Gene delivery efficiency and cytotoxicity of heterocyclic amine-modified PAMAM and PPI dendrimers

Component: Dendrimer Types; Description: • PAMAM (poly-amidoamine): G3 (32 surface amines, MW 6909) and G4 (64 surface amines, MW 14,215)<br>• PPI (poly-propylenimine): G4 (32 surface amines, MW 3513.9) and G5 (64 surface amines, MW 7168.1)

Component: Modifications; Description: Conjugation via amidation (EDC/HOBt coupling) of primary amines with:<br>• Histidine (imidazole ring, pKa ~6.0)<br>• 3-Pyridylacetic acid (pyridine ring, pKa ~5.2)<br>• Piperazine-2-carboxylic acid (piperazine ring, pKa ~5.6)

Component: Grafting Percentages; Description: 10%, 30%, 50% of surface primary amines (targeted); actual via TNBS assay (Table 1)

Component: Payload; Description: pRL-CMV-Luc plasmid DNA (Renilla luciferase reporter)

Component: Cell Model; Description: Neuro-2a (murine neuroblastoma) cells

Component: Controls; Description: Unmodified PPI (G4, G5) and PAMAM (G3, G4); bafilomycin A1 treatment for mechanism

Component: Complexation Ratio; Description: C/P (carrier/plasmid, wt/wt) ratios: 2, 4, 6

Parameter: Synthesis; Details: EDC/HOBt coupling; 24 h reaction; dialysis (6-8 kDa MWCO) for 72 h; freeze-dried

Parameter: Characterization; Details: FTIR (amide bond confirmation); ¹H NMR and ¹³C NMR (selected derivatives); TNBS assay (grafting percentage)

Parameter: DNA Condensation; Details: Ethidium bromide exclusion assay; stepwise addition of polymer to DNA (5 μg); fluorescence at 510/590 nm

Parameter: Buffering Capacity; Details: Acid-base titration (0.1 M HCl); pH range 12 → 3; buffering capacity (β) = ΔA/ΔpH (endosomal pH 4.5-7.5)

Parameter: Transfection; Details: 96-well plate; 1×10⁴ cells/well; 200 ng pDNA/well; 4 h exposure; 24 h post-transfection; luciferase assay (RLU/4000 cells)

Parameter: Bafilomycin A1 Treatment; Details: 200 nM, 1 h pre-treatment; luciferase assay as above

Parameter: Cytotoxicity; Details: MTT assay; 4 h exposure; 24 h post-treatment; 575/630 nm absorbance

Parameter: Particle Characterization; Details: DLS (size) and zeta potential (Malvern Nano ZS); C/P ratios 2, 4, 6

Parameter: Replicates; Details: ≥3 independent experiments; mean ± SD

Parameter: Statistical Tests; Details: Student's t-test; P ≤ 0.05 considered significant

Analysis Category: Grafting Efficiency; Methods: TNBS assay (2,4,6-trinitrobenzenesulfonic acid); absorbance at 410 nm; standard curve of unmodified dendrimers

Analysis Category: Chemical Characterization; Methods: FTIR (amide I band 1644-1649 cm⁻¹); ¹H NMR (D₂O); ¹³C NMR (amide bond confirmation)

Analysis Category: DNA Condensation; Methods: Ethidium bromide fluorescence quenching (Jasco FP-6200); 510 nm excitation/590 nm emission

Analysis Category: Buffering Capacity; Methods: Acid-base titration (0.1 M HCl); pH meter (JENWAY3310); β = ΔA/ΔpH

Analysis Category: Transfection Efficiency; Methods: Promega luciferase assay; Berthold Luminometer; RLU normalized to 4000 cells

Analysis Category: Cytotoxicity; Methods: MTT assay (5 mg/mL stock); DMSO solubilization; 575/630 nm absorbance

Analysis Category: Particle Size/Zeta Potential; Methods: Malvern Nano ZS (DLS); HBG buffer; 30 measurements per sample; n=3

Carrier: PPI4-His50; Targeted Grafting: 50%; Actual Grafting (%): 33.2 ± 0.85%

Carrier: PPI4-Pyr50; Targeted Grafting: 50%; Actual Grafting (%): 36.2 ± 2.0%

Carrier: PPI4-Pip50; Targeted Grafting: 50%; Actual Grafting (%): 37.1 ± 1.02%

Carrier: PPI5-Pyr50; Targeted Grafting: 50%; Actual Grafting (%): 40.2 ± 0.85%

Carrier: PPI5-Pip50; Targeted Grafting: 50%; Actual Grafting (%): 33.3 ± 1.67%

Carrier: PPI5-His50; Targeted Grafting: 50%; Actual Grafting (%): 46.9 ± 2.01%

Carrier: PAMAM4-Pip50; Targeted Grafting: 50%; Actual Grafting (%): 40.58 ± 1.78%

Carrier: G4 PPI; Unmodified: 3.99 ± 0.25; Modified (50%): PPI4-His50: 7.15; Fold Increase: 1.8×

Carrier: G5 PPI; Unmodified: 14.97 ± 1.52; Modified (50%): PPI5-Pip50: 22.72; Fold Increase: 1.5×

Carrier: G3 PAMAM; Unmodified: 7.24 ± 0.45; Modified (50%): PAMAM3-His50: 10.22; Fold Increase: 1.4×

Carrier: G4 PAMAM; Unmodified: 23.69 ± 0.75; Modified (50%): PAMAM4-Pip50: 48.97; Fold Increase: 2.1×

Carrier: PPI4-His50; C/P Ratio: C/P=6; Fold Increase: 3×; Significance: NS

Carrier: PPI5-Pyr50; C/P Ratio: C/P=6; Fold Increase: 22.7×; Significance: P < 0.001

Carrier: PPI5-His50; C/P Ratio: C/P=6; Fold Increase: 10.35×; Significance: P < 0.001

Carrier: PPI5-Pyr30; C/P Ratio: C/P=6; Fold Increase: 8.20×; Significance: P < 0.001

Carrier: PPI5-Pip50; C/P Ratio: C/P=6; Fold Increase: 4.75×; Significance: P < 0.001

Carrier: PAMAM3-Pip50; C/P Ratio: C/P=4; Fold Increase: 4.4×; Significance: -

Carrier: PAMAM4-Pip50; C/P Ratio: C/P=6; Fold Increase: 7.65×; Significance: -

Carrier: Best PPI vs. Best PAMAM; C/P Ratio: -; Fold Increase: 22.7× vs. 7.65×; Significance: PPI superior

Carrier: PPI5-Pyr50; Transfection Decrease: ~30-fold decrease; Significance: P < 0.001

Carrier: PAMAM4-Pip50; Transfection Decrease: ~8-fold decrease; Significance: P < 0.001

Carrier: PPI5 (unmodified); Viability: Baseline; vs. Unmodified: -

Carrier: PPI5 derivatives; Viability: >80%; vs. Unmodified: Significantly higher (P < 0.001)

Carrier: PAMAM4 derivatives; Viability: Variable; vs. Unmodified: Some lower than unmodified (not significant for transfection)

Carrier: PPI5-Pyr50 (C/P=6); Size (nm): 224.4 ± 5.0; Zeta Potential (mV): +27.2 ± 1.45

Carrier: PPI5-Pip50 (C/P=6); Size (nm): 298.2 ± 25.1; Zeta Potential (mV): +18.3 ± 1.07

Carrier: PPI5-His50 (C/P=6); Size (nm): 198.1 ± 4.9; Zeta Potential (mV): +27.1 ± 1.52

Carrier: PAMAM4-Pip50 (C/P=6); Size (nm): 144.1 ± 4.5; Zeta Potential (mV): +10.27 ± 0.79

Carrier: PAMAM4-Pip50 (C/P=4); Size (nm): 71.5 ± 0.9; Zeta Potential (mV): +25.6 ± 1.35

1. In vitro only: All experiments performed in Neuro-2a cells; no in vivo validation of transfection efficiency, biodistribution, or therapeutic efficacy.

2. Single cell line: Only one cell type (murine neuroblastoma) was tested; transfection efficiency may vary across different cell types.

3. Grafting efficiency lower than targeted: Actual grafting percentages were consistently lower than the targeted 10%, 30%, and 50% (e.g., 50% target yielded ~30-47% actual substitution), making precise structure-activity comparisons challenging.

4. Limited mechanistic characterization: While bafilomycin A1 confirmed proton sponge mechanism, the study did not quantify cellular uptake, endosomal escape efficiency, or intracellular trafficking of dendriplexes.

5. No in vivo toxicity: Cytotoxicity was only assessed in vitro by MTT; systemic toxicity, immunogenicity, and biocompatibility in vivo were not evaluated.

6. No comparison to commercial transfection reagents: The study did not benchmark modified dendrimers against Lipofectamine or other commercial reagents.

7. Limited structural characterization: FTIR, ¹H NMR, and ¹³C NMR were only performed on selected derivatives with best transfection activity, not on all synthesized carriers.

8. Particle size in HBG buffer: Size measurements were performed in HBG buffer, not in complete cell culture medium with serum, which may affect particle aggregation and size.

9. No siRNA delivery tested: The study focused on plasmid DNA delivery; siRNA delivery efficiency was not evaluated.

10. Transfection readout only luciferase: Only reporter gene (luciferase) expression was measured; functional delivery of therapeutic genes or protein expression kinetics was not assessed.

11. Mechanistic role of pKa not fully resolved: While the authors discuss pKa values of heterocyclic amines, a detailed correlation between pKa, buffering capacity, and transfection efficiency was not systematically established for all derivatives.

12. No surface morphology/TEM: Transmission electron microscopy of dendriplexes was not performed to confirm particle morphology and size distribution.

Report prepared based on the published Materials Science and Engineering C article. For full experimental details, supplementary data, and complete references, please refer to the original publication.