Something different to discuss – for the medical-revolution cynics among us. Cells from a human triple-negative breast cancer were implanted in mice under their mammary fat pads. Triple negative breast cancer is a nastier form of breast cancer which is harder to treat because these cells don’t respond to the usual anti-estrogenic drugs.
The mice were then allowed to eat only 70% as many calories as they would normally freely choose to eat. This is a particularly interesting study because it shows that calorie restriction inhibited the expression of certain micro RNAs even from foreign (non mouse) implanted breast cancer cells, and this apparently kept the cancer from spreading. Notably fatalities from cancers don’t usually come from the initial solid tumor but from the metastasized version, so this is potentially very useful.
The mechanism involves strengthening the matrix around the cancer cells. When these cancer cells have metastasized they produce more of these particular micro RNA’s which in turn appear to stop production of proteins that strengthen the extracellular matrix. In other words, the cancer cells probably use the micro RNA’s to degrade the cellular matrix around them in order to spread. The implications of this are both that the micro RNA’s could be used as a target for future drug development, and also that it may help explain why people who gain weight are more likely to have a recurrence. A link between weight and breast cancer is already well established. Dieting may especially help people undergoing radiation therapy, and other trials on this with patients have already started.
For the rest of us, it’s a bit more incentive not to eat the other half of the block of chocolate (til tomorrow). Of course “cutting calories” means being careful to avoid vitamin and mineral deficiencies too.
Fighting Cancer with Dietary Changes
Calorie restriction, a kind of dieting in which food intake is decreased by a certain percentage, has been touted as way to help people live longer. New research suggests that there may be other benefits, including improving outcomes for women in breast cancer. According to a study published May 26th in Breast Cancer Research and Treatment, the triple negative subtype of breast cancer — one of the most aggressive forms — is less likely to spread, or metastasize, to new sites in the body when mice were fed a restricted diet.
“The diet turned on a epigenetic program that protected mice from metastatic disease,” says senior author Nicole Simone, M.D., an associate professor in the department of Radiation Oncology at Thomas Jefferson University. Indeed, when mouse models of triple negative cancer were fed 30 percent less than what they ate when given free access to food, the cancer cells decreased their production of microRNAs 17 and 20 (miR 17/20). Researchers have found that this group of miRs is often increased in triple negative cancers that metastasize.
Breast cancer patients are often treated with hormonal therapy to block tumor growth, and steroids to counteract the side effects of chemotherapy. However, both treatments can cause a patient to have altered metabolism which can lead to weight gain. In fact, women gain an average of 10 pounds in their first year of treatment. Recent studies have shown that too much weight makes standard treatments for breast cancer less effective, and those who gain weight during treatment have worse cancer outcomes. “That’s why it’s important to look at metabolism when treating women with cancer,” says Dr. Simone.
In earlier studies, Dr. Simone and colleagues had shown that calorie restriction boosted the tumor-killing effects of radiation therapy. This study aimed to examine which molecular pathways were involved in this cooperative effect.
The investigators noticed that microRNAs — a type of RNA that regulates other genes in the cell — specifically miR 17 and 20, decreased the most when mice were treated with both radiation and calorie restriction. This decrease in turn increased the production of proteins involved in maintaining the extracellular matrix. “Calorie restriction promotes epigenetic changes in the breast tissue that keep the extracellular matrix strong,” says Dr. Simone. “A strong matrix creates a sort of cage around the tumor, making it more difficult for cancer cells to escape and spread to new sites in the body.”
Understanding the link to miR 17 also gives researchers a molecular target for diagnosing cancers that are more likely to metastasize and, potentially, for developing a new drug to treat the cancers. In theory, a drug that decreased miR 17 could have the same effect on the extracellular matrix as calorie restriction. However, targeting a single molecular pathway, such as the miR17 is unlikely to be as effective as calorie restriction, says Dr. Simone. Triple negative breast cancers tend to be quite different genetically from patient to patient. If calorie restriction is as effective in women as it is in animal models, then it would likely change the expression patterns of a large set of genes, hitting multiple targets at once without toxicity.
In order to test that this hypothesis is true in humans, Dr. Simone is currently enrolling patients in the CaReFOR (Calorie Restriction for Oncology Research) trial. As the first trial like it in the country, women undergoing radiation therapy for breast cancer receive nutritional counseling and are guided through their weight loss plan as they undergo their treatment for breast cancer.
Lianjin Jin, Meng Lim, Shuping Zhao, Yuri Sano, Brittany A. Simone, Jason E. Savage, Eric Wickstrom, Kevin Camphausen, Richard G. Pestell, Nicole L. Simone. The metastatic potential of triple-negative breast cancer is decreased via caloric restriction-mediated reduction of the miR-17~92 cluster. Breast Cancer Research and Treatment, 2014; DOI: 10.1007/s10549-014-2978-7