Abstract
Platelets are highly reactive fragments of megakaryocytes that play a fundamental role in thrombosis and hemostasis. Predictably, all conventional anti-platelet therapies elicit bleeding, raising the question whether the thrombotic activity of platelets can be targeted separately. In this study, we describe a novel approach of inhibiting platelet activation through the use of bispecific single-chain variable fragments (bi-scFvs), termed cis-acting platelet receptor inhibitors (CAPRIs) that harness the immunoreceptor tyrosine-based inhibition motif (ITIM)-containing co-inhibitory receptor G6b-B (G6B) to suppress immunoreceptor tyrosine-based (ITAM)-containing receptor-mediated platelet activation. CAPRI-mediated hetero-clustering of G6B with either the ITAM-containing GPVI-FcR γ-chain complex or FcγRIIA (CD32A) inhibited collagen- or immune complex-induced platelet aggregation. G6B-GPVI CAPRIs strongly and specifically inhibited thrombus formation on collagen under arterial shear, whereas G6B-CD32A CAPRI strongly and specifically inhibited thrombus formation to heparin-induced thrombocytopenia, vaccine-induced thrombotic thrombocytopenia and antiphospholipid syndrome complexes on Von Willebrand Factor-coated surfaces and photochemical-injured endothelial cells under arterial shear. Our findings provide proof-of-concept that CAPRIs are highly effective at inhibiting ITAM receptor-mediated platelet activation, laying the foundation for a novel family of anti-thrombotic therapeutics with potentially improved efficacy and fewer bleeding outcomes compared with current anti-platelet therapies. .