Title : Target Binding Properties and Cellular Activity of Afatinib ( BIBW 2992 ) , an Irreversible

Deregulation of the ErbB receptor network is well recognized as an oncogenic driver in epithelial cancers. Several targeted drugs have been developed, including antibodies and small molecule kinase inhibitors, each of them characterized by distinct patterns of ErbB receptor interactions. Understanding the precise pharmacological properties of these compounds is important for optimal use in clinical practice. Afatinib (BIBW 2992) is an ATP-competitive anilinoquinazoline derivative harboring a reactive acrylamide group and was designed to covalently bind and irreversibly block enzymatically active ErbB receptor family members. Here we show by X-ray crystallography the covalent binding of afatinib to wild-type EGFR and by mass spectrometry the covalent interaction with EGFR, EGFR, HER2 and ErbB-4. Afatinib potently inhibits the enymatic activity of ErbB-4 (EC50 = 1 nM) and the proliferation of cancer cell lines driven by multiple ErbB receptor aberrations at concentrations below 100 nM. BI 37781, a close analog of afatinib lacking the acrylamide group and thus incapable of covalent bond formation, had similar potency on cells driven by EGFR or EGFR, but less or no detectable activity on cells expressing EGFR T790M HER2 or ErbB-4. These results stress the importance of the acrylamide group and show that afatinib differs from approved ErbB targeting agents by irreversibly inhibiting the kinase activity of all ErbB family members. This article has not been copyedited and formatted. The final version may differ from this version. JPET Fast Forward. Published on August 10, 2012 as DOI: 10.1124/jpet.112.197756 at A PE T Jornals on A ril 0, 2017 jpet.asjournals.org D ow nladed from