Quality of Research Tools.

Drug discovery research is a complex undertaking conducted by teams of scientists representing the different areas involved. In addition to a strong familiarity with existing knowledge, key relevant concepts remain unknown as activities start. This is often an accepted risk, mitigated by gaining understanding in real time as the project develops. Chemicals play a role in all biology studies conducted in the context of drug discovery, whether endogenously or exogenously added to the system under study. Furthermore, new knowledge often flourishes at the interface of existing areas of expertise. Due to differences in their training, adding a chemist's perspective to research teams would at least avoid potentially costly mistakes and ideally make any biology research richer. Thus, it would seem natural that one such team member be a chemist. Still, as that may not always be the case, we present some suggestions to minimize the risk of irreproducibility due to chemistry-related issues during biology research supporting drug discovery and make these efforts more robust and impactful. These include discussions on identity and purity, target and species selectivity, and chemical modalities such as orthosteric or allosteric small molecules or antibodies. Given the immense diversity of potential chemical/biological system interactions, we do not intend to provide a foolproof guide to conduct biological experimentation. Investigate at your own peril!

cis-1-Oxo-heterocyclyl-4-amido cyclohexane derivatives as NPY5 receptor antagonists.

The NPY5 receptor binding and pharmacokinetic properties of a novel series of cis-1-oxo-heterocyclyl-4-amido-cyclohexane derivatives are described.

Discovery and structure-activity relationship of 1,3-cyclohexyl amide derivatives as novel mGluR5 negative allosteric modulators.

A novel series of trans-1,3-cyclohexyl diamides was discovered and characterized as mGluR5 negative allosteric modulators (NAMs) lacking an alkyne moiety. Conformational constraint of one of the amide bonds in the diamide template led to a spirooxazoline template. A representative compound (24d) showed good in vitro potency, high CNS penetration and, upon subcutaneous dosing, demonstrated efficacy in the mouse marble burying test, generally used as indicative of potential anxiolytic activity.

4-(1-Phenyl-1H-pyrazol-4-yl)quinolines as novel, selective and brain penetrant metabotropic glutamate receptor 4 positive allosteric modulators.

4-(1-Phenyl-1H-pyrazol-4-yl)quinoline (1) was identified by screening the Lundbeck compound collection, and characterized as having mGlu4 receptor positive allosteric modulator properties. Compound 1 is selective over other mGlu receptors and a panel of GPCRs, ion channels and enzymes, but has suboptimal lipophilicity and high plasma and brain non-specific binding. In view of the challenges at the hit-to-lead stage previously reported in the development of mGlu4 receptor positive allosteric modulators (PAMs), a thorough structure-mGlu4 PAM activity relationship study was conducted to interrogate the chemical tractability of this chemotype. The central pyrazole ring tolerates the addition of one or two methyl groups. The C-7 position of the quinoline ring provides a site tolerant to hydrophilic substituents, enabling the design of diverse analogs with good in vitro mGlu4 PAM potency and efficacy, as well as improved microsomal turnover in vitro, compared to 1. In spite of the excellent ligand efficiency of 1 (LE=0.43), optimization of in vitro potency for this series reached a plateau around EC(50)=200 nM.

6-Aryl-3-pyrrolidinylpyridines as mGlu5 receptor negative allosteric modulators.

A series of 6-aryl-3-pyrrolidinylpyridine analogs was explored as structurally novel negative allosteric modulators of the mGlu5 receptor lacking an alkyne or oxadiazole moiety. Compounds in this series were characterized by tractable SAR, good in vitro potencies and brain penetration in rodents.

Design and synthesis of 4-arylpiperidinyl amide and N-arylpiperdin-3-yl-cyclopropane carboxamide derivatives as novel melatonin receptor ligands.

Two series of 4-arylpiperidinyl amide and N-arylpiperdin-3-yl-cyclopropane carboxamide derivatives exhibiting diverse functionality at rat MT(1) and MT(2) receptors are reported. Compounds 11f and 18b (MT(1)/MT(2) agonist) have human microsomal intrinsic clearance comparable to ramelteon.

A case study of foliglurax, the first clinical mGluR4 PAM for symptomatic treatment of Parkinson's disease: translational gaps or a failing industry innovation model?

INTRODUCTION: Approximately 40% of Parkinson's disease (PD) patients that take mostly dopamine receptor agonists for motor fluctuations, experience the return of symptoms between regular doses. This is a phenomenon known as 'OFF periods.' Positive allosteric modulators (PAMs) of metabotropic glutamate receptor 4 (mGluR4) are a promising non-dopaminergic mechanism with potential to address the unmet need of patients suffering from OFF periods. Foliglurax is the first mGluR4 PAM that has advanced into clinical testing in PD patients. AREAS COVERED: We summarize the chemistry, pharmacokinetics, and preclinical pharmacology of foliglurax. Translational PET imaging studies, clinical efficacy data, and a competitive landscape analysis of available therapies are presented to the readers. In this Perspective article, foliglurax is used as a case study to illustrate the inherent R&D challenges that companies face when developing drugs. These challenges include the delivery of drugs acting through novel mechanisms, long-term scientific investment, and commercial success and shorter-term positive financial returns. EXPERT OPINION: Failure to meet the primary and secondary endpoints in a Phase 2 study led Lundbeck to discontinue the development of foliglurax. Understanding the evidence supporting compound progression into Phase 2 will enable the proper assessment of the therapeutic potential of mGluR4 PAMs.

Allosteric Modalities for Membrane-Bound Receptors: Insights from Drug Hunting for Brain Diseases.

Medicinal chemists are accountable for embedding the appropriate drug target profile into the molecular architecture of a clinical candidate. An accurate characterization of the functional effects following binding of a drug to its biological target is a fundamental step in the discovery of new medicines, informing the translation of preclinical efficacy and safety observations into human trials. Membrane-bound proteins, particularly ion channels and G protein-coupled receptors (GPCRs), are biological targets prone to allosteric modulation. Investigations using allosteric drug candidates and chemical tools suggest that their functional effects may be tailored with a high degree of translational alignment, making them molecular tools to correct pathophysiological functional tone and enable personalized medicine when a causative target-to-disease link is known. We present select examples of functional molecular fine-tuning of allosterism and discuss consequences relevant to drug design.

2-Arylpyrimidines: novel CRF-1 receptor antagonists.

The design, synthesis and structure-activity relationship studies of a novel series of CRF-1 receptor antagonists, the 2-arylpyrimidines, are described. The effects of substitution on the aromatic ring and the pyrimidine core on CRF-1 receptor binding were investigated. A number of compounds with K(i) values below 10 nM and lipophilicity in a minimally acceptable range for a CNS drug (cLogP<5) were discovered.

The design, synthesis and structure-activity relationships of 1-aryl-4-aminoalkylisoquinolines: a novel series of CRF-1 receptor antagonists.

The design, synthesis and structure-activity relationships of a novel series of CRF-1 receptor antagonist, the 1-aryl-4-alkylaminoisoquinolines, is described. The effects of substitution on the aromatic ring, the amino group and the isoquinoline core on CRF-1 receptor binding were investigated.

Metabolism-based identification of a potent thrombin receptor antagonist.

The metabolism of our prototypical thrombin receptor antagonist 1, Ki = 2.7 nM, was studied and three major metabolites (2, 4, and 5) were found. The structures of the metabolites were verified independently by synthesis. Compound 4 was shown to be a potent antagonist of the thrombin receptor with a Ki = 11 nM. Additionally, compound 4 showed a 3-fold improvement in potency with respect to 1 in an agonist-induced ex-vivo platelet aggregation assay in cynomolgus monkeys after oral administration; this activity was sustained with 60% inhibition observed at 24 h post-dose. Compound 4 was highly active in functional assays and showed excellent oral bioavailability in rats and monkeys. Compound 4 showed a superior rat enzyme induction profile relative to compound 1, allowing it to replace compound 1 as a development candidate.

The "Century of Biology" and the Evolving Role of Medicinal Chemists in Neuroscience.

Society expects that the wave of contemporary new discoveries in biological sciences will soon lead to novel treatments for human diseases, including many devastating brain disorders. Historically, medicinal chemists have contributed to drug discovery teams in ways that synergize with those from their partner sciences, and help transform new knowledge into the ultimate tangible asset: a new drug. The optimal balance of resources and the right strategy to minimize the risk of late clinical failure may differ for different therapeutic indications. Recent progress in the oncology and neuroscience therapeutic areas is compared and contrasted, in particular looking at the biological target space and functional attributes of recently FDA-approved drugs and those in the late clinical pipeline. Medicinal chemists are poised to have major influence in neuroscience drug research, and examples of areas of potential impact are presented, together with a discussion of the soft skills they bring to their project teams and why they have been so impactful.

Recent Developments in Group I Metabotropic Glutamate Receptor Allosteric Modulators for the Treatment of Psychiatric and Neurological Disorders (2014-May 2015).

In the last ~30 years, scientists have made great strides in understanding the biological function of group I metabotropic glutamate receptors (mGlu) in health and disease, as well as developing a broad array of potent and selective agents able to activate or inhibit these receptors. This article provides a comprehensive review of the most recent group I mGlu modulators published in patent and non-patent literatures from 2014 to May, 2015, including design, structure-activity relationship, in silico, in vitro and in vivo properties of key compounds. The current status of clinical mGlu5 negative allosteric modulators (NAMs) and the development of mGlu1 and mGlu5 PET ligands are also highlighted. While the therapeutic potential for group I mGlu modulating agents appears high, significant challenges remain. Strategies to reduce clinical development risks and mitigate important side effects, including psychotomimetic events observed with several mGlu5 NAMs and cellular toxicity associated with mGlu5 positive allosteric modulators (PAMs), while retaining therapeutic efficacy through approaches such as biased ligand signaling are discussed.

Metabotropic glutamate receptors as targets for new antipsychotic drugs: Historical perspective and critical comparative assessment.

In this review, we aim to present, discuss and clarify our current understanding regarding the prediction of possible antipsychotic effects of metabotropic glutamate (mGlu) receptor ligands. The number of preclinical trials clearly indicates, that this group of compounds constitutes an excellent alternative to presently used antipsychotic therapy, being effective not only to positive, but also negative and cognitive symptoms of schizophrenia. Although the results of clinical trials that were performed for the group of mGlu2/3 agonists were not so enthusiastic as in animal studies, they still showed that mGlu ligands do not induced variety of side effects typical for presently used antipsychotics, and were generally well tolerated. The lack of satisfactory effectiveness towards schizophrenia symptoms of mGlu2/3 activators in humans could be a result of variety of uncontrolled factors and unidentified biomarkers different for each schizophrenia patient, that should be taken into consideration in the future set of clinical trials. The subject is still open for further research, and the novel classes of mGlu5 or mGlu2/3 agonists/PAMs were recently introduced, including the large group of compounds from the third group of mGlu receptors, especially of mGlu4 subtype. Finally, more precise treatment based on simultaneous administration of minimal doses of the ligands for two or more receptors, seems to be promising in the context of symptoms-specific schizophrenia treatment.

Discovery of potent orally active thrombin receptor (protease activated receptor 1) antagonists as novel antithrombotic agents.

Structurally novel thrombin receptor (protease activated receptor 1, PAR-1) antagonists based on the natural product himbacine are described. The prototypical PAR-1 antagonist 55 showed a Ki of 2.7 nM in the binding assay, making it the most potent PAR-1 antagonist reported. 55 was highly active in several functional assays, showed excellent oral bioavailability in rat and monkey models, and showed complete inhibition of agonist-induced ex vivo platelet aggregation in cynomolgus monkeys after oral administration.

The antipsychotic-like effects in rodents of the positive allosteric modulator Lu AF21934 involve 5-HT1A receptor signaling: mechanistic studies.

RATIONALE: Diverse preclinical studies suggest the potential therapeutic utility of the modulation of the glutamatergic system in brain via metabotropic glutamate (mGlu) receptors. Lu AF21934, a positive allosteric modulator of the mGlu4 receptor, was previously shown to reverse behavioral phenotypes in animal models thought to mimic positive, negative, and cognitive symptoms of schizophrenia. OBJECTIVES: To begin elucidating the brain circuitry involved in mGlu4 receptor pharmacology and add mechanistic support to Lu AF21934-induced phenotypic responses, the potential involvement of 5-HT1A receptors in these antipsychotic-like effects was explored. The tests used were the following: MK-801-induced hyperactivity and 2,5-dimethoxy-4-iodoamphetamine (DOI)-induced head twitches in mice, for positive symptoms; MK-801-induced disruptions of social interactions for negative symptoms; and novel object recognition and spatial delayed alteration test for cognitive symptoms. The microdialysis studies in which the effect of Lu AF21934 on MK-801-induced dopamine and serotonin release was investigated. RESULTS: The effects caused by Lu AF2193 were inhibited by administration of the selective 5-HT1A receptor antagonist WAY100635 (0.1 mg/kg). That inhibition was observed across all models used. Moreover, the concomitant administration of sub-effective doses of Lu AF21934 and a sub-effective dose of the selective 5-HT1A receptor agonist tool compound (R)-(+)-8-hydroxy-DPAT hydrobromide (0.01 mg/kg) induced a clear antipsychotic-like effect in all the procedures used. Lu AF21934 (5 mg/kg) also inhibited MK-801-induced increase in dopamine and 5-HT release. CONCLUSIONS: The actions of Lu AF21934 are 5-HT1A receptor-dependent. Activation of the mGlu4 receptor may be a promising mechanism for the development of novel antipsychotic drugs, efficacious toward positive, negative, and cognitive symptoms.

Total Synthesis of (+)-Himbacine and (+)-Himbeline.

Himbacine (1), a complex piperidine alkaloid isolated from the bark of Australian magnolias, is a promising lead in Alzheimer's disease research due to its potent muscarinic receptor antagonist property. We have described here a highly efficient synthetic strategy that resulted in the total synthesis of himbacine (1) in about 10% overall yield and isohimbacine (1a), an unnatural isomer of himbacine, in 18% overall yield. The total synthesis of himbacine was initially approached using an intramolecular Diels-Alder reaction as the key step to generate intermediate 5 followed by a [3 + 2] cycloaddition with nitrone 4 to produce the isoxazolidine derivative 3. Methylation followed by catalytic reduction of 3 gave 12'-hydroxyhimbacine (20), which, upon dehydration, gave isohimbacine (1a) as the sole product. In an alternative approach, an all-encompassing intramolecular Diels-Alder reaction of an appropriately substituted tetraene derivative 31, which bears the entire latent carbon framework and functional group substitution of himbacine, gave the desired advanced tricyclic intermediate 33, which was readily converted to (+)-himbeline (2) and (+)-himbacine (1).

Potent non-peptide thrombin receptor antagonists.

Protease activated receptor-1 (PAR-1), also known as thrombin receptor, is present in a variety of cell types such as platelets and endothelial cells. PAR-1 is proteolytically activated by thrombin by cleavage at its extracellular domain, unmasking a new amino terminus, which internally binds to the proximal receptor, eliciting cellular activation. Inhibition of the cellular activation by thrombin is a potentially promising therapeutic approach for the treatment of thrombotic and vascular proliferative disorders such as atherosclerosis and restenosis. Reported herein is the pharmacology of potent, low molecular weight thrombin receptor antagonists from pyrroloquinazoline, benzimidazole, and himbacine series. In the radioligand binding assay, these compounds inhibited PAR-1 in a competitive manner. They also inhibited thrombin and agonist peptide induced human platelet aggregation in a dose-dependent manner. Additionally, these compounds showed dose-dependent inhibition of agonist-induced cytosolic Ca(+2) transients and thymidine incorporation in human coronary artery smooth muscle cells (hCASMC). The most potent compound among these antagonists showed a Ki of 12 nM in the radioligand binding assay and an IC50 of 70 nM in the platelet aggregation inhibition assay.

Chemical biology of mGlu4 receptor activation: dogmas, challenges, strategies and opportunities.

Drug design necessitates a clear understanding of the phenotypic response to be elicited by a given ligandtarget interaction. This relationship is relatively well understood for classical biological targets of drug action, but for some novel targets, notably those amenable to allosteric modulation, developing such understanding may represent a more challenging task. In order to gain knowledge on the nature of the functional response derived from mGlu4 receptor activation, its molecular and cell biology are reviewed, including signalling pathways involved, receptor localization in central nervous system and beyond, and potential genetic links to disease. Broadly held views for both, orthosteric agonists as well as allosteric modulators, are compared with specific observations for the case of mGlu4 receptor activation via orthosteric and allosteric mechanisms. First, sub-type selectivity and brain penetration of amino acid mGlu4 receptor agonists are discussed, followed by the quantification of functional allosteric effects, the potential role of heterodimers in the functional response, and the observation of supra-physiological efficacy of mGlu4 receptor PAMs. We show that, in our analysis, these attributes differ from those that may be expected by extrapolating from broad knowledge. In addition, recent progress with mGlu4 receptor radioligands and PET ligands is summarized.

Inhibitory actions of mGlu4 receptor ligands on cocaine-, but not nicotine-, induced sensitizing and conditioning locomotor responses in rats.

BACKGROUND: Male Wistar rats were used to verify the hypothesis that metabotropic glutamate 4 (mGlu4) receptor ligands may modulate the locomotor effects evoked by cocaine or nicotine. METHODS: The preferential mGlu4 receptor orthosteric agonist (2S)-2-amino-4-[hydroxy[hydroxy(4-hydroxy-3-methoxy-5-nitrophenyl)methyl]phosphoryl]butanoic acid (LSP1-2111) and the mGlu4 receptor positive allosteric modulator (+)-cis-N(1)-(3,4-dichlorophenyl)cyclohexane-1,2-dicarboxamide (Lu AF21934) were used in the study. Rats were given repeated pairings of a test environment with cocaine (10mg/kg), nicotine (0.4 mg/kg) or the respective vehicles for 5 days. On day 10, animals were challenged with cocaine (10mg/kg, cocaine sensitization), nicotine (0.4 mg/kg, nicotine sensitization) or vehicle (conditioned hyperlocomotion) in experimental cages. RESULTS: Given on day 10, LSP1-2111 (3mg/kg) as well as Lu AF21934 (2.5-5mg/kg) decreased the expression of cocaine sensitization. In another set of experiments, LSP1-2111 (3mg/kg) and Lu AF21934 (5mg/kg) administered on day 10 attenuated the conditioned hyperlocomotion in rats treated repeatedly with cocaine. Neither LSP1-2111 (1-3mg/kg) nor Lu AF21934 (2.5-5mg/kg) changed the expression of nicotine sensitization and conditioned hyperlocomotion in rats treated repeatedly with nicotine. None of the mGlu4 receptor agonist/modulator altered the basal locomotor activity or acute hyperactivity to cocaine or nicotine. CONCLUSIONS: The present data indicate that pharmacological stimulation of mGlu4 receptors reduces the cocaine-induced expression of sensitization as well as conditioned hyperactivity. In contrast, mGlu4 receptor activation seems to be devoid of any effect on the locomotor effects of nicotine.