Dios-Arg is a steroid-based cationic lipid that contains a diosgenin skeleton coupled to an L-arginine head group. It forms a complex with plasmid DNA and decreases plasmid DNA migration in an agarose-gel retardant assay at charge ratio greater than or equal to 4. Dios-Arg facilitates transfection of plasmid DNA into H1299 and HeLa cells in the presence and absence of fetal bovine serum, an effect that is reversed by the lipid raft-mediated endocytosis inhibitor methyl-β-cyclodextrin and the caveolae-mediated endocytosis inhibitor genistein . It has been used, coupled to 1,2-dioleoyl-sn-glycero-3-PE , to bind siRNA and plasmid DNA to form cationic lipid nanoparticles for intracellular transport. Dios-Arg is cytotoxic to H1299 and HeLa cells (IC50s = 83.5 and 74.1 µg/ml, respectively).