Information Filgotinib (GLPG0634) is a selectiveJAK1inhibitor withIC50of 10 nM, 28 nM, 810 nM, and 116 nM for JAK1, JAK2, JAK3, and TYK2, respectively. Phase 2. Targets JAK1 (Cell-free assay); JAK2 (Cell-free assay); TYK2 (Cell-free assay); JAK3 (Cell-free assay) 10 nM; 28 nM; 116 nM; 810 nM In vitro 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. In vivo Following oral administration, the absolute bioavailability is moderate in rats (45%) and high in mice (∼100%). Filgotinib (30 mg/kg daily (Rats); 50 mg/kg twice daily (Mice)) dose-dependently reduces inflammation, cartilage, and bone degradation in the CIA model in rats and mice.\xa0 Filgotinib (GLPG0634) in DSS-treated mice demonstrates that inhibition of JAK1 is sufficient for achieving strong efficacy in pre-clinical mouse model, correlated to the inhibition of STAT3 phosphorylation in the inflamed colon.