Automated multiple ligand screening by frontal affinity chromatography-mass spectrometry (FAC-MS)

High-throughput screening (HTS) efforts to discover "hits" typically rely on the large-scale parallel screening of individual compounds with attempts to screen mixtures of compounds typically and, unfortunately, giving rise to false positives and false negatives due to the nature of the HTS readout (% inhibition/activation above a defined threshold) that makes deconvolution virtually intractable. Bioaffinity screening methods have emerged as an alternative or orthogonal method to classic HTS. One of these methods, frontal affinity chromatography coupled to mass spectrometry detection (FAC-MS), although still a relatively new technique, is turning out to be a viable screening tool. However, to push FAC-MS more to the forefront as a moderate primary HTS system (or a secondary screening assay), automation needs to be addressed. An automated FAC-MS system is described using 2 columns containing immobilized hERbeta, whereby while 1 column is being regenerated, the other is being used. The authors are extrapolating that in a continuous 24-h operation, the number of ligands screened could potentially approach 10,000. In addition, preliminary structure-activity relationship binding information (typically not seen in early primary HTS) can be obtained by observing the rank order of the library members in the various mixtures.     

Just-in-time purification: an effective solution for cherry-picking and purifying active compounds from large legacy libraries

Many companies possess a compound collection consisting of purified compounds and of unpurified products from combinatorial libraries. Using commercial and proprietary compounds as examples, this report provides clear examples of the significant impact purification can have on the activity observed for a compound and highlights the need to retest the purified compounds prior to creating structure-activity relationships. Crude mixtures made with commercial compounds led to an increase in the number of false positives in the SXR-GAL4 assay as compared with their pure and purified counterparts. An examination of proprietary compounds in an HIV assay resulted in the purification of 61 active crude synthetic mixtures. Of these 61 compounds, 32 were 5-fold less active and 2 were 5-fold more active after purification. This report details a semiautomated process developed and implemented for cherry-picking, tracking, and selectively purifying compounds found active in high-throughput screening campaigns.     

On the prediction of statistical parameters in high-throughput screening using resampling techniques

A severe drawback in the high-throughput screening (HTS) process is the unintentional (random) presence of false positives and negatives. Their rates depend, among others, on the screening process being applied and the target class. Although false positives can be sorted out in subsequent process steps, their occurrence can lead to increased project cost. More fundamentally, it is not possible to rescue false nonhits. In this article, we investigate the prediction of the primary hit rate, hit confirmation rate, and false-positive and false-negative rates. Results for approximately 2800 compounds are considered that are tested as a pilot screen ahead of the primary screening work. This pilot screen is done at several concentrations and in replicates. The rates are predicted as a function of the proposed hit threshold by having the replicates serve as each other's confirmers, and confidence limits to the prediction are attached by means of a resampling scheme. A comparison of the rates resulting from the resampling with the primary hit rate and the confirmation rates obtained during the screening campaign shows how accurate this method is. Hence, the "optimal" compound concentration for the screen as well as the optimal hit threshold corresponding to low false rates can be determined prior to starting the subsequent screening campaign.     

Computer-Aided Design of Fragment Mixtures for NMR-Based Screening

Fragment-based drug discovery is widely applied both in industrial and in academic screening programs. Several screening techniques rely on NMR to detect binding of a fragment to a target. NMR-based methods are among the most sensitive techniques and have the further advantage of yielding a low rate of false positives and negatives. However, NMR is intrinsically slower than other screening techniques; thus, to increase throughput in NMR-based screening, researchers often assay mixtures of fragments, rather than single fragments. Herein we present a fast and straightforward computer-aided method to design mixtures of fragments taken from a library that have minimized NMR signal overlap. This approach enables direct identification of one or several active fragments without the need for deconvolution. Our approach entails encoding of NMR spectra into a computer-readable format that we call a fingerprint, and minimizing the global signal overlap through a Monte Carlo algorithm. The scoring function used favors a homogenous distribution of the global signal overlap. The method does not require additional experimental work: the only data required are NMR spectra, which are generally recorded for each compound as a quality control measure before its insertion into the library.     

Efficient hit-finding approaches for histone methyltransferases: the key parameters

For many novel epigenetics targets the chemical ligand space and structural information were limited until recently and are still largely unknown for some targets. Hit-finding campaigns are therefore dependent on large and chemically diverse libraries. In the specific case of the histone methyltransferase G9a, the authors have been able to apply an efficient process of intelligent selection of compounds for primary screening, rather than screening the full diverse deck of 900 000 compounds to identify hit compounds. A number of different virtual screening methods have been applied for the compound selection, and the results have been analyzed in the context of their individual success rates. For the primary screening of 2112 compounds, a FlashPlate assay format and full-length histone H3.1 substrate were employed. Validation of hit compounds was performed using the orthogonal fluorescence lifetime technology. Rated by purity and IC(50) value, 18 compounds (0.9% of compound screening deck) were finally considered validated primary G9a hits. The hit-finding approach has led to novel chemotypes being identified, which can facilitate hit-to-lead projects. This study demonstrates the power of virtual screening technologies for novel, therapeutically relevant epigenetics protein targets.     

Evaluation of fluorescent compound interference in 4 fluorescence polarization assays: 2 kinases, 1 protease,and 1 phosphatase

With the increasing use of fluorescence-based assays in high-throughput screening (HTS), the possibility of interference by fluorescent compounds needs to be considered. To investigate compound interference, a well-defined sample set of biologically active compounds, LOPAC, was evaluated using 4 fluorescein-based fluorescence polarization (FP) assays. Two kinase assays, a protease assay, and a phosphatase assay were studied. Fluorescent compound interference and light scattering were observed in both mixture- and single-compound testing under certain circumstances. In the kinase assays, which used low levels (1-3 nM) of fluorophore, an increase in total fluorescence, an abnormal decrease in mP readings, and negative inhibition values were attributed to compound fluorescence. Light scattering was observed by an increase in total fluorescence and minimal reduction in mP, leading to false positives. The protease and phosphatase assays, which used a higher concentration of fluorophore (20-1200 nM) than the kinase assays, showed minimal interference from fluorescent compounds, demonstrating that an increase in the concentration of the fluorophore minimized potential fluorescent compound interference. The data also suggests that mixtures containing fluorescent compounds can result in either false negatives that can mask a potential "hit" or false positives, depending on the assay format. Cy dyes (e.g., Cy3B and Cy5 ) excite and emit further into the red region than fluorescein and, when used in place of fluorescein in kinase 1, eliminate fluorescence interference and light scattering by LOPAC compounds. This work demonstrates that fluorescent compound and light scattering interferences can be overcome by increasing the fluorophore concentration in an assay or by using longer wavelength dyes.     

Identification of novel drug scaffolds for inhibition of SARS-CoV 3-Chymotrypsin-like protease using virtual and high-throughput screenings

We have used a combination of virtual screening (VS) and high-throughput screening (HTS) techniques to identify novel, non-peptidic small molecule inhibitors against human SARS-CoV 3CLpro. A structure-based VS approach integrating docking and pharmacophore based methods was employed to computationally screen 621,000 compounds from the ZINC library. The screening protocol was validated using known 3CLpro inhibitors and was optimized for speed, improved selectivity, and for accommodating receptor flexibility. Subsequently, a fluorescence-based enzymatic HTS assay was developed and optimized to experimentally screen approximately 41,000 compounds from four structurally diverse libraries chosen mainly based on the VS results. False positives from initial HTS hits were eliminated by a secondary orthogonal binding analysis using surface plasmon resonance (SPR). The campaign identified a reversible small molecule inhibitor exhibiting mixed-type inhibition with a K_i value of 11.1 μM. Together, these results validate our protocols as suitable approaches to screen virtual and chemical libraries, and the newly identified compound reported in our study represents a promising structural scaffold to pursue for further SARS-CoV 3CLpro inhibitor development.     

Enrichment of extremely noisy high-throughput screening data using a naïve Bayes classifier

The noise level of a high-throughput screening (HTS) experiment depends on various factors such as the quality and robustness of the assay itself and the quality of the robotic platform. Screening of compound mixtures is noisier than screening single compounds per well. A classification model based on na?ve Bayes (NB) may be used to enrich such data. The authors studied the ability of the NB classifier to prioritize noisy primary HTS data of compound mixtures (5 compounds/well) in 4 campaigns in which the percentage of noise presumed to be inactive compounds ranged between 81% and 91%. The top 10% of the compounds suggested by the classifier captured between 26% and 45% of the active compounds. These results are reasonable and useful, considering the poor quality of the training set and the short computing time that is needed to build and deploy the classifier.     

Affinity ligand selection from a library of small molecules: assay development, screening, and application

A facile and cost-effective process for screening synthetic libraries for an affinity ligand is described. A high throughput 96-well plate filtration method was designed to screen both discrete compounds and mixtures of compounds attached to a solid support. Human serum albumin (HSA) was used as a target protein to demonstrate the proof of concept. Detection and quantitation by fluorescence was accomplished with the use of fluorescamine to conjugate the protein in the filtrate. It is found that mixtures demonstrating low average binding reflect an overall lower hit rate of the components, whereas deconvolution of mixtures with high protein binding consistently provides a high hit rate. This differs from many of the previous experiences screening solid-phase mixtures in which high false positive rates are noted to occur. A total of 100K compounds were tested: 25K as discrete samples and 75K as mixtures. An overall hit rate of 8% was observed. Secondary screening of compounds measured specificity, recovery, and dynamic binding capacity. The effectiveness of the method is illustrated using an affinity column made with a representative lead compound. A similar purity was achieved in a single-step purification of HSA from serum as compared to that obtained by two steps of ion-exchange chromatography. The process for primary screening of a large number of compounds is simple, inexpensive, and applicable to any soluble target protein of known or unknown function from crude mixtures and may have additional utility as a generic chemical affinity tool for the functional characterization of novel proteins emerging from proteomics work.     

WaterLOGSY as a method for primary NMR screening: Practical aspects and range of applicability

WaterLOGSY represents a powerful method for primary NMR screening in the identification of compounds interacting with macromolecules, including proteins and DNA or RNA fragments. Several relay pathways are used constructively in the experiment for transferring bulk water magnetization to the ligand. The method is particularly useful for the identification of novel scaffolds of micromolar affinity that can be then optimized using directed screening, combinatorial chemistry, medicinal chemistry and structure-based drug design. The practical aspects and range of applicability of the WaterLOGSY experiment are analyzed in detail here. Competition binding and titration WaterLOGSY permit, after proper correction, the evaluation of the dissociation binding constant. The high sensitivity of the technique in combination with the easy deconvolution of the mixtures for the identification of the active components, significantly reduces the amount of material and time needed for the NMR screening process.     

新型高效微生态制品的研制

正交实验结果表明 ,4%淀粉水解液 ,10 %酵母提取液 ,2 0 %豆水解液 ,9%肝汤为双歧联菌株混合培养的最佳促生因子配方。经此优化培养基混合培养所得的双歧联菌株 ,制成冻干粉后 ,采用微囊化技术包裹成双歧杆菌微胶囊 ,其耐酸性强 ,肠溶性好 ,保存期长 ,由此可制得一系列新型高效微生态制品。     

Fragment-Based Screening Maps Inhibitor Interactions in the ATP-Binding Site of Checkpoint Kinase 2

Checkpoint kinase 2 (CHK2) is an important serine/threonine kinase in the cellular response to DNA damage. A fragment-based screening campaign using a combination of a high-concentration AlphaScreen™ kinase assay and a biophysical thermal shift assay, followed by X-ray crystallography, identified a number of chemically different ligand-efficient CHK2 hinge-binding scaffolds that have not been exploited in known CHK2 inhibitors. In addition, it showed that the use of these orthogonal techniques allowed efficient discrimination between genuine hit matter and false positives from each individual assay technology. Furthermore, the CHK2 crystal structures with a quinoxaline-based fragment and its follow-up compound highlight a hydrophobic area above the hinge region not previously explored in rational CHK2 inhibitor design, but which might be exploited to enhance both potency and selectivity of CHK2 inhibitors.     

How many deaths can be prevented by newborn screening for congenital adrenal hyperplasia?

BACKGROUND/AIMS: Congenital adrenal hyperplasia (CAH) is increasingly being included in newborn screening programs. Screening can prevent neonatal mortality in children with salt-wasting CAH, but the number of deaths prevented is not known. Cost-effectiveness analyses of screening require estimates of the probability of mortality in CAH. METHODS: We reviewed the literature to identify cohort studies of children with CAH ascertained clinically in the absence of screening. We abstracted the numbers of infant deaths attributable to CAH. We also addressed sex ratios among children with clinically detected CAH and the contribution of ascertainment bias to unbalanced ratios. RESULTS: The evidence suggests a probability of infant death due to adrenal crises in salt-wasting CAH of 4% or less in contemporary advanced economies without screening for CAH. This is lower than previous estimates, although the rate of mortality could be considerably higher in populations with limited clinical awareness or access. CONCLUSION: Although screening for CAH is conducted in a number of countries, further research is still needed to provide reliable estimates on the numbers of prevented deaths, along with evidence-based assessments of the potential benefits, harms, and costs of screening.     

富集培养及高质量DNA提取有利于从土壤宏基因组中获取新卤醇脱卤酶基因

目的:宏基因组技术作为一种不依赖于微生物纯培养的新方法,在挖掘新基因方面具有极大的潜力。本研究旨在建立一种从土壤中高效获取卤醇脱卤酶新基因的策略。方法:通过对现有DNA提取方法进行改进,同时结合富集培养途径以提高土壤宏基因组DNA质量和特异性;在此基础上,应用T-Coffee及CDEHOP程序设计特异引物并对目的基因进行扩增,同时采用正交法设计优化扩增条件,以提高获得卤醇脱卤酶基因的效率。结果:应用改进法提取的DNA质量较改进前有大幅度提高,其D260nm/D280nm及D260nm/D230nm值均大于1.8,且可以不经纯化直接用于PCR和相关酶切实验;PCR扩增目标基因的特异性增强,其中用经富集培养后所得DNA为模板扩增目标基因的特异性最强,TA克隆测序阳性结果比例最高。结论:富集培养和高质量DNA的获得有助于基于宏基因组途径获取新基因。     

ELISA microarray technology as a high-throughput system for cancer biomarker validation

A large gap currently exists between the ability to discover potential biomarkers and the ability to assess the real value of these proteins for cancer screening. One major challenge in biomarker validation is the inherent variability in biomarker levels. This variability stems from the diversity across the human population and the considerable molecular heterogeneity between individual tumors, even those that originate from a single tissue. An additional challenge with cancer screening is that most cancers are rare in the general population, meaning that assay specificity must be very high. Otherwise, the number of false positives will be much greater than the number of true positives. Due to these challenges associated with biomarker validation, it is necessary to analyze thousands of samples in order to obtain a clear idea of the utility of a screening assay. Enzyme-linked immunosorbent assay (ELISA) microarray technology can simultaneously quantify levels of multiple proteins and, thus, has the potential to accelerate validation of protein biomarkers for clinical use. This review will discuss current ELISA microarray technology and potential advances that could help to achieve the reproducibility and throughput that are required to evaluate cancer biomarkers.     

Screening and characterization of human monoglyceride lipase active site inhibitors using orthogonal binding and functional assays

Endocannabinoids such as 2-arachidonylglycerol (2-AG) are ligands for cannabinoid receptors that contribute to the transmission and modulation of pain signals. The antinociceptive effect of exogenous 2-AG suggests that inhibition of monoglyceride lipase (MGLL), the enzyme responsible for degrading 2-AG and arresting signaling, may be a target for pain modulation. Here we describe the characterization of MGLL ligands following a high-throughput screening campaign. Ligands were discovered using ThermoFluor, a label-free affinity-based screening tool that measures ligand binding via modulation of protein thermal stability. A kinetic fluorescent assay using the substrate 4-methylcoumarin butyrate was used to counterscreen confirmed HTS positives. A comparison of results from binding and inhibition assays allowed elucidation of compound mechanism of action. We demonstrate the limit of each technology and the benefits of using orthogonal assay techniques in profiling compounds.     

A rapid enzymatic assay for high-throughput screening of adenosine-producing strains

Adenosine is a major local regulator of tissue function and industrially useful as precursor for the production of medicinal nucleoside substances. High-throughput screening of adenosine overproducers is important for industrial microorganism breeding. An enzymatic assay of adenosine was developed by combined adenosine deaminase (ADA) with indophenol method. The ADA catalyzes the cleavage of adenosine to inosine and NH₃, the latter can be accurately determined by indophenol method. The assay system was optimized to deliver a good performance and could tolerate the addition of inorganic salts and many nutrition components to the assay mixtures. Adenosine could be accurately determined by this assay using 96-well microplates. Spike and recovery tests showed that this assay can accurately and reproducibly determine increases in adenosine in fermentation broth without any pretreatment to remove proteins and potentially interfering low-molecular-weight molecules. This assay was also applied to high-throughput screening for high adenosine-producing strains. The high selectivity and accuracy of the ADA assay provides rapid and high-throughput analysis of adenosine in large numbers of samples.     

A simple strategy for mitigating the effect of data variability on the identification of active chemotypes from high-throughput screening data

Among the several goals of a high-throughput screening campaign is the identification of as many active chemotypes as possible for further evaluation. Often, however, the number of concentration response curves (e.g., IC(50)s or K(i)s) that can be collected following a primary screen is limited by practical constraints such as protein supply, screening workload, and so forth. One possible approach to this dilemma is to cluster the hits from the primary screen and sample only a few compounds from each cluster. This introduces the question as to how many compounds must be selected from a cluster to ensure that an active compound is identified, if it exists at all. This article seeks to address this question using a Monte Carlo simulation in which the dependence of the success of sampling is directly linked to screening data variability. Furthermore, the authors demonstrate that the use of replicated compounds in the screening collection can easily assess this variability and provide a priori guidance to the screener and chemist as to the extent of sampling required to maximize chemotype identification during the triage process. The individual steps of the Monte Carlo simulation provide insight into the correspondence between the percentage inhibition and eventual IC(50) curves.     

Hypothesis testing in high-throughput screening for drug discovery

Following the success of small-molecule high-throughput screening (HTS) in drug discovery, other large-scale screening techniques are currently revolutionizing the biological sciences. Powerful new statistical tools have been developed to analyze the vast amounts of data in DNA chip studies, but have not yet found their way into compound screening. In HTS, characterization of single-point hit lists is often done only in retrospect after the results of confirmation experiments are available. However, for prioritization, for optimal use of resources, for quality control, and for comparison of screens it would be extremely valuable to predict the rates of false positives and false negatives directly from the primary screening results. Making full use of the available information about compounds and controls contained in HTS results and replicated pilot runs, the Z score and from it the p value can be estimated for each measurement. Based on this consideration, we have applied the concept of p-value distribution analysis (PVDA), which was originally developed for gene expression studies, to HTS data. PVDA allowed prediction of all relevant error rates as well as the rate of true inactives, and excellent agreement with confirmation experiments was found.