Unilateral Lung-Selective Gene Transfer Following the Administration of Naked Plasmid DNA onto the Pulmonary Pleural Surface in Mice

[Organ-, region- and cell-selective gene transfer using non-viral vectors]

Safety in gene therapy is an important issue since both viral and non-viral vectors have toxic side effects. Not only vectors themselves, but also distributions of produced proteins affect safety in gene therapy; thus, development of target-selective gene transfer methods is rational. We have developed organ-, region- and cell-selective gene transfer methods using non-viral vectors. To deliver foreign gene to liver parenchymal cells (hepatocytes), galactosylation of cationic liposome/plasmid DNA complex is useful strategy. Based on analyses for intrahepatic disposition characteristics and interaction with blood components, we formulated novel galactosylated lipoplex with regulated salt concentration to reduce particle size of lipoplex and to stabilize lipoplex simultaneously; as a consequence, we succeeded in improvement of hepatocyte-selective gene transfer after intraportal injection of the lipoplex in mice. On the other hand, administration routes are important for target-selective gene transfer. We discovered that simple instillation of naked plasmid DNA onto organ surface (the liver, kidney, spleen, stomach and lung) in mice and rats could result in effective and region-selective transgene expression. Neither physical force nor carriers are necessary for gene transfer onto organ surface mesothelial cells. To rationally improve transfection efficiency, mechanism of gene transfer should be elucidated. We clarified that Rac-mediated macropinocytosis was required for naked plasmid DNA transfer in gastric mesothelial cells.

[Development of drug delivery system by utilizing absorption from liver surface and its application]

Because it is difficult to achieve local drug activity following administration by the conventional intravenous and oral routes, I sought to develop a new route of administration utilizing drug absorption from the liver surface in order to target that organ. Although direct application to the liver surface should yield local drug distribution, drug absorption from the liver surface has not been reported in the literature. Therefore, we analyzed, as a model, the efficiency of absorption of several organic anions and dextrans of various molecular weights following application to the rat liver surface in vivo using a cylindrical diffusion cell. Each compound appeared gradually in the plasma, followed by excretion into the bile and/or urine, indicating the possibility of drug absorption from the liver surface. The absorption process from the liver surface may not involve a specific transport system because dose and transport inhibitors had no detectable effect. In addition, molecular weight was found to be a determinant of absorption through the liver surface. The efficiency of targeting desired region in the liver was enhanced considerably by application to the liver surface, compared to intravenous administration. Moreover, I have obtained several promising results from the application of this new drug delivery system to anticancer drugs and gene therapy. On the other hand, I have also clarified the characteristics of drug absorption from the surfaces of the kidney, stomach, cecum and small intestine, and plan to apply the physiological findings to other fields.