Abstract P4-15-08: Discovery of a potent inhibitor of CREB-mediated gene transcription that completely suppresses the growth of triple-negative breast cancer cells

Abstract

Abstract Background: Breast cancers are a heterogeneous group of diseases with distinct and complex mechanisms of pathogenesis. Triple-negative breast cancers (TNBC) form a subgroup of breast cancers with poor prognosis. TNBCs lack the expression of estrogen receptor (ER), progesterone receptor (PR) or HER2 and no targeted therapies exist. The cyclic-AMP (cAMP) response element binding protein (CREB) is a stimulus-induced transcription factor activated by multiple extracellular signals through phosphorylation. The transcription activity of CREB depends on its phosphorylation at Ser133 by mitogen- and stress-activated protein serine/threonine kinases, which are often dysregulated in TNBCs. The phosphorylated CREB (p-CREB) can then bind the mammalian transcription co-activator, CREB-binding protein (CBP), via the kinase-inducible domain (KID) in CREB and KID-interacting (KIX) domain in CBP. This binding event will further recruit other transcriptional machinery to the gene promoter to initiate CREB-dependent gene transcription. CREB is overexpressed in breast cancer tissues compared to normal mammary tissues and the level of expression inversely correlates with disease-free survival. Genetic studies have shown that inhibition of CREB's activity leads to decreased breast cancer cell proliferation. We describe here the discovery of a potent small molecule inhibitor of CREB-mediated gene transcription with in vitro and in vivo activity in TNBCs. Methods: The small molecule inhibitor (compound 1) was reporter earlier by us (Li and Xiao ChemBioChem 2009). Starting from this lead compound, we designed and synthesized a more potent compound 2. The in vitro antiproliferative activity and apoptosis induction were evaluated in MDA-MB-231 and MDA-MB-468 cells with MTT assays and flow cytometry, respectively. In vivo activity was investigated in a human xenograft model of MDA-MB-468. The CREB target gene expression was investigated by Western blot and qRT-PCR analysis. Results: Starting from compound 1, which is a low micromolar and cell-permeable inhibitor of CREB-mediated gene transcription, we designed and synthesized compound 2. Compound 2 potently inhibited CREB-mediated gene transcription with IC50 ∼80 nM. In vitro, this compound inhibited proliferation of MDA-MB-231 and MDA-MB-468 cells with concomitant activation of apoptosis and necrosis. In contrast, compound 2 was not toxic to normal human mammary epithelial cells. In vivo, compound 2 completely suppressed the growth of MDA-MB-468 cells at a dose not toxic to the mice. Conclusion: Compound 2 potently inhibited CREB-mediated gene transcription and TNBC cell growth in vitro and in vivo. These results suggest that CREB is a promising druggable target for TNBCs. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-15-08.