4-(1,3-Dimethoxyprop-2-ylamino)-2,7-dimethyl-8-(2, 4-dichlorophenyl)pyrazolo[1,5-a]-1,3,5-triazine: a potent, orally bioavailable CRF(1) receptor antagonist

Synthesis of new pyrazolo[1,2,3]triazines by cyclative cleavage of pyrazolyltriazenes

We describe the synthesis of so far synthetically not accessible 3,6-substituted-4,6-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines as nitrogen-rich heterocycles. The target compounds were obtained in five steps, including an amidation and a cyclative cleavage reaction as key reaction steps. The introduction of two side chains allowed a variation of the pyrazolo[3,4-d][1,2,3]triazine core with commercially available building blocks, enabling the extension of the protocol to gain other derivatives straightforwardly. Attempts to synthesize 3,7-substituted-4,7-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines, the regioisomers of the successfully gained 3,6-substituted 4,6-dihydro-3H-pyrazolo[3,4-d][1,2,3]triazines, were not successful under similar conditions due to the higher stability of the triazene functionality in the regioisomeric precursors and thus, the failure of the removal of the protective group.

Pyrazolotriazines: Biological activities, synthetic strategies and recent developments

Heterocyclic compounds create an important class of molecules that demonstrates various chemical spaces for the definition of effective medicines. Many N-heterocycles display numerous biological activities. Among condensed heterocycles, pyrazolotriazine derivatives have received the attention of researchers owing to the extensive spectrum of biological activities. The reactivity of identified compounds was similar to the free azoles and triazines. The pyrazolotriazine scaffold exhibited antiasthma, antiinflammatory, anticancer, antithrombogenic activity and showed activity for major depression and pathological anxiety. Pyrazolotriazine derivatives also exhibited antibacterial, anticancer, antimetabolites, antidiabetic, antiamoebic, anticonvulsant, antiproliferative activity, human carbonic anhydrase inhibition, cyclin-dependent kinase 2 inhibition, tyrosinase and urease inhibition, MAO-B inhibition, TTK inhibition, thymidine phosphorylase inhibition, tubulin polymerization inhibition, protoporphyrinogen oxidase inhibition, GABA_A agonistic activity, hCRF1 receptor antagonistic activity, and CGRP receptor antagonistic activity. This paper structurally categorized various pyrazolotriazines to isomeric classes into six groups that containing pyrazolo [1,5-d] [1,2,4] triazine, pyrazolo [5,1-c] [1,2,4] triazine, pyrazolo [3,4-e] [1,2,4] triazine, pyrazolo [4,3-e] [1,2,4] triazines, pyrazolo [1,5-a] [1,3,5] triazine, and pyrazolo [3,4-d] [1,2,3] triazine and expressed biological activity, the synthetic procedures for each class of pyrazolotriazines, structure-activity relationship and their mechanism of action. Generally, this review summarily indicated the past and present studies about the discovery of new lead compounds with good biological activity.

Synthesis of Purine Analogues: Photocatalyst-Free Visible-Light-Enhanced Annulation Approach to Pyrazolo[1,5-a][1,3,5]triazine-2,4-diamines

A new photocatalyst-free visible-light-enhanced strategy for the synthesis of pyrazolo[1,5-a][1,3,5]triazine-2,4-diamines via the formation of electron donor-acceptor (EDA) complexes is reported. The in situ generated pyrazolthiourea intermediates from 1H-pyrazol-3-amines and isothiocyanates undergo formal [4 + 2] annulation with 1,1,3,3-tetramethylguanidines (TMG) to deliver the corresponding products involved in three C-N bond formations in a one-pot protocol. The formation of EDA complex from pyrazolthiourea and TMG is confirmed by UV-vis spectroscopy and ¹H NMR experiments. Moreover, this mild reaction proceeds in the absence of any external transition metals, oxidants, bases, and ligands. This efficient methodology for the synthesis of purine analogues pyrazolo[1,5-a][1,3,5]triazine-2,4-diamines provides potential synthetic applications in the field of drug research and development.

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.

Selective corticotropin-releasing factor 1 receptor antagonist E2508 reduces restraint stress-induced defecation and visceral pain in rat models

N-Cyclopropylmethyl-7-(2,6-dimethoxy-4-methoxymethylphenyl)-2-ethyl-N-(tetrahydro-2H-pyran-4-ylmethyl)pyrazolo[1,5-a]pyridin-3-amine tosylate (E2508) is a newly discovered selective corticotropin-releasing factor 1 receptor antagonist. Here, we investigated the effects of E2508 on wrap restraint stress-induced defecation and visceral pain in rats. Oral pretreatment with E2508 dose-dependently decreased stool weights after 20min wrap restraint stress and significant effects were observed at doses of 30 and 100mg/kg. However, E2508 did not affect basal defecation at doses up to 100mg/kg. In contrast, alosetron, a 5-HT₃ receptor antagonist, decreased both wrap restraint stress-induced and basal stool output at a dose of 0.1mg/kg. In a rat visceral pain model, subcutaneous injections of both E2508 (0.01 and 0.1mg/kg) and alosetron (0.001 and 0.01mg/kg) significantly decreased the number of abdominal muscle contractions induced by colonic distention, suggesting these drugs reduced visceral pain. Together, these results demonstrate E2508 has the potential to be an effective therapy for the treatment of irritable bowel syndrome with a lower risk of adverse events such as constipation compared with the current clinically used 5-HT₃ receptor antagonist.

Synthesis, F-18 radiolabeling, and microPET evaluation of 3-(2,4-dichlorophenyl)-N-alkyl-N-fluoroalkyl-2,5-dimethylpyrazolo[1,5-a]pyrimidin-7-amines as ligands of the corticotropin-releasing factor type-1 (CRF1) receptor

A series of 3-(2,4-dichlorophenyl)-N-alkyl-N-fluoroalkyl-2,5-dimethylpyrazolo[1,5-a]pyrimidin-7-amines were synthesized and evaluated as potential positron emission tomography (PET) tracers for the corticotropin-releasing factor type-1 (CRF1) receptor. Compounds 27, 28, 29, and 30 all displayed high binding affinity (⩽1.2 nM) to the CRF1 receptor when assessed by in vitro competition binding assays at 23 °C, whereas a decrease in affinity (⩾10-fold) was observed with compound 26. The logP7.4 values of [(18)F]26-[(18)F]29 were in the range of ∼2.2-2.8 and microPET evaluation of [(18)F]26-[(18)F]29 in an anesthetized male cynomolgus monkey demonstrated brain penetrance, but specific binding was not sufficient enough to differentiate regions of high CRF1 receptor density from regions of low CRF1 receptor density. Radioactivity uptake in the skull, and sphenoid bone and/or sphenoid sinus during studies with [(18)F]28, [(18)F]28-d8, and [(18)F]29 was attributed to a combination of [(18)F]fluoride generated by metabolic defluorination of the radiotracer and binding of intact radiotracer to CRF1 receptors expressed on mast cells in the bone marrow. Uptake of [(18)F]26 and [(18)F]27 in the skull and sphenoid region was rapid but then steadily washed out which suggests that this behavior was the result of binding to CRF1 receptors expressed on mast cells in the bone marrow with no contribution from [(18)F]fluoride.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Synthesis and structure-activity relationships of 8-substituted-2-aryl-5-alkylaminoquinolines: Potent, orally active corticotropin-releasing factor-1 receptor antagonists

We previously reported a series of 8-methyl-2-aryl-5-alkylaminoquinolines as a novel class of corticotropin-releasing factor-1 (CRF(1)) receptor antagonists. A critical issue encountered for this series of compounds was low aqueous solubility at physiological pH (pH 7.4). To address this issue, derivatization at key sites (R(2), R(3), R(5), R(5'), and R(8)) was performed and the relationships between structure and solubility were examined. As a result, it was revealed that introduction of a methoxy substituent at the C(8) position had a positive impact on the solubility of the derivatives. Consequently, through in vivo and in vitro biological studies, compound 21d was identified as a potent, orally active CRF(1) receptor antagonist with improved physicochemical properties.

On the role of corticotropin-releasing hormone receptors in anxiety and depression

On the basis of extensive basic and clinical studies, corticotropin-releasing hormone (CRH) and its related family members are considered to play a pivotal role in stress-related disorders, such as anxiety and depression. CRH is regarded as the principal mediator in the brain of the stress response, as it mediates neuroendocrine, autonomic, and behavioral responses to stressful challenges. Recently, this neuropeptide family has expanded due to the discovery of two new members, urocortin II (also termed stresscopin-related peptide) and urocortin III (also termed stresscopin), which are selective agonists for the CRH receptor type 2. They show a discrete neuroanatomical localization and are involved in stress-coping responses, such as anxiolysis. Here, on the basis of recent developments, we suggest that CRH, the urocortins, and their receptors form a complex system in the brain, which is recruited during both the acute and the recovery phases of the stress response.

Synthesis and structure-activity relationships of pyrazolo[1,5-a]pyridine derivatives: potent and orally active antagonists of corticotropin-releasing factor 1 receptor

Design, synthesis, and structure-activity relationships of a series of 3-dialkylamino-7-phenyl pyrazolo[1,5-a]pyridines (I) as selective antagonists of the corticotropin-releasing factor 1 (CRF(1)) receptor are described. The most prominent compound to emerge from this work, 46 (E2508), exhibits potent in vitro activity, excellent drug-like properties, and robust oral efficacy in animal models of stress-related disorders. It has advanced into clinical trials.

Discovery of N-(1-ethylpropyl)-[3-methoxy-5-(2-methoxy-4-trifluoromethoxyphenyl)-6-methyl-pyrazin-2-yl]amine 59 (NGD 98-2): an orally active corticotropin releasing factor-1 (CRF-1) receptor antagonist

The design, synthesis, and structure-activity relationships of a novel series of pyrazines, acting as corticotropin releasing factor-1 (CRF-1) receptor antagonists, are described. Synthetic methodologies were developed to prepare a number of substituted pyrazine cores utilizing regioselective halogenation and chemoselective derivatization. Noteworthy, an efficient 5-step synthesis was developed for the lead compound 59 (NGD 98-2), which required no chromatography. Compound 59 was characterized as an orally bioavailable, brain penetrant, and highly selective CRF-1 receptor antagonist. Occupancy of rat brain CRF-1 receptors was quantified using ex vivo receptor occupancy assays, using both brain tissue homogenates as well as brain slices receptor autoradiography. Behaviorally, oral administration of 59 significantly antagonized CRF-induced locomotor activity at doses as low as 10 mg/kg and dose-dependently reduced the restraint stress-induced ACTH increases.

Biomimetic screening of class-B G protein-coupled receptors

The 41-amino acid peptide corticotropin releasing factor (CRF) is a major modulator of the mammalian stress response. Upon stressful stimuli, it binds to the corticotropin releasing factor receptor 1 (CRF(1)R), a typical member of the class-B G-protein-coupled receptors (GPCRs) and a prime target in the treatment of mood disorders. To chemically probe the molecular interaction of CRF with the transmembrane domain of its cognate receptor, we developed a high-throughput conjugation approach that mimics the natural activation mechanism of class-B GPCRs. An acetylene-tagged peptide library was synthesized and conjugated to an azide-modified high-affinity carrier peptide derived from the CRF C-terminus using copper-catalyzed dipolar cycloaddition. The resulting conjugates reconstituted potent agonists and were tested in situ for activation of the CRF(1) receptor in a cell-based assay. By use of this approach we (i) defined the minimal sequence motif that is required for full receptor activation, (ii) identified the critical functional groups and structure-activity relationships, (iii) developed an optimized, highly modified peptide probe with high potency (EC(50) = 4 nM) that is specific for the activation domain of the receptor, and (iv) probed the behavioral role of CRF receptors in living mice. The membrane recruitment by a high-affinity carrier enhanced the potency of the tethered peptides by >4 orders of magnitude and thus allowed the testing of very weak initial fragments that otherwise would have been inactive on their own. As no chromatography purification of the test peptides was necessary, a substantial increase in screening throughput was achieved. Importantly, the peptide conjugates can be used to probe the endogenous receptor in its native environment in vivo.

[(76) Br]BMK-152, a nonpeptide analogue, with high affinity and low nonspecific binding for the corticotropin-releasing factor type 1 receptor

Corticotropin-releasing factor (CRF), a neuropeptide, regulates endocrine and autonomic responses to stress through G-protein coupled receptors, CRF(1) or CRF(2) . A PET ligand able to monitor changes in CRF(1) receptor occupancy in vivo would aid in understanding the pathophysiology of stress-related diseases as well as in the clinical development of nonpeptide antagonists with therapeutic value. We have radiolabeled the CRF(1) receptor ligand, [8-(4-bromo-2,6-dimethoxyphenyl)-2,7-dimethylpyrazolo[1,5-α][1,3,5]triazin-4-yl]-N,N-bis-(2-methoxyethyl)amine (BMK-152) (ClogP = 2.6), at both the 3 and 4 position with [(76) Br]. Using in vitro autoradiography saturation studies the 4-[(76) Br]BMK-152 exhibited high affinity binding to both rat (K(d) = 0.23 ± 0.07 nM; n = 3) and monkey frontal cortex (K(d) = 0.31 ± 0.08 nM; n = 3) consistent with CRF(1) receptor regional distribution whereas with the 3-[(76) Br]BMK-152, the K(d) s could not be determined due to high nonspecific binding. In vitro autoradiography competition studies using [(125) I]Tyr(0) -o-CRF confirmed that 3-Br-BMK-152 (K(i) = 24.4 ± 4.9 nM; n = 3) had lower affinity (70-fold) than 4-Br-BMK-152 (K(i) = 0.35 ± 0.07 nM; n = 3) in monkey frontal cortex and similiar studies using [(125) I]Sauvagine confirmed CRF(1) receptor selectivity. In vivo studies with P-glycoprotein (PGP) knockout mice (KO) and their wild-type littermates (WT) showed that the brain uptake of 3-[(76) Br]BMK/4-[(76) Br]BMK was increased less than twofold in KO versus WT indicating that 3-[(76) Br]BMK-152/4-[(76) Br]BMK was not a Pgp substrate. Rat brain uptakes of 4-[(76) Br] BMK-152 from ex vivo autoradiography studies showed regional localization consistent with known published CRF(1) receptor distribution and potential as a PET ligand for in vivo imaging of CRF(1) receptors.

[¹²⁵I]YP20: a novel radioligand specific for the extracellular domain of the CRF₁ receptor

The peptide corticotropin-releasing factor (CRF) binds to the CRF₁ receptor via a two-domain mechanism such that the extracellular domain (ECD) of the receptor captures the CRF's C-terminus to facilitate the binding of CRF's N-terminus to the juxta-membrane or "J"-site. Known small molecule antagonists bind to the J-site while known CRF₁ receptor peptide radioligands bind to both sites. We report here the in vitro binding properties of the first radioligand that binds exclusively to the ECD of the CRF₁ receptor. This ligand, which we named [¹²⁵I]Yamada peptide 20 ([¹²⁵I]YP20), is a radiolabeled analog of a synthetic peptide first reported by Yamada et al. (2004). We confirmed its high affinity for the [¹²⁵I]CRF binding site on the hCRF₁ receptor and also found it to potently antagonize CRF-stimulated cAMP production in hCRF₁-CHO cells. Under optimized conditions, 20 pM [¹²⁵I]YP20 reproducibly bound to hCRF₁-CHO membranes with a pharmacology consistent with binding specific to the ECD of the CRF₁ receptor. Saturation binding studies revealed the presence of a high affinity site with an estimated K(d) of ≈0.9 nM. The kinetic association of 20 pM [¹²⁵I]YP20 binding best fit to a rapid component (t(1/2)=0.69 min) and a sluggish component (t(1/2)=42 min). [¹²⁵I]YP20's specific binding was rapidly reversible with dissociation kinetics also best described by two phases (t(1/2)=0.92 min and t(1/2)=11.7 min). While [¹²⁵I]YP20's binding kinetics are complex, its high affinity and pharmacological specificity indicate that it is an excellent radioligand for probing the ECD site of the CRF₁ receptor.

Allosteric modulators of class B G-protein-coupled receptors

Class B GPCR’s are activated by peptide ligands, typically 30-40 amino acid residues, that are involved in major physiological functions such as glucose homeostasis (glucagon and glucagon-like peptide 1), calcium homeostasis and bone turnover (parathyroid hormone and calcitonin), and control of the stress axis (corticotropin-releasing factor). Peptide therapeutics have been developed targeting these receptors but development of nonpeptide ligands, enabling oral administration, has proved challenging. Allosteric modulation of these receptors provides a potential route to developing nonpeptide ligands that inhibit, activate, or potentiate activation of these receptors. Here the known mechanisms of allosteric modulators targeting Class B GPCR’s are reviewed, particularly nonpeptide antagonists of the corticotropin-releasing factor 1 receptor and allosteric enhancers of the glucagon-like peptide-1 receptor. Also discussed is the potential for antagonist ligands to operate by competitive inhibition of one of the peptide binding sites, analogous to the Charniere mechanism. These mechanisms are then used to discuss potential strategies and management of pharmacological complexity in the future development of allosteric modulators for Class B GPCR’s.

Progress in corticotropin-releasing factor-1 antagonist development

Corticotropin releasing factor (CRF) receptor antagonists have been sought since the stress-secreted peptide was isolated in 1981. Although evidence is mixed concerning the efficacy of CRF(1) antagonists as antidepressants, CRF(1) antagonists might be novel pharmacotherapies for anxiety and addiction. Progress in understanding the two-domain model of ligand-receptor interactions for CRF family receptors might yield chemically novel CRF(1) receptor antagonists, including peptide CRF(1) antagonists, antagonists with signal transduction selectivity and nonpeptide CRF(1) antagonists that act via the extracellular (rather than transmembrane) domains. Novel ligands that conform to the prevalent pharmacophore and exhibit drug-like pharmacokinetic properties have been identified. The therapeutic utility of CRF(1) antagonists should soon be clearer: several small molecules are currently in Phase II/III clinical trials for depression, anxiety and irritable bowel syndrome.

Semi-remote production of Br-76 and preparation of high specific activity radiobrominated pharmaceuticals for PET studies

The PET radionuclide 76Br (t1/2=16.2 h) can be easily produced utilizing the nuclear reaction As(3He,2n)76Br. We use high-purity arsenic targets and isolate radioactive bromide by chromic acid oxidation followed by simple distillation of [76Br] hydrogen bromide using a semi-remote apparatus. Use of reagents with little or no carrier bromine yields high specific activity radiobrominated pharmaceuticals prepared from the distilled [76Br] hydrogen bromide.

Synthesis, structure-activity relationships, and in vivo evaluation of N3-phenylpyrazinones as novel corticotropin-releasing factor-1 (CRF1) receptor antagonists

Evidence suggests that corticotropin-releasing factor-1 (CRF(1)) receptor antagonists may offer therapeutic potential for the treatment of diseases associated with elevated levels of CRF such as anxiety and depression. A pyrazinone-based chemotype of CRF(1) receptor antagonists was discovered. Structure-activity relationship studies led to the identification of numerous potent analogues including 12p, a highly potent and selective CRF(1) receptor antagonist with an IC(50) value of 0.26 nM. The pharmacokinetic properties of 12p were assessed in rats and Cynomolgus monkeys. Compound 12p was efficacious in the defensive withdrawal test (an animal model of anxiety) in rats. The synthesis, structure-activity relationships and in vivo properties of compounds within the pyrazinone chemotype are described.

Synthesis and structure-activity relationships of 8-(pyrid-3-yl)pyrazolo[1,5-a]-1,3,5-triazines: potent, orally bioavailable corticotropin releasing factor receptor-1 (CRF1) antagonists

This report describes the syntheses and structure-activity relationships of 8-(substituted pyridyl)pyrazolo[1,5-a]-1,3,5-triazine corticotropin releasing factor receptor-1 (CRF(1)) receptor antagonists. These CRF(1) receptor antagonists may be potential anxiolytic or antidepressant drugs. This research resulted in the discovery of compound 13-15, which is a potent, selective CRF(1) antagonist (hCRF(1) IC(50) = 6.1 +/- 0.6 nM) with weak affinity for the CRF-binding protein and biogenic amine receptors. This compound also has a good pharmacokinetic profile in dogs. Analogue 13-15 is orally effective in two rat models of anxiety: the defensive withdrawal (situational anxiety) model and the elevated plus maze test. Analogue 13-15 has been advanced to clinical trials.

Involvement of vasopressin 3 receptors in chronic psychological stress-induced visceral hyperalgesia in rats

Visceral hypersensitivity and stress have been implicated in the pathophysiology of functional gastrointestinal disorders. We used a selective vasopressin 3 (V(3)) receptor antagonist SSR149415 to investigate the involvement of the vasopressin (AVP)/V(3) signaling system in the development of stress-induced visceral hyperalgesia in rats. Rats were exposed to a daily 1-h session of water avoidance stress (WAS) or sham WAS for 10 consecutive days. The visceromotor response to phasic colorectal distension (CRD, 10-60 mmHg) was assessed before and after stress. Animals were treated daily with SSR149415 (0.3, 1, or 3 mg/kg ip 30 min before each WAS or sham WAS session), with a single dose of SSR149415 (1 mg/kg ip), or the selective corticotropin-releasing factor 1 (CRF(1)) antagonist DMP-696 (30 mg/kg po) before CRD at day 11. Effects of a single dose of SSR149415 (10 mg/kg iv) on acute mechanical sensitization during repetitive CRD (12 distensions at 80 mmHg) were also assessed. In vehicle-treated rats, repeated WAS increased the response to CRD, indicating visceral hypersensitivity. Repeated administration of SSR149415 at 1 or 3 mg/kg completely prevented stress-induced visceral hyperalgesia. Similarly, a single dose of DMP-696 or SSR149415 completely blocked hyperalgesic responses during CRD. In contrast, a single dose of SSR149415 did not affect the acute hyperalgesic responses induced by repeated, noxious distension. These data support a major role for V(3) receptors in repeated psychological stress-induced visceral hyperalgesia and suggest that pharmacological manipulation of the AVP/V(3) pathway might represent an attractive alternative to the CRF/CRF(1) pathway for the treatment of chronic stress-related gastrointestinal disorders.

Neurobiology of stress-induced reproductive dysfunction in female macaques

It is now well accepted that stress can precipitate mental and physical illness. However, it is becoming clear that given the same stress, some individuals are very vulnerable and will succumb to illness while others are more resilient and cope effectively, rather than becoming ill. This difference between individuals is called stress sensitivity. Stress sensitivity of an individual appears to be influenced by genetically inherited factors, early life (even prenatal) stress, and by the presence or absence of factors that provide protection from stress. In comparison to other stress-related diseases, the concept of sensitivity versus resilience to stress-induced reproductive dysfunction has received relatively little attention. The studies presented herein were undertaken to begin to identify stable characteristics and the neural underpinnings of individuals with sensitivity to stress-induced reproductive dysfunction. Female cynomolgus macaques with normal menstrual cycles either stop ovulating (stress sensitive) or to continue to ovulate (stress resilient) upon exposure to a combined metabolic and psychosocial stress. However, even in the absence of stress, the stress-sensitive animals have lower secretion of the ovarian steroids, estrogen and progesterone, have higher heart rates, have lower serotonin function, have fewer serotonin neurons and lower expression of pivotal serotonin-related genes, have lower expression of 5HT2A and 2C genes in the hypothalamus, have higher gene expression of GAD67 and CRH in the hypothalamus, and have reduced gonadotropin-releasing hormone transport to the anterior pituitary. Altogether, the results suggest that the neurobiology of reproductive circuits in stress-sensitive individuals is compromised. We speculate that with the application of stress, the dysfunction of these neural systems becomes exacerbated and reproductive function ceases.

Conditional mouse mutants highlight mechanisms of corticotropin-releasing hormone effects on stress-coping behavior

Hypersecretion of central corticotropin-releasing hormone (CRH) has been implicated in the pathophysiology of affective disorders. Both, basic and clinical studies suggested that disrupting CRH signaling through CRH type 1 receptors (CRH-R1) can ameliorate stress-related clinical conditions. To study the effects of CRH-R1 blockade upon CRH-elicited behavioral and neurochemical changes we created different mouse lines overexpressing CRH in distinct spatially restricted patterns. CRH overexpression in the entire central nervous system, but not when overexpressed in specific forebrain regions, resulted in stress-induced hypersecretion of stress hormones and increased active stress-coping behavior reflected by reduced immobility in the forced swim test and tail suspension test. These changes were related to acute effects of overexpressed CRH as they were normalized by CRH-R1 antagonist treatment and recapitulated the effect of stress-induced activation of the endogenous CRH system. Moreover, we identified enhanced noradrenergic activity as potential molecular mechanism underlying increased active stress-coping behavior observed in these animals. Thus, these transgenic mouse lines may serve as animal models for stress-elicited pathologies and treatments that target the central CRH system.

Cyclopenta[d]pyrimidines and dihydropyrrolo[2,3-d]pyrimidines as potent and selective corticotropin-releasing factor 1 receptor antagonists

Two new classes of potent and selective CRF(1) receptor antagonists are presented. Exploration of general templates 3 and 4 through modifications of the top amine and bottom phenyl substituents led to optimization of the in vitro affinity and pharmacokinetic profiles. The typical alkyl chains present in the top region of CRF(1) antagonists were replaced by substituted heteroaryl moieties, leading to a dramatic improvement of the metabolic stability. This improvement was apparent when the compounds were dosed in vivo: several compounds exhibited low plasma clearance, good oral bioavailability, and high brain penetration. As a consequence of their outstanding pharmacokinetic profiles, these CRF(1) antagonists, as exemplified by compound 4 fi (4-(4-bromo-3-methyl-1H-pyrazol-1-yl)-7-(2,4-dichlorophenyl)-2-methyl-6,7-dihydro-5H-pyrrolo[2,3-d]pyrimidine), produced a dose-dependent "anxiolytic-like" effect when administered orally, decreasing the vocalization of rat pups.

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.

Activation of basolateral amygdala corticotropin-releasing factor 1 receptors modulates the consolidation of contextual fear

The basolateral amygdala complex (BLA) and central amygdala nucleus (CeA) are involved in fear and anxiety. In addition, the BLA contains a high density of corticotropin-releasing factor 1 (CRF(1)) receptors in comparison to the CeA. However, the role of BLA CRF(1) receptors in contextual fear conditioning is poorly understood. In the present study, we first demonstrated in rats that oral administration of DMP696, the selective CRF(1) receptor antagonist, had no significant effects on the acquisition of contextual fear but produced a subsequent impairment in contextual freezing suggesting a role of CRF(1) receptors in the fear memory consolidation process. In addition, oral administration of DMP696 significantly reduced phosphorylation of cyclic AMP response element-binding protein (pCREB) in the lateral and basolateral amygdala nuclei, but not in the CeA, during the post-fear conditioning period. We then demonstrated that bilateral microinjections of DMP696 into the BLA produced no significant effects on the acquisition of conditioned fear but reduced contextual freezing in a subsequent drug-free conditioned fear test. Importantly, bilateral microinjections of DMP696 into the BLA at 5 min or 3 h, but not 9 h, after exposure to contextual fear conditioning was also effective in reducing contextual freezing in the conditioned fear test. Finally, microinfusions of either DMP696 into the CeA or a specific corticotropin-releasing factor 2 receptor antagonist in the BLA were shown to have no major effects on disrupting either contextual fear conditioning or performance of contextual freezing in the drug-free conditioned fear test. Collectively, results implicate a role of BLA CRF(1) receptors in activating the fear memory consolidation process, which may involve BLA pCREB-induced synaptic plasticity.

Novel substituted tetrahydrotriazaacenaphthylene derivatives as potent CRF1 receptor antagonists

Corticotropin-releasing factor (CRF), a 41 amino acid peptide neurohormone synthesised by specific hypothalamic nuclei in the brain, is implicated in stress-related function. Antagonism of CRF(1) receptors is an attractive therapeutic approach for the treatment of depression and anxiety. Unsaturated tetrahydrotriazaacenaphthylenes of general structure 3 have been identified as potent and selective CRF(1) receptor antagonists with a suitable oral pharmacokinetic profile.

Differential activation of CRF receptor subtypes removes stress-induced memory deficit and anxiety

The objective of this study was to investigate the role of corticotropin-releasing factor receptors 1 (CRF(1)) and 2 (CRF(2)) in anxiety-like behavior and learning of C57BL/6J mice after exposure to a stressful stimulus. When C57BL/6J mice were exposed to immobilization (1 h) serving as stressful stimulus, context- and tone-dependent fear conditioning were impaired if the training followed immediately after immobilization. The stress-induced impairment of context-dependent fear conditioning was prevented by specific blockade of CRF(2) of the lateral septum (LS) with anti-sauvagine-30. Immobilization did not only affect conditioned fear, but also enhanced, through CRF(2) of the LS, anxiety-like behavior determined with the elevated plus maze. Recovery from stress-induced anxiety and impairment of context-dependent fear conditioning was observed after 1 h delay of training and required hippocampal CRF(1), as indicated by the finding that this recovery was prevented by blockade of intrahippocampal CRF(1). It was concluded that exposure to a stressor initially affected both anxiety-like behavior and contextual conditioned fear through septal CRF(2), while the later activation of hippocampal CRF(1) resulted in the return to baseline levels of both processes. Intraventricular injection of mouse urocortin 2, a CRF(2)-selective agonist, removed the stress-induced anxiety and learning impairment, but did not reduce the activation of the hypothalamic pituitary adrenal axis indicative of the hormonal stress response. We propose that the enhanced anxiety is the component of the stress response responsible for the memory deficit.

PET Imaging of CRF1 with [11C]R121920 and [11C]DMP696: is the target of sufficient density?

AIM

Overstimulation of the CRF type 1 receptor (CRF1) is implicated in anxiety and depressive disorders. The aim of this study was to investigate the in vivo binding characteristics of [11C]R121920 and [11C]DMP696 in the nonhuman primate for application in positron emission tomography (PET) studies of CRF1.

METHODS

PET imaging with the two novel CRF1 radioligands was performed in baboon. In vitro binding studies for CRF1 were performed in postmortem brain tissue of baboon and human to assess sufficiency of receptor density for PET.

RESULTS

Both [11C]R121920 and [11C]DMP696 distributed rapidly and uniformly throughout the brain. Washout was comparable across brain regions, without differences in volume of distribution between regions reported to have high and low in vitro CRF1 binding. Membrane-enriched tissue homogenate assay using [(125)I]Tyr(0)-sauvagine and specific CRF1 antagonists CP154,526 and SN003 in human occipital cortex yielded maximal binding (Bmax) of 63.3 and 147.3 fmol/mg protein, respectively, and in human cerebellar cortex yielded Bmax of 103.6 and 64.6 fmol/mg protein, respectively. Dissociation constants (K(D)) were subnanomolar. In baboon, specific binding was not detectable in the same regions; therefore, Bmax and K(D) were not measurable. Autoradiographic results were consistent except there was also detectable CRF1-specific binding in baboon cerebellum.

CONCLUSION

Neither [11C]R121920 nor [11C]DMP696 demonstrated quantifiable regional binding in vivo in baboon. In vitro results suggest CRF1 density in baboon may be insufficient for PET. Studies in man may generate more promising results due to the higher CRF1 density compared with baboon in cerebral cortex and cerebellum.

Corticotropin-releasing factor 1 antagonists selectively reduce ethanol self-administration in ethanol-dependent rats

BACKGROUND

Alcohol dependence is characterized by excessive alcohol consumption, loss of control over intake, and the presence of a withdrawal syndrome, which includes both motivational and physical symptoms. Similar to human alcoholics, ethanol-dependent animals display enhanced anxiety-like behaviors and enhanced ethanol self-administration during withdrawal, effects hypothesized to result from a dysregulation of corticotropin-releasing factor (CRF) stress systems. Here, we used an animal model of ethanol dependence to test the effects of CRF(1) receptor antagonists on excessive ethanol self-administration in dependent rats.

METHODS

Wistar rats, trained to orally self-administer ethanol, were exposed intermittently to ethanol vapors to induce ethanol dependence. Nondependent animals were exposed to control air. Following a 2-hour period of withdrawal, dependent and nondependent animals were systemically administered antalarmin, MJL-1-109-2, or R121919 (CRF(1) antagonists) and ethanol self-administration was measured.

RESULTS

The nonpeptide, small molecule CRF(1) antagonists selectively reduced excessive self-administration of ethanol in dependent animals during acute withdrawal. The antagonists had no effect on ethanol self-administration in nondependent rats.

CONCLUSIONS

These data demonstrate that CRF(1) receptors play an important role in mediating excessive ethanol self-administration in dependent rats, with no effect in nondependent rats. CRF(1) antagonists may be exciting new pharmacotherapeutic targets for the treatment of alcoholism in humans.

Corticotropin-releasing hormone and pro-opiomelanocortin gene expression in female monkeys with differences in sensitivity to stress

BACKGROUND/AIMS

The expressions of corticotropin-releasing hormone (CRH) and pro-opiomelanocortin (POMC) were assessed in brain tissue collected from nonstressed female cynomolgus monkeys previously categorized as highly stress resilient (HSR), medium stress resilient (MSR), or stress sensitive (SS) with respect to stress-induced anovulation.

METHODS

In situ hybridization and quantitative image analysis was used to measure mRNAs coding for CRH in the hypothalamic paraventricular nucleus (PVN) and thalamic center median-subfascicular complex (CM-Sf). Then, CRH neurons in the PVN were immunostained and the area of immunostaining was measured. Also, CRH fibers were immunostained in the central nucleus of the amygdala and the area of immunostaining was obtained. Finally, POMC mRNA expression was characterized in the hypothalamic infundibular nucleus. The groups were compared with ANOVA and Student-Newman-Keul's (SNK) post hoc comparison.

RESULTS

CRH mRNA was significantly elevated in the caudal PVN in the MSR and SS animals compared to HSR animals (p < 0.05, SNK). There was a significant increase in average and total CRH-positive area in the MSR and SS groups compared to the HSR group (p < 0.05, SNK). There was also a significant increase in CRH volume in the MSR and SS groups compared to the HSR group (p < 0.05, SNK). In the CM-Sf, the average CRH optical density was significantly higher in the MSR and SS groups than in the HSR group (p < 0.05, SNK). In the central nucleus of the amygdala, the area of CRH fiber staining was significantly higher in the SS group than in the MSR or HSR groups (p < 0.05, SNK). There was no difference between the groups in POMC mRNA expression in the mediobasal hypothalamus.

CONCLUSION

Macaques that exhibit immediate suppression of reproductive function upon stress are considered stress sensitive. These animals have elevated CRH in the hypothalamus and limbic structures, which may play a role in suppressing the hypothalamic-gonadal axis upon stress initiation.

Dissociation between opioid and CRF1 antagonist sensitive drinking in Sardinian alcohol-preferring rats

RATIONALE

The role of positive vs negative ethanol reinforcement in ethanol intake of Sardinian alcohol-preferring (sP) rats is unclear.

OBJECTIVES

To test the hypothesis that spontaneous ethanol self-administration of sP rats was sensitive to the opioid receptor antagonist naltrexone, whereas withdrawal-induced, but not spontaneous, ethanol self-administration would be sensitive to corticotropin-releasing factor(1) (CRF(1)) antagonists, implicating differential roles for positive and negative reinforcement, respectively.

METHODS

Male sP rats operantly (FR1, 30 min/day) self-administered ethanol (10% v/v) until responding stabilized. One group (n=11) was made ethanol dependent through intermittent ethanol vapor exposure. Both nondependent (n = 10) and dependent rats received the CRF(1) antagonist LWH-63 (5, 10, and 20 mg/kg, s.c.). Separate nondependent sP rats (n = 10) received the opioid antagonist naltrexone (16, 50, 150, and 450 microg/kg, s.c.). Finally, CRF(1) antagonists (MJL-1-109-2, LWH-63, and R121919) were studied for their actions on home-cage ethanol drinking in nondependent sP rats (n = 6-8/group) under continuous, limited-access, or stressed conditions.

RESULTS

Naltrexone potently reduced ethanol self-administration in nondependent sP rats. LWH-63 reduced heightened ethanol self-administration of vapor-sensitive, dependent sP rats. CRF(1) antagonists did not reduce ethanol intake in nondependent sP rats. R121919 (10 mg/kg, s.c.) retained antistress activity in sP rats, blunting novelty stress-induced suppression of ethanol intake.

CONCLUSIONS

Spontaneous ethanol self-administration of sP rats was opioid dependent with CRF(1) receptors implicated in withdrawal-induced drinking. Opioid and CRF(1) receptors play different roles in ethanol reinforcement and perhaps the ethanol addiction cycle. Such distinctions may apply to subtypes of alcoholic patients who differ in their motivation to drink and ultimately treatment response.