RESUMO
G protein-coupled receptors display multifunctional signaling, offering the potential for agonist structures to promote conformational selectivity for biased outputs. For ß2-adrenergic receptors (ß2AR), unbiased agonists stabilize conformation(s) that evoke coupling to Gαs (cyclic adenosine monophosphate [cAMP] production/human airway smooth muscle [HASM] cell relaxation) and ß-arrestin engagement, the latter acting to quench Gαs signaling, contributing to receptor desensitization/tachyphylaxis. We screened a 40-million-compound scaffold ranking library, revealing unanticipated agonists with dihydroimidazolyl-butyl-cyclic urea scaffolds. The S-stereoisomer of compound C1 shows no detectable ß-arrestin engagement/signaling by four methods. However, C1-S retained Gαs signaling-a divergence of the outputs favorable for treating asthma. Functional studies with two models confirmed the biasing: ß2AR-mediated cAMP signaling underwent desensitization to the unbiased agonist albuterol but not to C1-S, and desensitization of HASM cell relaxation was observed with albuterol but not with C1-S These HASM results indicate biologically pertinent biasing of C1-S, in the context of the relevant physiologic response, in the human cell type of interest. Thus, C1-S was apparently strongly biased away from ß-arrestin, in contrast to albuterol and C5-S C1-S structural modeling and simulations revealed binding differences compared with unbiased epinephrine at transmembrane (TM) segments 3,5,6,7 and ECL2. C1-S (R2 = cyclohexane) was repositioned in the pocket such that it lost a TM6 interaction and gained a TM7 interaction compared with the analogous unbiased C5-S (R2 = benzene group), which appears to contribute to C1-S biasing away from ß-arrestin. Thus, an agnostic large chemical-space library identified agonists with receptor interactions that resulted in relevant signal splitting of ß2AR actions favorable for treating obstructive lung disease.
Assuntos
Agonistas de Receptores Adrenérgicos beta 2/farmacologia , Relaxamento Muscular/efeitos dos fármacos , Miócitos de Músculo Liso/efeitos dos fármacos , Agonistas de Receptores Adrenérgicos beta 2/química , Animais , Linhagem Celular , Simulação por Computador , Cricetinae , Descoberta de Drogas , Epinefrina/química , Epinefrina/farmacologia , Células HEK293 , Humanos , Modelos Moleculares , Estrutura Molecular , Músculo Liso/efeitos dos fármacos , Ligação Proteica , Conformação Proteica , Sistema Respiratório , Bibliotecas de Moléculas PequenasRESUMO
The melanocortin receptors are involved in numerous physiological pathways, including appetite, skin and hair pigmentation, and steroidogenesis. In particular, the melanocortin-3 receptor (MC3R) is involved in fat storage, food intake, and energy homeostasis. Small-molecule ligands developed for the MC3R may serve as therapeutic lead compounds for treating disease states of energy disequilibrium. Herein, three previously reported pyrrolidine bis-cyclic guanidine compounds with five sites for molecular diversity (R1-R5) were subjected to parallel structure-activity relationship studies to identify the common pharmacophore of this scaffold series required for full agonism at the MC3R. The R2, R3, and R5 positions were required for full MC3R efficacy, while truncation of either the R1 or R4 positions in all three compounds resulted in full MC3R agonists. Two additional fragments, featuring molecular weights below 300 Da, were also identified that possessed full agonist efficacy and micromolar potencies at the mMC5R. These SAR experiments may be useful in generating new small-molecule ligands and chemical probes for the melanocortin receptors to help elucidate their roles in vivo and as therapeutic lead compounds.
Assuntos
Farmacóforo , Receptor Tipo 3 de Melanocortina , Receptor Tipo 3 de Melanocortina/agonistas , Receptor Tipo 3 de Melanocortina/metabolismo , Guanidina/farmacologia , Ligantes , Receptores de Melanocortina/metabolismo , Guanidinas , Relação Estrutura-AtividadeRESUMO
PURPOSE: Microphysiological systems (MPS), also known as "organs-on-chips" or "tissue chips," leverage recent advances in cell biology, tissue engineering, and microfabrication to create in vitro models of human organs and tissues. These systems offer promising solutions for modeling human physiology and disease in vitro and have multiple applications in areas where traditional cell culture and animal models fall short. Recently, the National Center for Advancing Translational Sciences (NCATS) at the National Institutes of Health (NIH) and the International Space Station (ISS) U.S. National Laboratory have coordinated efforts to facilitate the launch and use of these MPS platforms onboard the ISS. Here, we provide an introduction to the NIH Tissue Chips in Space initiative and an overview of the coordinated efforts between NIH and the ISS National Laboratory. We also highlight the current progress in addressing the scientific and technical challenges encountered in the development of these ambitious projects. Finally, we describe the potential impact of the Tissue Chips in Space program for the MPS field as well as the wider biomedical and health research communities.
Assuntos
Engenharia Tecidual/métodos , Ausência de Peso , Animais , Humanos , Microfluídica , Voo Espacial , Estados UnidosRESUMO
A novel and facile domino reaction has been developed to synthesize a variety of new derivatives from hydromorphone, amines and paraformaldehyde in good yields in a catalyst-free fashion with high atom efficiency. The products show a mixed MOR/DOR biological characteristic which makes them valuable for further study as opioid analgesics.
Assuntos
Analgésicos Opioides/farmacologia , Derivados da Morfina/farmacologia , Receptores Opioides delta/antagonistas & inibidores , Receptores Opioides kappa/agonistas , Receptores Opioides mu/agonistas , Analgésicos Opioides/administração & dosagem , Analgésicos Opioides/química , Animais , Relação Dose-Resposta a Droga , Humanos , Injeções Intraperitoneais , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Derivados da Morfina/administração & dosagem , Derivados da Morfina/química , Receptores Opioides kappa/deficiência , Receptores Opioides mu/antagonistas & inibidores , Receptores Opioides mu/deficiência , Relação Estrutura-AtividadeRESUMO
Bacterial topoisomerase functions are required for regulation of DNA supercoiling and overcoming the DNA topological barriers that are encountered during many vital cellular processes. DNA gyrase and topoisomerase IV of the type IIA bacterial topoisomerase family are important clinical targets for antibacterial therapy. Topoisomerase I, belonging to the type IA topoisomerase family, has recently been validated as a potential antitubercular target. The topoisomerase I activity has been shown to be essential for bacterial viability and infection in a murine model of tuberculosis. Mixture-based combinatorial libraries were screened in this study to identify novel bacterial topoisomerase I inhibitors. Using positional-scanning deconvolution, selective small-molecule inhibitors of bacterial topoisomerase I were identified starting from a polyamine scaffold. Antibacterial assays demonstrated that four of these small-molecule inhibitors of bacterial topoisomerase I are bactericidal against Mycobacterium smegmatis and Mycobacterium tuberculosis The MICs for growth inhibition of M. smegmatis increased with overexpression of recombinant M. tuberculosis topoisomerase I, consistent with inhibition of intracellular topoisomerase I activity being involved in the antimycobacterial mode of action.
Assuntos
Antituberculosos/farmacologia , DNA Topoisomerases Tipo I/metabolismo , Inibidores da Topoisomerase I/farmacologia , Antibacterianos/farmacologia , DNA Girase/genética , DNA Girase/metabolismo , DNA Topoisomerase IV/genética , DNA Topoisomerase IV/metabolismo , Testes de Sensibilidade Microbiana , Mycobacterium smegmatis/genética , Mycobacterium smegmatis/metabolismo , Mycobacterium tuberculosis/efeitos dos fármacos , Mycobacterium tuberculosis/metabolismoRESUMO
Arsenic is the most ubiquitous environmental toxin and carcinogen. Long-term exposure to arsenic is associated with human diseases including cancer, cardiovascular disease, and diabetes. Human As(III) S-adenosylmethionine (SAM) methyltransferases (hAS3MT) methylates As(III) to trivalent mono- and dimethyl species that are more toxic and potentially more carcinogenic than inorganic arsenic. Modulators of hAS3MT activity may be useful for the prevention or treatment of arsenic-related diseases. Using a newly developed high-throughput assay for hAS3MT activity, we identified 10 novel noncompetitive small molecule inhibitors. In silico docking analysis with the crystal structure of an AS3MT orthologue suggests that the inhibitors bind in a cleft between domains that is distant from either the As(III) or SAM binding sites. This suggests the presence of a possible allosteric and regulatory site in the enzyme. These inhibitors may be useful tools for future research in arsenic metabolism and are the starting-point for the development of drugs against hAS3MT.
Assuntos
Arsênio , Metiltransferases/antagonistas & inibidores , S-Adenosilmetionina , Bibliotecas de Moléculas Pequenas/farmacologia , Arsênio/química , Sítios de Ligação , Bioensaio , Cristalografia por Raios X , Avaliação Pré-Clínica de Medicamentos , Ativação Enzimática/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Humanos , Metiltransferases/química , Simulação de Acoplamento Molecular , S-Adenosilmetionina/química , Bibliotecas de Moléculas Pequenas/químicaRESUMO
Resistance to amikacin and other major aminoglycosides is commonly due to enzymatic acetylation by aminoglycoside 6'- N -acetyltransferase type I enzyme, of which type Ib [AAC(6')-Ib] is the most widespread among Gram-negative pathogens. Finding enzymatic inhibitors could be an effective way to overcome resistance and extend the useful life of amikacin. Small molecules possess multiple properties that make them attractive compounds to be developed as drugs. Mixture-based combinatorial libraries and positional scanning strategy led to the identification of a chemical scaffold, pyrrolidine pentamine, that, when substituted with the appropriate functionalities at five locations (R1 - R5), inhibits AAC(6')-Ib-mediated inactivation of amikacin. Structure-activity relationship (SAR) studies showed that while truncations to the molecule result in loss of inhibitory activity, modifications of functionalities and stereochemistry have different effects on the inhibitory properties. In this study, we show that alterations at position R1 of the two most active compounds, 2700.001 and 2700.003 , reduced inhibition levels, demonstrating the essential nature not only of the presence of an S -phenyl moiety at this location but also the distance to the scaffold. On the other hand, modifications on the R3, R4, and R5 positions have varied effects, demonstrating the potential for optimization. A correlation analysis between molecular docking values (ΔG) and the dose required for two-fold potentiation of compounds described in this and the previous studies showed a significant correlation between ΔG values and inhibitory activity. Highlights: Amikacin resistance in Gram-negatives is mostly caused by the AAC(6')-Ib enzymeAAC(6')-Ib has been identified in most Gram-negative pathogensInhibitors of AAC(6')-Ib could be used to treat resistant infectionsCombinatorial libraries and positional scanning identified an inhibitorThe lead compound can be optimized by structure activity relationship studies.
RESUMO
Resistance to amikacin and other major aminoglycosides is commonly due to enzymatic acetylation by the aminoglycoside 6'-N-acetyltransferase type I enzyme, of which type Ib [AAC(6')-Ib] is the most widespread among Gram-negative pathogens. Finding enzymatic inhibitors could be an effective way to overcome resistance and extend the useful life of amikacin. Small molecules possess multiple properties that make them attractive for drug development. Mixture-based combinatorial libraries and positional scanning strategy have led to the identification of a chemical scaffold, pyrrolidine pentamine, that, when substituted with the appropriate functionalities at five locations (R1-R5), inhibits AAC(6')-Ib-mediated inactivation of amikacin. Structure-activity relationship studies have shown that while truncations to the molecule result in loss of inhibitory activity, modifications of functionalities and stereochemistry have different effects on the inhibitory properties. In this study, we show that alterations at position R1 of the two most active compounds, 2700.001 and 2700.003, reduced inhibition levels, demonstrating the essential nature not only of the presence of an S-phenyl moiety at this location but also the distance to the scaffold. On the other hand, modifications on the R3, R4, and R5 positions had varied effects, demonstrating the potential for optimization. A correlation analysis between molecular docking values (ΔG) and the dose required for two-fold potentiation of the compounds described in this and the previous studies showed a significant correlation between ΔG values and inhibitory activity.
RESUMO
The formylpeptide receptor (FPR1) and formylpeptide-like 1 receptor (FPR2) are G protein-coupled receptors that are linked to acute inflammatory responses, malignant glioma stem cell metastasis, and chronic inflammation. Although several N-formyl peptides are known to bind to these receptors, more selective small-molecule, high-affinity ligands are needed for a better understanding of the physiologic roles played by these receptors. High-throughput assays using mixture-based combinatorial libraries represent a unique, highly efficient approach for rapid data acquisition and ligand identification. We report the superiority of this approach in the context of the simultaneous screening of a diverse set of mixture-based small-molecule libraries. We used a single cross-reactive peptide ligand for a duplex flow cytometric screen of FPR1 and FPR2 in color-coded cell lines. Screening 37 different mixture-based combinatorial libraries totaling more than five million small molecules (contained in 5,261 mixture samples) resulted in seven libraries that significantly inhibited activity at the receptors. Using positional scanning deconvolution, selective high-affinity (low nM K(i)) individual compounds were identified from two separate libraries, namely, pyrrolidine bis-diketopiperazine and polyphenyl urea. The most active individual compounds were characterized for their functional activities as agonists or antagonists with the most potent FPR1 agonist and FPR2 antagonist identified to date with an EC50 of 131 nM (4 nM K(i)) and an IC50 of 81 nM (1 nM K(i)), respectively, in intracellular Ca²âº response determinations. Comparative analyses of other previous screening approaches clearly illustrate the efficiency of identifying receptor selective, individual compounds from mixture-based combinatorial libraries.
Assuntos
Receptores de Formil Peptídeo/agonistas , Receptores de Formil Peptídeo/antagonistas & inibidores , Bibliotecas de Moléculas Pequenas/química , Aminoácidos/química , Animais , Cálcio/metabolismo , Linhagem Celular Tumoral , Dicetopiperazinas/síntese química , Dicetopiperazinas/química , Dicetopiperazinas/farmacologia , Relação Dose-Resposta a Droga , Citometria de Fluxo , Ensaios de Triagem em Larga Escala , Humanos , Peptídeos/química , Peptidomiméticos/química , Pirrolidinas/síntese química , Pirrolidinas/química , Pirrolidinas/farmacologia , Ratos , Bibliotecas de Moléculas Pequenas/síntese química , Bibliotecas de Moléculas Pequenas/farmacologia , EstereoisomerismoRESUMO
Structure-property relationships and structure-activity relationships play an important role in many research areas, such as medicinal chemistry and drug discovery. Such methods, however, have focused on providing post-hoc descriptions of such relationships based on known data. The ability for these descriptions to remain relevant when considering compounds of unknown activity, and thus the prediction of activity and property landscapes using existing data, remains little explored. In this study, we present a novel method of evaluating the ability of a compound comparison methodology to provide accurate information about a set of unknown compounds and also explore the ability of these predicted activity landscapes to prioritize active compounds over inactive. These methods are applied to three distinct and diverse sets of compounds, each with activity data for multiple targets, for a total of eight target-compound set pairs. Six methodologically distinct compound comparison methods were evaluated. We show that overall, all compound comparison methods provided an improvement in structure-activity relationship prediction over random and were able to prioritize compounds in a superior manner to random sampling, but the degree of success and therefore applicability varied markedly.
Assuntos
Algoritmos , Antiprotozoários/química , Modelos Estatísticos , Receptores Opioides/química , Bibliotecas de Moléculas Pequenas/química , Simulação por Computador , Bases de Dados de Compostos Químicos , Descoberta de Drogas , Humanos , Ligantes , Modelos Químicos , Estrutura Molecular , Antagonistas de Entorpecentes , Receptores Opioides/agonistas , Relação Estrutura-Atividade , Receptor de NociceptinaRESUMO
We present a general approach to describe the structure-activity relationships (SAR) of combinatorial data sets with activity for two biological endpoints with emphasis on the rapid identification of substitutions that have a large impact on activity and selectivity. The approach uses dual-activity difference (DAD) maps that represent a visual and quantitative analysis of all pairwise comparisons of one, two, or more substitutions around a molecular template. Scanning the SAR of data sets using DAD maps allows the visual and quantitative identification of activity switches defined as specific substitutions that have an opposite effect on the activity of the compounds against two targets. The approach also rapidly identifies single- and double-target R-cliffs, i.e., compounds where a single or double substitution around the central scaffold dramatically modifies the activity for one or two targets, respectively. The approach introduced in this report can be applied to any analogue series with two biological activity endpoints. To illustrate the approach, we discuss the SAR of 106 pyrrolidine bis-diketopiperazines tested against two formylpeptide receptors obtained from positional scanning deconvolution methods of mixture-based libraries.
Assuntos
Dicetopiperazinas/química , Dicetopiperazinas/farmacologia , Receptores de Formil Peptídeo/metabolismo , Relação Estrutura-Atividade , Bases de Dados de Produtos Farmacêuticos , Descoberta de Drogas/métodos , Humanos , Pirrolidinas/química , Pirrolidinas/farmacologiaRESUMO
A libraries from libraries approach is described for the synthesis of five different sulfonamide linked scaffolds. Four of the scaffolds are sulfonamides linked to heterocycles; piperazine, thiourea, cyclic guanidine, and dimethyl cyclic guanidine. The fifth scaffold is a polyamine linked sulfonamide. Three different diversity positions were effectively incorporated into each scaffold providing a number of different compounds with good yields and purity.
RESUMO
In the past 20 years, synthetic combinatorial methods have fundamentally advanced the ability to synthesize and screen large numbers of compounds for drug discovery and basic research. Mixture-based libraries and positional scanning deconvolution combine two approaches for the rapid identification of specific scaffolds and active ligands. Here we present a quantitative assessment of the screening of 32 positional scanning libraries in the identification of highly specific and selective ligands for two formylpeptide receptors. We also compare and contrast two mixture-based library approaches using a mathematical model to facilitate the selection of active scaffolds and libraries to be pursued for further evaluation. The flexibility demonstrated in the differently formatted mixture-based libraries allows for their screening in a wide range of assays.
Assuntos
Ensaios de Triagem em Larga Escala/métodos , Modelos Teóricos , Biblioteca de Peptídeos , Receptores de Formil Peptídeo/antagonistas & inibidores , Concentração Inibidora 50 , Ligantes , Peptídeos/química , Peptídeos/farmacologiaRESUMO
This article presents a combinatorial library method that consists of the synthesis and screening of mixture-based synthetic combinatorial libraries of peptide molecules to identify B and T cell epitopes. The protocols employ peptide libraries to identify peptides recognized by MAbs and T cells. The first protocol uses a positional scanning peptide library made up of hexapeptides to identify antigenic determinants recognized by MAbs. The 120 mixtures in the hexapeptide library are tested for their inhibitory activity in a competitive ELISA. The second protocol uses a decapeptide library to identify T cell peptide ligands. The 200 mixtures of the decapeptide library are tested for their ability to induce T cell activation. Support protocols cover optimization of the assay conditions for each MAb or T cell, to achieve the best level of sensitivity and reproducibility, and preparation of a hexapeptide library, along with deconvolution approaches. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Screening peptide library for antibody inhibition Basic Protocol 2: Screening a peptide library to identify CD4+ Or CD8+ T cell ligands Support Protocol 1: Optimizing antigen and antibody concentrations for screening assay Support Protocol 2: Preparing a positional scanning peptide library.
Assuntos
Epitopos de Linfócito T , Biblioteca de Peptídeos , Linfócitos B , Peptídeos , Reprodutibilidade dos TestesRESUMO
The spike proteins of enveloped viruses are transmembrane glycoproteins that typically undergo post-translational attachment of palmitate on cysteine residues on the cytoplasmic facing tail of the protein. The role of spike protein palmitoylation in virus biogenesis and infectivity is being actively studied as a potential target of novel antivirals. Here, we report that palmitoylation of the first five cysteine residues of the C-terminal cysteine-rich domain of the SARS-CoV-2 S protein are indispensable for infection, and palmitoylation-deficient spike mutants are defective in membrane fusion. The DHHC9 palmitoyltransferase interacts with and palmitoylates the spike protein in the ER and Golgi and knockdown of DHHC9 results in reduced fusion and infection of SARS-CoV-2. Two bis-piperazine backbone-based DHHC9 inhibitors inhibit SARS-CoV-2 S protein palmitoylation and the resulting progeny virion particles released are defective in fusion and infection. This establishes these palmitoyltransferase inhibitors as potential new intervention strategies against SARS-CoV-2.
Assuntos
COVID-19 , SARS-CoV-2 , Humanos , Lipoilação , Glicoproteína da Espícula de CoronavírusRESUMO
Research in low Earth orbit (LEO) has become more accessible. The 2020 Biomanufacturing in Space Symposium reviewed space-based regenerative medicine research and discussed leveraging LEO to advance biomanufacturing for regenerative medicine applications. The symposium identified areas where financial investments could stimulate advancements overcoming technical barriers. Opportunities in disease modeling, stem-cell-derived products, and biofabrication were highlighted. The symposium will initiate a roadmap to a sustainable market for regenerative medicine biomanufacturing in space. This perspective summarizes the 2020 Biomanufacturing in Space Symposium, highlights key biomanufacturing opportunities in LEO, and lays the framework for a roadmap to regenerative medicine biomanufacturing in space.
Assuntos
Materiais Biocompatíveis , Meio Ambiente Extraterreno , Manufaturas , Medicina Regenerativa , Inteligência Artificial , Automação , Bioengenharia , Humanos , Aprendizado de Máquina , PesquisaRESUMO
A 60-member 1,2,3-triazoles bearing biologically active sulfonamide moiety library was synthesized via azide-alkyne cycloaddition and examined for cytotoxic activity against human leukemia cell line HL-60. 25 of them were evaluated further in four additional cancer cell lines (HepG2, A549, PC3, SGC7901). Most of the 25 compounds showed moderate cytotoxic activities against the tested cell lines. Furthermore, the structure-activity relationships were discussed and a reliable 3D-QSAR model with good prediction (r²cv = 0.64, r² = 0.958) was generated on the basis of our synthesized 1,2,3-triazoles for their cytotoxic activities against the HL-60 cell line. The contour map of the CoMFA should aid in the design of new antitumor agents.
Assuntos
Antineoplásicos/síntese química , Antineoplásicos/farmacologia , Técnicas de Química Sintética/métodos , Relação Quantitativa Estrutura-Atividade , Sulfonamidas/síntese química , Sulfonamidas/farmacologia , Triazóis/química , Alcinos/química , Antineoplásicos/química , Azidas/química , Linhagem Celular Tumoral , Humanos , Concentração Inibidora 50 , Modelos Moleculares , Conformação Molecular , Sulfonamidas/químicaRESUMO
The central melanocortin-3 and melanocortin-4 receptors (MC3R, MC4R) are key regulators of body weight and energy homeostasis. Herein, the discovery and characterization of first-in-class small molecule melanocortin agonists with selectivity for the melanocortin-3 receptor over the melanocortin-4 receptor are reported. Identified via "unbiased" mixture-based high-throughput screening approaches, pharmacological evaluation of these pyrrolidine bis-cyclic guanidines resulted in nanomolar agonist activity at the melanocortin-3 receptor. The pharmacological profiles at the remaining melanocortin receptor subtypes tested indicated similar agonist potencies at both the melanocortin-1 and melanocortin-5 receptors and antagonist or micromolar agonist activities at the melanocortin-4 receptor. This group of small molecules represents a new area of chemical space for the melanocortin receptors with mixed receptor pharmacology profiles that may serve as novel lead compounds to modulate states of dysregulated energy balance.
Assuntos
Guanidina/metabolismo , Pirrolidinas/química , Receptor Tipo 3 de Melanocortina/agonistas , Algoritmos , Animais , Avaliação Pré-Clínica de Medicamentos , Metabolismo Energético/efeitos dos fármacos , Guanidina/análogos & derivados , Guanidina/farmacologia , Guanidina/uso terapêutico , Ensaios de Triagem em Larga Escala , Humanos , Camundongos , Camundongos Knockout , Isoformas de Proteínas/agonistas , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Pirrolidinas/metabolismo , Pirrolidinas/farmacologia , Pirrolidinas/uso terapêutico , Receptor Tipo 3 de Melanocortina/genética , Receptor Tipo 3 de Melanocortina/metabolismo , Bibliotecas de Moléculas Pequenas/química , Bibliotecas de Moléculas Pequenas/metabolismo , Bibliotecas de Moléculas Pequenas/farmacologia , Bibliotecas de Moléculas Pequenas/uso terapêutico , Relação Estrutura-AtividadeRESUMO
The melanocortin-4 receptor (MC4R) plays an important role in appetite. Agonist ligands that stimulate the MC4R decrease appetite, while antagonist compounds increase food consumption. Herein, a functional mixture-based positional scan identified novel MC4R antagonist sequences. Mixtures comprising a library of 12,960,000 tetrapeptides were screened in the presence and absence of the NDP-MSH agonist. These results led to the synthesis of 48 individual tetrapeptides, of which 40 were screened for functional activity at the melanocortin receptors. Thirteen compounds were found to possess nanomolar antagonist potency at the MC4R, with the general tetrapeptide sequence Ac-Aromatic-Basic-Aromatic-Basic-NH2. The most notable results include the identification of tetrapeptide 48 [COR1-25, Ac-DPhe(pI)-Arg-Nal(2')-Arg-NH2], an equipotent MC4R antagonist to agouti-related protein [AGRP(86-132)], more potent than miniAGRP(87-120), and possessing 15-fold selectivity for the MC4R versus the MC3R. These tetrapeptides may serve as leads for novel appetite-inducing therapies to treat states of negative energy balance, such as cachexia and anorexia.