Improvements in the Tolerability Profile of 2'-O-Methoxyethyl Chimeric Antisense Oligonucleotides in Parallel with Advances in Design, Screening, and Other Methods

Nucleic acid therapeutics as differentiation agents for myeloid leukemias

Differentiation therapy has proven to be a success story for patients with acute promyelocytic leukemia. However, the remaining subtypes of acute myeloid leukemia (AML) are treated with cytotoxic chemotherapies that have limited efficacy and a high likelihood of resistance. As differentiation arrest is a hallmark of AML, there is increased interest in developing differentiation-inducing agents to enhance disease-free survival. Here, we provide a comprehensive review of current reports and future avenues of nucleic acid therapeutics for AML, focusing on the use of targeted nucleic acid drugs to promote differentiation. Specifically, we compare and discuss the precision of small interfering RNA, small activating RNA, antisense oligonucleotides, and aptamers to modulate gene expression patterns that drive leukemic cell differentiation. We delve into preclinical and clinical studies that demonstrate the efficacy of nucleic acid-based differentiation therapies to induce leukemic cell maturation and reduce disease burden. By directly influencing the expression of key genes involved in myeloid maturation, nucleic acid therapeutics hold the potential to induce the differentiation of leukemic cells towards a more mature and less aggressive phenotype. Furthermore, we discuss the most critical challenges associated with developing nucleic acid therapeutics for myeloid malignancies. By introducing the progress in the field and identifying future opportunities, we aim to highlight the power of nucleic acid therapeutics in reshaping the landscape of myeloid leukemia treatment.

Safety and Tolerability of GalNAc3-Conjugated Antisense Drugs Compared to the Same-Sequence 2'-O-Methoxyethyl-Modified Antisense Drugs: Results from an Integrated Assessment of Phase 1 Clinical Trial Data

The triantennary N-acetylgalactosamine (GalNAc3) cluster has demonstrated the utility of receptor-mediated uptake of ligand-conjugated antisense drugs targeting RNA expressed by hepatocytes. GalNAc3-conjugated 2'-O-methoxyethyl (2'MOE) modified antisense oligonucleotides (ASOs) have demonstrated a higher potency than the unconjugated form to support lower doses for an equivalent pharmacological effect. We utilized the Ionis integrated safety database to compare four GalNAc3-conjugated and four same-sequence unconjugated 2'MOE ASOs. This assessment evaluated data from eight randomized placebo-controlled dose-ranging phase 1 studies involving 195 healthy volunteers (79 GalNAc3 ASO, 24 placebo; 71 ASO, 21 placebo). No safety signals were identified by the incidence of abnormal threshold values in clinical laboratory tests for either ASO group. However, there was a significant increase in mean alanine transaminase levels compared with placebo in the upper dose range of the unconjugated 2'MOE ASO group. The mean percentage of subcutaneous injections leading to local cutaneous reaction was 30-fold lower in the GalNAc3-conjugated ASO group compared with the unconjugated ASO group (0.9% vs. 28.6%), with no incidence of flu-like reactions (0.0% vs. 0.7%). Three subjects (4.2%) in the unconjugated ASO group discontinued dosing. An improvement in the overall safety and tolerability profile of GalNAc3-conjugated 2'MOE ASOs is evident in this comparison of short-term clinical data in healthy volunteers.

Integrated Assessment of Phase 2 Data on GalNAc3-Conjugated 2'-O-Methoxyethyl-Modified Antisense Oligonucleotides

Receptor-mediated delivery of an antisense oligonucleotide (ASO) using the ligand-conjugated antisense technology is establishing a new benchmark for antisense therapeutics. The triantennary N-acetylgalactosamine (GalNAc3) cluster is the first conjugated ligand to yield a marked increase in ASO potency for RNA targets expressed by hepatocytes, compared to the unconjugated form. In this study, we present an integrated safety assessment of data available from randomized, placebo-controlled, phase 2 studies for six GalNAc3-conjugated 2'-O-methoxyethyl (2'MOE)-modified ASOs. The total study population included 642 participants (130 placebo; 512 ASO) with up to 1 year of exposure. The primary measures were the incidence of signals from standardized laboratory tests and the mean test results over time. The GalNAc3-conjugated ASOs were well tolerated with no class effect identified across all doses tested compared to placebo. These results extend prior observations from phase 1 studies, now with treatment up to 1 year.

Recent Progress and Challenges in the Development of Antisense Therapies for Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is a dominant genetic disease in which the expansion of long CTG trinucleotides in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene results in toxic RNA gain-of-function and gene mis-splicing affecting mainly the muscles, the heart, and the brain. The CUG-expanded transcripts are a suitable target for the development of antisense oligonucleotide (ASO) therapies. Various chemical modifications of the sugar-phosphate backbone have been reported to significantly enhance the affinity of ASOs for RNA and their resistance to nucleases, making it possible to reverse DM1-like symptoms following systemic administration in different transgenic mouse models. However, specific tissue delivery remains to be improved to achieve significant clinical outcomes in humans. Several strategies, including ASO conjugation to cell-penetrating peptides, fatty acids, or monoclonal antibodies, have recently been shown to improve potency in muscle and cardiac tissues in mice. Moreover, intrathecal administration of ASOs may be an advantageous complementary administration route to bypass the blood-brain barrier and correct defects of the central nervous system in DM1. This review describes the evolution of the chemical design of antisense oligonucleotides targeting CUG-expanded mRNAs and how recent advances in the field may be game-changing by forwarding laboratory findings into clinical research and treatments for DM1 and other microsatellite diseases.

Natural antisense transcripts as drug targets

The recent discovery of vast non-coding RNA-based regulatory networks that can be easily modulated by nucleic acid-based drugs has opened numerous new therapeutic possibilities. Long non-coding RNA, and natural antisense transcripts (NATs) in particular, play a significant role in networks that involve a wide variety of disease-relevant biological mechanisms such as transcription, splicing, translation, mRNA degradation and others. Currently, significant efforts are dedicated to harnessing these newly emerging NAT-mediated biological mechanisms for therapeutic purposes. This review will highlight the recent clinical and pre-clinical developments in this field and survey the advances in nucleic acid-based drug technologies that make these developments possible.

Therapeutic Strategies in Huntington’s Disease: From Genetic Defect to Gene Therapy

Despite the identification of an expanded CAG repeat on exon 1 of the huntingtin gene located on chromosome 1 as the genetic defect causing Huntington’s disease almost 30 years ago, currently approved therapies provide only limited symptomatic relief and do not influence the age of onset or disease progression rate. Research has identified various intricate pathogenic cascades which lead to neuronal degeneration, but therapies interfering with these mechanisms have been marked by many failures and remain to be validated. Exciting new opportunities are opened by the emerging techniques which target the mutant protein DNA and RNA, allowing for “gene editing”. Although some issues relating to “off-target” effects or immune-mediated side effects need to be solved, these strategies, combined with stem cell therapies and more traditional approaches targeting specific pathogenic cascades, such as excitotoxicity and bioavailability of neurotrophic factors, could lead to significant improvement of the outcomes of treated Huntington’s disease patients.