Further evidence for a differential interaction of brivaracetam and levetiracetam with the synaptic vesicle 2A protein

Brivaracetam (BRV) and levetiracetam (LEV) are effective antiepileptic drugs that bind selectively to the synaptic vesicle 2A (SV2A) protein. BRV differs from LEV in preclinical studies in that it exhibits a more potent and complete seizure protection across animal models. We reported previously that an allosteric modulator of the SV2A protein had differential effects on BRV compared with LEV, suggesting that they act at different sites or with different conformations of the SV2A protein. If this is the case, then we hypothesized that mutations of specific amino acids in the SV2A protein may have differential effects on BRV and LEV binding by the modulator. Mutation of some amino acids identified previously in the binding site of racetams to the SV2A protein had marked effects on binding of both [H-3]BRV and [H-3]LEV (eg, W300F, F277A, G303A, F658A, Y462A, W666A, I663A, D670A, and V661A). However, 3 amino acids were identified (K694, I273, and S294) in which mutation lost the effect of the modulator on [H-3]LEV binding with no effect on the modulation of [H-3]BRV binding. These results confirm that BRV and LEV bind to the human synaptic vesicle 2A protein at closely related sites but interact with these sites in a different way.