title: Automated electrophysiology in the preclinical evaluation of drugs for potential QT prolongation.
abstract: BACKGROUND
  The human ether-a-go-go-related gene (hERG) potassium channel plays a major role in the electrical conductances involved in human heart repolarization. Drugs that decrease hERG K(+) currents are at risk to produce a prolongation of the cardiac action potential, resulting in an increase of the QT interval. Drug-induced QT prolongation or acquired long QT (aLQT) can lead to a fatal arrhythmia known as Torsade de Pointes (TdP). Electrophysiological methods are the best approach to evaluate potential drug candidates for hERG current inhibition. Here we identify limitations with the PatchXpress 7000A automated electrophysiology instrument and describe hERG protocol optimizations necessary for reliable preclinical assessment.
  
  
  METHODS
  The PatchXpress 7000A automated electrophysiology system was used to evaluate a group of drugs with known hERG activity under voltage clamp conditions. We used a recombinant cell line expressing hERG, and assessed the inhibition of hERG K(+) currents at different drug concentrations. These data were used to determine hERG IC(50) values and compare assay parameters under different recording conditions.
  
  
  RESULTS
  We found that due to limitations with the PatchXpress 7000A instrument, repeated compound additions were critical for achieving steady state drug concentrations that generated data comparable to standard patch clamp methods, particularly when similar voltage pulse protocols were implemented. Some discrepancies were observed between the PatchXpress 7000A and standard patch clamp techniques including shifts in IC(50) values for very hydrophobic compounds. Most hERG IC(50) values were within 3-fold of standard patch clamp IC(50) values.
  
  
  CONCLUSIONS
  Automation of electrophysiology technologies has greatly improved the throughput of assessing lead drug candidates for hERG liability. To maintain hERG data quality comparable to standard patch clamp techniques, the PatchXpress 7000A instrument limitations should be recognized and protocols optimized accordingly to ensure accuracy.
authors.affiliation: Hoffmann-La Roche, Inc., Non-clinical Drug Safety, Nutley, NJ 07110-1199, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Guo
authors.forename: Heather
authors.initials: H
authors.lastname: Guthrie
mesh_terms: D000818:Animals; D016466:CHO Cells / Q000187:drug effects / Q000502:physiology; D002317:Cardiovascular Agents / Q000009:adverse effects* / Q000145:classification; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D064420:Drug-Related Side Effects and Adverse Reactions; D004594:Electrophysiology / Q000295:instrumentation / Q000379:methods; D020128:Inhibitory Concentration 50; D008133:Long QT Syndrome / Q000139:chemically induced* / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D004364:Pharmaceutical Preparations / Q000145:classification; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects; D012371:Robotics / Q000295:instrumentation* / Q000379:methods; D016171:Torsades de Pointes / Q000139:chemically induced
chemical_list: D002317:Cardiovascular Agents; D004364:Pharmaceutical Preparations; D024642:Potassium Channels, Voltage-Gated