Skin-permeable quaternary nanoparticles with layer-by-layer structure enabling improved gene delivery

Skin is an attractive target for delivery of genetic therapeutics and vaccines. However, the effective delivery of nucleic acids through the skin is primarily limited by the highly organized structure of the stratum corneum. Herein we propose a novel strategy to overcome the formidable barrier of skin by using the skin-permeable LMWP/PGA/PEI/DNA quaternary nanoparticles (NPs) with a self-assembling layer-by-layer structure. The ternary layer of anionic poly(γ-glutamic acid) (PGA) coats the cationic nano-core of PEI/DNA, and the outermost layer is the cell-penetrating low molecular weight protamine (LMWP) peptide. The LMWP functions as a biological permeation enhancer, promoting not only skin permeation but also cell penetration. Our results showed that the cellular uptake and transfection level were greatly improved by the LMWP-modified quaternary NPs compared with the conventional PEI/DNA NPs, displaying a four-fold increase. Skin penetration of the quaternary NPs was significant, showing the high cumulative amount of percutaneous delivery up to 14% of the applied dose. Importantly, skin penetration efficiency of the quaternary NPs was further enhanced by a synergistic effect of LMWP and the chemical permeation enhancer sodium lauryl sulfate up to 23.8%. The results suggested that the skin-permeable NPs could be a promising approach for percutaneous gene delivery.