Catherine Roch

Recent trends in orexin research—2010 to 2015

Specific neurons in the lateral hypothalamus produce the orexin neuropeptides (orexin-A and orexin-B). The orexin-peptides are transported to areas of the brain regulating sleep-wake cycles, controlling food intake or modulating emotional states such as panic or anxiety. The orexin system, consisting of the two orexin-neuropeptides and two G-protein-coupled receptors (the orexin-1 and the orexin-2 receptor) is as well involved in reward and addictive behaviors. The review reflects on the most recent activities in the field of orexin research.

Substituted pyrrolidin-2-ones: Centrally acting orexin receptor antagonists promoting sleep. Part 2.

Starting from advanced pyrrolidin-2-one lead compounds, this novel series of small-molecule orexin receptor antagonists was further optimized by fine-tuning of the C-3 substitution at the γ-lactam ring. We discuss our design to align in vitro potency with metabolic stability and improved physicochemical/pharmacokinetic properties while avoiding P-glycoprotein-mediated efflux. These investigations led to the identification of the orally active 3-hydroxypyrrolidin-2-one 46, a potent and selective orexin-2 receptor antagonist, that achieved good brain exposure and promoted physiological sleep in rats.

Preparation, Antiepileptic Activity, and Cardiovascular Safety of Dihydropyrazoles as Brain-Penetrant T-Type Calcium Channel Blockers

A series of dihydropyrazole derivatives was developed as potent, selective, and brain-penetrating T-type calcium channel blockers. An optimized derivative, compound 6c, was advanced to in vivo studies, where it demonstrated efficacy in the WAG/Rij rat model of generalized nonconvulsive, absence-like epilepsy. Compound 6c was not efficacious in the basolateral amygdala kindling rat model of temporal lobe epilepsy, and it led to prolongation of the PR interval in ECG recordings in rodents.

The Use of Physiology-Based Pharmacokinetic and Pharmacodynamic Modeling in the Discovery of the Dual Orexin Receptor Antagonist ACT-541468

The identification of new sleep drugs poses particular challenges in drug discovery owing to disease-specific requirements such as rapid onset of action, sleep maintenance throughout major parts of the night, and absence of residual next-day effects. Robust tools to estimate drug levels in human brain are therefore key for a successful discovery program. Animal models constitute an appropriate choice for drugs without species differences in receptor pharmacology or pharmacokinetics. Translation to man becomes more challenging when interspecies differences are prominent. This report describes the discovery of the dual orexin receptor 1 and 2 (OX1 and OX2) antagonist ACT-541468 out of a class of structurally related compounds, by use of physiology-based pharmacokinetic and pharmacodynamic (PBPK-PD) modeling applied early in drug discovery. Although all drug candidates exhibited similar target receptor potencies and efficacy in a rat sleep model, they exhibited large interspecies differences in key factors determining their pharmacokinetic profile. Human PK models were built on the basis of in vitro metabolism and physicochemical data and were then used to predict the time course of OX2 receptor occupancy in brain. An active ACT-541468 dose of 25 mg was estimated on the basis of OX2 receptor occupancy thresholds of about 65% derived from clinical data for two other orexin antagonists, almorexant and suvorexant. Modeling predictions for ACT-541468 in man were largely confirmed in a single-ascending dose trial in healthy subjects. PBPK-PD modeling applied early in drug discovery, therefore, has great potential to assist in the identification of drug molecules when specific pharmacokinetic and pharmacodynamic requirements need to be met.

Discovery of Highly Potent Dual Orexin Receptor Antagonists via a Scaffold-Hopping Approach.

Starting from suvorexant (trade name Belsomra), we successfully identified interesting templates leading to potent dual orexin receptor antagonists (DORAs) via a scaffold‐hopping approach. Structure–activity relationship optimization allowed us not only to improve the antagonistic potency on both orexin 1 and orexin 2 receptors (Ox1 and Ox2, respectively), but also to increase metabolic stability in human liver microsomes (HLM), decrease time‐dependent inhibition of cytochrome P450 (CYP) 3A4, and decrease P‐glycoprotein (Pgp)‐mediated efflux. Compound 80 c [{(1S,6R)‐3‐(6,7‐difluoroquinoxalin‐2‐yl)‐3,8‐diazabicyclo[4.2.0]octan‐8‐yl}(4‐methyl‐[1,1′‐biphenyl]‐2‐yl)methanone] is a potent and selective DORA that inhibits the stimulating effects of orexin peptides OXA and OXB at both Ox1 and Ox2. In calcium‐release assays, 80 c was found to exhibit an insurmountable antagonistic profile at both Ox1 and Ox2, while displaying a sleep‐promoting effect in rat and dog models, similar to that of the benchmark compound suvorexant.

Orexin research: patent news from 2016

ABSTRACT Introduction: The orexin system consists of two G-protein-coupled receptors, orexin 1 and orexin 2 and two endogenous ligands, orexin A and orexin B . It is evolutionarily highly conserved. It is involved in the promotion of wakefulness as well as in anxiety and addictive disorders. In addition, its activation via the Ox1 receptor triggers apoptosis in several cancer cell lines. Dual orexin receptor antagonists are successfully used to treat primary insomnia. The major open questions are now related to the clinical validation of Ox1 selective antagonists. A strong rationale exists for orexin agonism in the treatment of narcolepsy with cataplexy. Areas covered: The patent applications from Thomson Reuters Integrity Database added in 2016 are summarized and discussed together with the most important findings published in the scientific literature. Expert opinion: The large number of patents shows the continuing interest in the orexin receptors as targets. The structural scope covered is narrow. Questions about novelty and inventiveness are evident. The additional information published on X-ray structures on both orexin receptors opens new ways of optimizing antagonists. It might also influence the efforts in the identification of orexin receptor agonists. Being potential treatments for narcolepsy with cataplexy.

Discovery and optimisation of 1-acyl-2-benzylpyrrolidines as potent dual orexin receptor antagonists

Starting from a thienopiperidine lead compound with high intrinsic clearance in rat and human liver microsomes and low aqueous solubility, a novel series of 1-acyl-2-benzylpyrrolidines were discovered as potent and competitive dual orexin receptor antagonists. Metabolic stability was improved to afford oral exposure, and aqueous solubility was increased by twentyfold, providing compounds suitable for preclinical evaluation. Compound 27 showed insurmountable antagonism at both orexin 1 and orexin 2 receptor subtypes and displayed a comparable sleep-promoting effect in the rat to almorexant and suvorexant.

Discovery of a Potent, Selective T-type Calcium Channel Blocker as a Drug Candidate for the Treatment of Generalized Epilepsies

We report here the discovery and pharmacological characterization of N-(1-benzyl-1H-pyrazol-3-yl)-2-phenylacetamide derivatives as potent, selective, brain-penetrating T-type calcium channel blockers. Optimization focused mainly on solubility, brain penetration, and the search for an aminopyrazole metabolite that would be negative in an Ames test. This resulted in the preparation and complete characterization of compound 66b (ACT-709478), which has been selected as a clinical candidate.

Milestones to the Discovery of T-type Calcium Channel Blockers for the Treatment of Generalized Epilepsies

We describe the discovery and optimization of new, brain-penetrant T-type calcium channel blockers. We present optimized compounds with excellent efficacy in a rodent model of generalized absence-like epilepsy. Along the fine optimization of a chemical series with a pharmacological target located in the CNS (target potency, brain penetration, and solubility), we successfully identified an Ames negative aminopyrazole as putative metabolite of this compound series. Our efforts culminated in the selection of compound 20, which was elected as a preclinical candidate.

Discovery and evaluation of Cav3.1-selective T-type calcium channel blockers

We identified and characterized a series of pyrrole amides as potent, selective Cav3.2-blockers. This series culminated with the identification of pyrrole amides 13b and 26d, with excellent potencies and/or selectivities toward the Cav3.1- and Cav3.3-channels. These compounds display poor physicochemical and DMPK properties, making their use difficult for in vivo applications. Nevertheless, they are well-suited for in vitro studies.