CYTOSTATIC AND CYTOTOXIC EFFECTS OF TUMOR-NECROSIS-FACTOR-ALPHA ON MCF-7 HUMAN BREAST-TUMOR CELLS ARE DIFFERENTLY INHIBITED BY GLUCOCORTICOID HORMONES

To investigate the mechanisms of growth inhibition exerted by TNF-alph a on tumor cells in vitro, we analyzed the cytokine effects on growth and cell-cycle parameters of cultured MCF-7 human breast cancer cells. TNF-alpha exerted a dose-dependent inhibition of MCF-7 cell growth, w hich reached its maximum at 1000 U/ml TNF-alpha concentrations. Flow-c ytometric analysis of cell nuclei revealed two main components in TNF- alpha activity: an earlier cytostatic effect (G1/S block), was followe d by nuclear shrinkage and cytolysis. The 55-60-kDa TNF-alpha receptor is involved in the growth inhibitory activity of the cytokine, since the H398 anti-55-kDa receptor antibody significantly counteracted the cytostatic and cytotoxic effects of TNF-alpha while an antibody (htr-9 ) with agonistic activity on the same receptor produced both cytostasi s and cytolysis. Culture conditions strongly influenced the MCF-7 cell response to TNF-alpha. Serum deprivation of log-growing (i.e., high S phase percentage) cultures potentiated the cytotoxic effect, while re duction in S phase cell percentage by preculture in serum-free medium resulted in a significant inhibition of TNF-alpha action. Mitogenic ho rmones, such as insulin and 17beta-estradiol + insulin, restored the s ensitivity of MCF-7 cells precultured in serum-free medium to both the cytostatic and cytolytic effects of TNF-alpha. The synthetic glucocor ticoid hormone dexamethasone, at micromolar concentrations, counteract ed the TNF-alpha effect on MCF-7 cell growth. Flow-cytometric analysis showed that dexamethasone did not antagonize the cytostatic activity of either TNF-alpha or htr-9 agonistic antibody, but only the subseque nt cytolysis. Our data demonstrate that TNF-alpha exerts both cytostat ic and cytotoxic effects on hormone-responsive MCF-7 breast cancer cel ls in vitro. The two distinct activities of the cytokine on cell proli feration and cell death can be differently modulated by mitogenic horm ones (i.e., insulin and 17-beta-estradiol) and antiinflammatory glucoc orticoids.