title: Polyethylenimine PEI F25-LMW allows the long-term storage of frozen complexes as fully active reagents in siRNA-mediated gene targeting and DNA delivery.
abstract: BACKGROUND
  Polyethylenimines (PEIs) are synthetic, charged polymers which function as transfection reagents based on their ability to compact DNA into complexes. Recently, PEI-mediated delivery of nucleic acids has been extended towards small interfering RNAs (siRNAs) which are instrumental in the induction of RNA interference (RNAi). Since RNAi represents a powerful method for specific gene silencing, the PEI-based delivery of siRNAs is a promising tool for novel putative therapeutic strategies.
  
  
  OBJECTIVE
  For therapeutic use, major requirements are the development of formulations which (i) are sufficiently stable in the presence of serum, and which can be (ii) easily and reproducibly manufactured and (iii) stored for a prolonged time with full retention of their integrity and bioactivity. In this paper, we explore the potential of PEI F25-LMW, a low-molecular weight PEI with superior transfection efficacy and low toxicity, towards these goals.
  
  
  RESULTS
  We have systematically analyzed and determined optimal DNA and siRNA complexation conditions with regard to various parameters including buffer concentration, ionic strength, pH and incubation time. As opposed to 22kDa linear PEI (L-PEI), the low-molecular weight (4-10kDa) PEI F25-LMW performs DNA transfection and siRNA gene targeting with identical efficacies in the presence of serum, thus emphasizing its usefulness in vivo. Furthermore, in contrast to other polyethylenimines, PEI F25-LMW-based DNA or siRNA complexes allow freeze/thawing and frozen storage for several months. Their activity is fully retained without requiring specific buffer conditions or the addition of any lyoprotectant. Physicochemical analysis and atomic force microscopy reveal a distinct size pattern with the presence of two complex subgroups and show that frozen PEI F25-LMW complexes remain stable with little increase in complex size, no changes regarding their zeta potential and cytotoxicity, and full retention of nucleic acid protection.
  
  
  CONCLUSIONS
  Frozen PEI F25-LMW-based complexes represent efficient and stable ready-to-use formulations of DNA- or siRNA-based gene therapy products.
authors.affiliation: Department of Pharmacology and Toxicology, Philipps-University School of Medicine, Marburg, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Höbel
authors.forename: Robert
authors.initials: R
authors.lastname: Prinz
authors.forename: Anastasia
authors.initials: A
authors.lastname: Malek
authors.forename: Beata
authors.initials: B
authors.lastname: Urban-Klein
authors.forename: Johannes
authors.initials: J
authors.lastname: Sitterberg
authors.forename: Udo
authors.initials: U
authors.lastname: Bakowsky
authors.forename: Frank
authors.initials: F
authors.lastname: Czubayko
authors.forename: Achim
authors.initials: A
authors.lastname: Aigner
mesh_terms: D002021:Buffers; D045744:Cell Line, Tumor; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D005615:Freezing; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D009994:Osmolar Concentration; D011094:Polyethyleneimine / Q000737:chemistry* / Q000633:toxicity; D034622:RNA Interference; D020871:RNA Stability; D034741:RNA, Small Interfering / Q000737:chemistry / Q000378:metabolism*; D044967:Serum / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
chemical_list: D002021:Buffers; D007202:Indicators and Reagents; D034741:RNA, Small Interfering; D011094:Polyethyleneimine; D004247:DNA