Polyethylenimine-mediated gene delivery to the lung and therapeutic applications

Abstract

Nonviral gene delivery is now considered a promising alternative to viral vectors. Among nonviral gene delivery agents, polyethylenimine (PEI) has emerged as a potent candidate for gene delivery to the lung. PEI has some advantages over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. However, intracellular (mainly the nuclear membrane) and extracellular obstacles still hamper its efficiency in vitro and in vivo, depending on the route of administration and the type of PEI. Nuclear delivery has been increased by adding nuclear localization signals. To overcome nonspecific interactions with biological fluids, extracellular matrix components and nontarget cells, strategies have been developed to protect polyplexes from these interactions and to increase target specificity and gene expression. When gene delivery into airway epithelial cells of the conducting airways is necessary, aerosolization of complexes seems to be better suited to guarantee higher transgene expression in the airway epithelial cells with lower toxicity than observed with either intratracheal or intravenous administration. Aerosolization, indeed, is useful to target the alveolar epithelium and pulmonary endothelium. Proof-of-principle that PEI-mediated gene delivery has therapeutic application to some genetic and acquired lung disease is presented, using as genetic material either plasmidic DNA or small-interfering RNA, although optimization of formulation and delivery protocols and limitation of toxicity need further studies.

Keywords: RNA interference; airway epithelial cells; gene therapy; gene transfer; lung; polyethylenimine.

Figure 1

Chemical structure of linear PEI, branched PEI and water-soluble lipopolymer (WSLP). Copyright © 2006. Reprinted with permission from Park TG, Jeong JH, Kim SW. 2006. Current status of polymeric gene delivery systems. Adv Drug Deliv Rev, 58:467–86.

Figure 2

Zeta potential (A) and size (B) of non-PEGylated (•) and PEGylated (•) linear PEI 22 kDa complexes prepared in 5% glucose at different N/P ratios were measured using a Malvern Zetasizer. Note that the grafting with PEG residues allows to partially shield the surface charge of the polyplexes. The size of the particles generated with the PEI-PEG conjugate at N/P above 3 was slightly bigger than that observed with PEI (125 vs 100 nm). Copyright © 2002. Reprinted with permission from Kichler A, Chillon M, Leborgne C, et al 2002. Intranasal gene delivery with a polyethylenimine-PEG conjugate. J Control Release, 81:379–88.

Figure 3

Electron microscopy of PEI/DNA complexes. PEI 25 kDNA complexes prepared in water (a) HBS (b) and 5% glucose (c) Copyright © 2005. Reprinted with permission from Rudolph C, Schillinger U, Ortiz A, et al 2005b. Aerosolized nanogram quantities of plasmid DNA mediate highly efficient gene delivery to mouse airway epithelium. Mol Ther, 12:493–501. Linear PEI 22 kDa complexes prepared in 150 mM NaCl (d) or 5% glucose (e) Copyright © 1998. Reprinted with permission from Goula D, Remy JS, Erbacher P, et al. 1998b. Size, diffusibility and transfection performance of linear PEI/DNA complexes in the mouse central nervous system. Gene Ther, 5:712–7.

Figure 4

Schematic representation of three strategies used for the formation of PEGylated ligand-containing PEI/DNA and PEI/siRNA complexes. (A) After PEGylation of PEI, the ligand reacts with functionalized distal end of the hydrophilic arm. The last step then consists of condensing the DNA/siRNA with the ligand-PEG-PEI conjugate. (B) PEI/DNA or PEI/siRNA complexes are first generated. The resulted polyplexes are modified by a heterobifunctional PEG which reacts with aminogroups of PEI. Ligands are finally incorporated into the complexes by conjugation with the distal end of the PEG. (C) The first step consists of covalently coupling the ligand to PEI. Addition of plasmid DNA or siRNA leads to the formation of ligand-PEI/DNA(siRNA) complexes which are subsequently modified with PEG chains. Modified with permission from Kichler A. 2004. Gene transfer with modified polyethylenimines. J Gene Med, 6:S3–S10.