High-Content Screening Analysis of the p38 Pathway: Profiling of Structurally Related p38α Kinase Inhibitors Using Cell-Based Assays

Activation of the P38/CREB/MMP13 axis is associated with osteoarthritis

Purposes

Osteoarthritis (OA) is a common joint disease characterized by the degradation of articular cartilage and joint inflammation. Interleukin-1ß induces P38/cAMP response element binding protein (CREB) pathway activation, resulting in increased expression of matrix metallopeptidase-13 (MMP13) in chondrocytes. However, the role of the P38/CREB/MMP13 axis is unclear in the progression of OA. In this study, we aimed to answer the following questions: (1) how does the P38/CREB/MMP13 axis in cartilage from patients with OA compare with control specimens? (2) Can the P38 agonist anisomycin (ANS) induce mouse OA?

Materials and methods

Surgical specimens of human cartilage were divided into OA and control groups. Surgical specimens of mouse cartilage were divided into control and ANS-induced groups. Safranin O staining of the cartilage tissues was performed to evaluate the extracellular matrix. Reverse transcription-polymerase chain reaction was performed using these tissues to investigate messenger RNA expressions of type II collagen, aggrecan, MMP13, and ADAM metallopeptidase with thrombospondin type 1 motif 5. Phosphorylated (p)-P38, p-CREB, and MMP13 were evaluated by Western blot analysis. Anisomycin was used to activate P38, and p-P38, p-CREB, and MMP13 were evaluated by immunofluorescence and Western blot analysis.

Results

Safranin O staining showed that the extracellular matrix degraded in humans with OA and ANS-induced mouse cartilage samples. The expressions of p-P38, p-CREB, and MMP13 were all upregulated in osteoarthritic cartilage or anisomycin-induced chondrocytes, suggesting that the P38/CREB/MMP13 axis may play a role in the progression of OA.

Conclusions

The P38/CREB/MMP13 axis is active in osteoarthritic chondrocytes and may cause the degeneration of cartilage. Effective new therapy directed against this pathway could be developed.

The development of high-content screening (HCS) technology and its importance to drug discovery

INTRODUCTION

High-content screening (HCS) was introduced about twenty years ago as a promising analytical approach to facilitate some critical aspects of drug discovery. Its application has spread progressively within the pharmaceutical industry and academia to the point that it today represents a fundamental tool in supporting drug discovery and development.

AREAS COVERED

Here, the authors review some of significant progress in the HCS field in terms of biological models and assay readouts. They highlight the importance of high-content screening in drug discovery, as testified by its numerous applications in a variety of therapeutic areas: oncology, infective diseases, cardiovascular and neurodegenerative diseases. They also dissect the role of HCS technology in different phases of the drug discovery pipeline: target identification, primary compound screening, secondary assays, mechanism of action studies and in vitro toxicology.

EXPERT OPINION

Recent advances in cellular assay technologies, such as the introduction of three-dimensional (3D) cultures, induced pluripotent stem cells (iPSCs) and genome editing technologies (e.g., CRISPR/Cas9), have tremendously expanded the potential of high-content assays to contribute to the drug discovery process. Increasingly predictive cellular models and readouts, together with the development of more sophisticated and affordable HCS readers, will further consolidate the role of HCS technology in drug discovery.

From Enzyme to Whole Blood: Sequential Screening Procedure for Identification and Evaluation of p38 MAPK Inhibitors

p38 mitogen-activated protein kinase (MAPK) is a pivotal enzyme in the biosynthesis of pro-inflammatory cytokines like IL-1 and TNF. Therefore, the success of anti-cytokine therapy for treatment of inflammatory processes qualified p38-MAPK as a solid target in drug research concerning chronic inflammatory diseases including infectious vascular, neurobiological, and autoimmune disorders. However, the discovery of new kinase inhibitors is limited by the need for a high biological activity combined with restricted activity to the target enzyme or pathway interaction. As a consequence, no p38 MAPK inhibitor has been introduced to the market so far, although several p38 inhibitors have proceeded into clinical trials. The development of novel inhibitor types and optimization of already known structural classes of MAPK inhibitors require appropriate testing systems reaching across these crucial parameters. As a new approach, we describe the sequential arrangement of three testing systems custom-tailored to the requirements of drug discovery programs with focus on p38 inhibition. Integrated analysis of the obtained results enables a concerted step-by-step selection of tested molecules in order to screen a compound library for the most suitable inhibitor. First, evaluation of the inhibitor's activity on the isolated p38 MAPK enzyme via an ELISA assay gives a first idea about the inhibitory potency of the molecule. Moreover, structure-activity relationships can be elucidated when comparing molecules within inhibitor series. Second, screening in living cells via a p38 substrate-specific MK2-EGFP translocation assay supplies further information about efficacy, but provides also a first notion concerning selectivity and toxicity. Third, efficacy is evaluated more specifically in vivo in LPS-stimulated human whole blood with regard to in vivo parameters, e.g., pharmacokinetic characteristics like plasma protein binding and cellular permeability. These three testing systems complement one another synergistically by providing a high overlap and predictability. Clear advantages of all presented systems are their realizability in an academic environment as well as their applicability for high-throughput screenings on a larger scale.

A p38 substrate-specific MK2-EGFP translocation assay for identification and validation of new p38 inhibitors in living cells: a comprising alternative for acquisition of cellular p38 inhibition data

The fundamental role of p38 mitogen-activated protein kinases (MAPKs) in inflammation underlines their importance as therapeutic targets for various inflammatory medical conditions, including infectious, vascular, neurobiological and autoimmune disease. Although decades of research have yielded several p38 inhibitors, most clinical trials have failed, due to lack of selectivity and efficacy in vivo. This underlines the continuous need to screen for novel structures and chemotypes of p38 inhibitors. Here we report an optimized MK2-EGFP translocation assay in a semi-automated image based High Content Analysis (HCA) system to screen a combinatorial library of 3362 proprietary compounds with extensive variations of chemotypes. By determining the levels of redistribution of MK2-EGFP upon activation of the Rac/p38 pathway in combination with compound treatment, new candidates were identified, which modulate p38 activity in living cells. Based on integrated analysis of TNFα release from human whole blood, biochemical kinase activity assays and JNK3 selectivity testing, we show that this cell based assay reveals a high overlap and predictability for cellular efficacy, selectivity and potency of tested compounds. As a result we disclose a new comprehensive short-list of subtype inhibitors which are functional in the low nanomolar range and might provide the basis for further lead-optimization. In accordance to previous reports, we demonstrate that the MK2-EGFP translocation assay is a suitable primary screening approach for p38-MAPK drug development and provide an attractive labor- and cost saving alternative to other cell based methods including determination of cytokine release from hPBMCs or whole blood.

Increasing the Content of High-Content Screening: An Overview

Target-based high-throughput screening (HTS) has recently been critiqued for its relatively poor yield compared to phenotypic screening approaches. One type of phenotypic screening, image-based high-content screening (HCS), has been seen as particularly promising.

In this article, we assess whether HCS is as high content as it can be. We analyze HCS publications and find that although the number of HCS experiments published each year continues to grow steadily, the information content lags behind. We find that a majority of high-content screens published so far (60−80%) made use of only one or two image-based features measured from each sample and disregarded the distribution of those features among each cell population. We discuss several potential explanations, focusing on the hypothesis that data analysis traditions are to blame. This includes practical problems related to managing large and multidimensional HCS data sets as well as the adoption of assay quality statistics from HTS to HCS. Both may have led to the simplification or systematic rejection of assays carrying complex and valuable phenotypic information.

We predict that advanced data analysis methods that enable full multiparametric data to be harvested for entire cell populations will enable HCS to finally reach its potential.

High-content single-cell analysis on-chip using a laser microarray scanner

High-content cellomic analysis is a powerful tool for rapid screening of cellular responses to extracellular cues and examination of intracellular signal transduction pathways at the single-cell level. In conjunction with microfluidics technology that provides unique advantages in sample processing and precise control of fluid delivery, it holds great potential to transform lab-on-a-chip systems for high-throughput cellular analysis. However, high-content imaging instruments are expensive, sophisticated, and not readily accessible. Herein, we report on a laser scanning cytometry approach that exploits a bench-top microarray scanner as an end-point reader to perform rapid and automated fluorescence imaging of cells cultured on a chip. Using high-content imaging analysis algorithms, we demonstrated multiplexed measurements of morphometric and proteomic parameters from all single cells. Our approach shows the improvement of both sensitivity and dynamic range by two orders of magnitude as compared to conventional epifluorescence microscopy. We applied this technology to high-throughput analysis of mesenchymal stem cells on an extracellular matrix protein array and characterization of heterotypic cell populations. This work demonstrates the feasibility of a laser microarray scanner for high-content cellomic analysis and opens up new opportunities to conduct informative cellular analysis and cell-based screening in the lab-on-a-chip systems.

Differential effects of p38MAP kinase inhibitors on the expression of inflammation-associated genes in primary, interleukin-1beta-stimulated human chondrocytes

BACKGROUND AND PURPOSE

A main challenge in the therapy of osteoarthritis (OA) is the development of drugs that will modify the disease. Reliable test systems are necessary to enable an efficient screening of therapeutic substances. We therefore established a chondrocyte-based in vitro cell culture model in order to characterize different p38MAPK inhibitors.

EXPERIMENTAL APPROACH

Interleukin-1beta (IL-1beta)-stimulated human OA chondrocytes were treated with the p38MAPK inhibitors Birb 796, pamapimod, SB203580 and the new substance CBS-3868. Birb 796- and SB203580-treated cells were analysed in a genome-wide microarray analysis. The efficacy of all inhibitors was characterized by quantitative gene expression analysis and the quantification of PGE(2) and NO release.

KEY RESULTS

Microarray analysis revealed inhibitor-specific differences in gene expression. Whereas SB203580 had a broad effect on chondrocytes, Birb 796 counteracted the IL-1beta effect more specifically. All p38MAPK inhibitors significantly inhibited the IL-1beta-induced gene expression of COX-2, mPGES1, iNOS, matrix metalloproteinase 13 (MMP13) and TNFRSF11B, as well as PGE(2) release. Birb 796 and CBS-3868 showed a higher efficacy than SB203580 and pamapimod at inhibiting the expression of COX-2 and MMP13 genes, as well as PGE(2) release. In the case of mPGES1 and TNFRSF11B gene expression, CBS-3868 exceeded the efficacy of Birb 796.

CONCLUSIONS AND IMPLICATIONS

Our test system could differentially characterize inhibitors of the same primary pharmaceutical target. It reflects processes relevant in OA and is based on chondrocytes that are mainly responsible for cartilage degradation. It therefore represents a valuable tool for drug screening in between functional in vitro testing and in vivo models.

Adherent cell assay results affected by variable z-position mixing

We demonstrate that modifying mixing dynamics after addition of organic solute into aqueous buffers dramatically affects cell morphology and protein expression. Variable z-position (VZP) or varying the height of aspiration and dispense positions during mixing eliminates artifactual effects. Here, we tested 4 adherent cell types and show effects of VZP on quantitative imaging, protein expression, viability, and morphology. The result: The quantitation of cytoplasmic fluorescence within the fields of interest of the phalloidin-actin stain assay improved by 47% and fluorescence variability emitted by cells expressing green fluorescence protein (GFP) fusion proteins decreased by 15%. Assays that perform measurement by averaged reading of the entire well are somewhat susceptible. For example, protein production decreased 8% on the hypoxia response element (HRE)-luciferase assay. VZP did not affect quantitative cell viability, deviate the half maximal effective dose concentration (EC(50)) values or alter expected curve patterns. VZP is a valuable systematic process for cellular assay workflows as it efficiently folds organic solute into the aqueous solution.

Review Article: High-Content Screening: A Decade of Evolution

In the past decade, high-content screening has become a highly developed approach to obtaining richly descriptive quantitative phenotypic data using automated microscopy. From early use in drug screening, the technique has evolved to embrace a diverse range of applications in both academic and industrial sectors and is now widely recognized as providing an efficient and effective approach to large-scale programs investigating cell biology in situ and in context.

Applications of high content screening in life science research

Over the last decade, imaging as a detection mode for cell based assays has opened a new world of opportunities to measure "phenotypic endpoints" in both current and developing biological models. These "high content" methods combine multiple measurements of cell physiology, whether it comes from sub-cellular compartments, multicellular structures, or model organisms. The resulting multifaceted data can be used to derive new insights into complex phenomena from cell differentiation to compound pharmacology and toxicity. Exploring the major application areas through review of the growing compendium of literature provides evidence that this technology is having a tangible impact on drug discovery and the life sciences.

IFN-gamma reverses IL-2- and IL-4-mediated T-cell steroid resistance

Corticosteroids are the most common therapeutic approach for control of tissue inflammation. Combination IL-2/IL-4 is known to induce T-cell steroid resistance. This can be reversed with IFN-gamma; however, the mechanism by which this occurs is unknown. In the current study, we found that treatment of peripheral blood mononuclear cells with combination IL-2/IL-4 for 48 hours, but not with IL-2 or IL-4 alone, abrogated dexamethasone (DEX)-induced glucocorticoid receptor (GCR)-alpha nuclear translocation in both CD4(+) and CD8(+) T cells. The presence of IL-4 significantly down-regulated IFN-gamma production by IL-2-stimulated cells. Importantly, addition of IFN-gamma to the IL-2/IL-4 combination restored GCRalpha nuclear translocation in response to DEX. Furthermore, DEX-induced mitogen-activated protein kinase (MAPK) phosphatase-1 induction, used as a readout for corticosteroid-induced transactivation, was significantly greater (P < 0.05) in media and IL-2/IL-4/IFN-gamma-treated conditions compared with IL-2/IL-4-treated cells. The combination of IL-2/IL-4 induced p38 MAPK activation in CD3(+) cells (30.5 +/- 5.7% cells expressed phospho-p38 MAPK versus no phospho-p38 MAPK expression after media treatment). The presence of the p38 MAPK inhibitor, SB203580, or IFN-gamma inhibited p38 MAPK phosphorylation and enhanced GCRalpha nuclear translocation in response to DEX. These data indicate that combination IL-2/IL-4 inhibits GCRalpha nuclear translocation in human T cells, and this effect is reversed by IFN-gamma via inhibition of p38 MAPK activation.

Biphenyl amide p38 kinase inhibitors 4: DFG-in and DFG-out binding modes

The biphenyl amides (BPAs) are a series of p38alpha MAP kinase inhibitors. Compounds are able to bind to the kinase in either the DFG-in or DFG-out conformation, depending on substituents. X-ray, binding, kinetic and cellular data are shown, providing the most detailed comparison to date between potent compounds from the same chemical series that bind to different p38alpha conformations. DFG-out-binding compounds could be made more potent than DFG-in-binding compounds by increasing their size. Unexpectedly, compounds that bound to the DGF-out conformation showed diminished selectivity. The kinetics of binding to the isolated enzyme and the effects of compounds on cells were largely unaffected by the kinase conformation bound.

High-throughput screening assays for the identification of chemical probes

High-throughput screening (HTS) assays enable the testing of large numbers of chemical substances for activity in diverse areas of biology. The biological responses measured in HTS assays span isolated biochemical systems containing purified receptors or enzymes to signal transduction pathways and complex networks functioning in cellular environments. This Review addresses factors that need to be considered when implementing assays for HTS and is aimed particularly at investigators new to this field. We discuss assay design strategies, the major detection technologies and examples of HTS assays for common target classes, cellular pathways and simple cellular phenotypes. We conclude with special considerations for configuring sensitive, robust, informative and economically feasible HTS assays.