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

Bioconjugate Chemistry (Impact Factor: 4.82). 02/2013; 24(3). DOI: 10.1021/bc300422a
Source: PubMed

ABSTRACT MUC1 variable number tandem repeats (VNTRs) conjugated to tumor-associated carbo-hydrate antigens (TACAs) have been shown to break self-tolerance in humanized MUC1 trans-genic 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 lig-and (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.

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