Purpose: Non-viral gene delivery systems such as poly-L-lysine (PLL) have low immunogenicity compared with viral vectors, but PLL suffers from poor biocompatibility, rapid degradation, and low transfection efficiency. PEGylation was explored to improve solubility, reduce cytotoxicity, and enhance cell permeability for gene delivery.
Hypothesis: If PLL is modified with polyethylene glycol (PEG) to form comb-shaped PEG-grafted PLL (PEG-g-PLL), then the resulting copolymer will condense DNA, reduce cytotoxicity, and increase transfection efficiency compared with PLL alone, with an optimal PEG grafting ratio.
Aims: Synthesize PEG-g-PLL with three PEG contents: 5, 10, and 25 mole% of ε-amino groups modified. - Characterize DNA condensation, complex size, and physicochemical properties. - Evaluate transfection efficiency and cytotoxicity in Hep G2 human carcinoma cells. - Compare with PLL alone and Lipofectin™, and investigate the role of endocytosis using chloroquine.
Delivery system:
Component: Polymer; Details: Poly-L-lysine (PLL, mol. wt. ≈ 25,000; 120 repeating units)
Component: Modification; Details: Methoxy PEG-carboxymethyl (mPEG-OCH₂CO₂H, mol. wt. ≈ 550) grafted to ε-amino groups of PLL
Component: Architecture; Details: Comb-shaped PEG-g-PLL copolymer
Component: PEG graft ratios; Details: 5, 10, and 25 mole%
Component: Payload; Details: Plasmid pSV-β-gal (β-galactosidase reporter gene)
Component: Complex formation; Details: Electrostatic interaction between plasmid DNA and cationic polymer
Component: Complex size; Details: ~300 nm at 1:3 DNA:polymer weight ratio (10 and 25 mole% PEG)
Component: Targeting ligand; Details: None
Component: Key feature; Details: PEG grafting to reduce cytotoxicity and improve transfection
Approach: In vitro only. No in vivo animal studies. - Cell line: Hep G2 human liver carcinoma cells. - Transfection: 96-well plates; plasmid DNA 10 µg/mL; PEG-g-PLL 1–50 µg/mL; 4 h incubation in MEM with 10% FBS; chloroquine 100 µM added in some experiments. - Controls: PLL alone, Lipofectin™. - No targeting ligand, no in vivo model, no disease context.
Key methods: Synthesis/characterization: ¹H NMR for PEG content. - DNA condensation: Ethidium bromide dye displacement assay; agarose gel electrophoresis. - Complex size: Dynamic laser light scattering. - Transfection: X-gal staining for β-galactosidase expression. - Cytotoxicity: MTT assay. - Mechanism: Chloroquine effect as indicator of endocytosis. - Duration: X-gal assay at 24–96 h.
Key results: Transfection: PEG-g-PLL showed 5- to 30-fold higher transfection efficiency than PLL alone. Optimal PEG content was 10 mole%; 25 mole% decreased efficiency. - Optimal ratio: Highest transfection at 1:3 DNA:PEG-g-PLL weight ratio. - Complex size: ~300 nm at 1:3 ratio for 10 and 25 mole% PEG. - Chloroquine effect: Transfection increased up to 30-fold with 100 µM chloroquine, suggesting endocytosis-mediated uptake. - Cytotoxicity: PEG-g-PLL showed lower cytotoxicity than PLL and Lipofectin™. - Expression duration: Early gene expression at 24 h and maintained up to 96 h. - Comparison: Lipofectin™ showed slightly higher transfection efficiency but higher cytotoxicity.
Interpretation: The authors claim that comb-shaped PEG-g-PLL is a promising non-viral gene carrier with low cytotoxicity, early gene expression, and sustained expression up to 96 h. The data suggest plasmid DNA/PEG-g-PLL complexes enter cells via endocytosis. Further work is proposed to attach cell-targeting ligands to PEG-modified carriers for in vitro and in vivo targeting.
Limitations: In vitro only: No in vivo validation, biodistribution, or therapeutic efficacy. - Single cell line: Hep G2 only; generalizability to other cell types not established. - No targeting ligand: Delivery relies on nonspecific electrostatic interactions. - Modest transfection vs Lipofectin™: Lipofectin™ achieved slightly higher transfection, though with greater toxicity. - Mechanism not fully resolved: Endocytosis inferred from chloroquine effect; no direct uptake/trafficking imaging. - No long-term safety or toxicity data. - No comparison with other non-viral carriers beyond PLL and Lipofectin™. - No in vivo serum stability or pharmacokinetic data. - Citation DOI absent in the supplied file.
