Abstract/Summary

Background: CLEC-2 is a platelet receptor with an important role in thrombo-inflammation but a minor role in haemostasis. Two endogenous ligands of CLEC-2 have been identified, the transmembrane protein podoplanin, and iron-containing porphyrin hemin, which is formed following haemolysis from red blood cells. Other exogenous ligands such as rhodocytin have contributed to our understanding of the role of CLEC-2. Objectives: To identify novel CLEC-2 small molecule ligands to aid therapeutic targeting of CLEC-2. Methods: ALPHA Screen technology has been used for development of a high throughput screening (HTS) assay recapitulating the podoplanin-CLEC-2 interaction. Light transmission aggregometry was used to evaluate platelet aggregation. Immunoprecipitation and western blot were used to evaluate direct phosphorylation of CLEC-2 and downstream protein phosphorylation. Autodock vina software was used to predict the molecular binding site of katacine and mass spectrometry to determine the polymeric nature of the ligand. Results and conclusions: We developed a CLEC-2-podoplanin interaction assay in a HTS format and screened 5016 compounds from an EU-Open screen library. We identified katacine, a mixture of polymers of proanthocyanidins, as a novel ligand for CLEC-2 and showed that it induces platelet aggregation and CLEC-2 phosphorylation via Syk- and Src kinases. Platelet aggregation induced by katacine is inhibited by the anti-CLEC-2 monoclonal antibody fragment AYP1 F(ab)’2. Katacine is a novel non-protein ligand of CLEC-2 that could contribute to a better understanding of CLEC-2 activation in human platelets.