Intracellular delivery of antisense oligonucleotides by tri-branched cyclic disulfide units.

Therapeutic oligonucleotides, such as antisense DNA, show promise in treating previously untreatable diseases. However, their applications are still hindered by the poor membrane permeability of naked oligonucleotides. Therefore, it is necessary to develop efficient methods for intracellular oligonucleotide delivery. Previously, our group successfully developed disulfide-based Membrane Permeable Oligonucleotides (MPON), which achieved enhanced cellular uptake and gene silencing effects through an endocytosis-free uptake mechanism.  Herein, we report a new molecular design for the next generation of MPON, called trimer MPON. The trimer MPON consists of a tri-branched backbone, three α-lipoic acid units, and a spacer linker between the oligonucleotides and tri-branched cyclic disulfide unit. We describe the design, synthesis, and functional evaluation of the trimer MPON, offering new insights into the molecular design for efficient oligonucleotide delivery.

Topological capture of mRNA for silencing gene expression.

We describe herein topological mRNA capture using branched oligodeoxynucleotides (ODNs) with multiple reactive functional groups. These fragmented ODNs efficiently formed topological complexes on template mRNA in vitro. In cell-based experiments targeting AcGFP mRNA, the bifurcated reactive ODNs showed a much larger gene silencing effect than the corresponding natural antisense ODN.

A 2'-modified uridine analog, 2'-O-(methylthiomethoxy)methyl uridine, for siRNA applications.

The medicinal applications of siRNAs have been intensively examined but are still hindered by their low molecular stability under biological conditions and off-target effects, etc. The introduction of chemical modifications to the nucleoside is a promising strategy for solving these limitations. Herein, we describe the development of a new uridine analog, U*, that has a (methylthiomethoxy)methoxy group at the 2' position. The phosphoramidite reagent corresponding to U* was easily synthesized and the RNA oligonucleotides containing U* were stably prepared using a standard protocol for oligonucleotide synthesis. The introduction of U* into the siRNA resulted in positive or negative effects on the targeted gene silencing in a position-dependent manner, and the positive effects were attributed to the improved stability under biological conditions. The thermodynamic analysis of the U*-modified RNAs revealed a slight destabilization of the dsRNA, based depending on which U was strategically utilized to restrain the off-target effects of the siRNA. This study describes a rare example of nucleoside analogs with a large substitution at the 2'-position in the context of an siRNA application and is informative for the development of other analogs to further improve the molecular properties of siRNAs for medicinal applications.