Effect of nomegestrol acetate on human estrogen sulfotransferase activity in the hormone-dependent MCF-7 and T-47D breast cancer cell lines.

Breast cancer cells possess all the enzymes involved in the last steps of estradiol (E2) bioformation, as well as in its transformation (e.g. sulfotransferases) for the conversion to estrogen sulfates (ES). As ES are biologically inactive, the formation of these conjugates is an important transformation pathway in the control of the hormone. In the present study, we explored the effect of nomegestrol acetate on the sulfotransferase activity in the hormone-dependent MCF-7 and T-47D human breast cancer cells. After 24-h incubation at 37 degrees C of physiological concentrations of estrone ([3H]-E1: 5 x 10(-9) mol/l), it was observed that the sulfotransferase activity was present in both cell lines, since the concentrations of estrogen sulfates found were 9.40 +/- 1.10 in MCF-7 cells and 6.65 +/- 0.72 in the T-47D cells. The presence of ES was found exclusively in the culture medium, which suggests that as soon as the sulfate is biosynthesized it is secreted into the medium. Nomegestrol acetate has a stimulatory effect on sulfotransferase activity: at low doses (5 x 10(-8) and 5 x 10(-7) mol/l) this compound strongly increases the activity of this enzyme by 60.6% and 83%, respectively, in the MCF-7 cells and by 69.2% at 5 x 10(-7) mol/l in T-47D cells. At a high concentration (5 x 10(-5) mol/l) the stimulatory effect of nomegestrol acetate on the sulfotransferase activity was only 5.4% and 6.1%, respectively, in MCF-7 and T-47D cells. In conclusion, the stimulation provoked at low doses by nomegestrol acetate on the estrogen sulfotransferase activity involved in the biosynthesis of the biologically inactive estrogen sulfates in hormone-dependent breast cancer cells is an important effect of this progestin and can open attractive clinical applications.

Activation of estrogen receptor alpha and ERbeta by 4-methylbenzylidene-camphor in human and rat cells: comparison with phyto- and xenoestrogens.

4-Methylbenzylidene-camphor (4-MBC) is an organic sunscreen that protects against UV radiation and may therefore help in the prevention of skin cancer. Recent results on the estrogenicity of 4-MBC have raised concerns about a potential of 4-MBC to act as an endocrine disruptor. Here, we investigated the direct interaction of 4-MBC with estrogen receptor (ER) alpha and ERbeta in a series of studies including receptor binding, ER transactivation and functional tests in human and rat cells. 4-MBC induced alkaline phosphatase activity, a surrogate marker for estrogenic activity, in human endometrial Ishikawa cells. Interestingly, 4-MBC induced weakly ERalpha and with a higher potency ERbeta mediated transactivation in Ishikawa cells at doses more than 1 microM, but showed no distinct binding affinity to ERalpha or ERbeta. In addition, 4-MBC was an effective antagonist for ERalpha and ERbeta. In an attempt to put 4-MBC's estrogenic activity into perspective we compared binding affinity and potency to activate ER with phyto- and xenoestrogens. 4-MBC showed lower estrogenic potency than genistein, coumestrol, resveratrol, bisphenol A and also camphor. Analysis of a potential metabolic activation of 4-MBC that could account for 4-MBC's more distinct estrogenic effects observed in vivo revealed that no estrogenic metabolites of 4-MBC are formed in primary rat or human hepatocytes. In conclusion, we were able to show that 4-MBC is able to induce ERalpha and ERbeta activity. However, for a hazard assessment of 4-MBC's estrogenic effects, the very high doses of 4-MBC required to elicit the reported effects, its anti-estrogenic properties as well as its low estrogenic potency compared to phytoestrogens and camphor has to be taken into account.