Non-invasive hERG channel screening based on electrical impedance tomography and extracellular voltage activation (EIT–EVA)

Abstract

hERG channel screening has been achieved based on electrical impedance tomography and extracellular voltage activation (EIT–EVA) to improve the non-invasive aspect of drug discovery. EIT–EVA screens hERG channels by considering the change in extracellular ion concentration which modifies the extracellular resistance in cell suspension. The rate of ion passing in cell suspension is calculated from the extracellular resistance R_ex, which is obtained from the EIT measurement at a frequency of 500 kHz. In the experiment, non-invasive screening is applied by a novel integrated EIT–EVA printed circuit board (PCB) sensor to human embryonic kidney (HEK) 293 cells transfected with the human ether-a-go-go-related gene (hERG) ion channel, while the E-4031 antiarrhythmic drug is used for hERG channel inhibition. The extracellular resistance R_ex of the HEK 293 cells suspension is measured by EIT as the hERG channels are activated by EVA over time. The R_ex is reconstructed into extracellular conductivity distribution change Δσ to reflect the extracellular K⁺ ion concentration change Δc resulting from the activated hERG channel. Δc is increased rapidly during the hERG channel non-inhibition state while Δc is increased slower with increasing drug concentration c_d. In order to evaluate the EIT–EVA system, the inhibitory ratio index (IR) was calculated based on the rate of Δc over time. Half-maximal inhibitory concentration (IC₅₀) of 2.7 nM is obtained from the c_d and IR dose–response relationship. The IR from EIT–EVA is compared with the results from the patch-clamp method, which gives R² of 0.85. In conclusion, EIT–EVA is successfully applied to non-invasive hERG channel screening.