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A bichromatic fluorescent reporter for cell-based screens of alternative splicing.

Alternative splicing is the primary source of proteome complexity in metazoans and its regulation shapes the proteome in response to shifting physiological requirements. We developed a bichromatic splicing reporter that uses a peculiar feature of some fluorescent protein coding regions to express two different fluorescent proteins from a single alternative splicing event. The mutually exclusive expression of different fluorescent proteins from a single reporter provides a uniquely sensitive approach for high-throughput screening and analysis of cell-specific splicing events in mixed cell cultures and tissues of transgenic animals. This reporter is applicable to the majority of alternative splicing patterns and can be used to quantify alternative splicing within single cells and to select cells that express specific splicing patterns. The ability to perform quantitative single-cell analysis of alternative splicing and high-throughput screens will enhance progress toward understanding splicing regulatory networks and identifying compounds that reverse pathogenic splicing defects.

Alternative Splicing↗

Ribonuclease activity of vaccinia DNA topoisomerase IB: kinetic and high-throughput inhibition studies using a robust continuous fluorescence assay.

Vaccinia type I DNA topoisomerase exhibits a strong site-specific ribonuclease activity when provided a DNA substrate that contains a single uridine ribonucleotide within a duplex DNA containing the sequence 5' CCCTU 3'. The reaction involves two steps: attack of the active site tyrosine nucleophile of topo I at the 3' phosphodiester of the uridine nucleotide to generate a covalent enzyme-DNA adduct, followed by nucleophilic attack of the uridine 2'-hydroxyl to release the covalently tethered enzyme. Here we report the first continuous spectroscopic assay for topoisomerase that allows monitoring of the ribonuclease reaction under multiple-turnover conditions. The assay is especially robust for high-throughput screening applications because sensitive molecular beacon technology is utilized, and the topoisomerase is released during the reaction to allow turnover of multiple substrate molecules by a single molecule of enzyme. Direct computer simulation of the fluorescence time courses was used to obtain the rate constants for substrate binding and release, covalent complex formation, and formation of the 2',3'-cyclic phosphodiester product of the ribonuclease reaction. The assay allowed rapid screening of a 500 member chemical library from which several new inhibitors of topo I were identified with IC(50) values in the range of 2-100 microM. Three of the most potent hits from the high-throughput screening were also found to inhibit plasmid supercoil relaxation by the enzyme, establishing the utility of the assay in identifying inhibitors of the biologically relevant DNA relaxation reaction. One of the most potent inhibitors of the vaccinia enzyme, 3-benzo[1,3]dioxol-5-yl-2-oxoproprionic acid, did not inhibit the closely related human enzyme. The inhibitory mechanism of this compound is unique and involves a step required for recycling the enzyme for steady-state turnover.

Anisotropy↗

Targeting hepatocyte-specific SLC2A8 blocks hepatic steatosis and dissociates TCA cycle flux inhibition from glutamine anaplerosis.

BACKGROUND: Excess TCA cycle and glutamine anaplerosis are hallmarks of metabolic dysfunction-associated steatotic liver disease and steatohepatitis. Blocking glutamine metabolism attenuates metabolic dysfunction-associated steatohepatitis. However, inhibiting TCA cycle flux by blocking plasma membrane carbohydrate transport is limited by the ubiquitous tissue distribution, function, and homology among the SLC2A family of facilitative carbohydrate transporters, and the potential for carbohydrate blockade to invoke or exacerbate glutamine anaplerosis. Here, we quantify alterations in hepatocyte carbon flux, define the broader metabolic consequences of hepatocyte-specific GLUT8/SLC2A8 inhibition, and delineate the antisteatotic efficacy of a novel small-molecule GLUT8-selective inhibitor. METHODS: We generated mice with floxed SLC2A8 alleles and expressed hepatocyte-specific Cre by breeding these mice with albumin-Cre transgenic mice, or by administering AAV8 encoding hepatocyte-specific iCre. We performed stable-isotope glucose, fructose, and glutamine metabolic labeling in isolated GLUT8WT and GLUT8LKO hepatocytes and performed metabolic phenotyping in lean and diet-induced obese GLUT8WT and GLUT8LKO mice. Finally, we performed high-throughput screening to identify a GLUT8-selective inhibitor, which we characterized using in vitro models of triglyceride accumulation. RESULTS: Hepatocyte-specific SLC2A8 deletion reduced diet-induced hepatic and peripheral fat accumulation and increased thermogenesis during ZT12-24 (eg, the dark phase). It also disrupted TCA cycle flux without inducing compensatory glutamine utilization. High-throughput screening identified a small-molecule, GLUT8-selective inhibitor, P20, which blocked hepatocyte TG accumulation and inflammation in in vitro steatotic and inflammatory models. CONCLUSIONS: Deleting the hepatocyte carbohydrate transporter GLUT8 suppresses TCA cycle flux without inducing compensatory glutamine anaplerosis. The net effect of this is liver protection against multiple forms of dietary insult. Given that selective pharmacological GLUT8 inhibition is feasible, GLUT8 may be a viable target to abate metabolic dysfunction-associated steatohepatitis and other complications of obesity.

Animals↗

Pharmacophore features distributions in different classes of compounds.

A pharmacophore analysis approach was used to investigate and compare different classes of compounds relevant to the drug discovery process (specifically, drug molecules, compounds in high throughput screening libraries, combinatorial chemistry building blocks and nondrug molecules). The distributions for a set of pharmacophore features including hydrogen bond acceptors, hydrogen bond donors, negatively ionizable centers, positively ionizable centers and hydrophobic points, were generated and examined. Significant differences were observed between the pharmacophore profiles obtained for the drug molecules and those obtained for the high-throughput screening compounds, which appear to be closely related to the nondrug pharmacophore distribution. It is suggested that the analysis of pharmacophore profiles could be used as an additional tool for the property-based optimization of compound selection and library design processes, thus improving the odds of success in lead discovery projects.

Journal Article↗

Inventory management and reagent supply for automated chemistry.

Developments in automated chemistry have kept pace with developments in HTS such that hundreds of thousands of new compounds can be rapidly synthesized in the belief that the greater the number and diversity of compounds that can be screened, the more successful HTS will be. The increasing use of automation for Multiple Parallel Synthesis (MPS) and the move to automated combinatorial library production is placing an overwhelming burden on the management of reagents. Although automation has improved the efficiency of the processes involved in compound synthesis, the bottleneck has shifted to ordering, collating and preparing reagents for automated chemistry resulting in loss of time, materials and momentum. Major efficiencies have already been made in the area of compound management for high throughput screening. Most of these efficiencies have been achieved with sophisticated library management systems using advanced engineering and data handling for the storage, tracking and retrieval of millions of compounds. The Automation Partnership has already provided many of the top pharmaceutical companies with modular automated storage, preparation and retrieval systems to manage compound libraries for high throughput screening. This article describes how these systems may be implemented to solve the specific problems of inventory management and reagent supply for automated chemistry.

Automation↗

JX401, A p38alpha inhibitor containing a 4-benzylpiperidine motif, identified via a novel screening system in yeast.

In vivo screening of compounds for potential pharmacological activity is more advantageous than in vitro screening. In vivo screens eliminate the isolation of compounds that cannot cross biological membranes, are cytotoxic, or are not specific to the target. However, animal-based or even cell-based systems are usually expensive, time-consuming, and laborious. Here we describe the identification of inhibitors of the mitogen-activated protein kinase p38alpha via a high throughput screen using yeast cells. p38alpha is hyperactive in inflammatory diseases, and various indications suggest that its inhibition would reverse inflammation. However, there are currently no p38alpha inhibitors in clinical use. Because the human p38alpha imposes severe growth retardation when expressed in yeast, we screened a library of 40,000 randomly selected small molecules for compounds that would restore a normal growth rate. We identified two compounds; both share a structural motif of 4-benzylpiperidine, and both were shown to be efficient and selective p38alpha inhibitors in vitro. They were also active in mammalian cells, as manifested by their ability to reversibly inhibit myoblast differentiation. Thus, the yeast screen identified efficient and specific p38alpha inhibitors that are capable of crossing biological membranes, are not toxic, and function in mammalian cells. The rapid and cost-efficient high-throughput screening used here could be applied for isolation of inhibitors of various targets.

Amino Acid Motifs↗

A multiparameter screening assay to assess the cytokine-induced expression of endothelial cell adhesion molecules.

Compounds which inhibit endothelial cell inflammatory responses are believed to be of therapeutic value. The cell adhesion molecules E-selectin, ICAM-1, and VCAM-1 play important roles in inflammatory reactions by mediating leukocyte-endothelial interactions. To identify compounds which inhibit the expression of these adhesion molecules following cytokine stimulation we developed an assay which measures E-selectin, ICAM-1, and VCAM-1 in the same experiment. For this, we have taken advantage of the technology of time-resolved fluorimetry, which allows detection of several parameters in parallel, employing anti-E-selectin antibody labeled with europium, and anti-ICAM-1 and anti-VCAM-1 labeled with samarium and terbium, respectively. These antibodies were used to detect the respective antigens in human endothelial cells stimulated with TNFalpha or IL-1beta. In cross-competition assays these antibodies were found to bind specifically to TNF- or IL-1-stimulated cells. This assay, in which three parameters are measured in the same experiment, proved to be robust with signal to noise ratios of 25-35 for E-Selectin, 4-8 for ICAM-1, and 3-9 for VCAM-1. The assay proved to be reproducible in high-throughput screening. The experience with this assay demonstrates that multiple parameters can be measured in an enzyme-linked immunosorbent assay-type assay on cells by using time-resolved fluorimetry. The possibility of obtaining several parameters from one experiment is feasible under high-throughput screening conditions and is of interest for other experimental setups in which the simultaneous measurement of several parameters is desired.

Antibodies↗

Genetic markers for retinitis pigmentosa.

OBJECTIVE: To review recent advances in the molecular genetics of retinitis pigmentosa with emphasis on the development of genetic markers that aids diagnosis and prognosis. DATA SOURCES AND EXTRACTION: Literature search of MEDLINE from 1988 to 2005 using the following key words: 'retinitis pigmentosa', 'rhodopsin', 'RP1', 'RPGR', and 'genetic counseling'. References of two genes--RHO and RP1--causing retinitis pigmentosa in the Chinese population were reviewed. STUDY SELECTION: Literature and data related to genetic markers for retinitis pigmentosa. DATA SYNTHESIS: The genetics of retinitis pigmentosa is complex. It can be sporadic or familial, with heterogeneous transmission modes. Retinitis pigmentosa is associated with nearly 40 chromosomal loci, where 32 candidate genes have been identified. A large number of mutations are known to cause retinitis pigmentosa. But no single mutation alone accounts for more than 10% of unrelated retinitis pigmentosa patients. Genetic tests for retinitis pigmentosa require screening for a consort of mutations in a large number of genes. High throughput screening technology such as denaturing high performance liquid chromatography and automated DNA sequencing should make such tests feasible. CONCLUSIONS: Rapid developments in the understanding of the genetics of retinitis pigmentosa have helped to establish genetic tests of clinical value. The complex mode of inheritance nonetheless makes genetic counselling difficult, even in the presence of positive genetic screening results.

Chromosome Mapping↗

A scalable high-content cytotoxicity assay insensitive to changes in mitochondrial metabolic activity.

Quantitative assessments of cell proliferation and cytotoxicity are key components of anticancer drug discovery. Advancements in genomics and combinatorial chemistry have increased the demand for cytotoxicity measurements, and almost all assays for cell proliferation that are compatible with high-throughput screening are single-parameter, homogeneous biochemical assays. Furthermore, the most popular methods currently in use are based on measurements of mitochondrial activity and therefore provide only an indirect measure of cell growth. Here we describe a high-content screening (HCS) methodology that permits the direct quantification of cell numbers as well as multiple measurements of drug activity in individual cells without the ambiguities of previously described homogenous metabolism-based assays. Using two human tumor cell lines, we compared our HCS method with a commonly used homogenous colorimetric assay that detects mitochondrial activity and found the colorimetric assay substantially underrepresented the cytotoxic effects of two mechanistically diverse, clinically used, anticancer drugs: a DNA-damaging agent, bleomycin, and a tubulin stabilizer, paclitaxel. Simultaneous evaluation of cell numbers, mitochondrial mass, and nuclear morphology by HCS provided an explanation for the differential toxicity. Furthermore, we expanded the scope of the HCS assay to include tubulin mass measurements in paclitaxel-treated cells as an example for a specific drug target. The data illustrate the utility of HCS as a powerful analysis tool compatible with the demands of high-throughput screening, and adaptable to include fluorescence-based markers of drug activity.

Antineoplastic Agents↗

Imaging Tetrahymena ribozyme splicing activity in single live mammalian cells.

Tetrahymena ribozymes hold promise for repairing genetic disorders but are largely limited by their modest splicing efficiency and low production of final therapeutic proteins. Ribozyme evolution in intact living mammalian cells would greatly facilitate the discovery of new ribozyme variants with high in vivo activity, but no such strategies have been reported. Here we present a study using a new reporter enzyme, beta-lactamase, to report splicing activity in single living cells and perform high-throughput screening with flow cytometry. The reporter ribozyme constructs consist of the self-splicing Tetrahymena thermophila group I intron ribozyme that is inserted into the ORF of the mRNA of beta-lactamase. The splicing activity in single living cells can be readily detected quantitatively and visualized. Individual cells have shown considerable heterogeneity in ribozyme activity. Screening of Tetrahymena ribozymes with insertions in the middle of the L1 loop led to identification of better variants with at least 4-fold more final in vivo activity than the native sequence. Our work has provided a new reporter system that allows high-throughput screening with flow cytometry of single living mammalian cells for a direct and facile in vivo selection of desired ribozyme variants.

Animals↗

Application of parallel liquid chromatography/mass spectrometry for high throughput microsomal stability screening of compound libraries.

Solution-phase and solid-phase parallel synthesis and high throughput screening have enabled biologically active and selective compounds to be identified at an unprecedented rate. The challenge has been to convert these hits into viable development candidates. To accelerate the conversion of these hits into lead development candidates, early assessment of the physicochemical and pharmacological properties of these compounds is being made. In particular, in vitro absorption, distribution, metabolism, and elimination (ADME) assays are being conducted at earlier and earlier stages of discovery with the goal of reducing the attrition rate of these potential drug candidates as they progress through development. In this report, we present an eight-channel parallel liquid chromatography/mass spectrometry (LC/MS) system in combination with custom Visual Basic and Applescript automated data processing applications for high throughput early ADME. The parallel LC/MS system was configured with one set of gradient LC pumps and an eight-channel multiple probe autosampler. The flow was split equivalently into eight streams before the multiple probe autosampler and recombined after the eight columns and just prior to the mass spectrometer ion source. The system was tested for column-to-column variation and for reproducibility over a 17 h period (approximately 500 injections per column). The variations in retention time and peak area were determined to be less than 2 and 10%, respectively, in both tests. The parallel LC/MS system described permits time-course microsomal incubations (t(o), t5, t15, t30) to be measured in triplicate and enables estimations of t 1/2 microsomal stability. The parallel LC/MS system is capable of analyzing up to 240 samples per hour and permits the complete profiling up to two microtiter plates of compounds per day (i.e., 176 test substrate compounds + sixteen controls).

Chromatography, High Pressure Liquid↗

Parallel analysis of v-Src mutant protein function using reverse transfection cell arrays.

The conversion of the genomic information produced by the recent sequencing projects into a comprehensive understanding of the human proteome has yet to occur. A new technology that represents a potential bridge between genomics and proteomics is reverse transfection. Reverse transfection cell microarrays are produced by overlaying cDNA arrays with mammalian cells, generating localized clusters of transfected cells with each cluster overexpressing a unique protein. This miniaturized cell-based microarray format affords parallel functional analysis of thousands of cDNA constructs in a high throughput format. In this report we document the development of a co-transfection methodology for reverse transfection applications. The demonstrated high co-transfection efficiency with a "marker" plasmid encoding for GFP enables the identification of transfected cells and eliminates the need for epitope-tagged constructs in cell-based high throughput screening applications using reverse transfection. This co-transfection method was used to study in parallel the structure/function of multiple versions of the v-Src protein using automated fluorescence microscopy. The wild-type v-Src protein and four mutants having insertions or deletions in the SH2 or SH3 domains displayed high levels of tyrosine kinase activity in HEK293T cells. Three other mutated v-Src proteins, including a kinase-dead version, were shown to be defective for tyrosine kinase activity. This reverse co-transfection approach is applicable for high throughput screening of both cDNA libraries and positional scanning recombinant protein libraries.

Cell Line↗

Miniaturizing the comet assay with 3D vertical comets.

BACKGROUND: The comet or single-cell gel electrophoresis assay is a sensitive method for the detection of DNA damage. The main drawback of comet sampling is the low cell density necessary to prevent nucleus overlap after electrophoresis, which limits large-scale high throughput screening. Another problem may be inconsistent comet focusing. We investigated whether an approach based on three-dimensional (3D) confocal microscopy might be beneficial for these concerns. METHODS: A vertical comet assay enabling three-dimensional confocal comet imaging of nuclei seeded at very high density was developed together with dedicated software algorithms to retrieve quantitative data at the single cell level. RESULTS: Three-dimensional confocal comet imaging greatly relieved the user interactions of our nonautomated two-dimensional comet sampling procedure. Batches of comets were blindly sampled, and confocal sectioning improved the clarity of the images and the accuracy of comet sampling. A 1-Gy dose response was readily established. The sampling speed was competitive with that of commercial packages. CONCLUSIONS: Vertical comet imaging is a new concept for fast and user-friendly comet sampling that allows miniaturization of the assay. It may become an essential step toward high throughput screening and exploit the benefits of confocal imaging.

Algorithms↗

Rational design of p53, an intrinsically unstructured protein, for the fabrication of novel molecular sensors.

The dominant paradigm of protein engineering is structure-based site-directed mutagenesis. This rational approach is generally more effective for the engineering of local properties, such as substrate specificity, than global ones such as allostery. Previous workers have modified normally unregulated reporter enzymes, including beta-galactosidase, alkaline phosphatase, and beta-lactamase, so that the engineered versions are activated (up to 4-fold) by monoclonal antibodies. A reporter that could easily be "reprogrammed" for the facile detection of novel effectors (binding or modifying activities) would be useful in high throughput screens for directed evolution or drug discovery. Here we describe a straightforward and general solution to this potentially difficult design problem. The transcription factor p53 is normally regulated by a variety of post-translational modifications. The insertion of peptides into intrinsically unstructured domains of p53 generated variants that were activated up to 100-fold by novel effectors (proteases or antibodies). An engineered p53 was incorporated into an existing high throughput screen for the detection of human immunodeficiency virus protease, an arbitrarily chosen novel effector. These results suggest that the molecular recognition properties of intrinsically unstructured proteins are relatively easy to engineer and that the absence of crystal structures should not deter the rational engineering of this class of proteins.

Alkaline Phosphatase↗

Discovery of compounds that will prevent tau pathology.

Tau is certainly a reasonable target for the development of compounds to prevent neurofibrillary pathology, particularly in the fronto-temporal dementias. Although the mechanism of the filamentous accumulations remains unclear, sufficient knowledge is in place to move forward with high throughput screens. In fact, the development of compounds from such screens will ultimately be the only way to validate the target. The dichotomy for such screens is that in vitro screens are easier to design, but require more assumptions as to the mechanism, in contrast to cell-based screens that are more difficult to design, but make fewer assumptions about mechanism. We have designed a moderate throughput for tau binding that relies on fluorescence detection in living cells and an in vitro cdk5/p25 tau phosphorylation high throughput screen.

Animals↗

Data management solutions for protein therapeutic research and development.

Protein therapeutics, including monoclonal antibodies, are a growing focus of drug discovery research organizations. High-throughput screening of large libraries of protein variants is therefore becoming increasingly important in R&D. As a result, there is a need to link large numbers of variant protein sequences with chemical and biological assay data. This integration will allow more efficient data mining and facilitate decision-making regarding hit identification, lead optimization and drug development. In this paper, we present an implementation in which a widely used small-molecule high-throughput screening data management system has been adapted to meet the unique needs of protein drug discovery and development.

Antibodies, Monoclonal↗

Development of new prostate specific monoclonal antibodies.

BACKGROUND: Despite the need for new prostate-specific diagnostic and therapeutic targets, very few unique prostate (cancer) specific antigens have been characterized. Monoclonal antibody (mAb) technology is a powerful tool to identify specific antigenic markers, which could be potential targets for cancer diagnostics or therapy. METHODS: Splenocytes from mice immunized with prostate cancer (PCa) homogenates of different origin were fused using standard techniques. Employing a differential high-throughput screening method followed by immediate screening in immunohistochemistry (IHC) a large number of hybridomas were screened for prostate (cancer) specificity. RESULTS: From 25 successful fusions approximately 300 clones were identified excreting PCa-reactive antibodies. Subsequent immunohistochemical fine-specificity analysis reduced this number to 26. Eventually, after extensive fine-specificity analysis, the number of mAbs appearing to define prostate-specific antigenic structures that might serve as new diagnostic or therapeutic targets was reduced to three. CONCLUSIONS: Using mAb technology combined with a high throughput screening method we have developed three mAbs (1.8, 2.26, and 3.10) directed against prostate associated antigens that might identify potential new therapeutic targets.

Animals↗

Urearetics: a small molecule screen yields nanomolar potency inhibitors of urea transporter UT-B.

Functional studies in knockout mice indicate a critical role for urea transporters (UTs) in the urinary concentrating mechanism and in renal urea clearance. However, potent and specific urea transport blockers have not been available. Here, we used high-throughput screening to discover high-affinity, small molecule inhibitors of the UT-B urea transporter. A collection of 50,000 diverse, drug-like compounds was screened using a human erythrocyte lysis assay based on UT-B-facilitated acetamide transport. Primary screening yielded approximately 30 UT-B inhibitors belonging to the phenylsulfoxyoxazole, benzenesulfonanilide, phthalazinamine, and aminobenzimidazole chemical classes. Screening of approximately 700 structurally similar analogs gave many active compounds, the most potent of which inhibited UT-B urea transport with an EC50 of approximately 10 nM, and approximately 100% inhibition at higher concentrations. Phenylsulfoxyoxazoles and phthalazinamines also blocked rodent UT-B and had good UT-B vs. UT-A specificity. The UT-B inhibitors did not reduce aquaporin-1 (AQP1)-facilitated water transport. In AQP1-null erythrocytes, "chemical UT-B knockout" by UT-B inhibitors reduced by approximately 3-fold UT-B-mediated water transport, supporting an aqueous pore pathway through UT-B. UT-B inhibitors represent a new class of diuretics, "urearetics," which are predicted to increase renal water and solute clearance in water-retaining states.

Animals↗