Janus kinases (JAKs) are non-receptor kinases that mediate signaling through cytokine receptors, often to members of the signal transducer and activator of transcription (Stat) family. ZM 39923 is an inhibitor of JAK3 (IC50 = 79 nM) that less potently inhibits epidermal growth factor receptor, JAK1, and cyclin-dependent kinase 4 (IC50s = 2.4, 40, and 10 μM, respectively). In the absence of the reducing agent dithiothreitol, ZM 39923 also inhibits human tissue transglutaminase 2 (TGM2) and the transglutaminase Factor XIIIa (IC50s= 10 and 25 nM, respectively). It breaks down in neutral buffer to form ZM 449829, which is also an inhibitor of JAK3, TGM2, and Factor XIIIa.
