Gold Nanoparticles Functionalized with Au-Se-Bonded Peptides Used as Gatekeepers for the Off-Target Release of Resveratrol in the Treatment of Triple-Negative Breast Cancer

Resveratrol has been garnering considerable attention as a promising chemopreventive and chemotherapeutic drug against metastatic tumors such as triple-negative breast cancer (TNBC). However, the potential in vivo application of resveratrol has been highly limited due to its poor solubility, rapid conjugation, low bioavailability, and bioactivity. In this study, a silica mesoporous nanoparticle (MSN)-based drug delivery system (DDS), named Au-Se@MSN, is developed to deliver the loaded resveratrol, endowing it with properties of targeted delivery, excellent bioavailability, and antioxidation of resveratrol. In Au-Se@MSN(RES), gold nanoparticles functionalized with selenol-modified uPA-specific peptides act as gatekeepers to avoid the interference of glutathione in the bloodstream and realize negligible premature release of resveratrol during delivery. Au-Se@MSN(RES) shows prolonged resveratrol release at the tumor site and endows resveratrol with a remarkable in vitro therapeutic effect. The pharmacological dose of resveratrol treatment on MDA-MB-231 cells was found to result in the generation of a high level of NAD(P)H other than H₂O₂, indicating reductive stress instead of oxidative stress involved in the resveratrol therapeutic process. In vivo experiments showed that Au-Se@MSN greatly improves the chemotherapeutic effect of resveratrol on mice bearing TNBC tumors, and damage to normal tissues and cells is negligible. Overall, Au-Se@MSN is a potential tool for further studies on the anticancer mechanism and clinical applications of resveratrol.

Rational construction of a new water soluble turn-on colorimetric and NIR fluorescent sensor for high selective Sec detection in Se-enriched foods and biosystems

As a naturally occurring amino acid, selenocysteine (Sec) plays a key role in a variety of cellular functions and Se-enriched foods. In this work, a robust water soluble fluorescence turn-on near-infrared (NIR) sensor NIR-Sec was constructed for Sec detection over biothiols in Se-enriched foods. Specifically, NIR-Sec contains a readily prepared water soluble NIR dicyanoisophorone fluorophore and a well-known response-site 2,4-dinitrobenzenesulfonyl moiety with strong intramolecular charge transfer (ICT) effect to quench the fluorescence intensity of NIR fluorophore. Upon addition of Sec, the NIR dicyanoisophorone fluorophore was released and a bright red emission at 663 nm was observed. Moreover, NIR-Sec toward Sec exhibited rapid response time (∼1 min), a large stoke shift (183 nm), and high selectivity and sensitivity (LOD: 52 nM). Impressively, NIR-Sec was successfully employed to detect and image Sec in Se-enriched foods and shrimp, indicating NIR-Sec could provide a robust tool for investigating the role of Sec in complex real-food samples.

Current status and future prospects of nanoscale metal–organic frameworks in bioimaging

The importance of diagnosis and in situ monitoring of lesion regions and transportation of bioactive molecules has a pivotal effect on successful treatment, reducing side effects, and increasing the chances of survival in the case of diseases.

A Fluorescent Probe for the Specific Staining of Cysteine Containing Proteins and Thioredoxin Reductase in SDS-PAGE

A naphthalimide-based fluorescent probe, Nap-I, with iodoacetamide as the alkylating group, has been synthesized, and its specific fluorescent staining of proteins containing cysteine (Cys) and selenocysteine (Sec) residues in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) has been evaluated. This molecule shows good fluorescence properties in the labeling of protein Cys/Sec residues, while reducing steric hindrance and minimizing changes in the water solubility of proteins. Reaction parameters, such as labeling time and pH, have been investigated, and the optimal labeling conditions for Cys-containing proteins have been determined. Thioredoxin reductase (TXNRD) is best stained at low pH. The probe Nap-I has been successfully used for the quantification of serum proteins and hemoglobin in Tan sheep serum, and TXNRD in Tan sheep liver and muscle has been labeled at low pH. Based on the probe Nap-I, we have also distinguished TXNRD1 and TXNRD2 by SDS-PAGE. The results showed that, compared with the normal microenvironment in which the protein resides, the lower the pH value, the greater the TXNRD activity.

Activatable Off-on Near-Infrared QCy7-based Fluorogenic Probes for Bioimaging

The activatable off-on near-infrared QCy7-based fluorogenic probes have emerged as powerful modalities for detecting and monitoring biological analytes and understanding their biological processes in cells and organisms. The use of biomarker-activated QCy7-based probes enables simple synthesis, minimum photo-damage to biological samples, and minimum background interference from biological systems. In this minireview, we aim to provide a rigorous but concise overview of activatable QCy7-based fluorogenic probes by reporting the significant progress made in recent years. The design strategies and the main applications of accurate detection and imaging of disease-related biomarkers (including ROS/RSS, enzymes, metal ions, and other related species) were reasonably analyzed and discussed. The potential challenges and prospects of activatable QCy7-based fluorogenic probes are also emphasized to further advance the development of new methods for biomarker detection and bioimaging.

An Au-Se nanoprobe for the evaluation of the invasive potential of breast cancer cells via imaging the sequential activation of uPA and MMP-2

Urokinase-type plasminogen activator (uPA) has been shown to activate matrix metalloproteinase-2 (MMP-2) that leads to the migration and invasion of breast cancer cells. Overexpressed uPA and MMP-2 are regarded as signs of malignant tumors in clinical practice. Therefore, real-time monitoring of the sequential activation of these two signal molecules may have important implications for the evaluation of the invasive potential and tumor progression of breast cancer. However, due to the complicated intracellular environment, visualizing the dynamic changes of protein expression levels in living cells with a noninvasive method is still a great challenge. Here, a novel gold-selenium (Au-Se) fluorescent nanoprobe with excellent selectivity and strong anti-interference capability was designed for the simultaneous in situ imaging of uPA and MMP-2 and real-time monitoring of their changes in living cells. The imaging results demonstrated that the nanoprobe achieved a better prevention of glutathione interference compared to the conventional Au-S nanoprobe, thus it could be applied to actually reflect the expression level of uPA and MMP-2 in different breast cancer cells. Furthermore, the Au-Se nanoprobe could visually present the activation process of the two signal molecules, which play a dual role of insuring the invasiveness evaluation of breast cancer cells. Overall, our work offers a visual biomarker detection method for the judgment of the degree of breast cancer malignancy, and also provides an effective strategy to investigate the relationships among signal molecules of other signaling pathways in the future.

A review of bioselenol-specific fluorescent probes: Synthesis, properties, and imaging applications

Bioselenols are important substances for the maintenance of physiological balance and offer anticancer properties; however, their causal mechanisms and effectiveness have not been assessed. One way to explore their physiological functions is the in vivo detection of bioselenols at the molecular level, and one of the most efficient ways to do so is to use fluorescent probes. Various types of bioselenol-specific fluorescent probes have been synthesized and optimized using chemical simulations and by improving biothiol fluorescent probes. Here, we review recent advances in bioselenol-specific fluorescent probes for selenocysteine (Sec), thioredoxin reductase (TrxR), and hydrogen selenide (H₂Se). In particular, the molecular design principles of different types of bioselenols, their corresponding sensing mechanisms, and imaging applications are summarized.

A differential study on oxidized/reduced ascorbic acid induced tumor cells’ apoptosis under hypoxia

The anticancer mechanism for reduced/oxidized ascorbic acid (AA/DHA) is of great significance for clinical cancer therapies.

Au nanoparticle-based probe for selenol in living cells and selenium-rich tea and rice

Selenocysteine (Sec) is a primary kind of reactive selenium species in cells, and its vital roles in physiological processes have been characterized. Therefore, the highly effective method for sensing Sec in metabolic processes and selenium-rich food must be developed. This study presents a new fluorescent probe, namely, GSH-NB@AuNPs, for highly selective detection of selenol based on the fluorescence quenching quality on the surface of gold nanoparticles (AuNPs). The probe consists of glutathione (GSH) and Nile blue (NB) moieties assembled on AuNPs. The probe exhibits excellent sensitivity and selectivity for Sec and is applied in imaging endogenous and exogenous Sec in living cells through confocal fluorescence microscopy. The proposed probe provides a promising and powerful method for detecting selenol in foodstuff (such as selenium-rich rice and tea) with the detection limit of 9.5 nM.

Monitoring NAD(P)H by an ultrasensitive fluorescent probe to reveal reductive stress induced by natural antioxidants in HepG2 cells under hypoxia

An ultrasensitive fluorescent probe for monitoring NAD(P)H and revealing reductive stress induced by natural antioxidants in HepG2 cells under hypoxia.

Reductive stress, the opposite of oxidative stress, represents a disorder in the redox balance state which is harmful to biological systems. For decades, the role of oxidative stress in tumor therapy has been the focus of attention, while the effects of reductive stress have been rarely studied. Here, we report the anti-cancer effects of reductive stress induced by three natural antioxidants (resveratrol, curcumin and celastrol). Considering the fact that the solid tumor microenvironment suffers from hypoxia, we performed cell experiments under hypoxic conditions. In order to observe the reductive stress, we first developed an ultrasensitive fluorescent probe (TCF-MQ) for specifically imaging NAD(P)H which is a marker of reductive stress. TCF-MQ responded to NAD(P)H rapidly and exhibited high sensitivity with a detection limit of 6 nM. With the help of TCF-MQ, we found that upon the treatment of HepG2 cells with pharmacological doses of three natural antioxidants under hypoxic conditions, high levels of NAD(P)H were produced before cell death. The excess NAD(P)H resulted in reductive stress instead of oxidative stress. In contrast, under normoxic conditions, there was no reductive stress involved in the process of cell death induced by three natural antioxidants. Therefore, we hypothesize that the mechanism of cancer cell death induced by natural antioxidants under hypoxia should be attributed to the reductive stress.

Engineering Self-Calibrating Nanoprobes with Two-Photon-Activated Fluorescence Resonance Energy Transfer for Ratiometric Imaging of Biological Selenocysteine

Selenocysteine (Sec) has proven to be the dominant active site of diverse selenoproteins that are directly linked with human health and disease. Thus, understanding the critical functions and dynamics of endogenous Sec at cellular and tissue levels is highly demanded. However, no method has been reported that is capable of providing reliable quantitative imaging analysis of Sec in living systems, especially in deep tissues, with low background signal and high sensitivity and imaging resolution simultaneously. To address this challenge, we herein report a novel class of engineered Sec-responsive fluorescent nanoprobes that combines two-photon excitation with Förster resonance energy transfer (FRET) mechanisms for direct, yet selective, sensing and imaging of biological Sec over abundant competing biothiols. Specifically, the two-photon excitation at the near-infrared window can minimize light scattering and background signals in tissues, thus offering improved spatial and temporal imaging of deep living tissues with reduced background interference. Moreover, a reasonable FRET donor-acceptor pair has further been designed and verified by theoretical calculation. The acceptor undergoes intramolecular rearrangement specifically in response to the nucleophilic attack of Sec, hence triggering remarkable FRET-mediated ratiometric fluorescence enhancement for sensitive and reliable quantification of Sec through self-calibration of two emission channels. These striking properties, along with good water solubility and biocompatibility, suggest that this strategy may serve as a valuable imaging tool for studying various Sec-related biological events in complex biological systems.

Excellent benzocoumarin-based ratiometric two-photon fluorescent probe for H2O2 detection

The level of hydrogen peroxide (H2O2) plays an essential role in regulating biological processes. The in vivo or in vitro detection of H2O2 in deep tissues by utilizing two-photon (TP) fluorescent probes can significantly alleviate the detection damage inflicted onto living organisms as well as facilitate high-resolution imaging when compared with one-photon (OP) fluorescent probes. However, few TP fluorescent probes possess both high fluorescence efficiency and easily distinguishable spectra for measuring H2O2. Therefore, an in-depth understanding of the relationship between the electronic structure and TP fluorescent properties and fabricating probes with excellent performance are still challenging. Consequently, we designed a series of benzocoumarin-based ratiometric TP fluorescent probes and corresponding product molecules for H2O2 detection. Thereafter, we theoretically evaluated the TP recognition performance of these compounds and studied the relationship between their molecular structure and TP performance by means of time-dependent density functional theory and quadratic response theory. Moreover, we determined their spectral properties and fluorescence efficiencies. Fortunately, in this study, we were able to propose an excellent TP probe BC-3 and the corresponding product molecule DCCA-3, which exhibit large TPA cross-sections in the NIR region (3420 GM/988 nm; 316 GM/939 nm) and large Stokes (116 nm; 60 nm) and emission (225 nm) shifts. Therefore, this probe enables the simultaneous NIR and TP imaging of H2O2, which is a unique ability and has never been previously reported. Moreover, we comprehensively investigated the effect of the benzene-fused position in the coumarin backbone on the transition dipole moment and nonradiative decay channels, explaining the fluorescence near-quenching mechanism of benzo[f]coumarin derivative DCCA-4 for the first time.

Size and surface controllable metal-organic frameworks (MOFs) for fluorescence imaging and cancer therapy

Benefiting from their porous structures, metal-organic frameworks (MOFs) have attracted intensive attention for use in drug release. However, the controllable synthesis of MOFs with proper particle sizes is still very challenging, which largely limits its applications. Here, UIO-66-NH2 with controlled particle sizes in the range of 20-200 nm has been achieved successfully. The amine on UIO-66-NH2 is demonstrated for the feasible post-modifying of UIO-66-NH2 to obtain multifunctional MOFs, overcoming the limitations of functional simplicity and broadening the range of applications. After covalent grafting the targeting reagent folic acid (FA) and the fluorescence imaging agent 5-carboxyfluorescein (5-FAM), UIO-66-NH2-FA-5-FAM/5-FU can target the cancer cells HePG-2 and display excellent fluorescence imaging in vitro. Moreover, the in vivo biodistribution and antitumor assays indicate that UIO-66-NH2-FA-5-FAM/5-FU can accumulate in the tumor and display stronger antitumor efficiency due to the long-time drug release. Taken together, this study integrates the imaging section and the treated section in a single platform successfully and the present approach can be a good use of therapeutic MOFs to achieve the desired objective, a better treatment.

Au-Se-Bond-Based Nanoprobe for Imaging MMP-2 in Tumor Cells under a High-Thiol Environment

The gold nanosensors based on the Au-S bond have been widely applied to biochemical detections. However, signal distortion caused by biothiols has been seldom mentioned and urgently needs to be solved. Herein, we designed a novel but easily assembled gold nanoprobe by coupling a selenol-modified peptide with FITC onto the gold nanoparticle's surface via an Au-Se bond for fluorescence imaging of a tumor marker matrix, metalloproteinases 2 (MMP-2). Compared to the Au-S probes, the Au-Se probes display high thermal stability and a very good anti-interference ability toward glutathione under simulated physiological conditions. More importantly, the Au-Se nanoprobe exhibits a high-fidelity fluorescent signal toward MMP-2, effectively avoiding interference caused by high levels of thiol compounds in vivo. In addition, in vivo experiments further proved that no significant signal intensity change for the tumor cells treated by the Au-Se probes was observed before and after eliminating glutathione. Hence, we believe such Au-Se probes with in vivo glutathione interfering resistance offer new routes and perspectives in biology and medicine in the future.

Sensitive and Selective Fluorescent Probe for Selenol in Living Cells Designed via a p Ka Shift Strategy

Selenocysteine (Sec) is a primary kind of reactive selenium species in cells, and its vital roles in physiological processes have been featured. Thus, the development of highly sensitive and selective methods for the sensing of Sec is of great significance. This work reports a turn-on fluorescent probe for selenol based on the unique fluorescence OFF-ON switching between the Schiff base (SB) and its complementary protonated Schiff base (PSB) form of merocyanine dyes. The probe consists of a merocyanine Schiff base fluorophore and a 2,4-dinitrobenzenesulfonamide moiety that reacts especially with selenol. The fluorescence turn-on response of MC-Sec is realized via the selective removal of the strongly electron withdrawing 2,4-dinitrobenzenesulfonyl group by Sec, leading to a shift in the p K_a of the imine nitrogen of the probe from 6.40 to 9.04 and thus significantly increasing the population of the fluorescent PSB form of the dye at physiological pH. MC-Sec shows good selectivity and sensitivity for Sec and has been applied in the imaging of exogenous and endogenous selenol in living cells by confocal fluorescence microscopy. The proposed mechanism should be useful for developing future probes directed to other target molecules by employing this simple but effective p K_a shift strategy.

Double-ratiometric fluorescence imaging of H2Se and O2˙− under hypoxia for exploring Na2SeO3-induced HepG2 cells' apoptosis

Sodium selenite (Na₂SeO₃), as an anti-tumor drug for inducing tumor cells' apoptosis, has been widely studied under normoxic conditions and has been shown to exhibit oxidative stress process-induced apoptosis. However, since the real tumor environment is hypoxic, the actual mechanism is still unclear. Hence, considering the main metabolite of Na₂SeO₃ in the metabolic process to be hydrogen selenide (H₂Se) and also that it can be converted to superoxide anion (O₂˙⁻) instantaneously in the presence of oxygen, a dual-ratiometric fluorescence imaging system for simultaneous monitoring of the changes of H₂Se and O₂˙⁻ induced by Na₂SeO₃-guided tumor cell apoptosis under hypoxic conditions was constructed. Two molecular probes NIR-H₂Se and dihydroethidium were used to detect H₂Se and O₂˙⁻, respectively, whereas Rhodamine 110 was used as the reference fluorophore. Notably, H₂Se levels significantly increased under hypoxic conditions, but there was no change in the level of O₂˙⁻, which is inconsistent with the results of the previous researches. Therefore, we hypothesize that the mechanism of Na₂SeO₃-induced apoptosis for tumor cells is caused by reductive stress; also, this method can be applied for the future study of other anti-cancer selenium compounds.

Sodium selenite (Na₂SeO₃), as an anti-tumor drug for inducing tumor cells' apoptosis, has been widely studied under normoxic conditions and has been shown to exhibit oxidative stress process-induced apoptosis.

A fast response and red emission probe for mammalian thioredoxin reductase

The first red emission probe, TRFS-red, for thioredoxin reductase was reported with improved response rate and sensitivity.