Lipophilic polylysines mediate efficient DNA transfection in mammalian cells

Low molecular weight (Mr approximately 3000) poly(L-lysine) (PLL) conjugated to N-glutarylphosphatidylethanolamine is an effective carrier to promote DNA-mediated transfection in cultured mammalian cells. The conjugates, named 'lipopolylysines', contained an average of two phospholipid groups per molecule of PLL. Similar conjugates of the non-degradable poly(D-lysine) also had a similar transfection activity, indicating that the degradation of the carrier is not required for the activity. Unconjugated polylysines had little activity. The transfection activity of the lipopolylysine has been optimized with respect to the DNA concentration, DNA/carrier ratio, incubation time and the presence of serum in the incubation medium. The binding of lipopolylysine with DNA was measured by the degree of retardation of DNA in agarose gel electrophoresis. It was found that at the optimal DNA/lipopolylysine ratio for transfection, all DNA were found in large complexes which did not enter the gel. The transfection activity of the lipopolylysine, under optimal conditions, was approximately 3-fold higher than that of lipofectin, a widely used commercial reagent. Moreover, lipopolylysine mediated transfection even in the presence of 10% calf serum; whereas the lipofectin lost about 70% of its activity under the same condition. However, unlike lipofectin the transfection activity of the lipopolylysine depended on scraping the treated cells. Furthermore, lipopolylysine only transfected attached monolayer cells, and not suspension cells.