Improving the Assessment of Heart Toxicity for All New Drugs Through Translational Regulatory Science

Assessment of corrected JT-peak (JTpc) and Tpeak-to-Tend (TpTec) as proarrhythmia biomarkers in non-human primates: Outcome from a HESI consortium

INTRODUCTION

Corrected QT interval (QTc)is an established biomarker for drug-induced Torsade de Pointe (TdP), but with concerns for a false positive signal. Clinically, JTpc and TpTec have emerged as ECG sub-intervals to differentiate predominant hERG vs. mixed ion channel blocking drugs that prolong QTc.

METHODS

In a multicentric, prospective, controlled study, different proarrhythmic drug effects on QTc, JTpc and TpTec were characterized with cynomolgus monkeys using telemetry in a Lead II configuration for internal and external telemetry.Drugs and vehicle were administered orally (PO) to group size of 4 to 8 animals, in 4 laboratories.

RESULTS

In monkeys, dofetilide (0.03-0.3 mg/kg) was associated with exposure dependent QTc and JTpc increase, but no significant TpTec effect. Similarly, quinidine (2-50 mg/kg) increased QTc and JTpc but did not change TpTec. Mexiletine (1-15 mg/kg) and verapamil (50 mg/kg) did not induce any significant effect on QTc, JTpc or TpTec.

DISCUSSION

Clinically, predominant hERG blockers (dofetilide and quinidine) prolong QTc, JTpc and TpTec and are associated with increased risk for TdP. Results from this study demonstrate that ECG changes after dofetilide and quinidine administration to telemetered monkeys differ from the clinical response, lacking the expected effects on TpTec. Potential explanations for the lack of translation include physio-pharmacology species differences or ECG recording and analysis methodology variations. Mixed ion channel blockers verapamil and mexiletine administered to monkeys showed no significant QTc, JTpc or TpTec prolongation as expected based on the similar clinical response for these agents.

Optimized J to T peak and T peak to T end measurements in nonclinical species administered moxifloxacin and amiodarone

INTRODUCTION

Cardiovascular safety and the risk of developing the potentially fatal ventricular tachyarrhythmia, Torsades de Pointes (TdP), have long been major concerns of drug development. TdP is associated with a delayed ventricular repolarization represented by QT interval prolongation in the electrocardiogram (ECG), typically due to block of the potassium channel encoded by the human ether-a-go-go related gene (hERG). Importantly however, not all drugs that prolong the QT interval are torsadagenic and not all hERG blockers prolong the QT interval. Recent clinical reports suggest that partitioning the QT interval into early (J to T peak; JTp) and late repolarization (T peak to T end; TpTe) components may be valuable for distinguishing low-risk mixed ion channel blockers (hERG plus calcium and/or late sodium currents) from high-risk pure hERG channel blockers. This strategy, if true for nonclinical animal models, could be used to de-risk QT prolonging compounds earlier in the drug development process.

METHODS

To explore this, we investigated JTp and TpTe in ECG data collected from telemetered dogs and/or monkeys administered moxifloxacin or amiodarone at doses targeting relevant clinical exposures. An optimized placement of the Tpeak fiducial mark was utilized, and all intervals were corrected for heart rate (QTc, JTpc, TpTec).

RESULTS

Increases in QTc and JTpc intervals with administration of the pure hERG blocker moxifloxacin and an initial QTc and JTpc shortening followed by prolongation with the mixed ion channel blocker amiodarone were detected as expected, aligning with clinical data. However, anticipated increases in TpTec by both standard agents were not detected.

DISCUSSION

The inability to detect changes in TpTec reduces the utility of these subintervals for prediction of arrhythmias using continuous single‑lead ECGs collected from freely moving dogs and monkeys.

Tpeak-Tend ECG Marker in Obesity and Cardiovascular Diseases: A Comprehensive Review

Globally, cardiovascular diseases are still the leading cause of death. Numerous methods are used to diagnose cardiovascular pathologies; there is still a place for straightforward and noninvasive techniques, such as electrocardiogram (ECG). Depolarization and repolarization parameters, including QT interval and its derivatives, are well studied. However, the Tpeak-Tend interval is a novel and promising ECG marker with growing evidence for its potential role in predicting malignant arrhythmias. In this review, we discuss the association between the Tpeak-Tend interval and several cardiovascular diseases, including long QT syndrome, cardiomyopathies, heart failure, myocardial infarction, and obesity, which constitutes one of the risk factors for cardiovascular diseases.

The New S7B/E14 Q&A Document Provides Additional Opportunities to Replace the Thorough QT Study

Since 2015, concentration-QTc (C-QTc) analysis has been used to exclude the possibility that a drug has a concerning effect on the QTc interval. This has enabled the replacement of the designated thorough QT (TQT) study with serial electrocardiograms (ECGs) in routine clinical pharmacology studies, such as the first-in-human (FIH) study. The E14 revision has led to an increased proportion of FIH studies with the added objective of QT evaluation, with the intention of replacing the TQT study. With the more recent revision of the S7B/E14 Q&A document in February 2022, nonclinical assays/studies can be brought into the process of regulatory decisions at the time of marketing application. If the hERG (human ether-a-go-go-related gene) and the non-rodent in vivo study are conducted according to the described best practices and are negative, the previous requirement that a QTc effect of >10 milliseconds must be excluded in healthy subjects at plasma concentrations 2-fold above what can be seen in patients can be reduced to covering the concentrations seen in patients. For drugs that cannot be safely given in high doses to healthy subjects, ECG evaluation is often performed at the therapeutic dose in patients. If a QTc effect of >10 milliseconds can be excluded, an argument can be made that the drug should be considered as having a low likelihood of proarrhythmic effects due to delayedrepolarization, if supported by negative best practices hERG and in vivo studies. In this article, we describe what clinicians involved in early clinical development need to understand in terms of the hERG and in vivo studies to determine whether these meet best practices and therefore can be used in an integrated clinical/nonclinical QT/QTc risk assessment.

New science, drug regulation, and emergent public health issues: The work of FDA's division of applied regulatory science

The U.S. Food and Drug Administration (FDA) Division of Applied Regulatory Science (DARS) moves new science into the drug review process and addresses emergent regulatory and public health questions for the Agency. By forming interdisciplinary teams, DARS conducts mission-critical research to provide answers to scientific questions and solutions to regulatory challenges. Staffed by experts across the translational research spectrum, DARS forms synergies by pulling together scientists and experts from diverse backgrounds to collaborate in tackling some of the most complex challenges facing FDA. This includes (but is not limited to) assessing the systemic absorption of sunscreens, evaluating whether certain drugs can convert to carcinogens in people, studying drug interactions with opioids, optimizing opioid antagonist dosing in community settings, removing barriers to biosimilar and generic drug development, and advancing therapeutic development for rare diseases. FDA tasks DARS with wide ranging issues that encompass regulatory science; DARS, in turn, helps the Agency solve these challenges. The impact of DARS research is felt by patients, the pharmaceutical industry, and fellow regulators. This article reviews applied research projects and initiatives led by DARS and conducts a deeper dive into select examples illustrating the impactful work of the Division.

Influence of antidepressant drugs on DNA methylation of ion channels genes in blood cells of psychiatric patients

Aim: This study investigated the influence of antidepressant drugs on methylation status of KCNE1, KCNH2 and SCN5A promoters and ECG parameters in adult psychiatric patients. Materials & methods: Electrocardiographic evaluation (24 h) and blood samples were obtained from 34 psychiatric patients before and after 30 days of antidepressant therapy. Methylation of promoter CpG sites of KCNE1, KCNH2 and SCN5A was analyzed by pyrosequencing. Results: Three CpG and four CpG sites of KCNE1 and SCN5A, respectively, had increased % methylation after treatment. Principal component analysis showed correlations of the methylation status with electrocardiographic variables, antidepressant doses and patient age. Conclusion: Short-term treatment with antidepressant drugs increase DNA methylation in KCNE1 and SCN5A promoters, which may induce ECG alterations in psychiatric patients.

Pharmacological characterisation of electrocardiogram J-Tpeak interval in conscious Guinea pigs

Drug-induced human ether-à-go-go-related gene (hERG) channel block and QT interval prolongation increase torsade de pointes (TdP) risk. However, some drugs block hERG channels and prolong QT interval with low TdP risk, likely because they block additional inward currents. We investigated the utility of J-T_peak interval, a novel biomarker of inward current block and TdP risk, in conscious telemetered guinea pigs. Electrocardiogram parameters were analysed in Hartley guinea pigs orally administered one of eight test compounds (dofetilide, flecainide, nifedipine, quinidine, quinine, ranolazine, sotalol, verapamil) or vehicle alone as controls. Heart rate-corrected QT (QTcX) and J-T_peak (J-T_peakcX) were calculated to evaluate the relations of QT-RR and J-T_peak-RR. Dofetilide and sotalol significantly increased ΔQTcX and ΔJ-T_peakcX intervals to similar degrees. Quinidine, quinine and flecainide also increased ΔQTcX and ΔJ-T_peakcX intervals, but the degrees of ΔJ-T_peakcX interval prolongation were shorter than those of ΔQTcX interval prolongation. Ranolazine showed slight increasing trends in ΔQTcX and ΔJ-T_peakcX intervals, but the differences were not significant. Verapamil and nifedipine did not increase the ΔQTcX or ΔJ-T_peakcX intervals. Based on the relations of ΔΔJ-T_peakcX and ΔΔQTcX intervals, dofetilide, sotalol and quinidine were classified as high risk for TdP, quinine, flecainide and ranolazine were classified as intermediate risk and verapamil and nifedipine were classified as low risk. These results supported the usefulness of J-T_peak interval assessment in conscious guinea pigs for predicting drug-induced balanced block of inward currents and TdP risk in early-stage preclinical studies.

Concentration-QT modelling of the novel DHFR inhibitor P218 in healthy male volunteers

AIMS

Given the increasing emergence of drug resistance in Plasmodium, new antimalarials are urgently required. P218 is an aminopyridine that inhibits dihydrofolate reductase being developed as a malaria chemoprotective drug. Assessing the effect of new compounds on cardiac intervals is key during early drug development to determine their cardiac safety.

METHODS

This double-blind, randomized, placebo-controlled, parallel group study evaluated the effect of P218 on electrocardiographic parameters following oral administration of seven single-ascending doses up to 1000 mg in 56 healthy volunteers. Participants were randomized to treatment or placebo at a 3:1 ratio. P218 was administered in the fasted state with standardized lunch served 4 hours after dosing. 12-lead ECGs were recorded in triplicate at regular intervals on the test day, and at 48, 72, 120, 168, 192 and 240 hours thereafter. Blood samples for pharmacokinetic evaluations were collected at similar time points. Concentration-effect modelling was used to assess the effect of P218 and its metabolites on cardiac intervals.

RESULTS

Concentration-effect analysis showed that P218 does not prolong the QTcF, J-Tpeak or TpTe interval at all doses tested. No significant changes in QRS or PR intervals were observed. Two-sided 90% confidence intervals of subinterval effects of P218 and its metabolites were consistently below the regulatory concern threshold for all doses. Study sensitivity was confirmed by significant shortening of QTcF after a meal.

CONCLUSION

Oral administration of P218 up to 1000 mg does not prolong QTcF and does not significantly change QRS or PR intervals, suggesting low risk for drug-induced proarrhythmia.

Human Induced Pluripotent Stem Cell as a Disease Modeling and Drug Development Platform-A Cardiac Perspective

A comprehensive understanding of the pathophysiology and cellular responses to drugs in human heart disease is limited by species differences between humans and experimental animals. In addition, isolation of human cardiomyocytes (CMs) is complicated because cells obtained by biopsy do not proliferate to provide sufficient numbers of cells for preclinical studies in vitro. Interestingly, the discovery of human-induced pluripotent stem cell (hiPSC) has opened up the possibility of generating and studying heart disease in a culture dish. The combination of reprogramming and genome editing technologies to generate a broad spectrum of human heart diseases in vitro offers a great opportunity to elucidate gene function and mechanisms. However, to exploit the potential applications of hiPSC-derived-CMs for drug testing and studying adult-onset cardiac disease, a full functional characterization of maturation and metabolic traits is required. In this review, we focus on methods to reprogram somatic cells into hiPSC and the solutions for overcome immaturity of the hiPSC-derived-CMs to mimic the structure and physiological properties of the adult human CMs to accurately model disease and test drug safety. Finally, we discuss how to improve the culture, differentiation, and purification of CMs to obtain sufficient numbers of desired types of hiPSC-derived-CMs for disease modeling and drug development platform.

Response to sertraline and antiepileptic drugs in pentylenetetrazole kindling in rats

Anti-epileptic drugs (AEDs) are the mainstay of epilepsy treatment but these may be a potential risk factor for behavioral disturbances particularly depression which requires treatment. In this study, the effect of antidepressant sertraline (SRT) in combination with AEDs sodium valproate (SV) and levetiracetam (LEV) on seizures, cognitive impairment and oxidative stress in rats was evaluated. After administration of 24th injection of pentylenetetrazole (PTZ), 77.8% rats were kindled. Administration of SRT showed no protective effect on kindling development while SV was 100% protective. With LEV 42.9% were kindled. On combining SRT with SV or LEV 25% and 20% rats were kindled. A significant increase in latency to reach platform zone in Morris water maze(MWM), and increased transfer latencies in Elevated plus maze(EPM) was observed in PTZ kindled rats as compared to normal control on day 49 and when LEV was combined with SRT. In EPM test, however none of the drug treatments had any effect on transfer latencies except LEV pretreated kindled group. In Passive avoidance (PA) test, kindling was associated with a significant decrease in retention time(p = 0.018) while LEV and SV had no effect. The PTZ kindled rats showed significantly higher malondialdehyde(MDA) levels in brain hippocampus(p = 0.0286) while both SRT and SV were associated with significantly lower MDA levels as compared to kindled control group. In case of glutathione (GSH), kindling had no significant effect. The use of sertraline for depression in persons with epilepsy on AEDs needs to be carefully evaluated and monitored due to likelihood of individual variation.

Electrocardiogram-based index for the assessment of drug-induced hERG potassium channel block

INTRODUCTION

Drug-induced block of the hERG potassium channel could predispose to torsade de pointes, depending on occurrence of concomitant blocks of the calcium and/or sodium channels. Since the hERG potassium channel block affects cardiac repolarization, the aim of this study was to propose a new reliable index for non-invasive assessment of drug-induced hERG potassium channel block based on electrocardiographic T-wave features.

METHODS

ERD_30% (early repolarization duration) and T_S/A (down-going T-wave slope to T-wave amplitude ratio) features were measured in 22 healthy subjects who received, in different days, doses of dofetilide, ranolazine, verapamil and quinidine (all being hERG potassium channel blockers and the latter three being also blockers of calcium and/or sodium channels) while undergoing continuous electrocardiographic acquisition from which ERD_30% and T_S/A were evaluated in fifteen time points during the 24 h following drug administration ("ECG Effects of Ranolazine, Dofetilide, Verapamil, and Quinidine in Healthy Subjects" database by Physionet). A total of 1320 pairs of ERD_30% and T_S/A measurements, divided in training (50%) and testing (50%) datasets, were obtained. Drug-induced hERG potassium channel block was modelled by the regression equation B_ECG(%) = a·ERD_30% + b·T_S/A+ c·ERD_30%·T_S/A + d; B_ECG(%) values were compared to plasma-based measurements, B_REF(%).

RESULTS

Regression coefficients values, obtained on the training dataset, were: a = -561.0 s^-1, b = -9.7 s, c = 77.2 and d = 138.9. In the testing dataset, correlation coefficient between B_ECG(%) and B_REF(%) was 0.67 (p < 10^-81); estimation error was -11.5 ± 16.7%.

CONCLUSION

B_ECG(%) is a reliable non-invasive index for the assessment of drug-induced hERG potassium channel block, independently from concomitant blocks of other ions.

Electrophysiological and ECG Effects of Perhexiline, a Mixed Cardiac Ion Channel Inhibitor, Evaluated in Nonclinical Assays and in Healthy Subjects

Perhexiline has been used to treat hypertrophic cardiomyopathy. In addition to its effect on carnitine-palmitoyltransferase-1, it has mixed ion channel effects through inhibition of several cardiac ion currents. Effects on cardiac ion channels expressed in mammalian cells were assayed using a manual patch-clamp technique, action potential duration (APD) was measured in ventricular trabeculae of human donor hearts, and electrocardiogram effects were evaluated in healthy subjects in a thorough QT (TQT) study. Perhexiline blocked several cardiac ion currents at concentrations within the therapeutic range (150-600 ng/mL) with IC₅₀ for hCav1.2 ∼ hERG < late hNav1.5. A significant APD shortening was observed in perhexiline-treated cardiomyocytes. The TQT study was conducted with a pilot part in 9 subjects to evaluate a dosing schedule that would achieve therapeutic and supratherapeutic perhexiline plasma concentrations on days 4 and 6, respectively. Guided by the results from the pilot, 104 subjects were enrolled in a parallel-designed part with a nested crossover comparison for the positive control. Perhexiline caused QTc prolongation, with the largest effect on ΔΔQTcF, 14.7 milliseconds at therapeutic concentrations and 25.6 milliseconds at supratherapeutic concentrations and a positive and statistically significant slope of the concentration-ΔΔQTcF relationship (0.018 milliseconds per ng/mL; 90%CI, 0.0119-0.0237 milliseconds per ng/mL). In contrast, the JTpeak interval was shortened with a negative concentration-JTpeak relationship, a pattern consistent with multichannel block. Further studies are needed to evaluate whether this results in a low proarrhythmic risk.

Differentiating multichannel block on the guinea pig ECG: Use of Tpeak-Tend and J-Tpeak

INTRODUCTION

The anaesthetised guinea pig is a well characterised assay for early assessment of drug effects on ventricular repolarisation and risk of Torsade de Pointes (TdP). We assessed whether a selective hERG blocker with known TdP risk could be differentiated from lower risk, balanced ion channel blockers in the guinea pig, using corrected QT (QTc) interval alongside novel electrocardiogram (ECG) biomarkers J-T_peakc and T_peak-T_end. Effects were compared with previous clinical investigations at similar plasma concentrations and with another index of TdP risk, the electromechanical window (EMW).

METHODS

Twenty-two Dunkin Hartley guinea pigs anaesthetised with sodium pentobarbitone were instrumented for haemodynamic measurement and ECG recording. Three ascending doses of vehicle (n = 6), dofetilide (2, 6 or 20 μg/kg; n = 7), ranolazine (2, 6 or 20 mg/kg; n = 5) or verapamil (0.1, 0.3 or 1.0 mg/kg; n = 4) were administered intravenously.

RESULTS

As reported in previous clinical studies, dofetilide induced dose-dependent increases in QTc interval, with increases in both J-T_peakC or T_peak-T_end, while verapamil caused no significant increase in QTc interval, J-T_peakC or T_peak-T_end. Ranolazine caused dose-dependent increases in QTc interval and corrected J-T_peakc, but had no effect on T_peak-T_end, which is in contrast to the effects reported in humans at similar concentrations. Only dofetilide caused a clear, dose-related decrease in the EMW.

DISCUSSION

These findings suggest that measurements of J-T_peakc and T_peak-T_end in addition to QT interval, may help differentiate pure hERG channel blockers with high risk of TdP from lower risk, multichannel blockers.

Myocardial repolarization time, J-point to T-peak and T-peak to T-end intervals, have different heart rate dependency and autonomic nerve interference in healthy prepubertal children

OBJECTIVE

The JT interval of the myocardial repolarization time can be divided into Jpoint to T-peak interval (JTp) and T-peak to T-end interval (Tpe). It is well known that the JT interval is dependent on the heart rate, but little is known regarding heart rate dependence for JTp and Tpe. The aim of the present study was to clarify the heart rate dependence of JTp and Tpe and to elucidate the interference of autonomic nervous activity with these parameters.

METHODS

We evaluated 50 prepubertal children (mean age: 6.4 ± 0.5 years; male:female, 22:28) without heart disease. JTp, Tpe, and the preceding RR intervals were measured using 120 consecutive beats (lead CM5). First, the relationships between the RR interval and JTp and Tpe were evaluated by Pearson's correlation coefficient. Second, to evaluate autonomic interference with JTp and Tpe, the degree of coherence between RR interval variability and JTp or Tpe variability was calculated using spectral analysis.

RESULTS

Significant positive correlations were observed between the RR interval and JTp (y = 0.116x + 105.5; r = 0.594, p < 0.001) and between the RR interval and Tpe (y = 0.037x + 44.7; r = 0.432, p < 0.001). Tpe variability had a lower degree of coherence with RR interval variability (range: 0.039-0.5 Hz) than with JTp variability (0.401 [interquartile range, 0.352-0.460] vs. 0.593 [0.503-0.664], respectively; p < 0.001).

CONCLUSIONS

Tpe had lower heart rate dependence and a lower degree of autonomic nervous interference than did JTp.

Comparing the consistency of electrocardiogram interval measurements by resting ECG versus 12-lead Holter

In clinical trials, traditionally only a limited number of 12-lead resting electrocardiograms (ECGs) can be recorded and, thus, long intervals may elapse between assessment timepoints and valuable information may be missed during times when patients' cardiac electrical activity is not being monitored. These limitations have led to the increasing use of Holter recorders which provide continuous data registrations while reducing the burden on patients and freeing up time for clinical trial staff to perform other tasks. However, there is a shortage of data comparing the two approaches. In this study, data from a randomized, double-blind, four-period, crossover thorough QT study in 40 healthy subjects were used to compare continuous 12-lead Holter recordings to standard 12-lead resting ECGs which were recorded in parallel. Heart rate and QT interval data were estimated by averaging three consecutive heartbeats. Values exceeding the sample average by more than 5% were tagged as outliers and excluded from the analysis. Visual comparisons of the ECG waveforms of the Holter signal showed a good correlation with resting ECGs at matching timepoints. Resting ECG data revealed sex differences that Holter data did not show. Specifically, women were found to have a longer QTcF of 20 ms, while men had a lower heart rate. We found that continuous recordings provided a more accurate reflection of changes in cardiac electrical activity over 24 hr. However, manual adjudication is still required to ensure the quality and accuracy of ECG data, and that only artifacts are removed thereby avoiding loss of true signals.

Translational Models and Tools to Reduce Clinical Trials and Improve Regulatory Decision Making for QTc and Proarrhythmia Risk (ICH E14/S7B Updates)

After multiple drugs were removed from the market secondary to drug-induced torsade de pointes (TdP) risk, the International Council for Harmonisation (ICH) released guidelines in 2005 that focused on the nonclinical (S7B) and clinical (E14) assessment of surrogate biomarkers for TdP. Recently, Vargas et al. published a pharmaceutical-industry perspective making the case that "double-negative" nonclinical data (negative in vitro hERG and in vivo heart-rate corrected QT (QTc) assays) are associated with such low probability of clinical QTc prolongation and TdP that potentially all double-negative drugs would not need detailed clinical QTc evaluation. Subsequently, the ICH released a new E14/S7B Draft Guideline containing Questions and Answers (Q&As) that defined ways that double-negative nonclinical data could be used to reduce the number of "Thorough QT" (TQT) studies and reach a low-risk determination when a TQT or equivalent could not be performed. We review the Vargas et al. proposal in the context of what was contained in the ICH E14/S7B Draft Guideline and what was proposed by the ICH E14/S7B working group for a "stage 2" of updates (potential expanded roles for nonclinical data and details for assessing TdP risk of QTc-prolonging drugs). Although we do not agree with the exact probability statistics in the Vargas et al. paper because of limitations in the underlying datasets, we show how more modest predictive value of individual assays could still result in low probability for TdP with double-negative findings. Furthermore, we expect that the predictive value of the nonclinical assays will improve with implementation of the new ICH E14/S7B Draft Guideline.

Intense bitterness of molecules: Machine learning for expediting drug discovery

Drug development is a long, expensive and multistage process geared to achieving safe drugs with high efficacy. A crucial prerequisite for completing the medication regimen for oral drugs, particularly for pediatric and geriatric populations, is achieving taste that does not hinder compliance. Currently, the aversive taste of drugs is tested in late stages of clinical trials. This can result in the need to reformulate, potentially resulting in the use of more animals for additional toxicity trials, increased financial costs and a delay in release to the market. Here we present BitterIntense, a machine learning tool that classifies molecules into "very bitter" or "not very bitter", based on their chemical structure. The model, trained on chemically diverse compounds, has above 80% accuracy on several test sets. Our results suggest that about 25% of drugs are predicted to be very bitter, with even higher prevalence (~40%) in COVID19 drug candidates and in microbial natural products. Only ~10% of toxic molecules are predicted to be intensely bitter, and it is also suggested that intense bitterness does not correlate with hepatotoxicity of drugs. However, very bitter compounds may be more cardiotoxic than not very bitter compounds, possessing significantly lower QPlogHERG values. BitterIntense allows quick and easy prediction of strong bitterness of compounds of interest for food, pharma and biotechnology industries. We estimate that implementation of BitterIntense or similar tools early in drug discovery process may lead to reduction in delays, in animal use and in overall financial burden.

Importance of electrocardiographic markers in predicting cardiac events in children

ECG is a common diagnostic tool in medical practice. Sudden cardiac death (SCD) is a rare but devastating event. The most common cause of SCD in the young is a primary arrhythmic event, which is often produced by malignant ventricular arrhythmia. Several electrocardiographic markers for ventricular repolarization and depolarization have been proposed to predict this arrhythmic risk and SCD in children. Although many of these parameters can easily be used in clinical practice, some of them need specific techniques for interpretation. In this review, we summarized the current knowledge regarding the clinical importance and the ability of these ECG parameters to predict adverse cardiac events in the pediatric population.

The association between body temperature and electrocardiographic parameters in normothermic healthy volunteers

Background

Previous studies reported that hypo‐ and hyperthermia are associated with several atrial and ventricular electrocardiographical parameters, including corrected QT (QTc) interval. Enhanced characterization of variations in QTc interval and normothermic body temperature aids in better understanding the underlying mechanism behind drug induced QTc interval effects. The analysis’ objective was to investigate associations between body temperature and electrocardiographical parameters in normothermic healthy volunteers.

Methods

Data from 3023 volunteers collected at our center were retrospectively analyzed. Subjects were considered healthy after review of collected data by a physician, including a normal tympanic body temperature (35.5‐37.5°C) and in sinus rhythm. A linear multivariate model with body temperature as a continuous was performed. Another multivariate analysis was performed with only the QT subintervals as independent variables and body temperature as dependent variable.

Results

Mean age was 33.8 ± 17.5 years and mean body temperature was 36.6 ± 0.4°C. Body temperature was independently associated with age (standardized coefficient [SC] = −0.255, P < .001), female gender (SC = +0.209, P < .001), heart rate (SC = +0.231, P < .001), P‐wave axis (SC = −0.051, P < .001), J‐point elevation in lead V4 (SC = −0.121, P < .001), and QTcF duration (SC = −0.061, P = .002). In contrast, other atrial and atrioventricular (AV) nodal parameters were not independently associated with body temperature. QT subinterval analysis revealed that only QRS duration (SC = −0.121, P < .001) was independently associated with body temperature.

Conclusion

Body temperature in normothermic healthy volunteers was associated with heart rate, P‐wave axis, J‐point amplitude in lead V4, and ventricular conductivity, the latter primarily through prolongation of the QRS duration.

Transdermal Testosterone Attenuates Drug-Induced Lengthening of Both Early and Late Ventricular Repolarization in Older Men

We have previously reported that transdermal testosterone attenuates drug-induced QT interval lengthening in older men. However, it is unknown whether this is due to modulation of early ventricular repolarization, late repolarization, or both. In a secondary analysis of a prospective, randomized, double-blind, placebo-controlled three-way crossover study, we determined if transdermal testosterone and oral progesterone attenuate drug-induced lengthening of early and late ventricular repolarization, represented by the electrocardiographic measurements J-T_peak c and T_peak -T_end , respectively, as well as T_peak -T_end /QT, a measure of transmural dispersion of repolarization. Male volunteers ≥ 65 years of age (n = 14) were randomized to receive transdermal testosterone 100 mg, oral progesterone 400 mg, or matching transdermal/oral placebo daily for 7 days. On the morning following the seventh day, subjects received intravenous ibutilide 0.003 mg/kg, after which electrocardiograms were performed serially. One subject was excluded due to difficulty in T-wave interpretation. Pre-ibutilide J-T_peak c was lower during the testosterone phase than during progesterone and placebo (216 ± 23 vs. 227 ± 28 vs. 227 ± 21 ms, P = 0.002). Maximum post-ibutilide J-T_peak c was also lower during the testosterone phase (233 ± 22 vs. 246 ± 29 vs. 248 ± 23 ms, P < 0.0001). Pre-ibutilide T_peak -T_end was not significantly different during the three phases, but maximum post-ibutilide T_peak -T_end was lower during the testosterone phase (80 ± 12 vs. 89 ± 18 vs. 86 ± 15 ms, P = 0.002). Maximum T_peak -T_end /QT was also lower during the testosterone phase (0.199 ± 0.023 vs. 0.216 ± 0.035 vs. 0.209 ± 0.031, P = 0.005). Progesterone exerted minimal effect on drug-induced lengthening of J-T_peak c, and no effect on T_peak -T_end or T_peak -T_end /QT. Transdermal testosterone attenuates drug-induced lengthening of both early and late ventricular repolarization in older men.

Discovery of Vixotrigine: A Novel Use-Dependent Sodium Channel Blocker for the Treatment of Trigeminal Neuralgia

Drugs that block voltage-gated sodium channels (NaVs) have utility in treating conditions including pain, epilepsy, and cardiac arrhythmias and as anesthetics (Lancet Neurol.20109413424; Expert Opin. Ther. Pat.201020755779). The identification of compounds with improved efficacy and safety is a key aim for the discovery of improved NaV blocking drugs (Comprehensive Medicinal Chemistry III; (Elsevier, 2017; pp 131-175). We report the identification of a novel class of brain penetrant and voltage-gated sodium channel blockers, leading to the discovery of vixotrigine, a use-dependent sodium channel blocker with activity in in vivo models of pain. Vixotrigine has excellent physiocochemical properties for drug development, and both preclinical and clinical data support a safety profile suitable for potential use in neuropathic pain and other conditions. It has shown efficacy in a Phase II study for pain associated with trigeminal neuralgia.

Summary of Torsades de Pointes (TdP) Reports Associated with Intravenous Drug Formulations Containing the Preservative Chlorobutanol

INTRODUCTION

Drug-induced torsades de pointes (TdP) is a potentially lethal ventricular arrhythmia that is associated with drugs that prolong the QT interval on the electrocardiogram (ECG) due to their interference with the cardiac potassium current, I_KR. Intravenous (IV) formulations of methadone have been associated with TdP and contain the preservative chlorobutanol, which, like methadone, blocks I_KR. The combinations of chlorobutanol with methadone or terfenadine, another I_KR blocker, produce synergistic I_KR block.

OBJECTIVE

The aim of this study was to examine and summarize the evidence available to address the question: what other IV drug formulations contain chlorobutanol and are they associated with TdP?

METHODS

IV drug products containing the preservative chlorobutanol were identified by searching the websites DailyMed ( https://dailymed.nlm.nih.gov/dailymed/index.cfm ) and Drugs@FDA ( https://www.accessdata.fda.gov/scripts/cder/daf/ ). For each drug identified, PubMed and the FDA's Adverse Event Reporting System (FAERS) were searched for reports of TdP and/or QT prolongation and FAERS data were analyzed for disproportionality of reports.

RESULTS

The search found nine drugs (methadone, epinephrine, papaverine, oxytocin, vasopressin, testosterone, estradiol, isoniazid, and desmopressin) that contain chlorobutanol 2.5 (n = 1) or 5.0 mg/mL. All nine drugs had reports of QT prolongation or TdP reported in FAERS and all but estradiol, testosterone, desmopressin, and isoniazid had reports of QT prolongation or TdP in PubMed. Two of the nine drugs (epinephrine and methadone) had positive signals (by disproportionality analysis) for TdP in FAERS (EB₀₅ 2.88 and 23.81, respectively) and four (methadone, epinephrine, papaverine, and vasopressin) were reported in published articles as the suspect drugs in cases of TdP.

CONCLUSION

The pharmacologic profile of chlorobutanol (synergistic I_KR block) and its association with reports of TdP and QT prolongation suggest the need for a full evaluation of its cardiac safety when used as a preservative in IV drug and vitamin formulations.

Blood pressure-related electrocardiographic findings in healthy young individuals

Purpose: Elevated blood pressure induces electrocardiographic changes and is associated with an increase in cardiovascular disease later in life compared to normal blood pressure levels. The purpose of this study was to evaluate the association between normal to high normal blood pressure values (90-139/50-89 mmHg) and electrocardiographic parameters related to cardiac changes in hypertension in healthy young adults.Methods: Data from 1449 volunteers aged 18-30 years collected at our centre were analyzed. Only subjects considered healthy by a physician after review of collected data with systolic blood pressure values between 90 and 139 mmHg and diastolic blood pressure values between 50 and 89 mmHg were included. Subjects were divided into groups with 10 mmHg systolic blood pressure increment between groups for analysis of electrocardiographic differences. Backward multivariate regression analysis with systolic and diastolic blood pressure as a continuous variable was performed.Results: The mean age was 22.7 ± 3.0 years, 73.7% were male. P-wave area, ventricular activation time, QRS-duration, Sokolow-Lyon voltages, Cornell Product, J-point-T-peak duration corrected for heart rate and maximum T-wave duration were significantly different between systolic blood pressure groups. In the multivariate model with gender, body mass index and cholesterol, ventricular rate (standardized coefficient (SC): +0.182, p < .001), ventricular activation time in lead V6 (SC= +0.065, p = .048), Sokolow-Lyon voltage (SC= +0.135, p < .001), and Cornell product (SC= +0.137, p < .001) were independently associated with systolic blood pressure, while ventricular rate (SC= +0.179, p < .001), P-wave area in lead V1 (SC= +0.079, p = .020), and Cornell product (SC= +0.091, p = .006) were independently associated with diastolic blood pressure.Conclusion: Blood pressure-related electrocardiographic changes were observed incrementally in a healthy young population with blood pressure in the normal range. These changes were an increased ventricular rate, increased atrial surface area, ventricular activation time and increased ventricular hypertrophy indices on a standard 12 lead electrocardiogram.

Classification of drug-induced hERG potassium-channel block from electrocardiographic T-wave features using artificial neural networks

BACKGROUND

Human ether-à-go-go-related gene (hERG) potassium-channel block represents a harmful side effect of drug therapy that may cause torsade de pointes (TdP). Analysis of ventricular repolarization through electrocardiographic T-wave features represents a noninvasive way to accurately evaluate the TdP risk in drug-safety studies. This study proposes an artificial neural network (ANN) for noninvasive electrocardiography-based classification of the hERG potassium-channel block.

METHODS

The data were taken from the "ECG Effects of Ranolazine, Dofetilide, Verapamil, and Quinidine in Healthy Subjects" Physionet database; they consisted of median vector magnitude (VM) beats of 22 healthy subjects receiving a single 500 μg dose of dofetilide. Fourteen VM beats were considered for each subject, relative to time-points ranging from 0.5 hr before to 14.0 hr after dofetilide administration. For each VM, changes in two indexes accounting for the early and the late phases of repolarization, ΔERD_30% and ΔT_{S /A} , respectively, were computed as difference between values at each postdose time-point and the predose time-point. Thus, the dataset contained 286 ΔERD_30% -ΔT_{S /A} pairs, partitioned into training, validation, and test sets (114, 29, and 143 pairs, respectively) and used as inputs of a two-layer feedforward ANN with two target classes: high block (HB) and low block (LB). Optimal ANN (OANN) was identified using the training and validation sets and tested on the test set.

RESULTS

Test set area under the receiver operating characteristic was 0.91; sensitivity, specificity, accuracy, and precision were 0.93, 0.83, 0.92, and 0.96, respectively.

CONCLUSION

OANN represents a reliable tool for noninvasive assessment of the hERG potassium-channel block.

Effects of the Fluoroquinolones Moxifloxacin and Levofloxacin on the QT Subintervals: Sex Differences in Ventricular Repolarization

Women are associated with longer electrocardiographic QT intervals and increased proarrhythmic risks of QT‐prolonging drugs. The purpose of this study was to characterize the differences in cardiac electrophysiology between moxifloxacin and levofloxacin in men and women and to assess the balance of inward and outward currents through the analysis of QT subintervals. Data from 2 TQT studies were used to investigate the impact of moxifloxacin (400 mg) and levofloxacin (1000 and 1500 mg) on QT subintervals using algorithms for measurement of J‐T_peak and T_peak‐T_end intervals. Concentration‐effect analyses were performed to establish potential relationships between the ECG effects and the concentrations of the 2 fluoroquinolones. Moxifloxacin was shown to be a more potent prolonger of QT interval corrected by Fredericia (QTcF) and had a pronounced effect on J‐T_peakc. Levofloxacin had little effect on J‐T_peakc. For moxifloxacin, the concentration‐effect modeling showed a greater effect for women on QTcF and J‐T_peakc, whereas for levofloxacin the inverse was true: women had smaller QTcF and J‐T_peakc effects. The different patterns in repolarization after administration of both drugs suggested a sex difference, which may be related to the combined I_Ks and I_Kr inhibitory properties of moxifloxacin versus I_Kr suppression only of levofloxacin. The equipotent inhibition of I_Ks and I_Kr appears to affect women more than men. Sex hormones are known to influence cardiac ion channel expression and differences in QT duration. Differences in I_Kr and I_Ks balances, influenced by sex hormones, may explain the results. These results support the impact of sex differences on the cardiac safety assessment of drugs.

Heart Rate Correction of the J-to-Tpeak Interval

Drug-induced changes of the J to T peak (JTp) and J to the median of area under the T wave (JT50) were reported to differentiate QT prolonging drugs that are predominant blockers of the delayed potassium rectifier current from those with multiple ion channel effects. Studies of drug-induced JTp/JT50 interval changes might therefore facilitate cardiac safety evaluation of new pharmaceuticals. It is not known whether formulas for QT heart rate correction are applicable to JTp and JT50 intervals. QT/RR, JTp/RR, and JT50/RR profiles were studied in 523 healthy subjects aged 33.5 ± 8.4 years (254 females). In individual subjects, 1,256 ± 220 electrocardiographic measurements of QT, JTp, and JT50 intervals were available including a 5-minute history of RR intervals preceding each measurement. Curvilinear, linear and log-linear regression models were used to characterize individual QT/RR, JTp/RR, and JT50/RR profiles both without and with correction for heart rate hysteresis. JTp/RR and JT50/RR hysteresis correction needs to be included but the generic universal correction for QT/RR hysteresis is also applicable to JTp/RR and JT50/RR profiles. Once this is incorporated, median regression coefficients of the investigated population suggest linear correction formulas JTpc = JTp + 0.150(1-RR) and JT50c = JT50 + 0.117(1-RR) where RR intervals of the underlying heart rate are hysteresis-corrected, and all measurements expressed in seconds. The established correction formulas can be proposed for future clinical pharmacology studies that show drug-induced heart rate changes of up to approximately 10 beats per minute.

Three-Dimensional Heart Model-Based Screening of Proarrhythmic Potential by in silico Simulation of Action Potential and Electrocardiograms

The proarrhythmic risk is a major concern in drug development. The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative has proposed the JTpeak interval on electrocardiograms (ECGs) and qNet, an in silico metric, as new biomarkers that may overcome the limitations of the hERG assay and QT interval. In this study, we simulated body-surface ECGs from patch-clamp data using realistic models of the ventricles and torso to explore their suitability as new in silico biomarkers for cardiac safety. We tested seven drugs in this study: dofetilide (high proarrhythmic risk), ranolazine, verapamil (QT increasing, but safe), bepridil, cisapride, mexiletine, and diltiazem. Human ventricular geometry was reconstructed from computed tomography (CT) images, and a Purkinje fiber network was mapped onto the endocardial surface. The electrical wave propagation in the ventricles was obtained by solving a reaction-diffusion equation using finite-element methods. The body-surface ECG data were calculated using a torso model that included the ventricles. The effects of the drugs were incorporated in the model by partly blocking the appropriate ion channels. The effects of the drugs on single-cell action potential (AP) were examined first, and three-dimensional (3D) body-surface ECG simulations were performed at free Cmax values of 1×, 5×, and 10×. In the single-cell and ECG simulations at 5× Cmax, dofetilide, but not verapamil or ranolazine, caused arrhythmia. However, the non-increasing JTpeak caused by verapamil and ranolazine that has been observed in humans was not reproduced in our simulation. Our results demonstrate the potential of 3D body-surface ECG simulation as a biomarker for evaluation of the proarrhythmic risk of candidate drugs.

Electrocardiographic conduction and repolarization markers associated with sudden cardiac death: moving along the electrocardiography waveform

The QT interval along with its heart rate corrected form (QTc) are well-established ECG markers that have been found to be associated with malignant ventricular arrhythmogenesis. However, extensive preclinical and clinical investigations over the years have allowed for novel clinical ECG markers to be generated as predictors of arrhythmogenesis and sudden cardiac death. Repolarization markers include the older QTc, QT dispersion and newer Tpeak - Tend intervals, (Tpeak - Tend) / QT ratios, T-wave alternans (TWA), microvolt TWA and T-wave area dispersion. Meanwhile, conduction markers dissecting the QRS complex, such as QRS dispersion (QRSD) and fragmented QRS, were also found to correlate conduction velocity and unidirectional block with re-entrant substrates in various cardiac conditions. Both repolarization and conduction parameters can be combined into the excitation wavelength (λ). A surrogate marker for λ is the index of Cardiac Electrophysiological Balance (iCEB: QT / QRSd). Other markers based on conduction-repolarization are [QRSD x (Tpeak-Tend) / QRSd] and [QRSD x (Tpeak-Tend) / (QRSd x QT)]. Advancement in technology permitted sophisticated electrophysiological analyses such as principal component analysis and periodic repolarization dynamics to further improve risk stratification. This was closely followed by other novel indices including ventricular ectopic QRS interval, the f99 index and EntropyXQT, which integrates mathematical and physical calculations for determining the risk markers. Though proven to be effective in limited patient cohorts, more clinical studies across different cardiac pathologies are required to confirm their validity. As such, this review seeks to encapsulate the development of old and new ECG markers along with their associated utility and shortcomings in clinical practice.

Assessment of Multi-Ion Channel Block in a Phase I Randomized Study Design: Results of the CiPA Phase I ECG Biomarker Validation Study

Balanced multi‐ion channel‐blocking drugs have low torsade risk because they block inward currents. The Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative proposes to use an in silico cardiomyocyte model to determine the presence of balanced block, and absence of heart rate corrected J‐T_peak (J‐T_peakc) prolongation would be expected for balanced blockers. This study included three balanced blockers in a 10‐subject‐per‐drug parallel design; lopinavir/ritonavir and verapamil met the primary end point of ΔΔJ‐T_peakc upper bound < 10 ms, whereas ranolazine did not (upper bounds of 8.8, 6.1, and 12.0 ms, respectively). Chloroquine, a predominant blocker of the potassium channel encoded by the ether‐à‐go‐go related gene (hERG), prolonged ΔΔQTc and ΔΔJ‐T_peakc by ≥ 10 ms. In a separate crossover design, diltiazem (calcium block) did not shorten dofetilide‐induced ΔQTc prolongation, but shortened ΔJ‐T_peakc and prolonged ΔT_peak‐T_end. Absence of J‐T_peakc prolongation seems consistent with balanced block; however, small sample size (10 subjects) may be insufficient to characterize concentration‐response in some cases.

The Cardiovascular Effects of a Meal: J-Tpeak and Tpeak -Tend Assessment and Further Insights Into the Physiological Effects

Meal intake leads to a significant and prolonged increase in cardiac output to supply the splanchnic vasculature. A meal is associated with sympathetic activation of the cardiovascular system, and food ingestion is correlated with an increase in heart rate, an increase in cardiac stroke volume, and QTc interval shortening for up to 7 hours. Given the complexity of the system, one or several of many mechanisms could explain this observation. The shortening of the QTc interval was correlated with a rise of C‐peptide following food ingestion, but the mechanisms by which C‐peptide may be involved in the modulation of cardiac repolarization are still unknown. This shortening of the myocardial action potential caused by the ingestion of food was further investigated in the present study by measuring the QRS, J‐T_peak, and T_peak‐T_end intervals in search of further clues to better understand the underlying mechanisms. A retrospective analysis was conducted based on data collected in a formal thorough QT/QTc study in which 32 subjects received a carbohydrate‐rich “continental” breakfast, moxifloxacin without food, and moxifloxacin with food. We assessed the effect of food on T‐wave morphology using validated algorithms for measurement of J‐T_peak and T_peak‐T_end intervals. Our findings demonstrate that a standardized meal significantly shortened J‐T_peak for 4 hours after a meal and to a much lesser extent and shorter duration (up to 1 hour) prolonged the T_peak‐T_end and QRS intervals. This suggests that the QTc shortening occurs mainly during phase 2 of the cardiac action potential. As there was no corresponding effect on T_peak‐T_end beyond the first hour, we conclude that a meal does not interfere with the outward correcting potassium channels but possibly with Ca²⁺ currents. An effect on mainly Ca²⁺ aligns well with our understanding of physiology whereby an increase in stroke volume, as observed after a meal, is associated with changes in Ca²⁺ cycling in and out of the sarcoplasmic reticulum during cardiac myocyte contraction.

Update on the ECG component of the CiPA initiative

The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative is validating a new paradigm for assessing proarrhythmic potential of drugs that goes beyond hERG block and QT prolongation. Based on in vitro data of the drug's effects on multiple cardiac ion channel currents, CiPA's in silico model of the human cardiomyocyte will classify drugs as low, intermediate or high risk for torsade de pointes. Under CiPA, early phase 1 ECG data will be used to determine if there are unexpected ion channel effects in humans compared to the in vitro ion channel data. CiPA's ECG biomarker working group identified the heart rate corrected J-Tpeak interval (J-Tpeakc, from the end of the QRS to the peak of the T-wave) as the best of 12 ECG biomarkers to detect late sodium current block in presence of hERG block. While predominant hERG blockers prolonged QTc and J-Tpeakc, "balanced" ion channel blocking drugs (hERG + late sodium and/or calcium block) prolonged QTc without prolonging J-Tpeakc. This manuscript reviews the ECG component of CiPA and provides a description of the ECG methods used in the CiPA ECG validation clinical study.

Arrhythmic hazard map for a 3D whole-ventricle model under multiple ion channel block

Background and Purpose

To date, proposed in silico models for preclinical cardiac safety testing are limited in their predictability and usability. We previously reported a multi‐scale heart simulation that accurately predicts arrhythmogenic risk for benchmark drugs.

Experimental Approach

We created a comprehensive hazard map of drug‐induced arrhythmia based on the electrocardiogram (ECG) waveforms simulated under wide range of drug effects using the multi‐scale heart simulator described here, implemented with cell models of human cardiac electrophysiology.

Key Results

A total of 9075 electrocardiograms constitute the five‐dimensional hazard map, with coordinates representing the extent of the block of each of the five ionic currents (rapid delayed rectifier potassium current (I_Kr), fast (I_Na) and late (I_Na,L) components of the sodium current, L‐type calcium current (I_Ca,L) and slow delayed rectifier current (I_Ks)), involved in arrhythmogenesis. Results of the evaluation of arrhythmogenic risk based on this hazard map agreed well with the risk assessments reported in the literature. ECG databases also suggested that the interval between the J‐point and the T‐wave peak is a superior index of arrhythmogenicity when compared to the QT interval due to its ability to characterize the multi‐channel effects compared with QT interval.

Conclusion and Implications

Because concentration‐dependent effects on electrocardiograms of any drug can be traced on this map based on in vitro current assay data, its arrhythmogenic risk can be evaluated without performing costly and potentially risky human electrophysiological assays. Hence, the map serves as a novel tool for use in pharmaceutical research and development.

Challenges in implementing and obtaining acceptance for J-Tpeak assessment as the clinical component of CiPA

INTRODUCTION

This paper is based on a presentation held at the Annual Safety Pharmacology Society meeting in September 2017, at which challenges for the clinical component of CiPA were presented. FDA has published an automated algorithm for measurement of the J-Tpeak interval on a median beat from a vector magnitude lead derived from a 12-lead ECG. CiPA proposes that J-Tpeak prolongation < 10 ms can be used for drugs with a QTc effect < 20 ms to differentiate between safe and unsafe delayed repolarization and to reduce the level of ECG monitoring in late stage clinical trials.

METHODS

We applied FDA's algorithm, complemented with iCOMPAS, to moxifloxacin and dolasetron data from the IQ-CSRC study with 9 subjects on active and 6 on placebo. The effect on QTcF and corrected J-Tpeak (J-Tpeak_c) was analyzed using concentration-effect modeling.

RESULTS

There was a good correlation between QTcF and J-Tpeak_c prolongation after oral dosing of 400 mg moxifloxacin with placebo-adjusted, change-from-baseline (ΔΔ) J-Tpeak_c of ~12 ms at concentrations that caused ΔΔQTcF of ~20 ms. On dolasetron, J-Tpeak_c was highly variable, no prolongation was seen and an effect on ΔΔJ-Tpeak_c > 10 ms could be excluded across the observed plasma concentration range.

DISCUSSION

In this limited analysis performed on the IQ-CSRC study waveforms using FDA's automated algorithm, J-Tpeak prolongation was observed on moxifloxacin, but not on dolasetron, despite clinical observations of proarrhythmias with both drugs. Challenges for the implementation of the J-Tpeak interval as a replacement or complement to the QTc interval, include to demonstrate that the proposed clinical algorithm using a J-Tpeak threshold of 10 ms, can be used to categorize drugs with a QT effect up to ~20 ms as having low pro-arrhythmic risk.

Drug-induced Proarrhythmia and Torsade de Pointes: A Primer for Students and Practitioners of Medicine and Pharmacy

Multiple marketing withdrawals due to proarrhythmic concerns occurred in the United States, Canada, and the United Kingdom in the late 1980s to early 2000s. This primer reviews the clinical implications of a drug's identified proarrhythmic liability, the issues associated with these safety-related withdrawals, and the actions taken by the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) and by regulatory agencies in terms of changing drug development practices and introducing new nonclinical and clinical tests to asses proarrhythmic liability. ICH Guidelines S7B and E14 were released in 2005. Since then, they have been adopted by many regional regulatory authorities and have guided nonclinical and clinical proarrhythmic cardiac safety assessments during drug development. While this regulatory paradigm has been successful in preventing drugs with unanticipated potential for inducing the rare but potentially fatal polymorphic ventricular arrhythmia torsade de pointes from entering the market, it has led to the termination of drug development programs for other potentially useful medicines because of isolated results from studies with limited predictive value. Research efforts are now exploring alternative approaches to better predict potential proarrhythmic liabilities. For example, in the domain of human electrocardiographic assessments, concentration-response modeling conducted during phase 1 clinical development has recently become an accepted alternate primary methodology to the ICH E14 "thorough QT/QTc" study for defining a drug's corrected QT interval prolongation liability under certain conditions. When a drug's therapeutic benefit is considered important at a public health level but there is also an identified proarrhythmic liability that may result from administration of the single drug in certain individuals and/or drug-drug interactions, marketing approval will be accompanied by appropriate directions in the drug's prescribing information. Health-care professionals in the fields of medicine and pharmacy need to consider the prescribing information in conjunction with individual patients' clinical characteristics and concomitant medications when prescribing and dispensing such drugs.

Traditional and novel electrocardiographic conduction and repolarization markers of sudden cardiac death

Sudden cardiac death, frequently due to ventricular arrhythmias, is a significant problem globally. Most affected individuals do not arrive at hospital in time for medical treatment. Therefore, there is an urgent need to identify the most-at-risk patients for insertion of prophylactic implantable cardioverter defibrillators. Clinical risk markers derived from electrocardiography are important for this purpose. They can be based on repolarization, including corrected QT (QTc) interval, QT dispersion (QTD), interval from the peak to the end of the T-wave (Tpeak - Tend), (Tpeak - Tend)/QT, T-wave alternans (TWA), and microvolt TWA. Abnormal repolarization properties can increase the risk of triggered activity and re-entrant arrhythmias. Other risk markers are based solely on conduction, such as QRS duration (QRSd), which is a surrogate marker of conduction velocity (CV) and QRS dispersion (QRSD) reflecting CV dispersion. Conduction abnormalities in the form of reduced CV, unidirectional block, together with a functional or a structural obstacle, are conditions required for circus-type or spiral wave re-entry. Conduction and repolarization can be represented by a single parameter, excitation wavelength (λ = CV × effective refractory period). λ is an important determinant of arrhythmogenesis in different settings. Novel conduction-repolarization markers incorporating λ include Lu et al.' index of cardiac electrophysiological balance (iCEB: QT/QRSd), [QRSD× (Tpeak - Tend)/QRSd] and [QRSD × (Tpeak - Tend)/(QRSd × QT)] recently proposed by Tse and Yan. The aim of this review is to provide up to date information on traditional and novel markers and discuss their utility and downfalls for risk stratification.

Translating New Science Into the Drug Review Process: The US FDA's Division of Applied Regulatory Science

In 2011, the US Food and drug Administration (FDA) developed a strategic plan for regulatory science that focuses on developing new tools, standards, and approaches to assess the safety, efficacy, quality, and performance of FDA-regulated products. In line with this, the Division of Applied Regulatory Science was created to move new science into the Center for Drug Evaluation and Research (CDER) review process and close the gap between scientific innovation and drug review. The Division, located in the Office of Clinical Pharmacology, is unique in that it performs mission-critical applied research and review across the translational research spectrum including in vitro and in vivo laboratory research, in silico computational modeling and informatics, and integrated clinical research covering clinical pharmacology, experimental medicine, and postmarket analyses. The Division collaborates with Offices throughout CDER, across the FDA, other government agencies, academia, and industry. The Division is able to rapidly form interdisciplinary teams of pharmacologists, biologists, chemists, computational scientists, and clinicians to respond to challenging regulatory questions for specific review issues and for longer-range projects requiring the development of predictive models, tools, and biomarkers to speed the development and regulatory evaluation of safe and effective drugs. This article reviews the Division's recent work and future directions, highlighting development and validation of biomarkers; novel humanized animal models; translational predictive safety combining in vitro, in silico, and in vivo clinical biomarkers; chemical and biomedical informatics tools for safety predictions; novel approaches to speed the development of complex generic drugs, biosimilars, and antibiotics; and precision medicine.

Mechanistic Model-Informed Proarrhythmic Risk Assessment of Drugs: Review of the "CiPA" Initiative and Design of a Prospective Clinical Validation Study

The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative is developing and validating a mechanistic-based assessment of the proarrhythmic risk of drugs. CiPA proposes to assess a drug's effect on multiple ion channels and integrate the effects in a computer model of the human cardiomyocyte to predict proarrhythmic risk. Unanticipated or missed effects will be assessed with human stem cell-derived cardiomyocytes and electrocardiogram (ECG) analysis in early phase I clinical trials. This article provides an overview of CiPA and the rationale and design of the CiPA phase I ECG validation clinical trial, which involves assessing an additional ECG biomarker (J-Tpeak) for QT prolonging drugs. If successful, CiPA will 1) create a pathway for drugs with hERG block / QT prolongation to advance without intensive ECG monitoring in phase III trials if they have low proarrhythmic risk; and 2) enable updating drug labels to be more informative about proarrhythmic risk, not just QT prolongation.

JT interval: What does this interval mean?

The JTp interval gained interest as a marker differentiating effects of drugs on cardiac ion channels. For JTp interval, both the beginning - identification of J point and identification of T wave end remains the subject of substantial variability. We aimed to analyze diagnostic and prognostic performance of JTp interval in the International LQTS Registry data. ECGs from 804 gene carriers and 1139 non-carriers from LQT1 families, 735 carriers and 1145 non-carriers from LQT2 families, and 238 carriers and 554 non-carriers from LQT3 families were evaluated. The diagnostic performance of JTpc was similar to QTc in LQT1 and LQT3 patients but inferior in LQT2 patients, whereas repolarization duration in general had limited diagnostic performance in LQT3 patients. The prognostic significance for predicting cardiac events in LQT1 and LQT2 patients was similar for JTpc and QTc. In LQT3 patients, JTpc fails to be associated with arrhythmic events.

Automated JTpeak analysis by BRAVO

Using BRAVO algorithm (AMPS-LLC, NY, v4.4.0), 5223 ECGs from a publicly available annotated dataset from a randomized clinical trial on four different compounds and placebo were analyzed. ECGs were automatically processed and JTp interval was computed on: 12 standard ECG leads, Vector Magnitude (VM), and root mean square (RMS) leads. On VM and RMS, JTp intervals were nearly identical (228 ± 29 vs. 227 ± 30 ms respectively, with correlation of 0.99, p < 0.0001). On lead II, JTp interval was about 10 ms longer, but highly correlated with that measured on VM (0.94, p < 0.0001). Similarly, on lead V5, JTp was about 8 ms longer than on VM, with a correlation of 0.95, p < 0.0001. When compared to the public available annotations, JTp by BRAVO generated longer (about 8 ms) measurement and evidenced outliers conducible to both the T-wave peak (in few ECGs presenting notched shapes) and, to a lesser degree, to the J point, due to variability of the two algorithms. Differences on the drug-induced effect from the four compounds were negligible.

Common Genetic Variant Risk Score Is Associated With Drug-Induced QT Prolongation and Torsade de Pointes Risk: A Pilot Study

BACKGROUND

Drug-induced QT interval prolongation, a risk factor for life-threatening ventricular arrhythmias, is a potential side effect of many marketed and withdrawn medications. The contribution of common genetic variants previously associated with baseline QT interval to drug-induced QT prolongation and arrhythmias is not known.

METHODS

We tested the hypothesis that a weighted combination of common genetic variants contributing to QT interval at baseline, identified through genome-wide association studies, can predict individual response to multiple QT-prolonging drugs. Genetic analysis of 22 subjects was performed in a secondary analysis of a randomized, double-blind, placebo-controlled, crossover trial of 3 QT-prolonging drugs with 15 time-matched QT and plasma drug concentration measurements. Subjects received single doses of dofetilide, quinidine, ranolazine, and placebo. The outcome was the correlation between a genetic QT score comprising 61 common genetic variants and the slope of an individual subject's drug-induced increase in heart rate-corrected QT (QTc) versus drug concentration.

RESULTS

The genetic QT score was correlated with drug-induced QTc prolongation. Among white subjects, genetic QT score explained 30% of the variability in response to dofetilide (r=0.55; 95% confidence interval, 0.09-0.81; P=0.02), 23% in response to quinidine (r=0.48; 95% confidence interval, -0.03 to 0.79; P=0.06), and 27% in response to ranolazine (r=0.52; 95% confidence interval, 0.05-0.80; P=0.03). Furthermore, the genetic QT score was a significant predictor of drug-induced torsade de pointes in an independent sample of 216 cases compared with 771 controls (r²=12%, P=1×10^-7).

CONCLUSIONS

We demonstrate that a genetic QT score comprising 61 common genetic variants explains a significant proportion of the variability in drug-induced QT prolongation and is a significant predictor of drug-induced torsade de pointes. These findings highlight an opportunity for recent genetic discoveries to improve individualized risk-benefit assessment for pharmacological therapies. Replication of these findings in larger samples is needed to more precisely estimate variance explained and to establish the individual variants that drive these effects.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01873950.

Automated Algorithm for J-Tpeak and Tpeak-Tend Assessment of Drug-Induced Proarrhythmia Risk

BACKGROUND

Prolongation of the heart rate corrected QT (QTc) interval is a sensitive marker of torsade de pointes risk; however it is not specific as QTc prolonging drugs that block inward currents are often not associated with torsade. Recent work demonstrated that separate analysis of the heart rate corrected J-Tpeakc (J-Tpeakc) and Tpeak-Tend intervals can identify QTc prolonging drugs with inward current block and is being proposed as a part of a new cardiac safety paradigm for new drugs (the "CiPA" initiative).

METHODS

In this work, we describe an automated measurement methodology for assessment of the J-Tpeakc and Tpeak-Tend intervals using the vector magnitude lead. The automated measurement methodology was developed using data from one clinical trial and was evaluated using independent data from a second clinical trial.

RESULTS

Comparison between the automated and the prior semi-automated measurements shows that the automated algorithm reproduces the semi-automated measurements with a mean difference of single-deltas <1 ms and no difference in intra-time point variability (p for all > 0.39). In addition, the time-profile of the baseline and placebo-adjusted changes are within 1 ms for 63% of the time-points (86% within 2 ms). Importantly, the automated results lead to the same conclusions about the electrophysiological mechanisms of the studied drugs.

CONCLUSIONS

We have developed an automated algorithm for assessment of J-Tpeakc and Tpeak-Tend intervals that can be applied in clinical drug trials. Under the CiPA initiative this ECG assessment would determine if there are unexpected ion channel effects in humans compared to preclinical studies. The algorithm is being released as open-source software.

TRIAL REGISTRATION

NCT02308748 and NCT01873950.

Electrocardiographic Biomarkers for Detection of Drug-Induced Late Sodium Current Block

BACKGROUND

Drugs that prolong the heart rate corrected QT interval (QTc) on the electrocardiogram (ECG) by blocking the hERG potassium channel and also block inward currents (late sodium or L-type calcium) are not associated with torsade de pointes (e.g. ranolazine and verapamil). Thus, identifying ECG signs of late sodium current block could aid in the determination of proarrhythmic risk for new drugs. A new cardiac safety paradigm for drug development (the "CiPA" initiative) will involve the preclinical assessment of multiple human cardiac ion channels and ECG biomarkers are needed to determine if there are unexpected ion channel effects in humans.

METHODS AND RESULTS

In this study we assess the ability of eight ECG morphology biomarkers to detect late sodium current block in the presence of QTc prolongation by analyzing a clinical trial where a selective hERG potassium channel blocker (dofetilide) was administered alone and then in combination with two late sodium current blockers (lidocaine and mexiletine). We demonstrate that late sodium current block has the greatest effect on the heart-rate corrected J-Tpeak interval (J-Tpeakc), followed by QTc and then T-wave flatness. Furthermore, J-Tpeakc is the only biomarker that improves detection of the presence of late sodium current block compared to using QTc alone (AUC: 0.83 vs. 0.72 respectively, p<0.001).

CONCLUSIONS

Analysis of the J-Tpeakc interval can differentiate drug-induced multichannel block involving the late sodium current from selective hERG potassium channel block. Future methodologies assessing drug effects on cardiac ion channel currents on the ECG should use J-Tpeakc to detect the presence of late sodium current block.

TRIAL REGISTRATION

NCT02308748 and NCT01873950.