Also, the tumours detected in these mice were three times smaller than in those in the control group.
The researchers engineered E. coli Nissle, a harmless type of bacteria found in the gut, into a probiotic that attaches to the surface of colorectal cancer cells. It then secretes an enzyme which converts glucosinolates from broccoli into cancer-fighting molecules.
Writing in the journal Nature Biomedical Engineering, the team from the National University of Singapore stated: "The engineered commensal Escherichia coli bound specifically to the heparan sulphate proteoglycan on colorectal cancer cells and secreted the enzyme myrosinase to transform host-ingested glucosinolates — natural components of cruciferous vegetables — to sulphoraphane, an organic small molecule with known anticancer activity."
The engineered microbes, coupled with glucosinolates, resulted in a 95% reduction of cancer cells in murine, human and colorectal adenocarcinoma cell lines in vitro.
"We also showed that murine models of colorectal carcinoma fed with the engineered microbes and the cruciferous vegetable diet displayed significant tumour regression and reduced tumour occurrence," they added.
However, the measures had no effect on cells from other types of cancer, such as breast and stomach cancer.
Lead author Dr Ho Chun-Loong hopes these probiotics can be used to prevent the development of cancer calls, and help clean up those remaining after the surgical removal of tumours.
Associate Professor Matthew Chang said: "One exciting aspect of our strategy is that it just capitalises on our lifestyle, potentially transforming our normal diet into a sustainable, low-cost therapeutic regimen. We hope that our strategy can be a useful complement to current cancer therapies."
Colorectal cancer is one of the most common cancers in the world. Although the five-year survival rates for earlier stages of the cancer are relatively good, survival rates decrease at later stages, and the risk of cancer recurrence increases considerably.
Source: Nature Biomedical Engineering
"Engineered commensal microbes for diet-mediated colorectal-cancer chemoprevention"
Authors: Ho Chun Loong, et al.