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-alpha 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, which reached its maximum at 1000 U/ml TNF-alpha concentrations. Flow-cytometric analysis of cell nuclei revealed two main components in TNF-alpha activity: an earlier cytostatic effect (G1/S block), was followed 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 cytostasis 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 reduction in S phase cell percentage by preculture in serum-free medium resulted in a significant inhibition of TNF-alpha action. Mitogenic hormones, such as insulin and 17 beta-estradiol+insulin, restored the sensitivity of MCF-7 cells precultured in serum-free medium to both the cytostatic and cytolytic effects of TNF-alpha. The synthetic glucocorticoid hormone dexamethasone, at micromolar concentrations, counteracted 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 subsequent cytolysis.(ABSTRACT TRUNCATED AT 250 WORDS)