S-equol promotes ferroptosis in triple negative breast cancer by coordinating NCOA4-mediated ferritinophagy and PPARγ-mediated lipid metabolism.

Triple negative breast cancer (TNBC) is a diverse and highly aggressive cancer characterized by a strong tendency to metastasize, poor prognosis, and a lack of effective therapeutic targets. S-equol, an active metabolinte produced by gut microbiota through the conversion of daidzein, has been proven to possess anticancer activity. This study aims to investigate the anticancer effects of S-equol on TNBC and to elucidate key targets and potential mechanisms. In vitro experiments utilized the TNBC cell lines, while in vivo experiments employed a nude mouse xenograft tumor model. By means of using CCK-8, colony formation, scratch, and transwell invasion assays, the biological function of S-equol was evaluated. In addition, bioinformatics methods were employed to explore the potential signaling pathways and target genes of S-equol. The in vitro results substantiated that S-equol significantly suppressed both the proliferation and metastatic capacity of TNBC cells. Moreover, the prediction results indicated that S-equol may exert its anti-TNBC effects through ferroptosis via the PI3K/AKT signaling pathway, with PPARγ identified as the key gene. In vitro and in vivo results collectively verified that S-equol triggers ferroptosis by influencing lipid peroxidation and Fe²+ levels, thereby suppressing the proliferation of TNBC. In terms of mechanism, the result that S-equol enhanced the sensitivity of TNBC to ferroptosis ensued from inhibiting the PI3K/AKT/mTOR pathway. This inhibition suppressed the reduction in lipid peroxidation mediated by PPARγ and GPX4, while promoting an increase in intracellular Fe²+ levels mediated by NCOA4, which were respectively reversed by PPARγ and STAT3 agonists, as well as autophagy inhibitor ULK101. The results of NCOA4 knockdown or PPARγ overexpression further verified the previous mechanism of S-equol. In conclusion, these findings revealed that S-equol promotes ferroptosis in TNBC by suppressing PPARγ-mediated lipid metabolism and promoting NCOA4-mediated ferritinophagy, which was largely dependent on the regulation of the PI3K/AKT/mTOR signaling pathways.