Structure-Activity Relationships at the Monoamine Transporters for a Novel Series of Modafinil (2-[(diphenylmethyl)sulfinyl]acetamide) Analogues

Series of (([1,1'-Biphenyl]-2-yl)methyl)sulfinylalkyl Alicyclic Amines as Novel and High Affinity Atypical Dopamine Transporter Inhibitors with Reduced hERG Activity

Currently, there are no FDA-approved medications for the treatment of psychostimulant use disorders (PSUD). We have previously discovered "atypical" dopamine transporter (DAT) inhibitors that do not display psychostimulant-like behaviors and may be useful as medications to treat PSUD. Lead candidates (e.g., JJC8-091, 1) have shown promising in vivo profiles in rodents; however, reducing hERG (human ether-à-go-go-related gene) activity, a predictor of cardiotoxicity, has remained a challenge. Herein, a series of 30 (([1,1'-biphenyl]-2-yl)methyl)sulfinylalkyl alicyclic amines was synthesized and evaluated for DAT and serotonin transporter (SERT) binding affinities. A subset of analogues was tested for hERG activity, and the IC50 values were compared to those predicted by our hERG QSAR models, which showed robust predictive power. Multiparameter optimization scores (MPO > 3) indicated central nervous system (CNS) penetrability. Finally, comparison of affinities in human DAT and its Y156F and Y335A mutants suggested that several compounds prefer an inward facing conformation indicating an atypical DAT inhibitor profile.

Enzymatic Resolution and Decarboxylative Functionalization of α-Sulfinyl Esters

α-Sulfinyl esters can be readily prepared through thiol substitution of α-bromo esters followed by oxidation to the sulfoxide. Enzymatic resolution with lipoprotein lipase provides both the unreacted esters and corresponding α-sulfinyl carboxylic acids in high yields and enantiomeric ratios. Subsequent decarboxylative halogenation, dihalogenation, trihalogenation and cross-coupling gives rise to functionalized sulfoxides. The method has been applied to the asymmetric synthesis of a potent inhibitor of 15-prostaglandin dehydrogenase.

Modifications to 1-(4-(2-Bis(4-fluorophenyl)methyl)sulfinyl)alkyl Alicyclic Amines That Improve Metabolic Stability and Retain an Atypical DAT Inhibitor Profile

Atypical dopamine transporter (DAT) inhibitors have shown therapeutic potential in the preclinical models of psychostimulant use disorders (PSUD). In rats, 1-(4-(2-((bis(4-fluorophenyl)methyl)sulfinyl)ethyl)-piperazin-1-yl)-propan-2-ol (JJC8-091, 3b) was effective in reducing the reinforcing effects of both cocaine and methamphetamine but did not exhibit psychostimulant behaviors itself. Improvements in DAT affinity and metabolic stability were desirable for discovering pipeline drug candidates. Thus, a series of 1-(4-(2-bis(4-fluorophenyl)methyl)sulfinyl)alkyl alicyclic amines were synthesized and evaluated for binding affinities at DAT and the serotonin transporter (SERT). Replacement of the piperazine with either a homopiperazine or a piperidine ring system was well tolerated at DAT (Ki range = 3-382 nM). However, only the piperidine analogues (20a-d) showed improved metabolic stability in rat liver microsomes as compared to the previously reported analogues. Compounds 12b and 20a appeared to retain an atypical DAT inhibitor profile, based on negligible locomotor activity in mice and molecular modeling that predicts binding to an inward-facing conformation of DAT.

Pharmacokinetics of Novel Dopamine Transporter Inhibitor CE-123 and Modafinil with a Focus on Central Nervous System Distribution

S-CE-123, a novel dopamine transporter inhibitor, has emerged as a potential candidate for cognitive enhancement. The objective of this study was to compare the tissue distribution profiles, with a specific focus on central nervous system distribution and metabolism, of S-CE-123 and R-modafinil. To address this objective, a precise liquid chromatography-high resolution mass spectrometry method was developed and partially validated. Neuropharmacokinetic parameters were assessed using the Combinatory Mapping Approach. Our findings reveal distinct differences between the two compounds. Notably, S-CE-123 demonstrates a significantly superior extent of transport across the blood-brain barrier (BBB), with an unbound brain-to-plasma concentration ratio (Kp,uu,brain) of 0.5, compared to R-modafinil's Kp,uu,brain of 0.1. A similar pattern was observed for the transport across the blood-spinal cord barrier. Concerning the drug transport across cellular membranes, we observed that S-CE-123 primarily localizes in the brain interstitial space, whereas R-modafinil distributes more evenly across both sides of the plasma membrane of the brain's parenchymal cells (Kp,uu,cell). Furthermore, our study highlights the substantial differences in hepatic metabolic stability, with S-CE-123 having a 9.3-fold faster metabolism compared to R-modafinil. In summary, the combination of improved BBB transport and higher affinity of S-CE-123 to dopamine transporters in comparison to R-modafinil makes S-CE-123 a promising candidate for further testing for the treatment of cognitive decline.

Modafinil, an atypical CNS stimulant?

Modafinil is a central nervous system stimulant approved for the treatment of narcolepsy and sleep disorders. Due to its wide range of biochemical actions, modafinil has been explored for other potential therapeutic uses. Indeed, it has shown promise as a therapy for cognitive disfunction resulting from neurologic disorders like ADHD, and as a smart drug in non-medical settings. The mechanism(s) of actions underlying the therapeutic efficacy of this agent remains largely elusive. Modafinil is known to inhibit the dopamine transporter, thus decreasing dopamine reuptake following neuronal release, an effect shared by addictive psychostimulants. However, modafinil is unique in that only a few cases of dependence on this drug have been reported, as compared to other psychostimulants. Moreover, modafinil has been tested, with some success, as a potential therapeutic agent to combat psychostimulant and other substance use disorders. Modafinil has additional, but less understood, actions on other neurotransmitter systems (GABA, glutamate, serotonin, norepinephrine, etc.). These interactions, together with its ability to activate selected brain regions, are likely one of the keys to understand its unique pharmacology and therapeutic activity as a CNS stimulant. In this chapter, we outline the pharmacokinetics and pharmacodynamics of modafinil that suggest it has an "atypical" CNS stimulant profile. We also highlight the current approved and off label uses of modafinil, including its beneficial effects as a treatment for sleep disorders, cognitive functions, and substance use disorders.

An FSCV Study on the Effects of Targeted Typical and Atypical DAT Inhibition on Dopamine Dynamics in the Nucleus Accumbens Shell of Male and Female Mice

Understanding the neurochemistry underlying sex differences in psychostimulant use disorders (PSUD) is essential for developing related therapeutics. Many psychostimulants, like cocaine, inhibit the dopamine transporter (DAT), which is largely thought to account for actions related to their misuse and dependence. Cocaine-like, typical DAT inhibitors preferentially bind DAT in an outward-facing conformation, while atypical DAT inhibitors, like modafinil, prefer a more inward-facing DAT conformation. Modafinil and R-modafinil have emerged as potential therapeutic options for selected populations of individuals affected by PSUD. In addition, analogs of modafinil (JJC8-088 and JJC8-091) with different pharmacological profiles have been explored as potential PSUD medications in preclinical models. In this work, we employ fast scan cyclic voltammetry (FSCV) to probe nucleus accumbens shell (NAS) dopamine (DA) dynamics in C57BL/6 male and female mice. We find that cocaine slowed DA clearance in both male and female mice but produced more robust increases in evoked NAS DA in female mice. R-Modafinil produced mild increases in evoked NAS DA and slowed DA clearance across the sexes. The modafinil analog JJC8-088, a typical DAT inhibitor, produced increases in evoked NAS DA in female and male mice. Finally, JJC8-091, an atypical DAT inhibitor, produced limited increases in evoked NAS DA and slowed DA clearance in both sexes. In this work we begin to tease out how sex differences may alter the effects of DAT targeting and highlight how this may help focus research toward effective treatment options for PSUD.

Are There Prevalent Sex Differences in Psychostimulant Use Disorder? A Focus on the Potential Therapeutic Efficacy of Atypical Dopamine Uptake Inhibitors

Psychostimulant use disorders (PSUD) affect a growing number of men and women and exert sizable public health and economic burdens on our global society. Notably, there are some sex differences in the onset of dependence, relapse rates, and treatment success with PSUD observed in preclinical and clinical studies. The subtle sex differences observed in the behavioral aspects of PSUD may be associated with differences in the neurochemistry of the dopaminergic system between sexes. Preclinically, psychostimulants have been shown to increase synaptic dopamine (DA) levels and may downregulate the dopamine transporter (DAT). This effect is greatest in females during the high estradiol phase of the estrous cycle. Interestingly, women have been shown to be more likely to begin drug use at younger ages and report higher levels of desire to use cocaine than males. Even though there is currently no FDA-approved medication, modafinil, a DAT inhibitor approved for use in the treatment of narcolepsy and sleep disorders, has shown promise in the treatment of PSUD among specific populations of affected individuals. In this review, we highlight the therapeutic potential of modafinil and other atypical DAT inhibitors focusing on the lack of sex differences in the actions of these agents.

Discovery and Development of Monoamine Transporter Ligands

Monoamine transporters (MATs) are targets of a wide range of compounds that have been developed as therapeutic treatments for various neuropsychiatric and neurodegenerative disorders such as depression, ADHD, neuropathic pain, anxiety disorders, stimulant use disorders, epilepsy, and Parkinson's disease. The MAT family is comprised of three main members - the dopamine transporter (DAT), the norepinephrine transporter (NET), and the serotonin transporter (SERT). These transporters are through reuptake responsible for the clearance of their respective monoamine substrates from the extracellular space. The determination of X-ray crystal structures of MATs and their homologues bound with various substrates and ligands has resulted in a surge of structure-function-based studies of MATs to understand the molecular basis of transport function and the mechanism of various ligands that ultimately result in their behavioral effects. This review focusses on recent examples of ligand-based structure-activity relationship studies trying to overcome some of the challenges associated with previously developed MAT inhibitors. These studies have led to the discovery of unique and novel structurally diverse MAT ligands including allosteric modulators. These novel molecular scaffolds serve as leads for designing more effective therapeutic interventions by modulating the activities of MATs and ultimately their associated neurotransmission and behavioral effects.

Psychostimulant Use Disorder, an Unmet Therapeutic Goal: Can Modafinil Narrow the Gap?

The number of individuals affected by psychostimulant use disorder (PSUD) has increased rapidly over the last few decades resulting in economic, emotional, and physical burdens on our society. Further compounding this issue is the current lack of clinically approved medications to treat this disorder. The dopamine transporter (DAT) is a common target of psychostimulant actions related to their use and dependence, and the recent availability of atypical DAT inhibitors as a potential therapeutic option has garnered popularity in this research field. Modafinil (MOD), which is approved for clinical use for the treatment of narcolepsy and sleep disorders, blocks DAT just like commonly abused psychostimulants. However, preclinical and clinical studies have shown that it lacks the addictive properties (in both behavioral and neurochemical studies) associated with other abused DAT inhibitors. Clinical availability of MOD has facilitated its off-label use for several psychiatric disorders related to alteration of brain dopamine (DA) systems, including PSUD. In this review, we highlight clinical and preclinical research on MOD and its R-enantiomer, R-MOD, as potential medications for PSUD. Given the complexity of PSUD, we have also reported the effects of MOD on psychostimulant-induced appearance of several symptoms that could intensify the severity of the disease (i.e., sleep disorders and impairment of cognitive functions), besides the potential therapeutic effects of MOD on PSUD.

New Drugs, Old Targets: Tweaking the Dopamine System to Treat Psychostimulant Use Disorders

The abuse of illicit psychostimulants such as cocaine and methamphetamine continues to pose significant health and societal challenges. Despite considerable efforts to develop medications to treat psychostimulant use disorders, none have proven effective, leaving an underserved patient population and unanswered questions about what mechanism(s) of action should be targeted for developing pharmacotherapies. As both cocaine and methamphetamine rapidly increase dopamine (DA) levels in mesolimbic brain regions, leading to euphoria that in some can lead to addiction, targets in which this increased dopaminergic tone may be mitigated have been explored. Further, understanding and targeting mechanisms underlying relapse are fundamental to the success of discovering medications that reduce the reinforcing effects of the drug of abuse, decrease the negative reinforcement or withdrawal/negative affect that occurs during abstinence, or both. Atypical inhibitors of the DA transporter and partial agonists/antagonists at DA D₃ receptors are described as two promising targets for future drug development.

Structure-activity relationships for a series of (Bis(4-fluorophenyl)methyl)sulfinylethyl-aminopiperidines and -piperidine amines at the dopamine transporter: Bioisosteric replacement of the piperazine improves metabolic stability

Despite considerable efforts to develop medications to treat psychostimulant use disorders, none have proven effective, leaving an underserved patient population and unanswered questions as to what mechanism(s) of action should be targeted for developing pharmacotherapies. Atypical dopamine transporter (DAT) inhibitors, based on (±)modafinil, have shown therapeutic potential in preclinical models of psychostimulant abuse. However, metabolic instability among other limitations to piperazine analogues 1-3 have impeded further development. Herein, bioisosteric substitutions of the piperazine ring were explored with a series of aminopiperidines (A) and piperidine amines (B) wherein compounds with either a terminal tertiary amine or amide were synthesized. Several lead compounds showed high to moderate DAT affinities and metabolic stability in rat liver microsomes. Aminopiperidines 7 (DAT Ki = 50.6 nM), 21b (DAT Ki = 77.2 nM) and 33 (DAT Ki = 30.0 nM) produced only minimal stimulation of ambulatory activity in mice, compared to cocaine, suggesting an atypical DAT inhibitor profile.

Modafinil and its structural analogs as atypical dopamine uptake inhibitors and potential medications for psychostimulant use disorder

Pharmacotherapeutics for treatment of psychostimulant use disorder are still an unmet medical goal. Recently, off label use of modafinil (MOD), an approved medication for treatment of sleep disturbances, has been tested as a therapeutic for cocaine and methamphetamine use disorder. Positive results have been found in subjects dependent on psychostimulants without concurrent abuse of other substances. Novel structural analogs of MOD have been synthesized in the search for compounds with potentially broader therapeutic efficacy than the parent drug. In the present report we review their potential efficacy as treatments for psychostimulant abuse and dependence assessed in preclinical tests. Results from these preclinical proof of concept studies reveal that some modafinil analogs do not possess typical cocaine-like neurochemical and behavioral effects. Further, they might blunt the reinforcing effects of psychostimulants in animal models, suggesting their potential efficacy as pharmacotherapeutics for treatment of psychostimulant use disorders.

Modafinil potentiates cocaine self-administration by a dopamine-independent mechanism: possible involvement of gap junctions

Modafinil and methylphenidate are medications that inhibit the neuronal reuptake of dopamine, a mechanism shared with cocaine. Their use as "smart drugs" by healthy subjects poses health concerns and requires investigation. We show that methylphenidate, but not modafinil, maintained intravenous self-administration in Sprague-Dawley rats similar to cocaine. Both modafinil and methylphenidate pretreatments potentiated cocaine self-administration. Cocaine, at self-administered doses, stimulated mesolimbic dopamine levels. This effect was potentiated by methylphenidate, but not by modafinil pretreatments, indicating dopamine-dependent actions for methylphenidate, but not modafinil. Modafinil is known to facilitate electrotonic neuronal coupling by actions on gap junctions. Carbenoxolone, a gap junction inhibitor, antagonized modafinil, but not methylphenidate potentiation of cocaine self-administration. Our results indicate that modafinil shares mechanisms with cocaine and methylphenidate but has a unique pharmacological profile that includes facilitation of electrotonic coupling and lower abuse liability, which may be exploited in future therapeutic drug design for cocaine use disorder.

Modulating the immune response with the wake-promoting drug modafinil: A potential therapeutic approach for inflammatory disorders

Modafinil is a psychostimulant drug approved by the FDA primarily for the treatment of sleep disorders such as narcolepsy, excessive daytime sleepiness and sleep apnea. Several documented but not yet approved uses for modafinil have been described over the last 30 years, including alleviating fatigue in neurological and neurodegenerative disorders. Recent evidence has suggested that modafinil may have an immunomodulatory effect. Here, we review the different effects of modafinil treatment in animal models of brain inflammation and peripheral immune function. We conclude that there is unequivocal evidence of an anti-inflammatory effect of modafinil in experimental animal models of brain inflammation and neurodegenerative disorders, including systemic inflammation and methamphetamine-induced neuroinflammation, Parkinson's disease, brain ischemia, and multiple sclerosis. Modafinil acts on resident glial cells and infiltrating immune cells, negatively affecting both innate and adaptive immune responses in the brain. We also review the outcomes of modafinil treatment on peripheral immune function. The results of studies on this subject are still controversial and far from conclusive, but point to a new avenue of research in relation to peripheral inflammation. The data reviewed here raise the possibility of modafinil being used as adjuvant treatment for neurological disorders in which inflammation plays an important role.

Pharmacokinetic and pharmacodynamic of the cognitive enhancer modafinil: Relevant clinical and forensic aspects

Modafinil is a nonamphetamine nootropic drug with an increasingly therapeutic interest due to its different sites of action and behavioral effects in comparison to cocaine or amphetamine. A review of modafinil (and of its prodrug adrafinil and its R-enantiomer armodafinil) chemical, pharmacokinetic, pharmacodynamic, toxicological, clinical and forensic aspects was performed, aiming to better understand possible health problems associated to its unconscious and unruled use. Modafinil is a racemate metabolized mainly in the liver into its inactive acid and sulfone metabolites, which undergo primarily renal excretion. Although not fully clarified, major effects seem to be associated to inhibition of dopamine reuptake and modulation of several other neurochemical pathways, namely noradrenergic, serotoninergic, orexinergic, histaminergic, glutamatergic and GABAergic. Due its wake-promoting effects, modafinil is used for the treatment of daily sleepiness associated to narcolepsy, obstructive sleep apnea and shift work sleep disorder. Its psychotropic and cognitive effects are also attractive in several other pathologies and conditions that affect sleep structure, induce fatigue and lethargy, and impair cognitive abilities. Additionally, in health subjects, including students, modafinil is being used off-label to overcome sleepiness, increase concentration and improve cognitive potential. The most common adverse effects associated to modafinil intake are headache, insomnia, anxiety, diarrhea, dry mouth and raise in blood pressure and heart rate. Infrequently, severe dermatologic effects in children, including maculopapular and morbilliform rash, erythema multiforme and Stevens-Johnson Syndrome have been reported. Intoxication and dependence associated to modafinil are uncommon. Further research on effects and health implications of modafinil and its analogs is steel needed to create evidence-based policies.

Structure-Activity Relationships of Novel Thiazole-Based Modafinil Analogues Acting at Monoamine Transporters

Atypical dopamine reuptake inhibitors, such as modafinil, are used for the treatment of sleeping disorders and investigated as potential therapeutics against cocaine addiction and for cognitive enhancement. Our continuous effort to find modafinil analogues with higher inhibitory activity on and selectivity toward the dopamine transporter (DAT) has previously led to the promising thiazole-containing derivatives CE-103, CE-111, CE-123, and CE-125. Here, we describe the synthesis and activity of a series of compounds based on these scaffolds, which resulted in several new selective DAT inhibitors and gave valuable insights into the structure-activity relationships. Introduction of the second chiral center and subsequent chiral separations provided all four stereoisomers, whereby the S-configuration on both generally exerted the highest activity and selectivity on DAT. The representative compound of this series was further characterized by in silico, in vitro, and in vivo studies that have demonstrated both safety and efficacy profile of this compound class.

Structure-Activity Relationships for a Series of (Bis(4-fluorophenyl)methyl)sulfinyl Alkyl Alicyclic Amines at the Dopamine Transporter: Functionalizing the Terminal Nitrogen Affects Affinity, Selectivity, and Metabolic Stability

Atypical dopamine transporter (DAT) inhibitors have shown therapeutic potential in preclinical models of psychostimulant abuse. In rats, 1-(4-(2-((bis(4-fluorophenyl)methyl)sulfinyl)ethyl)-piperazin-1-yl)-propan-2-ol (3b) was effective in reducing the reinforcing effects of both cocaine and methamphetamine but did not exhibit psychostimulant behaviors itself. While further development of 3b is ongoing, diastereomeric separation, as well as improvements in potency and pharmacokinetics were desirable for discovering pipeline drug candidates. Thus, a series of bis(4-fluorophenyl)methyl)sulfinyl)alkyl alicyclic amines, where the piperazine-2-propanol scaffold was modified, were designed, synthesized, and evaluated for binding affinities at DAT, as well as the serotonin transporter and σ₁ receptors. Within the series, 14a showed improved DAT affinity (K_i = 23 nM) over 3b (K_i = 230 nM), moderate metabolic stability in human liver microsomes, and a hERG/DAT affinity ratio = 28. While 14a increased locomotor activity relative to vehicle, it was significantly lower than activity produced by cocaine. These results support further investigation of 14a as a potential treatment for psychostimulant use disorders.

Distinct effects of (R)-modafinil and its (R)- and (S)-fluoro-analogs on mesolimbic extracellular dopamine assessed by voltammetry and microdialysis in rats

Psychostimulant use disorders remain an unabated public health concern worldwide, but no FDA approved medications are currently available for treatment. Modafinil (MOD), like cocaine, is a dopamine reuptake inhibitor and one of the few drugs evaluated in clinical trials that has shown promise for the treatment of cocaine or methamphetamine use disorders in some patient subpopulations. Recent structure-activity relationship and preclinical studies on a series of MOD analogs have provided insight into modifications of its chemical structure that may lead to advancements in clinical efficacy. Here, we have tested the effects of the clinically available (R)-enantiomer of MOD on extracellular dopamine levels in the nucleus accumbens shell, a mesolimbic dopaminergic projection field that plays significant roles in various aspects of psychostimulant use disorders, measured in vivo by fast-scan cyclic voltammetry and by microdialysis in Sprague-Dawley rats. We have compared these results with those obtained under identical experimental conditions with two novel and enantiopure bis(F) analogs of MOD, JBG1-048 and JBG1-049. The results show that (R)-modafinil (R-MOD), JBG1-048, and JBG1-049, when administered intravenously with cumulative drug-doses, will block the dopamine transporter and reduce the clearance rate of dopamine, increasing its extracellular levels. Differences among the compounds in their maximum stimulation of dopamine levels, and in their time course of effects were also observed. These data highlight the mechanistic underpinnings of R-MOD and its bis(F) analogs as pharmacological tools to guide the discovery of novel medications to treat psychostimulant use disorders.

Translating the atypical dopamine uptake inhibitor hypothesis toward therapeutics for treatment of psychostimulant use disorders

Medication-assisted treatments are unavailable to patients with cocaine use disorders. Efforts to develop potential pharmacotherapies have led to the identification of a promising lead molecule, JJC8-091, that demonstrates a novel binding mode at the dopamine transporter (DAT). Here, JJC8-091 and a structural analogue, JJC8-088, were extensively and comparatively assessed to elucidate neurochemical correlates to their divergent behavioral profiles. Despite sharing significant structural similarity, JJC8-088 was more cocaine-like, increasing extracellular DA concentrations in the nucleus accumbens shell (NAS) efficaciously and more potently than JJC8-091. In contrast, JJC8-091 was not self-administered and was effective in blocking cocaine-induced reinstatement to drug seeking. Electrophysiology experiments confirmed that JJC8-091 was more effective than JJC8-088 at inhibiting cocaine-mediated enhancement of DA neurotransmission. Further, when VTA DA neurons in DAT-cre mice were optically stimulated, JJC8-088 produced a significant leftward shift in the stimulation-response curve, similar to cocaine, while JJC8-091 shifted the curve downward, suggesting attenuation of DA-mediated brain reward. Computational models predicted that JJC8-088 binds in an outward facing conformation of DAT, similar to cocaine. Conversely, JJC8-091 steers DAT towards a more occluded conformation. Collectively, these data reveal the underlying molecular mechanism at DAT that may be leveraged to rationally optimize leads for the treatment of cocaine use disorders, with JJC8-091 representing a compelling candidate for development.

Effects of ( R)-Modafinil and Modafinil Analogues on Dopamine Dynamics Assessed by Voltammetry and Microdialysis in the Mouse Nucleus Accumbens Shell

Recent discoveries have improved our understanding of the physiological and pathological roles of the dopamine transporter (DAT); however, only a few drugs are clinically available for DAT-implicated disorders. Among those drugs, modafinil (MOD) and its ( R)-enantiomer (R-MOD) have been used off-label as therapies for psychostimulant use disorders, but they have shown limited effectiveness in clinical trials. Recent preclinical studies on MOD and R-MOD have led to chemically modified structures aimed toward improving their neurobiological properties that might lead to more effective therapeutics for stimulant use disorders. This study examines three MOD analogues (JJC8-016, JJC8-088, and JJC8-091) with improved DAT affinities compared to their parent compound. These compounds were investigated for their effects on the neurochemistry (brain microdialysis and FSCV) and behavior (ambulatory activity) of male Swiss-Webster mice. Our data indicate that these compounds have dissimilar effects on tonic and phasic dopamine in the nucleus accumbens shell and variability in producing ambulatory activity. These results suggest that small changes in the chemical structure of a DAT inhibitor can cause compounds such as JJC8-088 to produce effects similar to abused psychostimulants like cocaine. In contrast, other compounds like JJC8-091 do not share cocaine-like effects and have a more atypical DAT-inhibitor profile, which may prove to be an advancement in the treatment of psychostimulant use disorders.

Pharmacological classification of centrally acting drugs using EEG in freely moving rats: an old tool to identify new atypical dopamine uptake inhibitors

Atypical dopamine uptake inhibitors (DUIs) bind to the dopamine transporter and inhibit the reuptake of dopamine but have lower abuse potential than psychostimulants. Several atypical DUIs can block abuse-related effects of cocaine and methamphetamine, thus making them potential medication candidates for psychostimulant use disorders. The aim of the current study is to establish an in-vivo assay using EEG for the rapid identification of atypical DUIs with potential for medication development. The typical DUIs cocaine and methylphenidate dose-dependently decreased the power of the alpha, beta, and gamma bands. The atypical DUI modafinil and its F-analog, JBG1-049, decreased the power of beta, but in contrast to cocaine, none of the other frequency bands, while JHW007 did not significantly alter the EEG spectrum. The mu-opioid receptor agonists heroin and morphine dose-dependently decreased the power of gamma and increased power of the other bands. The effect of morphine on EEG power bands was antagonized by naltrexone. The NMDA receptor antagonist ketamine increased the power of all frequency bands. Therefore, typical and atypical DUIs and drugs of other classes differentially affected EEG spectra, showing distinctive features in the magnitude and direction of their effects on EEG. Comparative analysis of the effects of test drugs on EEG indicates a potential atypical profile of JBG1-049 with similar potency and effectiveness to its parent compound modafinil. These data suggest that EEG can be used to rapidly screen compounds for potential activity at specific pharmacological targets and provide valuable information for guiding the early stages of drug development. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Lauflumide (NLS-4) Is a New Potent Wake-Promoting Compound

Psychostimulants are used for the treatment of excessive daytime sleepiness in a wide range of sleep disorders as well as in attention deficit hyperactivity disorder or cognitive impairment in neuropsychiatric disorders. Here, we tested in mice the wake-promoting properties of NLS-4 and its effects on the following sleep as compared with those of modafinil and vehicle. C57BL/6J mice were intraperitoneally injected with vehicle, NLS-4 (64 mg/kg), or modafinil (150 mg/kg) at light onset. EEG and EMG were recorded continuously for 24 h after injections and vigilance states as well as EEG power densities were analyzed. NLS-4 at 64 mg/kg induced significantly longer wakefulness duration than modafinil at 150 mg/kg. Although no significant sleep rebound was observed after sleep onset for both treatments as compared with their vehicles, modafinil-treated mice showed significantly more NREM sleep when compared to NLS-4. Spectral analysis of the NREM EEG after NLS-4 treatment indicated an increased power density in delta activity (0.75–3.5 Hz) and a decreased power in theta frequency range (6.25–7.25 Hz), while there was no differences after modafinil treatment. Also, time course analysis of the delta activity showed a significant increase only during the first 2 time intervals of sleep after NLS-4 treatment, while delta power was increased during the first 9 time intervals after modafinil. Our results indicate that NLS-4 is a highly potent wake-promoting drug with no sign of hypersomnia rebound. As opposed to modafinil, recovery sleep after NLS-4 treatment is characterized by less NREM amount and delta activity, suggesting a lower need for recovery despite longer drug-induced wakefulness.

Characterization of the Neurochemical and Behavioral Effects of Solriamfetol (JZP-110), a Selective Dopamine and Norepinephrine Reuptake Inhibitor

Excessive sleepiness (ES) is associated with several sleep disorders, including narcolepsy and obstructive sleep apnea (OSA). A role for monoaminergic systems in treating these conditions is highlighted by the clinical use of US Food and Drug Administration-approved drugs that act on these systems, such as dextroamphetamine, methylphenidate, modafinil, and armodafinil. Solriamfetol (JZP-110) is a wake-promoting agent that is currently being evaluated to treat ES in patients with narcolepsy or OSA. Clinical and preclinical data suggest that the wake-promoting effects of solriamfetol differ from medications such as modafinil and amphetamine. The goal of the current studies was to characterize the mechanism of action of solriamfetol at monoamine transporters using in vitro and in vivo assays. Results indicate that solriamfetol has dual reuptake inhibition activity at dopamine (DA; IC₅₀ = 2.9 μM) and norepinephrine (NE; IC₅₀ = 4.4 μM) transporters, and this activity is associated in vivo with increased extracellular concentration of DA and NE as measured by microdialysis. Solriamfetol has negligible functional activity at the serotonin transporter (IC₅₀ > 100 μM). Moreover, the wake-promoting effects of solriamfetol are probably owing to activity at DA and NE transporters rather than other neurotransmitter systems, such as histamine or orexin. The dual activity of solriamfetol at DA and NE transporters and the lack of significant monoamine-releasing properties of solriamfetol might explain the differences in the in vivo effects of solriamfetol compared with modafinil or amphetamine. Taken together, these data suggest that solriamfetol may offer an important advancement in the treatment of ES in patients with narcolepsy or OSA.

Heterocyclic Analogues of Modafinil as Novel, Atypical Dopamine Transporter Inhibitors

Modafinil is a wake promoting compound with high potential for cognitive enhancement. It is targeting the dopamine transporter (DAT) with moderate selectivity, thereby leading to reuptake inhibition and increased dopamine levels in the synaptic cleft. A series of modafinil analogues have been reported so far, but more target-specific analogues remain to be discovered. It was the aim of this study to synthesize and characterize such analogues and, indeed, a series of compounds were showing higher activities on the DAT and a higher selectivity toward DAT versus serotonin and norepinephrine transporters than modafinil. This was achieved by substituting the amide moiety by five- and six-membered aromatic heterocycles. In vitro studies indicated binding to the cocaine pocket on DAT, although molecular dynamics revealed binding different from that of cocaine. Moreover, no release of dopamine was observed, ruling out amphetamine-like effects. The absence of neurotoxicity of a representative analogue may encourage further preclinical studies of the above-mentioned compounds.

Inhibitor mechanisms in the S1 binding site of the dopamine transporter defined by multi-site molecular tethering of photoactive cocaine analogs

Dopamine transporter (DAT) blockers like cocaine and many other abused and therapeutic drugs bind and stabilize an inactive form of the transporter inhibiting reuptake of extracellular dopamine (DA). The resulting increases in DA lead to the ability of these drugs to induce psychomotor alterations and addiction, but paradoxical findings in animal models indicate that not all DAT antagonists induce cocaine-like behavioral outcomes. How this occurs is not known, but one possibility is that uptake inhibitors may bind at multiple locations or in different poses to stabilize distinct conformational transporter states associated with differential neurochemical endpoints. Understanding the molecular mechanisms governing the pharmacological inhibition of DAT is therefore key for understanding the requisite interactions for behavioral modulation and addiction. Previously, we leveraged complementary computational docking, mutagenesis, peptide mapping, and substituted cysteine accessibility strategies to identify the specific adduction site and binding pose for the crosslinkable, photoactive cocaine analog, RTI 82, which contains a photoactive azide attached at the 2β position of the tropane pharmacophore. Here, we utilize similar methodology with a different cocaine analog N-[4-(4-azido-3-I-iodophenyl)-butyl]-2-carbomethoxy-3-(4-chlorophenyl)tropane, MFZ 2-24, where the photoactive azide is attached to the tropane nitrogen. In contrast to RTI 82, which crosslinked into residue Phe319 of transmembrane domain (TM) 6, our findings show that MFZ 2-24 adducts to Leu80 in TM1 with modeling and biochemical data indicating that MFZ 2-24, like RTI 82, occupies the central S1 binding pocket with the (+)-charged tropane ring nitrogen coordinating with the (-)-charged carboxyl side chain of Asp79. The superimposition of the tropane ring in the three-dimensional binding poses of these two distinct ligands provides strong experimental evidence for cocaine binding to DAT in the S1 site and the importance of the tropane moiety in competitive mechanisms of DA uptake inhibition. These findings set a structure-function baseline for comparison of typical and atypical DAT inhibitors and how their interactions with DAT could lead to the loss of cocaine-like behaviors.

Atypical dopamine transporter inhibitors R-modafinil and JHW 007 differentially affect D2 autoreceptor neurotransmission and the firing rate of midbrain dopamine neurons

Abuse of psychostimulants like cocaine that inhibit dopamine (DA) reuptake through the dopamine transporter (DAT) represents a major public health issue, however FDA-approved pharmacotherapies have yet to be developed. Recently a class of ligands termed "atypical DAT inhibitors" has gained attention due to their range of effectiveness in increasing extracellular DA levels without demonstrating significant abuse liability. These compounds not only hold promise as therapeutic agents to treat stimulant use disorders but also as experimental tools to improve our understanding of DAT function. Here we used patch clamp electrophysiology in mouse brain slices to explore the effects of two atypical DAT inhibitors (R-modafinil and JHW 007) on the physiology of single DA neurons in the substantia nigra and ventral tegmental area. Despite their commonalities of being DAT inhibitors that lack cocaine-like behavioral profiles, these compounds exhibited surprisingly divergent cellular effects. Similar to cocaine, R-modafinil slowed DA neuron firing in a D2 receptor-dependent manner and rapidly enhanced the amplitude and duration of D2 receptor-mediated currents in the midbrain. In contrast, JHW 007 exhibited little effect on firing, slow DAT blockade, and an unexpected inhibition of D2 receptor-mediated currents that may be due to direct D2 receptor antagonism. Furthermore, pretreatment with JHW 007 blunted the cellular effects of cocaine, suggesting that it may be valuable to investigate similar DAT inhibitors as potential therapeutic agents. Further exploration of these and other atypical DAT inhibitors may reveal important cellular effects of compounds that will have potential as pharmacotherapies for treating cocaine use disorders.

The Novel Modafinil Analog, JJC8-016, as a Potential Cocaine Abuse Pharmacotherapeutic

(±)Modafinil ((±)MOD) and its R-enantiomer (R-modafinil; R-MOD) have been investigated for their potential as treatments for psychostimulant addiction. We recently reported a series of (±)MOD analogs, of which JJC8-016 (N-(2-((bis(4-fluorophenyl)methyl)thio)ethyl)-3-phenylpropan-1-amine) was selected for further development. JJC8-016 and R-MOD were evaluated for binding across ~70 receptors, transporters, and enzymes. Although at a concentration of 10 μM, there were many hits for JJC8-016, binding affinities in the range of its DAT affinity were only observed at the serotonin transporter (SERT), dopamine D₂-like, and sigma₁ receptors. R-MOD was more selective, but had much lower affinity at the DAT (K_i=3 μM) than JJC8-016 (K_i=116 nM). In rats, systemic administration of R-MOD alone (10-30 mg/kg i.p.) dose-dependently increased locomotor activity and electrical brain-stimulation reward, whereas JJC8-016 (10-30 mg/kg i.p.) did not produce these effects. Strikingly, pretreatment with JJC8-016 dose-dependently inhibited cocaine-enhanced locomotion, cocaine self-administration, and cocaine-induced reinstatement of drug-seeking behavior, whereas R-MOD inhibited cocaine-induced reinstatement only at the high dose of 100 mg/kg. Notably, JJC8-016 alone neither altered extracellular dopamine in the nucleus accumbens nor maintained self-administration. It also failed to induce reinstatement of drug-seeking behavior. These findings suggest that JJC8-016 is a unique DAT inhibitor that has no cocaine-like abuse potential by itself. Moreover, pretreatment with JJC8-016 significantly inhibits cocaine-taking and cocaine-seeking behavior likely by interfering with cocaine binding to DAT. In addition, off-target actions may also contribute to its potential therapeutic utility in the treatment of cocaine abuse.

Synthesis of (R)-Modafinil via Organocatalyzed and Non-Heme Iron-Catalyzed Sulfoxidation Using H2O2 as an Environmentally Benign Oxidant

The first organocatalyzed sulfoxidation reaction towards enantioenriched (R)-modafinil (Armodafinil®), a drug against narcolepsy, is reported here. A series of chiral organocatalysts, e.g., different chiral BINOL-phosphates, or a fructose-derived N-substituted oxazolidinone ketone (Shi catalyst) were applied for the sulfoxidation reaction with environmentally friendly H2O2 as a convenient oxygen transferring agent. Furthermore, the potential of a biomimetic catalytic system consisting of FeCl3 and a dipeptide-based chiral ligand was demonstrated, which constitutes the most successful asymmetric non-heme iron-catalyzed synthesis of (R)-modafinil so far.

Novel and High Affinity 2-[(Diphenylmethyl)sulfinyl]acetamide (Modafinil) Analogues as Atypical Dopamine Transporter Inhibitors

The development of pharmacotherapeutic treatments of psychostimulant abuse has remained a challenge, despite significant efforts made toward relevant mechanistic targets, such as the dopamine transporter (DAT). The atypical DAT inhibitors have received attention due to their promising pharmacological profiles in animal models of cocaine and methamphetamine abuse. Herein, we report a series of modafinil analogues that have an atypical DAT inhibitor profile. We extended SAR by chemically manipulating the oxidation states of the sulfoxide and the amide functional groups, halogenating the phenyl rings, and/or functionalizing the terminal nitrogen with substituted piperazines, resulting in several novel leads such as 11b, which demonstrated high DAT affinity (K_i = 2.5 nM) and selectivity without producing concomitant locomotor stimulation in mice, as compared to cocaine. These results are consistent with an atypical DAT inhibitor profile and suggest that 11b may be a potential lead for development as a psychostimulant abuse medication.

The unique psychostimulant profile of (±)-modafinil: investigation of behavioral and neurochemical effects in mice

Blockade of dopamine (DA) reuptake via the dopamine transporter (DAT) is a primary mechanism identified as underlying the therapeutic actions of (±)-modafinil (modafinil) and its R-enantiomer, armodafinil. Herein, we explored the neurochemical and behavioral actions of modafinil to better characterize its psychostimulant profile. Swiss-Webster mice were implanted with microdialysis probes in the nucleus accumbens shell (NAS) or core (NAC) to evaluate changes in DA levels related to acute reinforcing actions of drugs of abuse. Additionally, subjective effects were studied in mice trained to discriminate 10 mg/kg cocaine (i.p.) from saline. Modafinil (17-300 mg/kg, i.p.) significantly increased NAS and NAC DA levels that at the highest doses reached ~300% at 1 h, and lasted > 6 h in duration. These elevated DA levels did not show statistically significant regional differences between the NAS and NAC. Modafinil produced cocaine-like subjective effects at 56-100 mg/kg when administered at 5 and 60 min before the start of the session, and enhanced cocaine effects when the two were administered in combination. Despite sharing subjective effects with cocaine, modafinil's psychostimulant profile was unique compared to that of cocaine and like compounds. Modafinil had lower potency and efficacy than cocaine in stimulating NAS DA. In addition, the cocaine-like subjective effects of modafinil were obtained at lower doses and earlier onset times than expected based on its dopaminergic effects. These studies suggest that although inhibition of DA reuptake may be a primary mechanism underlying modafinil's therapeutic actions, non DA-dependent actions may be playing a role in its psychostimulant profile.

Pharmacological Targeting the REV-ERBs in Sleep/Wake Regulation

The circadian clock maintains appropriate timing for a wide range of behaviors and physiological processes. Circadian behaviors such as sleep and wakefulness are intrinsically dependent on the precise oscillation of the endogenous molecular machinery that regulates the circadian clock. The identical core clock machinery regulates myriad endocrine and metabolic functions providing a link between sleep and metabolic health. The REV-ERBs (REV-ERBα and REV-ERBβ) are nuclear receptors that are key regulators of the molecular clock and have been successfully targeted using small molecule ligands. Recent studies in mice suggest that REV-ERB-specific synthetic agonists modulate metabolic activity as well as alter sleep architecture, inducing wakefulness during the light period. Therefore, these small molecules represent unique tools to extensively study REV-ERB regulation of sleep and wakefulness. In these studies, our aim was to further investigate the therapeutic potential of targeting the REV-ERBs for regulation of sleep by characterizing efficacy, and optimal dosing time of the REV-ERB agonist SR9009 using electroencephalographic (EEG) recordings. Applying different experimental paradigms in mice, our studies establish that SR9009 does not lose efficacy when administered more than once a day, nor does tolerance develop when administered once a day over a three-day dosing regimen. Moreover, through use of a time response paradigm, we determined that although there is an optimal time for administration of SR9009 in terms of maximal efficacy, there is a 12-hour window in which SR9009 elicited a response. Our studies indicate that the REV-ERBs are potential therapeutic targets for treating sleep problems as those encountered as a consequence of shift work or jet lag.

One-Pot Parallel Synthesis of Alkyl Sulfides, Sulfoxides, and Sulfones

A simple and cost-effective one-pot parallel synthesis approach to sulfides, sulfoxides, and sulfones from thiourea was elaborated. The method combines two procedures optimized to the parallel synthesis conditions: alkylation of thiourea with alkyl chlorides and mono or full oxidation of in situ generated sulfides with H2O2 or H2O2-(NH4)2MoO4. The experimental set up required commonly used lab equipment: conventional oven and ultrasonic bath; the work up includes filtration or extraction with chloroform. The method was evaluated on an 81 member library of drug-like sulfides, sulfoxides, and sulfones yielding the compounds on a 30-300 mg scale. A small-scale synthesis of 2-(benzhydrylsulfinyl)acetamide (modafinil) utilizing our approach resulted in similar efficiency to the published procedures.

R-modafinil attenuates nicotine-taking and nicotine-seeking behavior in alcohol-preferring rats

(±)-Modafinil (MOD) is used clinically for the treatment of sleep disorders and has been investigated as a potential medication for the treatment of psychostimulant addiction. However, the therapeutic efficacy of (±)-MOD for addiction is inconclusive. Herein we used animal models of self-administration and in vivo microdialysis to study the pharmacological actions of R-modafinil (R-MOD) and S-modafinil (S-MOD) on nicotine-taking and nicotine-seeking behavior, and mechanisms underlying such actions. We found that R-MOD is more potent and effective than S-MOD in attenuating nicotine self-administration in Long-Evans rats. As Long-Evans rats did not show a robust reinstatement response to nicotine, we used alcohol-preferring rats (P-rats) that display much higher reinstatement responses to nicotine than Long-Evans rats. We found that R-MOD significantly inhibited intravenous nicotine self-administration, nicotine-induced reinstatement, and nicotine-associated cue-induced drug-seeking behavior in P-rats. R-MOD alone neither sustained self-administration in P-rats previously self-administering nicotine nor reinstated extinguished nicotine-seeking behavior. The in vivo brain microdialysis assays demonstrated that R-MOD alone produced a slow-onset moderate increase in extracellular DA. Pretreatment with R-MOD dose-dependently blocked nicotine-induced dopamine (DA) release in the nucleus accumbens (NAc) in both naive and nicotine self-administrating rats, suggesting a DA-dependent mechanism underlying mitigation of nicotine's effects. In conclusion, the present findings support further investigation of R-MOD for treatment of nicotine dependence in humans.

Behavioral, biological, and chemical perspectives on atypical agents targeting the dopamine transporter

BACKGROUND

Treatment of stimulant-use disorders remains a formidable challenge, and the dopamine transporter (DAT) remains a potential target for antagonist or agonist-like substitution therapies.

METHODS

This review focuses on DAT ligands, such as benztropine, GBR 12909, modafinil, and DAT substrates derived from phenethylamine or cathinone that have atypical DAT-inhibitor effects, either in vitro or in vivo. The compounds are described from a molecular mechanistic, behavioral, and medicinal-chemical perspective.

RESULTS

Possible mechanisms for atypicality at the molecular level can be deduced from the conformational cycle for substrate translocation. For each conformation, a crystal structure of a bacterial homolog is available, with a possible role of cholesterol, which is also present in the crystal of Drosophila DAT. Although there is a direct relationship between behavioral potencies of most DAT inhibitors and their DAT affinities, a number of compounds bind to the DAT and inhibit dopamine uptake but do not share cocaine-like effects. Such atypical behavior, depending on the compound, may be related to slow DAT association, combined sigma-receptor actions, or bias for cytosol-facing DAT. Some structures are sterically small enough to serve as DAT substrates but large enough to also inhibit transport. Such compounds may display partial DA releasing effects, and may be combined with release or uptake inhibition at other monoamine transporters.

CONCLUSIONS

Mechanisms of atypical DAT inhibitors may serve as targets for the development of treatments for stimulant abuse. These mechanisms are novel and their further exploration may produce compounds with unique therapeutic potential as treatments for stimulant abuse.

Sulforaphane homologues: Enantiodivergent synthesis of both enantiomers, activation of the Nrf2 transcription factor and selective cytotoxic activity

Reported is an enantiodivergent approach for the synthesis of both enantiomers of sulforaphane (SFN) homologues with different chain lengths between the sulfinyl sulfur and the isothiocyanate groups and different substituents on the sulfinyl sulfur. The homologues were designed in order to unravel the effect of all the diversity elements included in sulforaphane's structure. The key step of the approach is the diastereoselective synthesis of both sulfinate ester epimers at sulfur, using as single chiral auxiliary the sugar derived diacetone-d-glucose. The approach allows the first synthesis of both enantiomers of 5-methylsulfinylpentyl isothiocyanate, and the biologically important 6-methylsulfinylhexyl isothiocyanate (6-HITC) found in Japanese horseradish, wasabi (Wasabia japonica). The ability of the synthesized compounds as inductors of phase II detoxifying enzymes has been studied by determining their ability to activate the cytoprotective transcription factor Nrf2. The cytotoxic activity of all the synthesized compounds against human lung adenocarcinoma (A549) and foetal lung fibroblasts (MRC-5) is also reported.

Elucidation of structural elements for selectivity across monoamine transporters: novel 2-[(diphenylmethyl)sulfinyl]acetamide (modafinil) analogues

2-[(Diphenylmethyl)sulfinyl]acetamide (modafinil, (±)-1) is a unique dopamine uptake inhibitor that binds the dopamine transporter (DAT) differently than cocaine and may have potential for the treatment of psychostimulant abuse. To further investigate structural requirements for this divergent binding mode, novel thio- and sulfinylacetamide and ethanamine analogues of (±)-1 were synthesized wherein (1) the diphenyl rings were substituted with methyl, trifluoromethyl, and halogen substituents and (2) substituents were added to the terminal amide/amine nitrogen. Halogen substitution of the diphenyl rings of (±)-1 gave several amide analogues with improved binding affinity for DAT and robust selectivity over the serotonin transporter (SERT), whereas affinity improved at SERT over DAT for the p-halo-substituted amine analogues. Molecular docking studies, using a subset of analogues with DAT and SERT homology models, and functional data obtained with DAT (A480T) and SERT (T497A) mutants defined a role for TM10 in the substrate/inhibitor S1 binding sites of DAT and SERT.

Modafinil attenuates reinstatement of cocaine seeking: role for cystine-glutamate exchange and metabotropic glutamate receptors

Modafinil may be useful for treating stimulant abuse, but the mechanisms by which it acts to do so are unknown. Indeed, a primary effect of modafinil is to inhibit dopamine transport, which typically promotes rather than inhibits motivated behavior. Therefore, we examined the role of nucleus accumbens extracellular glutamate and the group II metabotropic glutamate receptor (mGluR2/3) in modafinil effects. One group of rats was trained to self-administer cocaine for 10 days and extinguished, then given priming injections of cocaine to elicit reinstatement. Modafinil (300 mg/kg, intraperitoneal) inhibited reinstated cocaine seeking (but did not alter extinction responding by itself), and this effect was prevented by pre-treatment with bilateral microinjections of the mGluR2/3 antagonist LY-341495 (LY) into nucleus accumbens core. No reversal of modafinil effects was seen after unilateral accumbens core LY, or bilateral LY in the rostral pole of accumbens. Next, we sought to explore effects of modafinil on extracellular glutamate levels in accumbens after chronic cocaine. Separate rats were administered non-contingent cocaine, and after 3 weeks of withdrawal underwent accumbens microdialysis. Modafinil increased extracellular accumbens glutamate in chronic cocaine, but not chronic saline-pre-treated animals. This increase was prevented by reverse dialysis of cystine-glutamate exchange or voltage-dependent calcium channel antagonists. Voltage-dependent sodium channel blockade partly attenuated the increase in glutamate, but mGluR1 blockade did not. We conclude that modafinil increases extracellular glutamate in nucleus accumbens from glial and neuronal sources in cocaine-exposed rats, which may be important for its mGluR2/3-mediated antirelapse properties.

Synthesis and psychobiological evaluation of modafinil analogs in mice

Background and the purpose of the study

Modafinil, a novel wake-promoting agent with low potential for abuse and dependence, has a reliable structure to find some novel derivatives with better activity and lower potential for abuse and risk of dependency. This study was designed to evaluate psychobiological activity of some novel N-aryl modafinil derivatives.

Methods

Seven novel N-aryl modafinil derivatives were synthesized through three reactions: a) preparation of benzhydrylsulfanyl acetic acid through reaction of benzhydrol with thioglycolic acid, b) formation of desired amide by adding the substituted aniline to activated acid with EDC (1-ethyl-3-(3-dimethyl amino propyl) carbodiimide). This reaction was catalyzed by HOBt (N- hydroxylbenzotriazole), and c) oxidation of sulfur to sulfoxide group with H₂O₂. Then, their psychobiological effect on the performance of male albino mice were compared to that of modafinil as following: wakefulness by determining the effects of derivatives on phenobarbital-induced loss of the righting reflex (LOPR); exploratory activity by measuring activity in the open field test (OFT); depression by measuring immobility time (IT) during forced swimming test (FST) and the anxiogenic and anxiolytic like effects by using elevated plus-maze test (EPM). All tests were videotaped and analyzed for the frequency and duration of the behaviors during the procedures.

Conclusions

2-(Benzhydrylsulfonyl)-N-(4-chlorophenyl)acetamide (4c) showed comparable result in LOPR test. However, all analogs were found to be stimulant except 2-(benzhydrylsulfinyl)-N-phenylacetamide (4a). Also 4c led the most exploratory activity in mice among derivatives. FST results showed that 4a had the longest IT while modafinil, 2-(benzhydrylsulfinyl)-N-(3-chlorophenyl) acetamide (4b) and 2-(benzhydrylsulfinyl)-N-(4-ethylphenyl) acetamide (4d) had the shortest IT. In EPM, all derivatives showed anxiogenic-like behavior since they decreased open arms time and open arms entries and simultaneously increased close arms time.

Modafinil as a catecholaminergic agent: empirical evidence and unanswered questions

Modafinil, in its two clinical formulations (Provigil^® and Nuvigil^®), is a widely prescribed wake-promoting therapeutic agent. It binds competitively to the cell-membrane dopamine (DA) transporter and is dependent on catecholaminergic (dopaminergic and adrenergic) signaling for its wake-promoting effects. The clinical spectrum of effects for modafinil is distinct from the effects seen with other catecholaminergic agents. Relative to other commonly used agents that act through catecholaminergic mechanisms, modafinil has a relatively low abuse potential, produces wakefulness with an attenuated compensatory sleep recovery thereafter, and does not ameliorate cataplexy in narcolepsy. These clinically relevant phenomenological differences between modafinil and agents such as amphetamines and cocaine do not eliminate catecholaminergic effects as a possible mediator of its wake-promoting action; they merely reflect its unique pharmacological profile. Modafinil is an exceptionally weak, but apparently very selective, DA transporter inhibitor. The pharmacodynamic response to modafinil, as measured by DA levels in brain microdialyzate, is protracted relative to other agents that act via catecholaminergic mechanisms. The conformational constraints on the interaction of modafinil with the DA transporter – and probably, as a consequence, its effects on trace amine receptor signaling in the catecholaminergic cell – are unique among catecholaminergic agents. These unique pharmacological properties of modafinil should be considered both in seeking to thoroughly understand its putatively elusive mechanism of action and in the design of novel therapeutic agents.

The neurobiology of modafinil as an enhancer of cognitive performance and a potential treatment for substance use disorders

RATIONALE AND OBJECTIVES

Modafinil (MOD) and its R-enantiomer (R-MOD) are approved medications for narcolepsy and other sleep disorders. They have also been used, off-label, as cognitive enhancers in populations of patients with mental disorders, including substance abusers that demonstrate impaired cognitive function. A debated nonmedical use of MOD in healthy individuals to improve intellectual performance is raising questions about its potential abuse liability in this population.

RESULTS AND CONCLUSIONS

MOD has low micromolar affinity for the dopamine transporter (DAT). Inhibition of dopamine (DA) reuptake via the DAT explains the enhancement of DA levels in several brain areas, an effect shared with psychostimulants like cocaine, methylphenidate, and the amphetamines. However, its neurochemical effects and anatomical pattern of brain area activation differ from typical psychostimulants and are consistent with its beneficial effects on cognitive performance processes such as attention, learning, and memory. At variance with typical psychostimulants, MOD shows very low, if any, abuse liability, in spite of its use as a cognitive enhancer by otherwise healthy individuals. Finally, recent clinical studies have focused on the potential use of MOD as a medication for treatment of drug abuse, but have not shown consistent outcomes. However, positive trends in several result measures suggest that medications that improve cognitive function, like MOD or R-MOD, may be beneficial for the treatment of substance use disorders in certain patient populations.

Simple synthesis of modafinil derivatives and their anti-inflammatory activity

Simple synthesis of modafinil derivatives and their biological activity are described. The key synthetic strategies involve substitution and coupling reactions. We determined the anti-inflammatory effects of modafinil derivatives in cultured BV2 cells by measuring the inhibition of nitrite production and expression of iNOS and COX-2 after LPS stimulation. It was found that for sulfide analogues introduction of aliphatic groups on the amide part (compounds 11a–d) resulted in lower anti-inflammatory activity compared with cyclic or aromatic moieties (compounds 11e–k). However, for the sulfoxide analogues, introduction of aliphatic moieties (compounds 12a–d) showed higher anti-inflammatory activity than cyclic or aromatic fragments (compounds 12e–k) in BV-2 microglia cells.

R-modafinil (armodafinil): a unique dopamine uptake inhibitor and potential medication for psychostimulant abuse

BACKGROUND

(±)-Modafinil has piqued interest as a treatment for attention-deficit/hyperactivity disorder and stimulant dependence. The R-enantiomer of modafinil might have unique pharmacological properties that should be further investigated.

METHODS

(±)-Modafinil and its R-(-)- and S-(+)-enantiomers were synthesized and tested for inhibition of [(3)H] dopamine (DA) uptake and [(3)H]WIN 35428 binding in human dopamine transporter (DAT) wild-type and mutants with altered conformational equilibria. Data were compared with cocaine and the atypical DA uptake inhibitor, JHW 007. R- and S-modafinil were also evaluated in microdialysis studies in the mouse nucleus accumbens shell and in a cocaine discrimination procedure.

RESULTS

(±)-, R-, and S-modafinil bind to the DAT and inhibit DA uptake less potently than cocaine, with R-modafinil having approximately threefold higher affinity than its S-enantiomer. Molecular docking studies revealed subtle differences in binding modes for the enantiomers. R-modafinil was significantly less potent in the DAT Y156F mutant compared with wild-type DAT, whereas S-modafinil was affected less. Studies with the Y335A DAT mutant showed that the R- and S-enantiomers tolerated the inward-facing conformation better than cocaine, which was further supported by [2-(trimethylammonium)ethyl]-methanethiosulfonate reactivity on the DAT E2C I159C. Microdialysis studies demonstrated that both R- and S-modafinil produced increases in extracellular DA concentrations in the nucleus accumbens shell less efficaciously than cocaine and with a longer duration of action. Both enantiomers fully substituted in mice trained to discriminate cocaine from saline.

CONCLUSIONS

R-modafinil displays an in vitro profile different from cocaine. Future trials with R-modafinil as a substitute therapy with the potential benefit of cognitive enhancement for psychostimulant addiction are warranted.