Synthesis and biological studies of nociceptin derivatives containing the DTPA chelating group for further labeling with therapeutic radionuclides

Structure- and conformation-activity studies of nociceptin/orphanin FQ receptor dimeric ligands

The peptide nociceptin/orphanin FQ (N/OFQ) and the N/OFQ receptor (NOP) constitute a neuropeptidergic system that modulates various biological functions and is currently targeted for the generation of innovative drugs. In the present study dimeric NOP receptor ligands with spacers of different lengths were generated using both peptide and non-peptide pharmacophores. The novel compounds (12 peptide and 7 nonpeptide ligands) were pharmacologically investigated in a calcium mobilization assay and in the mouse vas deferens bioassay. Both structure- and conformation-activity studies were performed. Results demonstrated that dimerization did not modify the pharmacological activity of both peptide and non-peptide pharmacophores. Moreover, when dimeric compounds were obtained with low potency peptide pharmacophores, dimerization recovered ligand potency. This effect depends on the doubling of the C-terminal address sequence rather than the presence of an additional N-terminal message sequence or modifications of peptide conformation.

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.

Nociceptin inhibits uterine contractions in term-pregnant rats by signaling through multiple pathways

The actions of the endogenous peptide nociceptin (PNOC; previously abbreviated as N/OFQ) on the myometrium have not been investigated previously. Our aim was to study the presence and functional role of PNOC in the modulation of uterine contractility in pregnant rats at term. The presence of PNOC and its receptors (OPRL1; previously called NOP) in the uterus were detected by radioimmunoassay and radioligand-binding experiments. The PNOC-stimulated G protein activation was assessed by a [(35)S]GTPgammaS-binding technique. The effects of PNOC in uterine rings precontracted with KCl or oxytocin were also tested in vitro. Uterine levels of cAMP were measured by enzyme immunoassay. The K(+) channel blockers tetraethylammonium and paxilline were used to study the role of K(+) channels in mediating the uterine effects of PNOC. Both PNOC and OPRL1 were present in the uterus. PNOC revealed a maximum contraction inhibition of approximately 30%, which was increased to 40% by naloxone. Naloxone and pertussis toxin significantly attenuated the G protein-stimulating effect of PNOC. The uterine cAMP levels were elevated by PNOC and naloxone and after preincubation with pertussis toxin. Tetraethylammonium and paxilline reduced the contraction-inhibiting effect of PNOC and naloxone to approximately 10% and 15%, respectively. We presume that PNOC plays a role in regulating uterine contractility at term. Its effect is mediated partly by stimulatory heterotrimeric G (G(s)) proteins coupled to OPRL1 receptors and elevated cAMP levels, and also by Ca(2+)-dependent K(+) channels. Our results demonstrate a novel action and signaling pathway for PNOC that might be a potential drug target.

Temporal lobe epilepsy causes selective changes in mu opioid and nociceptin receptor binding and functional coupling to G-proteins in human temporal neocortex

There is no information concerning signal transduction mechanisms downstream of the opioid/nociceptin receptors in the human epileptic brain. The aim of this work was to evaluate the level of G-proteins activation mediated by DAMGO (a mu receptor selective peptide) and nociceptin, and the binding to mu and nociceptin (NOP) receptors and adenylyl cyclase (AC) in neocortex of patients with pharmacoresistant temporal lobe epilepsy. Patients with temporal lobe epilepsy associated with mesial sclerosis (MTLE) or secondary to tumor or vascular lesion showed enhanced [3H]DAMGO and [3H]forskolin binding, lower DAMGO-stimulated [35S]GTPgammaS binding and no significant changes in nociceptin-stimulated G-protein. [3H]Nociceptin binding was lower in patients with MTLE. Age of seizure onset correlated positively with [3H]DAMGO binding and DAMGO-stimulated [35S]GTPgammaS binding, whereas epilepsy duration correlated negatively with [3H]DAMGO and [3H]nociceptin binding, and positively with [3H]forskolin binding. In conclusion, our present data obtained from neocortex of epileptic patients provide strong evidence that a) temporal lobe epilepsy is associated with alterations in mu opioid and NOP receptor binding and signal transduction mechanisms downstream of these receptors, and b) clinical aspects may play an important role on these receptor changes.

Specificity and mobility of biomacromolecular, multivalent constructs for cellular targeting

Effective targeting of drugs to cells requires that the drug reach the target cell and interact specifically with it. In this study, we synthesized a biomacromolecular, multivalent construct intended to target glioblastoma tumors. The construct was created by linking three dodecapeptides, reported to bind the alpha 6beta1 integrin, with poly(ethylene glycol) linkers. The construct is intended to be delivered locally, and it demonstrates a more homogeneous and more rapid perfusion profile in comparison with quantum dots. The binding specificity of the construct was investigated by using glioblastoma cells and normal human astrocyte cells. The results reveal qualitative differences in binding between glioma and normal human astrocyte cells, with a moderate increase in binding avidity due to multivalency (0.79 microM for the trivalent construct versus 4.28 microM for the dodecapeptide). Overall, biomacromolecular constructs appear to be a promising approach for targeting with high biocompatibility, good perfusion abilities, and specificity.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

In vitro binding and functional studies of Ac-RYYRIK-ol and its derivatives, novel partial agonists of the nociceptin/orphanin F/Q receptor

Following the discovery of nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) and its endogenous ligand, an extensive search has started to find selective agonists and antagonists targeting this novel receptor-ligand system due to their therapeutic potentials. By the help of the combinatorial chemistry a series of hexapeptides with a general formula of Ac-RYY-R/K-W/I-R/K-NH(2) having high NOP receptor affinity and selectivity were identified. On the basis of this information we developed a number of novel compounds. The detailed structure-activity studies on the partial agonist Ac-RYYRIK-NH(2) are reported in this communication. Besides the modifications on N- and C-terminal, Arg-Cit exchange was performed on the template structure. The novel hexapeptides were analyzed in radioligand binding, functional biochemical [(35)S]GTPgammaS binding assays by using membranes from rat brains and Chinese hamster ovary cells expressing human NOP receptor. The agonist/antagonist properties were also tested on in the mouse vas deferens bioassay. C-terminal modification yielded a high affinity, selective and potent NOP ligand (Ac-RYYRIK-ol) with a partial agonist property. Several analogs of this compound were synthesized. The presence of the positively charged arginine residue at the first position turned out to be crucial for the biological activity of the hexapeptide. The N-terminal modifications with various acyl groups (ClAc, pivaloyl, formyl, benzoyl, mesyl) decreased the affinity of the ligand towards the receptor and the intrinsic activity for stimulating the G-protein activation was also decreased. The structure-activity studies on the hexapeptide derivatives provided some basic information on the structural requirements for receptor binding and activation.

Synthesis of enzymatically resistant nociceptin-related peptides containing a carbamic acid residue

Nociceptin, a 17-amino acid peptide (FGGFTGARKSARKLANQ, N/OFQ), is the endogenous ligand of the nociceptin/orphanin FQ (NOP) receptor. This receptor-ligand system is involved in various physiological as well as pathophysiological mechanisms, but owing to the peptidic structure, it is rapidly degraded by enzymes. The enzymatic digestion of nociceptin involves mainly aminopeptidases and yields Noc(2-17)-OH and other smaller fragments. We aimed at increasing the enzymatic stability against aminopeptidases in the case of peptide Noc(1-13)-NH(2), which possesses the minimum sequence capable of interacting with the NOP receptor. Therefore we developed a new procedure for the synthesis of peptides with the carbamic acid residue [...-NH-CH(R)-CO-NH-CO-NH-CH(Q)-CO-.]. A set of four carbamic acid-nociceptin derivatives were produced. The carbamic acid residue was incorporated into the inner part of the peptides, building on solid phase, by using a suitable dipeptide fragment with carbamic acid residue produced by a simple and efficient three-step solution phase procedure. Enzymatic stability of carbamic acid peptides was studied in the presence of aminopeptidase M (AP-M) and in rat brain membrane homogenate. The receptor-binding properties were also studied by radioligand binding assay on crude rat brain membranes and the activity of the ligands were analyzed on isolated mouse vas deferens (MVD) tissues. We found that incorporation of the carbamic acid residue into the N-terminal part of nociceptin significantly increases the resistance against AP-M. We observed the decrease of binding affinities to the NOP receptor in case of the peptides modified in the N-terminal portion. Consequently, the incorporation of the carbamic acid residue into peptides can be proposed as a promising and reasonable tool for increasing enzymatic stability, where the native molecule is less sensitive for carbamic acid residue-related structural change.