The research team, based at the Korea Institute of Radiological and Medical Sciences, set out to examine how metformin and phenformin influence ferroptosis triggered by cysteine deprivation, a metabolic stress that strips cancer cells of a raw material they desperately need. Cysteine is the precursor for glutathione, the cell’s master antioxidant, and also supplies sulfur for iron-sulfur cluster biogenesis. When cysteine runs out, glutathione synthesis collapses, the antioxidant enzyme glutathione peroxidase 4 loses support, and membranes become vulnerable to runaway lipid peroxidation, the biochemical signature of ferroptosis.

Working with H1299 human non-small cell lung cancer cells and HEYA8 ovarian cancer cells, the researchers cultured the cells in custom-made cysteine-free medium and then added metformin or phenformin at various concentrations. The results were unambiguous. Both drugs dose-dependently rescued cell viability that would otherwise have plummeted, and propidium iodide staining confirmed that the proportion of dead cells dropped sharply. Neither drug alone killed more than about ten percent of cells at the concentrations tested, yet in the cysteine-starved environment they acted as powerful survival shields.

To confirm that the cell death being blocked was genuinely ferroptotic, the team deployed a panel of death-pathway inhibitors. Ferrostatin-1 and liproxstatin-1, canonical ferroptosis inhibitors, strongly restored viability, as did deferoxamine, an iron chelator, consistent with iron-driven lipid peroxidation as the dominant death mechanism. The apoptosis inhibitor z-VAD-fmk had no effect. Intriguingly, necrostatin-1, a necroptosis inhibitor, also rescued viability and reduced lipid peroxidation, suggesting that cysteine deprivation kills cells through a hybrid program in which ferroptosis and necroptotic signaling overlap, with lipid peroxidation serving as a common mediator.

Flow cytometry with the fluorescent lipid peroxidation probe C11-BODIPY 581/591 revealed that metformin and phenformin dramatically suppressed the peroxidation wave triggered by cysteine withdrawal, and the mitochondrial probe MitoPeDPP showed that the protection extended to the mitochondrial membranes themselves. Because reactive oxygen species drive lipid peroxidation, the researchers next measured ROS with DCFH-DA and mitochondrial superoxide with MitoSOX. Cysteine deprivation sent both soaring; both drugs pulled the levels back down, even though neither drug altered ROS on its own.

Here is where the story becomes mechanistically fascinating. The canonical view of ferroptosis centers on the glutathione-glutathione peroxidase 4 axis: no cysteine means no glutathione, and no glutathione means an undefended membrane. Yet metformin did not restore glutathione levels, did not change the ratio of oxidized to reduced glutathione, and did not rescue glutathione peroxidase 4 protein expression. Its protective effect was entirely independent of the antioxidant system that ferroptosis researchers usually target. Something else was going on, and the trail led to the mitochondria.

Using FerroOrange and Mito-FerroGreen probes, the team found that cysteine deprivation caused ferrous iron to pile up both in the cell overall and specifically inside mitochondria, and that metformin and phenformin blunted both accumulations. This matters because cysteine starvation disrupts iron-sulfur cluster biogenesis, destabilizing cellular iron homeostasis and raising the pool of labile ferrous iron that catalyzes lipid-damaging radical reactions. Notably, rotenone, a direct inhibitor of mitochondrial Complex I, and CCCP, which dissipates the mitochondrial membrane potential, similarly reduced mitochondrial iron accumulation, implicating mitochondrial bioenergetics in the iron dysregulation.

The mitochondrial connection deepened when the researchers measured membrane potential with TMRE staining and oxygen consumption with an extracellular oxygen probe. Within just two hours of cysteine deprivation, before any substantial cell loss, mitochondria became hyperpolarized and oxygen consumption spiked, exactly the alterations previously shown to be required for this form of ferroptosis. Metformin and phenformin, both established Complex I inhibitors, suppressed the hyperpolarization and curbed the excess oxygen consumption. Ferrostatin-1 also attenuated the hyperpolarization and mitochondrial ROS, reinforcing that these mitochondrial changes are not bystanders but active participants in the death program.

The authors are careful about what these findings do and do not mean clinically. The concentrations of metformin that blocked ferroptosis in this study, in the millimolar range, far exceed the roughly 10 to 40 micromolar plasma levels achieved in patients, and micromolar metformin showed no detectable protection. The results should therefore be read primarily as mechanistic evidence that tuning mitochondrial bioenergetic activity can suppress cysteine deprivation-induced ferroptosis, not as a reason to expect metformin alone to shield tumors at therapeutic doses. They also note that other lung cancer cell lines, including A549, H460, H23, and H820, were far less sensitive to cysteine deprivation in the first place, underscoring how cell-type-specific these responses are. Adding another layer of complexity, prior studies have reported that metformin induces or enhances ferroptosis in lung, breast, and liver cancer models through pathways such as NRF2/HO-1 suppression and SLC7A11 destabilization, and has even shown anti-ferroptotic protection in diabetic osteoporosis and pancreatic beta-cell injury, making metformin’s role in ferroptosis regulation unmistakably context-dependent.

The broader implication is a caution flag for the ferroptosis field. As pharmaceutical interest surges in therapies that starve tumors of cysteine or block the SLC7A11/xCT cystine importer, the new data suggest that biguanides, and perhaps other mitochondrial modulators, could quietly undermine such strategies. The study also hints at unexplored territory: cyclosporine A, which blocks the mitochondrial permeability transition pore, protected cells without preventing hyperpolarization, raising the possibility that transient, low-conductance pore opening contributes to ferroptotic progression in ways that standard membrane potential measurements miss. For now, the message is clear: if you want to kill cancer cells by starving them of cysteine, you had better make sure their mitochondria, and any diabetes medication in the mix, are not working against you.

Subject of Research: Inhibition of cysteine deprivation-induced ferroptosis by the biguanide drugs metformin and phenformin through suppression of mitochondrial dysfunction

Article Title: Metformin Inhibits Ferroptotic Cell Death by Suppressing Cysteine Deprivation‐Induced Mitochondrial Dysfunction

Article References: Jang, S.-K., Kim, S., Kim, G., Hong, J., Park, I.-C., & Jin, H.-O. (2026). Metformin Inhibits Ferroptotic Cell Death by Suppressing Cysteine Deprivation‐Induced Mitochondrial Dysfunction. Pharmacology Research & Perspectives, 14(5), Article e70330. https://doi.org/10.1002/prp2.70330

Image Credits: AI Generated

DOI: 10.1002/prp2.70330

Keywords: metformin, phenformin, ferroptosis, cysteine deprivation, mitochondria, lipid peroxidation, reactive oxygen species, iron accumulation, cancer, biguanides, mitochondrial complex I, cell death

Ferroptosis is a form of regulated cell death that has captivated oncologists since its discovery. Unlike apoptosis, the tidy, programmed dismantling of a cell, ferroptosis is a violent, iron-driven process in which reactive oxygen species attack the fatty membranes that enclose cells. Lipid peroxidation spreads like a chemical wildfire until the membrane disintegrates. Under the microscope, cells dying by ferroptosis display shrunken mitochondria with increased membrane density and diminished cristae, the internal folds where respiration takes place. Because cancer cells run metabolically hot, accumulating oxidative stress as a byproduct of their rapid growth, they are often unusually vulnerable to this mode of death, making ferroptosis an attractive therapeutic lever.

The central antioxidant defense against ferroptosis is the glutathione peroxidase 4 enzyme, or GPX4, which detoxifies phospholipid hydroperoxides using glutathione as a cofactor. Starving cells of cysteine, the amino acid required to build glutathione, collapses this defense system. Cysteine depletion does more than drain glutathione: it also impairs the synthesis of coenzyme A, disrupting lipid metabolism, and destabilizes iron-sulfur clusters, which activates an iron-starvation response that increases iron uptake through the transferrin receptor. The result is an expanding pool of unliganded ferrous iron that fuels Fenton chemistry, generating a flood of reactive oxygen species and driving lethal lipid peroxidation. A compound called RSL3 can trigger the same endpoint more directly by binding to and inhibiting GPX4 outright.

Lapatinib, meanwhile, is an orally available small-molecule inhibitor that selectively blocks the tyrosine kinase activities of the epidermal growth factor receptor EGFR and its relative HER2, suppressing the downstream MAPK and PI3K/AKT survival pathways that tumors depend on. Previous studies had painted a confusing picture of its relationship with ferroptosis. In breast cancer cells, lapatinib promoted ferroptosis when combined with a lysosome-disrupting agent, accompanied by iron accumulation. More recently, it was reported to induce ferroptosis in osteosarcoma by disrupting glutamine uptake and glutathione synthesis. Yet in neuronal cells, lapatinib was found to suppress ferroptosis by restoring GPX4 expression. The new study set out to resolve how the drug behaves when ferroptosis is induced by cysteine deprivation in non-small cell lung cancer cells.

The research team, led by investigators at the Korea Institute of Radiological and Medical Sciences and collaborating institutions, worked with two human lung cancer cell lines, H1299 and H23. When the cells were deprived of cysteine for 24 hours, viability in H1299 cells collapsed to roughly 30 percent of control levels. Remarkably, adding lapatinib restored viability in a dose-dependent manner, climbing back to about 65 percent at a concentration of 10 micromolar. In H23 cells, where cysteine deprivation cut viability to about a quarter of normal, lapatinib again rescued the cells dose-dependently. Crucially, two other EGFR-targeting drugs, erlotinib and gefitinib, offered no such protection, indicating that the effect is not a generic property of this drug class.

To confirm that the cell death in question was truly ferroptosis, the researchers deployed a panel of benchmark compounds. Ferrostatin-1 and liproxstatin-1, both inhibitors of lipid peroxidation, and deferoxamine, an iron chelator, all significantly blunted the viability loss caused by cysteine deprivation, whereas z-VAD-fmk, an apoptosis blocker, had no effect. That pharmacological fingerprint pointed squarely at ferroptosis. The team then measured malondialdehyde, a major end product of lipid peroxidation, and used the C11-BODIPY fluorescent probe to visualize membrane oxidation directly. Cysteine deprivation drove both markers sharply upward, and lapatinib pulled them back down in both cell lines, confirming that the drug was suppressing the lipid peroxidation cascade at its core.

The mechanistic surprises deepened from there. Cysteine deprivation and lapatinib each independently raised intracellular reactive oxygen species and ferrous iron levels when given alone. Yet when lapatinib was combined with cysteine deprivation, it significantly reduced ROS generation even though intracellular ferrous iron remained elevated, comparable to levels seen with lapatinib alone. Even more counterintuitively, lapatinib further depleted glutathione and further reduced GPX4 protein expression under cysteine-deprived conditions, the opposite of what a ferroptosis-suppressing intervention would be expected to do through the canonical antioxidant pathway. The drug also protected cells from RSL3, the direct GPX4 inhibitor, while again lowering GPX4 expression further, demonstrating that its protective effect operates entirely independently of the glutathione-GPX4 axis.

The answer, the researchers found, lies in the mitochondria. Both cysteine deprivation and RSL3 treatment caused hyperpolarization of the mitochondrial membrane potential, detected by increased TMRE fluorescence, along with a marked rise in oxygen consumption, signatures of revved-up mitochondrial metabolism that have previously been linked to mitochondrial ROS generation and ferroptotic death. Lapatinib alone produced only modest increases in these parameters, but when co-administered with either ferroptotic stimulus, it significantly blunted both the membrane hyperpolarization and the surge in oxygen consumption. By restraining excessive mitochondrial metabolic activation, lapatinib appears to cut off the supply of mitochondrial ROS that sustains lipid peroxidation, rendering the accumulated ferrous iron insufficient to keep the ferroptotic fire burning.

Why would lapatinib calm mitochondrial respiration? The authors point to a tantalizing clue from a recent computational study predicting that lapatinib interacts with SLC1A5, a glutamine transporter. Glutaminolysis, the conversion of glutamine into alpha-ketoglutarate that feeds the tricarboxylic acid cycle, is indispensable for cysteine deprivation-induced ferroptosis, because it supplies the mitochondrial fuel that drives the respiratory surge. If lapatinib disrupts glutamine metabolism, reduced glutaminolysis would dampen mitochondrial activation and thereby limit ROS generation, a hypothesis consistent with the team’s observations. The precise molecular mechanism, however, remains to be worked out, and the researchers are careful to frame this as a hypothesis rather than a settled explanation.

The therapeutic implications cut in an uncomfortable direction. Ferroptosis induction is increasingly viewed as a way to overcome resistance to conventional agents such as cisplatin, docetaxel and sorafenib, and to amplify the effects of chemotherapy, radiotherapy and immunotherapy. If lapatinib suppresses ferroptosis that depends on mitochondrial metabolic activation, then combining it with such strategies could inadvertently blunt their efficacy and contribute to therapeutic resistance. The study also reinforces a broader lesson now echoing through the ferroptosis field: drug effects on this cell death pathway are exquisitely context-dependent, shaped by cell type, metabolic state and the specific trigger involved. A drug that kills by ferroptosis in one setting may protect against it in another, and clinicians designing rational combinations will need to account for that metabolic fine print.

Subject of Research: Context-dependent regulation of ferroptotic cell death by the EGFR/HER2 inhibitor lapatinib in non-small cell lung cancer cells

Article Title: Lapatinib suppresses cysteine deprivation-induced ferroptotic cell death by modulating mitochondrial function

Article References: Kim, G., Jang, S.-K., Kim, D.-G., Kim, H., Hong, J., Park, I.-C., & Jin, H.-O. (2026). Lapatinib suppresses cysteine deprivation-induced ferroptotic cell death by modulating mitochondrial function. Medical Oncology, 43(11), Article 294. https://doi.org/10.1007/s12032-026-03402-7

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03402-7

Keywords: lapatinib, ferroptosis, cysteine deprivation, mitochondria, GPX4, glutathione, lipid peroxidation, reactive oxygen species, non-small cell lung cancer, EGFR inhibitors, RSL3, mitochondrial membrane potential