Cationic lipid structure and formulation considerations for optimal gene transfection of the lung

Enhanced gene transduction to the lung using cationic lipids could be attai ned through optimization of the structure of the lipids and the formulation of the cationic lipid : plasmid DNA (pDNA) complexes. We have expanded on our earlier observation of the importance of the structural orientation of the cationic lipid headgroup. Through the synthesis of a number of matched pairs of cationic lipids differing only in the configuration of their headg roup, we confirmed that those harboring a T-shape headgroup are more active than their linear counterparts, at least when tested in the lungs of BALB/ c mice. Additionally, we demonstrated that not only are the structural cons iderations of these cationic lipids important, but also their protonation s tate, the free base being invariably more active than its salt counterpart. The salt forms of cationic lipids bound pDNA with greater avidity, which m ay have affected their subsequent intracellular dissolution and transit of the pDNA to the nucleus. Inclusion of a number of frequently used solutes i n the vehicle severely inhibited the gene transfection activity of the cati onic lipids. The selection of neutral co-lipids was also an important facto r for overall transfection activity of the formulation, with significant ga ins in transfection activity realized when diphytanoylphosphatidylethanolam ine or dilinoleoylphosphatidylethanolamine were used in lieu of dioleoylpho sphatidylethanolamine. Finally, we showed that a transacylation reaction co uld occur between the cationic lipid and neutral co-lipid which reduced the transfection activity of the complexes. It is the hope that as our underst anding of the many factors that influence the activity of these cationic li pid:pDNA complexes improves, formulations with much greater potency can be realized for use in the treatment of pulmonary diseases.