A recent study spearheaded by a scientist at the University of Manchester has revealed an intriguing new use for an old weapon in the battle against human disease: Common antibiotics have been shown to eradicate mitochondria in cancer stem cells, inhibiting the growth of  certain types of cancerous tumors.

The research team cautions that more studies will be required to assess the efficacy of antibiotics in a cancer treatment regime, but the team is encouraged by the findings and the prospect of inexpensive, widely available, and relatively benign antibiotic-based therapy for cancer.

According to the research paper, the team, which included scientists in New York and Philadelphia, tested four different types of antibiotics against 12 different cell lines of eight different types of tumor. The types of cancer examined included lung, breast, skin and brain cancers. The antibiotics were already in common use and included azithromycin (often used to treat pneumonia) and doxycycline (commonly prescribed for severe cases of acne).

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All four of the antibiotic classes tested eliminated the cancer stem cells in every test that was performed in the study.

The head of the research team, Professor Michael Lisanti, Director of the Breakthrough Breast Cancer Unit at the University of Manchester, was inspired to look into antibiotics as a cancer treatment after a conversation with his young daughter according to Science Daily. The girl asked him why doctors didn’t just use antibiotics to cure cancer, just as they did with other diseases.

Although there is an obvious answer to the question—most cancers are not caused by bacteria, and the mechanism by which antibiotics work attacks bacterial cells, not cancer cells—Lisanti stopped to think the question through and realized that the idea was worth further consideration.

Scientists knew from previous clinical trials that antibiotic treatment of cancer patients had improved one-year survival rates from 45% to 75%. The trials had been conducted to test the efficacy of antibiotic treatment of cancer patients afflicted with cancer-related bacterial infections, but, crucially, patients involved who were not infected also benefited from the drugs.

What Lisanti and his team found was that it is not the primary mechanism of the antibiotics that attacks the cancer stem cells, but rather a well-known side effect of the drugs, which can affect mitochondria, which are closely related to bacteria. The side effect is not considered significant enough to be dangerous to humans, but in stem cells, including cancer stem cells, mitochondria serve as the power source for division and replication.

Since it is run amuck that leads to cancer, disrupting that process is key to many cancer treatments. Many, however, have onerous side effects which disrupt healthy human cells along with cancerous cells. Antibiotics do not present that particular problem.

Since many of them have already gone through extensive testing and been approved for use in humans, the avenue to widespread use of antibiotics in cancer treatment may be much shorter than with more experimental treatments. And because they are already mass-produced and distributed broadly for their primary purpose, antibiotics are relatively inexpensive compared to other state-of-the-art cancer treatments.

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