Variability in high-throughput ion-channel screening data and consequences for cardiac safety assessment

Ryan C Elkins,Mark R Davies,Stephen J Brough,David J Gavaghan,Yi Cui,Najah Abi-Gerges,Gary R Mirams

doi:10.1016/j.vascn.2013.04.007

Abstract

IntroductionUnwanted drug interactions with ionic currents in the heart can lead to an increased pro-arrhythmic risk to patients in the clinic. It is therefore a priority for safety pharmacology teams to detect block of cardiac ion channels, and new technologies have enabled the development of automated and high-throughput screening assays using cell lines. As a result of screening multiple ion-channels there is a need to integrate information, particularly for compounds affecting more than one current, and mathematical electrophysiology in-silico action potential models are beginning to be used for this. MethodsWe quantified the variability associated with concentration-effect curves fitted to recordings from high-throughput Molecular Devices IonWorks® Quattro™ screens when detecting block of IKr (hERG), INa (NaV1.5), ICaL (CaV1.2), IKs (KCNQ1/minK) and Ito (Kv4.3/KChIP2.2), and the Molecular Devices FLIPR® Tetra fluorescence screen for ICaL (CaV1.2), for control compounds used at AstraZeneca and GlaxoSmithKline. We examined how screening variability propagates through in-silico action potential models for whole cell electrical behaviour, and how confidence intervals on model predictions can be estimated with repeated simulations. ResultsThere are significant levels of variability associated with high-throughput ion channel electrophysiology screens. This variability is of a similar magnitude for different cardiac ion currents and different compounds. Uncertainty in the Hill coefficients of reported concentration-effect curves is particularly high. Depending on a compound's ion channel blocking profile, the uncertainty introduced into whole-cell predictions can become significant. DiscussionOur technique allows confidence intervals to be placed on computational model predictions that are based on high-throughput ion channel screens. This allows us to suggest when repeated screens should be performed to reduce uncertainty in a compound's action to acceptable levels, to allow a meaningful interpretation of the data.

Highlights

Unwanted drug interactions with ionic currents in the heart can lead to an increased proarrhythmic risk to patients in the clinic
Each assay generates a histogram of reported minus log10 of IC50 (pIC50) and Hill coefficients, such as those shown in Fig. 2 for Cisapride in the hERG IonWorks screen
Those assays with multiple controls, which are hERG (Fig. 4), CaV1.2 FLuorometric Imaging Plate Reader (FLIPR) (Fig. 4), and slow delayed rectifier potassium current (IKs) (Fig. 5), demonstrate similar levels of variability in both pIC50 and Hill coefficients for all of the compounds considered. These results provide evidence that the second assumption we made in Section 2.4.2 about consistency in the spread of pIC50 and Hill coefficients is reasonable for these assays

Summary

Introduction

Unwanted drug interactions with ionic currents in the heart can lead to an increased proarrhythmic risk to patients in the clinic It is a priority for safety pharmacology teams to detect block of cardiac ion channels, and new technologies have enabled the development of automated and highthroughput screening assays using cell lines. Discovering that a lead compound carries a high cardiac risk at later stages of development is very costly At both AstraZeneca (AZ) and GlaxoSmithKline (GSK), results from HTS assays for multiple cardiac ion channels inform mathematical models for a compound's action on whole-cell electrophysiology (Davies et al, 2012; Mirams et al, 2011).

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