Gene delivery using liposome technology.

Development of more reliable liposomal formulations and preparation methods which can be used for gene therapy instead of commonly used viral vectors is expected. We have already developed the freeze-dried empty (non-drug-containing) liposomes (FDEL) method for mass-production of liposomal products. After these freeze-dried empty liposomes are rehydrated with aqueous drug solutions, many kinds of drugs can be encapsulated highly efficiently, and particle size can be controlled well. This study evaluated the usefulness of this FDEL method for preparation of liposomes containing DNA with a particular attention to the stability of DNA. When the liposomes were prepared by the conventional lipid-film method on a relatively large scale with use of a Potter-homogenizer (a teflon homogenizer), significant degradation and conformational change of DNA was observed during homogenization. Loss of DNA was also significant after extrusion for sizing and sterilization; residual DNA in the final preparation was hardly detected. When the FDEL method was used, on the other hand, no degradation, conformational change or loss of DNA was observed, and particle size was easily controlled. Moreover, there was no significant difference in luciferase activity between the lipid-film method used on a small scale with use of a vortex mixer and the FDEL method after transfection of tumor cells (HRA, HEC-1A and Colo320DM) by the liposomes containing DNA (PGV-C). These findings suggest that the FDEL method is very useful for preparation of liposomes containing DNA.