title: Plasmid CpG depletion improves degree and duration of tumor gene expression after intravenous administration of polyplexes.
abstract: OBJECTIVE
  Tumor gene expression after the intravenous (i.v.) administration of current polymer-based gene delivery systems is generally low and short-lived. Immune stimulatory CpG dinucleotides, present within the plasmid DNA of the polyplexes are likely to contribute to this. The effect of CpG replacement on the levels of transgene expression was studied, after the i.v. administration of polyethylenimine (PEI) polyplexes.
  
  
  METHODS
  Tumor transfection and immune stimulation of PEI polyplexes containing plasmid DNA encoding for luciferase and rich in CpG motifs was monitored and compared to polyplexes containing the same gene but devoid of CpG motifs. Lipoplexes based on 1,2-dioleyl-3-trimethylammonium-propane/dioleoylphosphatidylethanolamine liposomes were included as a control.
  
  
  RESULTS
  The replacement of CpGrich DNA by CpGfree DNA did neither affect the physical properties of the DNA complexes nor did it affect their in vitro transfection activity or cytotoxicity. The immune stimulation (interleukin-12) after i.v. administration of the PEI DNA complexes was low and unaffected by the presence of CpG motifs. The absence of CpG motifs within the different DNA complexes improved the degree and the duration of organ and tumor gene expression.
  
  
  CONCLUSIONS
  The depletion of CpG dinucleotides within the plasmid DNA of polyplexes enhances the degree and duration of in vivo transgene expression.
authors.affiliation: Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences (UIPS), Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands. h.k.dewolf@pharm.uu.nl
authors.forename: Holger K
authors.initials: HK
authors.lastname: de Wolf
authors.forename: Nina
authors.initials: N
authors.lastname: Johansson
authors.forename: Anh-Thy
authors.initials: AT
authors.lastname: Thong
authors.forename: Cor J
authors.initials: CJ
authors.lastname: Snel
authors.forename: Enrico
authors.initials: E
authors.lastname: Mastrobattista
authors.forename: Wim E
authors.initials: WE
authors.lastname: Hennink
authors.forename: Gert
authors.initials: G
authors.lastname: Storm
mesh_terms: D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D018899:CpG Islands / Q000235:genetics*; D004247:DNA / Q000008:administration & dosage / Q000737:chemistry; D016503:Drug Delivery Systems; D005079:Excipients; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D018014:Gene Transfer Techniques; D007249:Inflammation / Q000139:chemically induced / Q000473:pathology; D007275:Injections, Intravenous; D008081:Liposomes; D008297:Male; D051379:Mice; D008805:Mice, Inbred A; D010957:Plasmids / Q000008:administration & dosage* / Q000737:chemistry / Q000235:genetics*; D011108:Polymers; D014018:Tissue Distribution; D014162:Transfection; D019076:Transgenes / Q000187:drug effects
chemical_list: D005079:Excipients; D008081:Liposomes; D011108:Polymers; D004247:DNA