Researchers at Charité–Universitätsmedizin Berlin have developed a high-throughput approach that combines live-imaging and data analysis techniques to identify the best time of day to target breast cancer cells with specific drugs.
The method can be used to create detailed profiles showing how different types of cancer cells respond to different medications at various times. “This can help to identify the most effective combinations of drugs,” said study lead Adrián Enrique Granada, PhD, from the Charité Comprehensive Cancer Center (CCCC). “Overall, our findings indicate that personalized treatment plans based on individual circadian rhythms could substantially improve the efficacy of cancer treatment,” he added.
The circadian clock, or body clock, is a fundamental biological regulator of essential cellular processes in health and disease. Disruption of the circadian system, as often observed in shift workers, has been associated with multiple cancer subtypes. Recently, circadian-based therapeutic strategies have shown promising results, but at present uncovering the optimal treatment timings remains challenging, limiting their widespread adoption.
“Our research is timely in demonstrating how this circadian data can be harnessed to optimize treatment timing in patients,” said Granada.
The researchers used a range of experimental and data analysis approaches to create “time-of-day profiles” in a panel of breast cancer and healthy cell lines that were exposed to eight different chemotherapeutic agents. This deep phenotyping technique measured critical cellular factors underlying time-of-day responses, i.e., the circadian clock strength, growth dynamics, and drug response features.
Comparing tumor versus non-tumor time-of-day profiles allowed the researchers to identify candidate treatment timings that increase efficacy and reduce toxicity.
“We cultured cells from patients with triple-negative breast cancer to observe how they respond at different times of day to the medications administered,” explained Carolin Ector, a research associate in Granada’s working group and the study’s first author. “We used live imaging, a method of continuously monitoring living cells, and complex data analysis techniques to monitor and evaluate the circadian rhythms, growth cycles, and medication responses of these cancer cells in detail.”
The researchers report in Nature Communications that circadian clock strength varies among cancer cell models, challenging the common expectation that most cancer cells have a weak clock. They also showed that drug sensitivity varied throughout the day, but the variation depended on the drug–cell model.
For example, 5-fluorouracil had peak efficacy against a certain cancer cell line between 8 a.m. and 10 a.m. whereas, alisertib was most effective against the same cell line in the evening, at around 10 p.m. Of the 10 cell lines tested in combination with cisplatin, four were more sensitive in the morning, five were more sensitive in the afternoon, and one showed sensitivity peaks in both the morning and the afternoon.
In addition, the team quantified the extent of maximum and minimum treatment benefits by calculating the corresponding fold changes in time-of-day responses between the cancer and non-malignant cell models. By averaging these fold changes across cell lines and drugs, they established a ranking referred to as the “chronotherapeutic index,” which allowed them to pinpoint optimal treatment times to maximize cancer toxicity while minimizing impacts on healthy tissues. They found that, on average, drug efficacy could differ by 30% throughout the day.
“While these results are promising, further research is necessary to validate these findings and fully understand the underlying mechanisms before clinical application becomes routine,” said Ector.
Ector and Granada explained that before this approach can be widely implemented in the clinic, several steps are necessary. “Large-scale clinical trials with diverse patient populations are essential to validate the efficacy of circadian-based treatment strategies. Additionally, healthcare systems will need to adapt, including adjustments to hospital workflows, treatment scheduling, and patient monitoring technologies to support individualized timing.”
They added: “For many drugs, the broader use of programmable infusion systems, such as portable pumps tailored to a patient’s circadian rhythm, could be a practical solution. In the future, wearables that monitor circadian indicators like body temperature could further enhance this approach by helping to optimize both the timing and dosage of drug delivery based on real-time circadian data.”
For now, Ector, Granada, and colleagues plan to investigate how the circadian clock’s “status” functions as a global modulator of drug responses, independent of the time of day, and ultimately hope to uncover the molecular mechanisms driving circadian clock-dependent drug sensitivity.
“To achieve this, we are combining single-cell experiments with mathematical modeling to decipher the underlying regulatory mechanisms,” they said. “We plan to validate these models using single-cell microscopy, leveraging fluorescent reporters to monitor the circadian clock and track individual cell-fate decisions in real-time.”
