CHAPTER 4.4 – Cellular distribution of DOXIL® within selected tissues, assessed by confocal laser scanning microscopy

This chapter explores Confocal laser scanning (CLS) microscopic observations of pegylated liposome uptake in liver, spleen, and kidney. CLS microscopy is a research tool well suited for studying the spatial and temporal distribution of fluorescent compounds in cultured cells in vitro . The liver and spleen are the two major organs involved in the removal of sterically stabilized stealth liposomes from the blood after intravenous injection. Because of the fenestrated structure of the endothelium of the hepatic portal system, the liver is the major site of the removal of liposomes and free drug from the blood. Most of the liposomes and free drug are found in the spleen localized in red pulp macrophages. In lymph nodes, dendritic reticular cells and macrophages in the cortex and medulla take up a significant quantity of liposomes and drug. A scanned laser microscope (SCM) fluorescence image of doxorubicin shows kupffer cells; being fewer than the parenchymal, proportionately take up few doses of stealth liposomes and free drug. Doxorubicin in stealth liposomes (DOXIL) localized primarily in the small fenestrated endothelium close to portal veins in one hour. At 24 hours, DOXIL had continued to accumulate, and was most concentrated in periportal areas, most of the free doxorubicin was cleared from the liver.