Heme oxygenase (HO)-1 is known to metabolize heme into biliverdin/bilirubin, carbon monoxide, and ferrous iron, and it has been suggested to demonstrate cytoprotective effects against various stress-related conditions. HO-1 is commonly regarded as a survival molecule, exerting an important role in cancer progression and its inhibition is considered beneficial in a number of cancers. However, increasing studies have shown a dark side of HO-1, in which HO-1 acts as a critical mediator in ferroptosis induction and plays a causative factor for the progression of several diseases. Ferroptosis is a newly identified iron- and lipid peroxidation-dependent cell death. The critical role of HO-1 in heme metabolism makes it an important candidate to mediate protective or detrimental effects via ferroptosis induction. This review summarizes the current understanding on the regulatory mechanisms of HO-1 in ferroptosis. The amount of cellular iron and reactive oxygen species (ROS) is the determinative momentum for the role of HO-1, in which excessive cellular iron and ROS tend to enforce HO-1 from a protective role to a perpetrator. Despite the dark side that is related to cell death, there is a prospective application of HO-1 to mediate ferroptosis for cancer therapy as a chemotherapeutic strategy against tumors.

Heme oxygenases (HOs) act on heme degradation to produce carbon monoxide (CO), free iron, ferritin, and biliverdin. Upregulation of cellular HO-1 levels is signature of oxidative stress for its downstream effects particularly under pro-oxidative status. Subcellular traffics of HO-1 to different organelles constitute a network of interactions compromising a variety of effectors such as pro-oxidants, ROS, mitochondrial enzymes, and nucleic transcription factors. Some of the compartmentalized HO-1 have been demonstrated as functioning in the progression of cancer. Emerging data show the multiple roles of HO-1 in tumorigenesis from pathogenesis to the progression to malignancy, metastasis, and even resistance to therapy. However, the role of HO-1 in tumorigenesis has not been systematically addressed. This review describes the crosstalk between HO-1 and oxidative stress, and following redox regulation in the tumorigenesis. HO-1-regulated signaling pathways are also summarized. This review aims to integrate basic information and current progress of HO-1 in cancer research in order to enhance the understandings and facilitate following studies.

Ferroptosis is a form of oxidative cell death and has become a chemotherapeutic target for cancer treatment. BAY 11-7085 (BAY), which is a well-known IκBα inhibitor, suppressed viability in cancer cells via induction of ferroptotic death in an NF-κB-independent manner. This study was aimed to characterize the underlying mechanism by BAY and demonstrate its potential chemotherapeutic targets for cancer treatment. Reactive oxygen species scavenging, relief of lipid peroxidation, replenishment of glutathione and thiol-containing agents, as well as iron chelation, rescued BAY-induced cell death in human breast cancer cells (MDA-MB-231 and MDA-MB-468) and glioblastoma cells (DBTRG-05MG). The results from quantitative real-time PCR and western blotting analysis showed that BAY upregulated a variety of nuclear factor-E2-related factor 2 (Nrf2) target genes related to redox regulation, particularly heme oxygenase-1 (HO-1) and solute carrier family 7 membrane 1 (SLC7A11). Studies with pharmacological inhibitors and shRNA interventions suggested that the hierarchy of induction is Nrf2-SLC7A11-HO-1. The ferroptotic process induced by hHO-1 overexpression further indicated that HO-1 is a key mediator of BAY-induced ferroptosis that operates through cellular redox regulation and iron accumulation. Our study discovered that BAY induced ferroptosis via Nrf2-SLC7A11-HO-1 pathway and provided new insights to understand the mechanism of HO-1-induced ferroptosis, suggesting HO-1 as a new chemotherapeutic target for cancer treatment. Citation Format: Shih-Kai Chiang, Shuen-Ei Chen, Ling-Chu Chang. Heme oxygenase-1 mediates ferroptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2320.