Enhanced Renewal of Erythroid Progenitors in Myelodysplastic Anemia by Peripheral Serotonin.

Tryptophan as the precursor of several active compounds, including kynurenine and serotonin, is critical for numerous important metabolic functions. Enhanced tryptophan metabolism toward the kynurenine pathway has been associated with myelodysplastic syndromes (MDSs), which are preleukemic clonal diseases characterized by dysplastic bone marrow and cytopenias. Here, we reveal a fundamental role for tryptophan metabolized along the serotonin pathway in normal erythropoiesis and in the physiopathology of MDS-related anemia. We identify, both in human and murine erythroid progenitors, a functional cell-autonomous serotonergic network with pro-survival and proliferative functions. In vivo studies demonstrate that pharmacological increase of serotonin levels using fluoxetine, a common antidepressant, has the potential to become an important therapeutic strategy in low-risk MDS anemia refractory to erythropoietin.

Aligning Potency and Pharmacokinetic Properties for Pyridine-Based NCINIs.

Optimization of pyridine-based noncatalytic site integrase inhibitors (NCINIs) based on compound 2 has led to the discovery of molecules capable of inhibiting virus harboring N124 variants of HIV integrase (IN) while maintaining minimal contribution of enterohepatic recirculation to clearance in rat. Structure-activity relationships at the C6 position established chemical space where the extent of enterohepatic recirculation in the rat is minimized. Desymmetrization of the C4 substituent allowed for potency optimization against virus having the N124 variant of integrase. Combination of these lessons led to the discovery of compound 20, having balanced serum-shifted antiviral potency and minimized excretion in to the biliary tract in rat, potentially representing a clinically viable starting point for a new treatment option for individuals infected with HIV.

Implementation of ultrasonic sensing for high resolution measurement of binary gas mixture fractions.

We describe an ultrasonic instrument for continuous real-time analysis of the fractional mixture of a binary gas system. The instrument is particularly well suited to measurement of leaks of a high molecular weight gas into a system that is nominally composed of a single gas. Sensitivity < 5 × 10(-5) is demonstrated to leaks of octaflouropropane (C3F8) coolant into nitrogen during a long duration (18 month) continuous study. The sensitivity of the described measurement system is shown to depend on the difference in molecular masses of the two gases in the mixture. The impact of temperature and pressure variances on the accuracy of the measurement is analysed. Practical considerations for the implementation and deployment of long term, in situ ultrasonic leak detection systems are also described. Although development of the described systems was motivated by the requirements of an evaporative fluorocarbon cooling system, the instrument is applicable to the detection of leaks of many other gases and to processes requiring continuous knowledge of particular binary gas mixture fractions.

Discovery of BI 224436, a Noncatalytic Site Integrase Inhibitor (NCINI) of HIV-1.

An assay recapitulating the 3' processing activity of HIV-1 integrase (IN) was used to screen the Boehringer Ingelheim compound collection. Hit-to-lead and lead optimization beginning with compound 1 established the importance of the C3 and C4 substituent to antiviral potency against viruses with different aa124/aa125 variants of IN. The importance of the C7 position on the serum shifted potency was established. Introduction of a quinoline substituent at the C4 position provided a balance of potency and metabolic stability. Combination of these findings ultimately led to the discovery of compound 26 (BI 224436), the first NCINI to advance into a phase Ia clinical trial.

Preclinical profile of BI 224436, a novel HIV-1 non-catalytic-site integrase inhibitor.

BI 224436 is an HIV-1 integrase inhibitor with effective antiviral activity that acts through a mechanism that is distinct from that of integrase strand transfer inhibitors (INSTIs). This 3-quinolineacetic acid derivative series was identified using an enzymatic integrase long terminal repeat (LTR) DNA 3'-processing assay. A combination of medicinal chemistry, parallel synthesis, and structure-guided drug design led to the identification of BI 224436 as a candidate for preclinical profiling. It has antiviral 50% effective concentrations (EC50s) of <15 nM against different HIV-1 laboratory strains and cellular cytotoxicity of >90 µM. BI 224436 also has a low, ∼2.1-fold decrease in antiviral potency in the presence of 50% human serum and, by virtue of a steep dose-response curve slope, exhibits serum-shifted EC95 values ranging between 22 and 75 nM. Passage of virus in the presence of inhibitor selected for either A128T, A128N, or L102F primary resistance substitutions, all mapping to a conserved allosteric pocket on the catalytic core of integrase. BI 224436 also retains full antiviral activity against recombinant viruses encoding INSTI resistance substitutions N155S, Q148H, and E92Q. In drug combination studies performed in cellular antiviral assays, BI 224436 displays an additive effect in combination with most approved antiretrovirals, including INSTIs. BI 224436 has drug-like in vitro absorption, distribution, metabolism, and excretion (ADME) properties, including Caco-2 cell permeability, solubility, and low cytochrome P450 inhibition. It exhibited excellent pharmacokinetic profiles in rat (clearance as a percentage of hepatic flow [CL], 0.7%; bioavailability [F], 54%), monkey (CL, 23%; F, 82%), and dog (CL, 8%; F, 81%). Based on the excellent biological and pharmacokinetic profile, BI 224436 was advanced into phase 1 clinical trials.

Integrated strategies for identifying leads that target the NS3 helicase of the hepatitis C virus.

Future treatments for individuals infected by the hepatitis C virus (HCV) will likely involve combinations of compounds that inhibit multiple viral targets. The helicase of HCV is an attractive target with no known drug candidates in clinical trials. Herein we describe an integrated strategy for identifying fragment inhibitors using structural and biophysical techniques. Based on an X-ray structure of apo HCV helicase and in silico and bioinformatic analyses of HCV variants, we identified that one site in particular (labeled 3 + 4) was the most conserved and attractive pocket to target for a drug discovery campaign. Compounds from multiple sources were screened to identify inhibitors or binders to this site, and enzymatic and biophysical assays (NMR and SPR) were used to triage the most promising ligands for 3D structure determination by X-ray crystallography. Medicinal chemistry and biophysical evaluations focused on exploring the most promising lead series. The strategies employed here can have general utility in drug discovery.

Molecular dynamics simulations and structure-based rational design lead to allosteric HCV NS5B polymerase thumb pocket 2 inhibitor with picomolar cellular replicon potency.

The design and preliminary SAR of a new series of 1H-quinazolin-4-one (QAZ) allosteric HCV NS5B thumb pocket 2 (TP-2) inhibitors was recently reported. To support optimization efforts, a molecular dynamics (MD) based modeling workflow was implemented, providing information on QAZ binding interactions with NS5B. This approach predicted a small but critical ligand-binding induced movement of a protein backbone region which increases the pocket size and improves access to the backbone carbonyl groups of Val 494 and Pro 495. This localized backbone shift was consistent with key SAR results and was subsequently confirmed by X-ray crystallography. The MD protocol guided the design of inhibitors, exploiting novel H-bond interactions with the two backbone carbonyl groups, leading to the first thumb pocket 2 NS5B inhibitor with picomolar antiviral potency in genotype (gt) 1a and 1b replicons (EC50 = 120 and 110 pM, respectively) and with EC50 ≤ 80 nM against gt 2-6.

Monitoring drug self-aggregation and potential for promiscuity in off-target in vitro pharmacology screens by a practical NMR strategy.

A simple NMR assay was applied to monitor the tendency of compounds to self-aggregate in aqueous media. The observation of unusual spectral trends as a function of compound concentration appears to be signatory of the formation of self-assemblies. (1)H NMR resonances of aggregating compounds were sensitive to the presence of a range of molecular assemblies in solution including large molecular-size entities, smaller multimers, and mixtures of assembled species. The direct observation of aggregates via unusual NMR spectra also correlated with promiscuous behavior of molecules in off-target in vitro pharmacology assays. This empirical assay can have utility for predicting compound promiscuity and should complement predictive methods that principally rely on the computing of descriptors such as lipophilicity (cLogP) and topological surface area (TPSA). This assay should serve as a practical tool for medicinal chemists to monitor compound attributes in aqueous solution and various pharmacologically relevant media, as demonstrated herein.

Compound aggregation in drug discovery: implementing a practical NMR assay for medicinal chemists.

The pharmaceutical industry has recognized that many drug-like molecules can self-aggregate in aqueous media and have physicochemical properties that skew experimental results and decisions. Herein, we introduce the use of a simple NMR strategy for detecting the formation of aggregates using dilution experiments that can be performed on equipment prevalent in most synthetic chemistry departments. We show that (1)H NMR resonances are sensitive to large molecular-size entities and to smaller multimers and mixtures of species. Practical details are provided for sample preparation and for determining the concentrations of single molecule, aggregate entities, and precipitate. The critical concentrations above which aggregation begins can be found and were corroborated by comparisons with light scattering techniques. Disaggregation can also be monitored using detergents. This NMR assay should serve as a practical and readily available tool for medicinal chemists to better characterize how their compounds behave in aqueous media and influence drug design decisions.

A novel inhibitor-binding site on the HIV-1 capsid N-terminal domain leads to improved crystallization via compound-mediated dimerization.

Despite truly impressive achievements in the global battle against HIV there remains a need for new drugs directed against novel targets, and the viral capsid protein (CA) may represent one such target. Intense structural characterization of CA over the last two decades has provided unprecedented insight into the structure and assembly of this key viral protein. Furthermore, several inhibitor-binding sites that elicit antiviral activity have been reported on CA, two of which are located on its N-terminal domain (CANTD). In this work, the binding of a novel capsid-assembly inhibitor that targets a unique inhibitory site on CANTD is reported. Moreover, whereas cocrystallization of CANTD in complex with ligands has proven to be challenging in the past, the use of this inhibitor as a tool compound is shown to vastly facilitate ternary cocrystallizations with CANTD. This improvement in crystallization is likely to be achieved through the formation of a compound-mediated homodimer, the intrinsic symmetry of which greatly increases the prospect of generating a crystal lattice. While protein engineering has been used in the literature to support a link between the inherent symmetry of a macromolecule and its propensity to crystallize, to our knowledge this work represents the first use of a synthetic ligand for this purpose.

Optimization of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of HIV capsid assembly inhibitors 2: structure-activity relationships (SAR) of the C3-phenyl moiety.

Detailed structure-activity relationships of the C3-phenyl moiety that allow for the optimization of antiviral potency of a series of 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione inhibitors of HIV capsid (CA) assembly are described. Combination of favorable substitutions gave additive SAR and allowed for the identification of the most potent compound in the series, analog 27. Productive SAR also transferred to the benzotriazepine and spirobenzodiazepine scaffolds, providing a solution to the labile stereocenter at the C3 position. The molecular basis of how compound 27 inhibits mature CA assembly is rationalized using high-resolution structural information. Our understanding of how compound 27 may inhibit immature Gag assembly is also discussed.

Optimization of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of HIV capsid assembly inhibitors 1: addressing configurational instability through scaffold modification.

The optimization of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly that possess a labile stereocenter at C3 is described. Quaternization of the C3 position of compound 1 in order to prevent racemization gave compound 2, which was inactive in our capsid disassembly assay. A likely explanation for this finding was revealed by in silico analysis predicting a dramatic increase in energy of the bioactive conformation upon quaternization of the C3 position. Replacement of the C3 of the diazepine ring with a nitrogen atom to give the 1,5-dihydro-benzo[f][1,3,5]triazepine-2,4-dione analog 4 was well tolerated. Introduction of a rigid spirocyclic system at the C3 position gave configurationally stable 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione analog 5, which was able to access the bioactive conformation without a severe energetic penalty and inhibit capsid assembly. Preliminary structure-activity relationships (SAR) and X-ray crystallographic data show that knowledge from the 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly can be transferred to these new scaffolds.

Discovery and structural characterization of a new inhibitor series of HIV-1 nucleocapsid function: NMR solution structure determination of a ternary complex involving a 2:1 inhibitor/NC stoichiometry.

The nucleocapsid (NC) protein is an essential factor with multiple functions within the human immunodeficiency virus type 1 (HIV-1) replication cycle. In this study, we describe the discovery of a novel series of inhibitors that targets HIV-1 NC protein by blocking its interaction with nucleic acids. This series was identified using a previously described capsid (CA) assembly assay, employing a recombinant HIV-1 CA-NC protein and immobilized TG-rich deoxyoligonucleotides. Using visible absorption spectroscopy, we were able to demonstrate that this new inhibitor series binds specifically and reversibly to the NC with a peculiar 2:1 stoichiometry. A fluorescence-polarization-based binding assay was also developed in order to monitor the inhibitory activities of this series of inhibitors. To better characterize the structural aspect of inhibitor binding onto NC, we performed NMR studies using unlabeled and (13)C,(15)N-double-labeled NC(1-55) protein constructs. This allowed the determination of the solution structure of a ternary complex characterized by two inhibitor molecules binding to the two zinc knuckles of the NC protein. To the best of our knowledge, this represents the first report of a high-resolution structure of a small-molecule inhibitor bound to NC, demonstrating sub-micromolar potency and moderate antiviral potency with one analogue of the series. This structure was compared with available NC/oligonucleotide complex structures and further underlined the high flexibility of the NC protein, allowing it to adopt many conformations in order to bind its different oligonucleotide/nucleomimetic targets. In addition, analysis of the interaction details between the inhibitor molecules and NC demonstrated how this novel inhibitor series is mimicking the guanosine nucleobases found in many reported complex structures.

Human intestinal transporter database: QSAR modeling and virtual profiling of drug uptake, efflux and interactions.

PURPOSE: Membrane transporters mediate many biological effects of chemicals and play a major role in pharmacokinetics and drug resistance. The selection of viable drug candidates among biologically active compounds requires the assessment of their transporter interaction profiles. METHODS: Using public sources, we have assembled and curated the largest, to our knowledge, human intestinal transporter database (>5,000 interaction entries for >3,700 molecules). This data was used to develop thoroughly validated classification Quantitative Structure-Activity Relationship (QSAR) models of transport and/or inhibition of several major transporters including MDR1, BCRP, MRP1-4, PEPT1, ASBT, OATP2B1, OCT1, and MCT1. RESULTS: QSAR models have been developed with advanced machine learning techniques such as Support Vector Machines, Random Forest, and k Nearest Neighbors using Dragon and MOE chemical descriptors. These models afforded high external prediction accuracies of 71-100% estimated by 5-fold external validation, and showed hit retrieval rates with up to 20-fold enrichment in the virtual screening of DrugBank compounds. CONCLUSIONS: The compendium of predictive QSAR models developed in this study can be used for virtual profiling of drug candidates and/or environmental agents with the optimal transporter profiles.

Inhibition of HIV-1 capsid assembly: optimization of the antiviral potency by site selective modifications at N1, C2 and C16 of a 5-(5-furan-2-yl-pyrazol-1-yl)-1H-benzimidazole scaffold.

A uHTS campaign led to the discovery of a 5-(5-furan-2-ylpyrazol-1-yl)-1H-benzimidazole series that inhibits assembly of HIV-1 capsid. Synthetic manipulations at N1, C2 and C16 positions improved the antiviral potency by a . The X-ray structure of 33 complexed with the capsid N-terminal domain allowed identification of major interactions between the inhibitor and the protein.

HTS promiscuity analyses for accelerating decision making.

Frequent hitters are compounds that are detected as a "hit" in multiple high-throughput screening (HTS) assays. Such behavior is specific (e.g., target family related) or unspecific (e.g., reactive compounds) or can result from a combination of such behaviors. Detecting such hits while predicting the underlying reason behind their promiscuous behavior is desirable because it provides valuable information not only about the compounds themselves but also about the assay methodology and target classes at hand. This information can also greatly reduce cost and time during HTS hit profiling. The present study exemplifies how to mine large HTS data repositories, such as the one at Boehringer Ingelheim, to identify frequent hitters, gain further insights into the causes of promiscuous behavior, and generate models for predicting promiscuous compounds. Applications of this approach are demonstrated using two recent large-scale HTS assays. The authors believe this analysis and its concrete applications are valuable tools for streamlining and accelerating decision-making processes during the course of hit discovery.

Discovery of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly.

The discovery of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly is described. Synthesis of analogs of the 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione hit established structure-activity relationships. Replacement of the enamine functionality of the hit series with either an imidazole or a pyrazole ring led to compounds that inhibited both capsid assembly and reverse transcriptase. Optimization of the bicyclic benzodiazepine scaffold to include a 3-phenyl substituent led to lead compound 48, a pure capsid assembly inhibitor with improved antiviral activity.

Development of specific "drug-like property" rules for carboxylate-containing oral drug candidates.

The carboxylate moiety is an important pharmacophore in the medicinal chemist's arsenal and is sometimes an irreplaceable functionality in drug-target interactions. Thus, practical guidance on its use in the most optimized manner would be a welcome addition to rational drug design. Key physicochemical and ADMET-PK properties from a dataset of drugs containing a carboxylate (COOH) moiety were assembled and compared with those of a broader, general drug dataset. Our main objective was to identify features specific to COOH-containing oral drugs that could be converted into simple rules delineating the boundaries within which prospective COOH-containing chemical series and COOH-containing drug candidates would be reasonably expected to possess properties suitable for oral administration. These specific "drug-like" property rules include molecular weight, the number of rotatable bonds, the number of hydrogen bond donors and acceptors, predictions of lipophilic character (calculated log P and log D values), topological polar surface area (TPSA), and the pK(a) value of the carboxylate moiety. Similar to the various sets of criteria that have emerged over the past decade and which have significantly reshaped the way medicinal chemists think about preferred drug chemical space, we propose these specific COOH "drug-like" property rules as a guide for the design of superior COOH-containing drug candidates and as a tool to better manage the liabilities generally associated with the presence of a COOH moiety.

Investigation on the role of the tetrazole in the binding of thiotetrazolylacetanilides with HIV-1 wild type and K103N/Y181C double mutant reverse transcriptases.

The role of the tetrazole moiety in the binding of aryl thiotetrazolylacetanilides with HIV-1 wild type and K103N/Y181C double mutant reverse transcriptases was explored. Different acyclic, cyclic and heterocyclic replacements were investigated in order to evaluate the conformational and electronic contribution of the tetrazole ring to the binding of the inhibitors in the NNRTI pocket. The replacement of the tetrazole by a pyrazolyl group led to reversal of selectivity, providing inhibitors with excellent potency against the double mutant reverse transcriptase.

Thiotetrazole alkynylacetanilides as potent and bioavailable non-nucleoside inhibitors of the HIV-1 wild type and K103N/Y181C double mutant reverse transcriptases.

A series of aryl thiotetrazolylacetanilides were synthesized and found to be potent inhibitors of the HIV-1 wild type and K103N/Y181C double mutant reverse transcriptases. The incorporation of an alkynyl fragment on the aniline provided inhibitors with excellent cellular activity and extensive SAR led to the identification of one inhibitor having good oral bioavailability in rats.