GSK591 (GSK3203591), Alternative Names are EPZ015866, GSK3203591, is a potent selective inhibitor of the arginine methyltransferase PRMT5 (IC50=11 nM).

In an in vitro biochemical assay, GSK591 potently inhibits the PRMT5/MEP50 complex from methylating (histone) H4 with IC50 = 11 nM. In Z-138 cells, GSK591 inhibits the symmetric arginine methylation of SmD3 with EC50 = 56 nM. Further, GSK591 is selective for PRMT5 (up to 50 micromolar) relative to a panel of methyltransferases[1][2].

Selectivity profiling experiments: The lysates (5 mg of total protein each) are preincubated with 0 (DMSO control), 2.5 nM, 25 nM, 250 nM, 2.5 μM or 25 μM free compound (GSK690693 or GSK2141795) on an end-over-end shaker for 45 min at 4 °C. Subsequently, lysates are incubated with beads (coupled Akt probe or kinobeads) for 1 h at 4 °C, for both qualitative and quantitative experiments. The beads are washed with 1× CP buffer and collected by centrifugation. Bound proteins are eluted with 2× NuPAGE LDS sample buffer, and eluates are reduced and alkylated by 50 mM dithiothreitol and 55 mM iodoacetamide.