Opioid receptor-like 1 (ORL1) receptor binding and the biological properties of Ac-Arg-Tyr-Tyr-Arg-Ile-Arg-NH2 and its analogs

NOP-Targeted Peptide Ligands

The nociceptin/orphanin FQ (N/OFQ)-N/OFQ peptide (NOP) receptor system is widely distributed at both the peripheral and central level where it modulates important biological functions with increasing therapeutic implications. This chapter wants to provide a comprehensive and updated overview focused on the available structure-activity relationship studies on NOP receptor peptide ligands developed through different rational approaches. Punctual modifications and cyclizations of the N/OFQ sequence have been properly combined furnishing potent NOP selective ligands with different pharmacological activities (full and partial agonists, pure antagonists) and enhanced metabolic stability in vivo. The screening of peptide libraries provided a second family of NOP ligands that have been successfully optimized. Moreover, recent findings suggest the possibility to apply different multimerization strategies for the realization of multi-target NOP/opioid receptor ligands or tetrabranched N/OFQ derivatives with extraordinarily prolonged duration of action in vivo. The diverse approaches led to the identification of important pharmacological tools along with drug candidates currently in clinical development such as Rec 0438 (aka UFP-112) for the treatment of overactive bladder and SER 100 (aka ZP120) for the clinical management of systolic hypertension.

Synthesis and biological activity of small peptides as NOP and opioid receptors' ligands: view on current developments

The heptadecapeptide nociceptin, also called orphanin FQ (N/OFQ), is the endogenous agonist of the N/OFQ peptide receptor (NOP receptor) and is involved in several central nervous system pathways, such as nociception, reward, tolerance, and feeding. The discovery of small molecule ligands for NOP is being actively pursued for several therapeutic applications. This review presents overview of the several recently reported NOP ligands (agonists and antagonists), with an emphasis of the structural features that may be important for modulating the intrinsic activity of these ligands. In addition, a brief account on the characterization of newly synthesized ligands of NOP receptor with aminophosphonate moiety and β-tryptophan analogues will be presented.

Development of nociceptin receptor (NOP) agonists and antagonists

The nociceptin opioid (NOP) receptor is the most recently discovered member of the family of the opioid receptors; its endogenous agonist is the peptide nociceptin. Due to the subsequent elucidation of its physiological role in both central and peripheral nervous system and in some non-neural tissues, there is a rapidly growing interest in the pharmacological application of substances active on this receptor. Despite the current clinical use of a morphinane-based NOP/MOP mixed ligand (buprenorphine) as an analgesic and in the treatment of drug addictions, so far just a few clinical trials have been made with selective NOP ligands. However, the perspective of their utilization is rapidly growing. Agonists can find applications in the treatment of neuropathic pain, anxiety, cough, drug addition, urinary incontinence, anorexia, congestive heart failure, hypertension; and antagonists for pain, depression, Parkinson's disease, obesity, and as memory enhancers. Besides peptide ligands, which are still subjected to many pharmacological investigations, many different chemical classes of NOP ligands have been discovered: piperidines, nortropanes, spiropiperidines, 4-amino-quinolines and quinazolines, and others. The new advances in establishing structure-activity relationships, also with the help of modeling studies, can permit the development of more active and selective molecules.

Comparative biochemical and pharmacological characterization of a novel, NOP receptor selective hexapeptide, Ac-RYYRIR-ol

Nociceptin/orphanin FQ (N/OFQ) is an endogenous neuropeptide, which is widely distributed in central and peripheral nervous system. Some N/OFQ sequence unrelated hexapeptides can effectively bind to the N/OFQ peptide (NOP) receptor and they were used as template for structure-activity studies that lead to discovery of the new NOP selective ligands. In the present study, the pharmacological profile of the novel hexapeptide Ac-RYYRIR-ol was investigated using various in vitro assays including receptor binding and G-protein activation in rat brain membranes, mouse and rat vas deferens, guinea pig ileum, mouse colon and Ca(2+) mobilization assay in chinese hamster ovary (CHO) cells co-expressing the human recombinant NOP receptor and the C-terminally modified Galpha(qi5) protein. In rat brain membranes Ac-RYYRIR-ol displaced both [(3)H]nociceptin/OFQ and [(3)H]Ac-RYYRIK-ol with high affinity (pK(i) 9.35 and 8.81, respectively) and stimulated [(35)S]GTPgammaS binding showing however lower maximal effects than N/OFQ (alpha=0.28). The stimulatory effect of Ac-RYYRIR-ol was antagonized by the selective NOP receptor antagonist UFP-101. In the electrically stimulated mouse vas deferens Ac-RYYRIR-ol displayed negligible agonist activity while antagonizing in a competitive manner (pA(2) 7.99) the inhibitory effects of N/OFQ. Similar results were obtained in the rat vas deferens. In the mouse colon Ac-RYYRIR-ol produced concentration dependent contractile effects with similar potency and maximal effects as N/OFQ. Finally, in the Ca(2+) mobilization assay performed with CHO-hNOP-Galpha(qi5) cells Ac-RYYRIR-ol displayed lower potency and maximal effects (alpha=0.87) compared with N/OFQ. In conclusion, the novel NOP receptor selective hexapeptide Ac-RYYRIR-ol has been shown to have fine selectivity, high potency, furthermore agonist and antagonist effects toward the NOP receptors were measured in various assays; this is likely due to its partial agonist pharmacological activity.

Cell-penetrating peptide-conjugated XIAP-inhibitory cyclic hexapeptides enter into Jurkat cells and inhibit cell proliferation

X-Linked inhibitor of apoptosis protein (XIAP) is a member of the inhibitor of apoptosis protein family that is overexpressed in human cancers. There is great interest in the development of XIAP inhibitors, which are predicted to promote apoptosis in cancer cells and thus have therapeutic potential. A cyclic hexapeptide (CH), CPFKQC, which is one of the consensus motifs that can bind to the baculovirus IAP repeat 2 domain of XIAP, has been identified using phage-displayed combinatorial chemistry techniques [Tamm I, Trepel M, Cardo-Vila M, Sun Y, Welsh K, Cabezas E, Swatterthwait A, Arap W, Reed JC & Pasqualini R (2003) Peptides targeting caspase inhibitors. J Biol Chem278, 14401-14405]. In this study, we designed and synthesized covalently linked conjugates of CHs, cyclo[Cys-Pro-Xaa-Lys-Gln-Glu(-CO-)-NH2] (Xaa = various amino acids; cyclization via a peptide bond between the N-terminal amino group of Cys1 and the side-chain carboxylic acid of Glu6), and a cell-penetrating peptide (CPP), Ac-Cys-Trp-(Arg)8-Lys-NH2. CH-CPP conjugates (CHCPPs) with aromatic and hydrophobic Xaa residues, such as Phe (CHCPP 1), 2,6-dimethyl-phenylalanine (CHCPP 2) and 3-(1-naphthyl)-alanine/3-(2-naphthyl)-alanine (CHCPPs 3 and 4), potently inhibited the proliferation of Jurkat cells in a dose-dependent manner, whereas analogues with nonaromatic or less hydrophobic amino acids at the Xaa residue were less potent or caused no inhibition. A morphological study of nuclei after treatment with CHCPPs 1-4 revealed that nuclear fragmentation occurred, suggesting that these conjugates induce apoptosis. A kinetic study of the uptake of fluorescein-labelled CHCPP 2 into the cells showed that the conjugates were translocated within a few minutes. The cellular uptake of fluorescein isothiocyanate-labelled CHCPP 1 and CPP was greatly reduced in high-K+ buffers, suggesting that CPP and its conjugate are translocated by a mechanism associated with cell membrane potential. Competitive binding studies performed using fluorescence correlation spectroscopy demonstrated that CHCPP 1 binds to the baculovirus IAP repeat 2 domain of XIAP via the CH (Xaa = Phe) moiety. CHCPPs 1 and 2 showed the most potent inhibitory activity of the CHCPPs and embelin, a nonpeptide inhibitor of XIAP, suggesting that they are good templates for the design of a new class of anticancer drug.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.