Development of small-molecule fluorescent probes targeting neutrophils via N-formyl peptide receptors

N-Formyl peptide receptors (FPRs) are membrane receptors that are abundantly expressed in innate immune cells, including neutrophils and platelets, demonstrating potential new targets for immune system regulation and the treatment of inflammatory conditions. We report here the development and bio-physical validation of new FPR imaging agents as effective tools to track FPR distribution, localisation and functions, ultimately helping to establish FPR exact roles and functions in pathological and physiological conditions. The new series of probes feature a small molecule-based FPR address system conjugated to suitable fluorophores, resulting in highly specific FPR agents, including a partial agonist endowed with high affinity (i.e. low/sub-nanomolar potency) on FPR-transfected cells and human neutrophils. Preliminary imaging studies via multiphoton microscopy demonstrate that the probes enable the visualisation of FPRs in live cells, thus representing valid bio-imaging tools for the analysis of FPR-mediated signalling, such as the activation of neutrophils in inflammatory events.