Saint Louis University researchers have discovered a molecular breast cancer “switch” that allows aggressive tumors to grow, but also appears to be turned off by vitamin D.

The finding, reported in the Journal of Cell Biology, suggests the intriguing possibility that the “sunshine vitamin” may offer a safe and cost-effective way to combat so-called “triple-negative breast cancer,” a particularly virulent, hard-to-treat form of the disease that tends to strike younger women.

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In a study funded in part by a $500,000 Department of Defense grant, a team of Saint Louis researchers led by Susana Gonzalo identified a molecular pathway that, when activated, allows tumor cells to grow unchecked and makes them more resistant to current therapies.

But Gonzalo, an assistant professor of biochemistry and molecular biology, also found vitamin D and a class of drugs, known as protease inhibitors, can turn off that pathway, suggesting they may offer a new way to combat the cancer with less-toxic therapies.

What’s more, Gonzalo’s team discovered a set of three biomarkers that can help to identify patients who could benefit most from vitamin D treatment.

The research team examined how defects in the so-called BRCA1 breast cancer gene increase a woman’s risk for developing breast and ovarian cancers, including the triple-negative type. Chemotherapy is the most effective treatment, but can have profound negative side effects.

The experiments performed in Gonzalo's laboratory, in collaboration with those of Xavier Matias-Guiu and Adriana Duso (IRBLleida, Spain), determined not only that tumor cells proliferate as a result of several processes set in motion by BRCA1 defects, but also that vitamin D and protease inhibitors can shut them down.

Researchers now will test the effectiveness of using vitamin D and protease inhibitors — as single agents or in combination with different drugs — against breast cancers.

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