XMD17-109 is a selective ERK5 inhibitor (IC50 = 0.162 µM in an enzyme assay). It is selective for ERK5 over a panel of more than 200 kinases, inhibiting only ERK5 with greater than 90% target occupancy at a concentration of 10 µM. XMD17-109 inhibits ERK5 phosphorylation (IC50 = 0.09 µM in HeLa cells) and decreases...