Breast cancer stem cells, commonly called CSCs, represent a relatively small and adaptable population within a tumor. Unlike most rapidly dividing cancer cells, CSCs can self-renew, generate more differentiated tumor cells, and survive conditions that eliminate other malignant cells. These properties have been linked to recurrence, metastasis, and treatment failure. Although cancer metabolism has often been associated with increased glucose consumption and glycolysis, CSCs can also depend heavily on mitochondria, the organelles that generate ATP through oxidative phosphorylation. This reliance led the researchers to investigate POLG, the enzyme responsible for copying and repairing mitochondrial DNA.

POLG operates as a two-part molecular machine. The catalytic subunit is encoded by the POLG1 gene, while the accessory subunit is encoded by POLG2. Together, these proteins help replicate the small circular genome carried inside mitochondria. Mitochondrial DNA encodes essential components of the respiratory chain, the series of protein complexes that transfer electrons and use the released energy to produce ATP. If mitochondrial DNA is depleted or damaged, respiratory-chain assembly can fail, reducing energy production and altering the balance of reactive oxygen species inside the cell. The researchers therefore asked whether impairing POLG would interfere with the biology of breast cancer stem cells.

The experiments were initially performed in MCF-7 cells, an estrogen receptor-positive breast cancer model. Using genetic silencing, the investigators reduced expression of either POLG1 or POLG2. The effects on mitochondrial DNA were substantial: POLG1 silencing lowered mitochondrial DNA content by about 80%, while POLG2 silencing caused an approximately 70% reduction. These changes were accompanied by decreased levels of MTCO2, a protein encoded by mitochondrial DNA and required for respiratory-chain function. Measurements of mitochondrial membrane potential, respiration, and ATP production also indicated that the organelles were operating less efficiently after POLG disruption.

The mitochondrial defects were closely associated with a loss of stemness-related characteristics. In MCF-7 cells, silencing POLG1 reduced expression of OCT4, a transcription factor involved in maintaining cellular plasticity and self-renewal. The cells also formed roughly 70% fewer mammospheres, three-dimensional structures used as an in vitro indicator of mammary stem-cell activity. Their ability to generate colonies was markedly suppressed as well. Silencing POLG2 produced a similar pattern, reducing OCT4 expression, mammosphere formation, and clonogenic growth. Notably, these interventions did not substantially affect short-term growth in conventional two-dimensional cultures, suggesting that mitochondrial POLG activity may be particularly important for long-term self-renewal rather than immediate cell proliferation.

The study also examined how POLG disruption changed the chemical environment within mitochondria. Loss of mitochondrial membrane potential is a sign that the electrochemical gradient used to drive ATP synthesis has been weakened. At the same time, POLG1 and POLG2 silencing increased mitochondrial superoxide, a reactive oxygen species generated when electrons leak from the respiratory chain. This increase did not translate into a statistically significant rise in total cellular reactive oxygen species in every experiment, indicating that mitochondrial stress and whole-cell oxidative stress are not identical measurements. The results instead point to a localized disturbance in mitochondrial redox balance that may contribute to the loss of CSC-associated properties.

To test whether the genetic results could be reproduced with drugs, the researchers examined Alovudine, a nucleoside reverse transcriptase inhibitor developed for antiviral use. Alovudine can inhibit POLG as an off-target effect, although it is not a selective POLG-directed cancer drug. In the breast cancer cells, the compound reduced mammosphere and colony formation while lowering MTCO2 expression, mitochondrial respiration, and ATP generation. The authors emphasize that Alovudine caused hematological toxicities during antiviral development, making it unsuitable as an established cancer treatment on the basis of these experiments. Its role in the study was primarily to provide pharmacological support for the idea that POLG-dependent mitochondrial function is connected to cancer stemness.

The investigators then used a second compound, zalcitabine, also known as ddC, to determine whether the observations depended on a single drug. In MCF-7 cells, ddC impaired mitochondrial respiration, reduced MTCO2 levels, and suppressed both mammosphere and colony formation. The researchers extended the analysis to T47D, MDA-MB-231, MDA-MB-436, and MDA-MB-453 breast cancer cells, representing different biological subtypes and molecular characteristics. Across these models, ddC consistently reduced mammosphere formation, although its effects on ordinary monolayer growth varied. Non-tumoral MCF10A mammary epithelial cells showed limited viability changes under the tested conditions, a result that may indicate some degree of selectivity but cannot substitute for formal toxicity and therapeutic-index studies.

The molecular response to ddC also varied between cancer models. In MCF-7 cells, the compound markedly reduced the stemness-associated transcription factors SOX2 and NANOG. In MDA-MB-453 cells, SOX2 declined, whereas the effect on NANOG was more modest. Such differences are important because breast cancer is not a single disease: tumors differ in receptor status, genomic alterations, mitochondrial activity, and dependence on particular metabolic pathways. The researchers additionally analyzed clinical data from 458 patients with high-risk, estrogen receptor-positive, lymph node-positive luminal A breast cancer. Higher POLG1 expression was associated with poorer overall survival, with a hazard ratio of 1.34, and with shorter relapse-free, distant metastasis-free, and post-progression survival. These preliminary associations do not prove that POLG drives poor outcomes, and they require validation in independent patient cohorts using multivariable analyses.

The authors describe the work as a pilot study and stress that important questions remain unanswered. Much of the genetic evidence came from MCF-7 cells, and shRNA-based experiments can produce off-target effects that complicate interpretation. Neither Alovudine nor ddC is a fully selective POLG inhibitor, so their effects may involve additional molecular targets. The experiments were performed in cultured cells rather than animals or patients, meaning that the study does not yet demonstrate tumor suppression in a living organism or establish whether POLG inhibition can spare normal tissues. Future research will need to use independent genetic strategies, selective chemical probes, patient-derived models, xenografts, and orthotopic tumors. Nevertheless, the study identifies a compelling connection between mitochondrial DNA maintenance and breast cancer stem-cell behavior. By showing that POLG disruption can weaken mitochondrial respiration, alter redox balance, and suppress self-renewal across multiple models, the findings position POLG as a candidate biomarker and a possible target for therapies designed to attack the metabolically resilient cells that help breast tumors persist and return.

Subject of Research: Cells

Article Title: Investigating POLG-driven modulation of cancer stemness: a pilot study in breast cancer cells

News Publication Date: 24 August 2026

Web References: Aging, Volume 18; https://doi.org/10.18632/aging.206406; Aging-US

References: Chinigò et al., “Investigating POLG-driven modulation of cancer stemness: a pilot study in breast cancer cells,” Aging, DOI: 10.18632/aging.206406

Image Credits: Copyright © 2026 Chinigò et al.; Figure 2, distributed under the Creative Commons Attribution License (CC BY 4.0).

Keywords: breast cancer, cancer stem cells, cancer metabolism, POLG, POLG1, POLG2, mitochondrial DNA, mitochondrial function, oxidative phosphorylation, cancer stemness

Androgen deprivation therapy, a cornerstone in managing advanced prostate cancer, works by significantly reducing levels of male hormones, primarily testosterone, to inhibit tumor growth. While effective at controlling cancer progression, the treatment is well-documented for its adverse systemic effects, particularly the loss of muscle mass, decreased physical performance, and deteriorating quality of life. Yet, until now, the underlying biological mechanisms orchestrating these debilitating side effects were poorly understood.

The study’s authors employed cutting-edge molecular and functional analyses to explore how muscle mitochondria—organelles known as the powerhouses of the cell—respond to the hormonal alterations induced by ADT. Mitochondria play a pivotal role in energy production, cellular metabolism, and regulation of muscle function. Disruption in mitochondrial dynamics, number, or efficiency can significantly impair skeletal muscle performance and maintenance, potentially explaining the rapid physical decline observed in patients undergoing this therapy.

Using both biopsy samples from patients at various stages of ADT and complementary animal model studies, the researchers discovered that ADT triggered a marked reduction in mitochondrial content within muscle tissue. More strikingly, these mitochondria exhibited compromised bioenergetic function, with diminished oxidative phosphorylation capacity and increased indicators of mitochondrial damage and stress. This mitochondrial dysfunction was directly linked to decreased muscle strength and endurance measured through standardized physical tests.

Beyond mitochondrial alterations, the study illuminated how ADT induces systemic metabolic shifts that exacerbate muscle wasting. Hormonal deprivation was associated with increased inflammatory cytokines and oxidative stress markers, factors known to contribute to muscle catabolism. By integrating transcriptomic and proteomic profiling, the team identified downregulation of critical genes and proteins involved in mitochondrial biogenesis and muscle regeneration pathways, suggesting impaired muscle repair mechanisms during ADT.

One of the most remarkable aspects of this research is its exploration of how these molecular and physiological changes translate into profound impacts on lived experience. Quality of life assessments conducted alongside biological sampling revealed a strong correlation between mitochondrial impairment and patient-reported outcomes such as fatigue, mobility limitations, and general well-being. This establishes a direct link connecting cellular dysfunction to real-world functional decline, emphasizing the urgent need for targeted interventions.

Importantly, the study also broke new ground by identifying potential therapeutic avenues to mitigate muscle deterioration in men undergoing ADT. The authors propose that interventions aimed at preserving mitochondrial health—through pharmacological agents, exercise regimens tailored to enhance mitochondrial biogenesis, or nutritional strategies supporting mitochondrial function—could significantly improve physical function and quality of life. Preliminary data from pilot exercise trials support this notion, showing partial restoration of mitochondrial efficiency and muscle strength with specific resistance training protocols.

Further, the study challenges clinicians and researchers to reimagine the management of prostate cancer beyond tumor control alone. The findings advocate for a holistic treatment framework that concurrently addresses the systemic sequelae of androgen deprivation, aiming not just to extend survival but to preserve functional independence and life quality. Integrating mitochondrial biomarkers into clinical monitoring could refine patient stratification and treatment personalization, optimizing therapeutic outcomes.

Intriguingly, this research also raises broader questions about the generalizability of mitochondrial responses to hormone therapies across different cancers and patient populations. Understanding whether similar mitochondrial dysfunction patterns occur in other hormone-driven malignancies could open new interdisciplinary research avenues, advancing supportive care paradigms.

Technologically, the study exemplifies how advances in high-resolution mitochondrial imaging, single-cell RNA sequencing, and sophisticated functional assays can deepen mechanistic insights into treatment-induced tissue alterations. This multi-modal approach sets a new standard for translational oncology research, linking bench science with clinical impact.

From a societal perspective, the findings underscore the need to raise awareness about the hidden physiological costs of life-saving cancer treatments. Empowering patients through education about potential side effects and available mitigation strategies might improve adherence to therapy and overall health outcomes.

Looking ahead, the research community faces challenges in developing mitochondrial-focused therapeutics that are safe, effective, and accessible. The complexity of mitochondrial biology, coupled with patient variability, demands precision medicine approaches integrating genomics, metabolomics, and patient-reported data.

Ultimately, this landmark study by Caeiro, Anderson, Dash, and collaborators heralds a new era in understanding and managing the muscle-related side effects of androgen deprivation therapy. By illuminating the central role of mitochondrial health in mediating treatment outcomes, it provides a roadmap toward interventions that could transform the therapeutic landscape for prostate cancer survivors worldwide.

As oncology continues to evolve, embracing the interplay between systemic therapies and organ-specific aging processes, the integration of mitochondrial science into clinical practice promises to enhance survivorship care. This research not only charts a path for innovation but reaffirms the imperative of addressing quality of life as a fundamental goal alongside cancer control.

In sum, the 2026 study in Nature Communications offers powerful mechanistic explanations for the muscle deficits observed in ADT-treated prostate cancer patients, connecting mitochondrial dysfunction with physical decline and diminished life quality. Its insights pave the way for holistic, mitochondrial-centered care strategies poised to ameliorate the morbidity burden of hormone deprivation therapies. The coming years will undoubtedly witness transformed patient experiences grounded in the science illuminated by this seminal work.

Subject of Research: The impact of androgen deprivation therapy on muscle mitochondria, physical function, muscle mass, and quality of life in prostate cancer patients.

Article Title: Muscle mitochondria, function, mass, and quality of life in prostate cancer during androgen deprivation therapy

Article References:
Caeiro, L., Anderson, L.J., Dash, A. et al. Muscle mitochondria, function, mass, and quality of life in prostate cancer during androgen deprivation therapy. Nat Commun (2026). https://doi.org/10.1038/s41467-026-73542-x

Image Credits: AI Generated