Researchers at Heinrich-Heine-University Düsseldorf, led by Dennis Sohn and colleagues, report that pediatric medulloblastoma cells carrying functional, wild-type p53 do not simply die when bombarded with gamma irradiation. Instead, many of them enter senescence, a terminal and stable arrest of the cell cycle. These zombie-like cells stop dividing but refuse to die, lingering in the tissue for weeks. Crucially, the team showed that these irradiated, senescent tumor cells can then be selectively wiped out with senolytic drugs—compounds designed to eliminate senescent cells. The finding opens a potential two-step strategy: radiation first drives susceptible tumor cells into senescence, and senolytics then clear them away.

The study compared two SHH-activated medulloblastoma cell lines with fundamentally different genetic backgrounds. ONS76 cells carry wild-type p53, the master tumor suppressor that decides a cell’s fate after catastrophic DNA damage. UW228-3 cells carry a mutated, dysfunctional p53. When both lines were exposed to a 20 Gy dose of gamma irradiation, their responses diverged dramatically. UW228-3 cells detached from the culture dish and degraded completely within three to seven days. ONS76 cells, by contrast, remained attached for more than fifty days, flattening out and swelling enormously in both cell body and nucleus—classic hallmarks of senescence.

The molecular evidence followed the morphology. Irradiated ONS76 cells showed a dose-dependent stabilization of p53 and a strong increase in p21, the cyclin-dependent kinase inhibitor encoded by the CDKN1A gene that enforces the senescence arrest. They also accumulated senescence-associated beta-galactosidase activity, a lysosomal enzyme widely used as a senescence marker, and built up lipofuscin, the pigment-like cellular debris characteristic of aged or senescent cells. When the researchers knocked down p53 or p21 using siRNAs, the senescence program collapsed: far fewer cells became senescent and substantially more died instead. This established that radiation-induced senescence in these cells is strictly p53/p21-dependent.

The p53-mutated UW228-3 cells told the opposite story. They showed only a faint, transient rise in beta-galactosidase activity and never developed senescent morphology. Instead, measurements of lactate dehydrogenase release—a marker of plasma membrane destruction—and of DEVDase-like caspase activity revealed that they died by apoptosis, the controlled self-destruction pathway. A pan-caspase inhibitor, q-VD-OPh, completely abolished this cell death while leaving senescence untouched in the wild-type line. The team also employed a recently developed fluorescent lipofuscin binder, GLF16, alongside the amine-reactive viability dye Zombie-violet, allowing simultaneous flow cytometric quantification of senescent and dead cells with sharper discrimination than traditional staining.

The researchers then turned to c-Myc, a proto-oncogene that serves as a crucial negative prognostic factor in medulloblastoma and is known to antagonize p21. Using engineered ONS76 and UW228-3 lines that constitutively overexpress c-Myc, they found that the oncogene tipped the balance away from senescence. In irradiated ONS76/c-Myc cells, p21 protein levels dropped—though p21 mRNA levels did not, indicating that c-Myc interferes with p21 protein production or stability rather than its transcription. Fewer cells adopted senescent morphology, and more cells died, a death that q-VD-OPh could block even though it was not accompanied by elevated caspase activity. Notably, this c-Myc effect operated independently of p53 status. The senescent population in c-Myc-overexpressing cells also proved far more resistant to senolytic treatment, underscoring how oncogene dosage can shape therapeutic vulnerability.

The therapeutic payoff came in the final set of experiments. Seven days after irradiation, when the ONS76 cultures had become fully senescent, the researchers treated them with four senolytic compounds: the BCL-2 family inhibitors Navitoclax and Venetoclax, and the PI3K inhibitors PX-866 and BAY 80-6946 (Copanlisib), the latter already FDA-approved. All four killed the senescent cells in a dose-dependent manner. Navitoclax, however, also eliminated proliferating cells at the highest concentration tested, 30 µM—a reminder of the well-known toxicity problem that has complicated its clinical use, since healthy non-senescent cells are targeted at higher doses. The PI3K inhibitors, by contrast, showed a cleaner specificity for the senescent population.

The clinical logic behind this approach is compelling. Medulloblastoma is unusual among cancers in that relatively few tumors harbor p53 mutations, and in the SHH-activated subtype, p53 status actually defines two distinct risk groups: p53-mutated tumors carry a five-year overall survival of roughly 41 percent and are classified as high risk, while p53 wild-type tumors fare far better at about 81 percent. The new findings suggest that these two groups respond to radiotherapy in mechanistically different ways—senescence in the wild-type setting, apoptosis in the mutated one—a distinction invisible to standard proliferation-based cytotoxicity assays. Senolytic combination therapy would therefore primarily apply to the intermediate-risk, p53 wild-type group, where it could potentially improve outcomes further while reducing the radiation dose needed for tumor control.

The broader context strengthens the case. Senescent cells are not inert; they secrete a cocktail of cytokines and chemokines known as the senescence-associated secretory phenotype, or SASP, which drives chronic tissue microinflammation and can support tumor relapse. Craniospinal irradiation is associated with accelerated brain aging in survivors, and studies in glioblastoma have already shown that eliminating therapy-induced senescent cells with Navitoclax attenuates recurrence. Mouse studies of whole-brain irradiation likewise suggest that senolytic clearance protects cognitive function and the blood-brain barrier. Because senescence can be triggered at lower radiation doses than outright cell death, pairing senolytics with craniospinal irradiation might one day allow clinicians to cure tumors with less radiation exposure while simultaneously mopping up the senescent cells that radiation leaves behind.

Important caveats remain. The entire study was conducted in cell lines rather than animal models or patients, and the exact nature of the c-Myc-driven, caspase-inhibitable cell death observed in the overexpressing cells is still unclear. The authors themselves note that it would be intriguing to test whether JQ1, a bromodomain inhibitor that suppresses c-Myc signaling, could push c-Myc-high, p53 wild-type medulloblastoma cells back into a senescence-permissive state and thereby restore their susceptibility to senolytics. Still, the work is the first to document radiation-induced senescence in medulloblastoma cells and to demonstrate that these cells can be eliminated with existing senolytic drugs. If the strategy survives translation into preclinical models, it could reshape how one of pediatric oncology’s most grueling treatments is delivered—turning the very cells that radiation strands between life and death into targets for a second, cleaner strike.

Subject of Research: Radiation-induced cellular senescence in pediatric medulloblastoma and its targeting by senolytic drugs

Article Title: p53 wild-type/low c-Myc-expressing ONS76 pediatric medulloblastoma cells become senescent after gamma-irradiation and can be eliminated by senolytic substances

Article References: Sonntag, J., Preugschas, R.-L., Jazmati, D., Qin, N., Neuwahl, J., Matuschek, C., Remke, M., Budach, W., Hörner-Rieber, J., & Sohn, D. (2026). p53 wild-type/low c-Myc-expressing ONS76 pediatric medulloblastoma cells become senescent after gamma-irradiation and can be eliminated by senolytic substances. Cell Death Discovery, 12(1), Article 410. https://doi.org/10.1038/s41420-026-03404-4

Image Credits: AI Generated

DOI: 10.1038/s41420-026-03404-4

Keywords: medulloblastoma, senescence, senolytics, p53, c-Myc, p21, gamma irradiation, craniospinal irradiation, Navitoclax, PI3K inhibitors, SASP, pediatric brain tumor

The strategy grew out of a long-standing interest in cellular senescence, a stress response that permanently halts cell division. Senescent cells are famously double-edged. When a cell accumulates dangerous damage, senescence shuts it down before it can become cancerous, and during wound healing, senescent cells coordinate repair by broadcasting signals that recruit other cells to the injury site. The trouble begins when these cells overstay their welcome. Instead of quietly disappearing once their job is done, lingering senescent cells keep emitting inflammatory and profibrotic signals that drive chronic inflammation and scarring. Scott Lowe, who chairs the Cancer Biology and Genetics Program at MSK’s Sloan Kettering Institute and is a Howard Hughes Medical Institute investigator, has spent years probing this duality. The therapeutic dream, he explains, is to clear the harmful senescent cells while sparing the helpful ones—a goal that has proven difficult because senescent cells in different contexts can look deceptively similar.

The breakthrough came when the researchers examined macrophages, the scavenger immune cells that patrol tissues, in fibrotic environments. Within these populations, they identified a small subset expressing a surface protein called P-selectin alongside multiple molecular hallmarks of senescence. The team dubbed these cells MΦP+sen+—macrophages that are both P-selectin positive and senescence positive. What struck the scientists was their consistency: the same distinctive population appeared in fibrotic tumor niches in liver and lung cancers and in heavily scarred liver and lung tissue, and its presence correlated with poorer responses to immunotherapy in patients. Clemens Hinterleitner, a postdoctoral researcher and co-first author of the study, notes that finding this specific macrophage population so reliably in fibrotic tissue was remarkable, and that its presence signaled a compromised local immune environment.

These cells are far more than innocent bystanders. According to the study, MΦP+sen+ macrophages contribute to the fibrosis that forms a physical barrier around tumors, and they simultaneously dampen the activity of neighboring immune cells by sending out profibrotic and immunosuppressive signals. Co-first author Valentin Barthet describes them as actively erecting a wall that prevents the immune system from doing its job. The cells make up only about 3 to 5 percent of fibrotic tissue, yet experiments in mouse models of liver and lung fibrosis and fibrotic liver and lung cancers showed that selectively killing them or silencing their signals had a profound effect on fibrosis. The team validated the key findings in tumor samples from lung cancer patients treated at MSK and in human lung and liver cancer datasets, lending clinical weight to the mouse data.

The consequences of eliminating or disabling these macrophages were dramatic. The scar tissue shielding the tumor began to dissolve, and the suppression of other immune cells eased. Freed from both the physical and chemical barriers, checkpoint inhibitor immunotherapy—the class of drugs that unleashes T cells against cancer—suddenly worked in mice, shrinking tumors that had previously been resistant to treatment. In other words, the intervention did not attack the cancer cells directly. It removed the ecosystem support that allowed the tumor to hide, converting a cold, immune-excluded tumor microenvironment into one that existing therapies could penetrate.

Delivering a lethal payload to such a small and specific cell population posed a formidable engineering challenge, and this is where the collaboration with Daniel Heller’s biomedical engineering lab proved decisive. Heller’s group had previously developed a nanoparticle platform that targets P-selectin, and the team adapted it with new drugs and a new mission. The particles are roughly a thousand times smaller than the width of a human hair and are coated with fucoidan, a naturally occurring sugar molecule found in brown seaweed and sold as an anti-inflammatory supplement. Fucoidan binds specifically to P-selectin, ensuring that the nanoparticles are taken up not by just any macrophage but by the precise P-selectin-positive subset driving the fibrosis. When the targeted macrophages ingest and digest a particle, the drug inside is released—an effect Heller likens to soldiers springing from a Trojan Horse to launch a precision attack from within.

The researchers loaded the nanoparticles with two drugs that are potent against senescent cells but have been hampered by toxicity in clinical use. The first, Navitoclax, exploits a vulnerability in senescent cells’ survival machinery: these stressed cells block their own natural self-destruct program, and Navitoclax removes that block, causing them to die. The second, a BET inhibitor called dBET6, takes a different tack—it silences the inflammatory signals that senescent cells broadcast into surrounding tissue. With the alarm switched off, the cells stop producing the signals that drive fibrosis and immune suppression, even though the cells themselves survive. Both drugs had shown promise against cellular senescence in the laboratory but failed clinically because, when administered conventionally, they damage healthy cells and tissues throughout the body. In the mouse experiments, the nanoparticle-packaged versions appeared safe and did not produce the same toxicity, raising the possibility that targeted delivery could give both drugs a second chance in the clinic.

The implications may extend well beyond liver and lung cancer. Searching a large database of immune cell profiles, the researchers found the same harmful macrophage population associated with breast and colon cancers as well as chronic inflammatory diseases including osteoarthritis and rheumatoid arthritis. Aveline Filliol, a senior scientist in the Lowe Lab and co-corresponding author, points out that these macrophages also share important features with lipid-associated macrophages, a cell type found in the atherosclerotic plaques that cause heart disease—suggesting the platform could one day be adapted to deliver drugs to those cells as well. If MΦP+sen+ cells prove to be a common culprit across many diseases, a single nanoparticle platform, retargeted with different drug cargoes, could address an unusually wide range of conditions united by a shared cellular mechanism.

Beyond the specific findings, the work exemplifies an increasingly influential strategy in oncology: targeting the cancer ecosystem rather than the tumor cells alone. Cancer cells, Lowe argues, do not act in isolation; building a tumor-supportive environment requires coordinated interactions between malignant cells and the surrounding tissue, and disrupting those interactions represents a significant new frontier. The study also showcases the kind of interdisciplinary collaboration—between biologists and engineers, and between bench scientists and clinicians—that allowed the team to move from a biological observation to an engineering solution to validation in human tissue within a single institution. MSK is now seeking commercialization partners to advance the research into clinical trials, first in cancer and potentially in other fibrotic and inflammatory diseases. A patent application covering the use of fucoidan nanoparticles to treat senescence-associated pathologies has been published, and related intellectual property has been granted, signaling that the road from laboratory insight to patient benefit is already under construction. If the approach survives the rigors of human testing, it could offer a way to make immunotherapy work for the many patients it currently fails—and to treat the scarred, inflamed tissue that underlies diseases far beyond cancer.

Subject of Research: Senescence-directed nanoparticle targeting of fibrosis-driving macrophages to overcome immune exclusion in cancer

Article Title: Using nanoparticles to target fibrosis in cancer and other diseases

Article References: Using nanoparticles to target fibrosis in cancer and other diseases. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: nanoparticles, fibrosis, cellular senescence, macrophages, immunotherapy, cancer, P-selectin, fucoidan, Navitoclax, BET inhibitor, tumor microenvironment, checkpoint inhibitors