The Btk inhibitor AB‐95‐LH34 potently inhibits atherosclerotic plaque–induced thrombus formation and platelet procoagulant activity

BACKGROUND: New antithrombotic therapies with less effect on bleeding are needed for coronary artery disease. The Btk inhibitor ibrutinib blocks atherosclerotic plaque–mediated thrombus formation. However, it is associated with increased bleeding, possibly due to non–Btk‐mediated effects. Btk‐deficient patients do not have bleeding issues, suggesting selective Btk inhibition as a promising antithrombotic strategy. OBJECTIVES: To compare the antithrombotic effects of the highly selective Btk inhibitor AB‐95‐LH34 (LH34) with ibrutinib. METHODS: Glycoprotein VI and G‐protein coupled receptor‐mediated platelet function and signaling were analyzed in healthy human donor platelets by lumi‐aggregometry, flow adhesion, and western blot following 1 h treatment with inhibitors in vitro. RESULTS: LH34 showed similar inhibition of Btk‐Y223 phosphorylation as ibrutinib, but had no off‐target inhibition of Src‐Y418 phosphorylation. Similar dose‐dependent inhibition of aggregation to atherosclerotic plaque material was observed for both. However, in response to Horm collagen, which also binds integrin α2β1, LH34 exhibited less marked inhibition than ibrutinib. Both LH34 and ibrutinib inhibited platelet adhesion and aggregation to plaque material at arterial shear. Ibrutinib demonstrated the most potent effect, with complete blockade at high concentrations. Platelet activation (P‐selectin) and procoagulant activity (phosphatidylserine exposure) in thrombi were inhibited by LH34 and completely blocked by ibrutinib at high concentrations. Furthermore, plaque‐induced thrombin generation was reduced by higher concentrations of LH34 and ibrutinib. CONCLUSIONS: LH34 potently inhibits atherosclerotic plaque–induced thrombus formation and procoagulant platelet activity in vitro, with less off‐target inhibition of Src than ibrutinib, suggesting it is a promising antiplatelet therapy with the potential for reduced bleeding side effects.