The amount of sialyl-dimeric LeX antigen (NeuAc2-3Ga11-4(Fuc1- 3)GlcNAc1-3Gal1-4(Fuc1-3)GlcNAc1-) expressed on mucins in human colorectal carcinoma tissues increases upon tumors' progression to the metastatic phenotype. This was shown in surgically removed tumor tissues using immunochemical and immunohistochemical methods with a monoclonal antibody (MAb) FH6. Among other carbohydrate antigens related to ABO/Le blood group, a decrease in Ulex europeus agglutinin-I reactive mucin (presumably type 2 blood group H and LeY antigen) was seen in blood type O patients. Colon carcinoma cells lines having low and high MAb FH6 reactivity were selected in vitro. The cells expression less sialyl-dimeric LeX antigen produced liver and lung metastases at a higher incidence than a corresponding high expresser cell line when injected into nude mice. To further elucidate the role of sialyl-dimeric LeX antigens in determining human colorectal cancer metastasis, the following questions should be answered: (a) What is the structural basis for the increased expression of this antigen in human tumors and in human colon carcinoma cells selected in vitro? (b) How are these antigens synthesized and how are the structures regulated? (c) What are the biological functions of the mucins expressing blood group related antigens with respect to metastatic potential of the tumor cells? Are the functions modulated by changes in carbohydrate chains? (d) Is the metastatic behavior of human colon carcinoma cells in nude mice determined by different factors from the cells growing in situ in humans? To answer these questions, the structural basis for differential expression of sialyl-dimeric LeX antigens in tumor tissues at different stages of progression and in cell lines should be established. Three different types of mucins, i.e. mucins with sialyl-dimeric LeX antigens, mucins without sialyl-dimeric LeX antigen but containing ABO/Le blood group related antigens, and other mucins, will be purified from metastatic tumors and compared regarding their core polypeptide structures and carbohydrate profiles. Similar mucins from primary tumors which do not express sialyl-dimeric-LeX antigen will also be compared. Then, the question of whether similar changes in mucins are detectable on selected cell lines with different metastatic abilities will be addressed. If the previously selected cell lines do not show correlation with tumor tissues regarding their profiles in sialyl-dimeric LeX expression, additional variant cell lines representing carbohydrate changes occurring during colon carcinoma progression to the metastatic phenotype will be selected using a combination of a few MAbs with different specificities. These cells will be characterized for their metastatic behaviors in vivo and in vitro. Our long range goal is to determine how the production of sialyl-dimeric LeX antigen is regulated in situ, and to develop methods to reduce the amount, so that the tumor remains non-metastatic during the therapy.
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