Agitation during lipoplex formation harmonizes the interaction of siRNA to cationic liposomes.

We recently demonstrated that agitation during lipoplex formation (vorLTsiR) improves the gene knockdown effect of siRNA because the resultant decrease in lipoplex size leads to an enhanced uptake by cells. In furthering this line of research, the present study was focused on the interaction of siRNA to cationic liposomes during lipoplex preparation. A fluorescence resonance energy transfer (FRET) study indicated that the application of agitation in the presence of siRNA effectively reorganized positively charged lipids (DC-6-14 and DOPE) in an order that effectively promoted further electrostatic interaction between the negatively charged phosphate backbone of siRNA and the positively charged lipids in the cationic liposome membrane. A circular dichroism (CD) study indicated that the agitation did not bring about a change in the A-form helix of siRNA, therefore the interactions between the lateral anionic groups of siRNA - responsible for the characteristic bands of the A-form helix - and cationic liposomes were effectively promoted. Factorial design coupled with response surface methodology was used to statistically analyze the influence of vortex speed and time and siRNA dose on the in vitro gene knockdown effects of siRNA-lipoplex that were spontaneously formulated (spoLTsiR) along with that formulated under agitation (vorLTsiR). The analysis indicated that vortex speed plays the most important role in enhancing the gene knockdown effect of siRNA among the three variables, although all three are important. It was concluded that the high energy transmitted by applying agitation during lipoplex formation harmonized the interaction of siRNA to positively charged lipids (DC-6-14 and DOPE) in cationic liposomes, resulting in a superior gene knockdown efficacy of vorLTsiR compared to spoLTsiR. Our study suggests that the preparation procedure is one of the critical factors in producing the enhanced gene knockdown effect of siRNA.

Agitation during lipoplex formation improves the gene knockdown effect of siRNA.

The successful delivery of therapeutic siRNA to the designated target cells and their availability at the intracellular site of action are crucial requirements for successful RNAi therapy. In the present study, we focused on the siRNA-lipoplex preparation procedure and its effect on the gene-knockdown efficiency of siRNA in vitro. Agitation (vortex-mixing) during siRNA-lipoplex (vor-LTsiR) preparation and its effect on the gene-knockdown efficiency of stably expressed cell GFP was investigated, and their efficiency was compared with that of spontaneously formed lipoplex (spo-LTsiR). A dramatic difference in size between lipoplexes was observed at the N/P ratio of 7.62 (siRNA dose of 30 nM), even though both lipoplexes were positively charged. With the siRNA dose of 30 nM, vor-LTsiR accomplished a 50% gene-knockdown, while spo-LTsiR managed a similar knockdown effect at the 120 nM level, suggesting that the preparation procedure remarkably affects the gene-knockdown efficacy of siRNA. The uptake of vor-LTsiR was mainly via clathrin-mediated endocytosis, whereas that of spo-LTsiR was via membrane fusion. In addition, by inhibiting clathrin-mediated endocytosis, the gene-knockdown efficiency was significantly lowered. The size of the lipoplex, promoted by the preparation procedure, is likely to define the entry pathway, resulting in an increased amount of siRNA internalized in cells and an enhanced gene-knockdown efficacy. The results of the present study definitively show that a proper siRNA-lipoplex preparation procedure makes a significant contribution to the efficiency of cellular uptake, and thereby, to the gene-knockdown efficiency of siRNA.

Oxaliplatin encapsulated in PEG-coated cationic liposomes induces significant tumor growth suppression via a dual-targeting approach in a murine solid tumor model.

We recently designed a PEG-coated cationic liposome targeted to angiogenic vessels and showed, in a murine dorsal air sac model, potent anti-angiogenic activity of an oxaliplatin (l-OHP) formulation of this liposome. In the present study, we extended the l-OHP formulation to a murine tumor-xenograft model. Following three injections, l-OHP containing PEG-coated cationic liposomes showed substantial tumor growth suppression and increased survival time of tumor-bearing mice without apparent side effects, compared with other l-OHP containing PEG-coated neutral liposomes and free l-OHP. In vivo imaging showed a preferential tumor accumulation and a broader distribution of PEG-coated cationic liposomes, compared with PEG-coated neutral liposomes. In addition, PEG-coated cationic liposomes delivered larger amounts of l-OHP into the tumor tissue than other l-OHP formulations, correlating with its antitumor efficiency. In vitro studies indicated that PEG-coated cationic liposomes were internalized not only by tumor cells but also by endothelial cells, and consequently its l-OHP formulation displayed higher cytotoxicity towards both cell types as compared with l-OHP containing PEG-coated neutral liposomes. In summary, l-OHP containing PEG-coated cationic liposomes induced significant tumor growth suppression, presumably by delivering encapsulated l-OHP into both tumor endothelial cells and tumor cells. Such dual targeting approach, i.e. vascular-targeting and tumor-targeting with a single liposomal l-OHP formulation, may have great potential for overcoming some major limitations in conventional chemotherapy.