Oral administration of Bruton's tyrosine kinase inhibitors impairs GPVI-mediated platelet function

Abstract

The Tec family kinase Bruton's tyrosine kinase (Btk) plays an important signaling role downstream of immunoreceptor tyrosine-based activation motifs in hematopoietic cells. Mutations in Btk are involved in impaired B-cell maturation in X-linked agammaglobulinemia, and Btk has been investigated for its role in platelet activation via activation of the effector protein phospholipase Cγ2 downstream of the platelet membrane glycoprotein VI (GPVI). Because of its role in hematopoietic cell signaling, Btk has become a target in the treatment of chronic lymphocytic leukemia and mantle cell lymphoma; the covalent Btk inhibitor ibrutinib was recently approved by the US Food and Drug Administration for treatment of these conditions. Antihemostatic events have been reported in some patients taking ibrutinib, although the mechanism of these events remains unknown. We sought to determine the effects of Btk inhibition on platelet function in a series of in vitro studies of platelet activation, spreading, and aggregation. Our results show that irreversible inhibition of Btk with two ibrutinib analogs in vitro decreased human platelet activation, phosphorylation of Btk, P-selectin exposure, spreading on fibrinogen, and aggregation under shear flow conditions. Short-term studies of ibrutinib analogs administered in vivo also showed abrogation of platelet aggregation in vitro, but without measurable effects on plasma clotting times or on bleeding in vivo. Taken together, our results suggest that inhibition of Btk significantly decreased GPVI-mediated platelet activation, spreading, and aggregation in vitro; however, prolonged bleeding was not observed in a model of bleeding.

Acquired platelet antagonism: off‐target antiplatelet effects of malignancy treatment with tyrosine kinase inhibitors

“…In addition, evidence was obtained for reduced α IIb β 3 ‐dependent outside‐in signaling, linked to thrombus instability in vitro . Several studies have confirmed that Btk can act as a central target of ibrutinib in GPVI‐stimulated platelets, although downstream tyrosine kinases may be affected as well . In vitro , ibrutinib was found to fully inhibit the tyrosine phosphorylation of Src and PLCγ2 .…”

Effects of ibrutinib treatment on murine platelet function during inflammation and in primary hemostasis

“…In contrast, administration of ibrutinib analogs in non-human primates had no significant effect on bleeding time despite the ability to inhibit collagen-mediated platelet activation in vitro and ex vivo following treatment. 8 This begs the question as to whether ibrutinib alone is responsible for causing bleeding in patients. In the present study, we examined the impact of ibrutinib on platelet function in the context of inflammatory hemorrhage and primary hemostasis in mice.…”

Atrial fibrillation, anticoagulant stroke prophylaxis and bleeding risk with ibrutinib therapy for chronic lymphocytic leukaemia and lymphoproliferative disorders

“…In most trials, the frequency of grade 3 or 4 bleeding events has been low at c. 3-4%. These acquired defects are consistent with an on-target inhibition of BTK signalling downstream from both the platelet collagen receptor glycoprotein (GP)VI, and the von Willebrand factor receptor, GPIb-V-IX (Quek et al, 1998;Bye et al, 2015;Rigg et al, 2016). The utility of platelet function testing for patients on ibrutinib has not been established, but platelet aggregation responses to collagen (Kamel et al, 2015;Lipsky et al, 2015) and ristocetin are primarily affected (Kazianka et al, 2015).…”