Triple Reuptake Inhibitors as Potential Therapeutics for Depression and Other Disorders: Design Paradigm and Developmental Challenges.

Although first-line antidepressants offer therapeutic benefit, about 35% of depressed patients are not adequately treated, creating a large unmet medical need. These medicines mostly enhance the synaptic levels of serotonin and/or norepinephrine. Evidence from preclinical and clinical studies implicate dopamine hypofunction in the pathophysiology of depression. Triple reuptake inhibitors (TRIs), which elevate dopamine in addition to serotonin and norepinephrine, may demonstrate greater efficacy, with the reversal of anhedonia and improved tolerability. Medicinal chemistry efforts have resulted in more than 10 clinical candidates, although clinical candidates have failed to demonstrate superior efficacy compared to placebo or existing antidepressants. Hence, the successful development of future TRIs for depression will demand strong translational evidence, an optimal dosing regimen, and better tolerability. TRIs also hold therapeutic potential for other indications, with four candidates under clinical development for attention deficit hyperactivity disorder, binge eating disorder, cocaine addiction, obesity, and type 2 diabetes. Clinical studies have indicated a lower abuse potential for TRIs than psychostimulants.

Discovery of a tetracyclic quinoxaline derivative as a potent and orally active multifunctional drug candidate for the treatment of neuropsychiatric and neurological disorders.

We report the synthesis and structure-activity relationships of a class of tetracyclic butyrophenones that exhibit potent binding affinities to serotonin 5-HT(2A) and dopamine D2 receptors. This work has led to the discovery of 4-((6bR,10aS)-3-methyl-2,3,6b,9,10,10a-hexahydro-1H,7H-pyrido[3',4':4,5]pyrrolo[1,2,3-de]quinoxalin-8-yl)-1-(4-fluorophenyl)-butan-1-one 4-methylbenzenesulfonate (ITI-007), which is a potent 5-HT(2A) antagonist, postsynaptic D2 antagonist, and inhibitor of serotonin transporter. This multifunctional drug candidate is orally bioavailable and exhibits good antipsychotic efficacy in vivo. Currently, this investigational new drug is under clinical development for the treatment of neuropsychiatric and neurological disorders.

Synthesis and antiproliferative action of a novel series of maprotiline analogues.

The synthesis of a diverse library of compounds structurally related to maprotiline, a norepinephrine reuptake transporter (NET) selective antidepressant which has recently been identified as a novel in vitro antiproliferative agent against Burkitt's lymphoma (BL) cell lines is reported. A series of 9,10-dihydro-9,10-ethanoanthracenes were synthesised with modifications to the bridge of the dihydroethanoanthracene structure and with alterations to the basic side chain. A number of compounds were found to reduce cell viability to a greater extent than maprotiline in BL cell lines. In addition a related series of novel 9-substituted anthracene compounds were investigated as intermediates in the synthesis of 9,10-dihydro-9,10-ethanoanthracenes. These compounds proved the most active from the screen and were found to exert a potent caspase-dependant apoptotic effect in the BL cell lines, while having minimal effect on the viability of peripheral blood mononuclear cells (PBMCs). Compounds also displayed activity in multi-drug resistant (MDR) cells.

Synthesis and biological evaluation of novel 3,4-diaryl lactam derivatives as triple reuptake inhibitors.

A series of 3,4-diarylpyrrolidin-2-one was designed, prepared and evaluated as triple reuptake inhibitors for antidepressant. Most compounds exhibited comparable in vitro efficacy as norepinephrine and dopamine transporter reuptake inhibitors. Especially, 2i showed better potency than GBR-12909 (IC50=14 nM) which was used as reference compound for dopamine transporter. In addition, 2a and 2b showed inhibition (5.17 µM-85.6 nM) for three transporters.

First-in-class, dual-action, 3,5-disubstituted indole derivatives having human nitric oxide synthase (nNOS) and norepinephrine reuptake inhibitory (NERI) activity for the treatment of neuropathic pain.

A family of different 3,5-disubstituted indole derivatives having 6-membered rings were designed, synthesized, and demonstrated inhibition of human nitric oxide synthase (NOS) with norepinephrine reuptake inhibitory activity (NERI). The structure-activity relationship (SAR) within the cyclohexane ring showed the cis-isomers to be more potent for neuronal NOS and selective over endothelial NOS compared to their trans-counterparts. Compounds, such as cis-(+)-37, exhibited dual nNOS and NET inhibition (IC(50) of 0.56 and 1.0 µM, respectively) and excellent selectivity (88-fold and 12-fold) over eNOS and iNOS, respectively. The lead compound (cis-(+)-37) showed lack of any direct vasoconstriction or inhibition of ACh-mediated vasorelaxation in isolated human coronary arteries. Additionally, cis-(+)-37 was effective at reversing both allodynia and thermal hyperalgesia in a standard Chung (spinal nerve ligation) rat neuropathic pain model. Overall, the data suggest that cis-(+)-37 is a promising dual action development candidate having therapeutic potential for the treatment of neuropathic pain.

Efficient conversion of a nonselective norepinephrin reuptake inhibitor into a dual muscarinic antagonist-ß2-agonist for the treatment of chronic obstructive pulmonary disease.

Following interrogation of a wide-ligand profile database, a nonselective norepinephrin reuptake inhibitor was converted into a novel muscarinic antagonist using two medicinal chemistry transformations (M3/NRI selectivity of >1000). Conjugation to a ß(2) agonist motif furnished a molecule with balanced dual pharmacology, as demonstrated in a guinea pig trachea tissue model of bronchoconstriction. This approach provides new starting points for the treatment of chronic obstructive pulmonary disease and illustrates the potential for building selectivity into GPCR modulators that possess intrinsic promiscuity or reverse selectivity.

1-Heteroaryl-6-(3,4-dichlorophenyl)-3-azabicyclo[4.1.0]heptane: further insights into a class of triple re-uptake inhibitors.

Further exploration around the recently disclosed potent triple re-uptake inhibitor 6-(3,4-dichlorophenyl)-1-[(methyloxy)methyl]-3-azabicyclo[4.1.0]heptane led to the identification of a new series of potent triple re-uptake inhibitors endowed with good developability characteristics. The insertion of a further aryl moiety into the template allowed the 'titration' of the SERT/NET/DAT ratio leading to the identification of further tools in this important area.

Synthesis and neurotoxicity profile of 2,4,5-trihydroxymethamphetamine and its 6-(N-acetylcystein-S-yl) conjugate.

The purpose of the present study was to determine if trihydroxymethamphetamine (THMA), a metabolite of methylenedioxymethamphetamine (MDMA, "ecstasy"), or its thioether conjugate, 6-(N-acetylcystein-S-yl)-2,4,5-trihydroxymethamphetamine (6-NAC-THMA), play a role in the lasting effects of MDMA on brain serotonin (5-HT) neurons. To this end, novel high-yield syntheses of THMA and 6-NAC-THMA were developed. Lasting effects of both compounds on brain serotonin (5-HT) neuronal markers were then examined. A single intraventricular injection of THMA produced a significant lasting depletion of regional rat brain 5-HT and 5-hydroxyindoleacetic acid (5-HIAA), consistent with previous reports that THMA harbors 5-HT neurotoxic potential. The lasting effect of THMA on brain 5-HT markers was blocked by the 5-HT uptake inhibitor fluoxetine, indicating that persistent effects of THMA on 5-HT markers, like those of MDMA, are dependent on intact 5-HT transporter function. Efforts to identify THMA in the brains of animals treated with a high, neurotoxic dose (80 mg/kg) of MDMA were unsuccessful. Inability to identify THMA in the brains of these animals was not related to the unstable nature of the THMA molecule because exogenous THMA administered intracerebroventricularly could be readily detected in the rat brain for several hours. The thioether conjugate of THMA, 6-NAC-THMA, led to no detectable lasting alterations of cortical 5-HT or 5-HIAA levels, indicating that it lacks significant 5-HT neurotoxic activity. The present results cast doubt on the role of either THMA or 6-NAC-THMA in the lasting serotonergic effects of MDMA. The possibility remains that different conjugated forms of THMA or oxidized cyclic forms (e.g., the indole of THMA) play a role in MDMA-induced 5-HT neurotoxicity in vivo.

Synthesis of 2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues and their effects on monoamine uptake, nicotinic acetylcholine receptor function, and behavioral effects of nicotine.

Toward development of smoking cessation aids superior to bupropion (2), we describe synthesis of 2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues 5a-5h and their effects on inhibition of dopamine, norepinephrine, and serotonin uptake, nicotinic acetylcholine receptor (nAChR) function, acute actions of nicotine, and nicotine-conditioned place preference (CPP). Several analogues encompassing aryl substitutions, N-alkylation, and alkyl extensions of the morpholine ring 3-methyl group provided analogues more potent in vitro than (S,S)-hydroxybupropion (4a) as inhibitors of dopamine or norepinephrine uptake and antagonists of nAChR function. All of the new (S,S)-5 analogues had better potency than (S,S)-4a as blockers of acute nicotine analgesia in the tail-flick test. Two analogues with highest potency at α3ß4*-nAChR and among the most potent transporter inhibitors have better potency than (S,S)-4a in blocking nicotine-CPP. Collectively, these findings illuminate mechanisms of action of 2 analogues and identify deshydroxybupropion analogues 5a-5h as possibly superior candidates as aids to smoking cessation.

Synthesis and characterization of in vitro and in vivo profiles of hydroxybupropion analogues: aids to smoking cessation.

To create potentially superior aids to smoking cessation and/or antidepressants and to elucidate bupropion's possible mechanisms of action(s), 23 analogues based on its active hydroxymetabolite (2S,3S)-4a were synthesized and tested for their abilities to inhibit monoamine uptake and nAChR subtype activities in vitro and acute effects of nicotine in vivo. The 3',4'-dichlorophenyl [(+/-)-4n], naphthyl (4r), and 3-chlorophenyl or 3-propyl analogues 4s and 4t, respectively, had higher inhibitory potency and/or absolute selectivity than (2S,3S)-4a for inhibition of DA, NE, or 5HT uptake. The 3'-fluorophenyl, 3'-bromophenyl, and 4-biphenyl analogues 4c, 4d, and 4l, respectively, had higher potency for antagonism of alpha4beta2-nAChR than (2S,3S)-4a. Several analogues also had higher potency than (2S,3S)-4a as antagonists of nicotine-mediated antinociception in the tail-flick assay. The results suggest that compounds acting via some combination of DA, NE, or 5HT inhibition and/or antagonism of alpha4beta2-nAChR can potentially be new pharmacotherapeutics for treatment of nicotine dependence.

Structure-activity relationships of norepinephrine reuptake inhibitors with benzothiadiazine dioxide or dihydrosulfostyril cores.

Two related series of selective norepinephrine reuptake inhibitors were synthesized based on 3,4-dihydro-1H-2,1,3-benzothiadiazine 2,2-dioxide or 3,4-dihydrosulfostyril cores, and screened for monoamine reuptake inhibition. Structure-activity relationships were determined for the series' in vitro potency and selectivity versus serotonin or dopamine transporter inhibition, and analogs based on both cores were identified as potent and selective NRIs. The 3,4-dihydrosulfostyril series was further tested for microsome stability, and compound 16j, which was optimized for both potency and stability, showed efficacy in an in vivo model of thermoregulatory dysfunction.

Design, synthesis, and pharmacological evaluation of phenoxy pyridyl derivatives as dual norepinephrine reuptake inhibitors and 5-HT1A partial agonists.

Preclinical studies suggest that compounds with dual norepinephrine reuptake inhibitor (NRI) and 5-HT(1A) partial agonist properties may provide an important new therapeutic approach to ADHD, depression, and anxiety. Reported herein is the discovery of a novel chemical series with a favorable NRI and 5-HT(1A) partial agonist pharmacological profile as well as excellent selectivity for the norepinephrine transporter over the dopamine transporter.

Synthesis and biological evaluation of bupropion analogues as potential pharmacotherapies for cocaine addiction.

A series of bupropion (1a) analogues (1b-1ff) were synthesized, and their in vitro and in vivo pharmacological properties evaluated with the goal of developing a 1a analogue that had better properties for treating addictions. Their in vitro pharmacological properties were examined by [(3)H]dopamine ([(3)H]DA), [(3)H]serotonin ([(3)H]5HT), and [(3)H]norepinephrine ([(3)H]NE) uptake inhibition studies, and by binding studies at the dopamine, serotonin, and norepinephrine transporters using [(125)I]RTI-55 in cloned transporters. Several analogues showed increased [(3)H]DA uptake inhibition with reduced or little change in [(3)H]5HT and [(3)H]NE uptake inhibition relative to bupropion. Thirty-five analogues were evaluated in a 1 h locomotor activity observation test and 32 in an 8 h locomotor activity observation test and compared to the locomotor activity of cocaine. Twenty-four analogues were evaluated for generalization to cocaine drug discrimination after i.p. administration, and twelve analogues were tested in a time course cocaine discrimination study using oral administration. 2-(N-Cyclopropylamino)-3-chloropropiophenone (1x) had the most favorable in vitro efficacy and in vivo pharmacological profile for an indirect dopamine agonist pharmacotherapy for treating cocaine, methamphetamine, nicotine, and other drugs of abuse addiction.

Structure-activity relationships of the 1-amino-3-(1H-indol-1-yl)-3-phenylpropan-2-ol series of monoamine reuptake inhibitors.

The SAR of a series of 1-amino-3-(1H-indol-1-yl)-3-phenylpropan-2-ols as monoamine reuptake inhibitors, with a goal to improve both potency toward inhibiting the norepinephrine transporter and selectivity over the serotonin transporter, is reported. The effect of specific substitution on both the 3-phenyl group and the indole moiety were explored. This study led to the discovery of compound 20 which inhibited the norepinephrine transporter with an IC50 value of 4 nM while exhibiting 86-fold selectivity over the serotonin transporter.

N-[(3S)-Pyrrolidin-3-yl]benzamides as novel dual serotonin and noradrenaline reuptake inhibitors: impact of small structural modifications on P-gp recognition and CNS penetration.

The structure-activity relationship and the synthesis of novel N-[(3S)-pyrrolidin-3-yl]benzamides as dual serotonin and noradrenaline monoamine reuptake inhibitors (SNRI) is described. Preferred compound 9 aka PF-184,298 is a potent SNRI with good selectivity over dopamine reuptake inhibition (DRI), good in vitro metabolic stability, weak CYP inhibition and drug-like physicochemical properties consistent with CNS target space. Evaluation in an in vivo preclinical model of stress urinary incontinence showed 9 significantly increased urethral tone at free plasma concentrations consistent with its in vitro primary pharmacology.

Design, synthesis and evaluation of N-[(3S)-pyrrolidin-3-yl]benzamides as selective noradrenaline reuptake inhibitors: CNS penetration in a more polar template.

Derivatives of N-[(3S)-pyrrolidin-3-yl]benzamides are disclosed as a new series of noradrenaline reuptake inhibitors (NRI). Structure-activity relationships established that potent NRI activity could be achieved by appropriate substitution at the 2-position of the phenyl ring; consequently, selective NRIs and dual NSRIs were prepared. Benzamide 11e was identified as a potent NRI with good selectivity over SRI and DRI, good in vitro metabolic stability, weak CYP inhibition and low affinity for ion channels. Evaluation in vivo, in rat microdialysis experiments, showed 11e increased noradrenaline levels by up to 350% confirming good CNS penetration. Benzamide 11e was differentiated from previous NRIs as it was significantly less lipophilic (DeltaclogP -0.9).

Discovery of a new series of monoamine reuptake inhibitors, the 1-amino-3-(1H-indol-1-yl)-3-phenylpropan-2-ols.

A novel series of monoamine reuptake inhibitors, the 1-amino-3-(1H-indol-1-yl)-3-phenylpropan-2-ols, have been discovered by combining virtual and focused screening efforts with design techniques. Synthesis of the two diastereomeric isomers of the molecule followed by chiral resolution of each enantiomer revealed the (2R,3S)-isomer to be a potent norepinephrine reuptake inhibitor (IC(50)=28 nM) with excellent selectivity over the dopamine transporter and 13-fold selectivity over the serotonin transporter.

4-Piperidines and 3-pyrrolidines as dual serotonin and noradrenaline reuptake inhibitors: design, synthesis and structure-activity relationships.

Single enantiomer [(aryloxy)(pyridinyl)methyl]piperidine and pyrrolidine derivatives 5-9 are inhibitors of monoamine reuptake. Structure-activity relationships established that monoamine reuptake inhibition are functions of amine, pyridine isomer, aryloxy ring substitution and stereochemistry. Consequently, selective NRIs, selective SRIs, dual SNRIs and triple SNDRIs were all identified. Dual SNRIs 5l-a and 9c were evaluated in additional pharmacology and pharmacokinetic studies as representative examples from this series.

Design and synthesis of reboxetine analogs morpholine derivatives as selective norepinephrine reuptake inhibitors.

As part of a discovery effort aimed at identifying novel norepinephrine reuptake inhibitors (NRIs), a number of substituted morpholines were designed and synthesized. The target compounds contain vicinal stereogenic centers, and the program was greatly facilitated by the adoption of efficient synthetic routes which allowed for the late stage incorporation of structural and physicochemical diversity into the targets. Structure-activity relationships were developed by optimizing individual ring components of the structure for NRI potency and for selectivity against other monoamine reuptake transporters. Several novel morpholine derivatives with a potent and selective NRI profile are described.