Synergistic antitumor activity of etoposide and human interleukin-1 alpha against human melanoma cells.

To investigate the possibility of increased activity of cytotoxic anticancer drugs combined with cytokines, we treated human melanoma cells with combinations of etoposide (VP-16) and human recombinant interleukin-1 alpha (rIL-1 alpha). We evaluated the combined cytotoxic effects of VP-16 and rIL-1 alpha using A375-C6 cells, which are sensitive to rIL-1 alpha, and A375-C5 cells, a clonal variant line resistant to rIL-1 alpha. We used the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium-bromid e) assay and the inhibition of [3H]thymidine incorporation into DNA. We analyzed data using the median effects principle of Chou and Talalay (Chou's analysis). The calculated combination index values, at a dose ratio of VP-16 to rIL-1 alpha of 12:1 in simultaneous exposure, indicated synergistic cytotoxicity toward both A375-C6 cells and A375-C5 cells. We observed more pronounced synergism with VP-16 and rIL-1 alpha toward the A375-C5 IL-1 alpha-resistant melanoma cells. These results suggest that rIL-1 alpha combined with cytotoxic antitumor drugs may provide increased benefit in the treatment of malignant melanoma.