β3‐Adrenoceptor as a potential immuno‐suppressor agent in melanoma

Background and Purpose Stress‐related catecholamines have a role in cancer and β‐adrenoceptors; specifically, β2‐adrenoceptors have been identified as new targets in treating melanoma. Recently, β3‐adrenoceptors have shown a pleiotropic effect on melanoma micro‐environment leading to cancer progression. However, the mechanisms by which β3‐adrenoceptors promote this progression remain poorly understood. Catecholamines affect the immune system by modulating several factors that can alter immune cell sub‐population homeostasis. Understanding the mechanisms of cancer immune‐tolerance is one of the most intriguing challenges in modern research. This study investigates the potential role of β3‐adrenoceptors in immune‐tolerance regulation. Experimental Approach A mouse model of melanoma in which syngeneic B16‐F10 cells were injected in C57BL‐6 mice was used to evaluate the effect of β‐adrenoceptor blockade on the number and activity of immune cell sub‐populations (Treg, NK, CD8, MDSC, macrophages, and neutrophils). Pharmacological and molecular approaches with β‐blockers (propranolol and SR59230A) and specific β‐adrenoceptor siRNAs targeting β2‐ or β3‐adrenoceptors were used. Key Results Only β3‐, but not β2‐adrenoceptors, were up‐regulated under hypoxia in peripheral blood mononuclear cells and selectively expressed in immune cell sub‐populations including Treg, MDSC, and NK. SR59230A and β3‐adrenoceptor siRNAs increased NK and CD8 number and cytotoxicity, while they attenuated Treg and MDSC sub‐populations in the tumour mass, blood, and spleen. SR59230A and β3‐adrenoceptor siRNAs increased the ratio of M1/M2 macrophages and N1 granulocytes. Conclusions and Implications Our data suggest that β3‐adrenoceptors are involved in immune‐tolerance, which opens the way for new strategic therapies to overcome melanoma growth. Linked Articles This article is part of a themed section on Adrenoceptors—New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc