GSK 5959 exhibits >100-fold selectivity for BRPF1 (IC50 = 80 nM) over a panel of 35 other bromodomains, including BRPF2/3 and BET family bromodomains. Inhibits BRPF1 interaction with histone H3.3, which is involved in the epigenetic regulation of gene expression and have been implicated in human cancer.