498 Bruton’s tyrosine kinase (BTK) inhibitors impede platelet aggregation but not adhesion to collagen.

Abstract

OBJECTIVES/GOALS: The research objectives of this project are to elucidate the effects of Bruton’s tyrosine kinase inhibitors (BTKi) of varying target specificity on platelet function with regard to platelet aggregation, adhesion, spreading, and intracellular signaling as measured by kinase phosphorylation. METHODS/STUDY POPULATION: Blood from healthy volunteers was obtained and processed to obtain both washed platelets and platelet-rich plasma. The samples were then treated with one of the BTKi drugs or with vehicle (DMSO) at concentrations matching patient blood concentrations derived from clinical trials and pharmacokinetic studies. The incubated samples were then analyzed in an aggregometer using one of several agonists. Aggregation was stopped after five minutes with a perchloric acid-based lysis buffer. The samples were then analyzed by SDS-PAGE and immunoblotting to quantify BTK protein and BTK phosphorylation. Adhesion was assessed by incubating washed platelets treated with BTKi on microtiter wells coated with fibrinogen or collagen and quantifying adherent platelets by their endogenous acid phosphatase activity. RESULTS/ANTICIPATED RESULTS: We found that ibrutinib, zanubrutinib, and pirtobrutinib all completely inhibited collagen-induced platelet aggregation, whereas they did not inhibit aggregation induced by thrombin, ristocetin, arachidonic acid, or the PAR1 activator peptide SFLLRN (T6). Acalabrutinib inhibited collagen-induced platelet aggregation only at high concentrations (1-2 micromolar). At the lower concentration of 200 nanomolar, comparable to the concentration required for the other BTK inhibitors to completely inhibit platelet aggregation, acalabrutinib failed to inhibit aggregation but did inhibit auto-phosphorylation, indicating an impact on signaling. None of the BTKi drugs inhibited adhesion of platelets to collagen-coated surfaces. DISCUSSION/SIGNIFICANCE: Our data show the inhibitory effect of BTKi on collagen-induced platelet aggregation and signaling. However, it remains unclear whether the inhibition is due to an effect on BTK itself or other related kinases. Better insight into the mechanisms of platelet inhibition by BTKi may help guide the development of BTKi with a lower risk of hemorrhage.