Corticotrophin-releasing factor receptor antagonists

The therapeutic potential of CRF1 antagonists for anxiety

Preclinical studies suggest that the brain corticotropin-releasing factor (CRF) systems mediate anxiety-like behavioural and somatic responses through actions at the CRF1 receptor. CRF1 antagonists block the anxiogenic-like effects of CRF and stress in animal models. Cerebrospinal fluid levels of CRF are elevated in some anxiety disorders and normalise with effective treatment, further implicating CRF systems as a therapeutic target. Prototypical CRF1 antagonists are highly lipophilic, non-competitive antagonists of peptide ligands. Modification of the chemotype and the identification of novel pharmacophores are yielding more drug-like structures with increased hydrophilicity at physiological pHs. Newer compounds exhibit improved solubility, pharmacokinetic properties, potency and efficacy. Several clinical candidates have entered Phase I/II trials. However, unmet challenges await resolution during further discovery, clinical development and therapeutic application of CRF1 antagonists.

Recent developments in the psychobiology and pharmacotherapy of depression: optimising existing treatments and novel approaches for the future

Effective antidepressants include monoamine oxidase inhibitors and tricyclic antidepressants, selective serotonin re-uptake inhibitors and novel agents, including serotonin and noradrenaline re-uptake inhibitors. Although effective, current treatments most often produce partial symptomatic improvement (response) rather than symptom resolution and optimal functioning (remission). While current pharmacotherapies target monoaminergic systems, different symptoms of major depressive disorder (MDD) may have distinct neurobiological underpinnings and other neurobiological systems are likely involved in the pathogenesis of MDD. In this article a review of current pharmacotherapeutic options for MDD, current understanding of the neurobiology and pathogenesis of MDD and a review of new and promising directions in pharmacological research will be provided. It is generally accepted that no single neurotransmitter or system is responsible for the dysregulation found in MDD. While agents that affect monoaminergic systems will likely continue to be first-line treatments for MDD for the foreseeable future, a number of new and novel agents, including corticotropin-releasing factor antagonists, substance P antagonists and antiglucocorticoids show considerable promise for refining treatment options. In order to better understand the neurobiology and treatment response of MDD, it is probable that more sophisticated theory-driven typologies of MDD will have to be developed.

Role of CRF(1) and CRF(2) receptors in fear and anxiety

Fear and anxiety are common emotions that can be triggered by stress. This paper reviews the work examining the role played by specific corticotropin-releasing factor (CRF) receptors in mediating the expression of these emotions. Several lines of evidence taken from CRF(1) transgenic knockout mice, CRF(1) antisense oligonucleotide studies, and CRF(1) receptor antagonist work suggest that the anxiety inducing effects of CRF are mediated by the CRF(1) receptor. Of these three methodological approaches, the work using transgenic CRF(1) knockout mice appears to be the most consistent. In contrast, the work using specific CRF(1) antagonists has produced somewhat varied results that may be explained, in part, by the testing method. When animals are stressed prior to behavioral testing, CRF(1) receptor antagonists appear to have anxiolytic-like effects. In addition, chronic dosing with CRF(1) antagonists may have more potent anxiolytic-like effects, especially in animal models of spontaneous anxiety, than acute dosing procedures. Spontaneous anxiety is defined as behavior that is elicited entirely by the testing situation without current or prior aversive or explicitly induced stress. CRF(1) antisense oligonucleotide work is difficult to interpret because of potential toxicological side effects produced by the antisense oligonucleotide and, in some cases, the absence of verifiable reductions in CRF(1) receptor densities after treatment. Similar methods-CRF(2) knockouts, CRF(2) antisense oligonucleotides, and CRF(2) antagonists-were used to evaluate the function of CRF(2) receptors in emotionality. In comparison to the large number of CRF(1) receptor studies, fewer CRF(2) receptor investigations have been conducted and these studies have yielded mixed results. However, recent work demonstrating a robust reduction in CRF(2) receptors using a CRF(2) antisense oligonucleotide with minimal toxicity, and dose response studies using a peptide CRF(2) antagonist suggest that CRF(2) receptors play a role in stress-induced and spontaneous anxiety. Furthermore, inhibiting the actions of both CRF(1) and CRF(2) receptors produces a greater reduction in stress-induced behavior than inhibition of either receptor alone. Thus, current data suggest that CRF(1) and CRF(2) receptors are involved in the mediation of fear and anxiety behavior.

Drugs in development for social anxiety disorder: more to social anxiety than meets the SSRI

Individuals with social phobia (SP) fear and avoid a wide variety of social and performance situations in which they are exposed to unfamiliar persons or to possible scrutiny by others. The lifetime prevalence of SP is estimated to be as high as 13%. It is frequently co-morbid with and usually precedes the onset of other psychiatric illnesses and is associated with significant occupational and social impairment, including academic and vocational underachievement. Fortunately, there are effective treatments for this common and debilitating condition. There is currently considerable evidence for the efficacy of pharmacotherapy and especially the monoamine oxidase inhibitors (MAOIs) and selective serotonin re-uptake inhibitors (SSRIs) in the treatment of this disorder. However, SSRIs are generally preferred as the first-line treatment of choice due to the advantages of SSRIs over MAOIs in terms of safety and tolerability. Despite encouraging results, current treatments most often produce partial symptomatic improvement, rather than high end-state functioning. While current first line treatments for social phobia target the serotonergic system, it is important to remember that different social fears are likely to have different developmental roots and may be based on quite different neurobiological systems. In this article we provide a review of current pharmacotherapeutic options for SP, current knowledge of the neurobiology of SP, and a review of new and promising directions in pharmacological research. It is increasingly clear that serotonin (5-HT) is unlikely to be the whole story in SP and that other brain chemical systems, especially the dopaminergic, noradrenaline-corticotropin releasing hormone and gamma-aminobutyric acid (GABA) dependent systems, most probably have an important role to play in a substantial percentage of cases. A number of new and novel agents, including the substance P antagonists, GABA agonists and CRF antagonists show considerable promise in the treatment of SP. However, in order to enhance the understanding of the neurobiology and treatment response of SP, we need to develop more sophisticated theory-driven typologies of SP.

Corticotropin-releasing factor antagonists, binding-protein and receptors: implications for central nervous system disorders

Corticotrophin-releasing factor (CRF; interchangeable with corticotrophin-releasing hormone, CRH) is a neurohormone family of peptides which implements endocrine, physiological and behavioural responses to stressor exposure. Built-in biological diversity and selectivity of CRF system function is provided by multiple endogenous ligands and receptors which are heterogeneously distributed in both brain and peripheral tissues across species. At present, there are at least five distinct targets for CRF with unique cDNA sequences, pharmacology and localization. These fall into three distinct classes, encoded by three different genes and have been termed the CRF1 and CRF2 receptors and the CRF-binding protein. Significant gains in knowledge about the physiological role of CRF binding sites in brain have emerged recently due to the proliferation of novel, high-affinity, receptor-selective pharmacological tools as well as multiple knock-out and knock-in mutant mouse models. These results support a role for CRF binding sites in co-ordinating stress reactivity, emotionality and energy balance over the life-span of the organism.

Corticotropin-releasing factor antagonists in affective disorders

Following a search lasting nearly three decades, corticotropin-releasing factor (CRF), a 41 amino acid-containing peptide, was isolated and characterised in 1981. In the preceding 18 years, a concatenation was developed that appears to show that CRF integrates not only the endocrine, but also the autonomic, immunologic and behavioural responses of mammalian organisms to stress. Direct CNS administration of CRF to laboratory animals produces actions similar to those observed after exposure to stress. Moreover, CNS administration of peptidergic CRF antagonists blocks many of the behavioural responses to stress. Since both early untoward life events as well as recently experienced stress have been implicated in the pathophysiology of affective disorders, and because there is substantial evidence for CRF neuronal hyperactivity in patients with affective disorders, small molecule, lipophilic CRF antagonists have been hypothesised to possess antidepressant and/or anxiolytic activity. Within the last few years, a number of pharmaceutical companies have developed selective, small molecule CRF(1) receptor antagonists. These compounds block the effects of CRF both in vitro and in vivo. There is also evidence that these agents possess anxiolytic and antidepressant activity in animal behavioural models. Compounds that act upon the CRF system have been hypothesised to be of value not only for certain psychiatric disorders, but also in neurodegenerative and inflammatory disorders. Some of these CRF(1) receptor antagonists are currently undergoing clinical trials to determine their efficacy and tolerability in patients with mood and anxiety disorders.

Thiazolo[4,5-d]pyrimidine thiones and -ones as corticotropin-releasing hormone (CRH-R1) receptor antagonists

A series of thiazolo[4,5-d]pyrimidine thiones and -ones was prepared and discovered to have good binding affinity to the CRH-R1 receptor, thus showing promise as a new class of potential anxiolytics and/or antidepressants.

Purin-8-ones as corticotropin-releasing hormone (CRH-R1) receptor antagonists

A series of purin-8-ones was prepared and discovered to have excellent binding affinity to the CRH-R1 receptor. Structure-activity studies focused on amine side-chain optimization, urea substitution and pyridyl isostere incorporation. Thus, the highly potent purin-8-ones show promise as a new class of potential anxiolytics and/or antidepressants.

Use of the Suzuki reaction for the synthesis of aryl-substituted heterocycles as corticotropin-releasing hormone (CRH) antagonists

The Suzuki reaction has been used to synthesize a variety of aryl-substituted heterocyclic antagonists of the CRH1 receptor. Examples with several different heterocyclic cores are potent CRH receptor ligands.

Is there a future for neuropeptide receptor ligands in the treatment of anxiety disorders?

This review provides an overview of preclinical and clinical evidence of a role for the neuroactive peptides cholecystokinin (CCK), corticotropin-releasing factor (CRF), neuropeptide Y (NPY), tachykinins (i.e., substance P, neurokinin [NK] A and B), and natriuretic peptides in anxiety and/or stress-related disorders. Results obtained with CCK receptor antagonists in animal studies have been highly variable, and clinical trials with several of these compounds in anxiety disorders have been unsuccessful so far. However, future investigations using CCK receptor antagonists with better pharmacokinetic characteristics and animal models other than those validated with the classical anxiolytics benzodiazepines may permit a more precise evaluation of the potential of these compounds as anti-anxiety agents. Results obtained with peptide CRF receptor antagonists in animal models of anxiety convincingly demonstrated that the blockade of central CRF receptors may yield anxiolytic-like activity. However, the discovery of nonpeptide and more lipophilic CRF receptor antagonists is essential for the development of these agents as anxiolytics. Similarly, there is clear preclinical evidence that the central infusion of NPY and NPY fragments selective for the Y1 receptor display anxiolytic-like effects in a variety of tests. However, synthetic nonpeptide NPY receptor agonists are still lacking, thereby hampering the development of NPY anxiolytics. Unlike selective NK1 receptor antagonists, which have variable effects in anxiety models, peripheral administration of selective NK2 receptor antagonists and central infusion of natriuretic peptides produce clear anxiolytic-like activity. Taken as a whole, these findings suggest that compounds targeting specific neuropeptide receptors may become an alternative to benzodiazepines for the treatment of anxiety disorders.

Structural requirements for peptidic antagonists of the corticotropin-releasing factor receptor (CRFR): development of CRFR2beta-selective antisauvagine-30

Different truncated and conformationally constrained analogs of corticotropin-releasing factor (CRF) were synthesized on the basis of the amino acid sequences of human/rat CRF (h/rCRF), ovine CRF (oCRF), rat urocortin (rUcn), or sauvagine (Svg) and tested for their ability to displace [125I-Tyr0]oCRF or [125I-Tyr0]Svg from membrane homogenates of human embryonic kidney (HEK) 293 cells stably transfected with cDNA coding for rat CRF receptor, type 1 (rCRFR1), or mouse CRF receptor, type 2beta (mCRFR2beta). Furthermore, the potency of CRF antagonists to inhibit oCRF- or Svg-stimulated cAMP production of transfected HEK 293 cells expressing either rCRFR1 (HEK-rCRFR1 cells) or mCRFR2beta (HEK-mCRFR2beta cells) was determined. In comparison with astressin, which exhibited a similar affinity to rCRFR1 (Kd = 5.7 +/- 1.6 nM) and mCRFR2beta (Kd = 4.0 +/- 2.3 nM), [DPhe11,His12]Svg(11-40), [DLeu11]Svg(11-40), [DPhe11]Svg(11-40), and Svg(11-40) bound, respectively, with a 110-, 80-, 68-, and 54-fold higher affinity to mCRFR2beta than to rCRFR1. The truncated analogs of rUcn displayed modest preference (2- to 7-fold) for binding to mCRFR2beta. In agreement with the results of these binding experiments, [DPhe11, His12]Svg(11-40), named antisauvagine-30, was the most potent and selective ligand to suppress agonist-induced adenylate cyclase activity in HEK cells expressing mCRFR2beta.

Pyrazolo[1,5-a]pyrimidine CRF-1 receptor antagonists

A series of 3-phenylpyrazolo[1,5-a]pyrimidines was prepared and found to have affinity for the human CRF-1 receptor. The 3-dimensional structure of one of the most potent analogs in this series, 10d, was determined by X-ray crystallography and suggests the spatial requirements for potent CRF-1 receptor binding affinity in this series.