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Diabetes Drug Fights Breast Cancer
Sept. 14, 2009 - The next breakthrough breast cancer treatment may be a diabetes drug already on the shelves of nearly every pharmacy.
The drug is metformin, available generically and under brand names such as Glucophage and Fortamet. A growing body of evidence suggests that diabetes patients taking metformin are less likely to get cancer, and have better outcomes if they do get cancer, than those not taking the drug.
Now Harvard researcher Kevin Struhl, PhD, and colleagues find that metformin can kill breast cancer stem cells, thought to be the cells responsible for breast cancer spread and recurrence.
And in mice carrying human breast cancers, metformin made standard chemotherapy vastly more effective. Mice treated with the combination remain cancer-free for four months, unlike mice treated with either drug alone.
"We have discovered new properties of metformin that can be of some use in cancer treatment and even prevention," Struhl said at a news conference held to announce the findings.
While his current study looked at metformin's effects on breast cancer, Struhl says the drug may affect other types of cancer as well.
"Although our studies were pretty much done on breast cancer cells, a lot of the principles are not specific just to breast cancer," Struhl said. "A lot of data shows lower cancer risk -- not just breast cancer -- in people taking metformin for diabetes."
Metformin Kills Cancer Stem Cells
What's so special about yet another drug that kills cancer cells in mice?
For one thing, the kind of cancer cells metformin targets are cancer stem cells, which are resistant to standard chemotherapy.
"This is the first time it's been shown that metformin may have an effect on these very resistant cancer cells. It is very exciting research," Dana-Farber Cancer Institute researcher Jennifer A Ligibel, MD, said at the news conference.
The very existence of cancer stem cells has been debated. That debate is now "water under the bridge," Frank Rauscher, PhD, suggested at the news conference. Rauscher, a cancer researcher at the Wistar Institute, is editor-in-chief of Cancer Research, which published the Struhl study in today's advance online edition.
Struhl says cancer stem cells are "far more nasty" than regular cancer cells.
"The bulk of the cells in a tumor are cancer cells which grow but are killed by chemotherapy," Struhl says. "But there is also a small population of cancer stem cells, which are better able to form tumors on their own and more resistant to chemotherapy than cancer cells. After standard chemotherapy, they can remain and essentially regenerate the tumor, and the disease is back again."
Different researchers have recently described new compounds that selectively kill cancer stem cells. Whether these compounds might one day become safe and effective cancer drugs remains to be shown.
Struhl -- who, with Harvard Medical School, holds a patent on the combined use of metformin and low-dose chemotherapy -- says metformin is already known to be safe and merely needs to be proven effective in human clinical trials.
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October is National Breast Cancer Awareness Month, and a new study reveals why a high number of women with the disease still prefer to have the entire breast surgically removed instead of just the tumor. It's not always because doctors recommend it.
