Intratumoral Bacillus regulating colorectal cancer liver metastasis: links to lipid metabolism and APOE+ macrophages

Vollständiger Abstract

Worum geht es in dieser Arbeit?

Introduction Colorectal cancer liver metastasis (CRLM) develops in a hepatic niche where tumor cells encounter organ‑specific microbial, metabolic, and immune constraints. The role of intratumoral bacteria in this metastatic ecosystem remains incompletely defined. Methods We analyzed tumor and peritumoral tissues from 20 patients with non‑metastatic colorectal cancer (CRC) and 20 patients with CRLM by 5R 16S rDNA sequencing, untargeted metabolomics, and functional assays. Public datasets were used for single‑cell analysis of the tumor immune microenvironment. Results Primary colorectal lesions and paired liver metastases showed distinct microbial structures. Liver metastatic lesions had lower microbial diversity, and 73 genera differed between CRLM primary tumors and liver metastases. Bacillus was enriched in metastatic tumors and was associated with fatty‑acid‑related microbial pathways, serum CEA and CA19‑9 levels, and lipid‑related metabolites that accumulated in liver metastases. Bacillus supernatant increased SW480 and SW620 cell migration and proliferation in vitro , with the strongest activity at a multiplicity of infection (MOI)‑equivalent of 20. In an intrasplenic CRLM model, viable Bacillus and Bacillus supernatant increased metastatic tumor growth, whereas antibiotic intervention reduced this effect. Metabolomic profiling detected enrichment of lipids and lipid‑like molecules, including carnitine‑ and bile‑acid‑related metabolites, in liver metastatic lesions. Single‑cell analysis of public datasets showed remodeling of the tumor immune microenvironment (TIME) and identified APOE⁺ macrophages as lipid‑associated myeloid cells with broad ligand‑receptor communication with epithelial, immune, and stromal compartments. Discussion Together, these findings provide evidence that Bacillus promotes metastatic phenotypes and reveal associations among intratumoral Bacillus , lipid‑related metabolic alterations, and APOE + macrophage‑associated communication signatures in CRLM.