Development of a conformational histamine H 3 receptor biosensor for the synchronous screening of agonists and inverse agonists.

The histamine H receptor (HR) represents a highly attractive drug target for the treatment of various central nervous disorders but the discovery of novel HR targeting compounds relies on the assessment of highly amplified intracellular signaling events that do not only reflect HR modulation and carry the risk of high false-positive and -negative screening rates. To address these limitations, we designed an intramolecular HR biosensor based on the principle of bioluminescence-resonance-energy-transfer (BRET) that reports the receptor's real-time conformational dynamics and provides an advanced tool to screen for both, HR agonists and inverse agonists in a live cell screening-compatible assay format. This conformational G-protein-coupled receptor (GPCR) sensor allowed us to characterize the pharmacological properties of known and new H receptor ligands with unprecedented accuracy. Intriguingly, we found that one newly developed H receptor ligand possesses even stronger inverse agonistic activity than reference HR inverse agonists including the current gold standard pitolisant. Taken together, we describe here the design and validation of the first screening-compatible HR conformational biosensor that will aid in the discovery of novel HR ligands and can be employed to gain deeper insights into the (in-)activation mechanism of this highly attractive drug target.