Purpose: This study was designed to characterize the mechanisms regulating the expression of the human carcinoembryonic antigen promoter (pCEA), in terms of tissue-specific targeting for gene therapy. The promoter was subcloned to a luciferase reporter gene (pCEA/Luc) in our laboratory and compared with a virally controlled luciferase vector (pSV40/Luc).
Methods: Four human cancer cell lines (HeLa, SW480, Caco2, and SW1116) were transfected with either pCEA/Luc or pSV40/Luc. Cells were treated with interferon-gamma and assayed at 72 hours after treatment. Carcinoembryonic antigen level was measured by enzyme immunoassay. Luciferase expression was measured at 48 hours and one week after transfection by luminometry.
Results: Luciferase activity after transfection with pCEA/Luc was higher in CEA-positive cells than in CEA-negative cells (P < 0.0001). pCEA/Luc demonstrated higher activity than pSV40/Luc in CEA-positive cells (P < 0.0001), but not in CEA-negative cells. In Caco2 cells, which before confluence are CEA-negative, luciferase expression increased on reaching confluence (P < 0.0001). Well to moderately differentiated cells responded to the interferon-gamma treatment, but the increase in CEA secretion did not correspond to an increase in pCEA/Luc expression.
Conclusions: The expression of pCEA correlates well with the CEA production by the specific cell line offering a potential tissue-specific targeting strategy for colon cancer gene therapy. Furthermore, the tissue-specific CEA promoter has a higher and more persistent activity in CEA-positive human cancer cells than a viral promoter. The lack of response to interferon-gamma treatment suggests a different mechanism of action for interferon-gamma other than directly interacting with the promoter.