SB-674042

SB-674042 is a specific, high-affinity OX1 selective antagonist.

Characterisation of the binding of [3H]-SB-674042, a novel nonpeptide antagonist, to the human orexin-1 receptor.[Pubmed:14691055]

Br J Pharmacol. 2004 Jan;141(2):340-6.

1. This study characterises the binding of a novel nonpeptide antagonist radioligand, [(3)H]SB-674042 (1-(5-(2-fluoro-phenyl)-2-methyl-thiazol-4-yl)-1-((S)-2-(5-phenyl-(1,3,4)oxadiazo l-2-ylmethyl)-pyrrolidin-1-yl)-methanone), to the human orexin-1 (OX(1)) receptor stably expressed in Chinese hamster ovary (CHO) cells in both a whole cell assay and in a cell membrane-based scintillation proximity assay (SPA) format. 2. Specific binding of [(3)H]SB-674042 was saturable in both whole cell and membrane formats. Analyses suggested a single high-affinity site, with K(d) values of 3.76+/-0.45 and 5.03+/-0.31 nm, and corresponding B(max) values of 30.8+/-1.8 and 34.4+/-2.0 pmol mg protein(-1), in whole cell and membrane formats, respectively. Kinetic studies yielded similar K(d) values. 3. Competition studies in whole cells revealed that the native orexin peptides display a low affinity for the OX(1) receptor, with orexin-A displaying a approximately five-fold higher affinity than orexin-B (K(i) values of 318+/-158 and 1516+/-597 nm, respectively). 4. SB-334867, SB-408124 (1-(6,8-difluoro-2-methyl-quinolin-4-yl)-3-(4-dimethylamino-phenyl)-urea) and SB-410220 (1-(5,8-difluoro-quinolin-4-yl)-3-(4-dimethylamino-phenyl)-urea) all displayed high affinity for the OX(1) receptor in both whole cell (K(i) values 99+/-18, 57+/-8.3 and 19+/-4.5 nm, respectively) and membrane (K(i) values 38+/-3.6, 27+/-4.1 and 4.5+/-0.2 nm, respectively) formats. 5. Calcium mobilisation studies showed that SB-334867, SB-408124 and SB-410220 are all functional antagonists of the OX(1) receptor, with potencies in line with their affinities, as measured in the radioligand binding assays, and with approximately 50-fold selectivity over the orexin-2 receptor. 6. These studies indicate that [(3)H]SB-674042 is a specific, high-affinity radioligand for the OX(1) receptor. The availability of this radioligand will be a valuable tool with which to investigate the physiological functions of OX(1) receptors.

Mapping the binding pocket of dual antagonist almorexant to human orexin 1 and orexin 2 receptors: comparison with the selective OX1 antagonist SB-674042 and the selective OX2 antagonist N-ethyl-2-[(6-methoxy-pyridin-3-yl)-(toluene-2-sulfonyl)-amino]-N-pyridin-3-ylmet hyl-acetamide (EMPA).[Pubmed:20404073]

Mol Pharmacol. 2010 Jul;78(1):81-93.

The orexins and their receptors are involved in the regulation of arousal and sleep-wake cycle. Clinical investigation with almorexant has indicated that this dual OX antagonist is efficacious in inducing and maintaining sleep. Using site-directed mutagenesis, beta(2)-adrenergic-based OX(1) and OX(2) modeling, we have determined important molecular determinants of the ligand-binding pocket of OX(1) and OX(2). The conserved residues Asp(45.51), Trp(45.54), Tyr(5.38), Phe(5.42), Tyr(5.47), Tyr(6.48), and His(7.39) were found to be contributing to both orexin-A-binding sites at OX(1) and OX(2). Among these critical residues, five (positions 45.51, 45.54, 5.38, 5.42, and 7.39) were located on the C-terminal strand of the second extracellular loop (ECL2b) and in the top of TM domains at the interface to the main binding crevice, thereby suggesting superficial OX receptor interactions of orexin-A. We found that the mutations W214A(45.54), Y223A(5.38), F227A(5.42), Y317A(6.48), and H350A(7.39) resulted in the complete loss of both [(3)H]almorexant and [(3)H]N-ethyl-2-[(6-methoxy-pyridin-3-yl)-(toluene-2-sulfonyl)-amino]-N-pyridin-3 -ylmethyl-acetamide (EMPA) binding affinities and also blocked their inhibition of orexin-A-evoked [Ca(2+)](i) response at OX(2). The crucial residues Gln126(3.32), Ala127(3.33), Trp206(45.54), Tyr215(5.38), Phe219(5.42), and His344(7.39) are shared between almorexant and 1-(5-(2-fluoro-phenyl)-2-methyl-thiazol-4-yl)-1-((S)-2-(5-phenyl-(1,3,4)oxadiazol -2-ylmethyl)-pyrrolidin-1-yl)-methanone (SB-674042) binding sites in OX(1). The nonconserved residue at position 3.33 of orexin receptors was identified as occupying a critical position that must be involved in subtype selectivity and also in differentiating two different antagonists for the same receptor. In summary, despite high similarities in the ligand-binding pockets of OX(1) and OX(2) and numerous aromatic/hydrophobic interactions, the local conformation of helix positions 3.32, 3.33, and 3.36 in transmembrane domain 3 and 45.51 in ECL2b provide the structural basis for pharmacologic selectivity between OX(1) and OX(2).

Orexin-1 receptor-cannabinoid CB1 receptor heterodimerization results in both ligand-dependent and -independent coordinated alterations of receptor localization and function.[Pubmed:17015451]

J Biol Chem. 2006 Dec 15;281(50):38812-24.

Following inducible expression in HEK293 cells, the human orexin-1 receptor was targeted to the cell surface but became internalized following exposure to the peptide agonist orexin A. By contrast, constitutive expression of the human cannabinoid CB1 receptor resulted in a predominantly punctate, intracellular distribution pattern consistent with spontaneous, agonist-independent internalization. Expression of the orexin-1 receptor in the presence of the CB1 receptor resulted in both receptors displaying the spontaneous internalization phenotype. Single cell fluorescence resonance energy transfer imaging indicated the two receptors were present as heterodimers/oligomers in intracellular vesicles. Addition of the CB1 receptor antagonist SR-141716A to cells expressing only the CB1 receptor resulted in re-localization of the receptor to the cell surface. Although SR-141716A has no significant affinity for the orexin-1 receptor, in cells co-expressing the CB1 receptor, the orexin-1 receptor was also re-localized to the cell surface by treatment with SR-141716A. Treatment of cells co-expressing the orexin-1 and CB1 receptors with the orexin-1 receptor antagonist SB-674042 also resulted in re-localization of both receptors to the cell surface. Treatment with SR-141716A resulted in decreased potency of orexin A to activate the mitogen-activated protein kinases ERK1/2 only in cells co-expressing the two receptors. Treatment with SB-674042 also reduced the potency of a CB1 receptor agonist to phosphorylate ERK1/2 only when the two receptors were co-expressed. These studies introduce an entirely novel pharmacological paradigm, whereby ligands modulate the function of receptors for which they have no significant inherent affinity by acting as regulators of receptor heterodimers.

SB-674042 is a potent and selective non-peptide orexin OX1 receptor antagonist (Kd = 3.76 nM); exhibits 100-fold selectivity for OX1 over OX2 receptors.

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