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Amphiphilic core–shell nanoparticle, which is composed of a hydrophobic core and a branched polyethylenimine (PEI) shell, has been designed and synthesized as a novel gene delivery nanocarrier. In our previous study, we demonstrated that the core–shell nanoparticle was not only able to efficiently complex with plasmid DNA (pDNA) and protect it against enzymatic degradation, but also three times less cytotoxic, and threefold more efficient in gene transfection than branched 25 kDa PEI. This paper reports our further studies in the following three aspects: (1) the ability of the PEI-based nanoparticles to deliver gene in various mammalian cell lines; (2) intracellular distributions of the nanoparticles and their pDNA complexes in HeLa cells; and (3) incorporation of nuclear targeting agent into the nanoparticle/pDNA complexes to enhance the nuclear targeting ability. The PEI-based nanoparticles were able to transfect both human and non-human cell lines and their transfection efficiencies were cell-dependent. Within our four tested cell lines (MCF-7, BEL 7404, C6 and CHO-K1), gene transfer using PEI-based core–shell nanoparticles displayed gene expression levels comparable to, or even better than, the commercial Lipofectamine™ 2000. Confocal laser scanning microscopy showed that the nanoparticles and their pDNA complexes were effectively internalized into the HeLa cells. The in vitro time series experiments illustrated that both the nanoparticle/pDNA complexes and PEI-based nanoparticles were distributed in the cytoplasmic region after transfection for 10 and 60 min, respectively. Nuclear localization was also observed in both samples after transfection for 20 and 60 min, respectively. Incorporation of the high mobility group box 1 (HMGB1) protein for nuclear targeting has also been demonstrated with a simple approach: electrostatic complexation between the PEI-based nanoparticles and HMGB1. In the in vitro transfection study in MCF-7 cells, the expression level of the firefly luciferase gene encoded by the pDNA increased remarkably by up to eightfold when the HMGB1 protein was incorporated into the nanoparticle/pDNA complexes. Our results demonstrate that the PEI-based core–shell nanoparticles are promising nanocarriers for gene delivery.

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