Development of intracellular delivery methods for antisense DNAa nd siRNAi si mportant. Previously reported methods using liposomes or receptor-ligands take several hours or more to deliver oligonucleotides to the cytoplasm due to their retention in endosomes.Oligonucleotides modified with lowm olecular weight disulfide units at at erminus reach the cytoplasm 10 minutes after administration to cultured cells. This rapid cytoplasmic internalization of disulfide-modified oligonucleotides suggests the existence of an uptake pathway other than endocytosis.M echanistic analysis revealed that the modified oligonucleotides are efficiently internalizedi nto the cytoplasm through disulfide exchange reactions with the thiol groups on the cellular surface.T his approachs olves several critical problems with the currently available methods for enhancing cellular uptake of oligonucleotides and mayb ea n effective approachi nt he medicinal application of antisense DNAand siRNA.

Here, we report the applicability of diazirine-containing RNA photo-cross-linking probes for the identification of microRNA (miRNA) targets. The RNA cross-linking probes were synthesized by substituting the RNA nucleobases with nucleoside analogues such as 1-O-[3-(3-trifluoromethyl-3H-diazirin-3-yl)]benzyl-β-d-ribofuranose or 1-O-[4-(3-trifluoromethyl-3H-diazirin-3-yl)]benzyl-β-D-ribofuranose that carry aryl trifluoromethyl diazirine moieties. The probes were successfully cross-linked with synthetic RNAs containing the four natural nucleosides on the opposite site of the nucleoside analogues. Furthermore, it was found that miRNAs containing these analogues were effective in regulating the expression of their target genes. Thus, RNAs containing the nucleoside analogues are promising candidates as photo-cross-linking probes to identify the target mRNAs of miRNAs.

Messenger RNAs (mRNAs) with phosphorothioate modification (PS‐mRNA) to the phosphate site of A, G, C, and U with all 16 possible combinations were prepared, and the translation reaction was evaluated using an E. coli cell‐free translation system. Protein synthesis from PS‐mRNA increased in 12 of 15 patterns when compared with that of unmodified mRNA. The protein yield increased 22‐fold when the phosphorothioate modification at A/C sites was introduced into the region from the 5′‐end to the initiation codon. Single‐turnover analysis of PS‐mRNA translation showed that phosphorothioate modification increases the number of translating ribosomes, thus suggesting that the rate of translation initiation (rate of ribosome complex formation) is positively affected by the modification. The method provides a new strategy for improving translation by using non‐natural mRNA.

We herein report a new approach for RNA interference, so-called “build-up RNAi” approach, where single-strand circular RNAs with a photocleavable unit or disulfide moiety were used as siRNA precursors.

Development of intracellular delivery methods for antisense DNA and siRNA is important. Previously reported methods using liposomes or receptor‐ligands take several hours or more to deliver oligonucleotides to the cytoplasm due to their retention in endosomes. Oligonucleotides modified with low molecular weight disulfide units at a terminus reach the cytoplasm 10 minutes after administration to cultured cells. This rapid cytoplasmic internalization of disulfide‐modified oligonucleotides suggests the existence of an uptake pathway other than endocytosis. Mechanistic analysis revealed that the modified oligonucleotides are efficiently internalized into the cytoplasm through disulfide exchange reactions with the thiol groups on the cellular surface. This approach solves several critical problems with the currently available methods for enhancing cellular uptake of oligonucleotides and may be an effective approach in the medicinal application of antisense DNA and siRNA.