Polyamines and growth regulation of cultured human breast cancer cells by 17 beta-oestradiol.

The growth of ZR-75-1 cells, a line of human breast cancer cells in culture, is stimulated by oestradiol and inhibited by anti-oestrogens. Changes in growth rate caused by these agents are accompanied by changes in activity of ornithine decarboxylase, a rate-limiting enzyme for polyamine synthesis. Furthermore, the growth inhibition caused by tamoxifen, an anti-oestrogen, can be reversed by the addition of spermine, spermidine or putrescine to the cells. Insulin can also stimulate ZR-75-1 cell growth and this is again accompanied by an increase in ODC activity. The reduced cell growth rate observed when the cells become confluent is associated with a marked decrease in ornithine decarboxylase activity. Experiments performed with DFMO, a specific and irreversible inhibitor of ODC, show that this compound can prevent the stimulation of growth by oestradiol and that this may be overcome by the addition of putrescine to the cells. It would appear that increased ODC activity and polyamine synthesis are necessary components of the stimulation of breast cancer cell growth by oestradiol but that other growth regulatory stimuli also may act via this enzyme.