Estrogenic activity of a dieldrin/toxaphene mixture in the mouse uterus, MCF-7 human breast cancer cells, and yeast-based estrogen receptor assays: no apparent synergism

• Published in: Endocrinology (Philadelphia) 1997-04, Vol.138 (4), p.1520
• Main Authors: Ramamoorthy, K, Wang, F, Chen, I C, Norris, J D, McDonnell, D P, Leonard, L S, Gaido, K W, Bocchinfuso, W P, Korach, K S, Safe, S
• Format: Article
• Language: English
• Subjects: Animals; Binding, Competitive; Breast Neoplasms - metabolism; Cell Division - drug effects; Dieldrin - administration & dosage; Dieldrin - pharmacology; Drug Synergism; Estradiol - pharmacology; Female; Humans; Mice; Peroxidase - metabolism; Progesterone - metabolism; Rats; Receptors, Estrogen - analysis; Toxaphene - administration & dosage; Toxaphene - pharmacology; Transfection; Tumor Cells, Cultured; Uterus - drug effects; Uterus - metabolism
• ISSN: 0013-7227
• DOI: 10.1210/en.138.4.1520

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/