EGCG Inhibits Tumor Growth in Melanoma by Targeting JAK-STAT Signaling and Its Downstream PD-L1/PD-L2-PD1 Axis in Tumors and Enhancing Cytotoxic T-Cell Responses

Abstract

Over the last decade, therapies targeting immune checkpoints, such as programmed death-1 (PD-1), have revolutionized the field of cancer immunotherapy. However, low response rates and immune-related adverse events remain a major concern. Here, we report that epigallocatechin gallate (EGCG), the most abundant catechin in green tea, inhibits melanoma growth by modulating an immune response against tumors. In vitro experiments revealed that EGCG treatment inhibited interferon-gamma (IFN-γ)-induced PD-L1 and PD-L2 expression and JAK-STAT signaling. We confirmed that this effect was driven by inhibiting STAT1 gene expression and STAT1 phosphorylation, thereby downregulating the PD-L1/PD-L2 transcriptional regulator IRF1 in both human and mouse melanoma cells. Animal studies revealed that the in vivo tumor-inhibitory effect of EGCG was through CD8+ T cells and that the inhibitory effect of EGCG was comparable to anti-PD-1 therapy. However, their mechanisms of action were different. Dissimilar to anti-PD-1 treatment that blocks PD-1/PD-L1 interaction, EGCG inhibited JAK/STAT signaling and PD-L1 expression in tumor cells, leading to the re-activation of T cells. In summary, we demonstrate that EGCG enhances anti-tumor immune responses by inhibiting JAK-STAT signaling in melanoma. EGCG could be used as an alternative treatment strategy to target the PD-L1/PD-L2-PD-1 axis in cancers.

Modern aspects of the use of natural polyphenols in tumor prevention and therapy

“…In transformed cells, EGCG activates a mitochondria-mediated pathway of cell death, accompanied by the generation of ROS, a decrease in the transmembrane mitochondrial potential, and the release of apoptotic proteins ( Min and Kwon, 2014 ). Similar results have been obtained in pancreatic cancer, lung cancer, colon cancer, and melanoma cell lines, as well as in breast cancer xenograft animal models ( Gan et al, 2018 ; Khan and Mukhtar, 2018 ; Ravindran Menon et al, 2021 ; Romano and Martel, 2021 ). At concentrations of 5–20 μM, EGCG induced apoptosis only in melanoma cells, without any toxic effect on normal melanocytes ( Ravindran Menon et al, 2021 ).…”

“…Similar results have been obtained in pancreatic cancer, lung cancer, colon cancer, and melanoma cell lines, as well as in breast cancer xenograft animal models ( Gan et al, 2018 ; Khan and Mukhtar, 2018 ; Ravindran Menon et al, 2021 ; Romano and Martel, 2021 ). At concentrations of 5–20 μM, EGCG induced apoptosis only in melanoma cells, without any toxic effect on normal melanocytes ( Ravindran Menon et al, 2021 ). At concentrations of 10–80 mg/ml, EGCG induced apoptosis in hepatocellular carcinoma cells, but not in the normal liver cells ( Sojoodi et al, 2020 ).…”

Current insight into the regulation of PD-L1 in cancer

“…For example, in CHL and primary mediastinal large B-cell lymphoma (PMBCL), gp24.1 amplification increases PD-L1 expression and its induction by the JAK2-STAT1-IRF1 signaling pathway [ 33 ]. Moreover, in melanoma, epigallocatechin gallate decreases PD-L1 expression by restraining STAT1 gene expression and phosphorylation followed by downregulation of IRF1 expression [ 34 ]. The JAK inhibitor JAKi was used in HNSCC cells to block STAT1 phosphorylation, thereby inhibiting the increase in PD-L1 mRNA levels induced by combined 5-FU and IFN-γ treatment [ 35 ].…”

Anticarcinogenic potentials of tea catechins

“…PD-L1 was induced by epidermal growth factor (EGF) and interferon γ (IFN-γ). Studies were showing that EGCG could regulate the expression of PD-L1 by inhibiting the phosphorylation of STAT and preventing the Janus kinase (JAK)-STAT signaling pathway from activating the transcription factor of PD-L1/PD-L2 ( 125 ). PD-L1 mRNA level can also be controlled through the EGFR-Akt signaling pathway ( 124 ).…”