Effect of promegestone, tamoxifen, 4-hydroxytamoxifen and ICI 164,384 on the oestrone sulphatase activity of human breast cancer cells.

In the present study, we explored the effects on sulphatase activity by Promegestone (R-5020), Tamoxifen (TAM), 4-hydroxytamoxifen (4-OH-TAM) and ICI 164,384 in the T-47D hormone-dependent and MDA-MB-231 hormone-independent mammary cancer cell lines. Using homogenates of these cells it was observed that Promegestone has a significant effect on the inhibition of oestrone (E1) sulphatase activity. As this effect is competitive, it is suggested that there is a direct action of this compound on the enzyme. Tamoxifen has very little or no effect, 4-hydroxytamoxifen has an intermediate effect and ICI 164,384 is active in the enzyme inhibition, particularly with MDA-MB-231 cells. The present data could open new possibilities for human breast cancer treatment, as sulphatase is very active in the first step of the conversion of oestrone sulphate (E1S) to oestradiol (E2), and oestradiol is one of the principal carcinogenic factors in human hormone-dependent breast cancer.