SLC7A5 promotes colorectal cancer liver metastasis by reprogramming tryptophan metabolism through the Kyn/XANA‒AhR axis and reshaping the immune microenvironment.

backgroundColorectal cancer (CRC) is a leading cause of cancer-related death and is associated with high recurrence rates. Solute carrier family 7 member 5 (SLC7A5), a core transporter that facilitates the transmembrane movement of tryptophan, plays a role in various cancers. However, whether and how SLC7A5 promotes colorectal liver metastasis (CRLM) through tryptophan metabolism reprogramming and immune remodelling remain unexplored.

methodsWe integrated public datasets and clinical specimens to analyse SLC7A5 expression and prognosis, and validated its role in proliferation and metastasis using in vitro assays and in vivo models. Targeted metabolomics and isotope tracing identified kynurenine (Kyn) and xanthurenic acid (XANA) as downstream metabolites of SLC7A5. Single-cell RNA sequencing (scRNA-seq) and conditioned medium experiments were used to assess the impact of SLC7A5 on the tumour immune microenvironment (TIME).

resultsSLC7A5 expression increases sequentially in normal tissue, primary tumours and liver metastases, and higher SLC7A5 levels are associated with worse prognosis. SLC7A5 facilitates CRC cell growth, metastasis and epithelial‒mesenchymal transition (EMT) by promoting the production of Kyn and XANA and subsequent activation of the aryl hydrocarbon receptor (AhR). scRNA-seq analysis and conditioned medium experiments demonstrated that SLC7A5 knockdown reprograms the TIME by driving macrophages towards an antigen-presenting phenotype, alleviating CD8

conclusionsCollectively, our findings reveal that SLC7A5 drives CRLM through tryptophan/Kyn/XANA-AhR signalling and concomitant remodelling of the TIME, positioning SLC7A5 as a promising target for combination therapy with anti-PD-1 in CRLM.