New cardiac safety testing guidelines are being finalised, as part of the FDA’s Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative, which aim to remove the over-reliance on screening against the hERG channel by expanding the panel to include hNav1.5, hCav1.2, hKv4.3/KChiP2.2, hKir2.1 and hKv7.1/KCNE1 human cardiac ion channels. In addition, the CiPA working groups have recently identified two additional in vitro assays required for in silico models to reliably predict proarrhythmia. The first is a ‘late’ sodium current assay, as inhibition of persistent inward current can affect repolarisation and mitigate proarrhythmia (e.g. ranolazine). The second assay quantifies the degree of drug trapping in the hERG channel using the Milnes voltage protocol, which can improve the prediction of proarrhythmic risk.
Development of a robust hNaV1.9 high-throughput screening assay on the Sophion Qube384 platform. This is complemented by a suite of ion channel selectivity assays and sensory neuron recordings to create a versatile screening cascade to support NaV1.9 drug discovery programmes.
Optical voltage imaging of human iPSC-derived cardiomyocytes was used to assess electrophysiological effects of compounds beyond hERG inhibition. Action potential waveform analysis revealed compound-specific and concentration-dependent changes, enabling mechanistic differentiation of multichannel activity and demonstrating a human-relevant approach for translational cardiac safety assessment.