Expanding the available assays: adapting and validating In-Cell Westerns in microfluidic devices for cell-based assays

Heterotypic tumor spheroids: a platform for nanomedicine evaluation

Nanomedicine has emerged as a promising therapeutic approach, but its translation to the clinic has been hindered by the lack of cellular models to anticipate how tumor cells will respond to therapy. Three-dimensional (3D) cell culture models are thought to more accurately recapitulate key features of primary tumors than two-dimensional (2D) cultures. Heterotypic 3D tumor spheroids, composed of multiple cell types, have become more popular than homotypic spheroids, which consist of a single cell type, as a superior model for mimicking in vivo tumor heterogeneity and physiology. The stromal interactions demonstrated in heterotypic 3D tumor spheroids can affect various aspects, including response to therapy, cancer progression, nanomedicine penetration, and drug resistance. Accordingly, to design more effective anticancer nanomedicinal therapeutics, not only tumor cells but also stromal cells (e.g., fibroblasts and immune cells) should be considered to create a more physiologically relevant in vivo microenvironment. This review aims to demonstrate current knowledge of heterotypic 3D tumor spheroids in cancer research, to illustrate current advances in utilizing these tumor models as a novel and versatile platform for in vitro evaluation of nanomedicine-based therapeutics in cancer research, and to discuss challenges, guidelines, and future directions in this field.

The In-Cell Western immunofluorescence assay to monitor PROTAC mediated protein degradation

The In-Cell Western plate-based immunofluorescence assay is a useful methodology for monitoring protein levels and provides a facile moderate through-put method for PROTAC and degrader optimization. The method is compared to other reported assays used for PROTAC development. The advantages of this method are the greater through-put compared to Western blots due to its plate-based method and the ease to transfer between cells lines. Adherent cell lines are preferred, although suspension cells can be used following recommended modifications and precautions to the protocol. This method requires a high-quality antibody that recognizes the protein epitope in its cellular context, and in general provides data similar to Western blots with higher assay through-put.

Characterization of the SIM-A9 cell line as a model of activated microglia in the context of neuropathic pain

Resident microglia of the central nervous system are being increasingly recognized as key players in diseases such as neuropathic pain. Biochemical and behavioral studies in neuropathic pain rodent models have documented compelling evidence of the critical role of ATP mediated-P2X4R-brain-derived neurotrophic factor (BDNF) signaling pathway in the initiation and maintenance of pain hypersensitivity, a feature driving neuropathic pain-related behavior. The goal of this study was to develop and characterize an in vitro cell line model of activated microglia that can be subsequently utilized for screening neuropathic pain therapeutics. In the present study, we characterized the SIM-A9 microglia cell line for key molecules in the P2X4R-BDNF signaling axis using a combination of biochemical techniques and developed an ATP-activated SIM-A9 microglia model. We present three novel findings: first, SIM-A9 cells expressed P2X4R and BDNF proteins, second, ATP, but not LPS, was cytocompatible with SIM-A9 cells and third, exposure of cells to optimized ATP concentrations for defined periods increased intracellular expression of Iba1 and BDNF proteins. Increased Iba1 levels confirmed microglia activation and increased BDNF expression confirmed ATP-mediated stimulation of the P2X4R signaling pathway. We propose that this ATP-activated SIM-A9 cell line model system can be utilized for screening both small- as well as macro-molecular neuropathic pain therapeutics targeting BDNF and/or P2X4R knockdown.

Biomicrofluidic Systems for Hematologic Cancer Research and Clinical Applications

A persistent challenge in developing personalized treatments for hematologic cancers is the lack of patient specific, physiologically relevant disease models to test investigational drugs in clinical trials and to select therapies in a clinical setting. Biomicrofluidic systems and organ-on-a-chip technologies have the potential to change how researchers approach the fundamental study of hematologic cancers and select clinical treatment for individual patient. Here, we review microfluidics cell-based technology with application toward studying hematologic tumor microenvironments (TMEs) for the purpose of drug discovery and clinical treatment selection. We provide an overview of state-of-the-art microfluidic systems designed to address questions related to hematologic TMEs and drug development. Given the need to develop personalized treatment platforms involving this technology, we review pharmaceutical drugs and different modes of immunotherapy for hematologic cancers, followed by key considerations for developing a physiologically relevant microfluidic companion diagnostic tool for mimicking different hematologic TMEs for testing with different drugs in clinical trials. Opportunities lie ahead for engineers to revolutionize conventional drug discovery strategies of hematologic cancers, including integrating cell-based microfluidics technology with machine learning and automation techniques, which may stimulate pharma and regulatory bodies to promote research and applications of microfluidics technology for drug development.

Microphysiologic systems in female reproductive biology

Microphysiologic systems (MPS), including new organ-on-a-chip technologies, recapitulate tissue microenvironments by employing specially designed tissue or cell culturing techniques and microfluidic flow. Such systems are designed to incorporate physiologic factors that conventional 2D or even 3D systems cannot, such as the multicellular dynamics of a tissue-tissue interface or physical forces like fluid sheer stress. The female reproductive system is a series of interconnected organs that are necessary to produce eggs, support embryo development and female health, and impact the functioning of non-reproductive tissues throughout the body. Despite its importance, the human reproductive tract has received less attention than other organ systems, such as the liver and kidney, in terms of modeling with MPS. In this review, we discuss current gaps in the field and areas for technological advancement through the application of MPS. We explore current MPS research in female reproductive biology, including fertilization, pregnancy, and female reproductive tract diseases, with a focus on their clinical applications. Impact statement This review discusses existing microphysiologic systems technology that may be applied to study of the female reproductive tract, and those currently in development to specifically investigate gametes, fertilization, embryo development, pregnancy, and diseases of the female reproductive tract. We focus on the clinical applicability of these new technologies in fields such as assisted reproductive technologies, drug testing, disease diagnostics, and personalized medicine.

Adaptation of a Simple Microfluidic Platform for High-Dimensional Quantitative Morphological Analysis of Human Mesenchymal Stromal Cells on Polystyrene-Based Substrates

Multipotent stromal cells (MSCs, often called mesenchymal stem cells) have garnered significant attention within the field of regenerative medicine because of their purported ability to differentiate down musculoskeletal lineages. Given the inherent heterogeneity of MSC populations, recent studies have suggested that cell morphology may be indicative of MSC differentiation potential. Toward improving current methods and developing simple yet effective approaches for the morphological evaluation of MSCs, we combined passive pumping microfluidic technology with high-dimensional morphological characterization to produce robust tools for standardized high-throughput analysis. Using ultraviolet (UV) light as a modality for reproducible polystyrene substrate modification, we show that MSCs seeded on microfluidic straight channel devices incorporating UV-exposed substrates exhibited morphological changes that responded accordingly to the degree of substrate modification. Substrate modification also effected greater morphological changes in MSCs seeded at a lower rather than higher density within microfluidic channels. Despite largely comparable trends in morphology, MSCs seeded in microscale as opposed to traditional macroscale platforms displayed much higher sensitivity to changes in substrate properties. In summary, we adapted and qualified microfluidic cell culture platforms comprising simple straight channel arrays as a viable and robust tool for high-throughput quantitative morphological analysis to study cell-material interactions.

Single cell functional analysis of multiple myeloma cell populations correlates with diffusion profiles in static microfluidic coculture systems

Microfluidic cell culture systems are becoming increasingly useful for studying biology questions, particularly those involving small cell populations that are cultured within microscale geometries mimicking the complex cellular microenvironment. Depending on the geometry and spatial organization of these cell populations, however, paracrine signaling between cell types can depend critically on spatial concentration profiles of soluble factors generated by diffusive transport. In scenarios where single cell data are acquired to study cell population heterogeneities in functional response, uncertainty associated with concentration profiles can lead to interpretation bias. To address this issue and provide important evidence on how diffusion develops within typical microfluidic cell culture systems, a combination of experimental and computational approaches were applied to measure and predict concentration patterns within microfluidic geometries, and characterize the functional response of culture cells based on single-cell resolution transcription factor activation. Using a model coculture system consisting of multiple myeloma cells (MMCs) and neighboring bone marrow stromal cells (BMSCs), we measured concentrations of three cytokines (IL-6, VEGF, and TNF-α) in conditioned media collected from separate culture compartments using a multiplex ELISA system. A 3D numerical model was developed to predict biomolecular diffusion and resulting concentration profiles within the tested microsystems and compared with experimental diffusion of 20 kDa FITC-Dextran. Finally, diffusion was further characterized by controlling exogenous IL-6 diffusion and the coculture spatial configuration of BMSCs to stimulate STAT3 nuclear translocation in MMCs. Results showed agreement between numerical and experimental results, provided evidence of a shallow concentration gradient across the center well of the microsystem that did not lead to a bias in results, and demonstrated that microfluidic systems can be tailored with specific geometries to avoid spatial bias when desired.

MicroC(3): an ex vivo microfluidic cis-coculture assay to test chemosensitivity and resistance of patient multiple myeloma cells

Chemosensitivity and resistance assays (CSRAs) aim to direct therapies based upon ex vivo responses of patient tumor cells to chemotherapeutic drugs. However, successful CSRAs are yet to be developed. Here, we exposed primary CD138(+) multiple myeloma (MM) cells to bortezomib, a clinical proteasome inhibitor, in microfluidic-cis-coculture (MicroC(3)) incorporating the patient's own CD138(-) tumor-companion mononuclear cells to integrate some of the patients' own tumor microenvironment components in the CSRA design. Statistical clustering techniques segregated MicroC(3) responses into two groups which correctly identified all seventeen patients as either clinically responsive or non-responsive to bortezomib-containing therapies. In contrast, when the same patient MM samples were analyzed in the absence of the CD138(-) cells (monoculture), the tumor cell responses did not segregate into clinical response clusters. Thus, MicroC(3) identified bortezomib-therapy MM patient responses making it a viable CSRA candidate toward enabling personalized therapy.

Microengineered tumor models: insights & opportunities from a physical sciences-oncology perspective

Prevailing evidence has established the fundamental role of microenvironmental conditions in tumorigenesis. However, the ability to identify, interrupt, and translate the underlying cellular and molecular mechanisms into meaningful therapies remains limited, due in part to a lack of organotypic culture systems that accurately recapitulate tumor physiology. Integration of tissue engineering with microfabrication technologies has the potential to address this challenge and mimic tumor heterogeneity with pathological fidelity. Specifically, this approach allows recapitulating global changes of tissue-level phenomena, while also controlling microscale variability of various conditions including spatiotemporal presentation of soluble signals, biochemical and physical characteristics of the extracellular matrix, and cellular composition. Such platforms have continued to elucidate the role of the microenvironment in cancer pathogenesis and significantly improve drug discovery and screening, particularly for therapies that target tumor-enabling stromal components. This review discusses some of the landmark efforts in the field of micro-tumor engineering with a particular emphasis on deregulated tissue organization and mass transport phenomena in the tumor microenvironment.

Real-time optical pH measurement in a standard microfluidic cell culture system

The rapid growth of microfluidic cell culturing in biological and biomedical research and industry calls for fast, non-invasive and reliable methods of evaluating conditions such as pH inside a microfluidic system. We show that by careful calibration it is possible to measure pH within microfluidic chambers with high accuracy and precision, using a direct single-pass measurement of light absorption in a commercially available phenol-red-containing cell culture medium. The measurement is carried out using a standard laboratory microscope and, contrary to previously reported methods, requires no modification of the microfluidic device design. We demonstrate the validity of this method by measuring absorption of light transmitted through 30-micrometer thick microfluidic chambers, using an inverted microscope fitted with a scientific-grade digital camera and two bandpass filters. In the pH range of 7-8, our measurements have a standard deviation and absolute error below 0.05 for a measurement volume smaller than 4 nL.

Opportunities and challenges for use of tumor spheroids as models to test drug delivery and efficacy

Multicellular spheroids are three dimensional in vitro microscale tissue analogs. The current article examines the suitability of spheroids as an in vitro platform for testing drug delivery systems. Spheroids model critical physiologic parameters present in vivo, including complex multicellular architecture, barriers to mass transport, and extracellular matrix deposition. Relative to two-dimensional cultures, spheroids also provide better target cells for drug testing and are appropriate in vitro models for studies of drug penetration. Key challenges associated with creation of uniformly sized spheroids, spheroids with small number of cells and co-culture spheroids are emphasized in the article. Moreover, the assay techniques required for the characterization of drug delivery and efficacy in spheroids and the challenges associated with such studies are discussed. Examples for the use of spheroids in drug delivery and testing are also emphasized. By addressing these challenges with possible solutions, multicellular spheroids are becoming an increasingly useful in vitro tool for drug screening and delivery to pathological tissues and organs.

Organs-on-a-chip: a focus on compartmentalized microdevices

Advances in microengineering technologies have enabled a variety of insights into biomedical sciences that would not have been possible with conventional techniques. Engineering microenvironments that simulate in vivo organ systems may provide critical insight into the cellular basis for pathophysiologies, development, and homeostasis in various organs, while curtailing the high experimental costs and complexities associated with in vivo studies. In this article, we aim to survey recent attempts to extend tissue-engineered platforms toward simulating organ structure and function, and discuss the various approaches and technologies utilized in these systems. We specifically focus on microtechnologies that exploit phenomena associated with compartmentalization to create model culture systems that better represent the in vivo organ microenvironment.

Urine analysis in microfluidic devices

Microfluidics has attracted considerable attention since its early development in the 1980s and has experienced rapid growth in the past three decades due to advantages associated with miniaturization, integration and automation. Urine analysis is a common, fast and inexpensive clinical diagnostic tool in health care. In this article, we will be reviewing recent works starting from 2005 to the present for urine analysis using microfluidic devices or systems and to provide in-depth commentary about these techniques. Moreover, commercial strips that are often treated as chips and their readers for urine analysis will also be briefly discussed. We start with an introduction to the physiological significance of various components or measurement standards in urine analysis, followed by a brief introduction to enabling microfluidic technologies. Then, microfluidic devices or systems for sample pretreatments and for sensing urinary macromolecules, micromolecules, as well as multiplexed analysis are reviewed, in this sequence. Moreover, a microfluidic chip for urinary proteome profiling is also discussed, followed by a section discussing commercial products. Finally, the authors' perspectives on microfluidic-based urine analysis are provided. These advancements in microfluidic techniques for urine analysis may improve current routine clinical practices, particularly for point-of-care (POC) applications.

Microfluidic cell culture and its application in high-throughput drug screening: cardiotoxicity assay for hERG channels

Evaluation of drug cardiotoxicity is essential to the safe development of novel pharmaceuticals. Assessing a compound's risk for prolongation of the surface electrocardiographic QT interval and hence risk for life-threatening arrhythmias is mandated before approval of nearly all new pharmaceuticals. QT prolongation has most commonly been associated with loss of current through hERG (human ether-a-go-go related gene) potassium ion channels due to direct block of the ion channel by drugs or occasionally by inhibition of the plasma membrane expression of the channel protein. To develop an efficient, reliable, and cost-effective hERG screening assay for detecting drug-mediated disruption of hERG membrane trafficking, the authors demonstrate the use of microfluidic-based systems to improve throughput and lower cost of current methods. They validate their microfluidics array platform in polystyrene (PS), cyclo-olefin polymer (COP), and polydimethylsiloxane (PDMS) microchannels for drug-induced disruption of hERG trafficking by culturing stably transfected HEK cells that overexpressed hERG (WT-hERG) and studying their morphology, proliferation rates, hERG protein expression, and response to drug treatment. Results show that WT-hERG cells readily proliferate in PS, COP, and PDMS microfluidic channels. The authors demonstrated that conventional Western blot analysis was possible using cell lysate extracted from a single microchannel. The Western blot analysis also provided important evidence that WT-hERG cells cultured in microchannels maintained regular (well plate-based) expression of hERG. The authors further show that experimental procedures can be streamlined by using direct in-channel immunofluorescence staining in conjunction with detection using an infrared scanner. Finally, treatment of WT-hERG cells with 5 different drugs suggests that PS (and COP) microchannels were more suitable than PDMS microchannels for drug screening applications, particularly for tests involving hydrophobic drug molecules.

Automated high-throughput microchannel assays for cell biology: Operational optimization and characterization

Screening biological readouts in cell culture are increasing in frequency and throughput. In such assays, cell types may be rare and reagents or compounds may be expensive often resulting in a reduced number of conditions and/or replicates. "Tubeless" microfluidics offers a method to reduce this burden, as has been previously shown.1 In addition the In Cell Western (ICW) has recently been adapted to microfluidic cultures allowing high throughput analysis of immunocytochemistry (ICC) in microfluidic channels.2 Combining automated liquid handling in tubeless microfluidics with the ICW provides rapid and quantitative high throughput cell-based screens. Here we validate this platform using three parameters: operational robustness (pipetting reliability), cell seeding consistency, and cell staining consistency (both nuclear and antibody). Integration of liquid handling with microfluidics was found to be over 97% operationally robust. Cell seeding consistency between each microchannel and within each microchannel was found to be within a standard deviation of less than 5% and 6% respectively. Finally, through optimization of liquid handling steps, uniformity between all the channels was found for both nuclear and antibody staining. These results lay the foundation to perform most standard ICW assays using automated tubeless microfluidics.