Studies of the organ distribution in mice of teniposide liposomes designed for treatment of diseases in the mononuclear phagocytic system

Liposomes can be used for the delivery of drugs in cancer chemotherapy. After i.v. injection liposomes are to a large extent taken up by the mononuclear phagocytic system (MPS). When treating diseases in the MPS, such as the histiocytic syndromes, this property is of potential value for drug targeting and may lead to a more efficient therapy with less systemic toxicity. Teniposide (VM-26) is a potent anti-tumor drug. Its lipophilicity makes it suitable for liposomal formulation. Teniposide liposomes were prepared by dissolving egg phosphatidylcholine and dioleoyl phosphatidic acid (19:1 molar ratio) in methylene chloride together with teniposide. After solvent evaporation, the dry lipid film was dispersed in a glucose solution (50 mg/mL), and size calibration was obtained by filtration through polycarbonate filters. The amount of teniposide incorporated was 2.5 mol%. To investigate the organ distribution, teniposide liposomes containing radiolabeled teniposide or phospholipid were given i.v. to mice. By increasing the size of the vesicles, the MPS uptake could be modulated. When vesicles of 200 nm and 1 and 3 microns were injected, the drug levels in the spleen were increased 2.6-, 6.8-, and 21-fold 40 min after injection, compared with levels after injection of the commercial teniposide formulation. It was concluded that organ distribution of teniposide in mice could be modified by administering the drug in liposomal form with the potential of improved treatment of diseases engaging the MPS.