*3.4. Association of FA-PEG-Modified siRNA Lipoplexes with Cells*

To examine the effect of cationic lipid type on cellular association with FA-PEG-modified siRNA lipoplexes, we measured the siRNA amount taken up by KB cells at 3 h after transfection with FA-PEG-modified siRNA lipoplexes (Figure 4). In LP-HAPC, LP-OH, and LP-OH-C, the amount of siRNA in the cells decreased with increasing PEG-modification (Figure 4A–C). In contrast, 1–3 mol% FA-PEG-modification of LP-HAPC and LP-OH exhibited high cellular uptake of siRNA in the cells, compared with PEG-modified ones (Figure 4A,B). However, in LP-OH-C, with an increase of FA-PEG-modification, the amount of siRNA in the cells was decreased substantially, and LP-OH-C-3mol%FA-PEG2000 lipoplexes did not enhance cellular association compared with LP-OH-C-3mol%PEG2000 lipoplexes (Figure 4C). These results indicated that the cellular association of FA-PEG-modified siRNA lipoplexes might be strongly affected by cationic lipid type in cationic liposomes.

**Figure 4.** Effect of FA-PEG-modification of cationicliposomes on cellular association at 3 h after transfection of FA-PEG-modified siRNA lipoplexes. (**A**) LP-HAPC-1–3mol%PEG2000 and LP-HAPC-1–3mol%FA-PEG2000, (**B**) LP-OH-1–3mol%PEG2000 and LP-OH-1–3mol%FA-PEG2000, (**C**) LP-OH-C-1–3mol%PEG2000 and LP-OH-C-1–3mol%FA-PEG2000 were used. The siRNA lipoplexes were formed by mixing cationic liposomes with AF-siRNA, and they were added to KB cells at a final concentration of 50 nM siRNA. The association of siRNA lipoplexes with the cells was determined on the basis of Alexa Fluor®488-fluorescence by flow cytometry. Each column represents the mean fluorescent intensity + SD (*n* = 3).
