Synthesis, biological evaluation, structural-activity relationship, and docking study for a series of benzoxepin-derived estrogen receptor modulators

The estrogen receptors ERα and ERβ are recognized as important pharmaceutical targets for a variety of diseases including osteoporosis and breast cancer. A series of novel benzoxepin-derived compounds are described as potent selective modulators of the human estrogen receptor modulators (SERMs). We report the antiproliferative effects of these compounds on human MCF-7 breast tumor cells. These heterocyclic compounds contain the triarylethylene arrangement as exemplified by tamoxifen, conformationally restrained through the incorporation of the benzoxepin ring system. The compounds demonstrate potency at nanomolar concentrations in antiproliferative assays against an MCF-7 human breast cancer cell line with low cytotoxicity together with low nanomolar binding affinity for the estrogen receptor. The compounds also demonstrate potent antiestrogenic properties in the human uterine Ishikawa cell line. The effect of a number of functional group substitutions on the ER binding properties of the benzoxepin molecular scaffold is examined through a detailed docking and 2D-QSAR computational investigation. The best QSAR model developed for ERαβ selectivity yielded R² of 0.84 with an RMSE for the training set of 0.30. The predictive quality of the model was Q² of 0.72 and RMSE of 0.18 for the test set. One particular compound (26b) bearing a 4-fluoro substituent, exhibits 15-fold selectivity for ERβ and both our docking and QSAR studies converge on the correlation between enhanced lipophilicity and enhanced ERβ binding for this benzoxepin ring scaffold.