Characterization of ibrutinib as a non-covalent inhibitor of SRC-family kinases.

Ibrutinib is a BTK-targeted irreversible inhibitor. In this study, we demonstrate that ibrutinib potently inhibits SRC activity in a non-covalent manner via mass spectrometry and crystallography. The S345C mutation renders SRC to bind covalently with ibrutinib, and restores the potency of ibrutinib against the gatekeeper mutant. The co-crystal structure of ibrutinib/SRC shows Ser345 of SRC did not form covalent bond with ibrutinib, leading to a decrease of potency and loss of the ability to overcome the gatekeeper mutation of SRC. The X-ray crystallographic studies also provide structural insight into why ibrutinib behaves differently against gatekeeper mutants of different kinases.