title: Dendrimeric alkylated polyethylenimine nano-carriers with acid-cleavable outer cationic shells mediate improved transfection efficiency without increasing toxicity.
abstract: OBJECTIVE
  Improved polycation-based non-viral DNA vectors were sought by preparing dendrimers with polyethylenimine cores surrounded by various shells incorporating structural features intended to facilitate steps in transfection mechanisms. Dendrimeric vectors were designed with (a) an outer oligocation shell, intended to facilitate DNA release inside cells, (b) a hydrophobic C-16 alkyl shell, and (c) a polycationic core, the latter two intended to combine lipid-depletion and osmotic burst endosome escape mechanisms, respectively, and were (d) attached through an a acid-cleavable linker reported to hydrolyze at endosomal pH values.
  
  
  METHODS
  Vectors and DNA complexes were characterized by dynamic and static light scattering. Flow cytometry was used to quantitate transfection activity and cytotoxicity in CHO-K1 cells.
  
  
  RESULTS
  About 5-fold increased transfection activity was obtained for a vector constructed with an outer shell of oligocations attached through acid-cleavable linkers, relative to a control dendrimer with an acid-stable linker. The most effective oligocation component of outer shells tested was spermine. Neither modification was associated with increased cytotoxicity. This vector design did not permit an evaluation of the benefit of combining endosome release mechanisms.
  
  
  CONCLUSIONS
  Using acid-cleavable linkers to attach an outer shell of short, highly-charged oligocations to a PEI-based dendrimeric vector substantially increased transfection efficiency without increasing cytotoxicity.
authors.affiliation: Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota-Twin Cities, 308 Harvard St., SE, Minneapolis, Minnesota 55455, USA. wjsteele@ntu.edu.sg
authors.forename: Terry W J
authors.initials: TW
authors.lastname: Steele
authors.forename: Wayne Thomas
authors.initials: WT
authors.lastname: Shier
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000008:administration & dosage*; D050091:Dendrimers / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D011094:Polyethyleneimine / Q000737:chemistry*; D014162:Transfection
chemical_list: D050091:Dendrimers; D011094:Polyethyleneimine; D004247:DNA