Adenosine deaminase acting on RNA (ADAR)-mediated RNA editing has emerged as a powerful and precise technology for modifying RNA transcripts, enabling correction of disease-causing mutations without permanent changes to the genome. Recent advances in ADAR protein engineering, guide RNA design, and delivery methods have significantly improved editing efficiency and specificity, overcoming many initial limitations. These developments have expanded the therapeutic potential of ADAR-based editing across a range of conditions, including genetic disorders, cancer, metabolic diseases, and neurodegenerative disorders. Notably, several ADAR-based therapeutics have now entered early clinical trials, marking a critical milestone in translating this technology from bench to bedside. Moreover, its inherent programmability, reversibility, and transient nature make ADAR-mediated RNA editing a highly attractive platform for personalized medicine, enabling tailored interventions based on individual genetic profiles and disease contexts. This review provides a comprehensive comparison of recent innovative advancements in ADAR-based RNA editing technologies, their use in diverse contexts pertinent to human diseases, the key challenges that remain, and future directions for their therapeutic implementation.

Impaired angiogenesis is a common feature of several pathological conditions, including neuromuscular disorders. Such vascular defects not only contribute to disease progression but also may compromise the efficacy of systemically delivered therapies such as antisense oligonucleotides (ASOs) and adeno-associated virus vectors. Enhancing muscle vascularization is therefore an attractive strategy to improve both therapeutic delivery and tissue regeneration. Vascular endothelial growth factor A (VEGF-A) is the principal driver of angiogenesis, but its bioavailability is negatively regulated by VEGFR1/Flt-1, a high-affinity decoy receptor. Here, we investigated a splice-switching ASO (SSO) approach to downregulate Flt-1 expression in murine endothelial cells. We designed ASOs to induce skipping of an out-of-frame exon in the Flt1 transcript, triggering nonsense-mediated decay and reducing protein expression. Screening in C166 endothelial cells identified a lead SSO that efficiently skipped exon 5, resulting in robust Flt-1 downregulation, similar to levels achieved with a control siRNA. Functionally, Flt-1 knockdown enhanced endothelial cell proliferation, survival, and migration upon VEGF-A stimulation. These results provide proof-of-concept for targeting Flt-1 via exon skipping to promote angiogenesis, with potential applications in degenerative or ischemic contexts where vascularization is impaired.

In the fourth quarter of 2025, a press release announced the approval of the eighth small interfering RNA (siRNA)-based therapeutic. Redemplo (plozasiran), developed by Arrowhead Pharmaceuticals, is the third oligonucleotide-based medicine approved for the treatment of patients with familial chylomicronemia syndrome targeting apolipoprotein C-III. This approval represents the seventh approved siRNA drug based on GalNAc-mediated hepatocyte delivery and introduces the third distinct flavor of this delivery architecture to the clinic.

There is a current lack of harmonized regulatory guidance in evaluating the genotoxic potential of oligonucleotide-based therapeutics (ONTs). In particular, guidance has not established the circumstances under which it is acceptable to deviate from the standard test battery. In this study, we analyzed genotoxicity testing strategies and supporting rationales for 91 noncoding ONTs receiving European Scientific Advice between 2004 and 2024. While the standard test battery was performed for the majority of ONTs, reduced test approaches were proposed for 10 products. Furthermore, we examined both the positions of applicants and corresponding European Union (EU) regulatory opinions to identify critical considerations in evaluating genotoxicity. Our findings show that EU regulators see opportunities to deviate from the standard test battery for ONTs if sufficient evidence for class experience can be demonstrated. This was confirmed for several ONTs with well-characterized chemical modifications (ie, phosphorothioate, 2'-methoxyethyl, and 2'-Omethyl), making the standard battery redundant in these cases. Although all reported genotoxicity tests have been uniformly negative, uncertainty remains for future modifications. Ideally, what constitutes sufficient evidence for class experience should be defined in the upcoming International Council for Harmonisation guideline addressing the nonclinical safety evaluation of ONTs (ICH S13), which would allow regulators to accept reduced testing. Together with the industry sharing more knowledge and underlying data that support growing class experience, this development can promote a harmonized approach for future genotoxicity testing of noncoding ONTs.

Exon skipping antisense oligonucleotides (AONs) have been extensively studied as a promising method of treating Duchenne muscular dystrophy (DMD), yet the clinical efficacy of the conditionally approved AONs still remains low. Using phosphorothioated locked nucleic acid/2'-fluoro-RNA AONs, we aimed to increase AON efficiency by employing skeletal muscle-targeting conjugate molecules, cholesterol, and docosanoic acid to improve the biodistribution of the therapeutic. While conjugate molecules were able to induce high levels of skipping in an in vitro model, invivo studies in the hDMDdel52/mdx mouse model caused adverse symptomatic and systemic immune reactions, up to and including death, with little to no appreciable increase in exon skipping. Our study cautions against using these AON conjugates in an animal model due to severe toxicity.

Advances in backbone modifications are driving the development of nucleic acid therapeutics, yet there is still a need to establish compounds that avoid the potential dose-limiting toxicity of phosphorothioate internucleosidic linkages, particularly outside the central nervous system. We have developed a novel 7',5'-α-bc-DNA (abcDNA) scaffold, and here we benchmark the biophysical and invivo gene knockdown efficacy of gapmer antisense oligonucleotides (ASOs) containing abcDNA nucleotides. Melting curve analyses show gapmers with abcDNA bases in both wings maintain a good affinity for complementary RNA and demonstrate stable mismatch discrimination, in addition to a high degree of serum biostability. To assess invivo on-target activity and tolerability, mice were dosed systemically with abcDNA ASOs targeting Malat-1, with or without conjugation to palmitic acid. Multiple tissues were assessed for on-target knockdown efficiency by RT-PCR and in situ hybridization alongside biodistribution analysis by immunohistochemistry. abcDNA ASOs were well tolerated and performed at a comparable level to an equivalent 2'-O-methoxyethylribose gapmer. We also present the first invivo pharmacokinetic data generated using an enzyme-free nucleic acid nanorobotics method. Together, these data support the utility of abcDNA as a valuable addition to ASO technology that maintains a natural phosphodiester backbone, providing a combination of preferred biostability and on-target affinity with acceptable invivo tolerability.

In this study, we focused on N-1 impurities in antisense oligonucleotides. We evaluated their binding affinity to the therapeutic target RNA, which had the complementary sequence to the full-length N-mer desired product (DP), and their ability to recruit ribonuclease H (RNase H) using cell-free in vitro assays. The binding affinity of each N-1-mer to the target RNA was extremely low, with binding constants <1: 100 of that of the DP/RNA duplex. However, the degree of destabilization varied significantly depending on the position of the nucleotide defect within the N-1-mer, with differences of up to 5.1 kcal/mol (a 4,000-fold difference in binding constant). This weak binding capability to the target RNA suggests that the presence of the N-1-mer has little effect on DP activity. This study provides essential information for the dissemination of oligonucleotide therapeutics by providing a basis for considering the effect of N-1-mer impurities.

Pathogenic variants creating upstream open reading frames (uORFs) in the 5' untranslated region (5'UTR) of the ENG gene can disrupt translation from the main ORF and contribute to hereditary hemorrhagic telangiectasia (HHT). This is the case of the ENG c.-79C>T that introduces a uAUG shown to decrease endoglin expression and associates with HHT. Here, we investigated whether 2'-O-methyl (2'OMe) antisense oligonucleotides (ASOs) could restore protein levels by masking this aberrant uAUG or by targeting predicted secondary structures within the ENG 5'UTR. Several ASOs of varying lengths and backbone chemistries (full phosphodiester or full phosphorothioate) were designed to target the mutant region. Their effects were evaluated in HeLa cells transfected and in HUVECs transduced with wild-type or mutant ENG constructs. Transfection efficiency was verified by MALAT1 knockdown via qPCR, and endoglin protein levels were assessed by Western blot. Despite efficient ASO delivery and optimized experimental conditions, no reproducible increase in endoglin expression was observed upon ASO treatment. These findings highlight the limitations of steric-blocking ASOs targeting 5'UTR variants and underscore the need for deeper mechanistic understanding of uORF-mediated translational regulation.

Small interfering RNA (siRNA) therapeutics represent a transformative class of drugs, but their class-specific adverse events (CAE-siRNA) remain incompletely characterized. This study aimed to identify and quantify CAE-siRNA associated with U.S. Food and Drug Administration (FDA)-approved siRNA drugs (patisiran, givosiran, vutrisiran, inclisiran, and lumasiran) using real-world pharmacovigilance data, focusing on potential class-wide effects. A disproportionality analysis was conducted using the FDA Adverse Event Reporting System database (2014-2025Q2) accessed via the MY FAERS platform. The reporting odds ratio (ROR) with 95% confidence interval (CI) was calculated, with signals defined by a lower CI >1 and ≥3 cases. Sensitivity analyses included indication-matched populations (IMPs) and exclusion of concomitant medications. Causality was assessed using Bradford Hill criteria. Among 6200 siRNA-treated patients, 45 CAE-siRNA spanning 10 system organ classes were identified. Pain and pain in extremity, fatigue, and gastrointestinal disorders were the most frequently reported. Notably, patisiran was associated with an elevated risk of back pain (ROR: 2.28, 95% CI: 1.84-2.83), whereas givosiran exhibited significant signals for stress (ROR: 5.29, 95% CI: 3.64-7.70) and weight loss (ROR: 2.35, 95% CI: 1.74-3.16). Of particular concern, inclisiran demonstrated strong hepatic toxicity signals (ROR ranging from 9.11 to 86.06) along with discomfort (ROR: 3.60, 95% CI: 1.34-9.65). Sensitivity analyses confirmed robustness across subgroups. Furthermore, causality assessment supported a likely association between the hepatic toxicity and inclisiran. This study identified clinically relevant CAE-siRNA, particularly hepatic toxicity for inclisiran, supporting enhanced monitoring. While disproportionality analyses are hypothesis generating, these findings underscore the need for targeted pharmacovigilance to optimize the safety of this promising drug class.