CDO1 as a prognostic biomarker and therapeutic target in gastric cancer: Mechanistic insights into the PI3K/AKT-THBS1 axis and epigenetic reactivation by decitabine.

BACKGROUND: As a pivotal metabolic enzyme, cysteine dioxygenase type 1 (CDO1) exerts tumour-suppressive effects across diverse tumour types, and its expression is strongly correlated with clinical prognosis. However, the molecular mechanisms underlying CDO1-mediated tumour suppression in gastric cancer (GC), its relationship with the tumour-associated immune microenvironment, and pharmacological strategies to restore its expression remain poorly understood. METHODS: CDO1 expression and prognosis were evaluated by multi-omics and tissue microarray analyses. Tumour microenvironment and immune infiltration were analyzed using ESTIMATE and ssGSEA. Downstream pathways and interacting proteins were identified by transcriptomics, co-immunoprecipitation, and GST pull-down. CDO1 function was assessed by proliferation, apoptosis, and migration assays in gain- and loss-of-function models. In vivo tumorigenesis and CDO1-dependent decitabine efficacy were evaluated by subcutaneous xenografts. Patient-derived organoids were used to assess decitabine sensitivity and 5-FU synergy. RESULTS: Compared with normal controls, CDO1 expression was notably decreased in GC tissues, and its low expression was strongly linked to unfavourable prognosis, supporting its utility as a biomarker for prognosis. Elevated CDO1 levels correlated with an immune-active tumour microenvironment and reduced metastatic signatures. Mechanistically, CDO1 directly bound to PI3K p85α, disrupting p85α-p110α dimerization, thereby attenuating PI3K/AKT phosphorylation and downregulating THBS1 expression. CDO1 overexpression led to reduced proliferation, invasiveness, and EMT, accompanied by increased apoptosis. These effects were reversed by PI3K activation or THBS1 co-overexpression. Decitabine was identified as an agent that epigenetically restores CDO1 expression. Critically, CDO1 knockdown significantly attenuated the anti-tumour efficacy of decitabine in vivo, confirming that decitabine acts primarily through CDO1 reactivation. Decitabine synergized with 5-FU in both organoids and xenografts. CONCLUSIONS: Our data identify CDO1 as both a biomarker for prognosis and a tumour suppressor in gastric cancer. They reveal a CDO1-PI3K/AKT-THBS1 signalling axis and support the epigenetic reactivation of CDO1 by decitabine as a translatable therapeutic strategy. KEY POINTS: CDO1 is frequently downregulated in gastric cancer and serves as an independent favourable prognostic biomarker. CDO1 directly binds PI3K p85α, disrupting p85α-p110α dimerization to suppress the PI3K/AKT-THBS1 signalling axis. Decitabine epigenetically restores CDO1 expression, and its anti-tumour activity is critically CDO1-dependent in vivo. Combining decitabine with 5-FU synergistically overcomes gastric cancer growth in patient-derived organoids and subcutaneous xenograft models.