Abstracts

Rationale: Loss-of-function variants of SCN1A cause Dravet Syndrome (SMEI or EIEE6) and generalized epilepsy with febrile seizures plus (GEFS+), by decreasing Na_V1.1 expression or conductance in inhibitory interneurons. Studies of these and other channelopathies in mice reveal that Na_V1.1 is the dominant channel in inhibitory circuits while Na_V1.6 and Na_V1.2 are the dominant channels in excitatory pyramidal neurons. The loss of Na_V1.1 function results in hypo-excitability of inhibitory networks and subsequent hyperexcitability of excitatory networks leading to epilepsy and cognitive/motor developmental problems. A small molecule precision medicine therapy for Dravet Syndrome would ideally upregulate Na_V1.1 activity specifically without impacting other neuronal conductances or proteins. We have identified potent, isoform-selective, brain penetrant small molecule potentiators of Na_V1.1 channels that allow oral dosing and titration of interneuron activity. Such activators have the potential to directly address the underlying etiology of Dravet Syndrome with the potential to provide a safe and effective pharmacotherapy.

Methods: Automated patch clamp electrophysiology was used to screen and evaluate the potency, and selectivity of different compounds. Compounds were also evaluated electrophysiologically in brain slices from Scn1a heterozygous null mice (Scn1a^+/-) to assess the effects on interneuron activity and the inhibition/excitation balance. The compounds were then evaluated for efficacy through oral dosing in Scn1a^+/- mice in a modified 6Hz seizure assay.

Results: Novel, potent small molecules with favorable CNS drug properties have been developed that selectively potentiate Na_V1.1 channels over Na_V1.2, 1.6 and 1.5. In vitro electrophysiological characterization demonstrates these agents selectively destabilize the inactivated state of the Na_V1.1 channel. Ex vivo brain slices from Scn1a^+/- mice compound increased the maximum firing rate of fast spiking cortical PV+ interneurons and normalized the imbalance in spontaneous excitatory and inhibitory synaptic activity. In vivo, these compounds suppress seizures in Scn1a^+/- mice in a modified 6 Hz seizure model.

Conclusions: Selective Na_V1.1 potentiators restore the capability of inhibitory neurons to fire action potentials at high frequency and rebalance excitation in brain slices from Scn1a^+/- mice. Efficacy was confirmed in an Scn1a^+/- mouse seizure model suggesting a small molecule pharmaceutical with this profile could enable reversal of the fundamental neuronal imbalance in Dravet Syndrome and may have utility in other neurologic indications where interneuron function is impaired. This profile provides a new, mechanistically differentiated, class of voltage-gated sodium channel potentiators with the potential to provide a disease modifying therapy for Dravet Syndrome.

Funding: Please list any funding that was received in support of this abstract.: N/A.