The
Bruton's tyrosine kinase (Btk) inhibitor
ibrutinib has proven to be efficacious in the treatment of
B-cell chronic lymphocytic leukemia (B-CLL) and related diseases. However, a major adverse side effect of
ibrutinib is
bleeding, including major
hemorrhages. The
bleeding associated with
ibrutinib use is thought to be due to a combination of on-target irreversible Btk inhibition, as well as off-target inhibition of other
kinases, including EGFR, ITK, JAK3, and
Tec kinase. In this study, we investigated the effects of
ibrutinib vs
zanubrutinib (a more selective Btk inhibitor) on platelet activation,
glycoprotein expression, and
thrombus formation.
Ibrutinib, but not
zanubrutinib, induced a time- and dose-dependent shedding of GPIb-IX complex and
integrin αIIbβ3, but not of GPVI and GPV, from the platelet surface. The shedding of GPIbα and GPIX was blocked by
GM6001 and
TAPI-2, an ADAM17 inhibitor but not ADAM10 inhibitor.
Ibrutinib but not
zanubrutinib treatment of human platelets increased ADAM17 activation. Pretreatment of C57BL/6 mice with
ibrutinib (10 mg/kg), but not
zanubrutinib (10 mg/kg), inhibited ex vivo and in vivo
thrombus growth over time. Platelets from
ibrutinib-treated patients with CLL showed reduced GPIb-IX complex and
integrin αIIbβ3 surface expression and reduced ex vivo
thrombus formation under arterial flow, which was not observed in
zanubrutinib-treated patients. In mice,
ibrutinib, but not
zanubrutinib, led to increased soluble GPIbα and soluble αIIb levels in plasma. These data demonstrate that
ibrutinib induces shedding of GPIbα and GPIX by an ADAM17-dependent mechanism and
integrin αIIbβ3 by an unknown sheddase, and this process occurs in vivo to regulate
thrombus formation.