Bivalent argininamide-type neuropeptide y y(1) antagonists do not support the hypothesis of receptor dimerisation

Chemical pulldown combined with mass spectrometry to identify the molecular targets of antimalarials in cell-free lysates

Here, we provide a protocol using chemical pulldown combined with mass spectrometry (LC-MS/MS) to identify drug targets in Plasmodium falciparum. This approach works upon the principle that a resin-bound inhibitor selectively binds its molecular target(s) in cell-free lysates. We describe the preparation of drug beads and P. falciparum lysate, followed by chemical pulldown, sample fractionation, and LC-MS/MS analysis. We then detail how to identify specifically bound proteins by comparing protein enrichment in DMSO-treated relative to drug-treated lysates via quantitative proteomics. For complete details on the use and execution of this protocol, please refer to Milne et al. (2022).1.

Neuropeptide Y receptor interactions regulate its mitogenic activity

Neuropeptide Y (NPY) is a multifunctional neurotransmitter acting via G protein-coupled receptors - Y1R, Y2R and Y5R. NPY activities, such as its proliferative effects, are mediated by multiple receptors, which have the ability to dimerize. However, the role of this receptor interplay in NPY functions remains unclear. The goal of the current study was to identify NPY receptor interactions, focusing on the ligand-binding fraction, and determine their impact on the mitogenic activity of the peptide. Y1R, Y2R and Y5R expressed in CHO-K1 cells formed homodimers detectable on the cell surface by cross-linking. Moreover, Y1R and Y5R heterodimerized, while no Y2R/Y5R heterodimers were detected. Nevertheless, Y5R failed to block internalization of its cognate receptor in both Y1R/Y5R and Y2R/Y5R transfectants, indicating Y5R transactivation upon stimulation of the co-expressed receptor. These receptor interactions correlated with an augmented mitogenic response to NPY. In Y1R/Y5R and Y2R/Y5R transfectants, the proliferative response started at picomolar NPY concentrations, while nanomolar concentrations were needed to trigger proliferation in cells transfected with single receptors. Thus, our data identify direct and indirect heterotypic NPY receptor interactions as the mechanism amplifying its activity. Understanding these processes is crucial for the design of treatments targeting the NPY system.

Design of Stapled Oxyntomodulin Analogs Containing Functionalized Biphenyl Cross-Linkers

A panel of three lipid-modified, functionalized biphenyl cross-linkers (fBph) were synthesized and subsequently employed in the preparation of the stapled oxyntomodulin (OXM) analogs. In a luciferase-based reporter assay, these stapled OXM analogs showed varying degree of potency in activating GLP-1R and GCGR, presumably due to the disparate effect of the lipid chains on the local environment close to the ligand-receptor binding interface. In particular, the fBph-1 cross-linked peptide with the lipid chain attached to position-3 of the biphenyl cross-linker exhibited the highest dual agonist activity.

Heterodimerization of Dibenzodiazepinone-Type Muscarinic Acetylcholine Receptor Ligands Leads to Increased M2R Affinity and Selectivity

In search for selective ligands for the muscarinic acetylcholine receptor (MR) subtype M₂, the dimeric ligand approach, that is combining two pharmacophores in one and the same molecule, was pursued. Different types (agonists, antagonists, orthosteric, and allosteric) of monomeric MR ligands were combined by various linkers with a dibenzodiazepinone-type MR antagonist, affording five types of heterodimeric compounds ("DIBA-xanomeline," "DIBA-TBPB," "DIBA-77-LH-28-1," "DIBA-propantheline," and "DIBA-4-DAMP"), which showed high M₂R affinities (pK_i > 8.3). The heterodimeric ligand UR-SK75 (46) exhibited the highest M₂R affinity and selectivity [pK_i (M₁R-M₅R): 8.84, 10.14, 7.88, 8.59, and 7.47]. Two tritium-labeled dimeric derivatives ("DIBA-xanomeline"-type: [³H]UR-SK71 ([³H]44) and "DIBA-TBPB"-type: [³H]UR-SK59 ([³H]64)) were prepared to investigate their binding modes at hM₂R. Saturation-binding experiments showed that these compounds address the orthosteric binding site of the M₂R. The investigation of the effect of various allosteric MR modulators [gallamine (13), W84 (14), and LY2119620 (15)] on the equilibrium (13-15) or saturation (14) binding of [³H]64 suggested a competitive mechanism between [³H]64 and the investigated allosteric ligands, and consequently a dualsteric binding mode of 64 at the M₂R.

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.

Prototypic 18F-Labeled Argininamide-Type Neuropeptide Y Y1R Antagonists as Tracers for PET Imaging of Mammary Carcinoma

The neuropeptide Y (NPY) Y₁ receptor (Y₁R) selective radioligand (R)-N^α-(2,2-diphenylacetyl)-N^ω-[4-(2-[¹⁸F]fluoropropanoylamino)butyl]aminocarbonyl-N-(4-hydroxybenzyl)argininamide ([¹⁸F]23), derived from the high-affinity Y₁R antagonist BIBP3226, was developed for imaging studies of Y₁R-positive tumors. Starting from the argininamide core bearing amine-functionalized spacer moieties, a series of fluoropropanoylated and fluorobenzoylated derivatives was synthesized and studied for Y₁R affinity. The fluoropropanoylated derivative 23 displayed high affinity (K_i = 1.3 nM) and selectivity toward Y₁R. Radiosynthesis was accomplished via ¹⁸F-fluoropropanoylation, yielding [¹⁸F]23 with excellent stability in mice; however, the biodistribution study revealed pronounced hepatobiliary clearance with high accumulation in the gall bladder (>100 %ID/g). Despite the unfavorable biodistribution, [¹⁸F]23 was successfully used for imaging of Y₁R positive MCF-7 tumors in nude mice. Therefore, we suggest [¹⁸F]23 as a lead for the design of PET ligands with optimized physicochemical properties resulting in more favorable biodistribution and higher Y₁R-dependent enrichment in mammary carcinoma.

Mimicking of Arginine by Functionalized N(ω)-Carbamoylated Arginine As a New Broadly Applicable Approach to Labeled Bioactive Peptides: High Affinity Angiotensin, Neuropeptide Y, Neuropeptide FF, and Neurotensin Receptor Ligands As Examples

Derivatization of biologically active peptides by conjugation with fluorophores or radionuclide-bearing moieties is an effective and commonly used approach to prepare molecular tools and diagnostic agents. Whereas lysine, cysteine, and N-terminal amino acids have been mostly used for peptide conjugation, we describe a new, widely applicable approach to peptide conjugation based on the nonclassical bioisosteric replacement of the guanidine group in arginine by a functionalized carbamoylguanidine moiety. Four arginine-containing peptide receptor ligands (angiotensin II, neurotensin(8-13), an analogue of the C-terminal pentapeptide of neuropeptide Y, and a neuropeptide FF analogue) were subject of this proof-of-concept study. The N(ω)-carbamoylated arginines, bearing spacers with a terminal amino group, were incorporated into the peptides by standard Fmoc solid phase peptide synthesis. The synthesized chemically stable peptide derivatives showed high receptor affinities with Ki values in the low nanomolar range, even when bulky fluorophores had been attached. Two new tritiated tracers for angiotensin and neurotensin receptors are described.

Novel approaches to screening guanidine derivatives

INTRODUCTION

Compounds containing guanidine moiety, originating both from natural and synthetic sources, have found potential applications in both synthetic and medicinal chemistry. Indeed, guanidine functionality can be found in many natural and pharmaceutical products as well as in cosmetic ingredients produced by synthetic methods.

AREAS COVERED

This review covers the latest developments in the research undertaken for the therapeutic application of newly synthesized guanidine derivatives including: small peptides and peptidomimetics. This article encompasses the selected literature published in the last three decades with a focus on the novel approaches for screening of lead drug candidates with their pharmacological action.

EXPERT OPINION

Guanidines, as they are both organically based and also hydrophilic in nature, have undergone a mammoth amount of screening and testing to discover promising lead structures with a CN3 core, appropriate for potential future drug development. The compounds have the potential to be neurodegenerative therapeutic options, as well as: anti-inflammatory, anti-protozoal, anti-HIV, chemotherapeutic, anti-diabetic agents and so on. It is true that guanidine-based compounds of natural sources also, like synthetic and virtually designed drugs, have been of significant interest and have the potential to be useful therapeutic options in the future. As for now, however, there is not sufficient data to support their use in a number of the suggested areas, and further studies are required.

Synthesis and characterization of DMAP-modified NPY Y1 receptor antagonists as acyl-transfer catalysts

Starting from the working hypothesis that specific chemical labelling may be an attractive approach to detect and study G protein-coupled receptors (GPCRs) we synthesized catalytically active antagonists of the neuropeptide Y1 receptor (Y1R). An argininamide-type Y1R antagonist scaffold was combined with a DMAP moiety via spacers of different length and chemical nature. These hybrid compounds have Y1R affinities in the two-digit nanomolar range and are capable of catalysing acyl-transfer reaction to surrogates of bionucleophiles, as demonstrated in the absence of cells by using esters of fluorescent dyes as substrates in buffer. By contrast, selective staining of Y1Rs on living MCF-7 cells was not achieved due to significant non-catalysed (Y1R ligand independent) reaction with biomolecules and the limited density of Y1R on the cell surface. Although this may also depend on insufficient selectivity of the staining reagents, the results of this study suggest that the general applicability of catalytic staining to GPCRs has to be reconsidered, as this approach is hampered by a very low portion of receptor of interest compared to the total amount of membrane proteins.