Abstract
In many acute and chronic inflammatory disorders, recruitment of neutrophils plays a critical role in preventing disease severity and ensuring survival. On the other hand, neutrophil accumulation during inflammation can also favor disease progression in conditions such as autoimmune disorders and cancer or during ischemia-reperfusion injury. Therefore, blocking neutrophil influx has been considered an interesting therapeutic concept in diseases with overwhelming neutrophil responses. Using several in vivo and in vitro approaches we investigated the mode of action of ladarixin, a dual non-competitive inhibitor of chemokine receptors CXCR1 and CXCR2, in blocking neutrophil recruitment during inflammation. Examining neutrophil recruitment both in vivo in the mouse cremaster muscle via intravital microscopy and in vitro via flow chamber assays, we investigated the biological significance of the functional selectivity of the allosteric inhibitor, showing that ladarixin blocks neutrophil extravasation selectively at the level of vascular basement membrane penetration, a prerequisite for neutrophils to reach the inflamed tissue, without impairing rolling and adhesion to the inflamed endothelium. Mechanistically, ladarixin abolished neutrophil elastase translocation to the neutrophil surface, indispensable for neutrophil vascular basement membrane penetration and extracellular matrix degradation, in a selective and specific CXCR1/2-dependent fashion leading to reduced neutrophil elastase surface activity in mouse and primary human neutrophils. In brief, the allosteric CXCR1/2 inhibitor ladarixin effectively blocks neutrophil recruitment at the level of neutrophil extravasation without affecting firm adhesion. Clinically, this mode of action has interesting therapeutic potential to prevent neutrophil extravasation in inflammatory diseases including inflammatory bowel disease, psoriasis and other neutrophil-driven disorders.