ABSTRACT
XIAP is a key regulator of apoptosis, and its overexpression in cancer cells may contribute to their survival. The antiapoptotic function of XIAP derives from its BIR domains, which bind to and inhibit pro-apoptotic caspases. Most known IAP inhibitors are selective for the BIR3 domain and bind to cIAP1 and cIAP2 as well as XIAP. Pathways activated upon cIAP binding contribute to the function of these compounds. Inhibitors selective for XIAP should exert pro-apoptotic effects through competition with the terminal caspases. This paper details our synthetic explorations of a novel XIAP BIR2-selective benzazepinone screening hit with a focus on increasing BIR2 potency and overcoming high in vivo clearance. These efforts led to the discovery of benzoxazepinone 40, a potent BIR2-selective inhibitor with good in vivo pharmacokinetic properties which potentiates apoptotic signaling in a manner mechanistically distinct from that of known pan-IAP inhibitors.
Subject(s)
Heterocyclic Compounds/chemical synthesis , Heterocyclic Compounds/pharmacology , Inhibitor of Apoptosis Proteins/antagonists & inhibitors , X-Linked Inhibitor of Apoptosis Protein/antagonists & inhibitors , Alanine/analogs & derivatives , Alanine/chemical synthesis , Alanine/pharmacokinetics , Alanine/pharmacology , Animals , Antibodies, Monoclonal/pharmacology , Apoptosis/drug effects , Blotting, Western , Caspase 3/metabolism , Caspase 7/metabolism , Cell Line, Tumor , Cell Survival/drug effects , Crystallography, X-Ray , Female , Heterocyclic Compounds/pharmacokinetics , Humans , Inhibitor of Apoptosis Proteins/chemistry , Inhibitor of Apoptosis Proteins/metabolism , Mice , Mice, Nude , Models, Chemical , Models, Molecular , Molecular Structure , Oxazepines/chemical synthesis , Oxazepines/pharmacokinetics , Oxazepines/pharmacology , Protein Structure, Tertiary , Rats , Ubiquitin-Protein Ligases , X-Linked Inhibitor of Apoptosis Protein/chemistry , X-Linked Inhibitor of Apoptosis Protein/metabolism , Xenograft Model Antitumor AssaysABSTRACT
The mitogen-activated protein kinase (MAPK) signal transduction pathway plays a central role in regulating tumor cell growth, survival, differentiation, and angiogenesis. The key components of the Ras/Raf/MEK/ERK signal module are frequently altered in human cancers. Targeting this pathway represents a promising anticancer strategy. Small molecule inhibitors targeting MEK1/2 have shown promise in the clinic; however, ultimate clinical proof-of-concept remains elusive. Here, we report a potent and highly selective non-ATP-competitive MEK1/2 inhibitor, RO4927350, with a novel chemical structure and unique mechanism of action. It selectively blocks the MAPK pathway signaling both in vitro and in vivo, which results in significant antitumor efficacy in a broad spectrum of tumor models. Compared with previously reported MEK inhibitors, RO4927350 inhibits not only ERK1/2 but also MEK1/2 phosphorylation. In cancer cells, high basal levels of phospho-MEK1/2 rather than phospho-ERK1/2 seem to correlate with greater sensitivity to RO4927350. Furthermore, RO4927350 prevents a feedback increase in MEK phosphorylation, which has been observed with other MEK inhibitors. We show that B-Raf rather than C-Raf plays a critical role in the feedback regulation. The unique MAPK signaling blockade mediated by RO4927350 in cancer may reduce the risk of developing drug resistance. Thus, RO4927350 represents a novel therapeutic modality in cancers with aberrant MAPK pathway activation.
