Positive allosteric modulation of GABAA receptors by a novel antiepileptic drug cenobamate

Cenobamate is a novel antiepileptic drug under investigation for use in patients with focal (partial-onset) seizures. To understand its potential molecular mechanism of action, the effects of cenobamate on GABA(A) -mediated currents and GABA(A) receptors in rodent hippocampal neurons were examined. Cenobamate potentiated GABA-induced currents (I-GABA) in acutely isolated CA3 pyramidal cells in a concentration-dependent manner (EC50, 164 mu M), which was not affected by flumazenil, a benzodiazepine receptor antagonist. Cenobamate enhanced tonic GABA(A) currents (I-tonic), which is defined as a holding current shift by the GABA(A) receptor antagonist bicuculline (EC50, 36.63 mu M). At therapeutically relevant concentrations, cenobamate induced minimal changes in the frequency, amplitudes, and decay time of spontaneous inhibitory postsynaptic currents in the CA1 neurons. Flumazenil failed to affect cenobamate-potentiated I-tonic and I-phasic in CA1 neurons. Cenobamate showed positive allosteric modulation of GABA-induced I-GABA mediated by GABA(A) receptors. This effect was similar for all tested hGABA(A) receptors containing six different alpha subunits (alpha(1)beta(2)gamma(2) or alpha(2-6)beta(3)gamma(2)), with EC50 values ranging from 42 to 194 mu M. Cenobamate did not displace the binding of flunitrazepam, a benzodiazepine derivative, or flumazenil to GABA(A) receptors. The results showed that cenobamate, a novel antiepileptic drug, acts as a positive allosteric modulator of high-affinity GABA(A) receptors, activated by GABA at a site independent of the benzodiazepine binding site and efficiently enhances I-tonic inhibition in hippocampal neurons, which could be an underlying molecular mechanism stabilizing neural circuits of the epileptic hippocampus.