Design, synthesis of diaminopyrimidine inhibitors targeting IgE- and IgG-mediated activation of Fc receptor signaling.

Using cultured human mast cells (CHMC) the optimization of 2,4-diaminopyrimidine compounds leading to 22, R406 is described. Compound 22 is a potent upstream inhibitor of mast cell degranulation and its mechanism of action is via inhibition of Syk kinase. Compound 22 has significant activity in inhibiting both IgE- and IgG-mediated activation of Fc receptor (FcR) in mast cells and basophils, and in addition inhibits Syk kinase-dependent activity of FcR-mediated activation of monocytes, macrophages, neutrophils, and B cell receptor (BCR)-mediated activation of B lymphocytes.

Novel immunosuppression: R348, a JAK3- and Syk-inhibitor attenuates acute cardiac allograft rejection.

Background: Janus kinase (JAK)3 is crucial for signal transduction downstream of various cytokine receptors in immune cells. This is the first report on the novel JAK3 inhibitor R348.

Methods: (1) Detailed pharmacokinetic data were obtained in rats; (2) multiple in vitro enzyme inhibition assays were performed to characterize the drug; (3) prevention of acute rejection was investigated in animals treated with different doses of R348 or rapamycin for 5 days; and (4) cardiac allograft survival after a 10-day treatment period was studied for various regimens of R348, tacrolimus, or rapamycin; combination indices were calculated to evaluate drug interactions.

Immunotoxicity assessment for the novel Spleen tyrosine kinase inhibitor R406.

Spleen tyrosine kinase (Syk) is a novel pharmaceutical target for treatment of allergic, autoimmune, and neoplastic disorders. Previous studies have indicated that Syk signaling plays critical roles in regulating the lymphohematopoietic system. These observations prompted us to investigate whether inhibition of Syk would promote immunotoxicity.

Identification of the Syk kinase inhibitor R112 by a human mast cell screen.

Background: Activation of the IgE receptor, FcvarepsilonRI, in mast cells is the key mechanism initiating and propagating pathophysiological responses in allergic rhinitis.

Objective: Identify and characterize a small molecule inhibitor of IgE-dependent mast cell activation for the treatment of allergic diseases.

Methods: A cell-based high-throughput screen for small molecules that block IgE signaling was performed in cultured human mast cells.

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).