Allosteric effects of erythromycin pretreatment on thioridazine block of hERG potassium channels

Direct effects of antipsychotics on potassium channels

Schizophrenia (SCZ) and bipolar disorder (BD) and are severe psychiatric conditions that contribute to disability and increased healthcare costs globally. Although first-, second-, and third-generation antipsychotics are available for treating BD and SCZ, most have various side effects unrelated to their unique functions. Many antipsychotics affect K+ channels (Kv, KCa, Kir, K2P, and other channels), which change the functions of various organs. This review summarizes the biological actions of antipsychotics, including off-target side effects involving K+ channels.

hERG agonists pose challenges to web-based machine learning methods for prediction of drug-hERG channel interaction

Pharmacological blockade of the IKr channel (hERG) by diverse drugs in clinical use is associated with the Long QT Syndrome that can lead to life threatening arrhythmia. Various computational tools including machine learning models (MLM) for the prediction of hERG inhibition have been developed to facilitate the throughput screening of drugs in development and optimise thus the prediction of hERG liabilities. The use of MLM relies on large libraries of training compounds for the quantitative structure-activity relationship (QSAR) modelling of hERG inhibition. The focus on inhibition omits potential effects of hERG channel agonist molecules and their associated QT shortening risk. It is instructive, therefore, to consider how known hERG agonists are handled by MLM. Here, two highly developed online computational tools for the prediction of hERG liability, Pred-hERG and HergSPred were probed for their ability to detect hERG activator drug molecules as hERG interactors. In total, 73 hERG blockers were tested with both computational tools giving overall good predictions for hERG blockers with reported IC50s below Pred-hERG and HergSPred cut-off threshold for hERG inhibition. However, for compounds with reported IC50s above this threshold such as disopyramide or sotalol discrepancies were observed. HergSPred identified all 20 hERG agonists selected as interacting with the hERG channel. Further studies are warranted to improve online MLM prediction of hERG related cardiotoxicity, by explicitly taking into account channel agonism as well as inhibition.

The Strength of hERG Inhibition by Erythromycin at Different Temperatures Might Be Due to Its Interacting Features with the Channels

Erythromycin is one of the few compounds that remarkably increase ether-a-go-go-related gene (hERG) inhibition from room temperature (RT) to physiological temperature (PT). Understanding how erythromycin inhibits the hERG could help us to decide which compounds are needed for further studies. The whole-cell patch clamp technique was used to investigate the effects of erythromycin on hERG channels at different temperatures. While erythromycin caused a concentration-dependent inhibition of cardiac hERG channels, it also shifted the steady-state activation and steady-state inactivation of the channel to the left and significantly accelerated the onset of inactivation at both temperatures, although temperature itself caused a profound change in the dynamics of hERG channels. Our data also suggest that the binding pattern to S6 of the channels changes at PT. In contrast, cisapride, a well-known hERG blocker whose inhibition is not affected by temperature, does not change its critical binding sites after the temperature is raised to PT. Our data suggest that erythromycin is unique and that the shift in hERG inhibition may not apply to other compounds.

Calculations of the binding free energies of the Comprehensive in vitro Proarrhythmia Assay (CiPA) reference drugs to cardiac ion channels

The evaluation of the inhibitory activities of drugs on multiple cardiac ion channels is required for the accurate assessment of proarrhythmic risks. Moreover, the in silico prediction of such inhibitory activities of drugs on cardiac channels can improve the efficiency of the drug-development process. Here, we performed molecular docking simulations to predict the complex structures of 25 reference drugs that were proposed by the Comprehensive in vitro Proarrhythmia Assay consortium using two cardiac ion channels, the human ether-a-go-go-related gene (hERG) potassium channel and human NaV1.5 (hNaV1.5) sodium channel, with experimentally available structures. The absolute binding free energy (ΔGbind) values of the predicted structures were calculated by a molecular dynamics-based method and compared with the experimental half-maximal inhibitory concentration (IC50) data. Furthermore, the regression analysis between the calculated values and negative of the common logarithm of the experimental IC50 values (pIC50) revealed that the calculated values of four and ten drugs deviated significantly from the regression lines of the hERG and hNaV1.5 channels, respectively. We reconsidered the docking poses and protonation states of the drugs based on the experimental data and recalculated their ΔGbind values. Finally, the calculated ΔGbind values of 24 and 19 drugs correlated with their experimental pIC50 values (coefficients of determination=0.791 and 0.613 for the hERG and hNaV1.5 channels, respectively). Thus, the regression analysis between the calculated ΔGbind and experimental IC50 data ensured the realization of an increased number of reliable complex structures.

Electrophysiological and Proarrhythmic Effects of Hydroxychloroquine Challenge in Guinea-Pig Hearts

Hydroxychloroquine (HCQ), clinically established in antimalarial and autoimmune therapy, recently raised cardiac arrhythmogenic concerns when used alone or with azithromycin (HCQ+AZM) in Covid-19. We report complementary, experimental, studies of its electrophysiological effects. In patch clamped HEK293 cells expressing human cardiac ion channels, HCQ inhibited IKr and IK1 at a therapeutic concentrations (IC50s: 10 ± 0.6 and 34 ± 5.0 μM). INa and ICaL showed higher IC50s; Ito and IKs were unaffected. AZM slightly inhibited INa, ICaL, IKs, and IKr, sparing IK1 and Ito. (HCQ+AZM) inhibited IKr and IK1 (IC50s: 7.7 ± 0.8 and 30.4 ± 3.0 μM), sparing INa, ICaL, and Ito. Molecular induced-fit docking modeling confirmed potential HCQ-hERG but weak AZM-hERG binding. Effects of μM-HCQ were studied in isolated perfused guinea-pig hearts by multielectrode, optical RH237 voltage, and Rhod-2 mapping. These revealed reversibly reduced left atrial and ventricular action potential (AP) conduction velocities increasing their heterogeneities, increased AP durations (APDs), and increased durations and dispersions of intracellular [Ca2+] transients, respectively. Hearts also became bradycardic with increased electrocardiographic PR and QRS durations. The (HCQ+AZM) combination accentuated these effects. Contrastingly, (HCQ+AZM) and not HCQ alone disrupted AP propagation, inducing alternans and torsadogenic-like episodes on voltage mapping during forced pacing. O'Hara-Rudy modeling showed that the observed IKr and IK1 effects explained the APD alterations and the consequently prolonged Ca2+ transients. The latter might then downregulate INa, reducing AP conduction velocity through recently reported INa downregulation by cytosolic [Ca2+] in a novel scheme for drug action. The findings may thus prompt future investigations of HCQ's cardiac safety under particular, chronic and acute, clinical situations.

In vivo effects of the association of the psychoactive phenotiazine thioridazine on antitumor activity and hind limb paralysis induced by the native polypeptide crotamine

Crotamine is a cationic polypeptide composed by 42 amino acid residues with several pharmacological and biological properties, including the selective ability to enter and kill actively proliferating tumour cells, which led us to propose its use as a theranostic agent for cancer therapy. At the moment, the improvement of crotamine antitumoral efficacy by association with chemotherapeutic adjuvants is envisioned. In the present work, we evaluated the association of crotamine with the antitumoral adjuvant phenotiazine thioridazine (THD). In spite of the clear efficacy of these both compounds as anticancer agents in long-term in vivo treatment of animal model bearing implanted xenograph melanoma tumor, the expected mutual potentiation of the antitumor effects was not observed here. Moreover, this association revealed for the first time the influence of THD on crotamine ability to trigger the hind limb paralysis in mice, and this discovery may represent the first report suggesting the potential involvement of the CNS in the action of this snake polypeptide on the skeletal muscle paralysis, which was classically believed to be essentially limited to a direct action in peripheral tissues as the skeletal muscle. This is also supported by the observed ability of crotamine to potentiate the sedative effects of THD which action was consistently demonstrated to be based on its central action. The better characterization of crotamine properties in CNS may certainly bring important insights for the knowledge needed to pave the way toward the use of this molecule as a theranostic compound in human diseases as cancer.

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.

Antimicrobials and QT prolongation

Solithromycin, a ketolide/macrolide antibiotic, has recently been reported to be free of the expected QT-prolonging effect of macrolides. It appears that its keto substitution provides a structural basis for this observation, as the other two tested ketolides also have minimal QT effect.Among non-cardiovascular therapies, antimicrobials probably carry the greatest potential to cause cardiac arrhythmias. This is a result of their propensity to bind to the delayed rectifier potassium channel, IKr, inducing QT prolongation and risk of torsades de pointes ventricular tachycardia, their frequent interference with the metabolism of other QT prolongers and their susceptibility to metabolic inhibition by numerous commonly used drugs.Unfortunately, there is evidence that medical practitioners do not take account of the QT/arrhythmia risk of antimicrobials in their prescribing practices. Education on this topic is sorely needed. When a macrolide is indicated, a ketolide should be considered in patients with a QT risk.

Interaction among hERG channel blockers is a potential mechanism of death in caffeine overdose

Caffeine overdose death is due to cardiac arrest, but its mechanism has not been explored in detail. In this study, our data showed that caffeine significantly prolonged the heart rate-corrected QT interval (QTc) of rabbits in vivo (P<0.05; n=7). Caffeine was also found to be a hERG channel blocker with an IC₅₀ of 5.04mM (n=5). Although these two findings likely link caffeine overdose death with hERG channel blockade, the amount of caffeine consumption needed to reach the IC₅₀ is very high. Further study demonstrated that addition another hERG blocker could lower the consumption of caffeine significantly, no matter whether two hERG blockers share the same binding sites. Our data does not rule out other possibility, however, it suggests that there is a potential causal relationship between caffeine overdose death with hERG channel and the interaction among these hERG blockers.

The Role of Interaction Model in Simulation of Drug Interactions and QT Prolongation

Computational modelling is a cornerstone of Comprehensive In Vitro Proarrhythmia Assay and is re-increasingly being used in drug development. Electrophysiological effects of drug-drug interactions can be predicted in silico, e.g. with the use of in vitro cardiac ion channel data, PK profiles and human ventricular cardiomyocyte models. There are, however, several approaches with different assumptions used to assess the combined effect of multiple drugs, and there is no agreed standard interaction model. The aim of this study was to assess whether the choice of the drug-drug interaction (DDI) model (Bliss independence, Loewe additivity, or simple sum) influences the results of QT interval simulation trial. The Simcyp Simulator version 12.1 (Simcyp Ltd. [part of Certara], Sheffield, UK) and Cardiac Safety Simulator 2.0 (Simcyp Ltd. [part of Certara], Sheffield, UK) were used to simulate results of 8 virtual trials mimicking clinical studies and generate individual QTc data. The combined effect of inhibitory actions of drugs which were given simultaneously was calculated with use of three different interaction models. The PD effect of DDI was assessed and the differences between mean observed and mean predicted ΔQTcB values for terfenadine interactions were not statistically significant in all but one cases. Differences between the three DDI models are not statistically significant, implying that the choice of the DDI model, in the case of lack of synergy or antagonism, is irrelevant to the average predicted effect at the clinical level. However, in some cases, it can influence the verdict on combinatorial therapy safety for individual patients.

Mechanism Underlying Time-dependent Cross-phenomenon between Concentration-response Curves and Concentration Addition Curves: A Case Study of Sulfonamides-Erythromycin mixtures on Escherichia coli

Previous studies have identified a phenomenon in which the concentration-response curves (CRCs) for mixtures cross the curves for concentration addition model when predicting or judging joint toxic actions. However, mechanistic investigations of this phenomenon are extremely limited. In this study, a similar phenomenon was observed when we determined the joint toxic actions of sulfonamides (SAs) and erythromycin (ERY) on Escherichia coli (E. coli), which we named the "cross-phenomenon", and it was characterized by antagonism in the low-concentration range, addition in the medium-concentration range, and synergism in the high-concentration range. The mechanistic investigation of the cross-phenomenon was as follows: SAs and ERY could form a double block to inhibit the bacterial growth by exhibiting a synergistic effect; however, the hormetic effect of SAs on E. coli led to antagonism in the low-concentration range, resulting from the stimulation of sdiA mRNA expression by SAs, which increased the expression of the efflux pump (AcrAB-TolC) to discharge ERY. Furthermore, this cross-phenomenon was observed to be a time-dependent process induced by the increase of both the concentration and extent of stimulation of sdiA mRNA with exposure time. This work explains the dose-dependent and time-dependent cross-phenomenon and provides evidence regarding the interaction between hormesis and cross-phenomenon.