Durable suppression of seizures in a preclinical model of KCNT1 genetic epilepsy with divalent small interfering RNA

Abstract Objective Gain‐of‐function variants in the KCNT1 gene, which encodes a sodium‐activated potassium ion channel, drive severe early onset developmental epileptic encephalopathies including epilepsy of infancy with migrating focal seizures and sleep‐related hypermotor epilepsy. No therapy provides more than sporadic or incremental improvement. Here, we report suppression of seizures in a genetic mouse model of KCNT1 epilepsy by reducing Kcnt1 transcript with divalent small interfering RNA (siRNA), an emerging variant of oligonucleotide technology developed for the central nervous system. Methods The ATL‐201 molecule is two identical synthetic double‐stranded siRNAs, covalently linked, with 100% nucleotide base pair match to sequence present in both human KCNT1 and mouse Kcnt1 that does not contain any known pathogenic variant. ATL‐201 activity was tested in cortical neurons cultured from wild‐type mice and in mice homozygous for Kcnt1‐Y777H , the mouse ortholog to the human pathogenic KCNT1‐Y796H missense variant. Seizures and nest‐building behavior were measured in freely behaving Kcnt1‐Y777H mice. The number and duration of seizures were measured by electrocorticography in mice dosed with ATL‐201 or phosphate‐buffered saline in a 6‐month durability study and in a 2‐month dose–efficacy study. Results In vitro, ATL‐201 reduced KCNT1 transcript from whole‐cell lysate and eliminated potassium currents from KCNT1 channels in heterologous expression. ATL‐201 also eliminated sodium‐activated potassium currents recorded from individual cortical neurons. In vivo, ATL‐201 suppressed seizures in Kcnt1‐Y777H homozygous mice in a dose‐dependent manner with near‐complete suppression from 2 weeks to at least 4 months. Kcnt1‐Y777H mice had defects in nest building, whereas in ATL‐201‐treated mice nest building was equivalent to wild‐type mice. Significance Patients with KCNT1‐driven epilepsy experience up to hundreds of seizures per day and have severe impairment in cognitive, motor, and language development and high mortality. The dose‐dependent efficacy and long durability of ATL‐201 in mice show promise for ATL‐201 as a disease‐modifying treatment of KCNT1 epilepsy.