ENX-101, a GABA(A) receptor α2,3,5-selective positive allosteric modulator, displays antiseizure effects in rodent seizure and epilepsy models.

OBJECTIVE: γ-Aminobutyric acid type A (GABA(A)) receptor positive allosteric modulators (PAMs) that lack α-subunit selectivity, including benzodiazepines such as diazepam, exhibit antiseizure actions in animal models and in humans. ENX-101 is a deuterated analog of the ⍺2,3,5-selective GABA(A) receptor PAM L-838,417. The purpose of this study was to characterize the α-subunit selectivity of ENX-101 and evaluate its antiseizure potential in preclinical seizure and epilepsy models. METHODS: ENX-101 potentiation of GABA chloride current responses in cells expressing recombinant GABA(A) receptors were evaluated using an automated patch clamp assay. Antiseizure effects of ENX-101 were examined in the mouse 6 Hz test at 32 and 44 mA, amygdala kindled rats, and Genetic Absence Epilepsy Rat from Strasbourg (GAERS). RESULTS: ENX-101 displayed partial PAM activity with respect to diazepam at GABA(A) receptors containing α2, α3, or α5 subunits but did not enhance GABA responses of GABA(A) receptors containing α1 subunits. ENX-101 (30, 100, and 300 mg/kg, i.p.) and diazepam protected most animals in the 6 Hz model at 32 mA but was less effective at 44 mA. In amygdala kindled rats, ENX-101 (1-100 mg/kg, p.o.) reduced behavioral seizure severity and afterdischarge duration in a dose-dependent manner. ENX-101 (0.075-100 mg/kg, p.o.) caused dose-dependent, persistent (>130 min) inhibition of spontaneous spike-and-wave discharges (SWDs) in GAERS, whereas diazepam transiently inhibited discharges. ENX-101 did not cause motor impairment, as measured by performance in the rotarod assay. SIGNIFICANCE: ENX-101 is an α2,α3,α5-selective GABA(A) receptor PAM that has high potency and partial efficacy. The drug is highly effective in rodent seizure and epilepsy models. ENX-101 is most potent in the GAERS model of absence epilepsy, and active in the 6 Hz model and amygdala kindled rats. These results demonstrate that a partial, subtype-selective GABA(A) receptor PAM has activity in translationally validated preclinical epilepsy screening models. Clinical evaluation of ENX-101 as a treatment for focal and generalized epilepsies is warranted.