Identification of Styryl Sulfonyl Fluoride as a Near-Perfect Michael Acceptor for Diversified Protein Bioconjugations

Cysteine(Cys)-specific bioconjugation has widespread applications in the synthesis of protein conjugates,particularly for the functionalization of antibodies.Here,we report the discovery of transstyryl sulfonyl fluoride(SSF)as a near-perfect Michael acceptor for Cys-specific protein bioconjugation.Compared to maleimides,which are predominantly used,SSF exhibited better chemoselectivity,selfstability,and conjugate stability while maintaining comparable reactivity.Using SSF-derived probes,proteins can be readily modified on the Cys residue(s)to install functionalities,for example,fluorescent dyes,toxins,and oligonucleotides,without influencing the activity.Further applications of SSF-derived serum-stable antibody-drug conjugates and PD-L1 nanobody-oligo conjugates demonstrate the great translational value of SSF-based bioconjugation in drug development and single-cell sequencing.

Advances in targeted nanotherapeutics： From bioconjugation to biomimicry

Since the emergence of cancer nanomedicine, researchers have had intense interest in developing nanoparticles （NPs） that can specifically target diseased sites while avoiding healthy tissue to mitigate the off-target effects seen with conventional treatments like chemotherapy. Initial endeavors focused on the bioconjugation of targeting agents to NPs, and more recently, researchers have begun to develop biomimetic NP platforms that can avoid immune recognition to maximally accumulate in tumors. In this review, we describe the advantages and limitations of each of these targeting strategies. First, we review developments in bioconjugation strategies, where NPs are coated with biomolecules such as antibodies, aptamers, peptides, and small molecules to enable cell-specific binding. While bioconjugated NPs offer many exciting features and have improved pharmacokinetics and biodistribution relative to unmodified NPs, they are still recognized by the body as ＂foreign＂, resulting in their clearance by the mononuclear phagocytic system （MPS）. To overcome this limitation, researchers have recently begun to investigate biomimetic approaches that can hide NPs from immune recognition and reduce clearance by the MPS. These biomimetic NPs fall into two distinct categories： synthetic NPs that present naturally occurring structures, and NPs that are completely disguised by natural structures. Overall bioconjugated and biomimetic NPs have substantial potential to improve upon conventional treatments by reducing off-target effects through site-specific delivery. and they show great promise for future standards of care. Here, we provide a summary of each strategy, discuss considerations for their design moving forward, and highlight their potential clinical impact on cancer therapy.

4-Hydroxy-L-Proline as a General Platform for Stereoregular Aliphatic Polyesters:Controlled Ring-Opening Polymerization,Facile Functionalization,and Site-Specific Bioconjugation

Degradable polyesters have long been regarded as eco-friendly materials,useful for various applicationswhile meeting the growing needs of sustainability.However,it is still challenging to synthesize functional aliphatic polyesters from abundant and cheap renewable sources.Our present study reports a readily available and versatile platform for producing functional and stereoregular aliphatic polyesters from 4-hydroxy-L-proline(4-HYP).We synthesized a bicyclic bridged lactone monomer,namely,NR-PL,by a simple and scalable two-step process allowing facile side-chain functionalization and derivatization.The ring-opening homopolymerization and copolymerization for the generation of N^(R)-PL were controlled fully by using organobases such as 1,8-diazabicyclo[5.4.0]-undec-7-ene(DBU)without any detectable epimerization.This process afforded stereoregular polyesters PNRPE with molar mass(M_(n))up to 90 kg/mol and a narrow dispersity(Ð)generally below 1.10.The uniqueness of the backbone,which contains two chiral centers on a rigid propyl ring,together with the versatility of the side chain,offer tunable properties complementary to existing aliphatic polyesters.The utility of the polymers was showcased by the facile site-specific bioconjugation of PN^(EG3)PE,a water-soluble polyester,to a protein.This work might open numerous opportunities in creating functional and sustainable polyesters for a wide range of applications,including degradable plastics,drug delivery,and protein therapeutics.

Expeditious and scalable preparation of a Li-Thiele reagent for amine-based bioconjugation

Chemoselective amine bioco njugation has long been a challenge for native protein modification.Inspired by Thiele’s seminal discovery,Li and co-workers recently developed an orto-phthalaldehyde(OPA)based reagent for labeling the amino group of a protein.Here we report an expeditious and scalable synthesis of a Li-Thiele reagent featuring an arene construction strategy.The reagent contains an alkyne side chain as a handle for secondary modification.

Cysteine-Specific Bioconjugation and Stapling of Unprotected Peptides by Chlorooximes

Cyclic peptides have found applications in fields ranging from drug discovery to nanomaterials.Peptide stapling reagents crosslink two or more residues in peptides to generate macrocycles of diverse topology and introduce linker units that might directly impact the properties and biological functions of cyclic peptides.Herein,we demonstrate that chlorooxime derivatives are cysteine-specific peptide bioconjugation and stapling reagents that generate stable thiohydroximate linkages.

Optimization of the Process for Preparing Bivalent Polysaccharide Conjugates to Develop Multivalent Conjugate Vaccines against Streptococcus pneumoniae or Neisseria meningitidis and Comparison with the Corresponding Licensed Vaccines in Animal Models

Objective:This study aimed to describe,optimize and evaluate a method for preparing multivalent conjugate vaccines by simultaneous conjugation of two different bacterial capsular polysaccharides(CPs)with tetanus toxoid(TT)as bivalent conjugates.Methods:Different molecular weights(MWs)of polysaccharides,activating agents and capsular polysaccharide/protein(CP/Pro)ratio that may influence conjugation and immunogenicity were investigated and optimized to prepare the bivalent conjugate bulk.Using the described method and optimized parameters,a 20-valent pneumococcal conjugate vaccine and a bivalent meningococcal vaccine were developed and their effectiveness was compared to that of corresponding licensed vaccines in rabbit or mouse models.Results:The immunogenicity test revealed that polysaccharides with lower MWs were better for Pn1-TT-Pn3 and MenA-TT-MenC,while higher MWs were superior for Pn4-TT-Pn14,Pn6A-TT-Pn6B,Pn7F-TT-Pn23F and Pn8-TT-Pn11A.For activating polysaccharides,1-cyano-4-dimethylaminopyridinium tetrafluoroborate(CDAP)was superior to cyanogen bromide(CNBr),but for Pn1,Pn3 and MenC,N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride(EDAC)was the most suitable option.For Pn6A-TT-Pn6B and Pn8-TT-Pn11A,rabbits immunized with bivalent conjugates with lower CP/Pro ratios showed significantly stronger CP-specific antibody responses,while for Pn4-TT-Pn14,higher CP/Pro ratio was better.Instead of interfering with the respective immunological activity,our bivalent conjugates usually induced higher IgG titers than their monovalent counterparts.Conclusion:The result indicated that the described conjugation technique was feasible and efficacious to prepare glycoconjugate vaccines,laying a solid foundation for developing extended-valent multivalent or combined conjugate vaccines without potentially decreased immune function.

Synthesis and characterization of reporter molecules embedded core-shell nanoparticles as SERS nanotags

Surface-enhanced Raman scattering(SERS)spectroscopy is presented as a sensitive and spe-cific molecular tool for clinical diagnosis and prognosis monitoring of various diseases including cancer.In order for clinical application of SERS technique,an ideal method of bulk synthesis of SERS nanoparticles is necessary to obtain sensitive,stable and highly reproducible Raman signals.In this contribution,we determined the ideal conditions for bulk synthesis of Raman reporter(Ra)molecules embedded silver-gold core-shell nanoparticles(Au@Ra@AgNPs)using hydroquinone as reducing agent of silver nitrate.By using UV-Vis spectroscopy,Raman spectroscopy and transmission electron microscopy(TEM),we found that a 2∶1 ratio of silver nitrate to hydroquinone is ideal for a uniform silver coating with a strong and stable Raman signal.Through stability testing of the optimized Au@Ra@AgNPs over a two-week period,these SERS nanotags were found to be stable with minimal signal change occurred.The sta-bility of antibody linked SERS nanotags is also crucial for cancer and disease diagnosis,thus,we further conjugated the as-prepared SERS nanotags with anti-EpCAM antibody,in which the stability of bioconjugated SERS nanotags was tested over eight days.Both UV-Vis and SERS spectroscopy showed stable absorption and Raman signals on the anti-EpCAM conju-gated SERS nanotags,indicating the great potential of the synthesized SERS nanotags for future applications which require large,reproducible and uniform quantities in order for cancer biomarker diagnosis and monitoring.

Development of a novel multi-functional integrated bioconjugate effectively targeting K-Ras mutant pancreatic cancer

Folate receptor(FR)overexpression occurs in a variety of cancers,including pancreatic cancer.In addition,enhanced macropinocytosis exists in K-Ras mutant pancreatic cancer.Furthermore,the occurrence of intensive desmoplasia causes a hypoxic microenvironment in pancreatic cancer.In this study,a novel FR-directed,macropinocytosis-enhanced,and highly cytotoxic bioconjugate folate(F)-human serum albumin(HSA)-apoprotein of lidamycin(LDP)-active enediyne(AE)derived from lidamycin was designed and prepared.F-HSA-LDP-AE consisted of four moieties:F,HSA,LDP,and AE.F-HSA-LDP presented high binding efficiency with the FR and pancreatic cancer cells.Its uptake in wild-type cells was more extensive than in K-Ras mutant-type cells.By in vivo optical imaging,F-HSA-LDP displayed prominent tumor-specific biodistribution in pancreatic cancer xenograft-bearing mice,showing clear and lasting tumor localization for 360 h.In the MTT assay,F-HSA-LDP-AE demonstrated potent cytotoxicity in three types of pancreatic cancer cell lines.It also induced apoptosis and caused G2/M cell cycle arrest.F-HSALDP-AE markedly suppressed the tumor growth of AsPc-1 pancreatic cancer xenografts in athymic mice.At well-tolerated doses of 0.5 and 1 mg/kg,(i.v.,twice),the inhibition rates were 91.2%and 94.8%,respectively(P<0.01).The results of this study indicate that the F-HSA-LDP multi-functional bioconjugate might be effective for treating K-Ras mutant pancreatic cancer.

Studies on a Novel Minor-groove Targeting Artificial Nuclease:Synthesis and DNA Binding Behavior

Nucleases play an important role in molecular biology, for example, in DNA sequencing. Synthetic polyamide conjugates can be considered as a novel tool for the selective inhibition of gene expressions and also as potential drugs in anticancer or antiviral chemotherapy. In this article, the synthesis of a novel minor-groove targeting artificial nuclease, an oligopyrrol-containing compound, has been reported. It was found that this novel compound can bind DNA in AT-rich minor groove with high affinity and site specificity. DNA binding behavior was determined by using UV-Vis and CD. It is indicated that compound 6 can enhance the Tm, of DNA from 80.4 ℃ to 84. 4 ℃ and that it possesses a high binding constant value（Kb =3.05 × 10^4 L/mol）.

A versatile AIE fluorogen with selective reactivity to primary amines for monitoring amination,protein labeling,and mitochondrial staining

Specific bioconjugation for native primary amines is highly valuable for both chemistry and biomedical research.Despite all the efforts,scientists lack a proper strategy to achieve high selectivity for primary amines,not to mention the requirement of fast response in real applications.Herein,we report a chromone-based aggregation-induced emission(AIE)fluorogen called CMVMN as a self-reporting bioconjugation reagent for selective primary amine identification,and its applications for monitoring bioprocesses of amination and protein labeling.CMVMN is AIE-active and capable of solid-state sensing.Thus,its electrospun films are manufactured for visualization of amine diffusion and leakage process.CMVMN also shows good biocompatibility and potential mitochondria-staining ability,which provides new insight for organelle-staining probe design.Combined with its facile synthesis and good reversibility,CMVMN would not only show wide potential applications in biology,but also offer new possibilities for molecular engineering.

Click chemistry in the design of AIEgens for biosensing and bioimaging

The development of rapid,selective,and sensitivefluorescent sensors is essential for visualizing and quantifying biological molecules and processes in vitro,ex vitro,and in vivo,which is important for not only fundamental biological studies but the accurate diagnosis of diseases.The emergingfield of activity-based sensing(ABS),a sensing method that utilizes molecular reactivity for analyte detection possesses many advantages including high specificity,sensitivity and accuracy.The aggrega-tion caused quenching phenomenon which occurs in most conventionalfluorophores results in reduced labeling efficiency of the target analytes and low photobleaching resistance,therefore limiting the applications of the ABS strategy.In contrast,aggre-gation induced emission(AIE)active luminogens(AIEgens)provide exceptional molecular frameworks for ABS.Of the many reaction classes utilized in the AIEgen ABS approach,click chemistry has become increasing popular.In this review,the sensing concepts of the ABS approach with AIEgens and the principles of click chemistry are discussed,followed by a systematic summary of the application of specific click chemistry reactions in AIEgen ABS protocols for the detection of an array of target analytes.Furthermore,the utility of click chemistry in the construction of AIEgens for bioimaging will also be showcased throughout the review.

Viruses and Virus-Like Protein Assemblies--Chemically Programmable Nanoscale Building Blocks

Supramolecular proteins are generated using a limited set of twenty amino acids,but have distinctive functionalities which arise from the sequential arrangement of amino acids configured to exquisite three-dimensional structures.Viruses,virus-like particles,ferritins,enzyme complexes,cellular micro-compartments,and other supramolecular protein assemblies exemplify these systems,with their precise arrangements of tens to hundreds of molecules into highly organized scaffolds for nucleic acid packaging,metal storage,catalysis or sequestering reactions at the nanometer scale.These versatile protein systems,dubbed as bionanoparticles(BNPs),have attracted materials scientists to seek new opportunities with these pre-fabricated templates in a wide range of nanotechnology-related applications.Here,we focus on some of the key modification strategies that have been utilized,ranging from basic protein conjugation techniques to more novel strategies,to expand the functionalities of these multimeric protein assemblies.Ultimately,in combination with molecular cloning and sophisticated chemistries,these BNPs are being incorporated into many applications ranging from functional materials to novel biomedical drug designs.

Bacteriophage M13 as a Scaffold for Preparing Conductive Polymeric Composite Fibers

Using biological templates to build one-dimensional functional materials holds great promise in developing nanosized electrical devices,sensors,catalysts,and energy storage units.In this communication,we report a versatile assembly process for the preparation of water-soluble conductive polyaniline(PANi)/M13 composite nanowires by employing the bacteriophage M13 as a template.The surface lysine residues of M13 can be derivatized with carboxylic groups to improve its binding ability to the aniline;the resulting modifi ed M13 is denoted as m-M13.Highly negatively-charged poly(sulfonated styrene)was used both as a dopant acid and a stabilizing agent to enhance the stability of the composite fi bers in aqueous solution.A transparent solution of the conductive PANi/m-M13 composite fi bers can be readily obtained without any further purifi cation step.The fi bers can be easily fabricated into thin conductive fi lms due to their high aspect ratio and good solubility in aqueous solution.This synthesis discloses a unique and versatile way of using bionanorods to produce composite fi brillar materials with narrow dispersity,high aspect ratio,and high processibility,which may have many potential applications in electronics,optics,sensing,and biomedical engineering.

DNA alkylation promoted by an electron-rich quinone methide intermediate

Biological application of conjugates derived from oligonucleotides and quinone methides have pre- viously been limited by the slow exchange of their covalent self-adducts and subsequent alkylation of target nucleic acids. To enhance the rates of these processes, a new quinone methide precursor with an electron donating substituent has been prepared. Additionally, this substi- tuent has been placed para to the nascent exo-methylene group of the quinone methide for maximum effect. A conjugate made from this precursor and a 5＇-aminohex- yloligonucleotide accelerates formation of its reversible self-adduct and alkylation of its complementary DNA as predicted from prior model studies.

Improved Peptidyl Linkers for Self-Assembly of Semiconductor Quantum Dot Bioconjugates

We demonstrate improved peptide linkers which allow both conjugation to biomolecules such as DNA and self-assembly with luminescent semiconductor quantum dots.A hexahistidine peptidyl sequence was generated by standard solid phase peptide synthesis and modified with the succinimidyl ester of iodoacetamide to yield a thiol-reactive iodoacetyl polyhistidine linker.The reactive peptide was conjugated to dye-labeled thiolated DNA which was utilized as a model target biomolecule.Agarose gel electrophoresis and fluorescence resonance energy transfer analysis confirmed that the linker allowed the DNA to self-assemble with quantum dots via metal-affinity driven coordination.In contrast to previous peptidyl linkers that were based on disulfide exchange and were thus labile to reduction,the reactive haloacetyl chemistry demonstrated here results in a more stable thioether bond linking the DNA to the peptide which can withstand strongly reducing environments such as the intracellular cytoplasm.As thiol groups occur naturally in proteins,can be engineered into cloned proteins,inserted into nascent peptides or added to DNA during synthesis,the chemistry demonstrated here can provide a simple method for self-assembling a variety of stable quantum dot bioconjugates.

SURFACE FUNCTIONALIZATION OF POLYSTYRENE TO BIND WITH FMRF PEPTIDES FOR NOVEL BIOCOMPATIBILITY

A generic method was described to change surface biocompatibihty by introducing reactive functional groups onto surfaces of polymeric substrates and covalently binding them with biomolecules.A block copolymer with protected carboxylic acid functionality,poly（styrene-b-tert-butyl acrylate）（PS-PtBA）,was spin coated from solutions in toluene on a bioinert polystyrene（PS） substrate to form a bilayer structure：a surface layer of the poly（tert-butyl acrylate）（PtBA） blocks that order at the air-polymer interface and a bottom layer of the PS blocks that entangle with the PS substrate.The thickness of the PtBA layer and the area density of tert-butyl ester groups of PtBA increased linearly with the concentration of the spin coating solution until a 2 nm saturated monolayer coverage of PtBA was achieved at the concentration of 0.4%W/W.The protected carboxylic acid groups were generated by exposing the tert-butyl ester groups of PtBA to trifluoroacetic acid （TFA） for bioconjugation with FMRF peptides via amide bonds.The yield of the bioconjugation reaction for the saturated surface was calculated to be 37.1%based on X-ray photoelectron spectroscopy（XPS） measurements.The success of each functionalization step was demonstrated and characterized by XPS and contact angle measurements.This polymer functionalization/modification concept can be virtually applied to any polymeric substrate by choosing appropriate functional block copolymers and biomolecules to attain novel biocompatibility.

Highly photostable nanogels for fluorescence-based theranostics

A novel photo-crosslinkable nanogel is prepared from a biodegradable polymer template with intrinsic photoluminescence and high photostability.The fluorescent nanogels display excellent biodegradability and cytocompatibility owed to the facile synthesis scheme involving a solvent-and surfactant-free onepot reaction,derived entirely from biocompatible monomers citric acid,maleic acid,L-cysteine,and poly(ethylene glycol).The resultant nanogels are less than 200 nm in diameter with a narrow size distribution and monodispersity,and demonstrate long-term structural stability in biological buffer for two weeks.To gauge potential in theranostic applications,the fluorescent nanogels were surface functionalized with biologically active RGD peptides and encapsulated with active anti-cancer drug Doxorubicin,resulting in a pH-responsive controlled drug release in acidic pH resembling tumor environments.The strong fluorescence of the nanogels enabled tracking of targeted drug delivery,showing that drug-loaded nanogels homed into the cytoplasmic regions of prostate cancer cells to significantly induce cell death.These photo-crosslinkable and biodegradable nanogels pose as a strong candidate for theranostic medicine,demonstrating versatile functionalization,high stability in biological buffers,and capacity for real-time fluorescence-based monitoring of targeted drug delivery.

INTERACTION OF ANTIGEN AND ANTIBODY ON CORE-SHELL POLYMERIC MICROSPHERES

Monodispersed microspheres with polystyrene as the core and poly（acrylamide-co-N-acryloxysuccinirnide） as the shell were synthesized by a two-step surfactant-free emulsion copolymerization.The core-shell morphology of the microspheres was shown by scanning electron microscopy and transmission electron microscopy.Rabbit immunoglobulin G （as antigen） was covalently coupled onto the microspheres by the reaction between succinimide-activated ester groups on the shell of the microspheres and amino groups of the antigen molecules.The size of particles was characterized by dynamic light scattering technique and was found to vary upon bioconjugation and interaction with proteins.The binding process was shown to be specific to goat anti-rabbit immunoglobulin G（as antibody） and reversible upon the addition of free antigen into the system.

Biomimetic Recognition-Based Bioorthogonal Host-Guest Pairs for Cell Targeting and Tissue Imaging in Living Animals

Bioconjugation methods offer very important tools in studying biological systems.Synthetic host-guest pairs provide an alternative and complementary conjugation method to bioorthogonal reactions and biological association pairs.Nevertheless,macrocyclic hosts that can be used for in situ capture are limited and often rely on extremely high binding affinities.Herein,we report an alternative bioorthogonal host-guest pair that relies on highly selective molecular recognition in water.The host,namely amide naphthotube,possesses a biomimetic cavity with inward-directing hydrogen bonding sites and shows selective and strong binding to the guest(2-phenyl pyrimidine)even in biological media.Through anchoring the tetraphenyl ethylene-modi fied hosts to cell surfaces,the bioorthogonal host-guest pair can be applied in cell surface recognition,cell-cell interactions,and tissue imaging in mice.The bioorthogonality is originated from the high binding selectivity of the biomimetic macrocyclic host,which is different from other known host-guest pairs that have been applied in biological systems.This research provides a new noncovalent bioconjugation tool and a new concept for designing bioorthogonal host-guest pairs for biological applications.

Norvancomycin-capped silver nanoparticles: Synthesis and antibacterial activities against E. coli

The synthesis of norvancomycin (NVan)-capped silver nanoparticles (Ag@NVan) and their notable in vitro antibacterial activities against E. coli, a Gram-negative bacterial strain (GNB), are reported here. Mercaptoacetic acid-stabilized spherical silver nanoparticles with a diameter of 16±4 nm are prepared by a simple chemical reaction. The formation process of the silver nanoparticles is investigated by UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). NVan is then grafted to the terminal carboxyl of the mercaptoacetic acid in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC). The TEM images of single bacteria treated with Ag@NVan show that plenty of Ag@NVan aggregate in the cell wall of E. coli. A possible antibacterial mechanism is proposed that silver nanoparticles may help destroy the stability of the outer membrane of E. coli, which makes NVan easier to bind to the nether part of the peptidoglycan structure. The antibacterial activities of silver nanoparticles on their own, together with the rigid polyvalent interaction between Ag@NVan and cell wall, enables Ag@NVan to be an effective inhibitor of GNB. This kind of bionanocomposites might be used as novel bactericidal materials and we also provide an effective synthesis method for preparing functional bioconjugated nanoparticles here.