HERG patch clamp assay

Redfern et al. studied the occurrence of QT prolongation and the lethal arrhythmia torsades de pointes (see Chapter 16) in marketed drugs from the perspective of the therapeutic index [50]. This group proposed a therapeutic index of 30-fold, calculated from the free Cmax at the therapeutic dose and the in vitro potency in the manual hERG patch clamp assay. This level, or even higher, seems to be generally followed by the industry. 

However, when compound 15 was tested for h E RG K+ channel inhibition, a basic cardiovascular safety indicator related to the QT prolongation syndrome [32], and linked to ventricular fibrillation and sudden death [33], we were unpleasantly surprised. Although the lead compound 1 exhibited very weak binding to the hERG K+ channel (IC50 > 5000 nM), the optimized compound 15 was afairly potent hERG blocker with an inhibition concentration IC50 of 300 nM (in patch-clamp assay). 

Herg blockade is mesmerising the pharmaceutical industry, not just due to the implications for drug discovery, but also because the difficulty is understanding the interplay between displacement of dofetilide, patch clamp assays, dog telemetry and the occurrence of toursade des pointes in humans. Several groups have developed... 

Neurotoxicity—brain spheroids (central nervous system (CNS)) and dorsal root ganglia (DRG) neurite outgrowth (peripheral nervous system (PNS)) assay Cardiotoxicity—HERG patch clamp and/or HERG ligand assay... 

HERG ("Human-ether-a-go-go related gene) at low concentrations. Conformationally constrained isoquinuclidine analogs of BRL-32872 were also prepared to study the effects of molecular flexibility towards class III and class IV anti-arrhythmic properties [48]. Both standard microelectrode and patch clamp assays indicated that while both epimers displayed a pharmacological profile similar to BRL-32872, epimer 52b was more effective than 52a. 

Key words Cardiotoxicity, In vitro assays for cardiotoxicity, Cardiac safety, Functional flux assays, Fluorescence-based assays, hERG, Patch clamp, Alternative tests, Microelectrode array, hESC-derived cardiomyocytes, FLIPER, Q-T interval, HEK 293, CHO, Embryonic stem cells, Differentiation, hiPSCs, Drug interaction, Safety pharmacology, ICH guidelines, Arrhythmia... 

Each of these techniques can give quite different hERG IC50 values for the same compound. Eor example, terfenadine s IC50 has been measured at 30 nM in the patch-clamp assay, 4.8 pM in the rubidium flux assay, and 500 nM in a binding assay. Needless to say, numbers from different assays, different cells, or different labs for that matter, can t be directly compared. 

Tables.3 Hepatic metabolism, measured in liver microsomes and hERG IC50 (patch clamp data) of terfenadine and fexofenadine, determined and compared in early, routinely used in vitro profiling assays.

Rb+ efflux assay hERG-transfected ICa, (nM) Patch clamp Rb+ efflux assay [20]... 

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