Automated Screening of Cationic Lipid Formulations for Transfection

Automated Screening of Cationic Lipid Formulations for Transfection 

Department of Clinical Research, Tumor Biology Center, Freiburg, Germany 

A promising alternative to viral gene transfer is lipofection, the transfer of the negatively charged DNA material by cationic lipids (13-18). There is no restriction on the size of the therapeutic gene and no risk of immunogeni-city or infection (19). Thus, lipofection in vivo can be principally performed several times (20). Furthermore, cationic lipids can be synthesized in large quantities with relatively little effort. 

Despite the fact that many different cationic lipids have been synthesized and tested for transfection (25 34), relatively few systematic structure activity TE-relationship studies have been performed (35 39). As a result, no general relationship between chemical structure and TE could be drawn from these studies. One reason for this is that the chemical structure of a cationic lipid is not directly responsible for TE. TE rather depends on the biophysical characteristics of the cationic lipid aggregate (e.g., liposomes and lipoplexes), which, for its part, is dependent on the chemical structure of the lipids. In a previous study with analogs of the transfection lipid A-[l-(2,3-dioleoyloxy) propyl]-A,A,A-trimethylammoniumchloride (DOTAP) (40) which differ in their nonpolar hydrocarbon chains, it could be shown that the TE strongly depended on the biophysical properties of the resulting liposomes and lipoplexes (35). Minimal alterations of biophysical properties by using lipids with different hydrocarbon chains or by mixing the lipid with different neutral helper lipids could completely allow or prevent transfection. 

Cationic lipids cannot be dissolved in water and form aggregates in aqueous solution, such as bilayers. To prepare a homogeneous reagent, in most cases liposomes were made from cationic lipids in a first step. When it is not possible to form stable lipid bilayers (i.e., liposomes) using a single lipid, then it may be necessary to combine the cationic lipid with one or more so-called helper lipids like cholesterol (Choi) (41) or 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) (42). 

---