Abstract
Metabolic reprogramming is essential for colorectal cancer (CRC) progression, and recent studies have pointed to tryptophan metabolism as a crucial modulator of the tumor immune microenvironment. In this study, we performed untargeted metabolomics analyses and identified significant differences between CRC tissues and matched adjacent tissues, highlighting alterations in tryptophan metabolism. Targeted metabolomics, combined with public single-cell RNA sequencing datasets, further validated enhanced tryptophan metabolism activity in CRC, correlating closely with tumor purity and poor patient prognosis. Using multiple machine learning algorithms, we developed and validated a prognostic risk model based on key tryptophan metabolism-related genes across several independent cohorts. Single-cell transcriptomic analyses also revealed a distinct tumor cell subcluster (C1), characterized by elevated tryptophan metabolism and associated with tumor progression. Additionally, increased tryptophan metabolism correlated positively with M2 macrophage infiltration, and our in vitro co-culture assays confirmed that CRC cell-derived tryptophan metabolites could directly induce M2 macrophage polarization. Together, these results indicate that tryptophanmetabolism is pivotal in CRC development and immune escape, presenting potential novel targets for therapeutic intervention.