featuring the Echo Acoustic Technology
TITLES and AUTHORS
The introduction of Acoustic Droplet Ejection (ADE) liquid transfer technology has created a paradigm shift in compound handling for High Throughput Screening. Benefits of this technology include accurate, low volume transfers that eliminate the need for intermediate dilutions, conservation of compound and production of higher quality data. In addition non-contact transfers eliminate the use of pipette tips, saving hundreds of thousands of dollars in consumables. The benefits of using ADE technology are obvious and compelling. What is not obvious at first is how the introduction of this technology into the compound handling work flow can impact other steps in the process. We describe the evolution of the work flow in the Southern Research Institute High Throughput Screening Center when a Labcyte Echo 550 became part of the drug preparation process. Mixing and compound precipitation, evaporation control for nanoliter volumes transferred to assay plates, water absorption by source plates and automation of the process were all challenges addressed as the Echo ADE technology was integrated into work flow at Southern Research Institute.
KCC2, a neuronal-specific K-Cl cotransporter, plays a major role in maintaining intracellular Cl− concentration in neurons below its electrochemical equilibrium potential, thus favoring robust GABA hyperpolarizing or inhibitory responses. The pharmacology of the K-Cl cotransporter is dominated by loop diuretics such as furosemide and bumetanide, molecules used in clinical medicine because they inhibit the loop of Henle Na-K-2Cl cotransporter with much higher affinity. To identify molecules that affect KCC2 activity, we developed a fluorescence-based assay suitable for high-throughput screening (HTS) and used the assay to screen a library of 234,000 small molecules. We identified a large number of molecules that either decrease or increase the activity of the cotransporter. Here, we report the characterization of a small number of inhibitors, some of which inhibit KCC2 activity in the submicromolar range without substantially affecting NKCC1 activity. Using medicinal chemistry, we synthesized a number of variants, tested their effect on KCC2 function, and provide an analysis of structure/activity relationships. We also used one of the compounds to demonstrate competitive inhibition in regard to external [K+] versus noncompetitive inhibition in respect to external [Cl−].
We have developed a plate preparation workstation (the POD™ 810 plate assembler) that is controlled by an intellectual scheduler to increase the productivity of secondary screening labs. Dose-response analyses, such as IC50 determinations, are among the most important of the secondary screening assays and also among the most time-consuming and difficult. They are prone to poor precision due to serial dilutions, and erroneous results due to absorption of compounds. This workstation coordinates multiple assay plate preparation tools to optimize the throughput of any Echo® acoustic liquid handler. The intellectual scheduler plans multiple tasks simultaneously, according to the availability and need of each device in the workstation. We demonstrate that this plate assembler can set up assay plates for as many as 1400 12-point, six-log, dose-response curves each hour. The throughput and quality of results inherent with the POD plate assembler suggests using a larger number of compounds against a wider range of targets. This can increase the value of the libraries being screened and lead to faster identification of new drug candidates.
In this poster, we demonstrated the set up and best practices of using Acoustic Droplet Ejection (ADE) technology in a high throughput kinase assay. We designed a miniaturized kinase assay using the Labcyte® Echo® 555 liquid handler, Corning 1536-well microplates and the Promega Kinase-Glo® Plus Luminescence Kinase Assay. Optimal ATP concentration, kinase reaction time, amount of kinase for each reaction, and substrate concentration were determined. We showed the Z´-Factor of the assay and the IC50 curves of known kinase inhibitors. We discuss the advantages of combining the right set of hardware and assay technology.
The pre-dispensing of compound libraries by acoustic droplet ejection is a convenient way of preparing ”assay ready” compound plates. This method also allows for the direct (i.e. no pre-dilution necessary) and precise dispensing of the low volumes of compound DMSO solution required for assays in 1536 plates. However, questions arise about the effects of time, temperature and dispensed volume on assay performance and repeatability. These issues about the “shelf-life” of assay ready plates are of particular importance if large batches of plates need to be prepared several days in advance, e.g. for HTS screens. In an effort to validate this method of compound plate preparation for a particular screen and compound set, we pre-dispensed agonists of a nuclear hormone receptor in 25, 75 and 150 nL volumes of DMSO in triplicate 1536 plates at different time points prior to performing a TR-FRET agonist assay (plates prepared 2 weeks, 1 week, 2 days, 1 day, 0 days before and stored sealed at room temperature). In addition, we kept a 2 week old plate set at –18°C to see if storage temperature had an effect on compound activities. We present a comparison and interpretation of the assay potency and efficacy results between these plate sets.
Protein kinases comprise the largest family of mammalian enzymes, totaling at least 500. These ubiquitous enzymes play key roles in cellular regulation by catalyzing the reversible phosphorylation of more than 10,000 proteins.
Dysfunctional intracellular signaling through protein kinases is associated with about 400 human diseases, most notably cancers. As a result of the clinical success of the p210 Bcr-Abl inhibitor (Novartis’ Gleevec) for treatment of chronic myelogenous leukemia, pharma companies have applied massive resources to finding the next blockbuster kinase activity-modulating drug. And, as kinase-focused drug discovery enterprises expand, so does the need for discovery tools that automate and scale them.
At the Society for Biomolecular Screening’s (SBS) annual meeting held last month, companies collaborated in workshops, combining their technologies to address formidable challenges in kinase profiling and to facilitate selection of appropriate assay options.
In a workshop entitled “Assay Optimization and Kinase Profiling in micro HTS Format,” Labcyte (www.labcyte.com), Deerac Fluidics (www.deerac.com), Promega (www.promega.com), Corning Life Sciences (www.corning.com), and BMG Labtech (www.bmglabtech.com) teamed up to present a complete platform approach for kinase-assay development.
Using Labcyte’s ultralow volume-test technology, Corning Life Sciences’ specially developed dual assay plates, luminescent kinase-assay technology from Promega, Deerac Fluidics’ reagent-dispensing technology, and BMG Labtech’s PHERAstar luminescent-detection instrumentation, these companies demonstrated the complementarity and adaptability of their diverse technologies for the development of extremely low-volume, protein-kinase assays.
Successful development of robust and efficient compound screening assays is essential within the drug discovery process but this is often difficult to achieve when using primary cells. Additionally, data from the use of human tissue/primary cells needs to be maximised and so it is a requirement that we miniaturise our assays to achieve this. Previously we have assayed cytokine stimulated human chondrocytes prepared from human (OA) knee joints for nitric oxide (NO) production within a 96 well plate format. However we needed to further miniaturize this assay into 384 well plates to get as many data points as possible from a limited supply of tissue. This assay has long incubation times prior to NO detection and evaporation of liquid from peripheral wells was a major issue leading to poor data quality. To reduce this effect we used the MicroClime environmental lid (Fig 1) filled with assay buffer. The MicroClime lid has previously been used within AstraZeneca Charnwood filled with DMSO for the use in storage of compound plates (Fig 2). We describe here the development of a 384 well chondrocyte assay for the profiling of compounds and present data clearly showing that application of the MicroClime lid improves assay performance and efficiency.
Acoustic droplet ejection (ADE) moves nanoliter and picoliter volumes of liquid with sound1. ADE has been widely applied to DMSO-based solutions and has been demonstrated to improve screening results in drug discoveries and reduce the use of plastic consumables. With its excellent precision and accuracy in nanoliter liquid handling, ADE is a top choice for miniaturization in aqueous applications, such as protein arrays, PCR, live cell transfers and DNA sequencing. We show excellent ADE transfers of aqueous solutions of a wide variety with salt and buffer concentrations ranging from 0 to 200 mM. These solutions encompass most solutions of biological interest including such common solutions as PBS, PCR master mix, DMEM, and Tris-EDTA buffer. Further, we show that ADE can be used to transfer viscous solutions, such as those containing glycerol, which can be difficult to transfer with pipettes, nozzles and pin tools. ADE reduces cross contamination to zero since nothing contacts the solutions. We show examples of transferring various aqueous solutions with the Echo® 555 liquid handler and how it can be applied to genomic, proteomic and other research.
The serial dilution method is standard practice in the preparation of dose-response series for IC50 determination. However, it is well recognised that inadequacies in the liquid handling or mixing technique will affect the dilution ratio and hence the compound concentration and any errors will be compounded during each successive serial dilution, mix and transfer. A recent poll of end users ranked better precision, particularly at lower drug concentrations, and the reduction in compound precipitation as the improvements in dose-response analysis they most desired. In addition, it is now suspected that hydrophobic compounds may be lost from solution during aqueous serial dilutions and absorbed to intermediate plastic surfaces. This in turn adds to concern over the reliability of the results generated and the extent to which they are a true reflection of the potency of the compounds being evaluated. As part of the general drive to enhance the quality of screening data generated researchers are investigating strategies based on the direct dilution of micro-volumes of compound (i.e. on a volumetric basis). These investigations have been aided by the availability of low volume dispensing systems with good precision at low nL dispense volumes and a relatively wide dynamic range. Some groups are now reporting that IC50 values of compounds tend to be lower (more active) when the concentrations are made via direct dilutions. It is increasingly evident that direct dilution has a future role to play in dose-response analysis and where acoustic droplet ejection is preferentially deployed additional benefits will be derived in terms of reduced waste stream generated, less source material used and no cross-contamination.
Acoustic-based non contact droplet ejection compound transfer methods have become more widely utilized due to advantages demonstrated over traditional methods. These advantages include minimizing compound usage and subsequent conservation of compound bank as well as improved data quality through removal of serial dilution cross-contamination issues, reduction in false negative rates, lower consumable costs through reduced plastic and reagent wastage and lower final assay DMSO concentration for poorly tolerant assays.
Within the Lead Identification arena we have utilized acoustic based compound transfer where a requirement for flexible operation is appropriate software to enable easy design of transfer protocols. We have evaluated and utilized the Labcyte Echo™ Dose Response version 1.1.0 software for a range of direct microtiter to microtitre plate applications on the nanolitre transfer technology of the Labcyte® Echo™ 555 liquid handler.
The Echo™ dose-response software enables the user to define the layout of the source and destination plates, specify the number of points in the dose response curve, and transfer various concentrations and volumes of compounds to the destination plates. The software runs the liquid transfer as well as the DMSO back-fill, and generates a report of the survey and transfer results.
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