title: Long term stability of poly((2-dimethylamino)ethyl methacrylate)-based gene delivery systems.
abstract: OBJECTIVE
  To study the stability of polymer-plasmid complexes (polyplexes) both as an aqueous dispersion and in their lyophilized form.
  
  
  METHODS
  The characteristics of the polyplexes (size, charge and transfection potential) were monitored at different temperatures. Moreover, we studied possible changes in the secondary and tertiary structure of the plasmid by agarose gel electrophoresis and by CD spectroscopy to gain insight into the mechanism of polyplex degradation.
  
  
  RESULTS
  The polyplexes preserved almost their full transfection potential after aging in an aqueous solution of 20 mM Hepes (pH 7.4) containing 10% sucrose at 4 and 20 degrees C for 10 months. On the other hand, the polyplexes aged at 40 degrees C were rather unstable and lost their transfection capability with a half-life of around 2 months. During storage, conformational changes in the secondary and tertiary structure of DNA were observed. When naked plasmid DNA was aged at 40 degrees C as an aqueous solution and complexed with polymer just before the transfection experiment, a slower drop in its transfection capability was observed. The freeze-dried polyplexes using sucrose as lyoprotectant almost fully retained their transfection efficiency, even when aged at 40 degrees C for 10 months.
  
  
  CONCLUSIONS
  This study provides information about polyplex stability in aqueous dispersions on storage and demonstrates that freeze-drying is an excellent method to ensure long term stability.
authors.affiliation: Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.
authors.forename: J Y
authors.initials: JY
authors.lastname: Cherng
authors.forename: H
authors.initials: H
authors.lastname: Talsma
authors.forename: D J
authors.initials: DJ
authors.lastname: Crommelin
authors.forename: W E
authors.initials: WE
authors.lastname: Hennink
mesh_terms: D000818:Animals; D019556:COS Cells; D004587:Electrophoresis, Agar Gel; D005612:Freeze Drying; D015316:Genetic Therapy / Q000379:methods*; D007763:Lac Operon; D008689:Methacrylates / Q000494:pharmacology*; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000737:chemistry / Q000494:pharmacology*; D011108:Polymers / Q000494:pharmacology; D019163:Reducing Agents / Q000494:pharmacology*; D013395:Sucrose; D013696:Temperature; D013997:Time Factors; D014162:Transfection / Q000379:methods; D014867:Water
chemical_list: D008689:Methacrylates; D011108:Polymers; D019163:Reducing Agents; D014867:Water; D013395:Sucrose; C049840:2-(dimethylamino)ethyl methacrylate