In vivo microdialysis reveals that blockade of accumbal orexin OX2 but not OX1 receptors enhances dopamine efflux in the nucleus accumbens of freely moving rats

Treatment of Sleep, Motor and Sensory Symptoms with the Orexin Antagonist Suvorexant in Adults with Idiopathic Restless Legs Syndrome: A Randomized Double-Blind Crossover Proof-of-Concept Study

BACKGROUND AND OBJECTIVES

Current treatment guidelines for restless legs syndrome (RLS) recommend treatment be initiated with non-dopaminergic drugs. Given the potential role of orexins in the pathophysiology of RLS, we performed a pilot, proof-of-concept study to investigate the therapeutic effects of suvorexant, a dual orexin receptor antagonist (DORA), on sleep and sensory/motor symptoms in individuals with idiopathic RLS.

METHODS

This was a randomized, double-blind, crossover and placebo-controlled study. Inclusion criteria were diagnosis with idiopathic RLS, an International RLS Study Group Severity Rating Scale (IRLS) score > 15, and the absence of significant RLS symptoms before 9 pm. Following washout from any previous central nervous system (CNS)-active drugs, patients were randomized to receive either suvorexant or placebo for two consecutive 2-week treatment periods. Treatment was administered at 9 pm at a fixed dose of 10 mg/day during the first week, and 20 mg during the second week. Primary and coprimary endpoints were wake after sleep onset (WASO) and total sleep time (TST), respectively, while IRLS rating scale score, multiple suggested immobilization tests (m-SIT), and periodic limb movements (PLMs) were secondary endpoints. RLS severity was measured weekly using the IRLS and Clinical Global Improvement (CGI) scales. m-SIT were also performed between 8 pm and midnight at the end of each treatment phase and were followed by a sleep study.

RESULTS

A total of 41 participants were randomized, 40 of whom completed the study. Compared with placebo, treatment with suvorexant significantly improved RLS symptoms (according to IRLS total score, CGI, and the m-SIT), PLM during sleep, and PLM with arousal. Improvement of RLS symptoms was greater in those who had not been exposed to dopaminergic agents in the past. Sleep architecture also improved with significant changes in TST, WASO, sleep onset latency, sleep efficiency, non rapid-eye movement stage 1 (N1) %, non rapid-eye movement stage 2 (N2) %, and rapid eye movement (REM) %. Suvorexant was well tolerated in RLS, with few and mild adverse events.

CONCLUSIONS

Our results provide the first proof of evidence of the therapeutic efficacy of DORAs in improving sleep and sensory and motor symptoms in RLS. Given orexin's role in pain and sensory processing, potential mechanisms of action are discussed.

CLASSIFICATION OF EVIDENCE

The study provides class II evidence supporting the therapeutic efficacy of suvorexant in patients with RLS with sleep disturbance.

TRIAL REGISTRATION

EudraCT#: 2017-004580-12.

Abuse potential assessment of the dual orexin receptor antagonist daridorexant in rats

BACKGROUND

Drugs that act on the central nervous system (CNS) and have sedative effects can lead to abuse in humans. New CNS-active drugs often require evaluation of their abuse potential in dedicated animal models before marketing approval. Daridorexant is a new dual orexin receptor antagonist (DORA) with sleep-promoting properties in animals and humans. It was approved in 2022 in the United States and Europe for the treatment of insomnia disorder.

AIMS

Nonclinical evaluation of abuse potential of daridorexant using three specific rat models assessing reinforcement, interoception, and withdrawal.

METHODS

Reinforcing effects of daridorexant were assessed in an operant rat model of intravenous drug self-administration. Similarity of interoceptive effects to those of the commonly used sleep medication zolpidem was tested in an operant drug discrimination task. Withdrawal signs indicative of physical dependence were evaluated upon sudden termination of chronic daridorexant treatment. Rat experiments were conducted at a dose range resulting in daridorexant plasma concentrations equaling or exceeding those achieved at the clinically recommended dose of 50 mg in humans.

RESULTS

Daridorexant had no reinforcing effects, was dissimilar to zolpidem in the drug discrimination task, and did not induce any withdrawal-related signs upon treatment discontinuation that would be indicative of physical dependence.

OUTCOMES

Daridorexant showed no signs of abuse or dependence potential in rats. Our data indicate that daridorexant, like other DORAs, has a low potential for abuse in humans.