See Covering the Cover synopsis on page 2; See editorial on page 38.BACKGROUND AND AIMS: Dietary fat intake is associated with increased risk of colorectal cancer (CRC). We examined the role of high-fat diet (HFD) in driving CRC through modulating gut microbiota and metabolites. METHODS: HFD or control diet was fed to mice littermates in CRC mouse models of an azoxymethane (AOM) model and Apc min/þ model, with or without antibiotics cocktail treatment. Germ-free mice for fecal microbiota transplantation were used for validation. Gut microbiota and metabolites were detected using metagenomic sequencing and high-performance liquid chromatography-mass spectrometry, respectively. Gut barrier function was determined using lipopolysaccharides level and transmission electron microscopy. RESULTS: HFD promoted colorectal tumorigenesis in both AOMtreated mice and Apc min/þ mice compared with control diet-fed mice. Gut microbiota depletion using antibiotics attenuated colon tumor formation in HFD-fed mice. A significant shift of gut microbiota composition with increased pathogenic bacteria Alistipes sp. Marseille-P5997 and Alistipes sp. 5CPEGH6, and depleted probiotic Parabacteroides distasonis, along with impaired gut barrier function was exhibited in HFD-fed mice. Moreover, HFDmodulated gut microbiota promotes colorectal tumorigenesis in AOM-treated germ-free mice, indicating gut microbiota was essential in HFD-associated colorectal tumorigenesis. Gut metabolites alteration, including elevated lysophosphatidic acid, which was confirmed to promote CRC cell proliferation and impair cell junction, was also observed in HFD-fed mice. Moreover, transfer of stools from HFD-fed mice to germ-free mice without interference increased colonic cell proliferation, impaired gut barrier function, and induced oncogenic genes expression. CONCLUSIONS: HFD drives colorectal tumorigenesis through inducing gut microbial dysbiosis, metabolomic dysregulation with elevated lysophosphatidic acid, and gut barrier dysfunction in mice.

Author names in bold designate shared co-first authorship.

Insufficient T cell infiltration into noninflamed tumors, such as hepatocellular carcinoma (HCC), restricts the effectiveness of immune-checkpoint blockade (ICB) for a subset of patients. Epigenetic therapy provides further opportunities to rewire cancer-associated transcriptional programs, but whether and how selective epigenetic inhibition counteracts the immune-excluded phenotype remain incompletely defined. Here, we showed that pharmacological inhibition of histone deacetylase 8 (HDAC8), a histone H3 lysine 27 (H3K27)–specific isozyme overexpressed in a variety of human cancers, thwarts HCC tumorigenicity in a T cell–dependent manner. The tumor-suppressive effect of selective HDAC8 inhibition was abrogated by CD8+ T cell depletion or regulatory T cell adoptive transfer. Chromatin profiling of human HDAC8-expressing HCCs revealed genome-wide H3K27 deacetylation in 1251 silenced enhancer-target gene pairs that are enriched in metabolic and immune regulators. Mechanistically, down-regulation of HDAC8 increased global and enhancer acetylation of H3K27 to reactivate production of T cell–trafficking chemokines by HCC cells, thus relieving T cell exclusion in both immunodeficient and humanized mouse models. In an HCC preclinical model, selective HDAC8 inhibition increased tumor-infiltrating CD8+ T cells and potentiated eradication of established hepatomas by anti–PD-L1 therapy without evidence of toxicity. Mice treated with HDAC8 and PD-L1 coblockade were protected against subsequent tumor rechallenge as a result of the induction of memory T cells and remained tumor-free for greater than 15 months. Collectively, our study demonstrates that selective HDAC8 inhibition elicits effective and durable responses to ICB by co-opting adaptive immunity through enhancer reprogramming.