Information Selective JAK3 inhibitor 1 is an irreversibleJAK3inhibitor with Ki values of 0.07 nM, 320 nM, 740 nM for JAK3, JAK1 and JAK2 respectively. It is also selective over the other kinases possessing a cysteine in the same region as JAK3, such as BMX, EGFR, ITK, and BTK. Targets JAK3 (Cell-free assay); JAK1 (Cell-free assay); JAK2 (Cell-free assay) 0.07 nM(Ki); 320 nM(Ki); 740 nM(Ki) In vitro Selective JAK3 inhibitor 1 is a potent inhibitor of JAK3 (IC50 = 0.15 nM) was 4300-fold selective for JAK3 over JAK1 in enzyme assays, 67-fold [interleukin (IL)-2 versus IL-6] or 140-fold [IL-2 versus erythropoietin or granulocyte-macrophage colony-stimulating factor (GMCSF)] selective in cellular reporter assays and >35-fold selective in human peripheral blood mononuclear cell assays (IL-7 versus IL-6 or GMCSF). The compound blocks cytokine signaling through JAK3, but not through other JAK family enzymes. It inhibits IL-7, IL-15, and IL-2 signaling in T cells, but does not inhibit any other cytokine signaling pathways.