Preferentially Targeting the Endoplasmic Reticulum as a Unique Mechanism of Ferroptosis Induction by a Lipophilic Iron-Hinokitiol Complex

A strong correlation has been found between ferroptosis and various diseases, with iron overload being prominently implicated. However, few studies have specifically focused on triggering ferroptosis by directly eliciting iron overload via forming lipophilic iron complexes. Here, we show that the natural compound hinokitiol (HK) forms a stable, lipophilic 3:1 complex with Fe(III) (HK-Fe(III)), which rapidly enters HT-1080 cells via passive diffusion and delivers iron preferentially to the endoplasmic reticulum (ER). Notably, 10 μM HK-Fe(III) induces potent ferroptosis within 5 hours-substantially faster than classical inducers such as erastin, RSL3, and FINO2. Mechanistically, HK-Fe(III) specifically triggers ER peroxidation without significant involvement of mitochondria or lysosomes, and the ER-targeted antioxidant stobadine completely inhibits cell death. Enrichment of polyunsaturated fatty acids (PUFAs) in the ER enhanced the efficiency of HK-Fe(III)-induced ferroptosis by strengthening ER peroxidation, suggesting that ER peroxidation is a key factor in lipophilic iron complex-induced ferroptosis. HK-Fe(III) could also induce cognitive deficits and ferroptosis in hippocampal cells in mice, indicating its potential to establish animal models for neurodegenerative diseases through iron overload. This study identifies a unique ferroptosis mechanism based on ER-targeted iron delivery and ER peroxidation, and provides a rapid and potent inducer for studying ferroptosis in vitro and in vivo, with potential applications in disease modeling and therapy.