Diabetes drug appears to target cancer stem cells
US scientists have discovered that a drug called metformin which is commonly used to treat type-2 diabetes may target cancer stem cells, a subset of cells that are thought to initiate and fuel the growth of tumours.
Previous studies have suggested that people who take metformin may have a lowered risk of developing some forms of cancer - including breast cancer - and respond better to chemotherapy.
The study, which was carried out by researchers at Harvard Medical School and published in the journal Cancer Research, looked at the effects of a combination of metformin and the cancer drug doxorubicin when given to mice that had been implanted with different types of breast tumour.
The results suggested that the combination was more effective at shrinking the tumours and prolonging remission than chemotherapy alone, apparently because the diabetes drug targets cancer stem cells.
The study's authors believe that the results provide more support for the cancer 'stem cell' hypothesis, which suggests that a small subset of rogue stem cells within a tumour are capable of initiating and promoting recurrence, and are resistant to conventional anti-cancer therapies.
Senior author Professor Kevin Struhl, an expert in biological chemistry and molecular pharmacology at Harvard Medical School, claimed that metformin is "selective for cancer stem cells".
"There is a big desire to find drugs specific to cancer stem cells," he continued.
"The cancer stem cell hypothesis says you cannot cure cancer unless you also get rid of the cancer stem cells. From a purely practical point of view, this could be tested in humans. It's already used as a first-line diabetes drug."
Researchers carried out a series of studies on samples of human breast cancer cells in the laboratory, as well as in mice which received transplants of human breast cancer cells.
They found that the combination of metformin and doxorubicin was effective at killing both regular cancer cells and cancer stem cells in laboratory samples.
In mice which had been pre-treated with metformin before being transplanted with human breast cancer, the cancer stem cells were found to be unable to form tumours.
The researchers also found that in animals which already had established tumours, the combination of metformin and doxorubicin reduced the size of tumours and extended the length of time until relapse to a greater extent than with doxorubicin alone.
However, metformin was ineffective at treating tumours unless doxorubicin was administered at the same time.
Henry Scowcroft, Cancer Research UK's science information manager, commented: "This fascinating early study provides more support for the idea that cancers are caused by rogue stem cells.
"If the results are confirmed in larger trials it also suggests that it might be possible to use an existing drug to target cancer stem cells and help treat the disease at its roots. But this work was done in mice that were given transplanted tumours, and needs to be repeated on a larger scale to confirm its potential in patients.
"It's also important to remember that the idea that cancers are caused by rogue stem cells is relatively new, and may not hold true for all forms of the disease."