Targeting OXCT1-mediated ketone metabolism reprograms macrophages to promote antitumor immunity via CD8+ T cells in hepatocellular carcinoma

Abstract

Background & aims: The liver is the main organ of ketogenesis, while ketones are mainly metabolized in peripheral tissues via the critical enzyme OXCT1. We previously found that ketolysis is reactivated in hepatocellular carcinoma (HCC) cells through OXCT1 expression to promote tumor progression; however, whether OXCT1 regulates antitumor immunity remains unclear.

Methods: To investigate the expression pattern of OXCT1 in hepatocellular carcinoma in vivo, we conducted multiplex immunohistochemistry (mIHC) experiments on human HCC specimens. To explore the role of OXCT1 in mouse hepatocellular carcinoma tumor-associated macrophages (TAMs), we generated LysM^creOXCT1^f/f (OXCT1 conditional knockout in macrophages) mice.

Results: Here, we found that inhibiting OXCT1 expression in tumor-associated macrophages reduced CD8⁺ T-cell exhaustion through the succinate-H3K4me3-Arg1 axis. Initially, we found that OXCT1 was highly expressed in liver macrophages under steady state and that OXCT expression was further increased in TAMs. OXCT1 deficiency in macrophages suppressed tumor growth by reprogramming TAMs toward an antitumor phenotype, reducing CD8⁺ T-cell exhaustion and increasing CD8⁺ T-cell cytotoxicity. Mechanistically, high OXCT1 expression induced the accumulation of succinate, a byproduct of ketolysis, in TAMs, which promoted Arg1 transcription by increasing the H3K4 trimethylation (H3K4me3) level in the Arg1 promoter. In addition, Pimozide, an inhibitor of OXCT1, suppressed Arg1 expression as well as TAM polarization toward the protumor phenotype, leading to decreasing CD8⁺ T-cell exhaustion and deceleration of tumor growth. Finally, high expression of OXCT1 in macrophages was positively associated with poor survival in HCC patients.

Conclusions: In conclusion, our results demonstrate that OXCT1 epigenetically suppresses antitumor immunity, suggesting that suppressing OXCT1 activity in TAMs is an effective approach for treating liver cancer.

Impact and implications: The intricate metabolism of liver macrophages plays a critical role in shaping HCC progression and immune modulation. Targeting macrophage metabolism to counteract immune suppression presents a promising avenue for HCC. Here, we found that ketogenesis gene OXCT1 was highly expressed in tumor-associated macrophages and promoted tumor growth by reprogramming TAMs toward a protumor phenotype. And the strategic pharmacological intervention or genetic downregulation of OXCT1 in TAMs enhances the antitumor immunity and decelerated tumor growth. Our results suggest that suppressing OXCT1 activity in TAMs is an effective approach for treating liver cancer.

Keywords: CD8(+) T cell; Hepatocellular carcinoma; Macrophage reprogramming; OXCT1; Pimozide.