The Tumor Microenvironment Mediates the HIF-1α/PD-L1 Pathway to Promote Immune Escape in Colorectal Cancer.

The unsatisfactory efficacy of immunotherapy for colorectal cancer (CRC) remains a major challenge for clinicians and patients. The tumor microenvironment may promote CRC progression by upregulating the expression of hypoxia-inducing factor (HIF) and PD-L1. Therefore, this study explored the expression and correlation of HIF-1α and PD-L1 in the CRC microenvironment. The expression and correlation of HIF-1α and PD-L1 in CRC were analyzed using bioinformatics and Western blotting (WB). The hypoxia and inflammation of the CRC microenvironment were established in the CT26 cell line. CT26 cells were stimulated with two hypoxia mimics, CoCl2 and DFO, which were used to induce the hypoxic environment. Western blotting was used to assess the expression and correlation of HIF-1α and PD-L1 in the hypoxic environment.LPS stimulated CT26 cells to induce the inflammatory environment. WB and bioinformatics were used to assess the expression and correlation of TLR4, HIF-1α, and PD-L1 in the inflammatory environment. Furthermore, the impact of curcumin on the inflammatory environment established by LPS-stimulated CT26 cells was demonstrated through MTT, Transwell, molecular docking, network pharmacology and Western blotting assays. In this study, we found that the HIF-1α/PD-L1 pathway was activated in the hypoxic and inflammatory environment and promoted immune escape in CRC. Meanwhile, curcumin suppressed tumor immune escape by inhibiting the TLR4/HIF-1α/PD-L1 pathway in the inflammatory environment of CRC. These results suggest that combination therapy based on the HIF-1α/PD-L1 pathway can be a promising therapeutic option and that curcumin can be used as a potent immunomodulatory agent in clinical practice.