Discussion

The Corning® Epic® reader measures the response of unlabelled cells to a drug using dynamic mass redistribution (DMR). DMR is measured by the refraction of light from a biosensor integral to an Epic plate, but the cost of these high value plates has limited the use of this technology at scale. To enable its use in high throughput screening (HTS) we have successfully developed a 1536 format Epic® assay using a CHO-cell line over-expressing an orphan GPCR, but many challenges have been encountered throughout this process.

The first challenge was to make uncoated 1536 Epic® plates amenable for cell adhesion. Within AstraZeneca we have previously used commercially available 384 Epic® plates which have been coated with fibronectin, but for 1536 plates we wanted to investigate the application of this coating in house. Another challenge was to optimise the liquid handling capability for 1536 plates as the majority of equipment had previously been optimised only for 384 Epic® plates. Consideration of surface tension and low volumes within the well was imperative as we found that bubbles and evaporation were a problem during development. Even a small loss of liquid from each well had a significant effect on assay variability. We investigated multiple assay parameters to minimise this and a combination of these conditions successfully reduced variability, resulting in an assay that was of sufficient quality for screening.

To confirm that the 384 and 1536 formats generated identical data, a set of compounds were tested in concentration response assays to compare EC50 values. These data show that the 1536 assay format is fit for use in HTS, allowing us to maximise the number of compounds that can be screened against a target with significantly reduced screening costs.