Gene delivery system based on siRNA conjugates

Abstract

With high specificity and efficiency in target gene inhibition, small interfering RNAs (siRNAs) are promising tool for genomic therapeutics. To develop a siRNA delivery system with low cytotoxicity and high transfection efficiency, we prepared polyelectrolyte complex micelles (PECMs) of siRNA conjugated to poly(ethylene glycol) via a disulfide linkage (siRNA-PEG) using three kinds of condensing agents: amine-functionalized gold nanoparticles, cationic fusogenic peptide, Pluronic/poly(ethylenimine) nanocapsules. Gold nanoparticles chemically modified with primary amine groups could form stable polyelectrolyte complexes through electrostatic interactions with negatively charged siRNA-PEG conjugates having a cleavable di-sulfide linkage under reductive cytosol condition. The resultant core/shell type polyelectrolyte complexes surrounded by a protective PEG shell layer had a well dispersed nanostructure with a hydrodynamic diameter of 96.3 ± 25.9 nm, as determined by dynamic light scattering and transmission electron microscopy. Confocal laser scanning microscopy revealed that the nanosized polyelectrolyte complexes were efficiently internalized in human prostate carcinoma cells (PC-3 cells), and thus enhanced intracellular uptake of siRNA. Furthermore, the siRNA/gold complexes significantly inhibited the expression of a target gene within the cells without showing severe cytotoxicity. The current study demonstrated that positively charged gold nanoparticles could be potentially applied for intracellular delivery of siRNA. Anionic siRNA-PEG conjugate and cationic KALA spontaneously formed nano-sized PECMs (< 200 nm) that have an inner core of charge neutralized siRNA/KALA complex surrounded by a PEG corona. VEGF siRNA was used to demonstrate VEGF sequence-specific gene inhibition in PC-3 cells. The extent of gene silencing was gradually increased with increasing nitrogen to phosphate (N/P) ratio and the concentration of siRNA-PEG/KALA PECMs. These results suggest t...