Proteins and peptides bound to long-circulating liposomes.

Liposome formulations with prolonged circulation time have recently been developed as a potential sustained-release drug delivery system. Data shown in this report indicate that such formulations can also be used to prolong the circulation time of proteins and peptides by conjugating them to the surface of liposomes. Increase of the circulation halflife ranged from 2- to 150-fold depending on the protein/lipid ratio of the liposomal formulation, liposome size, and the lipid composition of liposomes. Since the proteins/peptides localize on the liposome surface, instead of being entrapped inside the liposomes, they are directly available for binding to its receptor molecules and express the biological activity. This strategy has been successfully applied to two proteins with known fast clearance rate, i.e. asialofetuin and ricin A-chain. The biological activities of both proteins are preserved when they are formulated in liposomes. Incorporation of a peptide, i.e. a-factor of the yeast Saccharomyces cerevisiae, into the liposome membrane also significantly enhanced the circulation time of the peptide.