GSKJ1 is a selective and potent histone demethylase inhibitor (GSK-J1) that has significant activity (IC50 60 nM for human JmjD3) in vitro and in cells using an ester derivative (GSK-J4: 1 µM < IC50 < 10 µM; e.g. 9 µM in primary human macrophages). The pyridine regio-isomer GSK-J2 displays significantly less on-target activity (IC50 > 100 µM for human JmjD3) and thus can be used as control for target effects in vitro, and as ester derivative (GSK-J5) in cells. Recent data has shown that GSK-J1 also shows some activity (IC50 950 nM for Jarid1b, IC50 1.76 uM for Jarid1c) against H3K4me3/2/1 demethylases.