Development of an oligonucleotide therapeutic for Dravet syndrome - Project Summary Dravet syndrome (DS) is a severe epileptic encephalopathy manifesting in the first year of life, characterized by febrile seizures, intellectual disability, and high risk of sudden unexpected death in epilepsy (SUDEP). Most DS patients lack one functional copy of SCN1A, the gene encoding the voltage-gated sodium channel NaV1.1. This monogenic nature in DS suggests SCN1A upregulation or replacement as obvious treatment strategies; yet despite considerable efforts, DS still lacks an FDA-approved disease-modifying drug. Here we propose to develop a new therapeutic target strategy for SCN1A upregulation, embodied by a new antisense oligonucleotide (ASO) that elevates NaV1.1 protein expression. This ASO blocks translation initiation of an upstream open reading frame (uORF), thereby directly increasing NaV1.1 protein production and elevating the steady state level of NaV1.1. Importantly, this ASO targets a different mechanism than current ASOs under testing that modulate a poison exon or an antisense regulatory gene. In side-by-side matched-dose comparisons to a poison exon-blocking ASO, this ASO provides superior rescue of mortality and heat-induced seizures in a DS mouse model. In this proposed project, we will characterize the pharmacokinetics and pharmacodynamics of this promising new DS-targeting ASO and closely related derivatives. The proposal is divided into two phases, R61 and R33. In the two-year R61 phase, we will establish our lead ASO compound. Activities in the R61 phase include: optimization of ASOs by varying the position along the transcript and the ASO chemistry, establishment of methods for biodistribution, description of ASO biodistribution and half-life, demonstration of Nav1.1 upregulation in mouse brains and human neurons, identification of the optimal dose for Nav1.1 upregulation, and last, generation and validation a large-scale batch of the lead ASO. In the R33 phase, we will apply our lead ASO to demonstrate efficacy and safety. R33 activities will include: evaluation of lead ASO in two DS animal models after administration in neonatal mice to test for disease prevention, evaluation of efficacy after administration into one animal model at P28 to test disease reversibility, and evaluation of the lead ASO biodistribution and safety. The ultimate goal of this proposal is to generate an industry-leading ASO that upregulates NaV1.1 through SCN1A uORF blockade and confers strong and safe rescue in multiple mouse models of DS. Furthermore, we hope this grant will help create a direct path to the clinic for the lead ASO either through the NIH Blueprint Neurotherapeutics Network-Biologic “Drug Discovery and Development for Disorders of the Nervous System” grant mechanism, or though an industrial partnership.
