hERG Channel Research Articles

Facilitation of hERG Activation by Its Blocker: A Mechanism to Reduce Drug-Induced Proarrhythmic Risk.

Modulation of the human Ether-à-go-go-Related Gene (hERG) channel, a crucial voltage-gated potassium channel in the repolarization of action potentials in ventricular myocytes of the heart, has significant implications on cardiac electrophysiology and can be either antiarrhythmic or proarrhythmic. For example, hERG channel blockade is a leading cause of long QT syndrome and potentially life-threatening arrhythmias, such as torsades de pointes. Conversely, hERG channel blockade is the mechanism of action of Class III antiarrhythmic agents in terminating ventricular tachycardia and fibrillation. In recent years, it has been recognized that less proarrhythmic hERG blockers with clinical potential or Class III antiarrhythmic agents exhibit, in addition to their hERG-blocking activity, a second action that facilitates the voltage-dependent activation of the hERG channel. This facilitation is believed to reduce the proarrhythmic potential by supporting the final repolarizing of action potentials. This review covers the pharmacological characteristics of hERG blockers/facilitators, the molecular mechanisms underlying facilitation, and their clinical significance, as well as unresolved issues and requirements for research in the fields of ion channel pharmacology and drug-induced arrhythmias.

Estrogen-induced phenotype in hiPSC-derived cardiomyocytes of a woman affected by both Long QT Syndrome Type 2 and Polycystic Ovary Syndrome

Abstract Introduction Long QT Syndrome (LQTS) is an arrhythmogenic disorder caused either by genetic alteration or by exogenous factors. Polycystic Ovary Syndrome (PCOS) is a disease associated with high levels of testosterone and low levels of estrogen (E2). It has been suggested that hormones can influence the occurrence of malignant cardiac events in LQTS type 2 (LQT2) women, carriers of mutations on the potassium channel (hERG). However, the precise mechanisms governing this process still need to be clarified. Purpose We studied a patient affected by both LQT2 and PCOS who started experiencing cardiac symptoms after initiation of hormonal replacement therapy. We observed a correlation with the occurrence of arrhythmic events and the irregular assumption of the hormonal replacement therapy, thus we aim to dissect the underlying mechanism in patient-in-a-dish cardiac cellular model. Methods Induced Pluripotent Stem Cells (hiPSC) were generated from a woman affected by both LQT2 and PCOS and from a healthy donor, and then differentiated into cardiomyocytes (hiPSC-CMs). hiPSC-CMs were stimulated with E2 10nM for five time points (1, 5, 10, 15 and 30 minutes). The expression of potassium channel hERG, and of the G-coupled estrogen receptor (GPER) regulating the fast non-genomic pathway, were quantified after E2 stimulation at different time points by In Cell Western (ICW). The Unstimulated sample were used to normalize GPER and hERG expression to 100%. Electrophysiological experiments were performed using the whole-cell patch-clamp technique in current-clamp mode to record spontaneous action potentials (APs). AP duration at 30%, 50% and 90% repolarization (APD30, APD50 and APD90) was quantified. During spontaneous activity, AP duration values were rate-corrected with Bazett’s formula, thus obtaining cAPD. Results LQT2 hiPSC-CMs express higher levels of GPER (p<0.05) and hERG (p<0.01) than healthy hiPSC-CMs. A significant decrease in GPER expression was detected during 10nM E2 stimulation in healthy cardiomyocytes at the five time points (p<0.0001), while any difference was detected in hERG expression levels. E2 stimulation at different time points did not affect neither GPER nor hERG expression in LQT2 hiPSC-CMs. In LQT2 hiPSC-CMs, APDC values were significantly increased (p<0.0001) compared to healthy cells; pre-incubation with E2 for 10 minutes significantly shortened cAPD50 and increased spontaneous firing rate. In healthy hiPSC-CMs, E2 had no effect. Conclusions The hiPSC-CM model reproduces the LQT2 clinical phenotype. cAPD50 shortening by E2 was unexpected based on the proarrhythmic effect in the patient. The mechanism of LQT2-specific effects of E2 are under investigation.

The impact of uncertainty in hERG binding mechanism on in silico predictions of drug-induced proarrhythmic risk.

Drug-induced reduction of the rapid delayed rectifier potassium current carried by the human Ether-à-go-go-Related Gene (hERG) channel is associated with increased risk of arrhythmias. Recent updates to drug safety regulatory guidelines attempt to capture each drug's hERG binding mechanism by combining in vitro assays with in silico simulations. In this study, we investigate the impact on in silico proarrhythmic risk predictions due to uncertainty in the hERG binding mechanism and physiological hERG current model. Possible pharmacological binding models were designed for the hERG channel to account for known and postulated small molecule binding mechanisms. After selecting a subset of plausible binding models for each compound through calibration to available voltage-clamp electrophysiology data, we assessed their effects, and the effects of different physiological models, on proarrhythmic risk predictions. For some compounds, multiple binding mechanisms can explain the same data produced under the safety testing guidelines, which results in different inferred binding rates. This can result in substantial uncertainty in the predicted torsade risk, which often spans more than one risk category. By comparison, we found that the effect of a different hERG physiological current model on risk classification was subtle. The approach developed in this study assesses the impact of uncertainty in hERG binding mechanisms on predictions of drug-induced proarrhythmic risk. For some compounds, these results imply the need for additional binding data to decrease uncertainty in safety-critical applications.

Abstract 11956: Arumenamide-787 Suppresses Arrhythmogenesis Associated With the J Wave Syndrome as Well as Hypothermia

Background: The J-wave syndromes (JWS), comprised of Brugada (BrS) and early repolarization syndromes (ERS), increase the risk of life-threatening ventricular arrhythmias in patients resulting in sudden cardiac death. There are limited therapeutic strategies to treat these life-threatening conditions. Present management is via an implantable cardioverter defibrillator and/or medication, including quinidine. However, these treatments may have serious side-effects. Thus, novel therapies are needed to treat JWS. In this study, we investigate the effects of ARumenamide-787 (AR-787) in suppressing the electrocardiographic and arrhythmic manifestations of JWS and hypothermia. Methods: We studied the effects of AR-787 on sodium current (I Na ) and the delayed-rectifier potassium current (I Kr ) in HEK-293 cells stably expressing the α- and β1-subunits of the cardiac (Na V 1.5) sodium channel or the hERG channel. In addition, we studied its effect on the transient outward potassium current (I to ) and calcium current (I Ca ) from dissociated canine ventricular myocytes, along with action potentials and ECG from coronary-perfused right (RV) and left (LV) ventricular wedge preparations. The I to agonist, NS5806, I Ca blocker, verapamil, and sodium current (I Na ) blocker, ajmaline, to induce the electrocardiographic and arrhythmic manifestations of JWS (prominent J waves/ST segment elevation, phase 2 reentry, and polymorphic VT/VF) in right and left canine ventricular wedge preparations. Results: AR-787 exerted pleiotropic effects on the cardiac ion channels. The predominant effect was an inhibition of I to and enhancement of I Na , with subtle effects to inhibit the I Kr and augment I Ca . AR-787 diminished the electrocardiographic J wave and prevented and/or suppressed all arrhythmic activity in canine RV and LV experimental models of BrS, ERS and hypothermia. We observed no arrhythmogenic effects of AR-787 on I Kr . Conclusions: Our findings point to AR-787 as a promising candidate for the pharmacologic treatment of JWS and hypothermia. AR-787 suppresses the electrocardiographic and arrhythmic manifestations of JWS and hypothermia without significant prolongation of the QT interval, as with the classic BrS drug, quinidine.

Abstract 12241: Low-Efficiency Gene Editing is Capable of Suppressing Arrhythmogenesis in Long QT Syndrome Type II: Computer Simulation Study

Background: Long QT Syndrome Type II (LQT2) is a congenital cause of arrhythmia and sudden cardiac death due to mutations in ion channel hERG responsible for the rapid inward rectifying potassium current (I Kr ). Progress in gene therapy may result in a viable treatment for LQT2. However, the gene transduction efficacy required to prevent cardiac arrhythmias in LQT2 is unknown. We used computer simulation to examine the minimum gene transduction efficacy necessary to suppress early afterdepolarizations (EADs). Hypothesis: Low transduction efficacy of hERG is sufficient to suppress EADs through electrotonic coupling between transduced I Kr (+) and non-transduced I Kr (-) cardiomyocytes (Fig 1A). Methods: Computational models of rabbit and human cardiac tissue were implemented in 2D (100 x 100 cells) and 3D (13 x 13 x 13 cells) with a multi-state Markov model for I Kr and a dynamic gap junction resistance model. Gene transduction efficacy was modeled by varying the percentage of I Kr (+) cardiomyocytes from 0-100%. Spatial heterogeneity in gene delivery was modeled by varying the cluster size of I Kr (+) cells from 1-400 cells. I Kr (+) cell clusters were distributed randomly in the tissue. Results: In 2D, EADs were suppressed with 14% I Kr (+) cells (rabbit model) and 12% I Kr (+) cells (human model) (Fig 1B). In 3D, the minimum transduction efficacy was further reduced to 10% (rabbit model) which likely reflects the impact of increased cell-cell coupling. Clustering I Kr (+) cells required greater transduction efficacy (Fig 1C). Detailed ionic current trajectory analysis suggests that the sufficiently large gap junction current from I Kr (+) cells during phase 2 of the action potential can prevent I Kr (-) cells from undergoing the Andronov-Hopf bifurcation that leads to EADs. Conclusions: Computational models suggest low-efficiency gene editing is a viable approach for suppressing arrhythmogenesis in LQT2 patients.

Contractility measurements for cardiotoxicity screening with ventricular myocardial slices of pigs.

Cardiotoxicity is one major reason why drugs do not enter or are withdrawn from the market. Thus, approaches are required to predict cardiotoxicity with high specificity and sensitivity. Ideally, such methods should be performed within intact cardiac tissue with high relevance for humans and detect acute and chronic side effects on electrophysiological behaviour, contractility, and tissue structure in an unbiased manner. Herein, we evaluate healthy pig myocardial slices and biomimetic cultivation setups (BMCS) as a new cardiotoxicity screening approach. Pig left ventricular samples were cut into slices and spanned into BMCS with continuous electrical pacing and online force recording. Automated stimulation protocols were established to determine the force-frequency relationship (FFR), frequency dependence of contraction duration, effective refractory period (ERP), and pacing threshold. Slices generated 1.3 ± 0.14 mN/mm2 force at 0.5 Hz electrical pacing and showed a positive FFR and a shortening of contraction duration with increasing pacing rates. Approximately 62% of slices were able to contract for at least 6 days while showing stable ERP, contraction duration-frequency relationship, and preserved cardiac structure confirmed by confocal imaging and X-ray diffraction analysis. We used specific blockers of the most important cardiac ion channels to determine which analysis parameters are influenced. To validate our approach, we tested five drug candidates selected from the Comprehensive in vitro Proarrhythmia Assay list as well as acetylsalicylic acid and DMSO as controls in a blinded manner in three independent laboratories. We were able to detect all arrhythmic drugs and their respective mode of action on cardiac tissue including inhibition of Na+, Ca2+, and hERG channels as well as Na+/Ca2+ exchanger. We systematically evaluate this approach for cardiotoxicity screening, which is of high relevance for humans and can be upscaled to medium-throughput screening. Thus, our approach will improve the predictive value and efficiency of preclinical cardiotoxicity screening.

Assembly of Cell-Free Synthesized Ion Channel Molecules in Artificial Lipid Bilayer Observed by Atomic Force Microscopy.

Artificial lipid bilayer systems, such as vesicles, black membranes, and supported lipid bilayers (SLBs), are valuable platforms for studying ion channels at the molecular level. The reconstitution of the ion channels in an active form is a crucial process in studies using artificial lipid bilayer systems. In this study, we investigated the assembly of the human ether-a-go-go-related gene (hERG) channel prepared in a cell-free synthesis system. AFM topographies revealed the presence of protrusions with a uniform size in the entire SLB that was prepared with the proteoliposomes (PLs) incorporating the cell-free-synthesized hERG channel. We attributed the protrusions to hERG channel monomers, taking into consideration the AFM tip size, and identified assembled structures of the monomer that exhibited dimeric, trimeric, and tetrameric-like arrangements. We observed molecular images of the functional hERG channel reconstituted in a lipid bilayer membrane using AFM and quantitatively evaluated the association state of the cell-free synthesized hERG channel.

Derivation of Highly Predictive 3D-QSAR Models for hERG Channel Blockers Based on the Quantum Artificial Neural Network Algorithm.

The hERG potassium channel serves as an annexed target for drug discovery because the associated off-target inhibitory activity may cause serious cardiotoxicity. Quantitative structure-activity relationship (QSAR) models were developed to predict inhibitory activities against the hERG potassium channel, utilizing the three-dimensional (3D) distribution of quantum mechanical electrostatic potential (ESP) as the molecular descriptor. To prepare the optimal atomic coordinates of dataset molecules, pairwise 3D structural alignments were carried out in order for the quantum mechanical cross correlation between the template and other molecules to be maximized. This alignment method stands out from the common atom-by-atom matching technique, as it can handle structurally diverse molecules as effectively as chemical derivatives that share an identical scaffold. The alignment problem prevalent in 3D-QSAR methods was ameliorated substantially by dividing the dataset molecules into seven subsets, each of which contained molecules with similar molecular weights. Using an artificial neural network algorithm to find the functional relationship between the quantum mechanical ESP descriptors and the experimental hERG inhibitory activities, highly predictive 3D-QSAR models were derived for all seven molecular subsets to the extent that the squared correlation coefficients exceeded 0.79. Given their simplicity in model development and strong predictability, the 3D-QSAR models developed in this study are expected to function as an effective virtual screening tool for assessing the potential cardiotoxicity of drug candidate molecules.

Utilizing Heteroatom Types and Numbers from Extensive Ligand Libraries to Develop Novel hERG Blocker QSAR Models Using Machine Learning-Based Classifiers.

The human ether-à-go-go-related gene (hERG) channel plays a crucial role in membrane repolarization. Any disruptions in its function can lead to severe cardiovascular disorders such as long QT syndrome (LQTS), which increases the risk of serious cardiovascular problems such as tachyarrhythmia and sudden cardiac death. Drug-induced LQTS is a significant concern and has resulted in drug withdrawals from the market in the past. The main objective of this study is to pinpoint crucial heteroatoms present in ligands that initiate interactions leading to the effective blocking of the hERG channel. To achieve this aim, ligand-based quantitative structure-activity relationships (QSAR) models were constructed using extensive ligand libraries, considering the heteroatom types and numbers, and their associated hERG channel blockage pIC50 values. Machine learning-assisted QSAR models were developed to analyze the key structural components influencing compound activity. Among the various methods, the KPLS method proved to be the most efficient, allowing the construction of models based on eight distinct fingerprints. The study delved into investigating the influence of heteroatoms on the activity of hERG blockers, revealing their significant role. Furthermore, by quantifying the effect of heteroatom types and numbers on ligand activity at the hERG channel, six compound pairs were selected for molecular docking. Subsequent molecular dynamics simulations and per residue MM/GBSA calculations were performed to comprehensively analyze the interactions of the selected pair compounds.

Pairwise biosynthesis of ion channels stabilizes excitability and mitigates arrhythmias

Coordinated expression of ion channels is crucial for cardiac rhythms, neural signaling, and cell cycle progression. Perturbation of this balance results in many disorders including cardiac arrhythmias. Prior work revealed association of mRNAs encoding cardiac NaV1.5 (SCN5A) and hERG1 (KCNH2), but the functional significance of this association was not established. Here, we provide a more comprehensive picture of KCNH2, SCN5A, CACNA1C, and KCNQ1 transcripts collectively copurifying with nascent hERG1, NaV1.5, CaV1.2, or KCNQ1 channel proteins. Single-molecule fluorescence in situ hybridization (smFISH) combined with immunofluorescence reveals that the channel proteins are synthesized predominantly as heterotypic pairs from discrete molecules of mRNA, not as larger cotranslational complexes. Puromycin disrupted colocalization of mRNA with its encoded protein, as expected, but remarkably also pairwise mRNA association, suggesting that transcript association relies on intact translational machinery or the presence of the nascent protein. Targeted depletion of KCHN2 by specific shRNA resulted in concomitant reduction of all associated mRNAs, with a corresponding reduction in the encoded channel currents. This co-knockdown effect, originally described for KCNH2 and SCN5A, thus appears to be a general phenomenon among transcripts encoding functionally related proteins. In multielectrode array recordings, proarrhythmic behavior arose when IKr was reduced by the selective blocker dofetilide at IC50 concentrations, but not when equivalent reductions were mediated by shRNA, suggesting that co-knockdown mitigates proarrhythmic behavior expected from the selective reduction of a single channel species. We propose that coordinated, cotranslational association of functionally related ion channel mRNAs confers electrical stability by co-regulating complementary ion channels in macromolecular complexes.

Diterpenoids from Euphorbia fischeriana with Kv1.3 Inhibitory Activity.

Euphorbia diterpenoids possess inhibitory effects of Kv1.3 ion channel, but most of this research has focused on diterpenoids with jatrophane-related or ingenane-related skeletons. In the present study, nine undescribed (1-9) and 16 known (10-25) diterpenoids, based on jatrophane, lathyrane, ingenane, abietane, and atisane skeletons, were identified from the methanol extract of the aerial parts of Euphorbia fischeriana. The structures were established by analysis of the spectroscopic data as well as by single-crystal X-ray diffraction analysis. Among the isolated diterpenoids, macrocyclic jatrophanes and lathyranes exerted Kv1.3 blocking activity. Compound 8 exhibited good selectivity on the inhibition of the Kv 1.3 channel rather than hERG channel, with a selectivity index over 7.0. The selective activity of lathyrane diterpenoids indicates that macrocyclic diterpenoids have the potential to be further investigated as therapeutic agents for the treatment of autoimmune diseases.

Systematical Evaluation of the Structure-Cardiotoxicity Relationship of 7-Azaindazole-based PI3K Inhibitors Designed by Bioisosteric Approach.

A growing concern of cardiotoxicity induced by PI3K inhibitors has raised the requirements to evaluate the structure-cardiotoxicity relationship (SCR) in the development process of novel inhibitors. Based on three bioisosteric 7-azaindazole-based candidate inhibitors namely FD269, FD268 and FD274 that give same order of inhibitory concentration 50% (IC50) magnitude against PI3Ks, in this work, we proposed to systematically evaluate the SCR of 7-azaindazole-based PI3K inhibitors designed by bioisosteric approach. The 24-h lethal concentrations 50% (LC50) of FD269, FD268 and FD274 against zebrafish embryos were 0.35, 4.82 and above 50μM (not detected), respectively. Determination of the heart rate, pericardial and yolk-sac areas and vascular malformation confirmed the remarkable reduction in the cardiotoxicity of from FD269 to FD268 and to FD274. The IC50s of all three compounds against the hERG channel were tested on the CHO cell line that constitutively expressing hERG channel, which were all higher than 20μM. The transcriptomic analysis revealed that FD269 and FD268 induced the up-regulation of noxo1b, which encodes a subunit of an NADPH oxidase evoking the oxidative stress. Furthermore, immunohistochemistry tests confirmed the structure-dependent attenuation of the overproduction of ROS and cardiac apoptosis. Our results verified the feasibility of bioisosteric replacement to attenuate the cardiotoxicity of 7-azaindazole-based PI3K inhibitors, suggesting that the screening for PI3K inhibitors with both high potency and low cardiotoxicity from bioisosteres would be a beneficial trial.

Translation reinitiation in c.453delC frameshift mutation of KCNH2 producing functional hERG K+ channels with mild dominant negative effect in the heterozygote patient-derived iPSC cardiomyocytes.

The c.453delC (p.Thr152Profs*14) frameshift mutation in KCNH2 is associated with an elevated risk of Long QT syndrome (LQTS) and fatal arrhythmia. Nevertheless, the loss-of-function mechanism underlying this mutation remains unexplored and necessitates an understanding of electrophysiology. To gain insight into the mechanism of the LQT phenotype, we conducted whole-cell patch-clamp and immunoblot assays, utilizing both a heterologous expression system and patient-derived induced pluripotent stem cell-cardiomyocytes (iPSC-CMs) with 453delC-KCNH2. We also explored the site of translational reinitiation by employing LC/MS mass spectrometry. Contrary to the previous assumption of early termination of translation, the findings of this study indicate that the 453delC-KCNH2 leads to an N-terminally truncated hERG channel, a potential from a non-canonical start codon, with diminished expression and reduced current (IhERG). The co-expression with wildtype KCNH2 produced heteromeric hERG channel with mild dominant-negative effect. Additionally, the heterozygote patient-derived iPSC-CMs exhibited prolonged action potential duration and reduced IhERG, which was ameliorated with the use of a hERG activator, PD-118057. The results of our study offer novel insights into the mechanisms involved in congenital LQTS associated with the 453delC mutation of KCNH2. The mutant results in the formation of less functional N-terminal-truncated channels with reduced amount of membrane expression. A hERG activator is capable of correcting abnormalities in both the heterologous expression system and patient-derived iPSC-CMs.

Impact of antipsychotics and antidepressants drugs on long QT syndrome induction related to hERG channel dysfunction: A systematic review

PurposeQT prolongation is one of the main unwanted cardiac effects caused by drugs, such as anti-psychotics and anti-depressants, inducing mainly via hERG channel dysfunction. The precise and underlying mechanism of adverse effects on hERG channel are still indecisive, but these effects limit their use in patients with cardiac risk factors. The aim of this review was studying mechanism of Long-term QT syndrome induction via hERG channel dysfunction by these Drugs. MethodSearch was performed in PubMed, and Scopus. All human, animals, and cell lines studies, English and full text publications were included. Among 1280 papers, 23 studies were eligible for more assessments. Quality of studies cheeked by two researchers independently. Key findingmost of studies were done on anti-psychotic drugs, especially typical class. Most used investigated method to long-term QT induction was patch clamp. Significanceresults suggests in susceptible cases with heart risk factors, these drugs should be taken with caution and monitored.

Targeted activation of human ether-à-go-go-related gene channels rescues electrical instability induced by the R56Q+/- long QT syndrome variant.

Long QT syndrome type 2 (LQTS2) is associated with inherited variants in the cardiac human ether-à-go-go-related gene (hERG) K+ channel. However, the pathogenicity of hERG channel gene variants is often uncertain. Using CRISPR-Cas9 gene-edited hiPSC-derived cardiomyocytes (hiPSC-CMs), we investigated the pathogenic mechanism underlying the LQTS-associated hERG R56Q variant and its phenotypic rescue by using the Type 1 hERG activator, RPR260243. The above approaches enable characterization of the unclear causative mechanism of arrhythmia in the R56Q variant (an N-terminal PAS domain mutation that primarily accelerates channel deactivation) and translational investigation of the potential for targeted pharmacologic manipulation of hERG deactivation. Using perforated patch clamp electrophysiology of single hiPSC-CMs, programmed electrical stimulation showed that the hERG R56Q variant does not significantly alter the mean action potential duration (APD90). However, the R56Q variant increases the beat-to-beat variability in APD90 during pacing at constant cycle lengths, enhances the variance of APD90 during rate transitions, and increases the incidence of 2:1 block. During paired S1-S2 stimulations measuring electrical restitution properties, the R56Q variant was also found to increase the variability in rise time and duration of the response to premature stimulations. Application of the hERG channel activator, RPR260243, reduces the APD variance in hERG R56Q hiPSC-CMs, reduces the variability in responses to premature stimulations, and increases the post-repolarization refractoriness. Based on our findings, we propose that the hERG R56Q variant leads to heterogeneous APD dynamics, which could result in spatial dispersion of repolarization and increased risk for re-entry without significantly affecting the average APD90. Furthermore, our data highlight the antiarrhythmic potential of targeted slowing of hERG deactivation gating, which we demonstrate increases protection against premature action potentials and reduces electrical heterogeneity in hiPSC-CMs.

P-Glycoprotein-Mediated Interaction Is a Risk Factor for QT Prolongation in Concomitant Use of Antipsychotics and SSRIs as P-Glycoprotein-Mediated Inhibitors: Analysis of the Japanese Adverse Drug Event Report Database.

The inhibition of human ether-a-go-go-related gene (hERG) channels is a known cause of QT prolongation triggered by antipsychotic drugs. Our previous studies suggest that P-glycoprotein (P-gp)-mediated drug interactions may lead to increased gastrointestinal absorption of pimozide and its accumulation in cardiomyocytes, thereby enhancing the inhibitory effect of hERG channels. There is a paucity of epidemiological studies examining the risk of QT prolongation by antipsychotic drugs in terms of P-gp-mediated interactions with concomitant drugs. Therefore, using the Japanese Adverse Event Reporting Database, we investigated whether the risk of QT prolongation triggered by antipsychotic drugs associated with hERG inhibition is affected by the concomitant use of selective serotonin reuptake inhibitors (SSRIs) associated with P-gp inhibition. The results showed that the frequency of QT prolongation increased when the antipsychotic drugs quetiapine and sulpiride, which are P-gp substrates, were combined with SSRIs with P-gp inhibition. In contrast, no association with QT prolongation was observed in patients on non-P-gp-substrate antipsychotics, irrespective of the P-gp inhibitory effect of the concomitant SSRI. These results suggest that P-gp-mediated interactions are a risk factor for antipsychotic-induced QT prolongation. There is a need for further investigation into the risks of specific drug combinations.

Transfer RNA-mediated restoration of potassium current and electrical correction in premature termination long-QT syndrome hERG mutants

Disease-causing premature termination codons (PTCs) individually disrupt the functional expression of hundreds of genes and represent a pernicious clinical challenge. In the heart, loss-of-function mutations in the hERG potassium channel account for approximately 30% of long-QT syndrome arrhythmia, a lethal cardiac disorder with limited treatment options. Premature termination of ribosomal translation produces a truncated and, for potassium channels, a potentially dominant-negative protein that impairs the functional assembly of the wild-type homotetrameric hERG channel complex. We used high-throughput flow cytometry and patch-clamp electrophysiology to assess the trafficking and voltage-dependent activity of hERG channels carrying patient PTC variants that have been corrected by anticodon engineered tRNA. Adenoviral-mediated expression of mutant hERG channels in cultured adult guinea pig cardiomyocytes prolonged action potential durations, and this deleterious effect was corrected upon adenoviral delivery of a human ArgUGA tRNA to restore full-length hERG protein. The results demonstrate mutation-specific, context-agnostic PTC correction and elevate the therapeutic potential of this approach for rare genetic diseases caused by stop codons.

New synthetic cannabinoids and the potential for cardiac arrhythmia risk

Synthetic cannabinoid receptor agonists (SCRAs) have been associated with QT interval prolongation. Limited preclinical information on SCRA effects on cardiac electrogenesis results from the rapid emergence of new compounds and restricted research availability. We used two machine-learning-based tools to evaluate seven novel SCRAs' interaction potential with the hERG potassium channel, an important drug antitarget. Five SCRAs were predicted to have the ability to block the hERG channel by both prediction tools; ADB-FUBIATA was predicted to be a strong hERG blocker. ADB-5Br-INACA and ADB-4en-PINACA showed varied predictions. These findings highlight potentially proarrhythmic hERG block by novel SCRAs, necessitating detailed safety evaluations.

Generation of patient-specific induced pluripotent stem cell lines with Type 2 Long QT Syndrome and the KCNH2 c.379C > T pathogenic variant

Type 2 Long QT Syndrome (LQT2) is a rare genetic heart rhythm disorder causing life-threatening arrhythmias. We derived induced pluripotent stem cell (iPSC) lines from two patients with LQT2, aged 18 and 6, both carrying a heterozygous missense mutation on the 3rd and 11th exons of KCNH2. The iPSC lines exhibited normal genomes, expressed pluripotent markers, and differentiated into trilineage embryonic layers. These patient-specific iPSC lines provide a valuable model to study the molecular and functional impact of the hERG channel gene mutation in LQT2 and to develop personalized therapeutic approaches for this syndrome.

Inhibition of the hERG Potassium Channel by a Methanesulphonate-Free E-4031 Analogue.

hERG (human Ether-à-go-go Related Gene)-encoded potassium channels underlie the cardiac rapid delayed rectifier (IKr) potassium current, which is a major target for antiarrhythmic agents and diverse non-cardiac drugs linked to the drug-induced form of long QT syndrome. E-4031 is a high potency hERG channel inhibitor from the methanesulphonanilide drug family. This study utilized a methanesulphonate-lacking E-4031 analogue, "E-4031-17", to evaluate the role of the methanesulphonamide group in E-4031 inhibition of hERG. Whole-cell patch-clamp measurements of the hERG current (IhERG) were made at physiological temperature from HEK 293 cells expressing wild-type (WT) and mutant hERG constructs. For E-4031, WT IhERG was inhibited by a half-maximal inhibitory concentration (IC50) of 15.8 nM, whilst the comparable value for E-4031-17 was 40.3 nM. Both compounds exhibited voltage- and time-dependent inhibition, but they differed in their response to successive applications of a long (10 s) depolarisation protocol, consistent with greater dissociation of E-4031-17 than the parent compound between applied commands. Voltage-dependent inactivation was left-ward voltage shifted for E-4031 but not for E-4031-17; however, inhibition by both compounds was strongly reduced by attenuated-inactivation mutations. Mutations of S6 and S5 aromatic residues (F656V, Y652A, F557L) greatly attenuated actions of both drugs. The S624A mutation also reduced IhERG inhibition by both molecules. Overall, these results demonstrate that the lack of a methanesulphonate in E-4031-17 is not an impediment to high potency inhibition of IhERG.