Effect of Protein Coatings on the Delivery Performance of Liposomes.

Abstract

Modifications of the surface properties of liposomal drug carriers, such as coating with therapeutic or targeting proteins, greatly impact their delivery performance. Many of the currently-used methods to associate proteins with the surface of the liposomes can be laborious, inefficient, and significantly change the delivery characteristics. In this dissertation, two relatively simple methods are explored for their ability to associate proteins with the liposome membrane and their impact on the liposome’s delivery properties. The first method that is characterized is the non-covalent conjugation of a polyhistidine (His)-tagged protein to the surface of liposomes containing nickel-chelating lipid. It is shown that the His-tagged model protein, yellow fluorescent protein (YFP-His), associates with the liposome membrane without impacting the stability or uptake properties of liposomes. Next, the effect of the liposome surface-associated protein antigen on the performance of a liposomal vaccine carrier that has previously shown to be efficient in inducing both cellular and humoral immune responses was tested. Not only was the cellular immune response uncompromised by this new liposome formulation, but also the humoral immune response to encapsulated antigen was enhanced. Thus, this study shows that additional antigens can be non-covalently coupled to the liposome membrane in this manner without impacting the delivery properties of the encapsulated antigen and while enhancing the overall immunogenicity of the vaccine. The second method investigated is the association of recombinant amphiphilic protein with the liposomal membrane via hydrophobic interaction. A truncated form of the amphiphilic protein apolipoprotein B (apoB), apoB23, was fused to YFP and used to associate YFP with the liposome membrane. The apoB23-YFP fusion protein did not affect the liposome’s properties in vitro. An apoB23 fusion protein was then prepared with a HER2-specific antibody fragment and used to coat the liposome membranes. The density at which apoB23 fusion proteins coated the liposome membrane, however, was low and no significant selectivity for HER2-overexpressing cells was observed with apoB23-αHER2-coated liposomes. Despite this, it was demonstrated that the apoB fusion protein could effectively associate with the liposome membrane without affecting the liposome’s characteristics and is suggestive of its utility in other targeting applications.