Ibrutinib is a bioavailable, small-molecule inhibitor of Bruton's tyrosine kinase (BTK) with potential antineoplastic activity. Upon oral administration, ibrutinib binds to and irreversibly inhibits BTK activity, thereby preventing both B-cell activation and B-cell-mediated signaling. This leads to an inhibition of the growth of malignant B cells that overexpress BTK. BTK, a member of the src-related BTK/Tec family of cytoplasmic tyrosine kinases, is required for B cell receptor signaling, plays a key role in B-cell maturation, and is overexpressed in a number of B-cell malignancies. The expression of BTK in tumor cells is also associated with increased proliferation and survival.

Ibrutinib is a highly selective Bruton's tyrosine kinase (Btk) irreversible inhibitor.PCI-32765 (Ibrutinib) is a selective and irreversible pyrrolopyrimidine-based inhibitor of BTK with IC50 of 0.5 nM. [1] PCI-32765 binds irreversibly to Cys-481 in BTK and thus is only active with other kinases with such a modifiable cysteine residue. In DOHH2 cells, in which the BCR pathway can be activated by anti-IgG, PCI-32765 inhibits autophosphorylation of BTK (IC50, 11 nM), BTK's physiological substrate, PLCg (IC50, 29 nm), and downstream ERK (IC50, 13 nm).