title: Chitosan-graft-branched polyethylenimine copolymers: influence of degree of grafting on transfection behavior.
abstract: BACKGROUND
  Successful non-viral gene delivery currently requires compromises to achieve useful transfection levels while minimizing toxicity. Despite high molecular weight (MW) branched polyethylenimine (bPEI) is considered the gold standard polymeric transfectant, it suffers from high cytotoxicity. Inversely, its low MW counterpart is less toxic and effective in transfection. Moreover, chitosan is a highly biocompatible and biodegradable polymer but characterized by very low transfection efficiency. In this scenario, a straightforward approach widely exploited to develop effective transfectants relies on the synthesis of chitosan-graft-low MW bPEIs (Chi-g-bPEI(x)) but, despite the vast amount of work that has been done in developing promising polymeric assemblies, the possible influence of the degree of grafting on the overall behavior of copolymers for gene delivery has been largely overlooked.
  
  
  RESULTS
  With the aim of providing a comprehensive evaluation of the pivotal role of the degree of grafting in modulating the overall transfection effectiveness of copolymeric vectors, we have synthesized seven Chi-g-bPEI(x) derivatives with a variable amount of bPEI grafts (minimum: 0.6%; maximum: 8.8%). Along the Chi-g-bPEI(x) series, the higher the degree of grafting, the greater the ζ-potential and the cytotoxicity of the resulting polyplexes. Most important, in all cell lines tested the intermediate degree of grafting of 2.7% conferred low cytotoxicity and higher transfection efficiency compared to other Chi-g-bPEI(x) copolymers. We emphasize that, in transfection experiments carried out in primary articular chondrocytes, Chi-g-bPEI(2.7%) was as effective as and less cytotoxic than the gold standard 25 kDa bPEI.
  
  
  CONCLUSIONS
  This work underlines for the first time the pivotal role of the degree of grafting in modulating the overall transfection effectiveness of Chi-g-bPEI(x) copolymers. Crucially, we have demonstrated that, along the copolymer series, the fine tuning of the degree of grafting directly affected the overall charge of polyplexes and, altogether, had a direct effect on cytotoxicity.
authors.affiliation: Unità Politecnico di Milano, Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali - INSTM, Milan, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Pezzoli
authors.forename: Francesca
authors.initials: F
authors.lastname: Olimpieri
authors.forename: Chiara
authors.initials: C
authors.lastname: Malloggi
authors.forename: Sabrina
authors.initials: S
authors.lastname: Bertini
authors.forename: Alessandro
authors.initials: A
authors.lastname: Volonterio
authors.forename: Gabriele
authors.initials: G
authors.lastname: Candiani
mesh_terms: D000818:Animals; D001672:Biocompatible Materials; D019556:COS Cells; D002417:Cattle; D002470:Cell Survival; D048271:Chitosan / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D002522:Chlorocebus aethiops; D019902:Chondrocytes / Q000378:metabolism; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D006367:HeLa Cells; D006801:Humans; D008970:Molecular Weight; D011094:Polyethyleneimine / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D011108:Polymers / Q000009:adverse effects / Q000138:chemical synthesis / Q000737:chemistry*; D014162:Transfection / Q000379:methods*
chemical_list: D001672:Biocompatible Materials; D011108:Polymers; C551320:chitosan-graft-polyethylenimine; D011094:Polyethyleneimine; D048271:Chitosan