Development of an In Vitro Model to Screen CYP1B1-Targeted Anticancer Prodrugs

Cytochrome P450 1B1 (CYP1B1) is an anticancer therapeutic target due to its overexpression in a number of steroid hormone–related cancers. One anticancer drug discovery strategy is to develop prodrugs specifically activated by CYP1B1 in malignant tissues to cytotoxic metabolites. Here, we aimed to develop an in vitro screening model for CYP1B1-targeted anticancer prodrugs using the KLE human endometrial carcinoma cell line. KLE cells demonstrated superior stability of CYP1B1 expression relative to transiently transfected cells and did not express any appreciable amount of cognate CYP1A1 or CYP1A2, which would have compromised the specificity of the screening assay. The effect of two CYP1B1-targeted probe prodrugs on KLE cells was evaluated in the absence and presence of a CYP1B1 inhibitor to chemically “knock out” CYP1B1 activity (CYP1B1 inhibited). Both probe prodrugs were more toxic to KLE cells than to CYP1B1-inhibited KLE cells and significantly induced G0/G1 arrest and decreased the S phase in KLE cells. They also exhibited pro-apoptotic effects in KLE cells, which were attenuated in CYP1B1-inhibited KLE cells. In summary, a KLE cell–based model has been characterized to be suitable for identifying CYP1B1-targeted anticancer prodrugs and should be further developed and employed for screening chemical libraries.

Matrix-Based Activity Pattern Classification as a Novel Method for the Characterization of Enzyme Inhibitors Derived from High-Throughput Screening

One of the central questions in the characterization of enzyme inhibitors is determining the mode of inhibition (MOI). Classically, this is done with a number of low-throughput methods in which inhibition models are fitted to the data. The ability to rapidly characterize the MOI for inhibitors arising from high-throughput screening in which hundreds to thousands of primary inhibitors may need to be characterized would greatly help in lead selection efforts. Here we describe a novel method for determining the MOI of a compound without the need for curve fitting of the enzyme inhibition data. We provide experimental data to demonstrate the utility of this new high-throughput MOI classification method based on nonparametric analysis of the activity derived from a small matrix of substrate and inhibitor concentrations (e.g., from a 4S × 4I matrix). Lists of inhibitors from four different enzyme assays are studied, and the results are compared with the previously described IC50-shift method for MOI classification. The MOI results from this method are in good agreement with the known MOI and compare favorably with those from the IC50-shift method. In addition, we discuss some advantages and limitations of the method and provide recommendations for utilization of this MOI classification method.

Functional Characterization of Acetylcholine Receptors Expressed in Human Neurons Differentiated from Hippocampal Neural Stem/Progenitor Cells

Neurotransmission mediated by acetylcholine receptors (AChRs) plays an important role in learning and memory functions in the hippocampus. Impairment of the cholinergic system contributes to Alzheimer’s disease (AD), indicating the importance of AChRs as drug targets for AD. To improve the success rates for AD drug development, human cell models that mimic the target brain region are important. Therefore, we characterized the functional expression of nicotinic and muscarinic AChRs (nAChRs and mAChRs, respectively) in human hippocampal neurons differentiated from hippocampal neural stem/progenitor cells (HIP-009 cells). Intracellular calcium flux in 4-week differentiated HIP-009 cells demonstrated that the cells responded to acetylcholine, nicotine, and muscarine in a concentration-dependent manner (EC50 = 13.4 ± 0.5, 6.0 ± 0.4, and 35.0 ± 2.5 µM, respectively). In addition, assays using subtype-selective compounds revealed that major AD therapeutic target AChR subtypes—α7 and α4β2 nAChRs, as well as M1 and M3 mAChRs—were expressed in the cells. Furthermore, neuronal network analysis demonstrated that potentiation of M3 mAChRs inhibits the spontaneous firing of HIP-009 neurons. These results indicate that HIP-009 cells are physiologically relevant for AD drug screening and hence are loadstars for the establishment of in vitro AD models.

One-Step Seeding of Neural Stem Cells with Vitronectin-Supplemented Medium for High-Throughput Screening Assays

Human neuronal cells differentiated from induced pluripotent cells have emerged as a new model system for the study of disease pathophysiology and evaluation of drug efficacy. Differentiated neuronal cells are more similar in genetics and biological content to human brain cells than other animal disease models. However, culture of neuronal cells in assay plates requires a labor-intensive procedure of plate precoating, hampering its applications in high-throughput screening (HTS). We developed a simplified method with one-step seeding of neural stem cells in assay plates by supplementing the medium with a recombinant human vitronectin (VTN), thus avoiding plate precoating. Robust results were obtained from cell viability, calcium response, and neurite outgrowth assays using this new method. Our data demonstrate that this approach greatly simplifies high-throughput assays using neuronal cells differentiated from human stem cells for translational research.

High-Throughput Platform for Identifying Molecular Factors Involved in Phenotypic Stabilization of Primary Human Hepatocytes In Vitro

Liver disease is a leading cause of morbidity worldwide and treatment options are limited, with organ transplantation being the only form of definitive management. Cell-based therapies have long held promise as alternatives to whole-organ transplantation but have been hindered by the rapid loss of liver-specific functions over a period of days in cultured hepatocytes. Hypothesis-driven studies have identified a handful of factors that modulate hepatocyte functions in vitro, but our understanding of the mechanisms involved remains incomplete. We thus report here the development of a high-throughput platform to enable systematic interrogation of liver biology in vitro. The platform is currently configured to enable genetic knockdown screens and includes an enzyme-linked immunosorbent assay–based functional assay to quantify albumin output as a surrogate marker for hepatocyte synthetic functions as well as an image-based viability assay that counts hepatocyte nuclei. Using this platform, we identified 12 gene products that may be important for hepatocyte viability and/or liver identity in vitro. These results represent important first steps in the elucidation of mechanisms instrumental to the phenotypic maintenance of hepatocytes in vitro, and we hope that the tools reported here will empower additional studies in various fields of liver research.

Functional Comparison of Neuronal Cells Differentiated from Human Induced Pluripotent Stem Cell–Derived Neural Stem Cells under Different Oxygen and Medium Conditions

Because neurons are difficult to obtain from humans, generating functional neurons from human induced pluripotent stem cells (hiPSCs) is important for establishing physiological or disease-relevant screening systems for drug discovery. To examine the culture conditions leading to efficient differentiation of functional neural cells, we investigated the effects of oxygen stress (2% or 20% O2) and differentiation medium (DMEM/F12:Neurobasal-based [DN] or commercial [PhoenixSongs Biologicals; PS]) on the expression of genes related to neural differentiation, glutamate receptor function, and the formation of networks of neurons differentiated from hiPSCs (201B7) via long-term self-renewing neuroepithelial-like stem (lt-NES) cells. Expression of genes related to neural differentiation occurred more quickly in PS and/or 2% O2 than in DN and/or 20% O2, resulting in high responsiveness of neural cells to glutamate, N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and ( S)-3,5-dihydroxyphenylglycine (an agonist for mGluR1/5), as revealed by calcium imaging assays. NMDA receptors, AMPA receptors, mGluR1, and mGluR5 were functionally validated by using the specific antagonists MK-801, NBQX, JNJ16259685, and 2-methyl-6-(phenylethynyl)-pyridine, respectively. Multielectrode array analysis showed that spontaneous firing occurred earlier in cells cultured in 2% O2 than in 20% O2. Optimization of O2 tension and culture medium for neural differentiation of hiPSCs can efficiently generate physiologically relevant cells for screening systems.

Combining Unique Multiplex Gateway Cloning and Bimolecular Fluorescence Complementation (BiFC) for High-Throughput Screening of Protein–Protein Interactions

Protein interaction networks are the basis for human metabolic and signaling systems. Interaction studies often use bimolecular fluorescence complementation (BiFC) to reveal the formation and cellular localization of protein complexes. However, large-scale studies were either far from native conditions in human cells or limited by laborious restriction/ligation cloning techniques. Here, we describe a new tool for protein interaction screening based on Gateway-compatible BiFC vectors. We made a set of four new vectors that permit fusion of candidate proteins to the N or C fragment of Venus in all fusion positions. We have validated the vectors and confirmed self-association of AHCY, AHCYL1, and galectin-3. In a high-throughput BiFC screen, we identified new AHCY interaction partners: galectin-3 and PUS7L. We also describe additional steps in protein interaction analysis, applied for AHCY–galectin-3 interaction. First, we classified the interaction in intracellular vesicles using CellCognition, machine learning free software. Then we identified the vesicles as endosomal pathway compartments, in line with known galectin-3 trafficking route. This offers a platform to rapidly identify and localize new protein interactions inside living cells, a prerequisite to validate in silico interactome data, and ultimately decode complex protein networks.

Rethinking Nuclear Receptors as Potential Therapeutic Targets for Retinal Diseases

Collectively, retinal diseases, including age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy, result in severe vision impairment worldwide. The absence and/or limited availability of successful drug therapies for these blinding disorders necessitates further understanding their pathobiology and identifying new targetable signaling pathways. Nuclear receptors are transcription regulators of many key aspects of human physiology, as well as pathophysiology, with reported roles in development, aging, and disease. Some of the pathways regulated by nuclear receptors include, but are not limited to, angiogenesis, inflammation, and lipid metabolic dysregulation, mechanisms also important in the initiation and development of several retinal diseases. Herein, we present an overview of the biology of three diseases affecting the posterior eye, summarize a growing body of evidence that suggests direct or indirect involvement of nuclear receptors in disease progression, and discuss the therapeutic potential of targeting nuclear receptors for treatment.