Preclinical characterization and target validation of the antimalarial pantothenamide MMV693183.

Drug resistance and a dire lack of transmission-blocking antimalarials hamper malaria elimination. Here, we present the pantothenamide MMV693183 as a first-in-class acetyl-CoA synthetase (AcAS) inhibitor to enter preclinical development. Our studies demonstrate attractive drug-like properties and in vivo efficacy in a humanized mouse model of Plasmodium falciparum infection. The compound shows single digit nanomolar in vitro activity against P. falciparum and P. vivax clinical isolates, and potently blocks P. falciparum transmission to Anopheles mosquitoes. Genetic and biochemical studies identify AcAS as the target of the MMV693183-derived antimetabolite, CoA-MMV693183. Pharmacokinetic-pharmacodynamic modelling predict that a single 30 mg oral dose is sufficient to cure a malaria infection in humans. Toxicology studies in rats indicate a > 30-fold safety margin in relation to the predicted human efficacious exposure. In conclusion, MMV693183 represents a promising candidate for further (pre)clinical development with a novel mode of action for treatment of malaria and blocking transmission.

Antimalarial pantothenamide metabolites target acetyl-coenzyme A biosynthesis in Plasmodium falciparum.

Malaria eradication is critically dependent on new therapeutics that target resistant Plasmodium parasites and block transmission of the disease. Here, we report that pantothenamide bioisosteres were active against blood-stage Plasmodium falciparum parasites and also blocked transmission of sexual stages to the mosquito vector. These compounds were resistant to degradation by serum pantetheinases, showed favorable pharmacokinetic properties, and cleared parasites in a humanized mouse model of P. falciparum infection. Metabolomics revealed that coenzyme A biosynthetic enzymes converted pantothenamides into coenzyme A analogs that interfered with parasite acetyl-coenzyme A anabolism. Resistant parasites generated in vitro showed mutations in acetyl-coenzyme A synthetase and acyl-coenzyme A synthetase 11. Introduction and reversion of these mutations in P. falciparum using CRISPR-Cas9 gene editing confirmed the roles of these enzymes in the sensitivity of the malaria parasites to pantothenamides. These pantothenamide compounds with a new mode of action may have potential as drugs against malaria parasites.

Structure-Guided Identification of Resistance Breaking Antimalarial N­Myristoyltransferase Inhibitors.

The attachment of myristate to the N-terminal glycine of certain proteins is largely a co-translational modification catalyzed by N-myristoyltransferase (NMT), and involved in protein membrane-localization. Pathogen NMT is a validated therapeutic target in numerous infectious diseases including malaria. In Plasmodium falciparum, NMT substrates are important in essential processes including parasite gliding motility and host cell invasion. Here, we generated parasites resistant to a particular NMT inhibitor series and show that resistance in an in vitro parasite growth assay is mediated by a single amino acid substitution in the NMT substrate-binding pocket. The basis of resistance was validated and analyzed with a structure-guided approach using crystallography, in combination with enzyme activity, stability, and surface plasmon resonance assays, allowing identification of another inhibitor series unaffected by this substitution. We suggest that resistance studies incorporated early in the drug development process help selection of drug combinations to impede rapid evolution of parasite resistance.

Antimalarial Inhibitors Targeting Serine Hydroxymethyltransferase (SHMT) with in Vivo Efficacy and Analysis of their Binding Mode Based on X-ray Cocrystal Structures.

Target-based approaches toward new antimalarial treatments are highly valuable to prevent resistance development. We report several series of pyrazolopyran-based inhibitors targeting the enzyme serine hydroxymethyltransferase (SHMT), designed to improve microsomal metabolic stability and to identify suitable candidates for in vivo efficacy evaluation. The best ligands inhibited Plasmodium falciparum (Pf) and Arabidopsis thaliana (At) SHMT in target assays and PfNF54 strains in cell-based assays with values in the low nanomolar range (3.2-55 nM). A set of carboxylate derivatives demonstrated markedly improved in vitro metabolic stability (t1/2 > 2 h). A selected ligand showed significant in vivo efficacy with 73% of parasitemia reduction in a mouse model. Five new cocrystal structures with PvSHMT were solved at 2.3-2.6 Å resolution, revealing a unique water-mediated interaction with Tyr63 at the end of the para-aminobenzoate channel. They also displayed the high degree of conformational flexibility of the Cys364-loop lining this channel.

Discovery and evaluation of a novel monocyclic series of CXCR2 antagonists.

Antagonism of the chemokine receptor CXCR2 has been proposed as a strategy for the treatment of inflammatory diseases such as arthritis, chronic obstructive pulmonary disease and asthma. Earlier series of bicyclic CXCR2 antagonists discovered at AstraZeneca were shown to have low solubility and poor oral bioavailability. In this Letter we describe the design, synthesis and characterisation of a new series of monocyclic CXCR2 antagonists with improved solubility and good pharmacokinetic profiles.

Discovery of AZD3199, An Inhaled Ultralong Acting ß2 Receptor Agonist with Rapid Onset of Action.

A series of dibasic des-hydroxy ß2 receptor agonists has been prepared and evaluated for potential as inhaled ultralong acting bronchodilators. Determination of activities at the human ß-adrenoreceptors demonstrated a series of highly potent and selective ß2 receptor agonists that were progressed to further study in a guinea pig histamine-induced bronchoconstriction model. Following further assessment by onset studies in guinea pig tracheal rings and human bronchial rings contracted with methacholine (guinea pigs) or carbachol (humans), duration of action studies in guinea pigs after intratracheal (i.t.) administration and further selectivity and safety profiling AZD3199 was shown to have an excellent over all profile and was progressed into clinical evaluation as a new ultralong acting inhaled ß2 receptor agonist with rapid onset of action.

Synthesis and evaluation of 8-oxoadenine derivatives as potent Toll-like receptor 7 agonists with high water solubility.

We report the discovery of novel series of highly potent TLR7 agonists based on 8-oxoadenines, 1 and 2 by introducing and optimizing various tertiary amines onto the N(9)-position of the adenine moiety. The introduction of the amino group resulted in not only improved water solubility but also enhanced TLR7 agonistic activity. In particular compound 20 (DSR-6434) indicated an optimal balance between the agonistic potency and high water solubility. It also demonstrated a strong antitumor effect in vivo by intravenous administration in a tumor bearing mice model.

In silico prediction of acyl glucuronide reactivity.

Drugs and drug candidates containing a carboxylic acid moiety, including many widely used non-steroidal anti-inflammatory drugs (NSAIDs) are often metabolized to form acyl glucuronides (AGs). NSAIDs such as Ibuprofen are amongst the most widely used drugs on the market, whereas similar carboxylic acid drugs such as Suprofen have been withdrawn due to adverse events. Although the link between these AG metabolites and toxicity is not proven, there is circumstantial literature evidence to suggest that more reactive acyl glucuronides may, in some cases, present a greater risk of exhibiting toxic effects. We wished therefore to rank the reactivity of potential new carboxylate-containing drug candidates, and performed kinetic studies on synthetic acyl glucuronides to benchmark our key compounds. Driven by the desire to quickly rank the reactivity of compounds without the need for lengthy synthesis of the acyl glucuronide, a correlation was established between the degradation half-life of the acyl glucuronide and the half life for the hydrolysis of the more readily available methyl ester derivative. This finding enabled a considerable broadening of chemical property space to be investigated. The need for kinetic measurements was subsequently eliminated altogether by correlating the methyl ester hydrolysis half-life with the predicted (13)C NMR chemical shift of the carbonyl carbon together with readily available steric descriptors in a PLS model. This completely in silico prediction of acyl glucuronide reactivity is applicable within the earliest stages of drug design with low cost and acceptable accuracy to guide intelligent molecular design. This reactivity data will be useful alongside the more complex additional pharmacokinetic exposure and distribution data that is generated later in the drug discovery process for assessing the overall toxicological risk of acidic drugs.

Substituted indole-1-acetic acids as potent and selective CRTh2 antagonists-discovery of AZD1981.

Novel indole-3-thio-, 3-sulfonyl- and 3-oxy-aryl-1-acetic acids are reported which are potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). Optimization required maintenance of high CRTh2 potency whilst achieving a concomitant reduction in rates of metabolism, removal of cyp p450 inhibition and minimization of aldose reductase and aldehyde reductase activity. High quality compounds suitable for in vivo studies are highlighted, culminating in the discovery of AZD1981 (22).

Design driven HtL: The discovery and synthesis of new high efficacy ß2-agonists.

The design and synthesis of a new series of high efficacy ß(2)-agonists devoid of the key benzylic alcohol present in previously described highly efficacious ß(2)-agonists is reported. A hypothesis for the unprecedented level of efficacy is proposed based on considerations of ß(2)-adrenoceptor crystal structure, other biophysical data and modeling studies.

Switching between agonists and antagonists at CRTh2 in a series of highly potent and selective biaryl phenoxyacetic acids.

A novel series of biaryl phenoxyacetic acids was discovered as potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). A hit compound 4 was discovered from high throughput screening. Modulation of multiple aryl substituents afforded both agonists and antagonists, with small changes often reversing the mode of action. Understanding the complex SAR allowed design of potent antagonists such as potential candidate 34.

Zwitterionic CRTh2 antagonists.

A novel series of zwitterions is reported that contains potent, selective antagonists of the chemoattractant receptor-homologous expressed on Th2 lymphocytes receptor (CRTh2 or DP2). A high quality lead compound 2 was discovered from virtual screening based on the pharmacophore features present in a literature compound 1. Lead optimization through side chain modification and preliminary changes around the acid are disclosed. Optimization of physicochemical properties (log D, MWt, and HBA) allowed maintenance of high CRTh2 potency while achieving low rates of metabolism and minimization of other potential concerns such as hERG channel activity and permeability. A step-change increase in potency was achieved through addition of a single methyl group onto the piperazine ring, which gave high quality compounds suitable for progression into in vivo studies.

Synthesis and biological evaluation of 8-oxoadenine derivatives as toll-like receptor 7 agonists introducing the antedrug concept.

Systemic administration of a Toll-like receptor 7 (TLR7) agonist is effective to in suppressing Th2 derived inflammation, however systemic induction of various cytokines such as IL-6, IL-12, and type I interferon (IFN) is observed. This cytokine induction would be expected to cause flu-like symptoms. We have previously reported adenine compounds (3, 4) as interferon inducing agents acting as TLR7 agonists. To identify potent anti-inflammatory compounds without systemic side effects, a labile carboxylic ester as an antedrug functionality onto the N(9)-benzyl group of the adenine was introduced. We found that 9e was a potent TLR7 agonist (EC(50) 50 nM) and rapidly metabolized by human plasma (T(1/2) 2.6 min) to the pharmacologically much less active carboxylic acid 16. Intratracheal administration of 9e effectively inhibited allergen-induced airway inflammation without inducing cytokines systemically. Therefore, the TLR7 agonist with antedrug characteristics 9e (SM-324405) is a novel candidate for immunotherapy of allergic diseases.

Evaluation of a series of bicyclic CXCR2 antagonists.

The CXCR2 SAR of a series of bicyclic antagonists such as the 2-aminothiazolo[4,5-d]pyrimidine 3b was investigated by systematic variation of the fused pyrimidine-based heterocyclic cores. Replacement of the aminothiazole ring with a 2-thiazolone alternative led to a series of thiazolo[4,5-d]pyrimidine-2(3H)-one antagonists with markedly improved biological and pharmacokinetic properties, which are suitable pharmacological tools to probe the in vivo effects of CXCR2 antagonism combined with the associated CCR2 activity.

From ATP to AZD6140: the discovery of an orally active reversible P2Y12 receptor antagonist for the prevention of thrombosis.

Starting from adenosine triphosphate (ATP), the identification of a novel series of P2Y(12) receptor antagonists and exploitation of their SAR is described. Modifications of the acidic side chain and the purine core and investigation of hydrophobic substituents led to a series of neutral molecules. The leading compound, 17 (AZD6140), is currently in a large phase III clinical trial for the treatment of acute coronary syndromes and prevention of thromboembolic clinical sequelae.

SAR studies on thiazolo[4,5-d]pyrimidine based CXCR2 antagonists involving a novel tandem displacement reaction.

As part of a Lead Optimisation programme to identify small molecule antagonists of the human CXCR2 receptor, a series of substituted thiazolo[4,5-d]pyrimidines was prepared via the application of a novel tandem displacement reaction.

Discovery of potent CRTh2 (DP2) receptor antagonists.

Starting with the weak agonist indomethacin, a series of potent, selective CRTh2 (DP(2)) antagonists have been discovered as potential treatments for asthma, allergic rhinitis and other inflammatory diseases.

Diastereoselective synthesis of cyclopropane amino acids using diazo compounds generated in situ.

A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3].

QSAR and the rational design of long-acting dual D2-receptor/beta 2-adrenoceptor agonists.

This paper describes the development of a QSAR model for the rational control of functional duration of topical long-acting dual D(2)-receptor/beta(2)-adrenoceptor agonists for the treatment of chronic obstructive pulmonary disease. A QSAR model highlighted the importance of lipophilicity and ionization in controlling beta(2) duration. It was found that design rules logD(7.4) > 2, secondary amine pK(a) > 8.0, yielded ultra-long duration compounds. This model was used successfully to guide the design of long- and ultra-long-acting compounds. The QSAR model is discussed in terms of the exosite model, and the plasmalemma diffusion microkinetic hypothesis, for the control of beta(2) duration. Data presented strongly suggests that beta(2) duration is primarily controlled by the membrane affinity of these compounds.

A novel one-pot method for the preparation of pyrazoles by 1,3-dipolar cycloadditions of diazo compounds generated in situ.

A convenient one-pot procedure for the preparation of pyrazoles by 1,3-dipolar cycloaddition of diazo compounds generated in situ has been developed. Diazo compounds derived from aldehydes were reacted with terminal alkynes to furnish regioselectively 3,5-disubstituted pyrazoles. Furthermore, the reaction of N-vinylimidazole and diazo compounds derived from aldehydes gave exclusively 3-substituted pyrazoles in a one-pot process.