Variability of manual patch clamp hERG data generated using standardized protocols and following ICH S7B Q&A 2.1 best practices

The most common mechanism of drug-induced QT_C prolongation and the potentially fatal arrhythmia Torsade de Pointes is block of hERG channels. Accordingly, the hERG assay is used to assess cardiac safety of new drugs in support of first-in-human studies. The recently updated ICH E14 Q&As 5.1 and 6.1 describe regulatory pathways to use hERG results obtained following best practice recommendations (ICH S7B Q&A 2.1) to complement clinical QT_C data that otherwise may not be adequate and inform labeling. However, the impact of protocol standardization on variability of hERG data has not been assessed. This is a critical data gap in implementation of the E14/S7B Q&As. This hERG dataset was collected as part of a HESI-coordinated international effort designed to generate cardiac ion channel data using physiologically relevant protocols when feasible and practical, following best practice recommendations in ICH S7B Q&As. Datasets for other cardiac ion channels are presented in a companion abstract (Yu et al.). Five laboratories established drug block potencies (IC₅₀s) for 28 clinical drugs in a two-phase study using manual patch clamp. Concentration verification was done to assess drug losses for all laboratories and drugs. Meta-analysis was used to estimate overall variability in IC₅₀s. Phase 1 study showed that hERG IC₅₀s were similar for four laboratories and systematically higher for one laboratory. The source of the systematic difference could not be identified and was not attributed to different extent of drug loss, drug delivery method, cell lines, or recording quality. The systematic difference disappeared during phase 2. Blind repeat testing of two phase 1 drugs was done by each laboratory to understand within the laboratory reproducibility. The overall variability (or reproducibility) of the hERG assay was estimated accounting for potency differences among different drugs and laboratory-specific tendencies. This variability indicates the resolution limit of the hERG assay under best practices to distinguish two IC₅₀s as different. Systematic differences in hERG IC₅₀s can occur following protocol standardization and ICH S7B best practice recommendations. The regulatory framework for identifying hERG-positive molecules should account for hERG data variability and may additionally need to account for laboratory-specific differences.