Jutta Rohrbacher | PubMed Health

PubMed2006

In-vitro experimental models for the risk assessment of antibiotic-induced QT prolongation.

The prolongation of the ventricular repolarization and proarrhythmic effects (Torsade de Pointes: TdP) of five reference antibiotics were compared in four in-vitro models. 1. Using the patch clamp technique on the human ether-a-gogo-related gene (HERG) current, the rank order for blockade of the HERG-current (IC(50)) was: sparfloxacin (44 microM)>telithromycin=moxifloxacin=erythromycin (+/-100 microM). 2. Assessing their effects on action potential duration (APD(90)) and incidence of early afterdepolarizations in isolated rabbit Purkinje fibers, the rank order was: sparfloxacin>moxifloxacin>telithromycin>erythromycin (prolongation of APD(90) at 100 microM: 83%, 48%, 33% and 17% from baseline compared to +5% with solvent, P<0.05, respectively). 3. Assessing the drug effects on the APD(60), triangulation, reverse use-dependency, and instability in isolated Langendorff-perfused rabbit hearts, the rank order was: moxifloxacin>erythromycin>sparfloxacin>telithromycin. 4. Assessing their torsadogenic potentials (scores of effects on QT-interval, peak of the T wave to end of T wave: T(p-e), T(p-e)/QT ratio, R wave on T wave (R on T) and TdP in isolated rabbit left ventricular wedge preparations, the rank order for their TdP risk score was: sparfloxacin>erythromycin>moxifloxacin>telithromycin. Additional experiments with grepafloxacin indicate that the rank order to detect grepafloxacin-induced long QT was the wedge preparation>the Purkinje fiber>HERG>the isolated heart, where the isolated heart was unable to detect grepafloxacin-induced APD prolongation. The present study demonstrates that the first three in-vitro models can be used to assess the ability of antibiotic compounds to delay ventricular repolarization. However, with respect to their known clinical effects on QT and TdP incidence, the wedge preparation appears to be more predictive and suitable for detecting torsadogenic action of antibiotics.

Action Potentials↗

PubMed2005

Identifying modulators of hERG channel activity using the PatchXpress planar patch clamp.

The authors used the PatchXpress 7000A system to measure compound activity at the hERG channel using procedures that mimicked the "gold-standard" conventional whole-cell patch clamp. A set of 70 compounds, including hERG antagonists with potencies spanning 3 orders of magnitude, were tested on hERG302-HEK cells using protocols aimed at either identifying compound activity at a single concentration or obtaining compound potency from a cumulative concentration dependence paradigm. After exposure to compounds and subsequent washout of the wells to determine reversibility of the block, blockade by a reference compound served as a quality control. Electrical parameters and voltage dependence were similar to those obtained using a conventional whole-cell patch clamp. Rank order of compound potency was also comparable to that determined by conventional methods. One exception was flunarizine, a particularly lipophilic compound. The PatchXpress accurately identified the activity of 29 moderately potent antagonists, which only weakly displace radiolabeled astemizole and are false negatives in the binding assay. Finally, no false hits were observed from a collection of relatively inactive compounds. High-quality data acquisition by PatchXpress should help accelerate secondary screening for ion channel modulators and the drug discovery process.

Cell Line↗