RNA Innovation Seminar: Lori Isom, Chair, Department of Pharmacology

“Dancing to a Different Tune: TANGO Provides Hope for Dravet Syndrome”
Lori Isom, Ph.D.
Chair, Department of Pharmacology
Maurice H. Seevers Collegiate Professor of Pharmacology
Professor of Molecular and Integrative Physiology
Professor of Neurology, University of Michigan Medical School

In-person: BSRB, ABC seminar rooms / zoom link

Abstract: Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy characterized by high seizure frequency and severity, intellectual disability, and a high risk of sudden unexpected death in epilepsy (SUDEP). Most DS patients carry de novo variants in SCN1A leading to haploinsufficiency of the voltage-gated sodium channel a subunit Nav1.1. Scn1a +/-  DS mouse models recapitulate many patient phenotypes, including severe seizures and SUDEP. DS mice have reduced excitability of parvalbumin-positive (PV+) fast-spiking interneurons, leading to disinhibition. Targeted Augmentation of Nuclear Gene Output (TANGO) was developed by our collaborators at Stoke Therapeutics to increase protein expression in diseases of haploinsufficiency using antisense oligonucleotide (ASO) technology. TANGO targets naturally occurring, non-productive alternative splicing events to reduce non-productive mRNA and increase productive mRNA and protein of the target gene by upregulating the wild-type allele. This approach has provided a unique opportunity to develop novel therapeutics to treat DS. We showed previously that a single, intracerebroventricular (ICV) dose at postnatal day (P)2 of the ASO STK-001, generated using TANGO technology to prevent inclusion of a nonsense-mediated decay or poison exon in Scn1a, exon 20N, increased productive Scn1a transcript and Nav1.1 expression and reduced the incidence of electrographic seizures and SUDEP in a mouse model of DS (SCIENCE TRANSLATIONAL MEDICINE, 2020, Vol 12, Issue 558, DOI: 10.1126/scitranslmed.aaz6100). Interestingly, de novo variants in SCN1A exon 20N were shown by others to increase its inclusion, resulting in haploinsufficiency and DS pathology in patients and in a mouse model. Our preclinical work led to a series of on-going clinical trials for STK-001. Here, we investigated the mechanism of a surrogate ASO that also targets exon 20N, ST-1001, in DS mouse brain. We tested the effects of a single ICV injection of ST-1001 at P2 on the subsequent electrophysiological properties of cortical pyramidal and PV+ fast-spiking interneurons in Scn1a +/- DS and Scn1a +/+ wild-type littermate control mice at P21-25. We show that, in untreated DS mice, intrinsic action potential (AP) firing properties of cortical pyramidal neurons were unchanged compared to controls while AP firing properties of PV+ interneurons showed depolarization block. In addition, sodium current density was reduced in DS PV+ interneurons. The frequency, but not amplitude, of inhibitory post-synaptic currents recorded in DS cortical pyramidal neurons was also reduced, suggesting reduced GABA release from interneurons. Single-dose ST-1001 ASO administration restored excitability and sodium current density in PV+ DS interneurons as well as restored GABAergic signaling to cortical pyramidal neurons. This new work provides key mechanisms for further development of precision medicine approaches to treat patients with DS and related developmental and epileptic encephalopathies. Our next experimental plan will include testing ST-1001 in a newly developed CRISPR transgenic rabbit model of DS as well as in DS patient-derived induced pluripotent stem cell neurons.