A Novel Topical Fluorescent Probe for Detection of Glioblastoma

Discovery of Fatty Acid Translocase CD36-Targeting Near-Infrared Fluorescent Probe Enables Visualization and Imaging-Guided Surgery for Glioma

Despite therapeutic advances in glioma, glioma-related mortality rates remain high due to its extremely poor prognosis and high recurrence. Near-infrared (NIR) fluorescence imaging technologies, using the clinically approved fluorescent probe 5-ALA, have gained prominence in facilitating visualization of glioma resection. However, the false-positive and false-negative results of 5-ALA decrease its sensitivity and specificity in detecting glioma, thereby hampering its use in glioma surgical navigation. Herein, a novel molecular probe MPA-Pip-abt-510 labeled with a NIR fluorescent dye MPA was developed, and its ability to target the CD36 protein, which is upregulated in glioma, was assessed. Fluorescent-labeled probes, conjugated to the CD36-targeting ligand abt-510, demonstrated high specificity and selectivity for CD36-positive tumor cells in vitro and tumor tissue in vivo. Biodistribution analysis of MPA-Pip-abt-510 revealed high tumor-specific accumulation in tumors, accompanied by minimal nonspecific uptake in background tissues, yielding a signal-to-noise ratio (SNR) of 6.6 ± 0.4 in a U87 subcutaneous glioma model 10 h postinjection. Meanwhile, quantitative analysis validated the high uptake of MPA-Pip-abt-510 in the U87 orthotopic tumor model, with a tumor-to-brain SNR of 5.4 ± 0.5, enabling the accurate identification of tumor tissue for surgical navigation. Moreover, pathological analysis of tumor and healthy brain tissues unveiled well-defined tumor boundaries, highlighting the capacity of the MPA-Pip-abt-510 probe to precisely visualize the CD36 protein at the molecular level. Given its rapid tumor-targeting abilities, durable retention, and accurate outlining of tumor boundaries, MPA-Pip-abt-510 emerges as a promising CD36-targeted fluorescence contrast agent and expands the toolbox of glioma fluorescent probes for surgical navigation.

Identification of a pancreatic juice-specific fluorescent probe through 411 probes activated by aminopeptidases/proteases or phosphatases/phosphodiesterases

BACKGROUND

This study is a retrospective review aimed to identify pancreatic juice-specific fluorescent probes to visualize pancreatic juice using a library of 381 aminopeptidase/protease-activatable fluorescent probes and 30 phosphatase/phosphodiesterase probes. In 2013, we developed a fluorescence imaging technique using a chymotrypsin probe to visualize pancreatic juice, linked to postoperative pancreatic fistula (POPF). This probe required addition of trypsin to convert pancreatic chymotrypsinogen to chymotrypsin. Recently we accessed libraries of enzyme-activatable fluorescent probes to find probes that facilitated target-specific imaging.

METHODS

Pancreatic juice and ascitic fluid samples were collected in eight patients undergoing pancreaticoduodenectomy. Reaction rates of pancreatic juice to background ascitic fluids were calculated for these 411 fluorescent probes.

RESULTS

Forty-four fluorescent probes were screened in terms of high reactivity with pancreatic juice. Only one candidate probe targeting ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) 1 was selected for a pancreatic juice-specific fluorescent probe. Inhibitor experiments and Western blotting supported the presence of ENPP1 in the pancreatic juice.

CONCLUSION

ENPP1-targeting fluorescent probe may have the potential to visualize pancreatic juice leakage during surgery. This finding may allow surgeons to suture leaking sites and decide the necessity of prophylactic abdominal drains; however, the role of ENPP1 in pancreatic juice remains to be clarified.

Dipeptidylpeptidase-4-targeted activatable fluorescent probes visualize senescent cells

Senescent cells promote cancer development and progression through chronic inflammation caused by a senescence-associated secretory phenotype (SASP). Although various senotherapeutic strategies targeting senescent cells have been developed for the prevention and treatment of cancers, technology for the in vivo detection and evaluation of senescent cell accumulation has not yet been established. Here, we identified activatable fluorescent probes targeting dipeptidylpeptidase-4 (DPP4) as an effective probe for detecting senescent cells through an enzymatic activity-based screening of fluorescent probes. We also determined that these probes were highly, selectively, and rapidly activated in senescent cells during live cell imaging. Furthermore, we successfully visualized senescent cells in the organs of mice using DPP4-targeted probes. These results are expected to lead to the development of a diagnostic technology for noninvasively detecting senescent cells in vivo and could play a role in the application of DPP4 prodrugs for senotherapy.

Activity-Based Fluorescence Diagnostics for Cancer

Fluorescence imaging is one of the most promising approaches to achieve intraoperative assessment of the tumor/normal tissue margins during cancer surgery. This is critical to improve the patients' prognosis, and therefore various molecular fluorescence imaging probes have been developed for the identification of cancer lesions during surgery. Among them, "activatable" fluorescence probes that react with cancer-specific biomarker enzymes to generate fluorescence signals have great potential for high-contrast cancer imaging due to their low background fluorescence and high signal amplification by enzymatic turnover. Over the past two decades, activatable fluorescence probes employing various fluorescence control mechanisms have been developed worldwide for this purpose. Furthermore, new biomarker enzymatic activities for specific types of cancers have been identified, enabling visualization of various types of cancers with high sensitivity and specificity. This Review focuses on recent advances in the design, function and characteristics of activatable fluorescence probes that target cancer-specific enzymatic activities for cancer imaging and also discusses future prospects in the field of activity-based diagnostics for cancer.

Advancement of fluorescent aminopeptidase probes for rapid cancer detection-current uses and neurosurgical applications

Surgical resection is considered for most brain tumors to obtain tissue diagnosis and to eradicate or debulk the tumor. Glioma, the most common primary malignant brain tumor, generally has a poor prognosis despite the multidisciplinary treatments with radical resection and chemoradiotherapy. Surgical resection of glioma is often complicated by the obscure border between the tumor and the adjacent brain tissues and by the tumor's infiltration into the eloquent brain. 5-aminolevulinic acid is frequently used for tumor visualization, as it exhibits high fluorescence in high-grade glioma. Here, we provide an overview of the fluorescent probes currently used for brain tumors, as well as those under development for other cancers, including HMRG-based probes, 2MeSiR-based probes, and other aminopeptidase probes. We describe our recently developed HMRG-based probes in brain tumors, such as PR-HMRG, combined with the existing diagnosis approach. These probes are remarkably effective for cancer cell recognition. Thus, they can be potentially integrated into surgical treatment for intraoperative detection of cancers.

Real-Time Fluorescence Imaging to Identify Cholangiocarcinoma in the Extrahepatic Biliary Tree Using an Enzyme-Activatable Probe

Introduction

Complete resection is the only possible treatment for cholangiocarcinoma in the extrahepatic biliary tree (eCCA), although current imaging modalities are limited in their ability to accurately diagnose longitudinal spread. We aimed to develop fluorescence imaging techniques for real-time identification of eCCA using an enzyme-activatable probe, which emits fluorescence immediately after activation by a cancer-specific enzyme.

Methods

Using lysates and small tissue fragments collected from surgically resected specimens, we selected the most specific probe for eCCA from among 800 enzyme-activatable probes. The selected probe was directly sprayed onto resected specimens and fluorescence images were acquired; these images were evaluated for diagnostic accuracy. We also comprehensively searched for enzymes that could activate the probe, then compared their expression levels in cancer and non-cancer tissues.

Results

Analyses of 19 samples (four cancer lysates, seven non-cancer lysates, and eight bile samples) and 54 tissue fragments (13 cancer tissues and 41 non-cancer tissues) revealed that PM-2MeSiR was the most specific fluorophore for eCCA. Fluorescence images of 7 patients were obtained; these images enabled rapid identification of cancerous regions, which closely matched histopathology findings in 4 patients. Puromycin-sensitive aminopeptidase was identified as the enzyme that might activate the probe, and its expression was upregulated in eCCA.

Conclusion

Fluorescence imaging with PM-2MeSiR, which may be activated by puromycin-sensitive aminopeptidase, yielded generally high accuracy. This technique may be useful for real-time identification of the spread of eCCA during surgery and endoscopic examinations.

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.

Protease Activated Probes for Real-Time Ratiometric Imaging of Solid Tumors

Surgery is the preferred treatment option for most solid tumors. However, inaccurate detection of cancer borders leads to either incomplete removal of malignant cells or excess excision of healthy tissue. While fluorescent contrast agents and imaging systems improve tumor visualization, they can suffer from low signal-to-background and are prone to technical artifacts. Ratiometric imaging has the potential to eliminate many of these issues such as uneven probe distribution, tissue autofluorescence, and changes in positioning of the light source. Here, we describe a strategy to convert quenched fluorescent probes into ratiometric contrast agents. Conversion of the cathepsin-activated probe, 6QC-Cy5, into a two-fluorophore probe, 6QC-RATIO, significantly improved signal-to-background in vitro and in a mouse subcutaneous breast tumor model. Tumor detection sensitivity was further enhanced using a dual-substrate AND-gate ratiometric probe, Death-Cat-RATIO, that fluoresces only after orthogonal processing by multiple tumor-specific proteases. We also designed and built a modular camera system that was coupled to the FDA-approved da Vinci Xi robot, to enable real-time imaging of ratiometric signals at video frame rates compatible with surgical workflows. Our results demonstrate that ratiometric camera systems and imaging probes have the potential to be clinically implemented to improve surgical resection of many types of cancer.

Diagnostic accuracy of intraoperative margin assessment techniques in surgery for head and neck squamous cell carcinoma: A meta-analysis

BACKGROUND

Positive margins following head and neck squamous cell carcinoma (HNSCC) surgery lead to significant morbidity and mortality. Existing Intraoperative Margin Assessment (IMA) techniques are not widely used due to limitations in sampling technique, time constraints and resource requirements. We performed a meta-analysis of the diagnostic performance of existing IMA techniques in HNSCC, providing a benchmark against which emerging techniques may be judged.

METHODS

The study was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines. Studies were included if they reported diagnostic metrics of techniques used during HNSCC surgery, compared with permanent histopathology. Screening, manuscript review and data extraction was performed by multiple independent observers. Pooled sensitivity and specificity were estimated using the bivariate random effects model.

RESULTS

From an initial 2344 references, 35 studies were included for meta-analysis. Sensitivity (Sens), specificity (Spec), diagnostic odds ratio (DOR) and area under the receiver operating characteristic curve (AUROC) were calculated for each group (n, Sens, Spec, DOR, AUROC): frozen section = 13, 0.798, 0.991, 309.8, 0.976; tumour-targeted fluorescence (TTF) = 5, 0.957, 0.827, 66.4, 0.944; optical techniques = 10, 0.919, 0.855, 58.9, 0.925; touch imprint cytology = 3, 0.925, 0.988, 51.1, 0.919; topical staining = 4, 0.918, 0.759, 16.4, 0.833.

CONCLUSIONS

Frozen section and TTF had the best diagnostic performance. Frozen section is limited by sampling error. TTF shows promise but involves administration of a systemic agent. Neither is currently in widespread clinical use. Emerging techniques must demonstrate competitive diagnostic accuracy whilst allowing rapid, reliable, cost-effective results.

Changes in calpain-2 expression during glioblastoma progression predisposes tumor cells to temozolomide resistance by minimizing DNA damage and p53-dependent apoptosis

BACKGROUND

Glioblastoma multiforme (GBM) is characterized by an unfavorable prognosis for patients affected. During standard-of-care chemotherapy using temozolomide (TMZ), tumors acquire resistance thereby causing tumor recurrence. Thus, deciphering essential molecular pathways causing TMZ resistance are of high therapeutic relevance.

METHODS

Mass spectrometry based proteomics were used to study the GBM proteome. Immunohistochemistry staining of human GBM tissue for either calpain-1 or -2 was performed to locate expression of proteases. In vitro cell based assays were used to measure cell viability and survival of primary patient-derived GBM cells and established GBM cell lines after TMZ ± calpain inhibitor administration. shRNA expression knockdowns of either calpain-1 or calpain-2 were generated to study TMZ sensitivity of the specific subunits. The Comet assay and ɣH2AX signal measurements were performed in order to assess the DNA damage amount and recognition. Finally, quantitative real-time PCR of target proteins was applied to differentiate between transcriptional and post-translational regulation.

RESULTS

Calcium-dependent calpain proteases, in particular calpain-2, are more abundant in glioblastoma compared to normal brain and increased in patient-matched initial and recurrent glioblastomas. On the cellular level, pharmacological calpain inhibition increased the sensitivities of primary glioblastoma cells towards TMZ. A genetic knockdown of calpain-2 in U251 cells led to increased caspase-3 cleavage and sensitivity to neocarzinostatin, which rapidly induces DNA strand breakage. We hypothesize that calpain-2 causes desensitization of tumor cells against TMZ by preventing strong DNA damage and subsequent apoptosis via post-translational TP53 inhibition. Indeed, proteomic comparison of U251 control vs. U251 calpain-2 knockdown cells highlights perturbed levels of numerous proteins involved in DNA damage response and downstream pathways affecting TP53 and NF-κB signaling. TP53 showed increased protein abundance, but no transcriptional regulation.

CONCLUSION

TMZ-induced cell death in the presence of calpain-2 expression appears to favor DNA repair and promote cell survival. We conclude from our experiments that calpain-2 expression represents a proteomic mode that is associated with higher resistance via "priming" GBM cells to TMZ chemotherapy. Thus, calpain-2 could serve as a prognostic factor for GBM outcome.

Apelin/APJ system: an emerging therapeutic target for neurological diseases

Apelin, an endogenous ligand for the G protein-coupled receptor APJ, is extensively expressed in various systems, especially the nervous system. This article reviews the role of apelin/APJ system in neurological diseases. In detail, apelin/APJ system can relieve acute brain injury including subarachnoid hemorrhage, traumatic brain injury, and ischemic stroke. Also, apelin/APJ system has therapeutic effects on chronic neurodegenerative disease models, involving the regulation of neurotrophic factors, neuroendocrine, oxidative stress, neuroinflammation, neuronal apoptosis, and autophagy. In addition, through different routes of administration, apelin/APJ system has a biphasic effect on depression, epilepsy, and pain. However, apelin/APJ system exacerbates the proliferation and invasion of glioblastoma. Thus, apelin/APJ system is expected to be a therapeutic target for the treatment of nervous system diseases.

An enzyme activated fluorescent probe for LTA4H activity sensing and its application in cancer screening

Early diagnosis of cancer is an efficient strategy to prevent tumor progression and improve the survival rate of patients. However, to discovery of reliable tumor-specific biomarkers remains a great challenge. Leukotriene A4 hydrolase (LTA₄H) is a bifunctional zinc metalloenzyme with epoxide hydrolase activity and aminopeptidase activity, which plays important roles in allergic and inflammatory reactions and showed strong relevance with carcinoma progression. We thus sought to investigate the possibility of application LTA₄H activity detection in cancer diagnosis. To achieve this, we herein develop an enzyme activated fluorescent probe for LTA₄H activity sensing by incorporating the specific recognition unit of LTA₄H with a red-emitting fluorophore. The acquired probe (named as ADMAB) showed high sensitivity and specificity toward LTA₄H in vitro. By further application of ADMAB in living cells, significantly elevated LTA₄H activity in cancer cell lines was observed when compared with normal cell lines and in vivo tracing A549 tumor in nude mice was also realized by ADMAB. Meanwhile, the wound-healing assay further revealed the importance of LTA₄H in tumor metastasis. Moreover, the LTA₄H activity in human serum sample was successfully detected by ADMAB and significantly elevated LTA₄H activity in patients diagnosed with cancer was firstly found, which demonstrated ADMAB to be a useful tool for cancer diagnosis and LTA₄H related biological study.

Development of an intraoperative breast cancer margin assessment method using quantitative fluorescence measurements

Breast-conserving surgery has become the preferred treatment method for breast cancer. Surgical margin assessment is performed during surgery, as it can reduce local recurrence in the preserved breast. Development of reliable and lower-cost ex vivo cancer detection methods would offer several benefits for patient care. Here, a practical and quantitative evaluation method for the ex vivo fluorescent diagnosis of breast lesions was developed and confirmed through a three-step clinical study. Gamma-glutamyl-hydroxymethyl rhodamine green (gGlu-HMRG) has been reported to generate fluorescence in breast lesions. Using this probe, we constructed a reliable and reproducible procedure for the quantitative evaluation of fluorescence levels. We evaluated the reliability of the method by considering reproducibility, temperature sensitivity, and the effects of other clinicopathological factors. The results suggest that the fluorescence increase of gGlu-HMRG is a good indicator of the malignancy of breast lesions. However, the distributions overlapped. A 5 min reaction with this probe could be used to distinguish at least part of the normal breast tissue. This method did not affect the final pathological examination. In summary, our results indicate that the methods developed in this study may serve as a feasible intraoperative negative-margin assessment tool during breast-conserving surgery.

Activatable Fluorophores for Imaging Immune Cell Function

Optical imaging has become an essential tool to study biomolecular processes in live systems with unprecedented spatial resolution. New fluorescent technologies and advances in optical microscopy have revolutionized the ways in which we can study immune cells in real time. For example, activatable fluorophores that emit signals after target recognition have enabled direct imaging of immune cell function with enhanced readouts and minimal background. In this Account, we summarize recent advances in the chemical synthesis and implementation of activatable fluorescent probes to monitor the activity and the role of immune cells in different pathological processes, from infection to inflammatory diseases or cancer. In addition to the contributions that our group has made to this field, we review the most relevant literature disclosed over the past decade, providing examples of different activatable architectures and their application in diagnostics and drug discovery. This Account covers the imaging of the three major cell types in the immune system, that is, neutrophils, macrophages, and lymphocytes. Attracted by the tunability and target specificity of peptides, many groups have designed strategies based on fluorogenic peptides whose fluorescence emission is regulated by the reaction with enzymes (e.g., MMPs, cathepsins, granzymes), or through Förster resonance energy transfer (FRET) mechanisms. Selective imaging of immune cells has been also achieved by targeting different intracellular metabolic routes, such as lipid biogenesis. Other approaches involve the implementation of diversity-oriented fluorescence libraries or the use of environmentally sensitive fluorescent scaffolds (e.g., molecular rotors). Our group has made important progress by constructing probes to image metastasis-associated macrophages in tumors, apoptotic neutrophils, or cytotoxic natural killer (NK) cells against cancer cells, among other examples. The chemical probes covered in this Account have been successfully validated in vitro in cell culture systems, and in vivo in relevant models of inflammation and cancer. Overall, the range of chemical structures and activation mechanisms reported to sense immune cell function is remarkable. However, the emergence of new strategies based on new molecular targets or activatable mechanisms that are yet to be discovered will open the door to track unexplored roles of immune cells in different biological systems. We anticipate that upcoming generations of activatable probes will find applications in the clinic to help assessing immunotherapies and advance precision medicine. We hope that this Account will evoke new ideas and innovative work in the design of fluorescent probes for imaging cell function.

Fluorescence Imaging Using Enzyme-Activatable Probes for Real-Time Identification of Pancreatic Cancer

Introduction

Radical resection is the only curative treatment for pancreatic cancer, which is a life-threatening disease. However, it is often not easy to accurately identify the extent of the tumor before and during surgery. Here we describe the development of a novel method to detect pancreatic tumors using a tumor-specific enzyme-activatable fluorescence probe.

Methods

Tumor and non-tumor lysate or small specimen collected from the resected specimen were selected to serve as the most appropriate fluorescence probe to distinguish cancer tissues from noncancerous tissues. The selected probe was sprayed onto the cut surface of the resected specimen of cancer tissue to acquire a fluorescence image. Next, we evaluated the ability of the probe to detect the tumor and calculated the tumor-to-background ratio (TBR) by comparing the fluorescence image with the pathological extent of the tumor. Finally, we searched for a tumor-specific enzyme that optimally activates the selected probe.

Results

Using a library comprising 309 unique fluorescence probes, we selected GP-HMRG as the most appropriate activatable fluorescence probe. We obtained eight fluorescence images of resected specimens, among which four approximated the pathological findings of the tumor, which achieved the highest TBR. Finally, dipeptidyl-peptidase IV (DPP-IV) or a DPP-IV-like enzyme was identified as the target enzyme.

Conclusion

This novel method may enable rapid and real-time visualization of pancreatic cancer through the enzymatic activities of cancer tissues.