Structural modification of small interfering ribonucleic acids for efficient gene delivery

Abstract

Gene silencing by RNA interference (RNAi) was discovered in C. elegans in 1998 as a response to long double-stranded (ds) RNA. The RNAi effect has been successfully extended to plants, Drosophila, and fungi. However, the introduction of long dsRNA into mammalian cells activates antiviral defense responses and nonspecific gene silencing. In 2001, RNAi-mediated gene silencing in mammalian cells was first reported by short, synthetic dsRNA, known as small interfering RNA (siRNA), which opened the door to RNAi technology for gene therapy. The synthetic siRNA has 19 ~ 21 base pairs with a 2-nucleotide overhang at both 3`-ends. The ability to easily design and customize siRNA sequences for any genes has made it more attractive for siRNA therapeutics. An siRNA is incorporated and unwound in RNA-induced silencing complex (RISC), and retains one strand of the siRNA duplex in cells. The RISC encapsulating a single strand siRNA guides the endonucleolytic cleavage of complementary mRNA, resulting in sequence-specific gene silencing. To achieve siRNA therapy, it is essential to transport exogenous siRNA into the cytoplasm of target cells due to endogenous RNAi pathway. To this end, viral vectors have been used for siRNA delivery owing to their ability to efficiently attach and transport own genomic materials into cells. They have shown high transfection efficiency. However, their clinical application has been restricted by the potential risks such as mutagenicity, inflammatory, and immunogenicity. These in-creasing concerns have led to the development of synthetic non-viral vectors. A variety of synthetic vectors based on cationic polymers, peptides, and lipids have been studied to form cationic nanocomplexes with poly-anionic nucleic acids by electrostatic interactions, which can facilitate cellular uptake through endocytosis. In general, plasmid DNA can be effectively condensed into stable complexes with sizes of approximately 200 nm upon contact with cationic carriers. ...