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 utilized for the detection of minimal disease or as a target of immunotherapeutic approaches. In preclinical models CEA has been found to be upregulated after exposure of cancer cells to 5-fluorouracil (5-FU). In the present study, the clonal distribution of CEA and its regulation by 5-FU at clonal level was investigated using human HT-29 colon cancer cells. Materials and Methods: The extent of CEA expression was measured in terms of: (a) antigen levels on plasma membrane by flow cytometry; (b) cytoplasm and membrane protein, by Western blot analysis; (c) transcript, by Northern blot analysis; (d) CEA shedding by radioimmunossay. Results: CEA protein and gene transcript were variably expressed among different clones. In all cases 5-FU was able to increase the percentage of CEA-positive cells, the amount of antigen either in the membrane ol cytosolic fractions, and the corresponding transcript. 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 preferential killing of CEA negative cells. The antimetabolite was capable of enhancing antigen expression also in other CEA-positive tumor cell lines with different basal levels of the marker Conclusions: The present findings could be of potential value to increase the sensitivity, of diagnostic processes based on detection of CEA positive tumor cells. Moreover, the antimetabolite might be included in immunotherapeutic protocols to facilitate recognition of CEA-positive cancer cells by immune responses.