L’ESSENTIEL
- Researchers have discovered that the human biological clock controls DNA repair.
- This finding suggests that radiotherapy may be more effective when administered in the afternoon or evening.
- This phenomenon, known as chronoradiotherapy, has been observed in prostate and breast cancers, but not in lung cancer.
Radiotherapy is a cornerstone of cancer treatment, and new research indicates that the timing of radiation sessions could significantly impact their effectiveness for certain malignancies.
The research, conducted by scientists at the Andalusian Centre for Molecular Biology and Regenerative Medicine (CABIMER) and the University of Seville, was published in the journal Nature Communications.
Radiotherapy: Afternoon Sessions May Be More Effective
The study focused on the DNA of tumor cells. Cancer cells often struggle to effectively repair their DNA, a weakness exploited by radiotherapy, which creates DNA breaks that the cells cannot fix.
Researchers found that DNA damage repair in human cells fluctuates throughout the day, following a circadian rhythm. “In other words, its effectiveness is not uniform, but varies depending on the time of day. During human circadian cycles, repair activity reaches its peak early in the morning, then gradually decreases until nightfall, before increasing again during the night,” the authors explained in a press release.
This regulation is linked to a key component of the biological clock: the CRY1 protein. “This protein acts as a temporal regulator and its abundance naturally varies throughout the day/night cycle.” When CRY1 levels are low – typically in the early morning – DNA repair is stimulated. Conversely, low levels – generally observed in the afternoon or evening – are associated with slower repairs, increasing the sensitivity of cancer cells to damaging agents like ionizing radiation. Based on these findings, radiotherapy sessions scheduled in the afternoon or evening may be more beneficial.
Chronoradiotherapy: Not All Cancers Respond
The Spanish researchers’ conclusions were supported by a review of patient medical records. The analysis showed that female patients with breast cancer whose tumors expressed high levels of CRY1 were more responsive to radiotherapy.
“a retrospective analysis of data from patients at the Virgen Macarena University Hospital highlighted a significant difference in overall survival depending on the timing of irradiation: treatment administered in the afternoon or evening, a period when CRY1 levels are naturally higher, made tumor samples more sensitive to radiotherapy and improved patient prognosis.”
A similar effect was observed in patients with prostate cancer. However, it was not present in those with lung cancer or gliomas.
The research team believes their work “opens the way to exploring the therapeutic potential of irradiation at specific times of the day, a phenomenon known as chronoradiotherapy.” This research highlights the complex interplay between the body’s natural rhythms and cancer treatment, potentially paving the way for more personalized and effective therapies.
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