Dual-targeting and pH/redox-responsive multi-layered nanocomplexes for smart co-delivery of doxorubicin and siRNA

Multi-layered nanocomplexes (MLNs) were designed here to provide smart co-delivery of doxorubicin (DOX) and vascular endothelial growth factor (VEGF) siRNA. The electrostatically self-assembled MLNs were constructed by TAT peptide modified mesoporous silica nanoparticles (TAT-MSN) as the cationic core for DOX loading, poly(allylamine hydrochloride)-citraconic anhydride (PAH-Cit) as the anionic inner layer, and galactose-modified trimethyl chitosan-cysteine (GTC) conjugate as the cationic outer layer to encapsulate siRNA. Their strong stability at pH 7.4 and 6.5 protected siRNA from degradation in the blood and tumor microenvironment. Galactose ligands on the GTC outer layers effectively facilitated the internalization of MLNs through receptor-mediated endocytosis. Afterwards, the endosomal/lysosomal acidity (pH 5.0) triggered the charge reversal of PAH-Cit, thereby inducing the disassembly of MLNs and their escape to the cytosol. Cytoplasmic glutathione further accelerated siRNA release through cleaving disulfide bonds in GTC layers, leading to high silencing efficiencies. Meanwhile, the exposed DOX-loaded cores were transported into the nuclei by virtue of TAT peptide and exhibited sustained release thereafter. As a result, potent antitumor efficacies of MLNs were noted following intravenous injection at a low dose with no apparent toxicity detected. Therefore, MLNs served as an effective and safe vector to maximize synergistic effect of chemodrugs and therapeutic genes.