Liposomes with temperature-responsive reversible surface properties.

Liposomes composed of egg phosphatidylcholine and cholesterol were modified with the temperature-responsive polymer poly(N-isopropylacrylamide-co-N, N-dimethylacrylamide) (P(NIPAAm-co-DMAAm)), and exhibited reversible surface properties with temperature. Completely reversible liposome aggregation due to P(NIPAAm-co-DMAAm) hydration/dehydration was demonstrated over four successive cycles of heating and cooling. The P(NIPAAm-co-DMAAm) polymer was hydrated during cooling, which dispersed the liposomes. The rigidity of the liposomal membrane was one of the factors in the reversible aggregation, as was the modification density of the polymer on the liposomes. A low density on relatively rigid liposomes could maintain the polymer property of reversible hydrated layers below critical solution temperature (LCST) boundary. Above the LCST, temperature-responsive polymers could also transport negatively charged liposomes into cells. The reversible behavior of the temperature-responsive polymer-modified liposomes has not been reported previously and could enable new applications for switching deposit forms as alternative drug carriers.

Enhanced cellular uptake and gene silencing activity of siRNA using temperature-responsive polymer-modified liposome.

Short interfering RNA (siRNA) delivery systems using nanoparticle carriers have been limited by inefficient intracellular delivery. One drawback is the poor cellular uptake of siRNA/particle complexes through the plasma membrane and release of the nucleic acids into the cytosol. In this study, to develop the temperature-responsive liposome as a novel carrier for siRNA delivery, we prepared lipoplexes and assessed cellular uptake of siRNA and gene silencing activity of target genes, compared with those of a commercial transfection reagent, Lipofectamine RNAiMAX, and non-modified or PEGylated liposomes. The temperature-responsive polymer, N-isopropylacrylamide-co-N,N'-dimethylaminopropylacrylamide [P(NIPAAm-co-DMAPAAm)]-modified liposome induced faster intracellular delivery because P(NIPAAm-co-DMAPAAm) exhibits a lower critical solution temperature (LCST) changing its nature from hydrophilic to hydrophobic above the LCST. The temperature-responsive liposomes showed significantly higher gene silencing activity than other carriers with less cytotoxicity. Furthermore, we showed that the temperature-responsive lipoplexes were internalized mainly via microtubule-dependent transport and also by the clathrin-mediated endocytosis pathway. This is the first report that temperature-responsive polymer-modified liposomes thermally enhanced silencing activity of siRNA. The dehydrated polymer on the liposomes, and its aggregation caused around the LCST, can probably be attributed to effective cellular uptake of the lipoplexes for gene silencing activity by interaction with the cell membrane.