Monitoring the action of redox-directed cancer therapeutics using a human peroxiredoxin-2-based probe

A guide to genetically-encoded redox biosensors: State of the art and opportunities

Genetically-encoded redox biosensors have become invaluable tools for monitoring cellular redox processes with high spatiotemporal resolution, coupling the presence of the redox-active analyte with a change in fluorescence signal that can be easily recorded. This review summarizes the available fluorescence recording methods and presents an in-depth classification of the redox biosensors, organized by the analytes they respond to. In addition to the fluorescent protein-based architectures, this review also describes the recent advances on fluorescent, chemigenetic-based redox biosensors and other emerging chemigenetic strategies. This review examines how these biosensors are designed, the biosensors sensing mechanism, and their practical advantages and disadvantages.

Modern optical approaches in redox biology: Genetically encoded sensors and Raman spectroscopy

The objective of the current review is to summarize the current state of optical methods in redox biology. It consists of two parts, the first is dedicated to genetically encoded fluorescent indicators and the second to Raman spectroscopy. In the first part, we provide a detailed classification of the currently available redox biosensors based on their target analytes. We thoroughly discuss the main architecture types of these proteins, the underlying engineering strategies for their development, the biochemical properties of existing tools and their advantages and disadvantages from a practical point of view. Particular attention is paid to fluorescence lifetime imaging microscopy as a possible readout technique, since it is less prone to certain artifacts than traditional intensiometric measurements. In the second part, the characteristic Raman peaks of the most important redox intermediates are listed, and examples of how this knowledge can be implemented in biological studies are given. This part covers such fields as estimation of the redox states and concentrations of Fe-S clusters, cytochromes, other heme-containing proteins, oxidative derivatives of thiols, lipids, and nucleotides. Finally, we touch on the issue of multiparameter imaging, in which biosensors are combined with other visualization methods for simultaneous assessment of several cellular parameters.

Genetically Encoded Biosensors for the Fluorescence Detection of O2 and Reactive O2 Species

The intracellular concentrations of oxygen and reactive oxygen species (ROS) in living cells represent critical information for investigating physiological and pathological conditions. Real-time measurement often relies on genetically encoded proteins that are responsive to fluctuations in either oxygen or ROS concentrations. The direct binding or chemical reactions that occur in their presence either directly alter the fluorescence properties of the binding protein or alter the fluorescence properties of fusion partners, mostly consisting of variants of the green fluorescent protein. Oxygen sensing takes advantage of several mechanisms, including (i) the oxygen-dependent hydroxylation of a domain of the hypoxia-inducible factor-1, which, in turn, promotes its cellular degradation along with fluorescent fusion partners; (ii) the naturally oxygen-dependent maturation of the fluorophore of green fluorescent protein variants; and (iii) direct oxygen binding by proteins, including heme proteins, expressed in fusion with fluorescent partners, resulting in changes in fluorescence due to conformational alterations or fluorescence resonance energy transfer. ROS encompass a group of highly reactive chemicals that can interconvert through various chemical reactions within biological systems, posing challenges for their selective detection through genetically encoded sensors. However, their general reactivity, and particularly that of the relatively stable oxygen peroxide, can be exploited for ROS sensing through different mechanisms, including (i) the ROS-induced formation of disulfide bonds in engineered fluorescent proteins or fusion partners of fluorescent proteins, ultimately leading to fluorescence changes; and (ii) conformational changes of naturally occurring ROS-sensing domains, affecting the fluorescence properties of fusion partners. In this review, we will offer an overview of these genetically encoded biosensors.

A Covalent Organic Framework Derived N-doped Carbon Nanozyme as the All-rounder for Targeted Catalytic Therapy and NIR-II Photothermal Therapy of Cancer

Nanomaterials with intrinsic enzyme-like activities (nanozymes) have gained significant attention in cancer catalytic therapy; however, developing metal-free nanozymes with multivariant enzyme-like activity as the "all-rounder" for cancer therapy remains challenging. Herein, a covalent organic framework (COF) derived carbon-based nanozyme is rationally devised to achieve synergistic catalytic therapy and second near-infrared (NIR-II) photothermal therapy of cancer. The developed nanozyme possesses multivariant enzyme-like activities, including oxidase (OXD)-like, catalase (CAT)-like, and peroxidase (POD)-like catalytic activities, which enables the nanozyme to produce adequate reactive oxygen species (ROS) for cancer cell killing. Furthermore, the nanozyme showed excellent photothermal converting activity that could kill cancer cells upon NIR-II laser irradiation, owing to the strong NIR-II absorption capacity of carbon-based materials. It is also worth noting that the nanozyme exhibited cytotoxicity specifically in tumor tissue profiting from the discrepant H2O2 level between tumor and normal tissue and the spatiotemporal controllability of laser irradiation. This work may inspire further development of intelligent nanozymes in biological applications across broad therapeutic and biomedical fields.

Nanoprobe-based molecular imaging for tumor stratification

The responses of patients to tumor therapies vary due to tumor heterogeneity. Tumor stratification has been attracting increasing attention for accurately distinguishing between responders to treatment and non-responders. Nanoprobes with unique physical and chemical properties have great potential for patient stratification. This review begins by describing the features and design principles of nanoprobes that can visualize specific cell types and biomarkers and release inflammatory factors during or before tumor treatment. Then, we focus on the recent advancements in using nanoprobes to stratify various therapeutic modalities, including chemotherapy, radiotherapy (RT), photothermal therapy (PTT), photodynamic therapy (PDT), chemodynamic therapy (CDT), ferroptosis, and immunotherapy. The main challenges and perspectives of nanoprobes in cancer stratification are also discussed to facilitate probe development and clinical applications.

Cuproptosis predicts the risk and clinical outcomes of lung adenocarcinoma

Copper is an essential microelement for the body and a necessary coregulator for enzymatic reactions, yet an unbalanced copper level promotes reactive oxidation and cytotoxicity, which ultimately induces cell death. Several small molecules targeting copper-induced cell death have been investigated, yet few showed promising therapeutic effects in clinical trials. In March 2022, Science first introduced the concept and mechanisms of cuproptosis, suggesting that copper-induced cell death targets the tricarboxylic acid (TCA) cycle via protein lipoylation. Does this novel form of cell death take part in tumorigenesis or tumor progression? Is cuproptosis related to clinical outcomes of diseases? Is there a cuproptosis-related panel for clinical practice in cancer treatment? Herein, based on 942 samples of lung adenocarcinoma (LUAD), we analyzed on gene set level the existence and predictive value of cuproptosis in disease diagnosis and treatment. We screened out and identified the “cupLA” panel which indicates the risk of LUAD occurrence, clinicopathological features of LUAD patients, and could guide clinicians to refine LUAD subtypes and make treatment choices.

Electrodes and electrocatalysts for electrochemical hydrogen peroxide sensors: a review of design strategies

H₂O₂ sensing is required in various biological and industrial applications, for which electrochemical sensing is a promising choice among various sensing technologies. Electrodes and electrocatalysts strongly influence the performance of electrochemical H₂O₂ sensors. Significant efforts have been devoted to electrode nanostructural designs and nanomaterial-based electrocatalysts. Here, we review the design strategies for electrodes and electrocatalysts used in electrochemical H₂O₂ sensors. We first summarize electrodes in different structures, including rotation disc electrodes, freestanding electrodes, all-in-one electrodes, and representative commercial H₂O₂ probes. Next, we discuss the design strategies used in recent studies to increase the number of active sites and intrinsic activities of electrocatalysts for H₂O₂ redox reactions, including nanoscale pore structuring, conductive supports, reducing the catalyst size, alloying, doping, and tuning the crystal facets. Finally, we provide our perspectives on the future research directions in creating nanoscale structures and nanomaterials to enable advanced electrochemical H₂O₂ sensors in practical applications.

Quantification of doping state of redox sensitive nanoparticles for probing the invasiveness of cancer cells using surface enhanced Raman scattering

Redox activity is known to regulate migration, invasion, metastasis, proliferation, and vascularization of cancer. Because cancer is heterogeneous, the role of redox activity in different cancers and cancer-related processes vary widely. In this study, water soluble, Tween 80-coated polyaniline (TPAni) nanoparticles were synthesized and used as nano-agents for sensing the redox activities of various cancer cells. To identify the relationship between the redox activity and the aggressiveness of cancer cells, two different cancer cell lines, derived from the same tissue but different with regards to aggressiveness, were selected for study. First, the cancer cell lines were incubated with TPAni nanoparticles, and an absorbance ratio obtained from the cell culture media was used as a colorimetric indicator of the redox activities of the cells. Simultaneously, hydrophobically modified filter papers coated with silver nanosnowflakes (SNSF) were used as sensing substrates for surface enhanced Raman scattering (SERS). SERS spectra obtained from varying concentrations of rhodamine 6G were used to confirm the detection limit of the SNSF-based SERS substrate. Cell culture media containing TPAni nanoparticles were treated with the SNSF-containing SERS substrates to examine the redox activities of the various cancer cell lines.The redox activities of cancer cell lines were confirmed by absorbance spectral analysis, and these redox activities were better identified via an SERS analysis method. A SNSF-containing SERS substrate, fabricated from SNSF and filter paper, was used to sense redox activity in cancer cell lines and to further identify correlations between redox activity and cancer cell line aggressiveness, as indicated by the use of EpCAM as a biomarker. Finally, potential of ​in vivo ​redox activity sensing was also confirmed.

Mitochondria-Targeting Chemodynamic Therapy Nanodrugs for Cancer Treatment

Mitochondria, as one of the most critical subcellular organelles of cancer cells, are very vulnerable and often on the verge of oxidative stress. The classic chemodynamic therapy (CDT) directly employs endogenous chemical energy to trigger reactive oxygen species (ROS) burst and destroy tumor cells. However, the effectiveness of CDT is restricted by the limited diffusion distance and short half-life of ROS. From this perspective, the treatment method (mitochondria-targeting chemodynamic therapy nanodrugs, M-CDT nanodrugs) that can generate high levels of ROS at the mitochondrial site is extremely efficient and promising for cancer treatment. Currently, many emerging M-CDT nanodrugs have been demonstrated excellent spatial specificity and anti-cancer efficacy. In this minireview, we review various proof-of-concept researches based on different M-CDT nanodrugs designs to overcome the limits of the efficacy of CDT, mainly divided into four strategies: supplying H₂O₂, non-H₂O₂ dependent CDT, eliminating GSH and enhancing by hyperthermia therapy (HT). These well-designed M-CDT nanodrugs greatly increase the efficacy of CDT. Finally, the progress and potential of M-CDT nanodrugs are discussed, as well as their limitations and opportunities.

Chemogenetic approaches to dissect the role of H2O2 in redox-dependent pathways using genetically encoded biosensors

Chemogenetic tools are recombinant enzymes that can be targeted to specific organelles and tissues. The provision or removal of the enzyme substrate permits control of its biochemical activities. Yeast-derived enzyme D-amino acid oxidase (DAAO) represents the first of its kind for a substrate-based chemogenetic approach to modulate H2O2 concentrations within cells. Combining these powerful enzymes with multiparametric imaging methods exploiting genetically encoded biosensors has opened new lines of investigations in life sciences. In recent years, the chemogenetic DAAO approach has proven beneficial to establish a new role for (patho)physiological oxidative stress on redox-dependent signaling and metabolic pathways in cultured cells and animal model systems. This mini-review covers established or emerging methods and assesses newer approaches exploiting chemogenetic tools combined with genetically encoded biosensors.

Redox-Sensitive Mapping of a Mouse Tumor Model Using Sparse Projection Sampling of Electron Paramagnetic Resonance

Aims: This work aimed to establish an accelerated imaging system for redox-sensitive mapping in a mouse tumor model using electron paramagnetic resonance (EPR) and nitroxyl radicals. Results: Sparse sampling of EPR spectral projections was demonstrated for a solution phantom. The reconstructed three-dimensional (3D) images with filtered back-projection (FBP) and compressed sensing image reconstruction were quantitatively assessed for the solution phantom. Mouse xenograft models of a human-derived pancreatic ductal adenocarcinoma cell line, MIA PaCa-2, were also measured for redox-sensitive mapping with the sparse sampling technique. Innovation: A short-lifetime redox-sensitive nitroxyl radical (¹⁵N-labeled perdeuterated Tempone) could be measured to map the decay rates of the EPR signals for the mouse xenograft models. Acceleration of 3D EPR image acquisition broadened the choices of nitroxyl radical probes with various redox sensitivities to biological environments. Conclusion: Sparse sampling of EPR spectral projections accelerated image acquisition in the 3D redox-sensitive mapping of mouse tumor-bearing legs fourfold compared with conventional image acquisition with FBP. Antioxid. Redox Signal. 36, 57-69.

Dissecting in vivo and in vitro redox responses using chemogenetics

Hydrogen peroxide (H2O2) is the most abundant reactive oxygen species (ROS) within mammalian cells. At low concentrations, H2O2 serves as a versatile cell signaling molecule that mediates vital physiological functions. Yet at higher concentrations, H2O2 can be a toxic molecule by promoting pathological oxidative stress in cells and tissues. Within normal cells, H2O2 is differentially distributed in a variety of subcellular locales. Moreover, many redox-active enzymes and their substrates are themselves differentially distributed within cells. Numerous reports have described the biological and biochemical consequences of adding exogenous H2O2 to cultured cells and tissues, but many of these observations are difficult to interpret: the effects of exogenous H2O2 do not necessarily replicate the cellular responses to endogenous H2O2. In recent years, chemogenetic approaches have been developed to dynamically regulate the abundance of H2O2 in specific subcellular locales. Chemogenetic approaches have been applied in multiple experimental systems, ranging from in vitro studies on the intracellular transport and metabolism of H2O2, all the way to in vivo studies that generate oxidative stress in specific organs in living animals. These chemogenetic approaches have exploited a yeast-derived d-amino acid oxidase (DAAO) that synthesizes H2O2 only in the presence of its d-amino acid substrate. DAAO can be targeted to various subcellular locales, and can be dynamically activated by the addition or withdrawal of its d-amino acid substrate. In addition, recent advances in the development of highly sensitive genetically encoded H2O2 biosensors are providing a better understanding of both physiological and pathological oxidative pathways. This review highlights several applications of DAAO as a chemogenetic tool across a wide range of biological systems, from analyses of subcellular H2O2 metabolism in cells to the development of new disease models caused by oxidative stress in vivo.

Screening compound libraries for H2O2-mediated cancer therapeutics using a peroxiredoxin-based sensor

Compounds that modulate H₂O₂ reaction networks have applications as targeted cancer therapeutics, as a subset of cancers exhibit sensitivity to this redox signal. Previous studies to identify therapeutics that induce oxidants have relied upon probes that respond to many different oxidants in cells, and thus do not report on only H₂O₂, a redox signal that selectively oxidizes proteins. Here we use a genetically encoded fluorescent probe for human peroxiredoxin-2 (Prx2) oxidation in screens for small-molecule compounds that modulate H₂O₂ pathways. We further characterize cellular responses to several compounds selected from the screen. Our results reveal that some, but not all, of the compounds enact H₂O₂-mediated toxicity in cells. Among them, SMER3, an antifungal, has not been reported as an oxidant-inducing drug. Several drugs, including cisplatin, that previously have been shown to induce reactive oxygen species (ROS) do not appear to oxidize Prx2, suggesting H₂O₂ is not among the ROS induced by those drugs.

Thiol-disulphide independent in-cell trapping for the identification of peroxiredoxin 2 interactors

Hydrogen peroxide (H2O2) acts as a signalling molecule by oxidising cysteine thiols in proteins. Recent evidence has established a role for cytosolic peroxiredoxins in transmitting H2O2-based oxidation to a multitude of target proteins. Moreover, it is becoming clear that peroxiredoxins fulfil their function in organised microdomains, where not all interactors are covalently bound. However, most studies aimed at identifying peroxiredoxin interactors were based on methods that only detect covalently linked partners. Here, we explore the applicability of two thiol-disulphide independent in-cell trapping methodological approaches in combination with mass spectrometry for the identification of interaction partners of peroxiredoxin 2 (Prdx2). The first is biotin-dependent proximity-labelling (BioID) with a biotin ligase A (BirA*)-fused Prdx2, which has never been applied on redox-active proteins. The second is crosslinker co-immunoprecipitation with an N-terminally His-tagged Prdx2. During the initial characterisation of the tagged Prdx2 constructs, we found that the His-tag, but not BirA*, compromises the peroxidase and signalling activities of Prdx2. Further, the Prdx2 interactors identified with each approach showed little overlap. We therefore concluded that BioID is a more reliable method than crosslinker co-immunoprecipitation. After a stringent mass spec data filtering, BioID identified 13 interactors under elevated H2O2 conditions, including subunit five of the COP9 signalosome complex (CSN5). The Prdx2:CSN5 interaction was further confirmed in a proximity ligation assay. Taken together, our results demonstrate that BioID can be used as a method for the identification of interactors of Prdxs, and that caution should be exercised when interpreting protein-protein interaction results using tagged Prdxs.

Genetically Encoded Fluorescent Redox Indicators for Unveiling Redox Signaling and Oxidative Toxicity

Redox-active molecules play essential roles in cell homeostasis, signaling, and other biological processes. Dysregulation of redox signaling can lead to toxic effects and subsequently cause diseases. Therefore, real-time tracking of specific redox-signaling molecules in live cells would be critical for deciphering their functional roles in pathophysiology. Fluorescent protein (FP)-based genetically encoded redox indicators (GERIs) have emerged as valuable tools for monitoring the redox states of various redox-active molecules from subcellular compartments to live organisms. In the first section of this review, we overview the background, focusing on the sensing mechanisms of various GERIs. Next, we review a list of selected GERIs according to their analytical targets and discuss their key biophysical and biochemical properties. In the third section, we provide several examples which applied GERIs to understanding redox signaling and oxidative toxicology in pathophysiological processes. Lastly, a summary and outlook section is included.

Peroxiredoxins wear many hats: Factors that fashion their peroxide sensing personalities

Peroxiredoxins (Prdxs) sense and assess peroxide levels, and signal through protein interactions. Understanding the role of the multiple structural and post-translational modification (PTM) layers that tunes the peroxiredoxin specificities is still a challenge. In this review, we give a tabulated overview on what is known about human and bacterial peroxiredoxins with a focus on structure, PTMs, and protein-protein interactions. Armed with numerous cellular and atomic level experimental techniques, we look at the future and ask ourselves what is still needed to give us a clearer view on the cellular operating power of Prdxs in both stress and non-stress conditions.

Miro1-mediated mitochondrial positioning supports subcellular redox status

Mitochondria are strategically trafficked throughout the cell by the action of microtubule motors, the actin cytoskeleton and adapter proteins. The intracellular positioning of mitochondria supports subcellular levels of ATP, Ca²⁺ and reactive oxygen species (ROS, i.e. hydrogen peroxide, H₂O₂). Previous work from our group showed that deletion of the mitochondrial adapter protein Miro1 leads to perinuclear clustering of mitochondria, leaving the cell periphery devoid of mitochondria which compromises peripheral energy status. Herein, we report that deletion of Miro1 significantly restricts subcellular H₂O₂ levels to the perinuclear space which directly affects intracellular responses to elevated mitochondrial ROS. Using the genetically encoded H₂O₂-responsive fluorescent biosensor HyPer7, we show that the highest levels of subcellular H₂O₂ map to sites of increased mitochondrial density. Deletion of Miro1 or disruption of microtubule dynamics with Taxol significantly reduces peripheral H₂O₂ levels. Following inhibition of mitochondrial complex 1 with rotenone we observe elevated spikes of H₂O₂ in the cell periphery and complementary oxidation of mitochondrial peroxiredoxin 3 (PRX3) and cytosolic peroxiredoxin 2 (PRX2). Conversely, in cells lacking Miro1, rotenone did not increase peripheral H₂O₂ or PRX2 oxidation but rather lead to increased nuclear H₂O₂ and an elevated DNA-damage response. Lastly, local levels of HyPer7 oxidation correlate with the size and abundance of focal adhesions (FAs) in MEFs and cells lacking Miro1 have significantly smaller focal adhesions and reduced phosphorylation levels of vinculin and p130Cas compared to Miro1^+/+ MEFs. Together, we present evidence that the intracellular distribution of mitochondria influences subcellular H₂O₂ levels and local cellular responses dependent on mitochondrial ROS.

Fluorescent probes for in vitro and in vivo quantification of hydrogen peroxide

Hydrogen peroxide (H2O2) plays essential roles in redox signaling and oxidative stress, and its dynamic concentration is critical to human health and diseases. Here we report the design, syntheses, and biological applications of HKPerox-Red and HKPerox-Ratio for quantitative measurement of H2O2. Both probes were successfully applied to detect endogenous H2O2 fluxes in living cells or zebrafish, and biological effects of multiple stress inducers including rotenone, arsenic trioxide, and starvation were investigated. As H2O2 is a common by-product for oxidase oxidation, a general assay was developed for ultrasensitive detection of various metabolites (glucose, uric acid, and sarcosine). Moreover, cellular H2O2 measurements were achieved for the first time by combining flow cytometry with live cell calibration. This study provides a pair of unique molecular tools for advanced H2O2 bio-imaging and assay development.

Defense Mechanism of Phosphorothioated DNA under Peroxynitrite-Mediated Oxidative Stress

DNA phosphorothioation (PT) exists in many pathogenic bacteria; however, the mechanism of PT-DNA resistance to the immune response is unclear. In this work, we meticulously investigated the peroxynitrite (PN) tolerance using PT-bioengineered E. coli strains. The in vivo experiment confirms that the S⁺ strain survives better than the S^- strain under moderately oxidative stress. The LCMS, IC, and GCMS experiments demonstrated that phosphorothioate partially converted to phosphate, and the byproduct included sulfate and elemental sulfur. When O,O-diethyl thiophosphate ester (DETP) was used, the reaction rate k₁ was determined to be 4.3 ± 0.5 M^-1 s^-1 in the first-order for both phosphorothioate and peroxynitrite at 35 °C and pH of 8.0. The IC₅₀ values of phosphorothioate dinucleotides are dramatically increased by 400-700-fold compared to DETP. The SH/OH Yin-Yang mechanism rationalizes the in situ DNA self-defense against PN-mediated oxidative stress at the extra bioenergetic cost of DNA modification.

Oxidative pentose phosphate pathway and glucose anaplerosis support maintenance of mitochondrial NADPH pool under mitochondrial oxidative stress

Mitochondrial NADPH protects cells against mitochondrial oxidative stress by serving as an electron donor to antioxidant defense systems. However, due to technical challenges, it still remains unknown as to the pool size of mitochondrial NADPH, its dynamics, and NADPH/NADP+ ratio. Here, we have systemically modulated production rates of H2O2 in mitochondria and assessed mitochondrial NADPH metabolism using iNap sensors, 13C glucose isotopic tracers, and a mathematical model. Using sensors, we observed decreases in mitochondrial NADPH caused by excessive generation of mitochondrial H2O2, whereas the cytosolic NADPH was maintained upon perturbation. We further quantified the extent of mitochondrial NADPH/NADP+ based on the mathematical analysis. Utilizing 13C glucose isotopic tracers, we found increased activity in the pentose phosphate pathway (PPP) accompanied small decreases in the mitochondrial NADPH pool, whereas larger decreases induced both PPP activity and glucose anaplerosis. Thus, our integrative and quantitative approach provides insight into mitochondrial NADPH metabolism during mitochondrial oxidative stress.

Real-time monitoring of peroxiredoxin oligomerization dynamics in living cells

Peroxiredoxins are most central to the cellular adaptation against oxidative stress. They act as oxidant scavengers, stress sensors, transmitters of signals, and chaperones, and they possess a unique quaternary switch that is intimately related to these functions. However, so far it has not been possible to monitor peroxiredoxin structural changes in the intact cellular environment. This study presents genetically encoded probes, based on homo-FRET (Förster resonance energy transfer between identical fluorophores) fluorescence polarization, that allow following these quaternary changes in real time, in living cells. We envisage that these probes can be used to address a broad range of questions related to the function of peroxiredoxins.

Peroxiredoxins are central to cellular redox homeostasis and signaling. They serve as peroxide scavengers, sensors, signal transducers, and chaperones, depending on conditions and context. Typical 2-Cys peroxiredoxins are known to switch between different oligomeric states, depending on redox state, pH, posttranslational modifications, and other factors. Quaternary states and their changes are closely connected to peroxiredoxin activity and function but so far have been studied, almost exclusively, outside the context of the living cell. Here we introduce the use of homo-FRET (Förster resonance energy transfer between identical fluorophores) fluorescence polarization to monitor dynamic changes in peroxiredoxin quaternary structure inside the crowded environment of living cells. Using the approach, we confirm peroxide- and thioredoxin-related quaternary transitions to take place in cellulo and observe that the relationship between dimer–decamer transitions and intersubunit disulfide bond formation is more complex than previously thought. Furthermore, we demonstrate the use of the approach to compare different peroxiredoxin isoforms and to identify mutations and small molecules affecting the oligomeric state inside cells. Mutagenesis experiments reveal that the dimer–decamer equilibrium is delicately balanced and can be shifted by single-atom structural changes. We show how to use this insight to improve the design of peroxiredoxin-based redox biosensors.

Early stratification of radiotherapy response by activatable inflammation magnetic resonance imaging

Tumor heterogeneity is one major reason for unpredictable therapeutic outcomes, while stratifying therapeutic responses at an early time may greatly benefit the better control of cancer. Here, we developed a hybrid nanovesicle to stratify radiotherapy response by activatable inflammation magnetic resonance imaging (aiMRI) approach. The high Pearson's correlation coefficient R values are obtained from the correlations between the T1 relaxation time changes at 24-48 h and the ensuing adaptive immunity (R = 0.9831) at day 5 and the tumor inhibition ratios (R = 0.9308) at day 18 after different treatments, respectively. These results underscore the role of acute inflammatory oxidative response in bridging the innate and adaptive immunity in tumor radiotherapy. Furthermore, the aiMRI approach provides a non-invasive imaging strategy for early prediction of the therapeutic outcomes in cancer radiotherapy, which may contribute to the future of precision medicine in terms of prognostic stratification and therapeutic planning.

MnTE-2-PyP Suppresses Prostate Cancer Cell Growth via H2O2 Production

Prostate cancer patients are often treated with radiotherapy. MnTE-2-PyP, a superoxide dismutase (SOD) mimic, is a known radioprotector of normal tissues. Our recent work demonstrated that MnTE-2-PyP also inhibits prostate cancer progression with radiotherapy; however, the mechanisms remain unclear. In this study, we identified that MnTE-2-PyP-induced intracellular H₂O₂ levels are critical in inhibiting the growth of PC3 and LNCaP cells, but the increased H₂O₂ levels affected the two cancer cells differently. In PC3 cells, many proteins were thiol oxidized with MnTE-2-PyP treatment, including Ser/Thr protein phosphatase 1 beta catalytic subunit (PP1CB). This resulted in reduced PP1CB activity; however, overall cell cycle progression was not altered, so this is not the main mechanism of PC3 cell growth inhibition. High H₂O₂ levels by MnTE-2-PyP treatment induced nuclear fragmentation, which could be synergistically enhanced with radiotherapy. In LNCaP cells, thiol oxidation by MnTE-2-PyP treatment was not observed previously and, similarly to PC3 cells, there was no effect of MnTE-2-PyP treatment on cell cycle progression. However, in LNCaP cells, MnTE-2-PyP caused an increase in low RNA population and sub-G₁ population of cells, which indicates that MnTE-2-PyP treatment may cause cellular quiescence or direct cancer cell death. The protein oxidative modifications and mitotic catastrophes caused by MnTE-2-PyP may be the major contributors to cell growth inhibition in PC3 cells, while in LNCaP cells, tumor cell quiescence or cell death appears to be major factors in MnTE-2-PyP-induced growth inhibition.

Ultrasensitive Genetically Encoded Indicator for Hydrogen Peroxide Identifies Roles for the Oxidant in Cell Migration and Mitochondrial Function

Hydrogen peroxide (H₂O₂) is a key redox intermediate generated within cells. Existing probes for H₂O₂ have not solved the problem of detection of the ultra-low concentrations of the oxidant: these reporters are not sensitive enough, or pH-dependent, or insufficiently bright, or not functional in mammalian cells, or have poor dynamic range. Here we present HyPer7, the first bright, pH-stable, ultrafast, and ultrasensitive ratiometric H₂O₂ probe. HyPer7 is fully functional in mammalian cells and in other higher eukaryotes. The probe consists of a circularly permuted GFP integrated into the ultrasensitive OxyR domain from Neisseria meningitidis. Using HyPer7, we were able to uncover the details of H₂O₂ diffusion from the mitochondrial matrix, to find a functional output of H₂O₂ gradients in polarized cells, and to prove the existence of H₂O₂ gradients in wounded tissue in vivo. Overall, HyPer7 is a probe of choice for real-time H₂O₂ imaging in various biological contexts.

Large-scale analyses identify a cluster of novel long noncoding RNAs as potential competitive endogenous RNAs in progression of hepatocellular carcinoma

The abnormal expression of noncoding RNAs has attracted increasing interest in the field of hepatocellular carcinoma progression. However, the underlying molecular mechanisms mediated by noncoding RNAs in these processes are unclear. Here, we obtained the expression profiles of long noncoding RNAs, microRNAs, and mRNAs from the Gene Expression Omnibus database and identified hepatocarcinogenesis-specific differentially expressed transcripts. Next, we identified significant Gene Ontology and pathway terms that the differentially expressed transcripts involved in. Using functional analysis and target prediction, we constructed a hepatocellular carcinoma-associated deregulated competitive endogenous RNA network to reveal the potential mechanisms underlying tumor progression. By analyzing The Cancer Genome Atlas dataset, six key long noncoding RNAs showed significant association with overall survival as well as strong correlation with some microRNAs and mRNAs in the competitive endogenous RNA network. We further validated the above results and determined their diagnostic and prognostic value in clinical samples. Importantly, by large-scale analyses, we identified a cluster of long noncoding RNAs, GBAP1, MCM3AP-AS1, SLC16A1-AS1, C3P1, DIO3OS, and HNF4A-AS1 as candidate biomarkers for the diagnosis and prognosis of hepatocellular carcinoma, which will improve our understanding of competitive endogenous RNA-mediated regulatory mechanisms underlying hepatocellular carcinoma development and will provide novel therapeutic targets in the future.

Aromatic Residues at the Dimer-Dimer Interface in the Peroxiredoxin Tsa1 Facilitate Decamer Formation and Biological Function

To prevent the accumulation of reactive oxygen species and limit associated damage to biological macromolecules, cells express a variety of oxidant-detoxifying enzymes, including peroxiredoxins. In Saccharomyces cerevisiae, the peroxiredoxin Tsa1 plays a key role in peroxide clearance and maintenance of genome stability. Five homodimers of Tsa1 can assemble into a toroid-shaped decamer, with the active sites in the enzyme being shared between individual dimers in the decamer. Here, we have examined whether two conserved aromatic residues at the decamer-building interface promote Tsa1 oligomerization, enzymatic activity, and biological function. When substituting either or both of these aromatic residues at the decamer-building interface with either alanine or leucine, we found that the Tsa1 decamer is destabilized, favoring dimeric species instead. These proteins exhibit varying abilities to rescue the phenotypes of oxidant sensitivity and genomic instability in yeast lacking Tsa1 and Tsa2, with the individual leucine substitutions at this interface partially complementing the deletion phenotypes. The ability of Tsa1 decamer interface variants to partially rescue peroxidase function in deletion strains is temperature-dependent and correlates with their relative rate of reactivity with hydrogen peroxide and their ability to interact with thioredoxin. Based on the combined results of in vitro and in vivo assays, our findings indicate that multiple steps in the catalytic cycle of Tsa1 may be impaired by introducing substitutions at its decamer-building interface, suggesting a multifaceted biological basis for its assembly into decamers.

The fluorescent protein sensor roGFP2-Orp1 monitors in vivo H2 O2 and thiol redox integration and elucidates intracellular H2 O2 dynamics during elicitor-induced oxidative burst in Arabidopsis

Hydrogen peroxide (H₂ O₂ ) is ubiquitous in cells and at the centre of developmental programmes and environmental responses. Its chemistry in cells makes H₂ O₂ notoriously hard to detect dynamically, specifically and at high resolution. Genetically encoded sensors overcome persistent shortcomings, but pH sensitivity, silencing of expression and a limited concept of sensor behaviour in vivo have hampered any meaningful H₂ O₂ sensing in living plants. We established H₂ O₂ monitoring in the cytosol and the mitochondria of Arabidopsis with the fusion protein roGFP2-Orp1 using confocal microscopy and multiwell fluorimetry. We confirmed sensor oxidation by H₂ O₂ , show insensitivity to physiological pH changes, and demonstrated that glutathione dominates sensor reduction in vivo. We showed the responsiveness of the sensor to exogenous H₂ O₂ , pharmacologically-induced H₂ O₂ release, and genetic interference with the antioxidant machinery in living Arabidopsis tissues. Monitoring intracellular H₂ O₂ dynamics in response to elicitor exposure reveals the late and prolonged impact of the oxidative burst in the cytosol that is modified in redox mutants. We provided a well defined toolkit for H₂ O₂ monitoring in planta and showed that intracellular H₂ O₂ measurements only carry meaning in the context of the endogenous thiol redox systems. This opens new possibilities to dissect plant H₂ O₂ dynamics and redox regulation, including intracellular NADPH oxidase-mediated ROS signalling.

Organometallic ruthenium anticancer complexes inhibit human peroxiredoxin I activity by binding to and inducing oxidation of its catalytic cysteine residue

Ruthenium arene anticancer complexes bind to human peroxiredoxin I, leading to oxidation of thiolate and failure of forming a disulfide bond.