@article {Majpet.110.178194, author = {Jian-Nong Ma and Michelle Owens and Magnus Gustafsson and Jacob Jensen and Ali Tabatabaei and Kara Schmelzer and Roger Olsson and Ethan S. Burstein}, title = {Characterization of Highly Efficacious Allosteric Agonists of the Human Calcium-Sensing Receptor}, elocation-id = {jpet.110.178194}, year = {2011}, doi = {10.1124/jpet.110.178194}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {We discovered structurally novel human calcium-sensing receptor (CaSR) allosteric agonists, and compared their pharmacology to phenylalkylamine calcimimetics. AC-265347 activated CaSR signaling in cellular proliferation and phosphatidyl inositol (PI) hydrolysis assays with potencies of 30 and 10 nM, respectively. (S)-AC-265347, the (S) enantiomer of AC-265347, was approximately 10 to 20-fold more potent than (R)-AC-265347. The phenylalkylamines cinacalcet and calindol had similar activity to AC-265347 in cellular proliferation assays, but less activity in PI assays. All compounds had reduced activity when extracellular Ca2+ was removed indicating they cooperate with Ca2+ to activate CaSRs, and all activated CaSR isoforms with the N-terminal extracellular domain deleted, indicating they interact with the transmembrane (TM) domains. In both cases AC-265347 and therefore (S)-AC-265347 were significantly more efficacious than the phenylalkylamines. Mutations E837A7.39 and I841A7.43 strongly reduced phenylalkylamine-induced signaling, but not AC-265347 or (S)-AC-265347 induced signaling, suggesting different modes of binding. AC-265347 and (S)-AC-265347 stimulated significantly greater responses than cinacalcet or calindol at each of four loss-of-function human polymorphic CaSR variants. AC-265347 did not inhibit the CYP2D6 cytochrome p450 isozyme, unlike cinacalcet which is a potent CYP2D6 inhibitor. In rats, AC-265347, (S)-AC-265347 and (R)-AC-265347 each reduced serum parathyroid hormone (PTH) with a rank order potency correlated to their in vitro potencies. AC-265347 and (S)-AC-265347 also reduced plasma ionizable calcium ([Ca2+]o). AC-265347 was orally active, and its plasma concentrations correlated well with its effects on serum PTH. Thus these highly efficacious CaSR allosteric agonists represent leads for developing therapeutic agents with potential advantages over existing therapies.}, issn = {0022-3565}, URL = {https://jpet.aspetjournals.org/content/early/2011/01/21/jpet.110.178194}, eprint = {https://jpet.aspetjournals.org/content/early/2011/01/21/jpet.110.178194.full.pdf}, journal = {Journal of Pharmacology and Experimental Therapeutics} }