Certain mucin epitopes are associated with tumors and are detected within the tandem repeat core of human mucin glycoprotein, MUC1, from malignant cells but not normal cells. Most of the known anti-MUC1 antibodies (Abs) recognize epitopes with the APDTRPAPG region of tandem repeat core, which is known as an immunodominant (ID) region of the MUC1. A new structural model of this ID-region is proposed based on NMR data. The Thr residue within the DTR motif of tandem repeat is O-glycosylated in vivo. Some Abs to MUC1 have shown a higher affinity to the DTR motif when Thr is glycosylated with core-type glycans. The attachment of peptide epitopes to the C-terminal effector region of the human C5a anaphylatoxin has been shown to improve the delivery of these antigens and simultaneously stimulate an immune response. Based on these findings, new MUC1-like immunogenic peptides with enhanced tumor selectivity will be developed to be used as immunogens for tumor vaccines and for producing immunodiagnostic reagents with improved selectivity. The structural model will be used to design, synthesize, and test conformationally constrained MUC1-like peptides and peptidomimetics with enhanced immunogenicity. The structural features of the carcinoma-associated epitopes (peptide and carbohydrate) in the ID-region of the MUC1 tandem repeat core will be evaluated by optical (ECD, FTIR, VCD) and NMR spectroscopy and by molecular modeling methods. To enhance epitope-specific Ab and/or cellular responses to the MUC1-like peptides, molecular constructs that include peptide and immunoadjuvant moieties will be designed and synthesized. A potent analog of the C-terminal effector region of the human C5a, YSFKPMPLaR, will be used as a molecular adjuvant. The immunogenecity of the MUC1 epitopes will be evaluated in vitro and in vivo. It was shown recently that human carcinoma cells contain an alternative sequence variant (substitutions of Asp by Glu) at a high incidence in the PDTR fragment. The origin and incidence of mutations in the ID-region of the MUC1 and the effects of these mutations on structure, antigenicity, and immunogenicity of tandem repeat peptides will be investigated. The existence of tumor-associated sequence variants raises the possibility for their use as immunogens for the generation of immunodiagnostic reagents with a higher degree of tumor selectivity and their application to therapy as more specific and efficient vaccines.
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