NA interference (RNAi) therapeutics use an endogenous mechanism whereby short interfering RNAs (siRNAs) direct the RNA-induced silencing complex (RISC) to sequence matched target transcripts for knockdown 1 . Both lipid nanoparticles and N-acetylgalactosamine (GalNAc) conjugates are clinically validated and approved delivery strategies for liver targets [2][3][4][5][6][7][8] . Building on nearly 2 decades of siRNA design and chemistry optimization [9][10][11][12] , we demonstrate here that, with suitable delivery solutions, the RNAi pathway can be harnessed in extrahepatic tissues, such as the central nervous system (CNS), eye and lung. Multiple CNS diseases, representing some of the highest unmet medical needs and greatest therapeutic challenges, have been associated with dominant gain-of-function mutations, making them suitable candidates for an RNAi-based silencing approach. As such, chemically modified siRNAs have demonstrated potent and sustained silencing in rodents and non-human primates (NHPs); however, using an invasive intracerebroventricular (ICV) administration approach 13 that is not suitable for repeated dosing in humans. Furthermore, technologies enabling siRNA delivery across the blood-brain barrier following a less challenging systemic administration are similarly being explored [14][15][16][17] , which are, however, still in early stages of discovery. In the eye, intravitreal (IVT) dosing of siRNAs has been evaluated in late-stage clinical studies, with few safety concerns, but did not advance further due to lack of efficacy 18 . Recently, the Coronavirus Disease 2019 (COVID-19) pandemic has highlighted the importance of optimizing siRNA delivery to the lung for the treatment of emergent viral respiratory diseases. Although earlier programs have already shown potential clinical benefits of siRNA-based therapeutics in the lung 19 , 2′-O-hexadecyl (C16) conjugates demonstrate enhanced delivery and siRNA uptake into the alveolar and bronchiolar epithelium. Taken together, this work highlights that the combination of a C16 lipophilic modification with our fully chemically modified, metabolically stable siRNAs achieves efficient delivery to the CNS, eye and lung, resulting in a robust and durable gene silencing in rodents and NHPs, with a favorable safety profile. We think that these advances have the potential to generate multiple candidates for investigating clinical safety and efficacy in humans. ResultsOptimization of the siRNA conjugate design. Lipophilic moieties represent one of the earliest approaches to improve cellular uptake and delivery of antisense oligonucleotides (ASOs) and siRNAs to the liver and various other organ systems 20 , including the CNS [21][22][23] . We reasoned that, by carefully optimizing the lipophilicity of chemically modified siRNAs, we could enhance intracellular delivery without compromising broad biodistribution, potency and safety. We used the 2′ position of the ribose sugar backbone to introduce
In Huntington’s disease (HD), the mutant Huntingtin (mHTT) is postulated to mediate template-based aggregation that can propagate across cells. It has been difficult to quantitatively detect such pathological seeding activities in patient biosamples, e.g. cerebrospinal fluids (CSF), and study their correlation with the disease manifestation. Here we developed a cell line expressing a domain-engineered mHTT-exon 1 reporter, which showed remarkably high sensitivity and specificity in detecting mHTT seeding species in HD patient biosamples. We showed that the seeding-competent mHTT species in HD CSF are significantly elevated upon disease onset and with the progression of neuropathological grades. Mechanistically, we showed that mHTT seeding activities in patient CSF could be ameliorated by the overexpression of chaperone DNAJB6 and by antibodies against the polyproline domain of mHTT. Together, our study developed a selective and scalable cell-based tool to investigate mHTT seeding activities in HD CSF, and demonstrated that the CSF mHTT seeding species are significantly associated with certain disease states. This seeding activity can be ameliorated by targeting specific domain or proteostatic pathway of mHTT, providing novel insights into such pathological activities.
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