Lipid/DNA complexes as an intermediate in the preparation of particles for gene transfer: An alternative to cationic liposome/DNA aggregates

When cationic liposomes are mixed with plasmid DNA an aggregation reaction occurs. The heterogeneous membrane structures which arise following this reaction are dependent on liposomal lipid composition, liposome/DNA ratio as well as the presence of added salts or proteins. The resulting structures are also unstable, resulting in time dependent changes in the physical attributes of the aggregates. Pharmaceutical development of the liposome/DNA aggregates will be challenging because of these factors. For these reasons we have pursued development of alternative lipid-based systems asa vehicle for gene transfer. The pivotal step that led to development of these novel systems was the identification and isolation of a hydrophobic cationic lipid/DNA complex. This complex can be used as an intermediate in the preparation of well-defined particles. The hydrophobic lipid/DNA complex and the liposome/DNA aggregates are both formed as a consequence of multivalent electrostatic interactions. In contrast to the liposome/DNA aggregates, however, we believe that the particles formed when using lipid/DNA complex intermediates are a consequence of hydrophobic interactions.