Bioconjugation with Maleimides: A Useful Tool for Chemical Biology

Residue-specific protein-glycan conjugation strategies for the development of pharmaceutically promising glycoconjugate vaccines: A recent update

Covalent coupling between a carbohydrate antigen and a protein carrier leads to the formation of pharmaceutically promising glycoconjugate vaccines. Most licensed glycoconjugate vaccines are acquired by random bioconjugation of native or sized glycans with the surface-exposed amino acid residues of proteins, such as lysine, cysteine, aspartic acid, glutamic amino acid, etc. In the last two decades, considerable momentum has been gained in the glycoconjugate vaccine development by discovering several residue-specific bioconjugation strategies. As a result, glycoconjugate chemistry reaches the verge of discovering well-defined and "real" homogeneous vaccines, which may be more potent to generate antimicrobial resistance against "bad-bugs". Through this literature survey, we intend to highlight the state of the art of residue-specific bioconjugation of proteins with glycans to obtain glycoconjugate vaccines. The review will also identify a potential roadmap to address the gap and the prospects in the medicinal domain.

Stoichiometric Control of Bismaleimide Conjugation of DNA to Silica Surfaces Through Quantitative Fluorescence Analysis of Thiolated DNA

Surface immobilization of DNA for biosensing or separations applications requires covalent attachment chemistry that is efficient, reproducible, and stable. In this work, an approach to link thiol-functionalized DNA to thiol-modified silica surfaces using N,N'-1,4-phenylene-bismaleimide is optimized by developing an efficient, one-pot synthesis of the maleimide-conjugated DNA followed by its immediate reaction with thiolated porous silica particles. The methodology takes advantage of a Michael addition reaction that couples a phenyl-bismaleimide cross-linking reagent and thiol-modified DNA to form a monomeric DNA-maleimide conjugate. The 1:1 stoichiometry of this reaction must be carefully controlled to avoid excess thiol-DNA, which generates unreactive bismaleimide-linked DNA dimers, or excess bismaleimide, which competes with the DNA-maleimide conjugate for reaction with the thiolated silica surface. To achieve control over the reaction forming the DNA conjugate, we adapt a fluorescence assay for free-thiols using 7-diethylamino-3-(4-maleimidophenyl)-4-methyl-coumarin (CPM) to determine the concentration of thiol-modified DNA that emerges from its synthesis, disulfide labeling, reduction to a thiol, and purification. The fluorescence response of the CPM reagent was calibrated using reduced glutathione as a standard, which allowed determination of the concentrations of thiolated-DNA and control over the stoichiometry of its reaction with a bismaleimide linker. The maleimide-conjugated DNA product thus formed was then reacted with thiolated-silica in order to bind the DNA to the internal surfaces of porous silica, whose surface populations were determined in individual particles by confocal Raman microscopy. Self-modeling curve resolution of the Raman spectra of surface-bound molecules validated the efficiency of the bismaleimide:thiolated DNA reaction, which provided stoichiometric control over formation of the monomeric DNA-maleimide conjugate and its optimized reaction with thiolated-silica surfaces.

Metal-free amination of alkenes based on maleimides

A metal-free amination of alkenes based on maleimides has been developed. This method features mild reaction conditions and broad substrate scope, and aminomaleimides with EWGs have been synthesized in up to 99% yield. The gram-scale reaction and successful derivatization of the products further demonstrate the applicability of this methodology.

Reversible Protein Labeling via Genetically Encoded Dithiolane-Containing Amino Acid and Organoarsenic Probes

Conventional protein labeling techniques often rely on irreversible covalent bonds, limiting dynamic control over protein modifications. Here, we present a reversible protein labeling strategy using genetically encoded dithiolane-containing amino acid (dtF) and organoarsenic conjugation chemistry. Using dithiarsolane dicarboxylic acid probe A2, we achieved near-quantitative labeling and ethanedithiol-mediated removal within 1 h at room temperature. A2 exhibited reduced toxicity with a 7-fold higher IC50 compared to arsenoxide, and its fluorescent derivative A2-FB showed no cytotoxicity up to 100 μM, enabling live-cell applications. This is the first demonstration of dithiol-arsenic chemistry at a single amino acid residue, providing a structural alternative to dicysteine motifs. Reversible labeling was validated in purified proteins (sfGFP-Y151dtF and MYO-K99dtF) and live Escherichia coli, offering a versatile tool for dynamic protein modifications and molecular tracking in biological systems.

Highly Enantioselective Organocatalytic Mannich Reaction of α-Benzylidene Succinimides with N-Boc Imines: Experimental and Theoretical Studies

The development of efficient and practical methods for the construction of chiral succinimide frameworks, which are the backbone of various natural products and widely studied in the field of pharmaceuticals, attracts considerable research attention. In this study, an asymmetric Mannich reaction of α-benzylidene succinimides with N-Boc imines was successfully performed using a bifunctional squaramide-type organocatalyst derived from quinine, affording the corresponding Mannich adduct with two contiguous stereocenters in high yields (up to 98%) with high diastereoselectivities (up to >20:1 dr) and excellent enantioselectivities (up to 99% ee). This protocol provides a direct approach to prepare chiral succinimide derivatives from simple starting material. Density Functional Theory (DFT) calculations with conformational search using an autosampling program revealed that the enantioselectivity profile was dominated by the deformation of the organocatalyst.

Peptide Multifunctionalization via Modular Construction of Trans-AB2C Porphyrin on Resin

Peptide multifunctionalization is a crucial technique to develop peptide-based agents for various purposes. Porphyrin-peptide conjugates are a class of popular multifunctional peptides renowned for their multifunctional and multimodal properties. However, the tedious synthetic works for porphyrin building blocks are involved in most previous studies. In this work, a modular solid-phase synthetic approach is reported to construct trans-AB2C porphyrin on peptide chains without presynthesized porphyrin building blocks. The products from this approach, which inherit both functionalities from the porphyrins and the modules employed for constructing porphyrins, show potential in biomedical and biomaterial applications. Furthermore, by extending this synthetic approach, the first example of "resin-to-resin" reaction is reported to link two peptides together along the construction of porphyrin motifs to give porphyrin-peptide conjugates with two different peptide chains.

Diverse reactivity of maleimides in polymer science and beyond

Maleimides are remarkably versatile functional groups, capable of participating in homo- and copolymerizations, Diels-Alder and (photo)cycloadditions, Michael additions, and other reactions. Their reactivity has afforded materials ranging from polyimides with high upper service temperatures to hydrogels for regenerative medicine applications. Moreover, maleimides have proven to be an enabling chemistry for pharmaceutical development and bioconjugation via straightforward modification of cysteine residues. To exert spatiotemporal control over reactions with maleimides, multiple approaches have been developed to photocage nucleophiles, dienes, and dipoles. Additionally, further substitution of the maleimide alkene (e.g., mono- and di-halo-, thio-, amino-, and methyl-maleimides, among other substituents) confers tunable reactivity and dynamicity, as well as responsive mechanical and optical properties. In this mini-review, we highlight the diverse functionality of maleimides, underscoring their notable impact in polymer science. This moiety and related heterocycles will play an important role in future innovations in chemistry, biomedical, and materials research.

Not So Bioorthogonal Chemistry

The advent of bioorthogonal chemistry has transformed scientific research, offering a powerful tool for selective and noninvasive labeling of (bio)molecules within complex biological environments. This innovative approach has facilitated the study of intricate cellular processes, protein dynamics, and interactions. Nevertheless, a number of challenges remain to be addressed, including the need for improved reaction kinetics, enhanced biocompatibility, and the development of a more diverse and orthogonal set of reactions. While scientists continue to search for veritable solutions, bioorthogonal chemistry remains a transformative tool with a vast potential for advancing our understanding of biology and medicine. This Perspective offers insights into reactions commonly classified as "bioorthogonal", which, however, may not always demonstrate the desired selectivity regarding the interactions between their components and the additives or catalysts used under the reaction conditions.

Metformin-encapsulating immunoliposomes conjugated with anti-TROP 2 antibody fragments for the active targeting of triple-negative breast cancer

Trophoblast cell-surface antigen 2 (TROP 2) has re-emerged as a promising biomarker in triple-negative breast cancer (TNBC), with high overexpression in many TNBC cases. However, despite its potential and approval as an antibody-drug-conjugate for TNBC treatment, TROP 2-targeted delivery systems are currently underexplored. Therefore, this study was aimed at exploiting the potential of TROP 2 targeting by encapsulating metformin (Met), an antidiabetic drug associated with tumor growth inhibitory properties, inside liposomes decorated with TROP 2-targeting single-chain variable fragments (scFvs). The optimization of scFv grafting resulted in Met-immunoliposomes with an average diameter of less than 200 nm, low polydispersity index (∼0.1), negative surface charge (<-10 mV), high Met drug loading (>150 mg g-1), and high affinity towards TROP 2 binding. Furthermore, Met-immunoliposomes were reproducible, and the scFv conjugation was stable in the presence of serum for five days. Their cellular uptake increased 4 folds in two-dimensional and 9 folds in three-dimensional TNBC models owing to the high affinity towards TROP 2 binding. Finally, it was observed that the therapeutic effect of Met in suppressing cancer cell growth and proliferation was superior when using anti-TROP 2 scFv-grafted Met-immunoliposomes, which completely stopped the spheroid growth and inhibited the expression of adenosine triphosphate. This study is one of the first reports to explore the combination of nanoparticle-based drug delivery systems to target the TROP 2 protein in TNBC, and to the best of our knowledge, this is the first report to specifically combine the use of scFvs with TROP 2 targeting to deliver therapeutics for TNBC treatment.

The Mysterious World of Non-Canonical Caps - What We Know and Why We Need New Sequencing Techniques

It was long believed that viral and eukaryotic mRNA molecules are capped at their 5' end solely by the N7-methylguanosine cap, which regulates various aspects of the RNA life cycle, from its biogenesis to its decay. However, the recent discovery of a variety of non-canonical RNA caps derived from metabolites and cofactors - such as NAD, FAD, CoA, UDP-glucose, UDP-N-acetylglucosamine, and dinucleoside polyphosphates - has expanded the known repertoire of RNA modifications. These non-canonical caps are found across all domains of life and can impact multiple aspects of RNA metabolism, including stability, translation initiation, and cellular stress responses. The study of these modifications has been facilitated by sophisticated methodologies such as liquid chromatography-mass spectrometry, which have unveiled their presence in both prokaryotic and eukaryotic organisms. The identification of these novel RNA caps highlights the need for advanced sequencing techniques to characterize the specific RNA types bearing these modifications and understand their roles in cellular processes. Unravelling the biological role of non-canonical RNA caps will provide insights into their contributions to gene expression, cellular adaptation, and evolutionary diversity. This review emphasizes the importance of these technological advancements in uncovering the complete spectrum of RNA modifications and their implications for living systems.

One-Step Maleimide-Based Dual Functionalization of Protein N-Termini

Maleimide derivatives are privileged reagents for chemically modifying proteins through the Michael addition reaction with cysteine due to their selectivity, operational simplicity, and commercial availability. However, since accessible free cysteine is rarely found in natural proteins, it is highly desirable to find alternative targets to enable direct bioconjugation of proteins with maleimides. In this study, we have developed an operationally simple and straightforward method for the N-terminal modification of proteins without the need for mutagenesis via a copper(II)-mediated [3+2] cycloaddition reaction with maleimides and 2-pyridinecarboxaldehyde (2-PCA) derivatives under non-denaturing conditions at pH 6 and 37 °C in aqueous media. Our method utilizes commercially available maleimides to attach diverse functionalities to various N-terminal amino acids. We demonstrate the preparation of a ternary protein complex cross-linked at the N-termini and dually modified trastuzumab equipped with monomethyl auristatin E (MMAE), a cytotoxic agent, and a Cy5 fluorophore (MMAE-Cy5-trastuzumab). MMAE-Cy5-trastuzumab retained human epidermal growth factor receptor 2 (HER2) recognition activity and exerted cytotoxicity against HER2-positive cells. Furthermore, MMAE-Cy5-trastuzumab allowed successful visualization of HER2-positive cancer cells in mouse tumors. This straightforward method will expand the accessibility of protein conjugates with well-defined structures in a wide range of research fields.

Cysteine-Specific 18F and NIR Dual Labeling of Peptides via Vinyltetrazine Bioorthogonal Conjugation for Molecular Imaging

Radiolabeled peptides are vital for positron emission tomography (PET) imaging, yet the 18F-labeling peptides remain challenging due to harsh conditions and time-consuming premodification requirements. Herein, we developed a novel vinyltetrazine-mediated bioorthogonal approach for highly efficient 18F-radiolabeling of a native peptide under mild conditions. This approach enabled radiosynthesis of various tumor-targeting PET tracers, including targeting the neurofibromin receptor (18F-P10a), the integrin αvβ3 (18F-P12a), and the platelet-derived growth factor receptor β (18F-ZPDGFRβ), with a radiochemical yield exceeding 90%. Preliminary evaluations revealed excellent hydrophilicity across these tracers, with 18F-P12a effectively visualizing integrin αvβ3 expression (tumor uptake: 1.57 ± 0.54%ID/g at 2 h). Additionally, we explored the potential for development of PET/near-infrared (NIR) dual-labeling agents using this method. The dual-modality agent 18F-Cy5-P12d enables specificity and colocalized imaging integrin αvβ3 expression (tumor uptake: 1.35 ± 0.24%ID/g at 2 h). Overall, this strategy offers a versatile platform for peptide radiolabeling and dual-modality agent development.

Dual-Performing Vinyltetrazine for Rapid, Selective Bioconjugation and Functionalization of Cysteine Proteins

Although methods for Cys-specific bioconjugation and functionalization of proteins have been developed and widely utilized in biomolecule engineering and therapeutic development, reagents for this purpose are generally designed to accomplish bioconjugation only. Consequently, additional clickable groups must be attached to these reagents to accomplish functionalization. Herein, we describe a new, simple, dual-performing bioconjugation-functionalization reagent, VMeTz, which possesses an electron-withdrawing tetrazine (Tz) substituted vinyl (V) moiety to serve as both a Michael receptor for selective conjugation with Cys and a site for click with TCO derivatives to introduce functionality. Critically, VMeTz contains a methyl group that prevents the formation of multiple Tz-containing Cys-adducts. Reactions of VMeTz with Cys-containing peptides and proteins both in vitro and in live cells produce single stable Michael adducts with high selectivity. Moreover, the Cys-VMeTz peptide and protein conjugates undergo facile click reactions with TCO-functionalized reagents for labeling and protein profiling. Furthermore, VMeTz selectively activates and delivers the TCO-caged toxic substances Dox and PROTAC ARV-771 to cancer cells to produce therapeutic effects that are comparable to those of the parent drugs. Collectively, the studies demonstrate that VMeTz is a useful reagent for therapeutically significant Cys-specific protein bioconjugation and functionalization.

Selective Protein (Post-)modifications through Dynamic Covalent Chemistry: Self-activated SNAr Reactions

SNAr reactions were remarkably accelerated using a pretargeting and activating unit based on dynamic covalent chemistry (DCvC). A Cys attack at the C-F bond on the aromatic ring of salicylaldehyde derivatives was only observed upon iminium formation with a neighboring Lys residue of model small peptides. Such self-activation was ascribed to the stronger electron-withdrawing capability of the iminium bond with respect to that of the parent aldehyde that stabilized the transition state of the reaction, together with the higher preorganization of the reactive groups in the cationic aldiminium species. This approach was further applied for the functionalization of two antibodies. In both cases, the presence of the aldehyde group in close proximity to the reactive C-F bond resulted in a noteworthy increase in bioconjugation yields, with excellent chemo-selectivity. Whereas the modification of an IgG1 antibody led to stochastic product distributions, microenvironment selectivity was noted when employing IgG4, in line with the lower number of Lys residues in the hinge region of the latter. Additionally, the postfunctionalization of the modified antibodies was attained through the dynamic covalent exchange of the tethered iminium derivative with hydrazides, representing an unprecedented "tag and modify" selective bioconjugation strategy based on DCvC.

Enantioselective Synthesis of Spiro[Indoline-3,4-Pyrrolo[3,4-b]Pyridines] Via an Organocatalysed Three-Component Cascade Reaction

Asymmetric synthesis of derivatives of spiro[indoline-3,4-pyrrolo[3,4-b]pyridines] were first developed through the organocatalytic cascade of Knoevenagel/Michael/cyclization reactions using a quinidine-derived squaramide. Under the optimized conditions, the three-component reactions of isatins, cyanoacetates, and 3-aminomaleimides yield the desired heterocycle-fused spirooxindoles in good yields (78-91 %) with 53 %-99 % enantiomeric excess (ee). Notably, this reaction enables a broad substrate scope under mild conditions and provides a convenient method for the enantioselective construction of diverse spirooxindoles combined with dihydropyridine and maleimide skeletons, which has great potential for the construction of new bioactive chemical entities.

Determination of degradation for sulfo-SIAB, SM(PEG)2, and sulfo-GMBS by RPLC-UV analysis

Bi-functional N-Hydroxysuccinimide (NHS) linkers are widely used in the conjugation processes linking an immunogen with a carrier protein capable of boosting immunity. A potential vaccine candidate against HIV-1, called fusion peptide (FP), is covalently linked to the recombinant tetanus toxoid heavy-chain fragment C (rTTHC) via this type of linker. A reversed-phase liquid chromatography (RPLC-UV) method was used to monitor the linker's degradation kinetics in various buffers, mimicking the steps in the conjugation process. The kinetics of the reactivities of the linkers are revealed in this study and can provide a good guidance to help effective conjugation process before these linkers are completely hydrolyze to the inactive degradants. Three cross-linkers degradation pathways were evaluated: Sulfosuccinimidyl (4-iodoacetyl) aminobenzoate (Sulfo-SIAB), PEGylated SMCC (SM(PEG)2), and N-γ-maleimidobutyryl-oxysulfosuccinimide ester (Sulfo-GMBS). We have reported kinetics for Sulfo-SIAB.

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.

Radio frequency gradient enhanced diffusion-edited semi-solid state NMR spectroscopy for detailed structural characterization of chemically modified hyaluronic acid hydrogels

Applications of functionalized hyaluronic acid (HA) hydrogels for numerous biomedical applications requires their detailed structural characterization. Since these materials are prepared by multistep chemical modifications in the solid phase and not amenable to characterization by standard analytical tools, we employed high-resolution solid-state NMR spectroscopy to gain detailed insights into the structures of the functionalized HA hydrogels. Divinyl sulfone crosslinked HA hydrogels were converted into maleimide-functionalized hydrogels, which were subjected to chemoselective thiol-maleimide reaction using L-cysteine as the protein mimetic thiol reagent. To overcome challenges associated with obtaining high-resolution NMR spectra of crosslinked hydrogels (such as line broadening and overlapping of signals of the hydrogel with those of residual reagents and solvents used during multi-step reaction processes on insoluble polymer matrices), we devised a radio frequency mediated diffusion-edited semi solid-state NMR technique. This technique enabled us to record NMR spectra of hydrogels exclusively by effectively suppressing signals associated with low molecular weight impurities. Thus, it became possible to perform in-depth characterization of these chemically modified HA hydrogels including quantification of reaction outcome for each reaction step.

A platform for mapping reactive cysteines within the immunopeptidome

The major histocompatibility complex class I antigen presentation pathways play pivotal roles in orchestrating immune responses. Recent studies have begun to explore the therapeutic potential of cysteines within the immunopeptidome, such as the use of covalent ligands to generate haptenated peptide neoepitopes for immunotherapy. In this work, we report a platform for mapping reactive cysteines on MHC-I-bound peptide antigens. We develop cell-impermeable sulfonated maleimide probes capable of capturing reactive cysteines on these antigens. Using these probes in chemoproteomic experiments, we discover that cysteines on MHC-I-bound antigens exhibit various degrees of reactivity. Moreover, interferon-gamma stimulation enhances the reactivity of cysteines at position 8 of 9-mer MHC-I-bound antigens. Finally, we demonstrate that targeting reactive cysteines on MHC-I-bound antigens with a maleimide-conjugated Fc-binding cyclic peptide contributes to the induction of antibody-dependent cellular phagocytosis.

Computational identification of PDL1 inhibitors and their cytotoxic effects with silver and gold nanoparticles

Immunotherapy is a promising treatment for cancer that aims to boost the immune system's response to cancer cells. This can be achieved by blocking Programmed cell death protein 1/Programmed death-ligand 1 (PD1/PDL1), which activates T cells. In this work, the aim was to find high-affinity drugs against PDL1 using computational tools and conjugate nanoparticles with them. The cytotoxic activity of the nanoparticle conjugated drugs was then tested. The screening of 100,000 drugs from the ZINC database and FDA-approved drugs was done computationally. The physicochemical properties and toxicity of the drugs were analyzed using SwissADME and ProTox-II, respectively. Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were synthesized using extracts of Catharanthus roseus flowers and Juglans regia shells, respectively. The characterization of AgNPs and AuNPs was performed using UV-Vis spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Their conjugation with the drugs Irinotecan, Imatinib, and Methotrexate was also confirmed using UV-Vis, FTIR, and Dynamic light scattering (DLS). The top screened drugs were ZINC1098661 and 3 FDA-approved drugs (Irinotecan, Imatinib, and Methotrexate). Docking studies revealed that Irinotecan had the highest binding affinity towards PDL1 when conjugated with silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs). The Irinotecan-PDL1 complex was confirmed as the most stable through molecular dynamics simulations. The result of the methylthiazol tetrazolium (MTT) assay showed that conjugated AgNPs and AuNPs with Irinotecan had a higher toxic effect on the A549 cancer cell line than AgNPs and AuNPs conjugated with Imatinib. This study provides a promising avenue for further investigation and development of nanoparticle-drug conjugates as a potential cancer immunotherapy strategy.

Fast and Selective Cysteine Conjugation Using para-Quinone Methides

An efficient and selective method for cysteine conjugation utilizing para-quinone methides (p-QMs) was developed. p-QM labeling exhibits high specificity toward the cysteine residue, as evidenced by its reactivity with various amino acid derivatives, peptides, and proteins. Notably, the p-QM-cysteine reactions display robust kinetics with rate constants up to 1.67 × 104 M-1·s-1. Furthermore, p-QM conjugation enables us to attach a fluorescent probe to a HER2 nanobody, resulting in selective labeling of HER2-positive SK-BR-3 cells.

The future of genetic medicines delivered via targeted lipid nanoparticles to leukocytes

Genetic medicines hold vast therapeutic potential, offering the ability to silence or induce gene expression, knock out genes, and even edit DNA fragments. Applying these therapeutic modalities to leukocytes offers a promising path for treating various conditions yet overcoming the obstacles of specific and efficient delivery to leukocytes remains a major bottleneck in their clinical translation. Lipid nanoparticles (LNPs) have emerged as the leading delivery system for nucleic acids due to their remarkable versatility and ability to improve their in vivo stability, pharmacokinetics, and therapeutic benefits. Equipping LNPs with targeting moieties can promote their specific cellular uptake and internalization to leukocytes, making targeted LNPs (tLNPs) an inseparable part of developing leukocyte-targeted gene therapy. However, despite the significant advancements in research, genetic medicines for leukocytes using targeted delivery approaches have not been translated into the clinic yet. Herein, we discuss the important aspects of designing tLNPs and highlight the considerations for choosing an appropriate bioconjugation strategy and targeting moiety. Furthermore, we provide our insights on limiting challenges and identify key areas for further research to advance these exciting therapies for patient care.

Astatine-211 radiolabelling chemistry: from basics to advanced biological applications

BACKGROUND

211At-radiopharmaceuticals are currently the subject of growing studies for targeted alpha therapy of cancers, which leads to the widening of the scope of the targeting vectors, from small molecules to peptides and proteins. This has prompted, during the past decade, to a renewed interest in developing novel 211At-labelling approaches and novel prosthetic groups to address the diverse scenarios and to reach improved efficiency and robustness of procedures as well as an appropriate in vivo stability of the label.

MAIN BODY

Translated from the well-known (radio)iodine chemistry, the long preferred electrophilic astatodemetallation using trialkylaryltin precursors is now complemented by new approaches using electrophilic or nucleophilic At. Alternatives to the astatoaryl moiety have been proposed to improve labelling stability, and the range of prosthetic groups available to label proteins has expanded.

CONCLUSION

In this report, we cover the evolution of radiolabelling chemistry, from the initial strategies developed in the late 1970's to the most recent findings.

Chemical Stability of mRNA/cDNA Complexes: Defining the Limits of mRNA Display

Messenger RNA (mRNA) display is being increasingly adopted for peptide drug candidate discovery. While many conditions have been reported for the affinity enrichment step and in some cases for peptide modification, there is still limited understanding about the versatility of peptide-puromycin-mRNA/cDNA (complementary DNA) complexes. This work explores the chemical stability of mRNA/cDNA hybrid complexes under a range of different fundamental chemical conditions as well as with peptide modification conditions reported in an mRNA display setting. We further compare the stability of full complexes originating from two different mRNA display systems (RaPID and cDNA-TRAP). Overall, these complexes were found to be stable under a broad range of conditions, with some edge conditions benefitting from encoding directly in cDNA rather than mRNA. This should allow for more and broader exploitation of late-stage peptide modification chemistry in mRNA display, with confidence regarding the stability of encoding, and potentially better hit-finding campaigns as a result.

Peptide and Protein Cysteine Modification Enabled by Hydrosulfuration of Ynamide

Efficient functionalization of peptides and proteins has widespread applications in chemical biology and drug discovery. However, the chemoselective and site-selective modification of proteins remains a daunting task. Herein, a highly efficient chemo-, regio-, and stereoselective hydrosulfuration of ynamide was identified as an efficient method for the precise modification of peptides and proteins by uniquely targeting the thiol group of cysteine (Cys) residues. This novel method could be facilely operated in aqueous buffer and was fully compatible with a wide range of proteins, including small model proteins and large full-length antibodies, without compromising their integrity and functions. Importantly, this reaction provides the Z-isomer of the corresponding conjugates exclusively with superior stability, offering a precise approach to peptide and protein therapeutics. The potential application of this method in peptide and protein chemical biology was further exemplified by Cys-bioconjugation with a variety of ynamide-bearing functional molecules such as small molecule drugs, fluorescent/affinity tags, and PEG polymers. It also proved efficient in redox proteomic analysis through Cys-alkenylation. Overall, this study provides a novel bioorthogonal tool for Cys-specific functionalization, which will find broad applications in the synthesis of peptide/protein conjugates.

Catalyst-Free, Three-Component Synthesis of Amidinomaleimides

Maleimide and amidine functionalities often appear in medicinal and natural product targets. We describe a catalyst-free, three-component coupling reaction for the synthesis of amidinomaleimides. This one-pot reaction fuses a broad range of secondary amines and aldehydes with azidomaleimides. The conditions are mild, simple, modular, high yielding, and amenable to aqueous solvents. Most reaction products can be sufficiently purified without column chromatography. The synthesis creates complex, multifunctional molecules with four different molecules, including a tripeptide, arrayed around an amidinomaleimide core.

Patterned graphene oxide via one-step thermal annealing for controlling collective cell migration

Graphene oxide (GO) is a two-dimensional metastable nanomaterial. Interestingly, GO formed oxygen clusterings in addition to oxidized and graphitic phases during the low-temperature thermal annealing process, which could be further used for biomolecule bonding. By harnessing this property of GO, we created a bio-interface with patterned structures with a common laboratory hot plate that could tune cellular behavior by physical contact. Due to the regional distribution of oxygen clustering at the interface, we refer to it as patterned annealed graphene oxide (paGO). In addition, since the paGO was a heterogeneous interface and bonded biomolecules to varying degrees, arginine-glycine-aspartic acid (RGD) was modified on it and successfully regulated cellular-directed growth and migration. Finally, we investigated the FRET phenomenon of this heterogeneous interface and found that it has potential as a biosensor. The paGO interface has the advantages of easy regulation and fabrication, and the one-step thermal reduction method is suitable for biological applications. We believe that this low-temperature thermal annealing method would make GO interfaces more accessible, especially for the development of nano-interfacial modifications for biological applications, revealing its potential for biomedical applications.

Cell-penetrating peptides with nanoparticles hybrid delivery vectors and their uptake pathways

Cell-penetrating peptides (CPPs) are molecules that improve the cellular uptake of various molecular payloads that do not easily traverse the cellular membrane. CPPs can be found in pharmaceutical and medical products. The vast majority of cell-penetrating chemicals that are discussed in published research are peptide based. The paper also delves into the various applications of hybrid vectors. Because CPPs are able to carry cargo across the cellular membrane, they are a viable candidate for use as a suitable carrier for a wide variety of cargoes, such as siRNA, nanoparticles, and others. In which we discuss the CPPs, their classification, uptake mechanisms, hybrid vector systems, nanoparticles and their uptake mechanisms, etc. Further in this paper, we discuss CPPs conjugated to Nanoparticles, Combining CPPs with lipids and polymeric Nanoparticles in A Conjugated System, CPPs conjugated to nanoparticles for therapeutic purposes, and potential therapeutic uses of CPPs as delivery molecules. Also discussed the preclinical and clinical use of CPPS, intracellular trafficking of nanoparticles, and activatable and bioconjugated CPPs.

Two-photon Dye-Based Fluorogenic Organic Nanoparticles as Intracellular Thiols Sensors

Optical bioimaging is an ever-growing field that benefits both from the fast progress of optical instrumentation and modalities, and from the development of light-emitting probes. The efficacy of molecular fluorescent dyes is crucial, yet hindered by limited brightness and hydrophilicity. Addressing these challenges, self-stabilized fluorogenic organic nanoparticles only made of pure dyes (dFONs) are introduced in this work. Comprising thiol-sensitive fluorogenic chromophores, these dFONs exhibit enhanced brightness exclusively in the presence of biological thiols, notably glutathione, overcoming the need for water-solubilizing moieties. Importantly, these nanoparticles demonstrate large fluorescence and one- and two-photon brightness, enabling sensitive bioimaging of intracellular thiols at micromolar concentrations. Notably, only the pristine fluorogenic nanoparticles can penetrate the cells and does not require to wash the cells before imaging, emphasizing their unique role as dye carriers, fluorogenic probes and ease of use. This work highlights the transformative potential of dFONs in advancing optical bioimaging, paving the way for the use of dFONs not just as tracers, but also now as biosensors and ultimately in the future as biomarkers.

Bioactive Hydrogels Based on Tyramine and Maleimide Functionalized Dextran for Tissue Engineering Applications

Hydrogels are widely used in tissue engineering due to their ability to form three-dimensional (3D) structures that support cellular functions and mimic the extracellular matrix (ECM). Despite their advantages, dextran-based hydrogels lack intrinsic biological activity, limiting their use in this field. Here, we present a strategy for developing bioactive hydrogels through sequential thiol-maleimide bio-functionalization and enzyme-catalyzed crosslinking. The hydrogel network is formed through the reaction of tyramine moieties in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2), allowing for tunable gelation time and stiffness by adjusting H2O2 concentrations. Maleimide groups on the hydrogel backbone enable the coupling of thiol-containing bioactive molecules, such as arginylglycylaspartic acid (RGD) peptides, to enhance biological activity. We examined the effects of hydrogel stiffness and RGD concentration on human mesenchymal stem cells (hMSCs) during differentiation and found that hMSCs encapsulated within these hydrogels exhibited over 88% cell viability on day 1 across all conditions, with a slight reduction to 60-81% by day 14. Furthermore, the hydrogels facilitated adipogenic differentiation, as evidenced by positive Oil Red O staining. These findings demonstrate that DexTA-Mal hydrogels create a biocompatible environment that is conducive to cell viability and differentiation, offering a versatile platform for future tissue engineering applications.

Exploring 2-Sulfonylpyrimidine Warheads as Acrylamide Surrogates for Targeted Covalent Inhibition: A BTK Story

Targeted covalent inhibitors (TCIs) directing cysteine have historically relied on a narrow set of electrophilic "warheads". While Michael acceptors remain at the forefront of TCI design strategies, they show variable stability and selectivity under physiological conditions. Here, we show that the 2-sulfonylpyrimidine motif is an effective replacement for the acrylamide warhead of Ibrutinib, for the inhibition of Bruton's tyrosine kinase. In a few iterations, we discovered new derivatives, which inhibit BTK both in vitro and in cellulo at low nanomolar concentrations, on par with Ibrutinib. Several derivatives also displayed good plasma stability and reduced off-target binding in vitro across 135 tyrosine kinases. This proof-of-concept study on a well-studied kinase/TCI system highlights the 2-sulfonylpyrimidine group as a useful acrylamide replacement. In the future, it will be interesting to investigate its wider potential for developing TCIs with improved pharmacologies and selectivity profiles across structurally related protein families.

Dual-Action Protein-siRNA Conjugates for Targeted Disruption of CD47-Signal Regulatory Protein α Axis in Cancer Therapy

A series of successes in RNA interference (RNAi) therapies for liver diseases using lipid nanoparticles and N-acetylgalactosamine have heralded a current era of RNA therapeutics. However, alternative delivery strategies are required to take RNAi out of the comfort zone of hepatocytes. Here we report SIRPα IgV/anti-CD47 siRNA (vS-siCD47) conjugates that selectively and persistently disrupt the antiphagocytic CD47/SIRPα axis in solid tumors. Conjugation of the SIRPα IgV domain protein to siRNAs enables tumor dash through CD47-mediated erythrocyte piggyback, primarily blocking the physical interaction between CD47 on cancer cells and SIRPα on phagocytes. After internalization of the vS-siCD47 conjugates within cancer cells, the detached free-standing anti-CD47 siRNAs subsequently attack CD47 through the RNAi mechanism. The dual-action approach of the vS-siCD47 conjugate effectively overcomes the "don't eat me" barrier and stimulates phagocyte-mediated tumor destruction, demonstrating a highly selective and potent CD47-blocking immunotherapy. This delivery strategy, employing IgV domain protein-siRNA conjugates with a dual mode of target suppression, holds promise for expanding RNAi applications beyond hepatocytes and advancing RNAi-based cancer immunotherapies for solid tumors.

Advancing Nitrile-Aminothiol Strategy for Dual and Sequential Bioconjugation

Nitrile-aminothiol conjugation (NATC) stands out as a promising biocompatible ligation technique due to its high chemo-selectivity. Herein we investigated the reactivity and substrate scope of NAT conjugation chemistry, thus developing a novel pH dependent orthogonal NATC as a valuable tool for chemical biology. The study of reaction kinetics elucidated that the combination of heteroaromatic nitrile and aminothiol groups led to the formation of an optimal bioorthogonal pairing, which is pH dependent. This pairing system was effectively utilized for sequential and dual conjugation. Subsequently, these rapid (≈1 h) and high yield (>90 %) conjugation strategies were successfully applied to a broad range of complex biomolecules, including oligonucleotides, chelates, small molecules and peptides. The effectiveness of this conjugation chemistry was demonstrated by synthesizing a fluorescently labelled antimicrobial peptide-oligonucleotide complex as a dual conjugate to imaging in live cells. This first-of-its-kind sequential NATC approach unveils unprecedented opportunities in modern chemical biology, showcasing exceptional adaptability in rapidly creating structurally complex bioconjugates. Furthermore, the results highlight its potential for versatile applications across fundamental and translational biomedical research.

Conjugating Hemoglobin and Albumin by Strain-Promoted Azide- Alkyne Cycloaddition

A one-to-one conjugate of cross-linked human hemoglobin and human serum albumin results from a strain-promoted alkyne-azide cycloaddition (SPAAC) of the modified proteins. Additions of a strained alkyne-substituted maleimide to the Cys-34 thiol of human serum albumin and an azide-containing cross-link between the amino groups of each β-unit at Lys-82 of human hemoglobin provide sites for coupling by the SPAAC process. The coupled hemoglobin-albumin conjugate can be readily purified from unreacted hemoglobin. The oxygen binding properties of the two-protein bioconjugate demonstrate oxygen affinity and cooperativity that are suitable for use in an acellular oxygen carrier.

Antibody Drug Conjugates for Cancer Therapy: From Metallodrugs to Nature-Inspired Payloads

This review highlights significant advancements in antibody-drug conjugates (ADCs) equipped with metal-based and nature-inspired payloads, focusing on synthetic strategies for antibody conjugation. Traditional methods such us maleimide and succinimide conjugation and classical condensation reactions are prevalent for metallodrugs and natural compounds. However, emerging non-conventional strategies such as photoconjugation are gaining traction due to their milder conditions and, in an aspect which minimizes side reactions, selective formation of ADC. The review also summarizes the therapeutic and diagnostic properties of these ADCs, highlighting their enhanced selectivity and reduced side effects in cancer treatment compared to non-conjugated payloads. ADCs combine the specificity of monoclonal antibodies with the cytotoxicity of chemotherapy drugs, offering a targeted approach to the elimination of cancer cells while sparing healthy tissues. This targeted mechanism has demonstrated impressive clinical efficacy in various malignancies. Key future advancements include improved linker technology for enhanced stability and controlled release of cytotoxic agents, incorporation of novel, more potent, cytotoxic agents, and the identification of new cancer-specific antigens through genomic and proteomic technologies. ADCs are also expected to play a crucial role in combination therapies with immune checkpoint inhibitors, CAR-T cells, and small molecule inhibitors, leading to more durable and potentially curative outcomes. Ongoing research and clinical trials are expanding their capabilities, paving the way for more effective, safer, and personalized treatments, positioning ADCs as a cornerstone of modern medicine and offering new hope to patients.

Fluorinated Tags to Study Protein Conformation and Interactions Using 19F NMR

The incorporation of fluorine atoms into a biomacromolecule provides a background-free and environmentally sensitive reporter of structure, conformation and interactions using 19F NMR. There are several methods to introduce the 19F reporter - either by synthetic incorporation via solid phase peptide synthesis; by suppressing the incorporation or biosynthesis of a natural amino acid and supplementing the growth media with a fluorinated counterpart during protein expression; and by genetic code expansion to add new amino acids to the amino acid alphabet. This review aims to discuss progress in the field of introducing fluorinated handles into biomolecules for NMR studies by post-translational bioconjugation or 'fluorine-tagging'. We will discuss the range of chemical tagging 'warheads' that have been used, explore the applications of fluorine tags, discuss ways to enhance reporter sensitivity and how the signal to noise ratios can be boosted. Finally, we consider some key challenges of the field and offer some ideas for future directions.

On-Demand Thio-Succinimide Hydrolysis for the Assembly of Stable Protein-Protein Conjugates

Chemical post-translational protein-protein conjugation is an important technique with growing applications in biotechnology and pharmaceutical research. Maleimides represent one of the most widely employed bioconjugation reagents. However, challenges associated with the instability of first- and second-generation maleimide technologies are yet to be fully addressed. We report the development of a novel class of maleimide reagents that can undergo on-demand ring-opening hydrolysis of the resulting thio-succinimide. This strategy enables rapid post-translational assembly of protein-protein conjugates. Thio-succinimide hydrolysis, triggered upon application of chemical, photochemical, or enzymatic stimuli, allowed homobifunctional bis-maleimide reagents to be applied in the production of stable protein-protein conjugates, with complete temporal control. Bivalent and bispecific protein-protein dimers constructed from small binders targeting antigens of oncological importance, PD-L1 and HER2, were generated with high purity, stability, and improved functionality compared to monomeric building blocks. The modularity of the approach was demonstrated through elaboration of the linker moiety through a bioorthogonal propargyl handle to produce protein-protein-fluorophore conjugates. Furthermore, extending the functionality of the homobifunctional reagents by temporarily masking reactive thiols included in the linker allowed the assembly of higher order trimeric and tetrameric single-domain antibody conjugates. The potential for the approach to be extended to proteins of greater biochemical complexity was demonstrated in the production of immunoglobulin single-domain antibody conjugates. On-demand control of thio-succinimide hydrolysis combined with the facile assembly of chemically defined homo- and heterodimers constitutes an important expansion of the chemical methods available for generating stable protein-protein conjugates.

Thermoreversible [2 + 2] Photodimers of Monothiomaleimides and Intrinsically Recyclable Covalent Networks Thereof

The development of intrinsically recyclable cross-linked materials remains challenged by the inherently unfavorable chemical equilibrium that dictates the efficiency of the reversible covalent bonding/debonding chemistry. Rather than having to (externally) manipulate the bonding equilibrium, we here introduce a new reversible chemistry platform based on monosubstituted thiomaleimides that can undergo complete and independent light-activated covalent bonding and on-demand thermal debonding above 120 °C. Specifically, repeated bonding/debonding of a small-molecule thiomaleimide [2 + 2] photodimer is demonstrated over five heat/light cycles with full conversion in both directions, thereby regenerating its initial monothiomaleimide constituents. This motivated the synthesis of multifunctional thiomaleimide reagents as precursors for the design of covalently cross-linked networks that display intrinsic switching between a monomeric and polymeric state. The resulting materials are shown to covalently dissociate and depolymerize upon heating both in solution and in bulk, thus transforming the densely photo-cross-linked material back into a viscous liquid. Temperature-regulated photorheology evidenced the intrinsic recyclability of the thiomaleimide-based thermosets during multiple cycles of UV cross-linking and thermal de-cross-linking. The thermally reversible photodimerization of thiomaleimides presents a new addition to the designer playground of dynamic polymer networks, providing interesting opportunities for the reprocessing and closed-loop recycling of covalently cross-linked materials.

Facile Access to Branched Multispecific Proteins

Approaches that leverage orthogonal chemical reactions to generate protein-protein conjugates have expanded access to bespoke chimeras. Although the literature is replete with examples of the semisynthesis of bispecific proteins, few methods exist for the semisynthesis of protein conjugates of higher complexity (i.e., greater than two-protein fusions). The recent emergence of trispecific cell engagers for immune cell redirection therapies necessitates the development of chemical methods for the construction of trispecific proteins that would otherwise be inaccessible via natural protein synthesis. Here, we demonstrate that 3-bromo-5-methylene pyrrolone (3Br-5MP) can be used to effect the facile chemical synthesis of trispecific peptides and proteins with exquisite control over the addition of each monomer. The multimeric complexes maintain epitope functionality both in human cells and upon immobilization. We anticipate that facile access to trispecific proteins using this 3Br-5MP will have broad utility in basic science research and will quicken the pace of research to establish novel, multimeric immune cell redirection therapies.

Long-distance tmFRET using bipyridyl- and phenanthroline-based ligands

With the great progress on determining protein structures over the last decade comes a renewed appreciation that structures must be combined with dynamics and energetics to understand function. Fluorescence spectroscopy, specifically Förster resonance energy transfer (FRET), provides a great window into dynamics and energetics due to its application at physiological temperatures and ability to measure dynamics on the ångström scale. We have recently advanced transition metal FRET (tmFRET) to study allosteric regulation of maltose binding protein and have reported measurements of maltose-dependent distance changes with an accuracy of ∼1.5 Å. When paired with the noncanonical amino acid Acd as a donor, our previous tmFRET acceptors were useful over a working distance of 10 to 20 Å. Here, we use cysteine-reactive bipyridyl and phenanthroline compounds as chelators for Fe2+ and Ru2+ to produce novel tmFRET acceptors to expand the working distance to as long as 50 Å, while preserving our ability to resolve even small maltose-dependent changes in distance. We compare our measured FRET efficiencies to predictions based on models using rotameric ensembles of the donors and acceptors to demonstrate that steady-state measurements of tmFRET with our new probes have unprecedented ability to measure conformational rearrangements under physiological conditions.

"Target-and-release" nanoparticles for effective immunotherapy of metastatic ovarian cancer

Immunotherapies such as checkpoint inhibitors (CPI) are effective in treating several advanced cancers, but these treatments have had limited success in metastatic ovarian cancer (OC). Here, we engineered liposomal nanoparticles (NPs) carrying a layer-by-layer (LbL) polymer coating that promotes their binding to the surface of OC cells. Covalent anchoring of the potent immunostimulatory cytokine interleukin-12 (IL-12) to phospholipid headgroups of the liposome core enabled the LbL particles to concentrate IL-12 in disseminated OC tumors following intraperitoneal administration. Shedding of the LbL coating and serum protein-mediated extraction of IL-12-conjugated lipids from the liposomal core over time enabled IL-12 to disseminate in the tumor bed following rapid NP localization in tumor nodules. Optimized IL-12 LbL-NPs promoted robust T cell accumulation in ascites and tumors in mouse models, extending survival compared to free IL-12 and remarkedly sensitizing tumors to CPI, leading to curative treatments and immune memory.

Maleimide functionalized polycaprolactone micelles for glutathione quenching and doxorubicin delivery

High glutathione production is known to be one of the defense mechanisms by which many cancer cells survive elevated oxidative stress. By explicitly targeting glutathione in these cancer cells and diminishing its levels, oxidative stress can be intensified, ultimately triggering apoptosis or programmed cell death. Herein, we developed a novel approach by creating maleimide-functionalized polycaprolactone polymers, specifically using 2,3-diiodomaleimide functionality to reduce the level of glutathione in cancer cells. Polycaprolactone was chosen to conjugate the 2,3-diiodomaleimide functionality due to its biodegradable and biocompatible properties. The amphiphilic block copolymer was synthesized using PEG as a macroinitiator to make corresponding polymeric micelles. The resulting 2,3-diiodomaleimide-conjugated polycaprolactone micelles effectively quenched glutathione, even at low concentrations (0.01 mg mL-1). Furthermore, we loaded these micelles with the anticancer drug doxorubicin (DOX), which exhibited pH-dependent drug release. We obtained a loading capacity (LC) of 3.5% for the micelles, one of the highest LC reported among functional PCL-based micelles. Moreover, the enhanced LC doesn't affect their release profile. Cytotoxicity experiments demonstrated that empty and DOX-loaded micelles inhibited cancer cell growth, with the DOX-loaded micelles displaying the highest cytotoxicity. The ability of the polymer to quench intracellular GSH was also confirmed. This approach of attaching maleimide to polycaprolactone polymers shows promise in depleting elevated glutathione levels in cancer cells, potentially improving cancer treatment efficacy.

DOTA-Based Plectin-1 Targeted Contrast Agent Enables Detection of Pancreatic Cancer in Human Tissue

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive and lethal malignancy with extremely poor patient survival rates. A key reason for the poor prognosis is the lack of effective diagnostic tools to detect the disease at curable, premetastatic stages. Tumor surgical resection is PDAC's first-line treatment, however distinguishing between cancerous and healthy tissue with current imaging tools remains a challenge. In this work, we report a DOTA-based fluorescent probe targeting plectin-1 for imaging PDAC with high specificity. To enable heterogeneous functionalization of the DOTA-core with multiple targeting peptide units and the fluorophore, a novel, fully clickable synthetic route that proceeds in one pot was developed. Extensive validation of the probe set the stage for PDAC detection in mice and human tissue. Altogether, these findings may pave the way for improved clinical understanding and early detection of PDAC progression as well as more accurate resection criteria.

Reversible Chemical Modification of Antibody Effector Function Mitigates Unwanted Systemic Immune Activation

Antibody effector functions including antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) are mediated through the interaction of the antibody Fc region with Fcγ receptors present on immune cells. Several approaches have been used to modulate antibody Fc-Fcγ interactions with the goal of driving an effective antitumor immune response, including Fc point mutations and glycan modifications. However, robust antibody-Fcγ engagement and immune cell binding of Fc-enhanced antibodies in the periphery can lead to the unwanted induction of systemic cytokine release and other dose-limiting infusion-related reactions. Creating a balance between effective engagement of Fcγ receptors that can induce antitumor activity without incurring systemic immune activation is an ongoing challenge in the field of antibody and immuno-oncology therapeutics. Herein, we describe a method for the reversible chemical modulation of antibody-Fcγ interactions using simple poly(ethylene glycol) (PEG) linkers conjugated to antibody interchain disulfides with maleimide attachments. This method enables dosing of a therapeutic with muted Fcγ engagement that is restored in vivo in a time-dependent manner. The technology was applied to an effector function enhanced agonist CD40 antibody, SEA-CD40, and experiments demonstrate significant reductions in Fc-induced immune activation in vitro and in mice and nonhuman primates despite showing retained efficacy and improved pharmacokinetics compared to the parent antibody. We foresee that this simple, modular system can be rapidly applied to antibodies that suffer from systemic immune activation due to peripheral FcγR binding immediately upon infusion.

Advances in organocatalyzed synthesis of organic compounds

The recent advancements in utilizing organocatalysts for the synthesis of organic compounds have been described in this review by focusing on their simplicity, effectiveness, reproducibility, and high selectivity which lead to excellent product yields. The organocatalytic methods for various derivatives, such as indoles, pyrazolones, anthrone-functionalized benzylic amines, maleimide, polyester, phthalimides, dihydropyrimidin, heteroaryls, N-aryl benzimidazoles, stilbenoids, quinazolines, quinolines, and oxazolidinones have been specifically focused. The review provides more understanding by delving into potential reaction mechanisms. We anticipate that this collection of data and findings on successful synthesis of diverse compound derivatives will serve as valuable resources and stimulating current and future research efforts in organocatalysis and industrial chemistry.

Impact of drug-linker on method selection for analytical characterization and purification of antibody-drug conjugates

In addition to traditional characterisation methods of hydrophobic interaction (HIC) and reverse phase (RP) chromatography, an anion exchange chromatography (AIEX) was developed to analyse and purify antibody drug conjugates (ADCs). Since different drug antibody ratio (DAR) species may impact biological activity, therapeutic index, PK parameters or even potential immunogenicity, homogenous ADC DAR demands have been significantly increasing. To accelerate linker designs, drug screening and ADC DAR purification for in vitro and in vivo studies, we built the analytical toolbox including HIC, RP, AIEX, icIEF, SEC, and MS for downstream ADC DAR purification using HIC and AIEX. The established analytical methods can quickly assess the quality of ADC DAR profiles and provide important information to select the proper ADC DAR purification method. Since drug-linker structures can significantly affect ADC physicochemical properties, and highly impact on selections of analytical methods, we applied both HIC and AIEX characterisation and purification platforms to achieve ADC DAR homogenous. Our experiments also implied that unlike HIC, AIEX could be used to separate DAR4 positional isomers.

Thermally Triggered Triazolinedione-Tyrosine Bioconjugation with Improved Chemo- and Site-Selectivity

A bioconjugation strategy is reported that allows the derivatization of tyrosine side chains through triazolinedione-based "Y-clicking". Blocked triazolinedione reagents were developed that, in contrast to classical triazolinedione reagents, can be purified before use, can be stored for a long time, and allow functionalization with a wider range of cargoes and labels. These reagents are bench-stable at room temperature but steadily release highly reactive triazolinediones upon heating to 40 °C in buffered media at physiological pH, showing a sharp temperature response over the 0 to 40 °C range. This conceptually interesting strategy, which is complementary to existing photo- or electrochemical bioorthogonal bond-forming methods, not only avoids the classical synthesis and handling difficulties of these highly reactive click-like reagents but also markedly improves the selectivity profile of the tyrosine conjugation reaction itself. It avoids oxidative damage and "off-target" tryptophan labeling, and it even improves site-selectivity in discriminating between different tyrosine side chains on the same protein or different polypeptide chains. In this research article, we describe the stepwise development of these reagents, from their short and modular synthesis to small-molecule model bioconjugation studies and proof-of-principle bioorthogonal chemistry on peptides and proteins.

Ultrafast Au(III)-Mediated Arylation of Cysteine

Through mechanistic work and rational design, we have developed the fastest organometallic abiotic Cys bioconjugation. As a result, the developed organometallic Au(III) bioconjugation reagents enable selective labeling of Cys moieties down to picomolar concentrations and allow for the rapid construction of complex heterostructures from peptides, proteins, and oligonucleotides. This work showcases how organometallic chemistry can be interfaced with biomolecules and lead to a range of reactivities that are largely unmatched by classical organic chemistry tools.

Non-symmetric stapling of native peptides

Stapling has emerged as a powerful technique in peptide chemistry. It enables precise control over peptide conformation leading to enhanced properties such as improved stability and enhanced binding affinity. Although symmetric stapling methods have been extensively explored, the field of non-symmetric stapling of native peptides has received less attention, largely as a result of the formidable challenges it poses - in particular the complexities involved in achieving the high chemo-selectivity and site-selectivity required to simultaneously modify distinct proteinogenic residues. Over the past 5 years, there have been significant breakthroughs in addressing these challenges. In this Review, we describe the latest strategies for non-symmetric stapling of native peptides, elucidating the protocols, reaction mechanisms and underlying design principles. We also discuss current challenges and opportunities this field offers for future applications, such as ligand discovery and peptide-based therapeutics.

ICLAMP: a novel technique to explore adenosine deamination via inosine chemical labeling and affinity molecular purification

Recent developments in sequencing and bioinformatics have advanced our understanding of adenosine-to-inosine (A-to-I) RNA editing. Surprisingly, recent analyses have revealed the capability of adenosine deaminase acting on RNA (ADAR) to edit DNA:RNA hybrid strands. However, edited inosines in DNA remain largely unexplored. A precise biochemical method could help uncover these potentially rare DNA editing sites. We explore maleimide as a scaffold for inosine labeling. With fluorophore-conjugated maleimide, we were able to label inosine in RNA or DNA. Moreover, with biotin-conjugated maleimide, we purified RNA and DNA containing inosine. Our novel technique of inosine chemical labeling and affinity molecular purification offers substantial advantages and provides a versatile platform for further discovery of A-to-I editing sites in RNA and DNA.