H-151 Blocks Ferroptosis Through Radical Trapping

H-151 is described as a covalent inhibitor of stimulator of interferon genes (STING). In this study, Yin et al. investigate an additional activity: suppression of ferroptosis through radical trapping, rather than through STING inhibition alone. The distinction matters because an effect on cell viability is not, by itself, evidence for a particular cell-death mechanism. Here, ferroptosis attribution is supported by ferroptosis-inducing treatments, rescue by established ferroptosis inhibitors, and measurements of lipid peroxidation. The paper does not investigate caspase-dependent or caspase-independent apoptosis as a mechanism.

Research Question

Does H-151 protect against ferroptosis because it inhibits STING, or can it suppress ferroptosis through a separate activity? The authors also ask whether any STING-independent effect is associated with radical trapping and whether H-151 can protect against renal ischemia–reperfusion injury (IRI), where the paper examines both STING signaling and ferroptosis-associated readouts.

Study Design and Methods

Cell-death mechanism experiments: The authors treated several mouse and human cell lines with RSL3 or ML-210, which inhibit GPX4, or with imidazole ketone erastin (IKE), a system xc− inhibitor. They measured viability and, for selected conditions, cell death. Fer-1 and deferoxamine served as ferroptosis-rescue comparators. Lipid peroxidation was assessed with BODIPY 581/591 C11 by flow cytometry and imaging. These experiments, rather than viability assays alone, form the central cellular evidence for a ferroptosis-related effect.

Testing STING dependence: The team compared wild-type cells with CRISPR-generated STING-knockout cells. HT-DNA stimulation and immunoblotting for STING-pathway readouts, including phosphorylated TBK1, assessed STING signaling. Persistence of H-151 protection in knockout cells tests whether STING is required for the cell-protective effect.

Testing radical trapping: A liposome-based FENIX assay measured oxidation of a fluorescent probe during radical-driven lipid oxidation; a lipid-free version tested radical trapping outside a membrane context. The authors also measured hydroxyl-radical-associated probe fluorescence in a Fenton reaction and assessed H-151 abundance by LC-MS under reaction conditions. A calcein assay tested iron chelation. These biochemical experiments address the proposed chemical activity; they are distinct from the cellular cell-death assays.

Animal study: Male mice underwent bilateral renal ischemia for 45 minutes followed by reperfusion. H-151 was given intraperitoneally at 5 mg/kg 12 hours before injury, and outcomes were assessed 24 hours later. The study measured serum creatinine and blood urea nitrogen, renal histology, TUNEL staining, 4-HNE staining, Ptgs2 expression and inflammatory readouts. Renal IRI was also tested in STING-knockout mice.

Main Findings

Reported findings: H-151, unlike the other tested STING inhibitors, protected cells from RSL3-associated viability loss; it also protected against ML-210 and IKE treatments in the tested cell lines. Cell-death measurements showed protection comparable to Fer-1 or deferoxamine in selected experiments. H-151 reduced BODIPY-detected lipid peroxidation, including in STING-knockout cells. STING deletion therefore did not eliminate the observed cellular protection, supporting a STING-independent component.

In biochemical assays, H-151 inhibited probe oxidation in both liposomal and lipid-free FENIX conditions. It reduced hydroxyl-radical-associated fluorescence in the Fenton system, and LC-MS showed reduced H-151 abundance when both Fe2+ and H2O2 were present. In the calcein assay, H-151 did not show the iron-chelating effect observed with deferoxamine. Together, these results support the authors’ conclusion that radical trapping, rather than iron chelation or STING inhibition alone, contributes to H-151’s suppression of lipid peroxidation. The exact reaction products and chemical intermediates were not identified.

In the mouse IRI model, H-151 treatment was associated with lower serum creatinine and blood urea nitrogen, reduced histological injury, and lower renal 4-HNE staining and Ptgs2 expression. STING-pathway and inflammatory readouts also decreased. H-151 retained an effect on renal-function measures in STING-knockout mice, consistent with a STING-independent contribution in vivo. These outcomes support protection in this acute, prophylactically treated model; they do not, on their own, establish which mechanism accounts for the in vivo benefit.

Interpretation and death-mode distinction: Ferroptosis is the paper’s mechanistic focus: the authors connect rescue from ferroptosis-inducing treatments with reduced lipid peroxidation and radical-trapping activity. STING inhibition is a separate inflammatory-signaling activity, supported by pathway readouts and the knockout experiments. By contrast, the study does not report caspase activation, caspase cleavage, or caspase-inhibition experiments, so it does not establish apoptosis or caspase dependence. TUNEL-positive cells were counted in injured kidneys, but TUNEL is not sufficient by itself to distinguish apoptosis from ferroptosis or to assign a death pathway. The tissue staining and injury markers are supporting in vivo observations, not a standalone demonstration of the mode of cell death.

Limitations

The authors identify several limits: efficacy was tested in one acute murine renal IRI model; H-151 was administered before injury, leaving post-injury treatment and the therapeutic window unresolved; and long-term efficacy and safety were not determined. The precise chemical intermediates and structural basis of radical scavenging were not characterized, and effects on other regulated cell-death forms and redox-dependent pathways were not examined. In addition, the in vivo ferroptosis evidence relies on associated lipid-peroxidation and gene-expression markers alongside functional and histological outcomes; the reported experiments do not isolate ferroptosis as the sole cause of H-151’s renal protection. Apoptosis was not mechanistically tested.

Source

Yin S, Li Y, Mei T, et al. “A STING inhibitor suppresses ferroptosis through radical-trapping antioxidant activity.” Cell Chemical Biology (2026). Read the source paper.