Diabetes drug metformin shows promise as a breast cancer treatment
(6 October 2009: VIDYYA MEDICAL NEWS SERVICE) -- Low doses of the commonly used diabetes drug metformin may be an effective treatment for breast cancer, primarily because the drug appears to target breast cancer stem cells, Harvard Medical School researchers reported online September 14 in Cancer Research. Cancer stem cells, also called tumor-initiating cells, are thought to be relatively rare cells that can give rise to new tumors and are resistant to standard cancer treatments.
In the study, the combination of metformin and the chemotherapy agent doxorubicin was more effective than either drug alone at eliminating cancer cells and cancer stem cells in cultured cell lines of four genetically distinct breast cancer types, including HER2-positive and triple-negative breast cancers. In a breast cancer mouse model, the drug combination eliminated tumors and prevented regrowth, whereas doxorubicin alone only reduced tumor size and did not prevent regrowth, and metformin alone had little effect.
“With both drugs, regression was quicker…and, more importantly, there was no relapse,” said senior author Dr. Kevin Struhl during a press briefing on the study.
When the researchers analyzed cell populations taken from the tumors of mice after three cycles of treatment, they found almost no cancer stem cells in the animals that received the drug combination but found the stem cells easily in tumors from mice given only doxorubicin. The highly beneficial effect of the combination treatment and the limited effect of either drug alone support the cancer stem cell hypothesis, Dr. Struhl said.
The results support previously published epidemiologic and laboratory studies that have suggested metformin has an anticancer effect, Dr. Jennifer Ligibel, a breast cancer researcher from Harvard University who was not involved with the study, said during the briefing. As a result, a large phase III clinical trial will test whether using metformin after standard treatment in women with early stage breast cancer can improve outcomes. The trial is being sponsored by NCI and coordinated by the National Cancer Institute of Canada. Trial investigators hope to start enrolling patients in the study next year, Dr. Ligibel said.
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