Discovery of Phosphoric Acid Mono-{2-[(E/Z)-4-(3,3-dimethyl-butyrylamino)-3,5-difluoro-benzoylimino]-thiazol-3-ylmethyl} Ester (Lu AA47070): A Phosphonooxymethylene Prodrug of a Potent and Selective hA2A Receptor Antagonist

A versatile approach to high-density microcrystals in lipidic cubic phase for room-temperature serial crystallography

Serial crystallography has emerged as an important tool for structural studies of integral membrane proteins. The ability to collect data from micrometre-sized weakly diffracting crystals at room temperature with minimal radiation damage has opened many new opportunities in time-resolved studies and drug discovery. However, the production of integral membrane protein microcrystals in lipidic cubic phase at the desired crystal density and quantity is challenging. This paper introduces VIALS (versatile approach to high-density microcrystals in lipidic cubic phase for serial crystallography), a simple, fast and efficient method for preparing hundreds of microlitres of high-density microcrystals suitable for serial X-ray diffraction experiments at both synchrotron and free-electron laser sources. The method is also of great benefit for rational structure-based drug design as it facilitates in situ crystal soaking and rapid determination of many co-crystal structures. Using the VIALS approach, room-temperature structures are reported of (i) the archaerhodopsin-3 protein in its dark-adapted state and 110 ns photocycle intermediate, determined to 2.2 and 1.7 Å, respectively, and (ii) the human A2A adenosine receptor in complex with two different ligands determined to a resolution of 3.5 Å.

A2A adenosine receptor agonists, antagonists, inverse agonists and partial agonists

The Gs-coupled A2A adenosine receptor (A2AAR) has been explored extensively as a pharmaceutical target, which has led to numerous clinical trials. However, only one selective A2AAR agonist (regadenoson, Lexiscan) and one selective A2AAR antagonist (istradefylline, Nouriast) have been approved by the FDA, as a pharmacological agent for myocardial perfusion imaging (MPI) and as a cotherapy for Parkinson's disease (PD), respectively. Adenosine is widely used in MPI, as Adenoscan. Despite numerous unsuccessful clinical trials, medicinal chemical activity around A2AAR ligands has accelerated recently, particularly through structure-based drug design. New drug-like A2AAR antagonists for PD and cancer immunotherapy have been identified, and many clinical trials have ensued. For example, imaradenant (AZD4635), a compound that was designed computationally, based on A2AAR X-ray structures and biophysical mapping. Mixed A2AAR/A2BAR antagonists are also hopeful for cancer treatment. A2AAR antagonists may also have potential as neuroprotective agents for treatment of Alzheimer's disease.

New aryl and acylsulfonamides as state-dependent inhibitors of Nav1.3 voltage-gated sodium channel

Voltage-gated sodium channels (Na_vs) play an essential role in neurotransmission, and their dysfunction is often a cause of various neurological disorders. The Na_v1.3 isoform is found in the CNS and upregulated after injury in the periphery, but its role in human physiology has not yet been fully elucidated. Reports suggest that selective Na_v1.3 inhibitors could be used as novel therapeutics to treat pain or neurodevelopmental disorders. Few selective inhibitors of this channel are known in the literature. In this work, we report the discovery of a new series of aryl and acylsulfonamides as state-dependent inhibitors of Na_v1.3 channels. Using a ligand-based 3D similarity search and subsequent hit optimization, we identified and prepared a series of 47 novel compounds and tested them on Na_v1.3, Na_v1.5, and a selected subset also on Na_v1.7 channels in a QPatch patch-clamp electrophysiology assay. Eight compounds had an IC₅₀ value of less than 1 μM against the Na_v1.3 channel inactivated state, with one compound displaying an IC₅₀ value of 20 nM, whereas activity against the inactivated state of the Na_v1.5 channel and Na_v1.7 channel was approximately 20-fold weaker. None of the compounds showed use-dependent inhibition of the cardiac isoform Na_v1.5 at a concentration of 30 μM. Further selectivity testing of the most promising hits was measured using the two-electrode voltage-clamp method against the closed state of the Na_v1.1-Na_v1.8 channels, and compound 15b displayed small, yet selective, effects against the Na_v1.3 channel, with no activity against the other isoforms. Additional selectivity testing of promising hits against the inactivated state of the Na_v1.3, Na_v1.7, and Na_v1.8 channels revealed several compounds with robust and selective activity against the inactivated state of the Na_v1.3 channel among the three isoforms tested. Moreover, the compounds were not cytotoxic at a concentration of 50 μM, as demonstrated by the assay in human HepG2 cells (hepatocellular carcinoma cells). The novel state-dependent inhibitors of Na_v1.3 discovered in this work provide a valuable tool to better evaluate this channel as a potential drug target.

New paradigms in purinergic receptor ligand discovery

The discovery and clinical implementation of modulators of adenosine, P2Y and P2X receptors (comprising nineteen subtypes) have progressed dramatically in ∼50 years since Burnstock's definition of purinergic signaling. Although most clinical trials of selective ligands (agonists and antagonists) of certain purinergic receptors failed, there is a renewed impetus to redirect efforts to new disease conditions and the discovery of more selective or targeted compounds with potentially reduced side effects, such as biased GPCR agonists. The elucidation of new receptor and enzyme structures is steering rational design of potent and selective agonists, antagonists, allosteric modulators and inhibitors. A2A adenosine receptor (AR) antagonists are being applied to neurodegenerative conditions and cancer immunotherapy. A3AR agonists have potential for treating chronic inflammation (e.g. psoriasis), stroke and pain, as well as cancer. P2YR modulators are being considered for treating inflammation, metabolic disorders, acute kidney injury, cancer, pain and other conditions, often with an immune mechanism. ADP-activated P2Y12R antagonists are widely used as antithrombotic drugs, while their repurposing toward neuroinflammation is considered. P2X3 antagonists have been in clinical trials for chronic cough. P2X7 antagonists have been in clinical trials for inflammatory diseases and depression (compounds that penetrate the blood-brain barrier). Thus, purinergic signaling is now recognized as an immense regulatory system in the body for rebalancing tissues and organs under stress, which can be adjusted by drug intervention for therapeutic purposes. The lack of success of many previous clinical trials can be overcome given more advanced pharmacokinetic and pharmacodynamic approaches, including structure-based drug design, prodrugs and biased signaling. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Thiazole: A Versatile Standalone Moiety Contributing to the Development of Various Drugs and Biologically Active Agents

For many decades, the thiazole moiety has been an important heterocycle in the world of chemistry. The thiazole ring consists of sulfur and nitrogen in such a fashion that the pi (π) electrons are free to move from one bond to other bonds rendering aromatic ring properties. On account of its aromaticity, the ring has many reactive positions where donor–acceptor, nucleophilic, oxidation reactions, etc., may take place. Molecules containing a thiazole ring, when entering physiological systems, behave unpredictably and reset the system differently. These molecules may activate/stop the biochemical pathways and enzymes or stimulate/block the receptors in the biological systems. Therefore, medicinal chemists have been focusing their efforts on thiazole-bearing compounds in order to develop novel therapeutic agents for a variety of pathological conditions. This review attempts to inform the readers on three major classes of thiazole-bearing molecules: Thiazoles as treatment drugs, thiazoles in clinical trials, and thiazoles in preclinical and developmental stages. A compilation of preclinical and developmental thiazole-bearing molecules is presented, focusing on their brief synthetic description and preclinical studies relating to structure-based activity analysis. The authors expect that the current review may succeed in drawing the attention of medicinal chemists to finding new leads, which may later be translated into new drugs.

Molecular Simulations and Drug Discovery of Adenosine Receptors

G protein-coupled receptors (GPCRs) represent the largest family of human membrane proteins. Four subtypes of adenosine receptors (ARs), the A1AR, A2AAR, A2BAR and A3AR, each with a unique pharmacological profile and distribution within the tissues in the human body, mediate many physiological functions and serve as critical drug targets for treating numerous human diseases including cancer, neuropathic pain, cardiac ischemia, stroke and diabetes. The A1AR and A3AR preferentially couple to the Gi/o proteins, while the A2AAR and A2BAR prefer coupling to the Gs proteins. Adenosine receptors were the first subclass of GPCRs that had experimental structures determined in complex with distinct G proteins. Here, we will review recent studies in molecular simulations and computer-aided drug discovery of the adenosine receptors and also highlight their future research opportunities.

Discovery and functional characterization of N-(thiazol-2-yl)-benzamide analogs as the first class of selective antagonists of the Zinc-Activated Channel (ZAC)

The Zinc-Activated Channel (ZAC) is an atypical member of the Cys-loop receptor (CLR) superfamily of pentameric ligand-gated ion channels, with its very different endogenous agonists and signalling properties. In this study, a compound library screening at ZAC resulted in the identification of 2-(5-bromo-2-chlorobenzamido)-4-methylthiazole-5-methyl ester (1) as a novel ZAC antagonist. The structural determinants for ZAC activity in 1 were investigated by functional characterization of 61 analogs at ZAC expressed in Xenopus oocytes by two-electrode voltage clamp electrophysiology, and couple of analogs exerting more potent ZAC inhibition than 1 were identified (IC₅₀ values: 1-3 μM). 1 and N-(4-(tert-butyl)thiazol-2-yl)-3-fluorobenzamide (5a, TTFB) were next applied in studies of the functional properties and the mode of action of this novel class of ZAC antagonists. TTFB was a roughly equipotent antagonist of Zn⁺- and H⁺-evoked ZAC signaling and of spontaneous ZAC activity, and the slow on-set of its channel block suggested that its ZAC inhibition is state-dependent. TTFB was found to be a selective ZAC antagonist, exhibiting no significant agonist, antagonist or modulatory activity at 5-HT₃A, α₃β₄ nicotinic acetylcholine, α₁β₂γ_2S GABA_A or α₁ glycine receptors at 30 μM. 1 displayed largely non-competitive antagonism of Zn²⁺-induced ZAC signalling, and TTFB was demonstrated to target the transmembrane and/or intracellular domains of the receptor, which collectively suggests that the N-(thiazol-2-yl)-benzamide analog acts a negative allosteric modulator of ZAC. We propose that this first class of selective ZAC antagonists could constitute useful pharmacological tools in future explorations of the presently poorly elucidated physiological functions governed by this CLR.

Binding Characterization of Agonists and Antagonists by MCCS: A Case Study from Adenosine A2A Receptor

Characterizing the structural basis of ligand recognition of adenosine A_2A receptor (AA_2AR) will facilitate its rational design and development of small molecules with high affinity and selectivity, as well as optimal therapeutic effects for pain, cancers, drug abuse disorders, etc. In the present work, we applied our reported algorithm, molecular complex characterizing system (MCCS), to characterize the binding features of AA_2AR based on its reported 3D structures of protein-ligand complexes. First, we compared the binding score to the reported experimental binding affinities of each compound. Then, we calculated an output example of residue energy contribution using MCCS and compared the results with data obtained from MM/GBSA. The consistency in results indicated that MCCS is a powerful, fast, and accurate method. Sequentially, using a receptor-ligand data set of 57 crystallized structures of AA_2ARs, we characterized the binding features of the binding pockets in AA_2AR, summarized the key residues that distinguish antagonist from agonist, produced heatmaps of residue energy contribution for clustering various statuses of AA_2ARs, explored the selectivity between AA_2AR and AA_1AR, etc. All the information provided new insights into the protein features of AA_2AR and will facilitate its rational drug design.

Classification models and SAR analysis on CysLT1 receptor antagonists using machine learning algorithms

Cysteinyl leukotrienes 1 (CysLT1) receptor is a promising drug target for rhinitis or other allergic diseases. In our study, we built classification models to predict bioactivities of CysLT1 receptor antagonists. We built a dataset with 503 CysLT1 receptor antagonists which were divided into two groups: highly active molecules (IC₅₀ < 1000 nM) and weakly active molecules (IC₅₀ ≥ 1000 nM). The molecules were characterized by several descriptors including CORINA descriptors, MACCS fingerprints, Morgan fingerprint and molecular SMILES. For CORINA descriptors and two types of fingerprints, we used the random forests (RF) and deep neural networks (DNN) to build models. For molecular SMILES, we used recurrent neural networks (RNN) with the self-attention to build models. The accuracies of test sets for all models reached 85%, and the accuracy of the best model (Model 2C) was 93%. In addition, we made structure-activity relationship (SAR) analyses on CysLT1 receptor antagonists, which were based on the output from the random forest models and RNN model. It was found that highly active antagonists usually contained the common substructures such as tetrazoles, indoles and quinolines. These substructures may improve the bioactivity of the CysLT1 receptor antagonists.

Towards high throughput GPCR crystallography: In Meso soaking of Adenosine A2A Receptor crystals

Here we report an efficient method to generate multiple co-structures of the A_2A G protein-coupled receptor (GPCR) with small-molecules from a single preparation of a thermostabilised receptor crystallised in Lipidic Cubic Phase (LCP). Receptor crystallisation is achieved following purification using a low affinity “carrier” ligand (theophylline) and crystals are then soaked in solutions containing the desired (higher affinity) compounds. Complete datasets to high resolution can then be collected from single crystals and seven structures are reported here of which three are novel. The method significantly improves structural throughput for ligand screening using stabilised GPCRs, thereby actively driving Structure-Based Drug Discovery (SBDD).

Prodrug approach: An overview of recent cases

In this review we highlight the most modern trends in the prodrug strategy. In drug research and development, the prodrug concept has found a number of useful applications. Selected examples of this approach are provided in this paper and they are classified according to the aim of their design.

Development of CINPA1 analogs as novel and potent inverse agonists of constitutive androstane receptor

Constitutive androstane receptor (CAR, NR1I3) and pregnane X receptor (PXR, NR1I2) are master regulators of endobiotic and xenobiotic metabolism and disposition. Because CAR is constitutively active in certain cellular contexts, inhibiting CAR might reduce drug-induced hepatotoxicity and resensitize drug-resistant cancer cells to chemotherapeutic drugs. We recently reported a novel CAR inhibitor/inverse agonist CINPA1 (11). Here, we have obtained or designed 54 analogs of CINPA1 and used a time-resolved fluorescence resonance energy transfer (TR-FRET) assay to evaluate their CAR inhibition potency. Many of the 54 analogs showed CAR inverse agonistic activities higher than those of CINPA1, which has an IC50 value of 687 nM. Among them, 72 has an IC50 value of 11.7 nM, which is about 59-fold more potent than CINPA1 and over 10-fold more potent than clotrimazole (an IC50 value of 126.9 nM), the most potent CAR inverse agonist in a biochemical assay previously reported by others. Docking studies provide a molecular explanation of the structure-activity relationship (SAR) observed experimentally. To our knowledge, this effort is the first chemistry endeavor in designing and identifying potent CAR inverse agonists based on a novel chemical scaffold, leading to 72 as the most potent CAR inverse agonist so far. The 54 chemicals presented are novel and unique tools for characterizing CAR's function, and the SAR information gained from these 54 analogs could guide future efforts to develop improved CAR inverse agonists.

History and perspectives of A2A adenosine receptor antagonists as potential therapeutic agents

Growing evidence emphasizes that the purine nucleoside adenosine plays an active role as a local regulator in different pathologies. Adenosine is a ubiquitous nucleoside involved in various physiological and pathological functions by stimulating A1 , A2A , A2B , and A3 adenosine receptors (ARs). At the present time, the role of A2A ARs is well known in physiological conditions and in a variety of pathologies, including inflammatory tissue damage and neurodegenerative disorders. In particular, the use of selective A2A antagonists has been reported to be potentially useful in the treatment of Parkinson's disease (PD). In this review, A2A AR signal transduction pathways, together with an analysis of the structure-activity relationships of A2A antagonists, and their corresponding pharmacological roles and therapeutic potential have been presented. The initial results from an emerging polypharmacological approach are also analyzed. This approach is based on the optimization of the affinity and/or functional activity of the examined compounds toward multiple targets, such as A1 /A2A ARs and monoamine oxidase-B (MAO-B), both closely implicated in the pathogenesis of PD.

Synthesis and SAR studies of analogues of 4-(3,3-dimethyl-butyrylamino)-3,5-difluoro-N-thiazol-2-yl-benzamide (Lu AA41063) as adenosine A2A receptor ligands with improved aqueous solubility

An adenosine A2A receptor antagonist may be useful for the treatment of Parkinson's disease. Synthesis and structure-activity studies starting from 4-(3,3-dimethylbutyrylamino)-3,5-difluoro-N-thiazol-2-yl-benzamide (Lu AA41063, 4) led to a novel series of human (h) A2A receptor antagonists with improved aqueous solubility. Compound 22 was identified as a key representative from the series, displaying submicromolar hA2A receptor affinity and excellent aqueous solubility. Compound 22 also displayed good in vitro pharmacokinetic properties and is considered a good starting point for further lead optimisation toward hA2A receptor antagonists with improved druggability properties.

Thiazole: a promising heterocycle for the development of potent CNS active agents

Thiazole is a valuable scaffold in the field of medicinal chemistry and has accounted to display a variety of biological activities. Thiazole and its derivatives have attracted continuing interest to design various novel CNS active agents. In the past few decades, thiazoles have been widely used to develop a variety of therapeutic agents against numerous CNS targets. Thiazole containing drug molecules are currently being used in treatment of various CNS disorders and a number of thiazole derivatives are also presently in clinical trials. A lot of research has been carried out on thiazole and their analogues, which has proved their efficacy to overcome several CNS disorders in rodent as well as primate models. The aim of present review is to highlights diverse CNS activities displayed by thiazole and their derivatives. SAR of this nucleus has also been well discussed. This review covers the recent updates present in literature and will surely provide a greater insight for the designing and development of potent thiazole based CNS active agents in future.

Identification of an aminothiazole with antifungal activity against intracellular Histoplasma capsulatum

As eukaryotes, fungi possess relatively few molecules sufficiently unique from mammalian cell components to be used as drug targets. Consequently, most current antifungals have significant host cell toxicity. Primary fungal pathogens (e.g., Histoplasma) are of particular concern, as few antifungals are effective in treating them. To identify additional antifungal candidates for the treatment of histoplasmosis, we developed a high-throughput platform for monitoring Histoplasma growth and employed it in a phenotypic screen of 3,600 commercially available compounds. Seven hit compounds that inhibited Histoplasma yeast growth were identified. Compound 41F5 has fungistatic activity against Histoplasma yeast at micromolar concentrations, with a 50% inhibitory concentration (IC50) of 0.87 μM, and has the greatest selectivity for yeast (at least 62-fold) relative to host cells. Structurally, 41F5 consists of an aminothiazole core with an alicyclic substituent at the 2-position and an aromatic substituent at the 5-position. 41F5 inhibits Histoplasma growth in liquid culture and similarly inhibits yeast cells within macrophages, the actual host environment of this fungal pathogen during infection. Importantly, 41F5 protects infected host cells from Histoplasma-induced macrophage death, making this aminothiazole hit compound an excellent candidate for development as an antifungal for Histoplasma infections.

Effective palladium-catalyzed hydroxycarbonylation of aryl halides with substoichiometric carbon monoxide

A protocol for the Pd-catalyzed hydroxycarbonylation of aryl iodides, bromides, and chlorides has been developed using only 1-5 mol % of CO, corresponding to a p(CO) as low as 0.1 bar. Potassium formate is the only stoichiometric reagent, acting as a mildly basic nucleophile and a reservoir of CO. The substoichiometric CO could be delivered to the reaction from an acyl-Pd(II) precatalyst, which provides both the CO and an active catalyst, and thereby obviates the need for handling a toxic gas.

RO4938581, a GABAAα5 modulator, displays strong CYP1A2 autoinduction properties in rats

Autoinduction in drug metabolism is a known phenomenon observed when a drug induces the enzymes responsible for its own metabolism. The potency, rate and extent of autoinduction following a given treatment paradigm may have therapeutic implications in clinic as well as for in vivo pharmacological assessments in animals. RO4938581, an imidazo-triazolo-benzodiazepine, is a novel GABAAα5 negative modulator recently pursued for the treatment of cognitive dysfunctions. As circulating plasma levels of RO4938581 were shown to decrease rapidly after repeated dosing in rats, with CYP1A2 being involved in the metabolism of the compound, we examined the potential role of RO4938581-mediated autoinduction of CYP1A2. Incubation of rat hepatocytes with RO4938581 revealed potent CYP1A2 induction with significant increase in enzymatic activity at concentrations of 0.1nM and RO4938581 was shown to be 700-fold more potent than β-napththoflavone. Ex vivo studies revealed a 7-fold increase in metabolic CYP1A2 activity in liver microsomes prepared from rats administered with 0.1mg/kg of RO4938581 24h before. This induction profile was reflected in vivo in pharmacokinetic studies in rats where an 8-fold reduction in plasma exposure was observed after a second dose. The reduction in plasma exposures due to CYP1A2 autoinduction were confirmed functionally in contextual fear conditioning paradigm in rats, where a positive pharmacological effect observed after acute drug administration disappeared completely after sub-chronic dosing. Together, these findings suggest that RO4938581 possesses potent CYP1A2 autoinductive properties in rats and may serve as a tool for mechanistic metabolism or drug-drug interaction studies encircling this enzyme in rats.

Stabilised G protein-coupled receptors in structure-based drug design: a case study with adenosine A2A receptor

The first example of structure-based drug design with stabilised GPCRs has enabled the identification of a preclinical candidate for the treatment of Parkinson's disease.

Hit-to-lead investigation of a series of novel combined dopamine D2 and muscarinic M1 receptor ligands with putative antipsychotic and pro-cognitive potential

We describe the discovery of a series of compounds based on 1-{3-[4-(2-oxo-2,3-dihydro-benzoimidazol-1-yl)-piperidin-1-yl]-propyl}-3,4-dihydro-1H-quinolin-2-one (3), showing combined D(2) receptor affinity and M(1) receptor agonism. Based on a strategy of controlling logP, we herein describe a hit-to-lead investigation with the aim of retaining the combined D(2)/M(1) profile, while removing the propensity of the compounds to inhibit the hERG channel, as well as at obtaining acceptable pharmacokinetic properties. Although a SAR was evident for all four parameters in question, it was not possible to separate hERG channel inhibition and D(2) receptor affinity by this effort; whilst it was feasible to obtain compounds with M(1) receptor agonism, acceptable clearance, and weak hERG inhibition.

The rationality for using prodrug approach in drug discovery programs for new xenobiotics: opportunities and challenges

The concept of prodrugs has been successfully executed for life cycle management options of several approved drugs and drugs in development. In addition to imparting ideal biopharmaceutical properties, such as solubility, permeability and lipophilicity, some prodrug concepts have also enabled site-specific drug delivery, prolonged the duration of therapeutic effect and improved therapeutic index. The strategic inclusion of prodrug concept during drug discovery and early development process brings in some unique challenges. The communication provides balanced perspectives on the rational use and challenges of prodrug concept during the drug discovery and development process.