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

Abstract

IntroductionDrugs 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.MethodsConcentration–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.ResultsThe 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.DiscussionThe 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.

Investigation of miscellaneous hERG inhibition in large diverse compound collection using automated patch-clamp assay

“…This permits applications of automated electrophysiology in primary screening. In addition to experimental approaches, to predict the hERG liability of lead candidates early in drug discovery, numerical in silico methods have been developed [12][13][14][15][16][17][18] . Since experimental data from a large collection of structurally diverse compounds were yet available, models was usually based on the existing data of limited number of hERG inhibitors generated using different methods.…”

The opportunities and challenges for biophysical modelling of beneficial and adverse drug actions on the heart

“…Voltage clamp experiments, performed as part of multiple ion channel screening, using cell lines, generate IC50 data that can be readily incorporated into computational models of varying levels of complexity. These models provide a unique method to link drug interactions at the molecular target level to predict altered function at increasingly integrated levels of function, from ionic currents to action potentials 31,32 , conduction (reentry) [33][34][35] and global heart rhythm itself (the ECG) [36][37][38][39] . This provides a quantitative link between pre-clinical protein kinetics assays and organ clinical indices.…”

CiPA: Ongoing testing, future qualification procedures, and pending issues

“…Each metric has advantages and disadvantages and only some of them can be obtained from patch clamp studies. For example, APD 90 can predict ECG QT interval prolongation, a potential precursor of proarrhythmia, and can be easily measured in experimental preparations for in silico model simulations (Beattie et al, 2013) but it fails to provide reliable information on proarrhythmic risk.…”