Category: Amino acid/peptide conjugates

The conjugation of different amino acids/peptides to various biologically active compounds has fetched the outstanding results as are very promising drug candidates.

N-terminus FITC labeling of peptides on solid support: the truth behind the spacer

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Fluorescein isothiocyanate (FITC) is an amine reactive derivative of fluorescein dye that has wide ranging application in biochemistry. It has been extensively used to label peptides and proteins. However, its use in solid phase peptide synthesis is restricted. Indeed, in acidic conditions required for linker cleavage, N-ter FITC-labeled peptides undergo a cyclization leading to the formation of a fluorescein with subsequent removal of the last amino acid. This can be avoided when a spacer such as amino hexanoic acid is used or if non-acidic cleavage is operated to release targeted peptide from the resin. (Tetrahedron Letters. Volume 50, Issue 3, 21 January 2009, Pages 260-263.)

Effects of Chemical Conjugation of l-Leucine to Chitosan on Dispersibility and Controlled Release of Drug from a Nanoparticulate Dry Powder Inhaler Formulation

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This study investigated l-leucine-conjugated chitosan as a drug delivery vehicle in terms of dispersibility and controlled release from a nanoparticulate dry powder inhaler (DPI) formulation for pulmonary delivery using diltiazem hydrochloride (DH) as the model drug. DH-loaded nanoparticles of chitosan and conjugate were prepared by water-in-oil emulsification followed by glutaraldehyde cross-linking. Nanoparticles were characterized by dynamic light scattering for particle size, X-ray photoelectron spectroscopy for surface composition, and twin stage impinger for drug dispersibility. The controlled release of DH was studied in phosphate-buffered saline (pH 7.3 ± 0.2, 37 °C) using UV spectrophotometry. The fine particle fractions of conjugated chitosan with and without drug were higher than those of nonconjugated chitosan nanoparticles. The conjugate nanoparticles were superior to those of unmodified chitosan in drug loading, entrapment efficiency, and controlled release profile. The higher dispersibility was attributed to the amphiphilic environment of the l-leucine conjugate and hydrophobic cross-links, and the release profile reflects the greater swelling. The conjugated chitosan nanoparticles could be useful, after appropriate testing for biodegradability and toxicity, as an alternative carrier for lung drug delivery with enhanced aerosolization and prolonged drug release from nanoparticulate DPI formulations. (Mol Pharm. 2016 May 2;13(5):1455-66. )

Carnosine-LVFFARK-NH2 Conjugate: A Moderate Chelator but Potent Inhibitor of Cu2+-Mediated Amyloid β-Protein Aggregation

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Aggregation of amyloid-β (Aβ) protein stimulated by Cu2+ has been recognized as a crucial step in the neurodegenerative process of Alzheimer’s disease. Hence, it is of significance to develop bifunctional agents capable of inhibiting Aβ aggregation as well as Cu2+-mediated Aβ toxicity. Herein, a novel bifunctional nonapeptide, carnosine-LVFFARK-NH2 ( Car-LK7), was proposed by integrating native chelator carnosine ( Car) and an Aβ aggregation inhibitor, Ac-LVFFARK-NH2 (LK7). Results revealed the bifunctionality of Car-LK7, including remarkably enhanced inhibition capability on Aβ aggregation as compared to LK7 and a moderate Cu2+ chelating affinity ( KD = 28.2 ± 2.1 μM) in comparison to the binding affinity for Aβ40 ( KD = 1.02 ± 0.13 μM). The moderate Cu2+ affinity was insufficient for Car-LK7 to sequester Cu2+ from Aβ40-Cu2+ species, but it was sufficient to form ternary Aβ40-Cu2+- Car-LK7 complexes. Formation of the ternary complexes directed the aggregation into small, unstructured aggregates with little β-sheet structure. Car-LK7 also showed higher activity on arresting Aβ40-Cu2+-catalyzed reactive oxygen species production than Car. Cell viability assays confirmed the prominent protection activity of Car-LK7 against Cu2+-mediated Aβ40 cytotoxicity; Car-LK7 could almost eliminate Aβ40 cytotoxicity at an equimolar dose (cell viability increased from 59% to 99%). The research has thus provided new insight into the design of potent bifunctional agents against metal-mediated amyloid toxicity by conjugating moderate metal chelators and existing inhibitors. (ACS Chem Neurosci. 2018 Nov 21;9(11):2689-2700.)

Genetically Encoded Cholesterol-Modified Polypeptides

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Biological systems use post-translational modifications (PTMs) to control the structure, location, and function of proteins after expression. Despite the ubiquity of PTMs in biology, their use to create genetically encoded recombinant biomaterials is limited. We have utilized a natural lipidation PTM (hedgehog-mediated cholesterol modification of proteins) to create a class of hybrid biomaterials called cholesterol-modified polypeptides (CHaMPs) that exhibit programmable self-assembly at the nanoscale. To demonstrate the biomedical utility of CHaMPs, we used this approach to append cholesterol to biologically active peptide exendin-4 that is an approved drug for the treatment of type II diabetes. The exendin-cholesterol conjugate self-assembled into micelles, and these micelles activate the glucagon-like peptide-1 receptor with a potency comparable to that of current gold standard treatments. (J Am Chem Soc. 2019 Jan 4. )

An intranasally delivered peptide drug ameliorates cognitive decline in Alzheimer transgenic mice

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Alzheimer’s disease (AD) is the most common neurodegenerative disease. Imbalance between the production and clearance of amyloid β (Aβ) peptides is considered to be the primary mechanism of AD pathogenesis. This amyloid hypothesis is supported by the recent success of the human anti‐amyloid antibody aducanumab, in clearing plaque and slowing clinical impairment in prodromal or mild patients in a phase Ib trial. Here, a peptide combining polyarginines (polyR) (for charge repulsion) and a segment derived from the core region of Aβ amyloid (for sequence recognition) was designed. The efficacy of the designed peptide, R8‐Aβ(25–35), on amyloid reduction and the improvement of cognitive functions were evaluated using APP/PS1 double transgenic mice. Daily intranasal administration of PEI‐conjugated R8‐Aβ(25–35) peptide significantly reduced Aβ amyloid accumulation and ameliorated the memory deficits of the transgenic mice. Intranasal administration is a feasible route for peptide delivery. The modular design combining polyR and aggregate‐forming segments produced a desirable therapeutic effect and could be easily adopted to design therapeutic peptides for other proteinaceous aggregate‐associated diseases.
Alzheimer’s disease (AD) is the most common neurodegenerative disease that causes dementia across multiple cognitive domains. Its incidence increases significantly with age and doubles every 5 years among the geriatric population ≧ 65 years of age. Despite remarkable scientific advancement and the vast resources invested in drug development, no effective therapy is currently available for AD. Thus, it is listed as one of the major unmet medical needs worldwide. Peptide drugs have been used with consistent benefits for many years and have advantages over small molecules, such as higher potency and fewer off‐target side effects (Craik et al, 2013). In addition, the properties of easy customization and synthesis under a well‐controlled environment make peptides excellent candidates for AD drug development. Neurodegenerative diseases encompass a heterogeneous group of neurological diseases characterized by synoptic and neuronal losses caused by multiple factors. Misfolded proteinaceous aggregates which exist in a variety of these diseases besides AD, including Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, are considered one of them, and may cause or contribute to these diseases through their prionlike property (Kim & Holtzman, 2010; de Calignon et al, 2012; Luk et al, 2012; Smethurst et al, 2016). In spite of the difference in the constituent proteins and complexity of assembly mechanism, the proteinaceous aggregates across these diseases share common structural conformations such as a β‐sheet conformation in the backbone (Funke & Willbold, 2012). This provides the basis for a rational design of therapeutic peptides for these misfolded aggregate‐associated diseases by applying a universal principle to reverse the process of formation. (EMBO Mol Med. 2017 May; 9(5): 703–715.)

A calorimetric evaluation of the interaction of amphiphilic prodrugs of idebenone with a biomembrane model

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Lipoamino acids (LAA) are useful promoieties to modify physicochemical properties of drugs, namely lipophilicity and amphiphilicity. The resulting membrane-like character of drug–LAA conjugates can increase the absorption profile of drugs through cell membranes and biological barriers. To show the role of amphiphilicity with respect to lipophilicity in the interaction of drugs with biomembranes, in the present study we evaluated the mode of such an interaction of lipophilic conjugates of LAA with the antioxidant drug idebenone (IDE). DSC analysis and transfer kinetic studies were carried out using dimyristoylphosphatidylcholine (DMPC) multilamellar liposomes (MLVs) as a model. For comparison, two esters of IDE with alkanoic acids were synthesized and included in the analysis. The experimental results indicate that based on their different structure, IDE–LAA conjugates interacted at different levels with respect to pure IDE with DMPC bilayers. In particular, a progressive penetration inside the vesicles was observed upon incubation of IDE–LAA compounds with empty liposomes. The enhanced amphiphilicity of the drug due to the LAA moieties caused more complex interactions with DMPC bilayers, compared to those registered with the native drug or IDE alkanoate esters.(J Colloid Interface Sci. 2006 Jul 15;299(2):626-35.)

Novel derivatives of abietic and dehydroabietic acid

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Abietic and dehydroabietic acid are interesting diterpenes with a highly diverse repertoire of associated bioactivities. They have, among others, shown antibacterial and antifungal activity, potentially valuable in the struggle against the increasing antimicrobial resistance and imminent antibiotic shortage. In this paper, we describe the synthesis of a set of 9 abietic and dehydroabietic acid derivatives containing amino acid side chains and their in vitro antimicrobial profiling against a panel of human pathogenic microbial strains. Furthermore, their in vitro cytotoxicity against mammalian cells was evaluated. The experimental results showed that the most promising compound was 10 [methyl N-(abiet-8,11,13-trien-18-yl)-d-serinate], with an MIC90 of 60 μg/mL against Staphylococcus aureus ATCC 25923, and 8 μg/mL against methicillin-resistant S. aureusStaphylococcus epidermidis and Streptococcus mitis. The IC50 value for compound 10 against Balb/c 3T3 cells was 45 μg/mL. ( 2017 Jan 1;25(1):132-137.)