Fluorescent probe disclosing hydroxyl radical generation in mitochondria and nucleoli of cells during ferroptosis

Ferroptosis, a recently discovered form of cell death driven by iron-dependent lipid peroxidation (LP), significantly contributes to the inhibition of cancer proliferation and chemo-resistance. The hydroxyl radical (•OH), generated by a Fe 2+ -catalyzed Fenton reaction in cells, can result in LP and is intrinsically involved in ferroptosis. However, the number of •OH generation sites in the cells remains unclear. Herein, we report a pyronine-based fluorescent probe for •OH with phenothiazine as the reactive group. The probe responded very rapidly to •OH (< 1 s), and exhibited excellent selectivity. The probe can simultaneously target the mitochondria and nucleoli of cells, and thus shed light on •OH generation at both sites during ferroptosis. By comparison, drugs that could not induce cell ferroptosis, such as β-lapachone and rapamycin, only stimulated •OH generation in the mitochondria of cells. •OH production at both sites may be a new biochemical characteristic of ferroptosis, which provides a distinct insight into the mechanisms of drug action. • A dual-targeted fluorescent probe of •OH is reported. • Generation of •OH was observed in mitochondria and nucleoli of cells during ferroptosis.