Photochemically controlled activation of STING by CAIX-targeting photocaged agonists to suppress tumor cell growth.

Controllable activation of the innate immune adapter protein - stimulator of interferon genes (STING) pathway is a critical challenge for the clinical development of STING agonists due to the potential "on-target off-tumor" toxicity caused by systematic activation of STING. Herein, we designed and synthesized a photo-caged STING agonist 2 with a tumor cell-targeting carbonic anhydrase inhibitor warhead, which could be readily uncaged by blue light to release the active STING agonist leading to remarkable activation of STING signaling. Furthermore, compound 2 was found to preferentially target tumor cells, stimulate the STING signaling in zebrafish embryo upon photo-uncaging and to induce proliferation of macrophages and upregulation of the mRNA expression of STING as well as its downstream NF-kB and cytokines, thus leading to significant suppression of tumor cell growth in a photo-dependent manner with reduced systemic toxicity. This photo-caged agonist not only provides a powerful tool to precisely trigger STING signalling, but also represents a novel controllable STING activation strategy for safer cancer immunotherapy.

Rational Design of Cu-Doped Tetrahedron of Spinel Oxide for High-Performance Nitric Oxide Electrochemical Sensor.

The real-time detection of nitric oxide (NO) in living cells is essential to reveal its physiological processes. However, the popular electrochemical detection strategy is limited to the utilization of noble metals. The development of new detection candidates without noble metal species still maintaining excellent catalytic performance has become a big challenge. Herein, we propose a spinel oxide doped with heteroatom-Cu-doped Co3O4 (Cu-Co3O4) for the sensitive and selective detection of NO release from the living cells. The material is strategically designed with Cu occupying the tetrahedral (Td) center of Co3O4 through the formation of a Cu-O bond. The introduced Cu regulates the local coordination environment and optimizes the electronic structure of Co3O4, hybridizing with the N 2p orbital to enhance charge transfer. The CuTd site can well inhibit the current response to nitrite (NO2-), resulting in a high improvement in the electrochemical oxidation of NO. The selectivity of Cu-Co3O4 can be markedly improved by the pore size of the molecular sieve and the negative charge on the surface. The rapid transmission of electrons is due to the fact that Cu-Co3O4 can be uniformly and densely in situ grown on Ti foil. The rationally designed Cu-Co3O4 sensor displays excellent catalytic activity toward NO oxidation with a low limit of detection of 2.0 nM (S/N = 3) and high sensitivity of 1.9 µA nM-1 cm-2 in cell culture medium. The Cu-Co3O4 sensor also shows good biocompatibility to monitor the real-time NO release from living cells (human umbilical vein endothelial cells: HUVECs; macrophage: RAW 264.7 cells). It was found that a remarkable response to NO was obtained in different living cells when stimulated by l-arginine (l-Arg). Moreover, the developed biosensor could be used for real-time monitoring of NO released from macrophages polarized to a M1/M2 phenotype. This cheap and convenient doping strategy shows universality and can be used for sensor design of other Cu-doped transition metal materials. The Cu-Co3O4 sensor presents an excellent example through the design of proper materials to implement unique sensing requirements and sheds light on the promising strategy for electrochemical sensor fabrication.

Construction of a multifunctional peptide nanoplatform for nitric oxide release and monitoring and its application in tumor-bearing mice.

As a "star molecule", nitric oxide (NO) either promotes or inhibits many physiological processes depending on its concentration. The in situ generation and monitoring of therapeutic gas molecules has been a problem that many researchers have been working to address due to the stochastic nature of gas molecule movement. There are still relatively few studies using short peptides as NO storage systems, and there are still challenges in monitoring NO release in situ with real-time imaging over long periods of time. In this work, a morphologically transformable NO release, diagnosis and treatment integrated multifunctional nanoplatform was fabricated. A new NO-activated probe (DPBTD) with emission in the first near infrared (NIR-I) region was encapsulated into the hydrophobic domains of Ac-KLVFFAL-NH2 peptide derivatives as a biosensor for NO release. Peptide scaffolds were endowed with the capacity of controlled NO release by the introduction of NO donor (organic nitrates). Interestingly, morphology of the nanoplatform could be transformed from one-dimensional (1D) nanowires to two-dimensional (2D) nanosheets via nanorods transition state under tip sonication, which was allowed for better cell uptake. Eventually, this nanocarrier was used for stimuli-responsive NO release, real-time imaging and treatment in tumor tissues of 4T1 tumor-bearing mice. This strategy expands the application potential of peptide-based nanomaterials and provides ideas for monitoring the progress of gas-mediated cancer therapy.

In Situ Reconstruction NiO Octahedral Active Sites for Promoting Electrocatalytic Oxygen Evolution of Nickel Phosphate.

Electrochemical activation strategy is very effective to improve the intrinsic catalytic activity of metal phosphate toward the sluggish oxygen evolution reaction (OER) for water electrolysis. However, it is still challenging to operando trace the activated reconstruction and corresponding electrocatalytic dynamic mechanisms. Herein, a constant voltage activation strategy is adopted to in situ activate Ni2 P4 O12 , in which the break of NiONi bond and dissolution of PO4 3- groups could optimize the lattice oxygen, thus reconstructing an irreversible amorphous Ni(OH)2 layer with a thickness of 1.5-3.5 nm on the surface of Ni2 P4 O12 . The heterostructure electrocatalyst can afford an excellent OER activity in alkaline media with an overpotential of 216.5 mV at 27.0 mA cm-2 . Operando X-ray absorption fine structure spectroscopy analysis and density functional theory simulations indicate that the heterostructure follows a nonconcerted proton-electron transfer mechanism for OER. This activation strategy demonstrates universality and can be used to the surface reconstruction of other metal phosphates.

Design of an activatable NIR-II nanoprobe for the in vivo elucidation of Alzheimer's disease-related variations in methylglyoxal concentrations.

Clear elucidation of the changes in Alzheimer's disease (AD)-related methylglyoxal (MGO) levels in vivo is significant yet highly challenging. Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) has gained increasing attention as an observation method in living organisms, but an MGO-activatable fluorescent probe that emits in this region for in vivo brain imaging is lacking because of the existence of the blood-brain barrier (BBB). Herein, a biocompatible Fe3O4 nanoparticle (IONP)-conjugated MGO-activatable NIR-II fluorescent probe (MAM) modified with the peptide T7 (HAIYPRH) (named TM-IONP) is reported for the in situ detection of MGO in a transgenic AD mouse model. In this system, the T7 peptide enhances BBB crossing and brain accumulation by specifically targeting transferrin receptors on the BBB. Due to the MAM probe, TM-IONPs emit fluorescence in the NIR-II region and display high selectivity with an MGO detection limit of 72 nM and a 10-fold increase in the fluorescence signal. After intravenous administration, the TM-IONPs are easily delivered to the brain and pass through the BBB without intervention, and as a result, the brains of AD mice can be noninvasively imaged for the first time by the in situ detection of MGO with a 24.2-fold enhancement in NIR-II fluorescence intensity compared with wild-type mice. Thus, this MGO-activated NIR-II-emitting nanoprobe is potentially useful for early AD diagnosis in clinic.

Dual-targeting prodrug nanotheranostics for NIR-â ¡ fluorescence imaging-guided photo-immunotherapy of glioblastoma.

Glioblastoma (GBM) therapy is severely impaired by the blood-brain barrier (BBB) and invasive tumor growth in the central nervous system. To improve GBM therapy, we herein presented a dual-targeting nanotheranostic for second near-infrared (NIR-II) fluorescence imaging-guided photo-immunotherapy. Firstly, a NIR-Ⅱ fluorophore MRP bearing donor-acceptor-donor (D-A-D) backbone was synthesized. Then, the prodrug nanotheranostics were prepared by self-assembling MRP with a prodrug of JQ1 (JPC) and T7 ligand-modified PEG5k-DSPE. T7 can cross the BBB for tumor-targeted delivery of JPC and MRP. JQ1 could be restored from JPC at the tumor site for suppressing interferon gamma-inducible programmed death ligand 1 expression in the tumor cells. MRP could generate NIR-II fluorescence to navigate 808 nm laser, induce a photothermal effect to trigger in-situ antigen release at the tumor site, and ultimately elicit antitumor immunogenicity. Photo-immunotherapy with JPC and MRP dual-loaded nanoparticles remarkably inhibited GBM tumor growth in vivo. The dual-targeting nanotheranostic might represent a novel nanoplatform for precise photo-immunotherapy of GBM.

NIR-I fluorescence imaging tumorous methylglyoxal by an activatable nanoprobe based on peptide nanotubes by FRET process.

Methylglyoxal (MGO), a glycolysis metabolite with high reactivity, can nonenzymatically modify proteins, lipids and nucleic acids etc., and it is closely related to the development of tumors. The accurate detection and high-performance optical imaging of MGO from deep tumor issues is of great significance for understanding their roles in tumor initiation and progression. Herein, we have presented a nanoprobe D/I-PNTs with emission in the first near infrared (NIR-I) region by employing a fluorescence resonance energy transfer (FRET) process between a far-red emission MGO probe and IR783 based on peptide nanotubes. The nanoplatform extended the emission range of MGO probe through FRET process and avoided complex molecular design and synthesis. The biocompatible peptide nanotubes improved the water solubility of MGO probe. D/I-PNTs was sensitive to MGO with a detection limit of 272 nM and enabled high-resolution NIR-I fluorescence imaging of MGO induced by glyoxalase I (GLO1) inhibitor in tumor with higher penetration depth (∼4 mm) than that in visible (Vis) region (∼3 mm). Most importantly, the FRET process based on the structure characteristics of peptide nanotubes can be a universal approach to realize the extension of emission wavelength and ratio detection of target analytes, which will be a promising strategy for bioimaging in deep tissue with high contrast.

An activatable and tumor-targeting NIR fluorescent probe for imaging of histone deacetylase 6 in cancer cells and in vivo.

An activatable and tumor-targeting near-infrared (NIR) fluorescent probe CyAc-RGD was synthesized for the imaging of histone deacetylase 6 (HDAC6). The probe exhibited higher sensitivity and specificity for HDAC6 detection in cancer cells. Moreover, CyAc-RGD demonstrated good tumor-targeting ability and realized HDAC6 imaging in vivo.

Activatable NIR-II Fluorescent Nanoprobe for Rapid Detection and Imaging of Methylglyoxal Facilitated by the Local Nonpolar Microenvironment.

Closely related to multiple chronic inflammation, especially type-2 diabetes (T2D), methylglyoxal (MGO) may be a potential key to visualize disease progression and treatment effects. On the other hand, lack of convenient and fast analytical methods cannot afford accurate MGO quantitative evaluation. In this work, an activatable second near-infrared region (NIR-II) fluorescent probe TDTCD was synthesized and its reaction mechanism with MGO was discussed. The desired NIR-II product preferred response solvents with small polarity. A novel activatable nanoprobe, MG-SLNP, for MGO was then constructed based on rational packaging to provide a local nonpolar microenvironment. The hydrophobic core of nanoparticles not only successfully improved the stability and water solubility but also greatly promoted the response rate while reacting with MGO. The comparison between NIR-II fluorescence and the traditional high-performance liquid chromatography method for T2D blood samples was discussed. A high-resolution viewing window, quick response, and good biocompatibility led to a satisfactory signal-to-noise ratio of MG-SLNP for real-time MGO bio-detection and imaging in vivo.

Nitric Oxide Prodrug Delivery and Release Monitoring Based on a Galactose-Modified Multifunctional Nanoprobe.

Nitric oxide (NO)-based cancer therapy has attracted much attention in recent years owing to its broad effects on cancer. Low concentrations of NO stimulate cancer cell progression, while its higher levels induce cell apoptosis, and thus, it has motivated the development of probes for in situ NO release monitoring. In this work, a galactose-modified benzothiadiazole-based fluorescent probe (GalNONP/C) was synthesized as both a NO-responsive nanoprobe and NO prodrug carrier. The probe exhibited far-red emission in the range from 550 to 800 nm, and the response showed acidity preference. The galactose on the probe enabled selective targeting of hepatocellular carcinoma (HCC) cells by binding to the asialoglycoprotein receptor (ASGPR) on the cell surface. The probe also delivered low-molecular weight NO prodrug JS-K into cells and monitored the real-time release of the generated NO. Furthermore, in vivo NO imaging with tumor targeting was demonstrated in HCC orthotopic transplantation nude mice and liver sections. Compared with the control experiment using a probe without NO prodrug loading, higher fluorescence response of NO was detected in the cell (3.0 times) and liver slices of the HCC tumor model (2.7 times). This strategy may pave the way to develop nanoprobes for in situ NO monitoring and therapy evaluation in NO-related cancer therapy.

A red-emissive D-A-D type fluorescent probe for lysosomal pH imaging.

Visual detection of pH changes in lysosomes is critical because lysosomes not only play an important role in diverse cellular functions but also are closely related to various physiological and pathological processes. Herein, we disclose a donor-acceptor-donor (D-A-D) type fluorescent probe DBTD for detecting pH fluctuation in lysosomes. DBTD was rationally designed by using benzothiadiazole as the electron acceptor and N,N-diethylamino groups as the electron donor. Owing to its unique D-A-D structure, DBTD displayed a red-emission centered at 614 nm. It showed a sensitive and a linear response to pH from 4.5 to 5.2 with a pKa of 5.0, which is very suitable for lysosomal pH imaging. The response was based on the intramolecular charge transfer (ICT) effect owing to the protonation of the diethylamino group. Furthermore, DBTD could accurately monitor lysosomal pH variations in SGC-7901 cells. More importantly, it was able to image the pH change in lysosomes during the autophagy process successfully, suggesting the great potential of DBTD acting as a powerful tool for monitoring lysosomal pH-related biological processes.

Imidazole-fused benzothiadiazole-based red-emissive fluorescence probe for lysosomal pH imaging in living cells.

Intracellular pH is a key physiological factor for controlling the activities and functions of cells and lysosome is a vital subcellular organelle. Thus, developing a novel lysosome-targeting fluorescence probe for selective and sensitive detection of lysosomal pH in living cells is very important. In this work, we synthesized a series of fluorescence probes based on imidazole-fused benzothiadiazole. The optical properties of these probes were easily adjusted by modifying the substituents with different electron-withdrawing/donating ability in imidazole moiety. All of them showed acid-response and decreased fluorescence intensity during pH values changing from 4.0 to 8.5. The introduction of morpholine group allowed them to specifically respond to the changes of lysosomal pH. Among them, probe MIBTAA possessed a suitable pKa value (5.3) and showed good linear response to pH (R2 = 0.9918) with red emission when pH changed from 4.4 to 5.6. The probe was successfully applied for monitoring pH variation in living cells induced by proton-pump inhibitor Baf-A1 and chloroquine, indicating its great potential for pH imaging in biological applications.

An activatable near-infrared fluorescent probe for methylglyoxal imaging in Alzheimer's disease mice.

Visual detection of the methylglyoxal (MGO) level in the brain is critical for understanding its role in the onset and progression of AD. Herein, we disclosed a NIR fluorescent probe, DBTPP, for detecting MGO by utilizing a thiadiazole-fused o-phenylenediamine moiety as a MGO-specific sensing unit. DBTPP exhibits a series of distinct advantages, such as NIR emission, high selectivity and sensitivity, excellent acid-stability, and a huge off-on ratio. The probe could accurately monitor both exogenous and endogenous MGO variations in SH-SY5Y cells. Besides, it was able to image the endogenous MGO in a transgenic AD mouse model successfully, suggesting the great potential of MGO as a biomarker for early AD diagnosis.

Imaging Tumorous Methylglyoxal by an Activatable Near-Infrared Fluorescent Probe for Monitoring Glyoxalase 1 Activity.

The accurate detection of tumorous methylglyoxal (MGO) and its detoxifier glyoxalase 1 (GLO1) in living systems is critical for understanding their roles in tumor initiation and progression. To date, the in situ fluorescence detection of endogenous MGO and GLO1 in tumor has not been reported. Herein we developed a near-infrared (NIR) fluorescent probe MEBTD to specifically detect tumorous MGO. Compared with previously reported MGO fluorescent probes, MEBTD exhibits several distinct advantages, including NIR emission, high selectivity with an MGO detection limit of 18 nM, and a 131-fold off-on ratio. The probe could sense GLO1 activity and monitor the therapeutic effect of GLO1 inhibitors by imaging tumorous MGO in a both a real-time and in situ manner, demonstrating that the biological effect of GLO1 inhibitors is dependent on the GLO1 activity. Furthermore, MEBTD enables the visualization of tumorous MGO induced by GLO1 inhibitors in vivo. To the best of our knowledge, MEBTD is the first NIR fluorescent probe for specifically imaging tumorous MGO in living animals, indicating the promising potential for tumor diagnosis and therapeutic evaluation.

Glycopeptide Nanofiber Platform for Aß-Sialic Acid Interaction Analysis and Highly Sensitive Detection of Aß.

The variation of amyloid ß peptide (Aß) concentration and Aß aggregation are closely associated with the etiology of Alzheimer's diseases (AD). The interaction of Aß with the monosialoganglioside-rich neuronal cell membrane has been suggested to influence Aß aggregation. Therefore, studies on the mechanism of Aß and sialic acids (SA) interaction would greatly contribute to better understanding the pathogenesis of AD. Herein, we report a novel approach for Aß-SA interaction analysis and highly sensitive Aß detection by mimicing the cell surface presentation of SA clusters through engineering of SA-modified peptide nanofiber (SANF). The SANF displayed well-ordered 1D nanostructure with high density of SA on surface. Using FAM-labeled Aß fragments of Aß1-16, Aß16-23, and Aß24-40, the interaction between Aß and SA was evaluated by the fluorescence titration experiments. It was found that the order of the SA-binding affinity was Aß1-16 > Aß24-40 > Aß16-23. Importantly, the presence of full-length Aß1-40 monomer triggered a significant fluorescence enhancement due to the multivalent binding of Aß1-40 to the nanofiber. This fluorescent turn-on response showed high selectivity and sensitivity for Aß1-40 detection and the method was further used for Aß aggregation process monitoring and inhibitor screening. The results suggest the proposed strategy is promising to serve as a tool for mechanism study and the early diagnosis of Alzheimer's disease.

Acid-Promoted D-A-D Type Far-Red Fluorescent Probe with High Photostability for Lysosomal Nitric Oxide Imaging.

To accurately monitor the variations of lysosomal nitric oxide (NO) under physiological condition remains a great challenge for understanding the biological function of NO. Herein, we developed a new chemotype probe, namely, MBTD, for acid-promoted and far-red fluorescence imaging of lysosomal NO in vitro and ex vivo. MBTD was rationally designed by incorporating o-phenylenediamino (OPD) moiety into the donor-acceptor-donor (D-A-D) type fluorophore based on a dual intramolecular charge transfer (ICT) mechanism. Compared to previously reported OPD-based NO probes, MBTD displays several distinct advantages including large stroke shift, huge on-off ratio with minimal autofluorescence, and high NO specificity. Particularly, MBTD exhibits an acid-promoted response to NO with high acid tolerance, which greatly improves the spatial resolution to lysosomal NO by excluding the background noise from other nonacidic organelles. Furthermore, MBTD displayed much longer-lived and more stable fluorescence emission in comparison with the commercialized NO probe. MBTD was employed for ratiometric examination of the exogenous or endogenous NO of macrophages. More importantly, MBTD was able to detect the variation of lysosomal NO level in an acute liver injury mouse model ex vivo, implying the potential of MBTD for real-time monitoring the therapeutic efficacy of drug candidates for the treatment of acute liver injury. MBTD as a novel type of NO probe might open a new avenue for precisely sensing lysosomal NO-related pathological and therapeutic process.

A Self-Assembled Ratiometric Polymeric Nanoprobe for Highly Selective Fluorescence Detection of Hydrogen Peroxide.

In this study, a dual-emission fluorescence resonance energy transfer (FRET) polymeric nanoprobe by single-wavelength excitation was developed for sensitive and selective hydrogen peroxide (H2O2) detection. Polymeric nanoprobe was prepared by simple self-assembly of functional lipopolymers, which were 4-carboxy-3-fluorophenylboronic acid (FPBA)-modified DSPE-PEG (DSPE-PEG-FPBA) and 7-hydroxycoumarin (HC)-conjugated DSPE-PEG (DSPE-PEG-HC). Subsequent binding of alizarin red S (ARS) to FPBA endowed the nanoprobe with a new fluorescence emission peak at around 600 nm. Because of the perfect match of the fluorescence emission spectra of HC with the absorbance spectra of ARS-FPBA, FRET was achieved between them. The sensing strategy for H2O2 was based on H2O2-induced deboronation reaction and boronic acid-mediated ARS fluorescence. Interaction between phenylboronic acid and ARS was revisited herein and it was found that electron-donating or -withdrawing group on phenylboronic acid (PBA) has significant influence on the fluorescence property of ARS, which enabled sensitive and selective H2O2 sensing. The nanoprobe displayed two well-separated emission bands (150 nm), providing high specificity and sensitivity for ratiometric detection of H2O2. Further application was exploited for the determination of glucose and the results demonstrated that the proposed strategy showed ratiometric response capability for glucose detection. The current method does not involve complicated organic synthesis and opens a new avenue for the construction of multifunctional polymeric fluorescent nanoprobe.