Ibrutinib (PCI-32765) selectively inhibits B-cell signaling and activation. It inhibits autophosphorylation of Btk (IC50=11 nM), phosphorylation of Btk's physiological substrate PLCγ (IC50=29 nM), and phosphorylation of a further downstream kinase, ERK (IC50=13 nM).
Ibrutinib (PCI-32765) inhibits BCR-activated primary B cell proliferation (IC50=8 nM). Following FcγR stimulation, Ibrutinib (PCI-32765) inhibits TNFα, IL-1β and IL-6 production in primary monocytes (IC50=2.6, 0.5, 3.9 nM, respectively).
Ibrutinib binds C481 (Cysteine481) of BTK with an ideal IC50 of 0.5 nM. Ibrutinib cannot form a covalent bond with the hydroxyl group of serine, C481S mutation increases the IC50 against BTK-C481S phosphorylation from 2.2 nM to 1 μM.