Ibrutinib treatment affects collagen and von Willebrand factor-dependent platelet functions

Abstract

Key Points• Ibrutinib affects collagen and VWF-mediated platelet activation.• The bleeding diathesis correlates with defects in collagen-induced platelet aggregation and firm adhesion on VWF at arterial shear rate.The oral Bruton's tyrosine kinase inhibitor, ibrutinib, has recently demonstrated high efficiency in patients with relapsed B-cell malignancies. Occurrence of bleeding events has been reported in a subgroup of ibrutinib-treated patients. We demonstrate that ibrutinib selectively inhibits platelet signaling and functions downstream of the collagen receptor glycoprotein VI and strongly affects firm platelet adhesion on von Willebrand factor (VWF) under arterial flow. A longitudinal study of 14 patients indicated a correlation between occurrence of bleeding events and decreased platelet aggregation in response to collagen in platelet-rich plasma and firm adhesion on VWF under arterial flow. The addition of 50% untreated platelets was sufficient to efficiently reverse the effects of ibrutinib, and platelet functions recovered after treatment interruption as physiological platelet renewal occurred. These data have important clinical implications and provide a basis for hemostasis management during ibrutinib treatment. (Blood. 2014;124(26):3991-3995) IntroductionThe Bruton tyrosine kinase (Btk) is an essential actor downstream of the B-cell receptor, and its covalent inhibitor, ibrutinib, has recently been approved for therapies of relapsed chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). [1][2][3][4][5][6][7][8] Bleeding has been reported in up to 50% of ibrutinib-treated patients. Most events were grade 1 to 2 (spontaneous bruising or petechiae), but in 5% of patients, they were of grade 3 or higher after trauma. [4][5][6] Platelets are the most important blood cells to prevent bleeding after vascular injury. Two Tec family kinases, Btk and Tec, are involved in platelet activation downstream of the collagen receptor glycoprotein VI (GPVI) via phospholipase Cg2 (PLCg2) phosphorylation and activation.9,10 Under arterial shear rate, interaction of platelets with the damaged vessel wall is largely mediated by binding of von Willebrand factor (VWF) to its receptor, the GPIb-IX-V complex. In a mouse model, Btk has been shown to play a role in VWF/GPIb-IX-V-induced platelet activation.11 To further characterize the bleeding events in ibrutinib-treated patients, we investigated the effect of this drug on platelet functions in vitro and ex vivo in 14 patients. Study designFor in vitro experiments, whole blood, platelet-rich plasma (PRP), or washed platelets from healthy donors free of antiplatelet medication were preincubated with ibrutinib (PCI-32765; Selleckchem) or dimethylsulfoxide for 10 or 30 minutes as indicated. For ex vivo experiments, blood samples were obtained before and 2 to 4 weeks after starting ibrutinib treatment (Imbruvica; Janssen-Cilaq Laboratories) in patients with CLL (420 mg daily) or MCL (560 mg daily) [4][5][6] (French compassionate use program) after informed consent, in ...

Comment on Lipsky et al.: Incidence and Risk Factors of Bleeding-Related Adverse Events in Patients with Chronic Lymphocytic Leukemia Treated with Ibrutinib

“…Concordant with recent reports implicating impaired collagen-induced platelet aggregation (assessed by formal platelet aggregation testing) as the likely cause of ibrutinib-associated bleeding, [2][3][4] the authors performed platelet aggregometry in 12 normal subjects, 14 subjects with treatment-naïve CLL, and 30 ibrutinib-treated subjects with CLL. In contradistinction to earlier reports, Lipsky et al found that patients with untreated CLL had significant baseline impairments in platelet aggregation to collagen and ADP, and that patients taking ibrutinib had a modest further reduction in collageninduced platelet aggregation, but an improvement in ADPinduced platelet aggregation.…”

“…Remaining mindful of ibrutinib's property as a potent, irreversible anti-platelet drug is highly useful in the clinic, particularly in the management of patients with severe thrombocytopenia and/or taking multiple antiplatelet agents, and in the treatment of patients presenting with acute bleeding or requiring emergency surgery, where transfusion of fresh platelets outside the 3 -4 hour ibrutinib plasma half-life window completely reverses the bleeding phenotype. 3 We and others have observed baseline defects in platelet aggregation in patients with CLL.…”

Targets for Ibrutinib Beyond B Cell Malignancies

“…The contribution of TEC to collagen signalling in the presence of BTK seems to be minor, as platelets from TEC KO mice have only a slight defect in the aggregation response to collagen 65. Platelet activation by vWF, the other activation pathway that is affected by ibrutinib treatment 20, also involves BTK 80. So far, no role for TEC has been described in this process, but it does not seem to compensate for absent BTK, because no phosphorylation of PLC γ 2 was found in platelets from BTK‐deficient mice after vWF stimulation, and no stable vWF‐dependent thrombus formation was observed in vivo in these mice 81.…”

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

“…Several labs have shown that ibrutinib can impair platelet activation in vitro, 4,5 and platelets taken from ibrutinibtreated patients have an impaired response to collagen and reduced adhesion to von Willebrand Factor (vWF) ex vivo. 6,7 It has therefore been suggested that ibrutinibinduced platelet dysfunction underlies bleeding in patients. 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.…”