Receptor subtypes Y1 and Y5 mediate neuropeptide Y induced feeding in the guinea-pig

1. Neuropeptide Y (NPY) is one of the most potent stimulants of food intake. It has been debated which receptor subtype mediates this response. Initially Y(1) was proposed, but later Y(5) was announced as a 'feeding' receptor in rats and mice. Very little is known regarding other mammals. The present study attempts to characterize the role of NPY in feeding behaviour in the distantly related guinea-pig. When infused intracerebroventricularly, NPY dose-dependently increased food intake. 2. PYY, (Leu(31),Pro(34))NPY and NPY(2 - 36) stimulated feeding, whereas NPY(13 - 36) had no effect. These data suggest that either Y(1) or Y(5) receptors or both may mediate NPY induced food intake in guinea-pigs. 3. The Y(1) receptor antagonists, BIBO 3304 and H 409/22 displayed nanomolar affinity for the Y(1) receptor (K(i) values 1.1+/-0.2 nM and 5.6+/-0.9 nM, respectively), but low affinity for the Y(2) or Y(5) receptors. When guinea-pigs were pretreated with BIBO 3304 and H 409/22, the response to NPY was inhibited. 4. The Y(5) antagonist, CGP 71683A had high affinity for the Y(5) receptor (K(i) 1.3+/-0.05 nM) without having any significant activities at the Y(1) and Y(2) receptors. When CGP 71683A was infused into brain ventricles, the feeding response to NPY was attenuated. 5. The present study shows that NPY stimulates feeding in guinea-pigs through Y(1) and Y(5) receptors. As the guinea-pig is very distantly related to the rat and mouse, this suggests that both Y(1) and Y(5) receptors may mediate NPY-induced hyperphagia also in other orders of mammals.     

Neuropeptide Y Y5 receptor antagonists as anti-obesity drugs

Neuropeptide Y (NPY) is present in the hypothalamus, where it is believed to play a key role in the control of food intake. Evidence for this assertion has come from studies demonstrating that acute administration of NPY into the hypothalamus or into the brain ventricles leads to increased food intake. In the case of chronic administration, the hyperphagic effects of NPY are prolonged, leading to the development of an obese state. NPY levels in the hypothalamus are temporally correlated with food intake and are markedly elevated in response to energy depletion. However, attempts to demonstrate an important role for NPY in the control of food intake using NPY knockout mice, NPY antisense oligodeoxynucleotides and anti-NPY antibodies has produced equivocal results. Despite this, many pharmaceutical companies have moved ahead with the search for antagonists of NPY receptor subtypes as appetite suppressant/anti-obesity agents. Antagonists of the NPY Y5 subtype seemed initially promising since analogs of NPY with high selectivity for this receptor strongly stimulated food intake. However, once again, attempts to inhibit the signaling of NPY through the NPY Y5 receptor produced equivocal effects on food intake. Many thousands of NPY Y5 antagonists have been made which fall into two main categories: those that influence food intake and those that do not. Those compounds that do inhibit food intake appear to do so by interactions with non-NPY Y5 related mechanisms. Thus, current evidence would suggest that antagonists of NPY acting through the NPY Y5 receptor subtype will not be useful appetite suppressant/anti-obesity agents.     

Neuropeptide Y2 receptors as drug targets for the central regulation of body weight

During the past decade, a detailed understanding has emerged of the aminergic and peptidergic neural pathways present within the brain that regulate appetite. Central among the peptide regulators is neuropeptide Y (NPY), a potent orexigenic agent that acts through five different receptor subtypes. Efforts to find novel appetite suppressant drugs that inhibit the interaction of NPY with either the NPY Y1 or NPY Y5 receptor subtypes have proven disappointing. Attempts have now been made to identify an NPY Y2 stimulator that will suppress appetite. Within the hypothalamus, NPY Y2 receptors have a predominantly presynaptic location where they act to inhibit NPY release. Stimulation of NPY Y2 receptors with synthetic peptide ligands or the gut derived peptide PY3-36 has been shown to reduce food intake. The NPY Y2 receptor has a wide distribution both within the brain and in the periphery. Stimulation of the NPY Y2 subtype at these sites produces a wide array of effects unrelated to changes in food intake. In consequence, the administration of both endogenous and exogenous agonists of the NPY Y2 receptor is likely to cause side effects, particularly regarding pituitary hormone release, as well as on the cardiovascular and gastrointestinal systems. The possibility that long-term NPY Y2 agonism could cause bone thinning and retinal angiogenesis are of particular concern and will need to be investigated as drug discovery moves forward.     

Central control of feeding behavior by neuropeptide Y

Obesity is a serious health problem in the Western societies, therefore its treatment has become the subject of intense interest in the scientific community. A significant number of recent publications enlist different central and peripheral factors which play important roles in the regulation of food intake, body weight and energy expenditure. Neuropeptide Y, a 36 amino acid peptide, which is quite abundant in the brain, seems to be one of the more important players in these regulations. Recently five NPY receptors have been cloned and pharmacological evidence strongly supports the existence of a sixth receptor. There are many contradictory findings regarding which NPY receptor mediates the effect of NPY on food intake. This article will review the effects of NPY on the regulation of food intake and energy expenditure and will discuss the pharmacological and molecular evidence as to which NPY receptor(s) mediate this effect. The review will also summarize the progress which has been made in the design of novel NPY-ergic ligands, especially NPY receptor antagonists, for potential use in the treatment of obesity.     

Neuropeptide Y receptor antagonists in obesity

Neuropeptide Y (NPY) is a 36 amino acid amidated peptide with high sequence homology to the endocrine peptides, peptide YY (PYY) and pancreatic polypeptide (PP). They appear to interact with a family of receptors that possess high affinity for one or more of these peptides. Five members of the receptor family have been cloned, with several additional members postulated through pharmacological evidence. All are members of the seven transmembrane domain-G-protein coupled receptor family. The Y1 receptor is the best characterised, with several nonpeptide antagonists available. This receptor appears to mediate a constriction of the peripheral vasculature and the 'anxiolytic' effects of centrally administered NPY. Less is known about the other receptors in the family. The Y2 receptor is believed to be presynaptic and mediates a reduction in neurotransmitter release. The Y4 receptor appears to be the receptor for pancreatic polypeptide, with high amounts of mRNA for this receptor found in the periphery, but lower levels in the brain. The Y5 receptor is expressed in the hypothalamus and has been postulated to be the receptor which mediates the increased food consumption seen following centrally administered NPY. Finally, the Y6 receptor has been cloned in the mouse and other species, but does not appear to encode a functional gene product in humans. Several types of nonpeptide Y1 and a series of Y5 antagonists have been described in the patent literature, though these compounds have limitations that will confine their use to preclinical studies. Nevertheless, considerable progress has been made in understanding the role of NPY and its receptors in experimental obesity. The next step will be the discovery of potent and selective nonpeptide antagonists, to add further credence to the therapeutic potential.     

Editorial Central & Peripheral Nervous Systems: Will neuropeptide Y receptor antagonists offer new therapeutic approaches?

Neuropeptide Y (NPY) and its receptors are widely distributed in the central and peripheral nervous systems. A multitude of biological effects have been attributed to NPY, and the peptide is, for instance, involved in regulation of food intake and is one of the most potent stimuli of ingestive behaviour. Moreover, it is a potent vasoconstrictor and is believed to be a regulator of central and peripheral cardiovascular function. NPY may be involved in pathophysiological states, like eating disorders and cardiovascular diseases. The peptide acts at multiple G-protein coupled receptors, several of which have been cloned and sequenced. Many pharmaceutical companies are in the process of developing drugs which act on NPY targets, and a number of peptide and non-peptide based NPY receptor antagonists have recently been described. Such compounds are essential in the investigation of the physiological role of NPY and some of them appear to be promising leads for drug development. The specific hypothalamic NPY receptor, which mediates food intake is a target of major interest for drug development. Some NPY receptor antagonists have been shown to inhibit NPY-evoked and natural feeding response. Similarly, NPY receptor antagonists which act specifically on hypothalamic NPY receptors could be evaluated for the treatment of anorexia or bulimia nervosa and obesity. Another set of potent NPY receptor antagonists have been shown to block NPY-mediated pressor and vasoconstrictor responses. Although there is a large arsenal of drugs for the treatment of cardiovascular disorders already on the market, vascular NPY receptor antagonists could also be examined as alternative therapeutics in this area.     

Inhibition of the Formation of the Alzheimer's β-Amyloid Peptide

Anorexia and body weight loss are characteristic of many diseases, including cancer and AIDS. Neuropeptides play a pivotal role in the physiological mechanisms regulating food intake and body weight. Neuropeptide Y (NPY) is a key molecule of the orexigenic network for energy intake and for normal adaptive feeding response to energy deficits. Therefore, the NPY receptors (notably, Y1 and Y5) may be one of the most significant target classes for treatment of anorexia and body weight loss. In addition, several anorexigenic peptides including corticotropin-releasing factor (CRF), cholecystokinin (CCK), leptin and melanocortin (MC) are emerging as potential targets for anorexia. Antagonists for CRF 2 receptor, CCK A receptor, MC 4 receptor and leptin receptor may be useful in stimulating food intake. The development of highly specific and selective non-peptide antagonists for these receptors is awaited. Anorexia is a crucial and critical disease. Increasing knowledge of its pathophysiology could lead to innovative new medicines for anorexia-cachexia syndrome.     

Identification of potent and selective neuropeptide Y Y(1) receptor agonists with orexigenic activity in vivo

Neuropeptide Y (NPY) binds to a family of G-protein coupled receptors termed Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). The use of various receptor subtype-selective agonists and antagonists has facilitated identification of the receptor subtypes responsible for mediating many of the biological effects of NPY. For example, the potent orexigenic activity of NPY is believed to be mediated by both the Y(1) and Y(5) receptor subtypes. Several selective Y(5) receptor agonists that stimulate food intake in rodents are available, but no selective Y(1) receptor agonist has been reported. We have identified several NPY analogs that bind the NPY Y(1) receptor with high affinity and exhibit full agonist activity, measured as inhibition of forskolin-stimulated cAMP production in cells expressing the cloned NPY Y(1) receptor. [D-Arg(25)]-NPY, [D-His(26)]-NPY, Des-AA(10--17)[Cys(7,21),Pro(34)]-NPY, Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac)]-NPY, Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac),Pro(34)]-NPY, Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac),D-His(26)]-NPY and Des-AA(11--18)[Cys(7,21),D-Lys(9)(Ac),D-His(26), Pro(34)]-NPY bind the NPY Y(1) receptor with K(i) values of 0.9 +/- 0.2, 2.0 +/- 0.3, 0.2 +/- 0.05, 0.7 +/- 0.1, 0.2 +/- 0.01, 2.2 +/- 0.3, and 1.2 +/- 0.3 nM, respectively, and inhibit forskolin-stimulated cAMP production with EC(50) values of 0.2 +/- 0.02, 0.5 +/- 0.04, 0.3 +/- 0.03, 0.5 +/- 0.05, 0.4 +/- 0.16, 5.3 +/- 0.32, and 5.1 +/- 0.97 nM, respectively. These peptides are highly selective for the NPY Y(1) receptor relative to the NPY Y(2), Y(4), and Y(5) receptors. [D-Arg(25)]-NPY, [D-His(26)]-NPY and Des-AA(11--18)[Cys(7,21), D-Lys(9)(Ac),D-His(26),Pro(34)]-NPY stimulate food intake dose-responsively in Long-Evans rats for at least 4 h after intracerebroventricular administration. Although the involvement of Y(1) receptors in several physiological activities, such as vasoconstriction and anxiolysis, remains to be investigated, adequate tools are now available.     

Structure-activity relationships of a series of pyrrolo[3,2-d]pyrimidine derivatives and related compounds as neuropeptide Y5 receptor antagonists

Neuropeptide Y (NPY) has been shown to play an important role in the regulation of food intake and energy balance. Pharmacological data suggests that the Y5 receptor subtype contributes to the effects of NPY on appetite, and therefore a Y5 antagonist might be a useful therapeutic agent for the treatment of obesity. In attempts to identify potential Y5 antagonists, a series of pyrrolo[3, 2-d]pyrimidine derivatives was prepared and evaluated for their ability to bind to Y5 receptors in vitro. We report here the synthesis and initial structure-activity relationship investigations for this class of compounds. The target compounds were prepared by a variety of synthetic routes designed to modify both the substitution and the heterocyclic core of the pyrrolo[3,2-d]pyrimidine lead 1. In addition to identifying several potent Y5 antagonists for evaluation as potential antiobesity agents, a pharmacophore model for the human Y5 receptor is presented.     

A typical Y1 receptor regulates feeding behaviors: effects of a potent and selective Y1 antagonist, J-115814

Neuropeptide Y (NPY) is a potent feeding stimulant. The orexigenic effect of NPY might be caused in part by the action of Y1 receptors. However, the existence of multiple NPY receptors including a possible novel feeding receptor has made it difficult to determine the relative importance of the Y1 receptor in feeding regulation. Herein we certified that the Y1 receptor is a major feeding receptor of NPY by using the potent and selective Y1 antagonist (-)-2-[1-(3-chloro-5-isopropyloxycarbonylaminophenyl)ethylamino]-6-[2-(5-ethyl-4-methyl-1,3-thiazol-2-yl)ethyl]-4-morpholinopyridine (J-115814) and Y1 receptor-deficient (Y1-/-) mice. J-115814 displaced (125)I-peptide YY binding to cell membranes expressing cloned human, rat, and murine Y(1) receptors with K(i) values of 1.4, 1.8, and 1.9 nM, respectively, and inhibited NPY (10 nM)-induced increases in intracellular calcium levels via human Y1 receptors (IC(50) = 6.8 nM). In contrast, J-115814 showed low affinities for human Y2 (K(i) > 10 microM), Y4 (K(i) = 640 nM) and Y5 receptors (K(i) = 6000 nM). Intracerebroventricular (ICV) (10-100 microg) and intravenous (IV) (0.3-30 mg/kg) administration of J-115814 significantly and dose-dependently suppressed feeding induced by ICV NPY (5 microg) in satiated Sprague-Dawley rats. Intraperitoneal (IP) administration of J-115814 (3-30 mg/kg) significantly attenuated spontaneous feeding in db/db and C57BL6 mice. Feeding induced by ICV NPY (5 microg) was unaffected by IP-injected J-115814 (30 mg/kg) in Y1-/- mice and was suppressed in wild-type and Y5-/- mice. These findings clearly suggest that J-115814 inhibits feeding behaviors through the inhibition of the typical Y1 receptor. We conclude that the Y1 receptor plays a key role in regulating food intake.     

Binding properties of three neuropeptide Y receptor subtypes from zebrafish: comparison with mammalian Y1 receptors

Neuropeptide Y (NPY) and peptide YY (PYY) are two related 36-amino-acid peptides found in all vertebrates and are involved in many physiological processes. Five receptor subtypes have been cloned in mammals (Y1, Y2, Y4, Y5, and y6). We have recently cloned three NPY/PYY receptor subtypes in zebrafish, called Ya, Yb, and Yc. Here we report on a direct comparison of the pharmacological properties of these three receptors in vitro using porcine NPY with alanine substitutions in positions 33–36 as ligands and three analogues with internal deletions: [Ahx^8–20]NPY, [Ahx^8–20, Pro³⁴]NPY, and [Ahx^5–24]NPY. In all cases, the zYc receptor was the most sensitive to the modifications of the NPY molecule and zYa was the least sensitive (except for the Arg → Ala replacement at position 33). Our data identified zYa as a receptor that can bind ligands specific for Y1, Y2, and Y4 receptors, while zYb and zYc were more Y1-like. All peptides with internal deletions bound to the zYa receptor with affinities similar to that of intact pNPY. Neither the Y1-selective antagonists BIBP3226 and SR120819A nor the Y2-selective BIIE0246 bound to any of the zebrafish receptors, although the amino acids identified as important for BIBP3226 binding were almost completely conserved. These results may prove helpful in molecular modeling of the three-dimensional receptor structure.     

Neuropeptide Y interaction with the adrenergic transmission line: a study of its effect on alpha-2 adrenergic receptors.

Neuropeptide Y (NPY), first isolated in 1982, is widely distributed among the neurons of the central and peripheral nervous systems, often in close association with catecholamines. Because of its wide distribution and concentrations in selected areas of the brain, NPY is considered a putative neurotransmitter with several possible physiological effects including modulation of blood pressure, food intake and pituitary hormone release at a central level. Peripherally, the peptide seems to be involved, via direct and indirect mechanisms, in noradrenaline (NA)-mediated vasoconstriction. The ability of NPY to interact with the catecholamine transmission line may underly a possible modulatory influence of NPY on catecholamine receptor characteristics. We recently observed interaction between alpha-2 adrenergic receptors and those for NPY at the presynaptic level. Additional data from our studies in spontaneously hypertensive rats suggest that impairment of these interactions may contribute to the hypertension in this strain.     

Increases in sucrose consumption, but not ethanol consumption, following ICV NPY administration

Neuropeptide Y (NPY) is a centrally acting neuromodulator that influences both consummatory behaviors and anxiety. NPY's effects on feeding are primarily regulated through Y5 receptors in hypothalamic sites, whereas NPY-induced anxiolysis appears to be mediated by Y1 receptors in the amygdala. Recently, NPY has been postulated to play a role in the regulation of ethanol consumption. The present study assessed the influence of intracerebroventricular (ICV) administration of NPY on the consumption of 10% ethanol or 2% sucrose in rats. Male Wistar rats were trained to self-administer 10% ethanol using the sucrose-substitution procedure and then implanted with an intracerebroventricular (ICV) cannula. The effects of NPY (0-15 microg) on ethanol consumption and sucrose consumption were then examined. ICV NPY infusion had no significant effects on the consumption of 10% ethanol, however, NPY significantly increased the consumption of 2% sucrose, [F(1, 11) = 6.18, p = 0.03]. These data suggest that ethanol intake and sucrose intake are differentially regulated by NPY. It is hypothesized that ICV infusion of NPY may be affecting both Y1 and Y5 receptors producing increased consummatory drive and anxiolysis, two factors that have opposing effects on subsequent ethanol consumption. Therefore, additional studies including site specific injection of NPY will be necessary to provide further insight into the role of NPY on ethanol consumption.     

Relevance of the neuropeptide Y system in the biology of cancer progression

The peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure, known as PP-fold. Within this family of peptides, NPY, a highly conserved 36-aminoacid residue peptide, is involved in the regulation of a wide range of physiological functions, such as food intake and energy metabolism, as well as in the promotion of some remarkable aspects of tumor progression, including cell proliferation, matrix invasion, metastatization, and angiogenesis. NPY exerts its biological effects through five G-protein coupled receptors, named Y1-, Y2-, Y4-, Y5-, and y6-R, which appear associated with different aspects of oncogenesis. Y1-R seems involved in the modulation of cancer cell proliferation, whereas Y2-R activation appears to promote angiogenesis. The development of NPY receptor subtype selective analogs has helped to elucidate the physiological and pathophysiological role and localization of each receptor and may contribute to a better understanding of the receptor-ligand interaction. The NPY system appears to be variously associated with specific tumors, including neural crest-derived tumors, breast and prostate cancers. In addition to NPY, PYY is also able to affect cancer cell growth in a dose-dependent manner and through Y-Rs. In conclusion, peptides of the NPY family and the related receptors play an important role in the progression of different cancer types, with some molecular specificity according to each step of this process. On this basis, future studies may be directed to the implementation of novel diagnostic and therapeutic approaches targeting this system.     

Neuropeptide Y (NPY) Y4 receptor selective agonists based on NPY(32-36): development of an anorectic Y4 receptor selective agonist with picomolar affinity

We have previously shown [Cys-Trp-Arg-Nva-Arg-Tyr-NH(2)](2), 1, to be a moderately selective neuropeptide Y (NPY) Y(4) receptor agonist. Toward improving the selectivity and potency for Y(4) receptors, we studied the effects of dimerizing H-Trp-Arg-Nva-Arg-Tyr-NH(2) using various diamino-dicarboxylic acids containing either di-, tri-, or tetramethylene spacers. These parallel dimers, 2A, 2B, 3, 4A, and 4B, and the corresponding linear tandem dimer and trimer analogues, 5 and 6, had enhanced selectivity and affinity for Y(4) receptors compared to 1 (Table 1). Substitution of Trp and Nva with Tyr and Leu, respectively, as in 2,7-d/l-diaminosuberic acid derivatized dimer, 7, resulted in a superior Y(4) selective agonist with picomolar affinity. Intraperitoneal (ip) injection of 7 potently inhibited food intake in fasted mice. Moreover, 7 (ip) inhibited the food intake in wild-type mice and not in Y(4)(-/-) knock-out mice, confirming that the actions of 7 on food intake are not due to global effects, but specifically mediated Y(4) receptors.     

Neuropeptide Y: multiple receptors and multiple roles in cardiovascular diseases

Neuropeptide Y (NPY), a sympathetic co-transmitter, acts through multiple G protein-coupled receptors (Y1 to y6) to elicit its vast range of effects in the cardiovascular, immune, and central and peripheral nervous systems. Initially, the focus of the function of NPY in the cardiovascular system involved its acute actions, such as vasoconstriction via the Y1 receptor. However, recent studies have shown that NPY is a potent growth and angiogenic factor, which acts on multiple receptor subtypes. To be more specific, NPY-mediated vascular smooth muscle cell growth, leading to neointima formation, involves Y1 and Y1 receptors, while the angiogenic effects of NPY include Y2 and Y5 receptor activation. The presence of dipeptidyl peptidase IV also influences the cardiovascular responses of NPY by acting as a converting enzyme, shifting NPY activities away from Y1. Thus, agonists and antagonists aimed at the NPY system represent a new avenue for drug treatment, which may help alleviate several cardiovascular disorders in which vascular remodeling plays a major role, such as atherosclerosis, restenosis following balloon angioplasty, hypertension and peripheral vascular disease.     

Agonists for neuropeptide Y receptors Y1 and Y5 stimulate different phases of feeding in guinea pigs

1. The stimulatory effect of neuropeptide Y (NPY) on food intake is well established but the roles of the receptor subtypes Y(1) and Y(5) have been difficult to define. We have studied the effects of two novel Y(1)-preferring and two Y(5)-preferring agonists on feeding in guinea pigs. 2. The Y(1)-preferring receptor agonists [Arg(6),Pro(34)]pNPY and [Phe(7),Pro(34)]pNPY had high affinity for the Y(1) receptor (K(i) values 0.07 and 0.04 nM, respectively) and nanomolar affinity for the Y(5) receptor. Administration of either compound into the third brain ventricle increased food intake equally to NPY. 3. The Y(5) agonist [Ala(31),Aib(32)]pNPY displayed a moderate affinity for the Y(5) receptor (K(i) 7.42 nM) and a low affinity for Y(1) (K(i) 1.7 micro M). This compound had only a modest effect on feeding. 4. The other Y(5)-preferring peptide [cPP(1-7),NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP had a higher affinity at the Y(5) receptor (K(i) 1.32 nM) and also at the Y(1) receptor (K(i) 85 nM). It potently stimulated feeding: the food consumption after administration of this peptide was two-fold compared to NPY. 5. Our results support the view that both the receptor subtypes Y(1) and Y(5) are involved in the stimulation of feeding. As the action profiles of the Y(1) and Y(5) agonists on feeding parameters were different, it seems that they influence different phases of eating.     

Neuropeptide Y receptor antagonists

A review of the patent literature for neuropeptide Y (NPY) antagonists is presented for the period of January 2000 to March 2001. This review focuses on antagonists of the Y(1) and Y(5) receptor subtypes, which have been of primary interest as anti-obesity agents. In contrast to the Y(5) receptor, there have been only a limited number of new chemical entities claimed as antagonists at the Y(1) receptor. This may suggest either a greater interest in the Y(5) subtype as a target for therapeutic intervention or difficulty in finding small, potent, non-peptide antagonists of the Y(1) receptor. Nevertheless, there are subnanomolar antagonists that are selective for both receptor subtypes available, which should prove to be useful in determining the roles of the Y(1) and Y(5) receptors in food intake, energy homeostasis, and other physiological functions.     

Synthesis of new benzoxazinone derivatives as neuropeptide Y5 antagonists for the treatment of obesity

Screening of our internal chemical collection against the neuropeptide Y5 (NPY Y5) receptor allowed the identification of a benzoxazine derivative 5f as a hit that showed moderate affinity (IC(50) = 300 nM). With the aim of improving the in vitro potency, a series of 2-benzoxazinone derivatives have been synthesized and tested for NPY Y5 activity. Most of the compounds were found to be potent and selective NPY Y5 antagonists having nanomolar binding affinities for the NPY Y5 receptor and showing functional antagonism in the forskolin-induced cyclic AMP test. Prelimminary studies in order to understand the structure-activity relationship were undertaken. Selected compounds were further evaluated for in vivo efficacy, affording the lead compound 2-[4-(8-methyl-2-oxo-4H-benzo[d][1,3]oxazin-1-yl)piperidin-1-yl]-N-(9-oxo-9H-fluoren-3-yl)acetamide 5p, which displayed in vivo activity reducing food intake in rodents.     

The role of neuropeptide Y in energy homeostasis

When administered into the brain, NPY acts at Y1 and Y5 receptors to increase food intake. The response occurs with a short latency and is quite robust, such that exogenous NPY is generally considered to be the most potent of a growing list of orexigenic compounds that act in the brain. The role of endogenous NPY is not so straightforward, however. Evidence from diverse types of experiments suggests that rather than initiating behavioral eating per se, endogenous NPY elicits autonomic responses that prepare the individual to better cope with consuming a calorically large meal.