New approaches to the pharmacological treatment of obesity: can they break through the efficacy barrier?

In this review we assess the range of centrally active anorectics that are either in human clinical trials, or are likely to be so in the near future. We describe their weight loss efficacy, mode of action at both pharmacological and behavioural levels, where understood, together with the range of side effects that might be expected in clinical use. We have however evaluated these compounds against the considerably more rigorous criteria that are now being used by the Federal Drugs Agency and European Medicines Agency to decide approvals and market withdrawals. Several trends are evident. Recent advances in the understanding of energy balance control have resulted in the exploitation of a number of new targets, some of which have yielded promising data in clinical trials for weight loss. A second major trend is derived from the hypothesis that improved weight loss efficacy over current therapy is most likely to emerge from treatments targeting multiple mechanisms of energy balance control. This reasoning has led to the development of a number of new treatments for obesity where multiple mechanisms are targeted, either by a single molecule, such as tesofensine, or through drug combinations such as qnexa, contrave, empatic, and pramlintide+metreleptin. Many of these approaches also utilise advances in formulation technology to widen safety margins. Finally, the practicality of peptide therapies for obesity has become better validated in recent studies and this may allow more rapid exploitation of novel targets, rather than awaiting the development of orally available small molecules. We conclude that novel, more efficacious and better tolerated treatments for obesity may become available in the near future.

Co-administration of SR141716 with peptide YY3-36 or oxyntomodulin has additive effects on food intake in mice.

BACKGROUND: SR141716 has been shown to significantly inhibit food intake and reduce body weight by antagonizing CB(1) receptors. The gut hormones peptide YY(3-36) (PYY(3-36)) and oxyntomodulin (OXM) inhibit food intake through Y(2) and Glucagon-Like-Peptide (GLP)-1 receptors respectively. OBJECTIVE: To determine the effects of co-administration of SR141716 with either PYY(3-36) or OXM in mice on food intake. METHODS: Mice (n = 14 per group) were fasted for 16 h prior to study days and given two intraperitoneal injections: study 1, vehicle-saline, SR141716-saline, vehicle-PYY3-36 or SR141716-PYY3-36; study 2: vehicle-saline, SR141716-saline, vehicle-OXM or SR141716-OXM. Food was returned and measured following injections. RESULTS: Co-administration of SR141716-PYY(3-36) or SR141716-OXM showed greater inhibition in food intake when compared with administration of SR141716, PYY(3-36) or OXM alone. CONCLUSION: Our data show that SR141716 in combination with PYY(3-36) or OXM reduces food intake additively in mice.

Monoamine receptors in the regulation of feeding behaviour and energy balance.

We evaluate the likely utility of drugs that interact, either directly or indirectly, with monoamine binding receptors for the treatment of obesity. We discuss ligands at dopaminergic, adrenergic, serotoninergic and histaminergic receptors and also drugs that either release or inhibit the reuptake of monoamine neurotransmitters. We review evidence from preclinical studies of receptor distribution and function, together with the consequences of gene deletion in transgenic mouse strains and the results from human studies where these are available. In addition we consider the side effect profiles that would be expected of these potential anti-obesity treatments. We conclude that compounds interacting with 5-HT(2C), 5-HT(6) and histamine H(3) receptors may be of particular interest as specific drug development targets for the treatment of appetite disturbance in obesity.

Serotonin 1B and 2C receptor interactions in the modulation of feeding behaviour in the mouse.

RATIONALE: To examine the functional relationship between 5-HT1B receptors (5-HT1B-R) and 5-HT2C receptors (5-HT2C-R) in the control of food intake. OBJECTIVES: To compare the hypophagic effect of the 5-HT(2C/1B)-R agonist m-chlorophenylpiperazine (mCPP), with that of the selective 5-HT1B-R agonist CP-94,253 in both wildtype (WT) and 5-HT2C knockout (KO) mice. METHODS: The hypophagic effects of mCPP (1, 3 and 5.6 mg/kg) and CP-94,253 (5, 10 and 20 mg/kg) were assessed in WT and 5-HT2C KO mice using the behavioural satiety sequence paradigm. The effects of pre-treatment with the selective 5-HT2C-R antagonist SB 242,084 (0.5 and 1.5 mg/kg) were assessed in two groups of WT mice, with each group given only mCPP or CP-94,253. RESULTS: The 5-HT(2C/1B) receptor agonist mCPP and the selective 5-HT1B receptor agonist CP-94,253 both suppressed food intake in WT mice. 5-HT2C KO mice were insensitive to the hypophagic effects of mCPP but were more sensitive to CP-94,253-induced hypophagia than WT controls. mCPP induced a significant increase in post-prandial activity in 5-HT2C KO mice, but this effect was absent in 5-HT2C KO mice who were given CP-94,253. Data from WT mice, who were pre-treated with the 5-HT2C receptor antagonist SB 242,084 and then challenged with either mCPP or CP-94,253, were similar to those obtained from 5-HT2C KO mice. CONCLUSIONS: 5-HT2C-R and 5-HT1B-R activation are each sufficient to induce a hypophagic response. However, concurrent 5-HT2C-R inactivation can potentiate the hypophagic response to 5-HT1B-R activation, consistent with an inhibitory role for the 5-HT2C-R in behaviour mediated by the activation of other 5-HT receptors. These results also confirm that 5-HT1B-R activation alone cannot account for the hyperactive response of 5-HT2C KO mice to mCPP.

Synthesis and biological evaluation of novel hexahydro-pyrido[3',2':4,5]pyrrolo[1,2-a]pyrazines as potent and selective 5-HT(2C) receptor agonists.

Further lead optimization efforts on previously described 1,2,3,4,10,10a-hexahydro-1H-pyrazino[1,2-a]indoles led to the new class of 5,5a,6,7,8,9-hexahydro-pyrido[3',2':4,5]pyrrolo[1,2-a]pyrazines culminating in the discovery of (5aR,9R)-2-[(cyclopropylmethoxy)methyl]-5,5a,6,7,8,9-hexahydro-9-methyl-pyrido[3', 2':4,5]pyrrolo[1,2-a]pyrazine 18 as a potent, full 5-HT(2C) receptor agonist with an outstanding selectivity profile and excellent hERG and phospholipidosis properties.

Identification of 4-methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles as 5-HT2C receptor agonists.

Synthesis and evaluation of the activity of new 4-methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles as 5-HT(2C) receptor agonists are described. Appropriately substituted, several analogs displayed selectivity against the other 5-HT(2) receptor subtypes of 1 order of magnitude or more. Selectivity was improved for several compounds versus the lead 1, increasing the therapeutic interest in this series of 5-HT(2C) receptor agonists.

Cannabinoids and the regulation of ingestive behaviour.

Over past centuries, Cannabis sativa (Delta(9)-tetrahydrocannabinol being the principal active ingredient) has been used extensively for both medicinal and recreational uses, and one widely reported effect is the onset of a ravenous appetite and eating behaviour. The pharmacological properties of such exogenous cannabinoids are mediated through the activation of two receptor subtypes, the CB(1) and CB(2) receptors. A number of endogenous ligands for these receptors, the endocannabinoids, have now also been identified allowing their effects on ingestive behaviour to be determined. In a number of species, including man, the administration of exogenous and endogenous cannabinoids leads to robust increases in food intake and can promote body weight gain. These effects are believed to be mediated through activation of the CB(1) receptor. Conversely, experiments with selective CB(1) receptor antagonists have demonstrated reductions in food intake and body weight with repeated compound administration. These reductions in body weight appear to be greater in obese animals and may be the result of a dual effect on both food intake and metabolic processes. Such findings have led to a number of pharmaceutical companies developing selective CB(1) receptor antagonists for the treatment of obesity. The most advanced compound is Sanofi-Synthelabo's inverse agonist, rimonabant (Acomplia; SR-141716), and early Phase III results have recently demonstrated significant reductions in body weight, waist circumference and improvement of lipid and glucose metabolism in overweight and obese humans. Accordingly, the cannabinoid system appears to have an important role in the regulation of ingestive behaviour in man and animals.

Indoline derivatives as 5-HT(2C) receptor agonists.

A series of 1-(1-indolinyl)-2-propylamines was synthesised and evaluated as 5-HT(2C) receptor agonists for the treatment of obesity. The general methods of synthesis of the precursor indoles are described. The functional efficacy and radioligand binding data for all of the compounds at 5-HT(2) receptor subtypes are reported. A number of compounds were found to reduce food intake in rats after oral administration.

mCPP-induced hyperactivity in 5-HT2C receptor mutant mice is mediated by activation of multiple 5-HT receptor subtypes.

The serotonin receptor agonist mCPP induces hyperlocomotion in 5-HT2C receptor knockout (KO) mice or in the presence of a 5-HT2C receptor antagonist. In the present group of experiments, we evaluate the role of 5-HT1A, 5-HT1B and 5-HT2A receptors in mCPP-induced hyperactivity in 5-HT2C KO mice. We also assess the ability of agonists at these receptors to induce hyperactivity in wildtype (WT) mice pre-treated with a selective 5-HT2C receptor antagonist. As previously reported, mCPP (3 mg/kg) induced hyperactivity in 5-HT2C KO mice. A combination of the 5-HT1B receptor agonist CP-94,253 (20 mg/kg) and the 5-HT1A receptor agonist 8-OH-DPAT (0.5 mg/kg) induced marked hyperactivity in WT but not in 5-HT2C KO mice, nor in mice treated with the selective 5-HT2C receptor antagonist, SB 242084 (1.5 mg/kg). Neither CP-94,253 nor 8-OH-DPAT had any intrinsic effect on locomotion in WTs. mCPP-induced hyperactivity was attenuated in 5-HT2C KO mice by the 5-HT1B receptor antagonist SB 224289 (2.5 mg/kg), and the 5-HT2A receptor antagonists ketanserin (0.3 mg/kg) and M100907 (0.01 mg/kg) but not by the 5-HT1A receptor antagonist WAY 100635 (1 mg/kg). The 5-HT(2A/2B/2C) receptor agonist, Ro 60-0175 (3 mg/kg), induced a modest increase in locomotor activity in WT mice pre-treated with SB 242084. However, the combination of Ro 60-0175 with CP-94,253 induced a substantial increase in activity in 5-HT2C KO mice, an effect comparable to mCPP-induced hyperactivity. Thus, joint activation of 5-HT1A and 5-HT1B receptors stimulates locomotion in WT mice but this response is dependent on a functional 5-HT2C receptor population and hence is absent in 5-HT2C KO mice. By contrast, mCPP-induced hyperactivity depends on the inactivation of a separate 5-HT2C receptor population and is mediated by 5-HT2A and 5-HT1B receptor activation.

Oral administration of the 5-HT2Creceptor agonist, mCPP, reduces body weight gain in rats over 28 days as a result of maintained hypophagia.

RATIONALE: The 5-HT(2C) receptor subtype has been implicated extensively in the regulation of ingestive behaviour. OBJECTIVE: To assess whether chronic administration of the preferential 5-HT(2C) receptor agonist, mCPP, reduces rat body weight gain and to determine if this effect is wholly or partially attributable to the effect of the drug on daily food intake. METHODS: Animals were orally dosed with mCPP (10 mg/kg P.O., b.i.d.) or d-fenfluramine (2.5 mg/kg P.O., b.i.d.) for 28 days. Further groups of animals received drug treatments for the first 14 days and then received vehicle for the remainder of the experiment. Locomotor activity was assessed on days 2, 14, and 28. In a second study, animals received mCPP or d-fenfluramine for a 14-day period (dose and route were identical to the previous study). A group of pair-fed controls were included to determine whether the effects on body weight gain were attributable entirely to drug-induced hypophagia. RESULTS: Both mCPP and d-fenfluramine reduced body weight relative to vehicle-treated controls over the 28-day period. Withdrawal of the drugs on day 14 resulted in a significant rebound weight gain. Neither mCPP nor d-fenfluramine induced significant changes in locomotor activity compared to controls on any of the days tested (2, 14 or 28). In the second, 14-day study, changes in the body weights of pair-fed controls closely paralleled those of their drug-treated counterparts. CONCLUSION: These data indicate that chronic oral treatment with mCPP and d-fenfluramine significantly reduces rat body weight gain, an effect that is reversible upon withdrawal and wholly attributable to maintained hypophagia.

Preferential effects of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight gain of obese (fa/fa) compared to lean Zucker rats.

RATIONALE: The selective CB(1) receptor antagonist, SR 141716, has been demonstrated to reduce food consumption in a range of animal species. OBJECTIVE: To assess the effect of chronic administration of SR 141716 on body weight and ingestive behaviour of lean and obese (fa/fa) Zucker rats. METHODS: Lean and obese Zucker rats were orally dosed with SR 141716 (3, 10, 30 mg/kg PO), sibutramine (5 mg/kg PO) or vehicle for one week. Pair-fed controls provided insight as to whether the effect of SR 141716 on body weight was attributable to drug-induced hypophagia. Subsequently, the effect of chronic oral administration of SR 141716 (1, 3, 10 mg/kg) was assessed for 28 days. At the end of this period, all animals were given vehicle for 14 days. The incidence of wet-dog shakes, yawning, scratching, and grooming behaviours, was assessed after acute administration and at weekly intervals thereafter for 4 weeks. RESULTS: SR 141716 dose-dependently decreased food intake and body weight gain in both lean and obese animals. The inhibition of food intake and body weight gain was greater in obese Zuckers than in lean Zucker controls. Changes in the body weights of pair-fed controls closely paralleled those of their drug-treated counterparts. Chronic 28-day treatment led to a maintained reduction of body weight gain. Withdrawal of SR 141716 on day 28 resulted in rebound hyperphagia and a significant weight gain. On acute administration, SR 141716 dose-dependently induced motor behaviours that showed tolerance upon repeated administration. CONCLUSION: These data indicate that chronic oral treatment with SR 141716 significantly reduces the food intake and body weight gain of obese and lean Zucker rats, an effect that is greater in obese animals and reversible upon drug withdrawal.

The muscarinic receptor agonist xanomeline has an antipsychotic-like profile in the rat.

The muscarinic receptor agonist xanomeline was examined and compared with the antipsychotics clozapine and/or haloperidol in the following in vivo rat models: apomorphine-induced disruption of prepulse inhibition (PPI), amphetamine-induced hyperlocomotion, and the conditioned emotional response (CER) test. The effects of xanomeline were also assessed ex vivo on dopamine turnover in the rat medial prefrontal cortex. Under conditions of varying dose and prepulse intensity, xanomeline, like haloperidol, had no effect on PPI. In contrast, the muscarinic receptor antagonist scopolamine and the muscarinic receptor agonist pilocarpine both induced significant dose-dependent deficits in PPI. Haloperidol and xanomeline, but not pilocarpine, dose dependently reversed apomorphine-induced disruption of PPI. Thus, xanomeline induced a clear antipsychotic-like effect in PPI, whereas pilocarpine appeared to induce a psychotomimetic-like effect. Xanomeline attenuated amphetamine-induced hyperactivity at doses that had no effect on spontaneous activity, possibly indicating a separation between attenuation of limbic hyperdopaminergic function and the induction of hypolocomotion. Haloperidol and clozapine also reversed amphetamine-induced hyperlocomotion, but at similar doses to those that reduced spontaneous locomotion. Clozapine, but not haloperidol had an anxiolytic-like effect in the CER test. The effects of xanomeline in the CER test were similar to those of clozapine, although at the anxiolytic dose it tended to disrupt baseline levels of lever pressing. Finally, haloperidol, clozapine, pilocarpine, and xanomeline, all induced an increase in dopamine turnover in medial prefrontal cortex. The antipsychotic-like effects of xanomeline in the animal models used here suggest that it may be a useful treatment for psychosis.

SB-243213; a selective 5-HT2C receptor inverse agonist with improved anxiolytic profile: lack of tolerance and withdrawal anxiety.

SB-243213 (5-methyl-1-[[-2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-6-trifluoromethylindoline hydrochloride) is a new, selective 5-hydroxytryptamine (5-HT)2C receptor inverse agonist. SB-243213 has high affinity for the human 5-HT2C receptor (pK(i) 9.37) and greater than a 100-fold selectivity over a wide range of neurotransmitter receptors, enzymes and ion channels. In in vitro functional studies, SB-243213 acted as an inverse agonist at the human 5-HT2C receptor with a pK(b) of 9.8. In in vivo studies, SB-243213 was a potent inhibitor of central 5-HT2C receptor-mediated function in rats, blocking meta-chlorophenylpiperazine-induced hypolocomotion with an ID50 of 1.1 mg/kg p.o. and a long duration of action (>8 h). In rats, SB-243213 exhibited anxiolytic-like activity in both the social interaction and Geller-Seifter conflict tests. Importantly, unlike diazepam, chronic administration of SB-243213 did not result in the development of either tolerance to the anxiolytic-like effects or withdrawal anxiogenesis. Furthermore, in rodents, SB-243213 did not affect seizure threshold, did not increase body weight or induce catalepsy, but attenuated the haloperidol-induced catalepsy. SB-243213 did not affect amphetamine-, MK-801- or phencyclidine-induced hyperactivity. In conclusion, SB-243213 may possess an improved anxiolytic profile compared to benzodiazepines. SB-243213 also modulates dopaminergic transmission, lacks pro-psychotic properties and may have utility in the treatment of schizophrenia and motor disorders.

Evidence that hypophagia induced by d-fenfluramine and d-norfenfluramine in the rat is mediated by 5-HT2C receptors.

The present series of studies is the first to investigate the pharmacological mechanisms underlying d-fenfluramine- and d-norfenfluramine-induced hypophagia in the rat using highly selective serotonin 5-HT2 receptor antagonists. Administration of d-fenfluramine, and its major metabolite d-norfenfluramine, suppresses food intake in animals. Both compounds stimulate the release of serotonin and are potent inhibitors of the re-uptake of 5-HT into nerve terminals. In addition, d-norfenfluramine also acts as a direct 5-HT(2B/2C) receptor agonist. Pre-treatment with the selective 5-HT2C receptor antagonist, SB-242084 (0.3-3 mg/kg), dose-dependently inhibited both d-fenfluramine- (3 mg/kg) and d-norfenfluramine-induced (2 mg/kg) hypophagia. In contrast, the hypophagic effect of d-fenfluramine and d-norfenfluramine was unaffected by prior treatment with the highly selective 5-HT2B receptor antagonists, SB-215505 (0.3-3 mg/kg) and RS-127445 (1-3 mg/kg) or the 5-HT2A receptor antagonists MDL 100,907 (0.003-0.03 mg/kg) and ketanserin (0.2, 0.5 mg/kg). In addition, the 5-HT1A receptor antagonist WAY-100635 (0.3, 1 mg/kg) and the 5-HT1B receptor antagonists GR-127935 (1, 2 mg/kg) and SB-224289 (2-10 mg/kg) did not affect d-fenfluramine-induced hypophagia. These data provide unequivocal evidence for an important role of the 5-HT2C receptor in the mediation of d-fenfluramine and d-norfenfluramine-induced hypophagia in the rat and do not support the involvement of 5-HT1A/1B/2A/2B receptors.

Modulation of 5-HT(2A) receptor-mediated head-twitch behaviour in the rat by 5-HT(2C) receptor agonists.

The pharmacology of several commonly described 5-hydroxytryptamine (5-HT)(2C) receptor agonists was investigated in vivo and in vitro at rat 5-HT(2A), 5-HT(2B), and 5-HT(2C) receptors. The 5-HT(2C) receptor agonist, (S)-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine fumarate (Ro 60-0175), did not induce a significant head-twitch response when given alone, yet when administered to rats subsequent to an acute challenge with the selective 5-HT(2C) receptor antagonist, 6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) pyridin-3-yl carbomyl] indoline (SB-242084), a robust head-twitch response was observed which was blocked by the selective 5-HT(2A) receptor antagonists R(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl-ethyl)]-4-piperidine-methanol (MDL 100907) or ketanserin. The preferential 5-HT(2C) receptor agonists Ro 60-0175, 6-chloro-2-[1-piperazinyl]-pyrazine HCl (MK-212), 1-(3-chlorophenyl)piperazine hydrochloride (mCPP), 1-(3-trifluoromethylphenyl)piperazine hydrochloride (TFMPP), and (S)-3-[(2,3-dihydro-5-methoxy-1H-inden-4-yl)oxy]-pyrollidine HCl (ORG-37684), the 5-HT(2A/2C) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI), the 5-HT(2B) receptor agonist 1-[5-thienylmethoxy-1-1H-3-indoyl] propan-2-amine hydrochloride (BW-723C86), and nor-D-fenfluramine were administered to rats subsequent to an acute challenge of SB-242084. Under such conditions, each agonist, with the exception of BW-723C86, induced a dose-dependent increase in the incidence of head twitches. The pharmacology of the same agonists was determined at cloned rat 5-HT(2) receptors using a fluorometric imaging plate reader (FLIPR). Both the in vivo and in vitro data suggest that for some ligands, previous reports have overestimated their in vivo selectivity for the 5-HT(2C) receptor.

1-[2-[(Heteroaryloxy)heteroaryl]carbamoyl]indolines: novel and selective 5-HT2C receptor inverse agonists with potential as antidepressant/anxiolytic agents.

Bisaryl ethers have been identified with excellent 5-HT2C affinity and selectivity over both 5-HT2A and 5-HT2B receptors. Compounds such as 11, 27 and 38 have potent oral activity in a centrally mediated pharmacodynamic model of 5-HT2C function and their potential as novel non-sedating anxiolytic and antidepressants is under investigation.

1-[2-[(Heteroarylmethoxy)aryl]carbamoyl]indolines are selective and orally active 5-HT2C receptor inverse agonists.

Bisarylmethoxyethers have been identified with nanomolar 5-HT2C affinity and selectivity over both 5-HT2A and 5-HT2B receptors. Compounds such as 1, 2, 8, 12, 14 and 18 have potent oral activity in a centrally mediated pharmacodynamic model of 5-HT2C function and their therapeutic potential is currently under further investigation.

Comparative effects of continuous infusion of mCPP, Ro 60-0175 and d-fenfluramine on food intake, water intake, body weight and locomotor activity in rats.

1. The aim of the study was to compare the effects of 14 day subcutaneous infusion of the 5-HT(2C) receptor agonists, m-chlorophenylpiperazine (mCPP, 12 mg kg(-1) day(-1)) and Ro 60-0175 (36 mg kg(-1) day(-1)) and the 5-HT releasing agent and re-uptake inhibitor, d-fenfluramine (6 mg kg(-1) day(-1)), on food and water intake, body weight gain and locomotion in lean male Lister hooded rats. 2. Chronic infusion of all three drugs significantly reduced food intake and attenuated body weight gain. In contrast, drug infusion did not lead to significant reductions in locomotor activity in animals assessed 2 and 13 days after pump implantation. 3. In a subsequent 14 day study that was designed to identify possible tolerance during days 7 - 14, animals were given a subcutaneous infusion of mCPP (12 mg kg(-1) day(-1)) or d-fenfluramine (6 mg kg(-1) day(-1)) for either 7 or 14 days. During the first 7 days both drugs significantly reduced body weight gain compared to saline-infused controls; however, from day 7 onwards animals withdrawn from drug treatment exhibited an increase in body weight such that by day 14 they were significantly heavier than their 14-day drug-treated counterparts. 4. Both mCPP and d-fenfluramine reduced daily food intake throughout the infusion periods. For 14-day treated animals this hypophagia was marked during the initial week of the study but only minor during the second week. In light of the sustained drug effect on body weight, the data suggest that weight loss by 5-HT(2C) receptor stimulation may be only partly dependent on changes in food consumption and that 5-HT(2C) receptor agonists may have effects on thermogenesis. 5. These data suggest tolerance does not develop to the effects of d-fenfluramine, mCPP and Ro 60-0175 on rat body weight gain.

Biarylcarbamoylindolines are novel and selective 5-HT(2C) receptor inverse agonists: identification of 5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]- 5-pyridyl]carbamoyl]-6-trifluoromethylindoline (SB-243213) as a potential antidepressant/anxiolytic agent.

The evolution, synthesis, and biological activity of a novel series of 5-HT(2C) receptor inverse agonists are reported. Biarylcarbamoylindolines have been identified with excellent 5-HT(2C) affinity and selectivity over 5-HT(2A) receptors. In addition, (pyridyloxypyridyl)carbamoylindolines have been discovered with additional selectivity over the closely related 5-HT(2B) receptor. Compounds from this series are inverse agonists at the human cloned 5-HT(2C) receptor, completely abolishing basal activity in a functional assay. The new series have reduced P450 inhibitory liability compared to a previously described series of 1-(3-pyridylcarbamoyl)indolines (Bromidge et al. J. Med. Chem. 1998, 41, 1598) from which they evolved. Compounds from this series showed excellent oral activity in a rat mCPP hypolocomotion model and in animal models of anxiety. On the basis of their favorable biological profile, 32 (SB-228357) and 40 (SB-243213) have been selected for further evaluation to determine their therapeutic potential for the treatment of CNS disorders such as depression and anxiety.

Measurement of anxiety in transgenic mice.

A wide range of approaches has been used to study anxiety in mice. All presuppose that aversive stimuli, such as foot shock or novelty, induce a central state of fear, which can be quantified through specific behavioural and physiological measures. This review discusses the validity of the various approaches in terms of their similarity to different human anxiety disorders, their ability to detect compounds which modulate human anxiety, and their relevance to animal defensive processes. The most commonly used models of anxiety suitable for screening transgenic and knockout mice are discussed, with an emphasis placed on controlling for factors which could confound results. As all models used to date have limitations and no single paradigm adequately models all aspects of anxiety, this review recommends the use of a broad range of anxiety models in order to provide a comprehensive characterisation of the behavioural phenotype of transgenic mice.