TAK-994, a Novel Orally Available Brain-Penetrant Orexin 2 Receptor-Selective Agonist, Suppresses Fragmentation of Wakefulness and Cataplexy-Like Episodes in Mouse Models of Narcolepsy.

Loss of orexin neurons is associated with narcolepsy type 1 (NT1), which is characterized by multiple symptoms including excessive daytime sleepiness and cataplexy. Orexin 2 receptor (OX2R) knockout (KO) mice, but not orexin 1 receptor (OX1R) KO mice, show narcolepsy-like phenotypes, thus OX2R agonists are potentially promising for treating NT1. In fact, in early proof-of-concept studies, intravenous infusion of danavorexton, an OX2R-selective agonist, significantly increased wakefulness in individuals with NT1. However, danavorexton has limited oral availability. Here, we report pharmacological characteristics of a novel OX2R agonist, TAK-994 [N-{(2S,3S)-1-(2-hydroxy-2-methylpropanoyl)-2-[(2,3',5'-trifluorobiphenyl-3-yl)methyl]pyrrolidin-3-yl}methanesulfonamide sesquihydrate]. TAK-994 activated recombinant human OX2R (EC50 value of 19 nM) with > 700-fold selectivity against OX1R and activated OX2R-downstream signaling similar to those by orexin peptides in vitro. Oral administration of TAK-994 promoted wakefulness in normal mice but not in OX2R KO mice. TAK-994 also ameliorated narcolepsy-like symptoms in two mouse models of narcolepsy: orexin/ataxin-3 mice and orexin-tTA;TetO diphtheria toxin A mice. The wake-promoting effects of TAK-994 in orexin/ataxin-3 mice were maintained after chronic dosing for 14 days. These data suggest that overall in vitro and in vivo properties, except oral availability, are very similar between TAK-994 and danavorexton. Preclinical characteristics of TAK-994 shown here, together with upcoming clinical study results, can improve our understanding for orally available OX2R agonists as new therapeutic drugs for NT1 and other hypersomnia disorders. SIGNIFICANCE STATEMENT: Narcolepsy type 1 (NT1) is caused by a loss of orexin neurons, and thus an orexin 2 receptor (OX2R) agonist is considered to address the underlying pathophysiology of NT1. Oral administration of TAK-994, a novel OX2R agonist, promoted wakefulness in normal mice, but not in OX2R knockout mice, and ameliorated fragmentation of wakefulness and cataplexy-like episodes in mouse models of narcolepsy. These findings indicate that TAK-994 is an orally available brain-penetrant OX2R-selective agonist with potential to improve narcolepsy-like symptoms.

Design and synthesis of aryl-piperidine derivatives as potent and selective PET tracers for cholesterol 24-hydroxylase (CH24H).

Cholesterol 24-hydroxylase (CH24H, CYP46A1) is a cytochrome P450 family enzyme that maintains the homeostasis of brain cholesterol. Soticlestat, a potent and selective CH24H inhibitor, is in development as a therapeutic agent for Dravet syndrome and Lennox-Gastaut syndrome. Herein, we report the discovery of aryl-piperidine derivatives as potent and selective CH24H positron emission tomography (PET) tracers which can be used for dose guidance of a clinical CH24H inhibitor and as a diagnostic tool for CH24H-related pathology. Starting from compound 1 (IC50 = 16 nM, logD = 1.7), which was reported as a CH24H inhibitor with lower lipophilicity, a18F-labeling site (3-fluoroazetidine) was incorporated by structure-based drug design (SBDD) utilizing the co-crystal structure of a compound 1 analog. Subsequent optimization to adjust key parameters for PET tracers, such as potency, lipophilicity, brain penetration, and unbound plasma protein binding, enabled compounds 3f (IC50 = 8.8 nM) and 3g (IC50 = 8.7 nM) as PET imaging candidates. Selectivity of these compounds for CH24H was validated by a brain distribution study using CH24H-WT and KO mice. In non-human primate PET imaging, [18F]3f and [18F]3g showed similar regional uptake in the brain, indicating that these tracers were specific to the CH24H-expressed regions and validated the expression of CH24H in the living brain by different tracers.

Discovery of Novel 3-Piperidinyl Pyridine Derivatives as Highly Potent and Selective Cholesterol 24-Hydroxylase (CH24H) Inhibitors.

Cholesterol 24-hydroxylase (CH24H or CYP46A1) is a brain-specific cytochrome P450 enzyme that metabolizes cholesterol into 24S-hydroxycholesterol (24HC) for regulating brain cholesterol homeostasis. For the development of a novel and potent CH24H inhibitor, we designed and synthesized 3,4-disubstituted pyridine derivatives using a structure-based drug design approach starting from compounds 1 (soticlestat) and 2 (thioperamide). Optimization of this series by focusing on ligand-lipophilicity efficiency value resulted in the discovery of 4-(4-methyl-1-pyrazolyl)pyridine derivative 17 (IC50 = 8.5 nM) as a potent and highly selective CH24H inhibitor. The X-ray crystal structure of CH24H in complex with compound 17 revealed a unique binding mode. Both blood-brain barrier penetration and reduction of 24HC levels (26% reduction) in the mouse brain were confirmed by oral administration of 17 at 30 mg/kg, indicating that 17 is a promising tool for the novel and selective inhibition of CH24H.

Discovery of novel 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives as γ-secretase modulators (Part 2).

γ-Secretase modulators (GSMs), which lower pathogenic amyloid beta (Aß) without affecting the production of total Aß or Notch signal, have emerged as a potential therapeutic agent for Alzheimer's disease (AD). A novel series of 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine derivatives was discovered and characterized as GSMs. Optimization of substituents at the 8-position of the core scaffold using ligand-lipophilicity efficiency (LLE) as a drug-likeness guideline led to identification of various types of high-LLE GSMs. Phenoxy compound (R)-17 exhibited especially high LLE as well as potent in vivo Aß42-lowering effect by single administration. Furthermore, multiple oral administration of (R)-17 significantly reduced soluble and insoluble brain Aß42, and ameliorated cognitive deficit in novel object recognition test (NORT) using Tg2576 mice as an AD model.

Design and synthesis of piperazine derivatives as a novel class of γ-secretase modulators that selectively lower Aß42 production.

Novel piperazine derivatives as γ-secretase modulators (GSMs) were prepared and tested for their ability to selectively lower Aß42 production. Lead compound 3, with selective Aß42-lowering activity, was modified by replacing its imidazolylphenyl moiety with an oxazolylphenyl moiety. Optimization of the urea group significantly improved mouse microsomal stability, while retaining both activity and selectivity. These efforts led to the successful identification of an orally available and brain-penetrant GSM, 6j, which selectively reduced brain Aß42 in mice.

Nickel-catalyzed decarbonylative addition of anhydrides to alkynes.

An intermolecular nickel-catalyzed addition reaction has been developed where phthalic anhydrides react with alkynes to afford substituted isocoumarins. A mechanistic rationale is proposed, implying reductive elimination of Ni(0) promoted by ZnCl(2) cocatalyst as the key step of the catalytic cycle.

Nickel-catalyzed decarbonylative addition of phthalimides to alkynes.

An intermolecular nickel-catalyzed addition reaction has been developed where N-arylphthalimides react with alkynes to afford substituted isoquinolones. A mechanistic rationale is proposed, implying nucleophilic attack of Ni(0) to an amide as the primary step of the catalytic cycle.