Oxymatrine reduces expression of programmed death-ligand 1 by promoting DNA demethylation in colorectal cancer cells

ABSTRACT

Background Colorectal cancer (CRC) represents an important neoplasm with high mortality. Although PD-L1/PD-1 system-based immunotherapy has benefits for a certain type of CRC, many efforts should be made to enhance the responses to anti-PD-1/PD-L1 drugs. DNA methylation has been critically implicated in the regulation of tumor immunity. Here, we examined the effects of the natural alkaloid oxymatrine on PD-L1 expression in CRC cells and to elucidate the underlying mechanism. Methods Human CRC SW620 and HCT116 cells were treated with interferon γ (IFNγ) and/or oxymatrine. Cell viability was determined using MTT assays. PD-L1 expression was detected by real-time PCR and Western blot analyses. DNA demethylase activity was measured using kits. Results Oxymatrine did not apparently affect the viability of normal human intestinal epithelial cells. IFNγ at 20 ng/ml increased the viability of CRC cells, but oxymatrine concentration-dependently reduced the viability in the absence or presence of IFNγ. IFNγ increased the mRNA and protein expression of PD-L1 in the two cell lines, but oxymatrine significantly abolished IFNγ-elevated PD-L1 levels at both mRNA and protein levels. Furthermore, DNA demethylase activity was remarkably increased in IFNγ-treated CRC cells, which was abolished by oxymatrine concentration-dependently. In addition, DNA methyltransferase inhibitor 5-azacytidine considerably abrogated oxymatrine-induced downregulation of PD-L1 mRNA and protein levels in IFNγ-stimulated CRC cells. Conclusion Oxymatrine suppressed viability and reduced PD-L1 expression in IFNγ-stimulated CRC cells, which was attributed to enhanced DNA demethylation. Our current discoveries suggested oxymatrine as an epigenetic modulatory agent for immunotherapy against CRC via PD-1/PD-L1 blockade (AU)