Lipid carrier compositions and methods for improved drug retention
Liposomal compositions which have enhanced retention properties for biological agents are characterized by an intrasomal osmolarity of 500 mOSM/kg or less and by containing substantially no cholesterol. The liposomes comprise vesicle forming lipids along with aggregation preventing components, and typically have transition temperatures of 38° C. or higher.
1 . A composition comprising liposomes, wherein said liposomes comprise at least one vesicle forming lipid and at least one aggregation preventing component and contain less than 20mol % of cholesterol,
wherein the said liposomes contain at least one encapsulated biologically active agent; and
wherein the intraliposomal aqueous medium has no osmolarity of 500 mOsm/kg or less.
2 . The composition of claim 1 wherein said liposomes have a transition temperature of 38° C. or greater.
3 . The composition of claim 1 wherein the liposomes are large unilamellar vesicles (LUV).
4 . The composition of claim 1 wherein the biologically active agent comprises an antineoplastic agent.
5 . The composition of claim 1 wherein the intraliposomal aqueous medium has an osmolarity of 300 mOsm/kg or less.
6 . The composition of claim 1 wherein the vesicle forming lipid comprises a diacylphosphoglyceride wherein the acyl moieties contain at least 16 carbons.
7 . The composition of claim 1 wherein said intraliposomal aqueous medium comprises citrate.
8 . The composition of claim 1 wherein the intraliposomal aqueous medium comprises TEA buffer.
9 . The composition of claim 1 wherein the at least one aggregation preventing component includes a hydrophilic polymer-lipid conjugate.
10 . The composition of claim 9 wherein the biologically active agent comprises FUDR and/or CPT-11.
11 . The composition of claim 1 which further comprises at least one pharmaceutically acceptable excipient.
12 . A method to administer a biologically active agent to a subject in need of such agent which method comprises administering to said subject an effective amount of the composition of claim 1 .
13 . A method to administer a biologically active agent to a subject in need of such agent which method comprises administering to said subject an effective amount of the composition of claim 11 .
14 . A method of making a liposome comprising an encapsulated pH gradient loadable agent comprising the steps of:
i) providing a liposome substantially free of cholesterol, said vesicle encapsulating one or more internal loading buffers having a known pH and having a concentration of less than 200 mM;
ii) suspending said liposome in an external buffer having a pH which is different than that of the internal loading buffer whereby a pH gradient is formed across a membrane of the liposome such that the pH gradient loadable agent is neutral when present in the exterior buffer and charged when present in the internal loading buffer;
iii) adding a pH gradient loadable agent to the mixture of ii) and incubating the mixture for a time sufficient for uptake of the agent into the liposome.
15 . A method of making a liposome comprising an encapsulated pH gradient loadable agent comprising the steps of:
i) providing a liposome comprising:
a) from about 2 to about 30 mol % of one or more aggregation preventing agents;
b) up to about 98 mol % of one or more vesicle-forming lipids;
c) one or more internal loading buffers encapsulated within the liposome having a known pH and having a concentration of less than 200 mM;
wherein the liposome contains substantially no cholesterol;
ii) suspending the liposome in an external buffer having a pH which is different than that of the internal loading buffer whereby a pH gradient is formed across the membrane of the liposome such that the pH gradient loadable agent is neutral when present in the exterior buffer and charged when present in the internal loading buffer;
iii) adding a pH gradient loadable agent to the mixture of ii) and incubating the mixture for a time sufficient for uptake of the agent into the liposome interior.