Small-molecule inhibitors that target bromodomains outside of the bromodomain and extra-terminal (BET) sub-family are lacking. Here, we describe highly potent and selective ligands for the bromodomain module of the human lysine acetyl transferase CBP/p300, developed from a series of 5-isoxazolyl-benzimidazoles. Our starting point was a fragment hit, which was optimized into a more potent and selective lead using parallel synthesis employing Suzuki couplings, benzimidazole-forming reactions, and reductive aminations. The selectivity of the lead compound against other bromodomain family members was investigated using a thermal stability assay, which revealed some inhibition of the structurally related BET family members. To address the BET selectivity issue, X-ray crystal structures of the lead compound bound to the CREB binding protein (CBP) and the first bromodomain of BRD4 (BRD4(1)) were used to guide the design of more selective compounds. The crystal structures obtained revealed two distinct binding modes. By varying the aryl substitution pattern and developing conformationally constrained analogues, selectivity for CBP over BRD4(1) was increased. The optimized compound is highly potent (K_d = 21 nM) and selective, displaying 40-fold selectivity over BRD4(1). Cellular activity was demonstrated using fluorescence recovery after photo-bleaching (FRAP) and a p53 reporter assay. The optimized compounds are cell-active and have nanomolar affinity for CBP/p300; therefore, they should be useful in studies investigating the biological roles of CBP and p300 and to validate the CBP and p300 bromodomains as therapeutic targets.

Tumor hypoxia confers resistance to many modalities of anticancer therapy. The endoplasmic reticulum (ER) is highly sensitive to severe hypoxic stress and results in the activation of the unfolded protein response. ATF4 is the main transcriptional regulator of the cellular hypoxic response to the UPR and activates genes that promote restoration of normal ER function and survival under hypoxia. Elevated expression of ATF4 is associated with resistance to current chemotherapeutic drugs including DNA-interactive and damaging agents, nonsteroidal anti-inflammatory drugs and proteasome inhibitors. ATF4 decreases the antitumor activity of chemotherapy by mechanisms involving expression of genes involved in oxidative stress resistance, redox homeostasis and inhibitors of apoptosis. ATF4 plays also a crucial role in resistance to proteasomal inhibitor bortezomib (PS-341) by the induction of prosurvival pathways, such as autophagy, that can relieve the protein overload in bortezomib treated cells. Inhibition of AT...

Hypoxia in the microenvironment of many solid tumours is an important determinant of malignant progression. The ISR (integrated stress response) protects cells from the ER (endoplasmic reticulum) stress caused by severe hypoxia. Likewise, autophagy is a mechanism by which cancer cells can evade hypoxic cell death. In the present paper we report that the autophagy-initiating kinase ULK1 (UNC51-like kinase 1) is a direct transcriptional target of ATF4 (activating transcription factor 4), which drives the expression of ULK1 mRNA and protein in severe hypoxia and ER stress. We demonstrate that ULK1 is required for autophagy in severe hypoxia and that ablation of ULK1 causes caspase-3/7-independent cell death. Furthermore, we report that ULK1 expression is associated with a poor prognosis in breast cancer. Collectively, the findings of the present study identify transcriptional up-regulation of ULK1 as a novel arm of the ISR, and suggest ULK1 as a potentially effective target for cancer therapy.

Introduction: Activating transcription factor 4 (ATF4) is a member of the activating transcription factor family. ATF4 expression is increased in response to a diverse array of microenvironmental stresses including amino acid depletion, oxidative stress and endoplasmic reticulum (ER) stress that are sensed by upstream eukaryotic translation initiation factor 2α (eIF2α) kinases. In tumours, ATF4 expression is detected in hypoxic- and nutrient-deprived regions where it promotes metabolic homeostasis and cancer cell survival by transcriptionally regulating amino acid uptake and biosynthesis, autophagy, redox balance and angiogenesis. Areas covered: The mechanism governing translational expression of ATF4 is discussed along with the physiological roles of ATF4 in growth and development. Conditions that result in ATF4 expression in tumours are described with a focus on the role of ATF4 in cancer progression and treatment resistance. Several approaches to target ATF4 are presented including strategies aimed at ...

The hypoxic areas of solid cancers represent a negative prognostic factor irrespective of which treatment modality is chosen for the patient. Still, after almost 80 years of focus on the problems created by hypoxia in solid tumours, we still largely lack methods to deal efficiently with these treatment-resistant cells. The consequences of this lack may be serious for many patients: Not only is there a negative correlation between the hypoxic fraction in tumours and the outcome of radiotherapy as well as many types of chemotherapy, a correlation has been shown between the hypoxic fraction in tumours and cancer metastasis. Thus, on a fundamental basis the great variety of problems related to hypoxia in cancer treatment has to do with the broad range of functions oxygen (and lack of oxygen) have in cells and tissues. Therefore, activation–deactivation of oxygen-regulated cascades related to metabolism or external signalling are important areas for the identification of mechanisms as potential targets for hypoxia-specific treatment. Also the chemistry related to reactive oxygen radicals (ROS) and the biological handling of ROS are part of the problem complex. The problem is further complicated by the great variety in oxygen concentrations found in tissues. For tumour hypoxia to be used as a marker for individualisation of treatment there is a need for non-invasive methods to measure oxygen routinely in patient tumours. A large-scale collaborative EU-financed project 2009–2014 denoted METOXIA has studied all the mentioned aspects of hypoxia with the aim of selecting potential targets for new hypoxia-specific therapy and develop the first stage of tests for this therapy. A new non-invasive PET-imaging method based on the 2-nitroimidazole [¹⁸F]-HX4 was found to be promising in a clinical trial on NSCLC patients. New preclinical models for testing of the metastatic potential of cells were developed, both in vitro (2D as well as 3D models) and in mice (orthotopic grafting). Low density quantitative real-time polymerase chain reaction (qPCR)-based assays were developed measuring multiple hypoxia-responsive markers in parallel to identify tumour hypoxia-related patterns of gene expression. As possible targets for new therapy two main regulatory cascades were prioritised: The hypoxia-inducible-factor (HIF)-regulated cascades operating at moderate to weak hypoxia (<1% O₂), and the unfolded protein response (UPR) activated by endoplasmatic reticulum (ER) stress and operating at more severe hypoxia (<0.2%). The prioritised targets were the HIF-regulated proteins carbonic anhydrase IX (CAIX), the lactate transporter MCT4 and the PERK/eIF2α/ATF4-arm of the UPR. The METOXIA project has developed patented compounds targeting CAIX with a preclinical documented effect. Since hypoxia-specific treatments alone are not curative they will have to be combined with traditional anti-cancer therapy to eradicate the aerobic cancer cell population as well.