L002 (NSC764414) is a novel selective, cell permeable and reversible inhibitor of p300 histone acetyl transferase (IC50 ~1.98 μM). It has no activity in histone methyltransferases tested, including DOT1, EZH1, G9a, PRMT1, SETD2, SET7-9, SMYD2, and SUV39H2 etc. L002 was shown to occupy Ac-CoA binding pocket of p300, and is less potent to CBP, PCAF, GCN5 and GNAT. It suppresses Histone H3 and H4 acetylation in triple negative breast cancer cell line MDAMB-468 as well as in HCT116 cell line and blocks p300-mediated STAT3 phosphorylation in pancreatic cancer cell line MIA Paca-2. L002 can suppress tumor growth and histone acetylation in a mouse MDA-MB-468 xenograft model.