GPCRdb in 2018: adding GPCR structure models and ligands.

G protein-coupled receptors are the most abundant mediators of both human signalling processes and therapeutic effects. Herein, we report GPCRome-wide homology models of unprecedented quality, and roughly 150 000 GPCR ligands with data on biological activities and commercial availability. Based on the strategy of 'Less model - more Xtal', each model exploits both a main template and alternative local templates. This achieved higher similarity to new structures than any of the existing resources, and refined crystal structures with missing or distorted regions. Models are provided for inactive, intermediate and active states-except for classes C and F that so far only have inactive templates. The ligand database has separate browsers for: (i) target selection by receptor, family or class, (ii) ligand filtering based on cross-experiment activities (min, max and mean) or chemical properties, (iii) ligand source data and (iv) commercial availability. SMILES structures and activity spreadsheets can be downloaded for further processing. Furthermore, three recent landmark publications on GPCR drugs, G protein selectivity and genetic variants have been accompanied with resources that now let readers view and analyse the findings themselves in GPCRdb. Altogether, this update will enable scientific investigation for the wider GPCR community. GPCRdb is available at http://www.gpcrdb.org.

Pharmacological characterization of novel small molecule agonists and antagonists for the orphan receptor GPR139.

The orphan G protein-coupled receptor GPR139 is predominantly expressed in the central nervous system and has attracted considerable interest as a therapeutic target. However, the biological role of this receptor remains somewhat elusive, in part due to the lack of quality pharmacological tools to investigate GPR139 function. In an effort to understand GPR139 signaling and to identify improved compounds, in this study we performed virtual screening and analog searches, in combination with multiple pharmacological assays. We characterized GPR139-dependent signaling using previously published reference agonists in Ca2+ mobilization and inositol monophosphate accumulation assays, as well as a novel real-time GPR139 internalization assay. For the four reference agonists tested, the rank order of potency was conserved across signaling and internalization assays: JNJ-63533054 > Compound 1a ¼ Takeda > AC4 > DL43, consistent with previously reported values. We noted an increased efficacy of JNJ-63533054-mediated inositol monophosphate signaling and internalization, relative to Compound 1a. We then performed virtual screening for GPR139 agonist and antagonist compounds that were screened and validated in GPR139 functional assays. We identified four GPR139 agonists that were active in all assays, with similar or reduced potency relative to known compounds. Likewise, compound analogs selected based on GPR139 agonist and antagonist substructure searches behaved similarly to their parent compounds. Thus, we have characterized GPR139 signaling for multiple new ligands using G protein-dependent assays and a new real-time internalization assay. These data add to the GPR139 tool compound repertoire, which could be optimized in future medical chemistry campaigns.

Discovery of a new class of orthosteric antagonists with nanomolar potency at extrasynaptic GABAA receptors.

Brain GABAΑ receptors are ionotropic receptors belonging to the class of Cys-loop receptors and are important drug targets for the treatment of anxiety and sleep disorders. By screening a compound library (2,112 compounds) at recombinant human α4ß1δ GABAΑ receptors heterologously expressed in a HEK cell line, we identified a scaffold of spirocyclic compounds with nanomolar antagonist activity at GABAΑ receptors. The initial screening hit 2027 (IC50 of 1.03 µM) was used for analogue search resulting in 018 (IC50 of 0.088 µM). 018 was most potent at α3,4,5-subunit containing receptors, thus showing preference for forebrain-expressed extrasynaptic receptors. Schild analysis of 018 at recombinant human α4ß1δ receptors and displacement of [3H]muscimol binding in rat cortical homogenate independently confirmed a competitive profile. The antagonist profile of 018 was further validated by whole-cell patch-clamp electrophysiology, where kinetic studies revealed a slow dissociation rate and a shallow hill slope was observed. Membrane permeability studies showed that 2027 and 018 do not cross membranes, thus making the compounds less attractive for studying central GABAΑ receptors effects, but conversely more attractive as tool compounds in relation to emerging peripheral GABAΑ receptor-mediated effects of GABA e.g. in the immune system.