@article {Woodjpet.119.261149, author = {Martyn Wood and Veronique Daniels and Laurent Provins and Christian Wolff and Rafal M Kaminski and Michel Gillard}, title = {Pharmacological profile of the novel antiepileptic drug candidate padsevonil {\textendash} interactions with synaptic vesicle 2 proteins and the GABAA receptor}, elocation-id = {jpet.119.261149}, year = {2019}, doi = {10.1124/jpet.119.261149}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {Padsevonil is an antiepileptic drug (AED) candidate synthesized in a medicinal chemistry program initiated to rationally design compounds with high affinity for synaptic vesicle 2 (SV2) proteins and low-to-moderate affinity for the benzodiazepine binding site on GABAA receptors. The pharmacological profile of padsevonil was characterized in binding and electrophysiological experiments. At recombinant SV2 proteins, padsevonil{\textquoteright}s affinity for SV2A was higher than that of levetiracetam and brivaracetam (pKi 8.5, 5.2 and 6.6, respectively). Unlike the latter AEDs, both selective SV2A ligands, padsevonil also displayed high affinity for the SV2B and SV2C isoforms (pKi 7.9 and 8.5, respectively). Padsevonil{\textquoteright}s interaction with SV2A differed from that of levetiracetam and brivaracetam; it exhibited slower binding kinetics {\textendash} dissociation t{\textonehalf} 30 min from the human protein at 37{\textdegree}C, compared with \<0.5 min for levetiracetam and brivaracetam {\textendash} and its binding was not potentiated by the allosteric modulator UCB1244283. At recombinant GABAA receptors, padsevonil displayed low-to-moderate affinity (pKi 6.4) for the benzodiazepine site, and in electrophysiological studies, its relative efficacy compared with zolpidem (full agonist reference drug) was 40\%, indicating partial agonist properties. In in vivo (mice) receptor occupancy studies, padsevonil exhibited SV2A occupancy at low (ED50 0.2 mg/kg), and benzodiazepine site occupancy at higher doses (ED50 36 mg/kg), supporting in vitro results. Padsevonil{\textquoteright}s selectivity for its intended targets was confirmed in profiling studies, where it lacked significant effects on a wide variety of ion channels, receptors, transporters and enzymes. Padsevonil is a first-in-class AED candidate with a unique target profile allowing for pre- and postsynaptic activity.SIGNIFICANCE STATEMENT Padsevonil is an antiepileptic drug candidate developed as a single molecular entity interacting with both pre- and postsynaptic targets. Results of in vitro and in vivo radioligand binding assays confirmed this target profile – padsevonil displayed nanomolar affinity for the three synaptic vesicle 2 protein isoforms (SV2A, B and C) and micromolar affinity for the benzodiazepine binding site on GABAA receptors. Furthermore, padsevonil showed higher affinity for, and slower binding kinetics at SV2A than the selective SV2A ligands, levetiracetam and brivaracetam.}, issn = {0022-3565}, URL = {https://jpet.aspetjournals.org/content/early/2019/10/16/jpet.119.261149}, eprint = {https://jpet.aspetjournals.org/content/early/2019/10/16/jpet.119.261149.full.pdf}, journal = {Journal of Pharmacology and Experimental Therapeutics} }