Butein suppresses PD-L1 expression via downregulating STAT1 in non-small cell lung cancer.

ABSTRACT

PD-L1 (programmed cell death ligand 1) is frequently up-regulated in tumors and is critical in tumor immune escape. In addition to antibodies that block the interaction between PD-L1 and PD-1 (programmed cell death protein 1), small-molecule compounds that suppress PD-L1 expression also exhibit significant anti-tumor effects, emerging as a new strategy targeting PD-L1. By using a cell-based screening model, we found that butein, a natural chalcone compound, significantly reduced the cytoplasm and cell surface expression of PD-L1. This effect was further validated in various non-small cell lung cancer (NSCLC) cell lines and primary cells derived from clinical NSCLC tissues. Butein inhibited PD-L1 transcription, but not the half-life of PD-L1 protein. Butein reduced STAT1 level and butein-induced PD-L1 suppression was eliminated by the absence of STAT1. By co-culture system, butein improved tumor elimination by increasing the killing ability of CD8+ T cells. By in vivo study, we further confirmed that butein downregulated PD-L1 expression and improved infiltration of CD8+ T cells in tumor tissues. Taken together, our study suggested that butein could suppress the transcription of PD-L1 via downregulating STAT1, providing a theoretical basis for the application of butein in anti-tumor therapy.