Liposomes Modified with Superhydrophilic Polymer Linked to a Nonphospholipid Anchor Exhibit Reduced Complement Activation and Enhanced Circulation

We report the synthesis of an acyl-anchored superhydrophilic polymer (SHP) for external surface modification of liposome surface. N¹-(2-aminoethyl)-N⁴-hexadecyl-2-tetradecylsuccinamide conjugated with SHP (HDAS-SHP) was synthesized and used for modifying the liposome surface. Unlike polyethylene glycol (PEG)-phospholipids, which are commonly used for manufacturing stealth liposomes, HDAS-SHP is devoid of both PEG and phosphoryl groups and possesses a zwitterionic polymeric chain. Circulation persistence of the ⁹⁹(m)Tc-labeled HDAS-SHP liposomes was documented by gamma camera imaging. After 24 h postinjection, approximately 30% of injected HDAS-SHP liposomes were present in blood as compared with only 4.5% of the plain liposomes. HDAS-SHP liposomes inhibited complement activation. They were found to be amenable to pH-gradient-based active loading of Adriamycin in a stable manner. At 37°C, HDAS-SHP liposomes provided better encapsulation efficiencies than the liposomes modified with DSPE-PEG₂₀₀₀. These results provide a strong basis for HDAS-SHP as a viable alternative to PEG-phospholipids for imparting stealth characteristics to drug delivery vehicles such as liposomes. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:114-123, 2015.