Additive estrogenic activities of a binary mixture of 2',4',6'-trichloro- and 2',3',4',5'-tetrachloro-4-biphenylol.
The estrogenic activity of 2',4',6'-trichloro-4-biphenylol (HO-PCB3), 2',3',4',5'-tetrachloro-4-biphenylol (HO-PCB4), and an equimolar mixture of both compounds (HO-PCB3/HO-PCB4) was investigated in the 21-day-old B6C3F1 mouse uterus, MCF-7 and MDA-MB-231 human breast cancer cells, HepG2 cells, and in a yeast-based reporter gene assay. Treatment of the animals with 17beta-estradiol (E2) (0.02 microg/kg/day x3) resulted in increased uterine wet weight, peroxidase activity and progesterone receptor binding. Treatment with 18, 73, 183 or 366 micromol/kg (x3) doses of HO-PCB3, HO-PCB4, or HO-PCB3/HO-PCB4 (equimolar) caused a dose-dependent increase in estrogenic activity; a maximal-induced response was not observed at any dose and the activity of the mixture was additive. Binding of E2, HO-PCB3, HO-PCB4, and HO-PCB3/HO-PCB4 to the mouse uterine estrogen receptor (ER) was determined in a competitive binding assay using [3H]E2 as the radioligand. The IC50 values were 1.1 x 10(-8), 3.4 x 10(-6), 9.9 x 10(-7), and 4.25 x 10(-6) m, respectively. HO-PCB3 and HO-PCB4 maximally induced MCF-7 cell proliferation, rat creatine kinase, and human complement C3 (C3-LUC) reporter gene activity at concentrations of 10(-5) to 10(-6) m, and these compounds were 10(3) to 10(4) less potent than E2. The HO-PCB3/HO-PCB4 mixture was active at the high concentration (10(-5) m) and was additive for these responses. HO-PCB3 and HO-PCB4 also exhibited estrogenic activity in human HepG2 cells cotransfected with C3-LUC and an ER expression plasmid, and the estrogenic activity of the HO-PCB mixture was additive. Similar results were obtained in yeast transformed with the human ER and a double estrogen responsive element upstream of the beta-gal reporter gene. The effects of variable ER expression on the potential synergistic interactions of HO-PCB3/HO-PCB4 were investigated in HepG2 cells cotransfected with C3-LUC (405 ng/well) and variable amounts of ER expression plasmid (270, 27, 2.7, or 0.27 ng/well). The results show that as ER levels decreased, the magnitude of the induction response by E2, HO-PCB3, HO-PCB4, and HO-PCB3/HO-PCB4 also decreased. However, the activities of the HO-PCB mixture were additive at high and low levels of ER. Similar results were obtained in MDA-MB-231 cells cotransfected with C3-LUC and variable amounts of ER expression plasmid. The results of this study demonstrate that for several estrogen-responsive assays in the mouse uterus; MCF-7, HepG2, and MDA-MBA-231 human cancer cells; and a yeast based-reporter gene assay, both HO-PCB3 and HO-PCB4 exhibited estrogenic activity. The estrogenic activity of an equimolar mixture of these compounds was additive at high and low levels of ER expression.
Ramamoorthy
K
K
Veterinary Physiology and Pharmacology, Texas A&M University, College Station, Texas 77843-4466, USA.
Vyhlidal
C
C
Wang
F
F
Chen
I
I
Safe
S
S
McDonnell
D P
DP
Leonard
L S
LS
Gaido
K W
KW
D000818:Animals; D001943:Breast Neoplasms; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms; D051379:Mice; D010544:Peroxidases / Q000032:analysis; D011078:Polychlorinated Biphenyls / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D011960:Receptors, Estrogen / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D011980:Receptors, Progesterone / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014599:Uterus / Q000187:drug effects* / Q000378:metabolism
D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D011078:Polychlorinated Biphenyls; D010544:Peroxidases