Merck-5

Merck 5, also known as Pyridone 6, is a potent and reversible ATP-competitive inhibitor of the JAK kinases (JAK1, JAK2, JAK3, and Tyk2) with IC(50) values in the low anomolar range. At higher values (IC(50) >100nM) Merck 5 also can inhibit ERK kinase family and appear to block IL-2 and IL-4 dependent proliferation of CTLL cells and inhibits the phosphorylation of STAT5. In research comparing Merck 5 (Pyridone 6) to the Jak inhibitor AG490, Merck 5 demonstrated much lower effective drug concentrations and faster kinetics and appear to be a more sensitive and specific inhibitor of JAK-STAT3 activity compared with AG490 and potently inhibited the growth of primary myeloma cells and myeloma-derived cell lines grown on bone marrow-derived stromal cells .