Tubeimoside-1 induces TFEB-dependent lysosomal degradation of PD-L1 and promotes antitumor immunity by targeting mTOR

Programmed cell death ligand 1(PD-L1)/programmed cell death protein 1(PD-1)cascade is an effective therapeutic target for immune checkpoint blockade(ICB)therapy.Targeting PD-L1/PD-1 axis by small-molecule drug is an attractive approach to enhance antitumor immunity.Using flow cytometry-based assay,we identify tubeimoside-1(TBM-1)as a promising antitumor immune modulator that negatively regulates PD-L1 level.TBM-1 disrupts PD-1/PD-L1 interaction and enhances the cytotoxicity of T cells toward cancer cells through decreasing the abundance of PD-L1.Furthermore,TBM-1 exerts its antitumor effect in mice bearing Lewis lung carcinoma(LLC)and B16 melanoma tumor xenograft via activating tumor-infiltrating T-cell immunity.Mechanistically,TBM-1 triggers PD-L1 lysosomal degradation in a TFEB-dependent,autophagy-independent pathway.TBM-1 selectively binds to the mammalian target of rapamycin(m TOR)kinase and suppresses the activation of m TORC1,leading to the nuclear translocation of TFEB and lysosome biogenesis.Moreover,the combination of TBM-1 and anti-CTLA-4 effectively enhances antitumor T-cell immunity and reduces immunosuppressive infiltration of myeloid-derived suppressor cells(MDSCs)and regulatory T(Treg)cells.Our findings reveal a previously unrecognized antitumor mechanism of TBM-1 and represent an alternative ICB therapeutic strategy to enhance the efficacy of cancer immunotherapy.