Int J Cancer. 2021 Aug 30. doi: 10.1002/ijc.33786. Online ahead of print.
ABSTRACT
Acidity in the tumor microenvironment has been reported to promote cancer growth and metastasis. In this study, we examined a potential relation between extracellular acidity and expression level of the immune checkpoint molecule PD-L1 in murine squamous cell carcinoma (SCC) and melanoma cell lines. PD-L1 expression in the tumor cells was upregulated by culturing in a low pH culture medium. Tumor-bearing mice were allowed to ingest sodium bicarbonate, resulting in neutralization of acidity in the tumor tissue, a decrease in PD-L1 expression in tumor cells, and suppression of tumor growth in vivo. Proton-sensing G protein-coupled receptors (GPCRs), T cell death-associated gene 8 (TDAG8) and ovarian cancer G-protein-coupled receptor 1 (OGR1), were upregulated by low pH, and essentially involved in the acidity-induced elevation of PD-L1 expression in the tumor cells. Human head and neck SCC RNAseq data from the Cancer Genome Atlas also suggested a statistically significant correlation between expression levels of the proton sensors and PD-L1 mRNA expression. These findings strongly suggest that neutralization of acidity in tumor tissue may result in reduction of PD-L1 expression, potentially leading to inhibition of an immune check point and augmentation of anti-tumor immunity.
PMID:34460096 | DOI:10.1002/ijc.33786
