Polyamidoamine dendron-bearing lipid assemblies: their morphologies and gene transfection ability.

Assembly morphology made from lipids is controlled by the balance between the polar headgroup and the hydrophobic tails. In this study, we showed the various generations of polyamidoamine dendron-bearing lipids could form various assembly morphologies. Furthermore, the effect of the assembly morphologies made from dendron-bearing lipids for transfection abilities were examined. We synthesized three novel dendron-bearing lipids, DL-U2-G1 (G1), DL-U2-G2 (G2), and DL-U2-G3 (G3), which included first, second, and third generation polyamidoamine dendrons, respectively. Transmission electron microscopy showed that lipoplexes (complexes with cationic lipids and plasmid DNA) comprising G1 had multilamellar structures. G2 presented as aggregates of cubic particles and G3 exhibited clusters of spherical micelles. The ability to form complexes with plasmid DNA was in the decreasing order G3 > G2 > G1; calcein release from endosomes was in the order G3 > G2, G1; and transfection activity followed the order G1 > G2, G3. Interaction of the lipoplexes with heparin suggests that G3 had a lower level of plasmid DNA dissociation from lipoplexes than G1 in vitro. These results suggest that the size of the DL-U2 headgroup determines assembly morphology and that the structure markedly affects transfection activity.

Development of an active targeting liposome encapsulated with high-density colloidal gold for transmission electron microscopy.

Active targeting of the liposome is an attractive strategy for drug delivery and in vivo bio-imaging. We previously reported the specific accumulation of Sialyl Lewis X (SLX) liposome to inflamed tissue in arthritic model mice or tumor-bearing mice. SLX-liposome encapsulation with fluorescent substances allows for the visualization of these liposomes by the time-dependent transvascular accumulation of fluorescent signals in the histological sections. In the present study, we developed a new SLX-liposome encapsulated with colloidal gold for transmission electron microscopic observation. We herein describe the characterization of the colloidal gold-loaded SLX-liposomes and demonstrate its specific targeting to the endothelial cells of tumor blood vessels in tumor-bearing mice.

E-selectin targeting to visualize tumors in vivo.

Generally angiogenic factors induce the expression of E-selectin in vascular endothelial cells in the tumors. In this study, we employed an anti-E-selectin monoclonal antibody to target tumors in vivo and evaluated an optical imaging reagent to visualize tumor regions. The anti-E-selectin antibody was conjugated on the surface of liposomes, which encapsulated the near-infrared fluorescent substances Cy3 or Cy5.5. The liposomes efficiently recognized human umbilical vein endothelial cells only when E-selectin was induced by angiogenic factors such as TNF-alpha in vitro. Cy5.5 encapsulated into liposomes that were conjugated with an anti-E-selectin antibody successfully visualized Ehrlich ascites tumor cells when transplanted into mice. Thus, E-selectin targeting with liposomes containing a near-infrared fluorescent dye was found effective in visualizing tumors in vivo. This strategy should be extremely useful as a method to identify sentinel lymphatic nodes and angiogenic tumors as well as use for drug delivery to tumor cells.

Accumulation of liposome with Sialyl Lewis X to inflammation and tumor region: application to in vivo bio-imaging.

We prepared the liposome binding Sialyl Lewis X (SLX) on the surface in order to specifically and efficiently deliver substances (fluorescent materials, chemical substances, proteins, genes, etc.) to inflammation or tumor regions. The liposome with SLX (SLX-Lipo-Cy5.5), in which fluorescent substance Cy5.5 was included, was administered intravenously to arthritis or Ehrlich Ascites Tumor (EAT) bearing mouse, and the accumulation of liposome was observed using two types of in vivo fluorescent imaging equipment. The result was that the accumulation of SLX-Lipo-Cy5.5 to inflammation or tumor regions was significantly higher than the control liposome without sugar chain (Lipo-Cy5.5) at 24 and 48 h after administration. In addition, it was confirmed that this accumulation showed a shift of liposome from blood vessels to the surrounding tissues. Thus, it was proven that this liposome is useful not only as an in vivo bio-imaging reagent but also as a drug delivery system (DDS).