ESTROGENIC ACTIVITY OF A DIELDRIN TOXAPHENE MIXTURE IN THE MOUSE UTERUS, MCF-7 HUMAN BREAST-CANCER CELLS, AND YEAST-BASED ESTROGEN-RECEPTORASSAYS - NO APPARENT SYNERGISM/

The estrogenic activity of dieldrin, toxaphene, and an equimolar mixtu re of both compounds (dieldrin/toxaphene) was investigated in the 21-d ay-old B6C3F1 mouse uterus, MCF-7 human breast cancer cells, and in ye ast-based reporter gene assays. Treatment of the animals with 17 beta- estradiol (E(2)) (0.0053 kg/day x3) resulted in a 3.1-, 4.8-, and 7.8- fold increase in uterine wet weight, peroxidase activity, and progeste rone receptor binding, respectively. In contrast, treatment with 2.5, 15 and 60 mu mol/Kg (x3) doses of toxaphene, dieldrin, or dieldrin/tox aphene (equimolar) did not significantly induce a dose dependent incre ase in ally of the E(2)-induced responses. The organochlorine pesticid es alone and the binary mixture did not bind to the mouse uterine estr ogen receptor (En) in a competitive binding assay using [H-3]E(2) as t he radioligand. In parallel studies, estrogenic a activities were dete rmined in MCF-7 cells by using a cell proliferation assay and by deter mining induction of chloramphenicol acetyl transferase (CAT) activity in MCF-7 cells transiently transfected with plasmids containing estrog en-responsive 5'-promotel regions from the rat creatine kinase B and h uman cathepsin D genes. E, caused a 24-fold increase in CAT activity i n MCF-7 cells transiently transfected with creatine kinase B and a 3.8 -fold increase in cells transiently transfected with the human catheps in D construct. Treatment of MCF-7 cells with dieldrin, toxaphene, or an equimolar mixture of dieldrin plus toxaphene 10(-8)-10(-5) M) did n ot significantly induce cell proliferation or CAT activity in the tran sient transfection experiment with both plasmids. The relative competi tive binding of the organochlorine pesticides was determined by incuba ting MCF-7 cells with 10(-9) M [3H]E, in the presence or absence of 2 x 10(-7) M unlabeled E(2) ito determine nonspecific binding), toxaphen e (10(-5) M), dieldrin (10(-5) M), and equimolar concentrations of the dieldrin plus toxaphene mixture (10(-5) M). The binding observed for [H-3]E(2) in the whole cell extracts was displaced by unlabeled E,, wh ereas the organochlorine pesticides acid binary mixture exhibited mini mal to nondetectable competitive binding activity. E(2) caused a 5000- fold induction of P-galactosidase (p-gal) activity in yeast transforme d with the human ER and a double estrogen responsive element upstream of the P-gal reporter gene. Treatment with 10(-6)-10(-4) M chlordane, dicldrin, toxaphene, or an equimolar mixture of dieldrin/toxaphene did not induce activity, whereas 10(-4) M endosulfan caused a 2000-fold i ncrease in beta-gal activity. Diethylstilbcstrol caused a 20-fold incr ease in activity in yeast transformed with the mouse ER and a single e strogen responsive element upstream of the beta-gal reporter gene. Die ldrin, chlordane, toxaphene, and endosulfan induced a 1.5- to 4-fold i ncrease in actitity at a concentration of 2.5x10(-5) M. Synergistic tr ansactivation 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-re sponsive 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 obser ved with a binary mixture of the two compounds.