposing the physical strain of tissue sectioning methods required for other high resolution light microscopy modalities. Identification and future measurements of these collagen fibers may be useful in predicting host immune response and device signal fidelity.

Analysis of fibroblast migration dynamics in idiopathic pulmonary fibrosis using image-based scaffolds of the lung extracellular matrix

Idiopathic pulmonary fibrosis (IPF) is characterized by a profound remodeling of the collagen in the extracellular matrix (ECM), where the fibers become both denser and more highly aligned. However, it is unknown how this reconfiguration of the collagen matrix affects disease progression. Here, we investigate the role of specific alterations in collagen fiber organization on cell migration dynamics by using biomimetic image-based collagen scaffolds representing normal and fibrotic lung, where the designs are derived directly from high-resolution second harmonic generation microscopy images. The scaffolds are fabricated by multiphoton-excited (MPE) polymerization, where the process is akin to three-dimensional printing, except that it is performed at much greater resolution (∼0.5 microns) and with collagen and collagen analogs. These scaffolds were seeded with early passaged primary human normal and IPF fibroblasts to enable the decoupling of the effect of cell-intrinsic characteristics (normal vs. IPF) versus ECM structure (normal vs. IPF) on migration dynamics. We found that the highly aligned IPF collagen structure promoted enhanced cell elongation and F-actin alignment along with increased cell migration speed and straightness relative to the normal tissues. Collectively, the data are consistent with an enhanced contact guidance mechanism on the aligned IPF matrix. Although cell intrinsic effects were observed, the aligned collagen matrix morphology had a larger effect on these metrics. Importantly, these biomimetic models of the lung cannot be synthesized by conventional fabrication methods. We suggest that the MPE image-based fabrication method will enable additional hypothesis-based testing studies of cell-matrix interactions in the context of tissue fibrosis.

Towards control of cellular decision-making networks in the epithelial-to-mesenchymal transition

We present the epithelial-to-mesenchymal transition (EMT) from two perspectives: experimental/technological and theoretical. We review the state of the current understanding of the regulatory networks that underlie EMT in three physiological contexts: embryonic development, wound healing, and metastasis. We describe the existing experimental systems and manipulations used to better understand the molecular participants and factors that influence EMT and metastasis. We review the mathematical models of the regulatory networks involved in EMT, with a particular emphasis on the network motifs (such as coupled feedback loops) that can generate intermediate hybrid states between the epithelial and mesenchymal states. Ultimately, the understanding gained about these networks should be translated into methods to control phenotypic outcomes, especially in the context of cancer therapeutic strategies. We present emerging theories of how to drive the dynamics of a network toward a desired dynamical attractor (e.g. an epithelial cell state) and emerging synthetic biology technologies to monitor and control the state of cells.

Probing cellular response to topography in three dimensions

Biophysical aspects of in vivo tissue microenvironments include microscale mechanical properties, fibrillar alignment, and architecture or topography of the extracellular matrix (ECM). These aspects act in concert with chemical signals from a myriad of diverse ECM proteins to provide cues that drive cellular responses. Here, we used a bottom-up approach to build fibrillar architecture into 3D amorphous hydrogels using magnetic-field driven assembly of paramagnetic colloidal particles functionalized with three types of human ECM proteins found in vivo. We investigated if cells cultured in matrices comprised of fibrils of the same size and arranged in similar geometries will show similar behavior for each of the ECM proteins tested. We were able to resolve spatial heterogeneities in microscale mechanical properties near aligned fibers that were not observed in bulk tissue mechanics. We then used this platform to examine factors contributing to cell alignment in response to topographical cues in 3D laminin-rich matrices. Multiple human cell lines extended protrusions preferentially in directions parallel or perpendicular to aligned fibers independently of the ECM coating. Focal adhesion proteins, as measured by paxillin localization, were mainly diffuse in the cytoplasm, with few puncta localized at the protrusions. Integrin β1 and fascin regulated protrusion extension but not protrusion alignment. Myosin II inhibition did not reduce observed protrusion length. Instead, cells with reduced myosin II activity generated protrusions in random orientations when cultured in hydrogels with aligned fibers. Similarly, myosin II dependence was observed in vivo, where cells no longer aligned along the abluminal surfaces of blood vessels upon treatment with blebbistatin. These data suggest that myosin II can regulate sensing of topography in 3D engineered matrices for both normal and transformed cells.

Macromolecular crowding tunes 3D collagen architecture and cell morphogenesis

Collagen I is the primary extracellular matrix component of most solid tumors and influences metastatic progression. Collagen matrix engineering techniques are useful for understanding how this complex biomaterial regulates cancer cell behavior and for improving in vitro cancer models. Here, we establish an approach to tune collagen fibril architecture using PEG as an inert molecular crowding agent during gelation and cell embedding. We find that crowding produces matrices with tighter fibril networks that are less susceptible to proteinase mediated degradation, but does not significantly alter matrix stiffness. The resulting matrices have the effect of preventing cell spreading, confining cells, and reducing cell contractility. Matrix degradability and fibril length are identified as strong predictors of cell confinement. Further, the degree of confinement predicts whether breast cancer cells will ultimately undergo individual or collective behaviors. Highly confined breast cancer cells undergo morphogenesis to form either invasive networks reminiscent of aggressive tumors or gland and lobule structures reminiscent of normal breast epithelia. This morphological transition is accompanied by expression of cell-cell adhesion genes, including PECAM1 and ICAM1. Our study suggests that cell confinement, mediated by matrix architecture, is a design feature that tunes the transcriptional and morphogenic state of breast cancer cells.

Perspective: Aligned arrays of electrospun nanofibers for directing cell migration

Cell migration plays an important role in a wide variety of biological processes, including embryogenesis, wound healing, inflammation, cancer metastasis, and tissue repair. Electrospun nanofibers have been extensively explored as scaffolds to manipulate cell migration owing to their unique characteristics in mimicking the hierarchical architecture of extracellular matrix. In particular, aligned arrays of electrospun nanofibers are capable of guiding and promoting the directional migration of cells. The physical parameters and properties of the aligned nanofibers, including their size, modulus, and surface chemistry, can all affect the migratory behaviors of cells, while the controlled release of growth factors and drugs from the nanofibers can also be utilized to influence cell migration. By manipulating cell migration, electrospun nanofibers have been applied to promote tissue repair and help eradicate tumors in vivo. In this perspective, we highlight recent developments in collecting electrospun nanofibers as aligned arrays and then illustrate how the aligned nanofibers can be utilized to manipulate cell migration.

Double-exclusive liquid repellency (double-ELR): an enabling technology for rare phenotype analysis

Double-exclusive liquid repellency (double-ELR) is an extreme wettability phenomenon in which adjacent regions selectively and completely repel immiscible liquids with different surface chemistries on a non-textured substrate (i.e., a substrate in absence of micro/nano-structures). Under double-ELR conditions, each liquid exhibits no physical contact (contact angle of 180°) with its non-preferred surface chemistry, thus enabling complete partitioning of adjacent fluidic volumes (e.g., between water and oil). This enables a new type of cell culture-based assay, where cell loss from common failure modes (e.g., biofouling from inadvertent cell adhesion, detrimental moisture loss/gain, and liquid handling dead volumes) is significantly mitigated. Importantly, the principles of double-ELR were leveraged to achieve underoil sweep patterning, a no-loss, robust and high-throughput distribution of sub-microliter volumes of aqueous media (and cells). In addition to high-efficiency distribution via sweep patterning, double-ELR can be used to construct "modular" (i.e., easily implemented and/or linked together with spatial and temporal control) higher-order architectures for in vitro imitation of physiologically relevant microenvironments that are of particular interest within the cell assay community, including multi-phenotype cultures with excellent spatial and temporal control, three-dimensional layered multi-phenotype cultures, cultures with selective mechanical cues of extracellular matrix (i.e., collagen fiber alignment), and spheroid cultures. Together, these features of double-ELR uniquely facilitate culture and high content analysis of limited cellular samples (e.g., a few hundred to a few thousand cells).

Decoupling the effects of stiffness and fiber density on cellular behaviors via an interpenetrating network of gelatin-methacrylate and collagen

The extracellular microenvironment provides critical cues that guide tissue development, homeostasis, and pathology. Deciphering the individual roles of these cues in tissue function necessitates the development of physically tunable culture platforms, but current approaches to create such materials have produced scaffolds that either exhibit a limited mechanical range or are unable to recapitulate the fibrous nature of in vivo tissues. Here we report a novel interpenetrating network (IPN) of gelatin-methacrylate (gelMA) and collagen I that enables independent tuning of fiber density and scaffold stiffness across a physiologically-relevant range of shear moduli (2-12 kPa), while maintaining constant extracellular matrix content. This biomaterial system was applied to examine how changes in the physical microenvironment affect cell types associated with the tumor microenvironment. By increasing fiber density while maintaining constant stiffness, we found that MDA-MB-231 breast tumor cells required the presence of fibers to invade the surrounding matrix, while endothelial cells (ECs) did not. Meanwhile, increasing IPN stiffness independently of fiber content yielded decreased invasion and sprouting for both MDA-MB-231 cells and ECs. These results highlight the importance of decoupling features of the microenvironment to uncover their individual effects on cell behavior, in addition to demonstrating that individual cell types within a tissue may be differentially affected by the same changes in physical features. The mechanical range and fibrous nature of this tunable biomaterial platform enable mimicry of a wide variety of tissues, and may yield more precise identification of targets which may be exploited to develop interventions to control tissue function.

The size-speed-force relationship governs migratory cell response to tumorigenic factors

Normal and transformed motile cells follow a common trend in which size and contractile forces are negatively correlated with cell speed. However, tumorigenic factors amplify the preexisting population heterogeneity and lead some cells to exhibit biomechanical properties that are more extreme than those observed with normal cells.

Tumor development progresses through a complex path of biomechanical changes leading first to cell growth and contraction and then cell deadhesion, scattering, and invasion. Tumorigenic factors may act specifically on one of these steps or have a wider spectrum of actions, leading to a variety of effects and thus sometimes to apparent contradictory outcomes. Here we used micropatterned lines of collagen type I/fibronectin on deformable surfaces to standardize cell behavior and measure simultaneously cell size, speed of motion and magnitude of the associated traction forces at the level of a single cell. We analyzed and compared the normal human breast cell line MCF10A in control conditions and in response to various tumorigenic factors. In all conditions, a wide range of biomechanical properties was identified. Despite this heterogeneity, normal and transformed motile cells followed a common trend whereby size and contractile forces were negatively correlated with cell speed. Some tumorigenic factors, such as activation of ErbB2 or loss of the βsubunit of casein kinase 2, shifted the whole population toward a faster speed and lower contractility state. Treatment with transforming growth factor β induced some cells to adopt opposing behaviors such as extremely high versus extremely low contractility. Thus tumor transformation amplified preexisting population heterogeneity and led some cells to exhibit biomechanical properties that were more extreme than those observed with normal cells.

Loss of miR-203 regulates cell shape and matrix adhesion through ROBO1/Rac/FAK in response to stiffness

Breast tumor progression is accompanied by changes in the surrounding extracellular matrix (ECM) that increase stiffness of the microenvironment. Mammary epithelial cells engage regulatory pathways that permit dynamic responses to mechanical cues from the ECM. Here, we identify a SLIT2/ROBO1 signaling circuit as a key regulatory mechanism by which cells sense and respond to ECM stiffness to preserve tensional homeostasis. We observed that Robo1 ablation in the developing mammary gland compromised actin stress fiber assembly and inhibited cell contractility to perturb tissue morphogenesis, whereas SLIT2 treatment stimulated Rac and increased focal adhesion kinase activity to enhance cell tension by maintaining cell shape and matrix adhesion. Further investigation revealed that a stiff ECM increased Robo1 levels by down-regulating miR-203. Consistently, patients whose tumor expressed a low miR-203/high Robo1 expression pattern exhibited a better overall survival prognosis. These studies show that cells subjected to stiffened environments up-regulate Robo1 as a protective mechanism that maintains cell shape and facilitates ECM adherence.

Concentric gel system to study the biophysical role of matrix microenvironment on 3D cell migration

The ability of cells to migrate is crucial in a wide variety of cell functions throughout life from embryonic development and wound healing to tumor and cancer metastasis. Despite intense research efforts, the basic biochemical and biophysical principles of cell migration are still not fully understood, especially in the physiologically relevant three-dimensional (3D) microenvironments. Here, we describe an in vitro assay designed to allow quantitative examination of 3D cell migration behaviors. The method exploits the cell's mechanosensing ability and propensity to migrate into previously unoccupied extracellular matrix (ECM). We use the invasion of highly invasive breast cancer cells, MDA-MB-231, in collagen gels as a model system. The spread of cell population and the migration dynamics of individual cells over weeks of culture can be monitored using live-cell imaging and analyzed to extract spatiotemporally-resolved data. Furthermore, the method is easily adaptable for diverse extracellular matrices, thus offering a simple yet powerful way to investigate the role of biophysical factors in the microenvironment on cell migration.

Modeling contact guidance and invasion by cancer cells

The first step in the spread of cancer is invasion by malignant cells of the normal tissue surrounding a tumor. There is considerable evidence both in vitro and in vivo that mechanical interactions with the tissue, in particular with the biopolymer network that makes up the extracellular matrix (ECM), are important factors in invasion. The interactions take two forms: (i) contractile cells on the surface of the tumor act on the nearby ECM and remodel it; in some cases, they align the fibers of the biopolymers; (ii) the aligned fibers can enhance invasion via contact guidance, the tendency of motile cells to follow alignment. Here, we give evidence, mainly for in vitro systems, that both effects are important. We discuss how alignment occurs in biopolymers such as collagen-I (a major component of the ECM). We propose a modeling framework for computing alignment and propose phenomenologic models for contact guidance. See all articles in this Cancer Research section, "Physics in Cancer Research."

3D culture assays of murine mammary branching morphogenesis and epithelial invasion

Epithelia are fundamental tissues that line cavities, glands, and outer body surfaces. We use three-dimensional (3D) embedded culture of primary murine mammary epithelial ducts, called "organoids," to recapitulate in days in culture epithelial programs that occur over weeks deep within the body. Modulating the composition of the extracellular matrix (ECM) allows us to model cell- and tissue-level behaviors observed in normal development, such as branching morphogenesis, and in cancer, such as invasion and dissemination. Here, we describe a collection of protocols for 3D culture of mammary organoids in different ECMs and for immunofluorescence staining of 3D culture samples and mammary gland tissue sections. We illustrate expected phenotypic outcomes of each assay and provide troubleshooting tips for commonly encountered technical problems.

A 3D tension bioreactor platform to study the interplay between ECM stiffness and tumor phenotype

Extracellular matrix (ECM) structure, composition, and stiffness have profound effects on tissue development and pathologies such as cardiovascular disease and cancer. Accordingly, a variety of synthetic hydrogel systems have been designed to study the impact of ECM composition, density, mechanics, and topography on cell and tissue phenotype. However, these synthetic systems fail to accurately recapitulate the biological properties and structure of the native tissue ECM. Natural three dimensional (3D) ECM hydrogels, such as collagen or hyaluronic acid, feature many of the chemical and physical properties of tissue, yet, these systems have limitations including the inability to independently control biophysical properties such as stiffness and pore size. Here, we present a 3D tension bioreactor system that permits precise mechanical tuning of collagen hydrogel stiffness, while maintaining consistent composition and pore size. We achieve this by mechanically loading collagen hydrogels covalently-conjugated to a polydimethylsiloxane (PDMS) membrane to induce hydrogel stiffening. We validated the biological application of this system with oncogenically transformed mammary epithelial cell organoids embedded in a 3D collagen I hydrogel, either uniformly stiffened or calibrated to create a gradient of ECM stiffening, to visually demonstrate the impact of ECM stiffening on transformation and tumor cell invasion. As such, this bioreactor presents the first tunable 3D natural hydrogel system that is capable of independently assessing the role of ECM stiffness on tissue phenotype.

Preferential, enhanced breast cancer cell migration on biomimetic electrospun nanofiber 'cell highways'

BACKGROUND

Aggressive metastatic breast cancer cells seemingly evade surgical resection and current therapies, leading to colonization in distant organs and tissues and poor patient prognosis. Therefore, high-throughput in vitro tools allowing rapid, accurate, and novel anti-metastatic drug screening are grossly overdue. Conversely, aligned nanofiber constitutes a prominent component of the late-stage breast tumor margin extracellular matrix. This parallel suggests that the use of a synthetic ECM in the form of a nanoscale model could provide a convenient means of testing the migration potentials of cancer cells to achieve a long-term goal of providing clinicians an in vitro platform technology to test the efficacy of novel experimental anti-metastatic compounds.

METHODS

Electrospinning produces highly aligned, cell-adhesive nanofiber matrices by applying a strong electric field to a polymer-containing solution. The resulting fibrous microstructure and morphology closely resembles in vivo tumor microenvironments suggesting their use in analysis of migratory potentials of metastatic cancer cells. Additionally, a novel interface with a gel-based delivery system creates CXCL12 chemotactic gradients to enhance CXCR4-expressing cell migration.

RESULTS

Cellular dispersions of MCF-10A normal mammary epithelial cells or human breast cancer cells (MCF-7 and MDA-MB-231) seeded on randomly-oriented nanofiber exhibited no significant differences in total or net distance traveled as a result of the underlying topography. Cells traveled ~2-5 fold greater distances on aligned fiber. Highly-sensitive MDA-MB-231 cells displayed an 82% increase in net distance traversed in the presence of a CXCL12 gradient. In contrast, MCF-7 cells exhibited only 31% increase and MCF-10A cells showed no statistical difference versus control or vehicle conditions. MCF-10A cells displayed little sensitivity to CXCL12 gradients, while MCF-7 cells displayed early sensitivity when CXCL12 concentrations were higher. MDA-MB-231 cells displayed low relative expression levels of CXCR4, but high sensitivity resulting in 55-fold increase at late time points due to CXCL12 gradient dissipation.

CONCLUSIONS

This model could create clinical impact as an in vitro diagnostic tool for rapid assessment of tumor needle biopsies to confirm metastatic tumors, their invasiveness, and allow high-throughput drug screening providing rapid development of personalized therapies.

Chemotaxis in cancer

Chemotaxis of tumour cells and stromal cells in the surrounding microenvironment is an essential component of tumour dissemination during progression and metastasis. This Review summarizes how chemotaxis directs the different behaviours of tumour cells and stromal cells in vivo, how molecular pathways regulate chemotaxis in tumour cells and how chemotaxis choreographs cell behaviour to shape the tumour microenvironment and to determine metastatic spread. The central importance of chemotaxis in cancer progression is highlighted by discussion of the use of chemotaxis as a prognostic marker, a treatment end point and a target of therapeutic intervention.

A 3D model of ovarian cancer cell lines on peptide nanofiber scaffold to explore the cell-scaffold interaction and chemotherapeutic resistance of anticancer drugs

RADA16-I peptide hydrogel, a type of nanofiber scaffold derived from self-assembling peptide RADA16-I, has been extensively applied to regenerative medicine and tissue repair in order to develop novel nanomedicine systems. In this study, using RADA16-I peptide hydrogel, a three-dimensional (3D) cell culture model was fabricated for in vitro culture of three ovarian cancer cell lines. Firstly, the peptide nanofiber scaffold was evaluated by transmission electron microscopy and atom force microscopy. Using phase contrast microscopy, the appearance of the representative ovarian cancer cells encapsulated in RADA16-I peptide hydrogel on days 1, 3, and 7 in 24-well Petri dishes was illustrated. The cancer cell-nanofiber scaffold construct was cultured for 5 days, and the ovarian cancer cells had actively proliferative potential. The precultured ovarian cancer cells exhibited nearly similar adhesion properties and invasion potentials in vitro between RADA16-I peptide nanofiber and type I collagen, which suggested that RADA16-I peptide hydrogel had some similar characteristics to type I collagen. The precultured ovarian cancer cells had two-fold to five-fold higher anticancer drug resistance than the conventional two-dimensional Petri dish culture. So the 3D cell model on peptide nanofiber scaffold is an optimal type of cell pattern for anticancer drug screening and tumor biology.