IDO1-mediated catabolism of tryptophan in gastric tumors: Its potential role in the axis of histopathology, differentiation and metastasis.

BACKGROUND: Indoleamine 2,3-Dioxygenase 1 (IDO1)-mediated tryptophan degradation, which is the rate-limiting enzyme of tryptophan/kynurenine pathway, may cause immune suppression in the tumor microenvironment, while potentiating proliferative and metastatic activity in the tumor focus, Phase studies of IDO1 inhibitors are ongoing, and our study aims to evaluate the potential contribution of IDO1 gene expression to the tryptophan/kynurenine pathway in tumor and tumor microenvironment foci in gastric cancer (GC) on a clinicopathological axis, METHOD: In the case-control study design, the determination of tryptophan and its metabolites in the serum of 51 GC and 49 healthy controls was made using High Pressure Liquid Chromatography-Fluorescence Detector (HPLC-FD). IDO1 expression in a total of 102 tissues with tumor and tumor microenvironment was detected by quantitative PCR (q-PCR).

RESULTS: In gastric tumors, 3,25-fold decreased expression of IDO1 was detected according to the tumor microenvironment (p=0,05), IDO1 expression was found to be more than 2 times higher in signet ring cell carcinoma (SRCC) and poorly differentiated tumors without distant organ metastasis (p<0,05), In GC, tryptophan level was found to be 1,6 times lower than in control (AUC:0889; cut off≤21,57; p<0001), Low tryptophan level was found in advanced tumor stage compared to early stage and in the presence of perineural invasion compared to its absence (p<0,05) The level of kynurenine was found to be approximately 1,8 times lower in SRCC (p=0,04), CONCLUSION: Increased tryptophan accumulation in the gastric tumor and its microenvironment, when catabolized via IDO1, exhibits histological type, tumor differentiation, and metastasis-promoting effects more prominently in aggressive subtypes such as SRCC.