Metabolome–Microbiome Reprogramming Under Circadian Disruption Accelerates Mammary Tumorigenesis

Background Circadian rhythm disruption (CRD), common in shift work and jet lag, is associated with aggressive breast cancer, yet the mechanisms linking circadian misalignment to tumor progression remain poorly understood. We investigated how CRD reshapes tumor immunometabolism and the intratumoral microbiome to promote immune evasion and metastasis. Methods Using a murine model of mammary tumorigenesis maintained under standard light–dark (LD) or CRD conditions, we performed untargeted metabolomics, 16S rRNA sequencing, flow cytometry, and integrative microbiome–metabolome modeling (MIMOSA2). Pharmacologic inhibition of arginase-1 (ARG1) was evaluated using nor-NOHA. Human breast cancer datasets and tumor samples were analyzed to assess clinical relevance. Results CRD significantly increased tumor burden and lung metastasis and induced extensive metabolic reprogramming within the tumor microenvironment. Immunosuppressive metabolites—including kynurenic acid, adenosine, xanthurenic acid, lactate, spermidine, and argininosuccinic acid—were markedly elevated, converging on the arginine–polyamine axis and driving ARG1 upregulation. ARG1 inhibition restored CD8⁺ T-cell infiltration, reduced immunosuppressive myeloid populations, and significantly decreased lung metastases. CRD also altered the intratumoral microbiome, enriching Firmicutes, Bacteroidetes, and Bacilli—taxa capable of producing or accumulating polyamines. Integrative analysis identified microbiome-driven regulation of key metabolites, including kynurenine and citrulline. Human tumor analyses confirmed associations between these microbial signatures, immune-modulatory pathways, and poor survival. Conclusions CRD promotes breast cancer progression through coordinated metabolic–microbial dysregulation that establishes an immunosuppressive tumor microenvironment. Targeting ARG1 and immunometabolic pathways may offer therapeutic opportunities for circadian disruption–associated breast cancer.