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CREB (cyclic AMP-response element-binding protein) is a downstream transcription factor of a multitude of signaling pathways emanating from receptor tyrosine kinases or G-protein coupled receptors.CREB can not be activated until it is phosphorylated at Ser133 and its subsequent binding to CREB-binding protein (CBP) through the kinase-inducible domain (KID) in CREB and KID-interacting (KIX) domain in CBP.In a cell-based CREB Renilla luciferase reporter assay, Naphthol AS-E inhibits CREB-mediated gene transcription with an IC ₅₀ of 2.29 µM. In HEK293T-based complementation assay, Naphthol AS-E dose-dependently inhibited Renilla luciferase activity with an IC ₅₀ of 2.9 µM by directly binding to CBP's KIX domain (K _d ~8.6 µM using a recombinant KIX).Naphthol AS-E exhibits low µM activity in inhibiting the proliferation of all these cancer cells, which is consistent with its cellular CREB inhibition potency. The average GI ₅₀ values for A549, MCF-7, MDA-MB-231 and MDA-MB-468 are approximately 2.9µM, 2.81µM, 2.35µM and 1.46µM, respectively.Naphthol AS-E (2.5 µM-10 µM; 48 hours) decreases the expression of anti-apoptotic protein Bcl-2. The expression of VEGF is also decreased.