Purpose: Gene carriers are often studied individually under different assay conditions, making direct structure–function comparisons difficult. The study compared dendritic poly(L-lysine) (KG6) and linear poly(L-lysine) (PLL) within the same experimental system to identify how carrier architecture affects DNA complex properties, cellular uptake, gene expression, and cytokine induction.
Hypothesis: If dendritic poly(L-lysine) KG6 has lowered pKa terminal amines and weaker DNA compaction than linear PLL, then despite lower cellular DNA uptake, KG6 will mediate higher gene expression through enhanced endosomal escape (proton sponge effect) and easier access of transcription machinery to weakly compacted DNA.
Aims: Compare physicochemical properties of DNA complexes formed with KG6 vs PLL (zeta potential, size, compaction, nuclease protection). - Quantify DNA binding and uptake into cells. - Compare in vitro gene expression efficiency. - Evaluate pro-inflammatory cytokine induction after intravenous administration. - Identify structural features of poly(L-lysine) carriers that determine efficacy.
Delivery system:
Component: Carriers; Details: Dendritic poly(L-lysine) KG6 (6th generation; 128 amines, 126 lysine residues) vs linear poly(L-lysine) PLL (Mw 15,000–30,000; ~170 amines/lysine residues)
Component: Payload; Details: Plasmid DNA PGV-C/CMV encoding luciferase; tetramethylrhodamine-labeled DNA for imaging
Component: Complexation; Details: Electrostatic binding at N/P ratio 8
Component: Size; Details: KG6-DNA: 887 ± 19 nm; PLL-DNA: 457 ± 20 nm in DMEM
Component: Zeta potential; Details: KG6-DNA: −1.0 ± 0.3 mV (neutral); PLL-DNA: +16.8 ± 0.5 mV (positive)
Component: Targeting ligand; Details: None
Component: Key feature; Details: Direct comparison of dendritic vs linear architecture in same assay system
Approach: In vitro: CHO cells; transfection in serum-free DMEM for 3 h, then 10% FBS DMEM for 24 h. - In vivo: Mice; intravenous injection of DNA complexes; blood collected for cytokine analysis. - Controls: Naked DNA; DOTAP/cholesterol liposomes for cytokine comparison. - No tumor model, no disease efficacy, no biodistribution. - Replicates: n = 3 for most measurements.
Key methods: Physicochemical characterization: Dynamic light scattering (size, zeta potential); ethidium bromide fluorescence titration for DNA compaction; DNase I protection assay; heparin dissociation. - Cellular uptake: Fluorescence microscopy with rhodamine-labeled DNA; quantitative real-time PCR for intracellular plasmid DNA. - Transfection: Luciferase assay normalized to total protein. - Cytokine induction: ELISA for TNF-α, IFN-γ, IL-1β, IL-12.
Key results: Zeta potential: KG6-DNA neutral (−1.0 ± 0.3 mV); PLL-DNA positive (+16.8 ± 0.5 mV). - Size: KG6-DNA 887 ± 19 nm; PLL-DNA 457 ± 20 nm. - DNA compaction: KG6 weaker (fluorescence plateau ~40%); PLL stronger (~20%). - Nuclease protection: PLL protected DNA better; KG6-DNA moderately digested and dissociated by heparin. - Uptake: PLL-mediated DNA uptake was 4-fold higher than KG6. - Transfection: KG6-mediated gene expression was 100-fold higher than PLL. - Cytokines: TNF-α elevated at 2 h for both carriers vs DNA alone, reduced by 6 h. No significant differences between KG6 and PLL for IFN-γ, IL-1β, or IL-12. DOTAP/cholesterol induced much higher cytokine levels.
Interpretation: The authors claim that dendritic poly(L-lysine) KG6 is structurally advantageous for gene delivery because its lowered pKa terminal amines promote endosomal escape via the proton sponge effect, and its weaker DNA compaction allows better access of RNA polymerase in the nucleus. Despite lower cellular uptake than linear PLL, KG6 yields 100-fold higher gene expression. Both poly(L-lysine) carriers induce low cytokine responses compared with cationic liposomes, supporting their potential for safer non-viral gene delivery.
Limitations: In vitro only for transfection: CHO cells only; no primary cells or other cell types. - In vivo only cytokine induction: No biodistribution, tumor efficacy, or survival. - No direct proof of proton sponge: Mechanism inferred, not directly visualized. - No viability/cytotoxicity data. - Serum-free transfection: Complexes delivered in serum-free DMEM; serum added afterward. - No targeting ligand: Delivery relies on nonspecific interactions. - Small sample size: n = 3. - No comparison with PEI or commercial reagents beyond DOTAP/cholesterol for cytokines. - No long-term expression or repeated dosing. - DMEM components affected complex properties and were not fully identified.
