A Comparative Study of Fluorescence Assays in Screening for BRD4.

Fluorescence assay technologies are commonly used in high-throughput screening because of their sensitivity and ease of use. Different technologies have their characteristics and the rationale for choosing one over the other can differ between projects because of factors such as availability of reagents, assay performance, and cost. Another important factor to consider is the assay susceptibility to artifacts, which is almost as important as the ability of the assay to pick up active compounds. Spending time and money on false positives or missing the opportunity to build chemistry around false negatives is something that every drug project tries to avoid. We used a BET family Bromodomain, BRD4(1), to explore the outcome of a screening campaign using three fluorescent assay technologies as primary assays. A diverse 7,038 compound set was screened in fluorescence lifetime, fluorescence polarization, and homogeneous time-resolved fluorescence to look at primary hit rates, compound overlap, and hit confirmation rates. The results show a difference between the fluorescence assay technologies with three separate hit lists and some overlap. The confirmed hits from each assay were further evaluated for translation into cells (NanoBRET™). Most of the actives confirmed in cells originated from compounds that overlapped between the assays. In addition, a well-annotated set of compounds with undesirable mechanism of inhibition was screened against BRD4(1) to compare the ability to discriminate true hits from artifact compounds. The results indicate a difference between the assays in their ability to generate false positives and negatives.

Prospectively Validated Proteochemometric Models for the Prediction of Small-Molecule Binding to Bromodomain Proteins.

The bromodomain-containing proteins are a ligandable family of epigenetic readers, which play important roles in oncological, cardiovascular, and inflammatory diseases. Achieving selective inhibition of specific bromodomains is challenging, due to the limited understanding of compound and target selectivity features. In this study we build and benchmark proteochemometric (PCM) classification models on bioactivity data for 15,350 data points across 31 bromodomains, using both compound fingerprints and binding site protein descriptors as input variables, achieving a maximum performance as measured by the Matthew's Correlation Coefficient (MCC) of 0.83 on the external test set. We also find that histone peptide binding data can be used as a target descriptor to build a high performing PCM model (MCC 0.80), showing the transferability of peptide interaction information to modeling small-molecule bioactivity. 1,139 compounds were selected for prospective experimental testing by performing a virtual screen using model predictions and implementing conformal prediction, which resulted in 319 correctly predicted compound-target pair actives and the correct prediction for certain selectivity profile combinations of the four bromodomains tested against. We identify that conformal prediction can be used to fine-tune the balance between hit retrieval and hit structural diversity in a virtual screening setting. PCM can be applied to future virtual screening and compound design, including off-target prediction for bromodomains.

In Situ Target Engagement Studies in Adherent Cells.

A prerequisite for successful drugs is effective binding of the desired target protein in the complex environment of a living system. Drug-target engagement has typically been difficult to monitor in physiologically relevant models, and with current methods, especially, while maintaining spatial information. One recent technique for quantifying drug-target engagement is the cellular thermal shift assay (CETSA), in which ligand-induced protein stabilization is measured after a heat challenge. Here, we describe a CETSA protocol in live A431 cells for p38α (MAPK14), where remaining soluble protein is detected in situ, using high-content imaging in 384-well, microtiter plates. We validate this assay concept using a number of known p38α inhibitors and further demonstrate the potential of this technology for chemical probe and drug discovery purposes by performing a small pilot screen for novel p38α binders. Importantly, this protocol creates a workflow that is amenable to adherent cells in their native state and yields spatially resolved target engagement information measurable at the single-cell level.

Exploring Binding Mechanisms in Nuclear Hormone Receptors by Monte Carlo and X-ray-derived Motions.

In this study, we performed an extensive exploration of the ligand entry mechanism for members of the steroid nuclear hormone receptor family (androgen receptor, estrogen receptor α, glucocorticoid receptor, mineralocorticoid receptor, and progesterone receptor) and their endogenous ligands. The exploration revealed a shared entry path through the helix 3, 7, and 11 regions. Examination of the x-ray structures of the receptor-ligand complexes further showed two distinct folds of the helix 6-7 region, classified as "open" and "closed", which could potentially affect ligand binding. To improve sampling of the helix 6-7 loop, we incorporated motion modes based on principal component analysis of existing crystal structures of the receptors and applied them to the protein-ligand sampling. A detailed comparison with the anisotropic network model (an elastic network model) highlights the importance of flexibility in the entrance region. While the binding (interaction) energy of individual simulations can be used to score different ligands, extensive sampling further allows us to predict absolute binding free energies and analyze reaction kinetics using Markov state models and Perron-cluster cluster analysis, respectively. The predicted relative binding free energies for three ligands binding to the progesterone receptor are in very good agreement with experimental results and the Perron-cluster cluster analysis highlighted the importance of a peripheral binding site. Our analysis revealed that the flexibility of the helix 3, 7, and 11 regions represents the most important factor for ligand binding. Furthermore, the hydrophobicity of the ligand influences the transition between the peripheral and the active binding site.

Structure-Based Drug Design of Mineralocorticoid Receptor Antagonists to Explore Oxosteroid Receptor Selectivity.

The mineralocorticoid receptor (MR) is a nuclear hormone receptor involved in the regulation of body fluid and electrolyte homeostasis. In this study we explore selectivity triggers for a series of nonsteroidal MR antagonists to improve selectivity over other members of the oxosteroid receptor family. A biaryl sulfonamide compound was identified in a high-throughput screening (HTS) campaign. The compound bound to MR with pKi =6.6, but displayed poor selectivity over the glucocorticoid receptor (GR) and the progesterone receptor (PR). Following X-ray crystallography of MR in complex with the HTS hit, a compound library was designed that explored an induced-fit hypothesis that required movement of the Met852 side chain. An improvement in MR selectivity of 11- to 79-fold over PR and 23- to 234-fold over GR was obtained. Given the U-shaped binding conformation, macrocyclizations were explored, yielding a macrocycle that bound to MR with pKi =7.3. Two protein-ligand X-ray structures were determined, confirming the hypothesized binding mode for the designed compounds.

Benzoxazepines Achieve Potent Suppression of IL-17 Release in Human T-Helper 17 (TH 17) Cells through an Induced-Fit Binding Mode to the Nuclear Receptor RORγ.

RORγt, an isoform of the retinoic acid-related orphan receptor gamma (RORc, RORγ), has been identified as the master regulator of T-helper 17 (TH 17) cell function and development, making it an attractive target for the treatment of autoimmune diseases. Validation for this target comes from antibodies targeting interleukin-17 (IL-17), the signature cytokine produced by TH 17 cells, which have shown impressive results in clinical trials. Through focused screening of our compound collection, we identified a series of N-sulfonylated benzoxazepines, which displayed micromolar affinity for the RORγ ligand-binding domain (LBD) in a radioligand binding assay. Optimization of these initial hits resulted in potent binders, which dose-dependently decreased the ability of the RORγ-LBD to interact with a peptide derived from steroid receptor coactivator 1, and inhibited the release of IL-17 secretion from isolated and cultured human TH 17 cells with nanomolar potency. A cocrystal structure of inverse agonist 15 (2-chloro-6-fluoro-N-(4-{[3-(trifluoromethyl)phenyl]sulfonyl}-2,3,4,5-tetrahydro-1,4-benzoxazepin-7-yl)benzamide) bound to the RORγ-LBD illustrated that both hydrophobic interactions, leading to an induced fit around the substituted benzamide moiety of 15, as well as a hydrogen bond from the amide NH to His479 seemed to be important for the mechanism of action. This structure is compared with the structure of agonist 25 (N-(2-fluorophenyl)-4-[(4-fluorophenyl)sulfonyl]-2,3,4,5-tetrahydro-1,4-benzoxazepin-6-amine ) and structures of other known RORγ modulators.

Cognitive functioning and cortisol profiles in first episode major depression.

Major Depressive Disorder (MDD) is often associated with high levels of stress and disturbances in the Hypothalamic Pituitary Adrenal (HPA) system, yielding high levels of cortisol, in addition to cognitive dysfunction. Previous studies have shown a relationship between cortisol profile and cognitive functioning in recurrent MDD in general. More specifically, the association between hypercortisolism and cognitive functioning, such as memory and Executive Functioning (EF), and also more recently cortisol suppression has been explored. However, no studies have investigated these relationships in patients diagnosed with first episode MDD. The aim of the present study was to examine the relationship between cortisol levels before and after the Dexamethasone suppression test (DST) and cognitive function in first episode MDD patients. Twenty-one patients meeting the DSM-IV criteria for a first episode of MDD diagnosis were included in the study. The control group was matched for age, gender and education level. Cortisol was measured in saliva collected with Salivette sampling devices. Saliva samples were collected 4 times during a 24 hours period over two consecutive days: at awakening, after 45 minutes, after 7 hours and at 11 pm. Dexamethasone (1.0 mg) was given orally on Day 1 at 11 pm. The neuropsychological test battery consisted of standardized tests measuring executive functioning (EF) and memory functioning. Cortisol levels did not differ significantly between patients and controls on Day 1, except for the last sample before Dexamethasone administration, where the control group showed higher levels. Both groups showed suppression after Dexamethasone. On Day 2 there was a significant difference between groups at the third sample, showing a significantly lower level in the control group, suggesting that the controls have a more effective suppression profile than the patients. There were no significant correlations between cortisol levels before or after Dexamethasone and cognitive measures. The results indicate impairment on HPA-axis functioning in first episode MDD patients, with less suppression functioning compared to healthy controls, but no relationship between cortisol profile and cognitive functioning in EF or Memory.

Cognitive functioning and cortisol suppression in recurrent major depression.

Major Depressive Disorder (MDD) is often associated with high levels of stress and disturbances in the hypothalamic-pituitary-adrenal (HPA) system, yielding high levels of cortisol in addition to cognitive dysfunction. The aim of the present study was to examine the relation between cortisol levels after the dexamethasone suppression test and cognitive function in recurrent unipolar MDD patients. Twenty-four patients meeting the Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.) criteria for a recurrent MDD diagnosis were included in the study. The control group was matched for age, sex, and education level. Cortisol was measured in saliva collected with Salivette sampling devices. Saliva samples were collected four times during a 24-hr period over two consecutive days: at awakening, after 45 min, after 7 hr, and at 11:00 p.m. One milligram of dexamethasone was given on Day 1 at 11:00 p.m. The neuropsychological test battery consisted of standardized tests measuring cognitive functioning within verbal and visual memory, as well as executive functioning. Cortisol levels did not differ between patients and controls on Day 1. Cortisol levels in patients were higher than in controls at awakening on Day 2 (D2S1), after dexamethasone administration the previous evening. All significant correlations between cognitive measures and cortisol at D2S1 were negative, indicating that low suppression after intake of dexamethasone is related to poor cognitive functioning. Significant relations were found in three of the cognitive tests measuring verbal memory, semantic fluency, and inhibition. The present findings indicate that dysregulation of the HPA-axis is related to poor verbal memory functioning. There was no firm evidence that abnormal cortisol levels were associated with inhibition difficulties.

Glucose and fatty acid metabolism in McA-RH7777 hepatoma cells vs. rat primary hepatocytes: responsiveness to nutrient availability.

The overabundance of dietary fats and simple carbohydrates contributes significantly to obesity and metabolic disorders associated with obesity. The liver balances glucose and lipid distribution, and disruption of this balance plays a key role in these metabolic syndromes. We investigated (1) how hepatocytes balance glucose and fatty acid metabolism when one or both nutrients are supplied in abundance and (2) whether rat hepatoma cells (McA-RH7777) reflect nutrient partitioning in a similar manner as compared with primary hepatocytes. Increasing media palmitate concentration increased fatty acid uptake, triglyceride synthesis and beta-oxidation. However, hepatoma cells had a 2-fold higher fatty acid uptake and a 2-fold lower fatty acid oxidation as compared with primary hepatocytes. McA-RH7777 cells did not synthesize significant amounts of glycogen and preferentially metabolized the glucose into lipids or into oxidation. In primary hepatocytes, the glucose was mostly spared from oxidation and instead partitioned into both de novo glycogen and lipid synthesis. Overall, lipid production was rapidly induced in response to either glucose or fatty acid excess and this may be one of the earliest indicators of metabolic syndrome development associated with nutrient excess.