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Biological Activity
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Description
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R788 (Fostamatinib) is a Syk inhibitor with IC50 of 41 nM. |
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Targets
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Syk |
Adenosine A3 receptor |
Adenosine transporter |
Monoamine transporter |
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IC50 |
41 nM |
81 nM |
1.84 μM |
2.74 μM [1] |
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In Vitro
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R788 is a prodrug of the spleen tyrosine kinase (Syk) inhibitor R-406. R406 is a competitive inhibitor for ATP binding with a Ki of 30 nM. R406 dose-dependently inhibits anti-IgE-mediated CHMC degranulation with an EC50 of 56 nM. R406 also inhibits the anti-IgE-induced production and release of LTC4 and cytokines and chemokines, including TNFα, IL-8, and GM-CSF. Inhibition of Syk by R406 results in inhibition of all phosphorylation events downstream of Syk signaling. Next to Fc?RI signaling in CHMC, R406 most potently inhibits the signaling of IL-4 and IL-2 receptors. R406 specifically inhibits FcγR signaling in human mast cells, macrophages, and neutrophils. R406 can inhibit local inflammatory injury mediated by immune complexes. [1] R406 induces apoptosis of the majority of examined DLBCL cell lines. In R406-sensitive DLBCL cell lines, R406 specifically inhibits both tonic- and ligand-induced BCR signaling (autophosphorylation of SYK525/526 and SYK-dependent phosphorylation of the B-cell linker protein [BLNK]). [2] |
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In Vivo
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Oral administration of R406 to mice reduces immune complex-mediated inflammation in a reverse-passive Arthus reaction and two antibody-induced arthritis models. [1] In another study, R788 effectively inhibits BCR signaling in vivo, resulting in reduced proliferation and survival of the malignant B cells and significantly prolongs survival of the treated animals. [3] R788 demonstrates a significant reduction in major inflammatory mediators such as TNFalpha, IL-1, IL-6 and IL-18, leading to reduced inflammation and bone degradation in models of rheumatoid arthritis. [4] |
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Clinical Trials
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R788 has entered in a phase III clinical trial in the treatment of rheumatoid arthritis. |
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Features
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Converted into its active metabolite R406 in vivo. |
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Protocol
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Kinase Assay
[1]
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| Fluorescence polarization kinase assay and Ki determination |
The fluorescence polarization reactions are performed. For Ki determination, duplicate 200-μL reactions are set up at eight different ATP concentrations from 200 μM (2-fold serial dilutions) in the presence of either DMSO or R406 at 125, 62.5, 31.25, 15.5, or 7.8 nM. At different time points, 20 μL of each reaction is removed and quenched to stop the reaction. For each concentration of R406, the rate of reaction at each concentration of ATP is determined and plotted against the ATP concentration to determine the apparent Km and Vmax (maximal rate). Finally the apparent Km (or apparent Ki/Vmax) is plotted against the inhibitor concentration to determine the Ki. |
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Cell Assay
[1]
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| Cell Lines |
Cultured human mast cells (CHMC) |
| Concentrations |
0 μM -100 μM |
| Incubation Time |
30 minutes |
| Methods |
Cultured human mast cells (CHMC) are derived from cord blood CD34+ progenitor cells and grown, primed, and stimulated and shown in supplemental data. Before stimulation, cells are incubated with R406 or DMSO for 30 minutes. Cells are then stimulated with either 0.25 to 2 mg/mL anti-IgE or anti-IgG or 2 μM ionomycin. For tryptase measurement, ～1500 cells per well are stimulated for 30 min in modified Tyrode's buffer. For LTC4 and cytokine production, 100,000 cells per well are stimulated for 1 or 7 hours, respectively. Tryptase activity is measured by luminescence readout of a peptide substrate, and LTC4 and cytokines are measured using Luminex multiplex technology. |
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Animal Study
[1]
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| Animal Models |
Balb/c mice with arthritis |
| Formulation |
35% TPGS, 60% PEG 400, 5% propylene glycol |
| Doses |
1 mg/kg or 5 mg/kg |
| Administration |
Orally b.i.d |
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References |
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[1] Braselmann S, et al. J Pharmacol Exp Ther, 2006, 319(3), 998-1008.
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[2] Chen L et al.Blood, 2008, 111(4), 2230-2237.
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[3] Suljagic M, et al. Blood, 2010, 116(23), 4894-4905.
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[4] Bajpai M. IDrugs, 2009, 12(3), 174-185.
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