The gene transfection and endocytic uptake pathways mediated by PEGylated PEI-entrapped gold nanoparticles

The development of gene vectors is the vital step in gene therapy. The cationic polymer polyethylenimine (PEI) is widely applied as an efficient and low cost nonviral gene vehicle. However, its further practical applications in gene therapy are limited due to its high cytotoxicity. To obtain safe and efficient gene vectors, hydrophilic polyethylene glycol (PEG) has been conjugated onto its surface due to its good biocompatibility, and the PEGylated PEI was used as a template to entrap gold nanoparticles (Au NPs) with different Au atom/PEI molar ratios (25:1, 50:1, 100:1, and 200:1, respectively). The formed PEGylated PEI-entrapped Au NPs (PEG-Au PENPs) and their cytotoxic effects as well as ability to transfect plasmid DNA (pDNAs) to HeLa cells were analyzed using Cell Counting Kit-8 (CCK-8) assay, flow cytometry and confocal microscopic imaging. To further understand cell internalization pathway of PEG-Au PENPs, several pharmacologic inhibitions of endocytic pathways were conducted. Our results revealed that the PEG-Au PENPs were not only able to transfect pDNAs into cells with decreased cytotoxicity, but also showed high transfection efficiency compared with PEI alone. The cellular uptake data indicated that the clathrin-mediated endocytosis is the main pathway in the internalization of the formed polyplexes. These findings suggested that the developed PEG-Au PENPs may serve as a safe gene carrier with non-compromised DNA transfection efficiency and promote the further development of efficient and safe gene delivery strategies based on nanoparticles.