BeKm-1, a Peptide Inhibitor of Human ether-a-go-go-Related Gene Potassium Currents, Prolongs QTc Intervals in Isolated Rabbit Heart

Abstract

Drug-induced cardiac arrhythmia, specifically Torsades de pointes, is associated with QT/QTc interval prolongation, thus prolongation of the QT interval is considered as a biomarker for Torsades de pointes risk (N Engl J Med 350:1013-1022, 2004). Specific inhibition of human ether-a-go-go-related gene (hERG) potassium channels has been recognized as the main mechanism for QT prolongation (Cardiovasc Res 58:32-45, 2003). This mechanism has been demonstrated for a variety of smallmolecule agents, which access the inner pore of the hERG channel preferentially from inside the cell. Peptide inhibitors of hERG, such as BeKm-1, interact with the extracellular amino acid residues close to the external pore region of the channel. In this study, the isolated rabbit heart was used to assess whether BeKm-1 could induce QTc prolongation like dofetilide and N- [4-[[1-[2-(6-methyl-2-pyridinyl) ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide (E-4031). Five hearts were perfused with 10 and 100 nM BeKm-1 sequentially. ECG parameters and left ventricular contractility were measured with spontaneously beating hearts. Both concentrations of BeKm-1 prolonged QTc intervals significantly and concentration-dependently (4.7 and 16.3% at 10 and 100 nM, respectively). When evaluated for their inhibitory effect in a hERG functional assay, BeKm-1, dofetilide, and E-4031 caused QTc prolongation at concentrations that caused significant hERG channel inhibition. Lastly, two polyclonal anti-hERG antibodies were also assessed in the hERG channel assay and found to be devoid of any inhibitory effect. These results indicated that the isolated rabbit heart assay can be used to measure QTc changes caused by specific hERG inhibition by peptides that specifically block the external pore region of the channel.

Functional Impact of BeKm-1, a High-Affinity hERG Blocker, on Cardiomyocytes Derived from Human-Induced Pluripotent Stem Cells

“…The effects of a mid-dose application of BeKm-1 on spontaneously beating hiPS-CMs consistently included cellular repolarization delay, negative chronotropic effects on APs, CaT, and monolayer contractions, which were accompanied with the higher rhythm variability of these parameters. This is in agreement with other studies investigating the effects of BeKm-1 on more integrated models [ 8 ]. Of note, negative chronotropic response is also in accordance with studies with common hERG blockers E4031 and dofetilide on hiPS-CMs [ 13 ] and on rabbit isolated hearts [ 14 ].…”

“…This reported value can be compared to some of the best hERG inhibitors: E4031 (IC 50 = 7.7 nM [ 5 ]), dofetilide (IC 50 = 12 nM [ 6 ]), and astemizole (IC 50 = 26 nM [ 7 ]). The proarrhythmic effect of BeKm-1 was evidenced in rabbit heart, a species expressing ERG channel, where it prolongs the QT interval in the electrocardiogram (ECG) [ 8 ]. Yet, the effect of BeKm-1 has never been tested on hiPS-CMs.…”

Oxytocin does not directly alter cardiac repolarization in rabbit or human cardiac myocytes

“… 2006 ), and it has demonstrated sensitivity to detect QT prolongation induced by BeKm-1, a specific peptide inhibitor of the hERG channel (Qu et al. 2011 ). Therefore, this isolated whole heart model can detect QTc prolongation caused by small or large molecules inhibitors that directly interfere with cardiac repolarization.…”

Proarrhythmic and Torsadogenic Effects of Potassium Channel Blockers in Patients

“…These models highlight the importance of Triangulation, Reverse use-dependence, Instability (of repolarization current), and Dispersion of Refractoriness, together known as the TRIaD model (2). Haraguchi et al who modeled transmural dispersion of repolarization (TDR) during ventricular tachycardia provide a good example of applying this approach to TdP (24 16). They found that arrhythmia risk in TdP is related to scroll wave stability, and is not directly associated with QT interval width.…”