Gut Microbe Metabolite ILA Blocks Colorectal Cancer by Shutting Down Tumor Energy Supply

Colorectal cancer (CRC) is the second leading cause of cancer death worldwide, and growing evidence links gut microbiome disruption to its progression. This study from Nanjing University investigated whether altered tryptophan (Trp) metabolism — specifically reduced levels of indole-3-lactic acid (ILA) — plays a causal role in CRC development and whether restoring ILA could suppress tumor growth.

The clinical discovery phase enrolled 132 participants (83 CRC patients, 49 healthy controls) whose fecal samples underwent metagenomic shotgun sequencing and targeted Trp metabolomics. CRC patients showed significant shifts in microbial community composition, with Bacteroides and Escherichia enriched in cancer patients, while Bifidobacterium, Lachnospiraceae, and Ruminococcaceae were depleted. Gut Metabolic Module analysis revealed disrupted Trp degradation pathways. Among 26 Trp metabolites measured, fecal ILA was significantly lower in CRC patients, and late-stage (III/IV) patients had even further reductions compared to early-stage patients. Critically, fecal ILA negatively correlated with tumor proliferation marker Ki67 (R²=−0.459, p=0.002, n=35), linking ILA depletion directly to tumor aggressiveness.

In vivo experiments used two mouse models: an AOM/DSS inflammation-driven colorectal adenocarcinoma model and an MC38 xenograft model in C57BL/6 mice. Exogenous ILA administration — both orally and intraperitoneally — significantly reduced tumor number, size, and total tumor load in AOM/DSS mice, with no difference in efficacy between delivery routes. Histological analysis confirmed reduced Ki67 and PCNA staining in ILA-treated tumors. In the xenograft model, ILA treatment significantly slowed tumor volume growth and reduced final tumor weight. Flow cytometry showed increased tumor-infiltrating CD8+ T cells with ILA treatment, consistent with prior immunological findings, though macrophage and MDSC proportions were unchanged.

Mechanistic studies in CRC cell lines (HCT116, SW480, HT29) demonstrated that ILA dose-dependently inhibited proliferation, migration, and colony formation, and promoted apoptosis. Seahorse metabolic flux assays revealed that ILA significantly suppressed glycolysis — reducing extracellular acidification rate (ECAR) — without substantially affecting mitochondrial oxidative phosphorylation. Proteomics and Western blot analyses identified STAT3 phosphorylation (p-STAT3) and its downstream target hexokinase 2 (HK2) as the primary effectors. Molecular docking and cellular thermal shift assays confirmed that ILA directly binds to STAT3 at its phosphorylation sites (Y705 and S727), reducing p-STAT3 levels and consequently downregulating HK2 expression and glucose uptake. Notably, AHR knockdown experiments confirmed this mechanism is AHR-independent, distinguishing ILA's action from other indole metabolites.

These findings establish ILA as a microbiome-derived tumor suppressor that acts through a previously uncharacterized STAT3-HK2-glycolysis axis. The convergence of clinical data, animal models, and mechanistic cell biology makes this a compelling candidate for therapeutic development, though translation to human clinical trials remains the critical next step.