An Old Breast Cancer Drug Could One Day Cure Superbug Infections

As our antibiotic options disappear, scientists are looking around to see what else is out there.

The "superbug" MRSA has long been the scourge of hospitals. The second-leading cause of infections acquired during a stay, it can result in dangerous bloodstream infections, surgical site infections, and pneumonia. What makes MRSA especially scary is that it's resistant to all penicillin-like antibiotics like the common drugs methicillin, amoxicillin and oxacillin.

But it turns out we may already have a cure for MRSA, and it’s been around since 1977, when it was approved for breast cancer treatment. Researchers from the University of California, San Diego School of Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences have found the common breast cancer drug tamoxifen can enhance white blood cell performance in both lab experiments and in mice.

The discovery is also important because, as lead researcher and pharmacy professor Dr. Victor Nizet pointed out in a statement, while the threat of antibiotic-resistant bacteria like MRSA grows, the development of new antibiotics has slowed. The finding demonstrates the value of taking a fresh look at known medicines to see if they are affective for illnesses that have no cure.

“We may have a cure for MRSA, and it’s been around since 1977.”

"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,” said Nizet. "Through this approach, we discovered that tamoxifen has pharmacological properties that could aid the immune system in cases where a patient is immunocompromised or where traditional antibiotics have otherwise failed."

Tamoxifen works by targeting the body’s estrogen receptors. About 80 percent of all breast cancers grow in response to the hormone estrogen, so finding a way to block the body’s estrogen production is crucial for cancer treatment. But the drug also helps the body produce molecules that help regulate a type of immune cell called neutrophils, which travel to an infection in the body and engulf the invading microorganism.

Here’s a video of a neutrophil in action:

To see if tamoxifen’s effects on neutrophils could help stave off infection, the researchers first applied the drug to the white blood cells in a lab container. They saw that neutrophils treated with tamoxifen were better at swallowing up bacteria because they made about three times more of the neutrophil extracellular traps -- the part of the neutrophil that reaches out to engulf the bacteria -- than the non-treated neutrophils.

The drug was then tested in mice. Researchers divided 12 mice into two groups and treated them with either tamoxifen or a control drug. The mice were then infected with MRSA, and the researchers treated them again with either the tamoxifen or the control drug. The control mice died after one day, while 35 percent of the mice treated with tamoxifen survived five days. Repeating the experiment, scientists found that eight hours after MRSA infection, mice who had been treated with tamoxifen had a bacterial count that was 100 times lower than the control group. The data helped researchers conclude that the drug helped clear the dangerous bacteria.

Hundreds of thousands of woman around the world use tamoxifen every day for breast cancer treatment, and the drug has often been investigated for its infection-fighting powers. Past studies have shown tamoxifen’s protective effects against hepatitis C and herpes, as well as the fungus that causes yeast infections.

Even though scientists know tamoxifen is safe for people to use, doctors shouldn't start using the drug off-label to fight infections, Nizet explained, saying further study is needed to see how tamoxifen battles infections in human beings.

"While physicians often use approved drugs 'off-label' in their best judgement for severe cases in which patients are doing poorly (failing conventional therapy), we feel the proper approach moving forward would be to conduct a trial of patients with antibiotic resistant infections in which tamoxifen would be added to the current standard-of-care (antibiotics) compared to standard-of-care alone,” Nizet concluded, saying that if tamoxifen were used to fight infections, it would only be used for a short time, until the patient's own immune system takes over.

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