Design and synthesis of tricyclic corticotropin-releasing factor-1 antagonists

Synthesis and Characterization of Azido- and Nitratoalkyl Nitropyrazoles as Potential Melt-Cast Explosives

Desirable advancements in the field of explosive materials include the development of novel melt-castable compounds with melting points ranging from 80 to 110 °C. This is particularly important due to the limited performance and high toxicity associated with TNT (trinitrotoluene). In this study, a series of innovative melt-castable explosives featuring nitratoalkyl and azidoalkyl functionalities attached to the 3-nitro-, 4-nitro-, 3,4-dinitropyrazole, or 3-azido-4-nitropyrazole scaffold are introduced. These compounds were synthesized using straightforward methods and thoroughly characterized using various analytical techniques, including single-crystal X-ray diffraction, IR spectroscopy, multinuclear nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, elemental analysis, and DTA. Furthermore, the energetic properties such as (theoretical) performance data, sensitivities, and compatibilities of the compounds were evaluated and compared among the different structures.

Identification of (6S)-cyclopropyl-6,7-dihydropyrazolo[1,5-a]pyrazine-5(4H)-carboxamines as new HBV capsid assembly modulators

GYH2-18 is a type II HBV CAM with 6,7-dihydropyrazolo[1,5-a]pyrazine-5(4H)-carboxamine (DPPC) skeleton discovered by Roche INC. A series of GYH2-18 derivatives were designed, synthesized and evaluated for their anti-HBV activity. Two compounds 2f and 3k exhibited excellent anti-HBV activity, low cytotoxicity and accepted oral PK profiles. Chiral separation of 2f and 3k was conducted successfully, and (6S)-cyclopropyl DPPC isomers 2f-1, 2f-3, 3k-1 and 3k-3 were identified to be much more active than the corresponding (6R)-ones. The preliminary structure-activity relationship, particle gel assay and molecular modeling studies were also discussed, which provide useful indications for guiding the further rational design of new (6S)-cyclopropyl DPPC analogues.

Design, Synthesis, and Biological Evaluation of Stable Colchicine-Binding Site Tubulin Inhibitors 6-Aryl-2-benzoyl-pyridines as Potential Anticancer Agents

We previously reported a potent tubulin inhibitor CH-2-77. In this study, we optimized the structure of CH-2-77 by blocking metabolically labile sites and synthesized a series of CH-2-77 analogues. Two compounds, 40a and 60c, preserved the potency while improving the metabolic stability over CH-2-77 by 3- to 4-fold (46.8 and 29.4 vs 10.8 min in human microsomes). We determined the high-resolution X-ray crystal structures of 40a (resolution 2.3 Å) and 60c (resolution 2.6 Å) in complex with tubulin and confirmed their direct binding at the colchicine-binding site. In vitro, 60c maintained its mode of action by inhibiting tubulin polymerization and was effective against P-glycoprotein-mediated multiple drug resistance and taxol resistance. In vivo, 60c exhibited a strong inhibitory effect on tumor growth and metastasis in a taxol-resistant A375/TxR xenograft model without obvious toxicity. Collectively, this work showed that 60c is a promising lead compound for further development as a potential anticancer agent.

Indazole, Pyrazole, and Oxazole Derivatives Targeting Nitric Oxide Synthases and Carbonic Anhydrases

Nitric oxide (NO) is an essential endogenous mediator with a physiological role in the central nervous system as neurotransmitter and neuromodulator. A growing number of studies have demonstrated that abnormal nitrergic signaling is a crucial event in the development of neurodegeneration. In particular, the uncontrolled production of NO by neuronal nitric oxide synthase (nNOS) is observed in several neurodegenerative diseases. Moreover, it is well recognized that specific isoforms of human carbonic anhydrase (hCA) physiologically modulate crucial pathways of signal processing and that low expression of CA affects cognition, leading to mental retardation, Alzheimer's disease, and aging-related cognitive impairments. In light of this, dual agents that are able to target both NOS (inhibition) and CA (activation) could be useful drug candidates for the treatment of Alzheimer's disease, aging, and other neurodegenerative diseases. In the present work, we show the design, synthesis, and in vitro biological evaluation of new nitrogen-based heterocyclic compounds. Among the tested molecules, 2-amino-3-(4-hydroxyphenyl)-N-(1H-indazol-5-yl)propanamide hydrochloride (10 b) was revealed to be a potent dual agent, able to act as a selective nNOS inhibitor and activator of the hCA I isoform.

Nitramines with varying sensitivities: functionalized dipyrazolyl-N-nitromethanamines as energetic materials

1,3-Dichloro-2-nitro-2-azapropane is an excellent precursor to dense energetic functionalized dipyrazolyl-N-nitromethanamines. This new family of energetic compounds was fully characterized by using (1)H, (13)C, and (15)N NMR and IR spectroscopy, differential scanning calorimetry, elemental analysis, and impact sensitivity tests. Additionally, single-crystal X-ray structuring was done for 3 and 5·CH3CN, which gave insight into structural characteristics. The experimentally determined densities of 2-9 fall between 1.69 and 1.90 g cm(-3). Heats of formation and detonation properties were calculated by using Gaussian 03 and EXPLO5 programs, respectively. The influence of different energetic moieties on the structural and energetic properties was established theoretically.

Binding kinetics redefine the antagonist pharmacology of the corticotropin-releasing factor type 1 receptor

Corticotropin-releasing factor (CRF) receptor antagonists are under preclinical and clinical investigation for stress-related disorders. In this study the impact of receptor-ligand binding kinetics on CRF₁ receptor antagonist pharmacology was investigated by measuring the association rate constant (k₁), dissociation rate constant (k₋₁), and kinetically derived affinity at 37°C. Three aspects of antagonist pharmacology were reevaluated: comparative binding activity of advanced compounds, in vivo efficacy, and structure-activity relationships. Twelve lead compounds, with little previously noted difference of affinity, varied substantially in their kinetic binding activity with a 510-fold range of kinetically derived affinity (k₋₁/k₁), 170-fold range of k₋₁, and 13-fold range of k₁. The k₋₁ values indicated previous affinity measurements were not close to equilibrium, resulting in compression of the measured affinity range. Dissociation was exceptionally slow for three ligands (k₋₁ t(1/2) of 1.6-7.2 h at 37°C). Differences of binding behavior were consistent with in vivo pharmacodynamics (suppression of adrenocorticotropin in adrenalectomized rats). Ligand concentration-effect relationships correlated with their kinetically derived affinity. Two ligands that dissociated slowly (53 and 130 min) produced prolonged suppression, whereas only transient suppression was observed with a more rapidly dissociating ligand (16 min). Investigating the structure-activity relationship indicated exceptionally low values of k₁, approaching 100,000-fold less than the diffusion-limited rate. Retrospective interpretation of medicinal chemistry indicates optimizing specific elements of chemical structure overcame kinetic barriers in the association pathway, for example, constraint of the pendant aromatic orthogonal to the ligand core. Collectively, these findings demonstrate receptor binding kinetics provide new dimensions for understanding and potentially advancing the pharmacology of CRF₁ receptor antagonists.

Distinct receptor subtypes mediate arginine vasopressin-dependent ACTH release and intracellular calcium mobilization in rat pituitary cells

In the present study, adrenocorticotropic hormone (ACTH) release and intracellular calcium ([Ca(2+)](i)) increase induced by arginine vasopressin (AVP) were characterized in collagenase-dispersed and 3-day cultured rat anterior pituitary cells. AVP and the selective vasopressin V(1b) receptor agonist, [1-deamino-4-cyclohexylalanine]AVP (d[Cha(4)]AVP) induced ACTH release with nanomolar potencies in both cell preparations, and produced a maximal stimulation that was about 1.5 fold greater in the 3-day cultured cells, indicating that the vasopressin V(1b) receptor-ACTH release pathway is enhanced over time in culture. In dispersed cells, AVP, oxytocin and d[Cha(4)]AVP induced [Ca(2+)](i) increases with nanomolar potencies. The selective vasopressin V(1a) receptors antagonist, SR49059 (100 nM), together with the selective oxytocin receptors antagonist (d(CH(2))(5)(1)Tyr(Me)(2),Thr(4),Orn(8),Tyr-NH(2)(9)-vasotocin (100 nM), inhibited the maximal AVP response by ~70%, without affecting the response to d[Cha(4)]AVP, suggesting that the V(1b) receptor was only partially responsible for the AVP-induced [Ca(2+)](i) increase. In contrast, in 3-day cultures, AVP induced an increase in [Ca(2+)](i), while oxytocin and d[Cha(4)]AVP did not. The response to AVP was completely antagonized by SR49059, whereas the vasopressin V(1b) receptor antagonists, SSR149415 and (d(CH(2))(5)(1)Tyr(Me)(2),Thr(4),Orn(8),Tyr-NH(2)(9))-vasotocin had no effect, indicating that the [Ca(2+)](i) increase was mediated exclusively by vasopressin V(1a) receptors. In conclusion, the enhancement of vasopressin V(1b) receptor-mediated ACTH release and the lack of a detectable vasopressin V(1b) receptor coupling to [Ca(2+)](i) increase in cultured cells suggests the activation of a different/additional signaling pathway in the molecular mechanism of ACTH release.

Corticotropin releasing factor receptor antagonists for major depressive disorder

INTRODUCTION

Major depressive disorder is a serious and common psychiatric illness, and many of the depressive patients benefit from pharmacological treatment. Available antidepressants produce remission in only about 30 -- 40% of the patients. Therefore, new concepts are being explored for the development of innovative antidepressants with higher efficacy.

AREAS COVERED

The use of corticotropin releasing factor type 1 (CRF1) receptor antagonists for depression is supported by abundant evidence of target validation, the availability of in vitro and in vivo assays and specific small ligands. Some of these compounds have advanced to clinical studies, with discouraging results so far in depression. This review covers the development of CRF1 receptor antagonists at different stages of the development pipeline of the pharmaceutical industry and its bottlenecks. Most of the available CRF1 receptor antagonists known so far share a common chemical scaffold. We present possible strategies to overcome obstacles in the discovery and development process at the levels of library screenings and clinical studies to find more diverse compounds.

EXPERT OPINION

CRF1 receptor antagonists are expected to be beneficial only for those patients with CRF overexpression and the need for tests to identify these individuals is discussed. New technical developments and diagnostic tools might eventually lead to a more successful treatment of major depression with CRF1 receptor antagonists.

Discovery of NBI-77860/GSK561679, a potent corticotropin-releasing factor (CRF1) receptor antagonist with improved pharmacokinetic properties

Antagonists of the corticotropin-releasing factor (CRF) neuropeptide may prove effective in treating stress and anxiety related disorders. In an effort to identify antagonists with improved physico-chemical properties a new series of CRF(1) antagonists were designed to substitute the propyl groups at the C7 position of the pyrazolo[1,5-a]pyrimidine core of 1 with heterocycles. Compound (S)-8d was identified as a high affinity ligand with a pK(i) value of 8.2 and a functional CRF(1) antagonist with pIC(50) value of 7.0 in the in vitro CRF ACTH production assay.

Allosteric ligands for G protein-coupled receptors: a novel strategy with attractive therapeutic opportunities

Allosteric receptor ligands bind to a recognition site that is distinct from the binding site of the endogenous messenger molecule. As a consequence, allosteric agents may attach to receptors that are already transmitter-bound. Ternary complex formation opens an avenue to qualitatively new drug actions at G protein-coupled receptors (GPCRs), in particular receptor subtype selective potentiation of endogenous transmitter action. Consequently, suitable exploitation of allosteric recognition sites as alternative molecular targets could pave the way to a drug discovery paradigm different from those aimed at mimicking or blocking the effects of endogenous (orthosteric) receptor activators. The number of allosteric ligands reported to modulate GPCR function is steadily increasing and some have already reached routine clinical use. This review aims at introducing into this fascinating field of drug discovery and at providing an overview about the achievements that have already been made. Various case examples will be discussed in the framework of GPCR classification (family A, B, and C receptors). In addition, the behavior at muscarinic receptors of hybrid derivatives incorporating both an allosteric and an orthosteric fragment in a common molecular skeleton will be illustrated.

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.

Allosteric antagonist binding sites in class B GPCRs: corticotropin receptor 1

The 41 amino acid neuropeptide, corticotropin-releasing factor (CRF) and its associated receptors CRF(1)-R and CRF(2)-R have been targeted for treating stress related disorders. Both CRF(1)-R and CRF(2)-R belong to the class B G-protein coupled receptors for which little information is known regarding the small molecule antagonist binding characteristics. However, it has been shown recently that different non-peptide allosteric ligands stabilize different receptor conformations for CRF(1)-R and hence an understanding of the ligand induced receptor conformational changes is important in the pharmacology of ligand binding. In this study, we modeled the receptor and identified the binding sites of representative small molecule allosteric antagonists for CRF(1)-R. The predicted binding sites of the investigated compounds are located within the transmembrane (TM) domain encompassing TM helices 3, 5 and 6. The docked compounds show strong interactions with H228 on TM3 and M305 on TM5 that have also been implicated in the binding by site directed mutation studies. H228 forms a hydrogen bond of varied strengths with all the antagonists in this study and this is in agreement with the decreased binding affinity of several compounds with H228F mutation. Also mutating M305 to Ile showed a sharp decrease in the calculated binding energy whereas the binding energy loss on M305 to Leu was less significant. These results are in qualitative agreement with the decrease in binding affinities observed experimentally. We further predicted the conformational changes in CRF(1)-R induced by the allosteric antagonist NBI-27914. Movement of TM helices 3 and 5 are dominant and generates three degenerate conformational states two of which are separated by an energy barrier from the third, when bound to NBI-27914. Binding of NBI-27914 was predicted to improve the interaction of the ligand with M305 and also enhanced the aromatic stacking between the ligand and F232 on TM3. A virtual ligand screening of ~13,000 compounds seeded with ~350 CRF(1)-R specific active antagonists performed on the NBI-27914 stabilized conformation of CRF(1)-R yielded a 44% increase in enrichment compared to the initially modeled receptor conformation at a 10% cutoff. The NBI-27914 stabilized conformation also shows a high enrichment for high affinity antagonists compared to the weaker ones. Thus, the conformational changes induced by NBI-27914 improved the ligand screening efficiency of the CRF(1)-R model and demonstrate a generalized application of the method in drug discovery.

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.

Structure-activity relationships and X-ray structures describing the selectivity of aminopyrazole inhibitors for c-Jun N-terminal kinase 3 (JNK3) over p38

c-Jun N-terminal kinase 3alpha1 (JNK3alpha1) is a mitogen-activated protein kinase family member expressed primarily in the brain that phosphorylates protein transcription factors, including c-Jun and activating transcription factor-2 (ATF-2) upon activation by a variety of stress-based stimuli. In this study, we set out to design JNK3-selective inhibitors that had >1000-fold selectivity over p38, another closely related mitogen-activated protein kinase family member. To do this we employed traditional medicinal chemistry principles coupled with structure-based drug design. Inhibitors from the aminopyrazole class, such as SR-3576, were found to be very potent JNK3 inhibitors (IC(50) = 7 nm) with >2800-fold selectivity over p38 (p38 IC(50) > 20 microm) and had cell-based potency of approximately 1 microm. In contrast, indazole-based inhibitors exemplified by SR-3737 were potent inhibitors of both JNK3 (IC(50) = 12 nm) and p38 (IC(50) = 3 nm). These selectivity differences between the indazole class and the aminopyrazole class came despite nearly identical binding (root mean square deviation = 0.33 A) of these two compound classes to JNK3. The structural features within the compounds giving rise to the selectivity in the aminopyrazole class include the highly planar nature of the pyrazole, N-linked phenyl structures, which better occupied the smaller active site of JNK3 compared with the larger active site of p38.

Antalarmin

In the mol­ecule of the title compund [systematic name: N-butyl-N-ethyl-2,5,6-trimethyl-7-(2,4,6-trimethyl­phen­yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine], C₂₄H₃₄N₄, the pyrrolopy­rimidine ring system is nearly planar, its five- and six-membered rings forming a dihedral angle of 5.3 (2)°. The benzene ring is nearly orthogonal to the central ring system. The N atom carrying the ethyl and n-butyl groups is flattened pyramidal.

5-tert-butyl-N-pyrazol-4-yl-4,5,6,7-tetrahydrobenzo[d]isoxazole-3-carboxamide derivatives as novel potent inhibitors of Mycobacterium tuberculosis pantothenate synthetase: initiating a quest for new antitubercular drugs

Pantothenate synthetase (PS) is one of the potential new antimicrobial targets that may also be useful for the treatment of the nonreplicating persistent forms of Mycobacterium tuberculosis. In this Letter we present a series of 5- tert-butyl- N-pyrazol-4-yl-4,5,6,7-tetrahydrobenzo[ d]isoxazole-3-carboxamide derivatives as novel potent Mycobacterium tuberculosis PS inhibitors, their in silico molecular design, synthesis, and inhibitory activity.

MPZP: a novel small molecule corticotropin-releasing factor type 1 receptor (CRF1) antagonist

The extrahypothalamic stress peptide corticotropin-releasing factor (CRF) system is an important regulator of behavioral responses to stress. Dysregulation of CRF and the CRF type 1 receptor (CRF(1)) system is hypothesized to underlie many stress-related disorders. Modulation of the CRF(1) system by non-peptide antagonists currently is being explored as a therapeutic approach for anxiety disorders and alcohol dependence. Here, we describe a new, less hydrophilic (cLogP approximately 2.95), small molecule, non-peptide CRF(1) antagonist with high affinity (K(i)=4.9 nM) and specificity for CRF(1) receptors: N,N-bis(2-methoxyethyl)-3-(4-methoxy-2-methylphenyl)-2,5-dimethyl-pyrazolo[1,5-a] pyrimidin-7-amine (MPZP). The compound was systemically administered to adult male rats in two behavioral models dependent on the CRF(1) system: defensive burying (0, 5, 20 mg/kg, n=6-11 for each dose) and alcohol dependence (0, 5, 10, 20 mg/kg, n=8 for each self-administration group). Acute administration of MPZP reduced burying behavior in the defensive burying model of active anxiety-like behavior. MPZP also attenuated withdrawal-induced excessive drinking in the self-administration model of alcohol dependence without affecting nondependent alcohol drinking or water consumption. The present findings support the proposed significance of the CRF(1) system in anxiety and alcohol dependence and introduce a promising new compound for further development in the treatment of alcohol dependence and stress-related disorders.

Allosteric ligands for the corticotropin releasing factor type 1 receptor modulate conformational states involved in receptor activation

Allosteric modulators of G-protein-coupled receptors can regulate conformational states involved in receptor activation ( Mol Pharmacol 58: 1412-1423, 2000 ). This hypothesis was investigated for the corticotropin-releasing factor type 1 (CRF(1)) receptor using a novel series of ligands with varying allosteric effect on CRF binding (inhibition to enhancement). For the G-protein-uncoupled receptor, allosteric modulation of CRF binding was correlated with nonpeptide ligand signaling activity; inverse agonists inhibited and agonists enhanced CRF binding. These data were quantitatively consistent with a two-state equilibrium underlying the modulation of CRF binding to the G-protein-uncoupled receptor. We next investigated the allosteric effect on CRF-stimulated G-protein coupling. Ligands inhibited CRF-stimulated cAMP accumulation regardless of their effect on the G-protein-uncoupled state. The modulators reduced CRF E(max) values, suggesting that they reduced the efficacy of a CRF-bound active state to couple to G-protein. Consistent with this hypothesis, the modulators inhibited binding to a guanine nucleotide-sensitive state. Together, the results are quantitatively consistent with a model in which 1) the receptor exists in three predominant states: an inactive state, a weakly active state, and a CRF-bound fully active state; 2) allosteric inverse agonists stabilize the inactive state, and allosteric agonists stabilize the weakly active state; and 3) antagonism of CRF signaling results from destabilization of the fully active state. These findings imply that nonpeptide ligands differentially modulate conformational states involved in CRF(1) receptor activation and suggest that different conformational states can be targeted in designing nonpeptide ligands to inhibit CRF signaling.

Central CRH system in depression and anxiety--evidence from clinical studies with CRH1 receptor antagonists

Basic and clinical studies provide convincing evidence that altered stress hormone regulation frequently observed in depression and anxiety are caused by elevated secretion of the hypothalamic neuropeptides corticotrophin releasing hormone (CRH) and vasopressin. CRH predominantly acts through CRH(1) receptors to produce a number of anxiety- and depression-like symptoms, which resulted in extensive validation of CRH(1) receptors as potential drug target. A number of orally available nonpeptidergic small molecules capable to pass the blood-brain barrier have been discovered; only some of these compounds entered clinical development. Here, we summarize results from clinical studies of two CRH(1) receptor antagonists. In the first study originally designed as a safety and tolerability trial in major depression, it was observed that the CRH(1) receptor antagonist NBI-30775/R121919 has a clinical profile comparable to the antidepressant paroxetine. In a second study the effect of another CRH(1) receptor antagonist, NBI-34041, upon stress hormone secretion in response to a psychosocial stressor was investigated. Administration of this compound reduced the stress-elicited secretion of cortisol. Both compounds, however, did not impair the CRH-induced release of ACTH and cortisol rejecting the possibility that the peripheral stress hormone system is impaired by CRH(1) receptor antagonists. From these studies we conclude that both CRH(1) receptor antagonists have psychotropic effects unrelated to their neuroendocrine action, which is in line with behavioral data obtained from transgenic mice. The results of the clinical studies underscore that CRH(1) receptor antagonists represent promising novel therapeutics in the psychopharmacology of depression and anxiety.

High-affinity CRF1 receptor antagonist NBI-34041: preclinical and clinical data suggest safety and efficacy in attenuating elevated stress response

There is an extensive evidence that corticotropin releasing factor (CRF) is hypersecreted in depression and anxiety, and blockade of CRF could have therapeutic benefit. We report preclinical data and the results of a clinical Phase I study with the novel nonpeptide CRF(1) antagonist NBI-34041/SB723620. Preclinical data conducted with different cell lines expressing human CRF receptors and in Wistar and Sprague-Dawley rats indicate that NBI-34041 is effective in reducing endocrine responses to pharmacological and behavioral challenge mediated by CRF(1) receptors. These specific properties and its well-documented safety profile enabled a clinical Phase I study with 24 healthy male subjects receiving NBI-34041 (10, 50, or 100 mg) or placebo for 14 days. Regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis was evaluated by intravenous stimulation with 100 microg of human CRF. Psychosocial stress response was investigated with the Trier Social Stress Test (TSST). Treatment with NBI-34041 did not impair diurnal adrenocorticotropic hormone (ACTH) and cortisol secretion or CRF evoked ACTH and cortisol responses but attenuated the neuroendocrine response to psychosocial stress. These results suggest that NBI-34041 is safe and does not impair basal regulation of the HPA system but improves resistance against psychosocial stress. NBI-34041 demonstrates that inhibition of the CRF system is a promising target for drug development against depression and anxiety disorders.

Single amino acid residue determinants of non-peptide antagonist binding to the corticotropin-releasing factor1 (CRF1) receptor

The molecular interactions between non-peptide antagonists and the corticotropin-releasing factor type 1 (CRF1) receptor are poorly understood. A CRF1 receptor mutation has been identified that reduces binding affinity of the non-peptide antagonist NBI 27914 (M276I in transmembrane domain 5). We have investigated the mechanism of the mutation's effect using a combination of peptide and non-peptide ligands and receptor mutations. The M276I mutation reduced binding affinity of standard non-peptide antagonists 5-75-fold while having no effect on peptide ligand binding. We hypothesized that the side chain of isoleucine, beta-branched and so rotationally constrained when within an alpha-helix, introduces a barrier to non-peptide antagonist binding. In agreement with this hypothesis, mutation of M276 to the rotationally constrained valine produced similar reductions of affinity as M276I mutation, whereas mutation to leucine (with an unbranched beta-carbon) minimally affected non-peptide antagonist affinity. Mutation to alanine did not appreciably affect non-peptide antagonist affinity, implying the methionine side chain does not contribute directly to binding. Three observations suggested M276I/V mutations interfere with binding of the heterocyclic core of the compounds: (1) all compounds affected by M276I/V mutations possess a planar heterocyclic core. (2) None of the M276 mutations affected binding of an acylic compound. (3) The mutations differentially affected affinity of two compounds that differ only by core methylation. These findings imply that non-peptide antagonists, and specifically the heterocyclic core of such molecules, bind in the vicinity of M276 of the CRF1 receptor. M276 mutations did not affect peptide ligand binding and this residue is distant from determinants of peptide binding (predominantly in the extracellular regions), providing molecular evidence for non-overlapping (allosteric) binding sites for peptide and non-peptide ligands within the CRF1 receptor.