Effects of the lipophilic core of polymer nanoassemblies on intracellular delivery and transfection of siRNA

Despite effective gene silencing in vitro, in vivo delivery and transfection of siRNA remain challenging due to the lack of carriers that protect siRNA stably in the body. This study is focused to elucidate the correlation between complex stability and transfection efficiency of siRNA carriers. The carriers were prepared by using polymer nanoassemblies made of a cationic branched polymer [poly(ethylene imine): bPEI] to which hydrophilic poly(ethylene glycol) polymers were tethered covalently. These polymer tethered nanoassemblies (TNAs) were further modified with lipophilic chains (palmitate: PAL) in the core to stabilize siRNA TNAs complexes through ionic and hydrophobic interactions in combination. The effects of PAL in the core of TNAs were investigated with respect to in vitro transfection, intracellular gene delivery, and toxicity of the complexes, using a human colon cancer HT29 cell line stably expressing a luciferase reporter gene. A commercial transfection agent (RNAiMax) was used as a control. TNAs entrapping siRNA showed the greatest complex stability in the absence of PAL although TNAs with a greater PAL content induced effective intracellular siRNA delivery, while luciferase expression decreased as the amount of PAL increased in the core of TNAs. These results demonstrate that lipophilic components in carriers affect not only complex stability but also intracellular distribution and transfection of siRNA in cancer cells.