Acetoacetate–GPR43 axis epigenetically silences IL-6/CSF1 to restrict TAMs-driven metastatic lung cancer

Abstract Background Metastasis remains the principal cause of cancer mortality, with the lungs representing one of the most frequent and clinically challenging sites. The tumor microenvironment, particularly tumor-associated macrophages (TAMs), plays a pivotal role in establishing and maintaining metastatic niches. Yet, how host ketone bodies influence the immune microenvironment to govern metastatic progression is poorly defined. Methods Pan-cancer gene expression analysis on the Home for Researchers platform to assess the activity of enzymes involved in acetoacetate synthesis and catabolism. Two murine metastatic Lung Cancer models were established to evaluate the role of acetoacetate in metastatic progression. Flow cytometry and immunohistochemistry were used to assess immune cell infiltration, particularly TAMs. Molecular modeling, Drug Affinity Responsive Target Stability, Cellular Thermal Shift Assay, receptor activation assays, inhibitor and small interfering RNA experiments were used to examine the interaction between acetoacetate and the G protein-coupled receptor 43 (GPR43). Immunofluorescence, RNA sequencing, quantitative PCR, Transwell, cytokine supplementation, dot and western blotting, methylated DNA immunoprecipitation–qPCR, and enzyme-linked immunosorbent assay were performed to investigate how acetoacetate regulates interleukin-6 (IL-6) and colony-stimulating factor 1 (CSF1), as well as the underlying epigenetic mechanisms. Results We uncover a previously unappreciated collapse of acetoacetate homeostasis in lung cancer, driven by the coordinated suppression of ketogenesis and increased ketolysis, resulting in a systemic acetoacetate deficiency. Restoring acetoacetate significantly limits metastatic lung cancer spread and reduces TAM infiltration within the tumor microenvironment. Mechanistically, we identify acetoacetate as an endogenous ligand for GPR43, linking metabolic sensing to immune regulation. Disruption of GPR43 signaling abolishes the anti-metastatic effects of acetoacetate, confirming a reliance on this pathway. Strikingly, acetoacetate–GPR43 signaling increases methionine adenosyltransferase 2A (MAT2A) and S-adenosylmethionine levels and induces region-specific DNA hypermethylation of pro-inflammatory cytokine genes, including IL6 and CSF1, thereby silencing their transcription. Restoring IL-6 and CSF1 reestablishes TAMs’ proliferation and migration, reactivating a pro-metastatic environment. Conclusions Our findings reveal a novel “metabolic–epigenetic–immune” axis, in which acetoacetate, through GPR43 signaling, reprograms the monocyte epigenome via DNA hypermethylation to suppress pro-metastatic inflammation. This study identifies the acetoacetate–GPR43 axis as a mechanistically grounded, potential therapeutic strategy for metastatic lung cancer and offers new insights into overcoming the limitations of current TAM-targeted therapies.