Inhibition of hERG K+ currents by antimalarial drugs in stably transfected HEK293 cells (original) (raw)
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European Journal of Pharmacology, 2006
The antipsychotic and anxiolytic phenothiazine, cyamemazine, was investigated for its effects on the hERG (human ether-à-go-go related gene) channel expressed in HEK 293 cells and on native I Na , I Ca , I to , I sus , or I K1 of human atrial myocytes. Moreover, cyamemazine and terfenadine were compared for their effects on the QT interval in anesthetized guinea pigs. Cyamemazine reduced hERG current amplitude with an IC 50 value of 470 nM. Cyamemazine 1 μM failed to significantly affect I Na , I to , I sus , or I K1 amplitudes and slightly decreased I Ca (18%). For comparison, haloperidol (30 nM) and olanzapine (300 nM) reduced hERG current amplitude by 44.2 ± 3.9% and 49.7 ± 4.2%, respectively. The cardiac safety ratio of cyamemazine, calculated from the IC 50 / receptor affinity ratios, is 81 and 313 against dopamine D 2 receptors and 5-HT 2A receptors, respectively. In guinea pigs, QT and QTcBazett were not significantly modified by intravenous cyamemazine when compared to the effects produced by the vehicle. Conversely, terfenadine (5 mg/kg iv) increased significantly QTcBazett (+ 58 ms), QTcFrediricia (+ 83 ms) and QTcVan de Water (+ 78 ms). In conclusion, cyamemazine concentrations required to inhibit hERG current exceed substantially those necessary to achieve therapeutic activity in humans. Moreover, cyamemazine, in contrast to terfenadine, does not delay cardiac repolarization in the anesthetized guinea pig. These non-clinical findings confirm the excellent cardiac safety records of cyamemazine during its 30 years of extensive therapeutic use.
Antimicrobial Agents and Chemotherapy, 2012
The in vitro cardiac properties of dihydroartemisinin (DHA) plus piperaquine phosphate (PQP) were compared with those of other antimalarial compounds. Results with antimalarial drugs, chosen on the basis of their free therapeutic maximum concentration in plasma (C max), were expressed as the fold of that particular effect with respect to their C max. The following tests were used at 37°C: hERG (human ether-à-go-go-related gene) blockade and trafficking, rabbit heart ventricular preparations, and sodium and slow potassium ion current interference (I Na and I Ks , respectively). Chloroquine, halofantrine, mefloquine, and lumefantrine were tested in the hERG studies, but only chloroquine, dofetilide, lumefantrine, and the combination of artemetherlumefantrine were used in the rabbit heart ventricular preparations, hERG trafficking studies, and I Na and I Ks analyses. A proper reference was used in each test. In hERG studies, the high 50% inhibitory concentration (IC 50) of halofantrine, which was lower than its C max , was confirmed. All the other compounds blocked hERG, with IC 50 s ranging from 3-to 30-fold their C max s. In hERG trafficking studies, the facilitative effects of chloroquine at about 30-fold its C max were confirmed and DHA blocked it at a concentration about 300-fold its C max. In rabbit heart ventricular preparations, dofetilide, used as a positive control, revealed a high risk of torsades de pointes, whereas chloroquine showed a medium risk. Neither DHA-PQP nor artemether-lumefantrine displayed an in vitro signal for a significant proarrhythmic risk. Only chloroquine blocked the I Na ion current and did so at about 30-fold its C max. No effect on I Ks was detected. In conclusion, despite significant hERG blockade, DHA-PQP and artemether-lumefantrine do not appear to induce potential torsadogenic effects in vitro, affect hERG trafficking, or block sodium and slow potassium ion currents.
Current protocols in pharmacology / editorial board, S.J. Enna (editor-in-chief) ... [et al.], 2012
In vitro electrophysiological safety studies have become an integral part of the drug development process since, in many instances, compound-induced QT prolongation has been associated with a direct block of human ether-a-go-go-related gene (hERG) potassium channels or its native current, the rapidly activating delayed rectifier potassium current (I(Kr)). Therefore, the in vitro hERG channel patch-clamp assay is commonly used as an early screen to predict the ability of a compound to prolong QT interval. The protocol described in this unit is designed to assess the effects of new chemical entities after acute or long-term exposure on the amplitude of I(Kr) in human embryonic kidney 293 (HEK293) cells stably transfected with the hERG channel (whole-cell configuration of the patch-clamp technique). Examples of results obtained with terfenadine, arsenic, pentamidine, erythromycin, and sotalol are provided for illustrative purposes.
Antimicrobial Agents and Chemotherapy, 2012
The in vitro cardiac properties of dihydroartemisinin (DHA) plus piperaquine phosphate (PQP) were compared with those of other antimalarial compounds. Results with antimalarial drugs, chosen on the basis of their free therapeutic maximum concentration in plasma (C max ), were expressed as the fold of that particular effect with respect to their C max . The following tests were used at 37°C: hERG (human ether-à-go-go-related gene) blockade and trafficking, rabbit heart ventricular preparations, and sodium and slow potassium ion current interference (I Na and I Ks , respectively). Chloroquine, halofantrine, mefloquine, and lumefantrine were tested in the hERG studies, but only chloroquine, dofetilide, lumefantrine, and the combination of artemetherlumefantrine were used in the rabbit heart ventricular preparations, hERG trafficking studies, and I Na and I Ks analyses. A proper reference was used in each test. In hERG studies, the high 50% inhibitory concentration (IC 50 ) of halofantrine, which was lower than its C max , was confirmed. All the other compounds blocked hERG, with IC 50 s ranging from 3-to 30-fold their C max s. In hERG trafficking studies, the facilitative effects of chloroquine at about 30-fold its C max were confirmed and DHA blocked it at a concentration about 300-fold its C max . In rabbit heart ventricular preparations, dofetilide, used as a positive control, revealed a high risk of torsades de pointes, whereas chloroquine showed a medium risk. Neither DHA-PQP nor artemether-lumefantrine displayed an in vitro signal for a significant proarrhythmic risk. Only chloroquine blocked the I Na ion current and did so at about 30-fold its C max . No effect on I Ks was detected. In conclusion, despite significant hERG blockade, DHA-PQP and artemether-lumefantrine do not appear to induce potential torsadogenic effects in vitro, affect hERG trafficking, or block sodium and slow potassium ion currents.
Journal of Biological Chemistry, 2012
Background: Inhibition of the cardiac hERG channel by essential pharmaceuticals is unpredictable and leads to fatal arrhythmias. Results: Pretreatment with a newly identified compound, VU0405601, reduces sensitivity of hERG to inhibition by multiple blockers and prevents arrhythmias. Conclusion: hERG-related arrhythmias are amenable to preventive therapy. Significance: A novel approach at ion channel modulation that impacts drug discovery and safety concerns is outlined. The human Ether-à-go-go-related gene (hERG)-encoded K ؉ current, I Kr is essential for cardiac repolarization but is also a source of cardiotoxicity because unintended hERG inhibition by diverse pharmaceuticals can cause arrhythmias and sudden cardiac death. We hypothesized that a small molecule that diminishes I Kr block by a known hERG antagonist would constitute a first step toward preventing hERG-related arrhythmias and facilitating drug discovery. Using a high-throughput assay, we screened a library of compounds for agents that increase the IC 70 of dofetilide, a well characterized hERG blocker. One compound, VU0405601, with the desired activity was further characterized. In isolated, Langendorff-perfused rabbit hearts, optical mapping revealed that dofetilide-induced arrhythmias were reduced after pretreatment with VU0405601. Patch clamp analysis in stable hERG-HEK cells showed effects on current amplitude, inactivation, and deactivation. VU0405601 increased the IC 50 of dofetilide from 38.7 to 76.3 nM. VU0405601 mitigates the effects of hERG blockers from the extracellular aspect primarily by reducing inactivation, whereas most clinically relevant hERG inhibitors act at an inner pore site. Structure-activity relationships surrounding VU0405601 identified a 3-pyridiyl and a naphthyridine ring system as key structural components important for preventing hERG inhibition by multiple inhibitors. These findings indicate that small molecules can be designed to reduce the sensitivity of hERG to inhibitors. The hERG 3 gene product forms the pore-forming subunit of the delayed rectifier I Kr , an important repolarizing current in the human heart (1, 2). Diminished repolarization either through genetic mutations in proteins that shape the action potential (AP), including ion channels or through inhibition by a pharmaceutical agent, can lead to AP prolongation and lengthening of the QT interval on the surface ECG. Mutations in the hERG gene (KCNH2) cause the relatively rare congenital long QT syndrome (LQTS), which can result in the Torsades de Pointes arrhythmia and sudden cardiac death (3, 4). Moreover, inhibition of I Kr either through class III antiarrhythmic drugs (5), through unintended block by agents prescribed for noncardiac conditions (6-8), or through over-the-counter drugs (9) can lead to the acquired LQTS (10). Consequently, arrhythmias associated with hERG inhibition have led to the withdrawal of otherwise successful drugs from the market. Indeed, the Food and Drug Administration has issued guidelines (ICH S6 and S7A) that require evaluation of novel chemical entities for their potential to induce QT prolongation early in drug development (11). It has been estimated that 50-70% of all lead compounds are eliminated at early stages due to hERG-related safety issues (12), thereby limiting the number of drugs that enter the development pipeline. On the other hand, hERG inhibition is not always predictive of proarrhythmic potential; for example, experience with clinically safe drugs like verapamil (13), which blocks hERG but does not alter APs due to simultaneous effects on calcium channels (14, 15), argues that it can be counterproductive to categorically avoid all hERG blockers. We hypothesized that a small mole-* This work was supported, in whole or in part, by National Institutes of Health Grants 1RO1HL090790 and RO3MH084820 (to S. K.), 1 U54 MH074427 (to C. D. W.
Molecular Pharmacology, 2005
A variety of drugs have been reported to cause acquired long-QT syndrome (LQTS) through inhibition of the I Kr channel. Screening compounds in early discovery and development stages against their ability to inhibit I Kr or the hERG channel has therefore become an indispensable procedure in the pharmaceutical industry. In contrast to numerous hERG channel blockers discovered during screening, so far only RPR260243 has been reported to enhance the hERG current. In this article, we describe several potent, mechanistically distinct hERG channel enhancers. One example is PD-118057 which produced average increases of 5.5 ± 1.1, 44.8 ± 3.1, and 111.1 ± 21.7% in the peak tail hERG current at 1, 3 and 10 µM, respectively, in HEK-293 cells. PD-118057 did not affect the voltage dependence and kinetics of gating parameters, nor did it require open conformation of the channel. In isolated guinea-pig cardiomyocytes, PD-118057 showed no major effect on I Na , I Ca,L , I K1 and I Ks. PD-118057 shortened the action potential duration and QT interval in arterially perfused rabbit ventricular wedge preparation in a concentration-dependent manner. Presence of 3-µM PD-118057 prevented APD and QT prolongation caused by dofetilide. Early after depolarizations induced by dofetilide were also completely eliminated by 3 µM PD-118057. While further investigation is warranted to evaluate the therapeutic value and safety profile of these compounds, our data support the notion that hERG activation by pharmaceuticals may offer a new approach in the treatment of delayed repolarization conditions which may occur in inherited or acquired LQTS, congestive heart failure and diabetes patients.
Potent Inhibition of hERG Channels by the Over-the-Counter Antidiarrheal Agent Loperamide
JACC: Clinical Electrophysiology, 2016
The aim of this study was to determine the in vitro electrophysiological properties of loperamide. The authors' hypothesis was that loperamide is a potent blocker of the current carried by the human ether-à-go-go-related gene (hERG) potassium channel. BACKGROUND Loperamide is a peripherally-acting m-opioid agonist available worldwide as an over-the-counter treatment for diarrhea. Like most opioids, it is not currently known to be proarrhythmic. Recent cases of torsade de pointes in association with high-dose loperamide raise concern given its structural similarity to methadone, another synthetic opioid with an established arrhythmia risk. METHODS Effects of loperamide on blockade of the hERG potassium channel ion current were assessed in Chinese hamster ovary cells (CHO) stably expressing hERG to elucidate current amplitude and kinetics. The concentration required to produce 50% inhibition (IC50) of hERG current was assessed from the amplitude of tail currents and the impact on action potential duration was assessed in isolated swine ventricular cardiomyocytes. RESULTS The 50% inhibitory concentration for loperamide inhibition of hERG ionic tail currents was approximately 40 nmol/l. In current-voltage measurements, loperamide reduced steady and tail currents and shifted the current activation to more negative potentials. Loperamide (10 nmol/l) also increased the action potential duration, assessed at 90% of repolarization, in ventricular myocytes by 16.4 AE 1.7% (n ¼ 6, p < 0.004). The maximum rate of rise of phase 0 of the action potential, however, was not significantly altered at any tested concentration of loperamide. CONCLUSIONS Loperamide is a potent hERG channel blocker. It significantly prolongs the action potential duration and suggests a causal association between loperamide and recent clinical cases of torsade de pointes.
Sulfonylureas blockade of neural and cardiac HERG channels
Febs Letters, 1998
The human ether-a-go-go-related gene (herg) encodes a K+ current (IHERG) which plays a fundamental role in heart excitability and in neurons by contributing to action potential repolarization and to spike-frequency adaptation, respectively. In this paper we show that IHERG, recorded in neuroblastoma cells and guinea-pig ventricular myocytes, was reversibly inhibited by the KATP channel blocker glibenclamide (IC50=74 μM). The voltage