Abstracts

Dravet Syndrome is a condition characterized by reduced expression of Na_V1.1 in inhibitory neurons. This reduction leads to hyperexcitability from impairment of inhibitory neuronal activity, ultimately resulting in epilepsy and multiple co-morbidities including serious cognitive and motor deficits. The non-seizure symptoms of the disorder emerge early in life and worsen over time, significantly impacting the overall disease burden. Therefore, there is a pressing need for therapeutic interventions that specifically target the non-seizure aspects of the condition.

To address this clinical need, we sought to develop precision medicine therapy that selectively enhances the activity of Na_V1.1 without affecting other neuronal functions or proteins. We have created small molecules that are potent, isoform-selective, and capable of penetrating the brain to potentiate Na_V1.1 channels. These molecules exhibit favorable CNS drug-like characteristics, enabling oral administration in vivo and normalize interneuron activity in ex vivo studies. By directly addressing the root cause of Dravet Syndrome, these compounds hold promise as disease-modifying pharmacotherapy, offering a potential correction of the underlying etiology.

Automated patch clamp electrophysiology was used to screen and evaluate the potency and selectivity of compounds. Compounds were also evaluated in brain slices from Scn1a heterozygous null mice (Scn1a^+/-) to assess the effects on interneuron excitability and synaptic inhibitory and excitatory balance. Efficacy was assessed after oral dosing in Scn1a^+/- mice in a 6Hz electrically induced seizure assay and in a rotorod motor performance assay.

XPC-1418 potently enhances Na_V1.1 channels, exhibiting more than 100-fold selectivity over Na_V1.2, 1.6, and 1.5. Biophysical analysis reveals that the compound specifically destabilizes the inactivated state of Na_V1.1 channels. In brain slices from Scn1a^+/- mice, XPC-1418 increases the firing activity of fast-spiking cortical PV+ interneurons and restores the balance between spontaneous excitatory and inhibitory synaptic input to pyramidal neurons. In in vivo experiments, XPC-1418 effectively suppresses 6Hz electrically induced seizures in Scn1a^+/- mice and normalized motor performance deficits as assessed by the rotarod assay.

Selective Na_V1.1 potentiators enhance the excitability of fast-spiking inhibitory neurons and restore the balance of excitation in brain slices from Scn1a^+/- mice. XPC-1418 effectively improves motor performance on the rotarod test in Scn1a^+/- mice, supporting the potential to alleviate non-seizure co-morbidities associated with Dravet Syndrome. The efficacy demonstrated in the 6Hz seizure model indicates target engagement and normalization of inhibitory activity in the brain through Na_V1.1 potentiation. With this unique profile, XPC-1418 represents a first-in-class mechanism for voltage-gated sodium channel potentiation, holding promise as a disease-modifying therapy for Dravet Syndrome.