Identifying druglike inhibitors of myelin-reactive T cells by phenotypic high-throughput screening of a small-molecule library

A real-time fluorometric method for the simultaneous detection of cell death type and rate

Several cell death assays have been developed based on a single biochemical parameter such as caspase activation or plasma membrane permeabilization. Our fluorescent apoptosis/necrosis (FAN) assay directly measures cell death and distinguishes between caspase-dependent apoptosis and caspase-independent necrosis of cells grown in any multiwell plate. Cell death is monitored in standard growth medium as an increase in fluorescence intensity of a cell-impermeable dye (SYTOX Green) after plasma membrane disintegration, whereas apoptosis is detected through caspase-mediated release of a fluorophore from its quencher (DEVD-amc). The assay determines the normalized percentage of dead cells and caspase activation per condition as an end-point measurement or in real time (automated). The protocol can be applied to screen drugs, proteins or siRNAs for interference with cell death while simultaneously detecting cell death modality switching between apoptosis and necrosis. Initial preparation may take up to 5 d, but the typical hands-on time is ∼2 h.

Protein reporter bioassay systems for the phenotypic screening of candidate drugs: a mouse platform for anti-aging drug screening

Recent drug discovery efforts have utilized high throughput screening (HTS) of large chemical libraries to identify compounds that modify the activity of discrete molecular targets. The molecular target approach to drug screening is widely used in the pharmaceutical and biotechnology industries, because of the amount of knowledge now available regarding protein structure that has been obtained by computer simulation. The molecular target approach requires that the structure of target molecules, and an understanding of their physiological functions, is known. This approach to drug discovery may, however, limit the identification of novel drugs. As an alternative, the phenotypic- or pathway-screening approach to drug discovery is gaining popularity, particularly in the academic sector. This approach not only provides the opportunity to identify promising drug candidates, but also enables novel information regarding biological pathways to be unveiled. Reporter assays are a powerful tool for the phenotypic screening of compound libraries. Of the various reporter genes that can be used in such assays, those encoding secreted proteins enable the screening of hit molecules in both living cells and animals. Cell- and animal-based screens enable simultaneous evaluation of drug metabolism or toxicity with biological activity. Therefore, drug candidates identified in these screens may have increased biological efficacy and a lower risk of side effects in humans. In this article, we review the reporter bioassay systems available for phenotypic drug discovery.

Use of primary human cells in high-throughput screens

Traditionally, the objective of high-throughput screening (HTS) has been to identify compounds that interact with a defined target protein as the starting point for a chemistry lead optimisation programme. To enable this it has become commonplace to express the drug target in a recombinant expression system and use this reagent as the source of the biological material to support the HTS campaign. In this chapter we describe an alternative HTS methodology with the objective of identifying compounds that mediate a change in a defined physiological end point as a consequence of compound activity in human primary cells. Rather than screening at a defined molecular target, such "phenotypic" screens permit the identification of compounds that act at any target protein within the cell to regulate the end point under study. As an example of such a screen we will describe an HTS campaign to identify compounds that promote the production of the cytokine interferon-alpha from human blood peripheral mononuclear cells (PBMCs) isolated from whole blood. We describe the procedures required to obtain and purify human PBMCs and the electrochemiluminescence-based assay technology used to detect interferon-alpha and highlight the challenges associated with this screening paradigm.

Lessons learnt from assembling screening libraries for drug discovery for neglected diseases

To enable the establishment of a drug discovery operation for neglected diseases, out of 2.3 million commercially available compounds 222 552 compounds were selected for an in silico library, 57 438 for a diverse general screening library, and 1 697 compounds for a focused kinase set. Compiling these libraries required a robust strategy for compound selection. Rules for unwanted groups were defined and selection criteria to enrich for lead-like compounds which facilitate straightforward structure-activity relationship exploration were established. Further, a literature and patent review was undertaken to extract key recognition elements of kinase inhibitors ("core fragments") to assemble a focused library for hit discovery for kinases. Computational and experimental characterisation of the general screening library revealed that the selected compounds 1) span a broad range of lead-like space, 2) show a high degree of structural integrity and purity, and 3) demonstrate appropriate solubility for the purposes of biochemical screening. The implications of this study for compound selection, especially in an academic environment with limited resources, are considered.