ABSTRACT
Bruton's tyrosine kinase (Btk) is a therapeutic target for rheumatoid arthritis, but the cellular and molecular mechanisms by which Btk mediates inflammation are poorly understood. Here we describe the discovery of CGI1746, a small-molecule Btk inhibitor chemotype with a new binding mode that stabilizes an inactive nonphosphorylated enzyme conformation. CGI1746 has exquisite selectivity for Btk and inhibits both auto- and transphosphorylation steps necessary for enzyme activation. Using CGI1746, we demonstrate that Btk regulates inflammatory arthritis by two distinct mechanisms. CGI1746 blocks B cell receptor-dependent B cell proliferation and in prophylactic regimens reduces autoantibody levels in collagen-induced arthritis. In macrophages, Btk inhibition abolishes FcγRIII-induced TNFα, IL-1ß and IL-6 production. Accordingly, in myeloid- and FcγR-dependent autoantibody-induced arthritis, CGI1746 decreases cytokine levels within joints and ameliorates disease. These results provide new understanding of the function of Btk in both B cell- or myeloid cell-driven disease processes and provide a compelling rationale for targeting Btk in rheumatoid arthritis.
Subject(s)
Arthritis, Experimental/drug therapy , Arthritis, Rheumatoid/drug therapy , B-Lymphocytes/drug effects , Benzamides/therapeutic use , Bridged Bicyclo Compounds, Heterocyclic/therapeutic use , Myeloid Cells/drug effects , Protein Kinase Inhibitors/therapeutic use , Agammaglobulinaemia Tyrosine Kinase , Animals , Arthritis, Experimental/immunology , Arthritis, Experimental/metabolism , Arthritis, Rheumatoid/immunology , Arthritis, Rheumatoid/metabolism , Autoantibodies/immunology , Autoantibodies/metabolism , B-Lymphocytes/immunology , B-Lymphocytes/metabolism , Benzamides/chemistry , Benzamides/pharmacology , Bridged Bicyclo Compounds, Heterocyclic/chemistry , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Cell Proliferation/drug effects , Enzyme Activation/drug effects , Interleukin-1beta/immunology , Interleukin-1beta/metabolism , Interleukin-6/immunology , Interleukin-6/metabolism , Mice , Myeloid Cells/immunology , Myeloid Cells/metabolism , Phosphorylation/drug effects , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/pharmacology , Protein-Tyrosine Kinases/chemistry , Protein-Tyrosine Kinases/pharmacology , Protein-Tyrosine Kinases/therapeutic use , Tumor Necrosis Factor-alpha/immunology , Tumor Necrosis Factor-alpha/metabolismABSTRACT
Inhibition of receptor tyrosine kinases (RTKs) such as vascular endothelial growth factor receptors (VEGFRs) and platelet-derived growth factor receptors (PDGFRs) has been validated by recently launched small molecules Sutent and Nexavar, both of which display activities against several angiogenesis-related RTKs. EphB4, a receptor tyrosine kinase (RTK) involved in the processes of embryogenesis and angiogenesis, has been shown to be aberrantly up regulated in many cancer types such as breast, lung, bladder and prostate. We propose that inhibition of EphB4 in addition to other validated RTKs would enhance the anti-angiogenic effect and ultimately result in more pronounced anti-cancer efficacy. Herein we report the discovery and SAR of a novel series of imidazo[1,2-a]pyrazine diarylureas that show nanomolar potency for the EphB4 receptor, in addition to potent activity against several other RTKs.
