p505-15 and Disease-Models--Animal

We describe the discovery of selective and potent Syk inhibitor 11, which exhibited favorable PK profiles in rat and dog and was found to be active in a collagen-induced arthritis model in rats. Compound 11 was selected for further profiling, but, unfortunately, in GLP toxicological studies it showed liver findings in rat and dog. Nevertheless, 11 could become a valuable tool compound to investigate the rich biology of Syk in vitro and in vivo.

Topics: Animals; Arthritis, Experimental; Collagen; Disease Models, Animal; Dogs; Dose-Response Relationship, Drug; Drug Discovery; Female; Humans; Intracellular Signaling Peptides and Proteins; Liver; Mice; Mice, Inbred C57BL; Models, Molecular; Molecular Conformation; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Rats; Rats, Inbred Lew; Structure-Activity Relationship; Syk Kinase

Design and optimization of benzo- and pyrido-thiazoles/isothiazoles are reported leading to the discovery of the potent, orally bioavailable Syk inhibitor 5, which was found to be active in a rat PK/PD model. Compound 5 showed acceptable overall kinase selectivity. However, in addition to Syk it also inhibited Aurora kinase in enzymatic and cellular settings leading to findings in the micronucleus assay. As a consequence, compound 5 was not further pursued.

Topics: Administration, Oral; Animals; Biological Availability; Disease Models, Animal; Dose-Response Relationship, Drug; Intracellular Signaling Peptides and Proteins; Microsomes, Liver; Models, Molecular; Molecular Structure; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Rats; Rats, Inbred Lew; Rats, Sprague-Dawley; Structure-Activity Relationship; Syk Kinase; Thiazoles

Based on genetic studies that establish the role of spleen tyrosine kinase (Syk) in immune function, inhibitors of this kinase are being investigated as therapeutic agents for inflammatory diseases. Because genetic studies eliminate both adapter functions and kinase activity of Syk, it is difficult to delineate the effect of kinase inhibition alone as would be the goal with small-molecule kinase inhibitors. We tested the hypothesis that specific pharmacological inhibition of Syk activity retains the immunomodulatory potential of Syk genetic deficiency. We report here on the discovery of (4-(3-(2H-1,2,3-triazol-2-yl)phenylamino)-2-((1R,2S)-2-aminocyclohexylamino) pyrimidine-5-carboxamide acetate (P505-15), a highly specific and potent inhibitor of purified Syk (IC50 1-2 nM). In human whole blood, P505-15 potently inhibited B cell antigen receptor-mediated B cell signaling and activation (IC50 0.27 and 0.28 μM, respectively) and Fcε receptor 1-mediated basophil degranulation (IC50 0.15 μM). Similar levels of ex vivo inhibition were measured after dosing in mice (Syk signaling IC50 0.32 μM). Syk-independent signaling and activation were unaffected at much higher concentrations, demonstrating the specificity of kinase inhibition in cellular systems. Oral administration of P505-15 produced dose-dependent anti-inflammatory activity in two rodent models of rheumatoid arthritis. Statistically significant efficacy was observed at concentrations that specifically suppressed Syk activity by ∼67%. Thus specific Syk inhibition can mimic Syk genetic deficiency to modulate immune function, providing a therapeutic strategy in P505-15 for the treatment of human diseases.

Topics: Adaptor Proteins, Signal Transducing; Animals; Arthritis, Experimental; B-Lymphocytes; Basophils; Biocatalysis; Blood; Cell Degranulation; Cell Line; Cell Line, Tumor; Cell Proliferation; Cyclohexylamines; Disease Models, Animal; Edema; Extracellular Signal-Regulated MAP Kinases; Female; Foot; Humans; Inhibitory Concentration 50; Intracellular Signaling Peptides and Proteins; Leukocytes; Lymphocyte Activation; Mice; Mice, Inbred BALB C; Molecular Structure; Phosphorylation; Precursor Cells, B-Lymphoid; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Pyrimidines; Rats; Rats, Inbred Lew; Receptors, Antigen, B-Cell; Signal Transduction; Syk Kinase; Synovitis