The nociceptin/orphanin FQ receptor partial agonist sunobinop promotes non-REM sleep in rodents and patients with insomnia.

The potent and partial agonist sunobinop activates the nociceptin/orphanin-FQ peptide receptor and promotes non-REM sleep in rodents and patients with insomnia.

Hyperthermia induced by transient receptor potential vanilloid-1 (TRPV1) antagonists in human clinical trials: Insights from mathematical modeling and meta-analysis.

Antagonists of the transient receptor potential vanilloid-1 (TRPV1) channel alter body temperature (Tb) in laboratory animals and humans: most cause hyperthermia; some produce hypothermia; and yet others have no effect. TRPV1 can be activated by capsaicin (CAP), protons (low pH), and heat. First-generation (polymodal) TRPV1 antagonists potently block all three TRPV1 activation modes. Second-generation (mode-selective) TRPV1 antagonists potently block channel activation by CAP, but exert different effects (e.g., potentiation, no effect, or low-potency inhibition) in the proton mode, heat mode, or both. Based on our earlier studies in rats, only one mode of TRPV1 activation - by protons - is involved in thermoregulatory responses to TRPV1 antagonists. In rats, compounds that potently block, potentiate, or have no effect on proton activation cause hyperthermia, hypothermia, or no effect on Tb, respectively. A Tb response occurs when a TRPV1 antagonist blocks (in case of hyperthermia) or potentiates (hypothermia) the tonic TRPV1 activation by protons somewhere in the trunk, perhaps in muscles, and - via the acido-antithermogenic and acido-antivasoconstrictor reflexes - modulates thermogenesis and skin vasoconstriction. In this work, we used a mathematical model to analyze Tb data from human clinical trials of TRPV1 antagonists. The analysis suggests that, in humans, the hyperthermic effect depends on the antagonist's potency to block TRPV1 activation not only by protons, but also by heat, while the CAP activation mode is uninvolved. Whereas in rats TRPV1 drives thermoeffectors by mediating pH signals from the trunk, but not Tb signals, our analysis suggests that TRPV1 mediates both pH and thermal signals driving thermoregulation in humans. Hence, in humans (but not in rats), TRPV1 is likely to serve as a thermosensor of the thermoregulation system. We also conducted a meta-analysis of Tb data from human trials and found that polymodal TRPV1 antagonists (ABT-102, AZD1386, and V116517) increase Tb, whereas the mode-selective blocker NEO6860 does not. Several strategies of harnessing the thermoregulatory effects of TRPV1 antagonists in humans are discussed.

Dibenzazepines and dibenzoxazepines as sodium channel blockers.

We have identified two related series of dibenzazepine and dibenzoxazepine sodium channel blockers, which showed good potency on Nav1.7 in FLIPR-based and electrophysiological functional assays.

N-Aryl azacycles as novel sodium channel blockers.

We have identified a new series of N-aryl azacycles as sodium channel blockers, which showed good potency on Nav1.7 in FLIPR-based and electrophysiological functional assays. Analogs from this series possessed selectivity over hERG, reasonable oral exposure in rat PK studies and are predicted to have limited CNS penetration.

Structure-activity relationship studies and discovery of a potent transient receptor potential vanilloid (TRPV1) antagonist 4-[3-chloro-5-[(1S)-1,2-dihydroxyethyl]-2-pyridyl]-N-[5-(trifluoromethyl)-2-pyridyl]-3,6-dihydro-2H-pyridine-1-carboxamide (V116517) as a clinical candidate for pain management.

A series of novel tetrahydropyridinecarboxamide TRPV1 antagonists were prepared and evaluated in an effort to optimize properties of previously described lead compounds from piperazinecarboxamide series. The compounds were evaluated for their ability to block capsaicin and acid-induced calcium influx in CHO cells expressing human TRPV1. The most potent of these TRPV1 antagonists were further characterized in pharmacokinetic, efficacy, and body temperature studies. On the basis of its pharmacokinetic, in vivo efficacy, safety, and toxicological properties, compound 37 was selected for further evaluation in human clinical trials.

Studies examining the relationship between the chemical structure of protoxin II and its activity on voltage gated sodium channels.

The aqueous solution structure of protoxin II (ProTx II) indicated that the toxin comprises a well-defined inhibitor cystine knot (ICK) backbone region and a flexible C-terminal tail region, similar to previously described NaSpTx III tarantula toxins. In the present study we sought to explore the structure-activity relationship of the two regions of the ProTx II molecule. As a first step, chimeric toxins of ProTx II and PaTx I were synthesized and their biological activities on Nav1.7 and Nav1.2 channels were investigated. Other tail region modifications to this chimera explored the effects of tail length and tertiary structure on sodium channel activity. In addition, the activity of various C-terminal modifications of the native ProTx II was assayed and resulted in the identification of protoxin II-NHCH3, a molecule with greater potency against Nav1.7 channels (IC50=42 pM) than the original ProTx II.

Roles of µ-opioid receptors and nociceptin/orphanin FQ peptide receptors in buprenorphine-induced physiological responses in primates.

Buprenorphine is known as a µ-opioid peptide (MOP) receptor agonist, but its antinociception is compromised by the activation of nociceptin/orphanin FQ peptide (NOP) receptors in rodents. The aim of this study was to investigate the roles of MOP and NOP receptors in regulating buprenorphine-induced physiological responses in primates (rhesus monkeys). The effects of MOP antagonist (naltrexone), NOP antagonist [(±)-1-[(3R*,4R*)-1-(cyclooctylmethyl)-3-(hydroxymethyl)-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397)], and NOP agonists [(1S,3aS)-8-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)-1-phenyl-1,3,8-triaza-spiro[4.5] decan-4-one (Ro 64-6198) and 3-endo-8-[bis(2-methylphenyl)methyl]-3-phenyl-8-azabicyclo[3.2.1]octan-3-ol (SCH 221510)] on buprenorphine were studied in three functional assays for measuring analgesia, respiratory depression, and itch in primates. Over the dose range of 0.01 to 0.1 mg/kg, buprenorphine dose-dependently produced antinociception, respiratory depression, and itch/scratching responses, and there was a ceiling effect at higher doses (0.1-1 mg/kg). Naltrexone (0.03 mg/kg) produced similar degrees of rightward shifts of buprenorphine's dose-response curves for all three endpoints. Mean pK(B) values of naltrexone (8.1-8.3) confirmed that MOP receptors mediated mainly buprenorphine-induced antinociception, respiratory depression, and itch/scratching. In contrast, J-113397 (0.1 mg/kg) did not change buprenorphine-induced physiological responses, indicating that there were no functional NOP receptors in buprenorphine-induced effects. More importantly, both NOP agonists, Ro 64-6198 and SCH 221510, enhanced buprenorphine-induced antinociception without respiratory depression and itch/ scratching. The dose-addition analysis revealed that buprenorphine in combination with the NOP agonist synergistically produced antinociceptive effects. These findings provided functional evidence that the activation of NOP receptors did not attenuate buprenorphine-induced antinociception in primates; instead, the coactivation of MOP and NOP receptors produced synergistic antinociception without other side effects. This study strongly supports the therapeutic potential of mixed MOP/NOP agonists as innovative analgesics.

Cysteine racemization during the Fmoc solid phase peptide synthesis of the Nav1.7-selective peptide--protoxin II.

Protoxin II is biologically active peptide containing the inhibitory cystine knot motif. A synthetic version of the toxin was generated with standard Fmoc solid phase peptide synthesis. If N-methylmorpholine was used as a base during synthesis of the linear protoxin II, it was found that a significant amount of racemization (approximately 50%) was observed during the process of cysteine residue coupling. This racemization could be suppressed by substituting N-methylmorpholine with 2,4,6-collidine. The crude linear toxin was then air oxidized and purified. Electrophysiological assessment of the synthesized protoxin II confirmed its previously described interactions with voltage-gated sodium channels. Eight other naturally occurring inhibitory knot peptides were also synthesized using this same methodology. The inhibitory potencies of these synthesized toxins on Nav1.7 and Nav1.2 channels are summarized.

Display of somatostatin-related peptides in the complementarity determining regions of an antibody light chain.

Peptide display in antibody complementarity determining regions (CDRs) offers several advantages over other peptide display systems including the potential to graft heterologous peptide sequences into multiple positions in the same backbone molecule. Despite the presence of six CDRs in an antibody variable domain, the majority of insertions reported have been made in heavy chain CDR3 (h-CDR3) which may be explained in part by the highly variable length and sequence diversity found in h-CDR3 in native antibodies. The ability to graft peptide sequences into CDRs is restricted by amino acids in these loops that make structural contacts to framework regions or are oriented towards the hydrophobic interior and are important for the proper folding of the antibody. To identify such positions in human kappa-light chain CDR1 (kappa-CDR1) and CDR2 (kappa-CDR2), we performed alignments of 1330 kappa-light chain variable region amino acid sequences and 19 variable region X-ray crystal structures. From analyses of these alignments, we predict insertion points where sequences can be grafted into kappa-CDR1 and kappa-CDR2 to prepare synthetic antibody molecules. We then tested these predictions by inserting somatostatin and somatostatin-related sequences into kappa-CDR1 and kappa-CDR2, and analyzing the expression and ability of the modified antibodies to bind to membranes containing somatostatin receptor 5. These results expand the repertoire of CDRs that can be used for the display of heterologous peptides in the CDRs of antibodies.

8-Substituted analogues of 3-(3-cyclopentyloxy-4-methoxy-benzyl)-8-isopropyl-adenine: highly potent and selective PDE4 inhibitors.

3-(3-Cyclopentyloxy-4-methoxy-benzyl)-8-isopropyl-adenine V11294 (1) has been identified as a lead structure, which selectively inhibits human lung PDE4 (436 nM) and is also active in a number of in vitro and in vivo models of inflammation. Here we describe the synthesis and pharmacology of a series of highly potent 8-[(benzyloxy)methyl]-substituted analogues, with potencies in the range 10-300 nM. In addition, several compounds showed interesting PDE4 subtype specificities, for example, the 3-thienyl derivative 5v, which showed 6-10 nM potency at PDE4B, D3, and D5 and a 20- to 200-fold selectivity over A and D2, respectively.

Synthesis and evaluation of pyridazinylpiperazines as vanilloid receptor 1 antagonists.

A structurally biased chemical library of pyridazinylpiperazine analogs was prepared in an effort to improve the pharmaceutical and pharmacological profile of the lead compound N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carboxamide (BCTC). The library was evaluated for VR1 antagonist activity in capsaicin-induced (CAP) and pH5.5-induced (pH) FLIPR assays in a human VR1-expressing HEK293 cell line. The most potent VR1 antagonists were found to have IC(50) values in the range of 9-200nM with improved pharmaceutical and pharmacological profiles versus the lead BCTC. These compounds represent possible second-generation BCTC analogs.

Design and synthesis of 4-phenyl piperidine compounds targeting the mu receptor.

Small molecule mu agonists based on the 4-phenyl piperidine scaffold were designed and synthesized to further investigate the therapeutic potential of loperamide analogs. The resulting compounds show excellent agonistic activity towards the human mu receptor with interesting SAR trends within the series.

1,3-Dihydro-2,1,3-benzothiadiazol-2,2-diones and 3,4-dihydro-1H-2,1,3-benzothidiazin-2,2-diones as ligands for the NOP receptor.

A series of 1,3-dihydro-2,1,3-benzothiadiazol-2,2-diones (I) and 3,4-dihydro-1H-2,1,3-benzothidiazin-2,2-diones (II) were prepared. While the five-member ring series (I) did not show good affinity for opioid receptors, the six-member ring series (II) exhibited extremely high affinity and selectivity for the NOP receptor and showed full agonist activity, as determined by stimulation of GTPgamma[35S] binding.

DiPOA ([8-(3,3-diphenyl-propyl)-4-oxo-1-phenyl-1,3,8-triazaspiro[4.5]dec-3-yl]-acetic acid), a novel, systemically available, and peripherally restricted mu opioid agonist with antihyperalgesic activity: I. In vitro pharmacological characterization and pharmacokinetic properties.

Mu opioid receptors are present throughout the central and peripheral nervous systems. Peripheral inflammation causes an increase in mu receptor levels on peripheral terminals of primary afferent neurons. Recent studies indicate that activation of peripheral mu receptors produces antihyperalgesic effects in animals and humans. Here, we describe the in vitro pharmacological and in vivo pharmacokinetic properties of a novel, highly potent, and peripherally restricted mu opioid agonist, [8-(3,3-diphenyl-propyl)-4-oxo-1-phenyl-1,3,8-triaza-spiro[4.5]dec-3-yl]-acetic acid (DiPOA). In a radioligand binding assay, DiPOA inhibited [(3)H]-diprenorphine binding to recombinant human mu receptors with a K(i) value of approximately 0.8 nM. The rank order of affinity for DiPOA binding to recombinant human opioid receptors was mu > kappa approximately ORL-1 >> delta. DiPOA showed potent agonist effects in a human mu receptor guanosine 5'-O-(3-[(35)S]thio)triphosphate functional assay, with an EC(50) value of approximately 33 nM and efficacy of approximately 85% [normalized to the mu agonist, [d-Ala2,MePhe4,Gly(ol)5]enkephalin]. Low potency agonist activity was also seen at ORL-1 and kappa receptors. DiPOA bound competitively to the opioid binding site of human mu receptors as demonstrated by a parallel rightward shift in its concentration-response curve in the presence of increasing concentrations of naltrexone. High and sustained (> or =5 h) plasma levels for DiPOA were achieved following intraperitoneal administration at 3 and 10 mg/kg; central nervous system penetration, however, was < or =4% of the plasma concentration, even at levels exceeding 1500 ng/ml. As such, DiPOA represents a systemically available, peripherally restricted small molecule mu opioid agonist that will aid in understanding the role played by mu opioid receptors in the periphery.

An efficient parallel synthesis of capsazepine and capsazepine analogs.

Capsazepine (CPZ, 1) is a well-known vanilloid receptor (VR1) antagonist that has been cited widely used in the literature. However the current synthetic methods used for the total synthesis of CPZ are lengthy, involve multiple purification steps, and produce low yields. Here we describe a new and highly efficient synthesis of benzazepine 3, a synthetic precursor of CPZ, in only two steps and 59% overall yield from a commercially available tetralone 2 via a Schmidt reaction as a key step. Moreover, we apply parallel synthesis techniques to prepare CPZ and CPZ analogs. Our approach enables the possibility of preparing larger, and more diverse libraries of CPZ analogs.

Design and synthesis of novel small molecule N/OFQ receptor antagonists.

Small molecule N/OFQ receptor antagonists were designed and synthesized to further investigate the therapeutic potential of N/OFQ receptor modulators. The resulting octahydrobenzimidazol-2-ones 14 and 23 show excellent antagonistic activity towards both N/OFQ and mu receptors with high affinity to the human N/OFQ receptor.

4-(2-pyridyl)piperazine-1-carboxamides: potent vanilloid receptor 1 antagonists.

A series of 4-(2-pyridyl)piperazine-1-carboxamide analogues based on the lead compound 1 was synthesized and evaluated for VR1 antagonist activity in capsaicin-induced (CAP) and pH (5.5)-induced (pH) FLIPR assays in a rat VR1-expressing HEK293 cell line. Potent VR1 antagonists were identified through SAR studies. From these studies, 18 was found to be very potent in the in vitro assay [IC(50)=4.8 nM (pH) and 35 nM (CAP)] and orally available in rat (F%=15.1).

Parallel synthesis of a biased library of thiazolidinones as novel sodium channel antagonists.

A biased chemical library containing 91 differentially substituted thiazolidinones was prepared in an effort to improve the pharmacology of a known anticonvulsant agent V102862. The collection was prepared in a single step multi-component condensation reaction that produced good yields and very high crude purity (75%-85%). Seven compounds, identified within the library were shown to be more potent than V102862, our parent reference compound, in an electrophysiological assay measuring sodium channel antagonism. The most potent compound, 3-(2-piperidinylethyl)-2-(3-(3-trifluoromethylphenoxy)phenyl)thiazolidinone, has a Ki of 90 nM.