Glycosylation, an effective synthetic strategy to improve the bioavailability of therapeutic peptides

Novel glycosylation zinc(II)-cryptolepine complexes perturb mitophagy pathways and trigger cancer cell apoptosis and autophagy in SK-OV-3/DDP cells

With the aim of shedding some light on the mechanism of action of zinc(II) complexes in antiproliferative processes and molecular signaling pathways, three novel glycosylated zinc(II)-cryptolepine complexes, i.e., [Zn(QA1)Cl₂] (Zn(QA1)), [Zn(QA2)Cl₂] (Zn(QA2)), and [Zn(QA3)Cl₂] (Zn(QA3)), were prepared by conjugating a glucose moiety with cryptolepine, followed by complexation of the resulting glycosylated cryptolepine compounds N-((1-(2-morpholinoethyl)-1H-1,2,3-triazol-4-yl)methyl)-benzofuro[3,2-b]quinolin-11-amine (QA1), 2-(4-((benzofuro[3,2-b]quinolin-11-ylamino)methyl)-1H-1,2,3-triazol-1-yl)ethan-1-ol (QA2), and (2S,3S,4R,5R,6S)-2-(4-((benzofuro[3,2-b]quinolin-11-ylamino)-methyl)-1H-1,2,3-triazol-1-yl)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol (QA3) with zinc(II), and their anticancer activity was evaluated. In MTT assays, Zn(QA1)-Zn(QA3) were more active against cisplatin-resistant ovarian SK-OV-3/DDP cancer cells (SK-OV-3cis) than ZnCl₂ and the QA1-QA3 ligands, with IC₅₀ values of 1.81 ± 0.50, 2.92 ± 0.32, and 1.01 ± 0.11 μM, respectively. Complexation of glycosylated cryptolepine QA3 with zinc(II) increased the antiproliferative activity of the ligand, suggesting that Zn(QA3) could act as a chaperone to deliver the active ligand intracellularly, in contrast with other cryptolepine metal complexes previously reported. In vivo and in vitro investigations suggested that Zn(QA3) exhibited enhanced anticancer activity with treatment effects comparable to those of the clinical drug cisplatin. Furthermore, Zn(QA1)-Zn(QA3) triggered SK-OV-3cis cell apoptosis through mitophagy pathways in the order Zn(QA1) > Zn(QA1) > Zn(QA2). These results demonstrate the potential of glycosylated zinc(II)-cryptolepine complexes for the development of chemotherapy drugs against cisplatin-resistant SK-OV-3cis cells.

Neurotensin analogs by fluoroglycosylation at Nω-carbamoylated arginines for PET imaging of NTS1-positive tumors

Since neurotensin (NT) receptors of subtype-1 (NTS1) are expressed by different types of malignant tumors, such as pancreatic adenocarcinoma, colorectal and prostate carcinoma, they represent an interesting target for tumor imaging by positron emission tomography (PET) and endoradiotherapy. Previously reported neurotensin-derived NTS1 ligands for PET were radiolabeled by modification and prelongation of the N-terminus of NT(8-13) peptide analogs. In this study, we demonstrate that modifying Arg8 or Arg9 by Nω-carbamoylation and subsequent fluoroglycosylation provides a suitable approach for the development of NT(8-13) analogs as PET imaging agents. The Nω-carbamoylated and fluoroglycosylated NT(8-13) analogs retained high NTS1 affinity in the one-digit nanomolar range as well as high metabolic stability in vitro. In vivo, the radioligand [18F]21 demonstrated favorable biokinetics in HT-29 tumor-bearing mice with high tumor uptake and high retention, predominantly renal clearance, and fast wash-out from blood and other non-target tissues. Therefore, [18F]21 has the potential to be used as molecular probe for the imaging of NTS1-expressing tumors by PET.

Expanding chemical space by para-C-H arylation of arenes

Biaryl scaffolds are privileged templates used in the discovery and design of therapeutics with high affinity and specificity for a broad range of protein targets. Biaryls are found in the structures of therapeutics, including antibiotics, anti-inflammatory, analgesic, neurological and antihypertensive drugs. However, existing synthetic routes to biphenyls rely on traditional coupling approaches that require both arenes to be prefunctionalized with halides or pseudohalides with the desired regiochemistry. Therefore, the coupling of drug fragments may be challenging via conventional approaches. As an attractive alternative, directed C−H activation has the potential to be a versatile tool to form para-substituted biphenyl motifs selectively. However, existing C–H arylation protocols are not suitable for drug entities as they are hindered by catalyst deactivation by polar and delicate functionalities present alongside the instability of macrocyclic intermediates required for para-C−H activation. To address this challenge, we have developed a robust catalytic system that displays unique efficacy towards para-arylation of highly functionalized substrates such as drug entities, giving access to structurally diversified biaryl scaffolds. This diversification process provides access to an expanded chemical space for further exploration in drug discovery. Further, the applicability of the transformation is realized through the synthesis of drug molecules bearing a biphenyl fragment. Computational and experimental mechanistic studies further provide insight into the catalytic cycle operative in this versatile C−H arylation protocol.

Biaryls are privileged structural motif used in the discovery and design of therapeutics with high affinity and specificity for a broad range of protein targets. Herein, the authors develop a robust strategy for para-C–H arylation of arenes with a range of (het)aryl iodides, including bioactive molecules.

Functional Characterization of a Regiospecific Sugar-O-Methyltransferase from Nocardia

Methyltransferases transfer a methyl group to a diverse group of natural products, thus providing structural diversity, stability, and altered pharmacological properties to the molecules. A limited number of regiospecific sugar-O-methyltransferases are functionally characterized. Thus, discovery of such an enzyme could solve the difficulties of biological production of methoxy derivatives of glycosylated molecules. In the current study, a regiospecific sugar-O-methyltransferase, ThnM1, belonging to the biosynthetic gene cluster (BGC) of 1-(α-L-(2-O-methyl)-6-deoxymannopyranosyloxy)-3,6,8-trimethoxynaphthalene produced by Nocardia sp. strain CS682, was analyzed and functionally characterized. ThnM1 demonstrated promiscuity to diverse chemical structures such as rhamnose-containing anthraquinones and flavonoids with regiospecific methylation at the 2′-hydroxyl group of the sugar moiety. Compared with other compounds, anthraquinone rhamnosides were found to be the preferred substrates for methylation. Thus, the enzyme was further employed for whole-cell biotransformation using engineered Escherichia coli to produce a methoxy-rhamnosyl derivative of quinizarin, an anthraquinone derivative. The structure of the newly generated derivative from Escherichia coli fermentation was elucidated by liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopic analyses and identified as quinizarin-4-O-α-l-2-O-methylrhamnoside (QRM). Further, the biological impact of methylation was studied by comparing the cytotoxicity of QRM with that of quinizarin against the U87MG, SNU-1, and A375SM cancer cell lines.

IMPORTANCE ThnM1 is a putative sugar-O-methyltransferase produced by the Nocardia sp. strain CS682 and is encoded by a gene belonging to the biosynthetic gene cluster (BGC) of 1-(α-l-(2-O-methyl)-6-deoxymannopyranosyloxy)-3,6,8-trimethoxynaphthalene. We demonstrated that ThnM1 is a promiscuous enzyme with regiospecific activity at the 2′-OH of rhamnose. As regiospecific methylation of sugars by chemical synthesis is a challenging step, ThnM1 may fill the gap in the potential diversification of natural products by methylating the rhamnose moiety attached to them.

Visible-Light-Promoted Stereoselective C(sp3 )-H Glycosylation for the Synthesis of C-Glycoamino Acids and C-Glycopeptides

The glycosylative modification of peptides could improve the pharmacological properties of peptide drugs and deliver them efficiently to the target sites. Compared with O-/N-glycosides, C-glycosides exhibit more metabolic stability. We here disclose the first example of visible-light-promoted and Cu-catalyzed stereoselective C-glycosylation. The mild reaction conditions are compatible with various carbohydrate substrates, as demonstrated with a series of monosaccharides and a disaccharide, and are amenable to the synthesis of a wide variety of C-glycoamino acids and C-glycopeptidomimetics with good yields and excellent stereoselectivities. The dual-functional photocatalyst formed in situ via coordination of the glycine derivative and the chiral phosphine Cu complex could not only catalyze the photoredox process but also control the stereoselectivity of the glycosylation reaction.

Overcoming the shortcomings of peptide-based therapeutics

Peptides have traditionally been perceived as poor drug candidates due to unfavorable characteristics mainly regarding their pharmacokinetic behavior, including plasma stability, membrane permeability and circulation half-life. Nonetheless, in recent years, general strategies to tackle those shortcomings have been established, and peptides are subsequently gaining increasing interest as drugs due to their unique ability to combine the advantages of antibodies and small molecules. Macrocyclic peptides are a special focus of drug development efforts due to their ability to address so called ‘undruggable’ targets characterized by large and flat protein surfaces lacking binding pockets. Here, the main strategies developed to date for adapting peptides for clinical use are summarized, which may soon help usher in an age highly shaped by peptide-based therapeutics. Nonetheless, limited membrane permeability is still to overcome before peptide therapeutics will be broadly accepted.

Strategies employed in the design of antimicrobial peptides with enhanced proteolytic stability

Due to the alarming developing rate of multidrug-resistant bacterial pathogens, the development and modification of antimicrobial peptides (AMPs) are unprecedentedly active. Despite the fact that considerable efforts have been expended on the discovery and design strategies of AMPs, the clinical translation of peptide antibiotics remains inadequate. A large number of articles and reviews credited the limited success of AMPs to their poor stability in the biological environment, particularly their poor proteolytic stability. In the past forty years, various design strategies have been used to improve the proteolytic stability of AMPs, such as sequence modification, cyclization, peptidomimetics, and nanotechnology. Herein, we focus our discussion on the progress made in improving the proteolytic stability of AMPs and the principle, successes, and limitations of various anti-proteolytic design strategies. It is of prospective significance to extend current insights into the degradation-related inactivation of AMPs and also alleviate/overcome the problem.

Effect and Mechanisms of Antibacterial Peptide Fraction from Mucus of C. aspersum against Escherichia coli NBIMCC 8785

Peptides isolated from the mucus of Cornu aspersum could be prototypes for antibiotics against pathogenic bacteria. Information regarding the mechanisms, effective concentration, and methods of application is an important tool for therapeutic, financial, and ecological regulation and a holistic approach to medical treatment. A peptide fraction with MW < 10 kDa was analyzed by MALDI-TOF-TOF using Autoflex™ III. The strain Escherichia coli NBIMCC 8785 (18 h and 48 h culture) was used. The changes in bacterial structure and metabolic activity were investigated by SEM, fluorescent, and digital image analysis. This peptide fraction had high inhibitory effects in surface and deep inoculations of E. coli of 1990.00 and 136.13 mm2/mgPr/µMol, respectively, in the samples. Thus, it would be effective in the treatment of infections involving bacterial biofilms and homogenous cells. Various deformations of the bacteria and inhibition of its metabolism were discovered and illustrated. The data on the mechanisms of impact of the peptides permitted the formulation of an algorithm for the treatment of infections depending on the phase of their development. The decrease in the therapeutic concentrations will be more sparing to the environment and will lead to a decrease in the cost of the treatment.

Development of Duramycin-Based Molecular Probes for Cell Death Imaging

Cell death is involved in numerous pathological conditions such as cardiovascular disorders, ischemic stroke and organ transplant rejection, and plays a critical role in the treatment of cancer. Cell death imaging can serve as a noninvasive means to detect the severity of tissue damage, monitor the progression of diseases, and evaluate the effectiveness of treatments, which help to provide prognostic information and guide the formulation of individualized treatment plans. The high abundance of phosphatidylethanolamine (PE), which is predominantly confined to the inner leaflet of the lipid bilayer membrane in healthy mammalian cells, becomes exposed on the cell surface in the early stages of apoptosis or accessible to the extracellular milieu when the cell suffers from necrosis, thus representing an attractive target for cell death imaging. Duramycin is a tetracyclic polypeptide that contains 19 amino acids and can bind to PE with excellent affinity and specificity. Additionally, this peptide has several favorable structural traits including relatively low molecular weight, stability to enzymatic hydrolysis, and ease of conjugation and labeling. All these highlight the potential of duramycin as a candidate ligand for developing PE-specific molecular probes. By far, a couple of duramycin-based molecular probes such as Tc-99 m-, F-18-, or Ga-68-labeled duramycin have been developed to target exposed PE for in vivo noninvasive imaging of cell death in different animal models. In this review article, we describe the state of the art with respect to in vivo imaging of cell death using duramycin-based molecular probes, as validated by immunohistopathology.

PSMA-Targeting Imaging and Theranostic Agents-Current Status and Future Perspective

In the past two decades, extensive efforts have been made to develop agents targeting prostate-specific membrane antigen (PSMA) for prostate cancer imaging and therapy. To date, represented by two recent approvals of [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]F-DCFPyL by the United States Food and Drug Administration (US-FDA) for positron emission tomography (PET) imaging to identify suspected metastases or recurrence in patients with prostate cancer, PSMA-targeting imaging and theranostic agents derived from small molecule PSMA inhibitors have advanced to clinical practice and trials of prostate cancer. The focus of current development of new PSMA-targeting agents has thus shifted to the improvement of in vivo pharmacokinetics and higher specific binding affinity with the aims to further increase the detection sensitivity and specificity and minimize the toxicity to non-target tissues, particularly the kidneys. The main strategies involve systematic chemical modifications of the linkage between the targeting moiety and imaging/therapy payloads. In addition to a summary of the development history of PSMA-targeting agents, this review provides an overview of current advances and future promise of PSMA-targeted imaging and theranostics with focuses on the structural determinants of the chemical modification towards the next generation of PSMA-targeting agents.

Chemical modifications to increase the therapeutic potential of antimicrobial peptides

The continued use of antibiotics has been accompanied by the rapid emergence and spread of antibiotic-resistant strains of bacteria. Antimicrobial peptides (AMPs), also known as host defense peptides, show multiple features as an ideal antimicrobial agent, including potent, rapid, and broad-spectrum antimicrobial activity, low promotion of antimicrobial resistance, potent anti-biofilm activity, and lethality against metabolically inactive microorganisms. However, several crucial drawbacks constrain the use of AMPs as clinical drugs, e.g., liability in vivo, toxicity when used systemically, and high production costs. Based on recent findings and our own experiences, here we summarize some chemical modifications and key design strategies to increase the therapeutic potential of AMPs, including 1) enhancing antimicrobial activities, 2) improving in vivo effectiveness, and 3) reduction in toxicity, which may facilitate the design and optimization of AMPs for the development of drug candidates. We also discuss the present challenges in the optimization of AMPs and future concerns about the resistance and cross-resistance to AMPs in the development of AMPs as therapeutic drugs.

Separation and purification of plant terpenoids from biotransformation

The production of plant terpenoids through biotransformation has undoubtedly become one of the research hotspots, and the continuous upgrading of the corresponding downstream technology is also particularly important. Downstream technology is the indispensable technical channel for the industrialization of plant terpenoids. How to efficiently separate high-purity products from complex microbial fermentation broths or enzyme-catalyzed reactions to achieve high separation rates, high returns and environmental friendliness has become the focus of research in recent years. This review mainly introduces the common separation methods of plant terpenoids based on biotransformation from the perspectives of engineering strain construction, unit separation technology, product properties and added value. Then, further attention was paid to the application prospects of intelligent cell factories and control in the separation of plant terpenoids. Finally, some current challenges and prospects are proposed, which provide possible directions and guidance for the separation and purification of terpenoids and even industrialization.

Allosteric Modulator Leads Hiding in Plain Site: Developing Peptide and Peptidomimetics as GPCR Allosteric Modulators

Allosteric modulators (AMs) of G-protein coupled receptors (GPCRs) are desirable drug targets because they can produce fewer on-target side effects, improved selectivity, and better biological specificity (e.g., biased signaling or probe dependence) than orthosteric drugs. An underappreciated source for identifying AM leads are peptides and proteins-many of which were evolutionarily selected as AMs-derived from endogenous protein-protein interactions (e.g., transducer/accessory proteins), intramolecular receptor contacts (e.g., pepducins or extracellular domains), endogenous peptides, and exogenous libraries (e.g., nanobodies or conotoxins). Peptides offer distinct advantages over small molecules, including high affinity, good tolerability, and good bioactivity, and specific disadvantages, including relatively poor metabolic stability and bioavailability. Peptidomimetics are molecules that combine the advantages of both peptides and small molecules by mimicking the peptide's chemical features responsible for bioactivity while improving its druggability. This review 1) discusses sources and strategies to identify peptide/peptidomimetic AMs, 2) overviews strategies to convert a peptide lead into more drug-like "peptidomimetic," and 3) critically analyzes the advantages, disadvantages, and future directions of peptidomimetic AMs. While small molecules will and should play a vital role in AM drug discovery, peptidomimetics can complement and even exceed the advantages of small molecules, depending on the target, site, lead, and associated factors.

Synthesis, Physicochemical Characterization, In Vitro 2D/3D Human Cell Culture, and In Vitro Aerosol Dispersion Performance of Advanced Spray Dried and Co-Spray Dried Angiotensin (1-7) Peptide and PNA5 with Trehalose as Microparticles/Nanoparticles for Targeted Respiratory Delivery as Dry Powder Inhalers

The peptide hormone Angiotensin (1—7), Ang (1—7) or (Asp-Arg-Val-Tyr-Ile-His-Pro), is an essential component of the renin–angiotensin system (RAS) peripherally and is an agonist of the Mas receptor centrally. Activation of this receptor in the CNS stimulates various biological activities that make the Ang (1—7)/MAS axis a novel therapeutic approach for the treatment of many diseases. The related O-linked glycopeptide, Asp-Arg-Val-Tyr-Ile-His-Ser-(O-β-D-Glc)-amide (PNA5), is a biousian revision of the native peptide hormone Ang (1—7) and shows enhanced stability in vivo and greater levels of brain penetration. We have synthesized the native Ang (1—7) peptide and the glycopeptide, PNA5, and have formulated them for targeted respiratory delivery as inhalable dry powders. Solid phase peptide synthesis (SPPS) successfully produced Ang (1—7) and PNA5. Measurements of solubility and lipophilicity of raw Ang (1—7) and raw PNA5 using experimental and computational approaches confirmed that both the peptide and glycopeptide have high-water solubility and are amphipathic. Advanced organic solution spray drying was used to engineer the particles and produce spray-dried powders (SD) of both the peptide and the glycopeptide, as well as co-spray-dried powders (co-SD) with the non-reducing sugar and pharmaceutical excipient, trehalose. The native peptide, glycopeptide, SD, and co-SD powders were comprehensively characterized, and exhibited distinct glass transitions (T_g) consistent with the amorphous glassy state formation with T_gs that are compatible with use in vivo. The homogeneous particles displayed small sizes in the nanometer size range and low residual water content in the solid-state. Excellent aerosol dispersion performance with a human DPI device was demonstrated. In vitro human cell viability assays showed that Ang (1—7) and PNA5 are biocompatible and safe for different human respiratory and brain cells.

Synthesis and In Vitro Characterization of Glycopeptide Drug Candidates Related to PACAP1-23

The search for efficacious treatment of neurodegenerative and progressive neuroinflammatory diseases continues, as current therapies are unable to halt or reverse disease progression. PACAP represents one potential therapeutic that provides neuroprotection effects on neurons, and also modulates inflammatory responses and circulation within the brain. However, PACAP is a relatively long peptide hormone that is not trivial to synthesize. Based on previous observations that the shortened isoform PACAP1-23 is capable of inducing neuroprotection in vitro, we were inspired to synthesize shortened glycopeptide analogues of PACAP1-23. Herein, we report the synthesis and in vitro characterization of glycosylated PACAP1-23 analogues that interact strongly with the PAC1 and VPAC1 receptors, while showing reduced activity at the VPAC2 receptor.

Facile access to C-glycosyl amino acids and peptides via Ni-catalyzed reductive hydroglycosylation of alkynes

C-Glycosyl peptides/proteins are metabolically stable mimics of the native glycopeptides/proteins bearing O/N-glycosidic linkages, and are thus of great therapeutical potential. Herein, we disclose a protocol for the syntheses of vinyl C-glycosyl amino acids and peptides, employing a nickel-catalyzed reductive hydroglycosylation reaction of alkyne derivatives of amino acids and peptides with common glycosyl bromides. It accommodates a wide scope of the coupling partners, including complex oligosaccharide and peptide substrates. The resultant vinyl C-glycosyl amino acids and peptides, which bear common O/N-protecting groups, are amenable to further transformations, including elongation of the peptide and saccharide chains.

C-Glycosyl peptides/proteins are metabolically stable mimics of the native glycopeptides/proteins of great therapeutic potential, but their chemical synthesis is challenging. Here, the authors report a protocol for the synthesis of vinyl C-glycosyl amino acids and peptides, via a Ni-catalyzed reductive hydroglycosylation reaction of alkyne derivatives of amino acids and peptides with glycosyl bromides.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

Therapeutic peptides for chemotherapy: Trends and challenges for advanced delivery systems

The past decades witnessed an increasing interest in peptides as clinical therapeutics. Rightfully considered as a potential alternative for small molecule therapy, these remarkable pharmaceuticals can be structurally fine-tuned to impact properties such as high target affinity, selectivity, low immunogenicity along with satisfactory tissue penetration. Although physicochemical and pharmacokinetic challenges have mitigated, to some extent, the clinical applications of therapeutic peptides, their potential impact on modern healthcare remains encouraging. According to recent reports, there are more than 400 peptides under clinical trials and 60 were already approved for clinical use. As the demand for efficient and safer therapy became high, especially for cancers, peptides have shown some exciting developments not only due to their potent antiproliferative action but also when used as adjuvant therapies, either to decrease side effects with tumor-targeted therapy or to enhance the activity of anticancer drugs via transbarrier delivery. The first part of the present review gives an insight into challenges related to peptide product development. Both molecular and formulation approaches intended to optimize peptide's pharmaceutical properties are covered, and some of their current issues are highlighted. The second part offers a comprehensive overview of the emerging applications of therapeutic peptides in chemotherapy from bioconjugates to nanovectorized therapeutics.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Developing mass spectrometry for the quantitative analysis of neuropeptides

INTRODUCTION

Neuropeptides are signaling molecules originating in the neuroendocrine system that can act as neurotransmitters and hormones in many biochemical processes. Their exact function is difficult to characterize, however, due to dependence on concentration, post-translational modifications, and the presence of other comodulating neuropeptides. Mass spectrometry enables sensitive, accurate, and global peptidomic analyses that can profile neuropeptide expression changes to understand their roles in many biological problems, such as neurodegenerative disorders and metabolic function.

AREAS COVERED

We provide a brief overview of the fundamentals of neuropeptidomic research, limitations of existing methods, and recent progress in the field. This review is focused on developments in mass spectrometry and encompasses labeling strategies, post-translational modification analysis, mass spectrometry imaging, and integrated multi-omic workflows, with discussion emphasizing quantitative advancements.

EXPERT OPINION

Neuropeptidomics is critical for future clinical research with impacts in biomarker discovery, receptor identification, and drug design. While advancements are being made to improve sensitivity and accuracy, there is still room for improvement. Better quantitative strategies are required for clinical analyses, and these methods also need to be amenable to mass spectrometry imaging, post-translational modification analysis, and multi-omics to facilitate understanding and future treatment of many diseases.

Eco-Friendly Synthesis of Peptides Using Fmoc-Amino Acid Chlorides as Coupling Agent Under Biphasic Condition

BACKGROUND

Agro-waste derived solvent media act as a greener process for the peptide bond formation using N^α-Fmoc-amino acid chloride and amino acid ester salt with in situ neutralization and coupling under biphasic condition. The Fmoc-amino acid chlorides are prepared by the reported procedure of freshly distilled SOCl₂ with dry CH₂Cl₂. The protocol found many added advantages such as neutralization of amino acid ester salt and not required additional base for the neutralization, and directly coupling take place with Fmoc-amino acid chloride gave final product dipeptide ester in good to excellent yields. The protocol occurs with complete stereo chemical integrity of the configuration of substrates. Here, we revisited Schotten-Baumann condition, instead of using inorganic base.

OBJECTIVE

To develop green protocol for the synthesis of peptide bond using Fmoc-amino acid chloride with amino acid esters salt.

METHODS

The final product isolated is analyzed in several spectroscopic and analytical techniques such as FT-IR, ¹H-, ¹³C-NMR, Mass spectrometry and RP-HPLC to check stereo integrity and purity of the product.

CONCLUSION

The present method developed greener using natural agro-waste (lemon fruit shell ash) derived solvent medium for the reaction and not required chemical entity.

A structural perspective on the design of decoy immune modulators

Therapeutic mAbs have dominated the class of immunotherapeutics in general and immune checkpoint inhibitors in particular. The high specificity of mAbs to the target molecule as well as their extended half-life and (or) the effector functions raised by the Fc part are some of the important aspects that contribute to the success of this class of therapeutics. Equally potential candidates are decoys and their fusions that can address some of the inherent limitations of mAbs, like immunogenicity, resistance development, low bio-availability and so on, besides maintaining the advantages of mAbs. The decoys are molecules that trap the ligands and prevent them from interacting with the signaling receptors. Although a few FDA-approved decoy immune modulators are very successful, the potential of this class of drugs is yet to be fully realized. Here, we review various strategies employed in fusion protein therapeutics with a focus on the design of decoy immunomodulators from the structural perspective and discuss how the information on protein structure and function can strategically guide the development of next-generation immune modulators.

A protecting group-free approach for synthesizing C-glycosides through glycosyl dithiocarbamates

The first protection/deprotection-free process for radical C-glycosylation has been achieved through one-step preparable glycosyl dithiocarbamates (GDTCs). The Giese-type reaction and radical allylation of unprotected GDTCs were successfully performed to obtain the corresponding α-C-glycosides stereoselectively under mild reaction conditions.

Dipyrrinato-Iridium(III) Complexes for Application in Photodynamic Therapy and Antimicrobial Photodynamic Inactivation

The generation of bio-targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo-)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N- and O-substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*-iridium(III) and ppy-iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl-η5 -cyclopentadienyl, ppy=2-phenylpyridyl). Similarly, electron-deficient [IrIII (dipy)(ppy)2 ] complexes could be used for post-functionalization, forming alkenyl, alkynyl and glyco-appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [IrIII (Cl)(Cp*)(dipy)] complexes and the glyco-substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.

Mammalian Neuropeptides as Modulators of Microbial Infections: Their Dual Role in Defense versus Virulence and Pathogenesis

The regulation of infection and inflammation by a variety of host peptides may represent an evolutionary failsafe in terms of functional degeneracy and it emphasizes the significance of host defense in survival. Neuropeptides have been demonstrated to have similar antimicrobial activities to conventional antimicrobial peptides with broad-spectrum action against a variety of microorganisms. Neuropeptides display indirect anti-infective capacity via enhancement of the host’s innate and adaptive immune defense mechanisms. However, more recently concerns have been raised that some neuropeptides may have the potential to augment microbial virulence. In this review we discuss the dual role of neuropeptides, perceived as a double-edged sword, with antimicrobial activity against bacteria, fungi, and protozoa but also capable of enhancing virulence and pathogenicity. We review the different ways by which neuropeptides modulate crucial stages of microbial pathogenesis such as adhesion, biofilm formation, invasion, intracellular lifestyle, dissemination, etc., including their anti-infective properties but also detrimental effects. Finally, we provide an overview of the efficacy and therapeutic potential of neuropeptides in murine models of infectious diseases and outline the intrinsic host factors as well as factors related to pathogen adaptation that may influence efficacy.

Computational avenues in oral protein and peptide therapeutics

Proteins and peptides are amongst the most sought-after biomolecules because of their exceptional potential to cater to a vast range of diseases. Although widely studied and researched, the oral delivery of these biomolecules remains a challenge. Alongside formulation strategies, approaches to overcome the inherent barriers for peptide absorption are being designed at the molecular level to establish a sound rationale and to achieve higher bioavailability. Computer-aided drug design (CADD) is a modern in silico approach for developing successful bio-formulations. CADD enables intricate study of the biomolecules in conjunction with their target sites or receptors at the molecular level. Knowledge of the molecular interactions of proteins and peptides makes way for the pre-screening of suitable formulation components and facilitates their delivery.

PepTherDia: database and structural composition analysis of approved peptide therapeutics and diagnostics

As of 2020, there were >100 approved peptides with therapeutic or diagnostic applications. However, a complete database providing information on marketed peptides is not freely available, making the peptide chemists' job of designing future peptide drug candidates challenging. Unlike the rules for small-molecule drugs, there is no general set of guidelines for designing a successful peptide-based drug. In this review, together with our freely available database (PepTherDia, http://peptherdia.herokuapp.com), we provide insights into what a successful peptide therapeutic or diagnostic agent looks like and lay the foundation for establishing a set of rules to help future medicinal chemists to design peptide candidates with increased approval rates.

Strategies to expand peptide functionality through hybridisation with a small molecule component

Combining different compound classes gives molecular hybrids that can offer access to novel chemical space and unique properties. Peptides provide ideal starting points for such molecular hybrids, which can be easily modified with a variety of molecular entities. The addition of small molecules can improve the potency, stability and cell permeability of therapeutically relevant peptides. Furthermore, they are often applied to create peptide-based tools in chemical biology. In this review, we discuss general methods that allow the discovery of this compound class and highlight key examples of peptide-small molecule hybrids categorised by the application and function of the small molecule entity.

Organic Solution Advanced Spray-Dried Microparticulate/Nanoparticulate Dry Powders of Lactomorphin for Respiratory Delivery: Physicochemical Characterization, In Vitro Aerosol Dispersion, and Cellular Studies

The purpose of this study was to formulate Lactomorphin (MMP2200) in its pure state as spray-dried(SD) powders, and with the excipient Trehalose as co-spray-dried(co-SD) powders; for intranasal and deep lung administration with Dry Powder Inhalers (DPI). Lactomorphin is a glycopeptide which was developed for the control of moderate to severe pain. Particles were rationally designed and produced by advanced spray drying particle engineering in a closed mode from a dilute organic solution. Comprehensive physicochemical characterization using different analytical techniques was carried out to analyze the particle size, particle morphology, particle surface morphology, solid-state transitions, crystallinity/non-crystallinity, and residual water content. The particle chemical composition was confirmed using attenuated total reflectance-Fourier-transform infrared (ATR-FTIR), and Confocal Raman Microscopy (CRM) confirmed the particles' chemical homogeneity. The solubility and Partition coefficient (LogP) of Lactomorphin were determined by the analytical and computational methodology and revealed the hydrophilicity of Lactomorphin. A thermal degradation study was performed by exposing samples of solid-state Lactomorphin to a high temperature (62 °C) combined with zero relative humidity (RH) and to a high temperature (62 °C) combined with a high RH (75%) to evaluate the stability of Lactomorphin under these two different conditions. The solid-state processed particles exhibited excellent aerosol dispersion performance with an FDA-approved human DPI device to reach lower airways. The cell viability resazurin assay showed that Lactomorphin is safe up to 1000 μg/mL on nasal epithelium cells, lung cells, endothelial, and astrocyte brain cells.

Peak Filtering, Peak Annotation, and Wildcard Search for Glycoproteomics

Glycopeptides in peptide or digested protein samples pose a number of analytical and bioinformatics challenges beyond those posed by unmodified peptides or peptides with smaller posttranslational modifications. Exact structural elucidation of glycans is generally beyond the capability of a single mass spectrometry experiment, so a reasonable level of identification for tandem mass spectrometry, taken by several glycopeptide software tools, is that of peptide sequence and glycan composition, meaning the number of monosaccharides of each distinct mass, e.g., HexNAc(2)Hex(5) rather than man5. Even at this level, however, glycopeptide analysis poses challenges: finding glycopeptide spectra when they are a tiny fraction of the total spectra; assigning spectra with unanticipated glycans, not in the initial glycan database; and finding, scoring, and labeling diagnostic peaks in tandem mass spectra. Here, we discuss recent improvements to Byonic, a glycoproteomics search program, that address these three issues. Byonic now supports filtering spectra by m/z peaks, so that the user can limit attention to spectra with diagnostic peaks, e.g., at least two out of three of 204.087 for HexNAc, 274.092 for NeuAc (with water loss), and 366.139 for HexNAc-Hex, all within a set mass tolerance, e.g., ± 0.01 Da. Also, new is glycan "wildcard" search, which allows an unspecified mass within a user-set mass range to be applied to N- or O-linked glycans and enables assignment of spectra with unanticipated glycans. Finally, the next release of Byonic supports user-specified peak annotations from user-defined posttranslational modifications. We demonstrate the utility of these new software features by finding previously unrecognized glycopeptides in publicly available data, including glycosylated neuropeptides from rat brain.

Synthesis and Cytotoxic Property of Annonaceous Acetogenin Glycoconjugates

Background

Annonaceous acetogenins (ACGs) are secondary metabolites produced by the Annonaceae family and display potent anticancer activity against various cancer cell lines. Squamocin and bullatacin are two examples of ACGs that show promising antitumor activity; however, preclinical data are not sufficient partly due to their being highly lipophilic and poorly soluble in water. These compounds also display high toxicity to normal cells. Due to these disadvantageous properties, the therapeutic potential of squamocin and bullatacin as antitumor agents has not been fully evaluated.

Methods

In order to enhance their water solubility and potentially improve their cancer targeting, squamocin and bullatacin were conjugated to a glucose or galactose to yield glycosylated derivatives by direct glycosylation or the Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction (the click reaction). The synthesized compounds were evaluated for their anticancer property against HeLa, A549 and HepG2 cancer cell lines using MTT assay.

Results

Nine glycosyl derivatives were synthesized and structurally characterized. Most of them show comparable in vitro cytotoxicity against HeLa, A549 and HepG2 cancer cell lines as their parent compounds squamocin and bullatacin. It appears that the type of sugar residue (glucose or galactose), the position at which the sugar residue is attached, and whether or not a linking spacer is present do not affect the potency of these derivatives much. The solubility of galactosylated squamocin 13 in phosphate buffer saline (PBS, pH = 7) is greatly improved (1.37 mg/mL) in comparison to squamocin (not detected in PBS).

Conclusion

The conjugation of a glucose or galactose to squamocin and bullatacin yields glycosyl derivatives with similar level of anticancer activity in tested cell lines. Further studies are needed to demonstrate whether or not these compounds show reduced toxicity to normal cells and their therapeutic potential as antitumor agents.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Glycosyl hydrolase catalyzed glycosylation in unconventional media

The reversible hydrolytic property of glycosyl hydrolases (GHs) as well as their acceptance of aglycones other than water has provided the abilities of GHs in synthesizing glycosides. Together with desirable physiochemical properties of glycosides and their high commercial values, research interests have been aroused to investigate the synthetic other than the hydrolytic properties of GHs. On the other hand, just like the esterification processes catalyzed by lipases, GH synthetic effectiveness is strongly obstructed by water both thermodynamically and kinetically. Medium engineering by involving organic solvents can be a viable approach to alleviate the obstacles caused by water. However, as native hydrolyases function in water-enriched environments, most GHs display poor catalytic performance in the presence of organic solvents. Some GHs from thermophiles are more tolerant to organic solvents due to their robust folded structures with strong residue interactions. Other than native sources, immobilization, protein engineering, employment of surfactant, and lyophilization have been proved to enhance the GH stability from the native state, which opens up the possibilities for GHs to be employed in unconventional media as synthases. KEY POINTS: • Unconventional media enhance the synthetic ability but destabilize GHs. • Viable approaches are discussed to improve GH stability from the native state. • GHs robust in unconventional media can be valuable industrial synthases.

Effect of hydroxylysine-O-glycosylation on the structure of type I collagen molecule: A computational study

Collagen undergoes many types of post-translational modifications (PTMs), including intracellular modifications and extracellular modifications. Among these PTMs, glycosylation of hydroxylysine (Hyl) is the most complicated. Experimental studies demonstrated that this PTM ceases once the collagen triple helix is formed and that Hyl-O-glycosylation modulates collagen fibrillogenesis. However, the underlying atomic-level mechanisms of these phenomena remain unclear. In this study, we first adapted the force field parameters for O-linkages between Hyl and carbohydrates and then investigated the influence of Hyl-O-glycosylation on the structure of type I collagen molecule, by performing comprehensive molecular dynamic simulations in explicit solvent of collagen molecule segment with and without the glycosylation of Hyl. Data analysis demonstrated that (i) collagen triple helices remain in a triple-helical structure upon glycosylation of Hyl; (ii) glycosylation of Hyl modulates the peptide backbone conformation and their solvation environment in the vicinity and (iii) the attached sugars are arranged such that their hydrophilic faces are well exposed to the solvent, while their hydrophobic faces point towards the hydrophobic portions of collagen. The adapted force field parameters for O-linkages between Hyl and carbohydrates will aid future computational studies on proteins with Hyl-O-glycosylation. In addition, this work, for the first time, presents the detailed effect of Hyl-O-glycosylation on the structure of human type I collagen at the atomic level, which may provide insights into the design and manufacture of collagenous biomaterials and the development of biomedical therapies for collagen-related diseases.

Genetically Encoded Quinone Methides Enabling Rapid, Site-Specific, and Photocontrolled Protein Modification with Amine Reagents

Site-specific modification of proteins with functional molecules provides powerful tools for researching and engineering proteins. Here we report a new chemical conjugation method which photocages highly reactive but chemically selective moieties, enabling the use of protein-inert amines for selective protein modification. New amino acids FnbY and FmnbY, bearing photocaged quinone methides (QMs), were genetically incorporated into proteins. Upon light activation, they generated highly reactive QM, which rapidly reacted with amine derivatives. This method features a rare combination of desired properties including fast kinetics, small and stable linkage, compatibility with low temperature, photocontrollability, and widely available reagents. Moreover, labeling via FnbY occurs on the β-carbon, affording the shortest linkage to protein backbone which is essential for advanced studies involving orientation and distance. We installed various functionalities onto proteins and attached a spin label as close as possible to the protein backbone, achieving high resolution in double electron-electron paramagnetic resonance distance measurements.

An Efficient Strategy for the Chemo-Enzymatic Synthesis of Bufalin Glycosides with Improved Water Solubility and Inhibition against Na+ , K+ -ATPase

In this study, bufalin was glycosylated by an efficient chemo-enzymatic strategy. Firstly, 2-chloro-4-nitrophenyl-1-O-β-D-glucoside (sugar donors) was obtained by chemical synthesis. Then, the glycosylation of the bufalin was achieved with the synthesized sugar donor under the catalysis of two glycosyltransferases (Loki and ASP). Finally, two glycosides, i. e., bufalin-3-O-β-D-glucopyranoside and bufalin-3-O-[β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside)], were obtained by preparative HPLC. Compared to our previously reported sole chemical (total yield 10 % in four steps) or enzymatic methods (30 %), our combined chemo-enzymatic strategy in this article greatly improves the yields of monoglycoside (68 %) and diglycoside (21 %) and decreased the experimental cost (90 %). Furthermore, we tested the water solubility of these glycosides and found that the water solubilities of the two glycosides were 13.1 and 53.7 times of bufalin, respectively. In addition, the inhibitory activity of these glycosides against Na⁺ , K⁺ -ATPase were evaluated. The mono-glycosylated compound showed more potent activity than bufalin, while the diglycosylated compound was less potent.

Effects of Glycosylation and d-Amino Acid Substitution on the Antitumor and Antibacterial Activities of Bee Venom Peptide HYL

Glycosylation is a promising strategy for modulating the physicochemical properties of peptides. However, the influence of glycosylation on the biological activities of peptides remains unknown. Here, we chose the bee venom peptide HYL as a model peptide and 12 different monosaccharides as model sugars to study the effects of glycosylation site, number, and monosaccharide structure on the biochemical properties, activities, and cellular selectivities of HYL derivatives. Some analogues of HYL showed improvement not only in cell selectivity and proteolytic stability but also in antitumor and antimicrobial activity. Moreover, we found that the helicity of glycopeptides can affect its antitumor activity and proteolytic stability, and the α-linked d-monosaccharides can effectively improve the antitumor activity of HYL. Therefore, it is possible to design peptides with improved properties by varying the number, structure, and position of monosaccharides. What's more, the glycopeptides HYL-31 and HYL-33 show a promising prospect for antitumor and antimicrobial drugs development, respectively. In addition, we found that the d-lysine substitution strategy can significantly improve the proteolytic stability of HYL. Our new approach provides a reference or guidance for the research of novel antitumor and antimicrobial peptide drugs.

Selective antagonism of cJun for cancer therapy

The activator protein-1 (AP-1) family of transcription factors modulate a diverse range of cellular signalling pathways into outputs which can be oncogenic or anti-oncogenic. The transcription of relevant genes is controlled by the cellular context, and in particular by the dimeric composition of AP-1. Here, we describe the evidence linking cJun in particular to a range of cancers. This includes correlative studies of protein levels in patient tumour samples and mechanistic understanding of the role of cJun in cancer cell models. This develops an understanding of cJun as a focal point of cancer-altered signalling which has the potential for therapeutic antagonism. Significant work has produced a range of small molecules and peptides which have been summarised here and categorised according to the binding surface they target within the cJun-DNA complex. We highlight the importance of selectively targeting a single AP-1 family member to antagonise known oncogenic function and avoid antagonism of anti-oncogenic function.

Tryptophan-galactosylamine conjugates inhibit and disaggregate amyloid fibrils of Aβ42 and hIAPP peptides while reducing their toxicity

Self-assembly of proteins into amyloid fibrils is a hallmark of various diseases, including Alzheimer's disease (AD) and Type-2 diabetes Mellitus (T2DM). Aggregation of specific peptides, like Aβ42 in AD and hIAPP in T2DM, causes cellular dysfunction resulting in the respective pathology. While these amyloidogenic proteins lack sequence homology, they all contain aromatic amino acids in their hydrophobic core that play a major role in their self-assembly. Targeting these aromatic residues by small molecules may be an attractive approach for inhibiting amyloid aggregation. Here, various biochemical and biophysical techniques revealed that a panel of tryptophan-galactosylamine conjugates significantly inhibit fibril formation of Aβ42 and hIAPP, and disassemble their pre-formed fibrils in a dose-dependent manner. They are also not toxic to mammalian cells and can reduce the cytotoxicity induced by Aβ42 and hIAPP aggregates. These tryptophan-galactosylamine conjugates can therefore serve as a scaffold for the development of therapeutics towards AD and T2DM.

Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

Impact of non-proteinogenic amino acids in the discovery and development of peptide therapeutics

With the development of modern chemistry and biology, non-proteinogenic amino acids (NPAAs) have become a powerful tool for developing peptide-based drug candidates. Drug-like properties of peptidic medicines, due to the smaller size and simpler structure compared to large proteins, can be changed fundamentally by introducing NPAAs in its sequence. While peptides composed of natural amino acids can be used as drug candidates, the majority have shown to be less stable in biological conditions. The impact of NPAA incorporation can be extremely beneficial in improving the stability, potency, permeability, and bioavailability of peptide-based therapies. Conversely, undesired effects such as toxicity or immunogenicity should also be considered. The impact of NPAAs in the development of peptide-based therapeutics is reviewed in this article. Further, numerous examples of peptides containing NPAAs are presented to highlight the ongoing development in peptide-based therapeutics.