Researchers have identified a mechanism explaining how chronic stress accelerates the growth of breast cancer stem cells.
Increasingly better understood and taken into account by the scientific community, chronic stress has already been the subject of numerous studies. All have demonstrated that a long and intense period of stress can have a lasting effect on the psychological and emotional well-being, as well as the physical health of people who are subjected to it. Previous research had, for example, suggested that exposure to stress could accelerate cancer growth by altering gene activity.
Others have suggested that exposure to stress may accelerate cancer growth due to its impact on gene activity.
New work, led by Dalian University in China and reported in the Journal of Clinical Investigation go further. By conducting a study on mice, its authors discovered how chronic stress could promote the development of breast cancer stem cells.
The role of epinephrine in tumor development
“You can kill all the cells you want in a tumor, but if the stem cells, or mother cells, are not killed, then the tumor will grow and metastasize. This is one of the first studies to specific link between chronic stress and breast cancer stem cell growth,” says Keith Kelley, professor emeritus in the Department of Animal Science and College of Medicine at the University of Illinois, and co-author of the study.
To establish a link between chronic stress and the development of stem cells, the researchers induced chronic stress in mice by placing them for a week in small pens limiting their movements. They were then inoculated with breast cancer cells. The mice were then divided into two groups: a control group and a group of stressed mice locked in small cages for an additional month. The scientists then found that mice suffering from chronic stress had larger and faster growing tumors than those in the control group.
After demonstrating the link between chronic stress, mood swings and increased growth of breast cancer stem cells, scientists turned their attention to the underlying biochemical foundations that cause stress and increase the growth of cancer cells.
For the authors of the study, the explanation is to be found on the side of epinephrine, one of the main stress hormones. They first noticed that epinephrine levels were higher in mice subjected to stress throughout the duration of the experiment, but also in those who had received treatment to inactivate the ADRB2 receptor for the hormone, the tumors were much smaller and had fewer stem cells.
“These data provide a new pathway that explains how elevated epinephrine caused by chronic stress promotes breast cancer progression by acting directly on cancer stem cells,” says Quentin Liu, of the Cancer Institute of Dalian Medical University in China.
Vitamin C, effective in targeting cancerous tumors
The researchers then assessed the clinical significance of their findings by measuring the presence of epinephrine in the blood of 83 breast cancer patients. Women with high levels of the stress hormone had significantly lower overall survival and disease-free survival than patients with low epinephrine.
In a final test, the researchers grew breast cancer cells in the lab and introduced a wide variety of cancer drugs. They discovered that when injected into stressed mice, vitamin C caused cancerous tumors to shrink.
Scientists have suspected the potential of vitamin C in the fight against cancer for decades and several clinical trials have shown positive results. This study provides a new understanding of its action in biochemical pathways relevant to breast cancer patients suffering from chronic stress, say its authors. “Taken together, these results show that vitamin C could be an effective new therapeutic agent for targeting cancer in patients suffering from chronic stress,” Dr. Liu concludes.
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