Divergent ferroptotic pathways in breast cancer cells: IGFBP6-regulated mitochondrial lipid peroxidation under erastin and omega-3 DHA treatment.

Breast cancer remains a major challenge and new therapeutic approaches are needed for its treatment. Ferroptosis is considered a promising alternative cell death mechanism to eliminate resistant cancer cells. In previous works, we identified that lower IGFBP6 gene expression in tumor tissue corresponds to a worse prognosis for breast cancer patients and, at the same, time makes them more sensitive to ferroptosis. In this study, we further investigated the mechanism of ferroptosis induction in IGFBP6 knockdown and control MDA-MB-231 breast cancer cells by the canonical ferroptosis inducer erastin and omega-3 docosahexaenoic acid (DHA). Our results indicate that there is a significant overlap between the mechanisms of action of both of these molecules, as they regulate the same subset of genes, and their action can be inhibited by canonical ferroptosis inhibitors. On the other hand, we also observed significant differences between the effects of erastin and DHA. The most notable of these are the additional activation of apoptosis-related genes by DHA and its minor peroxidation of mitochondrial lipid membranes. Interestingly, our kinetic analysis of ferroptosis induction showed that IGFBP6 knockdown cells began to die earlier and could hardly be rescued from erastin-induced ferroptosis by mitochondrial antioxidant SkQ1, in contrast to control cells. Overall, our data suggest that the action of DHA is less dependent on mitochondrial membrane peroxidation during ferroptosis induction, and this molecule can be a promising candidate for the treatment of breast cancer, especially in the case of reduced IGFBP6 gene expression in cancer cells.