Effect of 5-fluorouracil on carcinoembryonic antigen expression and shedding at clonal level in colon cancer cells

Background: The carcinoembryonic antigen (CEA) is a tumor marker largely ut ilized for the detection of minimal disease or as a target of immunotherape utic approaches. In preclinical models CEA has been found to be upregulated after exposure of cancer cells to 5-fluorouracil (5-FU). In the present st udy, the clonal distribution of CEA and its regulation by 5-FU at clonal le vel was investigated using human HT-29 colon cancer cells. Materials and Me thods: The extent of CEA expression was measured in terms of: (a) antigen l evels on plasma membrane by flow cytometry; (b) cytoplasm and membrane prot ein, by Western blot analysis; (c) transcript, by Northern blot analysis; ( d) CEA shedding by radioimmunossay. Results: CEA protein and gene transcrip t were variably expressed among different clones. In all cases 5-FU was abl e to increase the percentage of CEA-positive cells, the amount of antigen e ither in the membrane ol cytosolic fractions, and the corresponding transcr ipt. Moreover, a mal ked increase of CEA shedding was found in drug-treated cells with respect to that of controls. The increase of CEA induced by the antimetabolite was nor the result of a selection mechanism based on prefer ential killing of CEA negative cells. The antimetabolite was capable of enh ancing antigen expression also in other CEA-positive tumor cell lines with different basal levels of the marker Conclusions: The present findings coul d be of potential value to increase the sensitivity, of diagnostic processe s based on detection of CEA positive tumor cells. Moreover, the antimetabol ite might be included in immunotherapeutic protocols to facilitate recognit ion of CEA-positive cancer cells by immune responses.