Microprinted Stem Cell Niches Reveal Compounding Effect of Colony Size on Stromal Cells-Mediated Neural Differentiation

Inhibiting BRAF/EGFR/MEK suppresses cancer stemness and drug resistance of primary colorectal cancer cells

Drug resistance is a major barrier against successful treatments of cancer patients. Gain of stemness under drug pressure is a major mechanism that renders treatments ineffective. Identifying approaches to target cancer stem cells (CSCs) is expected to improve treatment outcomes for patients. To elucidate the role of cancer stemness in resistance of colorectal cancer cells to targeted therapies, we developed spheroid cultures of patient-derived BRAFmut and KRASmut tumor cells and studied resistance mechanisms to inhibition of MAPK pathway through phenotypic and gene and protein expression analysis. We found that treatments enriched the expression of CSC markers CD166, ALDH1A3, CD133, and LGR5 and activated PI3K/Akt pathway in cancer cells. We examined various combination treatments to block these activities and found that a triple combination against BRAF, EGFR, and MEK significantly reduced stemness and activities of oncogenic signaling pathways. This study demonstrates the feasibility of blocking stemness-mediated drug resistance and tumorigenic activities in colorectal cancer.

Therapeutic Targeting of Cancer Stem Cells Prevents Resistance of Colorectal Cancer Cells to MEK Inhibition

Drug resistance is a leading cause for the failure of cancer treatments. Plasticity of cancer cells to acquire stem cell-like properties enables them to escape drug toxicity through different adaptive mechanisms. Eliminating cancer stem cells (CSCs) can potentially improve treatment outcomes for patients. To determine the role of CSCs in resistance of colorectal cancer cells to targeted therapies and identify treatment strategies, we treated spheroids of BRAFmut and KRASmut colorectal cancer cells with inhibitors of the mitogen-activated protein kinase pathway and studied resistance mechanisms through gene and protein expression analyses. We found that treatments activated several oncogenic pathways and expression of CSC markers CD166 and ALDH1A3. We identified a specific combination treatment using trametinib and mithramycin A to simultaneously inhibit the CSC phenotype and activities of several pathways in cancer cells. This study demonstrates the feasibility of therapeutic targeting of CSCs as a strategy to block tumorigenic activities of cancer cells.

Therapeutic Targeting of Stromal-Tumor HGF-cMET Signaling in an Organotypic Triple Negative Breast Tumor Model

The tumor microenvironment (TME) promotes proliferation, drug resistance, and invasiveness of cancer cells. Therapeutic targeting of the TME is an attractive strategy to improve outcomes for patients, particularly in aggressive cancers such as triple negative breast cancer (TNBC) that have a rich stroma and limited targeted therapies. However, lack of preclinical human tumor models for mechanistic understanding of tumor-stromal interactions has been an impediment to identify effective treatments against the TME. To address this need, we developed a three-dimensional (3D) organotypic tumor model to study interactions of patient-derived cancer-associated fibroblasts (CAFs) with TNBC cells and explore potential therapy targets. We found that CAFs predominantly secreted hepatocyte growth factor (HGF) and activated MET receptor tyrosine kinase in TNBC cells. This tumor-stromal interaction promoted invasiveness, epithelial-to-mesenchymal transition, and activities of multiple oncogenic pathways in TNBC cells. Importantly, we established that TNBC cells become resistant to monotherapy and demonstrated a design-driven approach to select drug combinations that effectively inhibit pro-metastatic functions of TNBC cells. Our study also showed that HGF-MET from lung fibroblasts promotes colony formation by TNBC cells, suggesting that blocking HGF-MET signaling potentially could target both primary TNBC tumorigenesis and lung metastasis. Overall, we established the utility of our organotypic tumor model to identify and therapeutically target specific mechanisms of tumor-stromal interactions in TNBC toward the goal of developing targeted therapies against the TME. Implications: Leveraging a state-of-the-art organotypic tumor model, we demonstrated that CAFs-mediated HGF-MET signaling drive tumorigenic activities in TNBC and presents a therapeutic target.

The spatial self-organization within pluripotent stem cell colonies is continued in detaching aggregates

Colonies of induced pluripotent stem cells (iPSCs) reveal aspects of self-organization even under culture conditions that maintain pluripotency. To investigate the dynamics of this process under spatial confinement, we used either polydimethylsiloxane (PDMS) pillars or micro-contact printing of vitronectin. There was a progressive upregulation of OCT4, E-cadherin, and NANOG within 70 μm from the outer rim of iPSC colonies. Single-cell RNA-sequencing and spatial reconstruction of gene expression demonstrated that OCT4^high subsets, residing at the edge of the colony, have pronounced up-regulation of the TGF-β pathway, particularly of NODAL and its inhibitor LEFTY. Interestingly, after 5-7 days, iPSC colonies detached spontaneously from micro-contact printed substrates to form 3D aggregates. This new method allowed generation of embryoid bodies (EBs) of controlled size without enzymatic or mechanical treatment. Within the early 3D aggregates, radial organization and differential gene expression continued in analogy to the changes observed during self-organization of iPSC colonies. Early self-detached aggregates revealed up-regulated germline-specific gene expression patterns as compared to conventional EBs. However, there were no marked differences after further directed differentiation toward hematopoietic, mesenchymal, and neuronal lineages. Our results provide further insight into the gradual self-organization within iPSC colonies and at their transition into EBs.

Fndc5 knockdown significantly decreased the expression of neurotrophins and their respective receptors during neural differentiation of mouse embryonic stem cells

Fibronectin type III domain-containing-5 (Fndc5) is a trans-membrane protein which is involved in a variety of cellular events including neural differentiation of mouse embryonic stem cells (mESCs) as its knockdown and overexpression diminishes and facilitates this process, respectively. However, downstream targets of Fndc5 in neurogenesis are still unclear. Neurotrophins including NGF, BDNF, NT-3, and NT-4 are the primary regulators of neuronal survival, growth, differentiation, and repair. These biomolecules exert their actions through binding to two different receptor families, Trk and p75NTR. In this study, considering the fact that neurotrophins and their receptors play crucial roles in neural differentiation of ESCs, we sought to evaluate whether knockdown of Fndc5 decreased neural differentiation of mESCs by affecting the neurotrophins and their receptors expression. Results showed that at neural progenitor stage, the mRNA and protein levels of BDNF, Trk, and p75NTR receptors decreased following the Fndc5 knockdown. In mature neural cells, still, the expression of Trk and p75NTR receptors at mRNA and protein levels and BDNF and NGF expression only at protein levels showed a significant decrease in Fndc5 knockdown cells compared to control groups. Taken together, our results suggest that decreased efficiency of neural differentiation following the reduction of Fndc5 expression could be attributed to decreased levels of NGF and BDNF proteins in addition to their cognate receptors.

Cell-Inspired All-Aqueous Microfluidics: From Intracellular Liquid-Liquid Phase Separation toward Advanced Biomaterials

Living cells have evolved over billions of years to develop structural and functional complexity with numerous intracellular compartments that are formed due to liquid-liquid phase separation (LLPS). Discovery of the amazing and vital roles of cells in life has sparked tremendous efforts to investigate and replicate the intracellular LLPS. Among them, all-aqueous emulsions are a minimalistic liquid model that recapitulates the structural and functional features of membraneless organelles and protocells. Here, an emerging all-aqueous microfluidic technology derived from micrometer-scaled manipulation of LLPS is presented; the technology enables the state-of-art design of advanced biomaterials with exquisite structural proficiency and diversified biological functions. Moreover, a variety of emerging biomedical applications, including encapsulation and delivery of bioactive gradients, fabrication of artificial membraneless organelles, as well as printing and assembly of predesigned cell patterns and living tissues, are inspired by their cellular counterparts. Finally, the challenges and perspectives for further advancing the cell-inspired all-aqueous microfluidics toward a more powerful and versatile platform are discussed, particularly regarding new opportunities in multidisciplinary fundamental research and biomedical applications.

Synergistic Inhibition of Kinase Pathways Overcomes Resistance of Colorectal Cancer Spheroids to Cyclic Targeted Therapies

Cancer cells often adapt to single-agent treatments with chemotherapeutics. Activation of alternative survival pathways is a major mechanism of drug resistance. A potential approach to block this feedback signaling is using combination treatments of a pair of drugs, although toxicity has been a limiting factor. Preclinical tumor models to identify mechanisms of drug resistance and determine low but effective combination doses are critical to effectively suppress tumor growth with reduced toxicity to patients. Using our aqueous two-phase system microtechnology, we developed colorectal tumor spheroids in high-throughput and evaluated resistance of cancer cells to three mitogen-activated protein kinase inhibitors (MAPKi) in long-term cyclic treatments. Our quantitative analysis showed that the efficacy of MAPKi significantly reduced over time, leading to an increase in proliferation of HCT116 colorectal cancer cells and growth of spheroids. We established that resistance was due to feedback activation of PI3K/AKT/mTOR pathway. Using high-throughput, dose-dependent combinations of each MAPKi and a PI3K/mTOR inhibitor, we identified low-dose, synergistic combinations that blocked resistance to MAPKi and effectively suppressed the growth of colorectal tumor spheroids in long-term treatments. Our approach to study drug resistance offers the potential to determine high priority treatments to test in animal models.

RGD-Functionalized Nanofibers Increase Early GFAP Expression during Neural Differentiation of Mouse Embryonic Stem Cells

Stem cell differentiation toward a specific lineage is controlled by its microenvironment. Polymer scaffolds have long been investigated to provide microenvironment cues; however, synthetic polymers lack the specific signaling motifs necessary to direct cellular responses on their own. In this study, we fabricated random and aligned poly(ε-caprolactone) nanofiber substrates, surface-functionalized with RGD viastrain-promoted azide-alkyne cycloaddition, that were used to investigate the role of a covalently tethered bioactive peptide (RGD) and nanofiber orientation on neural differentiation of mouse embryonic stem cells. Gene and protein expression showed neural differentiation progression over 14 days, with similar expression on RGD random and aligned nanofibers for neurons and glia over time. The high levels of glial fibrillary acidic protein expression at early time points were indicative of neural progenitors, and occurred earlier than on controls or in previous reports. These results highlight the influence of RGD binding versus topography in differentiation.

Precision cell delivery in biphasic polymer systems enhances growth of keratinocytes in culture and promotes their attachment on acellular dermal matrices

Current approaches for precision deposition of cells are not optimized for moist environments or for substrates with complex surface topographic features, for example, the surface of dermal matrices and other biomaterials. To overcome these challenges, an approach is presented that utilizes cell confinement in phase-separating polymer solutions of polyethylene glycol and dextran to precisely deliver keratinocytes in well-defined colonies. Using this approach, keratinocyte colonies are produced with superior viability, proliferative capacity, and barrier formation compared with the same number of cells dispersedly seeded across substrate surfaces. It is further demonstrated that keratinocytes delivered in colonies to the surface of acellular dermal matrices form an intact epidermal basal layer more rapidly and more completely than cells delivered by conventional dispersed seeding. These findings demonstrate that delivery of keratinocytes in phase-separating polymer solutions holds potential for enhancing growth of keratinocytes in culture and production of functional skin equivalents.

Comparison of two different media for maturation rate of neural progenitor cells to neuronal and glial cells emphasizing on expression of neurotrophins and their respective receptors

Neural cells derived from embryonic stem cells (ESCs) have potential usefulness for the treatment of neurodegenerative disorders. Modulation of intrinsic growth factors expression such as neurotrophins and their respective receptors by these cells is necessary to obtain functional neural cells for transplantation. In present study, we compared neural differentiation potential of two different media, NB + 5%ES-FBS + N2B27 and Ko-DMEM + 5%ES-FBS for conversion of mESC derived neural progenitors (NPs) into mature neural cells with emphasis on effect of the these two media on neurotrophins and their respective receptors expression. Immunofluorescence staining, RT-qPCR and western blot analysis showed that the expression of neuronal specific markers, MAP2 and Tuj-1, in NB + 5%ES-FBS + N2B27 medium was significantly higher than the other medium. Western blot assay revealed that the expression of BDNF and NGF increased significantly in mature neural cells obtained from NB + 5%ES-FBS + N2B27 medium but decreased in neural cells from Ko-DMEM + 5%ES-FBS medium compared to mESCs. TrkB protein was not detectable in mESCs but its expression increased in neural cells obtained from both media although its expression in NB + 5%ES-FBS + N2B27 medium was significantly higher than the other medium. In contrast to TrkB, p75NTR protein was detectable in mESCs and is remained constant in neural cells cultured in NB + 5%ES-FBS + N2B27 medium but decreased significantly in the other medium. In conclusion, our results indicated that NB + 5%ES-FBS + N2B27 medium promoted neural differentiation process of mESCs and caused enhancement of neurotrophins protein expression in addition to their cognate receptors.

Teratogen screening with human pluripotent stem cells

Birth defects are a common occurrence in the United States and worldwide. Currently, evaluation of potential developmental toxicants (i.e., teratogens) relies heavily on animal-based models which do not always adequately mimic human development. In order to address this, researchers are developing in vitro human-based models which utilize human pluripotent stem cells (hPSCs) to assess the teratogenic potential of chemical substances. The field of human developmental toxicity assays includes a variety of platforms including monolayer, micropattern, embryoid body, and 3D organoid cultures. In this review, we will overview the field of human teratogenic assays, detail the most recent advances, and discuss current limitations and future perspectives.

Stem cell colony interspacing effect on differentiation to neural cells

Efforts to enhance the efficiency of neural differentiation of stem cells are primarily focused on exogenous modulation of physical niche parameters such as surface topography and extracellular matrix proteins, or addition of certain growth factors or small molecules to culture media. We report a novel neurogenic niche to enhance the neural differentiation of embryonic stem cells (ESCs) without any external intervention by micropatterning ESCs into spatially organized colonies of controlled size and interspacing. Using an aqueous two-phase system cell microprinting technology, we generated pairs of uniformly sized isolated ESC colonies at defined interspacing distances over a layer of differentiation-inducing stromal cells. Our comprehensive analysis of temporal expression of neural genes and proteins of cells in colony pairs showed that interspacing two colonies at approximately 0.66 times the colony diameter (0.66D) significantly enhanced neural differentiation of ESCs. Cells in these colonies displayed higher expression of neural genes and proteins and formed thick neurite bundles between the two colonies. A computational model of spatial distribution of soluble factors of cells in interspaced colony pairs showed that the enhanced neural differentiation is due to the presence of stable concentration gradients of soluble signalling factors between the two colonies. Our results indicate that culturing ESCs in colony pairs with defined interspacing is a promising approach to efficiently derive neural cells. Additionally, this approach provides a platform for quantitative studies of molecular mechanisms that regulate neurogenesis of stem cells.

In Vitro Microscale Models for Embryogenesis

Embryogenesis is a highly regulated developmental process requiring complex mechanical and biochemical microenvironments to give rise to a fully developed and functional embryo. Significant efforts have been taken to recapitulate specific features of embryogenesis by presenting the cells with developmentally relevant signals. The outcomes, however, are limited partly due to the complexity of this biological process. Microtechnologies such as micropatterned and microfluidic systems, along with new emerging embryonic stem cell-based models, could potentially serve as powerful tools to study embryogenesis. The aim of this article is to review major studies involving the culturing of pluripotent stem cells using different geometrical patterns, microfluidic platforms, and embryo/embryoid body-on-a-chip modalities. Indeed, new research opportunities have emerged for establishing in vitro culture for studying human embryogenesis and for high-throughput pharmacological testing platforms and disease models to prevent defects in early stages of human development.