DEGylation Enhanced the Stability of Peptide-siRNA Complexes in Serum

Small interfering RNA (siRNA) shows great therapeutic potential due to its ability to regulate gene expression in a highly selective manner, but this application has been limited by effective delivery, partly because of the low nuclease resistance of siRNA in the presence of serum, and inefficient cellular uptake. We previously reported a library of cell-penetrating and amino acid-pairing peptides that facilitate effective siRNA delivery to mammalian cells without causing cytotoxicity, but they are unstable within serum-containing medium. Here, we investigated the possibility of conjugating the peptide with diethylene glycol to improve its serum stability without compromising its gene-regulation capability. One of the most promising peptides, C6M1, was conjugated with diethylene glycol, and its incorporated siRNA complexes had excellent serum stability and highly efficient cellular uptake with negligible cytotoxicity. The gene-silencing ability of diethylene glycol conjugated-peptide/siRNA complexes was comparable to that of non-conjugated peptide/siRNA at both mRNA and protein levels. Our data demonstrate that conjugating peptides with diethylene glycol is a promising method for improving siRNA delivery by improving its serum stability.