RNA interference has been widely used for gene therapy of various infectious diseases and malignant tumors. However, its poor stability in serum has limited further clinic application. Here, we found that stability of siRNA in serum enhanced obviously when 3′-terminus of sense strand （siRNA-pS） was conjugated with peptide, while same conjugation at 3′-terminus of antisense strand brought no such effects. And it was also found that only the peptide residue in siRNA-pS could be cut off by RNase A. All these results indicated that nucleases in serum prefer to invade siRNA duplex through the 3′-end of sense strand.
Synthetic oligonucleotides including antisense oligonucleotides and siRNA have shown promising therapeutic potential.However,to realize the therapeutic potential of synthetic oligonucleotides,many obstacles have to be overcome,such as their poor biological stability,non-specific activity and inadequate cell membrane permeability.In this paper,the achievements by Lihe Zhang＇s group in the study of isonucleotide modified oligonucleotides and oligonucleotides conjugated with cell penetrating peptides are summarized.
Given its ability to knock down essentially any gene of interest, siRNA has been one of the promising candidates for gene therapy. However, like other nucleic-acid-based drugs, its poor cellular uptake poses a major challenge. Here we briefly summarize the use of cell penetrating peptides （CPPs） as a novel and promising approach for siRNA delivery. The main advantages of CPPs are their low toxicity and high efficiency.
