ESR1 and cancer: The cyclofenil-amide compound 13e is also identified as a promising lead compound of a clinically relevant ER conjugate with IC50 in MCF-7 cells of 187 nM, and ER binding affinity to ERα (IC50 = 19 nM) and ERβ (IC50 = 229 nM), which can target ER in the breast cancer cell and can thus deliver a cytotoxic agent CA4 to the cancer cell.