Going nuclear: Improved antisense oligonucleotide activity through conjugation with a nuclear importer

Antisense oligonucleotides (ASOs) are a promising class of therapeutics designed to modulate gene expression. Both key mechanisms of action for ASOs operate in the nucleus: splice-switching ASOs modify pre-mRNA, processed in the nucleus, and mRNA-degrading ASOs require RNase H, an enzyme predominantly active in the nucleus. Therefore, to achieve maximal efficacy, ASOs require efficient nuclear delivery. Current ASO therapeutics shuttle in and out of the nucleus inefficiently. In this work, we have synthesised ASO conjugates for active nuclear import, by covalent conjugation with a potent small-molecule nuclear importer, (+)-JQ1. (+)-JQ1 is a well-characterised high-affinity binder for members of the BET bromodomain family of proteins and was recently shown to transport cytoplasmic proteins into the nucleus. Our (+)-JQ1-ASO conjugates outperformed their unmodified counterparts for both splice-switching and mRNA knockdown in the nucleus, at all concentrations tested. In particular, we improved the performance of Oblimersen, a BCL-2 ASO drug that failed phase-III clinical trials, showing that this therapeutic may merit re-evaluation. This work shows that the covalent modification of ASOs with a small-molecule nuclear importer can significantly improve target engagement and pave the way for more effective therapeutics.