The selectivity of GSK 4027 against the wider bromodomain family is assessed in the BROMOscan panel (pKi of 8.9 and 8.9 for PCAF and GCN5, respectively). GSK 4027 displays equipotent activity against PCAF and GCN5 (Ki: 1.4 nM for both bromodomains). GSK 4027 also demonstrates potency toward BRD4 BD1 and BRD9 inTR-FRET assay with pIC50s of <4.3 and 5.1±0.08, respectively. Due to the encouraging measured artificial membrane permeability (500 nm/s), treatment of HEK293 cells with GSK 4027 displace full-length PCAF from histone H3.3 with little drop-off from the biochemical assay and a pIC50 7.2 (IC50 60 nM)[1].