Mitochondrial genome-encoded mitomiRs regulate cellular plasticity and susceptibility to ferroptosis in triple-negative breast cancer

Ferroptosis is a distinct form of regulated cell death promoted by iron-dependent lipid peroxidation. The metabolic plasticity of cancer cells determines their sensitivity to ferroptosis. Although mitochondrial dysfunction contributes to metabolic reprogramming in cancer cells, its role in ferroptosis remains to be identified. We identified that the mitochondrial genome encodes 13 miRNAs (mitomiRs) that are highly expressed in breast cancer cell lines and patient-derived tumor samples. Expression analysis revealed that mitomiRs are upregulated in basal-like triple-negative breast cancer (TNBC) cells compared to mesenchymal stem-like TNBC cells. Interestingly, 11 out of the 13 mitomiRs bind to the 3'UTR of zinc finger E-box-binding homeobox 1 (ZEB1), a transcription factor, involved in epithelial to mesenchymal transition (EMT) in breast cancer. Using mitomiR-3 mimic, inhibitor and sponges, we confirmed that mitomiR-3 indeed regulate ZEB1 expression in TNBC cells. Increased mesenchymal features in TNBC contributed to vulnerability to pro-ferroptotic metabolic reprogramming sensitizing to cell death in in vitro and in vivo models. Some of the challenges associated with pro-ferroptotic drugs includes lack of cancer cell specificity, low targeting ability, normal tissue toxicity contributing to their limited clinical application as cancer therapeutics. Here, we identified mitomiRs which are highly expressed in TNBC subtypes with low expression in normal breast cells making them an ideal candidate for selective inhibition for targeted therapy. Further, we demonstrated that the inhibition of mitomiRs in triple-negative breast cancer cells promote pro-ferroptotic metabolic reprogramming which can be exploited as novel vulnerability for targeted ferroptotic induction in cancer cells avoiding the normal tissue toxicity. Collectively, our results indicate a novel mechanism of mitochondrial miRNA mediated ferroptosis sensitivity in TNBC subtypes which could be exploited to develop potential miRNA-based therapeutics.