title: Amphiphilic, low molecular weight poly(ethylene imine) derivatives with enhanced stability for efficient pulmonary gene delivery.
abstract: BACKGROUND
  Poly(ethylene imine) (PEI) is a widely used transfection reagent for mammalian cells, but in vivo application of PEI 25 kDa is restricted by its toxicity. Low molecular weight (LMW) PEI is less toxic, but also less efficient than its high molecular weight equivalent, and prone to aggregation.
  
  
  METHODS
  A set of polymers was synthesized by coupling poly(ethylene glycol) (PEG) that contained either C(16/18) -chains (Cx-EO) or butyl-poly(propylene oxide)-co-poly(ethylene glycol) (ButPP). Critical micelle concentration (CMC) was determined for copolymers. Polyplexes were characterized by DNA binding ability, polyplex size and aggregation, hemolysis, and cytotoxicity. Transfection efficiency was tested in vitro and in vivo in mouse lungs.
  
  
  RESULTS
  Copolymers formed stable complexes with DNA, and showed enhanced complex stability in isotonic solution for at least 1 h. CMC was determined for Cx-EO-PEI 4.7 and 8.3 at 0.0019 and 0.0037 mM, respectively; membrane activity in a haemolysis assay was demonstrated for ButPP-PEI: both factors possibly enhance endosomal escape effect after PEGylation. IC(50) values of all synthesized polymers were in the range 6-33 ng/ml. Transfection efficiency of unmodified LMW-PEIs was equivalent or better than that of PEI 25 as a result of aggregation in vitro. Cells treated with polyplexes of amphiphilic polymers showed reduced transfection compared to PEI 25. After instillation in mouse lungs, highest transfection efficiency was demonstrated with Cx-EO copolymer of lowest molecular weight PEI.
  
  
  CONCLUSIONS
  A new set of polymers with low toxicity and high stability was synthesized, which contains promising candidates for pulmonary gene transfer, as documented by in vivo experiments in mice.
authors.affiliation: Department of Pharmaceutics and Biopharmacy, Philipps-Universität Marburg, Marburg, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Roesler
authors.forename: Felix P V
authors.initials: FP
authors.lastname: Koch
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmehl
authors.forename: Norbert
authors.initials: N
authors.lastname: Weissmann
authors.forename: Werner
authors.initials: W
authors.lastname: Seeger
authors.forename: Tobias
authors.initials: T
authors.lastname: Gessler
authors.forename: Thomas
authors.initials: T
authors.lastname: Kissel
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects; D004247:DNA / Q000235:genetics; D004912:Erythrocytes / Q000187:drug effects; D018014:Gene Transfer Techniques; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007097:Imines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D008168:Lung / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008823:Micelles; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D011095:Polyethylenes / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D013501:Surface-Active Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D014162:Transfection / Q000379:methods
chemical_list: D007097:Imines; D008823:Micelles; D011095:Polyethylenes; D013501:Surface-Active Agents; C505405:poly(ethylene imine); D004247:DNA