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Photodynamic therapy is an anti‐cancer treatment that requires illumination of photosensitizers to induce local cell death. Current near‐infrared organic photosensitizers are built from large and non‐modular structures that cannot be tuned to improve safety and minimize off‐target toxicity. This work describes a novel chemical platform to generate enzyme‐activatable near‐infrared photosensitizers. We optimized the Se‐bridged hemicyanine scaffold to include caging groups and biocompatible moieties, and generated cathepsin‐triggered photosensitizers for effective ablation of human glioblastoma cells. Furthermore, we demonstrated that enzyme‐activatable Se‐bridged hemicyanines are effective photosensitizers for the safe ablation of microtumors in vivo, creating new avenues in the chemical design of targeted anti‐cancer photodynamic therapy agents. [ABSTRACT FROM AUTHOR]

T cells are an essential part of the immune system with crucial roles in adaptive response and the maintenance of tissue homeostasis. Depending on their microenvironment, T cells can be differentiated into multiple states with distinct functions. This myriad of cellular activities have prompted the development of numerous smart probes, ranging from small molecule fluorophores to nanoconstructs with variable molecular architectures and fluorescence emission mechanisms. In this Tutorial Review, we summarize recent efforts in the design, synthesis and application of smart probes for imaging T cells in tumors and inflammation sites by targeting metabolic and enzymatic biomarkers as well as specific surface receptors. Finally, we briefly review current strategies for how smart probes are employed to monitor the response of T cells to anti-cancer immunotherapies. We hope that this Review may help chemists, biologists and immunologists to design the next generation of molecular imaging probes for T cells and anti-cancer immunotherapies. [ABSTRACT FROM AUTHOR]

The G protein‐coupled kisspeptin receptor (GPR54 or KISS1R) is an important mediator in reproduction, metabolism and cancer biology; however, there are limited fluorescent probes or antibodies for direct imaging of these receptors in cells and intact tissues, which can help to interrogate their multiple biological roles. Herein, we describe the rational design and characterization of a new acid‐resistant BODIPY‐based amino acid (Trp‐BODIPY PLUS), and its implementation for solid‐phase synthesis of fluorescent bioactive peptides. Trp‐BODIPY PLUS retains the binding capabilities of both short linear and cyclic peptides and displays notable turn‐on fluorescence emission upon target binding for wash‐free imaging. Finally, we employed Trp‐BODIPY PLUS to prepare some of the first fluorogenic kisspeptin‐based probes and visualized the expression and localization of GPR54 receptors in human cells and in whole mouse pancreatic islets by fluorescence imaging. [ABSTRACT FROM AUTHOR]

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near‐infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity‐based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild‐type and GzmA knock‐out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen‐driven recognition of cancer cells in real time. [ABSTRACT FROM AUTHOR]

The multiple applications of super‐resolution microscopy have prompted the need for minimally invasive labeling strategies for peptide‐guided fluorescence imaging. Many fluorescent reporters display limitations (e.g. large and charged scaffolds, non‐specific binding) as building blocks for the construction of fluorogenic peptides. Herein we have built a library of benzodiazole amino acids and systematically examined them as reporters for background‐free fluorescence microscopy. We have identified amine‐derivatized benzoselenadiazoles as scalable and photostable amino acids for the straightforward solid‐phase synthesis of fluorescent peptides. Benzodiazole amino acids retain the binding capabilities of bioactive peptides and display excellent signal‐to‐background ratios. Furthermore, we have demonstrated their application in peptide‐PAINT imaging of postsynaptic density protein‐95 nanoclusters in the synaptosomes from mouse brain tissues. [ABSTRACT FROM AUTHOR]

Increased levels of tumor‐associated macrophages (TAMs) are indicators of poor prognosis in most cancers. Although antibodies and small molecules blocking the recruitment of macrophages to tumors are under evaluation as anticancer therapies, these strategies are not specific for macrophage subpopulations. Herein we report the first enzyme‐activatable chemokine conjugates for effective targeting of defined macrophage subsets in live tumors. Our constructs exploit the high expression of chemokine receptors (e.g. CCR2) and the activity of cysteine cathepsins in TAMs to target these cells selectively over other macrophages and immune cells (e.g. neutrophils, T cells, B cells). Furthermore, we demonstrate that cathepsin‐activatable chemokines are compatible with both fluorescent and therapeutic cargos, opening new avenues in the design of targeted theranostic probes for immune cells in the tumor microenvironment. [ABSTRACT FROM AUTHOR]

Fungal infections caused by Candida species are among the most prevalent in hospitalized patients. However, current methods for the detection of Candida fungal cells in clinical samples rely on time‐consuming assays that hamper rapid and reliable diagnosis. Herein, we describe the rational development of new Phe‐BODIPY amino acids as small fluorogenic building blocks and their application to generate fluorescent antimicrobial peptides for rapid labelling of Candida cells in urine. We have used computational methods to analyse the fluorogenic behaviour of BODIPY‐substituted aromatic amino acids and performed bioactivity and confocal microscopy experiments in different strains to confirm the utility and versatility of peptides incorporating Phe‐BODIPYs. Finally, we have designed a simple and sensitive fluorescence‐based assay for the detection of Candida albicans in human urine samples. [ABSTRACT FROM AUTHOR]

Pilzinfektionen, die durch Candida‐Arten verursacht werden, gehören zu den häufigsten Infektionen bei Krankenhauspatienten. Die derzeitigen Methoden zum Nachweis von Candida‐Pilzzellen in klinischen Proben beruhen jedoch auf zeitaufwändigen Analysen, die eine schnelle und zuverlässige Diagnose erschweren. In diesem Beitrag beschreiben wir die rationale Entwicklung neuer Phe‐BODIPY‐Aminosäuren als kleine fluorogene Bausteine und ihre Anwendung zur Erzeugung fluoreszierender antimikrobieller Peptide für die schnelle Markierung von Candida‐Zellen im Urin. Mit Hilfe von computergestützten Berechnungen haben wir das fluorogene Verhalten von BODIPY‐substituierten aromatischen Aminosäuren analysiert und Bioaktivitäts‐ und konfokale Mikroskopieexperimente bei verschiedenen Stämmen durchgeführt, um den Nutzen und die Vielseitigkeit von Peptiden mit Phe‐BODIPYs zu bestätigen. Schließlich haben wir einen einfachen und sensitiven fluoreszensbasierten Test zum Nachweis von Candida albicans in menschlichen Urinproben entwickelt. [ABSTRACT FROM AUTHOR]

The detection and quantification of apoptotic cells is a key process in cancer research, particularly during the screening of anticancer therapeutics and in mechanistic studies using preclinical models. Intravital optical imaging enables high‐resolution visualisation of cellular events in live organisms; however, there are few fluorescent probes that can reliably provide functional readouts in situ without interference from tissue autofluorescence. We report the design and optimisation of the fluorogenic probe Apotracker Red for real‐time detection of cancer cell death. The strong fluorogenic behaviour, high selectivity, and excellent stability of Apotracker Red make it a reliable optical reporter for the characterisation of the effects of anticancer drugs in cells in vitro and for direct imaging of chemotherapy‐induced apoptosis in vivo in mouse models of breast cancer. [ABSTRACT FROM AUTHOR]

Fluorescent cyclic peptides are excellent chemical scaffolds to build optical agents for molecular imaging. In addition to their favorable physicochemical properties, they can be modified with multiple organic fluorophores and generate useful probes for biological assays targeting specific proteins, namely receptors or enzymes. In this article, we review recent advances in the synthetic approaches for the preparation of fluorescent cyclic peptides as well as some of their applications in biological imaging, from in vitro live‐cell imaging studies to in vivo characterization of preclinical models. [ABSTRACT FROM AUTHOR]

New chemotypes are obtained from tryptophan-containing diketopiperazines through selective C–C or C–N intramolecular oxidative couplings. The choice of the oxidant source dictates the outcome of the reaction. [ABSTRACT FROM AUTHOR]

The rational design and synthesis of a Trp-BODIPY cyclic peptide for the fluorescent labelling of apoptotic bodies is described. Affinity assays, confocal microscopy and flow cytometry analysis confirmed the binding of the peptide to negatively-charged phospholipids associated with apoptosis, and its applicability for the detection and characterisation of subcellular structures released by apoptotic cells. [ABSTRACT FROM AUTHOR]

A series of short tryptophan-phenylalanine peptides containing an iodo substituent on the phenyl ring was subjected to Pd-catalyzed CH activation reactions to give the corresponding aryl-indole coupled products. Two types of adducts were generated: cyclomonomer and cyclodimeric peptides; no evidence of oligo- or polymerization products was detected. Contrary to standard peptide macrocyclizations, the factors controlling the fate of the reaction are the number of amino acids between the aromatic residues and the regiochemistry of the parent iodo derivative, independent of both the concentration and the cyclization mode. The method is general and allows access to novel biaryl peptidic topologies, which have been fully characterized. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides are valuable agents to fight antibiotic resistance. These amphipatic species display positively charged and hydrophobic amino acids. Here, we enhance the local hydrophobicity of a model peptide derived from human lysozyme (107RKWVWWRNR115) by arylation of its tryptophan (Trp) residues, which renders a positive effect on Staphylococcus aureus and Staphylococcus epidermidis growth inhibition. This site-selective modification was accessed by solid-phase peptide synthesis using the non-proteinogenic amino acid 2-aryltryptophan, generated by direct C-H activation from protected Trp. The modification brought about a relevant increase in growth inhibition: S. aureus was fully inhibited by arylation of Trp 112 and by only 10% by arylation of Trp 109 or 111, respect to the non-arylated peptide. On the other hand, S. epidermidis was fully inhibited by the three arylated peptides and the parent peptide. The minimum inhibitory concentration was significantly reduced for S. aureus depending on the arylation site. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Tryptophan (Trp) and tryptophan derivatives are C2-arylated. A C--H activation process allows the preparation of both protected and unprotected arylated-Trp amino acids, directly from the amino acid precursor and aryl iodides. The obtained compounds are suitable for standard solid-phase peptide synthesis. [ABSTRACT FROM AUTHOR]

Cys-disulfide bonds contribute to the stabilization of peptide and protein structures. The synthesis of these molecules requires a proper protection of Cys residues, which is crucial to prevent side-reactions and also to achieve the correct Cys connectivity. Here we undertook a mechanistic study of a set of well-known acid-labile Cys protecting groups, as well other new promising groups, in order to better understand the nature of their acid-lability. The stability of the carbocation generated during the acid treatment was found to have a direct impact on the removal of the protective groups from the corresponding protected Cys-containing peptides. Hence a combination of steric and conjugative effects determines the stability of the carbocations generated. Here we propose diphenylmethyl (Dpm) as a promising protecting group on the basis of its intermediate relative carbocation stability. All the optimized geometries and energies presented in this study were determined using a B3LYP/6-31G(d,p) calculation. The results discussed herein may be of broader applicability for the development of new protecting groups. [ABSTRACT FROM AUTHOR]

To address the existing gap in the current set of acid-labile Cys-protecting groups for the Fmoc/tBu strategy, diverse Fmoc-Cys(PG)-OH derivatives were prepared and incorporated into a model tripeptide to study their stability against TFA. S-Dpm proved to be compatible with the commonly used S-Trt group and was applied for the regioselecive construction of disulfide bonds. [ABSTRACT FROM AUTHOR]

The prohibitin (PHB)-binding compound fluorizoline as well as PHB-downregulation activate the integrated stress response (ISR) in HEK293T and U2OS human cell lines. This activation is denoted by phosphorylation of eIF2α and increases in ATF4, ATF3, and CHOP protein levels. The blockage of the activation of the ISR by overexpression of GRP78, as well as an increase in IRE1 activity, indicate the presence of ER stress after fluorizoline treatment. The inhibition of the ER stress response in HEK293T and U2OS led to increased sensitivity to fluorizoline-induced apoptosis, indicating a pro-survival role of this pathway after fluorizoline treatment in these cell lines. Fluorizoline induced an increase in calcium concentration in the cytosol and the mitochondria. Finally, two different calcium chelators reduced fluorizoline-induced apoptosis in U2OS cells. Thus, we have found that fluorizoline causes increased ER stress and activation of the integrated stress response, which in HEK293T and U2OS cells are protective against fluorizoline-induced apoptosis. [ABSTRACT FROM AUTHOR]

This simple, mild, and versatile method allows the preparation of α-arylated indoles including amino acid derivatives directly from the corresponding indole or amino acid precursors. [ABSTRACT FROM AUTHOR]