Antisense Oligonucleotides Make Sense

1. In first-generation ASOs, the phosphate backbone linking the nucleotides is modified. One of the non-bridging oxygen atoms in the phosphodiester bond is replaced by a sulfur, methyl or amine group. These chemical modifications have improved the ASO stability by increasing the resistance of ASOs to nucleases. Unfortunately, the biologically active modified ASOs are highly toxic due, in particular, to their non-specific binding to proteins. This led researchers to develop new generations of ASOs that were both less toxic and more specific.


2. The second generation of ASOs is characterized by alkyl modifications at the 2′ position of the ribose. These ASOs are less toxic and have a slightly higher affinity for their target.


3. The third generation is more heterogeneous because it includes a large number of modifications aiming to improve binding-affinity, resistance to nucleases, and pharmacokinetic profile. The most common modifications include locked nucleic acids; phosphorodiamidate morpholino oligomers, in which the ribose is replaced by a morpholine moiety and the phosphodiester bond by a phosphorodiamidate bond; and peptide nucleic acids, in which the ribose-phosphate backbone is replaced by a polyamide backbone.

Several distinct mechanisms of ASOs are known: