Effects of different progestogens on human breast tumor cell growth

OBJECTIVE

To examine the effect of progestogens currently used in hormone therapy on growth of human breast tumor cells.

METHODS

MCF-7 cells were incubated in 10 nmol/l progestogens, including progesterone (P4), medroxyprogesterone acetate (MPA), norethisterone acetate (NETA), and cyproterone acetate (CPA), with or without 17β-estradiol (E(2), 1 nmol/l and 10 nmol/l), as well as E(2) alone. Cell proliferation, apoptosis, and the expression of caspase-3 and proliferating cell nuclear antigen (PCNA) were evaluated.

RESULTS

The ratios of apoptosis : proliferation significantly increased in cultures with progestogens alone, 1 nmol/l E(2) plus progestogens (except P4), and 10 nmol/l E(2) plus NETA. Caspase-3 significantly diminished in cultures with E(2) alone; this was completely reversed when progestogens were added. MPA alone or with 1 nmol/l E(2) and 10 nmol/l E(2) plus NETA significantly increased caspase-3. Using progestogens alone, except P4, significantly decreased PCNA expression.

CONCLUSIONS

The results demonstrate that various progestogens have different effects on growth of breast tumor cells, especially with the combined usage of E(2). Progestogen-induced apoptosis may be partly inhibited with the presence of E(2), but less severe with lower E(2) concentrations. Therefore, the choice of progestogens, as well as the doses of E(2) and/or progestogen, may influence breast cancer risk.

Estrogen sulfotransferases in breast and endometrial cancers

Estrogen sulfotransferase is significantly more active in the normal breast cell (e.g., Human 7) than in the cancer cell (e.g., MCF-7). The data suggest that in breast cancer sulfoconjugated activity is carried out by another enzyme, the SULT1A, which acts at high concentration of the substrates. In breast cancer cells sulfotransferase (SULT) activity can be stimulated by various progestins: medrogestone, promegestone, and nomegestrol acetate, as well as by tibolone and its metabolites. SULT activities can also be controlled by other substances including phytoestrogens, celecoxib, flavonoids (e.g., quercetin, resveratrol), and isoflavones. SULT expression was localized in breast cancer cells, which can be stimulated by promegestone and correlated with the increase of the enzyme activity. The estrogen sulfotransferase (SULT1E1), which acts at nanomolar concentration of estradiol, can inactivate most of this hormone present in the normal breast; however, in the breast cancer cells, the sulfotransferase denoted as SULT1A1 is mainly present, and this acts at micromolar concentrations of E(2). A correlation was postulated among breast cancer cell proliferation, the effect of various progestins, and sulfotransferase stimulation. In conclusion, it is suggested that factors involved in the stimulation of the estrogen sulfotransferases could provide new possibilities for the treatment of patients with hormone-dependent breast and endometrial cancers.