Pharmacological Profile of the Novel Antiepileptic Drug Candidate Padsevonil: Interactions with Synaptic Vesicle 2 Proteins and the GABA_A Receptor

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 GABA A receptors. The pharmacological profile of padsevonil was characterized in binding and electrophysiological experiments. At recombinant SV2 proteins, padsevonil's affinity for SV2A was greater 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's interaction with SV2A differed from that of levetiracetam and brivaracetam; it exhibited slower binding kinetics: dissociation t 1/2 30 minutes from the human protein at 37°C compared with ,0.5 minute for levetiracetam and brivaracetam. In addition, its binding was not potentiated by the allosteric modulator UCB1244283. At recombinant GABA A receptors, padsevonil displayed low to moderate affinity (pIC 50 #6.1) 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 ED 50 (0.2 mg/kg) and benzodiazepine site occupancy at higher doses (ED 50 36 mg/kg), supporting in vitro results. Padsevonil'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 presynaptic and postsynaptic activity. SIGNIFICANCE STATEMENTPadsevonil is an antiepileptic drug candidate developed as a single molecular entity interacting with both presynaptic 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 GABA A receptors. Furthermore, padsevonil showed greater affinity for and slower binding kinetics at SV2A than the selective SV2A ligands, levetiracetam, and brivaracetam.All studies described in this report were funded by UCB Pharma.

Functional characterization of the antiepileptic drug candidate, padsevonil, on GABAA receptors

“…2 Furthermore, unlike LEV and BRV, the interaction between Padsevonil and SV2A is not affected by UCB1244283, a positive allosteric modulator of SV2A, suggesting a different binding site for Padsevonil in the SV2A protein. [2][3][4] At recombinant GABA A Rs, Padsevonil displayed low-to-moderate affinity (pKi 6.4) for the benzodiazepine (BZD) binding site. This binding profile has been confirmed in receptor occupancy studies in vivo (mice), where Padsevonil exhibited SV2A occupancy at low doses (median effective dose [ED 50 ] 0.2 mg/kg), and BZD site occupancy at higher doses (ED 50 36 mg/kg).…”

“…The selective interaction of Padsevonil with its molecular targets, as intended in the rational drug discovery program, has been confirmed in both in vitro and in vivo studies. 2 Specifically, Padsevonil was designed to bind to the presynaptic SV2 proteins with high affinity and to postsynaptic GABA A Rs, with low-to-moderate affinity. In radioligand displacement studies, Padsevonil has been shown to bind to SV2A with nanomolar affinity (pKi 8.5) that is approximately 100-and 2000-fold greater than that of brivaracetam (BRV) and LEV, respectively.…”

“…In radioligand displacement studies, Padsevonil has been shown to bind to SV2A with nanomolar affinity (pKi 8.5) that is approximately 100-and 2000-fold greater than that of brivaracetam (BRV) and LEV, respectively. 2 Another major differentiating factor between Padsevonil and the SV2A selective ligands LEV and BRV is that Padsevonil also binds with high affinity to the B and C isoforms of SV2 proteins (pKi 7.9 and 8.5, respectively). 2 Padsevonil also demonstrates different binding properties to SV2A in that it displays significantly slower dissociation kinetics, translating into longer target occupancy.…”

“…2 Another major differentiating factor between Padsevonil and the SV2A selective ligands LEV and BRV is that Padsevonil also binds with high affinity to the B and C isoforms of SV2 proteins (pKi 7.9 and 8.5, respectively). 2 Padsevonil also demonstrates different binding properties to SV2A in that it displays significantly slower dissociation kinetics, translating into longer target occupancy. 2 Furthermore, unlike LEV and BRV, the interaction between Padsevonil and SV2A is not affected by UCB1244283, a positive allosteric modulator of SV2A, suggesting a different binding site for Padsevonil in the SV2A protein.…”

“…2 Padsevonil also demonstrates different binding properties to SV2A in that it displays significantly slower dissociation kinetics, translating into longer target occupancy. 2 Furthermore, unlike LEV and BRV, the interaction between Padsevonil and SV2A is not affected by UCB1244283, a positive allosteric modulator of SV2A, suggesting a different binding site for Padsevonil in the SV2A protein. [2][3][4] At recombinant GABA A Rs, Padsevonil displayed low-to-moderate affinity (pKi 6.4) for the benzodiazepine (BZD) binding site.…”