No assignee for this patent application, patent application serial number 768840, has been made.
Reporters obtained the following quote from the background information supplied by the inventors: "Liposomes are composed of at least one lipid bilayer membrane enclosing an aqueous internal compartment. Liposomes may be characterized by membrane type and by size. Small unilamellar vesicles (SUVs) have a single membrane and typically range between 0.02 and 0.25 .mu.m in diameter; large unilamellar vesicles (LUVs) are typically larger than 0.25 .mu.m. Oligolamellar large vesicles and multilamellar large vesicles have multiple, usually concentric, membrane layers and are typically larger than 0.25 .mu.m. Liposomes with several nonconcentric membranes, i.e., several small vesicles contained within a larger vesicle are termed multivesicular vesicles.
"Liposomes may be formulated to carry therapeutic agents, drugs or other active agents either contained within the aqueous interior space (water soluble active agents) or partitioned into the lipid bilayer (water-insoluble active agents). Liposomes may also be conjugated to, an antibody or targeting molecule that permits the delivery of active agent to a specific target site. Encapsulation of a drag in a liposome (1) reduces toxicity of the drug, (2) avoids the body's defenses that normally recognize foreign particles and target them for removal by the reticuloenclothelial system (RES) of the liver and spleen, and (3) allows targeting of the drag carrier to the therapeutic site of action, and once there, to release the drug rapidly so that it can act on the target tissue. Further, clearance of the liposome from blood by the cells of the reticuloendothelial system (RES) can be inhibited by incorporating polyethyleneglycol lipids into the liposome membrane; these lipids inhibit the protein adsorption that labels the liposome for RES uptake.
"Liposomes can be designed to be not leaky but will become so if a pore occurs in the liposome membrane, or if the membrane becomes fluid (e.g. undergoes a phase transition from a solid or gel phase to a liquid phase), or if the membrane degrades or dissolves. Such a breakdown in permeability can be induced by the application of electric fields (electroporation), or exposure of the liposome to enzymes or surfactants. Another met wolves raising the temperature of the membrane to temperatures in the vicinity of its gel to liquid phase transition temperature, where it appears that porous defects at phase boundary regions in the partially liquid and partially solid membrane allow for increased transport of water, ions and small molecules across the membrane. The clinical elevation of temperature in the body is called hyperthermia. This procedure has been used to raise the temperature at a target site in a subject and if temperature-sensitive liposomes can be delivered to the target site then this increase in temperature can trigger the release of liposome contents, giving rise to the selective delivery and release of therapeutic agents at the target site, as initially described by Yatvin et al., Science 204:188 (1979). This technique is limited, however, to conditions where the phase transition temperature of the liposome is higher (greater than 37.degree. C.) than the normal tissue temperature.
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