March 9, 2026, 11:54 am | Read time: 5 minutes

A glioblastoma develops from the glial cells (supporting tissue) of the brain. But what favors this disease? The only confirmed risk factor to date is previous radiation to the head.^.1 In addition, previous head injuries, toxins, and diet are associated with the development of the malignant brain tumor. Standard therapy is based on a combination of surgery, radiotherapy, and chemotherapy. A study has now discovered a new therapeutic approach that could slow down the growth of a glioblastoma.

Glioblastoma Adheres to the Circadian Rhythm

Researchers at Washington University in St. Louis focused their investigations on the circadian rhythm, also known colloquially in this study as the internal clock. It has the ability to synchronize important processes in the body over the course of a day. In other words, it is a natural clock for the change from daylight to dark. In this context, it regulates important processes such as sleeping and waking times, meal times, etc.

The reason why the scientists focused on the connection between the internal clock and the growth of glioblastoma is obvious. This is because the circadian rhythm is based on brain signals that coordinate the processes. “Our previous investigations have helped us to identify a pattern,” explains Dr. Maria Gonzalez-Aponte, first author of the study, in a press release. “Whether we are using clinical data from patients, harvested cells, or mice with glioblastoma model tumors, chemotherapy always worked best around the normal waking time. This gave us the idea that these tumors recognize the time of day.” Their research showed that glioblastoma also functions according to the circadian rhythm and even exploits it^.2

Disruption of the Circadian Rhythm

Shortly before you wake up, the brain sends a signal to the adrenal glands—a reaction to light and other environmental stimuli. This ensures that steroid hormones, known as glucocorticoids, are released. Their task is to regulate important metabolic and immune processes. They are also involved in the fight-or-flight response. The researchers suspected that the glioblastoma reacts to this surge of the hormone and thus synchronizes its own internal clock with the circadian rhythm of the host.

To prove this hypothesis, the scientists tested in mice whether the internal clock of the glioblastoma could be disrupted and thus reduce its growth. Using scientific methods, glioblastoma model tumors were formed in the brains of the animals. They were then kept in a cage in which the light and dark phases could be regulated. This made it possible to change the time at which the light was switched on. “Mice run more in their wheels at night than during the day,” explains Dr. Maria Gonzalez-Aponte, first author of the study, in a press release.^.3 When the mice started running in their wheels again, it was confirmation that the compulsion to resynchronize their circadian rhythm was working.

Observing the Cancer Cells

While the mice were getting used to their new schedule, the scientists constantly monitored the changes in the cancer cells in the brain. Using a novel method, they reproduced the expression of the clock genes in the cancer cells of the mice—and found that two of these clock genes changed in parallel with the resynchronization of the animals’ schedule. “We found that Bmal1 and Per2 do the same as the mouse in the running wheel. This means that the cancer cells resynchronize their circadian rhythm, while the mouse resynchronizes its locomotor activity,” says Gonzalez-Aponte. This is linked to the release of glucocorticoids.

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Significance for Treatment with Glucocorticoids

Glucocorticoids are just one of the circadian signals that have been shown to synchronize the clocks in cells throughout the body. Until now, they have also been used in high doses in the treatment of cancer, also known as DEX. Patients with glioblastoma are given this to reduce brain edema. However, not all patients experienced tumor-suppressing effects; some doctors report a more beneficial effect.

The researchers of the present study, therefore, suspect that the time of day plays a role in the administration, as this disrupts the circadian rhythm. For this reason, they conducted additional experiments to find out when the tumor size of the mice decreased or increased as a result of DEX. They found that the tumor size of the animals increased significantly when DEX was administered in the morning as opposed to in the evening.

Classification of the Study

“Glioblastomas are guided by hormones secreted by the same central clock in the host that controls the body’s regular circadian rhythm,” summarizes Dr. Erik D. Herzog, lead author of the study. “Blocking the daily increase in glucocorticoid signaling desynchronizes the circadian rhythms in glioblastoma with those of the host and dramatically slows the progression of the disease in tumor-bearing mice.” The time of day of the previously controversial administration of glucocorticoids could be decisive in disrupting the circadian rhythm in such a way that the growth of the glioblastoma is slowed down.

However, the scientists are aware of the limitations of their study. As the investigations are only based on experiments on mice, it is not clear whether the results would also apply to humans. However, as DEX is not a novel drug, it is possible to try administering DEX at different times of the day rather than in the morning in subsequent studies.

“The interaction between brain tumors and the circadian system is now a targeted mechanism for optimizing treatment,” Herzog explains the potential of the study results. “We believe that this feasible and transferable approach will ultimately personalize patient care by determining when cancer patients should be treated according to their individual circadian rhythms.”