Strategies to reduce the risk of drug-induced QT interval prolongation: a pharmaceutical company perspective

Thorough QTc Study of a Single Supratherapeutic Dose of Relebactam in Healthy Participants

The effects of supratherapeutic doses of intravenous (IV) relebactam on duration of ventricular depolarization and subsequent repolarization were assessed in a thorough QT/corrected QT study. This was a single-dose, double-blind (relebactam only), randomized, placebo- and positive-controlled, 3-period, balanced crossover study in healthy participants. Participants received in randomized order, and separated by a washout (≥4 days), a single dose of IV relebactam 1150 mg, oral moxifloxacin 400 mg (open-label positive control), and IV placebo. Least squares mean and 2-sided 90% confidence interval for change from baseline in population-derived corrected QT intervals for relebactam, moxifloxacin, and placebo were estimated for 24 hours. The upper limit of the 90% confidence interval of all least squares mean population-derived corrected QT treatment differences from placebo was not >10 milliseconds at any time point for 24 hours. Corrected QT assay sensitivity was confirmed with moxifloxacin treatment. Analysis of electrocardiogram parameters resulted in no additional cardiac safety concerns. Overall, a supratherapeutic dose of relebactam yielded no cardiac safety events; the 1150-mg supratherapeutic dose (4.6-fold above the 250-mg therapeutic dose) was not associated with QT prolongation or other abnormal cardiodynamic parameters. This study lends additional support to relebactam's use as a β-lactamase inhibitor in antimicrobial therapy.

Characterization and Validation of a Human 3D Cardiac Microtissue for the Assessment of Changes in Cardiac Pathology

Pharmaceutical agents despite their efficacy to treat disease can cause additional unwanted cardiovascular side effects. Cardiotoxicity is characterized by changes in either the function and/or structure of the myocardium. Over recent years, functional cardiotoxicity has received much attention, however morphological damage to the myocardium and/or loss of viability still requires improved detection and mechanistic insights. A human 3D cardiac microtissue containing human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs), cardiac endothelial cells and cardiac fibroblasts was used to assess their suitability to detect drug induced changes in cardiac structure. Histology and clinical pathology confirmed these cardiac microtissues were morphologically intact, lacked a necrotic/apoptotic core and contained all relevant cell constituents. High-throughput methods to assess mitochondrial membrane potential, endoplasmic reticulum integrity and cellular viability were developed and 15 FDA approved structural cardiotoxins and 14 FDA approved non-structural cardiotoxins were evaluated. We report that cardiac microtissues provide a high-throughput experimental model that is both able to detect changes in cardiac structure at clinically relevant concentrations and provide insights into the phenotypic mechanisms of this liability.

Relationships of Changes in Pharmacokinetic Parameters of Substrate Drugs in Drug-Drug Interactions on Metabolizing Enzymes and Transporters

A general objective of drug-drug interaction (DDI) studies is to determine whether potential interactions of new molecular entities with concomitantly administered other drugs exist and, if DDIs occur, whether dosage adjustments are required. A typical end point for DDI evaluations is the ratio of area under the plasma concentration-time curve (AUC) of substrate drugs (AUCR), whereas the ratios of maximal plasma concentration (C_max ) and terminal half-life (t_1/2 ) are also important to understand DDI mechanisms (C_max R and t_1/2 R, respectively). Because changes in substrate AUC by precipitant drugs ultimately result from alterations of C_max and t_1/2 , AUCR can be considered a hybrid parameter of C_max R and t_1/2 R, for example, AUCR ≈ C_max R  ×  t_1/2 R. The primary objective of this study was to investigate the relationships between AUCR, C_max R, and t_1/2 R in physiologically based pharmacokinetic model-predicted and clinically observed DDI results. First, the model-predicted results showed the excellent proportional relationship between AUCR and (C_max R × t_1/2 R) in DDI results of virtual substrates having a wide range of oral bioavailability with coadministration of ketoconazole, ritonavir, and rifampin. Second, the reasonable proportional relationships were also observed in the clinically observed DDI results of midazolam and statins (atorvastatin, cerivastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin, and simvastatin) with various inhibitors and inducers. Finally, these results suggest that utilization of the proportional relationship between AUCR and (C_max R × t_1/2 R) can provide an additional framework to further interpret DDI results reasonably and clearly. Furthermore, the proportional relationship can be purposely used to assess study design and pharmacokinetic analyses in DDI studies.

Alleviating CYP and hERG liabilities by structure optimization of dihydrofuran-fused tricyclic benzo[d]imidazole series - Potent, selective and orally efficacious microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors: Part-2

In an effort to identify CYP and hERG clean mPGES-1 inhibitors from the dihydrofuran-fused tricyclic benzo[d]imidazole series lead 7, an extensive structure-activity relationship (SAR) studies were performed. Optimization of A, D and E-rings in 7 afforded many potent compounds with human whole blood potency in the range of 160-950 nM. Selected inhibitors 21d, 21j, 21m, 21n, 21p and 22b provided selectivity against COX-enzymes and mPGES-1 isoforms (mPGES-2 and cPGES) along with sufficient selectivity against prostanoid synthases. Most of the tested analogs demonstrated required metabolic stability in liver microsomes, low hERG and CYP liability. Oral pharmacokinetics and bioavailability of lead compounds 21j, 21m and 21p are discussed in multiple species like rat, guinea pig, dog, and cynomolgus monkey. Besides, these compounds revealed low to moderate activity against human pregnane X receptor (hPXR). The selected lead 21j further demonstrated in vivo efficacy in acute hyperalgesia (ED₅₀: 39.6 mg/kg) and MIA-induced osteoarthritic pain models (ED₅₀: 106 mg/kg).

Discovery of furan and dihydrofuran-fused tricyclic benzo[d]imidazole derivatives as potent and orally efficacious microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors: Part-1

This letter describes the synthesis and biological evaluation of furan and dihydrofuran-fused tricyclic benzo[d]imidazole derivatives as novel mPGES-1 inhibitors, capable of inhibiting an increased PGE₂ production in the disease state. Structure-activity optimization afforded many potent mPGES-1 inhibitors having <50 nM potencies in the A549 cellular assay and adequate metabolic stability in liver microsomes. Lead compounds 8l and 8m demonstrated reasonable in vitro pharmacology and pharmacokinetic properties over other compounds. In particular, 8m revealed satisfactory oral pharmacokinetics and bioavailability in multiple species like rat, guinea pig, dog and cynomolgus monkey. In addition, the representative compound 8m showed in vivo efficacy by inhibiting LPS-induced thermal hyperalgesia with an ED₅₀ of 14.3 mg/kg in guinea pig.

Inter-individual variability and modeling of electrical activity: a possible new approach to explore cardiac safety?

Safety pharmacology aims to predict rare side effects of new drugs. We explored whether rare pro-arrhythmic effects could be linked to the variability of the effects of these drugs on ion currents and whether taking into consideration this variability in computational models could help to better detect and predict cardiac side effects. For this purpose, we evaluated how intra- and inter-individual variability influences the effect of hERG inhibition on both the action potential duration and the occurrence of arrhythmias. Using two computer simulation models of human action potentials (endocardial and Purkinje cells), we analyzed the contribution of two biological parameters on the pro-arrhythmic effects of several hERG channel blockers: (i) spermine concentration, which varies with metabolic status, and (ii) L-type calcium conductance, which varies due to single nucleotide polymorphisms or mutations. By varying these parameters, we were able to induce arrhythmias in 1 out of 16 simulations although conventional modeling methods to detect pro-arrhythmic molecules failed. On the basis of our results, taking into consideration only 2 parameters subjected to intra- and inter-individual variability, we propose that in silico computer modeling may help to better define the risks of new drug candidates at early stages of pre-clinical development.

Intravenous Dosing as an Alternate Approach to Safely Achieve Supratherapeutic Exposure for Assessments of Cardiac Repolarization: A Randomized Clinical Trial with Mavoglurant (AFQ056)

PURPOSE

The conduct of thorough QTc (TQT) studies is often challenging with compounds that are characterized by limited tolerability in healthy individuals. This is applicable to several central nervous system drugs, including mavoglurant acting as a selective allosteric modulator of metabotropic glutamate receptor 5. This TQT study describes the use of a single intravenous dosing regimen as an alternate approach allowing for sufficiently high C_max values while controlling tolerability.

METHODS

This study was a randomized, placebo- and active-controlled, 4-period, crossover, TQT study composed of 2 sequential phases. In the pilot phase, the safety and tolerability profile of 10-minute infusions of 25, 37.5, and 50 mg of mavoglurant was assessed in 36 healthy individuals. In the TQT phase, individuals received in random sequence single intravenous doses of mavoglurant (25 and 50 mg) and placebo and an oral dose of moxifloxacin (400 mg).

FINDINGS

Mavoglurant was well tolerated up to a single intravenous dose of 50 mg, and supratherapeutic C_max values were achieved that were approximately 2-fold higher than at the multiple maximum tolerated dose and more than 3-fold higher relative to therapeutic plasma concentrations. The upper bound of the 2-sided 90% CI of Fridericia-corrected placebo- and baseline-adjusted QTc intervals (QTcFs) did not exceed 10 milliseconds at any postdose time point for both mavoglurant doses. The pharmacokinetic and pharmacodynamic analysis confirmed the lack of an association between mavoglurant plasma concentrations and ΔΔQTcF data over the entire range of plasma concentration data at 25 and 50 mg of mavoglurant. An outlier analysis revealed no individuals with newly identified QTcF intervals >480 milliseconds or any QTcF prolongations >60 milliseconds compared with baseline in any of the treatment groups. Hence, the lack of any clinically relevant QTc prolongation was found for therapeutic and supratherapeutic single intravenous doses of 25 and 50 mg of mavoglurant.

IMPLICATIONS

This TQT study describes the use of single intravenous dosing as an alternate approach to achieve supratherapeutic plasma concentrations as required per the International Council for Harmonisation E14 guideline with compounds characterized by exposure related tolerability limitations. The increased C_max/AUC ratio compared with conventional oral dosing may contribute to a reduced incidence of adverse events that appear more related to overall exposure.

Administration of Non-Torsadogenic human Ether-à-go-go-Related Gene Inhibitors Is Associated with Better Survival for High hERG-Expressing Glioblastoma Patients

PURPOSE

Glioblastoma is the most malignant primary brain tumor, with a median survival of less than 2 years. More effective therapeutic approaches are needed to improve clinical outcomes.

EXPERIMENTAL DESIGN

Glioblastoma patient-derived cells (GPDC) were isolated from patient glioblastomas and implanted in mice to form xenografts. IHC was performed for human Ether-à-go-go-Related Gene (hERG) expression and tumor proliferation. Sphere-forming assays with the hERG blocker E-4031 were performed on a high and low hERG-expressing lines. A glioblastoma tissue microarray (TMA; 115 patients) was used to correlate hERG expression with patient survival. Clinical data were analyzed to determine whether patient survival was affected by incidental administration of hERG inhibitory drugs and the correlative effect of patient glioblastoma hERG expression levels.

RESULTS

hERG expression was upregulated in glioblastoma xenografts with higher proliferative indices. High hERG-expressing GPDCs showed a reduction in sphere formation when treated with hERG inhibitors compared with low hERG-expressing GPDCs. Glioblastoma TMA analysis showed worse survival for glioblastoma patients with high hERG expression versus low expression-43.5 weeks versus 60.9 weeks, respectively (P = 0.022). Furthermore, patients who received at least one hERG blocker had a better survival rate compared with patients who did not (P = 0.0015). Subgroup analysis showed that glioblastoma patients with high hERG expression who received hERG blockers had improved survival (P = 0.0458). There was no difference in survival for low hERG-expressing glioblastoma patients who received hERG blockers (P = 0.4136).

CONCLUSIONS

Our findings suggest that hERG is a potential glioblastoma survival marker, and that already approved drugs with non-torsadogenic hERG inhibitory activity may potentially be repurposed as adjuvant glioblastoma therapy in high hERG-expressing glioblastoma patients. Clin Cancer Res; 23(1); 73-80. ©2016 AACRSee related commentary by Arcangeli and Becchetti, p. 3.

Model-based evaluation of drug-induced QTc prolongation for compounds in early development

AIMS

Significant differences between dogs and humans have been observed in the concentration-QTc effect relationship of compounds with known pro-arrhythmic properties. These findings suggest that interspecies differences must be considered when evaluating drug effects. The aim of this study was to evaluate the performance of a model-based approach to assess the risk of QTc prolongation for three investigational compounds (NCE01, NCE02 and NCE03).

METHODS

Pharmacokinetic and pharmacodynamic data from experiments in conscious dogs and healthy subjects were included in this analysis. Pharmacokinetic modelling and deconvolution methods were applied to derive drug concentrations at the time of each QT measurement. An integrated pharmacokinetic-pharmacodynamic (PKPD) model was then used to describe QT prolongation. A threshold of ≥10 ms was used to characterize the probability of QTc prolongation.

RESULTS

The PKPD relationships of all three compounds were successfully described in both species. A strong effect was observed after administration of NCE01 to dogs and humans, with a slope of 0.0061 and 0.0662 ms nm(-1), respectively, and maximal probability of QTc prolongation ≥10 ms at peak concentration. For NCE02 and NCE03, QTc-shortening and borderline QT effects were observed both in dogs and humans, as described by negative or very shallow slopes (NCE02, -0.00098 and -0.01 ms nm(-1); NCE03, 0.00064 and -0.0002 ms nm(-1)).

CONCLUSIONS

Whilst NEC01 shows clear pro-arrhythmic effects, the liability for QT/QTc prolongation for NCE02 and NCE03 can be deemed low at the expected therapeutic exposure. Moreover, our results show the advantages of an integrated PKPD approach as the basis for translating pro-arrhythmic effects from dogs to humans.

Lack of effect of perampanel on QT interval duration: Results from a thorough QT analysis and pooled partial seizure Phase III clinical trials

INTRODUCTION

Perampanel is a selective, noncompetitive AMPA receptor antagonist approved as adjunctive treatment for partial seizures. To assess potential for delayed cardiac repolarization, a Phase I thorough QT study was performed, supplemented by plasma concentration-QT data modeled from 3 pooled Phase III studies.

METHODS

The Phase I thorough QT study (double-blind, combined fixed-sequence, parallel-group) quantified the effect of perampanel (6 mg once daily for 7 days, followed by dose escalation to a single 8-mg dose, a single 10-mg dose, then 12 mg once daily for 7 days), moxifloxacin positive control (single 400-mg dose on Day 16), and placebo on QT interval duration in healthy subjects (N = 261). Electrocardiograms were recorded at baseline, Day 7 (post 6 mg dose), and Day 16 (post 12 mg dose). Statistical comparisons were between the highest approved perampanel dose (12 mg) versus placebo, a "mid-therapeutic" dose (6 mg) versus placebo, and moxifloxacin versus placebo. Acknowledging that the Phase I thorough QT study could not incorporate a true "supratherapeutic" dose due to length of titration and tolerability concerns in healthy subjects, Phase III studies of perampanel included expanded electrocardiogram safety evaluations specifically intended to support concentration-QT response modeling. The lack of effect of perampanel on the QT interval is shown from pooled analysis of 3 double-blind, placebo-controlled, 19-week, Phase III studies with perampanel doses ≤ 12 mg (N = 1038, total perampanel; and N=442, placebo) in patients with partial seizures. QT measures were corrected for heart rate using Fridericia's (QTcF; the primary endpoint) and Bazett's (QTcB) formulas.

RESULTS

In the Phase I thorough QT study, the positive control moxifloxacin caused peak time-matched, baseline-adjusted, placebo-corrected (ΔΔ) QTcF of 12.15 ms at 4h postdose, confirming a drug effect on QTc interval and study assessment sensitivity. Mean baseline-adjusted (Δ) QTcF versus nominal time curves were comparable between perampanel 12 mg and placebo, with most ΔQTcF values being slightly negative. Healthy subjects receiving perampanel 6 and 12 mg doses for 7 days showed no evidence of effects on cardiac repolarization. Peak ΔΔQTcF was 2.34 ms at 1.5h postdose for perampanel 6 mg and 3.92 ms at 0.5h postdose for perampanel 12 mg. At every time point, the upper 95% confidence limit of ΔΔQTcF for perampanel 6 and 12 mg was <10 ms. Phase III studies revealed no clinically significant difference between patients with partial seizures treated with perampanel or placebo in QTcF and QTcB values >450 ms, with no dose-dependent increases or large incremental changes from baseline of >60 ms. Regression analysis of individual plasma perampanel concentrations versus corresponding QTc interval values in Phase I thorough QT and Phase III studies demonstrated no relationship between perampanel concentrations and QT interval duration.

CONCLUSION

Treatment with perampanel 6 mg and 12 mg for 7 days did not delay cardiac repolarization in healthy volunteers. In a population analysis of 1480 patients with partial seizures treated with perampanel doses ≤ 12 mg or placebo, no clinically significant trends in QT interval data were noted. Based on the thorough QT study and evaluations from pooled Phase III studies, there is no evidence of prolonged QT interval duration with perampanel treatment.

Mycobacterium tuberculosis gyrase inhibitors as a new class of antitubercular drugs

One way to speed up the TB drug discovery process is to search for antitubercular activity among compound series that already possess some of the key properties needed in anti-infective drug discovery, such as whole-cell activity and oral absorption. Here, we present MGIs, a new series of Mycobacterium tuberculosis gyrase inhibitors, which stem from the long-term efforts GSK has dedicated to the discovery and development of novel bacterial topoisomerase inhibitors (NBTIs). The compounds identified were found to be devoid of fluoroquinolone (FQ) cross-resistance and seem to operate through a mechanism similar to that of the previously described NBTI GSK antibacterial drug candidate. The remarkable in vitro and in vivo antitubercular profiles showed by the hits has prompted us to further advance the MGI project to full lead optimization.

Assessment of cardiomyocyte contraction in human-induced pluripotent stem cell-derived cardiomyocytes

Functional changes to cardiomyocytes are a common cause of attrition in preclinical and clinical drug development. Current approaches to assess cardiomyocyte contractility in vitro are limited to low-throughput methods not amenable to early drug discovery. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) were used to assess their suitability to detect drug-induced changes in cardiomyocyte contraction. Application of field stimulation and measurement of cardiac contraction (IonOptix edge detection) and Ca(2+) transients confirmed hiPS-CMs to be a suitable model to investigate drug-induced changes in cardiomyocyte contractility. Using a live cell, fast kinetic fluorescent assay with a Ca(2+) sensitive dye to test 31 inotropic and 20 non-inotropic compounds in vivo, we report that hiPS-CMs provide a high-throughput experimental model to detect changes in cardiomyocyte contraction that is applicable to early drug discovery with a sensitivity and specificity of 87% and 70%, respectively. Moreover, our data provide evidence of the detection of this liability at therapeutically relevant concentrations with throughput amenable to influencing chemical design in drug discovery. Measurement of multiple parameters of the Ca(2+) transient in addition to the number of Ca(2+) transients offered no insight into the mechanism of cardiomyocyte contraction.

Not-in-trial simulation I: Bridging cardiovascular risk from clinical trials to real-life conditions

AIMS

The assessment of heart rate-corrected QT (QTc) interval prolongation relies on the evidence of drug effects in healthy subjects. This study demonstrates the relevance of pharmacokinetic-pharmacodynamic (PKPD) relationships to characterize drug-induced QTc interval prolongation and explore the discrepancies between clinical trials and real-life conditions.

METHODS

d,l-Sotalol data from healthy subjects and from the Rotterdam Study cohort were used to assess treatment response in a phase I setting and in a real-life conditions, respectively. Using modelling and simulation, drug effects at therapeutic doses were predicted in both populations.

RESULTS

Inclusion criteria were shown to restrict the representativeness of the trial population in comparison to real-life conditions. A significant part of the typical patient population was excluded from trials due to weight and baseline QTc interval criteria. Relative risk was significantly different between sotalol users with and without heart failure, hypertension, diabetes and myocardial infarction (P < 0.01). Although drug effects do cause an increase in the relative risk of QTc interval prolongation, the presence of diabetes represented an increase from 4.0 [95% confidence interval (CI) 2.7-5.8] to 6.5 (95% CI 1.6-27.1), whilst for myocardial infarction it increased from 3.4 (95% CI 2.3-5.13) to 15.5 (95% CI 4.9-49.3).

CONCLUSIONS

Our findings show that drug effects on QTc interval do not explain the observed QTc values in the population. The prevalence of high QTc values in the real-life population can be assigned to co-morbidities and concomitant medications. These findings substantiate the need to account for these factors when evaluating the cardiovascular risk of medicinal products.

Chemotypes sensitivity and predictivity of in vivo outcomes for cytotoxic assays in THLE and HepG2 cell lines

In the present study, we demonstrate the utility of in vitro ATP depletion assays in both THLE and HepG2 cells for predicting the toxicological outcome in Exploratory Toxicology Studies across 446 Pfizer proprietary compounds. Our results suggest a higher likelihood of selecting suitable compounds for in vivo safety studies by using cytotoxicity assays in multiple cell-lines over a single cell line. In addition, we demonstrate that different cell-lines have different sensitivities to compounds depending on their ionization state, that is, acid, base or neutral. HepG2 cells are more sensitive for basic compounds, whereas THLE cells have a relatively higher sensitivity for the acidic and neutral compounds. These in vitro cytotoxicity assays when combined with physicochemical properties (cLogP >3 and topological polar surface area (TPSA) <75Å(2)), are the most effective means to prioritize compounds having a lower probability of causing adverse events in vivo.

Video image-based analysis of single human induced pluripotent stem cell derived cardiomyocyte beating dynamics using digital image correlation

Background

The functionality of a cardiomyocyte is primarily measured by analyzing the electrophysiological properties of the cell. The analysis of the beating behavior of single cardiomyocytes, especially ones derived from stem cells, is challenging but well warranted. In this study, a video-based method that is non-invasive and label-free is introduced and applied for the study of single human cardiomyocytes derived from induced pluripotent stem cells.

Methods

The beating of dissociated stem cell-derived cardiomyocytes was visualized with a microscope and the motion was video-recorded. Minimum quadratic difference, a digital image correlation method, was used for beating analysis with geometrical sectorial cell division and radial/tangential directions. The time series of the temporal displacement vector fields of a single cardiomyocyte was computed from video data. The vector field data was processed to obtain cell-specific, contraction-relaxation dynamics signals. Simulated cardiomyocyte beating was used as a reference and the current clamp of real cardiomyocytes was used to analyze the electrical functionality of the beating cardiomyocytes.

Results

Our results demonstrate that our sectorized image correlation method is capable of extracting single cell beating characteristics from the video data of induced pluripotent stem cell-derived cardiomyocytes that have no clear movement axis, and that the method can accurately identify beating phases and time parameters.

Conclusion

Our video analysis of the beating motion of single human cardiomyocytes provides a robust, non-invasive and label-free method to analyze the mechanobiological functionality of cardiomyocytes derived from induced pluripotent stem cells. Thus, our method has potential for the high-throughput analysis of cardiomyocyte functions.

Understanding, recognizing, and managing toxicities of targeted anticancer therapies

Answer questions and earn CME/CNE Advances in genomics and molecular biology have identified aberrant proteins in cancer cells that are attractive targets for cancer therapy. Because these proteins are overexpressed or dysregulated in cancer cells compared with normal cells, it was assumed that their inhibitors will be narrowly targeted and relatively nontoxic. However, this hope has not been achieved. Current targeted agents exhibit the same frequency and severity of toxicities as traditional cytotoxic agents, with the main difference being the nature of the toxic effects. Thus, the classical chemotherapy toxicities of alopecia, myelosuppression, mucositis, nausea, and vomiting have been generally replaced by vascular, dermatologic, endocrine, coagulation, immunologic, ocular, and pulmonary toxicities. These toxicities need to be recognized, prevented, and optimally managed.

Evaluation of an in silico cardiac safety assay: using ion channel screening data to predict QT interval changes in the rabbit ventricular wedge

INTRODUCTION

Drugs that prolong the QT interval on the electrocardiogram present a major safety concern for pharmaceutical companies and regulatory agencies. Despite a range of assays performed to assess compound effects on the QT interval, QT prolongation remains a major cause of attrition during compound development. In silico assays could alleviate such problems. In this study we evaluated an in silico method of predicting the results of a rabbit left-ventricular wedge assay.

METHODS

Concentration-effect data were acquired from either: the high-throughput IonWorks/FLIPR; the medium-throughput PatchXpress ion channel assays; or QSAR, a statistical IC50 value prediction model, for hERG, fast sodium, L-type calcium and KCNQ1/minK channels. Drug block of channels was incorporated into a mathematical differential equation model of rabbit ventricular myocyte electrophysiology through modification of the maximal conductance of each channel by a factor dependent on the IC50 value, Hill coefficient and concentration of each compound tested. Simulations were performed and agreement with experimental results, based upon input data from the different assays, was evaluated.

RESULTS

The assay was found to be 78% accurate, 72% sensitive and 81% specific when predicting QT prolongation (>10%) using PatchXpress assay data (77 compounds). Similar levels of predictivity were demonstrated using IonWorks/FLIPR data (121 compounds) with 78% accuracy, 73% sensitivity and 80% specificity. QT shortening (<-10%) was predicted with 77% accuracy, 33% sensitivity and 90% specificity using PatchXpress data and 71% accuracy, 42% sensitivity and 81% specificity using IonWorks/FLIPR data. Strong quantitative agreement between simulation and experimental results was also evident.

DISCUSSION

The in silico action potential assay demonstrates good predictive ability, and is suitable for very high-throughput use in early drug development. Adoption of such an assay into cardiovascular safety assessment, integrating ion channel data from routine screens to infer results of animal-based tests, could provide a cost- and time-effective cardiac safety screen.

A review of human pluripotent stem cell-derived cardiomyocytes for high-throughput drug discovery, cardiotoxicity screening, and publication standards

Drug attrition rates have increased in past years, resulting in growing costs for the pharmaceutical industry and consumers. The reasons for this include the lack of in vitro models that correlate with clinical results and poor preclinical toxicity screening assays. The in vitro production of human cardiac progenitor cells and cardiomyocytes from human pluripotent stem cells provides an amenable source of cells for applications in drug discovery, disease modeling, regenerative medicine, and cardiotoxicity screening. In addition, the ability to derive human-induced pluripotent stem cells from somatic tissues, combined with current high-throughput screening and pharmacogenomics, may help realize the use of these cells to fulfill the potential of personalized medicine. In this review, we discuss the use of pluripotent stem cell-derived cardiomyocytes for drug discovery and cardiotoxicity screening, as well as current hurdles that must be overcome for wider clinical applications of this promising approach.

Application of cardiac electrophysiology simulations to pro-arrhythmic safety testing

Concerns over cardiac side effects are the largest single cause of compound attrition during pharmaceutical drug development. For a number of years, biophysically detailed mathematical models of cardiac electrical activity have been used to explore how a compound, interfering with specific ion-channel function, may explain effects at the cell-, tissue- and organ-scales. With the advent of high-throughput screening of multiple ion channels in the wet-lab, and improvements in computational modelling of their effects on cardiac cell activity, more reliable prediction of pro-arrhythmic risk is becoming possible at the earliest stages of drug development. In this paper, we review the current use of biophysically detailed mathematical models of cardiac myocyte electrical activity in drug safety testing, and suggest future directions to employ the full potential of this approach.

Model for long QT syndrome type 2 using human iPS cells demonstrates arrhythmogenic characteristics in cell culture

Long QT syndrome (LQTS) is caused by functional alterations in cardiac ion channels and is associated with prolonged cardiac repolarization time and increased risk of ventricular arrhythmias. Inherited type 2 LQTS (LQT2) and drug-induced LQTS both result from altered function of the hERG channel. We investigated whether the electrophysiological characteristics of LQT2 can be recapitulated in vitro using induced pluripotent stem cell (iPSC) technology. Spontaneously beating cardiomyocytes were differentiated from two iPSC lines derived from an individual with LQT2 carrying the R176W mutation in the KCNH2 (HERG) gene. The individual had been asymptomatic except for occasional palpitations, but his sister and father had died suddenly at an early age. Electrophysiological properties of LQT2-specific cardiomyocytes were studied using microelectrode array and patch-clamp, and were compared with those of cardiomyocytes derived from control cells. The action potential duration of LQT2-specific cardiomyocytes was significantly longer than that of control cardiomyocytes, and the rapid delayed potassium channel (I_Kr) density of the LQT2 cardiomyocytes was significantly reduced. Additionally, LQT2-derived cardiac cells were more sensitive than controls to potentially arrhythmogenic drugs, including sotalol, and demonstrated arrhythmogenic electrical activity. Consistent with clinical observations, the LQT2 cardiomyocytes demonstrated a more pronounced inverse correlation between the beating rate and repolarization time compared with control cells. Prolonged action potential is present in LQT2-specific cardiomyocytes derived from a mutation carrier and arrhythmias can be triggered by a commonly used drug. Thus, the iPSC-derived, disease-specific cardiomyocytes could serve as an important platform to study pathophysiological mechanisms and drug sensitivity in LQT2.

Assessing the probability of drug-induced QTc-interval prolongation during clinical drug development

Early in the course of clinical development of new non-antiarrhythmic drugs, it is important to assess the propensity of these drugs to prolong the QT/QTc-interval. The current regulatory guidelines suggest using the largest time-matched mean difference between drug and placebo (baseline-adjusted) groups over the sampling interval, thereby neglecting any potential exposure-effect relationship and nonlinearity in the underlying physiological fluctuation in QT values. Thus far, most of the attempted models for characterizing drug-induced QTc-interval prolongation have disregarded the possibility of model parameterization in terms of drug-specific and system-specific properties. Using a database consisting of three compounds with known dromotropic activity, we built a bayesian hierarchical pharmacodynamic (PD) model to describe QT interval, encompassing an individual correction factor for heart rate, an oscillatory component describing the circadian variation, and a truncated maximum-effect model to account for drug effect. The explicit description of the exposure-effect relationship, incorporating various sources of variability, offers advantages over the standard regulatory approach.

On the relationship between block of the cardiac Na⁺ channel and drug-induced prolongation of the QRS complex

BACKGROUND AND PURPOSE

Inhibition of the human cardiac Na(+) channel (hNa(v) 1.5) can prolong the QRS complex and has been associated with increased mortality in patients with underlying cardiovascular disease. The safety implications of blocking hNa(v) 1.5 channels suggest the need to test for this activity early in drug discovery in order to design out any potential liability. However, interpretation of hNa(v) 1.5 blocking potency requires knowledge of how hNa(v) 1.5 block translates into prolongation of the QRS complex.

EXPERIMENTAL APPROACH

We tested Class I anti-arrhythmics, other known QRS prolonging drugs and drugs not reported to prolong the QRS complex. Their block of hNa(v) 1.5 channels (as IC(50) values) was measured in an automated electrophysiology-based assay. These IC(50) values were compared with published reports of the corresponding unbound (free) plasma concentrations attained during clinical use (fC(max)) to provide an IC(50) : fC(max) ratio. KEY RESULTS For 42 Class I anti-arrhythmics and other QRS prolonging drugs, 67% had IC(50) : fC(max) ratios <30. For 55 non-QRS prolonging drugs tested, 72% had ratios >100. Finally, we determined the relationship between the IC(50) value and the free drug concentration associated with prolongation of the QRS complex in humans. For 37 drugs, QRS complex prolongation was observed at free plasma concentrations that were about 15-fold lower than the corresponding IC(50) at hNa(v) 1.5 channels.

CONCLUSIONS AND IMPLICATIONS

A margin of 30- to 100-fold between hNa(v) 1.5 IC(50) and fC(max) appears to confer an acceptable degree of safety from QRS prolongation. QRS prolongation occurs on average at free plasma levels 15-fold below the IC(50) at hNa(v) 1.5 channels.

LINKED ARTICLE

This article is commented on by Gintant et al., pp. 254-259 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2011.01433.x.

Drug-induced long QT syndrome

The drug-induced long QT syndrome is a distinct clinical entity that has evolved from an electrophysiologic curiosity to a centerpiece in drug regulation and development. This evolution reflects an increasing recognition that a rare adverse drug effect can profoundly upset the balance between benefit and risk that goes into the prescription of a drug by an individual practitioner as well as the approval of a new drug entity by a regulatory agency. This review will outline how defining the central mechanism, block of the cardiac delayed-rectifier potassium current I(Kr), has contributed to defining risk in patients and in populations. Models for studying risk, and understanding the way in which clinical risk factors modulate cardiac repolarization at the molecular level are discussed. Finally, the role of genetic variants in modulating risk is described.

Safety profile of the fluoroquinolones: focus on levofloxacin

The fluoroquinolone class of antibacterial agents are among the most frequently prescribed drugs, with utility in a broad range of bacterial infections. Although very useful agents, the fluoroquinolones as a class are associated with a number of adverse events, some with considerable clinical significance. In the past 15-20 years, tolerability concerns have led to restrictions on the use of the fluoroquinolones and, in some instances, the withdrawal of agents from the market. This review focuses on the safety and tolerability of levofloxacin, a third-generation fluoroquinolone, relative to other fluoroquinolones. A literature search was performed of the MEDLINE database encompassing the dates 1980-2009, using as keywords the drug names levofloxacin and concurrently marketed fluoroquinolones combined with the words 'safety', 'adverse effect' or 'adverse drug reaction', or the name of the specific adverse effect. Adverse events commonly associated with the fluoroquinolones include gastrointestinal and CNS toxicity (most frequently headache and dizziness), as well as other adverse events including ECG abnormalities (for example QT interval prolongation), disrupted glucose metabolism, phototoxicity, tendon and joint disorders, hypersensitivity and skin disorders, and hepatic toxicity. Package inserts for the fluoroquinolones in Europe and the US contain warnings regarding these risks. US package inserts also carry 'black-box' warnings regarding the risk of tendon rupture and joint disorders with these agents; however, there is a substantial body of evidence to indicate that there are marked differences in the tolerability profiles of the individual agents within the fluoroquinolone class. These differences may be explained, at least in part, by structural differences: all fluoroquinolones share a basic quinolone core, with differences in specific side chains underlying the adverse event relationships. Furthermore, many of the fluoroquinolone-associated adverse effects and toxicities occur more frequently in patients with pre-existing risk factors, or in certain subpopulations. Notably, package inserts for the fluoroquinolones carry warnings regarding use in the elderly, paediatric patients and patients with pre-existing, or factors predisposing to, seizure disorders. Because of this, many adverse reactions with these agents could be prevented by improving patient screening and education. The recent withdrawal of gatifloxacin due to dysglycaemia makes it timely to review the safety and tolerability of the individual agents in this class. Overall, it appears that levofloxacin is relatively well tolerated, with low rates of clinically important adverse events such as CNS toxicity, cardiovascular toxicity and dysglycaemia.

Human embryonic stem cell-derived cardiomyocytes: demonstration of a portion of cardiac cells with fairly mature electrical phenotype

Cardiomyocytes (CMs) derived from human embryonic stem cells (hESC) provide a promising tool for the pharmaceutical industry. In this study the electrical properties and maturation of hESC-CM derived using two differentiation methods were compared and the suitability of hESC-CMs as a cell model for the assessment of drug-induced repolarization delay was evaluated. CMs were differentiated either in END-2 co-culture or by spontaneous differentiation. Action potentials (APs) were recorded from cells in spontaneously beating areas using the whole-cell patch-clamp technique. The hESC-CMs exhibited predominantly a ventricular-like phenotype with heterogeneous properties. Heterogeneity was indicative of the spectrum of hESC-CM maturation from embryonic-like with AP upstroke velocities <30 V/s and maximum diastolic potential (MDP) of close to -60 mV to more mature with values >150 V/s and -80 mV, respectively. The mean MDP was -70 mV and a significant difference was observed between the two differentiation methods (-66 versus -75 mV, P < 0.001). The age of the CMs did not correlate with phenotype maturation. The addition of the hERG blocker E-4031 and the sodium channel modulator veratridine significantly prolonged the AP duration. Furthermore, proarrhythmic indices were induced. In conclusion, the main observation was the heterogeneity in electrical properties of the hESC-CMs and this was observed with both differentiation methods. One-third of the hESC-CMs exhibited fairly mature electrophysiological properties, suggesting that mature CMs could be obtained from hESCs. However, improved differentiation methods are needed to produce homogeneous mature human CMs for pharmaceutical and toxicological applications.

An introduction to QT interval prolongation and non-clinical approaches to assessing and reducing risk

Owing to its association with Torsades de Pointes, drug-induced QT interval prolongation has been and remains a significant hurdle to the development of safe, effective medicines. Genetic and pharmacological evidence highlighting the pivotal role the human ether-a-go-go-related gene (hERG) channel was a critical step in understanding how to start addressing this issue. It led to the development of hERG assays with the rapid throughput needed for the short timescales required in early drug discovery. The resulting volume of hERG data has fostered in silico models to help chemists design compounds with reduced hERG potency. In early drug discovery, a pragmatic approach based on exceeding a given potency value has been required to decide when a compound is likely to carry a low QT risk, to support its progression to late-stage discovery. At this point, the in vivo efficacy and metabolism characteristics of the potential drug are generally defined, as well its safety profile, which includes usually a dog study to assess QT interval prolongation risk. The hERG and in vivo QT data, combined with the likely indication and the estimated free drug level for efficacy, are put together to assess the risk that the potential drug will prolong QT in man. Further data may be required to refine the risk assessment before making the major investment decisions for full development. The non-clinical data are essential to inform decisions about compound progression and to optimize the design of clinical QT studies.

Update on the evaluation of a new drug for effects on cardiac repolarization in humans: issues in early drug development

Following reports of death from cardiac arrhythmias with drugs like terfenadine and cisapride, the International Conference for Harmonization formulated a guidance (E14) document. This specifies that all new drugs must undergo a 'thorough QT/QTc' (TQT) study to detect drug-induced QT prolongation, a surrogate marker of ventricular tachycardia, especially torsades de pointes (TdPs). With better understanding of data from several completed TQT studies, regulatory requirements have undergone some changes since the E14 guidance was implemented in October 2005. This article reviews the implications of the E14 guidance and the changes in its interpretation including choice of baseline QT, demonstration of assay sensitivity, statistical analysis of the effect of new drug and positive control, and PK-PD modelling. Some issues like use of automated QT measurements remain unresolved. Pharmaceutical companies too are modifying Phase 1 studies to detect QTc liability early in order to save time and resources. After the E14 guidance, development of several drugs that prolong QTc by >5 ms is being abandoned by sponsors. However, all drugs that prolong the QT interval do not increase risk of TdP. Researchers in regulatory agencies, academia and industry are working to find better biomarkers of drug-induced TdP which could prevent many useful drugs from being prematurely abandoned. Drug-induced TdP is a rare occurrence. With fewer drugs that prolong QT interval reaching the licensing stage, knowing which of these drugs are torsadogenic is proving to be elusive. Thus, paradoxically, the effectiveness of the E14 guidance itself has made prospective validation of new biomarkers difficult.

Dog left ventricular midmyocardial myocytes for assessment of drug-induced delayed repolarization: short-term variability and proarrhythmic potential

BACKGROUND AND PURPOSE

Evaluation of the potential for delayed ventricular repolarization and proarrhythmia by new drugs is essential. We investigated if dog left ventricular midmyocardial myocytes (LVMMs) that can be used as a preclinical model to assess drug effects on action potential duration (APD) and whether in these cells, short-term variability (STV) or triangulation could predict proarrhythmic potential.

EXPERIMENTAL APPROACH

Beagle LVMMs and Purkinje fibres (PFs) were used to record APs. Effects of six reference drugs were assessed on APD at 50% (APD(50)) and 90% (APD(90)) of repolarization, STV(APD), triangulation (ratio APD(90)/APD(50)) and incidence of early afterdepolarizations (EADs) at 1 and 0.5 Hz.

KEY RESULTS

LVMMs provided stable recordings of AP, which were not affected by four sequential additions of dimethyl sulphoxide. Effects of dofetilide, d-sotalol, cisapride, pinacidil and diltiazem, but not of terfenadine, on APD in LVMMs were found to be comparable with those recorded in PFs. LVMMs, but not PFs, exhibited a proarrhythmic response to I(Kr) blockers. Incidence of EADs was not related to differences in AP prolongation or triangulation, but corresponded to beat-to-beat variability of repolarization, here quantified as STV of APD.

CONCLUSIONS AND IMPLICATIONS

LVMMs provide a suitable preclinical model to assess the effects of new drugs on APD and also yield additional information about putative indicators of proarrhythmia that add value to an integrated QT/TdP risk assessment. Our findings support the concept that increased STV(APD) may predict drug-induced proarrhythmia.

A HESI consortium approach to assess the human predictive value of non-clinical repolarization assays

Drug-induced ventricular arrhythmia and Torsades de Pointes remain a serious public health issues in bringing safe new pharmaceuticals to the market place. Under the auspices of the International Life Science Institute (ILSI)-Health and Environmental Sciences Institute (HESI), a consortium involving representatives from pharmaceutical companies, regulatory agencies and opinion leaders from the scientific and medical research communities has been initiated. The objectives are (1) to assess the concordance between signals in non-clinical repolarization assays and clinical QT interval prolongation; (2) to investigate the mechanisms for any discrepancy identified between non-clinical and clinical results and to determine viable and successful alternative approaches to identify these compounds; and (3) to assess the proarrhythmic potential of such compounds. At present, the consortium is conducting a retrospective analysis of non-clinical and clinical data from both FDA and contributing companies' databases and supplementing with a literature review. The overall objectives of these initial efforts are to establish a quantitative integrated risk assessment for each compound; to define criteria for concordance and apply them to the database in order to identify non-concordant compounds.

International Life Sciences Institute (Health and Environmental Sciences Institute, HESI) initiative on moving towards better predictors of drug-induced torsades de pointes

Knowledge of the cardiac safety of emerging new drugs is an important aspect of assuring the expeditious advancement of the best candidates targeted at unmet medical needs while also assuring the safety of clinical trial subjects or patients. Present methodologies for assessing drug-induced torsades de pointes (TdP) are woefully inadequate in terms of their specificity to select pharmaceutical agents, which are human arrhythmia toxicants. Thus, the critical challenge in the pharmaceutical industry today is to identify experimental models, composite strategies, or biomarkers of cardiac risk that can distinguish a drug, which prolongs cardiac ventricular repolarization, but is not proarrhythmic, from one that prolongs the QT interval and leads to TdP. To that end, the HESI Proarrhythmia Models Project Committee recognized that there was little practical understanding of the relationship between drug effects on cardiac ventricular repolarization and the rare clinical event of TdP. It was on that basis that a workshop was convened in Virginia, USA at which four topics were introduced by invited subject matter experts in the following fields: Molecular and Cellular Biology Underlying TdP, Dynamics of Periodicity, Models of TdP Proarrhythmia, and Key Considerations for Demonstrating Utility of Pre-Clinical Models. Contained in this special issue of the British Journal of Pharmacology are reports from each of the presenters that set out the background and key areas of discussion in each of these topic areas. Based on this information, the scientific community is encouraged to consider the ideas advanced in this workshop and to contribute to these important areas of investigations over the next several years.

Early clinical development: evaluation of drug-induced torsades de pointes risk

Drug-induced arrhythmias or QT interval prolongation is one of the two most common reasons for drugs to be denied regulatory approval or to have warnings imposed on their clinical labelling. The assessment of torsades de pointes (TdP) risk during clinical development of a new pharmaceutical compound has been an issue of debate since the original description of drug-induced proarrhythmia. TdP risk assessment is complicated by the very low incidence (e.g., <1/100,000 patient years of exposure) of clinical events for non-antiarrhythmic agents and thus the improbable likelihood of observing even one event during clinical development. Thus surrogate methods of determining risk are necessary. A clinical approach to the issue of TdP risk assessment during drug development has been developed and implemented internationally. These efforts have markedly reduced the likelihood that drugs with unknown TdP risks will be commercialized, have resulted in fostering extensive productive pre-clinical and clinical research, and subsequent improved understanding of drug-induced proarrhythmia. Current research efforts are directed to increasing the efficiency of clinical QT assessment and the impact of pre-clinical assessment on clinical development. This article describes the clinical evaluation of TdP risk during drug development and how pre-clinical assessment can impact the early clinical development TdP risk assessment.