Inhibition of cationic liposomes of [3H]thymidine incorporation into DNA of L1210 cells.

The in vitro cytotoxicity of cationic liposomes for L1210 cells was studied by measuring in two hours incubation their effect on [3H] thymidine incorporation into DNA. Liposomes prepared from the mixtures dipalmitoylphosphatidylcholine-cholesterol-stearylamine, egg yolk phosphatidyl-choline-cholesterol-stearylamine and egg yolk phosphatidyl-choline-stearylamine inhibit [3H] thymidine incorporation into L1210 cells DNA. The degree of inhibition increases with incubation time and the concentration of liposomes in the incubations. Liposomes of similar compositions, but without stearylamine (neutral liposomes), did not affect [3H] thymidine incorporation. On the other hand, fluorescence microscopy of cell incubated with liposomes containing 10 mM 6-carboxy fluorescein showed only cationic liposomes adsorbed on the surface of L1210 cells. It is concluded that the inhibition of [3H] thymidine incorporation due to cationic liposomes is partly related to their adsorption on the cell plasma membrane.