What was unclear was whether metformin helps diabetics deal better with their blood sugar levels and insulin sensitivity or whether it affects the cancer itself. The results of this study point strongly to the latter.
Mice in this study that simultaneously received metformin and doxorubicin, a common chemotherapy agent, showed reductions in tumor size in four types of breast cancer, as well as longer remission times.
On its own, metformin, which was given in lower doses than normal for diabetics, did not have such a striking effect, indicating that the two treatments in combination are key.
Scientists hope that the metformin-chemo combination will result in a need for less chemo, thereby reducing painful side effects.
"Basically the [current] chemo dose is set up to give you as much as you can possibly tolerate on the grounds that the more you kill, the better it is, but likely you're overdoing to do that," Struhl said. "If you could cut [chemotherapy] in half, for example, and use metformin, you might get equally good clinical results and cut side effects."
Researchers also hope that the metformin protocol could have similar synergistic effects in other types of cancers.
Although it's always wise to be cautious when interpreting studies done in mice, "some of the cells they were testing were actually of human origin, so even though they were tested for tumorigenicity in mice, it still has some relevance," Chernoff said.
Researchers are planning clinical trials, which will be the "ultimate test," Struhl said.
Researchers may also start looking at other drugs for similar effects. If other known drugs with good safety profiles prove effective, "that would be an incredible thing," Chernoff said.
All rights reserved