High potency silencing by single-stranded boranophosphate siRNA

Abstract

In RNA interference (RNAi), double-stranded short interfering RNA (ds-siRNA) inhibits expression from complementary mRNAs. Recently, it was demonstrated that short, single-stranded antisense RNA (ss-siRNA) can also induce RNAi. While ss-siRNA may offer several advantages in both clinical and research applications, its overall poor activity compared with ds-siRNA has prevented its widespread use. In contrast to the poor gene silencing activity of native ss-siRNA, we found that the silencing activity of boranophosphate-modified ss-siRNA is comparable with that of unmodified ds-siRNA. Boranophosphate ss-siRNA has excellent maximum silencing activity and is highly effective at low concentrations. The silencing activity of boranophosphate ss-siRNA is also durable, with significant silencing up to 1 week after transfection. Thus, we have demonstrated that boranophosphate-modified ss-siRNA can silence gene expression as well as native ds-siRNA, suggesting that boranophosphate-modified ss-siRNAs should be investigated as a potential new class of therapeutic agents.

Noncanonical Synthetic RNAi Inducers

“…siRNA shorter than canonical siRNA could also induce efficient silencing of target genes in mammalian cells acting via RNAi mechanism [87][88][89][90]. Short siRNAs have some benefits as inducers of RNAi such as reduction of immune response and decreased cost of the synthesis [76].…”

“…Early studies demonstrated that 5′-phosohorylated antisense siRNAs with 22-40 nt in length were able to induce gene silencing in Caenorhabditis elegans [92,93]. Several studies investigated the possibility of using antisense strand of siRNA 19-29 nt in length for transient knockdown of target genes in mammalian cells [88][89][90]. Antisense siRNA entered the RISC complex and provided mRNA cleavage but with lower efficiency in comparison with canonical siRNA.…”

“…Among the advantages of siRNAs, a lower price of synthesis and no side effects associated with the induction of interferon response should be considered [88].…”

“…Partial boranophosphate backbone (BP) modifications were designed to increase the stability and the silencing activity of the antisense siRNA [88]. BP-modified antisense siRNAs possess silencing activity comparable to unmodified double-stranded siRNAs.…”

“…Overall, in spite of lower silencing activity compared with canonical siRNA, antisense siRNA may be used in specific situations, for instance, to eliminate off-target silencing of genes in the case when the sense strand has substantial homology to nontarget genes [88].…”