Kazuo Watanabe, Makoto Kaneko, Yoshie Maitani

Folate-polymer-coated liposomes were developed for targeted chemotherapy using doxorubicin (DXR) as a model drug. Folate-poly(L-lysine) (F-PLL) conjugates with a folate modification degree of 16.7 mol% on epsilon amino groups of PLL were synthesized. DXR-loaded anionic liposomes were coated with F-PLL, and the cellular association of F-PLL-coated liposomes was evaluated by flow cytometry, and confocal microscopy in human nasopharyngeal carcinoma KB cells overexpressing folate receptors (FRs), and human lung adenocarcinoma A549 cells [FR (-)]. The existence of a polymer layer on the surface of F-PLL-coated liposomes was confirmed by zeta potential analysis. The KB cellular association of F-PLL-coated liposomal DXR was increased compared with that of PLL-coated liposomes and was inhibited in the presence of free folic acid. Twofold higher cytotoxicity of F-PLL-coated liposomal DXR was observed compared with that of the PLL-coated liposomal DXR in KB cells, but not in A549 cells, suggesting the presence of FR-mediated endocytosis. These results indicated that folate-targeted liposomes were prepared successfully by coating the folate-polymer conjugate F-PLL. This novel preparation method of folate-targeted liposomes is expected to provide a powerful tool for the development of a folate-targeting drug nanodevice as coating with ligand-polymer conjugates can be applicable to many kinds of particles, as well as to lipid-based particles.