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Influence of poly(ethylene glycol) grafting density and polymer length on liposomes: Relating plasma circulation lifetimes to protein binding |
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| Authors: | Nancy Dos Santos Christine Allen Malathi Anantha Ryan C. Gallagher Katarina Edwards Lacey Samuels Marcel B. Bally |
| Affiliation: | a Department of Advanced Therapeutics, British Columbia Cancer Agency, 675 West 10th Avenue, Vancouver, BC, Canada V5Z 1L3 b Department of Pathology and Laboratory Medicine, University of British Columbia, 2211 Wesbrook Mall, Vancouver, BC, Canada V6T 2B5 c Leslie Dan Faculty of Pharmacy, University of Toronto, 19 Russell Street, Toronto, ON, Canada M5S 2S2 d Department of Physical Chemistry, Uppsala University, Box 579, S-751 23 Uppsala, Sweden e Botany Department, University of British Columbia, 6270 University Blvd, Vancouver, BC, Canada V6T 1Z4 f Faculty of Pharmaceutical Sciences, University of British Columbia, 2146 East Mall, Vancouver, BC, Canada V6T 1Z3 |
| Abstract: | The incorporation of poly(ethylene glycol) (PEG)-conjugated lipids in lipid-based carriers substantially prolongs the circulation lifetime of liposomes. However, the mechanism(s) by which PEG-lipids achieve this have not been fully elucidated. It is believed that PEG-lipids mediate steric stabilization, ultimately reducing surface-surface interactions including the aggregation of liposomes and/or adsorption of plasma proteins. The purpose of the studies described here was to compare the effects of PEG-lipid incorporation in liposomes on protein binding, liposome-liposome aggregation and pharmacokinetics in mice. Cholesterol-free liposomes were chosen because of their increasing importance as liposomal delivery systems and their marked sensitivity to protein binding and aggregation. Specifically, liposomes containing various molecular weight PEG-lipids at a variety of molar proportions were analyzed for in vivo clearance, aggregation state (size exclusion chromatography, quasi-elastic light scattering, cryo-transmission and freeze fracture electron microscopy) as well as in vitro and in vivo protein binding. The results indicated that as little as 0.5 mol% of 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine (DSPE) modified with PEG having a mean molecular weight of 2000 (DSPE-PEG2000) substantially increased plasma circulation longevity of liposomes prepared of 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC). Optimal plasma circulation lifetimes could be achieved with 2 mol% DSPE-PEG2000. At this proportion of DSPE-PEG2000, the aggregation of DSPC-based liposomes was completely precluded. However, the total protein adsorption and the protein profile was not influenced by the level of DSPE-PEG2000 in the membrane. These studies suggest that PEG-lipids reduce the in vivo clearance of cholesterol-free liposomal formulations primarily by inhibition of surface interactions, particularly liposome-liposome aggregation. |
| Keywords: | ANOVA, analysis of variance AUC, area-under-the-curve BCA, bicinchoninic acid CH, cholesterol CHE, cholesteryl hexadecyl ether DDP, didodecylphosphate DOPE, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine DSPC, 1,2-distearoyl-sn-glycero-3-phosphatidylcholine DSPE, 1,2-distearoyl-sn-glycero-3-phosphatidylethanol-amine 3[H], tritium radiolabel HEPES, N-[2-hydroxyethyl]piperazine-N&prime -[2-ethanesulfonic acid] HBS, HEPES buffered saline, pH 7.4 LUV, large unilamellar vesicle MPS, mononuclear phagocytic system PAGE, polyacrylamide gel electrophoresis PB, protein binding (μmol protein/μmol lipid) PC, phosphatidylcholine PE, phosphatidylethanolamine PEG, poly(ethylene glycol) PK, pharmacokinetic QELS, quasielastic light scattering SDS, sodium dodecyl sulphate Tc, phase transition temperature |
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