DDIT3 inhibition by salvianolic acid B mitigates Fusobacterium nucleatum-mediated chemoresistance to 5-fluorouracil in colorectal cancer.

BACKGROUND

Fusobacterium nucleatum (Fn) drives chemotherapy resistance in colorectal cancer (CRC) by activating hypoxia-mimicking signaling pathways, yet the molecular mechanisms linking Fn to 5-fluorouracil (5-FU) resistance remain unclear. We investigated how Fn-induced hypoxia-related gene expression contributes to 5-FU resistance and identified a pharmacological strategy to overcome it.

METHODS

DEGs from Fn-infected CRC cells (GSE90944) were intersected with GSEA hypoxia-related genes, and Cox regression on TCGA-CRC data prioritized the top candidate, DDIT3. Its role in 5-FU resistance was characterized in vitro by Western blotting, qPCR, cell viability, and flow cytometry. LinkedOmics co-expression analysis mapped DDIT3-associated networks, and Salvia miltiorrhiza constituents were screened for DDIT3 inhibition.

RESULTS

DDIT3 was the most prognostically significant Fn-regulated hypoxia gene in CRC (HR: 1.544 [1.083-2.201], p = 0.016). Fn upregulated DDIT3 and activated the mitochondrial unfolded protein response (mitoUPR), suppressing 5-FU-induced ROS and reducing chemosensitivity; DDIT3 knockdown reversed these effects. A DDIT3-SLC3A2-CARS axis was identified as the key downstream pathway sustaining mitochondrial homeostasis. Salvianolic acid B (SAB) selectively suppressed this axis, restored ROS cytotoxicity, and improved 5-FU chemosensitivity in Fn-infected CRC cells.

CONCLUSIONS

Fn drives 5-FU resistance via DDIT3-mediated mitoUPR activation and ROS suppression through the DDIT3-SLC3A2-CARS axis. SAB disrupts this pathway, providing a rational basis for SAB-5-FU combination therapy in Fn-associated CRC.