Molecular determinants of hERG potassium channel inhibition by disopyramide

The Class la antiarrhythmic drug disopyramide (DISO) causes QT interval prolongation that is potentially dangerous in acquired Long QT Syndrome but beneficial in short QT syndrome, through inhibition of the hERG-encoded channels responsible for rapid delayed rectifier K+ current (I-Kr). In this study, alanine mutants of hERG S6 and pore helix residues and MthK-based homology modelling and ligand docking were used to investigate molecular determinants of DISO binding to hERG. Whole-cell hERG current (I-hERG) recordings were made at 37 degrees C from HEK-293 cells expressing WT or mutant hERG channels. WT outward I-hERG tails were inhibited with an IC50 of 7.3 mu M, whilst inward I-hERG tails in a high [K+](e) of 94 mM were blocked with an IC50 of 25.7 mu M. The IC50 for the Y652A mutation was similar to 55-fold that of WT I-hERG; this mutation also abolished a leftward shift in voltage-dependent I-hERG activation present for WT hERG. The IC50 for F656A I-hERG was similar to 51 fold its corresponding WT control. In contrast to previously studied methanesulphonanilide hERG inhibitors, neither the G648A S6 nor the T623A and S624A pore helical mutations modified DISO IC50. Computational docking with the hERG model showed that DISO did not exhibit a single unique binding pose: instead several low energy binding poses at the lower end of the pore cavity favoured interactions with Y652 and F656. In the WT hERG model DISO did not interact directly with residues at the base of the pore helix, consistent with the minimal effect of mutation of these residues on drug block. (C) 2011 Elsevier Ltd. All rights reserved.