Plasma Levels of Kynurenine, Soluble OX40 and Mir-138-5p Are Associated With Tumor-infiltrating Lymphocytes in Colorectal Cancer: An Exploratory Study.

Abstract

Colorectal cancer (CRC) is one of leading cancers in terms of incidence and mortality. Interaction of tumor cells with the surrounding microenvironment plays a crucial role in the development and progression of CRC. Many pathways such as the kynurenine pathway, OX40/OX40L-mediated signaling and microRNAs targeting PD-L1 may be involved in CRC development by affecting T cell activation, thus creating an immune-deficient microenvironment. Herein, our goal was to assess the association between plasma levels of tryptophan (TRP), kynurenine (KYN), KYN/TRP ratio, soluble OX40 (sOX40) and PD-L1-targeting miR-138-5p and CRC risk. Plasma concentrations of TRP and KYN were determined by HPLC; sOX40 was measured by ELISA whereas circulating miR-138-5p was measured by quantitative PCR in pathologically confirmed CRC patients and colonoscopy-verified CRC-free controls without polyps (control group 1) and with polyps (control group 2). We found significantly lower plasma levels of TRP in CRC patients compared to control groups which resulted in significantly higher KYN/TRP ratio in CRC patients than in the controls (p=0.007). Plasma levels of sOX40 did not significantly differ between groups. The levels of circulating miR-138-5p were significantly lower in CRC patients (relative median value 0.02) than in the control groups (relative median values 0.2 and 4.29, respectively) (p=0.03). Plasma levels of KYN and sOX40 were considerably higher in patients with no tumor-infiltrating lymphocytes (TILs) than those with TILs whereas circulating miR-138-5p had opposite expression pattern in plasma. The kynurenine pathway and miR-138-5p are associated with CRC risk and plasma levels of KYN, sOX40 and miR-138-5p are related to TILs, making them possible target molecules in possible immunotherapeutic targets for CRC.