Breakthroughs in neuroactive steroid drug discovery.

Endogenous and synthetic neuroactive steroids (NASs) or neurosteroids are effective modulators of multiple signaling pathways including receptors for the γ-aminobutyric acid A (GABAA) and glutamate, in particular N-methyl-d-aspartate (NMDA). These receptors are the major inhibitory and excitatory neurotransmitters in the central nervous system (CNS), and there is growing evidence suggesting that dysregulation of neurosteroid production plays a role in numerous neurological disorders. The significant unmet medical need for treatment of CNS disorders has increased the interest for these types of compounds. In this review, we highlight recent progress in the clinical development of NAS drug candidates, in addition to preclinical breakthroughs in the identification of novel NASs, mainly for GABAA and NMDA receptor modulation.

Novel triazines as potent and selective phosphodiesterase 10A inhibitors.

The identification of highly potent and orally active triazines for the inhibition of PDE10A is reported. The new analogs exhibit low-nanomolar potency for PDE10A, demonstrate high selectivity against all other members of the PDE family, and show desired drug-like properties. Employing structure-based drug design approaches, we investigated the selectivity of PDE10A inhibitors against other known PDE isoforms, by methodically exploring the various sub-regions of the PDE10A ligand binding pocket. A systematic assessment of the ADME and pharmacokinetic properties of the newly synthesized compounds has led to the design of drug-like candidates with good brain permeability and desirable drug kinetics (t(1/2), bioavailability, clearance). Compound 66 was highly potent for PDE10A (IC(50)=1.4 nM), demonstrated high selectivity (>200×) for the other PDEs, and was efficacious in animal models of psychoses; reversal of MK-801 induced hyperactivity (MED=0.1mg/kg) and conditioned avoidance responding (CAR; ID(50)=0.2 mg/kg).

SAGE-718: A First-in-Class N-Methyl-d-Aspartate Receptor Positive Allosteric Modulator for the Potential Treatment of Cognitive Impairment.

N-Methyl-d-aspartate receptor (NMDAR) positive allosteric modulators (PAMs) have received increased interest as a powerful mechanism of action to provide relief as therapies for CNS disorders. Sage Therapeutics has previously published the discovery of endogenous neuroactive steroid 24(S)-hydroxycholesterol as an NMDAR PAM. In this article, we detail the discovery of development candidate SAGE-718 (5), a potent and high intrinsic activity NMDAR PAM with an optimized pharmacokinetic profile for oral dosing. Compound 5 has completed phase 1 single ascending dose and multiple ascending dose clinical trials and is currently undergoing phase 2 clinical trials for treatment of cognitive impairment in Huntington's disease.

Synthesis and structure-activity relationship of novel lactam-fused chroman derivatives having dual affinity at the 5-HT(1A) receptor and the serotonin transporter.

The structure-activity relationship (SAR) for three series of lactam-fused chroman derivatives possessing 3-amino substituents was evaluated. Many compounds exhibited affinities for both the 5-HT(1A) receptor and the 5-HT transporter. Compounds 45 and 53 demonstrated 5-HT(1A) antagonist activities in the in vitro cAMP turnover model.

Novel benzofuran derivatives with dual 5-HT1A receptor and serotonin transporter affinity.

Several benzofuran derivatives linked to a 3-indoletetrahydropyridine through an alkyl chain were prepared and evaluated for serotonin transporter and 5-HT(1A) receptor affinities. Their design, synthesis and structure-activity relationships are described.

3-(Arylsulfonyl)-1-(azacyclyl)-1H-indoles are 5-HT(6) receptor modulators.

Novel 3-(arylsulfonyl)-1-(azacyclyl)-1H-indoles 6 were synthesized as potential 5-HT(6) receptor ligands, based on constraining a basic side chain as either a piperidine or a pyrrolidine. Many of these compounds had good 5-HT(6) binding affinity with K(i) values <10nM. Depending on substitution, both agonists (e.g., 6o: EC(50)=60nM, E(max)=70%) and antagonists (6y: IC(50)=17 nM, I(max)=86%) were identified in a 5-HT(6) adenylyl cyclase assay.

1-(2-Aminoethyl)-3-(arylsulfonyl)-1H-pyrrolopyridines are 5-HT(6) receptor ligands.

1-(2-Aminoethyl)-3-(arylsulfonyl)-1H-pyrrolopyridines were prepared. Binding assays indicated they are 5-HT(6) receptor ligands, among which 6f and 6g showed high affinity for 5-HT(6) receptors with K(i)=3.9 and 1.7 nM, respectively.

(S)-N-(5-Chlorothiophene-2-sulfonyl)-beta,beta-diethylalaninol a Notch-1-sparing gamma-secretase inhibitor.

Accumulation of beta-amyloid (Abeta), produced by the proteolytic cleavage of amyloid precursor protein (APP) by beta- and gamma-secretase, is widely believed to be associated with Alzheimer's disease (AD). Research around the high-throughput screening hit (S)-4-chlorophenylsulfonyl isoleucinol led to the identification of the Notch-1-sparing (9.5-fold) gamma-secretase inhibitor (S)-N-(5-chlorothiophene-2-sulfonyl)-beta,beta-diethylalaninol 7.b.2 (Abeta(40/42) EC(50)=28 nM), which is efficacious in reduction of Abeta production in vivo.

Novel 1-aminoethyl-3-arylsulfonyl-1H-pyrrolo[2,3-b]pyridines are potent 5-HT(6) agonists.

A series of 1-aminoethyl-3-arylsulfonyl-1H-pyrrolo[2,3-b]pyridines 10a-z was prepared as novel 5-HT(6) ligands. The best compounds were high affinity, full agonists at 5-HT(6) receptors. Several agonists demonstrated good selectivity over other serotonergic and dopaminergic receptors. Acute administration of selective agonist 10e significantly increased extracellular GABA concentrations in rat frontal cortex. This compound also reduced adjunctive drinking behavior in the rat schedule-induced polydipsia assay, possibly predictive of efficacy in obsessive compulsive disorder and other anxiety related disorders.

3,4-Dihydropyrimido(1,2-a)indol-10(2H)-ones as potent non-peptidic inhibitors of caspase-3.

Cysteine-dependant aspartyl protease (caspase) activation has been implicated as a part of the signal transduction pathway leading to apoptosis. It has been postulated that caspase-3 inhibition could attenuate cell damage after an ischemic event and thereby providing for a novel neuroprotective treatment for stroke. As part of a program to develop a small molecule inhibitor of caspase-3, a novel series of 3,4-dihydropyrimido(1,2-a)indol-10(2H)-ones (pyrimidoindolones) was identified. The synthesis, biological evaluation and structure-activity relationships of the pyrimidoindolones are described.

Synthesis and structure-activity relationship of a novel series of heterocyclic sulfonamide gamma-secretase inhibitors.

gamma-Secretase inhibitors have been shown to reduce the production of beta-amyloid, a component of the plaques that are found in brains of patients with Alzheimer's disease. A novel series of heterocyclic sulfonamide gamma-secretase inhibitors that reduce beta-amyloid levels in cells is reported. Several examples of compounds within this series demonstrate a higher propensity to inhibit the processing of amyloid precursor protein compared to Notch, an alternative gamma-secretase substrate.

Neuroactive Steroid N-Methyl-d-aspartate Receptor Positive Allosteric Modulators: Synthesis, SAR, and Pharmacological Activity.

Neuroactive steroids (NASs) play a pivotal role in maintaining homeostasis is the CNS. We have discovered that one NAS in particular, 24(S)-hydroxycholesterol (24(S)-HC), is a positive allosteric modulator (PAM) of NMDA receptors. Using 24(S)-HC as a chemical starting point, we have identified other NASs that have good in vitro potency and efficacy. Herein, we describe the structure activity relationship and pharmacokinetic optimization of this series that ultimately led to SGE-301 (42). We demonstrate that SGE-301 enhances long-term potentiation (LTP) in rat hippocampal slices and, in a dose-dependent manner, improves cognition in a rat social recognition study.

Correlating efficacy in rodent cognition models with in vivo 5-hydroxytryptamine1a receptor occupancy by a novel antagonist, (R)-N-(2-methyl-(4-indolyl-1-piperazinyl)ethyl)-N-(2-pyridinyl)-cyclohexane carboxamide (WAY-101405).

5-Hydroxytryptamine (5-HT)(1A) receptors play an important role in multiple cognitive processes, and compelling evidence suggests that 5-HT(1A) antagonists can reverse cognitive impairment. We have examined the therapeutic potential of a potent (K(i) = 1.1 nM), selective (>100-fold), orally bioavailable, silent 5-HT(1A) receptor antagonist (K(B) = 1.3 nM) (R)-N-(2-methyl-(4-indolyl-1-piperazinyl)-ethyl)-N-(2-pyridinyl)-cyclohexane carboxamide (WAY-101405). Oral administration of WAY-101405 was shown to be effective in multiple rodent models of learning and memory. In a novel object recognition paradigm, 1 mg/kg enhanced retention (memory) for previously learned information, and it was able to reverse the memory deficits induced by scopolamine. WAY-101405 (1 mg/kg) was also able to reverse scopolamine-induced deficits in a rat contextual fear conditioning model. In the Morris water maze, WAY-101405 (3 mg/kg) significantly improved learning in a paradigm of increasing task difficulty. In vivo microdialysis studies in the dorsal hippocampus of freely moving adult rats demonstrated that acute administration of WAY-101405 (10 mg/kg) increased extracellular acetylcholine levels. The selective radioligand [(3)H]WAY-100635, administered i.v., was used for in vivo receptor occupancy studies, where WAY-101405 occupied 5-HT(1A) receptors in the rat cortex, with an ED(50) value of 0.1 mg/kg p.o. Taken together, these studies demonstrate that WAY-101405 is a potent and selective, brain penetrant, orally bioavailable 5-HT(1A) receptor "silent" antagonist that is effective in preclinical memory paradigms at doses where approximately 90% of the postsynaptic 5-HT(1A) receptors are occupied. These results further support the rationale for use of this compound class in the treatment of cognitive dysfunction associated with psychiatric and neurological conditions.

Acylguanidine inhibitors of beta-secretase: optimization of the pyrrole ring substituents extending into the S1' substrate binding pocket.

The proteolytic enzyme beta-secretase (BACE-1) produces amyloid beta (Abeta) peptide, the primary constituent of neurofibrillary plaques, implicated in Alzheimer's disease, by cleavage of the amyloid precursor protein. A small molecule inhibitor of BACE-1, (diaminomethylene)-2,5-diphenyl-1H-pyrrole-1-acetamide (1, BACE-1 IC(50)=3.7 microM), was recently described, representing a new small molecule lead. Initial SAR investigation demonstrated the potential of accessing the nearby S(3) and S(1)(') substrate binding pockets of the BACE-1 enzyme by building substituents off one of the phenyl substituents and guanidinyl functional group. We report here the optimization of guanidinyl functional group substituents on 1, leading to potent submicromolar BACE-1 inhibitors.

Acylguanidine inhibitors of beta-secretase: optimization of the pyrrole ring substituents extending into the S1 and S3 substrate binding pockets.

Proteolytic cleavage of amyloid precursor protein by beta-secretase (BACE-1) and gamma-secretase leads to formation of beta-amyloid (A beta) a key component of amyloid plaques, which are considered the hallmark of Alzheimer's disease. Small molecule inhibitors of BACE-1 may reduce levels of A beta and thus have therapeutic potential for treating Alzheimer's disease. We recently reported the identification of a novel small molecule BACE-1 inhibitor N-[2-(2,5-diphenyl-pyrrol-1-yl)-acetyl]guanidine (3.a.1). We report here the initial hit-to-lead optimization of this hit and the SAR around the aryl groups occupying the S(1) and S(2') pockets leading to submicromolar BACE-1 inhibitors.

Studies toward the discovery of the next generation of antidepressants. Part 6: Dual 5-HT1A receptor and serotonin transporter affinity within a class of arylpiperazinyl-cyclohexyl indole derivatives.

Based on the previously reported discovery lead, 3-(cis-4-(4-(1H-indol-4-yl)piperazin-1-yl)cyclohexyl)-5-fluoro-1H-indole (2), a series of related arylpiperazin-4-yl-cyclohexyl indole analogs were synthesized then evaluated as 5-HT transporter inhibitors and 5-HT(1A) receptor antagonists. The investigation of the structure-activity relationships revealed the optimal pharmacophoric elements required for activities in this series. The best example from this study, 5-(piperazin-1-yl)quinoline analog (trans-20), exhibited equal binding affinities at 5-HT transporter (K(i)=4.9nM), 5-HT(1A) receptor (K(i)=6.2nM) and functioned as a 5-HT(1A) receptor antagonist.

Neuroactive Steroids. 2. 3α-Hydroxy-3ß-methyl-21-(4-cyano-1H-pyrazol-1'-yl)-19-nor-5ß-pregnan-20-one (SAGE-217): A Clinical Next Generation Neuroactive Steroid Positive Allosteric Modulator of the (γ-Aminobutyric Acid)A Receptor.

Certain classes of neuroactive steroids (NASs) are positive allosteric modulators (PAM) of synaptic and extrasynaptic GABAA receptors. Herein, we report new SAR insights in a series of 5ß-nor-19-pregnan-20-one analogues bearing substituted pyrazoles and triazoles at C-21, culminating in the discovery of 3α-hydroxy-3ß-methyl-21-(4-cyano-1H-pyrazol-1'-yl)-19-nor-5ß-pregnan-20-one (SAGE-217, 3), a potent GABAA receptor modulator at both synaptic and extrasynaptic receptor subtypes, with excellent oral DMPK properties. Compound 3 has completed a phase 1 single ascending dose (SAD) and multiple ascending dose (MAD) clinical trial and is currently being studied in parallel phase 2 clinical trials for the treatment of postpartum depression (PPD), major depressive disorder (MDD), and essential tremor (ET).

Synthesis and biological evaluation of novel compounds within a class of 3-aminochroman derivatives with dual 5-HT1A receptor and serotonin transporter affinity.

Compounds containing a 5-carbamoyl-8-fluoro-3-amino-3,4-dihydro-2H-1-benzopyran and a 3-alkylindole moiety linked through a common basic nitrogen were prepared and evaluated for 5-HT1A affinity, serotonin rat transporter affinity, and functional antagonist activity in vitro. 26a was found to be the most potent and selective compound in this series and was shown to possess neurochemical activity in vivo by producing acute and rapid increases in 5-HT in the rat frontal cortex.

Acylguanidines as small-molecule beta-secretase inhibitors.

BACE1 is an aspartyl protease responsible for cleaving amyloid precursor protein to liberate Abeta, which aggregates leading to plaque deposits implicated in Alzheimer's disease. We have identified small-molecule acylguanidine inhibitors of BACE1. Crystallographic studies show that these compounds form unique hydrogen-bonding interactions with the catalytic site aspartic acids and stabilize the protein in a flap-open conformation. Structure-based optimization led to the identification of potent analogs, such as 10d (BACE1 IC(50) = 110 nM).

Antiobesity-like effects of the 5-HT2C receptor agonist WAY-161503.

WAY-161503 ((4aR)-8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5(6H)-one), a 5-HT(2B/C) receptor agonist, was characterized in vitro using stable Chinese hamster ovary cell lines expressing each of the human 5-HT2 receptors and in vivo in animal models of obesity. WAY-161503 displaced both agonist ([125I]2,5-dimethoxy-4-iodoamphetamine (DOI)) and antagonist ([3H]mesulergine) radioligand binding to the human 5-HT2C receptor with derived Ki values of 3.3 +/- 0.9 and 32 +/- 6 nM, respectively. Relative to 5-HT2C receptor binding, WAY-161503 was approximately 6-fold less potent at human 5-HT2A receptors ([125I]DOI) with a derived Ki value of 18 nM and 20-fold less potent at human 5-HT2B receptors ([3H]5-HT) with a derived Ki value of 60 nM. In functional studies, WAY-161503 was a full agonist in stimulating 5-HT2C-receptor-coupled [3H]inositol phosphate (IP) formation and calcium mobilization with EC50 values of 8.5 nM and 0.8 nM, respectively. WAY-161503 was also a 5-HT2B agonist (EC50s of 6.9 and 1.8 nM for IP and calcium, respectively). In IP studies, WAY-161503 was a weak 5-HT(2A) partial agonist (EC50, 802 nM) yet potently stimulated calcium mobilization (EC50, 7 nM) in 5-HT2A receptor-expressing cells. Functionally, WAY-161503 also stimulated the phospholipase A2-coupled arachidonic acid release in 5-HT2C receptor expressing cells albeit with lower potency (EC50, 38 nM) and efficacy (Emax, 77%) compared with activation of the PLC pathway. In vivo, WAY-161503 produced dose-dependent decreases in 2-h food intake in 24 h fasted normal Sprague-Dawley rats, diet-induced obese mice, and obese Zuker rats with ED50 values of 1.9 mg/kg, 6.8 mg/kg, and 0.73 mg/kg, respectively. The reduction in food intake in normal Sprague-Dawley rats was reversed by administration of the 5-HT2C receptor antagonist SB-242084. Following chronic administration (10 days) in growing Sprague-Dawley rats, WAY-161503 decreased food intake and attenuated body weight gain. Finally, following chronic administration (15 days) of WAY-161503 to obese Zuker rats, the rats maintained a 30% decrease in food intake over the 15-day period combined with a 25 g decrease in body weight relative to vehicle-treated controls demonstrating a lack of tolerance to its anorectic effects.