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Breast cancer drug helps immune response against MRSA

The drug's immune-boosting ability was shown in lab in experiments with mice.

By Stephen Feller
Breast cancer drug helps immune response against MRSA
Tamoxifen helped mice infected with Methicillin-resistant Staphylococcus aureus, or MRSA, live about five times as long as those treated with a control drug. Photo by Flickr/National Institute of Allergy and Infectious Diseases

SAN DIEGO, Oct. 13 (UPI) -- The breast cancer drug tamoxifen boosts the immune system, and was shown to be effective against Methicillin-resistant Staphylococcus aureus, or MRSA, in lab experiments, according to researchers at the University of California San Diego.

Tamoxifen, which blocks estrogen receptors in breast tissue, is used by hundreds of thousands of women and men with advanced breast cancer. The drug's known effects on other cells led researchers to study other ways to use it.

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"While known for its efficacy against breast cancer cells, many other cell types are also exposed to tamoxifen," said Dr. Victor Nizet, a professor of pediatrics and pharmacy at the UCSD, in a press release. "The 'off-target effects' we identified in this study could have critical clinical implications given the large number of patients who take tamoxifen, often every day for years."

For patients with estrogen-receptor positive breast cancer, tamoxifen blocks the receptors, helping make other treatments such as chemotherapy and radiation more effective. Researchers focused, however, on the drug's 'off-target effect' on the production of a type fatty molecule called ceramide that enhances the ability of white blood cells called neutrophils to engulf and defeat bacteria.

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In the lab, researchers found that neutrophils treated with tamoxifen produced three times more neutrophil extracellular traps, or NETs, a group of proteins, enzymes and peptides neutrophils use to kill bacteria.

The researchers treated mice with tamoxifen to test its ability to boost the immune system. After exposing the rodents to MRSA, another dosage of tamoxifen was given and the mice were monitored for five days. Although none of the control mice live more than a day, about 35 percent of the mice treated with tamoxifen survived for five days. Five times fewer MRSA were found in peritoneal fluid taken from the mice's abdomens.

"The threat of multidrug-resistant bacterial pathogens is growing, yet the pipeline of new antibiotics is drying up," Nizet said. "We need to open the medicine cabinet and take a closer look at the potential infection-fighting properties of other drugs that we already know are safe for patients."

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The study is published in Nature Communications.

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