JAK3-IN-6 is a potent, selective irreversible Janus Associated Kinase 3 (JAK3) inhibitor, with an IC50 of 0.15 nM.

JAK3-IN-6 (compound 2), a potent inhibitor of JAK3 (0.15 nM) is 4300-fold selective for JAK3 over JAK1 in enzyme assays, 67-fold (IL-2 vs. IL-6) or 140-fold (IL-2 vs. EPO or GMCSF) selective in cellular reporter assays and >35-fold selective in human PBMC assays (IL-7 vs. IL-6 or GMCSF). Irreversible JAK3-IN-6 with a JAK1 selective inhibitor 3 (JAK1: 0.96 nM, JAK2: 14 nM, JAK3: >1500 nM, TYK2: 10 nM) are cross titrated to determine if there is an additive or synergistic effect of co-inhibiting JAK1 and JAK3 enzymes on IL-7 signaling in CD3+, CD4+ PBMCs. As shown, the predicted levels of pSTAT5 inhibition based on addition of JAK1 and JAK3 inhibition are very close to the measured effects of cross titrating each compound, demonstrating that there is an additive effect but no synergistic effect of inhibiting JAK1 and JAK3 on blocking STAT5 phosphorylation. Furthermore inhibition of either JAK1 or JAK3 alone is sufficient to fully inhibit pSTAT5[2].

[1]. ARYL SULFONOHYDRAZIDES. WO2017027400A1. [2]. Elwood F, et al. Evaluation of JAK3 Biology in Autoimmune Disease Using a Highly Selective, Irreversible JAK3 Inhibitor. J Pharmacol Exp Ther. 2017 May;361(2):229-244.