Description_x000D_ Packaging_x000D_ 5, 25 mg in glass bottle_x000D_ Biochem/physiol Actions_x000D_ 680C91 is a potent inhibitor of the enzyme tryptophan 2,3-dioxygenase (TDO), which directs the conversion of trypophan to kynurenin. Kynurenin has recently been identified as an endogenous lignd of the arylhydrocarbon receptor (AHR). TDO is highly expressed in glioma cells, and contributes to AHR-mediated glioma cell survival and suppression of anti-tumor immune responses.