Optogenetic Technologies Enable High Throughput Ion Channel Drug Discovery and Toxicity Screening

Abstract

The drug discovery process involving ion channels needs to rely on high-throughput screening (HTS) assays as well as fine-tuned characterization by electrophysiological measurements. Combining optogenetic tools with induced pluripotent stem-cells (iPSC)-derived cardiomyocytes can provide a reliable, cost-effective and highly time-resolved approach to induce electrogenic proteins activation. The aim of the OPTEL project, which combines the expertise of two leading European companies and one academic laboratory, was to develop integrated HTS-compatible platforms based on optogenetic tools (Channelrhodopsin, ChR2) for effective drug discovery in heterologous expression systems and iPS-derived cardiomyocytes. We generated HEK293 cell lines stably expressing ChR2 alone or with the cardiac sodium channel, NaV1.5 which proper functional expression was validated by fluorescence and manual patch-clamp. The best clones were used to implement light stimulation on an HTS automated patch-clamp platform (SynchroPatch 384PE, Nanion Technologies). We recorded light-induced currents and action potential-like responses in voltage and current-clamp, respectively, validating a new platform for high-throughput automated “opto-patch-clamp” assays. For optogenetic drug toxicity screening, commercially available iPSC-derived cardiomyocytes were infected with adeno-associated viruses to express ChR2 and analyzed by recording extracellular field potentials from 96 wells with a modified CardioExcyte96 system (Nanion Technologies). This was equipped with a custom designed 96 LED lid enabling pacing of cells and frequency-dependent drug screening over the physiological heart rate (1-3 Hz). Thereby we characterized adverse side effects of known ion channel blockers and pro-arrhythmogenic drugs on Na+, Ca2+ and K+ channels. These results validate new platforms that allow optogenetic control of electrical activity in HTS-compatible format with four different readouts: fluorescence, electrophysiology, impedance and extracellular field potentials. The use of these complementary readouts provides a new cost-effective and informative strategy in early stages of ion channel drug discovery, especially in the cardiac field.