An α_IIb β₃ antagonist prevents thrombosis without causing Fc receptor γ-chain IIa-mediated thrombocytopenia.

Essentials FcγRIIa-mediated thrombocytopenia is associated with drug-dependent antibodies (DDAbs). We investigated the correlation between α_IIb β₃ binding epitopes and induction of DDAbs. An FcγRIIa-transgenic mouse model was used to evaluate thrombocytopenia among anti-thrombotics. An antithrombotic with binding motif toward α_IIb β-propeller domain has less bleeding tendency. SUMMARY:Background Thrombocytopenia, a common side effect of Arg-Gly-Asp-mimetic antiplatelet drugs, is associated with drug-dependent antibodies (DDAbs) that recognize conformation-altered integrin α_IIb β₃ . Objective To explore the correlation between α_IIb β₃ binding epitopes and induction of DDAb binding to conformation-altered α_IIb β₃ , we examined whether two purified disintegrins, TMV-2 and TMV-7, with distinct binding motifs have different effects on induction of α_IIb β₃ conformational change and platelet aggregation in the presence of AP2, an IgG₁ inhibitory mAb raised against α_IIb β₃ . Methods We investigated the possible mechanisms of intrinsic platelet activation of TMV-2 and TMV-7 in the presence of AP2 by examining the signal cascade, tail bleeding time and immune thrombocytopenia in Fc receptor γ-chain IIa (FcγRIIa) transgenic mice. Results TMV-7 has a binding motif that recognizes the α_IIb β-propeller domain of α_IIb β₃ , unlike that of TMV-2. TMV-7 neither primed the platelets to bind ligand, nor caused a conformational change of α_IIb β₃ as identified with the ligand-induced binding site mAb AP5. In contrast to eptifibatide and TMV-2, cotreatment of TMV-7 with AP2 did not induce FcγRIIa-mediated platelet aggregation and the downstream activation cascade. Both TMV-2 and TMV-7 efficaciously prevented occlusive thrombosis in vivo. Notably, both eptifibatide and TMV-2 caused severe thrombocytopenia mediated by FcγRIIa, prolonged tail bleeding time in vivo, and repressed human whole blood coagulation indexes, whereas TMV-7 did not impair hemostatic capacity. Conclusions TMV-7 shows antiplatelet and antithrombotic activities resulting from a mechanism different from that of all other tested α_IIb β₃ antagonists, and may offer advantages as a therapeutic agent with a better safety profile.

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