JAK-IN-1 shows improved selectivity for JAK3 over JAK1. JAK-IN-1 is a JAK1/2/3 inhibitor with IC50s of 0.26, 0.8 and 3.2 nM, respectively.

JAK3:3.2 nM , JAK2:0.8 nM , JAK1:0.26 nM

JAK-IN-1 exhibits both mechanistic and functional activity in cell-based assays involving T-cells, a primary cell type where JAK3 has potential relevance. It effectively inhibits the proliferation of human CD4 and CD8 T cells in a dose-dependent fashion when stimulated by anti-CD3/anti-CD28 antibody-coated beads, which partially simulate the activation signals delivered to a T cell by an antigen-presenting cell.

JAK-IN-1 effectively inhibits IL-2-induced STAT5 phosphorylation in both a dose- and concentration-dependent fashion, achieving roughly 50% reduction at a dose of 10 mg/kg (plasma concentration approximately 480 nM). Demonstrating selectivity for JAK3 in vivo, JAK-IN-1 exhibits greater efficacy in inhibiting JAK1/JAK3-driven signaling compared to pathways involving JAK2 or the combination of JAK1, JAK2, and TYK2, as evaluated through whole blood assays. Additionally, JAK-IN-1 strongly suppresses IL-2 stimulated plasma concentrations corresponding to each administered dose.