Regulatory effects of Y4 receptor agonist (BVD-74D) on food intake

Illuminating the neuropeptide Y4 receptor and its ligand pancreatic polypeptide from a structural, functional, and therapeutic perspective

The neuropeptide Y4 receptor (Y4R), a rhodopsin-like G protein-coupled receptor (GPCR) and the hormone pancreatic polypeptide (PP) are members of the neuropeptide Y family consisting of four receptors (Y1R, Y2R, Y4R, Y5R) and three highly homologous peptide ligands (neuropeptide Y, peptide YY, PP). In this family, the Y4R is of particular interest as it is the only subtype with high affinity to PP over NPY. The Y4R, as a mediator of PP signaling, has a pivotal role in appetite regulation and energy homeostasis, offering potential avenues for the treatment of metabolic disorders such as obesity. PP as anorexigenic peptide is released postprandial from the pancreas in response to food intake, induces satiety signals and contributes to hamper excessive food intake. Moreover, this system was also described to be associated with different types of cancer: overexpression of Y4R have been found in human adenocarcinoma cells, while elevated levels of PP are related to the development of pancreatic endocrine tumors. The pharmacological relevance of the Y4R advanced the search for potent and selective ligands for this receptor subtype, which will be significantly progressed through the elucidation of the active state PP-Y4R cryo-EM structure. This review summarizes the development of novel PP-derived ligands, like Obinepitide as dual Y2R/Y4R agonist in clinical trials or UR-AK86c as small hexapeptide agonist with picomolar affinity, as well as the first allosteric modulators that selectively target the Y4R, e.g. VU0506013 as potent Y4R positive allosteric modulator or (S)-VU0637120 as allosteric antagonist. Here, we provide valuable insights into the complex physiological functions of the Y4R and PP and the pharmacological relevance of the system in appetite regulation to open up new avenues for the development of tool compounds for targeted therapies with potential applications in metabolic disorders.

Illuminating Neuropeptide Y Y4 Receptor Binding: Fluorescent Cyclic Peptides with Subnanomolar Binding Affinity as Novel Molecular Tools

The neuropeptide Y (NPY) Y4 receptor (Y4R), a member of the family of NPY receptors, is physiologically activated by the linear 36-amino acid peptide pancreatic polypeptide (PP). The Y4R is involved in the regulation of various biological processes, most importantly pancreatic secretion, gastrointestinal motility, and regulation of food intake. So far, Y4R binding affinities have been mostly studied in radiochemical binding assays. Except for a few fluorescently labeled PP derivatives, fluorescence-tagged Y4R ligands with high affinity have not been reported. Here, we introduce differently fluorescence-labeled (Sulfo-Cy5, Cy3B, Py-1, Py-5) Y4R ligands derived from recently reported cyclic hexapeptides showing picomolar Y4R binding affinity. With pKi values of 9.22-9.71 (radioligand competition binding assay), all fluorescent ligands (16-19) showed excellent Y4R affinity. Y4R saturation binding, binding kinetics, and competition binding with reference ligands were studied using different fluorescence-based methods: flow cytometry (Sulfo-Cy5, Cy3B, and Py-1 label), fluorescence anisotropy (Cy3B label), and NanoBRET (Cy3B label) binding assays. These experiments confirmed the high binding affinity to Y4R (equilibrium pKd: 9.02-9.9) and proved the applicability of the probes for fluorescence-based Y4R competition binding studies and imaging techniques such as single-receptor molecule tracking.

Cross talk about the role of Neuropeptide Y in CNS disorders and diseases

A peptide composed of a 36 amino acid called Neuropeptide Y (NPY) is employed in a variety of physiological processes to manage and treat conditions affecting the endocrine, circulatory, respiratory, digestive, and neurological systems. NPY naturally binds to G-protein coupled receptors, activating the Y-receptors (Y1-Y5 and y6). The findings on numerous therapeutic applications of NPY for CNS disease are presented in this review by the authors. New targets for treating diseases will be revealed by medication combinations that target NPY and its receptors. This review is mainly focused on disorders such as anxiety, Alzheimer's disease, Parkinson's disease, Huntington's disease, Machado Joseph disease, multiple sclerosis, schizophrenia, depression, migraine, alcohol use disorder, and substance use disorder. The findings from the preclinical studies and clinical studies covered in this article may help create efficient therapeutic plans to treat neurological conditions on the one hand and psychiatric disorders on the other. They may also open the door to the creation of novel NPY receptor ligands as medications to treat these conditions.

[3H]UR-JG102-A Radiolabeled Cyclic Peptide with High Affinity and Excellent Selectivity for the Neuropeptide Y Y4 Receptor

The family of human neuropeptide Y receptors (YRs) comprises four subtypes (Y1R, Y2R, Y4R, and Y5R) that are involved in the regulation of numerous physiological processes. Until now, Y4R binding studies have been predominantly performed in hypotonic sodium-free buffers using 125I-labeled derivatives of the endogenous YR agonists pancreatic polypeptide or peptide YY. A few tritium-labeled Y4R ligands have been reported; however, when used in buffers containing sodium at a physiological concentration, their Y4R affinities are insufficient. Based on the cyclic hexapeptide UR-AK86C, we developed a new tritium-labeled Y4R radioligand ([3H]UR-JG102, [3H]20). In sodium-free buffer, [3H]20 exhibits a very low Y4R dissociation constant (Kd 0.012 nM). In sodium-containing buffer (137 mM Na+), the Y4R affinity is lower (Kd 0.11 nM) but still considerably higher compared to previously reported tritiated Y4R ligands. Therefore, [3H]20 represents a useful tool compound for the determination of Y4R binding affinities under physiological-like conditions.

Stereochemistry-Driven Interactions of α,γ-Peptide Ligands with the Neuropeptide Y Y4-Receptor

The G-protein-coupled Y₄-receptor (Y₄R) and its endogenous ligand, pancreatic polypeptide (PP), suppress appetite in response to food intake and, thus, are attractive drug targets for body-weight control. The C-terminus of human PP (hPP), T³²-R³³-P³⁴-R³⁵-Y³⁶-NH₂, penetrates deep into the binding pocket with its tyrosine-amide and di-arginine motif. Here, we present two C-terminally amidated α,γ-hexapeptides (1a/b) with sequence Ac-R³¹-γ-CBAA³²-R³³-L³⁴-R³⁵-Y³⁶-NH₂, where γ-CBAA is the (1R,2S,3R)-configured 2-(aminomethyl)-3-phenylcyclobutanecarboxyl moiety (1a) or its mirror image (1b). Both peptides bind the Y₄R (K_i of 1a/b: 0.66/12 nM) and act as partial agonists (intrinsic activity of 1a/b: 50/39%). Their induced-fit binding poses in the Y₄R pocket are unique and build ligand-receptor contacts distinct from those of the C-terminus of the endogenous ligand hPP. We conclude that energetically favorable interactions, although they do not match those of the native ligand hPP, still guarantee high binding affinity (with 1a rivaling hPP) but not the maximum receptor activation.

PET Imaging of the Neuropeptide Y System: A Systematic Review

Neuropeptide Y (NPY) is a vastly studied biological peptide with numerous physiological functions that activate the NPY receptor family (Y₁, Y₂, Y₄ and Y₅). Moreover, these receptors are correlated with the pathophysiology of several diseases such as feeding disorders, anxiety, metabolic diseases, neurodegenerative diseases, some types of cancers and others. In order to deepen the knowledge of NPY receptors' functions and molecular mechanisms, neuroimaging techniques such as positron emission tomography (PET) have been used. The development of new radiotracers for the different NPY receptors and their subsequent PET studies have led to significant insights into molecular mechanisms involving NPY receptors. This article provides a systematic review of the imaging biomarkers that have been developed as PET tracers in order to study the NPY receptor family.

N-Terminus to Arginine Side-Chain Cyclization of Linear Peptidic Neuropeptide Y Y4 Receptor Ligands Results in Picomolar Binding Constants

The family of neuropeptide Y (NPY) receptors comprises four subtypes (Y₁R, Y₂R, Y₄R, Y₅R), which are addressed by at least three endogenous peptides, i.e., NPY, peptide YY, and pancreatic polypeptide (PP), the latter showing a preference for Y₄R. A series of cyclic oligopeptidic Y₄R ligands were prepared by applying a novel approach, i.e., N-terminus to arginine side-chain cyclization. Most peptides acted as Y₄R partial agonists, showing up to 60-fold higher Y₄R affinity compared to the linear precursor peptides. Two cyclic hexapeptides (18, 24) showed higher Y₄R potency (Ca²⁺ aequorin assay) and, with pK_i values >10, also higher Y₄R affinity compared to human pancreatic polypeptide (hPP). Compounds such as 18 and 24, exhibiting considerably lower molecular weight and considerably more pronounced Y₄R selectivity than PP and previously described dimeric peptidic ligands with high Y₄R affinity, represent promising leads for the preparation of labeled tool compounds and might support the development of drug-like Y₄R ligands.

Heterodimeric Analogues of the Potent Y1R Antagonist 1229U91, Lacking One of the Pharmacophoric C-Terminal Structures, Retain Potent Y1R Affinity and Show Improved Selectivity over Y4R

The cyclic dimeric peptide 1229U91 (GR231118) has an unusual structure and displays potent, insurmountable antagonism of the Y₁ receptor. To probe the structural basis for this activity, we have prepared ring size variants and heterodimeric compounds, identifying the specific residues underpinning the mechanism of 1229U91 binding. The homodimeric structure was shown to be dispensible, with analogues lacking key pharmacophoric residues in one dimer arm retaining high antagonist affinity. Compounds 11d-h also showed enhanced Y1R selectivity over Y4R compared to 1229U91.

Photochromic peptidic NPY Y4 receptor ligands

Photoresponsive NPY Y₄R ligands, containing an azobenzene, azopyrazole, diethienylethene or a fulgimide chromophore were prepared to explore structural requirements of Y₄R agonists on Y₄R binding.

In Search of NPY Y4R Antagonists: Incorporation of Carbamoylated Arginine, Aza-Amino Acids, or d-Amino Acids into Oligopeptides Derived from the C-Termini of the Endogenous Agonists

The cross-linked pentapeptides (2R,7R)-diaminooctanedioyl-bis(Tyr-Arg-Leu-Arg-Tyr-amide) ((2R,7R)-BVD-74D, (2R,7R)-1) and octanedioyl-bis(Tyr-Arg-Leu-Arg-Tyr-amide) (2) as well as the pentapeptide Ac-Tyr-Arg-Leu-Arg-Tyr-amide (3) were previously described as neuropeptide Y Y₄ receptor (Y₄R) partial agonists. Here, we report on a series of analogues of (2R,7R)-1 and 2 in which Arg², Leu³, or Arg⁴ were replaced by the respective aza-amino acids. The replacement of Arg² in 3 with a carbamoylated arginine building block and the extension of the N-terminus by an additional arginine led to the high-affinity hexapeptide Ac-Arg-Tyr-N^ω-[(4-aminobutyl)aminocarbonyl]Arg-Leu-Arg-Tyr-amide (35), which was used as a precursor for a d-amino acid scan. The target compounds were investigated for Y₄R functional activity in assays with complementary readouts: aequorin Ca²⁺ and β-arrestin 1 or β-arrestin 2 assays. In contrast to the parent compounds, which are Y₄R agonists, several ligands were able to suppress the effect elicited by the endogenous ligand pancreatic polypeptide and therefore represent a novel class of peptide Y₄R antagonists.

Pancreatic polypeptide is recognized by two hydrophobic domains of the human Y4 receptor binding pocket

Structural characterization of the human Y4 receptor (hY4R) interaction with human pancreatic polypeptide (hPP) is crucial, not only for understanding its biological function but also for testing treatment strategies for obesity that target this interaction. Here, the interaction of receptor mutants with pancreatic polypeptide analogs was studied through double-cycle mutagenesis. To guide mutagenesis and interpret results, a three-dimensional comparative model of the hY4R-hPP complex was constructed based on all available class A G protein-coupled receptor crystal structures and refined using experimental data. Our study reveals that residues of the hPP and the hY4R form a complex network consisting of ionic interactions, hydrophobic interactions, and hydrogen binding. Residues Tyr(2.64), Asp(2.68), Asn(6.55), Asn(7.32), and Phe(7.35) of Y4R are found to be important in receptor activation by hPP. Specifically, Tyr(2.64) interacts with Tyr(27) of hPP through hydrophobic contacts. Asn(7.32) is affected by modifications on position Arg(33) of hPP, suggesting a hydrogen bond between these two residues. Likewise, we find that Phe(7.35) is affected by modifications of hPP at positions 33 and 36, indicating interactions between these three amino acids. Taken together, we demonstrate that the top of transmembrane helix 2 (TM2) and the top of transmembrane helices 6 and 7 (TM6-TM7) form the core of the peptide binding pocket. These findings will contribute to the rational design of ligands that bind the receptor more effectively to produce an enhanced agonistic or antagonistic effect.

Replacement of Thr32 and Gln34 in the C-terminal neuropeptide Y fragment 25-36 by cis-cyclobutane and cis-cyclopentane β-amino acids shifts selectivity toward the Y(4) receptor

Neuropeptide Y (NPY) and pancreatic polypeptide (PP) control central and peripheral processes by activating the G protein coupled receptors YxR (x = 1, 2, 4, 5). We present analogs of the C-terminal fragments 25-36 and 32-36 of NPY and PP containing (1R,2S)-cyclobutane (βCbu) or (1R,2S)-cyclopentane (βCpe) β-amino acids, which display exclusively Y4R affinity. In particular, [βCpe(34)]-NPY-(25-36) is a Y4R selective partial agonist (EC50 41 ± 6 nM, Emax 71%) that binds Y4R with a Ki of 10 ± 2 nM and a selectivity >100-fold relative to Y1R and Y2R and >50-fold relative to Y5R. Comparably, [Y(32), βCpe(34)]-NPY(PP)-(32-36) selectively binds and activates Y4R (EC50 94 ± 21 nM, Emax 73%). The NMR structure of [βCpe(34)]-NPY-(25-36) in dodecylphosphatidylcholine micelles shows a short helix at residues 27-32, while the C-terminal segment R(33)βCpe(34)R(35)Y(36) is extended. The biological properties of the βCbu- or βCpe-containing NPY and PP C-terminal fragments encourage the future application of these β-amino acids in the synthesis of selective Y4R ligands.

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.