No abstract

Deregulation of the ErbB (proto-oncogene B of the avian erythroblastosis virus AEV-H strain) 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; N-[4-[(3-chloro-4-is an ATP-competitive anilinoquinazoline derivative harboring a reactive acrylamide group. It 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 epidermal growth factor receptor (EGFR) and by mass spectrometry the covalent interaction with EGFR, EGFR L858R/T790M , human epidermal growth factor receptor 2 (HER2), and ErbB-4. Afatinib potently inhibits the enymatic activity of ErbB-4 (EC 50 ϭ 1 nM) and the proliferation of cancer cell lines driven by multiple ErbB receptor aberrations at concentrations below 100 nM., 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 L858R , but less or no detectable activity on cells expressing EGFR L858R/ 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. They provide a mechanistic rationale for the distinct pharmacological features of this compound and explain the clinical activity seen in some patients who are resistant to antibody or kinase inhibitor therapy because of secondary mutations or ErbB receptor "reprogramming."

KRAS is the most frequently mutated driver of pancreatic, colorectal, and non-small cell lung cancers. Direct KRAS blockade has proven challenging and inhibition of a key downstream effector pathway, the RAF-MEK-ERK cascade, has shown limited success due to activation of feedback networks that keep the pathway in check. We hypothesized that inhibiting SOS1, a KRAS activator and important feedback node, represents an effective approach to treat KRAS-driven cancers. We report the discovery of a highly potent, selective and orally bioavailable small-molecule SOS1 inhibitor, BI-3406, that binds to the catalytic domain of SOS1 thereby preventing the interaction with KRAS. BI-3406 reduces formation of GTPloaded RAS and limits cellular proliferation of a broad range of KRAS-driven cancers.Importantly, BI-3406 attenuates feedback reactivation induced by MEK inhibitors and thereby enhances sensitivity of KRAS-dependent cancers to MEK inhibition. Combined SOS1 and MEK inhibition represents a novel and effective therapeutic concept to address KRAS-driven tumors. SignificanceTo date, there are no effective targeted pan-KRAS therapies. In-depth characterization of BI-3406 activity and identification of MEK inhibitors as effective combination partners provide an attractive therapeutic concept for the majority of KRAS mutant cancers, including those fueled by the most prevalent mutant KRAS oncoproteins G12D, G12V, G12C and G13D.Research.