Biocompatible Azide–Alkyne “Click” Reactions for Surface Decoration of Glyco‐Engineered Cells

Bio‐orthogonal copper (I)‐catalyzed azide–alkyne cycloaddition (CuAAC) has been widely used to modify azide‐ or alkyne‐bearing monosaccharides on metabolic glyco‐engineered mammalian cells. Here, we present a systematic study to elucidate the design space for the cytotoxic effects of the copper catalyst on NIH 3T3 fibroblasts and on HEK 293‐F cells. Monitoring membrane integrity by flow cytometry and RT‐PCR analysis with apoptotic and anti‐apoptotic markers elucidated the general feasibility of CuAAC, with exposure time of the CuAAC reaction mixture having the major influence on biocompatibility. A high labeling efficiency of HEK 293‐F cells with a fluorescent alkyne dye was rapidly achieved by CuAAC in comparison to copper free strain‐promoted azide–alkyne cycloaddition (SPAAC). The study details effective and biocompatible conditions for CuAAC‐based modification of glyco‐engineered cells in comparison to its copper free alternative.     

An Azide‐Modified Nucleoside for Metabolic Labeling of DNA

Metabolic incorporation of azido nucleoside analogues into living cells can enable sensitive detection of DNA replication through copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) and strain‐promoted azide–alkyne cycloaddition (SPAAC) “click” reactions. One major limitation to this approach is the poor chemical stability of nucleoside derivatives containing an aryl azide group. For example, 5‐azido‐2′‐deoxyuridine (AdU) exhibits a 4 h half‐life in water, and it gives little or no detectable labeling of cellular DNA. In contrast, the benzylic azide 5‐(azidomethyl)‐2′‐deoxyuridine (AmdU) is stable in solution at 37 °C, and it gives robust labeling of cellular DNA upon addition of fluorescent alkyne derivatives. In addition to providing the first examples of metabolic incorporation into and imaging of azide groups in cellular DNA, these results highlight the general importance of assessing azide group stability in bioorthogonal chemical reporter strategies.     

Opposite Modulation of Cell Migration by Distinct Subregions of Urokinase Connecting Peptide

Functional analysis of isolated protein domains may uncover cryptic activities otherwise missed. The serine protease urokinase (uPA) has a clear‐cut motogen activity that is catalytically independent and resides in its amino‐terminal growth factor domain (GFD, residues 1‐49) and connecting peptide region (CP, residues 132–158). To functionally dissect the CP region, we analysed the biological activity of two synthetic peptides corresponding to the N‐terminal [uPA‐(135–143), residues 135–143] and C‐terminal [uPA‐(144–158), residues 144–158] CP subregions. Most of the chemotactic activity of connecting peptide‐derived peptide (CPp, [uPA‐(135–158)]) for embryonic kidney HEK293/uPAR‐25 cells is retained by uPA‐(144–158) at nanomolar concentrations. In contrast, uPA‐(135–143) inhibits basal, CPp ‐, vitronectin‐ and fibronectin‐induced cell migration. Radioreceptor binding assays on intact HEK293 cells revealed that uPA‐(135–143) and uPA‐(144–158) are both able to compete with [¹²⁵I]‐CPp, albeit with different binding affinities. The consequences of phospho‐mimicking, S138E substitution, were studied using [138E]uPA‐(135–158) and [138E]uPA‐(135–143) peptides. Unlike CPp, [138E]uPA‐(135–158) and [138E]uPA‐(135–143) exhibit remarkable inhibitory properties. Finally, analysis of the conformational preferences of the peptides allowed to identify secondary structure elements exclusively characterising the stimulatory CPp and uPA‐(144–158) versus the inhibitory uPA‐(135–143), [138E]uPA‐(135–158) and [138E]uPA‐(135–143) peptides. In conclusion, these data shed light on the cryptic activities of uPA connecting peptide, revealing the occurrence of two adjacent regions, both competing for binding to cell surface but conveying opposite signalling on cell migration.     

A General Method for Artificial Metalloenzyme Formation through Strain‐Promoted Azide–Alkyne Cycloaddition

Strain‐promoted azide–alkyne cycloaddition (SPAAC) can be used to generate artificial metalloenzymes (ArMs) from scaffold proteins containing a p‐azido‐L ‐phenylalanine (Az) residue and catalytically active bicyclononyne‐substituted metal complexes. The high efficiency of this reaction allows rapid ArM formation when using Az residues within the scaffold protein in the presence of cysteine residues or various reactive components of cellular lysate. In general, cofactor‐based ArM formation allows the use of any desired metal complex to build unique inorganic protein materials. SPAAC covalent linkage further decouples the native function of the scaffold from the installation process because it is not affected by native amino acid residues; as long as an Az residue can be incorporated, an ArM can be generated. We have demonstrated the scope of this method with respect to both the scaffold and cofactor components and established that the dirhodium ArMs generated can catalyze the decomposition of diazo compounds and both Si?H and olefin insertion reactions involving these carbene precursors.     

Biotin-Functionalized Block Catiomers as an Active Targeting Approach in Gene Delivery

Recently, biotin (vitamin H) has been described as a ligand for active targeting and it has been found that many cancer cells overexpress the biotin receptor. In this study a biotin-conjugated block copolymer, biotin-poly(2-ethyl-2-oxazoline)-block-poly{N '-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (biotin-pEtOx-b-pASP(DEA) is synthesized by a living cationic polymerization of the pEtOx-block followed by the nucleophilic ringopening polymerization of the pASP-block. The biotin moiety is coupled to the pEtOx-b-pASP precursor by a Cu(I) mediated azide-alkyne click chemistry and finally, the diethylamine (DEA) side chain is introduced by a polymer analogous reaction. The final polymer P1 formed polyplexes in the presence of plasmid DNA that are characterized with respect to N/P ratio, size, zeta potential, and shape compared to a control polymer P2 without biotin. In addition, HEK293 cells are transfected with these polyplexes and the number of fluorescent HEK293 cells is evaluated to assess the influence of polymer nature on the activity of the micelles. Flow cytometric analysis revealed a significantly higher uptake of the biotin-PEtOx-PASP(DEA)/pDNA micelle than the PEtOx-PASP(DEA)/pDNA micelle against HEK293 cells at a low N/P ratio of 20, consistent with the transfection results whereas at higher N/P ratio no difference can be observed anymore between the two polymers.     

The inclusion of fetal bovine serum in gelatin/PCL electrospun scaffolds reduces short‐term osmotic stress in HEK 293 cells caused by scaffold components

Components of gelatin/polycaprolactone (PCL) electrospun scaffolds are released to surrounding media and cause osmotic changes that adversely affect cell viability and proliferation. In this study, the physiological properties of gelatin/PCL scaffolds were investigated by qRT‐PCR and by performing cellular studies on HEK 293 cells. Components released from gelatin/PCL scaffolds were found to induce osmotic stress response in these cells. However, osmotic stress was inhibited by adding fetal bovine serum (FBS) to scaffolds. In addition, focal adhesion related genes were found to be up‐regulated in HEK 293 cells on gelatin/PCL/20% FBS scaffolds, and this induced the down‐regulations of cell‐death related genes. Furthermore, the inclusion of 20% FBS improved the viabilities of HEK 293 cells on gelatin/PCL scaffolds. This study indicates that adding FBS to gelatin/PCL scaffolds improves scaffold bio‐affinity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Clonal selection of high producing,stably transfected HEK293 cell lines utilizing modified,high‐throughput FACS screening

BACKGROUND: Human embryonic kidney‐293 (HEK‐293) cells are commonly used as a transient expression host but their application in stable therapeutic protein production is limited. This is presumably due to the absence of a suitable amplifiable expression system and hence limited protein output compared with other mammalian cells such as Chinese hamster ovary cells. This paper describes a rapid clonal selection method for isolating HEK293 cell lines with high specific productivity, for a non‐amplifiable expression system, to achieve high‐level, scalable expression of recombinant antibodies. RESULTS: Flow cytometry utilizing cold capture of secreted protein on the cell surface was applied to isolate high expressing clones from a stable antibiotic resistant pool. The top three isolated clones showed a five‐ to seven‐fold improvement in volumetric outputs compared with the initial resistant pool (～20 mg L^?1) under batch conditions. In fed‐batch conditions using commercially available hydrolysate supplements, the final titre was further increased to 500–600 mg L^?1 in shaker flasks. One clone was scaled up to 25 L bag production using a similar hydrolysate feeding regime. The antibody titre reached 655 mg L^?1, and 12 g of antibody was recovered after purification, demonstrating scalability of the process. The process of clonal selection through to fed‐batch production of gram quantities was completed within 4 months. CONCLUSION: HEK‐293 cells can be used as a stable host for the production of biopharmaceuticals, producing gram quantities of recombinant proteins for preclinical development. Copyright © 2011 Society of Chemical Industry     

Synthesis and Characterization of the Nitrogen‐Rich Hyperbranched Polymers – Poly([1,2,3]‐Triazole‐[1,3,5]‐Triazine)s

Novel hyperbranched poly([1,2,3]‐triazole‐[1,3,5]‐triazine)s (HBP TT) were synthesized by a 1,3‐dipolar cycloaddition reaction from AB₂ monomer – 2‐azido‐4,6‐bis‐prop‐2‐yn‐1‐yloxy‐ [1,3,5]‐triazine (ABPOT). The monomer contains one azide group A and two terminal alkyne units B. Thermal polymerization of ABPOT in bulk or in DMF solution leads to hyperbranched polymers containing both 1,4‐ and 1,5‐disubstituted [1,2,3]‐triazoles. The monomer was also polymerized catalytically in the presence of Cu(I) salts under mild reaction conditions in DMSO solution and in bulk affording hyperbranched poly‐[1,2,3]‐triazoles 1,4‐disubstituted only. The reactions lead to the products soluble in aprotic polar solvents like DMSO or DMF. Side reactions can proceed in a few cases, particularly: (i) homocoupling of alkyne groups, leading to the formation of insoluble products as a result of cross‐linking, (ii) isomerization of propynyloxytriazine fragments to propynyl‐ or propadienyltriazinone ones, and (iii) hydrolysis of triple bonds without the loss of solubility. Heats of formation of monomer and synthesized polymers were calculated from their combustion heats. All products were characterized by NMR‐, IR‐spectroscopy, and size exclusion chromatography (SEC) data. The obtained results open the prospect for the use of HBP TT as the high‐enthalpy modifiers for energetic and non‐energetic binders.     

Lipocalin-2基因表达产物对人胚肾细胞增殖的影响

目的构建Lipocalin-2(Lcn-2)基因真核表达质粒PL-2,并检测其及前期原核表达的重组Lcn-2蛋白对人胚肾细胞HEK293增殖的影响。方法利用RT-PCR从鼠巨噬细胞RAW264.7中扩增Lcn-2基因,克隆入真核表达质粒pEGFP-C1中,构建重组质粒PL-2。转染HEK293细胞,通过荧光观察和RT-PCR鉴定Lcn-2基因的表达。将重组质粒PL-2和前期原核表达的重组Lcn-2蛋白作用于HEK293细胞,通过MTT法检测细胞增殖情况,Westernblot法检测细胞增殖核抗原(PCNA)的表达。结果重组真核表达质粒PL-2经酶切和测序鉴定,证明构建正确。经荧光观察和RT-PCR鉴定,转染重组质粒PL-2的HEK293细胞中有Lcn-2基因的表达。加入重组Lcn-2蛋白后,HEK293细胞较对照组明显增殖,细胞中PCNA的表达也较对照组明显升高,而重组质粒PL-2对HEK293细胞增殖以及细胞中PCNA的表达均无影响。结论已成功构建了Lcn-2基因真核表达质粒,其对HEK293细胞的增殖无影响,而原核表达的重组Lcn-2蛋白对HEK293细胞的增殖有一定的促进作用,推测Lcn-2基因的表达产物可能通过与细胞膜受体结合促进HEK293细胞的增殖。     

RNA聚合酶Ⅱ转录的ALU序列对HEK293细胞凋亡的影响

目的探讨RNA聚合酶Ⅱ转录的ALU序列对人胚肾293(HEK293)细胞凋亡的影响以及干扰素(IFN)在此机制中的作用。方法取对数生长期的HEK293细胞,分为6组,ALU-293组(瞬时转染重组质粒pcDNA3.1-ALU)、pcDNA3.1-293组[瞬时转染空质粒pcDNA3.1(-),作为阴性对照]、Poly I∶C-293组[瞬时转染dsRNA的多聚肌苷胞苷酸(Poly I∶C),作为阳性对照]、IFNβ-293组(加入1.65×104 U IFNβ,作为阳性对照)、空白对照组(未经处理的HEK293细胞)和HBs-293组(瞬时转染重组质粒pcDNA3.1-HBs),转染后48 h,采用MTT法检测细胞的增殖活性;Cellular DNA Fragmentation ELISA和DNA Ladder法检测细胞的凋亡情况;Real-time PCR检测细胞中IFNβ基因mRNA的水平。结果瞬时转染重组质粒pcDNA3.1-ALU能够抑制HEK293细胞增殖,并促使其凋亡,且细胞中IFNβmRNA的水平显著上调。结论 RNA聚合酶Ⅱ转录的ALU序列能够通过激活干扰素系统来诱导细胞凋亡。     

Synthesis of Modified 4H‐1,2,4‐Benzothiadiazine‐1,1‐dioxides and Determination of their Affinity and Selectivity for Different Types of KATP Channels

4H‐1,2,4‐Benzothiadiazine‐1,1‐dioxides with various substituents in positions 3, 5, and 7 were synthesized and tested as K_ATP channel agonists in artificial cell systems (CHO cells transfected with SUR1/Kir6.2, and HEK 293 transfected with SUR2B/Kir6.1) as model systems for insulin‐secreting pancreatic β‐cells and for smooth muscle cells, respectively. The effects of agonists were tested in intact cells using DiBAC4(3) [bis‐(1,3‐dibarbituric acid)trimethine oxanol] as a membrane potential dye, and the results compared with their binding affinity for the SUR2B‐type K_ATP channels using the radioligand [³H]P1075. Compounds with cycloalkyl and (cycloalkyl)methyl side chains in position 3 had higher affinities towards the SUR2B/Kir6.1 receptor compared with the parent compound diazoxide ( 1 a ). Compounds with bulky, nonpolar residues in position 3 exhibited remarkable selectivity for SUR2B‐type K_ATP channels. The compound substituted with a bulky (1‐adamantyl)methyl residue exhibited micromolar affinity and activity on SUR2B‐type K_ATP channels without being able to activate the SUR1‐type K_ATP channels.     

N-[2-Methyl-5-(triazol-1-yl)phenyl]pyrimidin-2-amine as a scaffold for the synthesis of inhibitors of Bcr-Abl

N‐[2‐Methyl‐5‐(triazol‐1‐yl)phenyl]pyrimidin‐2‐amine derivatives were synthesized and evaluated in vitro for their potential use as inhibitors of Bcr‐Abl. The design is based on the bioisosterism between the 1,2,3‐triazole ring and the amide group. The synthesis involves a copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) as the key step, with the exclusive production of anti‐(1,4)‐triazole derivatives. One of the compounds obtained shows general activity similar to that of imatinib; in particular, it was observed to be more effective in decreasing the fundamental function of cdc25A phosphatases in the K‐562 cell line.     

Cellular selectivity and biological impact of cytotoxic rhodium(III) and iridium(III) complexes containing methyl-substituted phenanthroline ligands

The antiproliferative properties and biological impact of octahedral iridium(III) complexes of the type fac‐[IrCl₃(DMSO)(pp)] containing pp=phenanthroline ( 1 ) and its 4‐ and 5‐methyl ( 2 , 3 ) and 4,7‐ and 5,6‐dimethyl derivatives ( 4 , 5 ) were investigated for both adherent and non‐adherent cells. A series of similar rhodium(III) complexes were studied for comparison purposes. The antiproliferative activity toward MCF‐7 cancer cells increases eightfold from IC₅₀=4.6 for 1 to IC₅₀=0.60 μM for 5 , and an even more pronounced 18‐fold improvement was established for the analogous rhodium complexes 6 and 8 , the respective IC₅₀ values for which are 1.1 and 0.06 μM . Annexin V/propidium iodide assays demonstrated that the 5,6‐dimethylphenanthroline complexes 5 and 8 both cause significant inhibition of Jurkat leukemia cell proliferation and invoke extensive apoptosis but negligible necrosis. The percentages of Jurkat cells exhibiting high levels of reactive oxygen species correlate with the percentages of cells undergoing apoptosis. The antiproliferative activity of 5 and 8 is strongly selective toward MCF‐7 and HT‐29 cancer cells over normal HFF‐1 and immortalized HEK‐293 cells. Complex 5 also exhibits high selectivity toward BJAB lymphoma cells relative to healthy leukocytes. Both 5 and 8 invoke permanent decreases in the adhesion and respiration of MCF‐7 cells.     

Strain-promoted alkyne-azide cycloadditions (SPAAC) reveal new features of glycoconjugate biosynthesis

We have shown that 4-dibenzocyclooctynol (DIBO), which can easily be obtained by a streamlined synthesis approach, reacts exceptionally fast in the absence of a Cu(I) catalyst with azido-containing compounds to give stable triazoles. Chemical modifications of DIBO, such as oxidation of the alcohol to a ketone, increased the rate of strain promoted azide-alkyne cycloadditions (SPAAC). Installment of a ketone or oxime in the cyclooctyne ring resulted in fluorescent active compounds whereas this property was absent in the corresponding cycloaddition adducts; this provides the first example of a metal-free alkyne-azide fluoro-switch click reaction. The alcohol or ketone functions of the cyclooctynes offer a chemical handle to install a variety of different tags, and thereby facilitate biological studies. It was found that DIBO modified with biotin combined with metabolic labeling with an azido-containing monosaccharide can determine relative quantities of sialic acid of living cells that have defects in glycosylation (Lec CHO cells). A combined use of metabolic labeling/SPAAC and lectin staining of cells that have defects in the conserved oligomeric Golgi (COG) complex revealed that such defects have a greater impact on O-glycan sialylation than galactosylation, whereas sialylation and galactosylation of N-glycans was similarly impacted. These results highlight the fact that the fidelity of Golgi trafficking is a critical parameter for the types of oligosaccharides being biosynthesized by a cell. Furthermore, by modulating the quantity of biosynthesized sugar nucleotide, cells might have a means to selectively alter specific glycan structures of glycoproteins.     

Systematic Investigation of Metabolic Oligosaccharide Engineering Efficiency in Intestinal Cells Using a Dibenzocyclooctyne-Monosaccharide Conjugate

Metabolic oligosaccharide engineering (MOE) of cells with synthetic monosaccharides can introduce functionality to the glycans of cell membranes. Unnatural sugars (e. g., peracetylated mannose-azide) can be expressed on the cell surface with the azide group in place. After MOE, the azide group can participate in a copper-free click reaction with an alkyne (e. g., dibenzocyclooctyne, DBCO) probe. This allows the metabolic fate of monosaccharides in cells to be understood. However, in a drug delivery context it is desirable to have azide groups on the probe (e. g. a drug delivery particle) and the alkyne (e. g. DBCO) on the cell surface. Consequently, the labelling efficiency of intestinal cell lines (Caco-2 and HT29-MTX-E12) treated with N-dibenzocyclooctyne-tetra-acetylmannosamine, and the concentration- and time-dependent labelling were determined. Furthermore, the labelling of mucus in HT29-MTX-E12 cells with DBCO was shown. This study highlights the potential for using MOE to target azide-functionalised probes to intestinal tissues for drug delivery applications.     

Nitrooxyacyl derivatives of salicylic acid: aspirin-like molecules that covalently inactivate cyclooxygenase-1

A recently described series of nitrooxyacyl derivatives of salicylic acid, displaying aspirin‐like anti‐inflammatory and platelet anti‐aggregatory properties, were evaluated for their abilities to inhibit cyclooxygenase (COX). A number of these compounds irreversibly inhibited both COX‐1 and COX‐2 isoforms when tested in isolated human platelets and monocytes. Further studies using COX‐1 expressed in human HEK293T cells showed that this inhibition mechanism is similar to that of aspirin; namely, the products are able to covalently bind to the Ser 530 residue present in the active cleft of the enzyme. Molecular modeling enabled us to rationalize this behavior. Because these products were previously found to display NO‐dependent properties in rat animal models, particularly as they decreased in vivo gastrotoxicity and induced in vitro vasodilation, they represent a new and interesting class of potential aspirin‐like antithrombotic agents worthy of further study.     

Click‐Chemistry‐Derived Tetracycline–Amino Acid Conjugates Exhibiting Exceptional Potency and Exclusive Recognition of the Reverse Tet Repressor

A click‐chemistry‐based synthesis of biologically active doxycycline–amino acid conjugates is described. Starting from 9‐aminodoxycycline derivatives and complementary functionalized amino acids, ligation was accomplished by copper(I)‐catalyzed azide–alkyne [3+2] cycloaddition (CuAAC). The final products were tested in a variety of TetR and revTetR systems, and the C‐terminally linked phenylalanine conjugate 12 c exhibited high selectivity for revTetR over TetR. Besides the unique property of the specific effector 12 c to effectively differentiate TetR and its reverse phenotype, the test compound proved to be almost devoid of any antibacterial activity; this will be highly beneficial for future applications to control gene expression in bacterial systems.     

人Makorin环指蛋白1基因沉默对HEK293细胞的影响

目的探讨特异性抑制人Makorin环指蛋白1(MKRN1)基因的表达对HEK293细胞的影响。方法用脂质体将前期筛选出的含最有效干扰序列的人MKRN1基因shRNA真核表达质粒,转染至HEK293细胞中,观察其对人端粒酶逆转录酶(hTERT)基因mRNA转录水平、蛋白表达水平及细胞增殖的影响。结果人MKRN1基因shRNA真核表达质粒转染HEK293细胞后,在mRNA和蛋白水平均能明显上调细胞hTERT基因的表达,且细胞明显增殖。结论抑制HEK293细胞中人MKRN1基因的表达,可导致hTERT基因mRNA转录水平和蛋白表达水平上调,并促进细胞增殖。     

Synthesis of Benzofuran,Benzothiophene, and Benzothiazole‐Based Thioamides and their Evaluation as KATP Channel Openers

Several series of benzofurans, benzothiophenes, and benzothiazoles, all featuring the thioamide group, were synthesized and tested as novel K_ATP channel openers in artificial cell systems: CHO cells transfected with SUR1/Kir6.2, and HEK 293 cells transfected with SUR2B/Kir6.1; these served as model systems for insulin‐secreting pancreatic β cells and smooth muscle cells, respectively. All compounds were investigated with respect to their binding affinity for the SUR2B‐type K_ATP channels using [³H]P1075 as radioligand. Selected compounds were also tested as agonists in intact cells using DiBAC₄(3) and DyeB (R7260) as membrane potential dyes. Remarkable affinity for SUR2B/Kir6.1 channels in the single‐digit micromolar range was observed. In addition, benzothiazole‐derived thioamides with sterically demanding, lipophilic substituents showed >100‐fold selectivity in favor of SUR2B/Kir6.1. A one‐carbon spacer between the heterocyclic skeleton and the thioamide moiety was observed to be crucial for affinity and selectivity. Two of the most potent and selective compounds were studied by crystal structure analyses.     

Multivalent Display and Receptor‐Mediated Endocytosis of Transferrin on Virus‐Like Particles

The structurally regular and stable self‐assembled capsids derived from viruses can be used as scaffolds for the display of multiple copies of cell‐ and tissue‐targeting molecules and therapeutic agents in a convenient and well‐defined manner. The human iron‐transfer protein transferrin, a high affinity ligand for receptors upregulated in a variety of cancers, has been arrayed on the exterior surface of the protein capsid of bacteriophage Qβ. Selective oxidation of the sialic acid residues on the glycan chains of transferrin was followed by introduction of a terminal alkyne functionality through an oxime linkage. Attachment of the protein to azide‐functionalized Qβ capsid particles in an orientation allowing access to the receptor binding site was accomplished by the Cu^I‐catalyzed azide–alkyne cycloaddition (CuAAC) click reaction. Transferrin conjugation to Qβ particles allowed specific recognition by transferrin receptors and cellular internalization through clathrin‐mediated endocytosis, as determined by fluorescence microscopy on cells expressing GFP‐labeled clathrin light chains. By testing Qβ particles bearing different numbers of transferrin molecules, it was demonstrated that cellular uptake was proportional to ligand density, but that internalization was inhibited by equivalent concentrations of free transferrin. These results suggest that cell targeting with transferrin can be improved by local concentration (avidity) effects.