The melanocortin MC1 receptor agonist BMS-470539 inhibits leucocyte trafficking in the inflamed vasculature

Background and purpose: Over three decades of research evaluating the biology of melanocortin (MC) hormones and synthetic peptides, activation of the MC type 1 (MC1) receptor has been identified as a viable target for the development of novel anti-inflammatory therapeutic agents. Here, we have tested a recently described selective agonist of MC1 receptors, BMS-470539, on leucocyte/post-capillary venule interactions in murine microvascular beds. Experimental approach: Intravital microscopy of two murine microcirculations were utilized, applying two distinct modes of promoting inflammation. The specificity of the effects of BMS-470539 was assessed using mice bearing mutant inactive MC1 receptors (the recessive yellow e/e colony). Key results: BMS-470539, given before an ischaemia-reperfusion protocol, inhibited cell adhesion and emigration with no effect on cell rolling, as assessed 90 min into the reperfusion phase. These properties were paralleled by inhibition of tissue expression of both CXCL1 and CCL2. Confocal investigations of inflamed post-capillary venules revealed immunostaining for MC1 receptors on adherent and emigrated leucocytes. Congruently, the anti-inflammatory properties of BMS-470539 were lost in mesenteries of mice bearing the inactive mutant MC1 receptors. Therapeutic administration of BMS-470539 stopped cell emigration, but did not affect cell adhesion in the cremasteric microcirculation inflamed by superfusion with platelet-activating factor. Conclusions and implications: Activation of MC1 receptors inhibited leucocyte adhesion and emigration. Development of new chemical entities directed at MC1 receptors could be a viable approach in the development of novel anti-inflammatory therapeutic agents with potential application to post-ischaemic conditions.