Further testing of compound 168 in a mastocytoma cell line expressing either murine TDO (P1.TDO) or IDO1 (P1.IDO1) showed that this compound displayed IC50 values of 5.46 μM against P1.TDO and 12.7 nM against P1.IDO1, with the assay being performed by measuring the secretion of L-kynurenine into the medium. Here, IDO1 is linked to mastocytoma.