Evaluation of the InteraX™ System Technology in a High-Throughput Screening Environment

The use of mammalian two-hybrid technologies for high-throughput drug screening

Developing agents that target protein-protein interactions (PPIs) is an emerging field in drug discovery. Although this target class has hitherto remained underexplored, it holds exceptional promise related to the large amount of potential PPI targets compared to single protein targets and it offers important opportunities to increase the specificity of therapeutic molecules. While several PPI modulating therapeutics have recently been reported and a number of these are in clinical trial, progress in the field has been hampered by the lack of efficient screening systems. Recently, a number of cellular approaches have been developed that complement classical in vitro screening methods and which exhibit a number of important assets related to the physiological context they provide. Here we discuss the utility of two-hybrid technologies towards high-throughput screening for PPI inhibitors, in particular those that operate in a mammalian cellular background. We review a number of cases where mammalian two-hybrids have been successfully applied to identify small molecule disruptors of PPIs and zoom in further on the MAPPIT (Mammalian Protein-Protein Interaction Trap) technology platform. The value of this approach for drug discovery is illustrated by recent data from MAPPIT-based screening projects.

Heterodimerisation of G protein-coupled receptors: implications for drug design and ligand screening

IMPORTANCE OF THE FIELD

In recent times many G protein-coupled receptors (GPCRs) have been shown to dimerise/oligomerise and, in some cases, such structural organization has been found to be essential for receptor function or to play a modulatory role in living cells. The fact that these complexes may display differential pharmacology through, for example, the formation of a new binding pocket or signalling properties, as well as different functions or regulation in physiological tissues, offers novel opportunities for drug discovery. As a consequence, it seems necessary to develop new approaches suitable for GPCR heterodimer identification and selective ligand screening.

AREAS COVERED IN THIS REVIEW

This review gives an overview of new strategies that have been developed in an effort to incorporate the possibilities added by GPCR hetero-oligomerisation on the screening of compounds as drug candidates.

WHAT THE READER WILL GAIN

The reader will gain a wider knowledge about how the current understanding of GPCR oligomeric structure and function has mandated that hetero-oligomeric receptors must be considered as novel targets in the identification of future lead compounds.

TAKE HOME MESSAGE

For the improvement of novel drug discovery, more structural and functional information on the process of receptor oligomerisation is needed, and the realisation that the function of GPCRs can be greatly influenced by other interacting receptors or proteins also demands consideration in the lead-compound developing process in order to achieve better therapeutic agents.

Identification of iNOS inhibitors using InteraX

Inducible nitric oxide synthase (iNOS) is active as a homodimer. A cell-based assay suitable for high-throughput screening (HTS) was generated to identify inhibitors of iNOS dimerization using the InteraX enzyme complementation technology of Applied Biosystems. The cells contain 2 chimeric proteins of complementing deletion mutants of beta-galactosidase, each fused to the oxygenase domain of human iNOS. The assay was characterized using known iNOS dimerization inhibitors, which gave a decrease in beta-galactosidase activity. Surprisingly, the assay was also able to identify compounds that have the same profile as known inhibitors of fully formed dimeric iNOS by causing an increase in beta-galactosidase activity. The iNOS InteraX assay was used to screen approximately 800,000 compounds in a 384-well format. After hit confirmation, 3359 compounds were taken forward for full IC50 determination in InteraX and cytotoxicity assays. Of these compounds 40.5% were confirmed as greater than 10-fold more active in InteraX compared to a cytotoxicity assay and were classified as potential iNOS dimerization inhibitors as they did not inhibit beta-galactosidase alone. In the same primary screen, 901 compounds gave a significant increase in beta-galactosidase activity. Many of these were known inhibitors of iNOS. After IC50 determination in InteraX and cytotoxicity assays, 182 novel compounds remained as potential arginine-competitive inhibitors of dimeric iNOS.

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.

Beta galactosidase complementation: a cell-based luminescent assay platform for drug discovery

Many cell-based assays interrogating cell pathway activation employ protocols that require microscopic imaging techniques. However, such assays are not in general widely adopted for primary screening. Protein complementation, particularly of enzymes, provides an alternative approach for cell pathway analysis, with a principal advantage that is amenable to high throughput screening using microtiter plate protocols. Notably, alpha complementation of the enzyme beta-galactosidase has been exploited as a technology in this regard, using substrates that generates luminescent signals. This review describes the various uses of this flexible technology to cell-based assay development.