Ursolic acid inhibits the proliferation of triple­negative breast cancer stem­like cells through NRF2­mediated ferroptosis.

Ursolic acid (UA), a pentacyclic triterpenoid that has been found in a broad variety of fruits, spices and medicinal plants, has various biological effects such as reducing inflammation, protecting cells from damage, and preserving brain function. However, its impact on ferroptosis in cancer stem­like cells remains unexplored. The present study investigated the effect of UA on MDA­MB­231 and BT­549 cell­derived triple­negative breast CSCs (BCSCs) and its potential ferroptosis pathway. The effects of ferroptosis on BCSCs were demonstrated by the detection of ferroptosis­related indexes including the intracellular level of glutathione, malondialdehyde, reactive oxygen species and iron. The effects of UA on the biological behaviors of BCSCs were analyzed by Cell Counting Kit­8, stemness indexes detection and mammosphere formation assay. The mechanism of UA induction on BCSCs was explored by reverse transcription­quantitative PCR and western blotting. BALB/c­nude mice were subcutaneously injected with MDA­MB­231­derived BCSCs to establish xenograft models to detect the effects of UA in vivo. The results revealed that BCSCs have abnormal iron metabolism and are less susceptible to ferroptosis. UA effectively reduces the stemness traits and proliferation of BCSCs in spheroids and mice models by promoting ferroptosis. It was observed that UA stabilizes Kelch­like ECH­associated protein 1 and suppresses nuclear factor erythroid­related factor 2 (NRF2) activation. These findings suggested that the ability of UA to trigger ferroptosis through the inhibition of the NRF2 pathway could be a promising approach for treating BCSCs, potentially addressing metastasis and drug resistance in triple­negative breast cancer (TNBC). This expands the clinical applications of UA and provides a theoretical basis for its use in TNBC treatment.