hERG Inhibition Assay

The hERG Inhibition Assay: predictive, sensitive & rapid

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The human ether-a-go-go related gene (hERG) encodes the inward rectifying voltage gated potassium channel in the heart (IKr) which is involved in cardiac repolarisation. Inhibition of the hERG current causes QT interval prolongation resulting in potentially fatal ventricular tachyarrhythmia called Torsade de Pointes.

The importance of the hERG ion channel for drug discovery programs stems from the observation that not only mutations, but also drug induced blockade of the channel, may cause repolarization abnormalities. Many drugs from different chemical classes and therapeutic areas have been shown to block the hERG-coded ion channel and may in turn potentially trigger torsades (). Other reasons for cardiac arrhythmias have been identified (; ; ; ), but hERG channel blockade has become the most frequent single cause for drug withdrawals (), and many drug discovery programs have been delayed (imposing significant costs on the pharmaceutical company) or stopped due to hERG channel liabilities of potential drug candidates. (Danker and Moller, 2014).

Whole-cell current amplitude and kinetics measurements verify the result of potential interactions of a test article with the product of the hERG gene, a human ion channel responsible for the IKr repolarizing current. IKr current inhibition has been shown to prolong the cardiac action potential, a phenomenon associated with increased risk of arrhythmia. IKr inhibition accounts for the vast majority of known cases of drug-induced QT-prolongation.

hERG1

Highlights:

•GLP-compliant manual patch-clamp
•Conducted at physiological temperature
•Part of the core battery of Safety Pharmacology tests required for IND submission
•Screens (non-GLP, faster study design) also available

 

Assay description:

Rapid delayed rectifying potassium (IKr) current inhibition assay

Cell line type:

HEK293 or CHO cells stably transfected with the human ERG (hERG) gene

Technique:

Manual patch-clamp, whole-cell configuration

GLP compliance:

Pre-IND (GLP-compliant) or exploratory designs (screen = non-GLP compliant)

Rationale:  

Part of the core battery of Safety Pharmacology tests required for IND submission Whole-cell current amplitude and kinetics measurements verify the results of the interactions of a test article with the product of the hERG gene, a K+-selective ion channel responsible for the IKr repolarizing current. IKr current inhibition has been shown to prolong the cardiac action potential, a phenomenon associated with increased risk of arrhythmia. IKr current inhibition accounts for the vast majority of known cases of drug-induced QT- prolongation.

Study Outline:

  • Number of cells exposed to the test article: 7 (screens: 3)
  • Number of concentrations of test article: 4 (screens: 3)
  • Method of test article exposure: cumulative concentrations in closed-circuit perfusion, or constant perfusion of individual concentrations
  • Voltage pulse: partial current-voltage relationship
  • A study includes positive and vehicle controls as well as a reference article

Study Outcome:

  • A quantitative assessment of IKr current inhibition
  • Determination of the IC50 value (if applicable)
  • Analysis of both amplitude and current kinetics as indicators of inhibition
  • FDA-ready hard copy  and e-report for electronic IND submission
  • Holistic interpretation of a positive signal, considering all other data generated

Recommended reading:

  1. Shah RR., Drug-induced QT interval prolongation-regulatory guidance and perspectives on hERG channels studies., Novartis Foundation Symp., 2005; 266:251-80.
  2. Sanguinetti MC. Mitcheson JS., Predicting drug-hERG channel interactions that cause acquired long QT syndrome., Trends in Pharmacological Sciences., 2005; 26(3): 119-24.