But the researchers -- who work at the University of Colorado -- aren’t making any promises yet.
"The value of this preclinical study is that it shows grape seed extract can attack cancer, and how it works, but much more investigation will be needed before these chemicals can be tested as a human cancer treatment and preventive," says Rajesh Agarwal, PhD, one of the researchers.
"With these results, we are not suggesting that people run out and buy and use grape seed extract," Agarwal says in a news release from the American Association for Cancer Research. "That could be dangerous since so little is known about doses and side effects."
Testing the Extract
In their study, the researchers began by testing various doses of grape seed extract on human colon cancer cells in test tubes.
The cancer cells treated with grape seed extract were more likely to halt their normal growth cycle and die, compared to those not treated with the extract.
Cancer cells that got the biggest doses of grape seed extract for the longest time were the most likely to halt their growth cycle.
Those results were "encouraging," the researchers write.
So the scientists took their experiment one step further.
They injected human colon cancer tumors under the skin of mice, then funneled grape seed extract into the mice’s mouths through a tube.
The tumors grew more slowly in those mice, compared to the tumors in mice that didn’t get grape seed extract.
The mice that got grape seed extract didn’t gain weight, change their diets, or show other side effects during the eight-week study.
Agarwal and his colleagues write that antioxidants called proanthocyanidins may be responsible for grape seed extracts’ effects.