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In this phase 3 trial, among children with later-onset spinal muscular atrophy, those who received nusinersen had improvement in motor-function scores and those who underwent a sham procedure did not.

The molecular mechanisms of toxicity of chemically modified phosphorothioate antisense oligonucleotides (PS-ASOs) are not fully understood. Here, we report that toxic gapmer PS-ASOs containing modifications such as constrained ethyl (cEt), locked nucleic acid (LNA) and 2′-O-methoxyethyl (2′-MOE) bind many cellular proteins with high avidity, altering their function, localization and stability. We show that RNase H1–dependent delocalization of paraspeckle proteins to nucleoli is an early event in PS-ASO toxicity, followed by nucleolar stress, p53 activation and apoptotic cell death. Introduction of a single 2′-O-methyl (2′-OMe) modification at gap position 2 reduced protein-binding, substantially decreasing hepatotoxicity and improving the therapeutic index with minimal impairment of antisense activity. We validated the ability of this modification to generally mitigate PS-ASO toxicity with more than 300 sequences. Our findings will guide the design of PS-ASOs with optimal therapeutic profiles.Chemical modification of PS-ASO therapeutics reduces binding to cellular proteins and decreases toxic side-effects.

In this phase 3 trial, among infants with spinal muscular atrophy, those who received nusinersen were more likely to achieve major motor milestones and less likely to need permanent assisted ventilation than those who underwent a sham procedure.

The increasing number of approved nucleic acid therapeutics demonstrates the potential to treat diseases by targeting their genetic blueprints in vivo. Conventional treatments generally induce therapeutic effects that are transient because they target proteins rather than underlying causes. In contrast, nucleic acid therapeutics can achieve long-lasting or even curative effects via gene inhibition, addition, replacement or editing. Their clinical translation, however, depends on delivery technologies that improve stability, facilitate internalization and increase target affinity. Here, we review four platform technologies that have enabled the clinical translation of nucleic acid therapeutics: antisense oligonucleotides, ligand-modified small interfering RNA conjugates, lipid nanoparticles and adeno-associated virus vectors. For each platform, we discuss the current state-of-the-art clinical approaches, explain the rationale behind its development, highlight technological aspects that facilitated clinical translation and provide an example of a clinically relevant genetic drug. In addition, we discuss how these technologies enable the development of cutting-edge genetic drugs, such as tissue-specific nucleic acid bioconjugates, messenger RNA and gene-editing therapeutics.This Review provides an overview of four platform technologies that are currently used in the clinic for delivery of nucleic acid therapeutics, describing their properties, discussing technical advancements that led to clinical approval, and highlighting examples of approved genetic drugs that make use of these technologies.

Despite the great success of anti-tumour necrosis factor-based therapies, the treatment of Crohn’s disease (CD) and ulcerative colitis (UC) still remains a challenge for clinicians, as these drugs are not effective in all patients, their efficacy may wane with time, and their use can increase the risk of adverse events and be associated with the development of new immune-mediated diseases. Therefore, new therapeutic targets are currently being investigated both in pre-clinical studies and in clinical trials. Among the technologies used to build new therapeutic compounds, the antisense oligonucleotide (ASO) approach is slowly gaining space in the field of inflammatory bowel diseases (IBDs), and three ASOs have been investigated in clinical trials. Systemic administration of alicaforsen targeting intercellular adhesion molecule-1, a protein involved in the recruitment of leukocytes to inflamed intestine, was not effective in CD, even though the same compound was of benefit when given as an enema to UC patients. DIMS0150, targeting nuclear factor (NF) κB-p65, a transcription factor that promotes pro-inflammatory responses, was very promising in pre-clinical studies and is currently being tested in clinical trials. Oral mongersen, targeting Smad7, an intracellular protein that inhibits transforming growth factor (TGF)-β1 activity, was safe and well tolerated by CD patients, and the results of a phase II clinical trial showed the efficacy of the drug in inducing clinical remission in patients with active disease. In this leading article, we review the rationale and the clinical data available regarding these three agents, and we discuss the challenge of using ASOs in IBD.

In a phase 2b trial involving patients with hypertriglyceridemia, the use of olezarsen (which targets APOC3 mRNA) for 6 months reduced triglyceride levels by approximately 50% as compared with placebo.

Angiopoietin-like 3 (ANGPTL3) inhibits endothelial lipase and lipoprotein lipase. Injection of antisense oligonucleotides targeting ANGPTL3 messenger RNA effects a reduction of atherogenic lipoproteins in humans and mice and a slowing of progression of atherosclerosis in mice.

Spinal muscular atrophy (SMA) is a rare autosomal recessive disorder characterized by muscle atrophy and weakness resulting from motor neuron degeneration in the spinal cord and brainstem. It is most commonly caused by insufficient levels of survival motor neuron (SMN) protein (which is critical for motor neuron maintenance) secondary to deletions or mutations in the SMN1 gene. Nusinersen (SPINRAZA™) is a modified antisense oligonucleotide that binds to a specific sequence in the intron, downstream of exon 7 on the pre-messenger ribonucleic acid (pre-mRNA) of the SMN2 gene. This modulates the splicing of the SMN2 mRNA transcript to include exon 7, thereby increasing the production of full-length SMN protein. Nusinersen is approved in the USA for intrathecal use in paediatric and adult patients with SMA. Regulatory assessments for nusinersen as a treatment for SMA are underway in the EU and several other countries. This article summarizes the milestones in the development of nusinersen leading to this first approval for SMA in paediatric and adult patients.

Phosphorothioates have found their usefulness in the general area of oligonucleotide therapeutic applications. Initially this modification was introduced into the antisense methodology because of the nuclease resistance of the phosphorothioate linkage in comparison with that of the phosphate linkage. However, as experimental data accumulated, it was detected that this chemical modification also facilitates cellular uptake and bioavailibity in vivo. Thus, today the majority of therapeutic oligonucleotides contain this modification. This review will discuss the historical development of this modification and present some of its chemical properties where they differ from those of the phosphate group. The antisense application will be discussed in the original context with cleavage of the target mRNA, but other target RNAs such as microRNAs and long noncoding RNAs will also be covered. It continues with applications where the target RNA should not be cleaved. A brief presentation of decoy oligonucleotides will be included, as well as some miscellaneous applications. Cellular uptake is a crucial step for oligonucleotides to reach their target and will be briefly reviewed. Lastly, a most surprising recent observation is the presence of phosphorothioate groups in bacterial DNA where functions still remain to be fully determined.

Recent advances in drug development have seen numerous successful clinical translations using synthetic antisense oligonucleotides (ASOs). However, major obstacles, such as challenging large-scale production, toxicity, localization of oligonucleotides in specific cellular compartments or tissues, and the high cost of treatment, need to be addressed. Thiomorpholino oligonucleotides (TMOs) are a recently developed novel nucleic acid analog that may potentially address these issues. TMOs are composed of a morpholino nucleoside joined by thiophosphoramidate internucleotide linkages. Unlike phosphorodiamidate morpholino oligomers (PMOs) that are currently used in various splice-switching ASO drugs, TMOs can be synthesized using solid-phase oligonucleotide synthesis methodologies. In this study, we synthesized various TMOs and evaluated their efficacy to induce exon skipping in a Duchenne muscular dystrophy (DMD) in vitro model using H2K mdx mouse myotubes. Our experiments demonstrated that TMOs can efficiently internalize and induce excellent exon 23 skipping potency compared with a conventional PMO control and other widely used nucleotide analogs, such as 2’-O-methyl and 2’-O-methoxyethyl ASOs. Notably, TMOs performed well at low concentrations (5−20 nM). Therefore, the dosages can be minimized, which may improve the drug safety profile. Based on the present study, we propose that TMOs represent a new, promising class of nucleic acid analogs for future oligonucleotide therapeutic development.