Molecular Basis for Kv1.5 Channel Block

Abstract

Kv1.5 channels conduct the ultrarapid delayed rectifier current (I Kur ) that contributes to action potential repolarization of human atrial myocytes. Block of these channels has been proposed as a treatment for atrial arrhythmias. Here we report a novel and potent inhibitor of Kv1.5 potassium channels, N-benzyl-N-pyridin-3-yl-methyl-2-(toluene-4-sulfonylamino)-benzamide hydrochloride (S0100176), which exhibits features consistent with preferential block of the open state. The IC 50 of S0100176 for Kv1.5 expressed in Xenopus oocytes was 0.7 M. Ala-scanning mutagenesis within the pore helix and the S6 segment, regions that form the walls of the central cavity, was combined with voltage clamp analysis to identify point mutations that altered drug affinity. This approach identified Thr-479, Thr-480, Val-505, Ile-508, and Val-512 as the most important residues for block by S0100176. Mutations of these key residues to Ala or other amino acids caused marked changes in the IC 50 of S0100176 (p < 0.01). For example, the IC 50 of S0100176 increased 362-fold for T480A, 26-fold for V505A, 150-fold for I508A, and 99-fold for V512A. We used modeling to dock S0100176 into the inner cavity of a Kv1.5 pore homology model that was generated based on the crystal structure of KcsA. The docking predicted that the five residues identified by the Ala scan were positioned less than 4.5 Å from the compound. Based on the homology models, the positions of the five amino acids identified to interact with S0100176 face toward the central cavity and overlap with putative binding sites for other blockers and voltage-gated potassium channels.

Side pockets provide the basis for a new mechanism of Kv channel–specific inhibition

“…1a) 6 . Unexpectedly, Psora-4 selectively blocks Kv1.3 and Kv1.5 with a half-maximum inhibitory concentration (IC 50 ) of 3 nM and 7 nM, respectively, whereas other K + channels, including the related Kv3.1, are only blocked in the micromolar range 12 .…”

“…The critical residues are highly conserved in Na + and Ca 2+ channels 2–5 and in Kv channels 6–9 , greatly challenging the discovery and development of subtype-specific channel inhibitors. In contrast, peptide toxin inhibitors that either modify gating or occlude the channel pore by binding the outer vestibule often have high subtype specificity because they have a rather large contact interface with extracellular regions of the channels that are not highly conserved 10,11 .…”

Pharmacophore Mapping for Kv1.5 Potassium Channel Blockers

“…The generally key residues, including Thr507, Leu510, Val514 of the S6 segment and Thr 479 near the selectivity filter, can influence the inhibitory effect [23,24]. Decher et al reported an Ala scanning mutagenesis to highlight the IC 50 reduction by I508A (150-fold), V512A (99-fold), coincidently the same with the presumption that Ile 508 and Val 512 of Kv1.5 were located in the positions equivalent to Tyr 652 and Phe 656 of the hERG potassium channel [45]. Their other studies disclosed that the binding site was located in Thr 479, Thr 480 in the selectivity filter and Ile 502, Val 505, Ile 508, Leu 510, Val 512, and Val 516 in the S6 domain [55].…”

“…All partial charges on the atoms of the Kv1.5 homology model were derived from the AMBER 8 force field parameters. Docking of the ligands into the active site around Ile508 and Val512 of Kv1.5 potassium channel (equivalent to Tyr652 and Phe656 of the hERG potassium channel [45]) was performed by DOCK 5.4 program [46].…”

Structure‐Based Virtual Screening and Electrophysiological Evaluation of New Chemotypes of Kv1.5 Channel Blockers

“…In recent years, there have been many novel types of K v 1.5 channel blockers reported that differ from traditional anti-arrhythmic agents. These K v 1.5 channel blockers include AVE0118, [14] S-0100176, [15] ISQ-1, [16] TAEA, [17] ICA-32 and analogues, [18][19][20] BMS34136, [21] as well as some benzopyran sulfonamide derivatives such as NIP-142. [22] FurtherAtrial fibrillation (AF) is the most prevalent nonfatal cardiac rhythm disorder associated with an increased risk of heart failure and stroke.…”