title: Evaluation of an in silico cardiac safety assay: using ion channel screening data to predict QT interval changes in the rabbit ventricular wedge.
abstract: BACKGROUND
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Computational Biology, Department of Computer Science, University of Oxford, Oxford OX1 3QD, UK. kylie.beattie@cs.ox.ac.uk
authors.forename: Kylie A
authors.initials: KA
authors.lastname: Beattie
authors.forename: Chris
authors.initials: C
authors.lastname: Luscombe
authors.forename: Geoff
authors.initials: G
authors.lastname: Williams
authors.forename: Jordi
authors.initials: J
authors.lastname: Munoz-Muriedas
authors.forename: David J
authors.initials: DJ
authors.lastname: Gavaghan
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
authors.forename: Gary R
authors.initials: GR
authors.lastname: Mirams
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D015195:Drug Design; D004562:Electrocardiography; D005260:Female; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D057166:High-Throughput Screening Assays / Q000379:methods; D020128:Inhibitory Concentration 50; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008133:Long QT Syndrome / Q000139:chemically induced* / Q000175:diagnosis; D008962:Models, Theoretical; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D011237:Predictive Value of Tests; D021281:Quantitative Structure-Activity Relationship; D011817:Rabbits; D012680:Sensitivity and Specificity
chemical_list: D007473:Ion Channels
keywords: AP (D); Action Potential (Duration); Action potential; Cardiac safety; Compound screening; Concentration for 50% Inhibition; ECG; ECVAM; European Centre for the Validation of Alternative Methods; FLIPR; FLuorescence Imaging Plate Reader; GSK; GlaxoSmithKline; I(Kr); I(Ks); IC(50); ICH; International Conference for Harmonization; Ion channels; Mathematical model; Methods; QSAR; QT interval; Quantitative Structure Activity Relationship; Rabbit ventricular wedge; TdP; Torsades de Pointes; electrocardiogram; hERG; human-Ether-a-go-go Related Gene; minus log(10) of IC(50); pIC(50); rapid delayed rectifier potassium current; slow delayed rectifier potassium current