Design, Synthesis, and Biological Evaluations of Novel Thiazolo[4,5-d]pyrimidine Corticotropin Releasing Factor (CRF) Receptor Antagonists as Potential Treatments for Stress Related Disorders and Congenital Adrenal Hyperplasia (CAH).

Corticotropin-releasing factor (CRF) is a key neuropeptide hormone that is secreted from the hypothalamus. It is the master hormone of the HPA axis, which orchestrates the physiological and behavioral responses to stress. Many disorders, including anxiety, depression, addiction relapse, and others, are related to over-activation of this system. Thus, new molecules that may interfere with CRF receptor binding may be of value to treat neuropsychiatric stress-related disorders. Also, CRF1R antagonists have recently emerged as potential treatment options for congenital adrenal hyperplasia. Previously, several series of CRF1 receptor antagonists were developed by our group. In continuation of our efforts in this direction, herein we report the synthesis and biological evaluation of a new series of CRF1R antagonists. Representative compounds were evaluated for their binding affinities compared to antalarmin. Four compounds (2, 5, 20, and 21) showed log IC50 values of -8.22, -7.95, -8.04, and -7.88, respectively, compared to -7.78 for antalarmin. This result indicates that these four compounds are superior to antalarmin by 2.5, 1.4, 1.7, and 1.25 times, respectively. It is worth mentioning that compound 2, in terms of IC50, is among the best CRF1R antagonists ever developed in the last 40 years. The in silico physicochemical properties of the lead compounds showed good drug-like properties. Thus, further research in this direction may lead to better and safer CRF receptor antagonists that may have clinical applications, particularly for stress-related disorders and the treatment of congenital adrenal hyperplasia.

Amino acid systems in the interpeduncular nucleus are altered in a sex-dependent manner during nicotine withdrawal.

Prior work in male rodents established that the medial habenula-interpeduncular nucleus (MHb-IPN) pathway modulates nicotine withdrawal. Specifically, withdrawal severity has been closely associated with inhibitory tone in the IPN via interneurons that release γ-aminobutyric acid (GABA). Inhibitory tone in the IPN is regulated by projections from the MHb that co-release glutamate and acetylcholine. Within the IPN, inhibitory tone is also regulated via corticotropin-releasing factor type 1 (CRF1) receptors that control GABA release from local interneurons. This study extends previous work by comparing sex differences in GABA, glutamate, as well serotonin levels in the IPN during precipitated nicotine withdrawal. Sex differences in withdrawal-induced neurochemical effects were also compared following systemic administration of a CRF1 receptor antagonist. The results revealed that there were no group differences in serotonin levels in the IPN. A major finding was that females displayed a larger withdrawal-induced increases in GABA levels in the IPN than males. Also, withdrawal increased IPN glutamate levels in a similar manner in females and males. Blockade of CRF1 receptors produced a larger suppression of the withdrawal-induced increases in GABA levels in the IPN of females versus males, an effect that was likely related to the robust increase in glutamate following administration of the CRF1 receptor antagonist in females. These data suggest that amino acid systems in the IPN modulate sex differences in the behavioral effects of nicotine withdrawal. Furthermore, our data imply that medications that target stress-induced activation of the IPN may reduce withdrawal severity, particularly in females.

Design, synthesis, structural optimization, SAR, in silico prediction of physicochemical properties and pharmacological evaluation of novel & potent thiazolo[4,5-d]pyrimidine corticotropin releasing factor (CRF) receptor antagonists.

Corticotropin-releasing factor (CRF) is a 41-amino-acid neuropeptide secreted from the hypothalamus and is the main regulator of the hypothalamus-pituitary-adrenocortical (HPA) axis. CRF is the master hormone which modulates physiological and behavioral responses to stress. Many disorders including anxiety, depression, addictive disorders and others are related to over activation of the CRF system. This suggests that new molecules which can interfere with CRF binding to its receptors may be potential candidates for neuropsychiatric drugs to treat stress-related disorders. Previously, three series of pyrimidine and fused pyrimidine CRF1 receptor antagonists were synthesized by our group and specific binding assays, competitive binding studies and determination of the ability to antagonize the agonist-stimulated accumulation of cAMP (the second messenger for CRF receptors) were reported. In continuation of our efforts in this direction, in the current manuscript, we report the synthesis & biological evaluation of a new series of CRF1 receptor antagonists. Seven compounds showed promising binding affinity with the best two compounds (compounds 6 & 43) displaying a superior binding affinity to all of our previous compounds. Compounds 6 & 43 have only 4 times and 2 times less binding affinity than the standard CRF antagonist antalarmin, respectively. Thus, our two best lead compounds (compound 6 & 43) can be considered potent CRF receptor antagonists with binding affinity of 41.0 & 19.2 nM versus 9.7 nM for antalarmin.

HIV-1 Tat Protein Promotes Neuroendocrine Dysfunction Concurrent with the Potentiation of Oxycodone's Psychomotor Effects in Female Mice.

Human immunodeficiency virus (HIV) is associated with neuroendocrine dysfunction which may contribute to co-morbid stress-sensitive disorders. The hypothalamic-pituitary-adrenal (HPA) or -gonadal (HPG) axes are perturbed in up to 50% of HIV patients. The mechanisms are not known, but we have found the HIV-1 trans-activator of transcription (Tat) protein to recapitulate the clinical phenotype in male mice. We hypothesized that HPA and/or HPG dysregulation contributes to Tat-mediated interactions with oxycodone, an opioid often prescribed to HIV patients, in females. Female mice that conditionally-expressed the Tat1-86 protein [Tat(+) mice] or their counterparts that did not [Tat(-) control mice] were exposed to forced swim stress (or not) and behaviorally-assessed for motor and anxiety-like behavior. Some mice had glucocorticoid receptors (GR) or corticotropin-releasing factor receptors (CRF-R) pharmacologically inhibited. Some mice were ovariectomized (OVX). As seen previously in males, Tat elevated basal corticosterone levels and potentiated oxycodone's psychomotor activity in females. Unlike males, females did not demonstrate adrenal insufficiency and oxycodone potentiation was not regulated by GRs or CRF-Rs. Rather OVX attenuated Tat/oxycodone interactions. Either Tat or oxycodone increased anxiety-like behavior and their combination increased hypothalamic allopregnanolone. OVX increased basal hypothalamic allopregnanolone and obviated Tat or oxycodone-mediated fluctuations. Together, these data provide further evidence for Tat-mediated dysregulation of the HPA axis and reveal the importance of HPG axis regulation in females. HPA/HPG disruption may contribute vulnerability to affective and substance use disorders.

HIV-1 Tat Dysregulates the Hypothalamic-Pituitary-Adrenal Stress Axis and Potentiates Oxycodone-Mediated Psychomotor and Anxiety-Like Behavior of Male Mice.

Human immunodeficiency virus (HIV) is associated with co-morbid affective and stress-sensitive neuropsychiatric disorders that may be related to dysfunction of the hypothalamic-pituitary-adrenal (HPA) stress axis. The HPA axis is perturbed in up to 46% of HIV patients, but the mechanisms are not known. The neurotoxic HIV-1 regulatory protein, trans-activator of transcription (Tat), may contribute. We hypothesized that HPA dysregulation may contribute to Tat-mediated interactions with oxycodone, a clinically-used opioid often prescribed to HIV patients. In transgenic male mice, Tat expression produced significantly higher basal corticosterone levels with adrenal insufficiency in response to a natural stressor or pharmacological blockade of HPA feedback, recapitulating the clinical phenotype. On acute exposure, HIV-1 Tat interacted with oxycodone to potentiate psychomotor and anxiety like-behavior in an open field and light-dark transition tasks, whereas repeated exposure sensitized stress-related psychomotor behavior and the HPA stress response. Pharmacological blockade of glucocorticoid receptors (GR) partially-restored the stress response and decreased oxycodone-mediated psychomotor behavior in Tat-expressing mice, implicating GR in these effects. Blocking corticotrophin-releasing factor (CRF) receptors reduced anxiety-like behavior in mice that were exposed to oxycodone. Together, these effects support the notion that Tat exposure can dysregulate the HPA axis, potentially raising vulnerability to stress-related substance use and affective disorders.

The effect of a corticotropin-releasing factor receptor 1 antagonist on the fear conditioning response in low- and high-anxiety rats after chronic corticosterone administration.

This study aimed to test the hypothesis that high-anxiety (HR) rats are more sensitive to the effects of chronic corticosterone administration and antalarmin (corticotropin-releasing factor (CRF) receptor 1, CRF1 antagonist) injections than low-anxiety (LR) rats, and this effect is accompanied by changes in CRF system activity in brain regions involved in the control of emotions and the hypothalamic-pituitary-adrenal (HPA) axis. Male rats were divided into LR (n = 25) and HR (n = 30) groups according to the duration of conditioned freezing in a contextual fear test. Chronic corticosterone administration (by injection, 20 mg/kg) for 21 d (except weekends) increased freezing duration and number of GR (glucocorticoid receptor)-immunoreactive nuclei in the basal amygdala (BA) and decreased GR-immunoreactive nuclei in the infralimbic cortex (IL), dentate gyrus (DG), and CA3 area, only in the HR group. Moreover, in this group, corticosterone administration decreased number of CRF-immunoreactive neurons of the parvocellular paraventricular hypothalamic nucleus (pPVN), DG, and CA1. Antalarmin (10 mg/kg, i.p., 2 injections) significantly attenuated conditioned fear responses, increased plasma corticosterone concentration, and decreased GR-immunoreactive nuclei in the BA, only in the HR group. Moreover, in this group, antalarmin increased number of GR-immunoreactive nuclei in the IL, DG, and CA3 and increased number of CRF-immunoreactive cells in the pPVN, DG, and CA1. Hence, antalarmin attenuated the fear response and restored HPA axis function in HR rats, which were more sensitive to corticosterone exposure. These data suggest that individual differences in central local CRF system activity may determine the neurobiological mechanisms related to mood and emotional disorders.

Corticotrophin-releasing factor mediates vasoactive intestinal peptide-induced hypophagia and changes in plasma parameters.

Vasoactive intestinal peptide (VIP) and corticotrophin-releasing factor (CRF) are anorexigenic neuropeptides that act in the hypothalamus to regulate food intake. Intracerebroventricular (ICV) microinjection of VIP promotes increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone, indicating that VIP activates hypothalamic-pituitary-adrenal axis. The aim of this study was to evaluate the interaction between VIP and CRF, by verifying the effects of ICV administration of VIP on the activity of neurons and CRF mRNA expression in paraventricular nucleus of hypothalamus (PVN). In addition, it was evaluated the effects of pretreatment with CRF type 1 receptor (CRFR1) antagonist (Antalarmin, ANT) or CRF type 2 receptor (CRFR2) antagonist (Antisauvagine-30, AS30) on VIP-induced changes on food intake and plasma parameters of male rats. Compared to Saline group, VIP increased not only the number of Fos-related antigens (FRA)-immunoreactive neurons in the PVN but also CRF mRNA levels in this nucleus. Both ANT and AS30 treatment attenuated the inhibition of food intake promoted by VIP, ANT showing a more pronounced effect. Both antagonists also attenuated VIP-induced reduction and enhancement of free fatty acids and corticosterone plasma levels, respectively, and only AS30 was able to attenuate the hyperglycemia. These results suggest that CRF is an important mediador of VIP effects on energy balance, and CRFR1 and CRFR2 are involved in these responses.

Corticotropin-releasing factor regulates caspase-3 and may protect developing zebrafish from stress-induced apoptosis.

The corticotropin-releasing factor (CRF) system is expressed in the earliest stages of zebrafish development, long before its canonical function in the endocrine stress response is realized, and yet its function during embryogenesis is unknown. We tested the hypothesis that CRF protects embryos from stress-induced apoptosis. Here we confirm that a 1 h heat shock applied at either 6 h post-fertilization (hpf) or 30 hpf elicits an increase in caspase-3 activity, a key effector of apoptosis. Temporal changes in the expression of crf and its binding protein (crf-bp) during recovery from heat shock indicate that the CRF system is responsive to stressors experienced as early as gastrulation. Next, we heat shocked embryos that were microinjected with crf mRNA, and showed that caspase-3 induction is significantly reduced in embryos that overexpress CRF relative to control embryos. In addition, incubating embryos in the presence of the CRF receptor type 1 (CRF-R1) antagonist, antalarmin, during recovery from heat shock significantly increased caspase-3 activity, suggesting that CRF regulates caspase-3 via a CRF-R1-dependent pathway. Finally, we show that most heat shock-induced mortality occurred during the first hour of recovery, long before a significant increase in caspase-3 activity was detected. Indeed, the delayed caspase-3 induction coincided with a mortality plateau, and neither CRF overexpression nor antalarmin treatment altered heat shock induced mortality, supporting previous in vitro evidence that CRF-mediated cytoprotection occurs through the slow and tightly controlled apoptotic pathway. This study provides novel in vivo evidence that CRF regulates stress-induced apoptosis in a vertebrate model species, and demonstrates for the first time a function for the CRF system in early development that precedes its role in the endocrine stress response.

CRHR1 exacerbates the glial inflammatory response and alters BDNF/TrkB/pCREB signaling in a rat model of global cerebral ischemia: implications for neuroprotection and cognitive recovery.

This study examined the impact of corticotropin-releasing hormone type 1 receptor (CRHR1) blockade using Antalarmin (ANT) on the expression of markers of neuroplasticity and inflammation, as well as neuroprotection and behavioral recovery following global cerebral ischemia. Male Wistar rats (N=50) were treated with ANT (2µg/2µl; icv) or a vehicle solution prior to a sham or four vessel (4VO) occlusion. Seven days post ischemia, anxiety was assessed in the Elevated Plus Maze and Open Field tests, and fear and spatial learning in a Y-Maze Passive Avoidance Task and the Barnes Maze. Thirty days post ischemia, brain derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) receptor expression, hippocampal neuronal death and inflammation were determined by analyzing immunoreactivity (ir) of neuron-specific nuclear protein (NeuN), microglia (IBA1, ionized calcium binding adaptor molecule 1), astrocytes (GFAP, glial fibrillary acidic protein) and TNFα (tumor necrosis factor alpha) a pro-inflammatory cytokine. Our findings revealed that ANT improved behavioral impairments, while conferring neuroprotection and blunting neuroinflammation in all hippocampal sub-regions post ischemia. We also observed reduced BDNF and TrkB mRNA and protein levels at the hippocampus, and increased expression at the hypothalamus and amygdala post ischemia, site-specific alterations which were regularized by pre-ischemic CRHR1 blockade. These findings support that CRHR1 actively contributes to altered brain plasticity, neuronal inflammation and injury and recovery of function following ischemic brain insults.

Milestones in CRH Research.

The Corticotropin-releasing Hormone (CRH) mammalian family members include CRH, urocortin I, Stresscopin (SCP) and Stresscopin-related peptide (SRP), along with the CRH receptors type 1 (CRHR1) and type 2 (CRHR2), and CRH-binding protein (CRH-BP). These family members differ in their tissue distribution and pharmacology. Several studies have provided evidence supporting an important role of this family in the regulation of the neuroendocrine and behavioral responses to stress. Regulation of the relative contribution of CRH and its homologs and the two CRH receptors in brain CRH pathways may be essential in coordinating physiologic responses to stress. The development of disorders related to heightened stress sensitivity and dysregulation of stress-coping mechanisms appears to involve regulatory mechanisms of the CRH family members. Therapeutic agents that target CRH family members may offer a new approach to the treatment of these disorders. The purpose of this review is to summarize the most significant discoveries related to CRH over time.

Early life stress is a risk factor for excessive alcohol drinking and impulsivity in adults and is mediated via a CRF/GABA(A) mechanism.

Childhood stress and trauma are associated with substance use disorders in adulthood, but the neurological changes that confer increased vulnerability are largely unknown. In this study, maternal separation (MS) stress, restricted to the pre-weaning period, was used as a model to study mechanisms of protracted effects of childhood stress/traumatic experiences on binge drinking and impulsivity. Using an operant self-administration model of binge drinking and a delay discounting assay to measure impulsive-like behavior, we report that early life stress due to MS facilitated acquisition of binge drinking and impulsivity during adulthood in rats. Previous studies have shown heightened levels of corticotropin releasing factor (CRF) after MS, and here, we add that MS increased expression levels of GABA(A) α2 subunit in central stress circuits. To investigate the precise role of these circuits in regulating impulsivity and binge drinking, the CRF1 receptor antagonist antalarmin and the novel GABA(A) α2 subunit ligand 3-PBC were infused into the central amygdala (CeA) and medial prefrontal cortex (mPFC). Antalarmin and 3-PBC at each site markedly reduced impulsivity and produced profound reductions on binge-motivated alcohol drinking, without altering responding for sucrose. Furthermore, whole-cell patch-clamp studies showed that low concentrations of 3-PBC directly reversed the effect of relatively high concentrations of ethanol on α2ß3γ2 GABA(A) receptors, by a benzodiazepine site-independent mechanism. Together, our data provide strong evidence that maternal separation, i.e. early life stress, is a risk factor for binge drinking, and is linked to impulsivity, another key risk factor for excessive alcohol drinking. We further show that pharmacological manipulation of CRF and GABA receptor signaling is effective to reverse binge drinking and impulsive-like behavior in MS rats. These results provide novel insights into the role of the brain stress systems in the development of impulsivity and excessive alcohol consumption.

The effect of obestatin on anxiety-like behaviour in mice.

Obestatin is a 23 amino acid-peptide, derived from the same preproghrelin-gene as ghrelin. Obestatin was originally reported as a ghrelin antagonist with anorexigenic activity, but later it was proven to be involved in multiple processes including sleep, memory retention, anxiety, morphine-induced analgesia and withdrawal. In the present study, in male CFLP mice, by using computerised open field (OF) and elevated plus maze (EPM) tests we have investigated the behavioural effects of the acute intracerebroventricular (icv) administration of obestatin alone, and following ghrelin receptor blockage with [d-Lys3]-Growth Hormone Releasing Peptide-6 ([d-Lys3]- GHRP6) or corticotropin-releasing hormone (CRH) receptor 1 antagonism with antalarmin. Plasma corticosterone levels were measured for each treatment group by using chemofluorescent assay. Our results in the EPM test showed that obestatin reduced the percent of time spent in the open arms. The basal locomotor activity (ambulation distance and time, rearing and jumping) was not influenced significantly neither in the obestatin-treated groups, nor in those receiving pre-treatment with antalarmin or [d-Lys3]-GHRP6. The percentage of central ambulation distance however was decreased by obestatin, while the percentage of time spent in the central zone showed a decreasing tendency. The administration of antalarmin or [d-Lys3]-GHRP6 have both reversed the effect of obestatin on central ambulation. Plasma corticosterone levels were elevated by obestatin, which effect was antagonised by the injection of antalarmin. These are the first results to indicate that obestatin exerts anxiogenic-like effect in mice, which might be mediated through ghrelin receptor and CRH activation.

Blocking of corticotrophin releasing factor receptor-1 during footshock attenuates context fear but not the upregulation of prepro-orexin mRNA in rats.

Hypothalamic neuropeptides called orexins (hypocretins) are well known for their roles in promoting arousal. Orexins have also been shown to play a role in fear and anxiety produced by the exposure of rats to an acute episode of moderately intense footshocks. Recent evidence indicates that stress activates orexin neurons through a corticotropin releasing factor (CRF) mechanism. In this study, we examined the effect of a CRF receptor-1 (CRF-R1) antagonist antalarmin (20mg/kg, i.p.) given before shock exposure on subsequent expression of contextual fear and the levels of prepro-orexin (ppOX) mRNA in the hypothalamus. Antalarmin decreased fear and ultrasonic vocalization expression to the shock context at 2 and 10 days after shock exposure. However, antalarmin did not prevent the increases in ppOX mRNA produced by the shock experience. This study provides evidence that blocking of CRF-R1 at the time of footshocks attenuates contextual fear. While an increase in the activity of the orexin system may contribute to fear, this activation does not appear to be sufficient for fear expression.

Involvements of stress hormones in the restraint-induced conditioned place preference.

The conditioned place preference (CPP) paradigm is widely used when examining the reinforcing effects of drugs. Some previous studies have shown that an acute stressor, such as restraint could also induce CPP. Although the modulating effects of stress hormones on various forms of learning are well known, the finding that a stressor has a potentially direct role in the reinforcement mechanism is novel. This study focused on the function of stress hormones in restraint-induced CPP in Wistar rats administered agonist or antagonist of 2 critical stress hormones prior to conditioning. Results showed that peripheral applications of corticosterone (CORT, 1, 3, 5, and 10 mg/kg, subcutaneously) failed to induce CPP. Furthermore, a glucocorticoid (GC) antagonist (mifepristone, 10, 40, or 100 mg/kg, sc) failed to block the restraint-induced CPP. Intracerebroventricular injection of a selective corticotropin-releasing factor receptor 1 (CRFR1) antagonist antalarmin (1 µg/5 µl), on the contrary, completely blocked the restraint-induced CPP. We concluded that CRFR1 plays an essential role in the neural mechanism of restraint-induced CPP. Negative feedback of CORT from peripheral sources may not be involved in this phenomenon.