The macrolide drug erythromycin does not protect the hERG channel from inhibition by thioridazine and terfenadine

Abstract

The macrolide antibiotic erythromycin has been associated with QT interval prolongation and inhibition of the hERG‐encoded channels responsible for the rapid delayed rectifier K+ current I(Kr). It has been suggested that low concentrations of erythromycin may have a protective effect against hERG block and associated drug‐induced arrhythmia by reducing the affinity of the pore‐binding site for high potency hERG inhibitors. This study aimed to explore further the notion of a potentially protective effect of erythromycin. Whole‐cell patch‐clamp experiments were performed in which hERG‐expressing mammalian (Human Embryonic Kidney; HEK) cells were preincubated with low to moderate concentrations of erythromycin (3 or 30 µM) prior to whole‐cell patch clamp recordings of hERG current (IhERG) at 37°C. In contrast to a previous report, exposure to low concentrations of erythromycin did not reduce pharmacological sensitivity of hERG to the antipsychotic thioridazine and antihistamine terfenadine. The IC50 value for IhERG tail inhibition by terfenadine was decreased by ~32‐fold in the presence of 3 µM erythromycin (p < .05 vs. no preincubation). Sensitivity to thioridazine remained unchanged (p > .05 vs. no preincubation). The effects of low concentrations of erythromycin were investigated for a series of pore blocking drugs, and the results obtained were consistent with additive and/or synergistic effects. Experiments with the externally acting blocker BeKm‐1 on WT hERG and a pore mutant (F656V) were used to explore the location of the binding site for erythromycin. Our data are inconsistent with the use of erythromycin for the management of drug‐induced QT prolongation.

Inhibition of the hERG potassium channel by phenanthrene: a polycyclic aromatic hydrocarbon pollutant

“…The F656V mutation was made to hERG1a as described in Ref. [ 31 ]. F656T was made using QuikChange (Agilent) mutagenesis using conditions described in Ref.…”

“…F656T was made using QuikChange (Agilent) mutagenesis using conditions described in Ref. [ 31 ] and the following primer sequences:…”

“…F656T was made using QuikChange (Agilent) mutagenesis using conditions described in Ref. [31] and the following primer sequences: forward-5′-GTA TGC TAG CAT CAC CGG CAA CGT GTCG-3′ reverse-5′-CGA CAC GTT GCC GGT GAT GCT AGC ATAC-3′ Experiments were performed on hERG1a current (I hERG1a ) except for the data in Fig. 2B, C, which were conducted using co-expressed hERG1a and 1b channels (I hERG1a/1b ) and Supplementary Fig.…”

Calculations of the binding free energies of the Comprehensive <i>in vitro</i> Proarrhythmia Assay (CiPA) reference drugs to cardiac ion channels

“…We excluded three drugs, namely erythromycin (classified as macrolides), as well as nifedipine and nitrendipine (both classified as dihydropyridines), from the dataset, because they might modulate the channels via different mechanisms from blockade of the pore. It is believed that erythromycin allosterically modulates the blockade by the other pore inhibitors by binding to an extracellular site in the hERG channel [34][35][36]. The mutation of Y652 of the hERG channel does not affect the binding of erythromycin, indicating that it does not penetrate the pore cavity [34].…”

Inhibition of The hERG Potassium Channel By The Polycyclic Aromatic Hydrocarbon Pollutant Phenanthrene

“…The F656V mutation was made to hERG1a as described in [31]. F656T was made using QuikChange (Agilent) mutagenesis using conditions described in [31] and the following primer sequences: forward − 5'-GTATGCTAGCATCACCGGCAACGTGTCG-3' reverse − 5'-CGACACGTTGCCGGTGATGCTAGCATAC-3' Experiments were performed on hERG1a current (I hERG1a ) except for the data in Fig. 2B and C, which were conducted using co-expressed hERG1a and 1b channels (I hERG1a/1b ), and supplementary Fig.…”