Research Update

UNA Modified siRNA for Improved Efficacy

TriLink is proud to introduce unlocked nucleic acid (UNA) oligonucleotides, flexible RNA mimics that enable modulation of affinity and specificity, as well as UNA modified siRNA, or UsiRNA, for improved gene knockdown. UNA is an RNA analogue also known as 2',3'-seco-RNA, where the C2'-C3' bond is absent, making the molecule very flexible. This gives UNA the property of decreased binding affinity towards a complementary strand. A 5-10°C decrease in melting temperature (Tm) is seen per UNA insertion with additive effect, allowing a gradual decrease in the thermostability by introduction into DNA or RNA oligonucleotides. UNA modifications can be strategically placed to induce either a lack of mismatch discrimination or an increase in mismatch discrimination.(1)

Due to these unique properties, UNA monomer substitution in an oligonucleotide permits modulation of the thermodynamic stability of various nucleic acid structures such as RNA:DNA duplexes, quadruplexes, aptamers and i-motifs. UNA has demonstrated utility in antisense oligonucleotide therapeutics, including single strand and gapmer oligonucleotides due to compatibility with RNase H activity.

Of particular interest are the UNA modified siRNAs, known as UsiRNAs, which show potent gene silencing and dramatically reduced off-target effects.(2) It was demonstrated by Marina Biotech that replacement of the two overhang bases with UNA, coupled with an additional UNA-U at the 5' end of the guide strand and a position 7 modification of the passenger strand with UNA greatly reduced the off-target effects and in many cases enhanced overall efficacy of the siRNA through reduced toxicity. This work was largely confirmed through the efforts of the laboratory of Jorgen Kjems at Aarhus University in Denmark along with numerous collaborators.(3) They investigated a large number of different modifications and discovered that UsiRNA performed best and stood out from the rest of the modifications as giving the most dependable reduction of off-target effects and hence overall efficacy.

To place an order for a UsiRNA, send us your siRNA sequences that currently have off-target effects. We will replace the appropriate bases with UNA. We expect that you will see a reduction in off-target effects in almost every case.

Learn more about UsiRNA
Learn more about UNA properties