Abstracts

Rationale: Perampanel, a structurally novel pyridone, is a potent, orally active AMPA receptor antagonist currently under development for the treatment of epilepsy. Perampanel inhibits AMPA-induced calcium influx into cultured rat cortical neurons in a concentration-dependent fashion with IC50 of 93 nM (Hanada T, et al., Epilepsia 2011;52:1331-1340). Perampanel caused complex effects on the concentration-response curve for AMPA in this assay so that its precise mode of inhibition was not defined. In the present study, we sought to characterize the mechanism of block through whole cell voltage-clamp recordings in cultured hippocampal neurons expressing native AMPA receptors. Methods: Cultures were obtained from E19 rat embryos and recordings were carried out at 10-25 days in culture. Agonists with and without perampanel were applied using a fast perfusion system at various concentrations [kainate (3, 10, and 100 μM), AMPA (10, 30, and 100 μM) and NMDA (10 and 100 nM)]. Results: Perampanel caused a concentration-dependent inhibition of inward AMPA receptor currents evoked by kainate and AMPA that was unaffected by agonist concentration, indicating a noncompetitive blocking mechanism. The mean IC50 value at all kainate concentrations was 692 ± 94 nM. At a concentration of 30 μM that completely abolished AMPA-evoked response, perampanel had no effect on NMDA-evoked responses. Perampanel inhibited AMPA-evoked responses to a similar extent regardless of the order of application (perampanel first or AMPA first). In addition, perampanel reduced the peak and steady state AMPA responses to the same extent. These observations indicate that perampanel binds with similar affinity to the open and closed states of AMPA receptors. Furthermore, perampanel had no effect on the decay time course of AMPA-evoked currents, indicating that it does not affect AMPA receptor desensitization. Conclusions: The results demonstrate that perampanel is a selective noncompetitive AMPA receptor antagonist that does not affect NMDA receptors. The drug inhibits AMPA receptors without influencing channel kinetics.