Precise structure manipulation of selective estrogen receptor modulators led to first-in-class thiophene-3-benzamide derivatives as potential ER-antagonists without uterotrophic activity

The present study introduces two sets of compounds: panel A, which features thiophene-3-benzamide, and panel B, which includes pyrazole-4-benzamide. We designed these compounds to target estrogen receptors (ER) while minimizing uterotrophic activities. The chemical structures of the two panels have been derived from structural modifications of the selective estrogen modulator, methyl-piperidinopyrazole (MPP). These modifications aim to reduce uterotrophic effects. In our design, we incorporated amide, amine, and ketone spacers between the three phenyl rings, substituting the central thiophene and pyrazole rings in the target ER antagonists. This structural strategy aims to alter the formation of tris-p-phenol metabolites, which are associated with the potential estrogenic activity of this class of compounds. The cytotoxicity of the compounds from panel A revealed significant activity against MCF7 cells, which are estrogen-dependent breast cancer cells. Importantly, these compounds demonstrated minimal cytotoxicity against other cell lines, including skin, osteosarcoma, and triple-negative breast cancer. Among the compounds tested, 5-benzoyl-thiophene-3-carboxamide 5a and 5-(4-chlorobenzoyl)-thiophene-3-carboxamide 5d exhibited the highest cytotoxicity against MCF7 cells, with IC₅₀ values of 7.38 μM and 8.50 μM, respectively. Furthermore, both 5a and 5d showed potential as antiestrogens, exhibiting no estrogenic activity in the uterine tissues of immature rats. In the dose-response experiment, the 5d antiestrogenic potency (EC₅₀ = 5.530 μM) was comparable to that of Tamoxifen (EC₅₀ = 7.625 μM). Molecular Docking and Molecular Dynamics simulations elucidated the antiestrogenic activity of 5d and inactivity of 5-fluorobenzoyl counterpart, 5e. The inactive derivative 5e in the active site exhibited an unfavorable conformation and unstable drug-receptor complex formation.