Fostamatinib (R788)(IC50 of 41 nM), which is a prodrug of the active metabolite R406, is a Syk inhibitor. It does not work on Lyn.

Syk:41 nM

在风湿性关节炎模型中,Fostamatinib 明显减少炎症介质,比如TNFalpha,IL-1,IL-6和IL-18,从而减少炎症和骨退化.Fostamatinib 能够有效抑制体内BCR信号,导致恶性B细胞的增殖和存活减少,并明显延长治疗组动物的存活.在逆转-被动阿瑟斯反应和双抗体诱导的关节炎小鼠模型中,口服Fostamatinib减少免疫复合物介导的炎症.

在人肥大细胞,巨噬细胞,和中性粒细胞中,Fostamatinib能够特异性抑制FcγR信号。在大部分DLBCL细胞系,Fostamatinib诱导细胞凋亡。Fostamatinib（EC50 =56 nM）以剂量依赖方式抑制抗- IgE介导的CHMC脱粒,它也会抑制抗-IgE诱导的LTC4,细胞因子以及趋化因子,包括TNFα,IL-8,和GM-CSF的产生与释放。

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 R788 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 R788, 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.

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 R788 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. (Only for Reference)