Pyridone 6 is a pan-JAK inhibitor, which potently inhibits the JAK kinase family, with IC 50 s 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.