Evaluation of α7 Nicotinic Acetylcholine Receptor Agonists and Positive Allosteric Modulators Using the Parallel Oocyte Electrophysiology Test Station

Neuronal acetylcholine receptors (nAChRs) of the alpha 7 subtype are ligand-gated ion channels that are widely distributed throughout the central nervous system and considered as attractive targets for the treatment of various neuropsychiatric and neurodegenerative diseases. Both agonists and positive allosteric modulators (PAMs) are being developed as means to enhance the function of alpha 7 nAChRs. The in vitro characterization of alpha 7 ligands, including agonists and PAMs, relies on multiple technologies, but only electrophysiological measurements assess the channel activity directly. Traditional electrophysiological approaches utilizing two-electrode voltage clamp or patch clamp in isolated cells have very low throughput to significantly impact drug discovery. Abbott (Abbott Park, IL) has developed a two-electrode voltage clamp-based system, the Parallel Oocyte Electrophysiology Test Station (POETs (TM)), that allows for the investigation of ligand-gated ion channels such as alpha 7 nAChRs in a higher-throughput manner. We describe the utility of this technology in the discovery of selective alpha 7 agonists and PAMs. With alpha 7 agonists, POETs experiments involved both single- and multiple-point concentration-response testing revealing diverse activation profiles (zero efficacy desensitizing, partial, and full agonists). In the characterization of alpha 7 PAMs, POETs testing has served as a reliable primary or secondary screen identifying compounds that fall into distinct functional types depending on the manner in which current potentiation occurred. Type I PAMs (eg, genistein, NS1738, and 5-hydroxyindole) increase predominantly the peak amplitude response, type II PAMs affect the peak current and current decay (eg, PNU-120,596 and 4-(naphthalen-1-yl)-3a, 4,5,9b-tetrahydro-3H- cyclopenta[c] quinoline-8-sulfonamide), and another type slowing the current decay kinetics in the absence of increases in the peak current. In summary, POETs technology allows for significant impact on higher throughput in the testing of alpha 7 agonists and PAMs and for identification of compounds with unique profiles that could prove valuable in identifying an optimum in vitro profile in the development of therapeutics for which the alpha 7 subtype is considered.