Introduction

Assays for hERG block of drug candidates are a crucial element of drug development.  Since CDI founder Dr. Craig January pioneered the HEK293 hERG screening test in 1997, several important drugs have been removed from the market due to their blocking effect on cardiac hERG channels, including Seldane (1998), Raxar (1999), Hismanal (1999), and Propulsid (2000).  These drugs, as well as other drug candidates, have been found to induce long QT syndrome (LQTS) in certain individuals and increase the potential for sudden death from arrhythmia.  Many more drugs have received black box warnings for the same effect. 

CDI’s Definitive Test…

Acute block of hERG channels by pharmaceuticals is a recognized developmental and clinical liability for which there is a recognized in vitro assay.  CDI's standard screening process uses the definitive in vitro assay for this effect using a tight-seal, whole-cell voltage clamp technique to generate complete room temperature concentration-response data on Test Article block of hERG channels stably expressed in HEK293 cells. 

CDI’s Non-GLP hERG Channel Assay specifications include:

• State-of-the-art patch clamp assay using the hERG channel gene expressed in HEK cells
• IC₅₀ determination from hERG tail current
• 4 drug concentrations tested bracketing the amount expected to produce 50% block (IC₅₀) of channel activity.
• 4 cells tested at each concentration
  

…with Definitive Results

Concentration-response data showing significant block of channel activity is fit with a Hill equation to derive the actual IC₅₀ as well as the coefficient of the relation.  Positive and negative controls are used in each assay to monitor experimental conditions. 

If your objective is to evaluate relative hERG block among candidate molecules, this same study can be used to test four compounds at a single concentration for the same price.  For this test, the selected concentration should be at least at the expected physiological concentration or above.  Instead of calculating IC₅₀, the study results include a relative ranking of the compounds for relative hERG channel block, if any.

Advantages

CDI Services for Drug Safety Screening & Discovery

• Accelerated drug development in key therapeutic target areas
• Extensive experience with drug-induced effects on ion channels
• Accurate, reliable screening results
• Rapid turnaround

A typical dose-response curve with IC₅₀ from a CDI study.

References

Vorperian VR, Zhou Z, Mohammad S, Hoon TJ, Studenik C and January CT.  1996. Torsades de Pointes with an antihistamine metabolite: Potassium channel blockade with desmethylastemizole.  J Am Coll Cardiol  28:1556-1561.

Zhou Z, Gong Q, Ye B, Fan Z, Makielski JC, Robertson GA and January CT. 1998. Properties of HERG channels stably expressed in HEK 293 cells studied at physiological temperature.  Biophys J 74:230-241.

Kamp TJ, January CT.  2004.  Inherited and Acquired Long QT Syndromes: New Insights and Evolving Technology. Drug Discovery Today.  1:45-51.

Rajamani S, Eckhardt LL, Valdivia CR, Klemens CA, Gillman BM, Anderson CL, Holzem KM, Delisle BP, Anson BD, Makielski JC, January CT.  2006. Drug-induced long QT syndrome:  hERG K+ channel block and disruption of protein trafficking by fluoxetine and norfluoxetine  Br J Pharmacol.  [In Press].