Stage‐Dependent Changes in Kynurenine Pathway Enzyme Expression Suggest Immune‐Related Involvement in Bladder Cancer Progression

L-tryptophan (Trp) metabolism through the L-kynurenine (Kyn) pathway contributes to immune escape in neoplasms, including bladder cancer (BC). Indoleamine 2,3-dioxygenase-1 (IDO1) is a key enzyme, and its catabolites-Kyn, 3-hydroxykynurenine (3HK), and 3-hydroxyanthranilate (3HAA)-depend on other enzymes and play a crucial role in immunomodulation. OBJECTIVES: We investigated the association between Kyn pathway enzyme expression and BC prognostic factors. METHODS: Data from 165 bc patients in the GEO DataSets were analyzed, comparing staging, tumor grade, progression, and recurrence with the expression of IDO1, arylformamidase (AFMID), kynurenine-oxoglutarate transaminase (KAT), kynureninase (KYNU), kynurenine 3-monooxygenase (KMO), 3-hydroxyanthranilate 3,4-dioxygenase (HAAO), and aminocarboxymuconate-semialdehyde decarboxylase (ACMSD). Predictive genes were further evaluated in RT4 (low-grade, non-invasive) and T24 (high-grade, invasive) BC cells treated with IFN-gamma and the IDO1 inhibitor INCB024360. Trp catabolites were quantified in the supernatant. RESULTS: Enzyme expression varied widely, especially for IDO1, AFMID, KAT, KMO, and KYNU. IDO1 correlated positively with KMO and negatively with KAT. High IDO1 and KMO levels were linked to advanced-stage disease, while KAT and KYNU were associated with earlier stages and lower tumor grade. RT4 and T24 cells showed distinct basal enzyme expression, with T24 cells being more responsive to IFN-gamma, increasing IDO1 and KYNU while decreasing KAT and KMO. These effects were inhibited by INCB024360. High Trp consumption increased Kyn and 3HAA but not 3HK. CONCLUSIONS: Kyn pathway enzyme expression varies with disease progression and may indicate immune activity by influencing tumor microenvironment catabolites. BC cell sensitivity to immune stimuli differs, potentially shaping distinct immune escape mechanisms.