R406, an orally available spleen tyrosine kinase inhibitor blocks fc receptor signaling and reduces immune complex-mediated inflammation.
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.
Braselmann
Sylvia
S
Rigel Pharmaceuticals, South San Francisco, CA 94080, USA.
Taylor
Vanessa
V
Zhao
Haoran
H
Wang
Su
S
Sylvain
Catherine
C
Baluom
Muhammad
M
Qu
Kunbin
K
Herlaar
Ellen
E
Lau
Angela
A
Young
Chi
C
Wong
Brian R
BR
Lovell
Scott
S
Sun
Thomas
T
Park
Gary
G
Argade
Ankush
A
Jurcevic
Stipo
S
Pine
Polly
P
Singh
Rajinder
R
Grossbard
Elliott B
EB
Payan
Donald G
DG
Masuda
Esteban S
ES
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
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