Corticotropin-releasing factor 1 receptor antagonists: a patent review

Structural and Functional Insights into CRF Peptides and Their Receptors

Corticotropin-releasing factor or hormone (CRF or CRH) and the urocortins regulate a plethora of physiological functions and are involved in many pathophysiological processes. CRF and urocortins belong to the family of CRF peptides (CRF family), which includes sauvagine, urotensin, and many synthetic peptide and non-peptide CRF analogs. Several of the CRF analogs have shown considerable therapeutic potential in the treatment of various diseases. The CRF peptide family act by interacting with two types of plasma membrane proteins, type 1 (CRF1R) and type 2 (CRF2R), which belong to subfamily B1 of the family B G-protein-coupled receptors (GPCRs). This work describes the structure of CRF peptides and their receptors and the activation mechanism of the latter, which is compared with that of other GPCRs. It also discusses recent structural information that rationalizes the selective binding of various ligands to the two CRF receptor types and the activation of receptors by different agonists.

Peripheral CRF-R1/CRF-R2 antagonist, astressin C, induces a long-lasting blockade of acute stress-related visceral pain in male and female rats

Peptide CRF antagonists injected peripherally alleviate stress-induced visceral hypersensitivity (SIVH) to colorectal distension (CRD) in rodents. Here we further evaluated the dose and time-dependent inhibitory activity of several long-acting peptide CRF receptor antagonists related to astressin on SIVH, focusing on astressin C (AstC), which previously showed high efficacy on stress-related alterations of HPA axis and gut secretomotor functions. Male and female Sprague-Dawley rats pretreated subcutaneously (SC) with AstC were injected intraperitoneally (IP) with CRF 15 min later. The visceromotor responses (VMR) to graded phasic CRD (10, 20, 40 and 60 mmHg) were monitored at basal, 15 min and up to 1-8 days after pretreatment. Two other astressin analogs, hexanoyl-astressin D (Hex-AstD) and [CαMeVal^19,32]-AstC, were also tested. The response to IP CRF was sex-dependent with female rats requiring a higher dose to exhibit visceral hyperalgesia. Pretreatment with AstC (30-1000 µg/kg) resulted in a dose-related inhibition of IP CRF-induced SIVH and diarrhea in both sexes. The highest dose prevented SIVH and diarrhea up to 5-7 days after a single SC injection and was lost on day 7 (females) and day 8 (males) but reinstated after a second injection of AstC on day 8 or 9 respectively. [CαMeVal^19,32]-AstC and Hex-AstD (1000 µg/kg in males) also prevented SIVH. These data show the potent long-lasting anti-hyperalgesic effect of AstC in an acute model of SIVH in both male and female rats. This highlights the potential of long-acting peripheral CRF antagonists to treat stress-sensitive irritable bowel syndrome.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

Brain and Gut CRF Signaling: Biological Actions and Role in the Gastrointestinal Tract

BACKGROUND

Corticotropin-releasing factor (CRF) pathways coordinate behavioral, endocrine, autonomic and visceral responses to stress. Convergent anatomical, molecular, pharmacological and functional experimental evidence supports a key role of brain CRF receptor (CRF-R) signaling in stress-related alterations of gastrointestinal functions. These include the inhibition of gastric acid secretion and gastric-small intestinal transit, stimulation of colonic enteric nervous system and secretorymotor function, increase intestinal permeability, and visceral hypersensitivity. Brain sites of CRF actions to alter gut motility encompass the paraventricular nucleus of the hypothalamus, locus coeruleus complex and the dorsal motor nucleus while those modulating visceral pain are localized in the hippocampus and central amygdala. Brain CRF actions are mediated through the autonomic nervous system (decreased gastric vagal and increased sacral parasympathetic and sympathetic activities). The activation of brain CRF-R2 subtype inhibits gastric motor function while CRF-R1 stimulates colonic secretomotor function and induces visceral hypersensitivity. CRF signaling is also located within the gut where CRF-R1 activates colonic myenteric neurons, mucosal cells secreting serotonin, mucus, prostaglandin E2, induces mast cell degranulation, enhances mucosal permeability and propulsive motor functions and induces visceral hyperalgesia in animals and humans. CRF-R1 antagonists prevent CRF- and stressrelated gut alterations in rodents while not influencing basal state.

DISCUSSION

These preclinical studies contrast with the limited clinical positive outcome of CRF-R1 antagonists to alleviate stress-sensitive functional bowel diseases such as irritable bowel syndrome.

CONCLUSION

The translational potential of CRF-R1 antagonists in gut diseases will require additional studies directed to novel anti-CRF therapies and the neurobiology of brain-gut interactions under chronic stress.

Discovery of 1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazoles as novel class of corticotropin releasing factor 1 receptor antagonists

A new class of corticotropin releasing factor 1 (CRF₁) receptor antagonists characterized by a tricyclic core ring was designed and synthesized. Novel tricyclic derivatives 2a-e were designed as CRF₁ receptor antagonists based on conformation analysis of our original 2-anilinobenzimidazole CRF₁ receptor antagonist. The synthesized tricyclic derivatives 2a-e showed CRF₁ receptor binding activity with IC₅₀ values of less than 400 nM, and the 1,2,3,4-tetrahydropyrimido-[1,2-a]benzimidazole derivative 2e was selected as a lead compound with potent in vitro CRF₁ receptor binding activity (IC₅₀ = 7.1 nM). To optimize the pharmacokinetic profiles of lead compound 2e, we explored suitable substituents on the 1-position and 6-position, leading to the identification of compound 42c-R, which exhibited potent CRF₁ receptor binding activity (IC₅₀ = 58 nM) with good oral bioavailability (F = 68% in rats). Compound 42c-R exhibited dose-dependent inhibition of [¹²⁵I]-CRF binding in the frontal cortex (5 and 10 mg/kg, p.o.) as well as suppression of locomotor activation induced by intracerebroventricular administration of CRF in rats (10 mg/kg, p.o.). These results suggest that compound 42c-R successfully binds CRF₁ receptors in the brain and exhibits the potential to be further examined for clinical studies.

In silico binding mechanism prediction of benzimidazole based corticotropin releasing factor-1 receptor antagonists by quantitative structure activity relationship, molecular docking and pharmacokinetic parameters calculation

Despite the various research efforts toward the treatment of stress-related disorders, the drug has not yet launched last 20 years. Corticotropin releasing factor-1 receptor antagonists have been point of great interest in stress-related disorders. In the present study, we have selected benzazole scaffold-based compounds as corticotropin releasing factor-1 antagonists and performed 2D and 3D QSAR studies to identify the structural features to elucidating the binding mechanism prediction. The best 2D QSAR model was obtained through multiple linear regression method with r² value of .7390, q² value of .5136 and pred_r² (predicted square correlation coefficient) value of .88. The contribution of 2D descriptor, T_2_C_1 was 60% (negative contribution) and 4pathClusterCount was 40.24% (positive contribution) in enhancing the activity. Also 3D QSAR model was statistically significant with q² value of .9419 and q²_se (standard error of internal validation) value of .19. Statistical parameters results prove the robustness and significance of both models. Further, molecular docking and pharmacokinetic analysis was performed to explore the scope of investigation. Docking results revealed that the all benzazole compounds show hydrogen bonding with residue Asn283 and having same hydrophobic pocket (Phe286, Leu213, Ile290, Leu287, Phe207, Arg165, Leu323, Tyr327, Phe284, and Met206). Compound B14 has higher activity compare to reference molecules. Most of the compounds were found within acceptable range for pharmacokinetic parameters. This work provides the extremely useful leads for structural substituents essential for benzimidazole moiety to exhibit antagonistic activity against corticotropin releasing factor-1 receptors.

Discovery of 4-chloro-2-(2,4-dichloro-6-methylphenoxy)-1-methyl-7-(pentan-3-yl)-1H-benzimidazole, a novel CRF1 receptor antagonist

Compound 1 exhibits potent binding inhibition activity against a corticotropin-releasing factor 1 (CRF₁) receptor (IC₅₀=9.5nM) and in vitro antagonistic activity (IC₅₀=88nM) but is rapidly metabolized by human hepatic microsomes (182μL/min/mg). Here we identified metabolically stable compounds with potent CRF binding inhibitory activity. Structure-activity relationship (SAR) studies considering in vitro metabolic stability revealed that 4-chloro-2-(2,4-dichloro-6-methylphenoxy)-1-methyl-7-(pentan-3-yl)-1H-benzimidazole 24d was more stable in human microsomes (87μL/min/mg) than compound 1. Compound 24d demonstrated potent CRF binding inhibitory activity (IC₅₀=4.1nM), in vitro antagonistic activity (IC₅₀=44nM), and slow dissociation from the CRF₁ receptor. Orally administered compound 24d (6-24μmol/kg) showed ex vivo CRF₁ receptor binding in the rat pituitary, olfactory bulb, and frontal cortex and suppressed stress-induced adrenocorticotropic hormone (ACTH) secretion. In this report, we discuss SAR studies on the metabolic stability as well as CRF binding inhibitory activity of the benzimidazole series as CRF₁ receptor antagonists and the pharmacological profiles of compound 24d.

Discovery of a 7-arylaminobenzimidazole series as novel CRF1 receptor antagonists

A promising lead compound 1 of a benzimidazole series has been identified as a corticotropin-releasing factor 1 (CRF1) receptor antagonist. In this study, we focused on replacement of a 7-alkylamino group of 1, predicted to occupy a large lipophilic pocket of a CRF1 receptor, with an aryl group. During the course of this examination, we established new synthetic approaches to 2,7-diarylaminobenzimidazoles. The novel synthesis of 7-arylaminobenzimidazoles culminated in the identification of compounds exhibiting inhibitory activities comparable to the alkyl analog 1. A representative compound, p-methoxyanilino analog 16g, showed potent CRF binding inhibitory activity against a human CRF1 receptor and human CRF1 receptor antagonistic activity (IC50=27nM, 56nM, respectively). This compound exhibited ex vivo (125)I-Tyr(0) ((125)I-CRF) binding inhibitory activity in mouse frontal cortex, olfactory bulb, and pituitary gland at 20mg/kg after oral administration. In this report, we discuss the structure-activity-relationship of these 7-arylamino-1H-benzimidazoles and their synthetic method.

P7, a novel antagonist of corticotropin releasing factor receptor type 1 (CRFR1) screened from phage display library

The corticotropin releasing factor (CRF) plays a central role in regulating the activities of hypothalamic-pituitary-adrenal (HPA) axis in the presence of a variety of stressful stimuli via binding to its type 1 receptors (CRFR1). Despite that many peptidic or non-peptidic antagonists of CRFR1 have been developed to serve as therapeutic tools to CRF-related pathologies, none of them have been utilized clinically. Targeting the extracellular domain 1 (EC1) of CRFR1, the CRF-binding site, represents a new strategy to inhibit the function of the receptor. However, no such agents have been identified up to now. Herein, by using an 87-amino acid fragment corresponding to the EC1 region as the bait, we screened the binding polypeptides from a phage display (Ph.D.-12) peptide library. After 3-round biopanning, positive clones were selected and the polypeptides carried by them were identified. 5 polypeptides were found to bind with the target specifically. Among them, the P7 exhibited the highest affinity. By evaluating the cAMP accumulation in the CRFR1 or CRFR2-expressing HEK293 cells, we demonstrated that P7 blocking the function of CRFR1, but not CRFR2. In addition, we also found that P7 and CRF act on CRFR1 competitively. Taken together, we reveal that P7, a novel polypeptide identified from phage display library, inhibits the function of CRFR1 effectively and specifically by binding at its EC1 domain. The new polypeptide might provide a promising agent for diagnostic or therapeutic utilities in CRF-related disorders.

Role of Corticotropin-releasing Factor Signaling in Stress-related Alterations of Colonic Motility and Hyperalgesia

The corticotropin-releasing factor (CRF) signaling systems encompass CRF and the structurally related peptide urocortin (Ucn) 1, 2, and 3 along with 2 G-protein coupled receptors, CRF₁ and CRF₂. CRF binds with high and moderate affinity to CRF₁ and CRF₂ receptors, respectively while Ucn1 is a high-affinity agonist at both receptors, and Ucn2 and Ucn3 are selective CRF₂ agonists. The CRF systems are expressed in both the brain and the colon at the gene and protein levels. Experimental studies established that the activation of CRF₁ pathway in the brain or the colon recaptures cardinal features of diarrhea predominant irritable bowel syndrome (IBS) (stimulation of colonic motility, activation of mast cells and serotonin, defecation/watery diarrhea, and visceral hyperalgesia). Conversely, selective CRF₁ antagonists or CRF₁/CRF₂ antagonists, abolished or reduced exogenous CRF and stress-induced stimulation of colonic motility, defecation, diarrhea and colonic mast cell activation and visceral hyperalgesia to colorectal distention. By contrast, the CRF₂ signaling in the colon dampened the CRF₁ mediated stimulation of colonic motor function and visceral hyperalgesia. These data provide a conceptual framework that sustained activation of the CRF₁ system at central and/or peripheral sites may be one of the underlying basis of IBS-diarrhea symptoms. While targeting these mechanisms by CRF₁ antagonists provided a relevant novel therapeutic venue, so far these promising preclinical data have not translated into therapeutic use of CRF₁ antagonists. Whether the existing or newly developed CRF₁ antagonists will progress to therapeutic benefits for stress-sensitive diseases including IBS for a subset of patients is still a work in progress.

Structures of class B G protein-coupled receptors: prospects for drug discovery

New members in the GPCR photo gallery! Crystal structures of class B G protein-coupled receptors, which bind peptide hormones, have been solved [see picture of the corticotropin-releasing factor receptor 1 (blue) and a bound allosteric nonpeptide antagonist (green)]. The structures provide a basis for a rational design of better drugs for diabetes, osteoporosis, migraine, or depression.