Reduction of tumor necrosis factor-α bioactivity by a human ovarian epithelial cancer cell line in vitro

OBJECTIVE: Our purpose was to determine the ability of an ovarian epithelial carcinoma cell line, Caov-3, to alter the bioactivity of exogenously added tumor necrosis factor-α. STUDY DESIGN: Caov-3 cells were cultured for up to 6 days in Dulbeccoʹs modified Eagleʹs medium containing 10% fetal calf serum. The control and tumor necrosis factor-α-treated cells were analyzed for proliferation, distribution throughout the cell cycle by flow cytometry, their ability to release bioactive tumor necrosis factor-α by L929 bioassay, and their ability to release immunoreactive tumor necrosis factor-α by a specific double sandwich enzyme-linked immunosorbent assay. RESULTS: Tumor necrosis factor-α induced a dose- and time-dependent inhibition of cell proliferation accompanied by accumulation of cells in late S and G2/M phases of the cell cycle. Tumor necrois factor-α bioactivity was undetectable in the media of control Caov-3 cell cultures, but these cells exhibited TNF-α messenger ribonucleic acid. After culture of the cells for 2 days in the presence of various doses of TNF-α (0.1, 1.0, 10, or 100 ng/ml), a significant decline (p< 0.01) in bioactivity was observed in all groups with the exception of 100 ng of TNF-α. Further declines in bioactivity were observed 2 and 4 days later. Addition of TNF-α to Caov-3 cells did not affect its immunoactivity, and Western blots of media revealed major bands of immunoactivity at −17 kd, the expected molecular size of TNF-α. CONCLUSION: These results indicate that Caov-3 ovarian carcinoma cells reduce the bioactivity of TNF-α, an important growth regulation, by a novel yet unknown mechanism to escape the modulatory effects of the normal immune response during cancer cell growth.