Scientists have figured out how disrupted cellular circadian rhythms lead to liver cancer and have found that by inhibiting key “clock” proteins, they can stop it from growing.

In a study published Jan. 3 in Proceedings of the National Academy of Sciences, researchers from the University of Southern California (USC) Keck School of Medicine explained how they identified the mechanism by which cancer cells hijack cells’ circadian rhythms to grow. They also showed that knocking down the genes for the clock proteins inhibited tumor growth in mice, suggesting a potential avenue for treatment.  

Many people are familiar with the concept of the circadian rhythm as it pertains to sleep, but it extends to individual cells, too. Cells release different proteins and peptides over the course of a 24-hour period. These patterns are dictated by circadian rhythm genes, like the aptly named CLOCK and BMAL1.

The proteins encoded by CLOCK and BMAL1 have been shown to be dysregulated in several cancer types including liver cancer, making a case for disrupting malignant cells’ circadian rhythms as a therapeutic strategy—one that some researchers are already testing out for prostate cancer, breast cancer and more.

In their new study, the USC researchers set out to establish a direct link between liver cancer and cellular circadian rhythms. They also wanted to see if manipulating the clock proteins could stop cancer cells from growing.

To do that, they started by knocking down the CLOCK and BMAL1 genes in liver cancer cells. This killed the cells and stopped tumor growth, indicating that the genes were necessary for cell proliferation. The researchers then looked more closely at the molecular mechanisms behind the CLOCK and BMAL1 proteins’ activity, analyzing how their inhibition altered phases of the cell cycle and caused the cells to die.

Their findings showed that the CLOCK and BMAL1 proteins drove transcription of the WEE1 protein, an enzyme involved in cell cycle regulation that’s highly expressed in many different cancer types—including liver cancer. Knocking down CLOCK and BMAL1 lowered the expression of WEE1 and also raised the level of another protein, P21, which collectively inhibits cancer cell proliferation and induces cancer cell death.

The scientists then turned to animal models. They injected groups of mice with regular liver cancer cells or cells where either the CLOCK or BMAL1 genes were knocked down. The impact was apparent when the researchers examined the size of the mice’s tumors. Tumors in the control animals were around four times the size of those without the BMAL1 gene, while the animals that were implanted with cells without the CLOCK gene showed little evidence of disease.  

The findings suggest that cancer cells are manipulating the clock proteins in a way that dysregulates the normal cell cycle, enabling them to grow unchecked. By showing that inhibiting the circadian rhythm genes staved off tumor growth, the scientists demonstrated a potential treatment strategy.   

Moving forward, the researchers will look more closely at the relationship between the circadian rhythm proteins and WEE1 as well as other genes that have been implicated in cancer development, such as the one for the tumor-repressing protein p53. Other studies have shown a connection between p53 function, DNA damage and clock protein activity as well as WEE1, noted Steve Kay, Ph.D., senior author and provost professor of neurology, biomedical engineering and quantitative computational biology at Keck.

“It makes sense for us to explore this co-regulatory circuitry, both for a deeper understanding of the mechanisms involved and perhaps eventually for using biomarker combinations to identify patients most likely to benefit from targeting a clock protein in a given cancer,” he said in an email to Fierce Biotech Research.

The current standard of care for liver cancer is a combination of Roche’s immunotherapy Tencentriq, an anti-PD-L1 antibody and Avastin, a drug that cuts off cancer blood vessel growth by inhibiting the growth factor VEGF. A recently approved immunotherapy combo from AstraZeneca—an anti-CTLA-4 antibody called Imjudo and PD-L1 antibody Imfinzi—showed a three-year survival rate of around 31%.  

The scientists hope to add to those options. They plan to work with collaborators at Synchronicity Pharma and the University of Florida Scripps Institute for Biomedical Research to test in patients some experimental compounds both alone and in combination with other agents such as WEE1 kinase inhibitors.

There’s also the potential to apply the findings beyond liver cancer. Kay’s lab studies how circadian rhythm proteins affect the development other types of cancer, with evidence to support targeting them in glioblastoma, acute myeloid leukemia, metastatic colorectal cancer and triple negative breast cancer.