Chronic Toxicity Assessment of 2′-O-Methoxyethyl Antisense Oligonucleotides in Mice

Advances in antisense oligonucleotide (ASO) chemistry and screening have enabled the design and selection of molecules that are optimized for a particular therapeutic application in terms of both potency and tolerability. The most-well studied of the chemically modified ASOs are single-stranded antisense inhibitors with phosphorothioate backbones and 2-O-methoxyethyl modifications (2-MOE ASO). The 2-MOE chemical modification in the design of the ASO has conferred increased hybridization affinity, increased stability, and/or enhanced tissue residence time, resulting in better potency and pharmacokinetics. Compound screening and selection are also important in optimizing the tolerability of intended therapeutic antisense inhibitors. In this study, we report the chronic toxicity of multiple 2-MOE ASOs in mice for several representative compounds that have progressed to later phases of clinical development. The results show that these 2-MOE ASOs selected for development have consistent behavior between sequences, have tolerability profiles suitable for chronic administration, and exhibit a relative lack of progression of findings observed in subchronic studies in mice.