AAV9-mediated targeting of natural antisense transcript as a novel treatment for Dravet Syndrome

Dravet syndrome (DS) is a severe childhood onset developmental and epileptic encephalopathy which leads to life-long disability. Symptoms usually manifest in the first year of life and include prolonged severe seizures, developmental delay and severe intellectual disability. DS patients have an increased mortality rate, including sudden unexpected death in epilepsy (SUDEP). Approximately 90% of patients carry a heterozygous loss-of-function mutation in the SCN1A gene, which encodes a voltage-gated sodium ion channel, Na _V 1.1. The Na _V 1.1 channel is expressed in the brain and at a lower level, in the heart. Previous studies have identified a long non-coding RNA (lncRNA) which specifically downregulates SCN1A gene expression. This natural antisense transcript (NAT) can be modulated by AntagoNATs, small synthetic oligonucleotides developed to inhibit NAT function. In a DS mouse model, AntagoNATs were shown to modulate Scn1a expression by targeting the Scn1a NAT, improving seizure frequency after repeated administration. Here, we have developed novel AntagoNATs and incorporated these into a clinically relevant adeno-associated virus serotype 9 (AAV9) gene therapy vector, to test in a DS mouse model ( Scn1a ^+/- ) and provide a one-off treatment approach.

Eighteen AntagoNATs were tested in vitro ; from the best performing candidates, we selected two AntagoNAT sequences (K & H) for in vivo testing as they had the highest homology (90%) to human SCN1A NAT. We administered both vectors to newborn Scn1a ^+/- mice via intracerebroventricular (ICV) and intravenous (IV) injection to target the brain and heart. AAV9-AntagoNAT-H significantly increased survival, decreased febrile seizures and reduced spontaneous seizure frequency compared to the PBS control group. When administered at P14 by ICV and IV injection, AAV9-AntagoNAT-H increased survival. In this proof-of-concept study, we have demonstrated for the first time the delivery of AntagoNAT technology via an AAV9 vector and thus offering the possibility of a one-time treatment for DS patients.