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1.  Investigational peptide and peptidomimetic μ and δ opioid receptor agonists in the relief of pain 
Introduction
Current methods for treating prolonged and neuropathic pain are inadequate and lead to toxicities that greatly diminish quality of life. Therefore, new approaches to the treatment of pain states are needed to address these problems.
Areas covered
The review primarily reviews approaches that have been taken in the peer-reviewed literature of multivalent ligands that interact with both μ and δ opioid receptors as agonists, and in some cases, also with pharmacophores for antagonist ligands that interact with other receptors as antagonists to block pain.
Expert opinion
Although there are a number of drugs currently on the market for the treatment of pain; none of them are 100% successful. In the authors’ opinion, it is clear that new directions and modalities are needed to better address the treatment of prolonged and neuropathic pain; one drug or class clearly is not the answer for all pain therapy. Undoubtedly, there are many different phenotypes of prolonged and neuropathic pain and this should be one avenue to further develop appropriate therapies.
doi:10.1517/13543784.2014.856879
PMCID: PMC4282681  PMID: 24329035
agonist; multifunctionality; multivalency; opioid; pain; receptors
2.  Multivalent Interactions: Synthesis and Evaluation of Melanotropin Multimers – Tools for Melanoma Targeting 
In order to develop agents for early detection and selective treatment of melanomas, high affinity and high specificity molecular tools are required. Enhanced specificity may be obtained by simultaneously binding to multiple cell surface targets via the use of multimeric analogs of naturally occurring ligands. Trimers targeting overexpressed melanocortin receptors have been found to be potential candidates for this purpose. In the present letter, we describe the synthesis and study of multimers based on a dendrimer-like scaffold. The binding affinity and activity results revealed that dendrimers promote multivalent interactions via statistical and/or cooperative effects on binding. Moreover, viability studies showed no significant toxicity at micromolar concentrations, which will allow these molecular complexes to be used in vivo. Finally, imaging studies showed effective internalization for all the molecules confirming their potential as delivery agents.
doi:10.1021/ml300312b
PMCID: PMC3601667  PMID: 23524643
Multivalent interactions; multimers; peptides; dendrimers; cancer; melanoma; targeted therapy; delivery
3.  Novel fentanyl-based dual μ/δ-opioid agonists for the treatment of acute and chronic pain 
Life sciences  2013;93(0):1010-1016.
Approximately one third of the adult U.S. population suffers from some type of on-going, chronic pain annually, and many more will have some type of acute pain associated with trauma or surgery. First-line therapies for moderate to severe pain include prescriptions for common mu opioid receptor agonists such as morphine and its various derivatives. The epidemic use, misuse and diversion of prescription opioids has highlighted just one of the adverse effects of mu opioid analgesics. Alternative approaches include novel opioids that target delta or kappa opioid receptors, or compounds that interact with two or more of the opioid receptors.
Aims
Here we report the pharmacology of a newly synthesized bifunctional opioid agonist (RV-Jim-C3) derived from combined structures of fentanyl and enkephalin in rodents. RV-Jim-C3 has high affinity binding to both mu and delta opioid receptors.
Main Methods
Mice and rats were used to test RV-Jim-C3 in a tailflick test with and without opioid selective antagonist for antinociception. RV-Jim-C3 was tested for anti-inflammatory and antihypersensitivity effects in a model of formalin-induced flinching and spinal nerve ligation. To rule out motor impairment, rotarod was tested in rats.
Key findings
RV-Jim-C3 demonstrates potent-efficacious activity in several in vivo pain models including inflammatory pain, antihyperalgesia and antiallodynic with no significant motor impairment.
Significance
This is the first report of a fentanyl-based structure with delta and mu opioid receptor activity that exhibits outstanding antinociceptive efficacy in neuropathic pain, reducing the propensity of unwanted side effects driven by current therapies that are unifunctional mu opioid agonists.
doi:10.1016/j.lfs.2013.09.016
PMCID: PMC3962292  PMID: 24084045
chronic pain; allodynia; hyperalgesia; inflammatory; mice; rat; fentanyl; mu opioid; delta opioid; spinal nerve ligation; formalin flinch; naloxone
4.  Synthesis and Crystallographic Study of N′-(1-benzylpiperidin-4-yl)acetohydrazide 
Journal of chemical crystallography  2010;40(11):961-964.
As part of a study into new Fentanyl-derived opioid compounds with potent analgesic activity and reduced side effects the starting material title compound, C14H21N3O (1), was synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The crystal structure is monoclinic Cc with unit cell parameters a = 14.1480(3) Å, b = 14.1720(4) Å, c = 27.6701(7) Å, β = 96.956(1)°, α = γ = 90°. The compound has crystallized with four crystallographically unique molecules in the asymmetric unit; each molecule has a very similar conformation and an analysis of the structure shows that although all four unique molecules overlay very well there is no evidence of pseudo-symmetry which would relate the molecules in the higher symmetry space group C2/c. The crystal packing consists of two separate hydrogen bonded chains which are linked together to form a thick 2D structure in the ab plane.
doi:10.1007/s10870-010-9771-1
PMCID: PMC4260262  PMID: 25505832
Organic compounds; Z′ > 1; Hydrogen bonding
5.  Proton sharing and transfer in some zwitterionic compounds based on 4-oxo-4-((1-phenethylpiperidin-4-yl)(phenyl)amino)alcanoic acids† 
CrystEngComm / RSC  2010;12(11):3651-3657.
Three compounds, each derived from Fentanyl and differing essentially only in the length of a carboxylic acid chain, were synthesized and yielded four crystal structures three of which share several structural similarities, including the length of the chain, while the fourth, with a shorter chain, is quite different. The chain length has a significant influence on the crystal structures formed. The ‘three atom’ chain compounds are all solvated zwitterions which feature a hydrogen-bonded ‘dimer’ between adjacent zwitterions. The formation of this large dimer leaves available a second carboxylate O atom to take part in hydrogen bonding interactions with solvent molecules. The shorter ‘two atom’ chain compound was difficult to crystallize and required the use of synchrotron radiation to measure X-ray diffraction data. It does not form the same dimer motif observed in the ‘three atom’ chain compounds and has not formally formed a zwitterion; although there is evidence of proton sharing or disorder X-ray data are insufficient to create a disordered model, and the compound was modeled as formally neutral based on O–H and N–H distances. Room temperature analyses showed the proton transfer behavior to be independent of crystal temperature, and nuclear magnetic resonance studies show proton transfer behavior in solution. The formation of a zwitterionic hydrogen-bonded dimer is implicated in providing some stability during crystal growth of the easily crystallized ‘three atom’ chain compounds.
doi:10.1039/B923698H
PMCID: PMC4241297  PMID: 25425961
6.  Recyclization reactions of 1-alkylpyrimidinium salts 
Heterocyclic communications  2011;17(3-4):129-133.
The reaction of 4-amino-2-benzyl-1-methyl-5-ethoxycarbonylpyrimidinium iodide (3) with alcoholic methylamine resulted in the formation of the methylimine of 2-amino-4-hydroxy-6-methylamino-5-phenylpyridine-3-carbaldehyde (5). Heating of the same pyrimidinium salt in benzylamine gave a mixture of products of two C–C recyclizations: 2-benzyl-4-benzylamino-5-carbamoylpyrimidine (7) and the benzylimine of 4-amino-2-benzyl-6-benzylaminopyrimidine-5-carbaldehyde (8). The reaction of 2-amino-1,4-dimethyl-5-ethoxycarbonylpyrimidinium iodide (10) with KOH ethanolic solution gave a single product of C–C-recyclization: 2-amino-5-acetyl-4-hydroxypyrimidine (11).
doi:10.1515/hc.2011.025
PMCID: PMC4230491  PMID: 25400328
pyrimidinium salt; recyclization
7.  Truncation of the peptide sequence in bifunctional ligands with mu and delta opioid receptor agonist and neurokinin 1 receptor antagonist activities 
Bioorganic & medicinal chemistry letters  2013;23(17):10.1016/j.bmcl.2013.06.065.
The optimization and truncation of our lead peptide-derived ligand TY005 possessing eight amino-acid residues was performed. Among the synthesized derivatives, NP30 (Tyr1-DAla2-Gly3-Phe4-Gly5-Trp6-O-[3′,5′-Bzl(CF3)2]) showed balanced and potent opioid agonist as well as substance P antagonist activities in isolated tissue-based assays, together with significant antinociceptive and antiallodynic activities in vivo.
doi:10.1016/j.bmcl.2013.06.065
PMCID: PMC3810412  PMID: 23899615
bifunctional compounds; opioid receptor agonists; neutokinin-1 receptor antagonists; Truncation of peptide sequence; NMR structure
8.  Synthesis and Characterization of Time-resolved Fluorescence Probes for Evaluation of Competitive Binding to Melanocortin Receptors 
Bioorganic & medicinal chemistry  2013;21(17):5029-5038.
Probes for use in time-resolved fluorescence competitive binding assays at melanocortin receptors based on the parental ligands MSH(4), MSH(7), and NDP-α-MSH were prepared by solid phase synthesis methods, purified, and characterized. The saturation binding of these probes was studied using HEK-293 cells engineered to overexpress the human melanocortin 4 receptor (hMC4R) as well as the human cholecystokinin 2 receptor (hCCK2R). The ratios of non-specific binding to total binding approached unity at high concentrations for each probe. At low probe concentrations, receptor-mediated binding and uptake was discernable, and so probe concentrations were kept as low as possible in determining Kd values. The Eu-DTPA-PEGO-MSH(4) probe exhibited low specific binding relative to non-specific binding, even at low nanomolar concentrations, and was deemed unsuitable for use in competition binding assays. The Eu-DTPA-PEGO probes based on MSH(7) and NDP-α-MSH exhibited Kd values of 27±3.9 nM and 4.2±0.48 nM, respectively, for binding with hMC4R. These probes were employed in competitive binding assays to characterize the interactions of hMC4R with monovalent and divalent MSH(4), MSH(7), and NDP-α-MSH constructs derived from squalene. Results from assays with both probes reflected only statistical enhancements, suggesting improper ligand spacing on the squalene scaffold for the divalent constructs. The Ki values from competitive binding assays that employed the MSH(7)-based probe were generally lower than the Ki values obtained when the probe based on NDP-α-MSH was employed, which is consistent with the greater potency of the latter probe. The probe based on MSH(7) was also competed with monovalent, divalent, and trivalent MSH(4) constructs that previously demonstrated multivalent binding in competitive binding assays against a variant of the probe based on NDP-α-MSH. Results from these assays confirm multivalent binding, but suggest a more modest increase in avidity for these MSH(4) constructs than was previously reported.
doi:10.1016/j.bmc.2013.06.052
PMCID: PMC3773999  PMID: 23890524
competition binding assays; fluorescent probes; melanocortin 4 receptor; saturation binding assays; time-resolved fluorescence
9.  Synthesis and Evaluation of Bivalent NDP-α-MSH(7) Peptide Ligands for Binding to the Human Melanocortin Receptor 4 (hMC4R) 
Bioconjugate chemistry  2007;18(4):1101-1109.
We demonstrate the potential utility of multivalent ligands as targeting agents for cancer imaging or therapy by determining the binding of homobivalent ligands to their corresponding receptors. This manuscript details the synthesis and evaluation of a series of bivalent ligands containing two copies of the truncated heptapeptide version of [Nle4-d-Phe7]-α-melanocyte stimulating hormone (NDP-α-MSH), referred to as MSH(7). These were connected with various semirigid linkers containing Pro-Gly repeats, with or without flexible poly(ethylene glycol) (PEGO) moieties at their termini. Modeling data suggest a distance of 20–50 Å between the ligand binding sites of two adjacent G-protein coupled receptors, GPCRs. These bivalent ligands were observed to bind with higher affinity compared to their monovalent counterparts. Data suggest these ligands may be capable of cross-linking adjacent receptors. An optimal linker length of 25 ± 10 Å, inferred from these ligands, correlated well with the inter-receptor distance estimated through modeling. Although there was no difference in maximal binding affinities between the ligands constructed with the Pro-Gly repeats versus those constructed with the PEGO inserts, the PEGO-containing ligands bound with high affinities over a greater range of linker lengths.
doi:10.1021/bc0603642
PMCID: PMC3538036  PMID: 17591746
10.  Design, synthesis and biological studies of efficient multivalent melanotropin ligands: tools towards melanoma diagnosis and treatment 
Journal of medicinal chemistry  2011;54(20):7375-7384.
In order to achieve early detection and specific cancer treatment we propose the use of multivalent interactions in which a series of binding events leads to increased affinity and consequently to selectivity. Using melanotropin (MSH) ligands, our aim is to target melanoma cells, which overexpress melanocortin receptors. In this study, we report the design and efficient synthesis of new trivalent ligands bearing MSH ligands. Evaluation of these multimers on a cell model engineered to overexpress melanocortin 4 receptors (MC4R) showed up to a 350-fold increase in binding compared to the monomer, resulting in a trivalent construct with nanomolar affinity starting from a micromolar affinity ligand. Cyclic adenosine monophosphate (cAMP) production was also investigated leading to more insights into the effects of multivalent compounds on transduction mechanisms.
doi:10.1021/jm2009937
PMCID: PMC3521580  PMID: 21928837
Binding; multiple interactions; multimeric ligand design; targeted therapy; cancer; melanoma
11.  Development and in vivo Quantitative Magnetic Resonance Imaging of Polymer Micelles Targeted to the Melanocortin 1 Receptor 
Journal of medicinal chemistry  2013;56(16):10.1021/jm4005576.
Recent emphasis has focused on the development of rationally-designed polymer-based micelle carriers for drug delivery. The current work tests the hypothesis that target specificity can be enhanced by micelles with cancer-specific ligands. In particular, we describe the synthesis and characterization of a new gadolinium texaphyrin (Gd-Tx) complex encapsulated in an IVECT™ micellar system, stabilized through Fe(III) crosslinking and targeted with multiple copies of a specific ligand for the melanocortin 1 receptor (MC1R), which has been evaluated as a cell-surface marker for melanoma. On the basis of comparative MRI experiments, we have been able to demonstrate that these Gd-Tx micelles are able to target MC1R-expressing xenograft tumors in vitro and in vivo more effectively than various control systems, including untargeted and/or uncrosslinked Gd-Tx micelles. Taken in concert, the findings reported herein support the conclusion that appropriately designed micelles are able to deliver contrast agent payloads to tumors expressing the MC1R.
doi:10.1021/jm4005576
PMCID: PMC3807968  PMID: 23863078
micelle; targeted therapy; melanoma; cancer; nanoparticles; MRI
12.  Fentanyl-related compounds and derivatives: current status and future prospects for pharmaceutical applications 
Future medicinal chemistry  2014;6(4):385-412.
Fentanyl and its analogs have been mainstays for the treatment of severe to moderate pain for many years. In this review, we outline the structural and corresponding synthetic strategies that have been used to understand the structure–biological activity relationship in fentanyl-related compounds and derivatives and their biological activity profiles. We discuss how changes in the scaffold structure can change biological and pharmacological activities. Finally, recent efforts to design and synthesize novel multivalent ligands that act as mu and delta opioid receptors and NK-1 receptors are discussed.
doi:10.4155/fmc.13.215
PMCID: PMC4137794  PMID: 24635521
13.  Synthesis and biological evaluation of new opioid agonist and neurokinin-1 antagonist bivalent ligands 
Bioorganic & medicinal chemistry  2011;19(20):6135-6142.
Newly designed bivalent ligands—opioid agonist/NK1-antagonists have been synthesized. The synthesis of new starting materials—carboxy-derivatives of Fentanyl (1a–1c) was developed. These products have been transformed to ‘isoimidium perchlorates’ (2a–c). The new isoimidium perchlorates have been successfully implemented in nucleophilic addition reactions, with L-tryptophan 3,5-bis(trifluoromethyl)benzyl ester to give the target compounds—amides (3a–c). Perchlorates (2a–c) successfully undergo reactions with other nucleophiles such as alcohols, amines or hydrazines. The obtained compound 3b exhibited μ-opioid agonist activity and NK1-antagonist activity and may serve as a useful lead compound for the further design of a new series of opioid agonist/NK1-antagonist compounds.
doi:10.1016/j.bmc.2011.08.027
PMCID: PMC4137774  PMID: 21925887
Analgesic; Bivalent ligands; μ-Opioids; NK1 antagonist; Fentanyl
14.  Discovery of Amphipathic Dynorphin A Analogues to Inhibit the Neuroexcitatory Effects of Dynorphin A through Bradykinin Receptors in the Spinal Cord 
We hypothesized that under chronic pain conditions, up-regulated dynorphin A (Dyn A) interacts with bradykinin receptors (BRs) in the spinal cord to promote hyperalgesia through an excitatory effect, which is opposite to the well known inhibitory effect of opioid receptors. Considering the structural dissimilarity between Dyn A and endogenous BR ligands, bradykinin (BK) and kallidin (KD), this interaction could not be predicted, but allowed us to discover a potential neuroexcitatory target. Well known BR ligands, BK, DALKD, and HOE140 showed different binding profiles at rat brain BRs than that previously reported. These results suggest that neuronal BRs in the rat central nervous system (CNS) may be pharmacologically distinct from those previously defined in non-neuronal tissues. Systematic structure-activity relationship (SAR) study at the rat brain BRs was performed and as a result, a new key structural feature of Dyn A for BR recognition was identified: amphipathicity. NMR studies of two lead ligands, Dyn A-(4-11) 7 and [des-Arg7]-Dyn A-(4-11) 14, which showed the same high binding affinity, confirmed that the Arg residue in position 7, which is known to be crucial for Dyn A’s biological activity, is not necessary, and that a type I β-turn structure at the C-terminal part of both ligands plays an important role in retaining good binding affinities at the BRs. Our lead ligand 14 blocked Dyn A-(2-13) 10-induced hyperalgesic effects and motor impairment in in vivo assays using naïve rats. In a model of peripheral neuropathy, intrathecal (i.th.) administration of ligand 14 reversed thermal hyperalgesia and mechanical hypersensitivity in a dose-dependent manner in nerve-injured rats. Thus ligand 14 may inhibit abnormal pain states by blocking the neuroexcitatory effects of enhanced levels of Dyn A, which are likely to be mediated by BRs in the spinal cord.
doi:10.1021/ja501677q
PMCID: PMC4021566  PMID: 24742335
pathological chronic pain states; hyperalgesia; dynorphin A; bradykinin receptor recognition; non-opioid; amphipathic pharmacophore
15.  Chiral Effect of a Phe Residue in Position 3 of the Dmt1-l(or d)-Tic2 Analogues on Opioid Functional Activities 
ACS Medicinal Chemistry Letters  2013;4(7):656-659.
In this letter, we describe a structure–activity relationships study, specifically related to the chirality of third amino acid residue in our H-Dmt-l(or d)-Tic analogues, of which C-terminus is attached to a piperidinyl moiety. Observed selectivities and functional activities of these analogues demonstrated that the chiralities of the second and third position residues are crucial for determining whether these ligands act as antagonists or agonists at the δ opioid receptor, but not at the μ opioid receptor.
doi:10.1021/ml400115n
PMCID: PMC3956057  PMID: 24648867
Dmt-Tic; opioid functional activities; structure−activity relationship; δ opioid receptor; chirality
16.  Synthesis and evaluation of cholecystokinin trimers: A multivalent approach to pancreatic cancer detection and treatment 
In the quest for novel tools for early detection and treatment of cancer, we propose the use of multimers targeting overexpressed receptors at the cancer cell surface. Indeed, multimers are prone to create multivalent interactions, more potent and specific than their corresponding monovalent versions, thus enabling the potential for early detection. There is a lack of tools for early detection of pancreatic cancer, one of the deadliest forms of cancer, but CCK2-R overexpression on pancreatic cancer cells makes CCK based multimers potential markers for these cells. In this Letter, we describe the synthesis and evaluation of CCK trimers targeting overexpressed CCK2-R.
doi:10.1016/j.bmcl.2013.02.022
PMCID: PMC4007200  PMID: 23489620
17.  Adventures in Peptides and Science With Students! The Joys of Research 
Biopolymers  2013;100(2):127-131.
doi:10.1002/bip.22179
PMCID: PMC3967710  PMID: 23616095
18.  Chiral Effect of a Phe Residue in Position 3 of the Dmt1-L(or D)-Tic2 Analogues on Opioid Functional Activities 
ACS medicinal chemistry letters  2013;4(7):656-659.
In this letter, we describe a structure–activity relationships study, specifically related to the chirality of third amino acid residue in our H-Dmt-L(or D)-Tic analogues, of which C-terminus is attached to a piperidinyl moiety. Observed selectivities and functional activities of these analogues demonstrated that the chiralities of the second and third position residues are crucial for determining whether these ligands act as antagonists or agonists at the δ opioid receptor, but not at the μ opioid receptor.
doi:10.1021/ml400115n
PMCID: PMC3956057  PMID: 24648867
Dmt-Tic; opioid functional activities; structure–activity relationship; δ opioid receptor; chirality
19.  Effect of anchoring 4-anilidopiperidines to opioid peptides 
We report here the design, synthesis, and in vitro characterization of new opioid peptides featuring a 4-anilidopiperidine moiety. Despite the fact that the chemical structures of fentanyl surrogates have been found suboptimal per se for the opioid activity, the corresponding conjugates with opioid peptides displayed potent opioid activity. These studies shed an instructive light on the strategies and potential therapeutic values of anchoring the 4-anilidopiperidine scaffold to different classes of opioid peptides.
doi:10.1016/j.bmcl.2013.03.065
PMCID: PMC3942532  PMID: 23623418
Opioid peptide; Dynorphine analog; Bivalent ligand; Fentanyl; Analgesic
20.  Biological Active Analogues of the Opioid Peptide Biphalin: Mixed α/β3-Peptides 
Journal of medicinal chemistry  2013;56(8):3419-3423.
Natural residues of the dimeric opioid peptide Biphalin were replaced by the corresponding homo-β3 amino acids. The derivative 1 containing hβ3 Phe in place of Phe showed good μ- and δ-receptor affinities ( Kiδ=0.72nM;Kiμ=1.1nM) and antinociceptive activity in vivo together with an increased enzymatic stability in human plasma.
doi:10.1021/jm301456c
PMCID: PMC3942533  PMID: 23547584
21.  α-Melanocyte-stimulating hormone regulates vascular NO availability and protects against endothelial dysfunction 
Cardiovascular Research  2012;97(2):360-368.
Aims
α-Melanocyte-stimulating hormone (α-MSH), derived from the precursor molecule pro-opiomelanocortin, exerts potent anti-inflammatory actions in the vasculature, but its role in circulatory regulation remains unclear. Therefore, we sought to investigate whether α-MSH could regulate the local control of blood vessel tone.
Methods and results
Using in vivo and ex vivo methods to assess vascular reactivity, we found that α-MSH improved endothelium-dependent vasodilatation in the mouse aorta and coronary circulation without directly contracting or relaxing blood vessels. α-MSH promoted vasodilatation by enhancing endothelial nitric oxide (NO) formation and by improving sensitivity to endothelium-independent blood vessel relaxation. Using cultured human endothelial cells to elucidate the involved molecular mechanisms, we show that α-MSH increased the expression and phosphorylation of endothelial NO synthase in these cells. The observed effects were regulated by melanocortin 1 (MC1) receptors expressed in the endothelium. In keeping with the vascular protective role of α-MSH, in vivo treatment with stable analogues of α-MSH ameliorated endothelial dysfunction associated with aging and diet-induced obesity in mice.
Conclusion
The present study identifies α-MSH and endothelial MC1 receptors as a new signalling pathway contributing to the regulation of NO availability and vascular function. These findings suggest applicability of α-MSH analogues for therapeutic use in pathological conditions that are characterized by vascular dysfunction.
doi:10.1093/cvr/cvs335
PMCID: PMC3543993  PMID: 23131503
Vasodilation; Nitric oxide; Endothelial function; Endothelial nitric oxide synthase; Melanocortin
22.  An Unusual Conformation of MSH Analogues Leads to a Selective Human Melanocortin 1 Receptor Antagonist for Targeting Melanoma Cells 
Biochemistry  2013;52(4):752-764.
γ-MSH (γ-melanocyte-stimulating hormone: H-Tyr-Val-Met-Gly-His-Phe-Arg-Trp-Asp-Arg-Phe-Gly-OH), with its exquisite specificity and potency, has recently created much excitement as a drug lead. However, this peptide like most peptides susceptible to proteolysis in vivo which potentially decreases its beneficial activities. In our continued effort to design a proteolytically stable with specific receptor binding ligand, we have engineered peptides by cyclizing γ-MSH using a thioether bridge. A number of novel cyclic truncated γ-MSH analogues were designed and synthesized, in which a thioether bridge was incorporated between a cysteine side chain and an N-terminal bromoacyl group. One of these peptides, cyclo-[(CH2)3CO-Gly1-His2-D-Phe3-Arg4-D-Trp5-Cys(S-)6]-Asp7-Arg8-Phe9-Gly10-NH2, demonstrated potent antagonist activity and receptor selectivity for the human melanocortin 1 receptor (hMC1R) (IC50 = 17 nM). This novel peptide is the most selective antagonist for the human hMC1R to date. Further pharmacological studies have shown that this peptide can specifically target melanoma cells. The NMR analysis of this peptide in a membrane–like environment revealed a new turn structure, specific to the hMC1R antagonist, at the C terminal, wherein the side chain and backbone conformation of D-Trp5 and Phe9 of the peptide are contributors to the hMC1R selectivity. Cyclization strategies represent an approach for stabilizing bioactive peptides while keeping their full potencies and should boost applications of peptide-based drugs in human medicine.
doi:10.1021/bi300723f
PMCID: PMC3641192  PMID: 23276279
α-MSH; γ-MSH; melanocortin receptors; melanotropin antagonist; hMC1R; steric constraints; selective ligands; melanoma
23.  Multivalent Interactions: Synthesis and Evaluation of Melanotropin Multimers—Tools for Melanoma Targeting 
To develop agents for early detection and selective treatment of melanomas, high affinity and high specificity molecular tools are required. Enhanced specificity may be obtained by simultaneously binding to multiple cell surface targets via the use of multimeric analogues of naturally occurring ligands. Trimers targeting overexpressed melanocortin receptors have been found to be potential candidates for this purpose. In the present letter, we describe the synthesis and study of multimers based on a dendrimer-like scaffold. The binding affinity and activity results revealed that dendrimers promote multivalent interactions via statistical and/or cooperative effects on binding. Moreover, viability studies showed no significant toxicity at micromolar concentrations, which will allow these molecular complexes to be used in vivo. Finally, imaging studies showed effective internalization for all of the molecules, confirming their potential as delivery agents.
doi:10.1021/ml300312b
PMCID: PMC3601667  PMID: 23524643
multivalent interactions; multimers; peptides; dendrimers; cancer; melanoma; targeted therapy; delivery
24.  Structure-Activity Relationships of Bifunctional Cyclic Disulfide Peptides Based on Overlapping Pharmacophores at Opioid and Cholecystokinin Receptors 
Peptides  2008;29(8):1413-1423.
Prolonged opioid exposure increases the expression of cholecystokinin (CCK) and its receptors in the central nervous system, where CCK may attenuate the antinociceptive effects of opioids. The complex interactions between opioid and CCK may play a role in the development of opioid tolerance. We designed and synthesized cyclic disulfide peptides and determined their agonist properties at opioid receptors and antagonist properties at CCK receptors. Compound 1 (Tyr-c[D-Cys-Gly-Trp-Cys]-Asp-Phe-NH2) showed potent binding and agonist activities at δ and µ opioid receptors while displaying some binding to CCK receptors. The NMR structure of the lead compound displayed similar conformational features of opioid and CCK ligands.
doi:10.1016/j.peptides.2008.03.022
PMCID: PMC2601673  PMID: 18502541
Multivalent Ligands; Bifunctional Peptides; Overlapping Pharmacophores; G-Protein Coupled Receptors; Pain; Tolerance; NMR Conformation
25.  Opioid and Melanocortin Receptors: Do They Have Opioid Overlapping Pharmacophores? 
Biopolymers  2008;90(3):433-438.
We have identified compound 1 as a novel ligand for opioid and melanocortin (MC) receptors, which is derived from the overlapping of a well known structure for the δ opioid receptor, 2,6-dimethyltyrosine (Dmt)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic), and a small molecule for the MC receptor, Tic-DPhe(p-Cl)-piperidin-4-yl-N-phenyl-propionamide. Ligand 1 showed that there is an overlapping pharmacophore between opioid and MC receptors through the Tic residue. The ligand displayed high biological activities at the δ opioid receptor (Ki = 0.38 nM in binding assay, EC50 = 0.48 nM in GTP-γ-S binding assay, IC50 = 74 nM in MVD) as an agonist instead of an antagonist and showed selective binding affinity (IC50 = 2.3 μM) at the MC-3 receptor rather than at the MC-5 receptor. A study of the structure-activity relationships demonstrated that the residues in positions 2, 3, and the C-terminus act as a pharmacophore for the MC receptors, and the residues in positions 1 and 2 act as a pharmacophore for the opioid receptors. Thus, this structural construct can be used to prepare chimeric structures with adjacent or overlapping pharmacophores for opioid and MC receptors.
doi:10.1002/bip.20814
PMCID: PMC2693099  PMID: 17657709
opioid receptor; melanocortin receptor; anti-opioid effect; multi-target drug; overlapping pharmacophores; antinociception; side effect; Dmt-Tic; fentanyl

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