Non-linear pharmacodynamics in the transfection efficiency of a non-viral gene delivery system

Transfection efficiencies using LipofectAMINE varied by more than three orders of magnitude depending on the concentrations of lipid and plasmid DNA (pDNA) used to prepare the lipoplexes. When lipoplexes were formed at lower concentrations a striking positive but non-linear relationship was found between dose and transfection efficiency, while at higher (i.e., normally used) concentrations a linear relationship was maintained. To determine the contribution of intracellular pharmacokinetics (PK) and pharmacodynamics (PD) to the observed nonlinearity, we quantified pDNA in whole cells and nuclei by real-time PCR and compared the results with the transfection efficiencies. There was no significant difference in the efficiency of intracellular PK; however, a remarkable difference was observed in the efficiency of PD. Analysis of individual cells by confocal laser scanning microscopy (CLSM) revealed that the amount of nuclear-delivered pDNA was higher for lipoplexes prepared at the normal concentration (NCL) compared to those of lipoplexes prepared at low concentration (LCL). Moreover, the size of the NCL was larger than that of the LCL. Both the size of the lipoplex particle and the dose appear to contribute to the non-linear efficiency of PD. These results emphasize the need to control not only intracellular PK, but also PD for the rational development of non-viral gene delivery systems.