Curcumin enhances breast cancer cell death by suppressing PD-L1 expression

Background: To investigate the effects of curcumin on the growth of breast cancer (BC) cells in vitro and to explore the role of Programmed death ligand 1 (PD-L1) in this process. Methods: Curcumin’s effects on the growth and apoptosis of MCF-7 and MDA-MB-231 breast cancer cells were assessed using cell counting kit-8 (CCK-8), flow cytometry and Western blotting. The inhibition of PD-L1 expression by curcumin was evaluated through co-transfection of PGL3-PD-L1 plasmids and luciferase activity. Additionally, the Phosphatidylinositol 3-Kinase (PI3K)/Protein Kinase B (AKT)/mechanistic target of rapamycin (mTOR) pathway was analyzed after treatment with curcumin and the PD-L1 inhibitor BMS202. Results: Curcumin had anti-proliferative and pro-apoptosis effects on human breast cancer cells. Curcumin significantly inhibited the expression level of both the PD-L1 protein and the PD-L1 mRNA in BC cells. The abundance of PD-L1 transcripts in the BC cells with curcumin decreased significantly, but increased with the increase in curcumin concentration. The activity of luciferase significantly decreased with the increase in concentration of the breast cancer cells transfected with PD-L1 promoter after treatment with curcumin. Curcumin also induced the inhibition of PD-L1 expression, and mediates the inhibition of the PI3K/AKT/mTOR axis. Conclusions: The combination of curcumin and PD-L1 inhibits the proliferation of BC cells and induces apoptosis, which may be related to curcumin’s inhibition of the activity of PD-L1 promoter and the downstream PI3K/AKT/mTOR axis.