The chemicals, called proanthocyanidins, inhibited the growth of human lung, colon and leukaemia cells in culture, without affecting healthy cells. They could also stop cancer from spreading, showed the tests.
The work by Catherine Neto at the University of Massachusetts-Dartmouth and colleagues is important as it is one of the first studies to look closely at the compounds in this fruit that are responsible for anti-cancer activity.
"Anti-cancer activity has been reported in the literature from way back but there is no good real data on the structures [in cranberries]," Neto told NutraIngredients.com.
There are several groups of antioxidant compounds in cranberries that could protect against cancer, she noted, including quercetin and ursolic acid.
But while cranberry extracts have previously been shown to inhibit human cancer cells, in most cases the researchers did not identify the active constituents responsible for such an effect.
Moreover, while proanthocyanidins from grapeseed have been linked to cancer inhibition, the structure of these chemicals is significantly different in cranberries compared with other berries.
"Unlike most fruit, cranberries contain PACs with A-type linkages between units, a structural feature identified in cranberry PACs with antibacterial adhesion properties and those with LDL-protective properties," write Neto and colleagues in the Journal of the Science of Food and Agriculture (DOI 10.1002/jsfa.2347).
"Previously published reports have suggested that cranberry proanthocyanidins have anti-cancer properties but there are few data on tumour growth inhibition by well-characterized cranberry proanthocyanidins," they note.
The authors isolated a proanthocyanidin-rich fraction of a whole cranberry extract made from fruit donated by US-based Decas Cranberries. The fractions were tested on several tumour cell lines and screened for their effect on tumour proliferation.
The study showed significant inihibition of the proliferation of cancer cells, not previously shown with other proanthocyanidins, as well as the blocking of tumour growth. "The activity was at no less than 100ug/mL concentration," said Neto.
"It's hard to say whether you would get these levels distributed to different tissues to the extent where you would have activity in vivo," she added.
But eating cranberries or taking supplements of extract could be helpful, she believes.
"There are so many compounds in cranberries capable of having some anti-cancer mechanism that when taken together there is potential for benefit," she said.
There are probably several mechanisms for the cranberry's anti-cancer action, said Neto, but further work needs to be done to clarify this.
"We're hoping to follow up with animal models. It's really important to do this. These compounds are not at all well-known so I think of this [new study] as opening a door."