CHOLESTEROL PHOSPHATE DERIVATIVES - SYNTHESIS AND INCORPORATION INTO A PHOSPHATASE AND CALCIUM-SENSITIVE TRIGGERED RELEASE LIPOSOME

A series of cholesterol derivatives that position a phosphate monoeste r at increasing distance from the sterol ring system was synthesized, and their utility as a triggered release liposome tested. Stable anion ic liposomes consisting of the novel cholesterol phosphate derivatives and dioleoylphosphatidylethanolamine (DOPE) can be induced to collaps e upon phosphatase-catalyzed removal of the phosphate group. Control l iposomes containing DOPE and cholesterol phosphate or phosphatidic aci d, which are not phosphatase substrates, do not undergo phosphatase-me diated collapse. The phosphatase-sensitive liposomes also collapse in the presence of calcium. The precise concentration of calcium that ind uces the collapse is controlled by the structure of the cholesterol ph osphate derivative. Plasmid DNA encoding luciferase, encapsulated in t he cholesterol derivative/DOPE liposomes, transfected cells in vitro. The level of transfection is dependent upon the cholesterol derivative and is mediated by both a calcium-independent and a calcium-dependent pathway; however, the involvement of phosphatase in the latter mechan ism is not yet resolved. The transfection efficiency is between 10(6) and 10(7) of luciferase activity in relative light units per milligram of protein, which is similar to transfection values reported using ot her triggered release liposomes.