POLARISED views and FRETting about probe modulation assays: Learning from High Throughput Screening

Fluorescent probe modulation assays are a widely used approach to monitor displacement or stabilisation of fluorescently labelled tool ligands by test compounds. These assays allow an optical read-out of probe-receptor binding and can be used to detect compounds that compete with the labelled ligand, either directly or indirectly. Probes for both orthosteric and allosteric sites are often employed. The method can also be used to identify test compounds that may stabilise the ternary complex, offering an opportunity to discover novel molecular glues. The utility of these fluorescence-based assays within high-throughput screening has been facilitated by the use of streptavidin labelled terbium as a donor and access to a range of different acceptor fluorophores. During 2023, the High-throughput Screening group at AstraZeneca carried out 8 high-throughput screens using these approaches. In this manuscript we will present the types of assays used, an overview of the timelines for assay development and screening, the application of orthogonal artefact methods to aid hit finding and the results of the screens in terms of hit rate and the number of compounds identified with IC₅₀ values of better than 30 µM. Learning across the development, execution and analysis of these screens will be presented.