Regulation of melatonin on the tumour microenvironment of human pancreatic adenocarcinoma

Abstract

<p> <span>Tumour immune microenvironment is a major reason leading to poor therapeutic response in pancreatic adenocarcinoma (PAAD). Tumour-associated neutrophils (TANs) was reported as an important modulator of tumour immunity in PAAD, however, whether TANs regulation can bepotentially a therapeutic target in PAAD remains unclear. Here we showed that pancreatic melatonin is critical for the regulation of TANs pheno-types and functions in PAAD. Pancreatic melatonin synthesis is suppressed, which correlates the overall survival of PAAD patients. Supplementa-tion of melatonin suppressed the orthotopic growth of pancreatic tumours in murine models, while blockade of melatonin pathway exacerbatedtumour progression. This effect of melatonin was independent to its cytotoxicity to tumour cells but was associated with TANs, and TANs deple-tion abolished the tumour suppressive effect of melatonin. Melatonin induced TANs infiltration and activation in PAAD tumour microenviron-ment, resulting in the induction of cell apoptosis of PAAD cells. The anti-tumour effect of melatonin-induced TANs was independent to cytotoxicT cell activation. Melatonin had minimal effect on neutrophil itself, but induced expression and secretion of CXCL2 from tumour cells as revealedby cytokine arrays. Knockdown of CXCL2 in tumour cells abolished the melatonin-induced neutrophils migration and activation in the co-culturesystem. Melatonin-induced neutrophils are observed to present an N1-like anti-tumour phenotype, with the increased neutrophil extracellulartraps (NETs) formation causing tumour cell apoptosis through cell-to-cell contact. Transcriptomics analysis revealed that sorted TANs frommelatonin-treated PAAD tumour showed increased metabolic pattern of fatty acid metabolism. Induction of fatty acid oxidation (FAO) inducedcellular ROS production in TANs, and presence of FAO inhibitor etomoxir significance block the ROS production as well as NETs formation insorted TANs, and abolished its cytotoxic effect on PAAD cells. Analysis on PAAD patient specimens revealed that CXCL2 expression was associ-ated with neutrophil infiltration in PAAD. Although expression of CXCL2 or NETs marker as individual factor was not correlated with the survivalof PAAD patients, the combination of CXCL2 with NETs marker, as well as the combination of TANs and NET markers can better predict patients'prognosis. In summary, pancreatic melatonin possesses anti-tumour effects on PAAD, by recruiting N1-like neutrophils into the microenvironmentwith beneficial NETs formation. Melatonin may be a potential as an adjacent supplement that benefits the survival of PAAD patients.</span> <br></p>