Complexing the Pre-assembled Brush-like siRNA with Poly(β-amino ester) for Efficient Gene Silencing

Small interfering RNA (siRNA) has been emerging as a highly selective and effective pharmaceutics for treating broad classes of diseases. However, the practical application of siRNA agent is often hampered by its poor crossing of the cellular membrane barrier and ineffective releasing from endosome to cytoplasm, leading to low gene silencing efficacy for clinical purposes. Thus far, cationic lipid and polymer-based vectors have been extensively explored for gene delivery. Yet condensing the rigid and highly negatively charged siRNA duplex to form a stable complex vehicle usually requires a large load of cationic carriers, prone to raising the toxicity issue for delivery. Herein, we develop a simple strategy that can efficiently condense the siRNAs into nanopartide vehicles for target gene regulation. In this approach, we first employ a DNA-grafted polycaprolactone (DNA-g-PCL) brush as template to organize the small rigid siRNAs into a large brush-like structure (siRNA-brush) through nucleic acid hybridization. Then, the siRNA-brush assembly is condensed by an ionizable and biodegradable polymer (poly(beta-amino ester), PBAE) under acidic buffer condition to form a stable nanopartide for siRNA delivery. Compared to the free siRNAs with poor complexing capability with PBAE, the large brush-like siRNA assemblies with more complicated topological architecture significantly promotes their electrostatic interaction with PBAE, enabling the formation of complexed nanoparticles at low weight ratio of polymer to siRNA. Additionally, PBAE/siRNA-brush complexes exhibit good biocompatibility and stability under physiological condition, as well as enhanced cellular internalization. When equipped with functional siRNAs, the obtained delivery system demonstrates excellent downregulation of target genes both in vitro and in vivo, through which the progression of hypertrophic scars can be retarded with negligible adverse effects in an xenografted mouse model.