Researchers discover backup pathway for essential amino acid that may help tumors resist treatment

Overview

Updated 1 hour ago

Every cell needs cysteine to build proteins, stabilize their three-dimensional structure, and defend against oxidative damage. For decades, biologists assumed cells could only get it by breaking down cystine with one of two enzymes — the disulfide reductase systems — and that at least one was essential for life.

Montana State University researchers bred mice lacking both systems. The mice lived. Their report in Nature Chemical Biology explains how: a backup chemical route breaks a carbon-sulfur bond inside cystine, freeing cysteine without the usual machinery. The same failsafe may help cancer cells survive chemotherapy and radiation, so disabling it could make tumors more vulnerable to treatment.

Why it matters

If cancer cells lean on this backup cysteine pathway to survive treatment, disabling it could make existing therapies far more lethal to tumors.

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Key Indicators

12 years

Research span from first clue to published mechanism

Schmidt's engineered mice survived without disulfide reductases in 2014; the mechanism was published in 2026.

Functioning disulfide reductase systems in surviving mice

Mice with no known cystine-reducing machinery survived — the result considered impossible.

Disulfide reductases once deemed essential

The two main systems cells use to convert cystine to cysteine, both of which can now fail without killing the cell.

Voices

Curated perspectives — historical figures and your fellow readers.

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People Involved

Ed Schmidt

Professor of genetics and development, Montana State University

Lead author of the Nature Chemical Biology paper

Peter Nagy

Research group leader, Hungarian National Institute of Oncology

Collaborator who provided analytical methods for the study

Organizations Involved

Montana State University

Public research university

Home institution of the discovery team

The land-grant university in Bozeman where the cysteine backup pathway was discovered.

Nature Chemical Biology

Peer-reviewed scientific journal

Venue of publication

A monthly journal covering chemical biology and biochemistry.

Hungarian National Institute of Oncology

National cancer research and treatment center

Collaborating institution

Budapest-based institute whose analytical methods helped identify the backup pathway.

Timeline

2014 September 2026

3 events Latest: Today

September 2026
Discovery reported publicly
Today Announcement

ScienceDaily and other outlets report the finding that a carbon-sulfur bond cleavage route can supply cysteine when disulfide reductases fail.
Today
Paper describing backup cysteine pathway appears
Publication

The study, led by Ed Schmidt with Peter Nagy's group, appears in Nature Chemical Biology with the DOI 10.1038/s41589-026-02213-1.
2 days ago
2014
Puzzling mice survive without essential enzymes
Discovery

Schmidt's engineered mice, lacking both disulfide reductases in their liver cells, survive — a result then considered impossible.
2014

Scenarios

Backup cysteine pathway confirmed in human tumors

Possible Resolves by End of 2027

Discussed by: The study's authors and independent cancer cell biology labs

Independent laboratories replicate the finding and show the carbon-sulfur bond cleavage pathway operates in human cancer cell lines and tumor samples, and that its activity correlates with resistance to chemotherapy and radiation. That would validate the discovery's clinical relevance and push drug discovery targeting the pathway.

Pathway-targeting drug enters human cancer trials

Unlikely Resolves by End of 2028

Discussed by: Ed Schmidt, Peter Nagy's Hungarian National Institute of Oncology group

Preclinical work identifies a compound that selectively blocks the carbon-sulfur bond cleavage pathway in tumor cells while sparing healthy tissue. A phase 1 trial begins recruiting cancer patients, likely combining the agent with an existing chemotherapy.

Backup pathway proves too essential to disable safely

Possible Resolves by Q2 2027

Discussed by: Toxicology observations that cysteine is indispensable to all cells, and that elevated cysteine can trigger mitochondrial iron overload and cell death

Preclinical studies show that suppressing the backup pathway damages healthy cells, because cysteine is required for protein synthesis and antioxidant defense in every tissue. The therapeutic approach is shelved or redirected toward cancers where cysteine metabolism is already disrupted.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

2005-2014

PARP inhibitors and the BRCA discovery (2005–2014)

Researchers found that cells with mutated BRCA genes had lost one DNA-repair backup, homologous recombination. Drugs blocking a second repair pathway, poly(ADP-ribose) polymerase (PARP), then killed cancer cells that normal cells tolerated — a concept called synthetic lethality.

Then

Phase 1 trials showed dramatic responses in BRCA-mutant ovarian and breast cancers; olaparib was approved in 2014.

Now

The principle of exploiting a cancer cell's missing backup system spawned a drug class and shaped how scientists hunt for vulnerabilities in other tumors.

Why this matters now

The cysteine discovery identifies a backup metabolic route cancer cells may lean on; disabling it could offer a similar synthetic-lethality approach to therapy.

1920s-1950s

The Warburg effect (1920s–1950s)

Otto Warburg observed that cancer cells metabolize glucose to lactate even when oxygen is present, an inefficient pathway for energy but one that yields building blocks for growth. The discovery framed cancer as a metabolic disease.

Then

Debate over whether the effect caused or merely accompanied malignancy lasted decades.

Now

The metabolic quirk became the basis of FDG-PET cancer imaging and continues to guide drugs that target tumor metabolism.

Why this matters now

Cancer metabolism discoveries routinely take years to reach the clinic; the cysteine pathway may follow the same slow arc from lab bench to therapy.

1960s-2000s

The unfolded protein response (1960s–2000s)

Cells detect misfolded proteins in the endoplasmic reticulum and activate the unfolded protein response (UPR) to restore balance. Cancer cells co-opt this stress-survival machinery to withstand chemotherapy, and drugs targeting the UPR entered trials — most notably for multiple myeloma.

Then

Proteins IRE1 and PERK emerged as drug targets; several inhibitors reached clinical testing.

Now

The UPR became a model of how cellular stress-survival pathways can be drugged to sensitize tumors to treatment.

Why this matters now

Like the UPR, the cysteine failsafe is a survival system cancers may exploit — and a candidate target for restoring sensitivity to therapy.