Cell-permeable. A reversible, p300/CBP (CREB-binding protein) histone acetyltransferase (HAT) inhibitor (Ki = 400 nM). Specific inhibition to p300 (86%) compared to N-acetyltransferase, PCAF, GCN5, Rtt109, Sas or MOZ histone acetyltransferases (<10%). Suppresses histone H3 and H4 acetylation in mouse fibroblast cell lines.