Potent and highly selective Bruton’s tyrosine kinase (BTK) inhibitor. Orally bioavailable and irreversible inhibitor of BTK (IC50 = 0.5 nM) with antineoplastic activity. Binds to and irreversibly inhibits BTK activity, preventing B cell activation and B cell-mediated signaling. This leads to an inhibition of the growth of malignant B cells that overexpress BTK. Shown to inhibit autophosphorylation of BTK (IC50 = 11nM), phosphorylation of PLCgamma (IC50 = 29nM), a substrate of BTK and phosphorylation of ERK (IC50 = 13nM).