Surface functionalization of liposomes with proteins and carbohydrates for use in anti-cancer applications

Liposomes can be used to exploit the altered biology of cancer thereby increasing delivery of liposome-associated anti-cancer drugs. In this dissertation, I explore methods that utilize the unique cancer expression of the polymeric glycosaminoglycan hyaluronan (HA) and the HA receptor CD44 to target liposomes to tumors, using liposomes functionalized with proteins or oligosaccharides on their surface. To make it easier to prepare protein-functionalized liposomes, a non-covalent protein/liposome association method based upon metal chelation/his 6 interaction was devised and characterized. I evaluated non-covalent attachment of the prodrug converting enzyme yeast cytosine deaminase, the far-red fluorescent protein mKate, two antigens ovalbumin and the membrane proximal region of an HIV GAG and hyaluronidase, a HA-degrading enzyme.;In Chapter 2, I describe the synthesis of hyaluronan-oligosaccharide (HA-O) lipid conjugates and their incorporation into liposomes to target CD44-overexpressing cancer cells. HA-O ligands of defined-length, up to 10 monosaccharides, were attached to lipids via various linkers by reductive amination. The HA-lipids were easily incorporated into liposomes but did not mediate binding of liposomes to CD44 overexpressing cells.;In Chapter 3, I evaluate the capacity of tris-NTA-Ni-lipids incorporated within a liposome bilayer to associate with his6-tagged proteins. Tris-NTA-lipids of differing structures and avidities were used to associate yeast cytosine deaminase and mKate to the surface of liposomes. Two tris-NTA-lipids and a mono-NTA lipid associated his-tagged proteins to a 1:1 molar ratio in solution. The proteins remained active while associated with the liposome surface. When challenged in vitro with fetal calf serum, tris-NTA-containing liposomes retained his-tagged proteins longer than mono-NTA. However, the tris-NTA/his6 interaction was found to be in a dynamic state; free yeast cytosine deaminase rapidly competed with pre-bound mKate for NTA occupancy. In the circulation of mice, his-tagged proteins associated with NTA-liposomes were cleared as rapidly as free protein.;In Chapter 4, I study the effect of NTA/his-tag avidity on immune response when NTA-containing liposomes are used as non-covalent, particulate adjuvants. Two his-tagged antigens, ovalbumin and the membrane proximal portion of HIV Gag, were associated with NTA-liposomes containing either mono-NTA or tris-NTA lipids. The immune response to each antigen was compared to control adjuvant formulations in which antigens were admixed with or covalently-conjugated to liposomes. The weaker antigen, the HIV Gag peptide, induced a stronger immune response when associated with NTA-containing liposomes than when admixed with liposomes. Ovalbumin preparations in which the protein was admixed with particles or non-covalently associated with NTA-liposomes elicited a higher immune response than free ovalbumin or ovalbumin admixed with the control adjuvant alum. For both antigens, NTA-liposome responses were less than the response to antigens covalently linked to the liposome.;In Chapter 5, I evaluate the potential for hyaluronidase to target conjugated liposomes to tumors or improve liposome motility within hyaluronan-rich tumors. Ovine hyaluronidase was modified using iminothiolane to introduce sulfhydryl groups into the enzyme. The enzyme was attached to liposomes via maleimide lipids or to maleimidehis10 in order to engineer non-covalent NTA-liposome association. Enzyme activity was retained after sulfhydryl addition and after attachment to liposomes. Liposome-conjugated hyaluronidase degraded an HA-gel at the same rate as admixed liposomes. When hyaluronidase-liposomes were injected intravenously in mice, the hyaluronidase conjugated-liposomes experienced faster clearance than control liposomes but slower clearance than free hyaluronidase.;As a whole, these studies may help develop universal methods for a range of protein therapeutics and anti-cancer targeting agents.