The Quest for the Best Dual Orexin Receptor Antagonist (Daridorexant) for the Treatment of Insomnia Disorders

Discovery of IDOR-1117-1680, a dual orexin receptor antagonist with fast onset and short duration of action for the treatment of insomnia

We describe the optimization of 2-acyl-1-biarylmethylpyrazolidines, a novel class of dual orexin receptor antagonists (DORAs) designed for the treatment of sleep disorders requiring a rapid onset (<30 min) and a short duration of action (2-4 h). Building on the previously identified lead compound DORA 4, our optimization program yielded several potent pyrazolidine DORAs with carefully tailored in vitro physicochemical and DMPK (drug, metabolism and pharmacokinetics) properties. In vivo studies in animals, combined with pharmacokinetic-pharmacodynamic (PK-PD) simulations, demonstrated that DORA 31 and DORA (R)-38 effectively induced sleep in dogs and met the in silico predicted requirements for rapid onset and short duration in humans. Further analysis of their covalent binding potential in human hepatocytes prioritized DORA 31 as the preferred molecule for additional safety and biopharmaceutical evaluation. In this report we summarize and present the results of all studies that supported the selection of DORA 31 (IDOR-1117-1680) as a preclinical development candidate.

Effects of daridorexant on rest/wake activity patterns and drinking in adult rats exposed to chronic ethanol vapor in adolescence

Disturbance in sleep and activity rhythms are significant health risks associated with alcohol use during adolescence. Many investigators support the theory of a reciprocal relationship between disrupted circadian rhythms, sleep patterns, and alcohol usage. However, in human studies it is difficult to disentangle other factors (i.e. lifestyle, psychiatric, genetic) when determining what is causal in the relationship between substance use and sleep/activity disruptions. To this end, we used an animal model of adolescent alcohol exposure whereby male and female Wistar rats are exposed to 5 weeks of intermittent alcohol vapor during adolescence (P22-P57). Five days after ethanol vapor rats were allowed to select to drink alcohol or water in a two-bottle choice procedure for a period of 5 h, 4 days a week for 6 weeks. Activity data was collected using a "Fitbit-like" device during vapor exposure, during acute withdrawal, and after 3 weeks of protracted withdrawal. Significant changes in rest/wake activity and circadian measures were seen during 24-h withdrawal and after 3 weeks of withdrawal. Four weeks following withdrawal, the effects of the dual orexin antagonist, Daridorexant, (DAX 30 mg, 100 mg, or vehicle control), on alcohol drinking and rest and activity rhythms were assessed over a 24 h period. Both daridorexant doses led to changes in circadian measures and rest/wake activity patterns. These results showed that daridorexant reduced activity, but it did not improve rest quality as measured by the mean inactive episode duration and inactive fragmentation ratio. Additionally, we did not find a significant difference in drinking behavior in animals treated with the orexin antagonist. Thus, it appears that data from this animal model do not support the use of this drug to improve adolescent alcohol-induced sleep disturbance and/or to decrease alcohol drinking.

Dual orexin receptor antagonists as promising therapeutics for Alzheimer's disease

We examine the relationship between sleep, glymphatics and Alzheimer's disease (AD), and recent work questioning glymphatic clearance during sleep. We highlight a need for understanding glymphatic and/or other mechanism of clearance during sleep, and review glymphatic flow measurement methods. Further, we explore dual orexin receptor antagonists (DORAs) potential to mitigate AD sleep disturbances and enhance clearance. Further research could elucidate a linkage between DORAs, improved sleep and reducing AD pathophysiology.

The potential use of daridorexant in eating disorders: beyond the treatment of insomnia?

A strong interplay exists between sleep and dietary habits, and sleep disturbances have been repeatedly documented in individuals with eating disorders (EDs). The orexin system - implicated in sleep regulation, energy homeostasis, and food reward - may represent a mechanist link between sleep alterations and disordered eating behaviors. Daridorexant is a dual orexin receptor antagonist (DORA) recently approved for the treatment of insomnia, with demonstrated efficacy and tolerability. Owing to its action on orexin neurons, the compound represents an intriguing option for addressing both sleep-related and core symptoms of EDs. By inhibiting motor hyperactivity, daridorexant may reduce excessive physical exercise in individuals with anorexia nervosa (AN) restricting type. Additionally, the compound may exert anti-binge effects, suggesting broad applicability in binge ED, bulimia nervosa, and binge/purging AN. In this framework, daridorexant emerges as a promising therapeutic option, offering a multifaceted approach to improving circadian rhythms, energy balance, and overall quality of life in individuals with diverse ED subtypes.

Clinical safety of daridorexant in insomnia treatment: Analysis of FDA adverse event reports

OBJECTIVE

Daridorexant, a novel dual orexin receptor antagonist, was approved by the FDA in 2022 for the treatment of insomnia in adults. The aim of this study is to delve into the adverse events (AEs) of daridorexant by analyzing data from the FAERS database, to assess its safety and effectiveness in clinical applications.

METHODS

This study selected data from the FAERS database from the first quarter of 2022 to the third quarter of 2023. Various data analysis methods were used, including the Reporting Odds Ratio (ROR), Proportional Reporting Ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), and Empirical Bayesian Geometric Mean (EBGM), to assess AEs related to daridorexant.

RESULTS

The study analyzed a total of 2,624,030 AE reports, of which 1318 were related to daridorexant. It identified 59 preferred terms (PTs) involving 23 system organ classes (SOCs). Signal mining identified new potential AEs related to daridorexant, including sleep-related psychiatric symptoms (nightmare, abnormal dreams, sleep terror, etc.), emotional and perceptual abnormalities (hallucination, depression, agitation), physiological and behavioral responses (palpitations, dry mouth, energy increased, etc.), suicide risk (suicidal ideation, intentional overdose), and other special concern AEs (tachyphrenia, sleep-related eating disorder, hypersensitivity).

CONCLUSION

Although some new potential AEs have been identified, these findings need further verification in broader datasets and long-term studies due to limitations in data sources and analysis methods. Future research should comprehensively assess the safety and effectiveness of daridorexant, providing more accurate guidance for medical professionals in the treatment of insomnia.

Discovery, synthesis and SAR of 2-acyl-1-biarylmethyl pyrazolidines, dual orexin receptor antagonists designed as fast and short-acting sleeping drugs

Dual orexin receptor antagonists (DORAs) are approved for the treatment of sleep onset and/or sleep maintenance insomnia. In the present disclosure, we report the discovery of a new class of DORAs designed to treat sleep disorders requiring a fast onset and a short duration of action (<4 h). We used early human pharmacokinetic-pharmacodynamic (PK-PD) predictions and in vivo experiments to identify DORAs eliciting this specific hypnotic profile. A high-throughput screening campaign revealed hits based on a rarely precedented tricyclic pyrazolidine scaffold. After unsuccessful structure-activity-relationship (SAR) studies on this hit series, a scaffold hopping exercise, aimed at reducing the molecular complexity of the tricyclic scaffold, resulted in the discovery of the 2-acyl-1-biarylmethylpyrazolidine series. SAR studies on this achiral series gave rise to the lead compound DORA 42. In vitro and in vivo parameters of DORA 42, and its PK-PD simulation for human use are detailed.

Discovery of Nivasorexant (ACT-539313): The First Selective Orexin-1 Receptor Antagonist (SO1RA) Investigated in Clinical Trials

The orexin system consists of two neuropeptides (orexins A and B) and two receptors (OX1 and OX2). Selective OX1 receptor antagonists (SO1RA) are gaining interest for their potential use in the treatment of CNS disorders, including substance abuse, eating, obsessive compulsive, or anxiety disorders. While blocking OX2 reduces wakefulness, the expected advantage of selectively antagonizing OX1 is the ability to achieve clinical efficacy without the promotion of sleep. Herein we report our discovery efforts starting from a dual orexin receptor antagonist and describe a serendipitous finding that triggered a medicinal chemistry program that culminated in the identification of the potent SO1RA ACT-539313. Efficacy in a rat model of schedule-induced polydipsia supported the decision to select the compound as a preclinical candidate. Nivasorexant (20) represents the first SO1RA to enter clinical development and completed a first proof of concept phase II clinical trial in binge eating disorder in 2022.

Pyrazole derivatives as selective orexin-2 receptor antagonists (2-SORA): synthesis, structure-activity-relationship, and sleep-promoting properties in rats

Selective orexin 2 receptor antagonists (2-SORA) such as seltorexant (15) are in clinical development for the treatment of insomnia and other conditions such as depression. Herein, we report our structure-activity-relationship (SAR) optimization efforts starting from an HTS hit (1) (N-(1-((5-acetylfuran-2-yl)methyl)-1H-pyrazol-4-yl)-5-(m-tolyl)oxazole-4-carboxamide) that was derived from an unrelated in-house GPCR-agonist program. Medicinal chemistry efforts focused on the optimization of orexin 2 receptor (OX2R) antagonistic activity, stability in liver microsomes, time dependent CYP3A4 inhibition, and aqueous solubility. Compounds were assessed for their brain-penetrating potential in in vivo experiments to select the most promising compounds for our in vivo sleep model. Our lead optimization efforts led to the discovery of the potent, brain penetrating and orally active, 2-SORA (N-(1-(2-(5-methoxy-1H-pyrrolo[3,2-b]pyridin-3-yl)ethyl)-1H-pyrazol-4-yl)-5-(m-tolyl)oxazole-4-carboxamide) 43 with efficacy in a sleep model in rats comparable to 15.

Targeting orexin receptors: Recent advances in the development of subtype selective or dual ligands for the treatment of neuropsychiatric disorders

Orexin-A and orexin-B, also named hypocretin-1 and hypocretin-2, are two hypothalamic neuropeptides highly conserved across mammalian species. Their effects are mediated by two distinct G protein-coupled receptors, namely orexin receptor type 1 (OX1-R) and type 2 (OX2-R), which share 64% amino acid identity. Given the wide expression of OX-Rs in different central nervous system and peripheral areas and the several pathophysiological functions in which they are involved, including sleep-wake cycle regulation (mainly mediated by OX2-R), emotion, panic-like behaviors, anxiety/stress, food intake, and energy homeostasis (mainly mediated by OX1-R), both subtypes represent targets of interest for many structure-activity relationship (SAR) campaigns carried out by pharmaceutical companies and academies. However, before 2017 the research was predominantly directed towards dual-orexin ligands, and limited chemotypes were investigated. Analytical characterizations, including resolved structures for both OX1-R and OX2-R in complex with agonists and antagonists, have improved the understanding of the molecular basis of receptor recognition and are assets for medicinal chemists in the design of subtype-selective ligands. This review is focused on the medicinal chemistry aspects of small molecules acting as dual or subtype selective OX1-R/OX2-R agonists and antagonists belonging to different chemotypes and developed in the last years, including radiolabeled OX-R ligands for molecular imaging. Moreover, the pharmacological effects of the most studied ligands in different neuropsychiatric diseases, such as sleep, mood, substance use, and eating disorders, as well as pain, have been discussed. Poly-pharmacology applications and multitarget ligands have also been considered.

The Present and Future of Synthetic Orexin Receptor Agonists

The neuropeptide orexin/hypocretin plays a crucial role in various physiological processes, including the regulation of sleep/wakefulness, appetite, emotion and the reward system. Dysregulation of orexin signaling has been implicated in hypersomnia, especially in narcolepsy, which is a chronic neurological disorder characterized by excessive daytime sleepiness (EDS), sudden loss of muscle tone while awake (cataplexy), sleep paralysis, and hallucinations. Small-molecule orexin receptor agonists have emerged as promising therapeutics for these disorders, and significant progress has been made in this field in the past decade. This review summarizes recent advances in the design and synthesis of orexin receptor agonists, with a focus on peptidic and small-molecule OX2R-selective, dual, and OX1R-selective agonists. The review discusses the key structural features and pharmacological properties of these agonists, as well as their potential therapeutic applications. DATA AVAILABILITY: No data was used for the research described in the article.

Number, Duration, and Distribution of Wake Bouts in Patients with Insomnia Disorder: Effect of Daridorexant and Zolpidem

BACKGROUND

Daridorexant, a dual orexin receptor antagonist approved in early 2022, reduces wake after sleep onset without reducing the number of awakenings in patients with insomnia. The objective of this post hoc analysis was to explore the effect of daridorexant on the number, duration, and distribution of night-time wake bouts, and their correlation with daytime functioning.

METHODS

Adults with insomnia disorder were randomized 1:1:1:1:1:1 to placebo, zolpidem 10 mg, or daridorexant 5, 10, 25, or 50 mg in a phase II dose-finding study, and 1:1:1 to placebo or daridorexant 25 or 50 mg in a pivotal phase III study. We analyzed polysomnography data for daridorexant 25 and 50 mg, zolpidem 10 mg, and placebo groups. Polysomnography was conducted at baseline, then on Days 1/2, 15/16, and 28/29 in the phase II study, and Months 1 and 3 in the phase III study. The number, duration, and distribution of wake bouts (≥ 0.5 min) were assessed.

RESULTS

Data from 1111 patients (phase II study: daridorexant 50 mg [n = 61], zolpidem 10 mg [n = 60], placebo [n = 60]; phase III study: daridorexant 25 mg [n = 310], daridorexant 50 mg [n = 310], placebo [n = 310]) were analyzed. Long wake bouts were defined as > 6 min. Compared with placebo, daridorexant 50 mg reduced overall wake time (p < 0.05; all time points, both studies), the odds of experiencing long wake bouts (p < 0.001; Months 1 and 3, phase III study), and the cumulative duration of long wake bouts (p < 0.01; all time points, both studies). Reductions in long wake bouts were sustained through the second half of the night and correlated with improvements in daytime functioning. An increase in the cumulative duration of short wake bouts was observed with daridorexant 50 mg (p < 0.01 vs placebo, Months 1 and 3, phase III study); this was uncorrelated with daytime functioning.

CONCLUSION

Daridorexant reduced the number and duration of longer wake bouts throughout the night compared with placebo, corresponding with improved daytime functioning.

CLINICAL TRIALS

Clinicaltrials.gov NCT02839200 (registered July 20, 2016), NCT03545191 (registered June 4, 2018).

Daridorexant, a Recently Approved Dual Orexin Receptor Antagonists (DORA) in Treatment of Insomnia

Insomnia is one of the major challenges in medical science nowadays as it leads to great socio-economic burden by impairing daytime function as well as the development of exhaustion, depression, and memory disturbance in affected individuals. Several important classes of drugs have been tried, including the BZDs and non-BZD hypnotics. Available drugs to combat this disease have the limitations of abuse potential, tolerance, and cognitive impairment. In some instances, withdrawal symptoms have been observed upon the abrupt cessation of those drugs. The Orexin system has been very recently targeted as a therapeutic option to overcome those limitations. Treatment of insomnia with Daridorexant as a Dual Orexin Receptor Antagonist (DORA) has been evaluated in several preclinical and clinical studies. Available information obtained from those studies has shown a promising future for this drug in the management of insomnia. Beyond its effectiveness in insomnia, it has been successfully used in patients suffering from obstructive sleep apnoea, chronic obstructed airway disease (COAD), Alzheimer's disease (AD), hypertension, and cardiovascular disorders. Larger studies need to address the safety issues as well as obtain robust pharmacovigilance information to safeguard the risk-benefit aspect of this drug in insomniac adults.

New Approved Drugs Appearing in the Pharmaceutical Market in 2022 Featuring Fragments of Tailor-Made Amino Acids and Fluorine

The strategic fluorination of oxidatively vulnerable sites in bioactive compounds is a relatively recent, widely used approach allowing us to modulate the stability, bio-absorption, and overall efficiency of pharmaceutical drugs. On the other hand, natural and tailor-made amino acids are traditionally used as basic scaffolds for the development of bioactive molecules. The main goal of this review article is to emphasize these general trends featured in recently approved pharmaceutical drugs.

The Metabolism of the Dual Orexin Receptor Antagonist Daridorexant

Daridorexant is a dual orexin receptor antagonist developed for the treatment of insomnia disorder and has shown improvement in sleep outcomes and daytime functioning. The present work describes its biotransformation pathways in vitro and in vivo and provides a cross-species comparison between the animal species used in preclinical safety assessments and man.Daridorexant clearance is driven by metabolism along seven distinct pathways. Metabolic profiles were characterized by downstream products while primary metabolic products were of minor importance. The metabolic pattern differed between rodent species, with the rat reflecting the human pattern better than the mouse.In rodents, daridorexant is mostly excreted via the bile after extensive metabolism while urinary excretion was negligible in the rat. Only traces of parent drug were detected in urine, bile or faeces.Daridorexant has three major metabolites which are well covered in these preclinical safety species. All of them retain some residual affinity towards orexin receptors. However, none of these is considered to contribute to the pharmacological effect of daridorexant as their active concentrations in human brain are too low.

Long-Term Safety and Tolerability of Daridorexant in Patients with Insomnia Disorder

BACKGROUND AND OBJECTIVE

Daridorexant is a dual orexin receptor antagonist for the treatment of insomnia. In two phase III, 12-week studies in patients with insomnia disorder, daridorexant improved sleep and daytime functioning while maintaining a favorable safety profile. The objective of this 40-week extension study was to assess the long-term safety and tolerability of daridorexant.

METHODS

Adults with insomnia disorder who completed the 12-week studies were invited to enroll in this double-blind extension study. Patients originally randomised to daridorexant (10 mg/25 mg/50 mg) remained on their respective treatments; patients randomised to placebo were re-randomised to daridorexant 25 mg or placebo. The 40-week treatment period was followed by a 7-day placebo run-out. The primary objective was to assess safety/tolerability. Exploratory objectives were to evaluate the efficacy of daridorexant on sleep (self-reported total sleep time) and daytime functioning (Insomnia Daytime Symptoms and Impacts Questionnaire).

RESULTS

In total, 804 patients were enrolled in the study, of whom 801 received at least one dose of the study treatment and 550 patients (68.4%) completed the study. Overall incidence of treatment-emergent adverse events was similar across groups (35-40%). Daridorexant did not induce next-morning sleepiness and no withdrawal-related symptoms or rebound were observed after treatment discontinuation. Improvements in sleep and daytime functioning were maintained through to the end of the study and were most pronounced with daridorexant 50 mg. Daridorexant 50 mg, compared with placebo, increased self-reported total sleep time by a least-squares mean of 20.4 (95% confidence interval [CI] 4.2, 36.5), 15.8 (95% CI - 0.8, 32.5) and 17.8 (95% CI - 0.4, 35.9) minutes and decreased (i.e., improved) Insomnia Daytime Symptoms and Impacts Questionnaire total scores by a least-squares mean of - 9.3 (95% CI - 15.1, - 3.6), - 9.5 (95% CI - 15.4, - 3.5) and - 9.1 (95% CI - 15.6, - 2.7), at weeks 12, 24 and 36 of the extension study, respectively.

CONCLUSIONS

Treatment with daridorexant, for up to 12 months, was generally safe and well tolerated. Exploratory efficacy analyses suggest that the sustained improvements in sleep and daytime functioning with daridorexant 50 mg support its use for long-term treatment of insomnia disorder, without concerns of new safety signals.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov (NCT03679884) [first posted: 21 September, 2018], https://clinicaltrials.gov/ct2/show/NCT03679884 .

Safety and efficacy of daridorexant in the treatment of insomnia: a systematic review and meta-analysis of randomized controlled trials

Daridorexant is a novel dual orexin receptor antagonist used in treating insomnia disorder. Daridorexant improves sleep quality without impairing daytime functioning. We assess the safety and efficacy of this novel drug in the treatment of insomnia. We performed a systematic search for electronic databases in SCOPUS, PubMed, Web of Science and the Cochrane library. Seven randomized controlled trials were included in this review, with 2425 participants enrolled. Daridorexant was superior to placebo in reducing wake time after sleep onset (MD = -13.26; 95% CI, -15.48 to -11.03; P < 0.00001), latency to persistent sleep (MD = -7.23; 95% CI, -9.60 to -4.85; P < 0.00001), with increasing the total sleep time (MD = 14.80; 95% CI, 11.18-18.42; P < 0.00001) and subjective total sleep time (MD = 14.80; 95% CI, 11.18-18.42], P < 0.00001). The 25 mg and 50 mg were the most officious doses. Treatment with daridorexant has resulted in a slightly higher incidence of adverse events [risk ratio (RR) = 1.19; 95% CI, 1.05-1.35;, P = 0.005], specifically somnolence (RR = 1.19; 95% CI, 1.13-3.23; P = 0.005) and fatigue (RR = 2.01; 95% CI, 1.21-3.36; P = 0.007). Daridorexant is superior to placebo in improving sleep quality. However, the drug resulted in a slightly higher incidence of adverse events, including somnolence and fatigue.

Orexin Receptor Antagonists and Insomnia

PURPOSE OF REVIEW

We review recent evidence on the use of orexin receptor antagonists (ORAs) for treating insomnia. We evaluate studies on five dual ORAs and one selective ORA.

RECENT FINDINGS

Research on suvorexant in recent years gradually focus on comorbid insomnia, while lemborexant and daridorexant were still being validated in primary insomnia. Almorexant is now mainly used as a commercial specific inhibitor of the orexin system in animal studies due to safety issues. Although filorexant has also shown a certain sleep-promoting effect, there are few clinical or experimental studies on sleep-related aspects of filorexant in recent years. As for selective ORAs, orexin receptor 2 antagonist seltorexant still has not yet reached phase 3. High-quality clinical trials in insomnia populations are needed which directly compare authorized ORAs and investigate non-approved ORAs, the use of ORAs in comorbid insomnia, and the orexin signaling system pathophysiology in insomnia.

A Comprehensive Review of Daridorexant, a Dual-Orexin Receptor Antagonist as New Approach for the Treatment of Insomnia

Insomnia affects 4.4-4.8% of the world's population, but because the effect of hypnotic drugs is limited and may cause harmful side-effects, scientists are turning their attention to developing drugs that act on the orexin system. Daridorexant, a selective dual-orexin receptor antagonist (DORA), has exhibited promising results in both animal and human studies. Its activity was evaluated based on the physiology-based pharmacodynamic and pharmacokinetic model. The use of daridorexant is considered safe, with no clinically significant side-effects including deprivation of next-morning residual effects. In this manuscript we conducted a comprehensive review of daridorexant including pharmacodynamics, animal and human research, pharmacokinetics and safety.

Daridorexant for the Treatment of Insomnia

Purpose of Review

Insomnia is a complex sleeping disorder that affects the lives of many individuals worldwide. Insomnia often occurs in the presence of coexisting comorbidities making it a complex disorder that requires a multifactorial approach to therapy. First-line therapy is cognitive-behavioral therapy for insomnia (CBT-I). Pharmacotherapy for insomnia falls into four classes based on mechanism of action: benzodiazepine receptor agonists (BZRAs), histamine receptor antagonists, melatonin receptor agonists, and dual orexin receptor antagonists (DORAs).

Recent Findings

Daridorexant is a dual orexin type 1 and types 2 (OX1 and OX2) receptor antagonist that was recently approved by the US FDA for the treatment of adults suffering from insomnia. It was shown to be effective in reducing insomnia symptoms, increasing daytime functioning, and improving the overall quality of sleep. Daridorexant offers patients relief from insomnia while avoiding the severe side effects and dependency issues of traditional treatments like benzodiazepines and sedatives.

Summary

In this article, we review the most recent data on insomnia treatments and summarize the safety and efficacy of daridorexant in treating insomnia.

Peptidomic Approaches and Observations in Neurodegenerative Diseases

Mass spectrometry (MS), with its immense technological developments over the last two decades, has emerged as an unavoidable technique in analyzing biomolecules such as proteins and peptides. Its multiplexing capability and explorative approach make it a valuable tool for analyzing complex clinical samples concerning biomarker research and investigating pathophysiological mechanisms. Peptides regulate various biological processes, and several of them play a critical role in many disease-related pathological conditions. One important example in neurodegenerative diseases is the accumulation of amyloid-beta peptides (Aβ) in the brain of Alzheimer’s disease (AD) patients. When investigating brain function and brain-related pathologies, such as neurodegenerative diseases, cerebrospinal fluid (CSF) represents the most suitable sample because of its direct contact with the brain. In this review, we evaluate publications applying peptidomics analysis to CSF samples, focusing on neurodegenerative diseases. We describe the methodology of peptidomics analysis and give an overview of the achievements of CSF peptidomics over the years. Finally, publications reporting peptides regulated in AD are discussed.

Hypocretins (orexins): The ultimate translational neuropeptides

The hypocretins (Hcrts), also known as orexins, are two neuropeptides produced exclusively in the lateral hypothalamus. They act on two specific receptors that are widely distributed across the brain and involved in a myriad of neurophysiological functions that include sleep, arousal, feeding, reward, fear, anxiety and cognition. Hcrt cell loss in humans leads to narcolepsy with cataplexy (narcolepsy type 1), a disorder characterized by intrusions of sleep into wakefulness, demonstrating that the Hcrt system is nonredundant and essential for sleep/wake stability. The causal link between Hcrts and arousal/wakefulness stabilisation has led to the development of a new class of drugs, Hcrt receptor antagonists to treat insomnia, based on the assumption that blocking orexin-induced arousal will facilitate sleep. This has been clinically validated: currently, two Hcrt receptor antagonists are approved to treat insomnia (suvorexant and lemborexant), with a New Drug Application recently submitted to the US Food and Drug Administration for a third drug (daridorexant). Other therapeutic applications under investigation include reduction of cravings in substance-use disorders and prevention of neurodegenerative disorders such as Alzheimer's disease, given the apparent bidirectional relationship between poor sleep and worsening of the disease. Circuit neuroscience findings suggest that the Hcrt system is a hub that integrates diverse inputs modulating arousal (e.g., circadian rhythms, metabolic status, positive and negative emotions) and conveys this information to multiple output regions. This neuronal architecture explains the wealth of physiological functions associated with Hcrts and highlights the potential of the Hcrt system as a therapeutic target for a number of disorders. We discuss present and future possible applications of drugs targeting the Hcrt system for the treatment of circuit-related neuropsychiatric and neurodegenerative conditions.

Orexin Signaling: A Complex, Multifaceted Process

The orexin system comprises two G protein-coupled receptors, OX1 and OX2 receptors (OX1R and OX2R, respectively), along with two endogenous agonists cleaved from a common precursor (prepro-orexin), orexin-A (OX-A) and orexin-B (OX-B). For the receptors, a complex array of signaling behaviors has been reported. In particular, it becomes obvious that orexin receptor coupling is very diverse and can be tissue-, cell- and context-dependent. Here, the early signal transduction interactions of the orexin receptors will be discussed in depth, with particular emphasis on the direct G protein interactions of each receptor. In doing so, it is evident that ligands, additional receptor-protein interactions and cellular environment all play important roles in the G protein coupling profiles of the orexin receptors. This has potential implications for our understanding of the orexin system's function in vivo in both central and peripheral environments, as well as the development of novel agonists, antagonists and possibly allosteric modulators targeting the orexin system.

Pharmacokinetic and pharmacodynamic interactions between daridorexant, a dual orexin receptor antagonist, and citalopram in healthy subjects

Daridorexant (ACT-541468) is a new dual orexin receptor antagonist being evaluated for the treatment of insomnia, which is a common comorbidity of depression and anxiety. Therefore, daridorexant is likely to be administered concomitantly with agents (e.g., citalopram) used to treat these disorders. In this single-centre, single-blind, randomized, placebo-controlled, sequential design Phase 1 study with the inclusion of two double-blind crossover parts, the pharmacokinetic (PK; blood sampling at regular intervals) and pharmacodynamic (PD; battery of objective and subjective PD tests performed at regular intervals) interactions between daridorexant (50 mg) and citalopram (20 mg, single dose and at steady state) as well as the safety/tolerability in healthy subjects were investigated. There were no relevant effects of citalopram (single dose/steady state) on daridorexant exposure and vice versa. PD variables measured after morning administration of daridorexant alone showed effects consistent with a sleep-promoting compound. Only co-administration of daridorexant with citalopram at steady state led to relevant changes in objective (unstable tracking) and subjective (visual analogue scale alertness and Karolinska Sleepiness Scale) PD endpoints compared to daridorexant alone. No serious or severe adverse events were reported, while no clinically relevant treatment-emergent effects on ECG parameters, clinical laboratory, or vital signs were observed. In conclusion, the co-administration of daridorexant and citalopram lead to only minor changes in PK parameters, while performance of PD assessments following co-administration were mainly driven by the expected central nervous system effects of daridorexant. Doses up to 50 mg daridorexant can be safely co-administered with citalopram.

Effect of Liver Cirrhosis on the Pharmacokinetics, Metabolism, and Tolerability of Daridorexant, A Novel Dual Orexin Receptor Antagonist

BACKGROUND AND OBJECTIVE

Daridorexant is a dual orexin receptor antagonist in clinical development for insomnia. As daridorexant is cleared mainly via cytochrome P450 (CYP) 3A4, the effect of hepatic impairment on the pharmacokinetics (PK), metabolism, and tolerability of daridorexant was evaluated. Sleep disorders are common in patients with liver cirrhosis and, therefore, sleep-promoting drugs with a better tolerability than currently available would be preferable, a premise that dual orexin receptor antagonists may fulfill.

METHODS

This was a single-dose, open-label, phase I study. Subjects with mild (Child-Pugh A, N = 8) or moderate (Child-Pugh B, N = 8) liver cirrhosis and matched healthy control subjects (N = 8) received 25 mg of daridorexant orally. Blood samples were collected for 72 h post-dose for PK assessments of daridorexant and three major metabolites.

RESULTS

Compared with healthy subjects, patients showed a decrease in total daridorexant area under the plasma concentration-time curve from zero to infinity (AUC_0-inf) and maximum plasma concentration with a geometric mean ratio (GMR, 90% confidence interval [CI]) of 0.51 (0.28-0.92) and 0.50 (0.35-0.72) in Child-Pugh A and 0.74 (0.39-1.41) and 0.42 (0.29-0.60) in Child-Pugh B patients, respectively. Furthermore, the median time to reach maximum plasma concentration was slightly delayed (1.0 h [90% CI 0.0-2.0] in Child-Pugh A patients and 0.5 h [90% CI 0.0-1.5] in Child-Pugh B patients), while for Child-Pugh B patients, a doubling in half-life was observed (GMR [90% CI]: 2.09 [1.32-3.30]). Considering the high plasma protein binding (> 99%) and a 1.9-fold to 2.3-fold increase in the unbound fraction in patients, the PK of unbound daridorexant was also assessed. Compared with healthy subjects, Child-Pugh B patients had a higher AUC_0-inf (GMR [90% CI] 1.60 [0.93-2.73]), a lower apparent plasma clearance (GMR [90% CI] 0.63 [0.37-1.07]), and the same doubling in the half-life observed for total daridorexant, whereas maximum plasma concentration and apparent volume of distribution were not different. Unbound daridorexant PK in Child-Pugh A patients did not differ from healthy subjects. In addition, the metabolic ratios (parent to metabolite), i.e., a marker of CYP 3A4 activity, of the two most abundant daridorexant metabolites were higher in patients with liver cirrhosis compared with healthy subjects. All treatment-emergent adverse events were transient and of mild or moderate intensity and no other treatment-related effects were apparent.

CONCLUSIONS

No safety issue of concern was detected following administration of 25 mg of daridorexant in the study population. Moderate liver cirrhosis causes impaired hepatic clearance of unbound daridorexant, which prolongs the half-life. A 25-mg dose of daridorexant should, therefore, not be exceeded in Child-Pugh B patients. A dose adjustment is not required in Child-Pugh A patients, while avoidance of daridorexant in patients with Child-Pugh C cirrhosis is recommended.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT03713242.

Nonclinical pharmacology of daridorexant: a new dual orexin receptor antagonist for the treatment of insomnia

Dual orexin receptor antagonists (DORAs) represent a novel type of sleep medication that provide an alternative to the traditionally used positive allosteric gamma-aminobutyric acid (GABA)-A receptor modulators. Daridorexant is a new DORA that exhibited in phase 3 trials in insomnia not only a beneficial effect on sleep variables, measured objectively and assessed subjectively, but also an improvement in daytime functioning. Daridorexant was discovered through a tailored research program aimed at identifying an optimized sleep-promoting molecule with pharmacokinetic properties appropriate for covering the whole night while avoiding next-morning residual activity at efficacious doses. By specific binding to both orexin receptors, daridorexant inhibits the actions of the wake-promoting orexin (also called hypocretin) neuropeptides. This mechanism avoids a more widespread inhibition of neuronal pathways and associated side effects that are intrinsic to positive allosteric GABA-A receptor modulators. Here, we review the general pharmacology of daridorexant, based on nonclinical pharmacology studies of daridorexant, unpublished or already described, or based on work with other DORAs. Some unique features of daridorexant will be highlighted, such as the promotion of natural and surmountable sleep, the preservation of memory and cognition, the absence of tolerance development or risk of physical dependence, and how it can benefit daytime functioning.