18 F‐FGln PET/CT Imaging of Glutamine Uptake Has Potential for Predicting Immunotherapy Response in Hepatocellular Carcinoma

ABSTRACT We investigated whether glutamine (Gln) uptake, imaged by 18 F‐(2S,4R)‐4‐fluoroglutamine ( 18 F‐FGln) PET/CT, could predict and modulate immunotherapy response in hepatocellular carcinoma (HCC). Analysis of the Cancer Genome Atlas (TCGA)‐Liver Hepatocellular Carcinoma (LIHC) dataset revealed that SLC1A5 expression—which encodes a primary Gln uptake channel in HCC cells—was significantly associated with poor prognosis, higher tumor grade, and an immunosuppressive tumor microenvironment. In murine HCC models, tumors with high 18 F‐FGln uptake exhibited elevated Slc1a5 expression and poor response to anti‐PD‐1 therapy, whereas low‐uptake tumors were more sensitive to immunotherapy. Genetic knockdown of Slc1a5 reduced 18 F‐FGln uptake, enhanced anti‐PD‐1 efficacy, increased cytotoxic T lymphocyte infiltration, and decreased regulatory T cell abundance. Transcriptomic and single‐cell analyses revealed activation of antitumor immune pathways and reprogramming toward an immune‐inflamed phenotype after Slc1a5 suppression. V‐9302 decreased tumor Gln uptake, as measured by 18 F‐FGln PET/CT, and sensitized HCC to PD‐1 blockade. In patient‐derived organoid‐T cell co‐culture systems, low‐SLC1A5 organoids were susceptible to PD‐1 blockade, whereas high‐SLC1A5 organoids were resistant, consistent with 18 F‐FGln PET/CT findings. These results identify Gln uptake as a checkpoint of immune evasion in HCC and support that 18 F‐FGln PET/CT has the potential to predict and monitor immunotherapy response.