title: Molecular basis of hERG potassium channel blockade by the class Ic antiarrhythmic flecainide.
abstract: The class Ic antiarrhythmic drug flecainide inhibits KCNH2-encoded "hERG" potassium channels at clinically relevant concentrations. The aim of this study was to elucidate the underlying molecular basis of this action. Patch clamp recordings of hERG current (IhERG) were made from hERG expressing cells at 37°C. Wild-type (WT) IhERG was inhibited with an IC50 of 1.49μM and this was not significantly altered by reversing the direction of K(+) flux or raising external [K(+)]. The use of charged and uncharged flecainide analogues showed that the charged form of the drug accesses the channel from the cell interior to produce block. Promotion of WT IhERG inactivation slowed recovery from inhibition, whilst the N588K and S631A attenuated-inactivation mutants exhibited IC50 values 4-5 fold that of WT IhERG. The use of pore-helix/selectivity filter (T623A, S624A V625A) and S6 helix (G648A, Y652A, F656A) mutations showed <10-fold shifts in IC50 for all but V625A and F656A, which respectively exhibited IC50s 27-fold and 142-fold their WT controls. Docking simulations using a MthK-based homology model suggested an allosteric effect of V625A, since in low energy conformations flecainide lay too low in the pore to interact directly with that residue. On the other hand, the molecule could readily form π-π stacking interactions with aromatic residues and particularly with F656. We conclude that flecainide accesses the hERG channel from the cell interior on channel gating, binding low in the inner cavity, with the S6 F656 residue acting as a principal binding determinant.
authors.affiliation: School of Physiology & Pharmacology, Medical Sciences Building, University Walk, Bristol BS8 1TD, UK.
authors.forename: Dario
authors.initials: D
authors.lastname: Melgari
authors.affiliation: School of Physiology & Pharmacology, Medical Sciences Building, University Walk, Bristol BS8 1TD, UK.
authors.forename: Yihong
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Physiology & Pharmacology, Medical Sciences Building, University Walk, Bristol BS8 1TD, UK.
authors.forename: Aziza
authors.initials: A
authors.lastname: El Harchi
authors.affiliation: School of Biochemistry, Medical Sciences Building, University Walk, Bristol BS8 1TD, UK.
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Dempsey
authors.affiliation: School of Physiology & Pharmacology, Medical Sciences Building, University Walk, Bristol BS8 1TD, UK. Electronic address: jules.hancox@bristol.ac.uk.
authors.forename: Jules C
authors.initials: JC
authors.lastname: Hancox
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage; D001145:Arrhythmias, Cardiac / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D005424:Flecainide / Q000008:administration & dosage*; D005786:Gene Expression Regulation / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D062105:Molecular Docking Simulation; D009154:Mutation; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D016171:Torsades de Pointes / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D015534:Trans-Activators / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D000071230:Transcriptional Regulator ERG
chemical_list: D000889:Anti-Arrhythmia Agents; C072312:ERG protein, human; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D005424:Flecainide
keywords: Flecainide; QT interval; Repolarization; Torsades de Pointes; hERG