Microfabricated mimics of in vivo structural cues for the study of guided tumor cell migration

Advancement in Cancer Vasculogenesis Modeling through 3D Bioprinting Technology

Cancer vasculogenesis is a pivotal focus of cancer research and treatment given its critical role in tumor development, metastasis, and the formation of vasculogenic microenvironments. Traditional approaches to investigating cancer vasculogenesis face significant challenges in accurately modeling intricate microenvironments. Recent advancements in three-dimensional (3D) bioprinting technology present promising solutions to these challenges. This review provides an overview of cancer vasculogenesis and underscores the importance of precise modeling. It juxtaposes traditional techniques with 3D bioprinting technologies, elucidating the advantages of the latter in developing cancer vasculogenesis models. Furthermore, it explores applications in pathological investigations, preclinical medication screening for personalized treatment and cancer diagnostics, and envisages future prospects for 3D bioprinted cancer vasculogenesis models. Despite notable advancements, current 3D bioprinting techniques for cancer vasculogenesis modeling have several limitations. Nonetheless, by overcoming these challenges and with technological advances, 3D bioprinting exhibits immense potential for revolutionizing the understanding of cancer vasculogenesis and augmenting treatment modalities.

Single clonal tracking on biomimetic microtextured platforms for real-time guided migration analysis of myeloid-derived suppressor cell dissemination characteristics ex vivo

Current strategies to undermine the deleterious influence of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment (TME) are lacking effective clinical solutions, in large part, due to insufficient knowledge on susceptible cellular and molecular targets. We describe here the application of biomimetic microfabricated platforms designed to analyze migratory phenotypes of MDSCs in the tumor niche ex vivo, which may enable accelerated therapeutic discovery. By mimicking the guided structural cues present in the physiological architecture of the TME, aligned microtopography substrates can elucidate potential interventions on migratory phenotypes of MDSCs at the single clonal level. Coupled with cellular and molecular biology analysis tools, our approach employs real-time tracking analysis of cell motility to probe the dissemination characteristics of MDSCs under guided migration conditions. These methods allow us to identify cellular subpopulations of interest based on their disseminative and suppressive capabilities. By doing so, we illustrate the potential of applying microscale engineering tools, in concert with dynamic live cell imaging and bioanalysis methods to uncover novel exploitable motility targets for advancing cancer therapy discovery. The inherent simplicity and extended application to a variety of contexts in tumor-associated cell migration render this method widely accessible to existing biological laboratory conditions and interests.

Shape of scaffold controlling the direction of cell migration

Cell migration plays an important role in the development and maintenance of multicellular organisms. Factors that induce cell migration and mechanisms controlling their expression are important for determining the mechanisms of factor-induced cell migration. Despite progress in the study of factor-induced cytotaxis, including chemotaxis and haptotaxis, precise control of the direction of cell migration over a wide area has not yet been achieved. Success in this area would update the cell migration assays, superior cell separation technologies, and artificial organs with high biocompatibility. The present study therefore sought to control the direction of cell migration over a wide area by adjusting the three-dimensional shape of the cell scaffold. The direction of cell migration was influenced by the shape of the cell scaffold, thereby optimizing cell adhesion and protrusion. Anisotropic arrangement of these three-dimensional shapes into a periodic structure induced unidirectional cell migration. Three factors were required for unidirectional cell migration: 1) the sizes of the anisotropic periodic structures had to be equal to or lower than the size of the spreading cells, 2) cell migration was restricted to a runway approximately the width of the cell, and 3) cells had to be prone to extension of long protrusions in one direction. Because the first two factors had been identified previously in studies of cell migration in one direction using two-dimensional shaped patterns, these three factors are likely important for the mechanism by which cell scaffold shapes regulate cell migration.

Microfluidic single-cell migration chip reveals insights into the impact of extracellular matrices on cell movement

Cell migration is a complex process that plays a crucial role in normal physiology and pathologies such as cancer, autoimmune diseases, and mental disorders. Conventional cell migration assays face limitations in tracking a large number of individual migrating cells. To address this challenge, we have developed a high-throughput microfluidic cell migration chip, which seamlessly integrates robotic liquid handling and computer vision to swiftly monitor the movement of 3200 individual cells, providing unparalleled single-cell resolution for discerning distinct behaviors of the fast-moving cell population. This study focuses on the ECM's role in regulating cellular migration, utilizing this cutting-edge microfluidic technology to investigate the impact of ten different ECMs on triple-negative breast cancer cell lines. We found that collagen IV, collagen III, and collagen I coatings were the top enhancers of cell movement. Combining these ECMs increased cell motility, but the effect was sub-additive. Furthermore, we examined 87 compounds and found that while some compounds inhibited migration on all substrates, significantly distinct effects on differently coated substrates were observed, underscoring the importance of considering ECM coating. We also utilized cells expressing a fluorescent actin reporter and observed distinct actin structures in ECM-interacting cells. ScRNA-Seq analysis revealed that ECM coatings induced EMT and enhanced cell migration. Finally, we identified genes that were particularly up-regulated by collagen IV and the selective inhibitors successfully blocked cell migration on collagen IV. Overall, the study provides insights into the impact of various ECMs on cell migration and dynamics of cell movement with implications for developing therapeutic strategies to combat diseases related to cell motility.

High-Throughput Cellular Heterogeneity Analysis in Cell Migration at the Single-Cell Level

Cancer cell migration represents an essential step toward metastasis and cancer deaths. However, conventional drug discovery focuses on cytotoxic and growth-inhibiting compounds rather than inhibitors of migration. Drug screening assays generally measure the average response of many cells, masking distinct cell populations that drive metastasis and resist treatments. Here, this work presents a high-throughput microfluidic cell migration platform that coordinates robotic liquid handling and computer vision for rapidly quantifying individual cellular motility. Using this innovative technology, 172 compounds were tested and a surprisingly low correlation between migration and growth inhibition was found. Notably, many compounds were found to inhibit migration of most cells while leaving fast-moving subpopulations unaffected. This work further pinpoints synergistic drug combinations, including Bortezomib and Danirixin, to stop fast-moving cells. To explain the observed cell behaviors, single-cell morphological and molecular analysis were performed. These studies establish a novel technology to identify promising migration inhibitors for cancer treatment and relevant applications.

In Situ Deployment of Engineered Extracellular Vesicles into the Tumor Niche via Myeloid-Derived Suppressor Cells

Extracellular vesicles (EVs) have emerged as a promising carrier system for the delivery of therapeutic payloads in multiple disease models, including cancer. However, effective targeting of EVs to cancerous tissue remains a challenge. Here, it is shown that nonviral transfection of myeloid-derived suppressor cells (MDSCs) can be leveraged to drive targeted release of engineered EVs that can modulate transfer and overexpression of therapeutic anticancer genes in tumor cells and tissue. MDSCs are immature immune cells that exhibit enhanced tropism toward tumor tissue and play a role in modulating tumor progression. Current MDSC research has been mostly focused on mitigating immunosuppression in the tumor niche; however, the tumor homing abilities of these cells present untapped potential to deliver EV therapeutics directly to cancerous tissue. In vivo and ex vivo studies with murine models of breast cancer show that nonviral transfection of MDSCs does not hinder their ability to home to cancerous tissue. Moreover, transfected MDSCs can release engineered EVs and mediate antitumoral responses via paracrine signaling, including decreased invasion/metastatic activity and increased apoptosis/necrosis. Altogether, these findings indicate that MDSCs can be a powerful tool for the deployment of EV-based therapeutics to tumor tissue.

Strategies for developing complex multi-component in vitro tumor models: Highlights in glioblastoma

In recent years, many research groups have begun to utilize bioengineered in vitro models of cancer to study mechanisms of disease progression, test drug candidates, and develop platforms to advance personalized drug treatment options. Due to advances in cell and tissue engineering over the last few decades, there are now a myriad of tools that can be used to create such in vitro systems. In this review, we describe the considerations one must take when developing model systems that accurately mimic the in vivo tumor microenvironment (TME) and can be used to answer specific scientific questions. We will summarize the importance of cell sourcing in models with one or multiple cell types and outline the importance of choosing biomaterials that accurately mimic the native extracellular matrix (ECM) of the tumor or tissue that is being modeled. We then provide examples of how these two components can be used in concert in a variety of model form factors and conclude by discussing how biofabrication techniques such as bioprinting and organ-on-a-chip fabrication can be used to create highly reproducible complex in vitro models. Since this topic has a broad range of applications, we use the final section of the review to dive deeper into one type of cancer, glioblastoma, to illustrate how these components come together to further our knowledge of cancer biology and move us closer to developing novel drugs and systems that improve patient outcomes.

Phenotypic and Functional Transformation in Smooth Muscle Cells Derived from a Superficial Thrombophlebitis-affected Vein Wall

BACKGROUND

Superficial thrombophlebitis (ST) is a frequent pathology, but its exact incidence remains to be determined. This study tested the hypothesis whether relationships exist among smooth muscle cells (SMCs) derived from ST, varicose great saphenous veins (VGSVs), and normal great saphenous veins (GSVs).

METHODS

Forty-one samples of ST, VGSVs, and GSVs were collected. SMCs were isolated and cultured. Proliferation, migration, adhesion, and senescence in SMCs from the three vein walls were compared by various methods. Bax, Bcl-2, caspase-3, matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and TIMP-2 messenger RNA (mRNA) and protein expressions were detected by fluorescence quantitative PCR and Western blot.

RESULTS

An obvious decrease in cytoskeletal filaments was observed in thrombophlebitic vascular smooth muscle cells (TVSMCs). The quantity of proliferation, migration, adhesion, and senescence in TVSMCs was significantly higher than in varicose vascular smooth muscle cells and normal vascular smooth muscle cells (NVSMCs) (all P < 0.05). Bax and caspase-3 mRNA and protein expression were decreased, while Bcl-2 mRNA and protein expression were increased in the TVSMCs compared with the varicose vascular smooth muscle cells and the NVSMCs (all P < 0.05). MMP-2, MMP-9, TIMP-1, and TIMP-2 mRNA and protein expression were significantly increased in the TVSMCs compared with the VVGSVs and the NVSMCs (all P < 0.05).

CONCLUSION

SMCs derived from ST are more dedifferentiated and demonstrate increased cell proliferation, migration, adhesion, and senescence, as well as obviously decreased cytoskeletal filaments. These results suggest that the phenotypic and functional differences could be related to the presence of atrophic and hypertrophic vein segments during the disease course among SMCs derived from ST, VGSVs, and GSVs.

Micropatterned growth surface topography affects extracellular vesicle production

Extracellular vesicles (EVs) are micro and nanoscale packages that circulate in all bodily fluids and play an important role in intercellular communication by shuttling biomolecules to nearby and distant cells. However, producing sufficient amounts of EVs for many types of in vitro studies using standard culture methods can be challenging, and despite the success of some bioreactors in increasing EV-production, it is still largely unknown how individual culture conditions can alter the production and content of EVs. In this study, we demonstrate a simple and inexpensive micropatterning technique that can be used to produce polystyrene microtracks over a 100 mm diameter growth surface area. We then demonstrate that these microtracks can play a significant role in increasing EV production using a triple-negative breast cancer cell line (MDA-MB-231) and that these changes in EV production correlate with increases in cellular aspect ratio, alignment of the cells' long axes to the microtracks, and single-cell migration rates. These findings have implications in both biomanufacturing of EVs and potentially in enhancing the biomimicry of EVs produced in vitro.

Bioprinting of in vitro tumor models for personalized cancer treatment: a review

Studying biological characteristics of tumors and evaluating the treatment effects require appropriate in vitro tumor models. However, the occurrence, progression, and migration of tumors involve spatiotemporal changes, cell-microenvironment and cell-cell interactions, and signal transmission in cells, which makes the construction of in vitro tumor models extremely challenging. In the past few years, advances in biomaterials and tissue engineering methods, especially development of the bioprinting technology, have paved the way for innovative platform technologies for in vitro cancer research. Bioprinting can accurately control the distribution of cells, active molecules, and biomaterials. Furthermore, this technology recapitulates the key characteristics of the tumor microenvironment and constructs in vitro tumor models with bionic structures and physiological systems. These models can be used as robust platforms to study tumor initiation, interaction with the microenvironment, angiogenesis, motility and invasion, as well as intra- and extravasation. Bioprinted tumor models can also be used for high-throughput drug screening and validation and provide the possibility for personalized cancer treatment research. This review describes the basic characteristics of the tumor and its microenvironment and focuses on the importance and relevance of bioprinting technology in the construction of tumor models. Research progress in the bioprinting of monocellular, multicellular, and personalized tumor models is discussed, and comprehensive application of bioprinting in preclinical drug screening and innovative therapy is reviewed. Finally, we offer our perspective on the shortcomings of the existing models and explore new technologies to outline the direction of future development and application prospects of next-generation tumor models.

Traversing behavior of tumor cells in three-dimensional platforms with different topography

Three-dimensional polydimethylsiloxane platforms were developed to mimic the extracellular matrix with blood vessels by having scaffolds with micropatterns, porous membrane and trenches. Precisely controlled physical dimensions, layouts, and topography as well as different surface chemical treatments were applied to study their influences on nasopharyngeal carcinoma cell (10-15 μm in diameter) migration in mimicked platforms over 15-hour of time-lapse imaging. By placing the pores at different distance from the edges of the trenches, pores with different trench sidewall exposures and effective sizes were generated. Pores right next to the trench sidewalls showed the highest cell traversing probability, most likely related to the larger surface contact area with cells along the sidewalls. Straight grating oriented perpendicular to trenches below the top layer increased cell traversing probability. Pore shape as well as pore size influenced the cell traversing probability and cells could not traverse through pores that were 6 μm or less in diameter, which is much smaller than the cell size. Trench depth of 15 μm could induce more cells to traverse through the porous membrane, while shallower trenches impeded cell traversing and longer time was needed for cells to traverse because 3 and 6 μm deep trenches were much smaller than cell size which required large cell deformation. Hydrophobic surface coating on the top layer and fibronectin in pores and trenches increased the cell traversing probability and reduced the pore size that cells could traverse from 8 to 6 μm, which indicated that cells could have larger deformation with certain surface coatings.

Reciprocal Signaling between Myeloid Derived Suppressor and Tumor Cells Enhances Cellular Motility and is Mediated by Structural Cues in the Microenvironment

Myeloid derived suppressor cells (MDSCs) have gained significant attention for their immunosuppressive role in cancer and their ability to contribute to tumor progression and metastasis. Understanding the role of MDSCs in driving cancer cell migration, a process fundamental to metastasis, is essential to fully comprehend and target MDSC-tumor cell interactions. This study employs microfabricated platforms, which simulate the structural cues present in the tumor microenvironment (TME) to elucidate the effects of MDSCs on the migratory phenotype of cancer cells at the single cell level. The results indicate that the presence of MDSCs enhances the motility of cancer-epithelial cells when directional cues (either topographical or spatial) are present. This behavior appears to be independent of cell-cell contact and driven by soluble byproducts from heterotypic interactions between MDSCs and cancer cells. Moreover, MDSC cell-motility is also impacted by the presence of cancer cells and the cancer cell secretome in the presence of directional cues. Epithelial dedifferentiation is the likely mechanism for changes in cancer cell motility in response to MDSCs. These results highlight the biochemical and biostructural conditions under which MDSCs can support cancer cell migration, and could therefore provide new avenues of research and therapy aimed at stemming cancer progression.

Phenotypic Plasticity of Invasive Edge Glioma Stem-like Cells in Response to Ionizing Radiation

Unresectable glioblastoma (GBM) cells in the invading tumor edge can act as seeds for recurrence. The molecular and phenotypic properties of these cells remain elusive. Here, we report that the invading edge and tumor core have two distinct types of glioma stem-like cells (GSCs) that resemble proneural (PN) and mesenchymal (MES) subtypes, respectively. Upon exposure to ionizing radiation (IR), GSCs, initially enriched for a CD133⁺ PN signature, transition to a CD109⁺ MES subtype in a C/EBP-β-dependent manner. Our gene expression analysis of paired cohorts of patients with primary and recurrent GBMs identified a CD133-to-CD109 shift in tumors with an MES recurrence. Patient-derived CD133⁻/CD109⁺ cells are highly enriched with clonogenic, tumor-initiating, and radiation-resistant properties, and silencing CD109 significantly inhibits these phenotypes. We also report a conserved regulation of YAP/TAZ pathways by CD109 that could be a therapeutic target in GBM.

Minata et al., in response to the proinflammatory environment induced by radiation, find that the tumor cells at the invasive edge acquire the expression of the CD109 protein concomitantly losing CD133. CD109 drives oncogenic signaling through the YAP/TAZ pathway, confers radioresistance to the cells, and represents a new potential therapeutic target for glioblastoma.

Guided migration analyses at the single-clone level uncover cellular targets of interest in tumor-associated myeloid-derived suppressor cell populations

Myeloid-derived suppressor cells (MDSCs) are immune cells that exert immunosuppression within the tumor, protecting cancer cells from the host’s immune system and/or exogenous immunotherapies. While current research has been mostly focused in countering MDSC-driven immunosuppression, little is known about the mechanisms by which MDSCs disseminate/infiltrate cancerous tissue. This study looks into the use of microtextured surfaces, coupled with in vitro and in vivo cellular and molecular analysis tools, to videoscopically evaluate the dissemination patterns of MDSCs under structurally guided migration, at the single-cell level. MDSCs exhibited topographically driven migration, showing significant intra- and inter-population differences in motility, with velocities reaching ~40 μm h⁻¹. Downstream analyses coupled with single-cell migration uncovered the presence of specific MDSC subpopulations with different degrees of tumor-infiltrating and anti-inflammatory capabilities. Granulocytic MDSCs showed a ~≥3-fold increase in maximum dissemination velocities and traveled distances, and a ~10-fold difference in the expression of pro- and anti-inflammatory markers. Prolonged culture also revealed that purified subpopulations of MDSCs exhibit remarkable plasticity, with homogeneous/sorted subpopulations giving rise to heterogenous cultures that represented the entire hierarchy of MDSC phenotypes within 7 days. These studies point towards the granulocytic subtype as a potential cellular target of interest given their superior dissemination ability and enhanced anti-inflammatory activity.

Suppression of LIM Kinase 1 and LIM Kinase 2 Limits Glioblastoma Invasion

The aggressive brain tumor glioblastoma (GBM) is characterized by rapid cellular infiltration of brain tissue, raising the possibility that disease progression could potentially be slowed by disrupting the machinery of cell migration. The LIM kinase isoforms LIMK1 and LIMK2 (LIMK1/2) play important roles in cell polarization, migration, and invasion and are markedly upregulated in GBM and many other infiltrative cancers. Yet, it remains unclear whether LIMK suppression could serve as a viable basis for combating GBM infiltration. In this study, we investigated effects of LIMK1/2 suppression on GBM invasion by combining GBM culture models, engineered invasion paradigms, and mouse xenograft models. While knockdown of either LIMK1 or LIMK2 only minimally influenced invasion in culture, simultaneous knockdown of both isoforms strongly reduced the invasive motility of continuous culture models and human GBM tumor-initiating cells (TIC) in both Boyden chamber and 3D hyaluronic acid spheroid invasion assays. Furthermore, LIMK1/2 functionally regulated cell invasiveness, in part, by disrupting polarized cell motility under confinement and cell chemotaxis. In an orthotopic xenograft model, TICs stably transduced with LIMK1/2 shRNA were implanted intracranially in immunocompromised mice. Tumors derived from LIMK1/2 knockdown TICs were substantially smaller and showed delayed growth kinetics and more distinct margins than tumors derived from control TICs. Overall, LIMK1/2 suppression increased mean survival time by 30%. These findings indicate that LIMK1/2 strongly regulate GBM invasive motility and tumor progression and support further exploration of LIMK1/2 as druggable targets. SIGNIFICANCE: Targeting the actin-binding proteins LIMK1 and LIMK2 significantly diminishes glioblastoma invasion and spread, suggesting the potential value of these proteins as therapeutic targets.

A versatile cancer cell trapping and 1D migration assay in a microfluidic device

Highly migratory cancer cells often lead to metastasis and recurrence and are responsible for the high mortality rates in many cancers despite aggressive treatment. Recently, the migratory behavior of patient-derived glioblastoma multiforme cells on microtracks has shown potential in predicting the likelihood of recurrence, while at the same time, antimetastasis drugs have been developed which require simple yet relevant high-throughput screening systems. However, robust in vitro platforms which can reliably seed single cells and measure their migration while mimicking the physiological tumor microenvironment have not been demonstrated. In this study, we demonstrate a microfluidic device which hydrodynamically seeds single cancer cells onto stamped or femtosecond laser ablated polystyrene microtracks, promoting 1D migratory behavior due to the cells' tendency to follow topographical cues. Using time-lapse microscopy, we found that single U87 glioblastoma multiforme cells migrated more slowly on laser ablated microtracks compared to stamped microtracks of equal width and spacing (p < 0.05) and exhibited greater directional persistence on both 1D patterns compared to flat polystyrene (p < 0.05). Single-cell morphologies also differed significantly between flat and 1D patterns, with cells on 1D substrates exhibiting higher aspect ratios and less circularity (p < 0.05). This microfluidic platform could lead to automated quantification of single-cell migratory behavior due to the high predictability of hydrodynamic seeding and guided 1D migration, an important step to realizing the potential of microfluidic migration assays for drug screening and individualized medicine.

Temperature-Controlled Orientation of Proteins on Temperature-Responsive Grafted Polymer Brushes: Poly(butyl methacrylate) vs Poly(butyl acrylate): Morphology, Wetting, and Protein Adsorption

Poly( n-butyl methacrylate) (PBMA) or poly( n-butyl acrylate) (PBA)-grafted brush coatings attached to glass were successfully prepared using atom-transfer radical polymerization "from the surface". The thicknesses and composition of the PBMA and PBA coatings were examined using ellipsometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. For PBMA, the glass-transition temperature constitutes a range close to the physiological limit, which is in contrast to PBA, where the glass-transition temperature is around -55 °C. Atomic force microscopy studies at different temperatures suggest a strong morphological transformation for PBMA coatings, in contrast to PBA, where such essential changes in the surface morphology are absent. Besides, for PBMA coatings, protein adsorption depicts a strong temperature dependence. The combination of bovine serum albumin and anti-IgG structure analysis with the principal component analysis of ToF-SIMS spectra revealed a different orientation of proteins adsorbed to PBMA coatings at different temperatures. In addition, the biological activity of anti-IgG molecules adsorbed at different temperatures was evaluated through tracing the specific binding with goat IgG.

Micro and Nanofabrication methods to control cell-substrate interactions and cell behavior: A review from the tissue engineering perspective

Cell-substrate interactions play a crucial role in the design of better biomaterials and integration of implants with the tissues. Adhesion is the binding process of the cells to the substrate through interactions between the surface molecules of the cell membrane and the substrate. There are several factors that affect cell adhesion including substrate surface chemistry, topography, and stiffness. These factors physically and chemically guide and influence the adhesion strength, spreading, shape and fate of the cell. Recently, technological advances enabled us to precisely engineer the geometry and chemistry of substrate surfaces enabling the control of the interaction cells with the substrate. Some of the most commonly used surface engineering methods for eliciting the desired cellular responses on biomaterials are photolithography, electron beam lithography, microcontact printing, and microfluidics. These methods allow production of nano- and micron level substrate features that can control cell adhesion, migration, differentiation, shape of the cells and the nuclei as well as measurement of the forces involved in such activities. This review aims to summarize the current techniques and associate these techniques with cellular responses in order to emphasize the effect of chemistry, dimensions, density and design of surface patterns on cell-substrate interactions. We conclude with future projections in the field of cell-substrate interactions in the hope of providing an outlook for the future studies.

Apoptotic Cell-Derived Extracellular Vesicles Promote Malignancy of Glioblastoma Via Intercellular Transfer of Splicing Factors

Aggressive cancers such as glioblastoma (GBM) contain intermingled apoptotic cells adjacent to proliferating tumor cells. Nonetheless, intercellular signaling between apoptotic and surviving cancer cells remain elusive. In this study, we demonstrate that apoptotic GBM cells paradoxically promote proliferation and therapy resistance of surviving tumor cells by secreting apoptotic extracellular vesicles (apoEVs) enriched with various components of spliceosomes. apoEVs alter RNA splicing in recipient cells, thereby promoting their therapy resistance and aggressive migratory phenotype. Mechanistically, we identified RBM11 as a representative splicing factor that is upregulated in tumors after therapy and shed in extracellular vesicles upon induction of apoptosis. Once internalized in recipient cells, exogenous RBM11 switches splicing of MDM4 and Cyclin D1 toward the expression of more oncogenic isoforms.

Cell migration in microengineered tumor environments

Recent advances in microengineered cell migration platforms are discussed critically with a focus on how cell migration is influenced by engineered tumor microenvironments, the medical relevance being to understand how tumor microenvironments may promote or suppress the progression of cancer. We first introduce key findings in cancer cell migration under the influence of the physical environment, which is systematically controlled by microengineering technology, followed by multi-cues of physico-chemical factors, which represent the complexity of the tumor environment. Recognizing that cancer cells constantly communicate not only with each other but also with tumor-associated cells such as vascular, fibroblast, and immune cells, and also with non-cellular components, it follows that cell motility in tumor microenvironments, especially metastasis via the invasion of cancer cells into the extracellular matrix and other tissues, is closely related to the malignancy of cancer-related mortality. Medical relevance of forefront research realized in microfabricated devices, such as single cell sorting based on the analysis of cell migration behavior, may assist personalized theragnostics based on the cell migration phenotype. Furthermore, we urge development of theory and numerical understanding of single or collective cell migration in microengineered platforms to gain new insights in cancer metastasis and in therapeutic strategies.

Elasticity patterns induced by phase-separation in polymer blend films

Systematical studies on the impact of the thickness of thin films composed of polystyrene (PS) or poly(ethylene oxide) (PEO) on the effective elasticity of polymer-decorated soft polydimethylsiloxane substrate were performed. For both investigated polymer films, elasticity parameter was determined from force-displacement curves recorded using atomic force microscopy. Effective stiffness of supported film grows monotonically with film thickness, starting from the value comparable to the elasticity of soft support and reaching plateau for polymer layers thicker than 200 nm. In contrary, for films cast on hard support no significant thickness dependence of elasticity was observed and the value of elasticity parameter was similar to the one of the substrate. Based on these results, non-conventional method to produce elasticity patterns of various shapes and dimensions induced by phase-separation process in symmetric and asymmetric PS:PEO blend films on soft support was demonstrated. Elevated PS domains were characterized by elasticity parameter 2 times higher than lower PEO matrix. In contrary, adhesion force was increased more than 3 times for PEO regions, as compared to PS areas.

Biocompatibility assay of cellular behavior inside a leaf-inspired biomimetic microdevice at the single-cell level

Inspired by recent studies, we created a biomimetic method to replicate the veinal microvasculature from a natural leaf into a lab-on-a-chip system, which could be further utilized as a biomimetic animal vessel as well as in vessel-derived downstream applications.

On-Chip Clonal Analysis of Glioma-Stem-Cell Motility and Therapy Resistance

Enhanced glioma-stem-cell (GSC) motility and therapy resistance are considered to play key roles in tumor cell dissemination and recurrence. As such, a better understanding of the mechanisms by which these cells disseminate and withstand therapy could lead to more efficacious treatments. Here, we introduce a novel micro-/nanotechnology-enabled chip platform for performing live-cell interrogation of patient-derived GSCs with single-clone resolution. On-chip analysis revealed marked intertumoral differences (>10-fold) in single-clone motility profiles between two populations of GSCs, which correlated well with results from tumor-xenograft experiments and gene-expression analyses. Further chip-based examination of the more-aggressive GSC population revealed pronounced interclonal variations in motility capabilities (up to ∼4-fold) as well as gene-expression profiles at the single-cell level. Chip-supported therapy resistance studies with a chemotherapeutic agent (i.e., temozolomide) and an oligo RNA (anti-miR363) revealed a subpopulation of CD44-high GSCs with strong antiapoptotic behavior as well as enhanced motility capabilities. The living-cell-interrogation chip platform described herein enables thorough and large-scale live monitoring of heterogeneous cancer-cell populations with single-cell resolution, which is not achievable by any other existing technology and thus has the potential to provide new insights into the cellular and molecular mechanisms modulating glioma-stem-cell dissemination and therapy resistance.

Engineered Models of Confined Cell Migration

Cells in the body are physically confined by neighboring cells, tissues, and the extracellular matrix. Although physical confinement modulates intracellular signaling and the underlying mechanisms of cell migration, it is difficult to study in vivo. Furthermore, traditional two-dimensional cell migration assays do not recapitulate the complex topographies found in the body. Therefore, a number of experimental in vitro models that confine and impose forces on cells in well-defined microenvironments have been engineered. We describe the design and use of microfluidic microchannel devices, grooved substrates, micropatterned lines, vertical confinement devices, patterned hydrogels, and micropipette aspiration assays for studying cell responses to confinement. Use of these devices has enabled the delineation of changes in cytoskeletal reorganization, cell-substrate adhesions, intracellular signaling, nuclear shape, and gene expression that result from physical confinement. These assays and the physiologically relevant signaling pathways that have been elucidated are beginning to have a translational and clinical impact.

The human PMR1 endonuclease stimulates cell motility by down regulating miR-200 family microRNAs

The motility of MCF-7 cells increases following expression of a human PMR1 transgene and the current study sought to identify the molecular basis for this phenotypic change. Ensemble and single cell analyses show increased motility is dependent on the endonuclease activity of hPMR1, and cells expressing active but not inactive hPMR1 invade extracellular matrix. Nanostring profiling identified 14 microRNAs that are downregulated by hPMR1, including all five members of the miR-200 family and others that also regulate invasive growth. miR-200 levels increase following hPMR1 knockdown, and changes in miR-200 family microRNAs were matched by corresponding changes in miR-200 targets and reporter expression. PMR1 preferentially cleaves between UG dinucleotides within a consensus YUGR element when present in the unpaired loop of a stem–loop structure. This motif is present in the apical loop of precursors to most of the downregulated microRNAs, and hPMR1 targeting of pre-miRs was confirmed by their loss following induced expression and increase following hPMR1 knockdown. Introduction of miR-200c into hPMR1-expressing cells reduced motility and miR-200 target gene expression, confirming hPMR1 acts upstream of Dicer processing. These findings identify a new role for hPMR1 in the post-transcriptional regulation of microRNAs in breast cancer cells.

Serine/Threonine Kinase MLK4 Determines Mesenchymal Identity in Glioma Stem Cells in an NF-κB-dependent Manner

Activation of nuclear factor κB (NF-κB) induces mesenchymal (MES) transdifferentiation and radioresistance in glioma stem cells (GSCs), but molecular mechanisms for NF-κB activation in GSCs are currently unknown. Here, we report that mixed lineage kinase 4 (MLK4) is overexpressed in MES but not proneural (PN) GSCs. Silencing MLK4 suppresses self-renewal, motility, tumorigenesis, and radioresistance of MES GSCs via a loss of the MES signature. MLK4 binds and phosphorylates the NF-κB regulator IKKα, leading to activation of NF-κB signaling in GSCs. MLK4 expression is inversely correlated with patient prognosis in MES, but not PN high-grade gliomas. Collectively, our results uncover MLK4 as an upstream regulator of NF-κB signaling and a potential molecular target for the MES subtype of glioblastomas.

Single-cell Migration Chip for Chemotaxis-based Microfluidic Selection of Heterogeneous Cell Populations

Tumor cell migration toward and intravasation into capillaries is an early and key event in cancer metastasis, yet not all cancer cells are imbued with the same capability to do so. This heterogeneity within a tumor is a fundamental property of cancer. Tools to help us understand what molecular characteristics allow a certain subpopulation of cells to spread from the primary tumor are thus critical for overcoming metastasis. Conventional in vitro migration platforms treat populations in aggregate, which leads to a masking of intrinsic differences among cells. Some migration assays reported recently have single-cell resolution, but these platforms do not provide for selective retrieval of the distinct migrating and non-migrating cell populations for further analysis. Thus, to study the intrinsic differences in cells responsible for chemotactic heterogeneity, we developed a single-cell migration platform so that individual cells' migration behavior can be studied and the heterogeneous population sorted based upon chemotactic phenotype. Furthermore, after migration, the highly chemotactic and non-chemotactic cells were retrieved and proved viable for later molecular analysis of their differences. Moreover, we modified the migration channel to resemble lymphatic capillaries to better understand how certain cancer cells are able to move through geometrically confining spaces.

Tapered microtract array platform for antimigratory drug screening of human glioblastoma multiforme

Understanding the effects of topographic characteristics on tumor cell migration is important for the development of new anti-migratory therapies. However, simplified in vitro culture systems often lead to inaccurate results regarding the efficacy of drugs. Histopathologically, glioblastoma multiform (GBM) cells migrate along the orientation of thin, elongated anatomical structures, such as white-matter tracts. Here, a tapered microtract array platform which mimics the anatomical features of brain tissue is introduced. This platform enables optimization of design for platform fabrication depending on topographic effects. By monitoring the migration of GBM cells on a simple tapered microtract, a saltatory migration resembling the migratory phenotype of human GBM cells in vivo is observed. The platform effectively induces the native characteristics and behavior of cells by topographic cues, allowing to observe the critical point for crawling to saltatory transition. Furthermore, this platform can be applied to efficiently screen anti-cancer drug by inhibiting associated signaling pathways on GBM cells. In conclusion, the microtract array platform reported here may provide a better understanding of the effects of topographic characteristics on cell migration, and may also be useful to determine the efficacy of antimigratory drugs for glioblastoma cells with cellular and molecular research and high-throughput screening.

Engineering strategies to mimic the glioblastoma microenvironment

Glioblastoma multiforme (GBM) is the most common and deadly brain tumor, with a mean survival time of only 21months. Despite the dramatic improvements in our understanding of GBM fueled by recent revolutions in molecular and systems biology, treatment advances for GBM have progressed inadequately slowly, which is due in part to the wide cellular and molecular heterogeneity both across tumors and within a single tumor. Thus, there is increasing clinical interest in targeting cell-extrinsic factors as way of slowing or halting the progression of GBM. These cell-extrinsic factors, collectively termed the microenvironment, include the extracellular matrix, blood vessels, stromal cells that surround tumor cells, and all associated soluble and scaffold-bound signals. In this review, we will first describe the regulation of GBM tumors by these microenvironmental factors. Next, we will discuss the various in vitro approaches that have been exploited to recapitulate and model the GBM tumor microenvironment in vitro. We conclude by identifying future challenges and opportunities in this field, including the development of microenvironmental platforms amenable to high-throughput discovery and screening. We anticipate that these ongoing efforts will prove to be valuable both as enabling tools for accelerating our understanding of microenvironmental regulation in GBM and as foundations for next-generation molecular screening platforms that may serve as a conceptual bridge between traditional reductionist systems and animal or clinical studies.

Microfabricated Systems and Assays for Studying the Cytoskeletal Organization, Micromechanics, and Motility Patterns of Cancerous Cells

Cell motions are driven by coordinated actions of the intracellular cytoskeleton - actin, microtubules (MTs) and substrate/focal adhesions (FAs). This coordination is altered in metastatic cancer cells resulting in deregulated and increased cellular motility. Microfabrication tools, including photolithography, micromolding, microcontact printing, wet stamping and microfluidic devices have emerged as a powerful set of experimental tools with which to probe and define the differences in cytoskeleton organization/dynamics and cell motility patterns in non-metastatic and metastatic cancer cells. In this review, we discuss four categories of microfabricated systems: (i) micropatterned substrates for studying of cell motility sub-processes (for example, MT targeting of FAs or cell polarization); (ii) systems for studying cell mechanical properties, (iii) systems for probing overall cell motility patterns within challenging geometric confines relevant to metastasis (for example, linear and ratchet geometries), and (iv) microfluidic devices that incorporate co-cultures of multiple cells types and chemical gradients to mimic in vivo intravasation/extravasation steps of metastasis. Together, these systems allow for creating controlled microenvironments that not only mimic complex soft tissues, but are also compatible with live cell high-resolution imaging and quantitative analysis of single cell behavior.

Phenotypic modulation of primary vascular smooth muscle cells by short-term culture on micropatterned substrate

Loss of contractility and acquisition of an epithelial phenotype of vascular smooth muscle cells (VSMCs) are key events in proliferative vascular pathologies such as atherosclerosis and post-angioplastic restenosis. There is no proper cell culture system allowing differentiation of VSMCs so that it is difficult to delineate the molecular mechanism responsible for proliferative vasculopathy. We investigated whether a micropatterned substrate could restore the contractile phenotype of VSMCs in vitro. To induce and maintain the differentiated VSMC phenotype in vitro, we introduced a micropatterned groove substrate to modulate the morphology and function of VSMCs. Later than 7(th) passage of VSMCs showed typical synthetic phenotype characterized by epithelial morphology, increased proliferation rates and corresponding gene expression profiles; while short-term culture of these cells on a micropatterned groove induced a change to an intermediate phenotype characterized by low proliferation rates, increased migration, a spindle-like morphology associated with cytoskeletal rearrangement and expression of muscle-specific genes. Microarray analysis showed preferential expression of contractile and smooth muscle cell-specific genes in cells cultured on the micropatterned groove. Culture on a patterned groove may provide a valuable model for the study the role of VSMCs in normal vascular physiology and a variety of proliferative vascular diseases.

3D printing of biomimetic microstructures for cancer cell migration

To understand the physical behavior and migration of cancer cells, a 3D in vitro micro-chip in hydrogel was created using 3D projection printing. The micro-chip has a honeycomb branched structure, aiming to mimic 3D vascular morphology to test, monitor, and analyze differences in the behavior of cancer cells (i.e. HeLa) vs. non-cancerous cell lines (i.e. 10 T1/2). The 3D Projection Printing system can fabricate complex structures in seconds from user-created designs. The fabricated microstructures have three different channel widths of 25, 45, and 120 microns wide to reflect a range of blood vessel diameters. HeLa and 10 T1/2 cells seeded within the micro-chip were then analyzed for morphology and cell migration speed. 10 T1/2 cells exhibited greater changes in morphology due to channel size width than HeLa cells; however, channel width had a limited effect on 10 T1/2 cell migration while HeLa cancer cell migration increased as channel width decreased. This physiologically relevant 3D cancer tissue model has the potential to be a powerful tool for future drug discoveries and cancer migration studies.

Cell migration in confined environments

We describe a protocol for measuring the speed of human neutrophils migrating through small channels, in conditions of mechanical confinement comparable to those experienced by neutrophils migrating through tissues. In such conditions, we find that neutrophils move persistently, at constant speed for tens of minutes, enabling precise measurements at single cells resolution, for large number of cells. The protocol relies on microfluidic devices with small channels in which a solution of chemoattractant and a suspension of isolated neutrophils are loaded in sequence. The migration of neutrophils can be observed for several hours, starting within minutes after loading the neutrophils in the devices. The protocol is divided into four main steps: the fabrication of the microfluidic devices, the separation of neutrophils from whole blood, the preparation of the assay and cell loading, and the analysis of data. We discuss the practical steps for the implementation of the migration assays in biology labs, the adaptation of the protocols to various cell types, including cancer cells, and the supplementary device features required for precise measurements of directionality and persistence during migration.