Fuchun Xie

The ITIM-containing receptor LAIR1 is essential for acute myeloid leukaemia development

Conventional strategies are not particularly successful in the treatment of leukaemia, and identification of signalling pathways crucial to the activity of leukaemia stem cells will provide targets for the development of new therapies. Here we report that certain receptors containing the immunoreceptor tyrosine-based inhibition motif (ITIM) are crucial for the development of acute myeloid leukaemia (AML). Inhibition of expression of the ITIM-containing receptor LAIR1 does not affect normal haematopoiesis but abolishes leukaemia development. LAIR1 induces activation of SHP-1, which acts as a phosphatase-independent signalling adaptor to recruit CAMK1 for activation of downstream CREB in AML cells. The LAIR1–SHP-1–CAMK1–CREB pathway sustains the survival and self-renewal of AML stem cells. Intervention in the signalling initiated by ITIM-containing receptors such as LAIR1 may result in successful treatment of AML.

Identification of a Potent Inhibitor of CREB-Mediated Gene Transcription with Efficacious in Vivo Anticancer Activity.

Recent studies have shown that nuclear transcription factor cyclic adenosine monophosphate response element binding protein (CREB) is overexpressed in many different types of cancers. Therefore, CREB has been pursued as a novel cancer therapeutic target. Naphthol AS-E and its closely related derivatives have been shown to inhibit CREB-mediated gene transcription and cancer cell growth. Previously, we identified naphthamide 3a as a different chemotype to inhibit CREB’s transcription activity. In a continuing effort to discover more potent CREB inhibitors, a series of structural congeners of 3a was designed and synthesized. Biological evaluations of these compounds uncovered compound 3i (666-15) as a potent and selective inhibitor of CREB-mediated gene transcription (IC50 = 0.081 ± 0.04 μM). 666-15 also potently inhibited cancer cell growth without harming normal cells. In an in vivo MDA-MB-468 xenograft model, 666-15 completely suppressed the tumor growth without overt toxicity. These results further support the potential of CREB as a valuable cancer drug target.

Small molecule inhibition of cAMP response element binding protein in human acute myeloid leukemia cells

The transcription factor CREB (cAMP Response-Element Binding Protein) is overexpressed in the majority of acute myeloid leukemia (AML) patients, and this is associated with a worse prognosis. Previous work revealed that CREB overexpression augmented AML cell growth, while CREB knockdown disrupted key AML cell functions in vitro. In contrast, CREB knockdown had no effect on long-term hematopoietic stem cell activity in mouse transduction/transplantation assays. Together, these studies position CREB as a promising drug target for AML. To test this concept, a small molecule inhibitor of CREB, XX-650-23, was developed. This molecule blocks a critical interaction between CREB and its required co-activator CBP (CREB Binding Protein), leading to disruption of CREB-driven gene expression. Inhibition of CBP–CREB interaction induced apoptosis and cell-cycle arrest in AML cells, and prolonged survival in vivo in mice injected with human AML cells. XX-650-23 had little toxicity on normal human hematopoietic cells and tissues in mice. To understand the mechanism of XX-650-23, we performed RNA-seq, ChIP-seq and Cytometry Time of Flight with human AML cells. Our results demonstrate that small molecule inhibition of CBP–CREB interaction mostly affects apoptotic, cell-cycle and survival pathways, which may represent a novel approach for AML therapy.

Identification, synthesis and evaluation of substituted benzofurazans as inhibitors of CREB-mediated gene transcription

Cyclic-AMP response-element binding protein (CREB) is a stimulus-activated transcription factor. Its transcription activity requires its binding with CREB-binding protein (CBP) after CREB is phosphorylated at Ser133. The domains involved for CREB-CBP interaction are kinase-inducible domain (KID) from CREB and KID-interacting domain (KIX) from CBP. Recent studies suggest that CREB is an attractive target for novel cancer therapeutics. To identify novel chemotypes as inhibitors of KIX-KID interaction, we screened the NCI-diversity set of compounds using a split renilla luciferase assay and identified 2-[(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thio]pyridine 1-oxide (compound 1, NSC228155) as a potent inhibitor of KIX-KID interaction. However, compound 1 was not particularly selective against CREB-mediated gene transcription in living HEK 293T cells. Further structure-activityrelationship studies identified 4-aniline substituted nitrobenzofurazans with improved selectivity.

Functional screening for G protein-coupled receptor targets of 14,15-epoxyeicosatrienoic acid

Epoxyeicosatrienoic acids (EETs) are potent vasodilators that play important roles in cardiovascular physiology and disease, yet the molecular mechanisms underlying the biological actions of EETs are not fully understood. Multiple lines of evidence suggest that the actions of EETs are in part mediated via G protein-coupled receptor (GPCR) signaling, but the identity of such a receptor has remained elusive. We sought to identify 14,15-EET-responsive GPCRs. A set of 105 clones were expressed in Xenopus oocyte and screened for their ability to activate cAMP-dependent chloride current. Several receptors responded to micromolar concentrations of 14,15-EET, with the top five being prostaglandin receptor subtypes (PTGER2, PTGER4, PTGFR, PTGDR, PTGER3IV). Overall, our results indicate that multiple low-affinity 14,15-EET GPCRs are capable of increasing cAMP levels following 14,15-EET stimulation, highlighting the potential for cross-talk between prostanoid and other ecosanoid GPCRs. Our data also indicate that none of the 105 GPCRs screened met our criteria for a high-affinity receptor for 14,15-EET.

Novel Type of Prodrug Activation through a Long-Range O,N-Acyl Transfer: A Case of Water-Soluble CREB Inhibitor.

CREB (cAMP response element binding protein) has been shown to play an important role in tumor initiation, progression, and metastasis. We discovered that naphthol AS-E, a cell-permeable CREB inhibitor, presented antiproliferative activity in a broad panel of cancer cell lines in vitro. However, it has limited aqueous solubility. In this report, we described a water-soluble inhibitor (compound 6) of CREB-mediated gene transcription with in vivo anticancer activity. Unexpectedly, compound 6 was found to be a prodrug of compound 12 necessitating an unprecedented long-range O,N-acyl transfer. The rate of this transfer was pH- and temperature-dependent. To the best of our knowledge, this is the first time to show that a long-range O,N-acyl transfer could be exploited as a prodrug activation strategy to improve aqueous solubility. This type of prodrug may be applicable to other structures with spatially arranged hydroxyl amide to improve their aqueous solubility.

Systemic Inhibition of CREB is Well-tolerated in vivo

cAMP-response element binding protein (CREB) is a nuclear transcription factor activated by multiple extracellular signals including growth factors and hormones. These extracellular cues activate CREB through phosphorylation at Ser133 by various protein serine/threonine kinases. Once phosphorylated, it promotes its association with transcription coactivators CREB-binding protein (CBP) and its paralog p300 to activate CREB-dependent gene transcription. Tumor tissues of different origins have been shown to present overexpression and/or overactivation of CREB, indicating CREB as a potential cancer drug target. We previously identified 666-15 as a potent inhibitor of CREB with efficacious anti-cancer activity both in vitro and in vivo. Herein, we investigated the specificity of 666-15 and evaluated its potential in vivo toxicity. We found that 666-15 was fairly selective in inhibiting CREB. 666-15 was also found to be readily bioavailable to achieve pharmacologically relevant concentrations for CREB inhibition. Furthermore, the mice treated with 666-15 showed no evidence of changes in body weight, complete blood count, blood chemistry profile, cardiac contractility and tissue histologies from liver, kidney and heart. For the first time, these results demonstrate that pharmacological inhibition of CREB is well-tolerated in vivo and indicate that such inhibitors should be promising cancer therapeutics.

Synthesis and Evaluation of an O-Aminated Naphthol AS-E as a Prodrug of CREB-mediated Gene Transcription Inhibition.

An O-aminated naphthol AS-E was designed as a prodrug to achieve reductive activation and improved aqueous solubility. During the synthesis of this designed compound, a novel transformation from aryl triflates and ethyl acetohydroximate to oxazoles was discovered. Although the initially designed O-amino naphthol AS-E was not made successfully, the eventually synthesized O-tert-butylamino derivative was found to be biologically inactive, suggesting that reductive N-O cleavage in this compound was not facile due to unfavorable steric and electronic effects.

Design, synthesis and biological evaluation of regioisomers of 666-15 as inhibitors of CREB-mediated gene transcription

cAMP-response element binding protein (CREB) is a nuclear transcription factor that has been implicated in the pathogenesis and maintenance of various types of human cancers. Identification of small molecule inhibitors of CREB-mediated gene transcription has been pursued as a novel strategy for developing cancer therapeutics. We recently discovered a potent and cell-permeable CREB inhibitor called 666-15. 666-15 is a bisnaphthamide and has been shown to possess efficacious anti-breast cancer activity without toxicity in vivo. In this study, we designed and synthesized a series of analogs of 666-15 to probe the importance of regiochemistry in naphthalene ring B. Biological evaluations of these analogs demonstrated that the substitution pattern of the alkoxy and carboxamide in naphthalene ring B is very critical for maintaining potent CREB inhibition activity, suggesting that the unique bioactive conformation accessible in 666-15 is critically important.

Synthesis of 14,15-EET from Arachidonic Acid Using Urea-Hydrogen Peroxide as the Oxidant

Abstract 14,15- Epoxyeicosatrienoic acid (14,15-EET) is an endogenous bioactive lipid with pharmacological benefits in multiple cardiovascular diseases. We describe here a practical synthesis of 14,15-EET from arachidonic acid using urea–hydrogen peroxide (UHP) as the oxidant. GRAPHICAL ABSTRACT