Optimizing the formulation of procationic liposomes-protamine-DNA complexes by response surface methodology

The procationic liposomes-protamine-DNA (PLPD) vectors we described here are non-viral vehicles for gene delivery comprised of polycation-condensed plasmid DNA and procationic liposomes made of phospholipids, cholesterol, and CHETA (Cholest-5-en-3beta-yl[2-[[4-[(carboxymethyl)dithio]-1-iminobutyl]amino]ethyl] carbamate, C36H61N3O4S2). Response surface methodology (RSM) was employed to optimize the formulation of PLPD. A three-factor, five-level RSM design was used for the optimization procedure, with the weight ratio of protamine/DNA (X1), the molar percent of CHETA (X2), and the weight ratio of CHETA/DNA (X3) in the procationic liposomes as the independent variables. PLPD size (Y1) and PLPD transfectivity (Y2) that was quantified as mU of beta-galactosidase per milligram of total protein were response variables. The simple factor experiment was utilized to define the experimental design region, and therefore the responses for the 15 formulations were obtained. Mathematical equations and response surface plots were used to relate the dependent and independent variables. The mathematical model predicted the optimized levels of X1, X2, and X3 through which the desired particle size and transfectivity were achieved. According to these levels, an optimized PLPD formulation was prepared, resulting in a particle size of 228.9 +/- 8.0 nm and transfectivity of 24.26 +/- 2.60 mU beta-galactosidase/mg protein.