Tumors devour glutathione as fuel, and an old drug may cut their supply

Cancer cells are eating glutathione. Not using it as a shield against oxidative damage, which is what a century of biochemistry would suggest, but actively breaking it down and burning it as metabolic fuel to sustain their growth.

That finding, published in Nature on March 18 by a team at the Wilmot Cancer Institute at the University of Rochester, reframes one of the most studied molecules in all of biology. Glutathione has been investigated almost exclusively for its antioxidant properties since its discovery 100 years ago. The Rochester group, led by associate professor Isaac Harris in the Department of Biomedical Genetics, has now shown it plays an entirely separate role in tumor metabolism - one that opens a previously unrecognized angle of attack against cancer.

Inside the tumor's pantry

The team, with co-first authors Fabio Hecht and Marco Zocchi, started by analyzing interstitial fluid extracted from human breast tumor samples donated to Wilmot's Biobank. What they found was surprising: abundant glutathione stored inside the tumor microenvironment. The nutrient landscape around tumors is generally sparse - most metabolites are scarce because cancer cells consume them with ruthless efficiency. Glutathione's abundance in this hostile, nutrient-depleted context was itself a significant clue that something unusual was happening with this particular molecule.

Further experiments in preclinical breast cancer models confirmed the suspicion and provided mechanistic detail. Cancer cells were actively importing glutathione from their surroundings and catabolizing it - dismantling the molecule and using its constituent amino acids and chemical energy as metabolic fuel to power cell division and growth. When the researchers blocked the cancer cells' ability to take up and process glutathione through genetic and pharmacological interventions, tumor growth slowed measurably.

The distinction from glutathione's antioxidant role is critical to understanding the finding. As an antioxidant, glutathione donates electrons to neutralize reactive oxygen species, protecting cells from oxidative damage. As a fuel source, it is being structurally dismantled for its molecular components and energy content. These are fundamentally different biochemical functions operating through different enzymatic pathways, and the cancer-specific fuel pathway may be targetable without disrupting the antioxidant function that healthy cells depend on for normal cellular maintenance.

The antioxidant supplement question

Glutathione is widely sold as a dietary supplement with broad health claims, available without prescription and marketed as supporting cellular health, skin brightening, and immune function. Harris was careful to note that the findings do not mean people should stop eating antioxidant-rich whole foods. Fruits, vegetables, and a balanced diet support weight management, reduce chronic inflammation, and bolster the immune system through multiple beneficial mechanisms.

But concentrated glutathione supplements present a different risk calculus. These pills, unregulated by the FDA for efficacy or precise dosing, deliver high concentrations of a molecule that tumors appear to consume avidly. The research does not prove that supplements cause cancer or accelerate existing tumors in humans - establishing that would require large clinical studies that have not been conducted. Still, the finding adds to a growing and increasingly concerning body of evidence suggesting caution with high-dose antioxidant supplementation.

This is not the first time an antioxidant marketed as health-promoting has been linked to tumor growth in laboratory settings. Last year, Harris's colleague Jeevisha Bajaj at Rochester discovered that taurine - another antioxidant available in foods, supplements, and popular energy drinks - drives the growth of leukemia cells, a finding also published in Nature. Earlier work by the Harris team, in collaboration with Tom Campbell and Erin Campbell, showed how a whole-food plant-based diet may reduce pro-tumor nutrient availability in the body, laying important groundwork for the current study by establishing the complex and sometimes counterintuitive links between antioxidants, dietary patterns, and cancer biology.

A drug candidate already exists

Using advanced high-throughput screening technology, the team searched for compounds that could inhibit a tumor's ability to metabolize glutathione as fuel. They identified a promising hit: a drug developed nearly a decade ago for a different therapeutic purpose entirely. The compound showed the ability to restrict tumors' use of glutathione in their experimental systems.

The researchers are now working with University of Rochester chemist Tom Driver, the Robert K. Boeckman Jr. and Mary H. Delton Family Distinguished Professor in Organic Chemistry, and Joshua Munger, professor of Biochemistry and Biophysics and a cancer metabolism specialist, to improve the existing compound's properties and to pinpoint the precise proteins involved in feeding glutathione to tumors. Additional key support comes from Wilmot investigators Brad Mills and Brian Altman.

The goal is to develop therapies that selectively starve tumors of this particular nutrient without collateral damage to healthy cells. Because normal cells and cancer cells appear to use glutathione through different biochemical pathways, there may be a therapeutic window - a dose range where the drug disrupts cancer metabolism while leaving normal antioxidant function essentially intact.

Plans include testing combinations of anti-cancer drugs alongside controlled dietary modifications that could further reduce glutathione availability to tumors. This multi-pronged approach reflects a broader strategic shift in oncology toward targeting tumor metabolism alongside or instead of relying solely on direct cytotoxic agents that kill both cancer and healthy cells.

How broad is this vulnerability?

The breast cancer results may extend to other tumor types. Preliminary data from the Harris lab suggests that many different cancers consume glutathione, including cancers that arise in tissues far removed from the breast. The degree of dependence likely varies by cancer type, genetic background, and the specific metabolic adaptations each tumor has evolved. Whether glutathione metabolism represents a universal tumor vulnerability or a feature of specific cancer subtypes will require systematic investigation across multiple cancer lineages.

The study also raises a mechanistic puzzle that warrants further investigation. Tumors exist in nutrient-poor environments where most metabolites are depleted. Yet they maintain high glutathione levels in their surrounding fluid. How are they acquiring and concentrating it? Cancer cells could be synthesizing it internally at elevated rates, importing it efficiently from surrounding tissue and blood supply, or both. The relative contribution of each source - and whether targeting one route alone is sufficient to meaningfully starve tumors - has not been fully resolved by this work.

Preclinical reality check

The tumor growth inhibition observed when glutathione uptake was blocked occurred in mouse models of breast cancer, not in human patients. Translating metabolic interventions from mice to humans is notoriously difficult and filled with examples of promising preclinical results that did not survive contact with human biology. Mice have different baseline metabolic rates, substantially different gut microbiomes, and different pharmacokinetics for drug absorption, distribution, and clearance. Many metabolic targets that look highly promising in preclinical models fail to show the same magnitude of effect in clinical trials.

The drug candidate itself needs substantial development work. Improving its potency, selectivity, pharmacological properties, and formulation will take years of medicinal chemistry optimization before it could enter first-in-human testing. And combination approaches involving dietary changes add another layer of practical complexity - controlling diet in clinical trial participants is substantially harder than controlling it in caged laboratory mice.

Still, the core finding stands on solid scientific ground. Glutathione's role as a tumor fuel source is supported by direct biochemical evidence from human tumor samples, validated in multiple independent preclinical models, and consistent with the emerging understanding that cancer metabolism is more complex, more opportunistic, and more adaptive than scientists previously appreciated. The research opens what Harris describes as a potentially entire new area of investigation into how cancer cells acquire nutrients that were never previously suspected of being tumor fuel.