title: R406, an orally available spleen tyrosine kinase inhibitor blocks fc receptor signaling and reduces immune complex-mediated inflammation.
abstract: Recent compelling evidence has lead to renewed interest in the role of antibodies and immune complexes in the pathogenesis of several autoimmune disorders, such as rheumatoid arthritis. These immune complexes, consisting of autoantibodies to self-antigens, can mediate inflammatory responses largely through binding and activating the immunoglobulin Fc receptors (FcRs). Using cell-based structure activity relationships with cultured human mast cells, we have identified the small molecule R406 [N4-(2,2-dimethyl-3-oxo-4H-pyrid[1,4]oxazin-6-yl)-5-fluoro-N2-(3,4,5-trimethoxyphenyl)-2,4-pyrimidinediamine] as a potent inhibitor of immunoglobulin E (IgE)- and IgG-mediated activation of Fc receptor signaling (EC(50) for degranulation = 56-64 nM). Here we show that the primary target for R406 is the spleen tyrosine kinase (Syk), which plays a key role in the signaling of activating Fc receptors and the B-cell receptor (BCR). R406 inhibited phosphorylation of Syk substrate linker for activation of T cells in mast cells and B-cell linker protein/SLP65 in B cells. R406 bound to the ATP binding pocket of Syk and inhibited its kinase activity as an ATP-competitive inhibitor (K(i) = 30 nM). Furthermore, R406 blocked Syk-dependent FcR-mediated activation of monocytes/macrophages and neutrophils and BCR-mediated activation of B lymphocytes. R406 was selective as assessed using a large panel of Syk-independent cell-based assays representing both specific and general signaling pathways. Consistent with Syk inhibition, oral administration of R406 to mice reduced immune complex-mediated inflammation in a reverse-passive Arthus reaction and two antibody-induced arthritis models. Finally, we report a first-inhuman study showing that R406 is orally bioavailable, achieving exposures capable of inhibiting Syk-dependent IgE-mediated basophil activation. Collectively, the results show R406 potential for modulating Syk activity in human disease.
authors.affiliation: Rigel Pharmaceuticals, South San Francisco, CA 94080, USA.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Braselmann
authors.forename: Vanessa
authors.initials: V
authors.lastname: Taylor
authors.forename: Haoran
authors.initials: H
authors.lastname: Zhao
authors.forename: Su
authors.initials: S
authors.lastname: Wang
authors.forename: Catherine
authors.initials: C
authors.lastname: Sylvain
authors.forename: Muhammad
authors.initials: M
authors.lastname: Baluom
authors.forename: Kunbin
authors.initials: K
authors.lastname: Qu
authors.forename: Ellen
authors.initials: E
authors.lastname: Herlaar
authors.forename: Angela
authors.initials: A
authors.lastname: Lau
authors.forename: Chi
authors.initials: C
authors.lastname: Young
authors.forename: Brian R
authors.initials: BR
authors.lastname: Wong
authors.forename: Scott
authors.initials: S
authors.lastname: Lovell
authors.forename: Thomas
authors.initials: T
authors.lastname: Sun
authors.forename: Gary
authors.initials: G
authors.lastname: Park
authors.forename: Ankush
authors.initials: A
authors.lastname: Argade
authors.forename: Stipo
authors.initials: S
authors.lastname: Jurcevic
authors.forename: Polly
authors.initials: P
authors.lastname: Pine
authors.forename: Rajinder
authors.initials: R
authors.lastname: Singh
authors.forename: Elliott B
authors.initials: EB
authors.lastname: Grossbard
authors.forename: Donald G
authors.initials: DG
authors.lastname: Payan
authors.forename: Esteban S
authors.initials: ES
authors.lastname: Masuda
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex / Q000502:physiology*; D001169:Arthritis, Experimental / Q000473:pathology; D001183:Arthus Reaction / Q000503:physiopathology; D001402:B-Lymphocytes / Q000187:drug effects / Q000502:physiology; D001491:Basophils / Q000187:drug effects; D015153:Blotting, Western; D002478:Cells, Cultured; D003461:Crystallography; D004311:Double-Blind Method; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D007074:Immunoglobulin G / Q000096:biosynthesis / Q000276:immunology; D007249:Inflammation / Q000188:drug therapy* / Q000473:pathology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects; D008407:Mast Cells / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D010078:Oxazines / Q000493:pharmacokinetics / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011725:Pyridines / Q000493:pharmacokinetics / Q000494:pharmacology*; D011961:Receptors, Fc / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects*; D013154:Spleen / Q000201:enzymology*; D013268:Stimulation, Chemical; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000936:Antigen-Antibody Complex; D004791:Enzyme Inhibitors; D007074:Immunoglobulin G; D008070:Lipopolysaccharides; C510788:N4-(2,2-dimethyl-3-oxo-4H-pyrid(1,4)oxazin-6-yl)-5-fluoro-N2-(3,4,5-trimethoxyphenyl)-2,4-pyrimidinediamine; D010078:Oxazines; D011725:Pyridines; D011961:Receptors, Fc; D011505:Protein-Tyrosine Kinases; D013755:Tetradecanoylphorbol Acetate