Characterization of a hERG Screen Using the IonWorks HT: Comparison to a hERG Rubidium Efflux Screen

Abstract

The introduction of parallel patch clamp instruments offers the promise of moderate-throughput, high-fidelity voltage clamp for drug screening assays. One such device, the IonWorks HT (Molecular Devices, Sunnyvale, CA), was evaluated and compared to conventional human ethera- go-go-related gene (hERG) patch clamp data and an alternative functional screen based on rubidium flux. Data generated by the IonWorks HT and rubidium assays were compared to determine if either offered superior predictive value compared to conventional patch clamp. Concentration-effect curves for a panel of known hERG blockers were shifted to higher concentrations on the IonWorks HT compared to conventional voltage clamp determinations. The magnitude of the potency shifts was compound-specific and ranged from no shift (e.g., quinidine) to over 200-fold (astemizole). When the extreme value for astemizole was disregarded, the potency shift for 13 other known reference standards was 12-fold or less, with an average shift of fivefold. The same subset of compounds in the rubidium efflux assay exhibited an average potency shift of 12-fold. To provide a simulation of how the IonWorks HT assay might perform in a single concentration screening mode, a panel of test compounds was evaluated. The IonWorks HT screen did not outperform the rubidium efflux screen in predicting conventional voltage clamp measurements. The most likely explanation appears to rest with variable and compound-specific potency shifts in the IonWorks HT assay. The variable potency shifts make it difficult to select a screening concentration that meets the criterion of a high positive predictive value while avoiding false-positives.

Pharmacological studies of Cav3.1 T-type calcium channels using automated patch-clamp techniques

“…A better correlation was observed with the values obtained in the present study than with the previously reported values, which is probably due to the differences in experimental conditions such as recording solutions and voltage protocols. The underestimated IC 50 values previously often observed due to the limited time for solution exchange and the adsorption of lipophilic test compounds (Guo and Guthrie 2005;Sorota et al 2005) were not observed in the present work. Also, the range of the IC 50 values extends over six orders of magnitude of concentrations with a slope of 0.96 determined by a linear regression, close to the unity line, indicating that the dynamic range of this method is broad enough for most of the test compounds to fall into this range.…”

Role of hERG potassium channel assays in drug development

“…Typically, hERG potencies measured by automated and manual electrophysiology are in good agreement; however, some compounds are known to appear less potent when tested by automated electrophysiology. [23][24][25][26] Discrepancies typically arise from hydrophobic compounds being adsorbed to the surface of the plate used to hold the compound or to the patch plate itself. Glass-coated compound plates can help to minimize the nonspecific binding to the compound plate but come at a significant cost.…”

Preclinical Drug Safety and Cardiac Ion Channel Screening

“…Using CHO cells that stably express hERG channels, IonWorks allows for assessment of approximately 200 data points per Patch plate and about 80 concentration-response curves per day [21][22][23][24]. A good pharmacological correlation with conventional MPC data was observed in terms of rank-order of compounds with hERG activity although the concentration-response curves were shifted to the right (within 3-to 5-fold).…”