Patchouli alcohol suppresses gastric cancer growth and immune evasion via inhibition of the NF-κB/PD-L1 axis

Objective This study aimed to investigate the anti-gastric cancer effect of Patchouli alcohol (PA), especially its influence on PD-L1-mediated immune evasion, and to elucidate the underlying molecular mechanisms. Methods A CCK-8 assay was used to evaluate the effects of PA on the viability of the gastric cancer cell lines HGC-27 and MKN-45. RT‒qPCR and western blotting were performed to analyze the mRNA and protein levels of NF-κB and PD-L1, respectively. In a coculture system of gastric cancer cells and peripheral blood mononuclear cells (PBMCs), the effect of PA pretreatment on the PBMC-induced apoptosis of cancer cells was analyzed by flow cytometry, and the cytotoxic activity of the PBMCs was assessed by a lactate dehydrogenase (LDH) release assay. Flow cytometry was also used to determine the proportions of CD3⁺CD8⁺ T cells and IFN-γ⁺CD8⁺ T cells. ELISA was used to measure the levels of IFN-γ, TNF-α, and granzyme B in the coculture supernatants. Immunofluorescence staining was conducted to assess NF-κB nuclear translocation. In a mouse xenograft model, tumor volume and weight were measured after 14 days of PA treatment. Histopathological changes and apoptosis were analyzed by HE and TUNEL staining. A luciferase reporter assay was used to examine the transcriptional regulation of PD-L1 by NF-κB. Results PA inhibited the viability of HGC-27 and MKN-45 cells in a dose- and time-dependent manner and significantly downregulated the expression of NF-κB and PD-L1 at both the mRNA and protein levels. In a PBMC coculture model, PA pretreatment enhanced the ability of PBMCs to induce apoptosis and directly kill gastric cancer cells. Furthermore, PA pretreatment increased the proportions of CD3⁺CD8⁺ T cells and IFN-γ⁺CD8⁺ T cells in a dose-dependent manner. Consistent with this immunostimulatory effect, PA increased the levels of IFN-γ, TNF-α, and granzyme B in the coculture supernatants. Mechanistically, western blotting analysis demonstrated that PA significantly reduced the protein levels of AKT, NF-κB, and PD-L1 in gastric cancer cells. Immunofluorescence staining further indicated that PA suppressed the nuclear translocation of NF-κB. In a mouse xenograft model, PA treatment significantly inhibited tumor growth, induced apoptosis, and downregulated NF-κB and PD-L1 protein expression in tumor tissues. Flow cytometry of tumor-infiltrating lymphocytes revealed increased proportions of CD3⁺CD8⁺ and IFN-γ⁺CD8⁺ T cells following PA treatment. Finally, luciferase reporter assays demonstrated that NF-κB directly regulates PD-L1 transcription by binding to its promoter region. Conclusion PA exerts antitumor effects in gastric cancer by suppressing the NF-κB/PD-L1 axis, thereby enhancing CD8⁺ T-cell–mediated cytotoxicity and inhibiting immune evasion.