Pain and RFamides

Opioid adjuvant strategy: improving opioid effectiveness

Future Medicinal Chemistry, 2016, 8(3), 339-354

Opioid analgesics continue to be the mainstay of pharmacologic treatment of moderate to severe pain. Many patients, particularly those suffering from chronic pain, require chronic high-dose analgesic therapy. Achieving clinical efficacy and tolerability of such treatment regimens is hampered by the appearance of opioid-induced side effects such as tolerance, hyperalgesia and withdrawal syndrome. Among the therapeutic options to improve the opioid effectiveness, this current review focuses on strategies combining opioids to other drugs that can modulate opioid-mediated effects. We will discuss about experimental evidences reported for several potential opioid adjuvants, including N-methyl-d-aspartate receptor antagonists, 5-HT7 agonists, sigma-1 antagonists, I2-R ligands, cholecystokinin antagonists, neuropeptide FF-R antagonists and toll-like receptor 4 antagonists.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

Pharmacology & Therapeutics, 2016, 160, 84-132

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Effects of systematic N-terminus deletions and benzoylations of endogenous RF-amide peptides on NPFF1R, NPFF2R, GPR10, GPR54 and GPR103

 Peptides, 2016, 71, 156-161

 Mammalian RF-amide peptides including RF-amide-related peptides-1 and -3, neuropeptides AF and FF, Prolactin releasing peptides, Kisspeptins and RFa peptides are currently considered endogenous peptides for the GPCRs NPFF1R, NPFF2R, GPR10, GPR54 and GPR103, respectively. While NPFF1R and NPFF2R displayed high affinity for all the RF-amide peptides, GPR10, GPR54 and GPR103 only bind their cognate ligands. Through a systematic and sequential N-terminus deletion and benzoylation of either RF-amide neuropeptide (RFRP-3, NPFF, Kp-10, PrRP20, and 26RFa), we report the corresponding impact on affinity and activity towards all the RF-amide receptors (NPFF1R, NPFF2R, GPR10, GPR54 and GPR103). Our results highlight the difficulty to develop selective peptide ligands for GPR10, GPR54 or GPR103 without a modification of the C-terminus RF-amide signature, but open the door to the design of new RF-amide peptides acting as agonist for one receptor and antagonist for another one.

Development of a Peptidomimetic Antagonist of Neuropeptide FF Receptors for the Prevention of Opioid-Induced Hyperalgesia, modulate nociception and morphine analgesia via NPFF receptors

ACS Chemical Neuroscience, 2015, 6(3), 438-445

Through the development of a new class of unnatural ornithine derivatives as bioisosteres of arginine, we have designed an orally active peptidomimetic antagonist of neuropeptide FF receptors (NPFFR). Systemic low-dose administration of this compound to rats blocked opioid-induced hyperalgesia, without any apparent side-effects. Interestingly, we also observed that this compound potentiated opioid-induced analgesia. This unnatural ornithine derivative provides a novel therapeutic approach for both improving analgesia and reducing hyperalgesia induced by opioids in patients being treated for chronic pain.

Graphical abstract

ACS Editor's choice ACS Editors' Choice

Effects of systematic N-terminus deletions and benzoylations of endogenous RF-amide peptides on NPFF1R, NPFF2R, GPR10, GPR54 and GPR103

Peptides, 2015, 71, 156-161

Mammalian RF-amide peptides including RF-amide-related peptides-1 and -3,neuropeptides AF and FF, Prolactin releasing peptides, Kisspeptins and RFa peptides are currently considered endogenous peptides for the GPCRs NPFF1R, NPFF2R, GPR10, GPR54 and GPR103, respectively. While NPFF1R and NPFF2R displayed high affinity for all the RF-amide peptides, GPR10, GPR54 and GPR103 only bind their cognate ligands. Through a systematic and sequential N-terminus deletion and benzoylation of either RF-amide neuropeptide (RFRP-3, NPFF, Kp-10, PrRP20, and 26RFa), we report the corresponding impact on affinity and activity towards all the RF-amide receptors (NPFF1R, NPFF2R, GPR10, GPR54 and GPR103). Our results highlight the difficulty to develop selective peptide ligands for GPR10, GPR54 or GPR103 without a modification of the C-terminus RF-amide signature, but open the door to the design of new RF-amide peptides acting as agonist for one receptor andantagonist for another one.

 

Neuropeptide FF receptors as novel targets for limbic seizure attenuation

Neuropharmacology, 2015, 95, 415-423

Neuropeptide Y (NPY) is a well established anticonvulsant and first-in-class antiepilepticneuropeptide. In this study, the controversial role of NPY1 receptors in epilepsy was reassessed by testing two highly selective NPY1 receptor ligands and a mixed NPY1/NPFF receptor antagonist BIBP3226 in a rat model for limbic seizures. While BIBP3226 significantly attenuated the pilocarpine-induced seizures, neither of the highly selective NPY1 receptor ligands altered the seizure severity. Administration of the NPFF1/NPFF2 receptor antagonist RF9 also significantly attenuated limbic seizure activity. To further prove the involvement of NPFF receptors in these seizure-modulating effects, low and high affinity antagonists for the NPFF receptors were tested. We observed that the low affinity ligand failed to exhibit anticonvulsant properties while the two high affinity ligands significantly attenuated the seizures. Continuous NPFF1receptor agonist administration also inhibited limbic seizures whereas bolus administration of the NPFF1 receptor agonist was without effect. This suggests that continuous agonist perfusion could result in NPFF1 receptor desensitization and mimic NPFF1 receptor antagonist administration. Our data unveil for the first time the involvement of the NPFF system in the management of limbic seizures.

Neuropeptide FF and prolactin-releasing peptide decrease cortical excitability through activation of NPFF receptors

Epilepsia, 2015, 56(3), 489-498

Objective
Drugs with a novel mechanism of action are needed to reduce the number of people with epilepsy that are refractory to treatment. Increasing attention is paid to neuropeptide systems and several anticonvulsant neuropeptides have already been described, such as galanin, ghrelin, and neuropeptide Y (NPY). Many others, however, have not been investigated for their ability to affect epileptic seizures. In this study, the potential anticonvulsant activities of three members of the RF-amide neuropeptide family, neuropeptide FF (NPFF), prolactin-releasing peptide (PrRP), and kisspeptin (Kp) and other receptor ligands (NPFF1/2R, GPR10, and GRP54, respectively) were tested in the motor cortex stimulation model.
Methods
A train of pulses with increasing intensity (0–10 mA over 150 s, 50 Hz, pulse width 2 msec) was delivered to the motor cortex of rats. The threshold intensity for eliciting a motor response (i.e., motor threshold) was determined through behavioral observation and used as a measure for cortical excitability. The threshold was determined before, during, and after the intracerebroventricular (i.c.v.) administration of various NPFF1/2R, GPR10, and GPR54 receptor ligands.
Results
NPFF and PrRP significantly increased the motor threshold by a maximum of 143 ± 27 and 83 ± 13 μA, respectively, for the doses of 1 nmol/h (p < 0.05). The increase of motor threshold by NPFF and PrRP was prevented by pretreatment and co-treatment with the NPFF1/2R antagonist RF9. Pretreatment with a selective NPFF1R antagonist also prevented the threshold increase induced by NPFF. Kp did not increase motor threshold.
Significance
Intracerebroventricular infusion of NPFF or PrRP decreases cortical excitability in rats through activation of NPFFRs. Furthermore, the NPFF1R is required for the NPFF-induced decrease in cortical excitability.

Endogenous mammalian RF-amide peptides, including PrRP, kisspeptin and 26RFa, modulate nociception and morphine analgesia via NPFF receptors

Neuropharmacology, 2013, 75, 164-171

Mammalian RF-amide peptides are encoded by five different genes and act through five different G protein-coupled receptors. RF-amide-related peptides-1 and -3, neuropeptides AF and FF, Prolactin releasing peptides, Kisspeptins and RFa peptides are currently considered endogenous peptides for NPFF1, NPFF2, GPR10, GPR54 and GPR103 receptors, respectively. However, several studies suggest that the selectivity of these peptides for their receptors is low and indicate that expression patterns for receptors and their corresponding ligands only partially overlap. In this study, we took advantage of the cloning of the five human RF-amide receptors to systematically examine their affinity for and their activation by all human RF-amide peptides. Binding experiments, performed on membranes from CHO cells expressing GPR10, GPR54 and GPR103 receptors, confirmed their high affinity and remarkable selectivity for their cognate ligands. Conversely, NPFF1 and NPFF2 receptors displayed high affinity for all RF-amide peptides. Moreover, GTPγS and cAMP experiments showed that almost all RF-amide peptides efficiently activate NPFF1 and NPFF2 receptors. As NPFF is known to modulate morphine analgesia, we undertook a systematic analysis in mice of the hyperalgesic and anti morphine-induced analgesic effects of a representative set of endogenous RF-amide peptides. All of them induced hyperalgesia and/or prevented morphine analgesia following intracerebroventricular administration. Importantly, these effects were prevented by administration of RF9, a highly selective NPFF1/NPFF2 antagonist. Altogether, our results show that all endogenous RF-amide peptides display pain-modulating properties and point to NPFF receptors as essential players for these effects.

Development of sub-nanomolar dipeptidic ligands of neuropeptide FF receptors

Bioorganic & Medicinal Chemistry Letters 2012, 22, 7471-7474

Based on our earlier reported neuropeptide FF receptors antagonist (RF9), we carried out an extensive structural exploration of the N-terminus part of the amidated dipeptide Arg-Phe-NH2 in order to establish a structure-activity relationships (SAR) study towards both NPFF receptor subtypes. This SAR led to the discovery of dipeptides (12, 35) with subnanomolar affinities towards NPFF1 receptor subtype, similar to endogenous ligand NPVF. More particularly, compound 12 exhibited a potent in vivo preventive effect on opioid-induced hyperalgesia at low dose. The significant selectivity of 12 toward NPFF1-R indicates that this receptor subtype may play a critical role in the anti-opioid activity of NPFF-like peptides.

Graphical abstract : Development of sub-nanomolar dipeptidic ligands of neuropeptide FF receptors

Involvement of neuropeptide FF receptors in neuroadaptive responses to acute and chronic opiate treatments

British Journal of Pharmacology 2012, 165, 424-435

BACKGROUND AND PURPOSE
Opiates remain the most effective compounds for alleviating severe pain across a wide range of conditions. However, their use is associated with significant side effects. Neuropeptide FF (NPFF) receptors have been implicated in several opiate-induced neuroadaptive changes including the development of tolerance. In this study, we investigated the consequences of NPFF receptor blockade on acute and chronic stimulation of opioid receptors in mice by using RF9, a potent and selective antagonist of NPFF receptors that can be administered systemically.
EXPERIMENTAL APPROACH
The effects of RF9 were investigated on opioid pharmacological responses including locomotor activity, antinociception, opioid-induced hyperalgesia, rewarding properties and physical dependence.
KEY RESULTS
RF9 had no effect on morphine-induced horizontal hyperlocomotion and slightly attenuated the decrease induced in vertical activity. Furthermore, RF9 dose-dependently blocked the long-lasting hyperalgesia produced by either acute fentanyl or chronic morphine administration. RF9 also potentiated opiate early analgesic effects and prevented the development of morphine tolerance. Finally, RF9 increased morphine-induced conditioned place preference without producing any rewarding effect by itself and decreased naltrexone-precipitated withdrawal syndrome following chronic morphine treatment.
CONCLUSION AND IMPLICATIONS
The NPFF system is involved in the development of two major undesirable effects: tolerance and dependence, which are clinically associated with prolonged exposure to opiates. Our findings suggest that NPFF receptors are interesting therapeutic targets to improve the analgesic efficacy of opiates by limiting the development of tolerance, and for the treatment of opioid dependence.