Shared immune perturbations in hepatocellular carcinoma-depression comorbidity and synergistic immunotherapeutic effects of fluoxetine combined with anti-PD-1

Background Hepatocellular carcinoma (HCC) often coexists with depression, elevating patient mortality by 39%. The tryptophan metabolic axis bridges tumor and neuropsychiatric immune dysfunction, yet the immunometabolic crosstalk underlying HCC-depression comorbidity remains poorly defined, and reliable combinatorial immunotherapies are absent. Methods We integrated public multi-omics datasets including TCGA, GEO, eQTLGen and FinnGen, and performed two-sample MR as well as genetic colocalization analyses to screen hub genes associated with HCC-depression comorbidity. GSEA/GSVA, single-cell and spatial transcriptomics were adopted to dissect gene expression and perturbed tryptophan immune pathways. In silico docking predicted fluoxetine binding to BTN3A3, GLCE and RBCK1. A Hepa1-6/CUMS comorbid mouse model combined with targeted tryptophan LC-MS metabolomics, flow cytometry and ELISA was used to verify combined therapeutic effects and tissue molecular alterations. Results Seven overlapping risk genes for HCC and depression were identified. BTN3A3 , GLCE and RBCK1 reached strict colocalization thresholds (SNP.PP.H4 > 0.90) and were predominantly expressed in T cells and M2 macrophages linked to tryptophan metabolism. Fluoxetine displayed stable binding affinity with all three hub proteins via molecular simulation. In vivo assays proved fluoxetine plus anti-PD-1 restrained tumor progression, alleviated depression-like phenotypes, normalized tissue GLCE/RBCK1 levels and restored disordered tryptophan metabolism and immunosuppressive microenvironment in comorbid mice. Conclusions This work characterizes tryptophan-mediated immune disturbance in HCC-depression comorbidity. GLCE and RBCK1 correlate with comorbid immunometabolic disorders. Fluoxetine combined with anti-PD-1 exerts synergistic immunoregulatory effects by reshaping tryptophan-related immune homeostasis, offering a preclinical metabolic immunotherapy strategy for concurrent HCC and depression.