In vitro activity: Pyridone 6 (also known as P6, CMP 6 or JAK Inhibitor I) is a pan-JAK (Janus-activated kinase) inhibitor, which potently inhibits the JAK kinase family, with IC50s of 1 nM for JAK2 and TYK2, 5 nM for JAK3, and 15 nM for JAK1, while displaying significantly weaker affinities (130 nM to>10 mM) for other protein tyrosine kinases. Pyridone 6 (P6) delayed the onset and reduced the magnitude of skin disease in an AD-like skin-disease model of NC/Nga mice. P6 reduced IFN-γ and IL-13, whereas it enhanced IL-17 and IL-22 expression. In vitro, P6 also inhibited both Th1 and Th2 development, whereas it promoted Th17 differentiation from naive T cells when present within a certain range of concentrations. This was probably because P6 strongly inhibited STAT1, STAT5, and STAT6 phosphorylation, whereas STAT3 phosphorylation was less efficiently suppressed by P6 at the same concentration. Furthermore, IL-22 protects keratinocytes from apoptosis induced by IFN-γ, and administration of IL-17 and IL-22 partially ameliorated skin diseases in NC/Nga mice. These results suggested that the JAK inhibitor P6 is therapeutic for AD by modulating the balance of Th2 and Th17.

Kinase Assay: Pyridone 6 (P6) is shown to inhibit kinase by interacting within the ATP-binding cleft of each JAK. The IC50 of Pyridone 6 is 3 nM for all of these cytokines; this is comparable to the reported IC50s of Pyridone 6 for JAK2, Tyk2, and JAK3. Pyridone 6 strongly inhibits Th2 and modestly inhibits Th1, whereas it enhances Th17 development when present within a certain range of concentrations. Pyridone 6 reduces IFN-γ and IL-13, whereas it enhances IL-17 and IL-22 expression. Pyridone 6 also inhibits both Th1 and Th2 development, whereas it promotes Th17 differentiation from naive T cells when present within a certain range of concentrations. Pyridone 6 (P6), is found to inhibit the JAKs in the low nanomolar range (IC50, 1-15 nM) and blocks IL-2-dependent proliferation of CTLL cells. Pyridone 6 is a reversible ATP inhibitor, and when tested against many other kinases, IC50s of>130 nM are required. Pyridone 6 inhibits osteoclast differentiation in mouse bone marrow macrophage (BMM) cultures stimulated by the receptor activator of nuclear factor-k B (NF-k B) ligand (RANKL) and co-cultures of bone marrow cells and osteoblasts. Pyridone 6 suppresses the expression of c-Fos and nuclear factor of activated T cells (NFAT) c1 in BMMs. Pyridone 6 also suppresses I-k B degradation and extracellular signal-regulated kinase (ERK) in mature osteoclasts, suggesting that these are the key molecules that pyridone 6 targets in the inhibition of osteoclast function

Cell Assay: Naive CD4+ T cells are treated with various concentrations of Pyridone 6 (10 and 30 nM) in RPMI 1640 medium 1 h before the appropriate cytokines are added to create each Th-differentiating condition. Immunoblotting is performed using antiphospho-STAT protein Abs or anti-total STAT protein Abs.