Degradable Polymers for Gene Delivery

Purpose: Non-viral gene delivery needs safe and effective carriers. PEI is effective but cytotoxic, while viral vectors raise safety concerns. Degradable poly(β-amino ester)s may provide effective gene delivery with reduced cytotoxicity. This study investigates how small changes in polymer synthesis ratio and end-group structure affect transfection efficacy and cell-type specificity.

Hypothesis: Small modifications to the monomer ratio used during polymerization and to the end-capping group structure will significantly alter gene delivery efficacy in a cell-type-dependent manner. Polymers synthesized at a lower acrylate:amine ratio (1.05:1) are expected to be generally more effective at low polymer:DNA weight ratios than those synthesized at 1.2:1.

Aims: Synthesize degradable poly(β-amino ester)s at two acrylate:amine monomer ratios: 1.05:1 and 1.2:1. - End-modify the base polymers with three different amine-containing small molecules: Poly 1, Poly 2, and Poly 3. - Evaluate gene delivery efficacy in COS-7 cancerous fibroblasts and IMR-90 human primary fibroblasts. - Compare efficacy with commercial reagents Lipofectamine 2000 and 25 kDa branched PEI. - Assess cell viability after transfection.

Delivery system: Polymer class: Degradable poly(β-amino ester)s. - Base polymer synthesis: 1,4-butanediol diacrylate + 5-amino-1-pentanol at molar ratios 1.05:1 and 1.2:1 in DMSO at 40 °C for 48 h. - End-modification: 1-(3-aminopropyl)-4-methylpiperazine (Poly 1), 1-(3-aminopropyl)pyrrolidine (Poly 2), or 4-aminophenyl disulfide (Poly 3) at room temperature for 24 h. - Payload: CMV-Luc plasmid DNA. - Polyplex formation: Self-assembly by electrostatic interaction in 25 mM sodium acetate buffer, pH 5. - Weight ratios tested: Polymer:DNA 20, 40, 60, and 100 (w/w). - Controls: 25 kDa branched PEI at w/w 1 (N/P ≈ 8) in 150 mM NaCl; Lipofectamine 2000 per manufacturer instructions. - Targeting ligand: None.

Approach: In vitro study using COS-7 cells and IMR-90 human primary fibroblasts. Cells were plated at 15,000 cells/well in 96-well plates, adhered overnight, then incubated with polyplexes for 4 h in complete media. Media was replaced, and luciferase expression was measured 48 h post-transfection. Protein content was measured by BCA assay. Gene delivery graphs show mean ± SD, n = 4. IMR-90 cells were used prior to passage eight.

Key methods: Gel permeation chromatography (GPC) for molecular weight and PDI. - Luciferase reporter gene expression (relative light units per gram protein). - BCA protein assay for normalization and viability assessment. - Visual inspection of cell viability. - Comparison with PEI and Lipofectamine 2000.

Key results: Molecular weight: 1.2:1 polymers had M_w ~6 kDa; 1.05:1 polymers had higher M_w ~6.5–8.5 kDa. - Low weight ratios (20 and 40 w/w): 1.05:1 polymers were generally more effective than 1.2:1 polymers. For Poly 1 at 20 w/w, the 1.05:1 ratio was more than 10-fold as effective in COS-7 cells and 400-fold more effective in IMR-90 cells. - High weight ratios (60 and 100 w/w): The trend was not seen; both synthesis ratios were comparable. Exception: Poly 2 in IMR-90 cells was only effective at the 1.05:1 ratio at any tested weight ratio. - Cell-type specificity: Poly 3 at 60 or 100 w/w gave very high delivery to COS-7 cells but very poor delivery to IMR-90 cells. Poly 3 (1.2:1, 60 w/w) gave 2-fold higher expression than Lipofectamine 2000 in COS-7 cells but >200-fold less expression in IMR-90 cells. - IMR-90 transfection: Poly 1 or Poly 2 at 1.05:1 and 100 w/w were most effective, achieving 8–10-fold higher transfection than Lipofectamine 2000 in serum-containing media. - Versus PEI: The polymers were up to 2–3 orders of magnitude more effective than 25 kDa branched PEI. - Viability: Cells remained viable and comparable to untreated controls by visual inspection and BCA protein content.

Interpretation: Small changes to polymer molecular weight and end-group chemical structure can significantly tune gene delivery efficacy and cell-type specificity. The degradable poly(β-amino ester)s were more effective than Lipofectamine 2000 or PEI for certain cancerous and primary fibroblasts. These materials may be useful for cancer therapeutics and regenerative medicine, and further structure exploration may yield safe, effective transfection reagents with natural proclivity for targeting certain cell types.

Limitations: In vitro only; no in vivo validation. - Only two cell types were tested: COS-7 and IMR-90. - Follow-up was limited to 48 h post-transfection. - Mechanisms of uptake, endosomal escape, and cell-type specificity were not quantified; the authors state these are being investigated. - No detailed serum stability, biodistribution, or long-term toxicity data. - No animal models or clinical translation data.