Radiation Therapy Triggers Copper-Driven Cell Death to Fight Resistant Tumors
Radiotherapy induces cuproptosis in cancer cells, and copper ionophores can restore radiation sensitivity in resistant tumors.
Summary
Researchers at MD Anderson discovered that radiotherapy (RT) triggers cuproptosis—a copper-dependent form of cell death—by raising mitochondrial copper levels through upregulation of the copper transporter CTR1 and depletion of mitochondrial glutathione. In radioresistant tumors, the transcription factor BACH1 is downregulated, which unleashes copper-sequestering proteins called metallothioneins (MT1E/X) that neutralize cuproptosis and confer resistance. Treating radioresistant cancer cells and tumor models with copper ionophores restored sensitivity to RT by enhancing cuproptosis. Clinical evidence from patient esophageal tumors confirmed that RT depletes cuproptosis hallmark proteins in vivo, validating the mechanism and opening a new therapeutic avenue against radioresistant cancers.
Detailed Summary
Radiotherapy remains one of the most widely used cancer treatments, yet a significant proportion of tumors develop resistance, leaving patients with limited options. Understanding the cell death mechanisms activated—or evaded—by radiation is critical to improving outcomes. This landmark study from MD Anderson Cancer Center identifies cuproptosis, a recently described copper-dependent cell death pathway, as a key mediator of RT's anti-tumor effects and a target for overcoming radioresistance.
The researchers demonstrated that RT elevates intracellular copper concentrations specifically within mitochondria, achieving this via two complementary mechanisms: upregulation of the copper importer CTR1 and depletion of mitochondrial glutathione, which normally chelates and sequesters copper. The resulting surge in mitochondrial copper triggers cuproptosis—characterized by aggregation of lipoylated mitochondrial proteins and loss of iron-sulfur (Fe-S) cluster proteins—distinct from apoptosis or ferroptosis. Critically, RT-induced cuproptosis was confirmed in patient esophageal tumor samples, where both lipoylated proteins and Fe-S cluster proteins were depleted after radiation treatment.
To understand radioresistance, the team performed RNA sequencing on radioresistant esophageal cancer cell lines and single-cell RNA sequencing on tumors from patients who did not respond to RT. Both datasets consistently pointed to downregulation of the transcription factor BACH1 as a driver of resistance. BACH1 normally represses MT1E and MT1X—metallothionein genes whose protein products sequester intracellular copper. When BACH1 is lost, MT1E/X expression rises, copper is buffered away from mitochondria, cuproptosis is suppressed, and tumors survive radiation.
Building on this mechanistic insight, the researchers tested whether copper ionophores—small molecules that shuttle copper into cells—could override the metallothionein defense and restore cuproptosis sensitivity. In radioresistant cell lines, cell line-derived xenografts (CDX), and patient-derived xenografts (PDX) of esophageal cancer, copper ionophore treatment combined with RT markedly enhanced tumor killing compared to either treatment alone. The synergy was dependent on cuproptosis induction, confirming the therapeutic rationale.
This study establishes a previously unrecognized mechanistic link between RT and cuproptosis and defines a BACH1→MT1E/X→copper sequestration axis as a tractable resistance pathway. The identification of copper ionophores as radiosensitizers with an established clinical safety profile (e.g., disulfiram/copper complexes are already in clinical trials) provides a potentially near-term translational strategy. Caveats include the focus on esophageal cancer models and the need for further validation across cancer types, as well as the complexity of in vivo copper homeostasis that may affect systemic delivery.
Key Findings
- RT elevates mitochondrial copper via CTR1 upregulation and glutathione depletion, directly triggering cuproptosis.
- RT depletes lipoylated proteins and Fe-S cluster proteins—cuproptosis hallmarks—in patient esophageal tumors.
- BACH1 downregulation in resistant tumors de-represses MT1E/X metallothioneins, sequestering copper and blocking cuproptosis.
- Copper ionophores synergize with RT to overcome radioresistance in cell lines, CDX, and patient-derived xenograft models.
- Cuproptosis induction by RT is independent of apoptosis and ferroptosis, identifying a distinct cell death axis.
Methodology
The study combined in vitro radioresistant cell line models, bulk RNA-seq, and single-cell RNA-seq from non-responsive esophageal cancer patients to identify resistance mechanisms. Functional validation used CRISPR/gene knockdown, copper ionophore treatments, and both CDX and PDX mouse models. Patient tumor biopsies were analyzed for cuproptosis protein hallmarks before and after RT.
Study Limitations
The mechanistic and xenograft studies focus predominantly on esophageal cancer, and generalizability to other tumor types requires further investigation. In vivo copper homeostasis is complex, and systemic copper ionophore delivery may have off-target metabolic effects not fully captured in these models.
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