Purpose: Intracellular protein and antibody delivery is limited by inefficient carriers, high toxicity, and a frequent requirement for serum-free conditions, especially in difficult-to-transfect cells such as immune cells, stem cells, and neurons. A simple noncovalent carrier that works in complete media and across diverse cell types is needed.
Hypothesis: If the polymeric peptide mimic PTDM (MePh₁₀-b-dG) is used to form noncovalent complexes with protein cargo, then it will deliver proteins and antibodies into diverse difficult-to-transfect cells more effectively than commercial amphiphilic carriers, including in serum-containing media and neurons.
Aims: Compare PTDM with four commercial amphiphilic carriers (Chariot, ProteoJuice, PULSin, Xfect) for GFP delivery. - Evaluate delivery in serum-free and complete media across five cell types. - Assess cellular viability associated with delivery. - Test antibody and antibody-fragment delivery into difficult-to-transfect neurons. - Establish PTDM as a broadly effective noncovalent protein delivery platform.
Delivery system:
Component: Carrier; Details: PTDM: MePh₁₀-b-dG, amphiphilic polymeric peptide mimic
Component: Architecture; Details: Hydrophobic MePh block + dense guanidinium (dG) block
Component: Complexation; Details: Noncovalent mixing; no conjugation or protein engineering
Component: Payloads; Details: GFP; polyclonal IgG-AF488; polyclonal F(ab′)₂-AF488
Component: Targeting ligand; Details: None
Component: Key feature; Details: Serum-compatible, noncovalent protein/antibody delivery
Component: Commercial comparators; Details: Chariot (Pep-1), ProteoJuice, PULSin, Xfect
Approach: In vitro only. No in vivo studies. - Cell types: HeLa, HUVEC, Jurkat T cells, hTERT MSCs, embryonic mouse hippocampal mHippoE cells. - Delivery conditions: 3 µg GFP; 30 min complexation; 4 h incubation; serum-free vs complete media (10% serum). - Antibody delivery: 5 nM IgG-AF488 or F(ab′)₂-AF488 into mHippoE cells for 4 h in complete media. - Controls: Untreated cells; commercial reagents individually optimized per manufacturer. - Replicates: n = 3 independent replicates; statistics by one-way ANOVA with Tukey post-test.
Key methods: Flow cytometry: % GFP-positive cells and median fluorescence intensity (MFI) after heparin wash to remove surface-bound complexes. - Confocal microscopy: Visualization of IgG-AF488 uptake in mHippoE neurons. - Viability assays: Cellular viability after delivery under serum-free and complete-media conditions. - Comparison: Side-by-side benchmarking against commercial carriers.
Key results: Commercial carriers: Xfect delivered GFP to all five cell types only in serum-free media; neurons were most challenging. PULSin delivered to all except neurons in serum-free media. ProteoJuice achieved only ~20% delivery in Jurkat cells. Chariot failed in all cell types. - Serum effect: In complete media, almost all commercial carriers lost efficacy; only PULSin with MSCs showed significant GFP delivery. - PTDM performance: PTDM delivered GFP effectively in every cell type in both serum-free and complete media. In mHippoE neurons, PTDM delivered to about half the population in complete media, whereas commercial carriers largely failed. - MFI: Commercial carriers showed low/no significant MFI in all cell types. PTDM produced significant MFI in all cell types in serum-free media and in MSCs and neurons in serum-containing media. - Antibody delivery: PTDM delivered IgG-AF488 and F(ab′)₂-AF488 to >90% of mHippoE neurons in complete media, with high MFI and no significant cytotoxicity. Confocal microscopy confirmed uptake into the cell body, excluding the nucleus. - Viability: Some serum-free conditions caused viability drops (PULSin in HeLa; PULSin, ProteoJuice, PTDM in Jurkat; PULSin and PTDM in mHippoE). Complete media eliminated most viability concerns.
Interpretation: The authors claim that PTDM is a promising noncovalent carrier for protein and antibody delivery, especially into difficult-to-transfect cells such as immune cells, stem cells, and neurons. PTDM outperformed commercial amphiphilic carriers in complete media and enabled efficient antibody delivery into neurons, addressing an unmet need in neuron biology and intracellular biologics delivery.
Limitations: In vitro only: No in vivo validation, biodistribution, or therapeutic efficacy. - Limited cargo set: GFP, IgG, and F(ab′)₂ only; no functional cytosolic delivery demonstrated in this study. - No mechanism: Membrane translocation and intracellular trafficking not resolved. - No quantitative cross-cargo comparison: Dye labeling differences preclude direct comparison of IgG, F(ab′)₂, and GFP amounts. - Single PTDM tested: Other PTDM structures or optimizations not explored. - Cell models: mHippoE is a murine hippocampal cell line, not primary human neurons. - Commercial comparators proprietary: Exact compositions and mechanisms unknown. - Small sample size: n = 3 independent replicates. - No long-term toxicity, immunogenicity, or repeat-dosing data. - No targeting ligand: Delivery relies on noncovalent complexation and passive interaction.
