In Vitro: GSK4028 is the enantiomeric negative control of GSK4027, which is a PCAF/GCN5 bromodomain chemical probe, the pIC50 of GSK4028 is 4.9. GSK4028 also demonstrates potency toward BRD4 BD1 and BRD9 inTR-FRET assay with pIC50s of <4.3 and 4.5±0.13, respectively.