Molecular optical imaging probes for early diagnosis of drug-induced acute kidney injury

In Situ Fluorescent and Photoacoustic Imaging of Golgi pH to Elucidate the Function of Transmembrane Protein 165

Golgi pH homeostasis affects many different biological processes, including glycosylation. Recent studies have demonstrated that transmembrane protein 165 (TMEM165) deficiency leads to Golgi glycosylation abnormalities by disturbing Golgi pH homeostasis. However, due to the lack of specific tools to measure Golgi pH in situ, evidence for TMEM165 involvement in H⁺ transport in the Golgi apparatus is still absent. Herein, the photoacoustic and fluorescent dual-mode probe CPH was developed for ratiometric detection of Golgi pH. CPH was proved to accumulate in the Golgi apparatus and reversibly image Golgi pH in real-time with high sensitivity in cells. Furthermore, we found that the absence of TMEM165 influenced H⁺ equilibrium and caused Golgi apparatus acidification. Our work provides strong evidence that TMEM165 regulates Golgi pH homeostasis. Moreover, we believe that CPH has the potential to be a practical tool to monitor Golgi pH in various biological processes.

Semiconducting Polymer Nanoreporters for Near-Infrared Chemiluminescence Imaging of Immunoactivation

Real-time in vivo imaging of immunoactivation is critical for longitudinal evaluation of cancer immunotherapy, which, however, is rarely demonstrated. This study reports semiconducting polymer nanoreporters (SPNRs) with superoxide anion (O₂ ^•- )-activatable chemiluminescence signals for in vivo imaging of immunoactivation during cancer immunotherapy. SPNRs are designed to comprise an SP and a caged chemiluminescence phenoxy-dioxetane substrate, which respectively serve as the chemiluminescence acceptor and donor to enable intraparticle chemiluminescence resonance energy transfer. SPNRs are intrinsically fluorescent but only become chemiluminescent upon activation by O₂ ^•- . Representing the first O₂ ^•- -activatable near-infrared chemiluminescent reporter, SPNR3 sensitively differentiates higher O₂ ^•- levels in immune cells from other cells including cancer and normal cells. Following systemic administration, SPNR3 passively accumulates into tumors in living mice and activates the chemiluminescence signals responding to the concentration of O₂ ^•- in the tumor microenvironment. Moreover, the enhancement of in vivo chemiluminescence signal after cancer immunotherapy is correlated with increased population of T cells in the tumor, proving its feasibility in tracking of T cell activation. Thus, SPNRs represent the first kind of chemiluminescent reporters competent for in vivo imaging of immunoactivation.

NIR Scaffold Bearing Three Handles for Biocompatible Sequential Click Installation of Multiple Functional Arms

Near-infrared (NIR) probes are ideal for fluorescence labeling and imaging of biological targets in living animals. However, the instability of common NIR dyes hampers the construction of NIR probes bearing multiple functional components such as biomolecules for specific targeting and imaging reagents for multimodality imaging. To overcome these limitations, we designed a novel NIR scaffold bearing two terminal alkynes as clickable handles and a chloride on the heptamethine backbone that allows nucleophilic substitution with an azide to generate the third clickable handle. This unique scaffold allows for facile installation of multiple functional arms for the construction of multifunctional NIR probes. Various biomacromolecules or imaging reagents can be introduced to the NIR scaffold by sequential one-pot click reactions under biocompatible conditions. The preclickable handle chloride on the NIR backbone does not interfere with the initial click reactions, and it can be easily transformed into an azide for a following click reaction. On the basis of this unique NIR scaffold, we developed a highly efficient method to construct diverse NIR probes containing multiple functional biomolecules including peptides, antibodies, nucleic acids, and NIR/PET (positron emission tomography) dual-modality imaging probes bearing tumor-targeting groups. NIR imaging or multimodality imaging using these probes was performed on live cells or tumor models on living mice.

H2S-activatable near-infrared afterglow luminescent probes for sensitive molecular imaging in vivo

Afterglow luminescent probes with high signal-to-background ratio show promise for in vivo imaging; however, such probes that can be selectively delivered into target sites and switch on afterglow luminescence remain limited. We optimize an organic electrochromic material and integrate it into near-infrared (NIR) photosensitizer (silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) containing nanoparticles, developing an H2S-activatable NIR afterglow probe (F12+-ANP). F12+-ANP displays a fast reaction rate (1563 ± 141 M-1 s-1) and large afterglow turn-on ratio (~122-fold) toward H2S, enabling high-sensitivity and -specificity measurement of H2S concentration in bloods from healthy persons, hepatic or colorectal cancer patients. We further construct a hepatic-tumor-targeting and H2S-activatable afterglow probe (F12+-ANP-Gal) for noninvasive, real-time imaging of tiny subcutaneous HepG2 tumors (<3 mm in diameter) and orthotopic liver tumors in mice. Strikingly, F12+-ANP-Gal accurately delineates tumor margins in excised hepatic cancer specimens, which may facilitate intraoperative guidance of hepatic cancer surgery.

A Renal-Clearable Macromolecular Reporter for Near-Infrared Fluorescence Imaging of Bladder Cancer

Bladder cancer (BC) is a prevalent disease with high morbidity and mortality; however, in vivo optical imaging of BC remains challenging because of the lack of cancer-specific optical agents with high renal clearance. Herein, a macromolecular reporter (CyP1) was synthesized for real-time near-infrared fluorescence (NIRF) imaging and urinalysis of BC in living mice. Because of the high renal clearance (ca. 94 % of the injection dosage at 24 h post-injection) and its cancer biomarker (APN=aminopeptidase N) specificity, CyP1 can be efficiently transported to the bladder and specially turn on its NIRF signal to report the detection of BC in living mice. Moreover, CyP1 can be used for optical urinalysis, permitting the ex vivo tracking of tumor progression for therapeutic evaluation and easy translation of CyP2 as an in vitro diagnostic assay. This study not only provides new opportunities for non-invasive diagnosis of BC, but also reveals useful guidelines for the development of molecular reporters for the detection of bladder diseases.

Nanoparticle-based Cell Trackers for Biomedical Applications

The continuous or real-time tracking of biological processes using biocompatible contrast agents over a certain period of time is vital for precise diagnosis and treatment, such as monitoring tissue regeneration after stem cell transplantation, understanding the genesis, development, invasion and metastasis of cancer and so on. The rationally designed nanoparticles, including aggregation-induced emission (AIE) dots, inorganic quantum dots (QDs), nanodiamonds, superparamagnetic iron oxide nanoparticles (SPIONs), and semiconducting polymer nanoparticles (SPNs), have been explored to meet this urgent need. In this review, the development and application of these nanoparticle-based cell trackers for a variety of imaging technologies, including fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, magnetic particle imaging, positron emission tomography and single photon emission computing tomography are discussed in detail. Moreover, the further therapeutic treatments using multi-functional trackers endowed with photodynamic and photothermal modalities are also introduced to provide a comprehensive perspective in this promising research field.

Reactive Oxygen Correlated Chemiluminescent Imaging of a Semiconducting Polymer Nanoplatform for Monitoring Chemodynamic Therapy

In chemodynamic therapy (CDT), real-time monitoring of reactive oxygen species (ROS) production is critical to reducing the nonspecific damage during CDT and feasibly evaluating the therapeutic response. However, CDT agents that can emit ROS-related signals are rare. Herein, we synthesize a semiconducting polymer nanoplatform (SPN) that can not only produce highly toxic ROS to kill cancer cells but also emit ROS-correlated chemiluminescent signals. Notably, the efficacy of both chemiluminescence and CDT can be significantly enhanced by hemin doping (∼10-fold enhancement for luminescent intensity). Such ROS-dependent chemiluminescence of SPN allows ROS generation within a tumor to be optically monitored during the CDT process. Importantly, SPN establishes an excellent correlation of chemiluminescence intensities with cancer inhibition rates in vitro and in vivo. Thus, our nanoplatform represents the first intelligent strategy that enables chemiluminescence-imaging-monitored CDT, which holds potential in assessing therapeutic responsivity and predicting treatment outcomes in early stages.

Cascaded Multiresponsive Self-Assembled 19F MRI Nanoprobes with Redox-Triggered Activation and NIR-Induced Amplification

Molecular probes featuring promising capabilities including specific targeting, high signal-to-noise ratio, and in situ visualization of deep tissues are in great demand for tumor diagnosis and therapy. ¹⁹F magnetic resonance imaging (MRI) techniques incorporating stimuli-responsive probes are anticipated to be highly beneficial for specific detection and imaging of tumors because of negligible background and deep tissue penetration. Herein, we report a cascaded multiresponsive self-assembled nanoprobe, which enables sequential redox-triggered and near-infrared (NIR) irradiation-induced ¹⁹F MR signal activation/amplification for sensing and imaging. Specifically, we designed and synthesized a cascaded multiresponsive ¹⁹F-bearing nanoprobe based on the self-assembly of amphiphilic redox-responsive ¹⁹F-containing polymers and NIR-absorbing indocyanine green (ICG) molecules. It could realize the activation of ¹⁹F signals in the reducing tumor microenvironment and subsequent signal amplification via the photothermal process. This stepwise two-stage activation/amplification of ¹⁹F signals was validated by ¹⁹F NMR and MRI both in vitro and in vivo. The multiresponsive ¹⁹F nanoprobes capable of cascaded ¹⁹F signal activation/amplification and photothermal effect exertion can provide accurate sensing and imaging of tumors.

Aggregation-induced emission luminogens for RONS sensing

The development of AIE bioprobes for RONS sensing in living systems is now summarized. We discuss some representative examples of AIEgen based bioprobes in terms of their molecular design, sensing mechanism and sensitive sensing in vitro and in vivo.

Chemiluminescence for bioimaging and therapeutics: recent advances and challenges

The current progress, design principles in bioimaging and therapeutic applications, and future perspectives of various chemiluminescent platforms are reviewed.

Imaging of peroxynitrite in drug-induced acute kidney injury with a near-infrared fluorescence and photoacoustic dual-modal molecular probe

A FRET-based probe for mapping the fluctuation of OONO⁻ in cisplatin-induced acute kidney injury was constructed.

In vivo pharmacodynamic evaluation of antidepressants based on flux mitochondrial Cys in living mice via near infrared fluorescence imaging

We proposed a new strategy for in vivo evaluation of antidepressants through NIRF imaging for mitochondrial Cys in the mouse brain.

A new FRET probe for ratiometric fluorescence detecting mitochondria-localized drug activation and imaging endogenous hydroxyl radicals in zebrafish

A new FRET probe has been prepared and successfully used for imaging hydroxyl radicals generated by drug activation and endogenous hydroxyl radicals in zebrafish.

Design of superior phototheranostic agents guided by Jablonski diagrams

This review summarizes how Jablonski diagrams guide the design of advanced organic optical agents and improvement of disease phototheranostic efficacies.

Molecular and nanoengineering approaches towards activatable cancer immunotherapy

This review summarizes the development of activatable immunotherapeutic nanoagents that activate antitumor immunity only in response to internal or external stimuli, which potentially enhance patient response rates while reducing immune-related adverse events during cancer immunotherapy.

Construction and bioimaging application of novel indole heptamethine cyanines containing functionalized tetrahydropyridine rings

IR780 as a commercially available dye with near-infrared emission has been extensively applied in fluorescent probes and bioimaging.

Modular Polymers as a Platform for Cell Surface Engineering: Promoting Neural Differentiation and Enhancing the Immune Response

Regulating cell behavior and cell fate are of great significance for basic biological research and cell therapy. Carbohydrates, as the key biomacromolecules, play a crucial role in regulating cell behavior. Herein, "modular" glycopolymers were synthesized by reversible addition-fragmentation chain transfer polymerization. These glycopolymers contain sugar units (glucose), anchoring units (cholesterol), "guest" units (adamantane) for host-guest interaction, and fluorescent labeling units (fluorescein). It was demonstrated that these glycopolymers can insert into cell membranes with high efficiency and their residence time on the membranes can be regulated by controlling their cholesterol content. Furthermore, the behavior of the engineered cells can be controlled by modifying with different functional β-cyclodextrins (CD-X) via host-guest interactions with the adamantane units. Host-guest interactions with the modular polymers were demonstrated using CD-RBITC (X = a rhodamine B isothiocyanate). The glycopolymers were modified with CD-S (X = seven sulfonate groups) and CD-M (X = seven mannose groups) and were then attached, respectively, to the surfaces of mouse embryonic stem cells for the promotion of neural differentiation and to the surfaces of cancer cells for the enhancement of the immune response. The combination of multiple anchors and host-guest interactions provides a widely applicable cell membrane modification platform for a variety of applications.

Responsive Exosome Nano-bioconjugates for Synergistic Cancer Therapy

Exosomes hold great potential in therapeutic development. However, native exosomes usually induce insufficient effects in vivo and simply act as drug delivery vehicles. Herein, we synthesize responsive exosome nano-bioconjugates for cancer therapy. Azide-modified exosomes derived from M1 macrophages are conjugated with dibenzocyclooctyne-modified antibodies of CD47 and SIRPα (aCD47 and aSIRPα) through pH-sensitive linkers. After systemic administration, the nano-bioconjugates can actively target tumors through the specific recognition between aCD47 and CD47 on the tumor cell surface. In the acidic tumor microenvironment, the benzoic-imine bonds of the nano-bioconjugates are cleaved to release aSIRPα and aCD47 that can, respectively, block SIRPα on macrophages and CD47, leading to abolished "don't eat me" signaling and improved phagocytosis of macrophages. Meanwhile, the native M1 exosomes effectively reprogram the macrophages from pro-tumoral M2 to anti-tumoral M1.

Biodegradable Inorganic Nanoparticles for Cancer Theranostics: Insights into the Degradation Behavior

Inorganic nanoparticles as a versatile nanoplatform have been broadly applied in the diagnosis and treatment of cancers due to their inherent superior physicochemical properties (including magnetic, thermal, optical, and catalytic performance) and excellent functions (e.g., imaging, targeted delivery, and controlled release of drugs) through surface functional modification or ingredient dopant. However, in practical biological applications, inorganic nanomaterials are relatively difficult to degrade and excrete, which induces a long residence time in living organisms and thus may cause adverse effects, such as inflammation and tissue cysts. Therefore, the development of biodegradable inorganic nanomaterials is of great significance for their biomedical application. This Review will focus on the recent advances of degradable inorganic nanoparticles for cancer theranostics with highlight on the degradation mechanism, aiming to offer an in-depth understanding of degradation behavior and related biomedical applications. Finally, key challenges and guidelines will be discussed to explore biodegradable inorganic nanomaterials with minimized toxicity issues, facilitating their potential clinical translation in cancer diagnosis and treatment.

An Ultrasensitivity Fluorescent Probe Based on the ICT-FRET Dual Mechanisms for Imaging β-Galactosidase in Vitro and ex Vivo

Emergence of fluorescence imaging with real-time and in situ manners has revolutionized the fields of tracing and defining enzymes in biological systems. β-galactosidase is a kind of enzyme that plays vital roles in controlling multitudes of cellular functions and participating in disease pathogenesis. Thus, building fluorescent probes with high sensitivity and fidelity for visualizing β-galactosidase in biological systems is very significative. Herein, we engineered the first ultrsensitivity ratiometric fluorescent probe CG based on ICT-FRET synergetic mechanisms for detecting β-galactosidase. The spectrum data show that probe CG has a fast response (<20 s), as well as a very low detection limit to β-galactosidase (0.081 U/mL). Moreover, by calculation of a serious of kinetic parameters including K_m (1.42 μM), k_cat (7.04 s^-1), and k_cat/K_m (4.96 μM^-1 s^-1), CG demonstrates high affinity and high catalytic efficiency to β-galactosidase. Because of its excellent water solubility, CG has well biocompatibility to visualize the β-galactosidase in living cells. Furthermore, for imaging in bioapplications, CG is capable of detecting β-galactosidase not only in overexpressed cell lines but also in transient expressed cell lines. Significantly, CG can monitor β-galactosidase ex vivo selectively. We hope ongoing work to employ CG can be as an ultrasensitive powerful tool for further seeking the physiological and pathological functions in biological organisms.

Activatable molecular agents for cancer theranostics

Theranostics that integrates diagnosis and treatment modalities has attracted great attention due to its abilities of personalized therapy and real-time monitoring of therapeutic outcome. Such a theranostic paradigm requires agents to simultaneously possess the capabilities of targeting, imaging, and treatment. Activatable molecular agents (AMAs) are promising for cancer theranostics, as they show a higher signal-to-noise ratio (SNR), real-time detection of cancer-associated biomarkers, lower normal tissue toxicity, and a higher therapeutic effect. This perspective summarizes the recent advancements of AMAs, which include imaging-guided chemotherapy, imaging-guided photodynamic therapy, and imaging-guided photothermal therapy. The molecular design principles, theranostic mechanisms, and biomedical applications of AMAs are described, followed by a discussion of potential challenges of AMAs in cancer theranostics.

Physicochemical-property guided design of a highly sensitive probe to image nitrosative stress in the pathology of stroke

In vivo real-time imaging of nitrosative stress in the pathology of stroke has long been a formidable challenge due to both the presence of the blood–brain barrier (BBB) and the elusive nature of reactive nitrogen species, while this task is also informative to gain a molecular level understanding of neurovascular injury caused by nitrosative stress during the stroke episode. Herein, using a physicochemical property-guided probe design strategy in combination with the reaction-based probe design rationale, we have developed an ultrasensitive probe for imaging nitrosative stress evolved in the pathology of stroke. This probe demonstrates an almost zero background fluorescence signal but a maximum 1000-fold fluorescence enhancement in response to peroxynitrite, the nitrosative stress marker. Due to its good physicochemical properties, the probe readily penetrates the BBB after intravenous administration, and quickly accumulates in mice brain to sense local vascular injuries. After accomplishing its imaging mission, the probe is easily metabolized and therefore won't cause safety concerns. These desirable features make the probe competent for the straightforward visualization of nitrosative stress progression in stroke pathology.

A brain–blood barrier permeable probe was developed for fluorogenically sensing nitrosative stress caused by brain vascular injury.

Engineering dithiobenzoic acid lactone-decorated Si-rhodamine as a highly selective near-infrared HOCl fluorescent probe for imaging drug-induced acute nephrotoxicity

A highly selective lysosome-targeting NIR fluorescent probe (Lyso-SiR-2S) for HOCl was constructed based on Si-rhodamine B spirodithiolactone. This probe was very effectively employed to sense HOCl produced in various living cells and to visualize fluctuations of endogenous HOCl resulting from GEN-induced acute kidney injury in vivo for the first time.

Activity-Based Optical Sensing Enabled by Self-Immolative Scaffolds: Monitoring of Release Events by Fluorescence or Chemiluminescence Output

Functional molecular scaffolds comprised of self-immolative adaptors are being used in widespread applications in the fields of enzyme activity analyses, signal amplification, and bioimaging. Optically detected chemical probes are very promising compounds for sensing and diagnosis, since they present several attractive features such as high specificity, low detection limits, fast response times, and technical simplicity. During the last two decades, we have developed several distinct molecular scaffolds that harness the self-immolative disassembly feature of these adaptors to amplify chromogenic output for diagnosis and drug delivery applications. In order to study the molecular behavior of the various amplification systems, an optical output, used to monitor the progress of the disassembly pattern, was required. Therefore, over the course of our research, diverse molecular scaffolds that produce an optical signal in response to a disassembly step, were evaluated. These optically active scaffolds have been incorporated into self-immolative dendrimers and self-immolative polymers to implement unique disassembly properties that result with linear and exponential signal amplification capabilities. In addition, some scaffolds, aimed for linker technology, were used in delivery systems to monitor release of drug molecules. The optical signal used to monitor the release event could be produced by analysis of reporter molecules with chromogenic or fluorogenic properties. Recently, we have also developed molecular scaffolds modified to produce a chemiluminescent signal to monitor the self-immolative disassembly step. The main advantage of these scaffolds over others is the use of chemiluminescence as an output signal. It is well-known that chemiluminescence is considered as one the most sensitive diagnostic methods due to its high signal-to-noise ratio. The unique structures of the self-immolative chemiluminescence scaffolds have been used in the design of three different distinctive concepts: self-immolative chemiluminescence polymers, auto-inductive amplification systems with chemiluminescence signal and monitoring of drug release by a chemiluminescence output. Furthermore, we reported the design and synthesis of the first theranostic prodrug for the monitoring of drug release achieved by a chemiluminescence mode of action. Quinone-methide elimination has proven to serve as a valuable functional tool for composing molecular scaffolds with self-immolative capabilities. Such scaffolds function as molecular adaptors that can almost simultaneously release a target molecule with an accompanied emission of a light signal that is used to monitor the release event. We anticipate that these self-immolative scaffolds will continue to find utility as functional linkers in various chemical and biological research areas such as drug delivery, theranostic applications, and as molecular sensors with signal amplification.

An Activatable Chemiluminescent Probe for Sensitive Detection of γ-Glutamyl Transpeptidase Activity in Vivo

Activatable chemiluminescent probes that show enhanced chemiluminescence upon interaction with a molecular target of interest have offered promising tools for sensing and bioimaging in terms of low background, high sensitivity, and improved penetration depth in biological tissues. Here, we reported a γ-glutamyl transpeptidase (GGT) activatable chemiluminescent probe for real-time detection of GGT activity in vitro and in living mice. The probe was designed by caging an electron-withdrawing acrylic group-substituted Schaap's phenoxy-dioxetane with a GGT-recognitive substrate (γ-Glu) and a self-immolative linker (p-aminobenzyl alcohol), which was initially chemiluminescence off. Upon interaction with GGT, strong chemiluminescence with a more than 800-fold turn-on ratio could be achieved in aqueous solution, allowing to specifically detect GGT activity with ultrahigh signal-to-background ratio and sensitivity in vitro and in live cells. We demonstrated that the probe was reliable to quantify the GGT in serum, permitting to accurately report the elevated levels of GGT in lipopolysaccharide-treated mouse serum. Moreover, through real-time chemiluminescence imaging of GGT activity, the designed probe was feasible to detect GGT-positive tumors in living mice after intravenous systemic administration. This study demonstrates the high potential of GGT-activatable chemiluminescent probe for serum assays and molecular imaging, which might find wide applications in diagnosis of GGT-related diseases.

Enlightening kidney pathophysiology

Understanding the mechanics of acute kidney injury from toxins, ischemia and sepsis remains challenging. Molecular probes with high renal clearance have now been developed for real-time optical detection of early-stage biomarkers of drug-induced acute kidney injury, and for the understanding of the mechanisms of injury.

Chemical Modulation of Bioengineered Exosomes for Tissue-Specific Biodistribution

The physicochemical properties of nanomaterials play a key role in tissue-specific targeting by reducing nonspecific background uptake as well as controlling biodistribution and clearance. Due to the strong influence of surface chemistry, chemical modulation of bioinert exosomes with chargeable and traceable small molecule fluorophores has a significant effect on the targeting, stability, and toxicity of the final conjugates. In this study, charge-variable exosomes are designed by conjugating their surface proteins with near-infrared fluorophores to control the in vivo fate of exosomes. Interestingly, zwitterionic fluorophore-labeled exosomes show rapid renal clearance with minimum to none nonspecific tissue uptake, whereas anionic exosomes are excreted through the hepatobiliary route with high uptake in the liver. The biodistribution and pharmacokinetics of exosome conjugates are comparable to their corresponding free fluorophores, demonstrating that the surface characteristics govern the fate of final conjugates in the living organism. Such unique surface properties of chemically modulated exosomes are confirmed in the lymphatic system after intradermal administration, which results in distinctive kinetic profiles in the secondary lymphoid tissues. This finding can subsequently serve as the foundation for developing tissue-specific exosome-based therapeutics.