Regulation of PD-L1 Expression by SAHA-Mediated Histone Deacetylase Inhibition in Lung Cancer Cells

Background/Objectives: The effects of PD-L1 are mediated via its binding to the PD-1 receptor, which mediates the signals intracellularly to suppress T-cell responses. The expression levels of PD-L1 on cancer cells are an important indicator of immunosuppression and cause poor prognosis in several types of cancers. Therefore, the identification and characterization of mechanisms that regulate the expression of PD-L1 in cancer patients is very critical. Method: Our experiment was designed to determine the impact of histone deacetylase (HDAC) inhibitor on PD-L1 expression to reverse tumor-induced immunosuppression using H460 and HCC827 lung cancer cell lines. These cells were treated with the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). PD-L1 expression levels were assessed along with key regulatory proteins, including p53, p21, acetyl-histones, DNMT3B, MGMT, and trimethyl histones. Results: In our experiments, suberoylanilide hydroxamic acid (SAHA) was able to reduce the expression of PD-L1 by 60% in a dose-dependent manner. While the level of PD-L1 was significantly reduced, a concurrent increase in levels of p53, p21, and acetyl histone levels were observed in H460 and HCC827 cells following SAHA treatment. Furthermore, SAHA treatment was able to decrease the levels of DNMT3B, MGMT, and tri-methyl histones. It appears that the decrease in PD-L1 expression observed is solely because of p53 or p21WAF1/CIP1-mediated negative control on the transcription process. Conclusion: Our results suggest that SAHA can be used along with immune checkpoint inhibitors to potentiate the therapeutic outcomes in patients with excessive immunosuppression due to PD-L1 expression.