A-366 is a highly selective peptide-competitive histone methyltransferase G9a inhibitor with IC50s of 3.3 and 38 nM for G9a and GLP, respectively.It is more than 1,000-fold selective for G9a and GLP over the other 21 methyltransferases. It is an inhibitor of the Spindlin1-H3K4me3 interaction with an IC50 of 182.6 nM.It exhibits high affinity for human H3R with a Ki value of 17 nM, and shows subtype selectivity between subgroups of the histaminergic and dopaminergic receptor families.