Synthesis and immunotherapeutic studies of carbohydrate-based cancer vaccines
Thompson, Pamela Sue
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Cancer remains a major cause of death throughout the world. Current treatment of cancer has primarily relied on a combination of therapies, in many cases surgical reduction of the tumor, followed by chemotherapy and radiation, which targets rapidly dividing cells. These treatments, however, do not only affect tumor cells, but also normal cells, resulting in severe side effects. As research has unraveled more details of the intrinsic underlying biological and immunological mechanisms of cancer, new approaches such as angiogenesis inhibitor therapy, gene therapy, and immunotherapy have emerged as possible treatments. The identification of tumor-associated antigens has made it possible to develop antigen-specific vaccines. It has been established that aberrant glycosylation is closely associated with a majority of human cancers. The low antigenicity of tumor-associated carbohydrate antigens signifies a hurdle in vaccine development. In this research, we have examined a three-component vaccine candidate which is able to break tolerance and induce humoral and cellular immune responses against the tumor-associated glycoprotein MUC1, generating CTLs and ADCC-mediating antibodies. This vaccine candidate, which is composed of the tumor-associated antigen MUC1, a promiscuous T-helper peptide derived from the polio virus, and a built-in adjuvant, the TLR2 ligand Pam3CysSK4, demonstrated a superior therapeutic anti-tumor effect in a mouse model of breast cancer. The synthesis of these glycolipopeptide vaccine candidates represents a formidable challenge due to the unique properties of the individual components. In this research, we have developed a highly efficient microwave-assisted liposome-mediated native chemical ligation protocol to obtain cancer vaccine candidates. In our efforts to further streamline the synthesis, we have successfully exploited microwave-assisted solid-phase peptide synthesis (MW-SPPS) for the linear construction of these glycolipopeptides. We applied this technology towards the synthesis of vaccine candidates which contain Pam3CysSK4 and aberrantly glycosylated long MUC1 peptide sequences. Immunization with these vaccine constructs resulted in the production of glycopeptide-specific IgG antibody responses, demonstrating that glycopeptide sequences from MUC1 can be processed and presented to MHC-II. Finally, a strategically protected sialyl-Tn antigen was synthesized in a stereoselective manner and was utilized during the linear assembly of a vaccine candidate via the newly developed MW-SPPS protocol.