Metastatic breast cancer is the proliferation of cancerous cells from a primary breast tumor site. The spread of these cancerous cells increases the difficulty of detection and treatment, leading to an overall reduced survival rate. One of the key indicators of breast cancer is the overexpression and aberrant glycosylation of Mucin 1 (MUC1), a large transmembrane protein located on the apical surface of human epithelial cells. Aberrant carbohydrate expression of Tumor-Associated Carbohydrate Antigens (TACAs) in breast cancer cells has been shown to indicate tumor progression and metastasis. MUC1 consists of a variable number tandem repeat (VNTR) domains that generally favor serine, threonine, and proline residues, the presence of which promote O-glycosylation. As a protective and cell signaling protein, its structure can be defined as densely O-glycosylated with long, and branched sugars. The overexpression, irregular intercellular localization, and aberrant glycosylation of this protein are associated with breast cancer progression. Breast cancer cell lines express truncated O-glycans, such as the Thomsen Nouvelle Antigen (Tn) antigen. It is hypothesized that TACAs like the Tn antigen allow MUC1 to be more exposed and open to interactions with carbohydrate binding proteins (lectins) that are overexpressed in metastatic cancers. In particular, the macrophage galactose type C lectin (MGL) recognizes Tn and sialylated Tn antigen, and facilitates the uptake of the antigen and regulation of T-cell immune response. The objective of our research was to prepare gram quantities of the Tn-α-O-Ser/Thr building blocks suitable for use in the solid-phase peptide synthesis of glycopeptide models of tumor-associated MUC1, as a step towards understanding how they affect cancer biology. The synthesis of Tn was completed through four key reactions: per-acetylation of D-galactal, one-pot azidochlorination reaction, glycosylation of Ser/Thr residue, and reductive acetylation of an azide group to an N-acetyl group. The purity of the final Ser/Thr-Tn building blocks was confirmed using RP-HPLC, MALDI-TOF mass spectrometry, 1H and 13C NMR. The availability of this building block will allow us to proceed to the next step, the synthesis of cancer-associated MUC1 glycopeptide models, with the long-term goal of studying the role of altered glycosylation of MUC1 in tumor progression and metastasis.

Synthesis of the glycosylated amino acid bearing the Thomsen nouvelle antigen

255th National Meeting (2018)

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