MCF-7aro/ERE, a novel cell line for rapid screening of aromatase inhibitors, ERα ligands and ERRα ligands

We have previously generated a breast cancer cell line, MCF-7aro, which over-expresses aromatase and is also ER positive. Recently, this MCF-7aro cell line was stably transfected with a promoter reporter plasmid, pGL3-Luc, containing three repeats of estrogen responsive element (ERE). Experiments using MCF-7aro/ERE have demonstrated that it is a novel, non-radioactive screening system for aromatase inhibitors (AIs), ERα ligands and ERRα ligands. The screening is carried out in a 96-well plate format. To evaluate this system, the cells were cultured overnight in charcoal–dextran stripped FBS medium supplemented with 0.1 nM testosterone or 17β-estradiol, and various concentrations of antiestrogens or AIs. We found that the luciferase activity was induced when the cells were cultured either in the presence of testosterone or 17β-estradiol. Furthermore, a 50% decrease in luciferase activity could be achieved when the cells were cultured in the presence of testosterone together with letrozole, anastrozole, tamoxifen or fulvestrant (concentrations being 75 nM, 290 nM, 100 nM, and 5 nM, respectively), compared to the testosterone-only cultured cells. Using this assay system, we confirmed that 3(2′-chlorophenyl)-7-methoxy-4-phenylcoumarin is an agonist of ER. Furthermore, genestein has been shown to be a ligand of ERRα because its binding could be blocked by an ERRα inverse agonist, XCT790. These results indicate that MCF-7aro/ERE is a novel cell line for rapid screening of AIs, ERα ligands and ERRα ligands.