Screening of environmental contaminants for ecdysteroid agonist and antagonist activity using the Drosophila melanogaster B-II cell in vitro assay

The B-II bioassay was developed as a rapid and reliable toot for detecting potential insect growth regulators acting as ecdysteroid receptor (ant)agon ists. Based on an ecdysteroid-responsive cell line from Drosophila melanoga ster, this microplate assay is ideally suited to the evaluation of environm ental contaminants as potential endocrine disrupters. Data are presented fo r about 80 potential environmental contaminants, including industrial chemi cals, pesticides, pharmaceuticals, phytoestrogens, and vertebrate steroids, and are compared with data for known (ant)agonists, Apart from androst-4-e ne-3,17-dione (a weak antagonist), vertebrate steroids were inactive at con centrations up to 10(-3) M. The vast majority of xenobiotics also showed no (ant)agonist activity. Among the industrial chemicals, antagonistic activi ty was observed for bisphenol A median effective concentration (EC50) of 1. 0 x 10(-4) M and diethylphthalate (EC50 of 2.0 x 10(-3) M). Some organochlo rine compounds also showed weak antagonistic activity, including o,p ' -dic hlorodiphenyldichloroethylene (DDE), p,p ' -DDE, dieldrin, and lindane (EC5 0 of 3.0 x 10(-5) M). For lindane, bisphenol A, and diethylphthalate, activ ity is not associated with impurities in the samples and, for lindane and b isphenol A at least, the compounds are able to compete with ecdysteroids fo r the ligand binding site on the receptor complex, albeit at concentrations very much higher than those found in the environment. The only pharmaceuti cal showing any detectable antagonist activity was 17 alpha -ethynylestradi ol. In the context of recent publications on potential endocrine disruption in marine and freshwater arthropods, these findings suggest that, for some compounds (e.g., diethylstilbestrol), ecdysteroid receptor-mediated respon ses are unlikely to be involved in producing chronic effects. The B-II assa y has a potentially valuable role to play in distinguishing between endocri ne-mediated, which normally occur at submicromolar concentrations, and phar macological effects in insects and crustaceans.