In vitro activity: In cell lines, GLPG0634 inhibits IL-2- and IL-4-induced JAK1/JAK3/γc signaling and IFN-αB2-induced JAK1/TYK2 type II receptor signaling with IC50 ranged from 150 to 760 nM. GLPG0634 shows higher selectivity for JAK/STAT signaling involving JAK1 than JAK2 kinase in a cellular context. Besides, GLPG0634 also inhibits the differentiation of Th1, Th2, and Th17 cells.

Kinase Assay: Recombinant JAK1, TYK2, JAK2, and JAK3 are used to develop activity assays in 50 mM HEPES (pH 7.5), 1 mM EGTA, 10 mM MgCl2, 2 mM DTT, and 0.01% Tween 20. The amount of JAK protein is determined per aliquot, maintaining initial velocity and linearity over time. The ATP concentration is equivalent to 4× the experimental Km value and the substrate concentration (ULight-conjugated JAK-1(Tyr1023) peptide) corresponds to the experimentally determined Km value. After 90 min incubation at room temperature (RT), the amount of phosphorylated substrate is measured by addition of 2 nM europium-anti-phosphotyrosine Ab and 10 mM EDTA in Lance detection buffer. Compound IC50 values are determined by preincubating the enzyme with compound at RT for 60 min, prior to the addition of ATP.

Cell Assay: GLPG0634 (50 mg/kg, o.p.) protects bone and cartilage from degradation, effectively reduces infiltration of T cells (CD3+ cells) and macrophages (F4/80+ cells) in the paw, and decreases the serum levels of all cytokines and chemokines measured, including IL-6, IP-10, XCL1, and MCP-1.