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Journal of Drug Targeting (J Drug Target)2013ReviewNon-viral Gene Delivery

Strategies on the nuclear-targeted delivery of genes

Jing Yao, Ying Fan, Yuanke Li, And Leaf HuangDOI 10.3109/1061186X.2013.830310

Summary

Non-viral gene delivery systems are safer than viral vectors but are highly inefficient at nuclear delivery. Only ~10–20% of applied plasmid DNA enters targeted cells, and only ~1–5% of the applied dose reaches the nucleus. The nuclear envelope is a major barrier to transgene delivery, and there is a need for “smart” non-viral vectors that can overcome multiple extracellular and intracellular barriers—especially nuclear transport—to enhance gene. Baseline inefficiency of non-viral vectors: Only 10–20% of applied plasmid DNA enters targeted cells, and only 1–5% enters the nucleus. - NLS enhancement: Addition of NLSs increased luciferase reporter gene expression.

Keywords

Targeted deliveryDNATransfectionPolyethylenimineViral vectorsPeptidesGene delivery
Purpose: Non-viral gene delivery systems are safer than viral vectors but are highly inefficient at nuclear delivery. Only ~10–20% of applied plasmid DNA enters targeted cells, and only ~1–5% of the applied dose reaches the nucleus. The nuclear envelope is a major barrier to transgene delivery, and there is a need for “smart” non-viral vectors that can overcome multiple extracellular and intracellular barriers—especially nuclear transport—to enhance gene expression.
Hypothesis: As a review article, this work does not test a single hypothesis. Its central thesis is:

If non-viral vectors are modified with peptides and small molecules that exploit natural nuclear transport mechanisms—such as nuclear localization signals (NLSs), cell-penetrating peptides, DNA-binding proteins, glucocorticoids, retinoic acid, and calcium phosphate—then nuclear translocation of therapeutic genes can be facilitated and gene expression efficacy can be significantly enhanced.

Aims: Primary Aim: To review the mechanisms of nuclear transport and the barriers hindering nuclear delivery of therapeutic genes. - Secondary Aims: - To summarize peptide-guided and small molecule–guided strategies for nuclear-targeted gene delivery. - To discuss lessons learned from viral nuclear transport mechanisms. - To highlight multifunctional envelope-type nano devices (MENDs) and other “smart” non-viral vectors. - To identify future directions for improving nuclear translocation of macromolecules.
Delivery system:

Component: Non-viral vectors; Examples Discussed: Poly-L-lysine (PLL), polyethyleneimine (PEI), liposomes, solid lipid nanoparticles (SLN), PLGA/PEI nanospheres, PAMAM dendrimers, calcium phosphate (CaP) nanoparticles, multifunctional envelope-type nano devices (MENDs)

Component: Payloads; Examples Discussed: Plasmid DNA (pDNA), siRNA, antisense oligodeoxynucleotides (ODNs), proteins (e.g., bovine serum albumin), luciferase reporter genes, GFP

Component: Peptide functionalization; Examples Discussed: TAT peptide (TATp), NLS peptides (e.g., SV40 large T-antigen), fusogenic peptides (GALA, KALA), histidine-rich peptides, octaarginine (R8), CR8C

Component: Small molecule functionalization; Examples Discussed: Dexamethasone (DEX), all-trans-retinoic acid (ATRA), calcium phosphate

Component: DNA-binding proteins; Examples Discussed: NF-κB p50, high mobility group box 1 (HMGB1), histones (H1, H2A, H2B)

Component: Targeting ligands; Examples Discussed: Transferrin, folate, anisamide (sigma receptor ligand), hyaluronic acid (HA)

Component: Key platforms; Examples Discussed: MEND, R8-MEND, T-MEND (tetra-lamellar MEND), lipid-coated CaP (LCP) nanoparticles

Approach: This is a narrative review synthesizing literature on nuclear-targeted gene delivery. No primary experimental data are presented. The review covers:
  • In vitro studies using cell lines such as HeLa, COS7, HepG2, HEK293, NIH3T3, B16F10, H460, U-87 MG, BT20, and PMSCs.
  • In vivo studies in mouse models, including tumor-bearing mice and metastatic lung tumor models.
  • Mechanistic discussions of endocytosis, endosomal escape, cytoplasmic transport, and nuclear import via nuclear pore complexes (NPCs).
Key methods: As a review, the “methods” are literature synthesis and comparative analysis. Headline data cited from primary studies were generated using:
  • Reporter gene assays: Luciferase and GFP expression.
  • Imaging: Confocal microscopy, MRI, magnetic separation.
  • Silencing assays: siRNA-mediated luciferase knockdown.
  • Biodistribution/efficacy: Tumor growth suppression, survival analysis in mice.
  • Cytotoxicity assays: Cell viability post-transfection.
  • Nuclear import analysis: Fluorescence localization, NPC transport studies.
Key results: Baseline inefficiency of non-viral vectors: Only 10–20% of applied plasmid DNA enters targeted cells, and only 1–5% enters the nucleus. - NLS enhancement: Addition of NLSs increased luciferase reporter gene expression by about 200-fold in HeLa and Cos7 cells without apparent cytotoxicity. - TATp-modified nanoparticles: TATp-conjugated superparamagnetic iron oxide particles enhanced transfection efficiency over 100-fold compared with unmodified particles. - Dexamethasone-PEI: DEX-conjugated low-molecular-weight PEI increased gene expression by an order of magnitude in HepG2 cells and at least two orders of magnitude in 293 cells. - PAMAM-DEX: Approximately 2-fold higher transfection efficiency than PAMAM in 293 cells. - HA/PEI₁₈₀₀-DEX/DNA ternary complexes: ~160 nm particles showed lowest cytotoxicity and highest transfection in B16F10 cells; suppressed tumor growth in vivo. - LCP nanoparticles: 3–4 fold higher silencing than liposome/polycation/DNA complexes; anisamide-targeted LCP achieved ~70% silencing in cultured tumor cells and ~50% in a xenograft model. A single IV dose of antiluciferase siRNA (0.12 mg/kg) reduced lung luciferase activity by 78% and prolonged mean survival by 27.8% in metastatic B16F10 tumor-bearing mice. - T-MEND: Transfection activity increased by several hundred-fold compared with conventional MEND in non-dividing JAWSII cells. - R8-MEND with 29DMAE: Transfection activity was almost 5-fold greater than R8-MEND containing protamine. - PNA-clamp NLS: Site-specific NLS attachment increased gene expression 7-fold. - NF-κB p50 coupling: Resulted in 31-fold augmentation of gene expression in mammalian cells. - HMG-1/PEI terplex: Transfection efficiency was 2.6–4.9-fold higher than PEI 25 kDa alone. - CaP with DOPA coating: Improved siRNA delivery 40-fold in vitro and 4-fold in vivo compared with lipid/protamine/DNA formulation.
Interpretation: The authors conclude that the nuclear envelope is a major barrier to non-viral gene delivery. Viral-inspired strategies—especially modification of non-viral vectors with peptides (NLS, TATp, fusogenic peptides) and small molecules (DEX, ATRA, CaP)—can significantly enhance nuclear translocation and gene expression. Multifunctional envelope-type nano devices (MENDs), particularly T-MENDs, achieve impressive nuclear transport by overcoming endosomal and nuclear membrane barriers via step-wise fusion. The authors expect that more intelligent and efficient non-viral vectors will be developed in the near future.
Limitations: Limitations inherent to the review:
  • No primary experimental data; conclusions are synthesized from existing literature.
  • No systematic search strategy or meta-analysis.
  • Focus is primarily on nuclear delivery; other barriers (e.g., extracellular stability, immune response) are discussed but less comprehensively.
  • Most cited studies are preclinical or in vitro; limited clinical translation data.

Limitations of the field highlighted by the authors:

  • Cytotoxicity: PLL and PEI show toxicity that increases with molecular weight; chloroquine addition increases toxicity.
  • PEGylation dilemma: PEGylation improves extracellular stability but inhibits endosomal escape and cellular uptake; reversible/exchangeable PEGylation is recommended.
  • NLS dissociation: NLSs may dissociate from DNA before reaching the nucleus.
  • Covalent NLS attachment: Chemical attachment of NLS peptides to DNA can occur at any location, potentially inhibiting gene expression.
  • Calcium phosphate safety concern: Ca²⁺ plays a role in cell signaling and injury; accumulation may increase risk of cell injury, though unpublished data suggest excess Ca²⁺ is pumped out or into mitochondria.
  • No large-animal validation: Most studies are in cell lines or mouse models; scalability and long-term safety remain unproven.

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