Patent ID: 7108863

Claim:
A liposome composition for intracellular delivery of a therapeutic agent, comprising liposomes consisting essentially of (i) a pH-sensitive lipid; (ii) between 1–20 mole percent of a lipid derivatized with a hydrophilic polymer, said polymer attached to said lipid by a bond effective to release the hydrophilic polymer in response to an existing or an induced physiologic condition; (iii) a targeting ligand; and (iv) an entrapped therapeutic agent; wherein said composition is adapted to bind to a target cell and to release said entrapped agent to achieve at least a two-fold increase in intracellular concentration of the agent, when compared to intracellular concentration of the agent delivered by similar liposomes lacking said releasable bond and/or said targeting ligand wherein, said releasable bond is a dithiobenzyl bond.