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Background and PurposeTRPM4 is a calcium‐activated non‐selective cation channel expressed in many tissues and implicated in several diseases, and has not yet been validated as a therapeutic target due to the lack of potent and selective inhibitors. We sought to discover a novel series of small‐molecule inhibitors by combining in silico methods and cell‐based screening assay, with sub‐micromolar potency and improved selectivity from previously reported TRPM4 inhibitors.Experimental ApproachHere, we developed a high throughput screening compatible assay to record TRPM4‐mediated Na+ influx in cells using a Na+‐sensitive dye and used this assay to screen a small set of compounds selected by ligand‐based virtual screening using previously known weakly active and non‐selective TRPM4 inhibitors as seed molecules. Conventional electrophysiological methods were used to validate the potency and selectivity of the hit compounds in HEK293 cells overexpressing TRPM4 and in endogenously expressing prostate cancer cell line LNCaP. Chemical chaperone property of compound 5 was studied using Western blots and electrophysiology experiments.Key ResultsA series of halogenated anthranilic amides were identified with TRPM4 inhibitory properties with sub‐micromolar potency and adequate selectivity. We also showed for the first time that a naturally occurring variant of TRPM4, which displays loss‐of‐expression and function, is rescued by the most promising compound 5 identified in this study.Conclusions and ImplicationsThe discovery of compound 5, a potent and selective inhibitor of TRPM4 with an additional chemical chaperone feature, revealed new opportunities for studying the role of TRPM4 in human diseases and developing clinical drug candidates.

Running Title: Investigating adenosine receptor selectivity of N 6 -modified agonists.Keywords: GPCRs; adenosine receptor; selectivity; G proteins; yeast. 2 AbstractA series of N 6 -bicyclic and N 6 -(2-hydroxy)cyclopentyl derivatives of adenosine were synthesized as novel A1R agonists and their A1R/A2R selectivity assessed using a simple yeast screening platform. We observed that the most selective, high potency ligands were achieved through N 6 -adamantyl substitution in combination with 5'-N-ethylcarboxamido or 5'-hydroxymethyl groups. In addition, we determined that 5'-(2-fluoro)thiophenyl derivatives all failed to generate a signaling response despite showing an interaction with the A1R. Some selected compounds were also tested on A1R and A3R in mammalian cells revealing that four of them are entirely A1R-selective agonists. By using in silico homology modeling and ligand docking, we provide insight into their mechanisms of recognition and activation of the A1R. We believe that given the broad tissue distribution, but contrasting signaling profiles, of adenosine receptor subtypes these compounds might have therapeutic potential.3

This report describes the synthesis and biological characterization of novel granisetron derivatives that are antagonists of the human serotonin (5-HT3A) receptor. Some of these substituted granisetron derivatives showed low nanomolar binding affinity and allowed the identification of positions on the granisetron core that might be used as attachment points for biophysical tags. A BODIPY fluorophore was appended to one such position and specifically bound to 5-HT3A receptors in mammalian cells.

The 5-HT3 receptor is a member of the Cys-loop family of transmitter receptors. It can function as a homopentamer (5-HT3A-only subunits) or as a heteropentamer. The 5-HT3AB receptor is the best characterized heteropentamer. This receptor differs from a homopentamer in its kinetics, voltage dependence, and single-channel conductance, but its pharmacology is similar. To understand the contribution of the 5-HT3B subunit to the binding site, we created homology models of 5-HT3AB receptors and docked 5-HT and granisetron into AB, BA, and BB interfaces. To test whether ligands bind in any or all of these interfaces, we mutated amino acids that are important for agonist and antagonist binding in the 5-HT3A subunit to their corresponding residues in the 5-HT3B subunit and vice versa. Changes in [3H]granisetron binding affinity (Kd) and 5-HT EC50 were determined using receptors expressed in HEK-293 cells and Xenopus oocytes, respectively. For all A-to-B mutant receptors, except T181N, antagonist binding was altered or eliminated. Functional studies revealed that either the receptors were nonfunctional or the EC50 values were increased. In B-to-A mutant receptors there were no changes in Kd, although EC50 values and Hill slopes, except for N170T mutant receptors, were similar to those for 5-HT3A receptors. Thus, the experimental data do not support a contribution of the 5-HT3B subunit to the binding pocket, and we conclude that both 5-HT and granisetron bind to an AA binding site in the heteromeric 5-HT3AB receptor.

Background and Purpose: The antimalarial compounds quinine, chloroquine and mefloquine affect the electrophysiological properties of Cys-loop receptors and have structural similarities to 5-HT 3 receptor antagonists. They may therefore act at 5-HT 3 receptors. Experimental Approach: The effects of quinine, chloroquine and mefloquine on electrophysiological and ligand binding properties of 5-HT 3A receptors expressed in HEK 293 cells and Xenopus oocytes were examined. The compounds were also docked into models of the binding site.

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