A fluorogenic, peptide-based probe for the detection of Cathepsin D in macrophages

Cathepsin D is a protease that is an effector in the immune response of macrophages, yet to date, only a limited number of probes have been developed for its detection. Herein, we report a water soluble, highly sensitive, pH insensitive fluorescent probe for the detection of Cathepsin D activity that provides a strong OFF/ON signal upon activation and with bright emission at 515 nm. The probe was synthesised using a combination of solid and solution-phase chemistries, with probe optimisation to increase its water solubility and activation kinetics by addition of a long PEG chain (5 kDa) at the C-terminus. A BODIPY fluorophore allowed detection of Cathepsin D across a wide pH range, important as the protease is active both at the low pH found in lysosomes and also in higher pH phagolysosomes, and in the cytosol. The probe was successfully used to detect Cathepsin D activity in macrophages challenged by exposure to bacteria.

Fluorophore-Tagged Poly-Lysine RAFT Agents: Controlled Synthesis of Trackable Cell-Penetrating Peptide-Polymers

The conjugation of a fluorophore and a variety of cell-penetrating peptides onto a RAFT agent allowed for the synthesis of polymers of defined sizes with quantifiable cell-uptake. Each peptide-RAFT agent was used to polymerize acrylamide, acrylate, and styrene monomers to form high or low molecular weight polymers (here 50 or 7.5 kDa) with the peptide having no influence on the RAFT agent's control. The incorporation of a single fluorophore per polymer chain allowed cellular analysis of the uptake of the size-specific peptide-polymers via flow cytometry and confocal microscopy. The cell-penetrating peptides had a direct effect on the efficiency of polymer uptake for both high and low molecular weight polymers, demonstrating the versatility of the strategy. These "all-in-one", synthetically accessible RAFT agents allow highly controlled preparation of synthetic peptide-polymer conjugates and subsequent quantification of their delivery into cells.

Moving into the red - a near infra-red optical probe for analysis of human neutrophil elastase in activated neutrophils and neutrophil extracellular traps

Neutrophils are the first immune cells recruited for defence against invading pathogens; however, their dysregulated activation and subsequent release of the enzyme human neutrophil elastase is associated with several, inflammation-based, diseases. Herein, we describe a FRET-based, tri-branched (one quencher, three fluorophores) near infrared probe that provides an intense OFF/ON amplified fluorescence signal for specific detection of human neutrophil elastase. The probe allowed selective detection of activated neutrophils and labelling of neutrophil extracellular traps.

Approved and investigational fluorescent optical imaging agents for disease detection in surgery

Fluorescent optical imaging is becoming an increasingly attractive imaging tool that physicians can utilise as it can detect previously 'unseen' changes in tissue at a cellular level that are consistent with disease. This is possible using a range of fluorescently labelled imaging agents that, once excited by specific wavelengths of light, can illuminate damaged and diseased tissues. For surgeons, such agents can permit dynamic, intraoperative imaging providing a real-time guide as they resect diseased tissue.

Solid-Phase Synthesis of s-Tetrazines

An efficient synthesis of s-tetrazines by solid-phase methods is described. This synthesis route was compatible with different solid-phase resins and linkers and did not require metal catalysts or high temperatures. Monosubstituted tetrazines were routinely synthesized using thiol-promoted chemistry, using dichloromethane as a carbon source, while disubstituted unsymmetrical aryl or alkyl tetrazines were synthesized using readily available nitriles. This efficient approach enabled the synthesis of s-tetrazines in high yields (70-94%), eliminating the classical solution-phase problems of mixtures of symmetrical and unsymmetrical tetrazines, with only a single final purification step required, and paves the way to the rapid synthesis of s-tetrazines with various applications in bioorthogonal chemistry and beyond.

Programmable and Flexible Fluorochromic Polymer Microarrays for Information Storage

Photoresponsive fluorochromic materials are regarded as an effective means for information storage. Their reversible changes of color and fluorescence facilitate the storage process and increase the possible storage capacity. Here, we propose an optically reconfigurable Förster resonance energy transfer (FRET) process to realize tunable emissions based on photochromic spiropyrans and common fluorophores. The kinetics of the photoisomerization of the spiropyran and the FRET process of the composite were systematically investigated. Through tuning the ratios of the acceptor spiropyran and donor fluorophore and external light stimuli, a programmable FRET process was developed to obtain tunable outputs. More importantly, flexible microarrays were fabricated from such fluorochromic mixtures by inkjet printing (230 ppi) and the dynamic FRET process could also be applied to generate tunable fluorescence in ready-made microstructures. The flexible patterns created using the microarrays could be used as novel optically readable media for information storage by altering the composition and optical performance of every feature within the microarray. A key aspect of information storage such is anti-counterfeiting, and these colorful displays can be fabricated and integrated in a simple and straightforward system. The reliable fabrication and programmable optical performances of these large-scale flexible polymer microarrays represent a substantial step toward high-density and high-security information storage platforms.

Attaching palladium catalysts to antibodies

Antibody-directed enzyme prodrug therapy (ADEPT) is a powerful concept in which antibody targeting is linked to enzymatic prodrug activation. The work herein describes the first steps in the development of a technology analogous to ADEPT but in which a palladium catalyst is attached of an antibody rather than an enzyme. Antibody-metal conjugates have been used in a variety of contexts including for radiotherapy; however, none of the metals attached to the antibodies have been used for catalytic purposes. This work represents the first example a metal being attached to an antibody for the purposes of carrying a functional catalyst.

Dyeing fungi: amphotericin B based fluorescent probes for multiplexed imaging

The clinically used antifungal polyene amphotericin B was conjugated, via the mycosamine and the aglycon moieties, to fluorophores. The Cy5 conjugated probe showed selective labelling of fungi in the presence of bacteria, allowing multiplexed imaging and identification of microbial species in a co-culture of fungi and Gram-positive and Gram-negative bacteria.

Solid-Phase Synthesis of Fluorescent Probes for Plasma Membrane Labelling

The cellular plasma membrane plays a fundamental role in biological processes, including cell growth, signaling and transport. The labelling of the plasma membrane with targeted fluorescent probes offers a convenient and non-invasive way to image the morphological changes and dynamics of a membrane in real-time and, despite many examples of fluorescent plasma membrane probes, a "universal targeting/anchoring moiety" is still required. In this study, a small number of stearic acid-based probes labelled with 6-carboxyfluorescein was designed and fabricated via solid-phase synthesis in which variations in both charge and hydrophobicity were explored. To ease the synthesis process, a gram-scale synthesis of the Fmoc-Lys(6-carboxyfluoresein diacetate)-OH building block was developed, allowing the discovery of optimal probes that carried a positively charged amino group and a stearic acid tail that exhibited intense plasma membrane brightness and robust retention.

Multifunctional, histidine-tagged polymers: antibody conjugation and signal amplification

A polymer scaffold, with multiple reactive centres, was synthesised by RAFT polymerisation and conjugated to the antibody herceptin. A hexahistidine RAFT agent enabled simple purification of polymer–protein conjugates.

Solid-phase synthesis of biocompatible N-heterocyclic carbene–Pd catalysts using a sub-monomer approach

Biocompatible N-heterocyclic carbene (NHC) based Pd ligands were assembled and loaded with Pd via solid-phase synthesis.

Tetrazine-mediated bioorthogonal prodrug-prodrug activation

The selective and biocompatible activation of prodrugs within complex biological systems remains a key challenge in medical chemistry and chemical biology. Herein we report, for the first time, a dual prodrug activation strategy that fully satisfies the principle of bioorthogonality by the symbiotic formation of two active drugs. This dual and traceless prodrug activation strategy takes advantage of the INVDA chemistry of tetrazines (here a prodrug), generating a pyridazine-based miR21 inhibitor and the anti-cancer drug camptothecin and offers a new concept in prodrug activation.

New substrates for stem cell control

The capacity to culture stem cells in a controllable, robust and scalable manner is necessary in order to develop successful strategies for the generation of cellular and tissue platforms for drug screening, toxicity testing, tissue engineering and regenerative medicine. Creating substrates that support the expansion, maintenance or directional differentiation of stem cells would greatly aid these efforts. Optimally, the substrates used should be chemically defined and synthetically scalable, allowing growth under defined, serum-free culture conditions. To achieve this, the chemical and physical attributes of the substrates should mimic the natural tissue environment and allow control of their biological properties. Herein, recent advances in the development of materials to study/manipulate stem cells, both in vitro and in vivo, are described with a focus on the novelty of the substrates' properties, and on application of substrates to direct stem cells.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

In-Cell Dual Drug Synthesis by Cancer-Targeting Palladium Catalysts

Transition metals have been successfully applied to catalyze non-natural chemical transformations within living cells, with the highly efficient labeling of subcellular components and the activation of prodrugs. In vivo applications, however, have been scarce, with a need for the specific cellular targeting of the active transition metals. Here, we show the design and application of cancer-targeting palladium catalysts, with their specific uptake in brain cancer (glioblastoma) cells, while maintaining their catalytic activity. In these cells, for the first time, two different anticancer agents were synthesized simultaneously intracellularly, by two totally different mechanisms (in situ synthesis and decaging), enhancing the therapeutic effect of the drugs. Tumor specificity of the catalysts together with their ability to perform simultaneous multiple bioorthogonal transformations will empower the application of in vivo transition metals for drug activation strategies.

Intracellular delivery of a catalytic organometallic complex

We show the intracellular delivery of a homogeneous palladium–peptide catalyst able to bioorthogonally activate a profluorophore inside living prostate cancer cells.

Tetrazine-Responsive Self-immolative Linkers

Molecules that undergo activation or modulation following the addition of benign external small-molecule chemical stimuli have numerous applications. Here, we report the highly efficient "decaging" of a variety of moieties by activation of a "self-immolative" linker, by application of water-soluble and stable tetrazine, including the controlled delivery of doxorubicin in a cellular context.

Copper Catalysis in Living Systems and In Situ Drug Synthesis

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has proven to be a pivotal advance in chemical ligation strategies with applications ranging from polymer fabrication to bioconjugation. However, application in vivo has been limited by the inherent toxicity of the copper catalyst. Herein, we report the application of heterogeneous copper catalysts in azide-alkyne cycloaddition processes in biological systems ranging from cells to zebrafish, with reactions spanning from fluorophore activation to the first reported in situ generation of a triazole-containing anticancer agent from two benign components, opening up many new avenues of exploration for CuAAC chemistry.

High-throughput Identification of Bacteria Repellent Polymers for Medical Devices

Medical devices are often associated with hospital-acquired infections, which place enormous strain on patients and the healthcare system as well as contributing to antimicrobial resistance. One possible avenue for the reduction of device-associated infections is the identification of bacteria-repellent polymer coatings for these devices, which would prevent bacterial binding at the initial attachment step. A method for the identification of such repellent polymers, based on the parallel screening of hundreds of polymers using a microarray, is described here. This high-throughput method resulted in the identification of a range of promising polymers that resisted binding of various clinically relevant bacterial species individually and also as multi-species communities. One polymer, PA13 (poly(methylmethacrylate-co-dimethylacrylamide)), demonstrated significant reduction in attachment of a number of hospital isolates when coated onto two commercially available central venous catheters. The method described could be applied to identify polymers for a wide range of applications in which modification of bacterial attachment is important.

Fortified interpenetrating polymers - bacteria resistant coatings for medical devices

Nanocapsule-mediated eugenol release from an interpenetrating polymer network coating reduces bacterial binding on medical devices.

Infections arising from contaminated medical devices are a serious global issue, contributing to antibiotic resistance and imposing significant strain on healthcare systems. Since the majority of medical device-associated infections are biofilm related, efforts are being made to generate either bacteria-repellent or antibacterial coatings aimed at preventing bacterial colonisation. Here, we utilise a nanocapsule mediated slow release of a natural antimicrobial to improve the performance of a bacteria repellent polymer coating. Poly(lauryl acrylate) nanocapsules containing eugenol (4-allyl-2-methoxyphenol) were prepared and entrapped within a interpenetrating network designed to repel bacteria. When coated on a catheter and an endotracheal tube, this hemocompatible system allowed slow-release of eugenol, resulting in notable reduction in surface-bound Klebsiella pneumoniae and methicillin resistant Staphylococcus aureus.

Fluorogenic Substrates for In Situ Monitoring of Caspase-3 Activity in Live Cells

The in situ detection of caspase-3 activity has applications in the imaging and monitoring of multiple pathologies, notably cancer. A series of cell penetrating FRET-based fluorogenic substrates were designed and synthesised for the detection of caspase-3 in live cells. A variety of modifications of the classical caspase-3 and caspase-7 substrate sequence Asp-Glu-Val-Asp were carried out in order to increase caspase-3 affinity and eliminate caspase-7 cross-reactivity. To allow cellular uptake and good solubility, the substrates were conjugated to a cationic peptoid. The most selective fluorogenic substrate 27, FAM-Ahx-Asp-Leu-Pro-Asp-Lys(MR)-Ahx, conjugated to the cell penetrating peptoid at the C-terminus, was able to detect and quantify caspase-3 activity in apoptotic cells without cross-reactivity by caspase-7.

Eliminating caspase-7 and cathepsin B cross-reactivity on fluorogenic caspase-3 substrates

11 FRET-based fluorogenic substrates were constructed using the pentapeptide template Asp-Glu-X2-Asp-X1', and evaluated with caspase-3, caspase-7 and cathepsin B. The sequence Asp-Glu-Pro-Asp-Ser was able to selectively quantify caspase-3 activity in vitro without notable caspase-7 and cathepsin B cross-reactivity, while exhibiting low μM KM values and good catalytic efficiencies (7.0-16.9 μM(-1) min(-1)).

Palladium-mediated in situ synthesis of an anticancer agent

Biocompatible heterogeneous Pd(0) catalysts were used in a Suzuki–Miyaura cross-coupling reaction to synthesise an anticancer agent in situ, leading to apoptosis of prostate cancer cells.

A labelled-ubiquicidin antimicrobial peptide for immediate in situ optical detection of live bacteria in human alveolar lung tissue

The in situ immediate detection of the presence of bacteria in the distal human lung is of significant clinical utility. Herein we describe the development and optimization of a bacterial binding fragment (UBI29-41) of the antimicrobial peptide, ubiquicidin (UBI), conjugated to an environmentally sensitive fluorophore to enable rapid live bacterial imaging within human lung tissue. UBI29-41 was modified for stability in the presence of human lung bronchoalveolar lavage fluid, for affinity to bacterial membranes and functionality in human lung tissue. The optimized cyclic structure yields an optical molecular Smartprobe for bacterial detection in human lung tissue.

Thermoresponsive hydrogel maintains the mouse embryonic stem cell “naïve” pluripotency phenotype

A chemically defined hydrogel HG21, which allows enzyme-free passaging, is a substitute for gelatin allowing standardised and inexpensive mESC culture.

A high-throughput polymer microarray approach for identifying defined substrates for mesenchymal stem cells

Mesenchymal stem cells (MSCs) hold great promise in regenerative medicine due to their wide multilineage potential as well as their ability to suppress/modulate the immune response. Maintaining these cells in vitro and expanding them on a clinically relevant scale remains a challenge that needs to be addressed to realise their full potential. Current culture methods for MSCs typically rely on animal sourced substrates and often result in a heterogeneous population of cells with varying degrees of differentiation capacity. Here, a high-throughput platform was used to identify synthetic substrates for MSC culture that not only facilitated growth but also maintained the MSC phenotype. Two polymers, PU157 (synthesised from poly(butyleneglycol) and 4,4'-methylenediphenyldiisocyanate with 3-(dimethylamino)-1,2-propanediol as a chain extender) and PA338 (N-methylaniline modified poly(methylmethacrylate-co-glycidylmethacrylate)) were able to maintain the growth and phenotype of human embryonic derived mesenchymal progenitors (hES-MPs) and adipose derived MSCs (ADMSCs) for five and ten passages, respectively. Cell phenotype and multipotency were confirmed by flow cytometry analysis of ten MSC markers and differentiation analysis. These new polymer substrates provide a chemically defined synthetic surface for efficient, long-term MSC culture.

Bacteria repelling poly(methylmethacrylate-co-dimethylacrylamide) coatings for biomedical devices†Electronic supplementary information (ESI) available: Polymer microarray screening, including analysis of bacterial adhesion by fluorescence microscopy and SEM, and chemical composition of bacteria repelling polymers identified in the screen; polymer synthesis and characterisation; preparation of catheter pieces and solvent studies, and details for confocal imaging/analysis. See DOI: 10.1039/c4tb01129eClick here for additional data file

A polymer microarray screen identified poly(methylmethacrylate-co-dimethylacrylamide) as a bacteria repelling surface, which substantially reduced binding of bacteria on coated catheters.

Nosocomial infections due to bacteria have serious implications on the health and recovery of patients in a variety of medical scenarios. Since bacterial contamination on medical devices contributes to the majority of nosocomical infections, there is a need for redesigning the surfaces of medical devices, such as catheters and tracheal tubes, to resist the binding of bacteria. In this work, polyurethanes and polyacrylates/acrylamides, which resist binding by the major bacterial pathogens underpinning implant-associated infections, were identified using high-throughput polymer microarrays. Subsequently, two ‘hit’ polymers, PA13 (poly(methylmethacrylate-co-dimethylacrylamide)) and PA515 (poly(methoxyethylmethacrylate-co-diethylaminoethylacrylate-co-methylmethacrylate)), were used to coat catheters and substantially shown to decrease binding of a variety of bacteria (including isolates from infected endotracheal tubes and heart valves from intensive care unit patients). Catheters coated with polymer PA13 showed up to 96% reduction in bacteria binding in comparison to uncoated catheters.

Photoluminescent carbon dots from 1,4-addition polymers

Photoluminescent carbon dots were synthesised directly by thermopyrolysis of 1,4-addition polymers, allowing precise control of their properties. The effect of polymer composition on the properties of the carbon dots was investigated by TEM, IR, XPS, elemental analysis and fluorescence analysis, with carbon dots synthesised from nitrogen-containing polymers showing the highest fluorescence. The carbon dots with high nitrogen content were observed to have strong fluorescence in the visible region, and culture with cells showed that the carbon dots were non-cytotoxic and readily taken up by three different cell lines.

Synthesis, biological evaluation, and structure-activity relationships for 5-[(E)-2-arylethenyl]-3-isoxazolecarboxylic acid alkyl ester derivatives as valuable antitubercular chemotypes

Tuberculosis (TB), mostly caused by Mycobacterium tuberculosis (Mtb), is one of the leading causes of death from infectious disease worldwide. Its coinfection with HIV and the emergence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) strains have further worsened the TB pandemic. Despite its global impact, TB is considered a neglected disease and no new anti-TB therapeutics have been introduced over the last four decades. The nonreplicating persistent form of TB (NRP-TB) is responsible for the length of the treatment and is the putative cause of treatment failure. Therefore, new anti-TB agents, which are active against both the replicating form of Mtb (R-TB) and NRP-TB, are urgently needed. Herein, we report the synthesis and structure-activity relationships (SAR) of a series of 5-[(E)-2-arylethenyl]-3-isoxazolecarboxylic acid alkyl esters as potent anti-TB agents. Several compounds had submicromolar minimum inhibitory concentrations (MIC) against R-TB and were active against NRP-TB in the low micromolar range, thus representing attractive lead compounds for the possible development of new anti-TB agents.

A 3D QSAR model of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core applying molecular dynamics simulations and ligand-protein docking

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme plays a crucial role in female hormonal regulation by catalysing the NADPH-dependent reduction of the less potent estrone E1 into the biologically active estradiol E2. Because 17beta-HSD1 is a key enzyme in E2 biosynthesis, it has emerged as an attractive drug target for inhibitor development. Herein we report the plausible binding modes and a 3D QSAR model of 17beta-HSD1 inhibitors based on a (di)cycloalkenothieno[2,3-d]pyrimidin-4(3H)-one core. Two generated enzyme complexes with potent inhibitors were subjected to molecular dynamics simulation to mimic the dynamic process of inhibitor binding. A set of 17beta-HSD1 inhibitors based on the thieno[2,3-d]pyrimidin-4(3H)-one core were docked into the resulting active site, and a CoMFA model employing the most extensive training set to date was generated. The model was validated with an external test set. Active site residues involved in inhibitor binding and CoMFA fields for steric and electrostatic interactions were identified. The model will be used to guide structural modifications of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core in order to improve the biological activity as well as in the design of novel 17beta-HSD1 inhibitors.

Active site analysis of 17beta-hydroxysteroid dehydrogenase type 1 enzyme complexes with SPROUT

Estrogens, especially estradiol, have been shown to stimulate the proliferation of hormone-dependent types of breast cancer cells. 17Beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme catalyses the synthesis of the active female estrogen, estradiol and is thus an attractive target for structure-based ligand design for the prevention and control of breast tumour growth. In this study, the active site of 17beta-HSD1 has been reviewed, and three crystal structure complexes (estradiol/NADP+, equilin/NADP+, dehydroepiandrosterone) of 17beta-HSD1 have been selected to be analysed for de novo ligand design. The boundary surface, hydrophobic interactions and hydrogen bonding sites in the ligand binding domain for each ligand complex were analysed to create a comprehensive image of the active site.

(Z)-1-Aryl-1-haloalkenes as intermediates in the Vilsmeier haloformylation of aryl ketones

[reaction: see text] Vilsmeier reagents give (Z)-1-aryl-1-haloalkenes from aryl ketones bearing an electron-donating substituent at the ortho- or para-position. These haloalkenes are intermediates in the Vilsmeier haloformylation of the aryl ketones. Another reaction mechanistic pathway is thus available in certain Vilsmeier haloformylations, in competition with the commonly accepted route by way of an enaminoketone.