PRT-060318, a novel Syk inhibitor, prevents heparin-induced thrombocytopenia and thrombosis in a transgenic mouse model.

Heparin-induced thrombocytopenia (HIT) is a major cause of morbidity and mortality resulting from the associated thrombosis. Extensive studies using our transgenic mouse model of HIT have shown that antibodies reactive with heparin-platelet factor 4 complexes lead to FcγRIIA-mediated platelet activation in vitro as well as thrombocytopenia and thrombosis in vivo. We tested PRT-060318 (PRT318), a novel selective inhibitor of the tyrosine kinase Syk, as an approach to HIT treatment. PRT318 completely inhibited HIT immune complex-induced aggregation of both human and transgenic HIT mouse platelets. Transgenic HIT model mice were treated with KKO, a mouse monoclonal HIT-like antibody, and heparin. The experimental group received orally dosed PRT318, whereas the control group received vehicle. Nadir platelet counts of PRT318-treated mice were significantly higher than those of control mice. When examined with a novel thrombosis visualization technique, mice treated with PRT318 had significantly reduced thrombosis. The Syk inhibitor PRT318 thus prevented both HIT immune complex-induced thrombocytopenia and thrombosis in vivo, demonstrating its activity in HIT.

[1]  R. Aster,et al.  Response of human platelets to activating monoclonal antibodies: importance of Fc gamma RII (CD32) phenotype and level of expression. , 1992, Blood.

[2]  M. Reilly,et al.  Prothrombotic factors enhance heparin‐induced thrombocytopenia and thrombosis in vivo in a mouse model , 2006, Journal of thrombosis and haemostasis : JTH.

[3]  A. Greinacher,et al.  The direct thrombin inhibitor hirudin , 2008, Thrombosis and Haemostasis.

[4]  D. Hoppensteadt,et al.  An update on heparins at the beginning of the new millennium. , 2000, Seminars in thrombosis and hemostasis.

[5]  Scott M. Taylor,et al.  The role of the human Fc receptor Fc gamma RIIA in the immune clearance of platelets: a transgenic mouse model. , 1999, Journal of immunology.

[6]  Heparin-induced thrombocytopenia: laboratory studies. , 1988, Blood.

[7]  A. Ichinose,et al.  Molecular and genetic mechanisms of factor XIII A subunit deficiency. , 2000, Seminars in thrombosis and hemostasis.

[8]  P. Hogarth,et al.  Riia Γ Platelet Receptors: De-itam-izing Fc Dual Itam-mediated Proteolytic Pathways for Irreversible Inactivation Of , 2022 .

[9]  W. Kisiel,et al.  Characterization of a murine monoclonal antibody that mimics heparin-induced thrombocytopenia antibodies. , 2000, Blood.

[10]  Ronald Levy,et al.  Inhibition of Syk with fostamatinib disodium has significant clinical activity in non-Hodgkin lymphoma and chronic lymphocytic leukemia. , 2010, Blood.

[11]  Yibing Yan,et al.  Specific Pharmacological Targeting of the Syk Kinase Activity in Platelets: A Novel, Safe Anti-Thrombotic Strategy , 2008 .

[12]  T. Lubowski.  Heparin-induced thrombocytopenia and thrombosis. , 1990, Connecticut medicine.

[13]  G. Arepally,et al.  Antibodies from patients with heparin-induced thrombocytopenia stimulate monocytic cells to express tissue factor and secrete interleukin-8. , 2001, Blood.

[14]  References , 1971 .

[15]  M. Weinblatt,et al.  Treatment of rheumatoid arthritis with a Syk kinase inhibitor: a twelve-week, randomized, placebo-controlled trial. , 2008, Arthritis and rheumatism.

[16]  Stefano Monti,et al.  SYK-dependent tonic B-cell receptor signaling is a rational treatment target in diffuse large B-cell lymphoma. , 2008, Blood.

[17]  J. Kelton,et al.  Heparin-induced thrombocytopenia: laboratory studies , 1988 .

[18]  M. Turner,et al.  The Fc receptor γ‐chain and the tyrosine kinase Syk are essential for activation of mouse platelets by collagen , 1997, The EMBO journal.

[19]  Y. Gruel,et al.  Induction of monocyte tissue factor expression by antibodies to heparin-platelet factor 4 complexes developed in heparin-induced thrombocytopenia. , 2001 .

[20]  T. Warkentin,et al.  Heparin‐induced thrombocytopenia: pathogenesis and management , 2003, British journal of haematology.

[21]  T. Kohlmann,et al.  Clinical features of heparin-induced thrombocytopenia including risk factors for thrombosis , 2005, Thrombosis and Haemostasis.

[22]  M. Poncz,et al.  Heparin-induced thrombocytopenia/thrombosis in a transgenic mouse model requires human platelet factor 4 and platelet activation through FcgammaRIIA. , 2001, Blood.

[23]  Y. Refaeli,et al.  Mouse models of non-Hodgkin lymphoma reveal Syk as an important therapeutic target. , 2009, Blood.

[24]  J. Bussel,et al.  Of mice and men: an open-label pilot study for treatment of immune thrombocytopenic purpura by an inhibitor of Syk. , 2009, Blood.

[25]  L. Rauova,et al.  Ultralarge complexes of PF4 and heparin are central to the pathogenesis of heparin-induced thrombocytopenia. , 2005, Blood.

[26]  J. Eble,et al.  The novel Syk inhibitor R406 reveals mechanistic differences in the initiation of GPVI and CLEC‐2 signaling in platelets , 2009, Journal of thrombosis and haemostasis : JTH.

[27]  D. Payan,et al.  R406, an Orally Available Spleen Tyrosine Kinase Inhibitor Blocks Fc Receptor Signaling and Reduces Immune Complex-Mediated Inflammation , 2006, Journal of Pharmacology and Experimental Therapeutics.

[28]  G. Visentin.  Heparin-Induced Thrombocytopenia: Molecular Pathogenesis , 1999, Thrombosis and Haemostasis.

[29]  Victor L. J. Tybulewicz,et al.  The SYK tyrosine kinase: a crucial player in diverse biological functions , 2010, Nature Reviews Immunology.

[30]  T. Warkentin,et al.  Heparin-Induced Thrombocytopenia: A Clinicopathologic Syndrome , 1999, Thrombosis and Haemostasis.

[31]  S. Neelamegham,et al.  Immune complexes formed following the binding of anti-platelet factor 4 (CXCL4) antibodies to CXCL4 stimulate human neutrophil activation and cell adhesion. , 2008, Blood.