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Oligosaccharies of Normal and Malignant Cells

Ajit P Varki

1 Collaborator(s)

Funding source

National Cancer Institute (NIH)
The long-term theme of this grant has been to compare and contrast oligosaccharides (glycans) of normal and malignant cells, and to define the pathological and therapeutic significance of the differences. Sialic acids (Sias) are attached to underlying glycans in various linkages, and can be modified in several ways. Altered expression of specific types and linkages of Sias are prominent features of human and murine tumors. All work in our lab is now focused on the biology and evolution of Sias and Sia-binding proteins in health and disease. Thus, the recent focus of this grant has been on "tumor-specific" changes in Sia-terminated glycans, and on their interactions with Sia-binding proteins such as Selectins and Siglecs. During the last funding period we completed all of our previously stated aims on Selectins and on alpha2-6-linked Sias in cancer, and also generated novel data about a human-specific diet- and antibody-mediated mechanism for chronic inflammation in tumor progression. The latter involves human metabolic incorporation of the non-human sialic acid N-glycolylneuraminic acid (Neu5Gc) from dietary sources (primarily red meats), in the face of human-specific circulating anti-Neu5Gc antibodies. We also now have preliminary evidence for a second mechanism of human-specific chronic inflammation, involving the reduced expression of inhibitory CD33-related Siglecs (CD33rSiglecs) on leukocytes. Given the known importance of chronic inflammation in carcinoma progression, these two human-specific mechanisms may help explain the unusual propensity of humans (as compared to other primates) to develop carcinomas, and have possible relevance for diagnosis, prognosis and therapy. Thus, the current proposal will focus only on the human-specific changes in Sia biology. The general hypothesis is that the human propensity to develop carcinomas is partly related to Neu5Gc incorporation into tumors in the face of anti-Neu5Gc antibody production, and also to relative leukocyte over-reactivity, arising due to human-specific reduction of CD33rSiglec expression. Our studies will focus on carcinomas of human or syngeneic mouse origin - growing in Cmah-/- mice with a human-like defect in Neu5Gc production and/or in mice with deletions or over-expression of myelomonocytic CD33rSiglecs. We will further explore the significance of Neu5Gc incorporation into primary and metastatic tumors in Cmah-/- mice, in the face of circulating anti-Neu5Gc antibodies, and use mouse models to explore the role of human myelomonocytic cell over-reactivity associated with reduced CD33rSiglec expression in chronic inflammation and progression of primary and metastatic human tumors. Finally, we will ask if the combination of Neu5Gc and anti-Neu5Gc antibodies interactions along with Siglec-deficiency-related myelomonocytic cell hyper-reactivity has even greater facilitating effect on progression of carcinomas. As time allows, we will also do pilot studies of human tumor samples for Neu5Gc expression and infiltrating leukocyte Siglec expression to see if either or both are predictive of prognosis and/or disease progression.

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