Synthesis and Immunological Evaluation of a MUC1 Glycopeptide Incorporated into l-Rhamnose Displaying Liposomes

Abstract

MUC1 variable number tandem repeats (VNTRs) conjugated to tumor-associated carbohydrate antigens (TACAs) have been shown to break self-tolerance in humanized MUC1 transgenic mice. Therefore, we hypothesize that a MUC1 VNTR TACA-conjugate can be successfully formulated into a liposome-based anti-cancer vaccine. The immunogenicity of the vaccine should be further augmented by incorporating surface displayed L-rhamnose (Rha) epitopes onto the liposomes to take advantage of a natural antibody-dependent antigen uptake mechanism. To validate our hypothesis we synthesized a 20-amino acid MUC1 glycopeptide containing a GalNAc-O-Thr (Tn) TACA by SPPS and conjugated it to a functionalized Toll-like receptor ligand (TLRL). An L-Rha-cholesterol conjugate was prepared using tetraethylene glycol (TEG) as a linker. The liposome-based anti-cancer vaccine was formulated by the extrusion method using TLRL-MUC1-Tn conjugate, Rha-TEG-cholesterol and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in a total lipid concentration of 30 mM. The stability, homogeneity and size characterization of the liposomes was evaluated by SEM and DLS measurements. The formulated liposomes demonstrated positive binding with both anti-Rha and mouse anti-human MUC1 antibodies. Groups of female BALB/c mice were immunized and boosted with a rhamnose-Ficoll (Rha-Ficoll) conjugate formulated with alum as adjuvant to generate the appropriate concentration of anti-Rha antibodies in the mice. Anti-Rha antibody titers were >25-fold higher in the groups of mice immunized with the Rha-Ficoll conjugate than the non-immunized control groups. The mice were then immunized with the TLRL-MUC1-Tn liposomal vaccine formulated either with or without the surface displaying Rha epitopes. Sera collected from the groups of mice initially immunized with Rha-Ficoll and later vaccinated with the Rha-displaying TLRL-MUC1-Tn liposomes showed a >8-fold increase in both anti-MUC1-Tn and anti-Tn antibody titers in comparison to the groups of mice that did not receive Rha-Ficoll. T-cells from BALB/c mice primed with a MUC1-Tn peptide demonstrated increased proliferation to the Rha-liposomal vaccine in the presence of antibodies isolated from Rha-Ficoll immunized mice compared to nonimmune mice, supporting the proposed effect on antigen presentation. The anti-MUC1-Tn antibodies in the vaccinated mice serum recognized MUC1 on human leukemia U266 cells. Because this vaccine uses separate rhamnose and antigenic epitope components, the vaccine can easily be targeted to different antigens or epitopes by changing the peptide without having to change the other components.

Synthesis of a Liposomal MUC1 Glycopeptide-Based Immunotherapeutic and Evaluation of the Effect of l-Rhamnose Targeting on Cellular Immune Responses

“…To overcome this problem, liposomes have been successfully used as carriers of a range of viral, bacterial and tumor antigens, and their efficient delivery to the antigen presenting cells (APCs) by this method is also well known. 4–9 …”

“…Anti-Rha antibodies were among the most abundant in humans and can also be generated in readily available non-transgenic mice. 9, 50, 51 In fact, Rha is now one of the most effective natural antibody eliciting molecules known 52 and Rha has been conjugated to lipids to recruit anti-Rha antibodies to tumor cells. 53, 54 …”

Synthesis of α-l-rhamnosyl ceramide and evaluation of its binding with anti-rhamnose antibodies

“…In order to prepare anti-rhamnose antibodies, two BALB/cJ mice were immunized and boosted with 1 μg rhamnose ovalbumin conjugate (Rha-Ova) 3a,c with Sigma Adjuvant System (1:1 ratio). The production of anti-Rha antibody was confirmed by ELISA (Figure 2).…”

“…1,2-Dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) (80%) and cholesterol (20%) were used to prepare the liposome. 3c The liposomes were formulated by the extrusion method in a total lipid concentration of 30 mM. Three batches of liposomes were prepared, the first displaying the α-L-RhaCer ( 1 , 10 nM) and the second displaying the ceramide 24 (10 nM).…”

“…Another advantage of studying the response to anti-Rha antibodies is that they can be generated in common laboratory mice rather than in proprietary mice. 3 …”