In vitro screening of inhibition of PPAR-γ activity as a first step in identification of potential breast carcinogens

Alcohol consumption and increased estrogen levels are major risk factors for breast cancer, and peroxisome proliferator-activated receptor γ (PPAR-γ) plays an important role in alcohol-induced breast cancer. PPAR-γ activity is inhibited by ethanol, leading to increased aromatase activity and estrogen biosynthesis ultimately leading to breast cancer. If other organic solvents inhibit PPAR-γ activity, they should also lead to increased oestrogen biosynthesis and thus be potential breast carcinogens. Ten commonly used hydrophilic organic solvents were first tested in a cell-based screening assay for inhibitory effects on PPAR-γ transactivation. The chemicals shown to inhibit PPAR-γ were tested with vectors encoding PPAR-γ with deleted AB domains and only the ligand-binding domain to rule out unspecific toxicity. Next, the effects on biosynthesis of estradiol, testosterone and oestrone sulphate were measured in the H295R steroidogenesis assay after incubation with the chemicals. Ethylene glycol, ethyl acetate, and dimethyl sulphoxide inhibited PPAR-γ transactivation in a dose-dependent manner. The inhibitory effect on PPAR-γ was specific for PPAR-γ since the AB domain of PPAR-γ was required for the inhibitory effect. In the second step, ethylene glycol significantly increased production of oestradiol by 19% (p <0.05) and ethyl acetate inhibited production of testosterone (p <0.05). We here show that screening of 10 commonly used organic solvents for the ability to inhibit PPAR-γ transactivation followed by a well-established steroidogenesis assay for production of sex hormones in exposed H295 R cells may provide a screening tool for potential breast carcinogens. This initial screening thus identified ethylene glycol and possibly ethyl acetate as potential breast carcinogens.