Exploring the Utility of Cell-Penetrating Peptides as Vehicles for the Delivery of Distinct Antimalarial Drug Cargoes.

The devastating impact of malaria includes significant mortality and illness worldwide. Increasing resistance of the causative parasite, Plasmodium, to existing antimalarial drugs underscores a need for additional compounds with distinct modes of action in the therapeutic development pipeline. Here we showcase peptide-drug conjugates (PDCs) as an attractive compound class, in which therapeutic or lead antimalarials are chemically conjugated to cell-penetrating peptides. This approach aims to enhance selective uptake into Plasmodium-infected red blood cells and impart additional cytotoxic actions on the intraerythrocytic parasite, thereby enabling targeted drug delivery and dual modes of action. We describe the development of PDCs featuring four compounds with antimalarial activity - primaquine, artesunate, tafenoquine and methotrexate - conjugated to three cell-penetrating peptide scaffolds with varied antiplasmodial activity, including active and inactive analogs of platelet factor 4 derived internalization peptide (PDIP), and a cyclic polyarginine peptide. Development of this diverse set of PDCs featured distinct and adaptable conjugation strategies, to produce conjugates with in vitro antiplasmodial activities ranging from low nanomolar to low micromolar potencies according to the drug cargo and bioactivity of the partner peptide. Overall, this study establishes a strategic and methodological framework for the further development of dual mode of action peptide-drug antimalarial therapeutics.

Selenium(II)-Nitrogen Exchange (SeNEx) Chemistry: A Good Chemistry Suitable for Nanomole-Scale Parallel Synthesis, DNA-encoded Library Synthesis, and Bioconjugation.

The continuous development of click reactions with new connecting linkage is crucial for advancing the frontiers of click chemistry. Selenium-nitrogen exchange (SeNEx) chemistry, a versatile chemistry in click chemistry, represents an all-encompassing term for nucleophilic substitution events that replace nitrogen at an electrophilic selenium(II) center, enabling the flexible and efficient assembly of linkages around a Se(II) core. Several SeNEx chemistries have been developed inspired by the biochemical reaction between Ebselen and cysteine residue, and demonstrated significant potential in on-plate nanomole-scale parallel synthesis, selenium-containing DNA-encoded library (SeDEL) synthesis, as well as peptide and protein bioconjugation. This concept aims to present the origins, advancements, and applications of selenium(II)-nitrogen exchange (SeNEx) chemistry while also outlining the potential directions for future research in this field.

Fluoroalcohols for chemical modification of biomolecules.

While their broad utility in various chemistry fields were well recognized for decades, fluoroalcohols have recently emerged as a unique solvent system for bioconjugation development. This review describes examples and roles of fluoroalcohols such as trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) for chemical modification of biomolecules such as polypeptides, nucleic acids, and saccharides. Many chemical modification processes were facilitated by notable functions of those fluoroalcohols such as a proton shuttle, reversible adduct formation with reactive species, and compatibility with electrochemistry/photochemistry. The usefulness of the fluoroalcohol solvents can be even promoted by its combination with a different solvent system for reaction enhancement and protein stabilization. The collection of the various chemical transformations in this review is an indication of the rapid growth of the solvent-assisted bioconjugation field.

Advances in biomacromolecule-functionalized magnetic particles for phytopathogen detection.

Due to the increasing crop losses caused by common and newly emerging phytopathogens, there is a pressing need for the development of rapid and reliable methods for phytopathogen detection and analysis. Leveraging advancements in biochemical engineering technologies and nanomaterial sciences, researchers have put considerable efforts on utilizing biofunctionalized magnetic micro- and nanoparticles (MPs) to develop rapid and reliable systems for phytopathogen detection. MPs facilitate the rapid, high-throughput analysis and in-field applications, while the biomacromolecules, which play key roles in the biorecognitions, interactions and signal amplification, determine the specificity, sensitivity, reliability, and portability of pathogen detection systems. The integration of MPs and biomacromolecules provides dimensionality- and composition-dependent properties, representing a novel approach to develop phytopathogen detection systems. In this review, we summarize and discuss the general properties, synthesis and characterization of MPs, and focus on biomacromolecule-functionalized MPs as well as their representative applications for phytopathogen detection and analysis reported over the past decade. Extensively studied bioreceptors, such as antibodies, phages and phage proteins, nucleic acids, and glycans that are involved in the recognitions and interactions, are covered and discussed. Additionally, the integration of MPs-based detection system with portable microfluidic devices to facilitate their in-field applications is also discussed. Overall, this review focuses on biomacromolecule-functionalized MPs and their applications for phytopathogen detection, aiming to highlight their potential in developing advanced biosensing systems for effective plant protection.

Perfect Partners: Biocatalytic Halogenation and Metal Catalysis for Protein Bioconjugation.

Flavin-dependent halogenases (FDHs) are the most extensively researched halogenases and show great potential for biotransformation applications. These enzymes use chloride, bromide, or iodide ions as halogen donors to catalyze the oxygen-dependent halogenation of electron-rich aryl moieties, requiring stochiometric amounts of FADH2 in the process. This makes FDH-catalyzed aryl halogenation a highly selective and environmentally friendly tool for the synthesis of aryl halides. The latter in turn serve as valuable intermediates for transition metal catalyzed cross coupling reactions for C-C bond formation. Previous research made extensive use of this approach to halogenate small molecules as building blocks for late-stage functionalization by transition-metal catalyzed cross-coupling reactions. Based on these results, several groups have managed to expand this research to protein targets over the past two years. Their work indicates an emerging methodology for bioconjugation using late-stage biocatalytic halogenation in conjunction with biorthogonal Suzuki-Miyaura cross-coupling. This strategy could present an attractive alternative to existing approaches due to the stability of the C-C bond bridging the generated biaryl moiety and the ease of late-stage enzymatic modification while maintaining excellent selectivity under mild conditions.

Emerging conjugation strategies and protein engineering technologies aim to improve ADCs in the fight against cancer.

Antibody drug conjugates are an exciting therapeutic modality that combines the targeting specificity of antibodies with potent cytotoxins to selectively kill cancer cells. The targeting component improves efficacy and protects non-target cells from the harmful effects of the payload. To date 15 ADCs have been approved by regulatory agencies for commercial use and shown to be valuable tools in the treatment of cancer.The assembly of an ADC requires the chemical ligation of a linker-payload to an antibody. Conventional conjugation methods targeting accessible lysines and cysteines have produced all the ADCs currently on the market. While successful, technologies aiming to improve the homogeneity and stability of ADCs are being developed and tested.Here we provide a review of developing methods for ADC construction. These include enzymatic methods, oligosaccharide remodelling, and technologies using genetic code expansion techniques. The virtues and limitations of each technology are discussed.Emerging conjugation technologies are being applied to produce new formats of ADCs with enhanced functionality including bispecific ADCs, dual-payload ADCs, and nanoparticles for targeted drug delivery. The benefits of these novel formats are highlighted.

Synthesis of Tumor Selective Indole and 8-Hydroxyquinoline Skeleton Containing Di-, or Triarylmethanes with Improved Cytotoxic Activity.

The reaction between glycine-type aminonaphthol derivatives substituted with 2- or 1-naphthol and indole or 7-azaindole has been tested. Starting from 2-naphthol as a precursor, the reaction led to the formation of ring-closed products, while in the case of a 1-naphthol-type precursor, the desired biaryl ester was isolated. The synthesis of a bifunctional precursor starting from 5-chloro-8-hydroxyquinoline, morpholine, and ethyl glyoxylate via modified Mannich reaction is reported. The formed Mannich base 10 was subjected to give bioconjugates with indole and 7-azaindole. The effect of the aldehyde component and the amine part of the Mannich base on the synthetic pathway was also investigated. In favor of having a preliminary overview of the structure-activity relationships, the derivatives have been tested on cancer and normal cell lines. In the case of bioconjugate 16, as the most powerful scaffold in the series bearing indole and a 5-chloro-8-hydroxyquinoline skeleton, a potent toxic activity against the resistant Colo320 colon adenocarcinoma cell line was observed. Furthermore, this derivative was selective towards cancer cell lines showing no toxicity on non-tumor fibroblast cells.

Evaluation of Kochetkov Hemiaminal hydrolysis under acidic, alkaline, and neutral conditions.

The most common precursors to synthetic glycoproteins are reducing end glycosyl amines. To afford these amines, a carbohydrate is reacted with an excess of an ammonia source to yield the ß-anomer, exclusively, in a reaction known as the Kochetkov amination. Although this process is the state-of-the-art method to synthesize non-functionalized, ß-amino (ßA) glycans, misconceptions surrounding the stability of these amines has limited their use in subsequent reactions. Here, we investigated the stability of seven amino sugars in the neutral, acidic, and basic conditions they would be subject to in common reactions using amines. In neutral and basic conditions, the amino sugars proved relatively stable with the fastest time to 50% hydrolysis being four days for only one carbohydrate. However, acidic conditions promoted rapid hydrolysis, with all amino sugars reaching over 97% hydrolysis within 2 h. Finally, we performed a bioconjugation using fluorescein isothiocyanate and ßA-difucosyllactose, revealing sufficient stability of the amino product for a successful subsequent reaction.

Bridging the gap: RNAylation conjugates RNAs to proteins.

In nature, the majority of known RNA-protein interactions are transient. Our recent study has depicted a novel mechanism known as RNAylation, which covalently links proteins and RNAs. This novel modification bridges the realms of RNA and protein modifications. This review specifically explores RNAylation catalyzed by bacteriophage T4 ADP-ribosyltransferase ModB, with a focus on its protein targets and RNA substrates in the context of Escherichia coli-bacteriophage T4 interaction. Additionally, we discuss the biological significance of RNAylation and present perspectives on RNAylation as a versatile bioconjugation strategy for RNAs and proteins.

Construction of HaloTag-based macromolecular probe for multiple logic gates and photoactivatable bioimaging.

Protein bioconjugation has emerged as one of the most valuable tools for the development of protein-based biochemical assays. Herein, we report a fluorescent macromolecular probe RF12_POI, in which the coumarin derivative RF12 is specifically conjugated onto the HaloTag fused protein of interest (POI) to achieve a dual stimuli-mediated fluorescence response. RF12 is first obtained by installing a photo-cleavable 1-ethyl-2-nitrobenzyl group onto the C7 hydroxy moiety of coumarin fluorophore with a HaloTag ligand attaching to the acid-labile 1,3-dioxane moiety. Upon stimulation, RF12_Halo exhibits a sequential fluorescence response to photon/H+ on both liquid and solid interfaces. Through the conjugation of RF12 onto the GFP_Halo protein, RF12_GFP_Halo presents a fluorescence resonance energy transfer (FRET) from photo-cleaved RF12 to GFP in the protein complex. Furthermore, by utilizing the stimuli-responsive fluorescence characteristics of coumarin derivatives RF12 (photon/H+) and RF16 (H2O2/H+), we construct RF12/RF16_POI based protein films and achieve multiple applications of logic circuits, including AND, OR, XOR, INHIBIT, Half-adder or Half-subtractor. In these circuits, the output value of I/I0 is dependent on the input sequence of photon, H2O2, and H+. Additionally, we evaluate the fluorescence labeling ability of RF12 to intracellular IRE1_Halo protein and demonstrate that RF12 containing the HaloTag ligand could be precisely retained in cells to track IRE1_Halo protein. Hence, we provide a unique structural design strategy to construct fluorescence dual-responsive macromolecules for information encryption and cellular protein visualization.

Late-stage Fluorination of Tyrosine Residues in Antiviral Protein Cyanovirin-N.

The applications of fluorinated molecules in chemical biology are rapidly expanding driven by the unique properties of C-F bonds, leading to increased interest in methodologies for controlled introduction of this atom. In this study, we present the first method for late-stage fluorination of tyrosine residues in proteins. Our results demonstrate that electrophilic fluorination using Selectfluor, a stable and non-toxic reagent, offers a straightforward and cost-effective method for labeling Cyanovirin-N (CVN), a 101-amino-acid lectin with effective antiviral activity. Uni- and bidimensional 1H, 13C and 19F NMR analyses, along with mass spectrometry, revealed chemoselective fluorination of the three tyrosine residues in CVN without affecting its overall structure or mannose-binding affinity. Additionally, we observed that other aromatic amino acids, such as tryptophan, phenylalanine, and histidine, are not fluorinated using this method. These findings advance our understanding of protein fluorination and its applications in studying structure, dynamics, and interactions, as well as other biological utilities.

Antibacterial activity of Au(I), Pt(II), and Ir(III) biotin conjugates prepared by the iClick reaction: influence of the metal coordination sphere on the biological activity.

A series of biotin-functionalized transition metal complexes was prepared by iClick reaction from the corresponding azido complexes with a novel alkyne-functionalized biotin derivative ([Au(triazolatoR,R')(PPh3)], [Pt(dpb)(triazolatoR,R')], [Pt(triazolatoR,R')(terpy)]PF6, and [Ir(ppy)(triazolatoR,R')(terpy)]PF6 with dpb = 1,3-di(2-pyridyl)benzene, ppy = 2-phenylpyridine, and terpy = 2,2':6',2''-terpyridine and R = C6H5, R' = biotin). The complexes were compared to reference compounds lacking the biotin moiety. The binding affinity toward avidin and streptavidin was evaluated with the HABA assay as well as isothermal titration calorimetry (ITC). All compounds exhibit the same binding stoichiometry of complex-to-avidin of 4:1, but the ITC results show that the octahedral Ir(III) compound exhibits a higher binding affinity than the square-planar Pt(II) complex. The antibacterial activity of the compounds was evaluated on a series of Gram-negative and Gram-positive bacterial strains. In particular, the neutral Au(I) and Pt(II) complexes showed significant antibacterial activity against Staphylococcus aureus and Enterococcus faecium at very low micromolar concentrations. The cytotoxicity against a range of eukaryotic cell lines was studied and revealed that the octahedral Ir(III) complex was non-toxic, while the square-planar Pt(II) and linear Au(I) complexes displayed non-selective micromolar activity.

Cell-Specific Optical Control of AMPA Glutamate Receptors with a Photoswitchable Tethered Antagonist.

AMPA receptors (AMPARs) are the main drivers of excitatory glutamatergic transmission in the brain, central to synaptic plasticity, and are key drug targets. However, AMPARs are expressed in virtually every neuron in the central nervous system and are activated with complex temporal dynamics, making it difficult to determine their functional roles with sufficient precision. Here we describe a cell specific, light-controllable competitive antagonist for the AMPA receptor called MP-GluAblock that combines the temporal precision of a photo-switchable ligand with the spatial and cellular specificity of a genetically-encoded membrane-anchor protein. This tool could pave the way for controlling endogenous AMPARs in neural circuits with cellular, spatial, and temporal specificity.

Exosome-drug conjugates delivery: a promising strategy for ameliorating the pharmacokinetic profile of artesunate.

Artesunate (ATS) is considered the most widely employed artemisnin derivative in the treatment of Plasmodium falciparum malaria. However, poor solubility and low bioavailability of ATS limit its further clinical application. Herein, we developed a new strategy based on the exosome (exo) - drug conjugation (EDC) using the milk-derived exosomes for ATS delivery. The Exo-ATS conjugates (EACs) which formed via a facile bio-conjugation of ATS to the exosomal surface, have been demonstrated to be able to not only boost the solubility and bioavailability of ATS but also enable a sustained-release of ATS from exosomes. Maximal improvement of 71.4-fold in the solubility of ATS was attained by EACs. The corresponding entrapment efficiency and drug loading capacities were found to be 90.3% and 73.9% for EACs, respectively. Further, in vivo pharmacokinetics study manifested that maximum 2.6-fold improved bioavailability of ATS was achieved by oral delivery of EACs. Moreover, EACs displayed a distinct sustained-release profile of maximum 36.2-fold prolonged half-life of ATS via intravenous delivery. We reported that for the first time the administration of EACs could be a potential drug delivery strategy aimed at ameliorating the pharmacokinetic profile of ATS based on our encouraging results and hoped that our work opened up a new avenue for the development of EDC delivery system.

Probing the Topological Effects on Stability Enhancement and Therapeutic Performance of Protein Bioconjugates: Tadpole, Macrocycle versus Figure-of-Eight.

Chemical topology provides a unique dimension for making therapeutic protein bioconjugates with native structure and intact function, yet the effects of topology remain elusive. Herein, the design, synthesis, and characterization of therapeutic protein bioconjugates in three topologies (i.e., tadpole, macrocycle, and figure-of-eight), are reported. The interferon α2b (IFN) and albumin binding domain (ABD) are selected as the model proteins for bioconjugation and proof-of-concept. The biosynthesis of these topological isoforms is accomplished via direct expression in cells using SpyTag-SpyCatcher chemistry and/or split-intein-mediated ligation for topology diversification. The corresponding topologies are proven with combined techniques of LC-MS, SDS-PAGE, and controlled proteolytic digestion. While the properties of these topological isoforms are similar in most cases, the figure-of-eight-shaped bioconjugate, f8-IFN-ABD, exhibits the best thermal stability and anti-aggregation properties along with prolonged half-life and enhanced tumor retention relative to the tadpole-shaped control, tadp-IFN-ABD, and the macrocyclic control, c-IFN-ABD, showcasing considerable topological effects. The work expands the topological diversity of proteins and demonstrates the potential advantages of leveraging chemical topology for functional benefits beyond multi-function integration in protein therapeutics.

Coupling enterotoxigenic Escherichia coli heat-stable peptide toxin with 8-arm PEG enhances immunogenicity.

Enterotoxigenic Escherichia coli (ETEC) strains, which produce the heat-stable enterotoxin (ST) either alone or in combination with the heat-labile enterotoxin, contribute to the bulk of the burden of child diarrheal disease in resource-limited countries and are associated with mortality. Developing an effective vaccine targeting ST presents challenges due to its potent enterotoxicity, non-immunogenicity, and the risk of autoimmune reaction stemming from its structural similarity to the human endogenous ligands, guanylin, and uroguanylin. This study aimed to assess a novel synthetic vaccine carrier platform employing a single chemical coupling step for making human ST (STh) immunogenic. Specifically, the method involved cross-linking STh to an 8-arm N-hydroxysuccinimide (NHS) ester-activated PEG cross-linker. A conjugate of STh with 8-arm structure was prepared, and its formation was confirmed through immunoblotting analysis. The impact of conjugation on STh epitopes was assessed using ELISAs with polyclonal and monoclonal antibodies targeting various epitopes of STh. Immunization of mice with the conjugate induced the production of anti-STh antibodies, exhibiting neutralizing activity against STh.

Covalent Lysozyme Immobilization on Enzymatic Cellulose Nanocrystals.

Nanostructured materials represent promising substrates for biocatalysts immobilization and activation. Cellulose nanocrystals (CNCs), accessible from waste and/or renewable sources, are sustainable and biodegradable, show high specific surface area for anchoring a high number of enzymatic units, and high thermal and mechanical stability. In this work, we present a holistic enzyme-based approach to functional antibacterial materials by bioconjugation between the lysozyme from chicken egg white and enzymatic cellulose nanocrystals. The neutral CNCs were prepared by endoglucanase hydrolysis from Avicel. We explore the covalent immobilization of lysozyme on the enzymatic CNCs and on their TEMPO oxidized derivatives (TO-CNCs), comparing immobilization yields, materials properties, and enzymatic activities. The materials were characterized by X-ray diffractometry (XRD), attenuated total reflectance Fourier Transform infrared spectroscopy (ATR-FTIR), bicinchoninic acid (BCA) assay, field-emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS). We demonstrate the higher overall efficiency of the immobilization process carried out on TO-CNCs, based on the success of covalent bonding and on the stability of the isolated biocojugates.

Accessing Therapeutically-Relevant Multifunctional Antisense Oligonucleotide Conjugates Using Native Chemical Ligation.

Antisense oligonucleotide (ASO) therapies hold significant promise in the realm of molecular medicine. By precisely targeting RNA molecules, ASOs offer an approach to modulate gene expression and protein production, making them valuable tools for treating a wide range of genetic and acquired diseases. As the precise intracellular targeting and delivery of ASOs is challenging, strategies for preparing ASO-ligand conjugates are in exceedingly high demand. This work leverages the utility of native chemical ligation to conjugate ASOs with therapeutically relevant chemical modifications including locked nucleic acids and phosphorothioate backbone modifications to peptides and sugars via a stable amide linkage. A suite of post-ligation functionalizations through modification of the cysteine ligation handle are highlighted, including chemoselective radical desulfurization, lipidation, and alkylation with a range of valuable handles (e.g. alkyne, biotin, and radionuclide chelating ligands), affording multifunctional constructs for further applications in biology and medicine. Application of the methodology to a clinically-relevant triantennary-GalNAc ASO conjugate and validation of its binding and functional activity underpins the applicability of the technique to oligonucleotide-based therapeutics.

Mutually Orthogonal Bioorthogonal Reactions: Selective Chemistries for Labeling Multiple Biomolecules Simultaneously.

Bioorthogonal click chemistry has played a transformative role in many research fields, including chemistry, biology, and medicine. Click reactions are crucial to produce increasingly complex bioconjugates, to visualize and manipulate biomolecules in living systems and for various applications in bioengineering and drug delivery. As biological (model) systems grow more complex, researchers have an increasing need for using multiple orthogonal click reactions simultaneously. In this review, we will introduce the most common bioorthogonal reactions and discuss their orthogonal use on the basis of their mechanism and electronic or steric tuning. We provide an overview of strategies to create reaction orthogonality and show recent examples of mutual orthogonal chemistry used for simultaneous biomolecule labeling. We end by discussing some considerations for the type of chemistry needed for labeling biomolecules in a system of choice.

Co-crosslinking strategy for dual functionalization of small magnetic nanoparticles with redox probes and biological probes.

Surface functionalization strategy is becoming a crucial bridge from magnetic nanoparticles (MNPs) to their broad bio-application. To realize the multiple functions of MNPs such as magnetic manipulation, target capture, and signal amplification in their use of electrochemical biosensing, co-crosslinking strategy was proposed here to construct dual-functionalized MNPs by combining ultra-sensitive redox moieties and specific biological probes. In this work, MNPs with a TEM size of 10 nm were synthesized by co-precipitation for amination and PEGylation to maintain colloid stability once dispersed in high-ionic-strength buffer (such as phosphate-buffered saline). Then, MNPs@IgG were prepared via the bis(sulfosuccinimidyl) suberate (BS3) cross-linker to conjugate these IgG onto the MNP surface, with a binding efficiency of 73%. To construct dual-functionalized MNPs, these redox probes of ferrocene-NHS (Fc) were co-crosslinked onto the MNP surface, together with IgG, by using BS3. The developed MNPs@Redox@IgG were characterized by SDS‒PAGE to identify IgG binding and by square wave voltammetry (SWV) to validate the redox signal. Additionally, the anti-CD63 antibodies were selected for the development of MNPs@anti-CD63 for use in the bio-testing of exosome sample capture. Therefore, co-crosslinking strategy paved a way to develop dual-functionalized MNPs that can be an aid of their potential utilization in diagnostic assay or electrochemical methods.