Discovery and Structure−Activity Relationship of (1R)-8-Chloro-2,3,4,5-tetrahydro-1-methyl-1H-3-benzazepine (Lorcaserin), a Selective Serotonin 5-HT2C Receptor Agonist for the Treatment of Obesity

High-fat and obesogenic diets: current and future strategies to fight obesity and diabetes

Obesity, diabetes and their associated diseases are some of the greatest challenges that the world health care systems already face and with prospects of overburdening their capacities and funding. Due to decreased energetic expenditure and increased caloric intake, particularly in saturated fats, the number of people afflicted by said conditions is increasing by the day. Due to the failure, to this day, to effectively and ubiquity prevent and revert these diseases, the research into new compounds and therapeutic strategies is vital. In this review, we explain the most common dietary models of obesity and diabetes and the novel avenues of research we believe will be taken in the next few years in obesity and diabetes research. We primarily focus on the role of mitochondria and how the modulation of mitochondrial function and number as well as several promising therapeutic strategies involving metabolic regulators can positively affect the obese and diabetic status.

The safety and efficacy of lorcaserin in the management of obesity

Lorcaserin represents a new serotonergic medication used as an adjunct to a reduced-calorie diet and increased physical activity treatment plan for chronic weight management in adult patients with an initial body mass index ≥ 30 kg/m 2 or in adult patients with an initial body mass index ≥ 27 kg/m 2 who have ≥ 1 comorbid condition associated with weight (eg, hypertension, dyslipidemia, or type 2 diabetes mellitus). In 2012, lorcaserin became the first obesity treatment medication to gain US Food and Drug Administration (FDA) approval since 1999. Lorcaserin is a centrally acting, selective serotonin C (5-HT2C) receptor full agonist that is associated with increased satiety and decreased food consumption in patients. The selectivity of lorcaserin for 5-HT2C receptors should reduce patient risk for the serious adverse complications that are associated with nonselective 5-HT agonist therapies, such as cardiac valvulopathy and pulmonary hypertension. The safety and efficacy of lorcaserin (10 mg twice daily) for ≥ 52 weeks has been evaluated in 3 separate Phase 3 trials. The primary outcome of patient weight loss in the 3 trials satisfied the FDA categorical benchmark but patient outcomes in the trials failed to achieve the FDA mean benchmark of patient weight loss. Secondary patient outcomes after lorcaserin therapy were favorable. Lorcaserin appears to be well tolerated in patients and the most common adverse events reported did not include serious complications. The incidence of FDA-defined valvulopathy in patients after 1 year of treatment was low and nonsignificant, but the statistical analysis of this safety endpoint was limited due to the small size of the study populations and high patient dropout rates. Continued post-marketing surveillance of patients taking lorcaserin is warranted.

Discovery of 1-(2,4-dichlorophenyl)-N-(piperidin-1-yl)-4-((pyrrolidine-1-sulfonamido)methyl)-5-(5-((4-(trifluoromethyl)phenyl)ethynyl)thiophene-2-yl)-1H-pyrazole-3-carboxamide as a novel peripherally restricted cannabinoid-1 receptor antagonist with significant weight-loss efficacy in diet-induced obese mice

After extensive synthetic efforts, we found that many structurally diverse bioisosteres could be generated via derivatizing the C-4 alkyl chain on the pyrazole ring of compound 3 (B/P = 1/33) with different electronegative groups. Especially when a sulfonamide or sulfamide moiety was added, resulting compounds exhibited not only potent CB1R activity but also a desired tPSA value over 90 Å(2), a threshold considered to possess a low probability to cross BBB, leading to the identification of compound 4 (B/P = 1/64) as a peripherally restricted CB1R antagonist. Apart from its significant weight-loss efficacy in DIO mice, compound 4 also displays 163 clean off-target profiles and is currently under development for treating obesity and the related metabolic syndrome.

Obesity pharmacotherapy: current perspectives and future directions

The rising tide of obesity and its related disorders is one of the most pressing health concerns worldwide, yet existing medicines to combat the problem are disappointingly limited in number and effectiveness. Recent advances in mechanistic insights into the neuroendocrine regulation of body weight have revealed an expanding list of molecular targets for novel, rationally designed antiobesity pharmaceutical agents. Antiobesity drugs act via any of four mechanisms: 1) decreasing energy intake, 2) increasing energy expenditure or modulating lipid metabolism, 3) modulating fat stores or adipocyte differentiation, and 4) mimicking caloric restriction. Various novel drug candidates and targets directed against obesity are currently being explored. A few of them are also in the later phases of clinical trials. This review discusses the development of novel antiobesity drugs based on current understanding of energy homeostasis

Lorcaserin: a novel serotonin 2C agonist for the treatment of obesity

BACKGROUND

Obesity has become an epidemic in the United States and its prevalence continues to increase. Adjunctive treatment with pharmacotherapy is often reserved for individuals who fail to achieve their intended weight goals with diet and exercise alone. Current approved therapies for weight loss include phentermine, diethylpropion, orlistat, and phentermine/topiramate. The objective of this paper was to review the place of lorcaserin, a novel serotonin 2C agonist, which was FDA approved in July 2012. Unlike contemporary lipase inhibitors and sympathomimetic amines, lorcaserin is purported to reduce food consumption and increase satiety.

SCOPE

A systematic review of the literature for all relevant articles was performed through January 2013 using MEDLINE, Web of Science, and International Pharmaceutical Abstracts using key words related to lorcaserin.

FINDINGS

Three phase III clinical studies have been published evaluating the efficacy and safety of lorcaserin in various obese populations. A higher proportion of patients receiving lorcaserin (∼47%) lost more than 5% body weight from baseline in comparison with the placebo group (∼25%; p < 0.05 in all studies). Those receiving the recommended dose of lorcaserin 10 mg twice daily lost on average ∼6 kg of body weight from baseline versus ∼3 kg with placebo. Patients with diabetes mellitus also saw significant reductions in their HbA1c with lorcaserin (∼0.9%) versus placebo (∼0.4%; p < 0.001). Lorcaserin is generally well tolerated with the most commonly experienced adverse events being nausea, dizziness, headache, upper respiratory tract infections, and nasopharyngitis. Cardiovascular evaluations showed no appreciable increase in valvulopathy with lorcaserin use versus placebo.

CONCLUSION

For now, pharmacists should continue to recommend the use of lorcaserin as a complement to, not in lieu of, ongoing lifestyle and behavioral modification.

Echocardiographic assessment of cardiac valvular regurgitation with lorcaserin from analysis of 3 phase 3 clinical trials

BACKGROUND

Lorcaserin is a selective 5-HT2C agonist evaluated for weight management in clinical trials. Echocardiographic monitoring was conducted to test the hypothesis that selective 5-HT2C agonism would avoid valvular heart disease.

METHODS AND RESULTS

Echocardiographic and weight change data from 5249 obese and overweight patients in 3 phase 3 trials were integrated. Treatment duration with 10 mg lorcaserin twice daily or placebo was 52 weeks. The proportions of patients who developed Food and Drug Administration-defined valvulopathy (≥ mild aortic or ≥ moderate mitral regurgitation) and changes in regurgitant grade at each heart valve were evaluated. Possible associations between weight or body mass index change and valvulopathy were explored. New valvulopathy was present in 2.04% of placebo and 2.37% of lorcaserin recipients at 52 weeks (risk difference, 0.33%; 95% confidence interval, -0.46 to 1.13; risk ratio, 1.16 [all patients with sufficient echocardiographic data, last-observation-carried-forward imputation] or 1.03 [patients who completed 52 weeks]). Changes in weight and body mass index were negatively associated with presence of valvulopathy at week 52 (P=0.02 and P=0.04, respectively); a 5% decrease in weight was associated with an odds ratio of 1.15 for Food and Drug Administration-defined valvulopathy. Most changes in regurgitation were ±1 grade in both treatment groups at all heart valves.

CONCLUSIONS

In 3 prospective placebo-controlled trials with integrated data for 5249 patients, the rate of echocardiographic valvulopathy was similar with lorcaserin and placebo. Point estimates for risk ratios ranged from 1.03 to 1.16 and may be at least partially influenced by greater weight loss in the lorcaserin group than in the placebo group.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00395135, NCT00603291, NCT00603902.

Structural basis for molecular recognition at serotonin receptors

Serotonin or 5-hydroxytryptamine (5-HT) regulates a wide spectrum of human physiology through the 5-HT receptor family. We report the crystal structures of the human 5-HT1B G protein-coupled receptor bound to the agonist antimigraine medications ergotamine and dihydroergotamine. The structures reveal similar binding modes for these ligands, which occupy the orthosteric pocket and an extended binding pocket close to the extracellular loops. The orthosteric pocket is formed by residues conserved in the 5-HT receptor family, clarifying the family-wide agonist activity of 5-HT. Compared with the structure of the 5-HT2B receptor, the 5-HT1B receptor displays a 3 angstrom outward shift at the extracellular end of helix V, resulting in a more open extended pocket that explains subtype selectivity. Together with docking and mutagenesis studies, these structures provide a comprehensive structural basis for understanding receptor-ligand interactions and designing subtype-selective serotonergic drugs.

Novel pyrimidoazepine analogs as serotonin 5-HT(2A) and 5-HT(2C) receptor ligands for the treatment of obesity

Obesity is one of the most serious public health problems worldwide in the 21st century. Current therapeutic treatment for obesity is mostly focused on preventive measures involving dietary control and physical exercises in combination with anti-obesity medications. However, most of these anti-obesity medications have little or no effect on weight loss, and some cases have demonstrated fatal side effects. Due to the urgent need for highly potent and selective anti-obesity agents, the serotonin receptors (5-HTR) have been the focus of much interest as a novel therapeutic target. In this report, we have developed pyrimidoazepine analogs targeting the 5-HT2A and 5-HT2C receptors and evaluated their biological activity in vitro and in vivo as novel anti-obesity agents. We were able to identify 6p as the most potent 5-HT2A and 5-HT2C ligand in vitro (IC50 = 3 nM and 2.3 nM, respectively), and this compound also demonstrated the greatest potency in vivo. In an acute obesity model, mice treated with 6p showed significant decrease in body weight gain and food intake over approximately 77-94% compared to a control group. In a chronic obesity model, mice treated with 6p also showed a marked decrease in food intake and body weight gain.

Synthesis of novel analogs of cabergoline: improving cardiovascular safety by removing 5-HT2B receptor agonism

The dopamine agonist cabergoline has been used to treat prolactinomas, Parkinson's disease, Cushing's disease and sexual dysfunction. However, its clinical use was severely curtailed when it was found that patients taking cabergoline had an increased risk of developing cardiac-valve regurgitation. This potentially life-threatening condition has been associated with drugs, such as cabergoline, that are 5-HT_2B receptor agonists. We prepared analogs of cabergoline and have identified several that have limited or no agonism at the 5-HT_2B receptor.

Design, synthesis, and pharmacological characterization of N- and O-substituted 5,6,7,8-tetrahydro-4H-isoxazolo[4,5-d]azepin-3-ol analogues: novel 5-HT(2A)/5-HT(2C) receptor agonists with pro-cognitive properties

The isoxazol-3-one tautomer of the bicyclic isoxazole, 5,6,7,8-tetrahydro-4H-isoxazolo[4,5-d]azepin-3-ol (THAZ), has previously been shown to be a weak GABA(A) and glycine receptor antagonist. In the present study, the potential in this scaffold has been explored through the synthesis and pharmacological characterization of a series of N- and O-substituted THAZ analogues. The analogues N-Bn-THAZ (3d) and O-Bn-THAZ (4d) were found to be potent agonists of the human 5-HT(2A) and 5-HT(2C) receptors. Judging from an elaborate pharmacological profiling at numerous other CNS targets, the 3d analogue appears to be selective for the two receptors. Administration of 3d substantially improved the cognitive performance of mice in a place recognition Y-maze model, an effect fully reversible by coadministration of the selective 5-HT(2C) antagonist SB242084. In conclusion, as novel bioavailable cognitive enhancers that most likely mediate their effects through 5-HT(2A) and/or 5-HT(2C) receptors, the isoxazoles 3d and 4d constitute interesting leads for further medicinal chemistry development.

Synergism between a serotonin 5-HT2A receptor (5-HT2AR) antagonist and 5-HT2CR agonist suggests new pharmacotherapeutics for cocaine addiction

Relapse to cocaine dependence, even after extended abstinence, involves a number of liability factors including impulsivity (predisposition toward rapid, unplanned reactions to stimuli without regard to negative consequences) and cue reactivity (sensitivity to cues associated with cocaine-taking which can promote cocaine-seeking). These factors have been mechanistically linked to serotonin (5-hydroxytryptamine, 5-HT) signaling through the 5-HT(2A) receptor (5-HT(2A)R) and 5-HT(2C)R; either a selective 5-HT(2A)R antagonist or a 5-HT(2C)R agonist suppresses impulsivity and cocaine-seeking in preclinical models. We conducted proof-of-concept analyses to evaluate whether a combination of 5-HT(2A)R antagonist plus 5-HT(2C)R agonist would have synergistic effects over these liability factors for relapse as measured in a 1-choice serial reaction time task and cocaine self-administration/reinstatement assay. Combined administration of a dose of the selective 5-HT(2A)R antagonist M100907 plus the 5-HT(2C)R agonist WAY163909, each ineffective alone, synergistically suppressed cocaine-induced hyperactivity, inherent and cocaine-evoked impulsive action, as well as cue- and cocaine-primed reinstatement of cocaine-seeking behavior. The identification of synergism between a 5-HT(2A)R antagonist plus a 5-HT(2C)R agonist to attenuate these factors important in relapse indicates the promise of a bifunctional ligand as an anti-addiction pharmacotherapeutic, setting the stage to develop new ligands with improved efficacy, potency, selectivity, and in vivo profiles over the individual molecules.

Synthesis and SAR of 2,3,3a,4-tetrahydro-1H-pyrrolo[3,4-c]isoquinolin-5(9bH)-ones as 5-HT2C receptor agonists

A series of 2,3,3a,4-tetrahydro-1H-pyrrolo[3,4-c]isoquinolin-5(9bH)-ones is described, several examples of which exhibit potent 5-HT(2C) agonism with excellent selectivity over the closely related 5-HT(2A) and 5-HT(2B) receptors. Compounds such as 38 and 44 were shown to be effective in reducing food intake in an acute rat feeding model.

Lorcaserin Hydrochloride

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are sent in print and are also available on-line. Monographs can be customized to meet the needs of a facility. Subscribers to The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X. A drug class review is now published monthly with The Formulary Monograph Service. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The November 2012 monograph topics are on vincristine sulfate liposome injection; ZIV-aflibercept; icosapent ethyl; prednisone delayed-release tablets; and elvitegravir, cobicistat, emtricitabine, tenofovir DF. The DUE/MUE is on vincristine sulfate liposome.

Novel therapeutics and targets for the treatment of diabetes

The microvascular complications of insufficiently controlled diabetes (neuropathy, retinopathy and nephropathy) and the marked increased risk of macrovascular events (e.g., stroke and myocardial infarction) have a dire impact on society in both human and economic terms. In Type 1 diabetes total β-cell loss occurs. In Type 2 diabetes, partial β-cell loss occurs before diagnosis, and the progressive β-cell loss during the life of the patient increases the severity of the disease. In patients with diabetes, increased insulin resistance in the muscle and liver are key pathophysiologic defects. In addition, defects in metabolic processes in the fat, GI tract, brain, pancreatic α-cells and kidney are detrimental to the overall health of the patient. This review addresses novel therapies for these deficiencies in clinical and preclinical evaluation, emphasizing their potential to address glucose homeostasis, β-cell mass and function, and the comorbidities of cardiovascular disease and obesity.

Identification of structural determinants of ligand selectivity in 5-HT₂ receptor subtypes on the basis of protein-ligand interactions

Drug selectivity is one of the most critical improvement steps in drug development. The 5-hydroxytryptamine 2 (5-HT₂) receptor has 3 subtypes that exhibit different pharmacological functions. Because of their high amino acid sequence similarity, designing small molecules that selectively activate only 1 receptor among the 3 subtypes is difficult. We performed homology modeling of the 5-HT₂ receptor subtypes using the β₂-adrenergic receptor as a template to identify differences in active sites that may influence 5-HT₂ receptor agonist selectivity. A subset of selective 5-HT₂ agonists was docked into the modeled protein structures to investigate their interactions with each receptor. Subtype-specific active site residues at positions xl2.54, 5.39, and 5.46 interacted differently with each ligand. Molecular dynamics simulations revealed that position 5.46 of the 5-HT(2A) receptor interacted more favorably with selective 5-HT(2A) agonists than with selective 5-HT(2B) agonists. These computationally obtained insights provided clues to improving agonist selectivity for specific pharmacological action at 5-HT₂ receptors.

Animal models to explore the effects of CNS drugs on food intake and energy expenditure

Obesity has reached epidemic proportions globally with an increasing incidence not just in Western cultures but also Mexico, Brazil, China and parts of Africa. In terms of pharmacological intervention, the track record of drug treatments for obesity is poor, especially in the case of centrally acting medicines, and there remains an unmet need for the development of safer compounds delivering superior efficacy. Animal models are of importance not only in detecting changes in food intake, energy expenditure and body weight but also providing confidence that these changes are behaviourally specific and not a result of drug-induced side effects. We review animal models of feeding behaviour that are used to aid our understanding of the control of body weight and energy regulation with special reference to CNS-acting drugs. The use of such models in the discovery of new drugs for the treatment of obesity is given particular emphasis. This article is part of a Special Issue entitled 'Central Control of Food Intake'.

The 5-HT2C receptor agonist lorcaserin reduces nicotine self-administration, discrimination, and reinstatement: relationship to feeding behavior and impulse control

Lorcaserin ((1R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine HCl) is a selective 5-HT(2C) receptor agonist with clinical efficacy in phase-III obesity trials. Based on evidence that this drug class also affects behaviors motivated by drug reinforcement, we compared the effect of lorcaserin on behavior maintained by food and nicotine reinforcement, as well as the stimulant and discriminative stimulus properties of nicotine in the rat. Acutely administered lorcaserin (0.3-3 mg/kg, subcutaneous (SC)) dose dependently reduced feeding induced by 22-h food deprivation or palatability. Effects up to 1 mg/kg were consistent with a specific effect on feeding motivation. Lorcaserin (0.6-1 mg/kg, SC) reduced operant responding for food on progressive and fixed ratio schedules of reinforcement. In this dose range lorcaserin also reversed the motor stimulant effect of nicotine, reduced intravenous self-administration of nicotine, and attenuated the nicotine cue in rats trained to discriminate nicotine from saline. Lorcaserin also reduced the reinstatement of nicotine-seeking behavior elicited by a compound cue comprising a nicotine prime and conditioned stimulus previously paired with nicotine reinforcement. Lorcaserin did not reinstate nicotine-seeking behavior or substitute for a nicotine cue. Finally, lorcaserin (0.3-1 mg/kg) reduced nicotine-induced increases in anticipatory responding, a measure of impulsive action, in rats performing the five-choice serial reaction time task. Importantly, these results indicate that lorcaserin, and likely other selective 5-HT(2C) receptor agonists, similarly affect both food- and nicotine-motivated behaviors, and nicotine-induced impulsivity. Collectively, these findings highlight a therapeutic potential for 5-HT(2C) agonists such as lorcaserin beyond obesity into addictive behaviors, such as nicotine dependence.

The utility of animal models to evaluate novel anti-obesity agents

The global incidence of obesity continues to rise and is a major driver of morbidity and mortality through cardiovascular and cerebrovascular diseases. Animal models used in the discovery of novel treatments for obesity range from straightforward measures of food intake in lean rodents to long-term studies in animals exhibiting obesity due to the continuous access to diets high in fat. The utility of these animal models can be extended to determine, for example, that weight loss is due to fat loss and/or assess whether beneficial changes in key plasma parameters (e.g. insulin) are evident. In addition, behavioural models such as the behavioural satiety sequence can be used to confirm that a drug treatment has a selective effect on food intake. Typically, animal models have excellent predictive validity whereby drug-induced weight loss in rodents subsequently translates to weight loss in man. However, despite this, at the time of writing orlistat (Europe; USA) remains the only drug currently marketed for the treatment of obesity, with sibutramine having recently been withdrawn from sale globally due to the increased incidence of serious, non-fatal cardiovascular events. While the utility of rodent models in predicting clinical weight loss is detailed, the review also discusses whether animals can be used to predict adverse events such as those seen with recent anti-obesity drugs in the clinic.

A one-year randomized trial of lorcaserin for weight loss in obese and overweight adults: the BLOSSOM trial

CONTEXT

Lorcaserin is a novel selective agonist of the serotonin 2C receptor.

OBJECTIVE

Our objective was to evaluate the effects of lorcaserin on body weight, cardiovascular risk factors, and safety in obese and overweight patients.

DESIGN AND SETTING

This randomized, placebo-controlled, double-blind, parallel arm trial took place at 97 U.S. research centers.

PATIENTS

Patients included 4008 patients, aged 18-65 yr, with a body mass index between 30 and 45 kg/m(2) or between 27 and 29.9 kg/m(2) with an obesity-related comorbid condition.

INTERVENTIONS

Patients were randomly assigned in a 2:1:2 ratio to receive lorcaserin 10 mg twice daily (BID), lorcaserin 10 mg once daily (QD), or placebo. All patients received diet and exercise counseling.

MAIN OUTCOME MEASURES

The ordered primary endpoints were proportion of patients achieving at least 5% reduction in body weight, mean change in body weight, and proportion of patients achieving at least 10% reduction in body weight at 1 yr. Serial echocardiograms monitored heart valve function.

RESULTS

Significantly more patients treated with lorcaserin 10 mg BID and QD lost at least 5% of baseline body weight (47.2 and 40.2%, respectively) as compared with placebo (25.0%, P < 0.001 vs. lorcaserin BID). Least squares mean (95% confidence interval) weight loss with lorcaserin BID and QD was 5.8% (5.5-6.2%) and 4.7% (4.3-5.2%), respectively, compared with 2.8% (2.5-3.2%) with placebo (P < 0.001 vs. lorcaserin BID; least squares mean difference, 3.0%). Weight loss of at least 10% was achieved by 22.6 and 17.4% of patients receiving lorcaserin 10 mg BID and QD, respectively, and 9.7% of patients in the placebo group (P < 0.001 vs. lorcaserin BID). Headache, nausea, and dizziness were the most common lorcaserin-related adverse events. U.S. Food and Drug Administration-defined echocardiographic valvulopathy occurred in 2.0% of patients on placebo and 2.0% on lorcaserin 10 mg BID.

CONCLUSIONS

Lorcaserin administered in conjunction with a lifestyle modification program was associated with dose-dependent weight loss that was significantly greater than with placebo.

Lorcaserin for the treatment of obesity

Obesity is a worldwide epidemic and there is an urgent need for the development of effective pharmacological therapies that target the metabolic and behavioral factors of body weight regulation. Serotonin (5-HT) has been implicated as a critical factor in the short-term (meal-by-meal) regulation of food intake and pharmaceutical companies have invested millions of dollars to discover and develop drug targets for the serotonergic pathway. Lorcaserin is a novel selective agonist of the 5-HT(2C) receptor for weight loss therapy. Preclinical and clinical studies indicate lorcaserin is well tolerated and not associated with cardiac valvulopathy or pulmonary hypertension suggesting that lorcaserin is a selective 5-HT(2C) receptor agonist and has little or no activation of the 5-HT(2B) and 5-HT(2A) receptors, respectively. Lorcaserin acts to alter energy balance through a reduction in energy intake and without an increase in energy expenditure and achieved the U.S. Food and Drug Administration guidelines for weight loss efficacy. It remains to be determined whether or not lorcaserin will be approved for the long-term management of obesity.

Lorcaserin, a 5-HT2C agonist, decreases nicotine self-administration in female rats

Lorcaserin, a selective 5-hydroxytryptamine(2C) (5-HT(2C)) agonist, has been shown to facilitate weight loss in obese populations. It was assessed for its efficacy in reducing nicotine self-administration in young adult female Sprague-Dawley rats. The effect of short-term doses (subcutaneous) on nicotine self-administration (0.03 mg/kg per infusion) with a fixed ratio 1 schedule was assessed in 3-h sessions. Short-term lorcaserin doses (0.3125-20 mg/kg) were administered in a counterbalanced order. Significant reduction of nicotine self-administration was achieved with all of the short-term doses in this range. Tests of lorcaserin on locomotor activity detected prominent sedative effects at doses greater than 1.25 mg/kg with more modest transient effects seen at 0.625 to 1.25 mg/kg. Long-term effects of lorcaserin on locomotor activity were tested with repeated injections with 0.625 mg/kg lorcaserin 10 times over 2 weeks. This low lorcaserin dose did not cause an overall change in locomotor activity relative to that of saline-injected controls. Long-term lorcaserin (0.625 mg/kg) significantly reduced nicotine self-administration over a 2-week period of repeated injections. Long-term lorcaserin at this same dose had no significant effects on food self-administration over the same 2-week period of repeated injections. These studies support development of the 5-HT(2C) agonist lorcaserin to aid tobacco smoking cessation.

Reversal of sibutramine-induced anorexia with a selective 5-HT(2C) receptor antagonist

RATIONALE

The monoamine reuptake inhibitor sibutramine reduces food intake but the receptor subtypes mediating the effects of sibutramine on feeding remain to be clearly identified.

OBJECTIVES

The involvement of the 5-HT(2C) receptor subtype in the satiety-enhancing effects of sibutramine was investigated by examining the effects of co-administration of sibutramine with the selective 5-HT(2C) receptor antagonist SB 242084

METHODS

Microstructural analyses of licking for a glucose solution by non-deprived, male rats were performed over a range of doses of sibutramine to identify a selective satiety-enhancing dose (experiment 1). Similar analyses were performed after administration of a vehicle control, two doses of SB 242084 alone or two doses of SB 242084 in combination with sibutramine (experiment 2).

RESULTS

Sibutramine at doses of 1-3 mg/kg selectively reduced glucose consumption via a reduction in the number of bouts of licking. Non-selective effects to increase latency to lick were only observed at the higher dose of 6 mg/kg. Co-administration of sibutramine (3 mg/kg) with SB 242084 (1 or 3 mg/kg) reversed the effect of sibutramine on bout number whereas either dose of SB 242084 alone had no significant effect.

CONCLUSIONS

We confirm behaviourally selective effects of sibutramine on feeding and provide further support for the satiety-enhancing effects of sibutramine. Our data also provide evidence for the involvement of the 5-HT(2C) receptor in the satiety-enhancing effects of sibutramine although additional targets may have an impact, and further investigation of the molecular mechanisms underlying the efficacy of sibutramine as an anorectic is warranted.

Lorcaserin, a 5-HT(2C) receptor agonist, reduces body weight by decreasing energy intake without influencing energy expenditure

CONTEXT

Lorcaserin, a selective 5-hydroxytryptamine (5-HT)(2C) receptor agonist, reduces body weight. It is unclear whether weight loss is due to reduced energy intake (EI) or also to enhanced energy expenditure (EE).

OBJECTIVE

This study tested the effect of lorcaserin on EI and EE.

DESIGN, PARTICIPANTS, AND INTERVENTION

In a double-blind, randomized, placebo-controlled trial, 57 (39 women) overweight and obese (body mass index, 27-45 kg/m(2)) adults were randomized to placebo (n = 28) or 10 mg twice daily lorcaserin (n = 29) for 56 d. Weight maintenance was imposed during d 1-7. Beginning on d 8, participants followed a diet and exercise plan targeting a 600 kcal/d deficit.

OUTCOMES

At baseline and after 7 and 56 d of treatment, we measured body weight, body composition (dual x-ray absorptiometry), blood pressure, heart rate, EI at lunch and dinner, subjective appetite ratings, and 24-h EE and 24-h-respiratory quotient (RQ), measured by indirect calorimetry in a respiratory chamber.

RESULTS

After 7 d of weight maintenance, EI was significantly (P < 0.01) reduced with lorcaserin but not placebo (mean ± sem for lorcaserin, -286 ± 86 kcal; placebo, -147 ± 89 kcal). After 56 d, lorcaserin resulted in significantly larger reductions in body weight (lorcaserin, -3.8 ± 0.4 kg; placebo, -2.2 ± 0.5 kg; P < 0.01), EI (lorcaserin, -470 ± 87 kcal; placebo, -205 ± 91 kcal; P < .05), and appetite ratings than in placebo. Changes in 24-h EE and 24-h RQ did not differ between groups, even after 24-h EE was adjusted for body weight and composition. Compared with placebo, lorcaserin had no effect on systolic or diastolic blood pressure or heart rate after 56 d.

CONCLUSIONS

Lorcaserin reduces body weight through reduced EI, not altered EE or RQ.

The use of serotonergic drugs to treat obesity--is there any hope?

Surgical interventional strategies for the treatment of obesity are being implemented at an increasing rate. The safety and feasibility of these procedures are questionable for most overweight or obese individuals. The use of long-term pharmacotherapy options, on the other hand, can target a greater portion of the obese population and provide early intervention to help individuals maintain a healthy lifestyle to promote weight loss. Medications that act on the central serotonergic pathways have been a relative mainstay for the treatment of obesity for the last 35 years. The clinical efficacy of these drugs, however, has been encumbered by the potential for drug-associated complications. Two drugs that act, albeit by different mechanisms, on the central serotonergic system to reduce food intake and decrease body weight are sibutramine and lorcaserin. Sibutramine is a serotonin and norepinephrine reuptake inhibitor, whereas lorcaserin is a selective 5HT_2C receptor agonist. The recent worldwide withdrawal of sibutramine and FDA rejection of lorcaserin has changed the landscape not only for serotonin-based therapeutics specifically, but for obesity pharmacotherapy in general. The purpose of this review is to focus on the importance of the serotonergic system in the control of feeding and its potential as a target for obesity pharmacotherapy. Advances in refining and screening more selective receptor agonists and a better understanding of the potential off-target effects of serotonergic drugs are needed to produce beneficial pharmacotherapy.

The use of lorcaserin in the management of obesity: a critical appraisal

Obesity is a chronic disease with a high prevalence in both developed and developing countries. Effective management of this worldwide epidemic will have a significant impact on the health care system globally. Lifestyle interventions, such as restricting calorie consumption and increasing physical activity, remain a major component of weight-reduction programs. The development of pharmacotherapy for the management of obesity is still at the infancy stage. Side effects have been the key issue for anti-obesity drugs previously withdrawn from the market. The focus of this review, lorcaserin, is a selective serotonin receptor agonist that is currently undergoing Phase III evaluations. The efficacy of this drug in reducing body weight and improving metabolic parameters of obese patients has been demonstrated in two recent clinical trials. The available evidence indicates that this drug does not show unwanted effects on heart valves or pulmonary artery pressure, and the treatment improves the risk factors for type 2 diabetes and cardiovascular diseases. Despite these promising results, additional experimental and clinical studies are critical for the approval of lorcaserin as a new anti-obesity monodrug therapy by the US Food and Drug Administration.

Discovery and development of 5-HT2C receptor agonists for obesity: is there light at the end of the tunnel?

Ever since the observation of late-onset obesity during the phenotypic characterization of the 5-HT2C knock-out mouse, the serotonin 5-HT2C receptor has been a drug target for obesity. Small-molecule agonists have repeatedly been shown to reduce food intake and body weight in rodent models of obesity. To date, however, only one compound, lorcaserin, has completed Phase III trials and currently awaits an US FDA decision following a negative advisory committee meeting. Agonist selectivity versus the highly homologous 5-HT2A and 5-HT2B receptors remains a significant hurdle. Ideally, a specific 5-HT2C agonist (completely devoid of 5-HT2A and 5-HT2B activity) would be preferred. The requirement of a basic amine coupled with larger, often aromatic, hydrophobic domains, to gain selectivity, often leads to additional challenges associated with cationic amphiphilic molecules such as hERG-channel inhibition and phospholipidosis. The success of future 5-HT2C agonists will depend on further improvements in selectivity (or attainment of complete specificity) and pharmaceutical properties to permit greater and sustained receptor stimulation, while avoiding side effects associated with the activation of other 5-HT receptors.

Novel 6,7,8,9-tetrahydro-5H-1,4,7,10a-tetraaza-cyclohepta[f]indene analogues as potent and selective 5-HT(2C) agonists for the treatment of metabolic disorders

The discovery of a novel series of 5-HT(2C) agonists based on a tricyclic pyrazolopyrimidine scaffold is described. Compounds with good levels of in vitro potency and moderate to good levels of selectivity with respect to the 5-HT(2A) and 5-HT(2B) receptors were identified. One of the analogues (7 g) was found to be efficacious in a sub-chronic weight loss model. A key limitation of the series of compounds was that they were found to be potent inhibitors of the hERG ion channel. Some compounds, bearing polar side chains were identified which showed a much reduced hERG liability however these compounds were sub-optimal in terms of their in vitro potency or selectivity.