Panaxadiol inhibits programmed cell deathligand 1 expression and tumor proliferation via hypoxia-inducible factor(HIF)-1a and STAT3 in human colon cancer cells

OBJECTIVE To investigate the potential anti-cancer activity of panaxadiol on PD-L1 expression and tumor proliferation in human colon cancer cells and to identify the underlying mechanism. METHODS HCT116, SW620, and HT29 cells were pretreated with panaxadiol(1, 3, 10, 30 μmol·L;) for 48 h to verify cell viability by MTT assay. HCT-116 cells were pretreated with panaxadiol(1, 3, 10 μmol·L;) for 12 h in Western blotting, flow cytometry analysis, and reverse transcription-PCR（RTPCR）. The interaction between panaxadiol and HIF-1α/STAT3 was studied by molecular docking and immunofluorescence. HCT-116/T-cell coculture model and T-cell killing assay were employed to investigated the immunosuppressive of HCT-116 cells. Colony cormation and Ed U labeling assay were performed to detect cell proliferation. Panaxadiol at a dose of 10 and 30 mg·kg;were orally administered in xenografted assay and Immunohistochemical analysis. RESULTS Panaxadiol showed little cytotoxicity according to the result of MTT assay and exerted a potent inhibitory activity against PD-L1 expression both on cell surface and protein/m RNA level in a dose-dependent manner. It was subsequently shown that panaxadiol inhibited STAT3 activation through JAK1,JAK2, and Src pathways. Simultaneously panaxadiol promoted degradation and depressed synthesis of HIF-αprotein induced by hypoxia. Moreover, pretrement of panaxadiol could restore the activity of cytotoxic T lymphocyte（CTL） and regain their capacity of tumor cell killing in a T cell/tumor cell co-culture system. Colony formation and Ed U labeling assays Further demonstrated that panaxadiol inhibited tumor proliferation. The Proliferation inhibitory effect in vivo of panaxadiol was also proved by xenograft assay. CONCLUSION Taken together, these studies reveal previously unknown characteristics of panaxadiol provide new perspectives into the mechanism of cancer inhibition of the compound.