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 polyethyleneglycol (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 DOX level in the plasma and tumor and a decrease in this level in the liver. The high amount of DOX entrapped demonstrated the usefulness of DOX liposomes for tumor cell uptake in vitro. The cell uptake of the liposomes depended on additional amounts of DOX and liposomal lipid. Furthermore, PEG modification of the surface of the liposomes facilitated the initial rate of liposome uptake into the tumor cells. This facilitation was attributed to the lipohydrophilic property of PEG and the fixed aqueous layer around the liposomes. Therefore, a higher amount of DOX entrapped in liposomes and PEG modification have been confirmed to be beneficial.