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

Abstract

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.