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hERG Channel (herg + channel)
Selected AbstractsEmbryonic Arrhythmia by Inhibition of HERG Channels: A Common Hypoxia-related Teratogenic Mechanism for Antiepileptic Drugs?EPILEPSIA, Issue 5 2002Faranak Azarbayjani Summary: ,Purpose: There is evidence that drug-induced embryonic arrhythmia initiates phenytoin (PHT) teratogenicity. The arrhythmia, which links to the potential of PHT to inhibit a specific potassium channel (Ikr), may result in episodes of embryonic ischemia and generation of reactive oxygen species (ROS) at reperfusion. This study sought to determine whether the proposed mechanism might be relevant for the teratogenic antiepileptic drug trimethadione (TMO). Methods: Effects on embryonic heart rhythm during various stages of organogenesis were examined in CD-1 mice after maternal administration (125,1,000 mg/kg) of dimethadione (DMO), the pharmacologically active metabolite of TMO. Palatal development was examined after administration of a teratogenic dose of DMO and after simultaneous treatment with DMO and a ROS-capturing agent (,-phenyl- N -tert-butyl-nitrone; PBN). The Ikr blocking potentials of TMO and DMO were investigated in HERG-transfected cells by using voltage patch-clamping tests. Results: DMO caused stage-specific (gestation days 9,13 only) and dose-dependent embryonic bradycardia and arrhythmia at clinically relevant maternal plasma concentrations (3,11 mM). Hemorrhage in the nasopharyngeal part of the embryonic palate (within 24 h) preceded cleft palate in fetuses at term. Simultaneous treatment with PBN significantly reduced the incidence of DMO-induced cleft palate, from 40 to 13%. Voltage patch-clamping studies showed that particularly DMO (70% inhibition), but also TMO, had Ikr blocking potential at clinically relevant concentrations. Conclusions: TMO teratogenicity, in the same way as previously shown for PHT, was associated with Ikr -mediated episodes of embryonic cardiac arrhythmia and hypoxia/reoxygenation damage. [source] The functional properties of the human ether-à-go-go -like (HELK2) K+ channelEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2002Andrea Becchetti Abstract The voltage-dependent K+ channels belonging to the ether-à-go-go family (eag, erg, elk) are widely expressed in the mammalian CNS. Their neuronal function, however, is poorly understood. Among the elk clones, elk2 is the most abundantly expressed in the brain. We have characterized the human ELK2 channel (HELK2) expressed in mammalian cell lines. Moreover, we have detected helk2 mRNA and ELK2-like currents in freshly dissociated human astrocytoma cells. HELK2 was inhibited by Cs+ in a voltage-dependent way (Kd was 0.7 mm, at ,120 mV). It was not affected by Way 123398 (5 µm), dofetilide (10 µm), quinidine (10 µm), verapamil (20 µm), haloperidol (2 µm), astemizole (1 µm), terfenadine (1 µm) and hydroxyzine (30 µm), compounds known to inhibit the biophysically related HERG channel. The crossover of the activation and inactivation curves produced a steady state ,window' current with a peak around ,20 mV and considerably broader than it usually is in voltage-dependent channels, including HERG. Similar features were observed in the ELK2 clone from rat, in the same experimental conditions. Thus, ELK2 channels are active within a wide range of membrane potentials, both sub- and suprathreshold. Moreover, the kinetics of channel deactivation and removal of inactivation was about one order of magnitude quicker in HELK2, compared to HERG. Overall, these properties suggest that ELK2 channels are very effective at dampening the neuronal excitability, but less so at producing adaptation of action potential firing frequency. In addition, we suggest experimental ways to recognize HELK2 currents in vivo and raise the issue of the possible function of these channels in astrocytoma. [source] The antihistamine fexofenadine does not affect IKr currents in a case report of drug-induced cardiac arrhythmiaBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2002Constanze R Scherer The human HERG gene encodes the cardiac repolarizing K+ current IKr and is genetically inactivated in inherited long QT syndrome 2 (LQTS2). The antihistamine terfenadine blocks HERG channels, and can cause QT prolongation and torsades de pointes, whereas its carboxylate fexofenadine lacks HERG blocking activity. In the present study the ability of fexofenadine to block the K897T HERG channel variant was investigated. The underlying single nucleotide polymorphism (SNP) A2960C was identified in a patient reported to develop fexofenadine-associated LQTS. K897T HERG channels produced wild-type-like currents in Xenopus oocytes. Even at a concentration of 100 ,M, fexofenadine did not inhibit wild-type or K897T HERG channels. Coexpression of wild-type and K897T HERG with the ß-subunit MiRP1, slightly changed current kinetics but did not change sensitivity to terfenadine and fexofenadine. Western blot analysis and immunostaining of transiently transfected COS-7 cells demonstrated that overall expression level, glycosylation pattern and subcellular localization of K897T HERG is indistinguishable from wild-type HERG protein, and not altered in the presence of 1 ,M fexofenadine. We provide the first functional characterization of the K897T HERG variant. We demonstrated that K897T HERG is similar to wild-type HERG, and is insensitive to fexofenadine. Although the polymorphism changes PKA and PKC phosphorylation sites, regulation of K897T HERG by these kinases is not altered. Our results strongly indicate that QT lengthening and cardiac arrhythmia in the reported case of drug-induced LQT are not due to the K897T exchange or to an inhibitory effect of fexofenadine on cardiac IKr currents. British Journal of Pharmacology (2002) 137, 892,900. doi:10.1038/sj.bjp.0704873 [source] Comparative Pharmacology of Guinea Pig Cardiac Myocyte and Cloned hERG (IKr) ChannelJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2004CHRISTINA DAVIE Ph.D. Introduction: This study used whole-cell, patch clamp techniques on isolated guinea pig ventricular myocytes and HEK293 cells expressing cloned human ether-a-go-go-related gene (hERG) to examine the action of drugs causing QT interval prolongation and torsades de pointes (TdP) in man. Similarities and important differences in drug actions on cardiac myocytes and cloned hERG IKr channels were established. Qualitative actions of the drugs on cardiac myocytes corresponded with results obtained from Purkinje fibers and measurement of QT interval prolongation in animal and human telemetry studies. Methods and Results: Adult guinea pig ventricular myocytes were isolated by enzymatic digestion. Cells were continuously perfused with Tyrode's solution at 33,35°C. Recordings were made using the whole-cell, patch clamp technique. Action potentials (APs) were elicited under current clamp. Voltage clamp was used to study the effect of drugs on IKr (rapidly activating delayed rectifier potassium current), INa (sodium current), and ICa (L-type calcium current). Dofetilide increased the myocyte action potential duration (APD) in a concentration-dependent manner, with a pIC50 of 7.3. Dofetilide 1 ,M elicited early afterdepolarizations (EADs) but had little affect on ICa or INa. E-4031 increased APD in a concentration-dependent manner, with a pIC50 of 7.2. In contrast, 10 ,M loratadine, desloratadine, and cetirizine had little effect on APD or IKr. Interestingly, cisapride displayed a biphasic effect on myocyte APD and inhibited ICa at 1 ,M. Even at this high concentration, cisapride did not elicit EADs. A number of AstraZeneca compounds were tested on cardiac myocytes, revealing a mixture of drug actions that were not observed in hERG currents in HEK293 cells. One compound, particularly AR-C0X, was a potent blocker of myocyte AP (pIC50 of 8.4). AR-C0X also elicited EADs in cardiac myocytes. The potencies of the same set of drugs on the cloned hERG channel also were assessed. The pIC50 values for dofetilide, E-4031, terfenadine, loratadine, desloratadine, and cetirizine were 6.8, 7.1, 7.3, 5.1, 5.2, and <4, respectively. Elevation of temperature from 22 to 35°C significantly enhanced the current kinetics and amplitudes of hERG currents and resulted in approximately fivefold increase in E-4031 potency. Conclusion: Our study demonstrates the advantages of cardiac myocytes over heterologously expressed hERG channels in predicting QT interval prolongation and TdP in man. The potencies of some drugs in cardiac myocytes were similar to hERG, but only myocytes were able to detect important changes in APD characteristics and display EADs predictive of arrhythmia development. We observed similar qualitative drug profiles in cardiac myocytes, dog Purkinje fibers, and animal and human telemetry studies. Therefore, isolated native cardiac myocytes are a better predictor of drug-induced QT prolongation and TdP than heterologously expressed hERG channels. Isolated cardiac myocytes, when used with high-throughput patch clamp instruments, may have an important role in screening potential cardiotoxic compounds in the early phase of drug discovery. This would significantly reduce the attrition rate of drugs entering preclinical and/or clinical development. The current kinetics and amplitudes of the cloned hERG channel were profoundly affected by temperature, significantly altering the potency of one drug (E-4031). This finding cautions against routine drug testing at room temperature compared to physiologic temperature when using the cloned hERG channel. [source] Combined hERG channel inhibition and disruption of trafficking in drug-induced long QT syndrome by fluoxetine: a case-study in cardiac safety pharmacologyBRITISH JOURNAL OF PHARMACOLOGY, Issue 5 2006J C Hancox Drug-induced prolongation of the rate-corrected QT interval (QTCI) on the electrocardiogram occurs as an unwanted effect of diverse clinical and investigational drugs and carries a risk of potentially fatal cardiac arrhythmias. hERG (human ether-à-go-go-related gene) is the gene encoding the ,-subunit of channels mediating the rapid delayed rectifier K+ current, which plays a vital role in repolarising the ventricles of the heart. Most QTCI prolonging drugs can inhibit the function of recombinant hERG K+ channels, consequently in vitro hERG assays are used widely as front-line screens in cardiac safety-testing of novel chemical entities. In this issue, Rajamani and colleagues report a case of QTCI prolongation with the antidepressant fluoxetine and correlate this with a dual effect of the drug and of its major metabolite norfluoxetine on hERG channels. Both compounds were found to produce an acute inhibition of the hERG channel by pharmacological blockade, but in addition they also were able to disrupt the normal trafficking of hERG protein to the cell membrane. Mutations to a key component of the drug binding site in the S6 region of the channel greatly attenuated channel block, but did not impair disruption of trafficking; this suggests that channel block and drug effects on trafficking were mediated by different mechanisms. These findings add to growing evidence for disruption of hERG channel trafficking as a mechanism for drug-induced long QT syndrome and raise questions as to possible limitations of acute screening methods in the assessment of QTcI prolonging liability of drugs in development. British Journal of Pharmacology (2006) 149, 457,459. doi:10.1038/sj.bjp.0706890 [source] Prospective Validation of a Comprehensive In silico hERG Model and its Applications to Commercial Compound and Drug DatabasesCHEMMEDCHEM, Issue 5 2010Munikumar Abstract Ligand-based in silico hERG models were generated for 2,644 compounds using linear discriminant analysis (LDA) and support vector machines (SVM). As a result, the dataset used for the model generation is the largest publicly available (see Supporting Information). Extended connectivity fingerprints (ECFPs) and functional class fingerprints (FCFPs) were used to describe chemical space. All models showed area under curve (AUC) values ranging from 0.89 to 0.94 in a fivefold cross-validation, indicating high model consistency. Models correctly predicted 80,% of an additional, external test set; Y-scrambling was also performed to rule out chance correlation. Additionally models based on patch clamp data and radioligand binding data were generated separately to analyze their predictive ability when compared to combined models. To experimentally validate the models, 50 of the predicted hERG blockers from the Chembridge database and ten of the predicted non-hERG blockers from an in-house compound library were selected for biological evaluation. Out of those 50 predicted hERG blockers, tested at a concentration of 10,,M, 18 compounds showed more than 50,% displacement of [3H]astemizole binding to cell membranes expressing the hERG channel. Ki values of four of the selected binders were determined to be in the micromolar and high nanomolar range (Ki (VH01)=2.0,,M, Ki (VH06)=0.15,,M, Ki (VH19)=1.1,,M and Ki (VH47)=18 ,M). Of these four compounds, VH01 and VH47 showed also a second, even higher affinity binding site with Ki values of 7.4,nM and 36,nM, respectively. In the case of non-hERG blockers, all ten compounds tested were found to be inactive, showing less than 50,% displacement of [3H]astemizole binding at 10,,M. These experimentally validated models were then used to virtually screen commercial compound databases to evaluate whether they contain hERG blockers. 109,784 (23,%) of Chembridge, 133,175 (38,%) of Chemdiv, 111,737 (31,%) of Asinex and 11,116 (18,%) of the Maybridge database were predicted to be hERG blockers by at least two of the models, a prediction which could, for example, be used as a pre-filtering tool for compounds with potential hERG liabilities. [source] Comparative Pharmacology of Guinea Pig Cardiac Myocyte and Cloned hERG (IKr) ChannelJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2004CHRISTINA DAVIE Ph.D. Introduction: This study used whole-cell, patch clamp techniques on isolated guinea pig ventricular myocytes and HEK293 cells expressing cloned human ether-a-go-go-related gene (hERG) to examine the action of drugs causing QT interval prolongation and torsades de pointes (TdP) in man. Similarities and important differences in drug actions on cardiac myocytes and cloned hERG IKr channels were established. Qualitative actions of the drugs on cardiac myocytes corresponded with results obtained from Purkinje fibers and measurement of QT interval prolongation in animal and human telemetry studies. Methods and Results: Adult guinea pig ventricular myocytes were isolated by enzymatic digestion. Cells were continuously perfused with Tyrode's solution at 33,35°C. Recordings were made using the whole-cell, patch clamp technique. Action potentials (APs) were elicited under current clamp. Voltage clamp was used to study the effect of drugs on IKr (rapidly activating delayed rectifier potassium current), INa (sodium current), and ICa (L-type calcium current). Dofetilide increased the myocyte action potential duration (APD) in a concentration-dependent manner, with a pIC50 of 7.3. Dofetilide 1 ,M elicited early afterdepolarizations (EADs) but had little affect on ICa or INa. E-4031 increased APD in a concentration-dependent manner, with a pIC50 of 7.2. In contrast, 10 ,M loratadine, desloratadine, and cetirizine had little effect on APD or IKr. Interestingly, cisapride displayed a biphasic effect on myocyte APD and inhibited ICa at 1 ,M. Even at this high concentration, cisapride did not elicit EADs. A number of AstraZeneca compounds were tested on cardiac myocytes, revealing a mixture of drug actions that were not observed in hERG currents in HEK293 cells. One compound, particularly AR-C0X, was a potent blocker of myocyte AP (pIC50 of 8.4). AR-C0X also elicited EADs in cardiac myocytes. The potencies of the same set of drugs on the cloned hERG channel also were assessed. The pIC50 values for dofetilide, E-4031, terfenadine, loratadine, desloratadine, and cetirizine were 6.8, 7.1, 7.3, 5.1, 5.2, and <4, respectively. Elevation of temperature from 22 to 35°C significantly enhanced the current kinetics and amplitudes of hERG currents and resulted in approximately fivefold increase in E-4031 potency. Conclusion: Our study demonstrates the advantages of cardiac myocytes over heterologously expressed hERG channels in predicting QT interval prolongation and TdP in man. The potencies of some drugs in cardiac myocytes were similar to hERG, but only myocytes were able to detect important changes in APD characteristics and display EADs predictive of arrhythmia development. We observed similar qualitative drug profiles in cardiac myocytes, dog Purkinje fibers, and animal and human telemetry studies. Therefore, isolated native cardiac myocytes are a better predictor of drug-induced QT prolongation and TdP than heterologously expressed hERG channels. Isolated cardiac myocytes, when used with high-throughput patch clamp instruments, may have an important role in screening potential cardiotoxic compounds in the early phase of drug discovery. This would significantly reduce the attrition rate of drugs entering preclinical and/or clinical development. The current kinetics and amplitudes of the cloned hERG channel were profoundly affected by temperature, significantly altering the potency of one drug (E-4031). This finding cautions against routine drug testing at room temperature compared to physiologic temperature when using the cloned hERG channel. [source] Dexrazoxane protects the heart from acute doxorubicin-induced QT prolongation: a key role for IKsBRITISH JOURNAL OF PHARMACOLOGY, Issue 1 2010J Ducroq Introduction:, Doxorubicin, an anthracycline widely used in the treatment of a broad range of tumours, causes acute QT prolongation. Dexrazoxane has been shown to prevent the QT prolongation induced by another anthracycline, epirubicin, but has not yet been reported to prevent that induced by doxorubicin. Thus, the present study was designed to test whether the acute QT effects induced by doxorubicin could be blocked by dexrazoxane and to explore the mechanism. Results were compared with those obtained with a reference human ether-a-go-go (hERG) channel blocker, moxifloxacin. Methods:, The effects of moxifloxacin (100 µM) and doxorubicin (30 µM), with or without dexrazoxane (from 3 to 30 µM), have been evaluated on the QTc interval in guinea-pig isolated hearts and on IKr (rapid component of the delayed rectifier current) and IKs (slow component of the delayed rectifier current) currents stably expressed in human embryonic kidney 293 cells. Results:, Moxifloxacin (100 µM), a potent hERG blocker, prolonged QTc by 22%, and this effect was not prevented by dexrazoxane. Doxorubicin (30 µM) also prolonged QTc by 13%, did not significantly block hERG channels and specifically inhibited IKs (IC50: 4.78 µM). Dexrazoxane significantly reduced the doxorubicin-induced QTc prolongation and prevented doxorubicin-induced inhibition of IKs. Conclusion and implications:, Doxorubicin acutely prolonged the QT interval in guinea-pig heart by selective IKs blockade. This effect was prevented by dexrazoxane. This result is important because it illustrates the danger of neglecting IKs in favour of hERG screening alone, for early preclinical testing for possible induction of torsade de pointes. This article is part of a themed section on QT safety. To view this issue visit http://www3.interscience.wiley.com/journal/121548564/issueyear?year=2010 [source] Combined hERG channel inhibition and disruption of trafficking in drug-induced long QT syndrome by fluoxetine: a case-study in cardiac safety pharmacologyBRITISH JOURNAL OF PHARMACOLOGY, Issue 5 2006J C Hancox Drug-induced prolongation of the rate-corrected QT interval (QTCI) on the electrocardiogram occurs as an unwanted effect of diverse clinical and investigational drugs and carries a risk of potentially fatal cardiac arrhythmias. hERG (human ether-à-go-go-related gene) is the gene encoding the ,-subunit of channels mediating the rapid delayed rectifier K+ current, which plays a vital role in repolarising the ventricles of the heart. Most QTCI prolonging drugs can inhibit the function of recombinant hERG K+ channels, consequently in vitro hERG assays are used widely as front-line screens in cardiac safety-testing of novel chemical entities. In this issue, Rajamani and colleagues report a case of QTCI prolongation with the antidepressant fluoxetine and correlate this with a dual effect of the drug and of its major metabolite norfluoxetine on hERG channels. Both compounds were found to produce an acute inhibition of the hERG channel by pharmacological blockade, but in addition they also were able to disrupt the normal trafficking of hERG protein to the cell membrane. Mutations to a key component of the drug binding site in the S6 region of the channel greatly attenuated channel block, but did not impair disruption of trafficking; this suggests that channel block and drug effects on trafficking were mediated by different mechanisms. These findings add to growing evidence for disruption of hERG channel trafficking as a mechanism for drug-induced long QT syndrome and raise questions as to possible limitations of acute screening methods in the assessment of QTcI prolonging liability of drugs in development. British Journal of Pharmacology (2006) 149, 457,459. doi:10.1038/sj.bjp.0706890 [source] | ||||||||||