Antisense oligonucleotide therapy for SCN2A gain-of-function epilepsy

Abstract

The clinical spectrum associated with SCN2A de novo mutations (DNMs) continues to expand and includes autism spectrum disorder with or without seizures, in addition to early and late seizure onset developmental and epileptic encephalopathies (DEEs). Recent biophysical studies on SCN2A variants suggest that the majority of early seizure onset DEE DNMs cause gain of function. Gain of function in SCN2A, the principal sodium channel of excitatory pyramidal neurons, would result in heightened neuronal activity and is likely to underlie the pathology seen in early seizure onset DEE patients. Supratherapeutic dosing of the non-selective sodium channel blocker phenytoin, is effective in controlling seizures in these patients but does not impact neurodevelopment, raising the idea that more profound and specific reduction in SCN2A function could significantly improve clinical outcome. To test the potential therapeutic benefit of reducing SCN2A in early seizure onset DEE we centrally administered an antisense oligonucleotide (ASO) targeting mouse Scn2a (Scn2a ASO) to a mouse model of human SCN2A early seizure onset DEE. Mice were genetically engineered to harbour the human equivalent SCN2A p.R1882Q mutation (Q/+), one of the most recurrent mutations in early seizure onset DEE. Q/+ mice presented with spontaneous seizures at postnatal day (P) 1 and did not survive beyond P30. Intracerebroventricular Scn2a ASO administration into Q/+ mice between P1-2 (that reduced Scn2a mRNA levels by 50%) significantly extended lifespan and markedly reduced spontaneous seizures occurrence. Across a range of cognitive and motor behavioural tests, Scn2a ASO treated Q/+ mice were largely indistinguishable from wildtype (+/+) mice. Further improvements in survival and behaviour were seen by adjustment of dosing regimens during development. Scn2a ASO efficacy was also evident at the cellular level. Whole cell patch clamp recording showed that Scn2a ASO administration reversed changes in neuronal excitability in layer 2/3 pyramidal neurons of Q/+ mice to levels seen in +/+ mice. Safety was assessed in +/+ mice and showed a developmental stage dependent tolerability and a favourable therapeutic index. This study suggests that a human SCN2A gapmer ASO could profoundly and safely impact early seizure onset DEE patients and heralds a new era of precision therapy in neurodevelopmental disorders.

The atlas of RNase H antisense oligonucleotide distribution and activity in the CNS of rodents and non-human primates following central administration

“…It is important to note that healthy, wild-type animals were used in the studies presented herein. Theoretically, a disease condition could affect the activity and distribution of ASOs, but we have not observed decreased ASO activity in a variety of neurodegenerative and neurodevelopmental disease models ( 11 , 16 , 35 , 43 ). However, we recommend that each disease model should be evaluated for activity and tolerability of ASOs independently.…”

“…The Malat1 ASO is the standard 5–10–5 MOE-gapmer design that is frequently used in preclinical research ( 8 , 10 , 12–14 , 16–18 ) as well as in ongoing clinical trials ( 19 , 20 ). Other studies using similar ASO chemistries have also shown broad ASO distribution in mice and NHP ( 8 , 24 , 35 ). The dose of Malat1 ASO used in NHPs herein is comparable to the doses used for human ASO drug candidates when tested in NHPs or in experimental NHP-specific compounds shown reduce target RNA ( 20 , 36 , 37 ).…”

“…The mechanism governing this, be it differences in cellular uptake, trafficking or RNase H1 activity for example, requires further investigation. It is important to note, however, that despite lower sensitivity of neurons compared to glia, ASOs do efficiently knock down targets specifically expressed in neurons ( 35 ). More work is required to fully characterize the sensitivity of the major CNS cell types and subtypes to ASOs.…”

Paradoxical hyperexcitability from NaV1.2 sodium channel loss in neocortical pyramidal cells

“…Similar EEG patterns have been observed with conditional heterozygous expression of Scn2a in excitatory, but not inhibitory, neocortical neurons (Ogiwara et al, 2018). However, changes in action potential (AP) output, a feature common to many models of Na V -channelopathy-mediated epilepsy (Goff and Goldberg, 2019;Li et al, 2020;Lopez-Santiago et al, 2017;Martin et al, 2010;Tai et al, 2014), have not been observed in mature Scn2a +/À pyramidal cells (Shin et al, 2019;Spratt et al, 2019).…”

Paradoxical hyperexcitability from NaV1.2 sodium channel loss in neocortical pyramidal cells

“…Similar EEG patterns have been observed in mice with conditional heterozygous expression of Scn2a in excitatory, but not inhibitory neocortical neurons (Ogiwara et al, 2018). However, changes in action potential (AP) output, a feature common to many models of Na V -channelopathy-mediated epilepsy (Goff and Goldberg, 2019; Li et al, 2020; Lopez-Santiago et al, 2017; Martin et al, 2010; Tai et al, 2014), have not been observed in mature Scn2a +/- pyramidal cells (Shin et al, 2019; Spratt et al, 2019).…”