The design and synthesis of gold nanoparticles and its interaction with mammalian cells in culture.

Abstract

Cancer is a disease characterized by accelerated cell growth, resulting in healthy tissue being destroyed by the processes of invasion and metastasis. Non-viral gene delivery approaches have been extensively studied as a basic tool for intracellular gene transfer and gene therapy especially for genetic aberrations including cancer. Gold nanoparticles have attracted strong biomedical interest for drug delivery due to their low toxic nature, surface plasmon resonance and capability of increasing the stability of the payload. In the present study the synthesis of photoluminescent nanoparticles consisting of a gold core coated with polyethyleneimine, poly-L-lysine, cysteine and chitosan is reported. These functionalized gold nanoparticles (FAuNPs) were investigated at different pH values and ionic strength to identify the optimum conditions to produce stable monodisperse nanoparticles. FAuNPs showed good stability at low ionic strength which is important for the flexibility of the polymer chain. All nanoparticle/polymer formulations remained in the size range 11.9-195 nm with narrow particle distributions and low PDI (<1.2). TEM images revealed nanoparticles that were spherical and monodispersed. Nanoparticle and pDNA complexation was efficiently demonstrated in the band shift and ethidium bromide intercalation assays respectively. The serum nuclease digestion assay revealed that the nanoparticles provided partial protection to the complexed plasmid DNA (pCMV-luc). MTT cytotoxicity experiments indicated that the FAuNPs elicited a dose dependent cytotoxic effect with the four mammalian cell lines (HepG2, HEK293, HeLa and Caco2) tested responding differently. Au-PEI/pDNA maintained over 80% cell viability across all cell lines, while the Au-cys/pDNA exhibited a significant 91.8% (p<0.001) in Caco2 cells, Au-Chit/pDNA 126% (p<0.01) in HepG2 cells and Au-PLL/pDNA 104% in Hela cells. Transfection studies were accomplished using the luciferase reporter gene assay. Results showed that the FAuNPs produced greater transgene activity than the cationic polymer/DNA complexes on their own. This was evident for the Au-PEI/pDNA complex which produced a 12 fold increase in the HEK293 cells and a 9 fold increase in the HepG2 cells, compared to the PEI/pDNA complexes alone. The results of this study suggest that FAuNPs low cytotoxicity coupled with the ability to parametrically control particle size and surface properties, make these nanoparticles suitable non-viral gene delivery vectors. However further engineering and modifications of the FAuNPs may be required to enable in vivo gene delivery.