Superior Silencing by 2 ',4 '-BNA(NC)-Based Short Antisense Oligonucleotides Compared to 2 ',4 '-BNA/LNA-Based Apolipoprotein B Antisense Inhibitors

The duplex stability with target mRNA and the gene silencing potential of a novel bridged nucleic acid analogue are described. The analogue, 2 ',4 '-BNA(NC) antisense oligonucleotides (AONs) ranging from 10-to 20-nt-long, targeted apolipoprotein B. 2 ',4 '-BNA(NC) was directly compared to its conventional bridged (or locked) nucleic acid (2 ',4 '-BNA/LNA)-based counterparts. Melting temperatures of duplexes formed between 2 ',4 '-BNA(NC)-based antisense oligonucleotides and the target mRNA surpassed those of 2 ',4 '-BNA/LNA-based counterparts at all lengths. An in vitro transfection study revealed that when compared to the identical length 2 ',4 '-BNA/LNA-based counterpart, the corresponding 2 ',4 '-BNA(NC)-based antisense oligonucleotide showed significantly stronger inhibitory activity. This inhibitory activity was more pronounced in shorter (13-, 14-, and 16-mer) oligonucleotides. On the other hand, the 2 ',4 '-BNA(NC)-based 20-mer AON exhibited the highest affinity but the worst IC50 value, indicating that very high affinity may undermine antisense potency. These results suggest that the potency of AONs requires a balance between reward term and penalty term. Balance of these two parameters would depend on affinity, length, and the specific chemistry of the AON, and fine-tuning of this balance could lead to improved potency. We demonstrate that 2 ',4 '-BNA(NC) may be a better alternative to conventional 2 ',4 '-BNA/LNA, even for "short" antisense oligonucleotides, which are attractive in terms of drug-likeness and cost-effective bulk production.