DOES THE AMOUNT OF AN ANTITUMOR AGENT ENTRAPPED IN LIPOSOMES INFLUENCE ITS TISSUE DISTRIBUTION AND CELL UPTAKE

The effects of the amount of a drug entrapped in liposomes and polyeth yleneglycol (PEG) modification on the tissue distribution in vivo and cell uptake in vitro have been examined. An increase in the amount of doxorubicin (DOX) entrapped in liposomes induced an increase in the DO X level in the plasma and tumor and a decrease in this level in the li ver. The high amount of DOX entrapped demonstrated the usefulness of D OX liposomes for tumor cell uptake in vitro. The cell uptake of the li posomes depended on additional amounts of DOX and liposomal lipid. Fur thermore, PEG modification of the surface of the liposomes facilitated the initial rate of liposome uptake into the tumor cells. This facili tation was attributed to the lipo-hydrophilic property of PEG and the fixed aqueous layer around the liposomes. Therefore, a higher amount o f DOX entrapped in liposomes and PEG modification have been confirmed to be beneficial. (C) 1998 Elsevier Science Ireland Ltd. All rights re served.