The expanded CAG repeat in the huntingtin gene as target for therapeutic RNA modulation throughout the HD mouse brain

Abstract

The aim of these studies was to demonstrate the therapeutic capacity of an antisense oligonucleotide with the sequence (CUG)7 targeting the expanded CAG repeat in huntingtin (HTT) mRNA in vivo in the R6/2 N-terminal fragment and Q175 knock-in Huntington’s disease (HD) mouse models. In a first study, R6/2 mice received six weekly intracerebroventricular infusions with a low and high dose of (CUG)7 and were sacrificed 2 weeks later. A 15–60% reduction of both soluble and aggregated mutant HTT protein was observed in striatum, hippocampus and cortex of (CUG)7-treated mice. This correction at the molecular level resulted in an improvement of performance in multiple motor tasks, increased whole brain and cortical volume, reduced levels of the gliosis marker myo-inositol, increased levels of the neuronal integrity marker N-aceyl aspartate and increased mRNA levels of the striatal marker Darpp-32. These neuroanatomical and neurochemical changes, together with the improved motor performance, suggest that treatment with (CUG)7 ameliorates basal ganglia dysfunction. The HTT-lowering was confirmed by an independent study in Q175 mice using a similar (CUG)7 AON dosing regimen, further demonstrating a lasting reduction of mutant HTT protein in striatum, hippocampus and cortex for up to 18 weeks post last infusion along with an increase in motor activity. Based on these encouraging results, (CUG)7 may thus offer an interesting alternative HTT-lowering strategy for HD.

Huntingtin Lowering Strategies for Disease Modification in Huntington’s Disease

“…In addition, as shown in Table 1, allele-selective ASOs targeting single nucleotide polymorphisms in linkage to the CAG expansion have been developed (Skotte et al, 2014), and a clinical trial by Wave Life Sciences is already underway (Hersch et al, 2017). Biomarin also has an allele-selective ASO in pre-clinical development that directly targets the expanded CAG repeat (Datson et al, 2017).…”

Genetics, Mechanisms, and Therapeutic Progress in Polyglutamine Spinocerebellar Ataxias

“…Similar repeat-targeting AONs were tested in SCA7 cell lines, where ataxin-7 downregulation was achieved with varying efficiency based on the specific chemistry used [ 220 ]. To our knowledge, the CAG repeat-targeting AONs have not yet been tested in animal models of SCA, but positive results have been obtained where these types of AONs were injected in the brains of HD mice [ 251 ]. Specifically, CAG repeat-targeting AONs reduced mutant huntingtin (HTT) protein with 15 to 60% throughout the mouse brain, and corresponding improvements in motor tasks were reported [ 251 ].…”

Gene suppression approaches to neurodegeneration

“…One potential drawback of this strategy is that other polyQ-containing proteins may be affected, and the potency of CAG targeting therapies is not as great as for other approaches. BioMarin Pharmaceuticals have, however, very recently carried out a study showing that an ASO with sequence (CUG)7 successfully targeted the expanded CAG repeat in mutant Htt mRNA in two different mouse models of HD and that this led to phenotypic improvement [ 85 ].…”