The estrogenic activity of
dieldrin,
toxaphene, and an equimolar mixture of both compounds (
dieldrin/
toxaphene) was investigated in the 21-day-old B6C3F1 mouse uterus, MCF-7 human
breast cancer cells, and in yeast-based reporter gene assays. Treatment of the animals with 17beta-estradiol (E2) (0.0053 kg/day x3) resulted in a 3.1-, 4.8-, and 7.8-fold increase in uterine wet weight,
peroxidase activity, and
progesterone receptor binding, respectively. In contrast, treatment with 2.5, 15 and 60 micromol/kg (x3) doses of
toxaphene,
dieldrin, or
dieldrin/
toxaphene (equimolar) did not significantly induce a dose-dependent increase in any of the E2-induced responses. The organochlorine pesticides alone and the binary mixture did not bind to the mouse uterine
estrogen receptor (ER) in a competitive binding assay using [3H]E2 as the radioligand. In parallel studies, estrogenic activities were determined in MCF-7 cells by using a cell proliferation assay and by determining induction of
chloramphenicol acetyl
transferase (CAT) activity in MCF-7 cells transiently transfected with plasmids containing
estrogen-responsive 5'-promoter regions from the rat
creatine kinase B and human
cathepsin D genes. E2 caused a 24-fold increase in CAT activity in MCF-7 cells transiently transfected with
creatine kinase B and a 3.8-fold increase in cells transiently transfected with the human
cathepsin D construct. Treatment of MCF-7 cells with
dieldrin,
toxaphene, or an equimolar mixture of
dieldrin plus
toxaphene (10(-8)-10(-5) M) did not significantly induce cell proliferation or CAT activity in the transient transfection experiment with both plasmids. The relative competitive binding of the organochlorine pesticides was determined by incubating MCF-7 cells with 10(-9) M [3H]E2 in the presence or absence of 2 x 10(-7) M unlabeled E2 (to determine nonspecific binding),
toxaphene (10(-5) M),
dieldrin (10(-5) M), and equimolar concentrations of the
dieldrin plus
toxaphene mixture (10(-5) M). The binding observed for [3H]E2 in the whole
cell extracts was displaced by unlabeled E2, whereas the organochlorine pesticides and binary mixture exhibited minimal to nondetectable competitive binding activity. E2 caused a 5000-fold induction of
beta-galactosidase (beta-gal) activity in yeast transformed with the human ER and a double
estrogen responsive
element upstream of the beta-gal reporter gene. Treatment with 10(-6)-10(-4) M
chlordane,
dieldrin,
toxaphene, or an equimolar mixture of
dieldrin/
toxaphene did not induce activity, whereas 10(-4) M
endosulfan caused a 2000-fold increase in beta-gal activity.
Diethylstilbestrol caused a 20-fold increase in activity in yeast transformed with the mouse ER and a single
estrogen responsive
element upstream of the beta-gal reporter gene.
Dieldrin,
chlordane,
toxaphene, and
endosulfan induced a 1.5- to 4-fold increase in activity at a concentration of 2.5 x 10(-5) M. Synergistic transactivation was not observed for any equimolar binary mixture of the pesticides at concentrations of either 2.5 x 10(-5) M or 2.5 x 10(-4) M. The results of this study demonstrate that for several
estrogen-responsive assays in the mouse uterus, MCF-7 human
breast cancer cells, and yeast-based reporter gene assays, the activities of both
dieldrin and
toxaphene were minimal, and no synergistic interactions were observed with a binary mixture of the two compounds.