Differential effects of progestogens, by type and regimen, on estrogen-metabolizing enzymes in human breast cancer cells.
OBJECTIVE
To investigate the in vitro effects of five progestogens commonly used in hormone replacement therapy (HRT) on estrogen-metabolizing enzymes in human breast cancer cells.


METHODS
The human hormone-dependent breast cancer cell lines T47D, MCF-7, and MCF-7aro were cultured with estradiol (E(2)) and progestogens. The mRNA levels of estrogen-metabolizing enzymes were determined by RT-PCR or Northern blot, and enzyme activities by radiolabeled substrates. Cell proliferation was measured by bromodeoxyuridine incorporation. In vitro models for continuous combined regimen (CCR) and sequential combined regimen (SCR) were established to mimic the in vivo conditions of HRT.


RESULTS
Medroxyprogesterone acetate (MPA) plus E(2) (10(-8)M) stimulated the mRNA levels and activities of estrogen-activating enzymes aromatase (at 10(-8)M MPA), 17beta-hydroxysteroid dehydrogenase type 1 (17betaHSD1) (at 10(-6)M), and sulfatase (at 10(-8) to 10(-6)M) compared to E(2) only. Progesterone also stimulated enzyme activity, but to a lower magnitude. Levonorgestrel, norethindrone, and dienogest showed no enzyme stimulation. The estrogen-inactivating enzymes 17beta-hydroxysteroid dehydrogenase type 2 and sulfotransferase were not affected by any of the progestogens tested. However, all the progestogens (at 10(-8) to 10(-6)M) inhibited E(2)-stimulated cell proliferation. While increased aromatase and 17betaHSD1 activities were observed in the CCR model, no significant enzyme stimulation was observed in the SCR model.


CONCLUSIONS
The present study suggested that progestogens exert different actions on estrogen-metabolizing enzymes in breast cancer cells dependent on the specific progestogen and regimen used. Further studies are needed to elucidate whether MPA, a progestogen currently used in HRT, leads to a higher risk of breast cancer development than other progestogens.
Xu
Bing
B
Department of Obstetrics and Gynecology, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, 465 Kajii-cho, Kamigyo-ku, Kyoto 602-8566, Japan.
Kitawaki
Jo
J
Koshiba
Hisato
H
Ishihara
Hiroaki
H
Kiyomizu
Miyo
M
Teramoto
Mariko
M
Kitaoka
Yui
Y
Honjo
Hideo
H
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D001141:Aromatase / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004338:Drug Combinations; D006801:Humans; D017258:Medroxyprogesterone Acetate / Q000008:administration & dosage; D011372:Progestins / Q000494:pharmacology*; D043266:Steryl-Sulfatase / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D004338:Drug Combinations; D011372:Progestins; D017258:Medroxyprogesterone Acetate; D015067:17-Hydroxysteroid Dehydrogenases; D001141:Aromatase; D043266:Steryl-Sulfatase