title: Molecular determinants of human ether-à-go-go-related gene 1 (hERG1) K+ channel activation by NS1643.
abstract: Human ether-à-go-go-related gene 1 (hERG1) channels conduct the rapid delayed rectifier K+ current, I(Kr), an important determinant of action potential repolarization in mammals, including humans. Reduced I(Kr) function caused by mutations in KCNH2 or drug block of hERG1 channels prolongs the QT interval of the electrocardiogram and increases the risk of ventricular fibrillation and sudden cardiac death. Several activators of hERG1 channels have been discovered in recent years. These compounds shorten the duration of cardiac action potentials and have been proposed as a new therapeutic approach for the treatment of acquired or congenital long QT syndrome. We defined previously the mechanism of action of 1,3-bis-(2-hydroxy-5-trifluoromethyl-phenyl)-urea (NS1643), a compound that increases hERG1 currents by shifting the voltage-dependence of inactivation to more positive potentials. Here, we use scanning mutagenesis of hERG1 and functional characterization of 56 mutant channels heterologously expressed in Xenopus laevis oocytes to define the molecular determinants of the binding site for NS1643. Most point mutations did not alter response to the drug; however, 10 mutant channels had reduced sensitivity, and F619A and I567A exhibited enhanced activation by the drug. Some of these residues form a cluster and, together with molecular modeling, suggest that NS1643 binds to a pocket near the extracellular ends of the S5/S6 segments of two adjacent hERG1 channel subunits. This putative binding site differs from the sites described previously for two other hERG1 activators, (3R,4R)-4-[3-(6-methoxy-quinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluoro-phenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid (RPR260243) and 2-(4-[2-(3,4-dichloro-phenyl)-ethyl]-phenylamino)-benzoic acid (PD-118057).
authors.affiliation: Department of Drug Discovery Portfolio Management, NeuroSearch A/S, Pederstrupvej 93, 2750 Ballerup, Denmark. mgr@neurosearch.dk
authors.forename: Morten
authors.initials: M
authors.lastname: Grunnet
authors.forename: Jennifer
authors.initials: J
authors.lastname: Abbruzzese
authors.forename: Frank B
authors.initials: FB
authors.lastname: Sachse
authors.forename: Michael C
authors.initials: MC
authors.lastname: Sanguinetti
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D003408:Cresols / Q000494:pharmacology*; D051638:Ether-A-Go-Go Potassium Channels / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D006801:Humans; D008958:Models, Molecular; D010671:Phenylurea Compounds / Q000494:pharmacology*; D017354:Point Mutation / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects; D014982:Xenopus laevis / Q000235:genetics
chemical_list: D000889:Anti-Arrhythmia Agents; D003408:Cresols; D051638:Ether-A-Go-Go Potassium Channels; C496884:KCNH1 protein, human; D010671:Phenylurea Compounds; C507624:1,3-bis(2-hydroxy-5-trifluoromethylphenyl)urea