Additive effects of ziprasidone and d,l-sotalol on the action potential in rabbit Purkinje fibres and on the hERG potassium current

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

PURPOSE

QT 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.

METHOD

Search 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 FINDING

most of studies were done on anti-psychotic drugs, especially typical class. Most used investigated method to long-term QT induction was patch clamp.

SIGNIFICANCE

results suggests in susceptible cases with heart risk factors, these drugs should be taken with caution and monitored.

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

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

Deconstructing the Pharmacovigilance Hype Cycle

Data science is making increasing contributions to pharmacovigilance. Although the technical innovation of these works are indisputable, efficient progress in real-world pharmacovigilance signal detection may be hampered by corresponding technology life cycle effects, with a resulting tendency to conclude that, with large enough datasets and intricate algorithms, "the numbers speak for themselves," discounting the importance of clinical and scientific judgment. A practical consequence is overzealous declarations regarding the safety or lack of safety of drugs. We describe these concerns through a critical discussion of key results and conclusions from case studies selected to illustrate these points.

Twenty-Four-Hour Measures of Heart Rate-Corrected QT Interval, Peak-to-End of the T-Wave, and Peak-to-End of the T-Wave/Corrected QT Interval Ratio During Antipsychotic Treatment

PURPOSE/BACKGROUND

Prolonged ventricular repolarization, measured by heart rate-corrected QT interval (QTc) prolongation, might be a biomarker for risk of torsade de pointes (TdP) and sudden cardiac death. However, the predictive value of QTc has been challenged, and a component of QTc, peak-to-end of the T-wave (Tpe), and a high Tpe/QT ratio might be superior biomarkers because they better reflect increased transmural dispersion of ventricular myocyte repolarization, which can lead to TDP. The purpose of this pilot study was to provide the first measurements of heart rate, QTc, Tpe, Tpe/QTc, and their variability over 24 hours in medication-free patients with schizophrenia, during treatment with ziprasidone or other antipsychotic drugs, and healthy controls.

METHODS

Subjects included 12 patients treated with ziprasidone, 30 treated with other antipsychotic drugs, 3 unmedicated patients, and 15 normal controls. Subjects underwent 24-hour analog Holter recording, and the recordings were digitized. A cardiologist blind to treatment selected multiple 10-cycle segments throughout each recording and measured the electrocardiogram metrics.

RESULTS

Variability in QTc, Tpe, and Tpe/QTc over the 24 hours was present in all groups; 91.1% of patients and 100% of controls had 1 or more QTc values of 450 milliseconds or greater. Mean QTc length was significantly greater in the ziprasidone-treated than the non-ziprasidone-treated patients (P = 0.02). Mean Tpe was not elevated in the ziprasidone patients, whereas mean Tpe/QTc was lower (P < 0.01).

CONCLUSIONS

The large variability in QTc, Tpe, and Tpe/QTc observed supports the need for 24-hour electrocardiogram recordings to provide an accurate assessment of risk of TdP. Heart rate-corrected QT interval alone does not capture the risk of TdP.

Lengthening of cardiac repolarization in isolated guinea pigs hearts by sequential or concomitant administration of two IKr blockers

Block of I(Kr) is of major concern in drug safety. The objective of this study was to assess prolongation of cardiac repolarization during the combined use of two I(Kr) blockers when administered concomitantly or sequentially. (1) When isolated hearts from male guinea pigs were perfused concomitantly with two I(Kr) blockers, prolongation of monophasic action potential duration measured at 90% (MAPD(90)) was less than the summation of effects observed for each drug perfused alone. (2) In sequential administration, when ketoconazole or erythromycin was perfused first, they antagonized MAPD(90)-prolonging effects of domperidone. This effect was absent when domperidone or dofetilide was perfused first. Patch-clamp experiments confirmed that the order of sequential perfusion impacts the decrease in HERG tail amplitude. In conclusion, this study does not support the concept that potentiation of drug effects is observed during the combined administration of two I(Kr) blockers. Furthermore, order of administration of two I(Kr) blockers together may be an important factor in drug-induced long QT syndrome.

Collation, assessment and analysis of literature in vitro data on hERG receptor blocking potency for subsequent modeling of drugs' cardiotoxic properties

The assessment of the torsadogenic potency of a new chemical entity is a crucial issue during lead optimization and the drug development process. It is required by the regulatory agencies during the registration process. In recent years, there has been a considerable interest in developing in silico models, which allow prediction of drug-hERG channel interaction at the early stage of a drug development process. The main mechanism underlying an acquired QT syndrome and a potentially fatal arrhythmia called torsades de pointes is the inhibition of potassium channel encoded by hERG (the human ether-a-go-go-related gene). The concentration producing half-maximal block of the hERG potassium current (IC(50)) is a surrogate marker for proarrhythmic properties of compounds and is considered a test for cardiac safety of drugs or drug candidates. The IC(50) values, obtained from data collected during electrophysiological studies, are highly dependent on experimental conditions (i.e. model, temperature, voltage protocol). For the in silico models' quality and performance, the data quality and consistency is a crucial issue. Therefore the main objective of our work was to collect and assess the hERG IC(50) data available in accessible scientific literature to provide a high-quality data set for further studies.

Additive effects of combined application of multiple hERG blockers

Pro-arrhythmia by noncardiac drugs has become an important safety concern in the pharmaceutical industry. The most common underlying mechanism for induction of arrhythmias by noncardiac drugs is off-target block of the native cardiac repolarizing current, I Kr. The pore-forming subunit of I Kr is encoded by the human ether-a-go-go related gene (hERG), and in vitro measurements of hERG activity has become a standard component of drug safety evaluations. hERG/I Kr channels are blocked by a wide array of different chemical series; therefore, patients could be exposed to multiple blockers. There are few published studies addressing whether multiple blockers will exert independent actions on hERG channels. Whole cell patch clamp was used to evaluate the potential for cooperative effects when 2 hERG blocking agents were applied simultaneously. Cisapride, quinidine, fluvoxamine, and BeKm-1 were selected as representative agents binding to: (1) hydrophobic residues in the inner vestibule (cisapride and quinidine, the most frequent sites of interaction), (2) an extracellular segment near the pore (BeKm-1) or, (3) an unknown site (fluvoxamine). No synergistic blocking actions were seen. In some cases block was slightly less than additive. On balance, the results are consistent with additive and independent actions with simultaneous application of 2 hERG blockers.

Protriptyline block of the human ether-à-go-go-related gene (HERG) K+ channel

Protriptyline, a tricyclic antidepressant for psychiatric disorders, can induce prolonged QT, torsades de pointes, and sudden death. We studied the effects of protriptyline on human ether-à-go-go-related gene (HERG) channels expressed in Xenopus oocytes and HEK293 cells. Protriptyline induced a concentration-dependent decrease in current amplitudes at the end of the voltage steps and HERG tail currents. The IC(50) for protriptyline block of HERG current in Xenopus oocytes progressively decreased relative to the degree of depolarization, from 142.0 microM at -40 mV to 91.7 microM at 0 mV to 52.9 microM at +40 mV. The voltage dependence of the block could be fit with a monoexponential function, and the fractional electrical distance was estimated to be delta=0.93. The IC(50) for the protriptyline-induced blockade of HERG currents in HEK293 cells at 36 degrees C was 1.18 microM at +20 mV. Protriptyline affected channels in the activated and inactivated states, but not in the closed states. HERG blockade by protriptyline was use-dependent, exhibiting a more rapid onset and a greater steady-state block at higher frequencies of activation. Our findings suggest that inhibition of HERG currents may contribute to the arrhythmogenic side effects of protriptyline.

Action potential experiments complete hERG assay and QT-interval measurements in cardiac preclinical studies

INTRODUCTION

The ICHS7B guideline focused on hERG and QT assays, although other factors have also been linked with the induction of severe arrhythmias. Thus, the aim of the present study was to demonstrate that two in vitro action potential recordings constitute convincing models of predictive drug-induced Torsades de pointes (TdP) and re-entry arrhythmias.

METHODS

The effects of D,L-sotalol, flecainide and quinidine were investigated on potassium (hERG) and sodium (Na(V)1.5) currents transfected in HEK-293 cells to determine the repercussion of the blockade of these currents on rabbit Purkinje fibre (PF) and atrial action potentials. Atrial conduction velocity was also investigated as a model of re-entry arrhythmias.

RESULTS

hERG channels were blocked by D,L-sotalol, quinidine and flecainide (IC(50): 69, 0.33 and 0.74 micromol/L, respectively). D,L-sotalol (30 micromol/L) induced reverse-use dependent increases in action potential duration (APD(90): +31.7% and +81.2% at 1 and 0.2 Hz) and triangulation (APD(90-40): +34.7% and +73.6% at 1 and 0.2 Hz) in PF but not in atria. Quinidine (10 micromol/L) also increased APD(90) (+14.5% and +68.5% at 1 and 0.2 Hz) and APD(90-40) (+73.3% and +152.1% at 1 and 0.2 Hz) in PF. Flecainide (10 micromol/L) shortened APD(90) in PF (-26.0% and - 22.2% at 1 and 0.2 Hz). Quinidine and flecainide blocked Na(V)1.5 channels by 32.3% and 73.1%, respectively, and produced decreases in dV/dt(max) which were more marked in atria (-20.4% and -31.9%) compared to PF (-12.8% and 22.4%) at 1 Hz. Finally, quinidine and flecainide decreased atrial conduction speed by 14.6% and 30.8%, respectively.

CONCLUSION

Results obtained with flecainide demonstrate that use of the hERG channel alone should not be considered as a useful single assay. Rabbit Purkinje fiber action potentials can be considered as a comparable model for detection of reverse-use dependent APD prolongation and triangulation whereas the rabbit atria can be considered as a useful model for detection of sodium channel blockade associated with decreases in dV/dt(max) and conduction velocity.

Insights for Human Ether-a-Go-Go-Related Gene Potassium Channel Inhibition Using Recursive Partitioning and Kohonen and Sammon Mapping Techniques

The human ether-a-go-go related gene (hERG) can be inhibited by marketed drugs, and this inhibition may lead to QT prolongation and possibly fatal cardiac arrhythmia. We have collated literature data for 99 diverse hERG inhibitors to generate Kohonen maps, Sammon maps, and recursive partitioning models. Our aim was to investigate whether these computational models could be used either individually or together in a consensus approach to predict the binding of a prospectively selected test set of 35 diverse molecules and at the same time to offer further insights into hERG inhibition. The recursive partitioning model provided a quantitative prediction, which was markedly improved when Tanimoto similarity was included as a filter to remove molecules from the test set that were too dissimilar to the training set (r2 = 0.83, Spearman rho = 0.75, p = 0.0003 for the 18 remaining molecules, >0.77 similarity). This model was also used to screen and prioritize a database of drugs, recovering several hERG inhibitors not used in model building. The mapping approaches used molecular descriptors required for hERG inhibition that were not reported previously and in particular highlighted the importance of molecular shape. The Sammon map model provided the best qualitative classification of the test set (95% correct) compared with the Kohonen map model (81% correct), and this result was also superior to the consensus approach. This study illustrates that patch clamping data from various literature sources can be combined to generate valid models of hERG inhibition for prospective predictions.

Block of hERG channel by ziprasidone: biophysical properties and molecular determinants

Ziprasidone, an antipsychotic agent, delays cardiac repolarization and, thus, prolongs the QT interval of the cardiac ECG. In this study, we examined the biophysical properties and the molecular determinants of the ziprasidone block of wild-type hERG potassium channels stably expressed in HEK-293 cells or wild-type and mutant hERG channels expressed in Xenopus oocytes. In stably transfected HEK-293 cells, ziprasidone blocked wild-type hERG current in a voltage- and concentration-dependent manner (IC(50)=120nM, 0mV, 37 degrees C). Ziprasidone showed minimal tonic block of hERG current estimated during a depolarizing voltage (-20 or +30mV) or evaluated by the envelope of tails test (+30mV). Rate of the block onset was rapid, but not significantly affected by test potentials ranging from -20 to +30mV (time constant (tau)=114+/-14ms at +30mV). The time constant of the slow component of hERG current deactivation (at -50mV) was significantly increased by ziprasidone (tau=1776+/-90 versus 1008+/-71ms, P<0.01). Time course of channel inactivation was slowed by ziprasidone in a voltage-dependent manner. The V(1/2) values for steady-state activation and inactivation of hERG channel in HEK-293 cells were not significantly altered by ziprasidone. In Xenopus oocytes, ziprasidone exhibited less potent block of wild-type hERG current (IC(50)=2.8microM, 0mV, 23 degrees C). Mutation of the aromatic residues (Tyr-652 or Phe-656) located in the S6 domain of hERG dramatically reduced the potency of channel block by ziprasidone (IC(50)>0.4 and 1mM at 0mV for Y652A and F656A, respectively). In conclusion, ziprasidone preferentially binds to and blocks open hERG channels. Tyr-652 and Phe-656 are two critical residues in the ziprasidone-binding site.

Methodology used in safety pharmacology: appraisal of the state-of-the-art, the regulatory issues and new directions

This is the second focused issue of the Journal of Pharmacological and Toxicological Methods that is devoted exclusively to methodology, opinions and regulatory issues related to Safety Pharmacology. This issue of the Journal highlights a record number of articles and abstracts from the 4th Annual Safety Pharmacology Society (SPS) meeting that was held in Covington, Kentucky September 27-29, 2004. The focus of this issue of the Journal is to present a description of currently used fundamental pharmacological methods as outlined in the regulatory guidance documents for pre-clinical safety testing of drugs (ICH S7A and S7B). This issue features articles that discuss methods related to in vivo and in vitro CNS, respiratory and cardiovascular core battery studies. Additionally, articles are included that discuss species differences and recording issues in EKG measurement; automated (HTS) electrophysiology methods for assessing drug-induced hERG blockade (i.e., PatchXpress 7000A and hERG-lite); methods that describe and validate the use of the guinea pig as a safety pharmacology screening model; methods used to predict QTc prolongation and mathematical models that describe beat-to-beat instability of QT duration; supplemental studies that assess and discuss emerging renal biomarkers and renal function and food effects on gastrointestinal transit time; pro-arrhythmia models, cardiac function assessment using 3-D echocardiography and a description of a novel open field motor activity system to assess the possible CNS effects of drugs. Thus, this issue of the Journal of Pharmacological and Toxicological Methods should be a primary resource aid to individuals in academia and industry that are interested in understanding Safety Pharmacology methods. It provides a comprehensive overview of current and advanced methods used in Safety Pharmacology studies today.