In vitro activity: KG-501 is a potent inhibitor of CREB (cAMP response element-binding protein) with an IC50 of 6.89 μM. KG-501 (2-naphthol-AS-E-phosphate), targeted a surface distal to the CREB binding groove that includes Arg-600, a residue that is required for the CREB:CBP interaction. When added to live cells, KG-501 disrupted the CREB: CBP complex and attenuated target gene induction in response to cAMP agonist. These results demonstrate the ability of small molecules to interfere with second-messenger signaling cascades by inhibiting specific protein-protein interactions in the nucleus.

Kinase Assay: KG-501, which directly targets the KIX domain of CBP, results in a disrupted CREB-CBP complex, inhibits CREB-target gene induction, and inhibits IL-1β-mediated angiogenic activity in NSCLC. KG-501 disrupts phospho (Ser-133) CREB binding to KIX with a Ki of ~90 μM, using concentrations of CREB that are within the linear range of the binding assay.

Cell Assay: Treatment of HEK293T cells with KG-501 also blocks induction of endogenous CREB target genes (NR4A2, αCG, c-fos, and RGS2) by forskolin, indicating that KG-501 likely exerts a general effect on CREB activity. KG-501 can also inhibit NF-κB transcription activity because NF-κB also uses CBP as a cofactor to regulate gene expression. The migration of HUVECs induced by CM from A549 cells treated with IL-1β plus 10 μM of KG-501 is significantly lower than that induced by CM from A549 cells treated with IL-1β alone. At 10 μM, KG-501 suppresses the expression of all of the IL-1β–induced CXC chemokine genes except CXCL8. For the protein level, KG-501 significantly suppresses IL-1β–induced CXCL5 protein secretion. Similar effects of KG-501 are also observed in the H1734 cell line.