Patent ID: 7244449

Claim:
A composition for treating a tumor in a subject, comprising liposomes composed of a vesicle-forming lipid and between about 1–20 mole percent of a vesicle-forming lipid derivatized with polyethyleneglycol having a molecular weight between 500–5,000 Daltons, said polymer being distributed on both sides of the liposomes' bilayer membranes; and entrapped in the liposomes, a topoisomerase inhibitor at a concentration of at least about 0.10 μmole drug per μmole lipid, said liposomes having an inside/outside ion gradient sufficient to retain the topoisomerase inhibitor within the liposomes at the specified concentration, and wherein the topoisomerase inhibitor is selected from the group consisting of MPE-camptothecin, topotecan, and (7-(2-N-isopropylamino)ethyl)-(20S)-camptothecin.