Salicylates are interference compounds in TR-FRET assays.

Given the importance of high-throughput screening in drug discovery, the identification of compounds that interfere with assay readouts is crucial. The pursuit of false positives wastes time and money, while distracting development teams from more promising leads. In the context of TR-FRET assays, most interfering compounds are dyes or aggregators. In the course of our studies on the PD1-PDL2 interaction, we discovered that salicylic acids, an extremely common compound subclass in screening libraries, interfere with TR-FRET assays. While the precise mechanism of interference was not established, our data suggest that interaction of the salicylate with the cryptand-ligated europium FRET donor is responsible for the change in assay signal.