title: Novel ortho ester-based, pH-sensitive cationic lipid for gene delivery in vitro and in vivo.
abstract: BACKGROUND
  Cationic lipoplexes are less toxic than viral gene vectors and more convenient to prepare but their efficiencies of gene delivery are generally lower.
  
  
  OBJECTIVE
  To develop ortho ester-based, pH-sensitive lipoplexes for efficient gene delivery both in cultured cells and in vivo.
  
  
  METHODS
  A novel cationic and acid-labile lipid (DOC) containing a cationic headgroup and a cholesterol-derived lipid tail joined together by an acid-labile ortho ester linker was designed and synthesized. DOC was formulated into liposomes with the conical helper lipid DOPE, and then into lipoplexes with plasmid DNA encoding a luciferase reporter gene. The physicochemical properties of the lipoplexes (size, surface charge and pH-sensitivity) were characterized. Gene delivery by DOC/DOPE/DNA lipoplexes was also evaluated in CV-1 cells and in CD-1 mice following intratracheal injection. Lipoplexes consisting of the acid-stable cationic lipid DC-Chol were characterized as a control.
  
  
  RESULTS
  DOC formed cationic lipoplexes with DOPE and DNA. After incubation at acidic pH 4.6, DOC/DOPE/DNA lipoplexes lost their positive charges and aggregated with one another as a result of DOC hydrolysis. Both in CV-1 cell culture and in CD-1 mice, DOC/DOPE/DNA lipoplexes increased the luciferase gene expression by 5- to 10-fold compared with the analogous but acid-stable DC-Chol/DOPE/DNA lipoplexes.
  
  
  CONCLUSIONS
  Incorporation of an acid-labile ortho ester linker into a cationic lipid is a viable approach to enhance gene delivery by the corresponding lipoplexes both in cultured cells and in vivo.
authors.affiliation: Department of Pharmaceutics and Medicinal Chemistry, Thomas J. Long School of Pharmacy and Health Sciences, University of the Pacific , Stockton, CA , USA and.
authors.forename: Xin
authors.initials: X
authors.lastname: Guo
authors.forename: Lucie
authors.initials: L
authors.lastname: Gagne
authors.forename: Haigang
authors.initials: H
authors.lastname: Chen
authors.forename: Francis C
authors.initials: FC
authors.lastname: Szoka
mesh_terms: D000818:Animals; D002412:Cations; D002460:Cell Line; D002784:Cholesterol / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D004247:DNA / Q000008:administration & dosage; D004983:Ethanolamines / Q000138:chemical synthesis / Q000737:chemistry*; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008081:Liposomes / Q000138:chemical synthesis / Q000737:chemistry*; D051379:Mice; D010714:Phosphatidylethanolamines / Q000008:administration & dosage; D014132:Trachea; D014162:Transfection / Q000379:methods*
chemical_list: C410262:1,2-dioleoyl-glycero-3-phosphatidyl ethanolamine; D002412:Cations; D004983:Ethanolamines; D008081:Liposomes; C000595431:N,N-dimethyl-(4-methoxy-(cholest-5-en-3-oxy)hept-3,5-dioxa-yl)amine; D010714:Phosphatidylethanolamines; D004247:DNA; D002784:Cholesterol
keywords: Acid-labile; cationic liposome; endosome; intratracheal; lipoplex