Inhibitory Effects of a Novel μ-Opioid Receptor Nonpeptide Antagonist, UD-030, on Morphine-Induced Conditioned Place Preference

Although opioids are widely used to treat moderate to severe pain, opioid addiction and the opioid overdose epidemic are becoming more serious. Although opioid receptor antagonists/partial agonists, such as naltrexone and buprenorphine, have relatively low selectivity for the μ-opioid receptor (MOP), they have been used for the management of opioid use disorder. The utility of highly selective MOP antagonists remains to be evaluated. Here, we biologically and pharmacologically evaluated a novel nonpeptide ligand, UD-030, as a selective MOP antagonist. UD-030 had more than 100-fold higher binding affinity for the human MOP (K_i = 3.1 nM) than for δ-opioid, κ-opioid, and nociceptin receptors (K_i = 1800, 460, and 1800 nM, respectively) in competitive binding assays. The [³⁵S]-GTPγS binding assay showed that UD-030 acts as a selective MOP full antagonist. The oral administration of UD-030 dose-dependently suppressed the acquisition and expression of morphine-induced conditioned place preference in C57BL/6J mice, and its effects were comparable to naltrexone. These results indicate the UD-030 may be a new candidate for the treatment of opioid use disorder, with characteristics that differ from traditional medications that are in clinical use.

High-dose naloxone, an experimental tool uncovering latent sensitisation: pharmacokinetics in humans

BACKGROUND

Naloxone, an opioid receptor antagonist, is used as a pharmacological tool to detect tonic endogenous activation of opioid receptors in experimental pain models. We describe a pharmacokinetic model linking naloxone pharmacokinetics to its main metabolite after high-dose naloxone infusion.

METHODS

Eight healthy volunteers received a three-stage stepwise high-dose i.v. naloxone infusion (total dose 3.25 mg kg^-1). Naloxone and naloxone-3-glucuronide (N3G) plasma concentrations were sampled from infusion onset to 334 min after infusion discontinuation. Pharmacokinetic analysis was performed using non-linear mixed effect models (NONMEM). The predictive performances of Dowling's and Yassen's models were evaluated, and target-controlled infusion simulations were performed.

RESULTS

Three- and two-compartment disposition models with linear elimination kinetics described the naloxone and N3G concentration time-courses, respectively. Two covariate models were developed: simple (weight proportional) and complex (with the shallow peripheral volume of distribution linearly increasing with body weight). The median prediction error (MDPE) and wobble for Dowling's model were -32.5% and 33.4%, respectively. For Yassen's model, the MDPE and wobble were 1.2% and 19.9%, respectively.

CONCLUSIONS

A parent-metabolite pharmacokinetic model was developed for naloxone and N3G after high-dose naloxone infusion. No saturable pharmacokinetics were observed. Whereas Dowling's model was inaccurate and over-predicted naloxone concentrations, Yassen's model accurately predicted naloxone pharmacokinetics. The newly developed covariate models may be used for high-dose TCI-naloxone for experimental and clinical practice.

CLINICAL TRIALS REGISTRATION

NCT01992146.

The role of oxycodone/naloxone in the management of patients with pain and opioid-induced constipation

INTRODUCTION

Common opioid adverse effects (AE) of the gastrointestinal tract include opioid-induced constipation (OIC) and opioid-induced bowel dysfunction (OIBD) with traditional laxatives being of limited efficacy, having AEs and not addressing the pathophysiology of OIC or OIBD. Targeted treatment comprises of PAMORA (peripherally acting mu-opioid receptor antagonists) and a combination of an opioid receptor agonist with its antagonist, namely prolonged-release oxycodone with prolonged-release naloxone (OXN) tablets at a fixed ratio of 2:1. Oxycodone provides analgesia, whereas naloxone prevents binding or displaces it from opioid receptors located in the gut wall. Areas covered: The authors review the role of OXN in the management of patients with pain and OIC. A literature search was performed using the search terms 'oxycodone/naloxone' and 'opioid-induced constipation' using the PubMed database up to October 2018. Expert opinion: OXN delivers analgesia comparable (or superior versus placebo and in observational studies) to oxycodone alone and other opioids with a limited or decreased disturbing effect on bowel function. OXN in daily doses of up to 160 mg/80 mg provides effective analgesia with little negative impact on bowel function. OXN may be successfully used in patients with chronic pain, to prevent or treat symptoms of OIC and OIBD.

Kappa opioid receptor antagonism: Are opioids the answer for treatment resistant depression?

Introduction:

Past trials of buprenorphine (BUP) in the treatment of major depressive disorder (MDD) have displayed favorable results, although its clinical utility was limited by the risk of abuse or physical dependence. By combining BUP with samidorphan (SAM), the euphoric high is negated by an opposing mechanism, which theoretically reduces addictive-like properties while allowing the antidepressant properties to remain. As such, the objective of this article is to analyze the results of BUP/SAM premarketing clinical trials as adjunctive treatment for treatment-resistant MDD.

Methods:

A comprehensive PubMed/MEDLINE search was conducted through November 9, 2017, using the following search terms: depression, samidorphan, buprenorphine, ALKS-5461. Additional data were obtained from Clinicaltrials.gov and resources included in the present study. All English-language clinical trials evaluating the combination of BUP/SAM in the treatment of MDD were included.

Results:

A few premarketing studies have evaluated the efficacy and safety of BUP/SAM combination as adjunctive treatment in patients with treatment-resistant MDD. The FORWARD-1 through FORWARD-5 trials concluded (1) the most effective dosing ratio of BUP/SAM to reduce abuse potential was 1:1; (2) statistically significant changes in scores from baseline on the Montgomery-Asberg Depression Rating Scale were noted for the 2 mg/2 mg dose compared with placebo; and (3) the most commonly reported adverse effects were nausea, dizziness, and fatigue.

Discussion:

Buprenorphine/samidorphan has shown favorable results for efficacy and tolerability in premarketing studies evaluating its use as adjunctive therapy for treatment-resistant MDD. Its novel mechanism targeting the opioid pathway may serve as a promising antidepressant devoid of abuse potential.

Efficacy and safety of naloxegol in patients with opioid-induced constipation and laxative-inadequate response

BACKGROUND

Treatment options for patients with opioid-induced constipation (OIC) and inadequate response to laxatives (LIR) are few.

OBJECTIVE

Assess the efficacy and safety of orally administered naloxegol in patients with prospectively confirmed OIC and LIR.

METHODS

We analyzed pooled data from two identical randomized, double-blind, placebo-controlled, Phase 3 trials of naloxegol in patients with non-cancer pain, OIC and LIR in which naloxegol (12.5 mg, n = 240; 25 mg, n = 241) or placebo (n = 239) were administered daily. We assessed the response rates, time to first post-dose laxation, spontaneous bowel movements (SBMs), OIC symptoms and patient-reported outcomes over 12 weeks.

RESULTS

OIC response rates for the naloxegol 25-mg (p < 0.001) and the 12.5-mg (p = 0.005) LIR dose groups were higher than placebo. Median times to first post-dose SBM were 7.6, 19.2 and 41.1 hours for the naloxegol 25 mg, naloxegol 12.5 mg and placebo groups, respectively. Other SBM measures, daily symptoms of OIC, and both the Patient Assessment of Constipation - Symptoms and Patient Assessment of Constipation-Quality of Life scores improved from baseline with naloxegol treatment. Changes from baseline in opioid dose, pain scores and opioid withdrawal scores were similar among treatment groups.

CONCLUSIONS

Naloxegol was efficacious, generally safe and well tolerated in the patients with OIC and LIR, while preserving opioid analgesia. ClinicalTrials.gov identifiers: NCT01309841; NCT01323790.

The effects of renal impairment on the pharmacokinetics, safety, and tolerability of naloxegol

The impact of renal impairment on the pharmacokinetics of a 25-mg oral dose of naloxegol was examined in patients with renal impairment classified as moderate, severe, or end-stage renal disease (ESRD) and compared with healthy subjects (n = 8/group). Geometric mean area under the plasma concentration-time curve (AUC) was increased in patients with moderate (1.7-fold) or severe (2.2-fold) impairment, and maximum plasma concentrations (Cmax ) were elevated in patients with moderate (1.1-fold) or severe (1.8-fold) impairment. These findings were driven by higher exposures in two patients in each of the moderate and severe impairment groups; exposures in all other patients were similar to the control group. Overall exposures in ESRD patients were similar and Cmax was 29% lower versus normal subjects. Renal impairment minimally affected other plasma pharmacokinetic parameters. As renal clearance was a minor component of total clearance, exposure to naloxegol was unaffected by the degree of renal impairment, with no correlation between either AUC or Cmax and estimated glomerular filtration rate (eGFR). Hemodialysis was an ineffective means to remove naloxegol. Naloxegol was generally well tolerated in all groups. Renal impairment could adversely affect clearance by hepatic and gut metabolism, resulting in the increased exposures observed in outliers of the moderate and severe renal impairment groups.

The effects of mild or moderate hepatic impairment on the pharmacokinetics, safety, and tolerability of naloxegol

Naloxegol is a peripherally acting µ-opioid receptor antagonist (PAMORA) in development for the treatment of opioid-induced constipation (OIC). The pharmacokinetics of a single oral 25-mg dose of naloxegol in plasma was assessed in patients with mild (Child-Pugh class A) or moderate (Child-Pugh class B) hepatic impairment and compared with healthy volunteers. Participants were matched for sex, age, and body mass index. Hepatically impaired patients exhibited a 17%-18% decrease in area under the plasma concentration versus time curve (AUC) despite similar maximum plasma concentrations (Cmax ). This was an unexpected finding given that naloxegol is primarily cleared by the hepatic route. Time to Cmax was shorter in patients with moderate impairment (0.6 hours) versus those with mild impairment (2.3 hours) or normal subjects (2.0 hours). Mean apparent terminal half-life (t½ ) was shorter in patients with mild (9.6 hours) and moderate (7.5 hours) hepatic impairment versus healthy subjects (11.3 hours). Reductions in enterohepatic recycling of naloxegol because of hepatic impairment may explain the observed decreases in AUC and t½ observed in these patients. Naloxegol was generally well tolerated, and mild or moderate hepatic impairment appeared to have minimal effect on its pharmacokinetics and safety.

A novel delta opioid receptor antagonist, SoRI-9409, produces a selective and long-lasting decrease in ethanol consumption in heavy-drinking rats

BACKGROUND

Naltrexone, a compound with high affinity for the mu opioid receptor (MOP-R) reduces alcohol consumption. SoRI-9409 is a derivative of naltrexone that has highest affinity at delta opioid receptors (DOP-Rs). We have investigated the effects of SoRI-9409 on ethanol consumption to determine the consequences of altering the naltrexone compound to a form with increased efficacy at DOP-Rs.

METHODS

Effects of the opioid receptor antagonists, SoRI-9409 (0-30 mg/kg, IP), naltrexone (0-30 mg/kg, IP), or naltrindole (0-10 mg/kg, IP) on ethanol consumption was measured in high- and low-ethanol-consuming rats with two different drinking paradigms. SoRI-9409-, naltrexone-, and naltrindole-mediated inhibition of DOP-R-stimulated [(35)S]GTP gamma S binding was measured in brain membranes prepared from high-ethanol-consuming rats. The effects of SoRI-9409 on morphine-mediated analgesia, conditioned place preference, and anxiety were also examined.

RESULTS

In high- but not low-ethanol-consuming animals, SoRI-9409 is threefold more effective and selective at reducing ethanol consumption when compared with naltrexone or naltrindole for up to 24 hours. SoRI-9409 administered daily for 28 days continuously reduced ethanol consumption, and when the administration of SoRI-9409 was terminated, the amount of ethanol consumed remained lower compared with vehicle-treated animals. Furthermore, SoRI-9409 inhibits DOP-R-stimulated [(35)S]GTP gamma S binding in brain membranes of high-ethanol-consuming rats.

CONCLUSIONS

SoRI-9409 causes selective and long-lasting reductions of ethanol consumption. This suggests that compounds that have high affinity for DOP-Rs such as SoRI-9409 might be promising candidates for development as a novel therapeutic for the treatment of alcoholism.

Tonic inhibitory control exerted by opioid peptides in the paraventricular nuclei of the hypothalamus on regional hemodynamic activity in rats

1. Systemic and regional cardiovascular changes were measured following bilateral microinjection of specific and selective opioid-receptor antagonists into the paraventricular nuclei of the hypothalamus (PVN) of awake, freely moving rats. 2. PVN microinjection of increasing doses of the specific opioid antagonist naloxone - methiodide (1 - 5.0 nmol), or a selective mu-opioid receptor antagonist, beta-funaltrexamine (0.05 - 0.5 nmol), evoked important cardiovascular changes characterized by small and transient increases in heart rate (HR) and mean arterial pressure (MAP), vasoconstriction in renal and superior mesenteric vascular beds and vasodilation in the hindquarter vascular bed. 3. No significant cardiovascular changes were observed following PVN administration of the highly selective delta-opioid-receptor antagonist, ICI 174864 (0.1 - 1 nmol), or the selective kappa-opioid-receptor antagonist, nor-binaltorphine (0.1 - 1 nmol). 4. Most of the cardiovascular responses to naloxone (3 nmol) and beta-funaltrexamine (0.5 nmol) were attenuated or abolished by an i.v. treatment with a specific vasopressin V(1) receptor antagonist. 5. These results suggest that endogenous opioid peptides and mu-type PVN opioid receptors modulate a tonically-active central depressor pathway acting on systemic and regional haemodynamic systems. Part of this influence could involve a tonic inhibition of vasopressin release.