hERG Channel Research Articles

Hysteretic hERG channel gating current recorded at physiological temperature

Cardiac hERG channels comprise at least two subunits, hERG 1a and hERG 1b, and drive cardiac action potential repolarization. hERG 1a subunits contain a cytoplasmic PAS domain that is absent in hERG 1b. The hERG 1a PAS domain regulates voltage sensor domain (VSD) movement, but hERG VSD behavior and its regulation by the hERG 1a PAS domain have not been studied at physiological temperatures. We recorded gating charge from homomeric hERG 1a and heteromeric hERG 1a/1b channels at near physiological temperatures (36 ± 1 °C) using pulse durations comparable in length to the human ventricular action potential. The voltage dependence of deactivation was hyperpolarized relative to activation, reflecting VSD relaxation at positive potentials. These data suggest that relaxation (hysteresis) works to delay pore closure during repolarization. Interestingly, hERG 1a VSD deactivation displayed a double Boltzmann distribution, but hERG 1a/1b deactivation displayed a single Boltzmann. Disabling the hERG 1a PAS domain using a PAS-targeting antibody similarly transformed hERG 1a deactivation from a double to a single Boltzmann, highlighting the contribution of the PAS in regulating VSD movement. These data represent, to our knowledge, the first recordings of hERG gating charge at physiological temperature and demonstrate that VSD relaxation (hysteresis) is present in hERG channels at physiological temperature.

Identification and New Indication of Melanin-Concentrating Hormone Receptor 1 (MCHR1) Antagonist Derived from Machine Learning and Transcriptome-Based Drug Repositioning Approaches.

Melanin-concentrating hormone receptor 1 (MCHR1) has been a target for appetite suppressants, which are helpful in treating obesity. However, it is challenging to develop an MCHR1 antagonist because its binding site is similar to that of the human Ether-à-go-go-Related Gene (hERG) channel, whose inhibition may cause cardiotoxicity. Most drugs developed as MCHR1 antagonists have failed in clinical development due to cardiotoxicity caused by hERG inhibition. Machine learning-based prediction models can overcome these difficulties and provide new opportunities for drug discovery. In this study, we identified KRX-104130 with potent MCHR1 antagonistic activity and no cardiotoxicity through virtual screening using two MCHR1 binding affinity prediction models and an hERG-induced cardiotoxicity prediction model. In addition, we explored other possibilities for expanding the new indications for KRX-104130 using a transcriptome-based drug repositioning approach. KRX-104130 increased the expression of low-density lipoprotein receptor (LDLR), which induced cholesterol reduction in the gene expression analysis. This was confirmed by comparison with gene expression in a nonalcoholic steatohepatitis (NASH) patient group. In a NASH mouse model, the administration of KRX-104130 showed a protective effect by reducing hepatic lipid accumulation, liver injury, and histopathological changes, indicating a promising prospect for the therapeutic effect of NASH as a new indication for MCHR1 antagonists.

Synthesis, molecular docking, ADMET study and in vitro pharmacological research of 7-(2-chlorophenyl)-4-(4-methylthiazol-5-yl)-4,6,7,8-tetrahydroquinoline-2,5(1H,3H)-dione as a promising non-opioid analgesic drug

Introduction: The discovery of novel drugs that can block the transmission of pain signals for treating the pain of various etiologies is an urgent topic in pharmaceutics. The aim of this paper is to synthesize and to investigate in vitro and in silico characteristics of a promising novel compound: 7-(2-chlorophenyl)-4-(4-methylthiazol-5-yl)-4,6,7,8-tetrahydroquinoline-2,5(1H,3H)-dione (HSV-DKH-0450).
 Materials and methods: The specific activity and the inhibitory mechanism of HSV-DKH-0450 were studied using the HEK293 culture cells expressing the IPTG-induced TRPA1 ion channels. Cardiotoxicity was determined by estimating the binding of HSV-DKH-0450 to the hERG channel. Inhibition of human liver cytochromes was determined by the effect on the activity of cytochromes 1A2, 2C9, 2D6, 2C8, and 3A4. Cellular toxicity was assessed by the effect on the viability of human hepatocytes. ADMET properties were evaluated using admetSAR and SwissADME web-based tools. Molecular docking was carried out using AutoDock Vina tools to predict the binding affinity of all HSV-DKH-0450 stereoisomers toward the TRPA1 and TRPV1 receptors.
 Results and discussion: In silico predictions of ADMET properties of HSV-DKH-0450 showed that it has optimal pharmaceutical profiles. A series of in vitro pharmacological studies revealed that HSV-DKH-0450 is a promising antagonist of the TRPA1 ion channel with the IC50 of 91.3 nM. The molecular docking of HSV-DKH-0450 stereoisomers against the TRPA1 and TRPV1 receptors demonstrates that they all are characterized by an approximately similar high binding affinity.
 Conclusion: The obtained data for substance HSV-DKH-0450 look promising for its further development as a potential therapeutic agent for pain relief.

Overcoming undesirable hERG affinity by incorporating fluorine atoms: A case of MAO-B inhibitors derived from 1 H-pyrrolo-[3,2-c]quinolines

The incorporation of the fluorine motif is a strategy widely applied in drug design for modulating the activity, physicochemical parameters, and metabolic stability of chemical compounds. In this study, we attempted to reduce the affinity for ether-à-go-go-related gene (hERG) channel by introducing fluorine atoms in a group of 1H-pyrrolo[3,2-c]quinolines that are capable of inhibiting monoamine oxidase type B (MAO-B). A series of structural modifications guided by in vitro evaluation of MAO-B inhibition and antitargeting for hERG channels were performed, which led to the identification of 1-(3-chlorobenzyl)-4-(4,4-difluoropiperidin-1-yl)-1H-pyrrolo[3,2-c]quinoline (26). Compound 26 acted as a reversible MAO-B inhibitor exhibiting selectivity over 45 targets, enzymes, transporters, and ion channels, and showed potent glioprotective properties in cultured astrocytes. In addition, the compound demonstrated good metabolic stability in rat liver microsomes assay, a favorable safety profile, and brain permeability. It also displayed procognitive effects in the novel object recognition test in rats and antidepressant-like activity in forced swim test in mice. The findings of the study suggest that reversible MAO-B inhibitors can have potential therapeutic applications in Alzheimer's disease.

Absence of developmental or reproductive toxicity in rats for MB-102, a fluorescent tracer agent for point-of-care measurement of glomerular filtration rate

The fluorescent tracer agent MB-102 was designed for the direct, real-time measurement of glomerular filtration rate. Previous studies, both in vitro and in vivo (rats, rabbits and dogs) have assessed single dose toxicity, phototoxicity, local tolerance, hERG channel changes, mutation, chromosomal aberration, micronuclease assays, and CNS and cardiovascular safety. The resulting safety/toxicology profile allowed FDA clearance to conduct Phase I and II human clinical studies. Herein we report on maternal toxicity and potential effects on embryo-fetal development and toxicokinetics of MB-102 administered daily via intravenous (bolus) injection into pregnant rats during organogenesis gestation day 6–17. Mortality, clinical observations, body weight, food consumption, reproductive performance, necropsy, and cesarean section findings were assessed. Blood samples were evaluated toxicokinetically. No significant findings were noted in any endpoints. The only clinical findings were skin, eye or pelage discoloration in the two higher dose groups, which were considered related to the color and fluorescent properties of MB-102 and deemed non-adverse. Exposure, assessed by Cmax and AUC(0-6), increased in a dose-dependent manner from 9 to 225 mg/kg/day. Thus, intravenous administration of MB-102 was not associated with any adverse developmental or reproductive toxicities in pregnant rats.

Postmarketing pharmacovigilance: Remdesivir and cardiovascular events.

Postmarketing pharmacovigilance: Remdesivir and cardiovascular events.

HERG1 Potassium Channel Expression in Colorectal Adenomas: Comparison with Other Preneoplastic Lesions of the Gastrointestinal Tract.

Preneoplastic lesions represent a useful target for early diagnosis and follow-up of gastrointestinal malignancies. hERG1 channel expression was tested by immunohistochemistry (IHC) in a cohort of colorectal adenoma samples belonging to Italian subjects. Overall, hERG1 was expressed in 56.5% of cases with both high staining intensity and a high percentage of positive cells. Moreover, hERG1 was expressed in a higher percentage of dysplastic adenomas with respect to hyperplastic lesions, and the proportion of positive samples further increased in patients with high-grade dysplasia. Comparing hERG1 expression in other preneoplastic lesions of the GI tract (gastric dysplasia and Barrett’s esophagus), it emerged that in all the conditions, hERG1 was expressed with a diffused pattern, throughout the cell, with variable staining intensity within the samples. The highest expression was detected in gastric dysplasia samples and the lowest in Barrett’s esophagus at similar levels observed in colorectal adenomas. Our results show that hERG1 is aberrantly expressed in human preneoplastic lesions of the gastrointestinal tract and has a different pattern of expression and role in the different sites. Overall, the detection of hERG1 expression in preneoplastic lesions could represent a novel diagnostic or prognostic marker of progression in the gastrointestinal tract.

Neurotoxic and cardiotoxic effects of N-methyl-1-(naphthalen-2-yl)propan-2-amine (methamnetamine) and 1-phenyl-2-pyrrolidinylpentane (prolintane)

Two synthetic phenylethylamines, N-methyl-1-(naphthalen-2-yl)propan-2-amine (MNA) and 1-phenyl-2-pyrrolidinylpentane (prolintane), are being abused by people seeking hallucinogens for pleasure. These new psychotropic substances may provoke problems because there is no existing information about their toxicity and pharmacological behaviors. Therefore, we evaluated the safety of nerves and cardiovascular systems by determining toxicity after MNA and prolintane drugs administrations to mice and rat. Consequently, side effects such as increased spontaneous motion and body temperature were observed in oral administration of MNA. In addition, both substances reduced motor coordination levels. The IHC tests were conducted to see whether the immune response also shows abnormalities in brain tissue compared to the control group. It has been confirmed that the length of allograft inflammatory factor 1(IBA-1), an immune antibody known as microglia marker, has been shortened. We identified that a problem with the contact between synapses and neurons might be possibly produced. In the assessment of the cardiac toxicity harmfulness, no substances have been confirmed to be toxic to myocardial cells, but at certain concentrations, they have caused the QT prolongation, an indicator of ventricular arrhythmia. In addition, the hERG potassium channel, the biomarker of the QT prolongation, has been checked for inhibition. The results revealed that the possibility of QT prolongation through the hERG channel could not be excluded, and the two substances can be considered toxic that may cause ventricular arrhythmia. In sum, this study demonstrated that the possibility of toxicity in MNA and prolintane compounds might bring many harmful effects on nerves and hearts.

Combining multi-dimensional molecular fingerprints to predict the hERG cardiotoxicity of compounds

Recently, drug toxicity has become a critical problem with heavy medical and economic burdens. Acquired long QT syndrome (acLQTS) is an acquired cardiac ion channel disease caused by drugs blocking the hERG channel. Therefore, it is necessary to avoid cardiotoxicity in drug design, and computer models have been widely used to fix this predicament. In this study, we collected a hERG inhibitor dataset containing 8671 compounds, and then, these compounds were featurized by traditional molecular fingerprints (including Baseline2D, ECFP4, PropertyFP, and 3DFP) and the newly proposed molecular dynamics fingerprint (MDFP). Subsequently, regression prediction models were established by using four machine learning algorithms based on these fingerprints and the combined multi-dimensional molecular fingerprints (MultiFP). After cross-validation and independent test dataset validation, the results show that the best model was built by the consensus of four algorithms with MultiFP, and this model bests recently published methods in terms of hERG cardiotoxicity prediction with a RMSE of 0.531 and a R2 of 0.653 on the test dataset. Feature importance analysis and correlation analysis identified some novel structural features and molecular dynamics features that are highly associated with the hERG inhibition of compounds. Our findings provide new insight into multi-dimensional molecular fingerprints and consensus models for hERG cardiotoxicity prediction.

Cardiotoxicity assessment of 31 herbal formulae by activity of hERG potassium channel in HEK 293 cells

Objectives: Drug-induced blockade of the human ether-à-go-go related gene (hERG) potassium ion channel causes acquired long QT syndrome, which is known to cause cardiac arrhythmias and be fatal. To establish safety evidence of herbal formulae, we evaluated the effects of 31 herbal formulae on hERG channel activity.Methods: The current through hERG channel was measured by changing the membrane voltage before and after treatment with 31 herbal formulae in HEK 293 cell overexpressing hERG channel using a whole-cell patch clamp system. The current-voltage curves and the activity curves were fitted, and the hERG activity and 50% inhibitory concentration (IC50) according to each herbal formula were calculated.Results: Chokyungjongok-tang, Oncheong-eum, and Cheongsangbangpung-tang strongly inhibited the hERG activity, with IC50 values of 67.67, 141.2, and 296.3 μg/mL, respectively. Yeonkyopaedok-san, Eunkyo-san, Ukgan-san gajinphibanha, Daegunjoong-tang (except Oryzae gluten), Insamyangyoung-tang, Banhahubak-tang, SokyungHwalhyul-tang, Jodeung-san, Hyeonggaeyeongyo-tang, and Bangkeehwangkee-tang weakly inhibited hERG activity, with IC50 values ranging from 400 to 1000 μg/mL. The other 18 herbal formulae showed very weak hERG activity inhibition of less than 50% at the highest concentration (1000 μg/mL).Conclusion: This study provided safety information on cardiotoxicity by cardiac arrhythmia risk assessment of herbal formulae, and is expected to be a reference data for predicting the safety and risk of herbal formulae.

Discovery and structure–activity relationships of a novel oxazolidinone class of bacterial type II topoisomerase inhibitors

There is an increasingly urgent and unmet medical need for novel antibiotic drugs that tackle infections caused by multidrug-resistant (MDR) pathogens. Novel bacterial type II topoisomerase inhibitors (NBTIs) are of high interest due to limited cross-resistance with fluoroquinolones, however analogues with Gram-negative activity often suffer from hERG channel inhibition. A novel series of bicyclic-oxazolidinone inhibitors of bacterial type II topoisomerase were identified which display potent broad-spectrum anti-bacterial activity, including against MDR strains, along with an encouraging in vitro safety profile. In vivo proof of concept was achieved in a A. baumannii mouse thigh infection model.

Molecular dynamics simulations suggest possible activation and deactivation pathways in the hERG channel

The elusive activation/deactivation mechanism of hERG is investigated, a voltage-gated potassium channel involved in severe inherited and drug-induced cardiac channelopathies, including the Long QT Syndrome. Firstly, the available structural data are integrated by providing a homology model for the closed state of the channel. Secondly, molecular dynamics combined with a network analysis revealed two distinct pathways coupling the voltage sensor domain with the pore domain. Interestingly, some LQTS-related mutations known to impair the activation/deactivation mechanism are distributed along the identified pathways, which thus suggests a microscopic interpretation of their role. Split channels simulations clarify a surprising feature of this channel, which is still able to gate when a cut is introduced between the voltage sensor domain and the neighboring helix S5. In summary, the presented results suggest possible activation/deactivation mechanisms of non-domain-swapped potassium channels that may aid in biomedical applications.

Discovery of ASP5878: Synthesis and structure–activity relationships of pyrimidine derivatives as pan-FGFRs inhibitors with improved metabolic stability and suppressed hERG channel inhibitory activity

Fibroblast growth factor receptor 3 (FGFR3) is an attractive therapeutic target for the treatment of bladder cancer patients harboring genetic alterations in FGFR3. We identified pyrimidine derivative ASP5878 (27) with improved metabolic stability and suppressed human ether-á-go-go related gene (hERG) channel inhibitory activity by the optimization of lead compound 1. Based on prediction of the metabolites of 1, an ether linker was introduced in place of the ethylene linker to improve metabolic stability. Moreover, conversion of the phenyl moiety into the pyrazole ring resulted in the suppression of hERG channel inhibitory activity, possibly due to the weaker π-π stacking interaction with Phe656 in the hERG channel by a reduction in π-electrical density of the aromatic ring. ASP5878 showed potent in vitro FGFR3 enzyme and cell growth inhibitory activity, and in vivo FGFR3 autophosphorylation inhibitory activity. Moreover, ASP5878 did not affect the hERG current up to 10 µM by in vitro patch-clamp assay, and a single oral dose of ASP5878 at 1, 10, and 100 mg/kg did not induce serious adverse effects on the central nervous, cardiovascular, and respiratory systems in dogs. Furthermore, ASP5878 exhibited lower total clearance than hepatic blood flow and high oral bioavailability in rats and dogs, and moderate brain penetration in rats.

Multi-Scale modeling of state-dependent drug binding to the hERG channel

The hERG channel plays an important role in the repolarization phase of the cardiac action potential. Blockage of the channel conductance can lead to prolongation of the cardiac action potential and the QT interval on the surface electrocardiogram, which may result in deadly arrhythmias. hERG channel blockade is a leading cause for drug withdrawal from the drug development pipeline or marketplace. However, not all hERG-blocking and QT-prolonging drugs cause arrhythmia. Therefore, understanding the molecular mechanisms of drug interactions with the hERG channel and the subsequent modulation of the channel gating leading to different pro-arrhythmia outcomes is crucial for drug design and development.

Exploring drug arrythmogenicity via atomistic simulations of state-specific hERG-channel block

Expressed primarily in cardiac myocytes, the hERG channel (Kv11.1) is a voltage-gated potassium channel that facilitates a repolarizing K+ current during the cardiac action potential (CAP). In response to changes in membrane potential, the hERG channel undergoes transitions from closed to open and inactivated states. Utilizing atomistic molecular modeling and docking simulations, we aim to assess the state-specific binding of drugs to the hERG channel utilizing structural models of open and inactivated hERG channels.

A hydrophobic nexus at the PAS-cap/globular PAS/CNPhd interface tunes deactivation kinetics of hERG channels

Slow deactivation is a critical biophysical property of human ether-à -go-go related gene (hERG) channels, mediating the cardiac current IKr during repolarization of the ventricular action potential. Disruption of interactions between the intracellular N-terminal Per-Arnt-Sim (PAS) and C-terminal cyclic nucleotide-binding homology (CNBh) domains can impair slow deactivation and is associated with long QT syndrome (LQTS). The PAS-cap (residues 1-25), an essential mediator of slow deactivation, is composed of an unstructured segment (residues 1-12) and an amphipathic α-helix (residues 13-25).

PAS and CNBH domain interactions in hERG channels investigated with surface plasmon resonance

Human ether-á-go-go-related gene (hERG) potassium channels play a key role in the regulation of cardiac repolarization, neuronal excitability, and tumorigenesis. hERG channels contain N-terminal Per-Arnt-Sim (PAS) and C-terminal cyclic nucleotide-binding homology (CNBH) domains. Structural, functional and fluorescence-based studies established that the hERG PAS and CNBH domains from adjacent subunits interact. Moreover, many long-QT syndrome (LQTS)-linked mutations are located at the interface between these domains.

Conformation sensitive antibody reveals an altered cytosolic PAS/CNBH assembly during hERG channel gating

The human ether-à -go-go-related gene (hERG) K+ channel has a crucial function in cardiac repolarization and mutations or channel block can give rise to long QT syndrome and catastrophic ventricular arrhythmias. The cytosolic assembly formed by the N-terminal Per-Arnt-Sim (PAS) and C-terminal cyclic nucleotide binding homology (CNBh) domains is the defining structural feature of hERG and related KCNH channels. However, the molecular role of these two domains in channel gating remains unclear. We have previously shown that single-chain fragment variable (scFv) antibody fragments can modulate hERG function by binding to the PAS domain.

Effect of the membrane environment on pharmacologic inhibition of hERG channel activity

The human-ether-a-go-go related gene (hERG) encodes the voltage-gated K+ channel Kv11.1, which is responsible for the rapidly activating delayed rectifier K+ current in cardiac myocytes. hERG channels play a significant role in membrane repolarization during phase three of the cardiac action potential. In addition to being a target for many class III antiarrhythmic agents, these channels are also the unintended target of many other pharmacological compounds, which can produce acquired long QT syndrome, leading to polymorphic ventricular tachycardia.

Voltage dependent block of the cardiac potassium channel hERG by calcium and hydrogen

Reduction of the current carried by the cardiac potassium channel HERG can lead to Long QT syndrome, an arrhythmia characterized by a rapid heart rate and reduced cardiac output, which can, in certain situations, be fatal. The effects of various extracellular electrolytes on the biophysical properties of the HERG channel have been studied in some detail. In particular, increases in extracellular divalent ions such as Ca2+, Mg2+, and Zn2+ as well as increases in extracellular H+ have been shown to slow channel activation, increase channel deactivation, and shift the G-V curve to more positive voltages.