ESR1 and breast carcinoma: In contrast, in MCF7 human breast cancer cells, transfected with the same ERE-Luc reporter construct, the aGLP1-E2 compound showed weak transcriptional activity (<1.5-fold) compared to E2 (4-fold), further confirming our in vivo finding that aGLP1-E2 does not stimulate breast ER activity (Fig. 1C).