Screening of some anti-androgenic endocrine disruptors using a recombinant cell-based in vitro bioassay

The present work describes the development and optimization of a cell-based androgen reporter assay using the Chinese hamster ovarian cell line (CHO K1) in the 96-well format. The recent reports on increasing exposure of humans and wild-life to environmental endocrine disrupting chemicals (ED) prompt the need for high throughput screening systems for such compounds in environmental and biological samples. To this end, CHO cells were cotransfected with plasmids encoding mouse mammary tumour virus-neomycin-luciferase and human androgen receptor (hAR), and a stable cell line was established. After selection with neomycin, a highly active clone was obtained which stably expressed both the hAR and the androgen-responsive luciferase reporter. Stimulation of the cells with androgens for 24 h resulted in about 15-fold stimulation of luciferase activity, with the minimum effective dose of testosterone being 0.1 nmol/l. Potent steroidal and non-steroidal anti-androgens, such as hydroxyflutamide and cyproterone acetate, significantly inhibited the androgen-induced transactivation. Non-androgenic steroids like estradiol, progesterone, dexamethasone and cortisol showed weak activity at high concentrations. RT-PCR and western blot confirmed proper transcription and translation as well as stable expression of the AR gene in the cells. About 60 different chemicals (mostly pesticides or their metabolites, and common industrial chemicals) were screened with the cell line for their ability to stimulate luciferase activity or inhibit that evoked by 0.1 nmol/l R1881, used as a positive androgenic control. About 10 highly potent anti-androgenic chemicals were identified. The most potent anti-androgenic compounds identified in our assay included bisphenol A, alpha-hexachlorocyclohexane, vinclozolin and 4,4-DDE. These compounds had alone either no effect or were weak agonists (with cytotoxic effects at very high concentrations), but none showed any significant agonistic activity. In conclusion, we demonstrate that the bioassay based on this cell line provides a reliable test for detecting androgenic and anti-androgenic compounds. The 96-well plate format makes the assay suitable for high throughput screening.