Research

Structural, functional and biological studies on O-glycosylated antigens and glycosyltransferases abnormally expressed in cancer cells

The most abundant form of O-linked glycosylation in higher eukaryotes, termed ‘‘mucin-type’’, is characterized by the covalent linkage of an α-N-acetylgalactosamine residue (GalNAc) to the hydroxyl group of Ser/Thr residues. Mucin core O-glycosylation is catalyzed by a group of UDP-GalNAc:polypeptide N-acetylgalactosaminyl-transferases (ppGalNAc-Ts) (EC. 2.4.1.41). Subsequent elongation of O-linked sugar chains is achieved by the transfer of additional saccharide units, catalyzed by specific glycosyltransferases. Malignant transformation of epithelial cells is commonly associated with changes in the expression level and/or glycosylation pattern of mucins, including exposure of simple mucin-type carbohydrates, such as Tn, sialyl-Tn and TF antigens. These determinants contribute to the phenotype and biology of cancer cells and are involved in their metastatic activity. Moreover, they are considered among the most specific cancer-associated structures, and are thus being evaluated as promising targets for tumor immunotherapy. We have recently identified some apomucins and glycosyltransferases, which are abnormally expressed in certain cancer cells. One of these enzymes, ppGalNAc-T13, is probably associated to the aggressiveness of some tumors. In this project we investigate the molecular mechanisms underlying the regulation of the initial steps of mucin-type O-glycosylation in human cancer, and evaluate how this abnormal process influences malignant cell behavior.

Cross-reactive interactions between cancer and parasites: The possible involvement of simple mucin-type O-glycosylated antigens

In the last years, different groups independently reported that certain parasite infections reduced the incidence of cancer. For instance, in patients with hydatid disease the prevalence of cancer was significantly lower than in normal subjects. Furthermore, a lower level of colon cancer induced by 1,2-dimethylhydrazine has been reported in rats chronically infected with Trypanosoma cruzi, compared to a non-infected control group. In the same direction, Balb/C mice infected with T. cruzi CH4 strain developed anti-tumor activity which inhibited the growth and metastasis of a subsequently transplanted solid L5178Y-R lymphoma. Presumably, tumor cells and these parasites expose similar antigenic determinants, and hence, some parasite antigens induced an effective cross-reacting immune response against cancer cells. This is in agreement with data reported by our laboratory regarding the expression of simple mucin-type antigens by some parasites. In particular, we have shown Tn and sialyl-Tn antigen expression in different parasites, raising the interesting possibility that these antigens act by altering the host susceptibility to cancer. On the basis of this hypothesis, we investigate whether these parasitic antigens are able to induce an effective immune response capable of inhibit the malignant tumors growth in animal models.

Glycoprotein engeneering towards the design of anti-tumor vaccines

This project aims to develop a new approach for the production of glycosylated hemi-synthetic vaccines for anti-tumor immunotherapy. Our strategy will be based on the directed enzymatic glycosylation of a mucin-like protein from parasitic origin. The proof of concept of this strategy will be obtained using the tumor-associated Tn antigen. Tn-based vaccines will be prepared by in vitro glycosylation of the mucin-type parasite C317 protein using several recombinant ppGalNAc-Ts, including those specifically expressed by cancer cells. The fact that C317 comes from an evolutionary distant organism should overcome tolerance issues encountered with human-mucin based cancer therapeutic approaches. If successful, this innovative procedure could have broad applications in the development of anti-tumoral and anti-parasite glycoprotein-based vaccines.