Radiation therapy for colon cancer works better when specific protein blocked: study

Researchers at Washington University School of Medicine in St. Louis have discovered a way to make radiation therapy for colorectal cancer more effective by inhibiting a protein found in cancer cells in the gut.

By studying cells, mice and tumor samples from patients with cancer, the scientists targeted an enzyme known as indoleamine 2,3 dioxygenase 1 (IDO1), report agencies.

In the study, the researchers treated colon cancer cell lines with radiation and found that the cells made more IDO1 protein after a single dose. They also looked at tumor samples from patients with colorectal cancer and found that radiation caused those cells to make more of the protein.

Further experiments suggested the protein might be protecting cancer cells from the effects of radiation. Then they turned to using techniques to block the IDO1 gene, as well as the drug epacadostat to block the protein's activity, and found that combining the strategies contributed to tumor shrinkage in 40 percent of the tumors they studied. 

In mice, combining radiation with inhibition of the protein also resulted in tumors located away from the primary cancer shrinking or growing more slowly.

In other experiments, the combination therapy prevented recurrence of the cancers.

"It acted almost like a vaccine," said Matthew A. Ciorba, an associate professor of medicine and director of the Inflammatory Bowel Disease Center at Washington University. "Mice that received the combined therapies were less likely to develop other cancers of the same type."

The researchers now are testing the approach in people with colorectal cancer.

As the protein is also overexpressed in other abdominal and pelvic cancers, Ciorba explained that blocking its activity may be helpful in other types of cancer, too.

The findings are published online on Tuesday in the journal Cancer Immunology Research.