Cellular hERG Assays - hERG Ion Channel Cell Lines

hERG ion channel cell lines for cardiac safety screening

Despite their effectiveness in blocking target ion channels, all drugs must avoid blocking one channel: a cardiac K channel termed hERG (Human Ether-á-go-go-Related-Gene). Because only patch-clamp assays provide the data required by ICH guidelines, drug discovery requires assays that are rapid and reliable. Invitrogen now provides hERG-expressing cell lines for safety screening assays.


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The hERG potassium channel is expressed in the mammalian heart and is crucial for repolarization and relaxation of cardiac muscle during every heartbeat. Potassium efflux occurs when the channel is open and the cardiac myocyte membrane potential is positive to the equilibrium potential for potassium; roughly –90 mV.

Human mutations of this gene increase susceptibility to QT-interval prolongation on an electrocardiogram. This prolonged interval can lead to lethal ventricular arrhythmias. Carriers may be asymptomatic until a sudden startle stimulus (e.g., an alarm or an unexpected telephone call) causes fainting (if awake) or sudden onset of ventricular arrhythmia. Mutations typically decrease the amount of protein expressed on the cell surface; i.e., they encode trafficking-deficient proteins. A diversity of drugs from widely-differing chemical scaffolds block this channel. Patients admitted for QT-interval prolongation or ventricular arrhythmia are typically screened for medications; therapeutically-relevant levels of prescription drugs have been shown to block hERG channels expressed in recombinant cell lines in patch-clamp assays. Such findings have led to the withdrawal of 10–20 marketed drugs, and a recommendation from the ICH that all Investigational New Drugs be tested in such patch-clamp assays to assess hERG block liability before they are administered to humans.

We offer two cell lines utilizing Invitrogen’s proprietary inducible expression technology, T-REx™, where there is little or no expression of hERG current until doxycyline is added. Twenty-four to forty-eight hours after addition of doxycyline, large currents are obtained from a majority of the cells examined in traditional patch-clamp assays.



Figure 1. Inducible expression of hERG current in hERG T-REx™ 293 Cells. For 15 cells patch-clamped without exposure to doxycycline, there was no outward tail current measured during the voltage step protocol used to define the current-voltage curves in 12 of the 15 cells. Following 48 hr of induction, all 22 cells tested had outward hERG current. The mean (± S.D.) amplitude of the tail current for the step from +40 to -70 mV is shown.



Figure 2. Example of currents recorded from hERG-T-REx™293 cells in patch-clamp assay. Left: Cells were held at -90 mV and stepped in 10 mV increments from -70 to +40 mV, then back to -70 mV to elicit tail currents. Right: the peak current during the step (diamonds) and during the step back to -70 mV (the tail current; boxes) are plotted.



Figure 3. Radioligand association and displacement. Using radiolabelled astemizole, the KD for the specific binding to 293 cell membranes following 48 hr of induction is 3.5 nM; the Bmax value of 7.6 pmol/mg protein equals or exceeds that of commercially available hERG-expressing cell lines. These levels of expression allow straightfoward and accurate profiling of compounds for hERG liability, as shown using the known hERG antagonists astemizole, E4031, and cisapride.
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