Interaction of Liposomes Bearing a Lipophilic Doxorubicin Prodrug with Tumor Cells

摘要

When used as nanosized carriers, liposomes enable targeted delivery and decrease systemic toxic-ity of antitumor agents significantly. However, slow unloading of liposomes inside cells diminishes the treat-ment efficiency. The problem could be overcome by the adoption of lipophilic prodrugs tailored for incorpo-ration into lipid bilayer of liposomes. We prepared liposomes of egg yolk phosphatidylcholine and yeast phos-phatidylinositol bearing a diglyceride conjugate of an antitumor antibiotic doxorubicin (a lipophilic prodrug, DOX-DG) in the membrane to study how these formulations interact with tumor cells. We also prepared liposomes of rigid bilayer-forming lipids, such as a mixture of dipalmitoylphosphatidylcholine and choles-terol, bearing DOX in the inner water volume, both pegylated (with polyethylene glycol (PEG) chains exposed to water phase) and non-pegylated. Efficiency of binding of free and liposomal doxorubicin with tumor cells was evaluated in vitro using spectrofluorimetry of cell extracts and flow cytometry. Intracellular traffic of the formulations was investigated by confocal microscopy; co-localization of DOX fluorescence with organelle trackers was estimated. All liposomal formulations of DOX were shown to distribute to organelles retarding its transport to nucleus. Intracellular distribution of liposomal DOX depended on lipo-some structure and pegylation. We conclude that the most probable mechanism of the lipophilic prodrug pen-etration into a cell is liposome-mediated endosomal pathway.