Blocking TCA Cycle Enhances T Cell Antitumor Response by Inhibiting the Thrombospondin 2 Signaling Pathway Associated With Endoplasmic Reticulum Stress

PURPOSE The tricarboxylic acid (TCA) cycle occurs within the mitochondrial matrix plays a critical role in mitochondrial metabolism, providing energy essential for tumor cell proliferation and survival. Despite its significance, there is currently no established connection between the tumor cell TCA cycle and the immune response within the tumor microenvironment. In this study, we use head and neck squamous cell carcinoma (HNSCC) cells as a research model to investigate the role of tumor cell TCA cycle in regulating antitumor immunity. METHODS CPI-613 (devimistat), a novel systemic therapeutic that targets the TCA cycle by inhibiting pyruvate dehydrogenase (PDH) and ketoglutarate dehydrogenase (KGDH), was used to treat HNSCC cells. MOC2 ER-BioIDHA cells was generated by transfecting MOC2 cells with ER-BioIDHA construct. Conditioned medium (CM) from cells with or without CPI-613 treatment were collected and incubated with streptavidin beads, followed by liquid chromatography-mass spectrometry (LC/MS) analysis. Molecular alterations were examined by Western blotting and immunohistochemistry. Immune response was assessed by flow cytometry. RESULTS Our LC/MS results demonstrate that CPI-613 effectively prevents HNSCC cells from secreting thrombospondin-2 (THBS2), a glycoprotein strongly associated with poor prognosis and immune evasion in HNSCC patients. Mechanistically, CPI-613 induces endoplasmic reticulum (ER) stress and triggers the expression level of XBP1s, which transcriptionally suppresses the expression of THBS2 gene. In addition, THBS2 interacts with the membrane protein CD36 presented on the intratumoral CD8+ T cells and activates the downstream signaling pathways of AKT and AMPK. This activation, in turn, enhances the T cell-mediated antitumor immunity. CONCLUSION Our research uncovers a novel mechanism whereby CPI-613 enhances the immune response through the inhibition of THBS2 signaling associated with ER stress. These findings offer insights into the immunomodulatory effects of TCA cycle inhibition and establish a robust basis for considering CPI-613 as a promising treatment strategy for HNSCC.