title: Association of hydrophobically-modified poly(ethylene glycol) with fusogenic liposomes.
abstract: We present results on using cooperative interactions to shield liposomes by incorporating multiple hydrophobic anchoring sites on polyethylene glycol (PEG) polymers. The hydrophobically-modified PEGs (HMPEGs) are comb-graft polymers with strictly alternating monodisperse PEG blocks (M(w)=6, 12, or 35 kDa) bonded to C18 stearylamide hydrophobes. Cooperativity is varied by changing the degree of oligomerization at a constant ratio of PEG to stearylamide. Fusogenic liposomes prepared from N-C12-DOPE:DOPC 7:3 (mol:mol) were equilibrated with HMPEGs. Affinity for polymer association to liposomes increases with the degree of oligomerization; equilibrium constants (given as surface coverage per equilibrium concentration of free polymer) for 6 kDa PEG increased from 6.1+/-0.8 (mg/m(2))/(mg/ml) for 2.5 loops to 78.1+/-12.2 (mg/m(2))/(mg/ml) for 13 loops. In contrast, the equilibrium constant for distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG5k) was 0.4+/-0.1 (mg/m(2))/(mg/ml). The multi-loop HMPEGs demonstrate higher levels of protection from complement binding than DSPE-PEG5k. Greater protection does not correlate with binding strength alone. The best shielding was by HMPEG6k-DP3 (with three 6 kDa PEG loops), suggesting that PEG chains with adequate surface mobility provide optimal protection from complement opsonization. Complement binding at 30 min and 12 h demonstrates that protection by multi-looped PEGs is constant whereas DSPE-PEG5k initially protects but presumably partitions off of the surface at longer times.
authors.affiliation: Department of Chemical Engineering, Princeton University, Engineering Quadrangle, Princeton, NJ 08544, USA.
authors.forename: Debra T
authors.initials: DT
authors.lastname: Auguste
authors.forename: Robert K
authors.initials: RK
authors.lastname: Prud'homme
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Ahl
authors.forename: Paul
authors.initials: P
authors.lastname: Meers
authors.forename: Joachim
authors.initials: J
authors.lastname: Kohn
mesh_terms: D000327:Adsorption; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes / Q000737:chemistry*; D008970:Molecular Weight; D011092:Polyethylene Glycols / Q000737:chemistry*
chemical_list: D008081:Liposomes; D011092:Polyethylene Glycols