1-Methyltryptophan is a chemical compound that is an inhibitor of the tryptophan catabolic enzyme indoleamine 2,3-dioxygenase (IDO or INDO EC 1.13.11.52).

The L-isomer (L-1MT) inhibits IDO weakly but also serves as an enzyme substrate.

The D-isomer (D-1MT) does not inhibit IDO at all, but it can inhibit the IDO-related enzyme IDO2[2] and restore mTOR signaling in cells starved of tryptophan due to IDO activity.

[3] D-1MT is also known as indoximod and is was in clinical trials for cancer treatment, such as for advanced melanoma, in 2017.

[4][needs update] A U.S. patent covering salt and prodrug formulations of indoximod was issued to NewLink Genetics on August 15, 2017 providing exclusivity until at least 2036.