ESR1 and breast cancer: We first tested the ability of T6I-29-1A to reduce the transcription of canonical ERα target genes including GREB1, CCND1, PGR, and CA12. T47D breast cancer cells were treated for 16 h with veh (DMSO), 1 nM E2 or 1 nM E2 + 1 μM T6I-29-1A, ICI, Laso, or RAD1901 and gene expression was measured by qPCR and normalized to E2-only treatment.