Estimation of both the potency and efficacy of alpha7 nAChR agonists from single-concentration responses

The assessment of functional properties is a crucial step in the screening of potential new drug candidates. The development of moderate to high throughput electrophysiological recording systems such as OpusXpress (Molecular Devices) has facilitated the process of testing new drugs to a large degree. However, while the simple screening of multiple drugs at a single concentration identifies "hits" and "misses", the generation of full concentration-response studies is still a bottleneck in drug development. The alpha7 nicotinic acetylcholine receptor displays a unique concentration dependence of response kinetics which permits estimates of EC50 and Imax values for experimental drugs to be generated from single-concentration responses. This method is based on the analysis of 13 different concentration-response studies utilizing either human or rat alpha7 nAChR. Each experimental response was first normalized to an ACh control, and then a transformation of the pooled data was generated which, based on the relationship between the net charge and peak current to their respective EC50 values defined the "functional concentration" (the test concentration relative to the EC50 for the given agonist). At low functional concentrations, net charge is large relative to peak current amplitude and at higher functional concentration this relationship reverses. For any single-concentration response, the ratio of net charge to peak current can be used to estimate functional concentration. Efficacy can then be estimated by comparing the observed (net charge) response to the expected value for a full agonist at the estimated functional concentration. This extended analysis, combined with automated recording methods, should greatly increase the efficiency with which promising new drug candidates can be characterized.