Metamifop-induced human breast cancer cells proliferation: Revealing a proliferation mechanism distinct from 17β-estradiol.

The potential endocrine-disrupting effects of AOPP herbicides have garnered increasing attention, yet the mechanisms and extent of metamifop endocrine disruption in humans remain unclear. This study aims to investigate the effects of metamifop herbicide on the proliferation effects of human breast cancer cells (MCF-7) and to explore its molecular mechanisms underlying such effects. For this, MCF-7 cells were exposed to metamifop (10-10 M) and 17β-estradiol (E2, 1 nmol/L) for 24-72 h. CCK-8 assay indicate that metamifop significantly increased cell proliferation rates in the low-dose treatment group, similar to E2. The 5-ethynyl-2-deoxyuridine (EdU) assay further confirmed that MCF-7 cells treated with metamifop exhibited a proliferation phase proportion of 26.42%, while the E2-treated group reached 22.51%, indicating its pro-proliferative effect. Additionally, cell cycle analysis revealed that both E2 and metamifop treatment significantly encourage cell proliferation by faster the transition from G1 to S phase. Notably, these results collectively indicate that, similar to E2, metamifop significantly enhances the viability and proliferation of MCF-7 cells. Further investigation into the potential mechanisms, transcriptomic analysis and dual luciferase reporter assays indicated that metamifop did not activate ER-mediated transcriptional activity, distinct from E2. Finally, metamifop was validated that may influence MCF-7 cell proliferation by regulating key genes in the estrogen signaling pathway and the relative proteins expression. Conclusion, this study suggested that the estrogen-like endocrine-disrupting response induced by metamifop, potentially mediated via non-classical estrogen signaling pathways (e.g., GPER1-KMT2D axis), rather than direct ERα activation. These findings provide scientific evidence for assessing metamifop endocrine-disrupting effects and environmental risks.