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Special Issue "Advances in Peptide and Peptidomimetic Design Inspiring Basic Science and Drug Discovery: A Themed Issue Honoring Professor Victor J. Hruby on the Occasion of His 80th Birthday"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Medicinal Chemistry".

Deadline for manuscript submissions: closed (31 March 2019)

Special Issue Editors

Guest Editor
Prof. Henry Mosberg

Tom D. Rowe Professor of Medicinal Chemistry, Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109, United States
Website | E-Mail
Interests: GPCR; opioids; bifunctional ligands; peptidomimetics
Guest Editor
Dr. Tomi Sawyer

Merck & Co., Inc., Boston, MA, USA
Website | E-Mail
Interests: peptide and proteomimetic chemistry; GPCR, kinase, protease and protein–protein interaction drug discovery; medicinal chemistry; structure-based design; cell permeability
Guest Editor
Prof. Carrie Haskell-Luevano

Philip S. Portoghese Endowed Chair in Chemical Neuroscience, Institute for Translational Neuroscience Scholar, Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota, United States
Website | E-Mail
Interests: GPCR; neuropeptide; peptide; obesity; feeding behavior; melanocortin; melanotropin

Special Issue Information

Dear Colleagues,

Fueled by a wide-ranging, probing curiosity complemented by an energetic, engaging personality and a highly collaborative approach to science, Prof. Victor J. Hruby’s research accomplishments have spanned a staggering breadth of scientific endeavors resulting in well over 1300 publications, numerous patents, and a worldwide reputation as a preeminent scholar.

Victor was born in Valley City, North Dakota and received his B.S. and M.S. degrees with A. William Johnson at the University of North Dakota. He then went to Cornell University for graduate studies with A. T. Blomquist.  After receiving his Ph.D., Dr. Hruby joined the Cornell University Medical College as an Instructor, working with Prof. Vincent duVigneaud, Nobel Laureate. He moved to the University of Arizona in 1968 as an Assistant Professor and rose through the academic ranks to be Regents Professor in the Department of Chemistry and Biochemistry in 1989. He is now Emeritus Regents Professor and has remained very active in both mentoring and collaborative work at the University of Arizona and throughout the world.

Prof. Hruby’s many accomplishments include: (i) the rational design of novel, extensively used and highly cited ligands for opioid, melanocortin, oxytocin, glucagon, and neurokinin receptors; (ii) the development and application of approaches for incorporating conformational constraints into peptides to improve selectivity and bioavailability and to aid elucidation of bioactive conformations; and (iii) key contributions to combinatorial chemistry, and the application of biophysical methods (e.g., NMR, X-ray crystallography, fluorescence, Plasmon waveguide resonance spectroscopy) to the determination of  biomolecular structure and mechanism. 

Molecules is highly pleased to host a Special Issue honoring Prof. Victor J. Hruby on the occasion of his 80th birthday for his outstanding achievements to advance peptide and peptidomimetic design, as well as inspire both basic science and drug discovery.

Prof. Henry Mosberg
Dr. Tomi Sawyer
Prof. Carrie Haskell-Luevano
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Peptide
  • peptidomimetic
  • macrocyclic peptides
  • conformationally-constrained peptides
  • receptor targets
  • structural biology
  • biophysical chemistry
  • computational modeling
  • structure-activity, opioids
  • melanocortins
  • oxytocin
  • glucagon
  • neurokinins

Published Papers (13 papers)

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Research

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Open AccessArticle
Incorporation of Putative Helix-Breaking Amino Acids in the Design of Novel Stapled Peptides: Exploring Biophysical and Cellular Permeability Properties
Molecules 2019, 24(12), 2292; https://doi.org/10.3390/molecules24122292
Received: 22 May 2019 / Revised: 14 June 2019 / Accepted: 16 June 2019 / Published: 20 June 2019
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Abstract
Stapled α-helical peptides represent an emerging superclass of macrocyclic molecules with drug-like properties, including high-affinity target binding, protease resistance, and membrane permeability. As a model system for probing the chemical space available for optimizing these properties, we focused on dual Mdm2/MdmX antagonist stapled [...] Read more.
Stapled α-helical peptides represent an emerging superclass of macrocyclic molecules with drug-like properties, including high-affinity target binding, protease resistance, and membrane permeability. As a model system for probing the chemical space available for optimizing these properties, we focused on dual Mdm2/MdmX antagonist stapled peptides related to the p53 N-terminus. Specifically, we first generated a library of ATSP-7041 (Chang et al., 2013) analogs iteratively modified by L-Ala and D-amino acids. Single L-Ala substitutions beyond the Mdm2/(X) binding interfacial residues (i.e., Phe3, Trp7, and Cba10) had minimal effects on target binding, α-helical content, and cellular activity. Similar binding affinities and cellular activities were noted at non-interfacial positions when the template residues were substituted with their d-amino acid counterparts, despite the fact that d-amino acid residues typically ‘break’ right-handed α-helices. d-amino acid substitutions at the interfacial residues Phe3 and Cba10 resulted in the expected decreases in binding affinity and cellular activity. Surprisingly, substitution at the remaining interfacial position with its d-amino acid equivalent (i.e., Trp7 to d-Trp7) was fully tolerated, both in terms of its binding affinity and cellular activity. An X-ray structure of the d-Trp7-modified peptide was determined and revealed that the indole side chain was able to interact optimally with its Mdm2 binding site by a slight global re-orientation of the stapled peptide. To further investigate the comparative effects of d-amino acid substitutions we used linear analogs of ATSP-7041, where we replaced the stapling amino acids by Aib (i.e., R84 to Aib4 and S511 to Aib11) to retain the helix-inducing properties of α-methylation. The resultant analog sequence Ac–Leu–Thr–Phe–Aib–Glu–Tyr–Trp–Gln–Leu–Cba–Aib–Ser–Ala–Ala–NH2 exhibited high-affinity target binding (Mdm2 Kd = 43 nM) and significant α-helicity in circular dichroism studies. Relative to this linear ATSP-7041 analog, several d-amino acid substitutions at Mdm2(X) non-binding residues (e.g., d-Glu5, d-Gln8, and d-Leu9) demonstrated decreased binding and α-helicity. Importantly, circular dichroism (CD) spectroscopy showed that although helicity was indeed disrupted by d-amino acids in linear versions of our template sequence, stapled molecules tolerated these residues well. Further studies on stapled peptides incorporating N-methylated amino acids, l-Pro, or Gly substitutions showed that despite some positional dependence, these helix-breaking residues were also generally tolerated in terms of secondary structure, binding affinity, and cellular activity. Overall, macrocyclization by hydrocarbon stapling appears to overcome the destabilization of α-helicity by helix breaking residues and, in the specific case of d-Trp7-modification, a highly potent ATSP-7041 analog (Mdm2 Kd = 30 nM; cellular EC50 = 600 nM) was identified. Our findings provide incentive for future studies to expand the chemical diversity of macrocyclic α-helical peptides (e.g., d-amino acid modifications) to explore their biophysical properties and cellular permeability. Indeed, using the library of 50 peptides generated in this study, a good correlation between cellular permeability and lipophilicity was observed. Full article
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Open AccessArticle
Novel pH Selective, Highly Lytic Peptides Based on a Chimeric Influenza Hemagglutinin Peptide/Cell Penetrating Peptide Motif
Molecules 2019, 24(11), 2079; https://doi.org/10.3390/molecules24112079
Received: 2 May 2019 / Revised: 22 May 2019 / Accepted: 24 May 2019 / Published: 31 May 2019
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Abstract
Delivery of macromolecular cargos such as siRNA to the cytosol after endocytosis remains a critical challenge. Numerous approaches including viruses, lipid nanoparticles, polymeric constructs, and various peptide-based approaches have yet to yield a general solution to this delivery issue. In this manuscript, we [...] Read more.
Delivery of macromolecular cargos such as siRNA to the cytosol after endocytosis remains a critical challenge. Numerous approaches including viruses, lipid nanoparticles, polymeric constructs, and various peptide-based approaches have yet to yield a general solution to this delivery issue. In this manuscript, we describe our efforts to design novel endosomolytic peptides that could be used to facilitate the release of cargos from a late endosomal compartment. These amphiphilic peptides, based on a chimeric influenza hemagglutinin peptide/cell-penetrating peptide (CPP) template, utilize a pH-triggering mechanism in which the peptides are protonated after acidification of the endosome, and thereby adopt an alpha-helical conformation. The helical forms of the peptides are lytically active, while the non-protonated forms are much less or non-lytically active at physiological pH. Starting from an initial lead peptide (INF7-Tat), we systematically modified the sequence of the chimeric peptides to obtain peptides with greatly enhanced lytic activity that maintain good pH selectivity in a red blood cell hemolysis assay. Full article
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Open AccessArticle
ACPred: A Computational Tool for the Prediction and Analysis of Anticancer Peptides
Molecules 2019, 24(10), 1973; https://doi.org/10.3390/molecules24101973
Received: 1 April 2019 / Revised: 7 May 2019 / Accepted: 17 May 2019 / Published: 22 May 2019
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Abstract
Anticancer peptides (ACPs) have emerged as a new class of therapeutic agent for cancer treatment due to their lower toxicity as well as greater efficacy, selectivity and specificity when compared to conventional small molecule drugs. However, the experimental identification of ACPs still remains [...] Read more.
Anticancer peptides (ACPs) have emerged as a new class of therapeutic agent for cancer treatment due to their lower toxicity as well as greater efficacy, selectivity and specificity when compared to conventional small molecule drugs. However, the experimental identification of ACPs still remains a time-consuming and expensive endeavor. Therefore, it is desirable to develop and improve upon existing computational models for predicting and characterizing ACPs. In this study, we present a bioinformatics tool called the ACPred, which is an interpretable tool for the prediction and characterization of the anticancer activities of peptides. ACPred was developed by utilizing powerful machine learning models (support vector machine and random forest) and various classes of peptide features. It was observed by a jackknife cross-validation test that ACPred can achieve an overall accuracy of 95.61% in identifying ACPs. In addition, analysis revealed the following distinguishing characteristics that ACPs possess: (i) hydrophobic residue enhances the cationic properties of α-helical ACPs resulting in better cell penetration; (ii) the amphipathic nature of the α-helical structure plays a crucial role in its mechanism of cytotoxicity; and (iii) the formation of disulfide bridges on β-sheets is vital for structural maintenance which correlates with its ability to kill cancer cells. Finally, for the convenience of experimental scientists, the ACPred web server was established and made freely available online. Full article
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Open AccessArticle
The Characteristics of PD-L1 Inhibitors, from Peptides to Small Molecules
Molecules 2019, 24(10), 1940; https://doi.org/10.3390/molecules24101940
Received: 25 April 2019 / Revised: 17 May 2019 / Accepted: 19 May 2019 / Published: 20 May 2019
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Abstract
The programmed cell death ligand protein 1 (PD-L1) is a member of the B7 protein family and consists of 290 amino acid residues. The blockade of the PD-1/PD-L1 immune checkpoint pathway is effective in tumor treatment. Results: Two pharmacophore models were generated based [...] Read more.
The programmed cell death ligand protein 1 (PD-L1) is a member of the B7 protein family and consists of 290 amino acid residues. The blockade of the PD-1/PD-L1 immune checkpoint pathway is effective in tumor treatment. Results: Two pharmacophore models were generated based on peptides and small molecules. Hypo 1A consists of one hydrogen bond donor, one hydrogen bond acceptor, two hydrophobic points and one aromatic ring point. Hypo 1B consists of one hydrogen bond donor, three hydrophobic points and one positive ionizable point. Conclusions: The pharmacophore model consisting of a hydrogen bond donor, hydrophobic points and a positive ionizable point may be helpful for designing small-molecule inhibitors targeting PD-L1. Full article
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Open AccessArticle
Aza-Amino Acids Disrupt β-Sheet Secondary Structures
Molecules 2019, 24(10), 1919; https://doi.org/10.3390/molecules24101919
Received: 1 May 2019 / Revised: 15 May 2019 / Accepted: 17 May 2019 / Published: 18 May 2019
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Abstract
Cα to N substitution in aza-amino acids imposes local conformational constraints, changes in hydrogen bonding properties, and leads to adaptive chirality at the nitrogen atom. These properties can be exploited in mimicry and stabilization of peptide secondary structures and self-assembly. Here, the effect [...] Read more.
Cα to N substitution in aza-amino acids imposes local conformational constraints, changes in hydrogen bonding properties, and leads to adaptive chirality at the nitrogen atom. These properties can be exploited in mimicry and stabilization of peptide secondary structures and self-assembly. Here, the effect of a single aza-amino acid incorporation located in the upper β-strand at a hydrogen-bonded (HB) site of a β-hairpin model peptide (H-Arg-Tyr-Val-Glu-Val-d-Pro-Gly-Orn-Lys-Ile-Leu-Gln-NH2) is reported. Specifically, analogs in which valine3 was substituted for aza-valine3 or aza-glycine3 were synthesized, and their β-hairpin stabilities were examined using Nuclear Magnetic Resonance (NMR) spectroscopy. The azapeptide analogs were found to destabilize β-hairpin formation compared to the parent peptide. The aza-valine3 residue was more disruptive of β-hairpin geometry than its aza-glycine3 counterpart. Full article
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Open AccessArticle
Rapid Discovery of Illuminating Peptides for Instant Detection of Opioids in Blood and Body Fluids
Molecules 2019, 24(9), 1813; https://doi.org/10.3390/molecules24091813
Received: 15 April 2019 / Revised: 3 May 2019 / Accepted: 5 May 2019 / Published: 10 May 2019
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Abstract
The United States is currently experiencing an opioid crisis, with more than 47,000 deaths in 2017 due to opioid overdoses. Current approaches for opioid identification and quantification in body fluids include immunoassays and chromatographic methods (e.g., LC-MS, GC-MS), which require expensive instrumentation and [...] Read more.
The United States is currently experiencing an opioid crisis, with more than 47,000 deaths in 2017 due to opioid overdoses. Current approaches for opioid identification and quantification in body fluids include immunoassays and chromatographic methods (e.g., LC-MS, GC-MS), which require expensive instrumentation and extensive sample preparation. Our aim was to develop a portable point-of-care device that can be used for the instant detection of opioids in body fluids. Here, we reported the development of a morphine-sensitive fluorescence-based sensor chip to sensitively detect morphine in the blood using a homogeneous immunoassay without any washing steps. Morphine-sensitive illuminating peptides were identified using a high throughput one-bead one-compound (OBOC) combinatorial peptide library approach. The OBOC libraries contain a large number of random peptides with a molecular rotor dye, malachite green (MG), that are coupled to the amino group on the side chain of lysine at different positions of the peptides. The OBOC libraries were then screened for fluorescent activation under a confocal microscope, using an anti-morphine monoclonal antibody as the screening probe, in the presence and absence of free morphine. Using this novel three-step fluorescent screening assay, we were able to identify the peptide-beads that fluoresce in the presence of an anti-morphine antibody, but lost fluorescence when the free morphine was present. After the positive beads were decoded using automatic Edman microsequencing, the morphine-sensitive illuminating peptides were then synthesized in soluble form, functionalized with an azido group, and immobilized onto microfabricated PEG-array spots on a glass slide. The sensor chip was then evaluated for the detection of morphine in plasma. We demonstrated that this proof-of-concept platform can be used to develop fluorescence-based sensors against morphine. More importantly, this technology can also be applied to the discovery of other novel illuminating peptidic sensors for the detection of illicit drugs and cancer biomarkers in body fluids. Full article
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Open AccessFeature PaperArticle
Triazolopeptides Inhibiting the Interaction between Neuropilin-1 and Vascular Endothelial Growth Factor-165
Molecules 2019, 24(9), 1756; https://doi.org/10.3390/molecules24091756
Received: 29 March 2019 / Revised: 3 May 2019 / Accepted: 4 May 2019 / Published: 6 May 2019
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Abstract
Inhibiting the interaction of neuropilin-1 (NRP-1) with vascular endothelial growth factor (VEGF) has become an interesting mechanism for potential anticancer therapies. In our previous works, we have obtained several submicromolar inhibitors of this interaction, including branched pentapeptides of general structure Lys(Har)-Xxx-Xxx-Arg. With the [...] Read more.
Inhibiting the interaction of neuropilin-1 (NRP-1) with vascular endothelial growth factor (VEGF) has become an interesting mechanism for potential anticancer therapies. In our previous works, we have obtained several submicromolar inhibitors of this interaction, including branched pentapeptides of general structure Lys(Har)-Xxx-Xxx-Arg. With the intent to improve the proteolytic stability of our inhibitors, we turned our attention to 1,4-disubstituted 1,2,3-triazoles as peptide bond isosteres. In the present contribution, we report the synthesis of 23 novel triazolopeptides along with their inhibitory activity. The compounds were synthesized using typical peptide chemistry methods, but with a conversion of amine into azide completely on solid support. The inhibitory activity of the synthesized derivatives spans from 9.2% to 58.1% at 10 μM concentration (the best compound Lys(Har)-GlyΨ[Trl]GlyΨ[Trl]Arg, 3, IC50 = 8.39 μM). Synthesized peptidotriazoles were tested for stability in human plasma and showed remarkable resistance toward proteolysis, with half-life times far exceeding 48 h. In vitro cell survival test resulted in no significant impact on bone marrow derived murine cells 32D viability. By means of molecular dynamics, we were able to propose a binding mode for compound 3 and discuss the observed structure–activity relationships. Full article
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Open AccessArticle
Small AntiMicrobial Peptide with In Vivo Activity Against Sepsis
Molecules 2019, 24(9), 1702; https://doi.org/10.3390/molecules24091702
Received: 30 March 2019 / Revised: 15 April 2019 / Accepted: 17 April 2019 / Published: 1 May 2019
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Abstract
Antimicrobial peptides (AMPs) are considered as potential therapeutic sources of future antibiotics because of their broad-spectrum activities and alternative mechanisms of action compared to conventional antibiotics. Although AMPs present considerable advantages over conventional antibiotics, their clinical and commercial development still have some limitations, [...] Read more.
Antimicrobial peptides (AMPs) are considered as potential therapeutic sources of future antibiotics because of their broad-spectrum activities and alternative mechanisms of action compared to conventional antibiotics. Although AMPs present considerable advantages over conventional antibiotics, their clinical and commercial development still have some limitations, because of their potential toxicity, susceptibility to proteases, and high cost of production. To overcome these drawbacks, the use of peptides mimics is anticipated to avoid the proteolysis, while the identification of minimalist peptide sequences retaining antimicrobial activities could bring a solution for the cost issue. We describe here new polycationic -amino acids combining these two properties, that we used to design small dipeptides that appeared to be active against Gram-positive and Gram-negative bacteria, selective against prokaryotic versus mammalian cells, and highly stable in human plasma. Moreover, the in vivo data activity obtained in septic mice reveals that the bacterial killing effect allows the control of the infection and increases the survival rate of cecal ligature and puncture (CLP)-treated mice. Full article
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Open AccessArticle
A Stapled Peptide Mimic of the Pseudosubstrate Inhibitor PKI Inhibits Protein Kinase A
Molecules 2019, 24(8), 1567; https://doi.org/10.3390/molecules24081567
Received: 30 March 2019 / Revised: 17 April 2019 / Accepted: 19 April 2019 / Published: 20 April 2019
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Abstract
Kinases regulate multiple and diverse signaling pathways and misregulation is implicated in a multitude of diseases. Although significant efforts have been put forth to develop kinase-specific inhibitors, specificity remains a challenge. As an alternative to catalytic inhibition, allosteric inhibitors can target areas on [...] Read more.
Kinases regulate multiple and diverse signaling pathways and misregulation is implicated in a multitude of diseases. Although significant efforts have been put forth to develop kinase-specific inhibitors, specificity remains a challenge. As an alternative to catalytic inhibition, allosteric inhibitors can target areas on the surface of an enzyme, thereby providing additional target diversity. Using cAMP-dependent protein kinase A (PKA) as a model system, we sought to develop a hydrocarbon-stapled peptide targeting the pseudosubstrate domain of the kinase. A library of peptides was designed from a Protein Kinase Inhibitor (PKI), a naturally encoded protein that serves as a pseudosubstrate inhibitor for PKA. The binding properties of these peptide analogs were characterized by fluorescence polarization and surface plasmon resonance, and two compounds were identified with KD values in the 500–600 pM range. In kinase activity assays, both compounds demonstrated inhibition with 25–35 nM IC50 values. They were also found to permeate cells and localize within the cytoplasm and inhibited PKA activity within the cellular environment. To the best of our knowledge, these stapled peptide inhibitors represent some of the highest affinity binders reported to date for hydrocarbon stapled peptides. Full article
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Open AccessArticle
Development of Highly Selective 1,2,3-Triazole-containing Peptidic Polo-like Kinase 1 Polo-box Domain-binding Inhibitors
Molecules 2019, 24(8), 1488; https://doi.org/10.3390/molecules24081488
Received: 29 March 2019 / Revised: 12 April 2019 / Accepted: 14 April 2019 / Published: 16 April 2019
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Abstract
Members of the polo-like kinase (Plk) family of serine/threonine protein kinases play crucial roles in cell cycle regulation and proliferation. Of the five Plks (Plk1–5), Plk1 is recognized as an anticancer drug target. Plk1 contains multiple structural components that are important for its [...] Read more.
Members of the polo-like kinase (Plk) family of serine/threonine protein kinases play crucial roles in cell cycle regulation and proliferation. Of the five Plks (Plk1–5), Plk1 is recognized as an anticancer drug target. Plk1 contains multiple structural components that are important for its proper biological function. These include an N-terminal catalytic domain and a C-terminal non-catalytic polo-box domain (PBD). The PBD binds to phosphothreonine (pT) and phosphoserine-containing sequences. Blocking PBD-dependent interactions offers a potential means of down-regulating Plk1 function that is distinct from targeting its ATP-binding site. Previously, we demonstrated by tethering alkylphenyl chains from the N(π)-position of the His residue in the 5-mer PLHSpT, that we were able to access a hydrophobic “cryptic” binding pocket on the surface of the PBD, and in so doing enhance binding affinities by approximately 1000-fold. More recently, we optimized these PBD-ligand interactions using an oxime ligation-based strategy. Herein, using azide-alkyne cycloaddition reactions, we explore new triazole-containing PBD-binding antagonists. Some of these ligands retain the high PBD-binding affinity of the parent peptide, while showing desirable enhanced selectivity for the PBD of Plk1 relative to the PBDs of Plk2 and Plk3. Full article
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Open AccessArticle
Structure–Activity Relationships of the Tetrapeptide Ac-His-Arg-(pI)DPhe-Tic-NH2 at the Mouse Melanocortin Receptors: Modification at the (pI)DPhe Position Leads to mMC3R Versus mMC4R Selective Ligands
Molecules 2019, 24(8), 1463; https://doi.org/10.3390/molecules24081463
Received: 28 February 2019 / Revised: 1 April 2019 / Accepted: 4 April 2019 / Published: 13 April 2019
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Abstract
The five melanocortin receptors (MC1R–MC5R) are involved in numerous biological pathways, including steroidogenesis, pigmentation, and food intake. In particular, MC3R and MC4R knockout mice suggest that the MC3R and MC4R regulate energy homeostasis in a non-redundant manner. While MC4R-selective agonists have been utilized [...] Read more.
The five melanocortin receptors (MC1R–MC5R) are involved in numerous biological pathways, including steroidogenesis, pigmentation, and food intake. In particular, MC3R and MC4R knockout mice suggest that the MC3R and MC4R regulate energy homeostasis in a non-redundant manner. While MC4R-selective agonists have been utilized as appetite modulating agents, the lack of MC3R-selective agonists has impeded progress in modulating this receptor in vivo. In this study, the (pI)DPhe position of the tetrapeptide Ac-His-Arg-(pI)DPhe-Tic-NH2 (an MC3R agonist/MC4R antagonist ligand) was investigated with a library of 12 compounds. The compounds in this library were found to have higher agonist efficacy and potency at the mouse (m) MC3R compared to the MC4R, indicating that the Arg-DPhe motif preferentially activates the mMC3R over the mMC4R. This observation may be used in the design of new MC3R-selective ligands, leading to novel probe and therapeutic lead compounds that will be useful for treating metabolic disorders. Full article
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Review

Jump to: Research

Open AccessFeature PaperReview
Current Mechanistic and Pharmacodynamic Understanding of Melanocortin-4 Receptor Activation
Molecules 2019, 24(10), 1892; https://doi.org/10.3390/molecules24101892
Received: 21 April 2019 / Revised: 15 May 2019 / Accepted: 15 May 2019 / Published: 16 May 2019
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Abstract
In this work we summarize our understanding of melanocortin 4 receptor (MC4R) pathway activation, aiming to define a safe and effective therapeutic targeting strategy for the MC4R. Delineation of cellular MC4R pathways has provided evidence for distinct MC4R signaling events characterized by unique [...] Read more.
In this work we summarize our understanding of melanocortin 4 receptor (MC4R) pathway activation, aiming to define a safe and effective therapeutic targeting strategy for the MC4R. Delineation of cellular MC4R pathways has provided evidence for distinct MC4R signaling events characterized by unique receptor activation kinetics. While these studies remain narrow in scope, and have largely been explored with peptidic agonists, the results provide a possible correlation between distinct ligand groups and differential MC4R activation kinetics. In addition, when a set of small-molecule and peptide MC4R agonists are compared, evidence of biased signaling has been reported. The results of such mechanistic studies are discussed. Full article
Open AccessReview
Peptide Conjugates with Small Molecules Designed to Enhance Efficacy and Safety
Molecules 2019, 24(10), 1855; https://doi.org/10.3390/molecules24101855
Received: 27 April 2019 / Revised: 10 May 2019 / Accepted: 12 May 2019 / Published: 14 May 2019
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Abstract
Peptides constitute molecular diversity with unique molecular mechanisms of action that are proven indispensable in the management of many human diseases, but of only a mere fraction relative to more traditional small molecule-based medicines. The integration of these two therapeutic modalities offers the [...] Read more.
Peptides constitute molecular diversity with unique molecular mechanisms of action that are proven indispensable in the management of many human diseases, but of only a mere fraction relative to more traditional small molecule-based medicines. The integration of these two therapeutic modalities offers the potential to enhance and broaden pharmacology while minimizing dose-dependent toxicology. This review summarizes numerous advances in drug design, synthesis and development that provide direction for next-generation research endeavors in this field. Medicinal studies in this area have largely focused upon the application of peptides to selectively enhance small molecule cytotoxicity to more effectively treat multiple oncologic diseases. To a lesser and steadily emerging extent peptides are being therapeutically employed to complement and diversify the pharmacology of small molecule drugs in diseases other than just cancer. No matter the disease, the purpose of the molecular integration remains constant and it is to achieve superior therapeutic outcomes with diminished adverse effects. We review linker technology and conjugation chemistries that have enabled integrated and targeted pharmacology with controlled release. Finally, we offer our perspective on opportunities and obstacles in the field. Full article
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