4,4-Disubstituted cyclohexylamine NK(1) receptor antagonists I

A series of novel 4,4-disubstituted cyclohexylamine based NK(1) antagonists is described. The effect of changes to the C(1)-C(4) relative stereochemistry on the cyclohexane ring and replacements for the flexible linker are discussed, leading to the identification of compounds with high affinity and good in vivo duration of action.     

1-Phenyl-8-azabicyclo[3.2.1]octane ethers: a novel series of neurokinin (NK1) antagonists

1-Phenyl-8-azabicyclo[3.2.1]octane ethers are NK(1) receptor antagonists. Substitution at the 6-exo-position led to high affinity NK(1) antagonists with a prolonged duration of action in vivo. Incorporation of an alpha-methyl substituent in the pendent benzyl ether side chain gave compounds with increased selectivity over the hERG channel.     

A constitutively active form of neurokinin 1 receptor and neurokinin 1 receptor-mediated apoptosis in glioblastomas

Previous studies have shown that neurokinin 1 receptor (NK1R) occurs naturally in human glioblastomas and its stimulation causes cell proliferation. In the present study we show that stimulation of NK1R in human U373 glioblastoma cells by substance P increases Akt phosphorylation by 2.5-fold, with an EC₅₀ of 57 nM. Blockade of NK1R lowers basal phosphorylation of Akt, indicating the presence of a constitutively active form of NK1R; similar results are seen in U251 MG and DBTRG-05 glioblastoma cells. Linkage of NK1R to Akt implicates NK1R in apoptosis of glioblastoma cells. Indeed, treatment of serum-starved U373 cells with substance P reduces apoptosis by 53 ± 1% ( p  <   0.05), and treatment with NK1R antagonist L-733,060 increases apoptosis by 64 ± 16% ( p  <   0.01). Further, the blockade of NK1R in human glioblastoma cells with L-733,060 causes cleavage of Caspase-3 and proteolysis of poly (ADP-ribose) polymerase. Experiments designed to elucidate the mechanism of NK1R-mediated Akt phosphorylation revealed total involvement of non-receptor tyrosine kinase Src and phosphatidyl-3-kinase, a partial involvement of epidermal growth factor receptor, and no involvement of mitogen-activated protein/extracellular signal-related kinase. Taken together, the results of the present study indicate a key role for NK1R in glioblastoma apoptosis.     

New insights into the antidepressant actions of substance P (NK1 receptor) antagonists

Considerable progress has been made in understanding the neural circuits involved the antidepressant and anxiolytic efficacy of substance P (NK, receptor) antagonists (SPAs). Progress has been hampered by species differences in the pharmacology of the NK1 receptor, and the availability of NK1R-/- mice has been a particularly useful resource in overcoming this difficulty. Using neuroanatomical, behavioural, and electrophysiological techniques, studies have now established that pharmacological blockade or deletion of the NK1 receptor produces an antidepressant and anxiolytic-like profile in a range of behavioural assays that is distinct from that of established drugs. There is evidence from focal injection studies that some of these effects may be mediated directly by blockade of NK, receptors in the amygdala and its projections to the hypothalamus, periaqueductal gray, and reticulopontine nucleus. Substance P and NK1 receptors are also intimately associated with ascending 5-HT and norepinephrine projections to the forebrain, and alterations in the function of these systems are also likely to be related to the antidepressant efficacy of SPAs. Unlike some established drugs, SPAs are generally well tolerated and do not induce sedation or motor impairment in preclinical species. These findings are consistent with a novel antidepressant mechanism of action of SPAs.     

Design and synthesis of potential dual NK1/NK3 receptor antagonists

The tachykinin NK₁ and NK₃ receptors are a novel drug target for schizophrenia in order to treat not only the positive and cognitive symptoms, but also the associated co-morbid depression and sleep disturbances associated with the disease. A novel class of peptidomimetic derivatives based on a versatile phenylglycine central core was synthesized and tested in vitro as dual NK₁/NK₃ receptor antagonists. From this series emerged compounds with good NK₁ receptor affinity, although only modest dual NK₁/NK₃ receptor affinity was observed with one of these analogs.     

Topological analysis of the complex formed between neurokinin A and the NK2 tachykinin receptor

Neurokinin A stimulates physiological responses in the peripheral and central nervous systems upon interacting primarily with the tachykinin NK2 receptor (NK2R). In this study, the structure of NKA bound to the NK2R is characterised by use of fluorescence resonance energy transfer. Four fluorescent NKA analogues with Texas red introduced at amino acid positions 1, 4, 7 and 10 were prepared. When bound to a NK2R carrying enhanced green fluorescent protein at the N-terminus, all peptides reduce green fluorescent protein fluorescence from 10% to 50% due to energy transfer. The derived donor-acceptor distances are 46, 55, 59 and 69 A for the fluorophore linked to positions 1-10, respectively. The monotonic increase in distance clearly indicates that the peptide adopts an extended structure when bound to its receptor. The present data are used, in combination with rhodopsin structure, fluorescence studies, photoaffinity labelling and site-directed mutagenesis data to design a computer model of the NKA-NK2R complex. We propose that the N-terminus of NKA is exposed and accessible to the extracellular medium. Subsequent amino acids of the NKA peptide become progressively more buried residues up to approximately one-third of the transmembrane-spanning domain.     

Synthesis and SAR of sulfoxide substituted carboxyquinolines as NK3 receptor antagonists

The neurokinin-3 (NK3) receptor is regarded as a potential novel target for treating patients with schizophrenia. Herein we report the synthesis and SAR of a series of C3-alkylsulfoxide substituted quinolines as potent NK3 receptor antagonists. These compounds have excellent NK3 functional activity, good selectivity and drug-like properties. Several key compounds have good in vitro/in vivo DMPK characteristics, and are active in a gerbil locomotor activity model.     

Design,synthesis and evaluation of [3H]PF-7191, a highly specific nociceptin opioid peptide (NOP) receptor radiotracer for in vivo receptor occupancy (RO) studies

Herein we report the identification of (+)-N-(2-((1H-pyrazol-1-yl)methyl)-3-((1R,3r,5S)-6′-fluoro-8-azaspiro[bicyclo[3.2.1]octane-3,1′-isochroman]-8-yl)propyl)-N-[³H]-methylacetamide {[³H]PF-7191 [(+)-11]} as a promising radiotracer for the nociceptin opioid peptide (NOP) receptor. (+)-11 demonstrated high NOP binding affinity (K_i = 0.1 nM), excellent selectivity over other opioid receptors (>1000×) and good brain permeability in rats (C_b,u/C_p,u = 0.29). Subsequent characterization of [³H](+)-11 showed a high level of specific binding and a brain bio-distribution pattern consistent with known NOP receptor expression. Furthermore, the in vivo brain binding of [³H](+)-11 in rats was inhibited by a selective NOP receptor antagonist in a dose–responsive manner. This overall favorable profile indicated that [³H](+)-11 is a robust radiotracer for pre-clinical in vivo receptor occupancy (RO) measurements and a possible substrate for carbon-11 labeling for positron emission tomography (PET) imaging in higher species.     

Convergent QSAR studies on a series of NK3 receptor antagonists for schizophrenia treatment

The dopamine hypothesis states that decreased dopaminergic neurotransmission reduces schizophrenia symptoms. Neurokinin-3 receptor (NK₃) antagonists reduce dopamine release and have shown positive effects in pre-clinical and clinical trials. We employed 2D and 3D-QSAR analysis on a series of 40 non-peptide NK₃ antagonists. Multivariate statistical analysis, PCA and HCA, were performed to rational training/test set splitting and PLS regression was employed to construct all QSAR models. We constructed one highly predictive CoMFA model (q^2?=?0.810 and r^2?=?0.929) and acceptable HQSAR and CoMSIA models (HQSAR q^2?=?0.644 and r^2?=?0.910; CoMSIA q^2?=?0.691, r^2?=?0.911). The three different techniques provided convergent physicochemical results. All models indicate cyclopropane, piperidine and di-chloro-phenyl ring attached to cyclopropane ring and also the amide group attached to the piperidine ring could play an important role in ligand–receptor interactions. These findings may contribute to develop potential NK₃ receptor antagonists for schizophrenia.     

Identification of novel NK1/NK3 dual antagonists for the potential treatment of schizophrenia

During the lead optimization of NK(1)/NK(3) receptor antagonists program, a focused exploration of molecules bearing a lactam moiety was performed. The aim of the investigation was to identify the optimal position of the carbonyl and hydroxy methyl group in the lactam moiety, in order to maximize the in vitro affinity and the level of insurmountable antagonism at both NK(1) and NK(3) receptors. The synthesis and biological evaluation of these novel lactam derivatives, with potent and balanced NK(1)/NK(3) activity, were reported in this paper.     

Neurokinin-1 (NK-1) receptor antagonists abrogate methamphetamine-induced striatal dopaminergic neurotoxicity in the murine brain

Methamphetamine (METH) is an addictive substance that also causes extensive neural degeneration in the central nervous system. Because METH augments striatal substance P (SP) levels, we hypothesized that this neuropeptide plays a role in methamphetamine-induced toxicity and neural damage in the striatum. In this study we present evidence demonstrating that signaling through the neurokinin-1 (NK-1) receptor by SP plays an important role in methamphetamine-induced toxicity in the striatum. We tested the effects of the selective NK-1 receptor antagonists WIN-51,708 and L-733,060 on several markers of dopaminergic terminal toxicity in the mouse striatum. Administration of NK-1 receptor antagonist prevented the loss of dopamine transporters assessed by autoradiography and western blotting, the loss of tissue dopamine assessed by high-pressure liquid chromatography, and the loss of tyrosine hydroxylase, as well as the induction of glial fibrillary acidic protein determined by western blotting. Pre-treatment with NK-1 receptor antagonist had no effect on METH-induced hyperthermia. Pre-exposure of mice to either of the NK-1 receptor antagonists alone was without effect on all of these neurochemical markers. These results provide the first evidence that tachykinins, particularly SP, acting through NK-1 receptors, play a crucial role in the pathogenesis of nigrostriatal dopaminergic terminal degeneration induced by METH. This finding could lead to novel therapeutic strategies to offset drug addictions as well as in the treatment of a number of disorders including Parkinson's and Huntington's diseases.     

Development of potent antagonists for formyl peptide receptor 1 based on Boc-Phe-d-Leu-Phe-d-Leu-Phe-OH

While stimulation of formyl peptide receptors (FPRs) on the surface of human neutrophils induces several immune responses, under conditions of continuous activation of the receptor by agonists such as formyl-Met-Leu-Phe-OH (fMLP), neutrophil-dependent tissue damage ensues. Thus, FPR antagonists could be anticipated as drugs for FPR-related disease. In this study, Boc-Phe-d-Leu-Phe-d-Leu-Phe-OH (Boc-FlFlF), one of several FPR subtype selective antagonists, was chosen and the positions at the Phe residues were optimized. We found that substitution with unnatural amino acids resulted in an improvement of two orders of magnitude. The most potent antagonist indicated FPR subtype selectivity at 1 μM. In addition to finding a potent antagonist, the structure–activity trends observed in this study should be valuable in designing a new type of FPR subtype selective antagonist.     

Scaffold hopping of fused piperidine-type NK3 receptor antagonists to reduce environmental impact

Neurokinin-3 receptor (NK3R) plays a pivotal role in the release of gonadotropin-releasing hormone in the hypothalamus–pituitary–gonadal (HPG) axis. To develop novel NK3R antagonists with less environmental toxicity, a series of heterocyclic scaffolds for the triazolopiperazine substructure in an NK3R antagonist fezolinetant were designed and synthesized. An isoxazolo[3,4–c]piperidine derivative exhibited moderate NK3R antagonistic activity and favorable properties that were decomposable under environmental conditions.     

VIP receptor antagonists inhibit mammary carcinogenesis in C3(1)SV40T antigen mice

The effects of a vasoactive intestinal peptide (VIP) receptor antagonist on mammary carcinogenesis were investigated using the C3(1)SV40T antigen (ag) mice. Ten microg/day VIPhybrid (VIPhyb) administered daily subcutaneously increased significantly the survival of C3(1)SV40Tag mice. At 5.2 months, VIPhyb significantly reduced the mammary tumor burden in C3(1)SV40Tag mice relative to control animals. 125I-VIP bound with high affinity to mouse mammary tumor homogenate. Because (Lys15, Arg16, Leu27)VIP1-7GRF8-27 (VPAC1 selective) but not Ro25-1553 (VPAC2 selective) inhibited specific 125I-VIP binding to mammary tumor membranes with high affinity, VPAC1 receptors predominate. By RT-PCR, VPAC1 receptor mRNA was detected in mammary tumors. By Western blot, a major 60 Kdalton band was detected in mammary tumor extracts using VPAC1 receptor antisera. By immunocytochemistry, VPAC1-R immunostaining was detected in the cytosol and plasma membrane but not the nucleus of fixed mammary tumor tissue. Using laser capture microdissected tumor cells and surface enhanced laser desorption/ionization (SELDI) techniques on mammary tumor cells, the proteomic profile was altered in mice treated with VIPhyb. Because VPAC1 receptor antagonists increase the survival and reduce the tumor burden in C3(1)SV40Tag mice, they may function as chemopreventive agents in mammary cancer.     

Discovery of 2,5-diarylnicotinamides as selective orexin-2 receptor antagonists (2-SORAs)

The orexin (or hypocretin) system has been identified as a novel target for the treatment of insomnia due to the wealth of biological and genetic data discovered over the past decade. Recently, clinical proof-of-concept was achieved for the treatment of primary insomnia using dual (OX₁R/OX₂R) orexin receptor antagonists. However, elucidation of the pharmacology associated with selective orexin-2 receptor antagonists (2-SORAs) has been hampered by the lack of orally bioavailable, highly selective small molecule probes. Herein, the discovery and optimization of a novel series of 2,5-diarylnicotinamides as potent and orally bioavailable orexin-2 receptor selective antagonists is described. A compound from this series demonstrated potent sleep promotion when dosed orally to EEG telemetrized rats.     

Norbornyllactone-substituted xanthines as adenosine A(1) receptor antagonists

During the search for second-generation adenosine A(1) receptor antagonist alternatives to the clinical candidate 8-(3-oxa-tricyclo[3.2.1.0(2,4)]oct-6-yl)-1,3-dipropyl-3,7-dihydro-purine-2,6-dione (BG9719), we developed a series of novel xanthines substituted with norbornyl-lactones that possessed high binding affinities for adenosine A(1) receptors and in vivo activity.     

Towards rational design of cannabinoid receptor 1 (CB1) antagonists for peripheral selectivity

CB1 receptor antagonists that are peripherally restricted were targeted. Compounds with permanent charge as well as compounds that have increased polar surface area were made and tested against CB1 for binding and activity. Sulfonamide and sulfamide with high polar surface area and good activity at CB1 were rationally designed and pharmacologically tested. Further optimization of these compounds and testing could lead to the development of a new class of therapeutics to treat disorders where the CB1 receptor system has been implicated.     

Truncation of the peptide sequence in bifunctional ligands with mu and delta opioid receptor agonist and neurokinin 1 receptor antagonist activities

The optimization and truncation of our lead peptide-derived ligand TY005 possessing eight amino-acid residues was performed. Among the synthesized derivatives, NP30 (Tyr¹-DAla²-Gly³-Phe⁴-Gly⁵-Trp⁶-O-[3′,5′-Bzl(CF₃)₂]) showed balanced and potent opioid agonist as well as substance P antagonist activities in isolated tissue-based assays, together with significant antinociceptive and antiallodynic activities in vivo.     

New azole antagonists with high affinity for the P2Y1 receptor

Five-membered-ring heterocyclic urea mimics have been found to be potent and selective antagonists of the P2Y₁ receptor. SAR of the various heterocyclic replacements is presented, as well as side-chain SAR of the more potent thiadiazole ring system which leads to thiadiazole 4c as a new antiplatelet agent.