Old drugs with new skills: fenoprofen as an allosteric enhancer at melanocortin receptor 3.

The efficiency of drug research and development has paradoxically declined over the last decades despite major scientific and technological advances, promoting new cost-effective strategies such as drug repositioning by systematic screening for new actions of known drugs. Here, we performed a screening for positive allosteric modulators (PAMs) at melanocortin (MC) receptors. The non-steroidal anti-inflammatory drug fenoprofen, but not the similar compound ibuprofen, presented PAM activity at MC3, MC4, and MC5 receptors. In a model of inflammatory arthritis, fenoprofen afforded potent inhibition while ibuprofen was nearly inactive. Fenoprofen presented anti-arthritic actions on cartilage integrity and synovitis, effects markedly attenuated in Mc3r-/- mice. Fenoprofen displayed pro-resolving properties promoting macrophage phagocytosis and efferocytosis, independently of cyclooxygenase inhibition. In conclusion, combining repositioning with advances in G-protein coupled receptor biology (allosterism) may lead to potential new therapeutics. In addition, MC3 PAMs emerged as a viable approach to the development of innovative therapeutics for joint diseases.

Terbinafine is a novel and selective activator of the two-pore domain potassium channel TASK3.

Two-pore domain potassium channels (K2Ps) are characterized by their four transmembrane domain and two-pore topology. They carry background (or leak) potassium current in a variety of cell types. Despite a number of important roles there is currently a lack of pharmacological tools with which to further probe K2P function. We have developed a cell-based thallium flux assay, using baculovirus delivered TASK3 (TWIK-related acid-sensitive K+ channel 3, KCNK9, K2P9.1) with the aim of identifying novel, selective TASK3 activators. After screening a library of 1000 compounds, including drug-like and FDA approved molecules, we identified Terbinafine as an activator of TASK3. In a thallium flux assay a pEC50 of 6.2 ( ±0.12) was observed. When Terbinafine was screened against TASK2, TREK2, THIK1, TWIK1 and TRESK no activation was observed in thallium flux assays. Several analogues of Terbinafine were also purchased and structure activity relationships examined. To confirm Terbinafine's activation of TASK3 whole cell patch clamp electrophysiology was carried out and clear potentiation observed in both the wild type channel and the pathophysiological, Birk-Barel syndrome associated, G236R TASK3 mutant. No activity at TASK1 was observed in electrophysiology studies. In conclusion, we have identified the first selective activator of the two-pore domain potassium channel TASK3.

A "Target Class" Screen to Identify Activators of Two-Pore Domain Potassium (K2P) Channels.

Two-pore domain potassium (K2P) channels carry background (or leak) potassium current and play a key role in regulating resting membrane potential and cellular excitability. Accumulating evidence points to a role for K2Ps in human pathophysiologies, most notably in pain and migraine, making them attractive targets for therapeutic intervention. However, there remains a lack of selective pharmacological tools. The aim of this work was to apply a "target class" approach to investigate the K2P superfamily and identify novel activators across all the described subclasses of K2P channels. Target class drug discovery allows for the leveraging of accumulated knowledge and maximizing synergies across a family of targets and serves as an additional approach to standard target-based screening. A common assay platform using baculovirus (BacMam) to transiently express K2P channels in mammalian cells and a thallium flux assay to determine channel activity was developed, allowing the simultaneous screening of multiple targets. Importantly, this system, by allowing precise titration of channel function, allows optimization to facilitate the identification of activators. A representative set of channels (THIK-1, TWIK-1, TREK-2, TASK-3, and TASK-2) were screened against a library of Food and Drug Administration (FDA)-approved compounds and the LifeArc Index Set. Activators were then analyzed in concentration-response format across all channels to assess selectivity. Using the target class approach to investigate the K2P channels has enabled us to determine which of the K2Ps are amenable to small-molecule activation, de-risk multiple channels from a technical point of view, and identify a diverse range of previously undescribed pharmacology.

Design and synthesis of 6-phenylnicotinamide derivatives as antagonists of TRPV1.

6-Phenylnicotinamide (2) was previously identified as a potent TRPV1 antagonist with activity in an in vivo model of inflammatory pain. Optimization of this lead through modification of both the biaryl and heteroaryl components has resulted in the discovery of 6-(4-fluorophenyl)-2-methyl-N-(2-methylbenzothiazol-5-yl)nicotinamide (32; SB-782443) which possesses an excellent overall profile and has been progressed into pre-clinical development.

The physiology and pharmacology of the orexins.

Orexin-A and orexin-B are two peptides derived by proteolytic cleavage from a 130 amino acid precursor prepro-orexin, which recently were isolated from the rat hypothalamus. Orexin-A is fully conserved across mammalian species, whilst rat and human orexin-B differ by 2 amino acids. These peptides bind to two G(q)-coupled receptors, termed OX(1) and OX(2). The receptors are 64% homologous and highly conserved across species. Orexin-A is equipotent at OX(1) and OX(2), whilst orexin-B displays moderate ( approximately 10-fold) selectivity for OX(2). Prepro-orexin is found in the hypothalamus and, to a markedly lesser extent, the testes, adrenals, and myenteric plexus. However, orexin-A and orexin-B are found throughout the CNS, due to extrahypothalamic projections, as well as in the adrenals and small intestine. OX(1) is expressed mainly in the hypothalamus and locus coeruleus, as well as other brain regions and the spinal cord. OX(2) is expressed in the hypothalamus, cortex, spinal cord, and a few discrete brain nuclei. Both receptors are also expressed in the gut. The orexins modulate feeding behaviour and energy homeostasis, as well as associated drinking behaviours, and also regulate the sleep-wake cycle. Moreover, disruption of prepro-peptide expression or mutations in the gene encoding OX(2) result in a narcoleptic phenotye in various animal models, whilst several clinical studies have linked disruption of the orexin system to narcolepsy in humans. The orexins also have cardiovascular and neuroendocrine effects. This review further details the pharmacology and localisation of these peptides and summarises the evidence for their role in the physiology outlined above.

A High-Throughput Electrophysiology Assay Identifies Inhibitors of the Inwardly Rectifying Potassium Channel Kir7.1.

Kir7.1 is an inwardly rectifying potassium channel that has been implicated in controlling the resting membrane potential of the myometrium. Abnormal uterine activity in pregnancy plays an important role in postpartum hemorrhage, and novel therapies for this condition may lie in manipulation of membrane potential. This work presents an assay development and screening strategy for identifying novel inhibitors of Kir7.1. A cell-based automated patch-clamp electrophysiology assay was developed using the IonWorks Quattro (Molecular Devices, Sunnyvale, CA) system, and the iterative optimization is described. In total, 7087 compounds were tested, with a hit rate (>40% inhibition) of 3.09%. During screening, average Z' values of 0.63 ± 0.09 were observed. After chemistry triage, lead compounds were resynthesized and activity confirmed by IC50 determinations. The most potent compound identified (MRT00200769) gave rise to an IC50 of 1.3 µM at Kir7.1. Compounds were assessed for selectivity using the inwardly rectifying potassium channel Kir1.1 (ROMK) and hERG (human Ether-à-go-go Related Gene). Pharmacological characterization of known Kir7.1 inhibitors was also carried out and analogues of VU590 tested to assess selectivity at Kir7.1.

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

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)oxadiazol-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.

Pharmacology of vanilloids at recombinant and endogenous rat vanilloid receptors.

This study compared the actions of members of five different chemical classes of vanilloid agonists at the recombinant rat vanilloid VR1 receptor expressed in HEK293 cells, and at endogenous vanilloid receptors on dorsal root ganglion cells and sensory nerves in the rat isolated mesenteric arterial bed. In mesenteric beds, vanilloids elicited dose-dependent vasorelaxation with the rank order of potency: resiniferatoxin>>capsaicin=olvanil>phorbol 12-phenyl-acetate 13-acetate 20-homovanillate (PPAHV)>isovelleral. Scutigeral was inactive. Responses were abolished by capsaicin pretreatment and inhibited by ruthenium red. In VR1-HEK293 cells and dorsal root ganglion neurones, Ca(2+) responses were induced by resiniferatoxin>capsaicin=olvanil>PPAHV; all four were full agonists. Isovelleral and scutigeral were inactive. The resiniferatoxin-induced Ca(2+) response had a distinct kinetic profile. Olvanil had a Hill coefficient of approximately 1 whilst capsaicin, resiniferatoxin and PPAHV had Hill coefficients of approximately 2 in VR1-HEK293 cells. The capsaicin-induced Ca(2+) response was inhibited in a concentration-dependent manner by ruthenium red>capsazepine>isovelleral. These data show that resiniferatoxin, capsaicin, olvanil and PPAHV, but not scutigeral and isovelleral, are agonists at recombinant rat VR1 receptors and endogenous vanilloid receptors on dorsal root ganglion neurones and in the rat mesenteric arterial bed. The vanilloids display the same relative potencies (resiniferatoxin>capsaicin=olvanil>PPAHV) in all of the bioassays.

Inhibition of C6 glioma cell proliferation by anandamide, 1-arachidonoylglycerol, and by a water soluble phosphate ester of anandamide: variability in response and involvement of arachidonic acid.

It has previously been shown that the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) inhibit the proliferation of C6 glioma cells in a manner that can be prevented by a combination of capsazepine (Caps) and cannabinoid (CB) receptor antagonists. It is not clear whether the effect of 2-AG is due to the compound itself, due to the rearrangement to form 1-arachidonoylglycerol (1-AG) or due to a metabolite. Here, it was found that the effects of 2-AG can be mimicked with 1-AG, both in terms of its potency and sensitivity to antagonism by Caps and CB receptor antagonists. In order to determine whether the effect of Caps could be ascribed to actions upon vanilloid receptors, the effect of a more selective vanilloid receptor antagonist, SB366791 was investigated. This compound inhibited capsaicin-induced Ca(2+) influx into rVR1-HEK293 cells with a pK(B) value of 6.8+/-0.3. The combination of SB366791 and CB receptor antagonists reduced the antiproliferative effect of 1-AG, confirming a vanilloid receptor component in its action. 1-AG, however, showed no direct effect on Ca(2+) influx into rVR1-HEK293 cells indicative of an indirect effect upon vanilloid receptors. Identification of the mechanism involved was hampered by a large inter-experimental variation in the sensitivity of the cells to the antiproliferative effects of 1-AG. A variation was also seen with anandamide, which was not a solubility issue, since its water soluble phosphate ester showed the same variability. In contrast, the sensitivity to methanandamide, which was not sensitive to antagonism by the combination of Caps and CB receptor antagonists, but has similar physicochemical properties to anandamide, did not vary between experiments. This variation greatly reduces the utility of these cells as a model system for the study of the antiproliferative effects of anandamide. Nevertheless, it was possible to conclude that the antiproliferative effects of anandamide were not solely mediated by either its hydrolysis to produce arachidonic acid or its CB receptor-mediated activation of phospholipase A(2) since palmitoyltrifluoromethyl ketone did not prevent the response to anandamide. The same result was seen with the fatty acid amide hydrolase inhibitor palmitoylethylamide. Increasing intracellular arachidonic acid by administration of arachidonic acid methyl ester did not affect cell proliferation, and the modest antiproliferative effect of umbelliferyl arachidonate was not prevented by a combination of Caps and CB receptor antagonists.

Characterization of SB-705498, a potent and selective vanilloid receptor-1 (VR1/TRPV1) antagonist that inhibits the capsaicin-, acid-, and heat-mediated activation of the receptor.

Vanilloid receptor-1 (TRPV1) is a nonselective cation channel, predominantly expressed by sensory neurons, which plays a key role in the detection of noxious painful stimuli such as capsaicin, acid, and heat. TRPV1 antagonists may represent novel therapeutic agents for the treatment of a range of conditions including chronic pain, migraine, and gastrointestinal disorders. Here we describe the in vitro pharmacology of N-(2-bromophenyl)-N'-[((R)-1-(5-trifluoromethyl-2-pyridyl)pyrrolidin-3-yl)]urea (SB-705498), a novel TRPV1 antagonist identified by lead optimization of N-(2-bromophenyl)-N'-[2-[ethyl(3-methylphenyl)amino]ethyl]urea (SB-452533), which has now entered clinical trials. Using a Ca(2+)-based fluorometric imaging plate reader (FLIPR) assay, SB-705498 was shown to be a potent competitive antagonist of the capsaicin-mediated activation of the human TRPV1 receptor (pK(i) = 7.6) with activity at rat (pK(i) = 7.5) and guinea pig (pK(i) = 7.3) orthologs. Whole-cell patch-clamp electrophysiology was used to confirm and extend these findings, demonstrating that SB-705498 can potently inhibit the multiple modes of receptor activation that may be relevant to the pathophysiological role of TRPV1 in vivo: SB-705498 caused rapid and reversible inhibition of the capsaicin (IC(50) = 3 nM)-, acid (pH 5.3)-, or heat (50 degrees C; IC(50) = 6 nM)-mediated activation of human TRPV1 (at -70 mV). Interestingly, SB-705498 also showed a degree of voltage dependence, suggesting an effective enhancement of antagonist action at negative potentials such as those that might be encountered in neurons in vivo. The selectivity of SB-705498 was defined by broad receptor profiling and other cellular assays in which it showed little or no activity versus a wide range of ion channels, receptors, and enzymes. SB-705498 therefore represents a potent and selective multimodal TRPV1 antagonist, a pharmacological profile that has contributed to its definition as a suitable drug candidate for clinical development.

Discovery of SB-705498: a potent, selective and orally bioavailable TRPV1 antagonist suitable for clinical development.

Small molecule antagonists of the vanilloid receptor TRPV1 (also known as VR1) are disclosed. Pyrrolidinyl ureas such as 8 and 15 (SB-705498) emerged as lead compounds following optimisation of the previously described urea SB-452533. Pharmacological studies using electrophysiological and FLIPR-Ca2+-based assays showed that compounds such as 8 and 15 were potent antagonists versus the multiple chemical and physical modes of TRPV1 activation (namely capsaicin, acid and noxious heat). Furthermore, 15 possessed suitable developability properties to enable progression of this compound into in vivo studies and subsequently clinical development.

N-Tetrahydroquinolinyl, N-quinolinyl and N-isoquinolinyl biaryl carboxamides as antagonists of TRPV1.

Starting from the high throughput screening hit (3), novel N-tetrahydroquinolinyl, N-quinolinyl and N-isoquinolinyl carboxamides have been identified as potent antagonists of the ion channel TRPV1. The N-quinolinylnicotinamide (46) showed excellent potency at human, guinea pig and rat TRPV1, a favourable in vitro DMPK profile and activity in an in vivo model of inflammatory pain.

Discovery of small molecule antagonists of TRPV1.

Small molecule antagonists of the vanilloid receptor 1 (TRPV1, also known as VR1) are disclosed. Ureas such as 5 (SB-452533) were used to explore the structure activity relationship with several potent analogues identified. Pharmacological studies using electrophysiological and FLIPR Ca(2+) based assays showed compound 5 was an antagonist versus capsaicin, noxious heat and acid mediated activation of TRPV1. Study of a quaternary salt of 5 supports a mode of action in which compounds from this series cause inhibition via an extracellularly accessible binding site on the TRPV1 receptor.