Cryo-EM structures of adenosine receptor A3AR bound to selective agonists.

The adenosine A3 receptor (A3AR), a key member of the G protein-coupled receptor family, is a promising therapeutic target for inflammatory and cancerous conditions. The selective A3AR agonists, CF101 and CF102, are clinically significant, yet their recognition mechanisms remained elusive. Here we report the cryogenic electron microscopy structures of the full-length human A3AR bound to CF101 and CF102 with heterotrimeric Gi protein in complex at 3.3-3.2 Å resolution. These agonists reside in the orthosteric pocket, forming conserved interactions via their adenine moieties, while their 3-iodobenzyl groups exhibit distinct orientations. Functional assays reveal the critical role of extracellular loop 3 in A3AR's ligand selectivity and receptor activation. Key mutations, including His3.37, Ser5.42, and Ser6.52, in a unique sub-pocket of A3AR, significantly impact receptor activation. Comparative analysis with the inactive A2AAR structure highlights a conserved receptor activation mechanism. Our findings provide comprehensive insights into the molecular recognition and signaling of A3AR, paving the way for designing subtype-selective adenosine receptor ligands.

GPR84 regulates pulmonary inflammation by modulating neutrophil functions.

Acute lung injury (ALI) is an acute, progressive hypoxic respiratory failure that could develop into acute respiratory distress syndrome (ARDS) with very high mortality rate. ALI is believed to be caused by uncontrolled inflammation, and multiple types of immune cells, especially neutrophils, are critically involved in the development of ALI. The treatment for ALI/ARDS is very limited, a better understanding of the pathogenesis and new therapies are urgently needed. Here we discover that GPR84, a medium chain fatty acid receptor, plays critical roles in ALI development by regulating neutrophil functions. GPR84 is highly upregulated in the cells isolated from the bronchoalveolar lavage fluid of LPS-induced ALI mice. GPR84 deficiency or blockage significantly ameliorated ALI mice lung inflammation by reducing neutrophils infiltration and oxidative stress. Further studies reveal that activation of GPR84 strongly induced reactive oxygen species production from neutrophils by stimulating Lyn, AKT and ERK1/2 activation and the assembly of the NADPH oxidase. These results reveal an important role of GPR84 in neutrophil functions and lung inflammation and strongly suggest that GPR84 is a potential drug target for ALI.

Discovery of orally effective and safe GPR40 agonists by incorporating a chiral, rigid and polar sulfoxide into ß-position to the carboxylic acid.

GPR40 is primarily expressed in pancreatic islet ß-cells, and its activation by endogenous ligands of medium to long-chain free fatty acids or synthetic agonists is clinically proved to improve glycemic control by stimulating glucose-dependent insulin secretion. However, most of the reported agonists are highly lipophilic, which might cause lipotoxicity and the off-target effects in CNS. Particularly, the withdrawal of TAK-875 from clinical trials phase III due to liver toxicity concern threw doubt over the long-term safety of targeting GPR40. Improving the efficacy and the selectivity, thus enlarging the therapeutic window would provide an alternative to develop safe GPR40-targeted therapeutics. Herein, by employing an innovative "three-in-one" pharmacophore drug design strategy, the optimal structural features for GPR40 agonist was integrated into one functional group of sulfoxide, which was incorporated into the ß-position of the propanoic acid core pharmacophore. As a result, the conformational constraint, polarity as well as chirality endowed by the sulfoxide significantly enhanced the efficacy, selectivity and ADMET properties of the novel (S)- 2-(phenylsulfinyl)acetic acid-based GPR40 agonists. The lead compounds (S)-4a and (S)-4s exhibited robust plasma glucose-lowering effects and insulinotropic action during an oral glucose tolerance test in C57/BL6 mice, excellent pharmacokinetic profile and little hepatobiliary transporter inhibition, marginal cell toxicities against human primary hepatocyte at 100 µM.