Nanoassemblies with Effective Serum Tolerance Capability Achieving Robust Gene Silencing Efficacy for Breast Cancer Gene Therapy.

The transfection efficiency of siRNA mediated by cationic polymers is limited due to the instability of polymers/siRNA complexes in the presence of serum. Poly(ethylene glycol) (PEG) is usually applied to modify cationic polymers, so as to reduce protein and cell adsorption and then to improve siRNA transfection efficiency. However, the polymers' modification with PEG mostly consumes the free amino of the polymers, which can, in turn, reduce the charge density and limit their siRNA transfection efficacy. Here, a new PEG modification strategy that need not consume the surface aminos of polymers is proposed. Catechol-PEG polymers are coated on the surface of phenylboronic acid (PBA)-modified Generation 5 (G5) poly(amidoamine) dendrimers (G5PBA) via reversible boronate esters to establish PEG-modified dendrimer/siRNA nanoassemblies for efficient siRNA delivery. The PEG/G5PBA/siRNA nanoassemblies have positive charge and show excellent gene silencing efficacy in the absence of serum in vitro. More importantly, the PEG/G5PBA/siRNA nanoassemblies also exhibit excellent serum resistance and gene silencing efficacy in serum-containing medium. Furthermore, the effective antiserum and gene silencing efficacy elicited by these nanoassemblies lead to excellent antitumor effects in vivo. This proposed strategy constitutes an important approach to reach an excellent gene silencing efficacy in the presence of serum.