Long circulating liposomal platform utilizing hydrophilic polymer-based surface modification: preparation, characterisation, and biological evaluation.

[Display omitted] • HPMA-based copolymers with cholesterol hydrophobic anchors were synthesized and used to modify the surface of liposomes. • Long circulation properties of the polymer-coated liposomes were demonstrated in rabbits even after repeated administration. • Neither antibody response nor complement activation was detected. • HPMA-based copolymers represent an excellent alternative to PEG for the coating of liposomes. • HPMA-based copolymers-modified liposomes represent a suitable way for a new liposomal drug delivery platform. Liposomes are one of the most important drug delivery vectors, nowadays used in clinics. In general, polyethylene glycol (PEG) is used to ensure the stealth properties of the liposomes. Here, we have employed hydrophilic, biocompatible and highly non-fouling N -(2-hydroxypropyl) methacrylamide (HPMA)-based copolymers containing hydrophobic cholesterol anchors for the surface modification of liposomes, which were prepared by the method of lipid film hydration and extrusion through 100 nm polycarbonate filters. Efficient surface modification of liposomes was confirmed by transmission electron microscopy, atomic force microscopy, and gradient ultracentrifugation. The ability of long-term circulation in the vascular bed was demonstrated in rabbits after i.v. application of fluorescently labelled liposomes. Compared to PEGylated liposomes, HPMA-based copolymer-modified liposomes did not induce specific antibody formation and did not activate murine and human complement. Compared with PEGylated liposomes, HPMA-based copolymer-modified liposomes showed a better long-circulating effect after repeated administration. HPMA-based copolymer-modified liposomes thus represent suitable new candidates for a generation of safer and improved liposomal drug delivery platforms. [ABSTRACT FROM AUTHOR]