Potential Gastric Cancer Biomarker in Gastric Juice: Adenosine and Its Role in the Immune Evasion Mechanism of Gastric Cancer

Adenosine, a common cellular metabolite, can remodel the tumor immune microenvironment. Although gastric juice is considered a potential biomarker for gastric cancer (GC), sufficient verification is still lacking. This study aims to explore the potential of gastric juice-derived adenosine as a cancer biomarker. Adenosine levels in gastric juice, blood, and tissues from patients with GC and normal controls were quantified using non-targeted metabolomics and assay kits. Structure–explorative–interactive–SAR algorithm was used to analyze and predict the binding between adenosine and adenosine A1 receptor (ADORA1). Tumor immune estimation resource algorithm was employed to examine the correlation between ADORA1 and M2 macrophage infiltration and interleukin-6 (IL-6) levels. The binding affinity between adenosine and ADORA1 was validated using the cellular thermal shift assay. The messenger RNA and protein expression levels of ADORA1, CD86, and CD206 were examined via reverse transcription–quantitative polymerase chain reaction and Western blot. The protein expression of ADORA1 in tissue samples was assessed by immunohistochemistry. Flow cytometry was employed to measure the expression of surface markers on macrophages. Levels of cytokines and IL-6 were determined using an enzyme-linked immunosorbent assay. The chemotaxis of M2 macrophages was evaluated through Transwell. In vivo validation was conducted using a primary GC mouse model. Adenosine was highly expressed in gastric juice and tissues of patients with GC, while no significant difference was observed in the blood. Adenosine showed a strong binding affinity for ADORA1, and its expression level was positively correlated with adenosine concentration. Moreover, ADORA1 expression in GC cells was significantly and positively associated with M2 macrophage polarization and IL-6 secretion. However, the polarization of M1 macrophages and migration of M2 macrophages remained largely unchanged during this process. Our study innovatively reveals that gastric juice adenosine holds promise as a biomarker for GC diagnosis and the cancer immune landscape.