Background Cholangiocarcinoma (CCA) is an aggressive malignancy of the biliary tract that carries an unfavorable prognosis. Recurrent, hotspot mutations in the IDH1 gene are found in 10–20% of CCAs and can be targeted with mutant IDH1 inhibitors, though objective responses leading to a reduction in tumor size are rare.1 2 Mutant IDH1 has neomorphic enzymatic activity that results in the production of the oncometabolite D-2-hydroxyglutarate (D-2-HG).3 D-2-HG promotes biliary tumor formation through cancer cell-intrinsic effects,4–6 but D-2-HG can also act as a paracrine factor released by IDH1-mutant cancer cells into the tumor microenvironment to promote tumor growth through non-cell intrinsic mechanisms.7 8 We have performed studies to determine the paracrine effects of D-2-HG on fibroblasts to further examine the CCA tumor microenvironment.
Methods To determine if fibroblasts are paracrine targets of D-2-HG in the CCA TME, we treated LX-2 hepatic stellate fibroblast cells with 0–50mM exogenous D-2-HG and utilized liquid chromatography-mass spectrometry to quantify the amount of intracellular D-2-HG. D-2-HG treated LX-2 fibroblasts and controls were then examined for changes in gene expression across 579 immune-related genes using the Nanostring platform. In partnership with Tempus, bulk RNA sequencing of IDH1-mutant (N=52) and wild type (N=403) CCA patient tumor samples was performed and CIBERSORT was used for deconvolution of gene expression data to define tumor-infiltrating immune cell populations.
Results Intracellular D-2-HG was increased in LX-2 cells treated with exogenous D-2-HG compared to controls (figure 1A). D-2-HG treated fibroblasts showed significant changes in immune-related gene expression with significant increases in expression of genes involved in immunometabolism, TLR signaling, and inflammasome signaling—as indicated by unsupervised hierarchical clustering (figure 1B). The most upregulated gene in D-2-HG-conditioned LX-2 fibroblasts is SPP1 (figure 1C). We further identified that human IDH1-mutant CCA samples have a unique tumor immune microenvironment (figure 2A) and a significantly higher number of infiltrating M2 macrophages compared to wild-type controls (figure 2B).
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