Evaluation of the Indazole Analogs of 5-MeO-DMT and Related Tryptamines as Serotonin Receptor 2 Agonists

Herein, we report the synthesis and characterization of a novel set of substituted indazole-ethanamines and indazole-tetrahydropyridines as potent serotonin receptor subtype 2 (5-HT2) agonists. Specifically, we examine the 5-HT2 pharmacology of the direct indazole analogs of 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) and related serotonergic tryptamines, and highlight the need for rigorous characterization of 5-HT2 subtype selectivity for these analogs, particularly for the 5-HT2B receptor subtype. Within this series, the potent analog VU6067416 (19d) was optimized to have suitable preclinical pharmacokinetic properties for in vivo dosing, although potent 5-HT2B agonist activity precluded further characterization for this series. Additionally, in silico docking studies suggest that the high potency of 19d may be a consequence of a halogen-bonding interaction with Phe2345.38 in the 5-HT2A orthosteric pocket.

Development of a Selective and High Affinity Radioligand, [3H]VU6013720, for the M4 Muscarinic Receptor

M4 muscarinic receptors are highly expressed in the striatum and cortex, brain regions that are involved in diseases such as Parkinson's disease, schizophrenia, and dystonia. Despite potential therapeutic advantages of specifically targeting the M4 receptor, it has been historically challenging to develop highly selective ligands, resulting in undesired off-target activity at other members of the muscarinic receptor family. Recently, we have reported first-in-class, potent, and selective M4 receptor antagonists. As an extension of that work, we now report the development and characterization of a radiolabeled M4 receptor antagonist, [3H]VU6013720, with high affinity (pKd of 9.5 ± 0.2 at rat M4, 9.7 at mouse M4, and 10 ± 0.1 at human M4 with atropine to define nonspecific binding) and no significant binding at the other muscarinic subtypes. Binding assays using this radioligand in rodent brain tissues demonstrate loss of specific binding in Chrm4 knockout animals. Dissociation kinetics experiments with various muscarinic ligands show differential effects on the dissociation of [3H]VU6013720 from M4 receptors, suggesting a binding site that is overlapping but may be distinct from the orthosteric site. Overall, these results demonstrate that [3H]VU6013720 is the first highly selective antagonist radioligand for the M4 receptor, representing a useful tool for studying the basic biology of M4 as well for the support of M4 receptor-based drug discovery. SIGNIFICANCE STATEMENT: This manuscript describes the development and characterization of a novel muscarinic (M) acetylcholine subtype 4 receptor antagonist radioligand, [3H]VU6013720. This ligand binds to or overlaps with the acetylcholine binding site, providing a highly selective radioligand for the M4 receptor that can be used to quantify M4 protein expression in vivo and probe the selective interactions of acetylcholine with M4 versus the other members of the muscarinic receptor family.

Development of a Peripherally Restricted 5-HT2B Partial Agonist for Treatment of Pulmonary Arterial Hypertension

Ligands for the serotonin 2B receptor (5-HT2B) have shown potential to treat pulmonary arterial hypertension in preclinical models but cannot be used in humans because of predicted off-target neurological effects. The aim of this study was to develop novel systemically restricted compounds targeting 5-HT2B. Here, we show that mice treated with VU6047534 had decreased RVSP compared with control treatment in both the prevention and intervention studies using Sugen-hypoxia. VU6047534 is a novel 5-HT2B partial agonist that is peripherally restricted and able to both prevent and treat Sugen-hypoxia-induced pulmonary arterial hypertension. We have synthesized and characterized a structurally novel series of 5-HT2B ligands with high potency and selectivity for the 5-HT2B receptor subtype. Next-generation 5-HT2B ligands with similar characteristics, and predicted to be systemically restricted in humans, are currently advancing to investigational new drug-enabling studies.

2B Determined: The Future of the Serotonin Receptor 2B in Drug Discovery

The cardiotoxicity associated with des-ethyl-dexfenfluramine (norDF) and related agonists of the serotonin receptor 2B (5-HT2B) has solidified the receptor's place as an "antitarget" in drug discovery. Conversely, a growing body of evidence has highlighted the utility of 5-HT2B antagonists for the treatment of pulmonary arterial hypertension (PAH), valvular heart disease (VHD), and related cardiopathies. In this Perspective, we summarize the link between the clinical failure of fenfluramine-phentermine (fen-phen) and the subsequent research on the role of 5-HT2B in disease progression, as well as the development of drug-like and receptor subtype-selective 5-HT2B antagonists. Such agents represent a promising class for the treatment of PAH and VHD, but their utility has been historically understudied due to the clinical disasters associated with 5-HT2B. Herein, it is our aim to examine the current state of 5-HT2B drug discovery, with an emphasis on the receptor's role in the central nervous system (CNS) versus the periphery.

Alkylation of NH-sulfoximines under Mitsunobu-type conditions

Previously described approaches for the alkylation of NH-sulfoximines typically rely either on transition metal catalysis, or the use of traditional alkylation reagents and strong bases. Herein, we report a straightforward alkylation of diverse NH-sulfoximines under simple Mitsunobu-type conditions, despite the unusually high pK_a of the NH center.

Identification of Potent, Selective, and Peripherally Restricted Serotonin Receptor 2B Antagonists from a High-Throughput Screen

Antagonists of the serotonin receptor 2B (5-HT2B) have shown great promise as therapeutics for the treatment of pulmonary arterial hypertension, valvular heart disease, and related cardiopathies. Herein, we describe a high-throughput screen campaign that led to the identification of highly potent and selective 5-HT2B antagonists. Furthermore, selected compounds were profiled for their predicted ability to cross the blood-brain barrier. Two exemplary compounds, VU0530244 and VU0631019, were predicted to have very limited potential for brain penetration in human subjects, a critical profile for the development of 5-HT2B antagonists devoid of centrally-mediated adverse effects.

DARK Classics in Chemical Neuroscience: Methaqualone

Commonly known as "Quaaludes," methaqualone (1) is a sedative-hypnotic medication, with effects resembling barbiturates and other downers, that exerts its effects through modulation of γ-aminobutyric acid type A receptors (GABA_AR). Following the discovery of the sedative and euphoric effects of methaqualone (1), it was quickly adopted by pharmaceutical companies and promoted by clinicians around the world as a "safe" sleeping pill option, and for a period it was available over the counter. The popularity of methaqualone (1) soared worldwide, and many people began to use it recreationally for its sedative-hypnotic-like psychoactive effects. Not long after its introduction, many individuals began to misuse the drug leading to overdoses and drug dependence which brought to light methaqualone's (1) addictive nature. In this review, the background, synthesis, pharmacology, metabolism, and pharmacokinetics of methaqualone (1) will be covered along with its discovery, history, and the derivatives that are currently available around the world through manufacture in clandestine laboratories.

Synthesis and characterization of chiral 6-azaspiro[2.5]octanes as potent and selective antagonists of the M4 muscarinic acetylcholine receptor

In this manuscript, we report a series of chiral 6-azaspiro[2.5]octanes and related spirocycles as highly potent and selective antagonists of the muscarinic acetylcholine receptor subtype 4 (mAChR₄). Chiral separation and subsequent X-ray crystallographic analysis of early generation analogs revealed the R enantiomer to possess excellent human and rat M₄ potency, and further structure-activity relationship (SAR) studies on this chiral scaffold led to the discovery of VU6015241 (compound 19). Compound 19 is characterized by high M₄ potency and selectivity across multiple species, excellent aqueous solubility, and moderate brain exposure in rodents after intraperitoneal administration.

Discovery of VU6028418: A Highly Selective and Orally Bioavailable M4 Muscarinic Acetylcholine Receptor Antagonist

Herein, we report the SAR leading to the discovery of VU6028418, a potent M4 mAChR antagonist with high subtype-selectivity and attractive DMPK properties in vitro and in vivo across multiple species. VU6028418 was subsequently evaluated as a preclinical candidate for the treatment of dystonia and other movement disorders. During the characterization of VU6028418, a novel use of deuterium incorporation as a means to modulate CYP inhibition was also discovered.

Discovery of the First Selective M4 Muscarinic Acetylcholine Receptor Antagonists with in Vivo Antiparkinsonian and Antidystonic Efficacy

Nonselective antagonists of muscarinic acetylcholine receptors (mAChRs) that broadly inhibit all five mAChR subtypes provide an efficacious treatment for some movement disorders, including Parkinson's disease and dystonia. Despite their efficacy in these and other central nervous system disorders, antimuscarinic therapy has limited utility due to severe adverse effects that often limit their tolerability by patients. Recent advances in understanding the roles that each mAChR subtype plays in disease pathology suggest that highly selective ligands for individual subtypes may underlie the antiparkinsonian and antidystonic efficacy observed with the use of nonselective antimuscarinic therapeutics. Our recent work has indicated that the M₄ muscarinic acetylcholine receptor has several important roles in opposing aberrant neurotransmitter release, intracellular signaling pathways, and brain circuits associated with movement disorders. This raises the possibility that selective antagonists of M₄ may recapitulate the efficacy of nonselective antimuscarinic therapeutics and may decrease or eliminate the adverse effects associated with these drugs. However, this has not been directly tested due to lack of selective antagonists of M₄. Here, we utilize genetic mAChR knockout animals in combination with nonselective mAChR antagonists to confirm that the M₄ receptor activation is required for the locomotor-stimulating and antiparkinsonian efficacy in rodent models. We also report the synthesis, discovery, and characterization of the first-in-class selective M₄ antagonists VU6013720, VU6021302, and VU6021625 and confirm that these optimized compounds have antiparkinsonian and antidystonic efficacy in pharmacological and genetic models of movement disorders.

Discovery of a novel class of heteroaryl-pyrrolidinones as positive allosteric modulators of the muscarinic acetylcholine receptor M1

This Letter describes the synthesis and optimization of a series of heteroaryl-pyrrolidinone positive allosteric modulators (PAMs) of the muscarinic acetylcholine receptor M₁ (mAChR M₁). Through the continued optimization of M₁ PAM tool compound VU0453595, with a focus on replacement of the 6,7-dihydro-5H-pyrrolo[3,4-b]pyridin-5-one with a wide variety of alternative 4,5-dihydropyrrolo-fused heteroaromatics, the generation of M₁ PAMs with structurally novel chemotypes is disclosed. Two compounds from these subseries, 8b (VU6005610) and 20a (VU6005852), show robust selectivity for the M₁ mAChR, and no M₁ agonism. Both compounds have favorable preliminary PK profiles in vitro;8b additionally demonstrates high brain exposure in a rodent IV cassette model.

DARK Classics in Chemical Neuroscience: Carfentanil

Because of its remarkable potency and relative ease of synthesis, carfentanil (1) has recently emerged as a problematic contaminant in other drugs of abuse. Carfentanil and its close analogs, currently approved only for large animal veterinary medicine, have found use both as illicit additives to the clandestine manufacture of scheduled drugs and as chemical weapons. In this Review, the background, synthesis, manufacture, metabolism, pharmacology, approved indications, dosage, and adverse effects of carfentanil will be discussed along with its emergence as a key player in the ongoing opioid crisis.

1086 Non-Linear Associations Between Depression and Sleep Duration in an International Sample of 16,997 Respondents

Introduction

Abnormal sleep duration is common in people with depression and can be both a risk-factor and a symptom of depression. Here we determine the prevalence of depression likelihood and assess associations between long and short sleep duration in an international convenience sample.

Methods

N=16,997 respondents (age range: 8-98y, mean age 39.7y ±13.1 SD; 43% female) completed the 10-item Harvard Department of Psychiatry National Depression Screening Day Scale (HANDS) online from October 7 to October 13, 2019. Higher total scores on the HANDS indicate higher likelihood of major depressive episode with scores >8 indicate the presence of a major depressive disorder is likely. Additional questions were added to the survey including the question “During the past two weeks, how many hours of actual sleep did you average at night?” Answer choices ranged from “less than 5 hours” to “more than 10h” in half-hour increments.

Results

Respondents came from 115 different countries with the majority of respondents from Canada (48%) and the United States (38%). Sixty-four percent of the sample were recommended for further evaluation for depression. Of those recommended, 66% reported <7h of sleep per night and 3% reported >9h. Those who reported 7-9h of sleep per night had the lowest depression scores (9.2 points) compared to those who reported <7h (11.8 points) and >9h (13.7 points), F(2,15366)=434.81, p<0.001. The amount of sleep associated with the lowest depression scores was 7.5h (8.6 points) with <5h associated with the highest depression scores (15.5 points).

Conclusion

We found a high prevalence of depression likelihood in 64% of an international convenience sample, with 69% of those not meeting the recommended 7-9h of sleep per night. Both short and long sleep were associated with higher levels of depression with 7.5h of sleep associated with the lowest depression scores. Future research on depression should focus on sleep interventions aimed at improving both short and long sleep duration.

Support

N/A.

Synthesis of Substituted 6,7-Dihydro-5H-pyrrolo[2,3-c]pyridazines/pyrazines via Catalyst-Free Tandem Hydroamination-Aromatic Substitution

Herein, we report an efficient and operationally simple synthesis of 6,7-dihydro-5H-pyrrolo[2,3-c]pyridazines and 6,7-dihydro-5H-pyrrolo[2,3-b]pyrazines via a tandem hydroamination-S_NAr sequence that makes use of mild reagents under catalyst-free conditions in moderate to high yields. This chemistry expands the known scope of pyridazine/pyrazine chemistry and can be applied toward the synthesis of novel drug-like molecules with favorable bioactivity and pharmacokinetic properties.

The C. elegans CHP1 homolog, pbo-1, functions in innate immunity by regulating the pH of the intestinal lumen

Caenorhabditis elegans are soil-dwelling nematodes and models for understanding innate immunity and infection. Previously, we developed a novel fluorescent dye (KR35) that accumulates in the intestine of C. elegans and reports a dynamic wave in intestinal pH associated with the defecation motor program. Here, we use KR35 to show that mutations in the Ca²⁺-binding protein, PBO-1, abrogate the pH wave, causing the anterior intestine to be constantly acidic. Surprisingly, pbo-1 mutants were also more susceptible to infection by several bacterial pathogens. We could suppress pathogen susceptibility in pbo-1 mutants by treating the animals with pH-buffering bicarbonate, suggesting the pathogen susceptibility is a function of the acidity of the intestinal pH. Furthermore, we use KR35 to show that upon infection by pathogens, the intestinal pH becomes neutral in a wild type, but less so in pbo-1 mutants. C. elegans is known to increase production of reactive oxygen species (ROS), such as H₂O_2, in response to pathogens, which is an important component of pathogen defense. We show that pbo-1 mutants exhibited decreased H₂O₂ in response to pathogens, which could also be partially restored in pbo-1 animals treated with bicarbonate. Ultimately, our results support a model whereby PBO-1 functions during infection to facilitate pH changes in the intestine that are protective to the host.

Innate immunity is critical for host defense against pathogens. However, questions remain about how the host senses and responds to pathogen invasion. Using a pH-sensitive fluorescent dye and a Caenorhabditis elegans pathogen infection model we show that pathogens induce changes in pH of the worm intestine. We also show that intestinal pH directly affects production of reactive oxygen species (e.g. H₂O₂) important for pathogen defense. Our results show that pH regulation is an important component of the innate immune response to pathogens.

Dual Pharmacophores Explored via Structure-Activity Relationship (SAR) Matrix: Insights into Potent, Bifunctional Opioid Ligand Design

Short-acting μ-opioid receptor (MOR) agonists have long been used for the treatment of severe, breakthrough pain. However, selective MOR agonists including fentanyl and morphine derivatives are limited clinically due to high risks of dependence, tolerance, and respiratory depression. We recently reported the development of a long-acting, bifunctional MOR agonist/δ-opioid receptor (DOR) antagonist analgesic devoid of tolerance or dependence in mice (AAH8, henceforth referred to as 2B). To address the need for short-acting treatments for breakthrough pain, we present a series of novel, short-acting, high-potency MOR agonist/DOR antagonist ligands with antinociceptive activity in vivo. In this study, we utilized a two-dimensional structure-activity relationship matrix to identify pharmacological trends attributable to combinations of two key pharmacophore elements within the chemotype. This work enhances our ability to modulate efficacy at MOR and DOR, accessing a variety of bifunctional profiles while maintaining high affinity and potency at both receptors.

The Muscarinic Acetylcholine Receptor M5: Therapeutic Implications and Allosteric Modulation

The muscarinic acetylcholine receptor (mAChR) subtype 5 (M₅) was the most recent mAChR to be cloned and has since emerged as a potential therapeutic target for a number of indications. Early studies with knockout animals have provided clues to the receptor's role in physiological processes related to Alzheimer's disease, schizophrenia, and addiction, and until recently, useful subtype-selective tools to further probe the pharmacology of M₅ have remained elusive. Small-molecule allosteric modulators have since gained traction as a means by which to selectively examine muscarinic pharmacology. This review highlights the discovery and optimization of M₅ positive allosteric modulators (PAMs) and negative allosteric modulators (NAMs).

Discovery of Tricyclic Triazolo- and Imidazopyridine Lactams as M1 Positive Allosteric Modulators

This Letter describes the chemical optimization of a new series of muscarinic acetylcholine receptor subtype 1 (M₁) positive allosteric modulators (PAMs) based on novel tricyclic triazolo- and imidazopyridine lactam cores, devoid of M₁ agonism, e.g., no M₁ ago-PAM activity, in high expressing recombinant cell lines. While all the new tricyclic congeners afforded excellent rat pharmacokinetic (PK) properties (CL_p < 8 mL/min/kg and t_1/2 > 5 h), regioisomeric triazolopyridine analogues were uniformly not CNS penetrant ( K_p < 0.05), despite a lack of hydrogen bond donors. However, removal of a single nitrogen atom to afford imidazopyridine derivatives proved to retain the excellent rat PK and provide high CNS penetration ( K_p > 2), despite inclusion of a basic nitrogen. Moreover, 24c was devoid of M₁ agonism in high expressing recombinant cell lines and did not induce cholinergic seizures in vivo in mice. Interestingly, all of the new M₁ PAMs across the diverse tricyclic heterocyclic cores possessed equivalent CNS MPO scores (>4.5), highlighting the value of both "medicinal chemist's eye" and experimental data, e.g., not sole reliance (or decision bias) on in silico calculated properties, for parameters as complex as CNS penetration.

Structure-Activity Relationships of Pan-Gαq/11 Coupled Muscarinic Acetylcholine Receptor Positive Allosteric Modulators

Recent years have seen a large increase in the discovery of allosteric ligands targeting muscarinic acetylcholine receptors (mAChRs). One of the challenges in screening such compounds is to understand their mechanisms of action and define appropriate parameter estimates for affinity, cooperativity and efficacy. Herein we describe the mechanisms of action and structure-activity relationships for a series of "pan-G_q-coupled" muscarinic acetylcholine (ACh) receptor (mAChR) positive allosteric modulators (PAMs). Using a combination of radioligand binding, functional inositol phosphate accumulation assays, receptor alkylation and operational data analysis, we show that most compounds in the series derive their variable potency and selectivity from differential cooperativity at the M₁, M₃ and M₅ mAChRs. None of the PAMs showed greater than 10-fold subtype selectivity for the agonist-free receptor, but VU6007705, VU6007678, and VU6008555 displayed markedly increased cooperativity compared to the parent molecule and M₅ mAChR-preferring PAM, ML380 (αβ > 100), in the presence of ACh. Most of the activity of these PAMs derives from their ability to potentiate ACh binding affinity at mAChRs, though VU6007678 was notable for also potentiating ACh signaling efficacy and robust allosteric agonist activity. These data provide key insights for the future design of more potent and subtype-selective mAChR PAMs.

Discovery and Optimization of Potent and CNS Penetrant M5-Preferring Positive Allosteric Modulators Derived from a Novel, Chiral N-(Indanyl)piperidine Amide Scaffold

The pharmacology of the M₅ muscarinic acetylcholine receptor (mAChR) is the least understood of the five mAChR subtypes due to a historic lack of selective small molecule tools. To address this shortcoming, we have continued the optimization effort around the prototypical M₅ positive allosteric modulator (PAM) ML380 and have discovered and optimized a new series of M₅ PAMs based on a chiral N-(indanyl)piperidine amide core with robust SAR, human and rat M₅ PAM EC₅₀ values <100 nM and rat brain/plasma K_p values of ∼0.40. Interestingly, unlike M₁ and M₄ PAMs with unprecedented mAChR subtype selectivity, this series of M₅ PAMs displayed varying degrees of PAM activity at the other two natively G_q-coupled mAChRs, M₁ and M₃, yet were inactive at M₂ and M₄.

Discovery, Characterization, and Effects on Renal Fluid and Electrolyte Excretion of the Kir4.1 Potassium Channel Pore Blocker, VU0134992

The inward rectifier potassium (Kir) channel Kir4.1 (KCNJ10) carries out important physiologic roles in epithelial cells of the kidney, astrocytes in the central nervous system, and stria vascularis of the inner ear. Loss-of-function mutations in KCNJ10 lead to EAST/SeSAME syndrome, which is characterized by epilepsy, ataxia, renal salt wasting, and sensorineural deafness. Although genetic approaches have been indispensable for establishing the importance of Kir4.1 in the normal function of these tissues, the availability of pharmacological tools for acutely manipulating the activity of Kir4.1 in genetically normal animals has been lacking. We therefore carried out a high-throughput screen of 76,575 compounds from the Vanderbilt Institute of Chemical Biology library for small-molecule modulators of Kir4.1. The most potent inhibitor identified was 2-(2-bromo-4-isopropylphenoxy)-N-(2,2,6,6-tetramethylpiperidin-4-yl)acetamide (VU0134992). In whole-cell patch-clamp electrophysiology experiments, VU0134992 inhibits Kir4.1 with an IC₅₀ value of 0.97 µM and is 9-fold selective for homomeric Kir4.1 over Kir4.1/5.1 concatemeric channels (IC₅₀ = 9 µM) at -120 mV. In thallium (Tl⁺) flux assays, VU0134992 is greater than 30-fold selective for Kir4.1 over Kir1.1, Kir2.1, and Kir2.2; is weakly active toward Kir2.3, Kir6.2/SUR1, and Kir7.1; and is equally active toward Kir3.1/3.2, Kir3.1/3.4, and Kir4.2. This potency and selectivity profile is superior to Kir4.1 inhibitors amitriptyline, nortriptyline, and fluoxetine. Medicinal chemistry identified components of VU0134992 that are critical for inhibiting Kir4.1. Patch-clamp electrophysiology, molecular modeling, and site-directed mutagenesis identified pore-lining glutamate 158 and isoleucine 159 as critical residues for block of the channel. VU0134992 displayed a large free unbound fraction (f_u) in rat plasma (f_u = 0.213). Consistent with the known role of Kir4.1 in renal function, oral dosing of VU0134992 led to a dose-dependent diuresis, natriuresis, and kaliuresis in rats. Thus, VU0134992 represents the first in vivo active tool compound for probing the therapeutic potential of Kir4.1 as a novel diuretic target for the treatment of hypertension.

Preparation of Unsymmetrical 1,2,4,5-Tetrazines via a Mild Suzuki Cross-Coupling Reaction

N-Alkyl substituted chlorotetrazines were coupled with various boronic acids under Suzuki conditions in high yield at room temperature, giving a mild and straightforward synthetic route toward diverse unsymmetrical 1,2,4,5-tetrazines, a rare heteroarene. This chemistry not only expands the known substrate scope of tetrazine cross-coupling reactions but also allows for the synthesis of novel, tetrazine-containing biologically active molecules with improved DMPK properties.

Classics in Chemical Neuroscience: Memantine

Memantine was the first breakthrough medication for the treatment of moderate to severe Alzheimer's disease (AD) patients and represents a fundamentally new mechanism of action (moderate-affinity, uncompetitive, voltage-dependent, N-methyl-d-aspartate (NMDA) receptor antagonist that exhibits fast on/off kinetics) to modulate glutamatergic dysfunction. Since its approval by the FDA in 2003, memantine, alone and in combination with donepezil, has improved patient outcomes in terms of cognition, behavioral disturbances, daily functioning, and delaying time to institutionalization. In this review, we will highlight the historical significance of memantine to AD (and other neuropsychiatric disorders) as well as provide an overview of the synthesis, pharmacology, and drug metabolism of this unique NMDA uncompetitive antagonist that clearly secures its place among the Classics in Chemical Neuroscience.

Discovery and optimization of 3-(4-aryl/heteroarylsulfonyl)piperazin-1-yl)-6-(piperidin-1-yl)pyridazines as novel, CNS penetrant pan-muscarinic antagonists

This letter describes the synthesis and structure activity relationship (SAR) studies of structurally novel M4 antagonists, based on a 3-(4-aryl/heteroarylsulfonyl)piperazin-1-yl)-6-(piperidin-1-yl)pyridazine core, identified from a high-throughput screening campaign. A multi-dimensional optimization effort enhanced potency at human M4 (hM4 IC50s<200nM), with only moderate species differences noted, and with enantioselective inhibition. Moreover, CNS penetration proved attractive for this series (rat brain:plasma Kp=2.1, Kp,uu=1.1). Despite the absence of the prototypical mAChR antagonist basic or quaternary amine moiety, this series displayed pan-muscarinic antagonist activity across M1-5 (with 9- to 16-fold functional selectivity at best). This series further expands the chemical diversity of mAChR antagonists.

Synthesis and evaluation of 4,6-disubstituted pyrimidines as CNS penetrant pan-muscarinic antagonists with a novel chemotype

This letter describes the synthesis and structure activity relationship (SAR) studies of structurally novel M₄ antagonists, based on a 4,6-disubstituted core, identified from a high-throughput screening campaign. A multi-dimensional optimization effort enhanced potency at both human and rat M₄ (IC₅₀s<300nM), with no substantial species differences noted. Moreover, CNS penetration proved attractive for this series (brain:plasma K_p,uu=0.87), while other DMPK attributes were addressed in the course of the optimization effort, providing low in vivo clearance in rat (CL_p=5.37mL/min/kg). Surprisingly, this series displayed pan-muscarinic antagonist activity across M_1-5, despite the absence of the prototypical basic or quaternary amine moiety, thus offering a new chemotype from which to develop a next generation of pan-muscarinic antagonist agents.

Classics in Chemical Neuroscience: Xanomeline

Xanomeline (1) is an orthosteric muscarinic acetylcholine receptor (mAChR) agonist, often referred to as M₁/M₄-preferring, that received widespread attention for its clinical efficacy in schizophrenia and Alzheimer's disease (AD) patients. Despite the compound's promising initial clinical results, dose-limiting side effects limited further clinical development. While xanomeline, and related orthosteric muscarinic agonists, have yet to receive approval from the FDA for the treatment of these CNS disorders, interest in the compound's unique M₁/M₄-preferring mechanism of action is ongoing in the field of chemical neuroscience. Specifically, the promising cognitive and behavioral effects of xanomeline in both schizophrenia and AD have spurred a renewed interest in the development of safer muscarinic ligands with improved subtype selectivity for either M₁ or M₄. This Review will address xanomeline's overall importance in the field of neuroscience, with a specific focus on its chemical structure and synthesis, pharmacology, drug metabolism and pharmacokinetics (DMPK), and adverse effects.

Effects of N-Substitutions on the Tetrahydroquinoline (THQ) Core of Mixed-Efficacy μ-Opioid Receptor (MOR)/δ-Opioid Receptor (DOR) Ligands

N-Acetylation of the tetrahydroquinoline (THQ) core of a series of μ-opioid receptor (MOR) agonist/δ-opioid receptor (DOR) antagonist ligands increases DOR affinity, resulting in ligands with balanced MOR and DOR affinities. We report a series of N-substituted THQ analogues that incorporate various carbonyl-containing moieties to maintain DOR affinity and define the steric and electronic requirements of the binding pocket across the opioid receptors. 4h produced in vivo antinociception (ip) for 1 h at 10 mg/kg.

Rapid Synthesis of Boc-2',6'-dimethyl-l-tyrosine and Derivatives and Incorporation into Opioid Peptidomimetics

The unnatural amino acid 2',6'-dimethyl-l-tyrosine has found widespread use in the development of synthetic opioid ligands. Opioids featuring this residue at the N-terminus often display superior potency at one or more of the opioid receptor types, but the availability of the compound is hampered by its cost and difficult synthesis. We report here a short, three-step synthesis of Boc-2',6'-dimethyl-l-tyrosine (3a) utilizing a microwave-assisted Negishi coupling for the key carbon-carbon bond forming step, and employ this chemistry for the expedient synthesis of other unnatural tyrosine derivatives. Three of these derivatives (3c, 3d, 3f) have not previously been examined as Tyr(1) replacements in opioid ligands. We describe the incorporation of these tyrosine derivatives in a series of opioid peptidomimetics employing our previously reported tetrahydroquinoline (THQ) scaffold, and the binding and relative efficacy of each of the analogues at the three opioid receptor subtypes: mu (MOR), delta (DOR), and kappa (KOR).

Asymmetric synthesis and in vitro and in vivo activity of tetrahydroquinolines featuring a diverse set of polar substitutions at the 6 position as mixed-efficacy μ opioid receptor/δ opioid receptor ligands

We previously reported a small series of mixed-efficacy μ opioid receptor (MOR) agonist/δ opioid receptor (DOR) antagonist peptidomimetics featuring a tetrahydroquinoline scaffold and showed the promise of this series as effective analgesics after intraperitoneal administration in mice. We report here an expanded structure-activity relationship study of the pendant region of these compounds and focus in particular on the incorporation of heteroatoms into this side chain. These analogues provide new insight into the binding requirements for this scaffold at MOR, DOR, and the κ opioid receptor (KOR), and several of them (10j, 10k, 10m, and 10n) significantly improve upon the overall MOR agonist/DOR antagonist profile of our previous compounds. In vivo data for 10j, 10k, 10m, and 10n are also reported and show the antinociceptive potency and duration of action of compounds 10j and 10m to be comparable to those of morphine.

Synthesis and evaluation of 4-substituted piperidines and piperazines as balanced affinity μ opioid receptor (MOR) agonist/δ opioid receptor (DOR) antagonist ligands

In this letter, we describe a series of 4-substituted piperidine and piperazine compounds based on tetrahydroquinoline 1, a compound that shows balanced, low nanomolar binding affinity for the mu opioid receptor (MOR) and the delta opioid receptor (DOR). We have shown that by changing the length and flexibility profile of the side chain in this position, binding affinity is improved at both receptors by a significant degree. Furthermore, several of the compounds described herein display good efficacy at MOR, while simultaneously displaying DOR antagonism. The MOR agonist/DOR antagonist has shown promise in the reduction of negative side effects displayed by selective MOR agonists, namely the development of dependence and tolerance.

Opioid peptidomimetics: leads for the design of bioavailable mixed efficacy μ opioid receptor (MOR) agonist/δ opioid receptor (DOR) antagonist ligands

We have previously described opioid peptidomimetic, 1, employing a tetrahydroquinoline scaffold and modeled on a series of cyclic tetrapeptide opioid agonists. We have recently described modifications to these peptides that confer a μ opioid receptor (MOR) agonist, δ opioid receptor (DOR) antagonist profile, which has been shown to reduce the development of tolerance to the analgesic actions of MOR agonists. Several such bifunctional ligands have been reported, but none has been demonstrated to cross the blood-brain barrier. Here we describe the transfer of structural features that evoked MOR agonist/DOR antagonist behavior in the cyclic peptides to the tetrahydroquinoline scaffold and show that the resulting peptidomimetics maintain the desired pharmacological profile. Further, the 4R diastereomer of 1 was fully efficacious and approximately equipotent to morphine in the mouse warm water tail withdrawal assay following intraperitoneal administration and thus a promising lead for the development of opioid analgesics with reduced tolerance.

Sleeping beauty-mediated somatic mutagenesis implicates CSF1 in the formation of high-grade astrocytomas

The Sleeping Beauty (SB) transposon system has been used as an insertional mutagenesis tool to identify novel cancer genes. To identify glioma-associated genes, we evaluated tumor formation in the brain tissue from 117 transgenic mice that had undergone constitutive SB-mediated transposition. Upon analysis, 21 samples (18%) contained neoplastic tissue with features of high-grade astrocytomas. These tumors expressed glial markers and were histologically similar to human glioma. Genomic DNA from SB-induced astrocytoma tissue was extracted and transposon insertion sites were identified. Insertions in the growth factor gene Csf1 were found in 13 of the 21 tumors (62%), clustered in introns 5 and 8. Using reverse transcription-PCR, we documented increased Csf1 RNAs in tumor versus adjacent normal tissue, with the identification of transposon-terminated Csf1 mRNAs in astrocytomas with SB insertions in intron 8. Analysis of human glioblastomas revealed increased levels of Csf1 RNA and protein. Together, these results indicate that SB-insertional mutagenesis can identify high-grade astrocytoma-associated genes and they imply an important role for CSF1 in the development of these tumors.

Whole-body sleeping beauty mutagenesis can cause penetrant leukemia/lymphoma and rare high-grade glioma without associated embryonic lethality

The Sleeping Beauty (SB) transposon system has been used as a somatic mutagen to identify candidate cancer genes. In previous studies, efficient leukemia/lymphoma formation on an otherwise wild-type genetic background occurred in mice undergoing whole-body mobilization of transposons, but was accompanied by high levels of embryonic lethality. To explore the utility of SB for large-scale cancer gene discovery projects, we have generated mice that carry combinations of different transposon and transposase transgenes. We have identified a transposon/transposase combination that promotes highly penetrant leukemia/lymphoma formation on an otherwise wild-type genetic background, yet does not cause embryonic lethality. Infiltrating gliomas also occurred at lower penetrance in these mice. SB-induced or accelerated tumors do not harbor large numbers of chromosomal amplifications or deletions, indicating that transposon mobilization likely promotes tumor formation by insertional mutagenesis of cancer genes, and not by promoting wide-scale genomic instability. Cloning of transposon insertions from lymphomas/leukemias identified common insertion sites at known and candidate novel cancer genes. These data indicate that a high mutagenesis rate can be achieved using SB without high levels of embryonic lethality or genomic instability. Furthermore, the SB system could be used to identify new genes involved in lymphomagenesis/leukemogenesis.

lin-35/Rb and the CoREST ortholog spr-1 coordinately regulate vulval morphogenesis and gonad development in C. elegans

Using a genetic screen to identify genes that carry out redundant functions during development with lin-35/Rb, the C. elegans Retinoblastoma family ortholog, we have identified a mutation in spr-1. spr-1 encodes the C. elegans ortholog of human CoREST, a protein containing Myb-like SANT and ELM2 domains, which functions as part of a transcriptional regulatory complex. CoREST recruits mediators of transcriptional repression, including histone deacetylase, and demethylase, and interacts with the tumor suppression protein REST. spr-1/CoREST was previously shown in C. elegans to suppress defects associated with loss of the presenilin sel-12, which functions in the proteolytic processing of LIN-12/Notch. Here we show that lin-35 and spr-1 coordinately regulate several developmental processes in C. elegans including the ingression of vulval cells as well as germline proliferation. We also show that loss of lin-35 and spr-1 hypersensitizes animals to a reduction in LIN-12/Notch activity, leading to the generation of proximal germline tumors. This defect, which is observed in lin-35; spr-1; lin-12(RNAi) and lin-35; spr-1; hop-1(RNAi) triple mutants is likely due to a delay in the entry of germ cells into meiosis.

lin-35/Rb and xnp-1/ATR-X function redundantly to control somatic gonad development in C. elegans

In screens for genetic modifiers of lin-35/Rb, the C. elegans retinoblastoma protein (Rb) homolog, we have identified a mutation in xnp-1. Mutations in xnp-1, including a presumed null allele, are viable and, in general, appear indistinguishable from the wild type. In contrast, xnp-1 lin-35 double mutants are typically sterile and exhibit severe defects in gonadal development. Analyses of the abnormal gonads indicate a defect in the lineages that generate cells of the sheath and spermatheca. xnp-1 encodes the C. elegans homolog of ATR-X, a human disease gene associated with severe forms of mental retardation and urogenital developmental defects. xnp-1/ATR-X is a member of the Swi2/Snf2 family of ATP-dependent DEAD/DEAH box helicases, which function in nucleosome remodeling and transcriptional regulation. Expression of an xnp-1 Colon, two colons GFP promoter fusion is detected throughout C. elegans development in several cell types including neurons and cells of the somatic gonad. Our findings demonstrate a new biological role for Rb family members in somatic gonad development and implicate lin-35 in the execution of multiple cell fates in C. elegans. In addition, our results suggest a possible conserved function for xnp-1/ATR-X in gonadal development across species.

Acute effects of caffeine ingestion on signal-averaged electrocardiograms

BACKGROUND

Although moderate caffeine ingestion has not been shown to be arrhythmogenic, caffeine toxicity can cause severe cardiac arrhythmias, including atrial fibrillation and ventricular tachycardia. Atrial fibrillation and ventricular tachycardia have been associated with prolongation of P-wave and QRS complex durations on signal-averaged electrocardiograms. This study investigated acute effects of caffeine ingestion on signal-averaged P-wave and QRS complexes.

METHODS AND RESULTS

Signal-averaged electrocardiograms were obtained from 12 normal subjects (6 men, 6 women; ages 21 to 26 years) before and after ingestion of caffeine (5 mg/kg body weight) or placebo in a randomized, double-blind, crossover fashion. Electrocardiograms for signal averaging were recorded from electrodes left in a constant location. After bandpass filtering (30 to 300 Hz) and amplification, signals were sampled over 7.2 minutes at 2000 Hz. Signal-averaged P-wave and QRS complex durations did not significantly change after placebo ingestion. After caffeine ingestion QRS duration prolonged in 9 of 11 subjects at 90 minutes (mean +/- SEM = 0.8+/-0.3 ms, P< .02) and in 8 of 9 after 3 hours (1.1+/-0.2 ms, P< .001). No significant change in P-wave duration or heart rate was found after caffeine ingestion at any test interval. Average caffeine level in saliva 90 minutes after ingestion was 6.6+/-1.6 (SD) microg/dL.

CONCLUSIONS

Although probably not arrhythmogenic in normal subjects, moderate caffeine ingestion does produce a small but statistically significant prolongation of signal-averaged QRS complexes. Further prolongation caused by excessive caffeine intake may be a factor in the genesis of arrhythmias associated with caffeine toxicity.

Hemodynamic effects of acute caffeine ingestion in young adults

This study investigated hemodynamic effects of acute caffeine ingestion in young adults 21 to 26 years of age. Data showed an increase in heart rate corrected velocity of circumferential fiber shortening at an indexed afterload up to 4.5 hours following caffeine consumption.