The role of tumor-derived lipid metabolites in the immune microenvironment of hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality worldwide, characterized by complex molecular alterations and immunosuppressive tumor microenvironment (TME) formation. Recent studies have highlighted the critical role of lipid metabolic reprogramming in shaping TME, promoting tumor progression, and resistance to immune checkpoint blockades (ICBs) therapy. However, the crosstalk regulators between tumor cells and immune cells, rewiring the anti-tumor immunity in HCC TME remain poorly understood. Here, we used liquid chromatography-mass spectrometry (LC-MS/MS) to investigate the profile of lipid metabolites in tumor interstitial fluids (TIF) reflecting the nutrient availability and accumulation of tumor-derived metabolites from TME. Compared to paired-non-tumor TIF, arachidonic acid (ARA), one of the omega-6 polyunsaturated fatty acids (PUFA), was remarkably accumulated in TME. In addition, we reported that hepatic FADS1 expression was significantly upregulated in HCC tissues and was associated with increased levels of ARA in HCC TME. Utilizing a hepatic Fads1 knockout (KO) model, we found that the absence of Fads1 led to a marked reduction in ARA levels in tumor TIF, effectively reshaping the HCC microenvironment from 'cold'—characterized by immune evasion and suppression—to 'hot,' which was associated with enhanced CD8+ T cells infiltration and activation. Notably, FADS1 inhibition mediated by selective inhibitor D5D-IN-326 or a recombinant adeno-associated virus 8 (AAV8) with FADS1 shRNAs exhibited an increased presence and functionality of CXCR6+ tissue-resident memory (TRM) CD8+ T cells using high-parameter flow cytometry. Unexpectedly, the ARA metabolism pathway, screened by pooled CRISPR-Cas9 library targeting 3,017 metabolic genes, as a disadvantageous factor inhibited the formation of liver TRM in the lymphocytic choriomeningitis virus (LCMV) infection model. Further investigation revealed that ARA selectively mediated the metabolic dysfunction of CXCR6+ TRM induced by interleukin-15 (IL-15), a cytokine involved in maintaining the mitochondrial respiration of memory CD8+ T cells. This metabolic dysregulation was characterized by disrupted OXPHOS, leading to reduced anti-tumor immunity and persistence of CXCR6+ TRM. By targeting FADS1, we were able to rebuild the metabolic fitness of CXCR6+ TRM by reducing the ARA accumulation in the HCC microenvironment. From a clinical perspective, the positive correlation between FADS1 and ARA level in TIF was validated, which showed the negative association with CXCR6+ TRM infiltration; moreover, we established the model combining normalized FADS1 expression score and CXCR6+ TRM density to predict the prognosis of HCC patients (n = 89). Importantly, our findings suggested that inhibiting FADS1 not only modulated lipid metabolism but also served as a potential strategy to enhance the efficacy of immunotherapies in HCC. Specifically, FADS1 inhibition was found to synergize with anti-programmed cell death protein 1 (anti-PD-1) therapy and glypican-3 chimeric antigen receptor T (GPC3-CAR-T) cell therapy, both of which were emerging therapeutic approaches in HCC. The combination of FADS1 inhibition with these immunotherapies resulted in improved tumor suppression and prolonged survival of pre-clinical HCC mouse models. In conclusion, our study uncovers a novel link between lipid metabolic reprogramming and immune modulation in HCC. Targeting FADS1 offers a promising approach to enhance anti-tumor immunity and improve the efficacy of existing immunotherapies, providing a new selection for therapeutic intervention in HCC.