Purpose: Non-viral gene delivery needs safer and more effective polymeric vectors. Poly(β-amino ester)s (PBAEs) are promising, but previous studies had not systematically modified all three structural elements—backbone, side chain, and end group—within one library to analyze how small structural changes affect transfection and cytotoxicity.
Hypothesis: Systematic small changes to PBAE backbone hydrophobicity, side-chain hydrophobicity, and end-group chemistry will produce dramatic changes in transfection efficacy and cytotoxicity. Balancing overall polymer hydrophobicity will be crucial, and optimized end-modified PBAEs will outperform commercial non-viral reagents.
Aims: Synthesize a 320-member library of end-modified PBAEs with systematic variations in diacrylate backbone, amino alcohol side chain, and end-capping amine. - Characterize base polymer molecular weights and solubility. - Screen transfection efficacy and cytotoxicity in COS-7 cells at different polymer:DNA weight ratios. - Analyze structure–function relationships for backbone, side-chain, and end-group effects. - Compare lead PBAE formulations with FuGENE HD and Lipofectamine 2000.
Delivery system:
Component: Polymer class; Details: End-modified poly(β-amino ester)s (PBAEs)
Component: Library size; Details: 320 polymers
Component: Backbone monomers; Details: 8 diacrylates: B3, B3m, B4, B5, B6, BL1, BL2, BH1
Component: Side-chain monomers; Details: 4 amino alcohols: S3o, S3, S4, S5
Component: End groups; Details: 10 primary-amine-containing end-capping amines: E1–E12 (some sequential)
Component: Payload; Details: Plasmid DNA: CMV-Luc (luciferase) and EGFP-N1 (GFP)
Component: Nanoparticle formation; Details: Self-assembly in 25 mM sodium acetate buffer (pH 5.2); polymer:DNA wt/wt ratios 30–150, most optimal at 60
Component: Targeting ligand; Details: None
Component: Cell model; Details: COS-7 cells; in vitro only
Approach: In vitro only. No in vivo animal studies. - Cell line: COS-7 (African green monkey kidney fibroblast-like cells). - Transfection format: 96-well plates; 15,000 cells/well; 600 ng CMV-Luc DNA and 36 µg polymer (60 wt/wt) for library screen; EGFP-N1 DNA tested at 30, 60, and 90 wt/wt for selected polymers. - Controls: FuGENE HD, Lipofectamine 2000, untreated cells. - Replicates: n = 4 for luminescence and MTS; n = 4 for flow cytometry. - Disease context: General gene delivery; no specific disease model.
Key methods: Polymer synthesis and characterization: Michael addition; GPC for molecular weight; ¹H NMR for end-group modification. - Transfection efficacy: BrightGlo luciferase assay (RLU/well) and flow cytometry for % GFP-positive cells. - Cytotoxicity: CellTiter 96 AQueous One MTS assay for metabolic activity. - Solubility: Absorbance at 620 nm in 25 mM sodium acetate. - Statistical analysis: One-way and two-way ANOVA; linear regression; Spearman correlation.
Key results: Library: 320 end-modified PBAEs synthesized; base polymer Mw ranged from ~2,000 to 48,000 Da. - Optimal ratio: Most polymers achieved maximal luminescence at 60 wt/wt polymer:DNA; B3-S5 end-modified polymers sometimes required 125–150 wt/wt. - Hydrophobicity effects: Increasing hydrophobicity of backbone or side chain generally increased transfection. Side chain accounted for 45% of variance (p < 0.0001); diacrylate backbone accounted for 8.5% (p < 0.0001); interaction accounted for 9% (p < 0.0001). - Most effective side chain: S5 (most hydrophobic) was generally optimal; S4 and S3 were better than S3o. - End-group effects: E9-containing polymers were highly toxic; E10 and E12 often low efficacy; E5 generally better than E12 by >1 log order. Same base polymer with different end groups varied >3 log orders in luminescence. - Lead formulations vs. commercial reagents: Optimized PBAEs achieved ~3-fold higher luminescence (2.2 × 10⁶ RLU/well vs 8.1 × 10⁵) and 2-fold higher transfection by flow cytometry (76.7% vs 42.9%) compared with FuGENE HD and Lipofectamine 2000, with comparable or reduced toxicity. - Top six polymers: B3-S5-E1, B3-S5-E5, B3m-S5-E7, B4-S5-E3, B4-S5-E4, B4-S5-E7; at 60 wt/wt they achieved 64–77% GFP-positive cells.
Interpretation: The authors claim that balancing polymer hydrophobicity is crucial for PBAE-mediated gene delivery. Increasing backbone or side-chain hydrophobicity improves transfection, but excess hydrophobicity can reduce the need for a hydrophobic pairing. Optimized end-modified PBAEs are superior to FuGENE HD and Lipofectamine 2000 in COS-7 cells and are potentially useful non-viral gene delivery reagents.
Limitations: In vitro only: No in vivo validation, biodistribution, or therapeutic efficacy. - Single cell line: COS-7 cells only; generalizability to primary or human disease-relevant cells is not established. - No targeting ligand: Delivery relies on nonspecific electrostatic interactions. - Library screen at one ratio: Full 320-polymer library screened mainly at 60 wt/wt; only a subset tested across multiple ratios. - No long-term expression or safety data. - No mechanistic uptake/trafficking studies. - No direct in vivo comparison to commercial reagents. - No therapeutic gene payload: Reporter genes only (luciferase, GFP).
