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Drugs that target a protein called indoleamine 2,3-dioxygenase (or IDO for short) are showing promise in early clinical trials for unleashing the immune system against cancer, and may boost the effectiveness of existing immunotherapies.
IDO breaks down the crucial amino acid tryptophan, thereby staving immune cells and suppressing immune responses and potentially damaging inflammation. However, it can also block the body’s natural immune response to cancer and allow tumours to grow unchecked. Some tumours even produce IDO to shield themselves from the immune system.
New drugs, called IDO inhibitors, can potentially boost the effectiveness of treatments called immunotherapies, which bolster the immune response against cancer. IDO inhibitors include drugs such as indoximod, which in combination with an anti-PD1 drug shrank the tumours in more than half of the people with advanced melanoma in the trial. Another IDO inhibitor is called epacadostat, which could boost response rates to anti-PD-1 drugs in lung and kidney cancers. In a clinical trial with kidney cancer, epacadostat plus pembrolizumab shrank tumours in 47% of people in the trial.
This Nature article reviews the research to date with IDO inhibitors