A novel Lyn-binding peptide inhibitor blocks eosinophil differentiation, survival, and airway eosinophilic inflammation

Receptor antagonists block all receptor-coupled signaling pathways indiscriminately. We introduce a novel class of peptide inhibitors that is designed to block a specific signal from a receptor while keeping other signals intact. This concept was tested in the model of IL-5 signaling via Lyn kinase. We have previously mapped the Lyn-binding site of the IL-5/GM- CSF receptor common β (βe) subunit. In the present study, we designed a peptide inhibitor using the Lyn-binding sequence. The peptide was N-stearated to enable cellular internalization. The stearated peptide blocked the hinding of Lyn to the βe receptor and the activation of Lyn. The lipopeptide did not affect the activation of Janus kinase 2 or its association with βe. The inhibitor blocked the Lyn-dependent functions of IL-5 in vitro (e.g., eosinophil differentiation from stem cells and eosinophil survival). It did not affect eosinophil degranulation. When applied in vivo, the Lyn-binding peptide significantly inhibited airway eosinophil influx in a mouse model of asthma. The lipopeptide had no effect on basophil histamine release or on the proliferation of B cells and T cells. To our knowledge, this is the first report on an inhibitor of IL-5 that blocks eosinophil differentiation, survival, and airway eosinophilic inflammation. This novel strategy to develop peptide inhibitors can be applied to other receptors.