Monitoring Gq-coupled receptor response through inositol phosphate quantification with the IP-One assay

G-protein-coupled receptors (GPCRs) are transmembrane proteins that play a key role in the signal transduction of extracellular stimuli. GPCRs associate to a complex assembly of intracellular proteins regulating a large variety of signaling pathways. In particular, the production of inositol 1,4,5 triphosphate (IP3) signs the activation of Gq-coupled receptors. However, its very short half-life makes its assessment too challenging for drug screening operations and the monitoring of calcium release, triggered by IP3, has been extensively used as a downstream readout of this signaling pathway. Recently, a new homogeneous time-resolved fluorescence (HTRF) assay, detecting a downstream metabolite of IP3, inositol monophosphate (IP1), has overcome the drawbacks of the IP3 quantification, allowing its use in primary or secondary screening.

This review provides an overview of the use of the IP-One assay in screening processes, providing comparisons with results obtained with other existing techniques traditionally used to investigate Gq-coupled receptors. Moreover, the review highlights two key features of the IP-One assay, the discrimination of slow acting compounds and the characterization of inverse agonists, which are impossible to achieve using calcium release.

The IP-One assay is well established to perform screening in the pharmaceutical industry. A number of criteria can be taken into account, including the impact of the sensitivity improvement of the assay, to position the IP-One assay in the different stages of the drug screening process. Moreover, the IP-One assay can be used as a valuable solution to investigate new research concepts such as ligand-biased signaling or receptor heteromerization.