When Oxidants Meet Telomeres: A Rigorous Audit of Redox Control in Cancer

Two of the most defining features of cancer — the reactivation of telomerase, the enzyme that rebuilds chromosome ends, and a profoundly rewired redox metabolism — almost always travel together in tumor cells. Yet the scientific literature connecting them has grown into a tangled thicket of thousands of papers, many of which appear to contradict one another. A new review published in Molecular Biology Reports by Mohsen Tatar of Golestan University of Medical Sciences and colleagues takes on that thicket with an unusually disciplined tool: a framework that dissects every claimed redox–telomere link along four axes that are routinely conflated — the exposure used, the experimental model, the strength of the causal test, and how molecularly direct the evidence actually is. When the field is read through that lens, the authors argue, much of the apparent disagreement dissolves into differences in experimental design rather than genuine biological conflict.

The review organizes the sprawling literature into five distinct propositions: redox control of telomerase activity, the reverse control of redox metabolism by the telomerase reverse transcriptase TERT, oxidative damage to telomeric DNA itself, redox-associated alternative lengthening of telomeres (ALT), and the therapeutic translation of all of the above. Each proposition is then graded separately for causal strength and molecular directness — two qualities the authors emphasize can vary completely independently. A finding can be causally robust yet mechanistically indirect, resting on a chain of downstream events; or it can be chemically precise yet demonstrated only in a test tube. Recognizing this independence, they contend, is the first step toward cleaning up a literature that has often graded studies on a single, misleading scale.

One of the sharpest methodological criticisms in the review targets a design that appears throughout the redox–telomerase literature: pretreating cells with millimolar concentrations of a thiol antioxidant such as N-acetylcysteine or glutathione before exposing them to a thiol-reactive electrophile. The problem, the authors explain, is one of chemical ambiguity. At those concentrations, the added thiol can simply quench the electrophile directly in the culture medium, a brute-force chemical reaction that has nothing to do with restoring the cell’s own antioxidant capacity. A rescue observed under those conditions cannot distinguish between genuine redox regulation of telomerase and trivial chemical neutralization of the insult. Because so many headline claims about antioxidants modulating telomerase rest on exactly this design, the finding casts a long shadow over a substantial fraction of the field.

What survives the audit? The authors identify the peroxide-driven, Src kinase–dependent phosphorylation of TERT at tyrosine 707, which triggers export of the enzyme from the nucleus via the Ran transport pathway, as among the best-supported redox findings. Hydrogen peroxide activates Src family kinases, phosphorylation at that specific residue promotes nuclear export, and the pathway satisfies necessity tests — blocking the kinase or the export machinery prevents the effect. Similarly well-supported is the glutathione depletion-and-repletion paradigm, in which lowering cellular glutathione alters telomerase activity and restoring it rescues the phenotype. Yet even these strongest findings, the review notes, remain pathway-mediated rather than chemically direct, and several were established in transfected systems or non-cancer cells such as endothelial cells and fibroblasts, leaving open questions about how faithfully they recapitulate events in an intact tumor.

Perhaps the most striking conclusion of the entire appraisal is a negative one. Despite decades of work, the authors identified no study that causally links a residue-resolved oxidative modification of endogenous TERT — a specific cysteine or tyrosine chemically modified by a defined reactive species inside a living cancer cell — to an altered outcome in telomerase assembly, subcellular localization, or catalytic activity. The distinction matters because redox biology has matured into a chemistry-first discipline: modern chemoproteomic tools can now identify which cysteines in a proteome are reactive, which ones get oxidized under defined conditions, and what functional consequences follow. TERT, with its multiple regulatory phosphorylation sites and its dependence on assembly with the telomerase RNA component, dyskerin and other partners, is precisely the kind of protein where such residue-level resolution should be achievable — and has not yet been delivered.

In contrast, the most molecularly direct chemistry in the entire field sits not on the protein but on the telomeric DNA itself. Guanine-rich telomeric repeats are exquisitely vulnerable to oxidation, and the review assembles a compelling body of biochemical work showing that the identity and position of an oxidative lesion govern nearly everything that matters: binding by the shelterin proteins TRF1 and TRF2, folding of the telomeric G-quadruplex structures that regulate telomerase access, recruitment of repair glycosylases such as OGG1 and the NEIL family, and the ability of telomerase to extend the chromosome end. An 8-oxoguanine lesion at one position of a G-quadruplex can destabilize the structure and promote telomerase extension, while the same lesion elsewhere blocks it — a position-dependent logic revealed through single-molecule and biochemical assays.

Even more provocative are recent findings showing that telomeric oxidation can drive dysfunction without any detectable shortening of the telomere. In work highlighted by the review, a single acute burst of targeted 8-oxoguanine damage at telomeres was sufficient to trigger rapid premature senescence, with telomere length remaining essentially unchanged. This decouples telomere dysfunction from the classical model in which telomeres erode gradually with each cell division, suggesting that a discrete oxidative event can flip the shelterin-bound chromosome end into a damage-signaling state essentially overnight. For cancer biology, the implication is double-edged: oxidative stress can push premalignant cells toward senescence, but it can also, under other conditions, push telomeres toward the recombination-based ALT pathway that a subset of tumors uses to elongate their chromosome ends.

On the therapeutic front, the review delivers a sobering translational parallel to its mechanistic gap. Imetelstat, the lipid-conjugated oligonucleotide that directly targets the telomerase RNA template, has now established randomized phase 3 efficacy in lower-risk myelodysplastic syndromes and has earned regulatory approval in the United States and a positive assessment in Europe. Yet the review points out that its redox engagement — whether the drug’s effects intersect with the oxidative stress programs that co-occur in treated tumors — has never been measured, nor have telomere pharmacodynamics been tracked in a way that connects clinical response to telomere biology at the molecular level. The most clinically successful telomerase-targeting agent, in other words, is as much of a black box with respect to redox as endogenous TERT is with respect to residue-level oxidation.

The review also surveys a crowded pipeline of redox-active agents with claimed telomerase effects: disulfiram and its copper diethyldithiocarbamate complex, which has been reported to induce both mitochondrial and telomerase dysfunction in lung cancer models; glutathione synthesis inhibitors such as butionine sulfoximine tested in combination regimens; the nucleoside analog 6-thio-deoxyguanosine, now in a phase 3 trial in non-small cell lung cancer, which recent structural work suggests stalls telomerase in a non-productive complex; and G-quadruplex ligands whose mechanisms have required substantial reevaluation. The authors’ framework provides a way to grade each of these claims, and the grades are frequently humbling: many rest on pharmacological exposures at concentrations far from physiological, in cell lines of uncertain provenance, with telomerase activity measured by the TRAP assay, which is itself known to be vulnerable to artifacts from redox-active compounds in the lysates.

What would close the gaps? The authors set out a concrete measurement agenda. For the protein side, it means deploying residue-resolved chemoproteomics and structural methods such as cryo-electron microscopy to catch endogenous TERT in the act of being oxidatively modified, and then testing causality with precisely engineered non-oxidizable mutants. For the telomere side, it means mapping lesion identity and position in cells, not just in synthetic oligonucleotides, and tracking how those lesions propagate through shelterin binding, repair, and telomerase extension. For the clinic, it means measuring telomere pharmacodynamics and redox biomarkers in imetelstat-treated patients. Until those measurements exist, the review concludes, the field should resist the temptation to narrate a tidy story of oxidants and telomeres — because the honest story, carefully audited, is one of strong chemistry at the chromosome end, plausible but unproven signaling at the enzyme, and a translational success whose deepest mechanisms remain to be written.

Subject of Research: Redox regulation of telomerase and telomeres in cancer

Article Title: Redox regulation of telomerase and telomeres in cancer: a critical appraisal of exposure, causality and molecular directness

Article References: Tatar, M., Khorrami, M., Kazemi, F., Masoumi, M., Babaei, S., & Khorrami, M. (2026). Redox regulation of telomerase and telomeres in cancer: a critical appraisal of exposure, causality and molecular directness. Molecular Biology Reports, 53(1), Article 1638. https://doi.org/10.1007/s11033-026-12826-3

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12826-3

Keywords: telomerase, TERT, telomeres, redox biology, oxidative stress, cancer, 8-oxoguanine, glutathione, ALT, imetelstat, DNA damage, G-quadruplex