Immunoregulatory role of melatonin in cancer.

Melatonin is a ubiquitous indole amine that plays a fundamental role in the regulation of the biological rhythm. Disrupted circadian rhythm alters the expression of clock genes and deregulates oncogenes, which finally promote tumor development and progression. An evidence supporting this notion is the higher risk of developing malignancies among night shift workers. Circadian secretion of the pineal hormone also synchronizes the immune system via a reciprocal association that exists between the immune system and melatonin. Immune cells are capable of melatonin biosynthesis in addition to the expression of its receptors. Melatonin induces big changes in different immune cell proportions, enhances their viability and improves immune cell metabolism in the tumor microenvironment. These effects might be directly mediated by melatonin receptors or indirectly through alterations in hormonal and cytokine release. Moreover, melatonin induces apoptosis in tumor cells via the intrinsic and extrinsic pathways of apoptosis, while it protectsthe immune cells. In general, melatonin has a profound impact on immune cell trafficking, cytokine production and apoptosis induction in malignant cells. On such a basis, using melatonin and resynchronization of sleep cycle may have potential implications in immune function enhancement against malignancies, which will be the focus of the present paper.