Complex gel permeation assays for screening combinatorial libraries

Utilization of Microarrayed Compound Screening (μARCS) to Identify Inhibitors of p56lck Tyrosine Kinase

Protein tyrosine kinases play critical roles in cell signaling and are considered attractive targets for drug discovery. The authors have applied μARCS (microarrayed compound screening) technology to develop a high-throughput screen for finding inhibitors of the p56lck tyrosine kinase. Initial assay development was performed in a homogeneous time-resolved (LANCE™) format in 96-well microplates and then converted into the gel-based μARCS format. The μARCS methodology is a well-less screening format in which 8640 compounds are arrayed on a microplate-sized piece of polystyene and subsequently assayed by placing reagents cast in agarose gels in contact with these compound sheets. A blotting paper soaked with adenosine triphosphate is applied on the gel to initiate the kinase reaction in the gel. Using this screening methodology, 300,000 compounds were screened in less than 40 h. Substantial reagent reduction was achieved by converting this tyrosine kinase assay from a 96-well plate assay to μARCS, resulting in significant cost savings. ( Journal of Biomolecular Screening 2004: 12-21)

The fall and rise of pharmacology--(re-)defining the discipline?

Pharmacology is an integrative discipline that originated from activities, now nearly 7000 years old, to identify therapeutics from natural product sources. Research in the 19th Century that focused on the Law of Mass Action (LMA) demonstrated that compound effects were dose-/concentration-dependent eventually leading to the receptor concept, now a century old, that remains the key to understanding disease causality and drug action. As pharmacology evolved in the 20th Century through successive biochemical, molecular and genomic eras, the precision in understanding receptor function at the molecular level increased and while providing important insights, led to an overtly reductionistic emphasis. This resulted in the generation of data lacking physiological context that ignored the LMA and was not integrated at the tissue/whole organism level. As reductionism became a primary focus in biomedical research, it led to the fall of pharmacology. However, concerns regarding the disconnect between basic research efforts and the approval of new drugs to treat 21st Century disease tsunamis, e.g., neurodegeneration, metabolic syndrome, etc. has led to the reemergence of pharmacology, its rise, often in the semantic guise of systems biology. Against a background of limited training in pharmacology, this has resulted in issues in experimental replication with a bioinformatics emphasis that often has a limited relationship to reality. The integration of newer technologies within a pharmacological context where research is driven by testable hypotheses rather than technology, together with renewed efforts in teaching pharmacology, is anticipated to improve the focus and relevance of biomedical research and lead to novel therapeutics that will contain health care costs.

Micro-patterned porous substrates for cell-based assays

In the search for new therapeutic chemicals, lab-on-a-chip systems have recently emerged as innovative and efficient tools for cell-based assays and high throughput screening. Here, we describe a novel, versatile and simple device for cell-based assays at the bench-top. We created spatial variations of porosity on the surface of a membrane filter by microcontact printing with a biocompatible polymer (PDMS). We called such systems Micro-Printed Membranes (μPM). Active compounds dispensed on the porous areas, where the membrane pores are not clogged by the polymer, can cross the membrane and reach cells growing on the opposite side. Only cells immediately below those porous areas could be stimulated by chemicals. We performed proof-of-principle experiments using Hoechst nuclear staining, calcein-AM cell viability assay and destabilization of the cytoskeleton organisation by cytochalasin B. Resulting fluorescent staining properly matched the drops positioning and no cross-contaminations were observed between adjacent tests. This well-less cell-based screening system is highly flexible by design and it enables multiple compounds to be tested on the same cell tissue. Only low sample volumes in the microlitre range are required. Moreover, chemicals can be delivered sequentially and removed at any time while cells can be monitored in real time. This allows the design of complex, sequential and combinatorial drug assays. μPMs appear as ideal systems for cell-based assays. We anticipate that this lab-on-chip device will be adapted for both manual and automated high content screening experiments.

High-throughput cellular microarray platforms: applications in drug discovery, toxicology and stem cell research

Cellular microarrays are powerful experimental tools for high-throughput screening of large numbers of test samples. Miniaturization increases assay throughput while reducing reagent consumption and the number of cells required, making these systems attractive for a wide range of assays in drug discovery, toxicology, stem cell research and potentially therapy. Here, we provide an overview of the emerging technologies that can be used to generate cellular microarrays, and we highlight recent significant advances in the field. This emerging and multidisciplinary approach offers new opportunities for the design and control of stem cells in tissue engineering and cellular therapies and promises to expedite drug discovery in the biotechnology and pharmaceutical industries.

Compound transfer efficiency from polystyrene surfaces: application to microarrayed compound screening

In microarrayed compound screening (microARCS), compounds are spotted and dried onto a polystyrene sheet (ChemCard)ata high density and introduced into the assay by contacting with agarose gels that contain reagents for the assay. The authors have conducted studies to characterize the compound transfer process using 59 compounds of diverse properties. The amount of compounds remaining on the ChemCard was determined by liquid chromatography/mass spectrometry after incubation with agarose gels for predetermined time periods. The results showed good correlation with kinetics of compound transfer to phosphate-buffered saline (PBS) buffer, but only moderate correlation with equilibrium solubility of compounds in PBS buffer. These observations indicate that the major factor determining compound transfer efficiency is the kinetics of dissolution of compounds, rather than equilibrium solubility and diffusion of compounds in the gel. Compounds of lower ClogP showed a higher rate of transfer to agarose gels and vice versa. Other compound properties such as molecular weight, size, acid-base, and H-bonding properties did not significantly affect compound transfer. Importantly, the majority of the compounds studied show greater than 20% transfer after a 10-min incubation with agarose gels, providing sufficient amounts of compounds for screening purposes.

Microarrayed compound screening (microARCS) to identify activators and inhibitors of AMP-activated protein kinase

A novel and innovative high-throughput screening assay was developed to identify both activators and inhibitors of AMP-activated protein kinase (AMPK) using microarrayed compound screening (microARCS) technology. Test compounds were arrayed at a density of 8640 on a polystyrene sheet, and the enzyme and peptide substrate were introduced into the assay by incorporating them into an agarose gel followed by placement of the gels onto the compound sheet. Adenosine triphosphate (ATP) was delivered via a membrane, and the phosphorylated biotinylated substrate was captured onto a streptavidin affinity membrane (SAM trade mark ). For detection, the SAM trade mark was removed, washed, and imaged on a phosphor screen overnight. A library of more than 700,000 compounds was screened using this format to identify novel activators and inhibitors of AMPK.

A cell-based microarrayed compound screening format for identifying agonists of G-protein-coupled receptors

The identification of agonist and antagonist leads for G-protein-coupled receptors (GPCRs) is of critical importance to the pharmaceutical and biotechnology industries. We report on the utilization of a novel, high-density, well-less screening platform known as microarrayed compound screening microARCS) that tests 8640 compounds in the footprint of a standard microtiter plate for the identification of novel agonists for a specific G-protein-coupled receptor. Although receptors coupled to the G alpha(q) protein can readily be assessed by fluorescence-based Ca(2+) release measurements, many GPCRs that are coupled to G alpha(s) or G alpha(i/o) proteins are not amenable to functional evaluation in such a high-throughput manner. In this study, the human dopamine D(4.4) receptor, which normally couples through the G alpha(i/o) protein to inhibit adenylate cyclase and to reduce levels of intracellular cAMP, was coupled to intracellular Ca(2+) release by stably coexpressing this receptor with a chimeric G(alpha qo5) protein in HEK-293 cells. In microARCS format, the cells expressing D(4.4) receptor and G alpha(qo5) protein were preloaded with fluo-4, cast into a 1% agarose gel, placed above the compound sheets, and imaged successively using a ViewLux charge-coupled device imaging system. Dopamine and other agonists evoked an increase in fluorescence response that appeared as bright spots in a time- and concentration-dependent manner. Utilizing this technology, a library of 260,000 compounds was rapidly screened and led to the identification of several novel agonists. These agonists were further characterized using a fluorometric imaging plate reader assay. Excellent confirmation rates coupled with enhanced efficiency and throughput enable microARCS to serve as an alternative platform for the screening and identification of novel GPCR agonists.

Going to the well no more: lawn format assays for ultra-high-throughput screening

Screening in a 'well-less' or lawn format provides a means to screen large compound collections against many targets in a fast, versatile and cost effective manner. The development of generic lawn format assays to screen various gene families against large compound collections should facilitate the identification of hits and tools to use in drug discovery and chemogenomic endeavours. Lawn format holds particular promise for screening GPCRs and selected enzyme families with potential use in other gene families.

Study on molecular mechanism and 3D-QSAR of influenza neuraminidase inhibitors

Neuraminidase (NA) is a critical enzyme of the influenza virus and many inhibitors targeting to this enzyme are quite efficient and encouraging as anti-influenza agents. In this paper the binding model of five series of inhibitors to NA was examined using molecular simulation method. The resulted conformation and orientation of the compounds were directly put into CoMSIA study. The most significant amino acid residues at binding sites and the requirement for features of substituents were applied to direct design of new inhibitors. The robust QSAR model and its three-dimensional contour map provided guidelines to building novel compounds with new scaffold and for structural optimization of current molecules.

Application of Micro Arrayed Compound Screening (microARCS) to identify inhibitors of caspase-3

Micro Arrayed Compound Screening (microARCS) is a miniaturized ultra-high-throughput screening platform developed at Abbott Laboratories. In this format, 8,640 discrete compounds are spotted and dried onto a polystyrene sheet, which has the same footprint as a 96-well plate. A homogeneous time-resolved fluorescence assay format (LANCE) was applied to identify the inhibitors of caspase-3 using a peptide substrate labeled with a fluorescent europium chelate and a dabcyl quencher. The caspase-3 enzyme was cast into a thin agarose gel, which was placed on a sheet containing test compounds. A second gel containing caspase substrate was then laid above the enzyme gel to initiate the reaction. Caspase-3 cleaves the substrate and separates the europium from the quencher, giving rise to a time-resolved fluorescent signal, which was detected using a ViewLux charge-coupled device imaging system. Potential inhibitors of caspase-3 appeared as dark spots on a bright fluorescent background. Results from the microARCS assay format were compared to those from a conventional 96-well plate-screening format.

Microarray compound screening (microARCS) to identify inhibitors of HIV integrase

A novel high-throughput strand transfer assay has been developed, using Microarray Compound Screening (microARCS) technology, to identify inhibitors of human immunodeficiency virus (HIV) integrase. This technology utilizes agarose matrices to introduce a majority of the reagents throughout the assay. Integration of biotinylated donor DNA with fluorescein isothiocyanate (FITC)-labeled target DNA occurs on a SAM membrane in the presence of integrase. An anti-FITC antibody conjugated to alkaline phosphatase (AP) was used to do an enzyme-linked immunosorbent assay with the SAM. An agarose gel containing AttoPhos, a substrate of AP, was used for detection of the integrase reactions on the SAM. For detection, the AttoPhos gel was separated from the SAM after incubation and then the gel was imaged using an Eagle Eye II closed-circuit device camera system. Potential integrase inhibitors appear as dark spots on the gel image. A library of approximately 250,000 compounds was screened using this HIV integrase strand transfer assay in microARCS format. Compounds from different structural classes were identified in this assay as novel integrase inhibitors.