Cell-permeable. JAK Inhibitor, Pyridone 6 is a potent, reversible, ATP-competitive JAK inhibitor. It inhibits JAK1, 2, and 3 with IC₅₀ values of 15, 1, and 5 nM, respectively. Displays significantly weaker affinities (IC₅₀s = 130 nM - > 10 μM) for other protein tyrosine kinases. It was shown to block IL-2 and IL-4-dependent proliferation of mouse T-cell lymphoma cells with IC₅₀ values of 50-100 nM.