Protein expression following non-viral delivery of plasmid DNA coding for basic FGF and BMP-2 in a rat ectopic model

Abstract

Non-viral delivery of genes involved in stimulation of bone formation has been pursued for clinical bone repair, but no effort has been made to assess protein expression levels after in vivo delivery. This is critical to better understand gene delivery efficiencies and to compare different modes of non-viral delivery. This study investigated expression levels of basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) after delivering expression vectors (plasmid DNA) with polymeric carriers in a rat subcutaneous implant model. The polymers used were a 2 kDa molecular weight polyethylenimine modified with linoleic acid (PEI-LA) and the 25 kDa PEI (PEI25) used for non-viral gene delivery in animal models. The PEI-LA mediated delivery of the plasmid DNAs in 293T cells led to ∼3.5 and ∼13 ng/106 cells/day secretion of bFGF and BMP-2 in vitro, respectively. Using the reporter protein, Green Fluorescence Protein (GFP), transfection in implants was readily detected by the presence of GFP-positive cells and a polymeric carrier was needed for this GFP expression. No bFGF and BMP-2 were detected in the scaffolds due to high background in detection assays and/or rapid diffusion of the secreted proteins from the implant site. However, using an ex vivo culture system, significant levels of BMP-2, but not bFGF, secretion were observed from the scaffolds. The BMP-2 secretion from PEI-LA delivered expression vector was equivalent and/or superior to PEI25 depending on the plasmid DNA implant dose. Gelatin scaffolds were able to sustain ∼0.3 ng/sponge/day BMP-2 secretion as compared to collagen scaffolds (∼0.1 ng/sponge/day). These values were equivalent to secretion rates reported with some viral delivery systems from independent studies.