Short- and long-term synergistic effects of human tumor necrosis factor and interferon-gamma on A549 human lung cancer cells maintained in three-dimensional culture.

We have studied the short- and long-term effects of human recombinant tumor necrosis factor (TNF) and TNF/recombinant human interferon-gamma (IFN-gamma) mixtures on A549 human lung carcinoma cells maintained in organotypic culture. Continuous treatments with 2 x 10; 2 x 10(2); 2 x 10(3) and 2 x 10(4) U/ml TNF or with mixtures of TNF/IFN-gamma at 2 x 10(2) and 10(3) U/ml, respectively, were administered. Nodule growth, cell proliferation and cell survival were studied. On the 2nd day of treatment with TNF, only the highest dose (2 x 10(4) U/ml) diminished cell proliferation significantly, as measured by tritiated thymidine uptake into DNA. On the 10th day, only the lowest TNF dose (2 x 10 U/ml) induced no significant growth inhibition. Necrosis and nodule disintegration were apparent in the 2 x 10(4) U/ml-treated nodules where DNA synthesis decreased. In this case, using agar cloning assays, no cell survival could be observed. Similar results could be obtained with TNF at low concentration (2 x 10(2) U/ml) in combination with INF-gamma (10(3) U/ml), showing a synergistic effect on inhibition of cell proliferation. In the long-term experiments, with the lower TNF doses, in situ evidence of regrowth was observed (outgrowing zones in the nodules) on about the 40th day of treatment, and nodule recovery was confirmed by the resumption of DNA synthesis measured on the 50th day of treatment. No regrowth, however, occurred when the IFN-gamma/TNF combination was used, and the nodules disintegrated completely on the 35th day of treatment without evidence of any cellular survival.