Probiotic Metabolites Show Anti-Tumor Effects in Colorectal Cancer Cells

Colorectal cancer remains one of the deadliest malignancies worldwide, and despite advances in surgery, chemotherapy, targeted therapies, and immunotherapy, outcomes for advanced-stage disease remain stubbornly poor. Now, a new study published in Frontiers in Cellular and Infection Microbiology suggests that metabolites derived from probiotic bacteria could offer a novel adjunct strategy by targeting the gut–tumor axis, the intricate communication network linking the intestinal microbiome with tumor progression. Using an ambitious systems biology approach that integrates network pharmacology, transcriptomics, proteomics, metabolomics, and microbiome profiling, researchers led by Haoyu Li of Hankou University, Chunguang Hou of Huangshi Hospital of Traditional Chinese Medicine, and Yan Pan of Hubei Normal University have mapped how twelve probiotic-derived metabolites modulate key molecular pathways in colorectal cancer cells.

The research team began by identifying twelve key metabolites produced by probiotic bacteria, including short-chain fatty acids such as butyrate, acetate, and propionate, indole derivatives like indole-3-acetic acid and indole-3-propionic acid, lactic acid, bacteriocins, hydrogen peroxide, reuterin, exopolysaccharides, and conjugated linoleic acid. These metabolites are low-molecular-weight bioactive molecules that probiotic organisms release into the gut environment, where they can influence epithelial barrier integrity, immune surveillance, and inflammatory signaling. Using computational target prediction databases including SwissTargetPrediction, STITCH, and BindingDB, the researchers predicted 428 putative molecular targets for these metabolites. When intersected with 1,236 colorectal cancer-associated genes compiled from GeneCards, DisGeNET, and OMIM, the analysis revealed 162 overlapping genes representing potential therapeutic targets.

Protein–protein interaction network analysis of these 162 genes, conducted using the STRING database and visualized in Cytoscape, produced a densely connected network of 1,984 edges with an average node degree of 24.5. Topological algorithms identified ten hub genes central to colorectal cancer biology: TP53, AKT1, MAPK1, PIK3CA, NFKB1, TNF, IL6, STAT3, BAX, and CASP3. Functional enrichment analysis confirmed significant involvement of these genes in inflammatory response, apoptotic process, and immune regulation, with Kyoto Encyclopedia of Genes and Genomes pathway analysis highlighting enrichment in NF-κB signaling, PI3K–Akt signaling, MAPK signaling, and apoptosis pathways. These pathways serve as critical nodes linking microbial activity with tumor progression and immune regulation, positioning them as prime targets for microbiome-based interventions.

To validate these computational predictions experimentally, the team treated four human colorectal cancer cell lines—HCT116, HT-29, Caco-2, and SW480—with sodium butyrate at concentrations ranging from 1 to 5 millimolar, along with indole-3-acetic acid at 50 to 200 micromolar, for periods of 24, 48, or 72 hours. Dose-response experiments identified 5 millimolar sodium butyrate as the optimal concentration for inducing significant anti-proliferative and pro-apoptotic effects. At this concentration, cell viability dropped by 42.3 percent in HCT116 cells, 38.7 percent in HT-29 cells, 35.5 percent in Caco-2 cells, and 40.1 percent in SW480 cells after 48 hours, all with p-values below 0.001. Estimated IC50 values ranged from 4.2 to 5.6 millimolar depending on cell type, indicating moderate sensitivity across the panel.

Flow cytometric analysis using Annexin V-FITC and propidium iodide staining revealed a dramatic increase in apoptotic cell populations. Total apoptosis in HCT116 cells rose from 8.6 percent in untreated controls to 32.4 percent following butyrate treatment. Remarkably, when the researchers combined sodium butyrate with indole-3-acetic acid at 100 micromolar, apoptosis climbed to 41.2 percent, suggesting a synergistic pro-apoptotic effect between these two probiotic-derived metabolites. Indole-3-acetic acid alone demonstrated moderate anti-proliferative effects of 20 to 28 percent across the cell lines, but its capacity to amplify butyrate-induced apoptosis points toward the therapeutic potential of metabolite combinations.

Transcriptomic profiling by RNA sequencing identified 1,248 differentially expressed genes, including 652 upregulated and 596 downregulated. Pro-apoptotic genes BAX and CASP3 were upregulated with log2 fold changes of +1.8 to +2.3, while pro-inflammatory genes IL6, TNF, and NFKB1 were significantly downregulated with log2 fold changes of −1.5 to −2.1. Gene set enrichment analysis confirmed suppression of NF-κB signaling and activation of apoptosis pathways. Quantitative proteomics by liquid chromatography–tandem mass spectrometry identified 3,562 proteins, of which 412 were differentially expressed. Key downregulated proteins included AKT1 at −1.6-fold, MAPK1 at −1.4-fold, and EGFR at −1.3-fold, while apoptotic regulators CASP3 and BAX were upregulated at +1.7-fold and +1.5-fold respectively, corroborating the transcriptomic findings and highlighting coordinated suppression of PI3K–Akt and MAPK survival pathways.

Multiplex cytokine profiling using the Luminex xMAP platform demonstrated significant immunomodulatory effects. Pro-inflammatory cytokines IL-6, TNF-α, and IL-1β decreased by 48.2 percent, 44.7 percent, and 39.5 percent respectively, while anti-inflammatory IL-10 increased by 26.3 percent. Untargeted metabolomics identified 186 significantly altered metabolites, with intracellular butyrate levels increasing by 2.8-fold and oxidative stress markers decreasing by approximately 35 percent, suggesting improved cellular redox balance. Pathway analysis indicated modulation of energy metabolism and lipid biosynthesis, consistent with the metabolic reprogramming expected from short-chain fatty acid signaling.

Perhaps most strikingly, 16S rRNA sequencing of microbial communities from an in vitro gut fermentation model revealed substantial restructuring following probiotic metabolite treatment. At the phylum level, Firmicutes increased from 42.3 percent to 51.7 percent and Actinobacteriota from 6.8 percent to 11.4 percent, while Proteobacteria decreased from 18.5 percent to 11.2 percent and Fusobacteriota from 7.6 percent to 4.1 percent. At the genus level, beneficial taxa including Lactobacillus and Bifidobacterium increased by 2.4-fold and 1.9-fold respectively, whereas the colorectal cancer-associated genus Fusobacterium decreased by approximately 41 percent. Alpha diversity, measured by the Shannon index, rose from 2.8 to 3.6, indicating restoration of microbial richness and evenness. Beta-diversity analysis demonstrated clear separation between treated and control communities, confirming treatment-induced restructuring of the microbiota toward a healthier ecosystem.

The integrated multi-omics analysis revealed coordinated regulation across all molecular layers. Butyrate functions as a histone deacetylase inhibitor, promoting epigenetic activation of tumor-suppressive pathways while suppressing pro-inflammatory NF-κB signaling. Indole derivatives contribute to immune modulation by reducing pro-inflammatory cytokine expression and enhancing anti-inflammatory responses through aryl hydrocarbon receptor activation. The convergence of transcriptomic, proteomic, metabolomic, and microbiome data on the NF-κB, PI3K–Akt, MAPK, and apoptosis pathways strengthens the robustness of the findings and provides a systems-level framework for understanding how probiotic-derived metabolites modulate the gut–tumor axis.

Despite these compelling results, the researchers acknowledge important limitations. The study was conducted primarily using in vitro colorectal cancer cell models and lacks validation in clinical patient samples. The absence of in vivo experiments limits assessment of host–microbiome interactions under physiological conditions, and inter-individual variability in microbiome composition, metabolite production, dietary factors, and tumor heterogeneity may influence therapeutic responses. The team notes that future investigations should incorporate animal models, well-characterized clinical cohorts, and patient-derived tumor tissues to confirm the translational relevance of the identified molecular signatures. Nevertheless, by demonstrating that probiotic-derived metabolites can simultaneously suppress tumor cell survival, activate apoptosis, reduce inflammation, and restore beneficial microbial communities, this study provides a novel systems-based strategy for microbiome-informed precision oncology in colorectal cancer management.

Subject of Research: Probiotic Metabolites Show Anti-Tumor Effects in Colorectal Cancer Cells

Article Title: Targeting the gut–tumor axis: probiotic therapy as an adjunct strategy in colorectal cancer treatment

Article References: Li, H., Hou, C., & Pan, Y. (2026). Targeting the gut–tumor axis: probiotic therapy as an adjunct strategy in colorectal cancer treatment. Frontiers in Cellular and Infection Microbiology, 16, Article 1873871. https://doi.org/10.3389/fcimb.2026.1873871

Image Credits: AI Generated

DOI: 10.3389/fcimb.2026.1873871

Keywords: Targeting, tumor, axis, probiotic, therapy, adjunct, strategy, colorectal, cancer, treatment, scientific research