2,3,7,8-Tetrachlorodibenzo-p-dioxin causes an extensive alteration of 17 beta-estradiol metabolism in MCF-7 breast tumor cells.
MCF-7 breast tumor cells form multicellular foci in vitro when supplemented with 17 beta-estradiol (E2). In the presence of E2 and the aryl hydrocarbon-receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), MCF-7 cells grow to confluence but do not form foci. To investigate the role of E2 metabolism in this antiestrogenic effect of TCDD, analyses were performed by capillary GC/MS. The results revealed that pretreatment of MCF-7 cultures with TCDD (10 nM) rapidly depletes E2. In untreated cultures supplemented with 10 nM E2, the concentration of free E2 decreased to 4 nM in the first 12 hr, followed by a slower rate of decline. After 3 days most E2 in the medium was in conjugated form(s); 1.7 nM was present as free E2, and 2.9 nM was released by treatment with glucuronidase/sulfatase. In TCDD-treated cultures, E2 declined to 290 pM in 12 hr and after 2 days was not detected (less than 100 pM) either as free steroid or after treatment with glucuronidase/sulfatase. Intracellular E2 and estrone were likewise depleted by pretreatment with TCDD. Microsomes from TCDD-treated cells showed highly elevated aryl hydrocarbon-hydroxylase activity and catalyzed hydroxylations of E2 at C-2, C-4, C-15 alpha, and C-6 alpha with a combined rate of 0.85 nmol/min per nmol of cytochrome P-450 at saturating E2. These results suggest that depletion of E2 by enhanced metabolism accounts for the antiestrogenic activity of TCDD in MCF-7 cells.
Spink
D C
DC
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
Lincoln
D W
DW
Dickerman
H W
HW
Gierthy
J F
JF
D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D001943:Breast Neoplasms; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004147:Dioxins / Q000494:pharmacology*; D004958:Estradiol / Q000378:metabolism*; D004967:Estrogens / Q000302:isolation & purification; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006900:Hydroxylation; D007700:Kinetics; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*
D004147:Dioxins; D004967:Estrogens; D000072317:Polychlorinated Dibenzodioxins; D004958:Estradiol; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases