The Design and Characterization of Temperature-Sensitive Liposomes

The usual strategy for targeting liposomes is to attach a ligand specific for a determinant on the target cell. Alternative methods of liposome targeting use the inherent tendency of liposomes to be taken up by phagocytes or localized in specific anatomical compartments. The majority of the liposomes are taken up by the liver and spleen. Compartmental targeting has shown promise for delivering steroids to arthritic joints, and anticancer drugs to peritoneal and lymphatic sites. Small unilamellar vesicles (SUV) have apparent transition temperatures several degrees below those predicted from the T_m of the component lipids in large unilamellar vesicles (LUY) or in multilamellar vesicles (MLV). The chapter describes techniques used to make temperature-sensitive SUV, LUY, and MLV. It discusses two methods for assaying temperature-sensitive release. One uses the fluorescent dye carboxyfluorescein; the other, radiolabeled water soluble tracer molecules. The chapter illustrates the in vivo application of temperature sensitive liposomes.