NMR-based screening: a powerful tool in fragment-based drug discovery

In silico identification of putative druggable pockets in PRL3, a significant oncology target

Protein tyrosine phosphatases (PTP) have emerged as targets in diseases characterized by aberrant phosphorylations such as cancers. The activity of the phosphatase of regenerating liver 3, PRL3, has been linked to several oncogenic and metastatic pathways, particularly in breast, ovarian, colorectal, and blood cancers. Development of small molecules that directly target PRL3, however, has been challenging. This is partly due to the lack of structural information on how PRL3 interacts with its inhibitors. Here, computational methods are used to bridge this gap by evaluating the druggability of PRL3. In particular, web-based pocket prediction tools, DoGSite3 and FTMap, were used to identify binding pockets using structures of PRL3 currently available in the Protein Data Bank. Druggability assessment by molecular dynamics simulations with probes was also performed to validate these results and to predict the strength of binding in the identified pockets. While several druggable pockets were identified, those in the closed conformation show more promise given their volume and depth. These two pockets flank the active site loops and roughly correspond to pockets predicted by molecular docking in previous papers. Notably, druggability simulations predict the possibility of low nanomolar affinity inhibitors in these sites implying the potential to identify highly potent small molecule inhibitors for PRL3. Putative pockets identified here can be leveraged for high-throughput virtual screening to further accelerate the drug discovery against PRL3 and development of PRL3-directed therapeutics.

Identification of isoform/domain-selective fragments from the selection of DNA-encoded dynamic library

DNA-encoded chemical library (DEL) has emerged to be a powerful ligand screening technology in drug discovery. Recently, we reported a DNA-encoded dynamic library (DEDL) approach that combines the principle of traditional dynamic combinatorial library (DCL) with DEL. DEDL has shown excellent potential in fragment-based ligand discovery with a variety of protein targets. Here, we further tested the utility of DEDL in identifying low molecular weight fragments that are selective for different isoforms or domains of the same protein family. A 10,000-member DEDL was selected against sirtuin-1, 2, and 5 (SIRT1, 2, 5) and the BD1 and BD2 domains of bromodomain 4 (BRD4), respectively. Albeit with modest potency, a series of isoform/domain-selective fragments were identified and the corresponding inhibitors were derived by fragment linking.

NMR as a "Gold Standard" Method in Drug Design and Discovery

Studying disease models at the molecular level is vital for drug development in order to improve treatment and prevent a wide range of human pathologies. Microbial infections are still a major challenge because pathogens rapidly and continually evolve developing drug resistance. Cancer cells also change genetically, and current therapeutic techniques may be (or may become) ineffective in many cases. The pathology of many neurological diseases remains an enigma, and the exact etiology and underlying mechanisms are still largely unknown. Viral infections spread and develop much more quickly than does the corresponding research needed to prevent and combat these infections; the present and most relevant outbreak of SARS-CoV-2, which originated in Wuhan, China, illustrates the critical and immediate need to improve drug design and development techniques. Modern day drug discovery is a time-consuming, expensive process. Each new drug takes in excess of 10 years to develop and costs on average more than a billion US dollars. This demonstrates the need of a complete redesign or novel strategies. Nuclear Magnetic Resonance (NMR) has played a critical role in drug discovery ever since its introduction several decades ago. In just three decades, NMR has become a "gold standard" platform technology in medical and pharmacology studies. In this review, we present the major applications of NMR spectroscopy in medical drug discovery and development. The basic concepts, theories, and applications of the most commonly used NMR techniques are presented. We also summarize the advantages and limitations of the primary NMR methods in drug development.

Genomics, Computational Biology and Drug Discovery for Mycobacterial Infections: Fighting the Emergence of Resistance

Tuberculosis (TB) and leprosy are mycobacterial infections caused by Mycobacterium tuberculosis and Mycobacterium leprae respectively. These diseases continue to be endemic in developing countries where the cost of new medicines presents major challenges. The situation is further exacerbated by the emergence of resistance to many front-line antibiotics. A priority now is to design new antimycobacterials that are not only effective in combatting the diseases but are also less likely to give rise to resistance. In both these respects understanding the structure of drug targets in M. tuberculosis and M. leprae is crucial. In this review we describe structure-guided approaches to understanding the impacts of mutations that give rise to antimycobacterial resistance and the use of this information in the design of new medicines.

Analysis of metabolome changes in the HepG2 cells of apatinib treatment by using the NMR-based metabolomics

Neovascularization is required for the growth of tumors, vascular endothelial growth factor (VEGF) and related signal pathways are important in tumor angiogenesis. Apatinib is a highly selective and potent antiangiogenesis drug targeting the receptor of VEGFR2, blocking downstream signal transduction and inhibiting angiogenesis of tumor tissue. Apatinib has a wide range of antitumor activities in vitro and in vivo, but its effect on metabolic changes has not deeply research at present. Nowadays, our research first systematically studied the metabolic changes affected by apatinib in the HepG2 cells at the half-maximal inhibitory concentration value. We used the metabolomics by using ¹ H nuclear magnetic resonance (¹ H-NMR) to analyze the HepG2 cell culture media. Multivariable Statistics was applied to analyze the ¹ H-NMR spectra of the cell media, including principal component analysis, partial least squares discriminant analysis (PLS-DA) and orthogonal PLS-DA (OPLS-DA). Compared with the uncultured and cultured media (negative/positive control), the metabolic phenotypes were changed in the apatinib treatment with a continuous effect over time. The metabolic pathway analysis is shown that the mainly disturbed metabolic pathways pyruvate metabolism, alanine, aspartate, and glutamate metabolism and amino acid metabolism associated with them in the apatinib treatment. The differential metabolites which were identified from the reconstructed OPLS-DA loading plots also reflected in these disturbed metabolic pathways. Our works could allow us to well understand the therapeutic effect of apatinib, especially in metabolism.

Structure Based Identification of Potential Inhibitors of NS3 Protein of Zika Virus

Background:

The re-emerging Zika virus has posed a serious threat to human health due to its association with the neurological disorders. The NS3 protein of Zika virus plays a pivotal role in the genome replication and thus may prove to be a critical target for the drug designing studies.

Objective:

The present study was conceptualized to analyze the crystal structure of NS3 protein of Zika virus followed by the identification of it’s potential inhibitors.

Methods:

Crystal structure of the NS3 protein was evaluated in detail. Docking of the NS3 protein was done with 130 different ligands including dengue virus inhibitors and their similar compounds along with some approved drugs. The drug likeliness properties were checked for non drug compounds.

Results:

Structural analysis of the NS3 protein revealed three important sites namely ATP- and RNAbinding sites as well as a central cavity. The selected ten ligands (ZINC05487635, ZINC0092398, ZINC13345444, 4-methoxyphenyl 4-chloro-3-nitrobenzoate, Luteolin, Ivermectin, Suramin, Dasatinib, Panduratin A, and ARDP0009) showed a higher binding affinity for the NS3 protein and good drug likeliness properties.

Conclusion:

These inhibitors could possibly act as potential lead molecules for future drug designing studies. Our present computational data is envisaged to be useful for gathering experimental evidences towards the development of potential therapeutic molecules against this arthropod mediated pathogen.

Solution NMR Spectroscopy in Target-Based Drug Discovery

Solution NMR spectroscopy is a powerful tool to study protein structures and dynamics under physiological conditions. This technique is particularly useful in target-based drug discovery projects as it provides protein-ligand binding information in solution. Accumulated studies have shown that NMR will play more and more important roles in multiple steps of the drug discovery process. In a fragment-based drug discovery process, ligand-observed and protein-observed NMR spectroscopy can be applied to screen fragments with low binding affinities. The screened fragments can be further optimized into drug-like molecules. In combination with other biophysical techniques, NMR will guide structure-based drug discovery. In this review, we describe the possible roles of NMR spectroscopy in drug discovery. We also illustrate the challenges encountered in the drug discovery process. We include several examples demonstrating the roles of NMR in target-based drug discoveries such as hit identification, ranking ligand binding affinities, and mapping the ligand binding site. We also speculate the possible roles of NMR in target engagement based on recent processes in in-cell NMR spectroscopy.

Proteintemplat-gesteuerte Fragmentligationen - von der molekularen Erkennung zur Wirkstofffindung

Proteintemplat‐gesteuerte Fragmentligationen sind ein neuartiges Konzept zur Unterstützung der Wirkstofffindung und können dazu beitragen, die Wirksamkeit von Proteinliganden zu verbessern. Es handelt sich dabei um chemische Reaktionen zwischen niedermolekularen Verbindungen (“Fragmenten”), die die Oberfläche eines Proteins als Reaktionsgefäß verwenden, um die Bildung eines Proteinliganden mit erhöhter Bindungsaffinität zu katalysieren. Die Methode nutzt die molekulare Erkennung kleiner reaktiver Fragmente durch die Proteine sowohl zur Assemblierung der Liganden als auch zur Identifizierung bioaktiver Fragmentkombinationen. Chemische Synthese und Bioassay werden dabei in einem Schritt vereint. Dieser Aufsatz diskutiert die biophysikalischen Grundlagen der reversiblen und irreversiblen Fragmentligationen und gibt einen Überblick über die Methoden, mit denen die durch das Proteintemplat gebildeten Ligationsprodukte detektiert werden können. Der chemische Reaktionsraum und aktuelle Anwendungen wie auch die Bedeutung dieses Konzeptes für die Wirkstofffindung werden erörtert.

Protein-Templated Fragment Ligations-From Molecular Recognition to Drug Discovery

Protein-templated fragment ligation is a novel concept to support drug discovery and can help to improve the efficacy of protein ligands. Protein-templated fragment ligations are chemical reactions between small molecules ("fragments") utilizing a protein's surface as a reaction vessel to catalyze the formation of a protein ligand with increased binding affinity. The approach exploits the molecular recognition of reactive small-molecule fragments by proteins both for ligand assembly and for the identification of bioactive fragment combinations. In this way, chemical synthesis and bioassay are integrated in one single step. This Review discusses the biophysical basis of reversible and irreversible fragment ligations and gives an overview of the available methods to detect protein-templated ligation products. The chemical scope and recent applications as well as future potential of the concept in drug discovery are reviewed.

Protein-Templated Formation of an Inhibitor of the Blood Coagulation Factor Xa through a Background-Free Amidation Reaction

Protein‐templated reactions enable the target‐guided formation of protein ligands from reactive fragments, ideally with no background reaction. Herein, we investigate the templated formation of amides. A nucleophilic fragment that binds to the coagulation factor Xa was incubated with the protein and thirteen differentially activated dipeptides. The protein induced a non‐catalytic templated reaction for the phenyl and trifluoroethyl esters; the latter was shown to be a completely background‐free reaction. Starting from two fragments with millimolar affinity, a 29 nm superadditive inhibitor of factor Xa was obtained. The fragment ligation reaction was detected with high sensitivity by an enzyme activity assay and by mass spectrometry. The reaction progress and autoinhibition of the templated reaction by the formed ligation product were determined, and the structure of the protein–inhibitor complex was elucidated.

Design of Potent and Druglike Nonphenolic Inhibitors for Catechol O-Methyltransferase Derived from a Fragment Screening Approach Targeting the S-Adenosyl-l-methionine Pocket

A fragment screening approach designed to target specifically the S-adenosyl-l-methionine pocket of catechol O-methyl transferase allowed the identification of structurally related fragments of high ligand efficiency and with activity on the described orthogonal assays. By use of a reliable enzymatic assay together with X-ray crystallography as guidance, a series of fragment modifications revealed an SAR and, after several expansions, potent lead compounds could be obtained. For the first time nonphenolic and small low nanomolar potent, SAM competitive COMT inhibitors are reported. These compounds represent a novel series of potent COMT inhibitors that might be further optimized to new drugs useful for the treatment of Parkinson's disease, as adjuncts in levodopa based therapy, or for the treatment of schizophrenia.

Targeting tuberculosis using structure-guided fragment-based drug design

Fragment-based drug discovery is now widely used in academia and industry to obtain small molecule inhibitors for a given target and is established for many fields of research including antimicrobials and oncology. Many molecules derived from fragment-based approaches are already in clinical trials and two - vemurafenib and venetoclax - are on the market, but the approach has been used sparsely in the tuberculosis field. Here, we describe the progress of our group and others, and examine the most recent successes and challenges in developing compounds with antimycobacterial activity.

Recent contributions of structure-based drug design to the development of antibacterial compounds

According to a Pew Research study published in February 2015, there are 37 antibacterial programs currently in clinical trials in the United States. Protein structure-based methods for guiding small molecule design were used in at least 34 of these programs. Typically, this occurred at an early stage (drug discovery and/or lead optimization) prior to an Investigational New Drug (IND) application, although sometimes in retrospective studies to rationalize biological activity. Recognizing that structure-based methods are resource-intensive and often require specialized equipment and training, the NIAID has funded two Structural Genomics Centers to determine structures of infectious disease species proteins with the aim of supporting individual investigators' research programs with structural biology methods.

An NMR-Guided Screening Method for Selective Fragment Docking and Synthesis of a Warhead Inhibitor

Selective hits for the glutaredoxin ortholog of Brucella melitensis are determined using STD NMR and verified by trNOE and (15)N-HSQC titration. The most promising hit, RK207, was docked into the target molecule using a scoring function to compare simulated poses to experimental data. After elucidating possible poses, the hit was further optimized into the lead compound by extension with an electrophilic acrylamide warhead. We believe that focusing on selectivity in this early stage of drug discovery will limit cross-reactivity that might occur with the human ortholog as the lead compound is optimized. Kinetics studies revealed that lead compound 5 modified with an ester group results in higher reactivity than an acrylamide control; however, after modification this compound shows little selectivity for bacterial protein versus the human ortholog. In contrast, hydrolysis of compound 5 to the acid form results in a decrease in the activity of the compound. Together these results suggest that more optimization is warranted for this simple chemical scaffold, and opens the door for discovery of drugs targeted against glutaredoxin proteins-a heretofore untapped reservoir for antibiotic agents.

Hitting the target: fragment screening with acoustic in situ co-crystallization of proteins plus fragment libraries on pin-mounted data-collection micromeshes

Acoustic droplet ejection (ADE) is a powerful technology that supports crystallographic applications such as growing, improving and manipulating protein crystals. A fragment-screening strategy is described that uses ADE to co-crystallize proteins with fragment libraries directly on MiTeGen MicroMeshes. Co-crystallization trials can be prepared rapidly and economically. The high speed of specimen preparation and the low consumption of fragment and protein allow the use of individual rather than pooled fragments. The Echo 550 liquid-handling instrument (Labcyte Inc., Sunnyvale, California, USA) generates droplets with accurate trajectories, which allows multiple co-crystallization experiments to be discretely positioned on a single data-collection micromesh. This accuracy also allows all components to be transferred through small apertures. Consequently, the crystallization tray is in equilibrium with the reservoir before, during and after the transfer of protein, precipitant and fragment to the micromesh on which crystallization will occur. This strict control of the specimen environment means that the crystallography experiments remain identical as the working volumes are decreased from the few microlitres level to the few nanolitres level. Using this system, lysozyme, thermolysin, trypsin and stachydrine demethylase crystals were co-crystallized with a small 33-compound mini-library to search for fragment hits. This technology pushes towards a much faster, more automated and more flexible strategy for structure-based drug discovery using as little as 2.5 nl of each major component.

Fragment-based identification of a locus in the Sec7 domain of Arno for the design of protein-protein interaction inhibitors

By virtual screening using a fragment-based drug design (FBDD) approach, 33 fragments were selected within small pockets around interaction hot spots on the Sec7 surface of the nucleotide exchange factor Arno, and then their ability to interfere with the Arno-catalyzed nucleotide exchange on the G-protein Arf1 was evaluated. By use of SPR, NMR, and fluorescence assays, the direct binding of three of the identified fragments to Arno Sec7 domain was demonstrated and the promiscuous aggregate behavior evaluated. Then the binding mode of one fragment and of a more active analogue was solved by X-ray crystallography. This highlighted the role of stable and transient pockets at the Sec7 domain surface in the discovery and binding of interfering compounds. These results provide structural information on how small organic compounds can interfere with the Arf1-Arno Sec7 domain interaction and may guide the rational drug design of competitive inhibitors of Arno enzymatic activity.

Fragment-based drug discovery using NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy has evolved into a powerful tool for fragment-based drug discovery over the last two decades. While NMR has been traditionally used to elucidate the three-dimensional structures and dynamics of biomacromolecules and their interactions, it can also be a very valuable tool for the reliable identification of small molecules that bind to proteins and for hit-to-lead optimization. Here, we describe the use of NMR spectroscopy as a method for fragment-based drug discovery and how to most effectively utilize this approach for discovering novel therapeutics based on our experience.

Drugging challenging targets using fragment-based approaches

Fragment-based approaches have now become firmly established in the drug discovery armoury. After notable early successes against protein kinases, the versatility and power of fragment-based approaches are increasingly being demonstrated on more diverse and difficult protein targets. This review highlights seven examples including targeting protein-protein interactions, a RNA polymerase and a DNA-binding protein. It shows how fragment-based approaches using small libraries have been successful when large HTS screens have failed. It also highlights the range of biophysical approaches being used and the interplay between experimental and in silico screens. The examples all show the iterative way in which potency is built up by synthetic elaboration of the initial fragment hits.

NMR metabolomics and drug discovery

NMR is an integral component of the drug discovery process with applications in lead discovery, validation, and optimization. NMR is routinely used for fragment-based ligand affinity screens, high-resolution protein structure determination, and rapid protein-ligand co-structure modeling. Because of this inherent versatility, NMR is currently making significant contributions in the burgeoning area of metabolomics, where NMR is successfully being used to identify biomarkers for various diseases, to analyze drug toxicity and to determine a drug's in vivo efficacy and selectivity. This review describes advances in NMR-based metabolomics and discusses some recent applications.

Formation of the RFX gene regulatory complex induces folding of the interaction domain of RFXAP

Major histocompatibility complex class II (MHCII) molecules have a central role in the mammalian adaptive immune response against infection. The level of the immune response is directly related to the concentration of MHCII molecules in the cell, which have a central role in initiating the immune response. MHCII molecules are therefore a potential target for the development of immunosuppressant drugs for the treatment of organ transplant rejection and autoimmune disease. The expression of MHCII molecules is regulated by a cell specific multiprotein complex. The RFX complex is the key DNA binding component of this complex. The RFX complex is composed of three proteins-RFX5, RFXAP, and RFXB-all of which are required for activation of expression of the MHCII genes. Little is currently known about the precise regions of the RFX proteins that are required for complex formation, or their structure. We have therefore identified the key regions of RFX5, RFXAP, and RFXB, which are required to form the RFX complex and have characterized the individual domains and the complexes they form using NMR and circular dichroism spectroscopy and isothermal titration calorimetry. Our results support a model for the assembly of the RFX complex in which the interaction between RFX5 and RFXAP promote folding of a poorly structured region ofRFXAP, which is required for high affinity binding of RFXB to the RFX5.RFXAP complex.

Development and NMR validation of minimal pharmacophore hypotheses for the generation of fragment libraries enriched in heparanase inhibitors

A combined strategy based on the development of pharmacophore hypotheses and NMR approaches is reported for the identification of novel inhibitors of heparanase, a key enzyme involved in tumor metastasis through the remodeling of the subepithelial and subendothelial basement membranes, resulting in the dissemination of metastatic cancer cells. Several pharmacophore hypotheses were initially developed from the most active heparanase inhibitors known to date and, after their application to a pool of 27 known heparanase inhibitors and a database of 1,120 compounds approved by the FDA, a four-point pharmacophore model was selected as the most predictive. This model was subsequently applied to a database of 686 chemical fragments, and a subset of 100 fragments accomplishing completely or partially the four-point model was selected to perform nuclear magnetic resonance experiments to validate the hypothesis. The experimental studies confirmed the reliability of our pharmacophore model, its applicability to in silico databases in order to reduce the number of compounds to be experimentally screened, and the possibility of generating fragment libraries enriched in heparanase inhibitors.

Perspectives on NMR in drug discovery: a technique comes of age

In the past decade, the potential of harnessing the ability of nuclear magnetic resonance (NMR) spectroscopy to monitor intermolecular interactions as a tool for drug discovery has been increasingly appreciated in academia and industry. In this Perspective, we highlight some of the major applications of NMR in drug discovery, focusing on hit and lead generation, and provide a critical analysis of its current and potential utility.

Cofactor chemogenomics

Cofactors are organic molecules, most of them originating from vitamins, that bind to enzymes making them able to catalyze defined reactions. A cofactor-based chemogenomics approach exploits the presence of a cofactor-binding domain to develop compound scaffolds tailored to mimic the cofactor and to replace it within target enzyme classes. As a result, a loss of function is observed. An expansion of the cofactor scaffold to include structural/chemical features derived from the substrate, that usually binds at cofactor adjacent sites, increases the specificity of the enzyme fishing. This approach has been so far applied only to NAD(P)(+)-dependent enzymes. However, it is suitable for all other cofactors, with difficulties, for some of them, originated by very tight binding. In the case of cofactors covalently bound to the enzyme, the competition between the natural cofactor and the cofactor scaffold mimic can only occur during enzyme folding.