Visualizing glioma margins by real-time tracking of γ-glutamyltranspeptidase activity

Next-generation agents for fluorescence-guided glioblastoma surgery

Glioblastoma is a fast-growing and aggressive form of brain cancer. Even with maximal treatment, patients show a low median survival and are often subjected to a high recurrence incidence. The currently available treatments require multimodal management, including maximal safe surgical resection, followed by radiation and chemotherapy. Because of the infiltrative glioblastoma nature, intraoperative differentiation of cancer tissue from normal brain parenchyma is very challenging, and this accounts for the low rate of complete tumor resection. For these reasons, clinicians have increasingly used various intraoperative adjuncts to improve surgical results, such as fluorescent agents. However, most of the existing fluorophores show several limitations such as poor selectivity, photostability, photosensitization and high costs. This could limit their application to successfully improve glioblastoma resection. In the present perspective, we highlight the possibility to develop next-generation fluorescent tools able to more selectively label cancer cells during surgical resection.

Mitocytosis Mediated by an Enzyme-Activable Mitochondrion-Disturbing Polymer-Drug Conjugate Enhances Active Penetration in Glioblastoma Therapy

The application of nanomedicines for glioblastoma (GBM) therapy is hampered by the blood-brain barrier (BBB) and the dense glioblastoma tissue. To achieve efficient BBB crossing and deep GBM penetration, this work demonstrates a strategy of active transcellular transport of a mitochondrion-disturbing nanomedicine, pGBEMA22-b-pSSPPT9 (GBEPPT), in the GBM tissue through mitocytosis. GBEPPT is computer-aided designed and prepared by self-assembling a conjugate of an amphiphilic block polymer and a drug podophyllotoxin (PPT). When GBEPPT is delivered to the tumor site, overexpressed γ-glutamyl transpeptidase (GGT) on the brain-blood endothelial cell, or the GBM cell triggered enzymatic hydrolysis of γ-glutamylamide on GBEPPT to reverse its negative charge to positive. Positively charged GBEPPT rapidly enter into the cell and target the mitochondria. These GBEPPT disturb the homeostasis of mitochondria, inducing mitocytosis-mediated extracellular transport of GBEPPT to the neighboring cells via mitosomes. This intracellular-to-intercellular delivery cycle allows GBEPPT to penetrate deeply into the GBM parenchyma, and exert sustainable action of PPT released from GBEPPT on the tumor cells along its penetration path at the tumor site, thus improving the anti-GBM effect. The process of mitocytosis mediated by the mitochondrion-disturbing nanomedicine may offer great potential in enhancing drug penetration through malignant tissues, especially poorly permeable solid tumors.

Stimuli-Responsive Polymer-Based Nanosystems for Cancer Theranostics

Stimuli-responsive polymers can respond to internal stimuli, such as reactive oxygen species (ROS), glutathione (GSH), and pH, biological stimuli, such as enzymes, and external stimuli, such as lasers and ultrasound, etc., by changing their hydrophobicity/hydrophilicity, degradability, ionizability, etc., and thus have been widely used in biomedical applications. Due to the characteristics of the tumor microenvironment (TME), stimuli-responsive polymers that cater specifically to the TME have been extensively used to prepare smart nanovehicles for the targeted delivery of therapeutic and diagnostic agents to tumor tissues. Compared to conventional drug delivery nanosystems, TME-responsive nanosystems have many advantages, such as high sensitivity, broad applicability among different tumors, functional versatility, and improved biosafety. In recent years, a great deal of research has been devoted to engineering efficient stimuli-responsive polymeric nanosystems, and significant improvement has been made to both cancer diagnosis and therapy. In this review, we summarize some recent research advances involving the use of stimuli-responsive polymer nanocarriers in drug delivery, tumor imaging, therapy, and theranostics. Various chemical stimuli will be described in the context of stimuli-responsive nanosystems. Accordingly, the functional chemical groups responsible for the responsiveness and the strategies to incorporate these groups into the polymer will be discussed in detail. With the research on this topic expending at a fast pace, some innovative concepts, such as sequential and cascade drug release, NIR-II imaging, and multifunctional formulations, have emerged as popular strategies for enhanced performance, which will also be included here with up-to-date illustrations. We hope that this review will offer valuable insights for the selection and optimization of stimuli-responsive polymers to help accelerate their future applications in cancer diagnosis and treatment.

Near-infrared imaging of hepatocellular carcinoma and its medicinal treatment with a γ-glutamyl transpeptidase-monitoring fluorescence probe

Herein, the Near-infrared imaging of hepatocellular carcinoma (HCC) and its medicinal treatment was achieved with a γ-glutamyl transpeptidase (GGT)-monitoring fluorescence probe KYZ-GGT which consisted of the typical recognition group γ-glutamyl and the structurally modified signal reporting group hemicyanine-thioxanthene. Compared with the recently reported probes, KYZ-GGT suggested practical and steady capability for monitoring the GGT level in the cellular, xenograft, induced as well as medicinal treatment HCC models. It realized the mitochondrial targeting intracellular imaging to reflect the GGT dynamics in the induction or medicinal treatment of HCC. In the xenograft and induced model mice with multiple factors, KYZ-GGT showed stable performance for visualizing the HCC status. In the medicinal treatment of the long-period-induced HCC model mice verified by the serum indexes and histopathological analysis, KYZ-GGT successfully imaged the medicinal treatment process of HCC with two marketed drugs (Sorafenib and Lenvatinib) respectively, with an applicative penetration depth. The information here was meaningful for investigating effective medicinal strategies for overcoming HCC.

Activatable probes with potential for intraoperative tumor-specific fluorescence-imaging guided surgery

Owing to societal development and aging population, the impact of cancer on human health and quality of life has increased. Early detection and surgical treatment are the most effective approaches for most cancer patients. As the scope of conventional tumor resection is determined by auxiliary examination and surgeon experience, there is often insufficient recognition of tiny tumors. The ability to detect such tumors can be improved by using fluorescent tumor-specific probes for surgical navigation. This review mainly describes the design principles and mechanisms of activatable probes for the fluorescence imaging of tumors. This type of probe is nonfluorescent in normal tissue but exhibits obvious fluorescence emission upon encountering tumor-specific substrates, such as enzymes or bioactive molecules, or changes in the microenvironment, such as a low pH. In some cases, a single-factor response does not guarantee the effective fluorescence labeling of tumors. Therefore, two-factor-activatable fluorescence imaging probes that react with two specific factors in tumor cells have also been developed. Compared with single biomarker testing, the simultaneous monitoring of multiple biomarkers may provide additional insight into the role of these substances in cancer development and aid in improving the accuracy of early cancer diagnosis. Research and progress in this field can provide new methods for precision medicine and targeted therapy. The development of new approaches for early diagnosis and treatment can effectively improve the prognosis of cancer patients and help enhance their quality of life.

Recent Progress in Fluorescent Probes for Real-Time Monitoring of Glioblastoma

Treating glioblastoma (GBM) by resecting to a large extent can prolong a patient's survival by controlling the tumor cells, but excessive resection may produce postoperative complications by perturbing the brain structures. Therefore, various imaging procedures have been employed to successfully diagnose and resect with utmost caution and to protect vital structural or functional features. Fluorescence tagging is generally used as an intraoperative imaging technique in glioma cells in collaboration with other surgical tools such as MRI and navigation methods. However, the existing fluorescent probes may have several limitations, including poor selectivity, less photostability, false signals, and intraoperative re-administration when used in clinical and preclinical studies for glioma surgery. The involvement of smart fluorogenic materials, specifically fluorescent dyes, and biomarker-amended cell-penetrable fluorescent probes have noteworthy advantages for precise glioma imaging. This review outlines the contemporary advancements of fluorescent probes for imaging glioma cells along with their challenges and visions, with the anticipation to develop next-generation smart glioblastoma detection modalities.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

A water-soluble fluorescent probe for the determination of γ-glutamyltransferase activity and its application in tumor imaging

γ-glutamyltransferase (GGT), an important tumor marker, is highly expressed in tumor tissues, and precise detection of its activity provides a vital indicator for the diagnosis and treatment. In this work, a "lighting-on" probe (TCF-GGT) was elaborated to detect endogenous GGT with high selectivity and sensitivity. Dicyanomethyldifuranyl (TCF-OH) was employed as the fluorescence reporter and short peptide glutathione (GSH) worked as the GGT-active trigger, the introduction of which prevented the initial proton transfer of TCF-OH contributing to a blank sensing background. A bright red fluorescence could be switched on upon GGT catalytic hydrolysis, avoiding the potential interference from background. There displayed an excellent water-solubility, and little organic solvent was required during the exploration, which otherwise avoided the potential damage to enzyme and organism. TCF-GGT has been proved to be workable at cellular and organism level with highly effective imaging and a short metabolic cycle, which is expected to offer an alternative solution or reference to the early diagnosis and treatment of tumor.

Constructing a novel fluorescence detection method for γ-glutamyltranspeptidase and application on visualizing liver injury

Liver injury is a serious threat to human health, and γ-glutamyltranspeptidase (GGT) is proven to be one of the clinical biomarkers of liver injury. The conventional detection method of GGT activity in serum suffers from the complex operation, expensive equipment, and incapability of dynamically monitoring in biological samples. Herein, in consideration of the excellent characteristics of fluorescent probes, such as simple operation, high sensitivity, low cost, and good biocompatibility, a novel fluorescence detection method for GGT based on the combination of probe Rho-GGT and glutamic acid 5-hydrazide (glutamlhydrine) was designed. This method was applied to liver injury model mice to construct the relationship between the fluorescence signal, GGT activity, and the occurrence or development stage of liver injury. The fluorescence detection method combined with clinical indexes could more accurately characterize the situation of liver fibrosis, and evaluate the efficacy of liver fibrosis drugs, which could help provide important information for accurate diagnosis and early treatment of liver injury. The successful implementation of this project would promote the accurate in situ detection of GGT in liver injury, which was expected to guide pre-clinical diagnosis and clinical practice.

A water-soluble fluorescent probe for real-time visualization of γ-glutamyl transpeptidase activity in living cells

γ-glutamyl transpeptidase (GGT) is a kind of cell-surface enzyme that is overexpressed in many cancer cells. It is of great significance to develop an ideal tool for the diagnosis of GGT-rich cancer cells. Here, we reported a simple-structured but effective imaging probe for the detection of GGT activity. In the presence of GGT, the γ-glutamyl linkage could be cleaved specifically to produce amino-substituted product, resulting in significant fluorescence enhancement at 578 nm. Moreover, we successfully employed the probe to monitor GGT activity in HepG2 cells. We envisaged that such a simple but effective imaging tool could improve the practical applications for bioimaging.

Nanoscale Drug Delivery Systems in Glioblastoma

Glioblastoma is the most aggressive cerebral tumor in adults. However, the current pharmaceuticals in GBM treatment are mainly restricted to few chemotherapeutic drugs and have limited efficacy. Therefore, various nanoscale biomaterials that possess distinct structure and unique property were constructed as vehicles to precisely deliver molecules with potential therapeutic effect. In this review, nanoparticle drug delivery systems including CNTs, GBNs, C-dots, MOFs, Liposomes, MSNs, GNPs, PMs, Dendrimers and Nanogel were exemplified. The advantages and disadvantages of these nanoparticles in GBM treatment were illustrated.

In Situ Sprayed Starvation/Chemodynamic Therapeutic Gel for Post-Surgical Treatment of IDH1 (R132H) Glioma

Complete resection of isocitrate dehydrogenase 1 (IDH1) (R132H) glioma is unfeasible and the classic post-surgical chemo/radiotherapy suffers from high recurrence and low survival rate. IDH1 (R132H) cells are sensitive to low concentrations of glucose and high concentrations of reactive oxygen species (ROS) due to inherent metabolism reprograming. Hence, a starvation/chemodynamic therapeutic gel is developed to combat residual IDH1 (R132H) tumor cells after surgery. Briefly, glucose oxidase (GOx) is mineralized with manganese-doped calcium phosphate to form GOx@MnCaP nanoparticles, which are encapsulated into the fibrin gel (GOx@MnCaP@fibrin). After spraying gel in the surgical cavity, GOx catalyzes the oxidation of glucose in residual IDH1 (R132H) cells and produces H₂ O₂ . The generated H₂ O₂ is further converted into highly lethal hydroxyl radicals (•OH) by a Mn²⁺ -mediated Fenton-like reaction to further kill the residual IDH1 (R132H) cells. The as-prepared starvation/chemodynamic therapeutic gel shows much higher therapeutic efficacy toward IDH1 (R132H) cells than IDH1 (WT) cells, and achieves long-term survival.

Activatable molecular probes for fluorescence-guided surgery, endoscopy and tissue biopsy

The real-time, dynamic optical visualization of lesions and margins ensures not only complete resection of the malignant tissues but also better preservation of the vital organs/tissues during surgical procedures. Most imaging probes with an "always-on" signal encounter high background noise due to their non-specific accumulation in normal tissues. By contrast, activatable molecular probes only "turn on" their signals upon reaction with the targeted biomolecules that are overexpressed in malignant cells, offering high target-to-background ratios with high specificity and sensitivity. This review summarizes the recent progress of activatable molecular probes in surgical imaging and diagnosis. The design principle and mechanism of activatable molecular probes are discussed, followed by specific emphasis on applications ranging from fluorescence-guided surgery to endoscopy and tissue biopsy. Finally, potential challenges and perspectives in the field of activatable molecular probe-enabled surgical imaging are discussed.

Sensing and imaging of exosomal CD26 secreted from cancer cells and 3D colorectal tumor model using a novel near-infrared fluorogenic probe

Cancer-derived exosomes or their specific components hold great promise for early diagnosis and precise staging of cancers. This work aimed to construct a novel enzyme-activatable fluorescent substrate for real-time detection and in situ imaging of a key exosomal surface protein CD26 in various biological systems, as well as to reveal the relevance of exosomal CD26 to the tumorigenesis. For these purposes, a group of Gly-Pro amides deriving from several near-infrared fluorophores were designed on the basis of the unique prolyl-cleaving dipeptidease activity of CD26, while molecular docking simulations were applied to assess the possibility of the designed amides as CD26 specific substrates. Following virtual screening and experimental validation, it was observed that GP-ACM displayed the best combination of high sensitivity and excellent specificity to CD26. The sensing and imaging ability of GP-ACM towards CD26 were examined in a range of biological systems, such as living cells, in situ tissues, and the exosomes secreted from cancer cells. Under physiological conditions, GP-ACM can be readily hydrolyzed by CD26 to release the fluorescent product ACM. The fluorescent product emits strong near-infrared fluorescence signals around 660 nm, which can be easily captured by the devices equipped with a fluorescence detector. GP-ACM prolyl-cleaving reaction shows excellent specificity and rapid response towards CD26, while its fluorescent product ACM displays good chemical stability and outstanding photostability. With the help of GP-ACM, CD26 in living cells, tissues and the tumor-secreted exosomes can be real-time monitored and in-situ imaged, while further investigations reveal that the exosomal CD26 activities are abnormally elevated with the progression of colon tumor. Collectively, the present study offers a practical optical assay for real-time monitoring CD26 activities in multiple complex biological systems including the exosomes secreted by tumor cells. The simplicity and effectiveness of this assay hold great potential for facilitating fundamental researches and clinical diagnosis of exosomal CD26 associated diseases.

Nanoprobe-mediated precise imaging and therapy of glioma

Gliomas are the most common primary brain tumors in adults, accounting for 80% of primary intracranial tumors. Due to the heterogeneous and infiltrating nature of malignant gliomas and the hindrance of the blood-brain barrier (BBB), it is very difficult to accurately image and differentiate the malignancy grade of gliomas, thus significantly influencing the diagnostic accuracy and subsequent surgery or therapy. In recent years, the rapid development of emerging nanoprobes has provided a promising opportunity for the diagnosis and treatment of gliomas. After rational component regulation and surface modification, functional nanoprobes could efficiently cross the BBB, target gliomas, and realize single-modal or multimodal imaging of gliomas with high clarity. Moreover, these contrast nanoagents could also be conjugated with therapeutic drugs and cure cancerous tissues at the same time. Herein, we focus on the design strategies of nanoprobes for effective crossing of the BBB, and introduce the recent advances in the precise imaging and therapy of gliomas using functional nanoprobes. Finally, we also discuss the challenges and future directions of nanoprobe-based diagnosis and treatment of gliomas.

Manipulation of immune‒vascular crosstalk: new strategies towards cancer treatment

Tumor vasculature is characterized by aberrant structure and function, resulting in immune suppressive profiles of tumor microenvironment through limiting immune cell infiltration into tumors, endogenous immune surveillance and immune cell function. Vascular normalization as a novel therapeutic strategy tends to prune some of the immature blood vessels and fortify the structure and function of the remaining vessels, thus improving immune stimulation and the efficacy of immunotherapy. Interestingly, the presence of "immune‒vascular crosstalk" enables the formation of a positive feedback loop between vascular normalization and immune reprogramming, providing the possibility to develop new cancer therapeutic strategies. The applications of nanomedicine in vascular-targeting therapy in cancer have gained increasing attention due to its specific physical and chemical properties. Here, we reviewed the recent advances of effective routes, especially nanomedicine, for normalizing tumor vasculature. We also summarized the development of enhancing nanoparticle-based anticancer drug delivery via the employment of transcytosis and mimicking immune cell extravasation. This review explores the potential to optimize nanomedicine-based therapeutic strategies as an alternative option for cancer treatment.

In Vivo Imaging of Senescent Vascular Cells in Atherosclerotic Mice Using a β-Galactosidase-Activatable Nanoprobe

Senescence-associated diseases have severely diminished the quality of life and health of patients. However, a sensitive assay of these diseases remains limited due to a lack of straightforward methods. Considering that senescence-associated β-galactosidase (SA-β-Gal) is overexpressed in senescent cells, the detection of SA-β-Gal in senescent cells and tissues might be a feasible strategy for the early diagnosis of SA diseases. In this study, a β-galactosidase-activatable nanoprobe BOD-L-βGal-NPs was developed for the imaging of senescent cells and vasculature in atherosclerotic mice via real-time monitoring of β-Gal. BOD-L-βGal-NPs was fabricated by encapsulating a newly designed NIR ratiometric probe BOD-L-βGal within a poly(lactic-co-glycolic) acid (PLGA) core. Nanoprobe BOD-L-βGal-NPs showed good accumulation in arteries, thus successfully visualizing senescent cells and vasculature in atherosclerotic mice by tail vein injection. Our findings indicated that nanoprobe BOD-L-βGal-NPs holds great potential for the early diagnosis and therapy of atherosclerosis and other aging-associated diseases.

Aggregation Enhanced Responsiveness of Rationally Designed Probes to Hydrogen Sulfide for Targeted Cancer Imaging

Activatable molecular probes hold great promise for targeted cancer imaging. However, the hydrophobic nature of most conventional probes makes them generate precipitated agglomerate in aqueous media, thereby annihilating their responsiveness to analytes and precluding their practical applications for bioimaging. This study reports the development of two small molecular probes with unprecedented aggregation enhanced responsiveness to H₂S for in vivo imaging of H₂S-rich cancers. The subtle modulation of the equilibrium between hydrophilicity and lipophilicity by N-methylpyridinium endows these designed probes with the capability of spontaneously self-assembling into nanoprobes under physiological conditions. Such probes in an aggregated state, rather than a molecular dissolved state, show NIR fluorescence light up and photoacoustic signals turn on upon H₂S specific activation, allowing in vivo visualization and differentiation of cancers based on differences in H₂S content. Thus, our study presents an effective design strategy which should pave the way to molecular design of optimized probes for precision cancer diagnostics.

In vivo detection of γ-glutamyl-transferase up-regulation in glioma using hyperpolarized γ-glutamyl-[1-13C]glycine

Glutathione (GSH) is often upregulated in cancer, where it serves to mitigate oxidative stress. γ-glutamyl-transferase (GGT) is a key enzyme in GSH homeostasis, and compared to normal brain its expression is elevated in tumors, including in primary glioblastoma. GGT is therefore an attractive imaging target for detection of glioblastoma. The goal of our study was to assess the value of hyperpolarized (HP) γ-glutamyl-[1-¹³C]glycine for non-invasive imaging of glioblastoma. Nude rats bearing orthotopic U87 glioblastoma and healthy controls were investigated. Imaging was performed by injecting HP γ-glutamyl-[1-¹³C]glycine and acquiring dynamic ¹³C data on a preclinical 3T MR scanner. The signal-to-noise (SNR) ratios of γ-glutamyl-[1-¹³C]glycine and its product [1-¹³C]glycine were evaluated. Comparison of control and tumor-bearing rats showed no difference in γ-glutamyl-[1-¹³C]glycine SNR, pointing to similar delivery to tumor and normal brain. In contrast, [1-¹³C]glycine SNR was significantly higher in tumor-bearing rats compared to controls, and in tumor regions compared to normal-appearing brain. Importantly, higher [1-¹³C]glycine was associated with higher GGT expression and higher GSH levels in tumor tissue compared to normal brain. Collectively, this study demonstrates, to our knowledge for the first time, the feasibility of using HP γ-glutamyl-[1-¹³C]glycine to monitor GGT expression in the brain and thus to detect glioblastoma.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

A molecular design strategy toward enzyme-activated probes with near-infrared I and II fluorescence for targeted cancer imaging

The advance of cancer imaging requires innovations to establish novel fluorescent scaffolds that are excitable and emit in the near-infrared region with favorable Stokes shifts. Nevertheless, the lack of probes with these optimized optical properties presents a major bottleneck in targeted cancer imaging. By coupling of boron dipyrromethene platforms to enzymic substrates via a self-immolative benzyl thioether linker, we here report a strategy toward enzyme-activated fluorescent probes to satisfy these requirements. This strategy is applicable to generate various BODIPY-based probes across the NIR spectrum via introducing diverse electron-withdrawing substituents at the 3-position of the BODIPY core through a vinylene unit. As expected, such designed probes show advantages of two-channel ratiometric fluorescence and light-up NIR (I and II) emission with large Stokes shifts upon enzyme activation, enabling targeted cancer cell imaging and accurate tumor location by real-time monitoring of enzyme activities. This strategy is promising in engineering activatable molecular probes suitable for precision medicine.

Enzyme-activatable polymer-drug conjugate augments tumour penetration and treatment efficacy

A tumour microenvironment imposes barriers to the passive diffusion of molecules, which renders tumour penetration an unresolved obstacle to an effective anticancer drug delivery. Here, we present a γ-glutamyl transpeptidase-responsive camptothecin-polymer conjugate that actively infiltrates throughout the tumour tissue through transcytosis. When the conjugate passes on the luminal endothelial cells of the tumour blood vessels or extravasates into the tumour interstitium, the overexpressed γ-glutamyl transpeptidase on the cell membrane cleaves the γ-glutamyl moieties of the conjugate to generate positively charged primary amines. The resulting cationic conjugate undergoes caveolae-mediated endocytosis and transcytosis, which enables transendothelial and transcellular transport and a relatively uniform distribution throughout the tumour. The conjugate showed a potent antitumour activity in mouse models that led to the eradication of small solid tumours (~100 mm³) and regression of large established tumours with clinically relevant sizes (~500 mm³), and significantly extended the survival of orthotopic pancreatic tumour-bearing mice compared to that with the first-line chemotherapeutic drug gemcitabine.

Boosting often overlooked long wavelength emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of orthotopic glioblastoma

Rare-earth nanoparticles (RE NPs) with narrow long wavelength emissions have been recently investigated for their potential application for fluorescence imaging in the second near-infrared window (NIR-II). Previously these RE NPs have a very limited application in the diagnosis and treatment of deep-seated tumors such as brain tumors, due to their weak fluorescence in the range of 1300-1700 nm. Herein, we report a significant enhancement of more than 10 times regular emission of NaNdF₄ nanoparticles at 1340 nm wavelength by coating them with an inert layer of NaLuF₄, followed by sensitizing with a near-infrared dye (IR-808). We deliver these highly bright nanoparticles into the brain by using focused ultrasound to temporarily open the blood-brain barrier (BBB), and then detect the orthotopic glioblastoma by fluorescence imaging at 1340 nm. The images obtained from long wavelength fluorescence (i.e. 1340 nm) exhibited better resolution and contrast compared to the short wavelength fluorescence (i.e. 1060 nm). Our study not only provides insights for enhancing often overlooked emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of deep-seated tumors, but also demonstrates great potential of focused ultrasound based technology in delivering nanotheranostic agents.

Ratiometric Detection of γ-Glutamyltransferase in Human Colon Cancer Tissues Using a Two-Photon Probe

γ-Glutamyltransferase (GGT) plays a role in cleaving the γ-glutamyl bond of glutathione. The GGT is known to be overexpressed in some tumors and has been recognized as a potential biomarker for malignant tumors. Colon cancer is one of the most common cancers worldwide; however, there is no quantitative method for detecting cancer cells in human colon tissues. In this study, we report a ratiometric two-photon probe for GGT that can be applied in human colon tissues. The probe (Probe 2) showed high fluorescence efficiency, marked fluorescence changes, excellent kinetics, and selectivity for the GGT in live colon cells. Additionally, we obtained ratiometric two-photon microscopy images of GGT activity in human colon tissue. We used this method to compare normal and cancer tissues based on their ratio values; the ratio value was higher in cancer tissue than in normal tissue. This study provides a method for quantitative analysis of GGT, particularly in human colon cancer, which will be useful for studying GGT-related diseases and diagnosing colon cancer.

Point-of-care Ratiometric Fluorescence Imaging of Tissue for the Diagnosis of Ovarian Cancer

During a minimally invasive tumor resection procedure, it is still a challenge to rapidly and accurately trace tiny malignant tumors in real time. Fluorescent molecular imaging is considered an efficient method of localizing tumors during surgery due to its high sensitivity and biosafety. On the basis of the fact that γ-glutamyltranspeptidase (GGT) is overexpressed in ovarian cancer, we herein designed a highly sensitive ratiometric fluorescent GGT-responsive probe Py-GSH for rapid tumor detection.

Methods: The GGT response probe (Py-GSH) was constructed by using GSH group as a response group and pyrionin B as a fluorescent reporter. Py-GSH was characterized for photophysical properties, response speed and selectivity of GGT and response mechanism. The anti-interference ability of ratiometric probe Py-GSH to probe concentration and excitation power was evaluated both in vitro and in tissue. The biocompatibility and toxicity of the ratiometric probe was examined using cytoxicity test. The GGT levels in different lines of cells were determined by ratiometric fluorescence imaging and cytometry analysis.

Results: The obtained probe capable to rapidly monitored GGT activity in aqueous solution with 170-fold ratio change. By ratiometric fluorescence imaging, the probe Py-GSH was also successfully used to detect high GGT activity in solid tumor tissues and small peritoneal metastatic tumors (~1 mm in diameter) in a mouse model. In particular, this probe was further used to determine whether the tissue margin following clinical ovarian cancer surgery contained tumor.

Conclusion: In combination of ratiometric fluorescence probes with imaging instrument, a point-of-care imaging method was developed and may be used for surgical navigation and rapid diagnosis of tumor tissue during clinical tumor resection.

Enhanced γ-Glutamyltranspeptidase Imaging That Unravels the Glioma Recurrence in Post-radio/Chemotherapy Mixtures for Precise Pathology via Enzyme-Triggered Fluorescent Probe

Accurate pathological diagnosis of gliomas recurrence is crucial for the optimal management and prognosis prediction. The study here unravels that our newly developed γ-glutamyltranspeptidase (GGT) fluorescence probe (Figure 1A) imaging in twenty recurrent glioma tissues selectively recognizes the most malignant portion from treatment responsive tissues induced by radio/chemo-therapy (Figure 1B). The overexpression of GGT in recurrent gliomas and low level in radiation necrosis were validated by western blot analysis and immunohistochemistry. Furthermore, the ki-67 index evaluation demonstrated the significant increase of malignancy, aided by the GGT-responsive fluorescent probe to screen out the right specimen through fast enhanced imaging of enzyme activity. Importantly, our GGT-targeting probe can be used for accurate determination of pathologic evaluation of tumor malignancy, and eventually for guiding the following management in patients with recurrent gliomas.

Recent Advances in the Development of Optical Imaging Probes for γ-Glutamyltranspeptidase

γ-Glutamyltranspeptidase (GGT) is a cell-membrane-bound protease that participates in cellular glutathione and cysteine homeostasis, which are closely related to many physiological and pathological processes. The accurate measurement of GGT activity is useful for the early diagnosis of diseases. In the past few years, many efforts have been made to build optical imaging probes for the detection of GGT activity both in vitro and in vivo. In this Minireview, recent advances in the development of various optical imaging probes for GGT, including activatable fluorescence probes, ratiometric fluorescence probes, and activatable bioluminescence probes, are summarized. This review starts from the instruction of the GGT enzyme and its biological functions, followed by a discussion of activatable fluorescence probes that show off-on fluorescence in response to GGT. GGT-activatable two-photon fluorescence imaging probes with improved imaging depth and spatial resolution are also discussed. Ratiometric fluorescence probes capable of accurately reporting on GGT levels through a self-calibration mechanism are discussed, followed by describing GGT-activatable bioluminescence probes that can offer a high signal-to-background ratio to detect GGT in living mice. Finally, current challenges and further perspectives for the development of molecular imaging probes for GGT are addressed.

Mitochondria-targeting BODIPY-loaded micelles as novel class of photosensitizer for photodynamic therapy

In this paper, a series of novel BODIPY-based photosensitizers have been designed and synthesized for photodynamic therapy. BODIPY3 was screened out as the most potential photosensitizer due to its excellent optical properties, high singlet oxygen efficiency and good photostability. However, as an organic photosensitizer, BODIPY3 still suffered from the drawbacks of insolubility and instability in aqueous system. In view of these problems, DSPE-PEG2000 was used to trap BODIPY3 into the hydrophobic core of micelles to obtain well-dispersing nano complexes BODIPY3-PEG₃ in aqueous system. More importantly, BODIPY3-PEG₃ not only has better solubility and stability in aqueous media but can generate significant singlet oxygen (¹O₂, one of the reactive oxygen species, the real cytotoxic agent in photodynamic therapy) in living cells and exhibit high light cytotoxicity to three cancer cell lines. The mechanism studies indicated the mitochondrial localization of BODIPY3-PEG₃ was able to generate ROS in mitochondria, which further result in mitochondrial dysfunction and photoinduced apoptosis via caspase-8 and caspase-3 pathway.

Dual-channel near-infrared fluorescent probe for real-time tracking of endogenous γ-glutamyl transpeptidase activity

We developed a curcuminoid difluoroboron-based fluorescent probe for tracking endogenous GGT activity with dual-channel light-up near-infrared (NIR) imaging.

Selective tracking of ovarian-cancer-specific γ-glutamyltranspeptidase using a ratiometric two-photon fluorescent probe

Real-time tracking of GGT enzymatic activity in human ovarian cancer cells is a reliable method for accurate prediction of cancer diagnosis and management.