Apoptosis in cultured human colon cancer cells induced by combined treatments with 5-fluorouracil, tumor necrosis factor-alpha and interferon-alpha.

Biochemical analysis using nick end-labeling was performed to investigate the effect of various combinations of 5-fluorouracil, natural human tumor necrosis factor-alpha and natural human interferon-alpha on the induction of apoptosis in RPMI 4788 human colon cancer cells. After treatment with 5-fluorouracil (1 mM) for 48 h, the number of nick end-positive cells was significantly increased in comparison to the situation without treatment. When tumor cells were treated with 1 mM 5-fluorouracil, 2.86 Japan Reference Units (JRU)/ml natural human tumor necrosis factor-alpha and 1 x 10(3) IU/ml natural human interferon-alpha in combination for 48 h, the number of nick end-positive cells was significantly higher than that after treatment with 5-fluorouracil alone. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay revealed a significant decrease of relative viability, as compared to treatment with 5-fluorouracil (1 mM), 5-fluorouracil + natural human tumor necrosis factor-alpha, or 5-fluorouracil + natural human interferon-alpha for 48 h. Pretreatment with 5-fluorouracil (1 mM) for 24 h prior to treatment with natural human tumor necrosis factor-alpha (2.86 JRU/ml) and natural human interferon-alpha (10(3) IU/ml) for 24 h resulted in a significant increase of nick end-positive cells compared to pretreatment with natural human tumor necrosis factor-alpha and natural human interferon-alpha prior to treatment with 5-fluorouracil for 24 h (p < 0.05). These results suggest that 5-fluorouracil alone can induce apoptosis in RPMI 4788 tumor cells and that this effect can be enhanced by combination with natural human tumor necrosis factor-alpha and natural human interferon-alpha.