Cell-permeable. A potent, non-competitive inhibitor of p300 and PCAF (p300/CBP-associated factor) histone acetyltransferase (HAT) activities (IC₅₀~8.5 µM and ~5 µM, respectively. Inhibits SUMOylation of RanGAP1-C2 with an IC₅₀ = 2.2 µM