Antagonistic properties of centrally truncated analogs of [D-Trp(32)]NPY

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.

Manipulating Y receptor subtype activation of short neuropeptide Y analogs by introducing carbaboranes

Short selective neuropeptide Y (NPY) analogs are highly attractive because of their facile synthesis. Based on the reduced-size NPY analog [Pro(30), Nle(31), Bpa(32), Leu(34)]NPY 28-36 position 32 was identified as a key position to alter the preferential activation pattern of the human neuropeptide Y receptors (hYRs). By replacing benzoylphenylalanine (Bpa) by a biphenylalanine (Bip) the photostability was first improved while the biological activity was maintained. SAR-studies showed that both aromatic rings have a high influence on the preferential hYR subtype activation. Interestingly, replacement of Bpa(32) by a strongly hydrophobic moiety changed the hYR subtype preference of the analog. Whereas the parent compound is able to activate the human neuropeptide Y1 receptor (hY1R) subtype, the introduction of an N(ε)-ortho-carbaboranyl propionic acid modified lysine resulted in a loss of activity at the hY1R but in an increased activity at both the hY2R and the hY4R. However, subsequent receptor internalization studies with this novel analog revealed that receptor internalization can neither be triggered at the hY2R nor at the hY4R suggesting a biased ligand. Surprisingly, investigations by (1)H NMR spectroscopy revealed structural changes in the side chains of residues Pro(30) and Leu(34) which nicely correlates with the shift from hY1R/hY4R to hY2R/hY4R activation preference. Thus, position 32 has been identified to switch the bioactive conformation and subsequently influences receptor subtype activation behavior.

GR231118 (1229U91) and other analogues of the C-terminus of neuropeptide Y are potent neuropeptide Y Y1 receptor antagonists and neuropeptide Y Y4 receptor agonists

GR231118, BW1911U90, Bis(31/31')[[Cys31, Trp32, Nva34] neuropeptide Y(31-36)] (T-190) and [Trp-Arg-Nva-Arg-Tyr]2-NH2 (T-241) are peptide analogs of the C-terminus of neuropeptide Y that have recently been shown to be antagonists of the neuropeptide Y Y1 receptor. In this study, the activity of these peptides at each of the cloned neuropeptide Y receptor subtypes is determined in radioligand binding assays and in functional assays (inhibition of forskolin-stimulated cAMP formation). GR231118 is a potent antagonist at the human and rat neuropeptide Y Y1 receptors (pA2 = 10.5 and 10.0, respectively; pKi = 10.2 and 10.4, respectively), a potent agonist at the human neuropeptide Y Y4 receptor (pEC50 = 8.6; pKi = 9.6) and a weak agonist at the human and rat neuropeptide Y Y2 and Y5 receptors. GR231118 also has high affinity for the mouse neuropeptide Y Y6 receptor (pKi = 8.8). Therefore, GR231118 is a relatively selective neuropeptide Y Y1 receptor antagonist, but has appreciable activity at the neuropeptide Y Y4 and Y6 receptors as well. BW1911U90, T-190 and T-241 are moderately potent neuropeptide Y Y1 receptor antagonists (pA2 = 7.1, 5.8 and 6.5, respectively; pKi = 8.3, 6.5 and 6.8, respectively) and neuropeptide Y Y4 receptor agonists (pEC50 = 6.8, 6.3 and 6.6, respectively; pKi; 8.3, 7.7 and 8.3, respectively). These data suggest that the C-terminus of neuropeptide Y and related peptides is sufficient for activation of the neuropeptide Y Y4 receptor, but is not sufficient for activation of the neuropeptide Y Y1 receptor. Because BW1911U90, T-190 and T-241 are significantly less potent at the cloned human neuropeptide Y Y1 receptor than at the neuropeptide Y receptor in human erythroleukemia cells, these cells may express a novel neuropeptide Y receptor with high affinity for these peptides.

Neuropeptide Y family of hormones: receptor subtypes and antagonists

Neuropeptide Y (NPY) is the most abundant peptide present in the mammalian central and peripheral nervous system. NPY exhibits a variety of potent central and peripheral effects including those on feeding, memory, blood pressure, cardiac contractility and intestinal secretions. Classical pharmacological studies have shown that NPY effects are mediated by four different receptor subtypes, Y-1, Y-1-like, Y-2, and Y-3. However, the existence of numerous atypical activities provide strong evidence for the occurrence of additional NPY receptor subtypes. Pharmacological studies have further been facilitated by the recent cloning and expression of Y-1, Y-2, Y-4 (PP-1) and Y-5 receptors. Moreover, the cloned Y-5 receptor has been suggested to be the long awaited Y-1-like receptor involved in feeding. Structure-activity studies have laid a good foundation towards the development of receptor selective compounds, and to date potent Y-1 selective peptide and nonpeptide antagonists have been developed. The need to clone numerous receptor subtypes and to develop receptor selective compounds for physiological and perhaps clinical use is expected to keep NPY research active for many years to come.

Synthesis, structure, and antagonistic properties of des-Asn29[D-Trp28,32]NPY(27-36)

We have previously reported that [D-Trp32]NPY and its centrally truncated analogues such as des-AA7-24[D-Trp5,32,Aoc6]NPY can competitively antagonize NPY effects on rat hypothalamus and Y1 (SK-N-MC AND HEL) cells, respectively. In continuation of this work, we performed structure-activity studies with C-terminal decapeptide sequence keeping D-Trp at position 32 to develop lower molecular weight Y1-selective antagonists. This study led to the development of des-Asn29[D-Trp28,32]NPY(27-36), which bound to both Y1 (SK-N-MC, Ki > or = 10 microM) and Y2 (SK-N-BE2, Ki = 1.01 +/- 0.03 microM) receptors. This peptide did not exhibit any agonist activity at Y1 receptors, and exhibited comparable potencies in antagonizing the effects of NPY on the synthesis of cAMP and mobilization of [Ca2+]i in HEL cells. However, in SK-N-MC cells, it was more potent in antagonizing the mobilization of [Ca2+]i than inhibition of cAMP synthesis. Substitution of Nva for Gln34 to increase the hydrophobicity without altering the carbon skeleton substantially increased Y1 affinity (Ki = 0.33 +/- 0.15 microM) and imparted Y1 selectivity (Ki for Y2 affinity = 3.16 +/- 0.50). Moreover, this peptide exhibited good antagonistic potency in HEL cells. 2D NMR studies of des-Asn29[D-Trp28,32]NPY(27-36) revealed the existence of a fairly stable loop-like structure between residues 27 and 32 and a less stable one between residues 32 and 36. The increased Y1 affinity of des-Asn29[D-Trp28,32,Nva34]NPY(27-36) may be due to the stabilization of the 32-36 loop by Nva34. It appears therefore that stabilization of the loop structures in these peptides should result in the development of more potent Y1 receptor antagonists. Our investigations also suggest that HEL cells express a homogeneous population of NPY Y1 receptors whereas SK-N-MC cells express high- and low-affinity Y1 receptors coupled to Ca2+ and cAMP, respectively.