Abstract
In this study, two new types of theranostic polymer/superparamagnetic iron oxide nanoparticle (SPION) nanocomplexes were designed and studied for their gene delivery capability. In the first part of this study, SPION was synthesized by thermal decomposition and used to prepare SPEI/SPION (~150nm in diameter) via layer-by-layer deposition process. Via the electrostatic interactions, SPEI/SPION complexed with plasmid DNA (pDNA) and protected it from DNAse degradation, as analyzed using gel electrophoresis. Efficient cellular uptake of SPEI/SPION/pDNA was confirmed by prussian blue staining of SPION. Efficient in vitro transfection efficiency of SPEI/SPION/pDNA was observed using fluorescent reported gene on two mammalian cell lines. The transfection efficiency (72 hr post-transfection) was up to 90% and 50% in 293T and MCF7 cells respectively under serum-free transfection condition. It is worth of mentioning that SPEI/SPION/pDNA maintained efficient gene delivery capability even in serum-containing transfection condition. Additionally, external magnetic field was found to further promote the gene delivery efficiency. In second part of this study, water-soluble SPION was synthesized by co-precipitation method and subsequently conjugated with pyridyl disulfide-containing linker (2-(pyridyldithio)-ethylamine hydrochloride, PDS). The presence of PDS in the resultant hydrophobic SPION-PDS was confirmed by FTIR spectrum. SPION-ss-PEI800 was then prepared by PEI800-SH conjugation onto the surface of SPION-PDS. The as-synthesized SPION-ss-PEI800 possess small size (150 nm in diameter), well dispersion in water and capable of effectively interacting with small interfering RNA (siRNA). The in vitro transfection results show that SPION-ss-PEI800 could deliver siRNA into cytoplasm and successfully knock down the expression of enhanced green fluorescent protein (eGFP) or vascular endothelial cell growth factor (VEGF) gene. 24 hr after transfection, the most significant VEGF gene silencing was observed (74.5% knock down) using ELISA assay. 42 hr after transfection, the level of VEGF remained low (50.0% knock down). In contrast, the gene silencing effect by the control treatment (scramble siRNA) was not significant (14% and 8% VEGF knockdown for 24 or 42 hr post-transfection respectively) as expected. The results verified the specificity of VEGF gene knockdown by SPION-ss-PEI800/siRNA. In the future, we will explore the potential of using SPION-PDS as a universal carrier system for thiol-containing molecules conjugation and the biomedical applications.