Therapeutic failure and tumor relapse have been a major challenge to cure cancer and is thought to be caused by a sub-population of tumorigenic cells, termed cancer stem cells (CSC). CSC are characterized by an increased iron metabolism participating in their intrinsic drug-resistance capacity. Hence, combining therapies targeting both CSC and cancer cells appears as an attractive strategy to reduce tumor relapse, and improve clinical outcomes. Ferroptosis is a form of non-apoptotic cell death, defined by the iron-dependent accumulation of lipid-based reactive oxygen species. Due to their iron-dependency nature, CSC are very sensitive to ferroptosis, and Salinomycin, a lysosomal iron-targeting drug, has been shown to eliminate efficiently CSC. However, the underlying molecular mechanisms are still to be fully elucidated.

Using a well-established model of breast cancer stem cells (HMLER CD24low/CD44high), we systematically investigate the role of endoplasmic reticulum in ferroptosis induced by Salinomycin. This investigation involves mechanistic analyses conducted notably through western blot and flow cytometry techniques. Additionally, we explored the hypothesis of morphological changes using electron microscopy and fluorescent microscopy images.

We identified that Salinomycin-induced ferroptosis in breast CSC is partly due to endoplasmic reticulum stress. Indeed, many molecular actors of endoplasmic reticulum stress are found dysregulated by Salinomycin in our context. Moreover, if an endoplasmic reticulum stress inhibitor is added simultaneously with Salinomycin, partial protection against ferroptosis is observed. The use of microscopy also demonstrated the morphological alterations experienced by this organelle in cells treated with Salinomycin.

Our findings provide experimental evidence supporting the role of endoplasmic reticulum as a key player of Salinomycin-induced ferroptosis, opening new therapeutic opportunities for breast cancer treatment. This suggests that combining Salinomycin with an inducer of endoplasmic reticulum stress could be a promising strategy to enhance treatment efficacy.