Endocytosis and transcytosis of an immunoliposome-based brain drug delivery system

J Drug Target. 2000;8(6):435-46. doi: 10.3109/10611860008997919.


Immunoliposomes conjugated with the OX26 monoclonal antibody to the rat transferrin receptor can be used for brain delivery of small molecules. In the present study the uptake of OX26-immunoliposomes by target cells as well as their transcytosis across the blood-brain barrier was investigated. Microscopy of RG2 rat glioma cells incubated with fluorescence labeled OX26-immunoliposomes revealed intracellular co-localization of liposomal cargo, the liposomal membrane bilayer and the OX26 monoclonal antibody. The distinct particulate staining pattern was indicative for accumulation of OX26-immunoliposomes within endosomal or lysosomal compartments. Prolonged incubations demonstrated endosomal release of the liposomal cargo propidium iodide to the cytoplasm. A maximum of 50% of propidium iodide was released from the endosomal compartment after 24 hours of incubation. Transcytosis was studied using an in vitro model of the blood-brain barrier consisting of immortalized RBE4 rat brain endothelial cells. OX26-immunoliposomes did permeate across the RBE4 cell monolayer and showed a permeability coefficient of P(app) = 1.6 x 10(-5) ml/s. Transport was inhibited at low temperature, by competition with free OX26 or by exchanging the OX26 monoclonal antibody for an unspecific isotype antibody. Transcytosis of OX26-immunolipsomes was confirmed in vivo by the brain perfusion and capillary depletion technique. OX26-immunoliposomes were detected within the post-vascular compartment of brain parenchyma (PS product = 2.4 microl/g/min.) and were not associated with the brain microvasculature.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibiotics, Antineoplastic / pharmacokinetics*
  • Antibodies, Monoclonal / pharmacokinetics*
  • Blood-Brain Barrier / physiology
  • Brain / metabolism*
  • Cells, Cultured
  • Daunorubicin / pharmacokinetics*
  • Drug Delivery Systems / methods*
  • Endocytosis / physiology
  • Endosomes / metabolism*
  • Liposomes
  • Rats
  • Receptors, Transferrin / metabolism*
  • Tumor Cells, Cultured


  • Antibiotics, Antineoplastic
  • Antibodies, Monoclonal
  • Liposomes
  • Receptors, Transferrin
  • Daunorubicin