Rapid intraoperative visualization of breast lesions with γ-glutamyl hydroxymethyl rhodamine green

Ex vivo fluorescence-guided resection margin assessment in breast cancer surgery using a topically applied, cathepsin-activatable imaging agent

Up to 40 % of breast cancer patients have a tumor-positive resection margin (TPRM) - defined as cancer cells at the surface of the resected specimen - after breast-conserving surgery (BCS), necessitating re-resection or boost radiation. To prevent these additional treatments, intraoperative near-infrared (NIR) fluorescence imaging with the topically applied, cathepsin-activatable imaging agent AKRO-6qcICG might be used to detect TPRMs and guide additional resection. Here, to validate its performance, the agent is topically applied to all surfaces of freshly resected breast cancer specimens (n = 11 patients) and to 3-5 mm thick tissue slices of the specimens (n = 26 patients). NIR fluorescence images of the resection surfaces and tissue slices are acquired and correlated to final histopathology. AKRO-6qcICG detects TPRMs with a sensitivity, specificity, PVV, and NPV of 100 %, 67 %, 10 %, and 100 %, respectively. On the tissue slices, the fluorescence signal has a median tumor-to-background ratio of 1.8. These findings indicate that topically applied AKRO-6qcICG can visualize TPRMs ex vivo with a high sensitivity and NPV, with sufficient contrast to adjacent healthy breast tissue.

γ-Glutamyltranspeptidase (GGT) Sensitive Fluorescence Probes for Cancer Diagnosis; Brief Review

Millions of deaths occur each year due to the late diagnosis of abnormal cellular growth within the body. However, the devastating impact of this can be significantly reduced if cancer metastasis is detected early through the use of enzymatic biomarkers. Among several biomarkers, γ-glutamyltranspeptidase (GGT) stands out as a member of the aminopeptidase family. It is primarily found on the surface of cancer cells such as glioma, ovarian, lung, and prostate cancer, without being overexpressed in normal cells or tissues. Recent years have witnessed significant progress in the field of cancer monitoring and imaging. Fluorescence sensing techniques have been employed, utilizing organic small molecular probes with enzyme-specific recognition sites. These probes emit a fluorescent signal upon interacting with GGT, enabling the imaging, identification, and differentiation of normal and cancerous cells, tissues, and organs. This review article presents a concise overview of recent progress in fluorescent probes developed for the selective detection of GGT, focusing on their applications in cancer imaging. It highlights the observed alterations in the fluorescence and absorption spectra of the probes before and after interaction with GGT. Additionally, the study investigates the changes in the probe molecule's structure following enzyme treatment, evaluates the sensor's detection limit, and consolidated imaging studies conducted using confocal fluorescence analysis. This comprehensive survey is expected to contribute to the advancement of sensing techniques for biomarker detection and cancer imaging, providing valuable insights for refining methodologies and inspiring future developments in this field.

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.

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.

Characterization of a fluorescence imaging probe that exploits metabolic dependency of ovarian clear cell carcinoma

The purpose of this study is to clarify the metabolic dependence of ovarian clear cell carcinoma (CCC) by comparing normal tissues and to examine the applicability of fluorescence imaging probe to exploit these metabolic differences. Enhanced glutathione synthesis was supported by the increased uptake of related metabolites and elevated expression levels of genes. Accumulation of intracellular iron and lipid peroxide, induction of cell death by inhibition of the glutathione synthesis pathway indicated that ferroptosis was induced. The activation of γ-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG), a fluorescent imaging probe that recognizes γ-glutamyl transferase, which is essential for the synthesis of glutathione, was investigated in fresh-frozen surgical specimens. gGlu-HMRG detected extremely strong fluorescent signals in the tumor lesions of CCC patients, compared to normal ovaries or endometrium. These results revealed that CCC occurs in the stressful and unique environment of free radical-rich endometrioma, and that glutathione metabolism is enhanced as an adaptation to oxidative stress. Furthermore, a modality that exploits these metabolic differences would be useful for distinguishing between CCC and normal tissues.

Rapid imaging of thymoma and thymic carcinoma with a fluorogenic probe targeting γ-glutamyltranspeptidase

In recent years, thoracoscopic and robotic surgical procedures have increasingly replaced median sternotomy for thymoma and thymic carcinoma. In cases of partial thymectomy, the prognosis is greatly improved by ensuring a sufficient margin from the tumor, and therefore intraoperative fluorescent imaging of the tumor is especially valuable in thoracoscopic and robotic surgery, where tactile information is not available. γ-Glutamyl hydroxymethyl rhodamine green (gGlu-HMRG) has been applied for fluorescence imaging of some types of tumors in the resected tissues, and here we aimed to examine its validity for the imaging of thymoma and thymic carcinoma. 22 patients with thymoma or thymic carcinoma who underwent surgery between February 2013 and January 2021 were included in the study. Ex vivo imaging of specimens was performed, and the sensitivity and specificity of gGlu-HMRG were 77.3% and 100%, respectively. Immunohistochemistry (IHC) staining was performed to confirm expression of gGlu-HMRG's target enzyme, γ-glutamyltranspeptidase (GGT). IHC revealed high GGT expression in thymoma and thymic carcinoma in contrast to absent or low expression in normal thymic parenchyma and fat tissue. These results suggest the utility of gGlu-HMRG as a fluorescence probe for intraoperative visualization of thymomas and thymic carcinomas.

Quantitative Micro-Elastography Enables In Vivo Detection of Residual Cancer in the Surgical Cavity during Breast-Conserving Surgery

Breast-conserving surgery (BCS) is commonly used for the treatment of early-stage breast cancer. Following BCS, approximately 20% to 30% of patients require reexcision because postoperative histopathology identifies cancer in the surgical margins of the excised specimen. Quantitative micro-elastography (QME) is an imaging technique that maps microscale tissue stiffness and has demonstrated a high diagnostic accuracy (96%) in detecting cancer in specimens excised during surgery. However, current QME methods, in common with most proposed intraoperative solutions, cannot image cancer directly in the patient, making their translation to clinical use challenging. In this proof-of-concept study, we aimed to determine whether a handheld QME probe, designed to interrogate the surgical cavity, can detect residual cancer directly in the breast cavity in vivo during BCS. In a first-in-human study, 21 BCS patients were scanned in vivo with the QME probe by five surgeons. For validation, protocols were developed to coregister in vivo QME with postoperative histopathology of the resected tissue to assess the capability of QME to identify residual cancer. In four cavity aspects presenting cancer and 21 cavity aspects presenting benign tissue, QME detected elevated stiffness in all four cancer cases, in contrast to low stiffness observed in 19 of the 21 benign cases. The results indicate that in vivo QME can identify residual cancer by directly imaging the surgical cavity, potentially providing a reliable intraoperative solution that can enable more complete cancer excision during BCS.

SIGNIFICANCE

Optical imaging of microscale tissue stiffness enables the detection of residual breast cancer directly in the surgical cavity during breast-conserving surgery, which could potentially contribute to more complete cancer excision.

Colourful fluorescence-based carbon dots for tumour imaging-guided nanosurgery

Fluorescent-intraoperative navigation is a visual technique that allows surgeons to accurately distinguish malignant and normal tissues during surgery. It has the advantages of immediacy, high resolution, and high specificity. However, a single fluorescent source cannot provide sufficient surgical information. Multicolour carbon dots (CDs) are more suitable since they provide outstanding water solubility, photostability, and multicolour-fluorescence imaging. Here, we prepared an optical probe with CD-based multicolour-fluorescence imaging via a hydrothermal method. CDs can be endocytosed by tumour cells, and after intravenous injection, they can effectively accumulate at the tumour site. In a pancreatic cancer mouse model, we demonstrated the multicolour-fluorescence imaging capabilities of CDs, which aided the accurate resection of tumours under fluorescent-intraoperative navigation. Stereoscopic fluorescence microscopy imaging and H&E staining proved that the removed tissue belonged to the pancreatic tumour. This study emphasizes the potential of CDs for fluorescence-guided intraoperative resection and expands the application of CDs in biological fields.

Fluorescence Imaging Using Enzyme-Activatable Probes for Detecting Diabetic Kidney Disease and Glomerular Diseases

A clear identification of the etiology of glomerular disease is essential in patients with diabetes. Renal biopsy is the gold standard for assessing the underlying nephrotic pathology; however, it has the risk for potential complications. Here, we aimed to investigate the feasibility of urinary fluorescence imaging using an enzyme-activatable probe for differentiating diabetic kidney disease and the other glomerular diseases. Hydroxymethyl rhodamine green (HMRG)-based fluorescent probes targeting gamma-glutamyl transpeptidase (GGT) and dipeptidyl-peptidase (DPP) were used. Urinary fluorescence was compared between groups which were classified by their histopathological diagnoses (diabetic kidney disease, glomerulonephritis, and nephrosclerosis) as obtained by ultrasound-guided renal biopsy. Urinary fluorescence was significantly stronger in patients with diabetic kidney disease compared to those with glomerulonephritis/nephrosclerosis after DPP-HMRG, whereas it was stronger in patients with nephrosclerosis than in patients with glomerulonephritis after GGT-HMRG. Subgroup analyses of the fluorescence performed for patients with diabetes showed consistent results. Urinary fluorescence imaging using enzyme-activatable fluorescence probes thus represents a potential noninvasive assessment technique for kidney diseases in patients with diabetes.

Rapid imaging of lung cancer using a red fluorescent probe to detect dipeptidyl peptidase 4 and puromycin-sensitive aminopeptidase activities

Rapid identification of lung-cancer micro-lesions is becoming increasingly important to improve the outcome of surgery by accurately defining the tumor/normal tissue margins and detecting tiny tumors, especially for patients with low lung function and early-stage cancer. The purpose of this study is to select and validate the best red fluorescent probe for rapid diagnosis of lung cancer by screening a library of 400 red fluorescent probes based on 2-methyl silicon rhodamine (2MeSiR) as the fluorescent scaffold, as well as to identify the target enzymes that activate the selected probe, and to confirm their expression in cancer cells. The selected probe, glutamine-alanine-2-methyl silicon rhodamine (QA-2MeSiR), showed 96.3% sensitivity and 85.2% specificity for visualization of lung cancer in surgically resected specimens within 10 min. In order to further reduce the background fluorescence while retaining the same side-chain structure, we modified QA-2MeSiR to obtain glutamine-alanine-2-methoxy silicon rhodamine (QA-2OMeSiR). This probe rapidly visualized even borderline lesions. Dipeptidyl peptidase 4 and puromycin-sensitive aminopeptidase were identified as enzymes mediating the cleavage and consequent fluorescence activation of QA-2OMeSiR, and it was confirmed that both enzymes are expressed in lung cancer. QA-2OMeSiR is a promising candidate for clinical application.

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.

Development of a fluorescent probe library enabling efficient screening of tumour-imaging probes based on discovery of biomarker enzymatic activities

Fluorescent probes that can selectively detect tumour lesions have great potential for fluorescence imaging-guided surgery. Here, we established a library-based approach for efficient screening of probes for tumour-selective imaging based on discovery of biomarker enzymes. We constructed a combinatorial fluorescent probe library for aminopeptidases and proteases, which is composed of 380 probes with various substrate moieties. Using this probe library, we performed lysate-based in vitro screening and/or direct imaging-based ex vivo screening of freshly resected clinical specimens from lung or gastric cancer patients, and found promising probes for tumour-selective visualization. Further, we identified two target enzymes as novel biomarker enzymes for discriminating between tumour and non-tumour tissues. This library-based approach is expected to be an efficient tool to develop tumour-imaging probes and to discover new biomarker enzyme activities for various tumours and other diseases.

Efficient methodology to develop tumor-imaging fluorescent probes based on screening with our newly constructed probe library for aminopeptidase/protease (380 probes) and clinical samples has been established.

Rapid Visualization of Deeply Located Tumors In Vivo by Intravenous Administration of a γ-Glutamyltranspeptidase-Activated Fluorescent Probe

We previously showed that spraying the fluorescent probe gGlu-HMRG (γ-glutamyl hydroxymethyl rhodamine green) can visualize even tiny tumors on the mesentery and peritoneal wall of tumor-bearing mice. However, during surgery, repeated spraying is necessary to detect tumors located deep within organs. Here, we examine whether deeply located tumors can be stained by intravenous administration of this probe. In mice bearing subcutaneous tumors, intravenous administration of gGlu-HMRG resulted in a rapid and specific increase of fluorescence in the tumor, which was visible to the naked eye within 5 min, and the maximum fluorescence intensity ratio of tumor to normal tissue (T/N = 4.3) was reached at 30 min. In mice bearing lung tumors, the T/N ratio reached approximately 20 at 30 min after administration, and deeply located tumors were clearly visualized. These results suggest that intravenous administration of gGlu-HMRG may be a useful technique in fluorescence-guided surgery of tumors.

Rapid visualization of mammary gland tumor lesions of dogs using the enzyme-activated fluorogenic probe; γ-glutamyl hydroxymethyl rhodamine green

Since gamma-glutamyl transpeptidase (GGT) is highly and locally expressed in human breast cancer, a GGT-enzymatically activatable fluorescent probe, gamma-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG), has been developed to detect the human breast cancer area with high performance. In this study, GGT expression and the efficacy of gGlu-HMRG on visualization were investigated in canine mammary gland tumors (MGT). Seventeen non-fixed fresh-frozen MGT specimens and each peritumoral control tissue were utilized. The GGT mRNA levels were highly observed in the tumor specimens compared with the control. GGT immunostaining was mostly observed on the cell membrane and cytosol of the alveolar and duct mammary epithelium of MGT tissues. These signals were strongly positive in several cases while they were mild to not observed in other cases. When gGlu-HMRG solution was dropped to the non-fixed tissue pieces of MGT or control tissues, the fluorescence intensities (FIs) were measured using Maestro in-vivo imaging device. FIs in MGT tissues were significantly higher than each control tissue 20 min after treatment. Based on Youden index method said that the maximum sensitivity and specificity of FI was 82.4% and 82.4%. These findings suggest that GGT is highly expressed in several MGTs in dogs and gGlu-HMRG could visualize at least a part of MGT tissues in dogs. Nevertheless, it should be needed to assess the false-negative areas more carefully in canine than human cases.

Development of intraoperative assessment of margins in breast conserving surgery: a narrative review

OBJECTIVE

We intend to provide an informative and up-to-date summary on the topic of intraoperative assessment of margins in breast conserving surgery (BCS). Conventional methods as well as cutting-edge technologies are analyzed for their advantages and limitations in the hope that clinicians can turn to this for reference. This review can also offer guidance for technicians in the future design of intraoperative margin assessment tools.

BACKGROUND

Achieving negative margins during BCS is one of the vital factors for preventing local recurrence. Conducting intraoperative margin assessment can ensure negative margins to a large extent and possibly relieve patients of the anguish of re-interventions. In recent years, innovative methods for margin assessment during BCS are advancing rapidly. And there is a lack of summary regarding the development of intraoperative margin assessment in BCS.

METHODS

A PubMed search with keywords "intraoperative margin assessment" and "breast conserving surgery" was conducted. Relevant publications were screened manually for its title, abstract and even full text to determine its true relevance. Publications on neo-adjuvant therapy and intraoperative radiotherapy were excluded. References from the searched articles and other supplementary articles were also looked into.

CONCLUSIONS

Conventional methods for margin assessment yields stable outcome but its use is limited because of the demand on pathology staff and the trade-off between time and precision. Conventional imaging techniques pass the workload to radiologists at the cost of a significantly low duration of time. Involving artificial intelligence for image-based assessment is a further improvement. However, conventional imaging is inherently flawed in that occult lesions can't show on the image and the showing ones are ambiguous and open to interpretation. Unconventional techniques which base their judgment on cellular composition are more reassuring. Nonetheless, unconventional techniques should be subjected to clinical trials before putting into practice. And studies regarding comparison between conventional methods and unconventional methods are also needed to evaluate their relative efficacy.

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.

Clinical usefulness of a novel fluorescence technique for the intraoperative diagnosis of surgical margins in patients with breast cancer

In both 5- and 15-min data, FI was significantly higher in malignant tissues than in benign tissues. The diagnostic accuracy was similar at 5 and 15 min. Therefore, the 5-min FI was enough applying in the further analyses.

Biofunctional chemistry and reactivity of biogenic acrolein for cancer diagnosis and therapy

Acrolein holds excellent potential as a biomarker in various oxidative stress-related diseases, including cancer, Alzheimer's, Parkinson's, and inflammatory disorders. Consequently, a direct method to target and visualize acrolein in biological systems might be essential to provide tools for diagnosis and therapeutic purposes. Previously, we discovered 1,3-dipolar cycloaddition between aryl azides and acrolein, which proceeds without a catalyst to give α-diazocarbonyl derivatives. The reaction proceeds with high reactivity and selectivity even under physiological conditions. We have successfully utilized the reaction as a robust method for detecting acrolein generated by cancer cells. This review discusses the utilization of the endogenous acrolein reaction with aryl azide to (1) distinguish breast cancer from normal tissue during breast-conserving surgery and (2) treat cancer through selective prodrug activation in a mouse model without causing adverse effects. The methods have potential clinical application for breast-conserving surgery and are highly advantageous for cancer therapy.

Rapid fluorescence imaging of human hepatocellular carcinoma using the β-galactosidase-activatable fluorescence probe SPiDER-βGal

Fluorescence imaging of tumours facilitates rapid intraoperative diagnosis. Thus far, a promising activatable fluorescence probe for hepatocellular carcinoma (HCC) has not been developed. Herein, the utility of the fluorescence imaging of HCC using a β-galactosidase (β-Gal)-activatable fluorescence probe SPiDER-βGal was examined. β-Gal activity was measured in cryopreserved tissues from 68 patients. Live cell imaging of HCC cell lines and imaging of tumour-bearing model mice were performed using SPiDER-βGal. Furthermore, fluorescence imaging was performed in 27 freshly resected human HCC specimens. In cryopreserved samples, β-Gal activity was significantly higher in tumour tissues than in non-tumour tissues. Fluorescence was observed in HCC cell lines. In mouse models, tumours displayed stronger fluorescence than normal liver tissue. In freshly resected specimens, fluorescence intensity in the tumour was significantly higher than that in non-tumour liver specimens as early as 2 min after spraying. Receiver operating characteristic curves were generated to determine the diagnostic value of SPiDER-βGal 10 min after its spraying; an area under the curve of 0.864, sensitivity of 85.2%, and specificity of 74.1% were observed for SPiDER-βGal. SPiDER-βGal is useful for the rapid fluorescence imaging of HCC. Fluorescence imaging guided by SPiDER-βGal would help surgeons detect tumours rapidly and achieve complete liver resection.

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.

Matrix metalloprotease-14 is a target enzyme for detecting peritoneal metastasis in gastric cancer

BACKGROUND

Accurate diagnosis of peritoneal metastasis in gastric cancer (GC) is important to determine the appropriate treatment. This study aimed to examine whether matrix metalloprotease-14 (MMP-14) was a candidate enzyme in fluorescence imaging for the diagnosis of peritoneal metastasis in GC.

METHODS

GC and normal peritoneal (NP) tissues from 96 and 20 patients, respectively were evaluated for MMP-14 expression. Live cell imaging of GC cell lines (NUGC4, MKN45, MKN74, HGC-27, and Kato-III) was performed using the MMP-14-activatable fluorescence probe; BODIPY-MMP. Furthermore, the overall survival (OS) was calculated in all patients (n = 96).

RESULTS

MMP-14 expression was significantly higher in GC tissues (median: 3.57 ng/mg protein; range:0.64-24.4 ng/mg protein) than in NP tissues (median: 1.34 ng/mg protein; median: 0.53-3.09 ng/mg protein) (P < 0.01). Receiver operating characteristic curves showed that the area under the curve, sensitivity, and specificity were 0.907, 84.4%, and 90.0%, respectively. In live cell imaging using the BODIPY-MMP, fluorescence was observed in five GC cell lines. In the analysis of OS, the high expression of the MMP-14 group had a significantly poorer OS rate than the low expression of the MMP-14 group (P = 0.02). In the multivariate analyses, MMP-14 expression was an independent risk factor for OS (hazard ratio: 2.33; 95 % confidence interval: 1.05-5.45; P = 0.04).

CONCLUSION

MMP-14 is a promising enzyme in intraoperative fluorescence imaging for peritoneal metastasis in GC, especially in patients with poor prognosis.

A versatile toolbox for investigating biological processes based on quinone methide chemistry: From self-immolative linkers to self-immobilizing agents

Quinone methide (QM) species have been included in the design of various functional molecules. In this review, we present a comprehensive overview of bioanalytical tools based on QM chemistry. In the first part, we focus on self-immolative linkers that have been incorporated into functional molecules such as prodrugs and fluorescent probes. In the latter half, we outline how the highly electrophilic property of QMs, enabling them to react rapidly with neighboring nucleophiles, has been applied to develop inhibitors or labeling probes for enzymes, as well as self-immobilizing fluorogenic probes with high spatial resolution. This review systematically summarizes the versatile QM toolbox available for investigating biological processes.

A Novel Topical Fluorescent Probe for Detection of Glioblastoma

PURPOSE

Five-aminolevulinic acid (5-ALA) is widely used as an intraoperative fluorescent probe for radical resection of high-grade glioma, and thus aids in extending progression-free survival of patients. However, there exist some cases where 5-ALA fails to fluoresce. In some other cases, it may undergo fluorescence quenching but cannot be orally readministered during surgery. This study aimed to develop a novel hydroxymethyl rhodamine green (HMRG)-based fluorescence labeling system that can be repeatedly administered as a topical spray during surgery for the detection of glioblastoma.

EXPERIMENTAL DESIGN

We performed a three-stage probe screening using tumor lysates and fresh tumor tissues with our probe library consisting of a variety of HMRG probes with different dipeptides. We then performed proteome and transcript expression analyses to detect candidate enzymes responsible for cleaving the probe. Moreover, in vitro and ex vivo studies using U87 glioblastoma cell line were conducted to validate the findings.

RESULTS

The probe screening identified proline-arginine-HMRG (PR-HMRG) as the optimal probe that distinguished tumors from peritumoral tissues. Proteome analysis identified calpain-1 (CAPN1) to be responsible for cleaving the probe. CAPN1 was highly expressed in tumor tissues which reacted to the PR-HMRG probe. Knockdown of this enzyme suppressed fluorescence intensity in U87 glioblastoma cells. In situ assay using a mouse U87 xenograft model demonstrated marked contrast of fluorescence with the probe between the tumor and peritumoral tissues.

CONCLUSIONS

The novel fluorescent probe PR-HMRG is effective in detecting glioblastoma when applied topically. Further investigations are warranted to assess the efficacy and safety of its clinical use.

β-Galactosidase is a target enzyme for detecting peritoneal metastasis of gastric cancer

Diagnosis of peritoneal metastasis in gastric cancer (GC) is essential for determining appropriate therapeutic strategies and avoiding non-essential laparotomy or gastrectomy. Recently, a variety of activatable fluorescence probes that can detect enzyme activities have been developed for cancer imaging. The aim of this study was to identify the key enzyme involved in peritoneal metastasis in GC. The enzymatic activity of gamma-glutamyl transpeptidase, dipeptidyl peptidase IV, and β-galactosidase (β-Gal) was assessed in lysates prepared from preserved human GC (n = 89) and normal peritoneal (NP; n = 20) samples. β-Gal activity was significantly higher in the human GC samples than in NP samples, whereas no differences were observed in the activities of the other enzymes. Therefore, we used SPiDER-βGal, a fluorescent probe that can be activated by β-Gal, for imaging GC cell lines, peritoneal metastasis in a mouse model, and fresh human resected GC samples (n = 13). All cell lines showed fluorescence after applying SPiDER-βGal, and metastatic nodules in the mice gradually developed high fluorescence that could be visualized with SPiDER-βGal. The human GC samples showed significantly higher fluorescence than NP samples. β-Gal is a useful target enzyme for fluorescence imaging of peritoneal metastasis in GC.

Application of Acrolein Imines to Organic Synthesis, Biofunctional Studies, and Clinical Practice

N-alkyl unsaturated imines derived from acrolein, a toxin produced during oxidative stress, and biogenic alkyl amines occur naturally and are considered biologically relevant compounds. However, despite the recent conceptual and technological advances in organic synthesis, research on the new reactivity of these compounds is lacking. This personal account discusses research on the reactivity that has been overlooked in acrolein imines, including the discovery of new methods to synthesize biologically active compounds, the determination of new functions of relevant imines and their precursors, i. e., aldehydes and amines, and the application of these methods for clinical diagnosis.

Rapid and Sensitive Detection of Cancer Cells with Activatable Fluorescent Probes for Enzyme Activity

Fluorescence (FL)-guided detection of cancer is one of the most promising approaches to achieve intraoperative assessment of surgical margins. Enzymes, such as aminopeptidase, carboxypeptidase, and glycosidase, whose activities are increased in cancer, have attracted great interest as imaging targets for rapid and sensitive visualization of cancerous tissues with fluorescent probes. Activatable probes, which are initially nonfluorescent but become strongly fluorescent upon rapid one-step cleavage of their substrate moiety by the target enzyme, are especially promising for practical clinical application during surgical or endoscopic procedures due to the highly amplified FL change generated by enzyme-catalyzed turnover at lesion sites. Here, we describe robust protocols for using activatable fluorescent probes targeting cancer-associated enzyme activities to visualize cultured cancer cells, metastatic cancer in a mouse model, and cancerous lesions in surgical specimens from patients.

Rapid and Accurate Visualization of Breast Tumors with a Fluorescent Probe Targeting α-Mannosidase 2C1

Accurate detection of breast tumors and discrimination of tumor from normal tissues during breast-conserving surgery are essential to reduce the risk of misdiagnosis or recurrence. However, existing probes show substantial background signals in normal breast tissues. In this study, we focus on glycosidase activities in breast tumors. We synthesized a series of 12 fluorescent probes and performed imaging-based evaluation on surgically resected human breast specimens. Among them, the α-mannosidase-reactive fluorescent probe HMRef-αMan detected breast cancer with 90% sensitivity and 100% specificity. We identified α-mannosidase 2C1 as the target enzyme and confirmed its overexpression in various breast tumors. We found that fibroadenoma, the most common benign breast lesion in young woman, tends to have higher α-mannosidase 2C1 activity than malignant cancer. Combined application of green-emitting HMRef-αMan and a red-emitting γ-glutamyltranspeptidase probe enabled efficient dual-color, dual-target optical discrimination of malignant and benign tumors.

γ-Glutamyltranspeptidase (GGT)-Activatable Fluorescence Probe for Durable Tumor Imaging

γ-Glutamyltranspeptidase (GGT) is overexpressed in several types of cancer. Existing GGT-targeting fluorescence probes can image these cancers, but the fluorescent hydrolysis product leaks from the target cancer cells during prolonged incubation or fixation. Here, we present a functionalized fluorescence probe for GGT, 4-CH₂ F-HMDiEtR-gGlu, which is designed to generate an azaquinone methide intermediate during activation by GGT; this intermediate reacts with intracellular nucleophiles to generate a fluorescent adduct that is trapped inside the cells, without loss of the target enzyme activity. Application of the probe to patient-derived xenograft (PDX) mice enabled in vivo cancer imaging for a prolonged period and was also compatible with fixation and immunostaining of the cancer tissue.

Use of autofluorescence and fluorescent probes as a potential diagnostic tool for oral cancer: A systematic review

INTRODUCTION

The prognosis of patients with Oral squamous cell carcinoma (OSCC) are directly related to the stage of development of the tumor at the time of diagnosis, but it is estimated an average delay in diagnosis of 2-5 months. New non-invasive techniques for the early diagnosis of OSCC are being developed, such as methodologies to detect spectral changes of tumor cells. We conducted a systematic review to analyze the potential use of autofluorescence and/or fluorescent probes for OSCC diagnosis.

MATERIAL AND METHODS

Four databases (PubMed, Scopus, Embase and Web of Science) were used as research sources. Protocol was registered with PROSPERO. It was included studies that evaluated tissue autofluorescence and/or used fluorescent probes as a method of diagnosing and/or treatment of oral cancer in humans.

RESULTS

Forty-five studies were selected for this systematic review, of which 28 dealt only with autofluorescence, 18 on fluorescent probes and 1 evaluated both methods. The VELscope® was the most used device for autofluorescence, exhibiting sensitivity (33%-100%) and specificity (12%-88.6%). 5-Aminolevulinic acid (5-ALA) was the most used fluorescent probe, exhibiting high sensitivity (90%-100%) and specificity (51.3%-96%). Hypericin, rhodamine 6 G, rhodamine 610, porphyrin and γ-glutamyl hydroxymethyl rhodamine green have also been reported.

CONCLUSION

Thus, the autofluorescence and fluorescent probes can provide an accurate diagnosis of oral cancer, assisting the dentist during daily clinical activity, but it is not yet possible to suggest that this method may replace histopathological examination.

Accuracy of gross intraoperative margin assessment for breast cancer: experience since the SSO-ASTRO margin consensus guidelines

Gross intraoperative assessment can be used to ensure negative margins at the time of surgery. Previous studies of this technique were conducted before the introduction of consensus guidelines defining a “positive” margin. We performed a retrospective study examining the accuracy of this technique since these guidelines were published. We identified all specimens that were grossly examined at the time of breast conserving surgery from January 2014 to July 2020. Gross and final microscopic diagnoses were compared and the performance of intraoperative examination was assessed in terms of false positive and false negative rates. Logistic regression models were used to examine the effect of clinicopathologic covariates on discordance. 327 cases were reviewed. Gross exam prompted re-excision in 166 cases (61%). The rate of false negative discordance was 8.6%. In multivariate analysis, multifocality on final pathology was associated with discordance. We consider the false negative rate acceptable for routine clinical use; however, there is an ongoing need for more accurate methods for the intraoperative assessment of margins.

Molecular design strategy of fluorogenic probes based on quantum chemical prediction of intramolecular spirocyclization

Fluorogenic probes are essential tools for real-time visualization of dynamic intracellular processes in living cells, but so far, their design has been largely dependent on trial-and-error methods. Here we propose a quantum chemical calculation-based method for rational prediction of the fluorescence properties of hydroxymethyl rhodamine (HMR)-based fluorogenic probes. Our computational analysis of the intramolecular spirocyclization reaction, which switches the fluorescence properties of HMR derivatives, reveals that consideration of the explicit water molecules is essential for accurate estimation of the free energy difference between the open (fluorescent) and closed (non-fluorescent) forms. We show that this approach can predict the open-closed equilibrium (pK_cycl values) of unknown HMR derivatives in aqueous media. We validate this pK_cycl prediction methodology by designing red and yellow fluorogenic peptidase probes that are highly activated by γ-glutamyltranspeptidase, without the need for prior synthesis of multiple candidates.

ɤ-glutamyl hydroxymethyl rhodamine green fluorescence as a prognostic indicator for lung cancer

OBJECTIVE

ɤ-glutamyltranspeptidase is an enzyme expressed in various malignancies including lung cancer. It rapidly activates non-fluorescent ɤ-glutamyl hydroxymethyl rhodamine green to highly fluorescent hydroxymethyl rhodamine green. The resultant tumor fluorescence is therefore an indicator of cellular ɤ-glutamyltranspeptidase activity. We have explored the use of ɤ-glutamyl hydroxymethyl rhodamine green as an intraoperative imaging tool for visualizing cancers. Herein, we evaluated the potential of the tumor fluorescence as a postoperative prognostic indicator.

METHODS

We included patients with non-small cell lung cancer who had undergone radical resection from 2012 to 2014 in the study. We assessed the fluorescence intensity of the resected tumor and normal lung tissue by ex vivo imaging using ɤ-glutamyl hydroxymethyl rhodamine green.

RESULTS

Sixty-seven patients were eligible for the study (adenocarcinomas, n = 44; squamous cell carcinoma, n = 14; other histologies, n = 8). The pathological stages were I, II, III, and IV in 39, 15, 12, and 1 patient, respectively. Based on the fluorescence of the tumor tissue, the patients were divided into high fluorescence (n = 33) and low fluorescence (n = 34) groups. The 5-year overall survival rate was significantly higher in the high fluorescence group (72.7%) compared to the low fluorescence group (47.1%, P = 0.025). Similarly, pathological stage I patients of the high fluorescence group had higher 5-year overall survival (85.7% vs. 44.4%, P = 0.009) and recurrence-free survival (76.2% vs. 44.4% P = 0.044) rates compared to those of the low fluorescence group.

CONCLUSIONS

ɤ-glutamyl hydroxymethyl rhodamine green fluorescence is a good postoperative prognostic indicator in patients with non-small cell lung cancer.

Emerging Technologies for Real-Time Intraoperative Margin Assessment in Future Breast-Conserving Surgery

Clean surgical margins in breast-conserving surgery (BCS) are essential for preventing recurrence. Intraoperative pathologic diagnostic methods, such as frozen section analysis and imprint cytology, have been recognized as crucial tools in BCS. However, the complexity and time-consuming nature of these pathologic procedures still inhibit their broader applicability worldwide. To address this situation, two issues should be considered: 1) the development of nonpathologic intraoperative diagnosis methods that have better sensitivity, specificity, speed, and cost; and 2) the promotion of new imaging algorithms to standardize data for analyzing positive margins, as represented by artificial intelligence (AI), without the need for judgment by well-trained pathologists. Researchers have attempted to develop new methods or techniques; several have recently emerged for real-time intraoperative management of breast margins in live tissues. These methods include conventional imaging, spectroscopy, tomography, magnetic resonance imaging, microscopy, fluorescent probes, and multimodal imaging techniques. This work summarizes the traditional pathologic and newly developed techniques and discusses the advantages and disadvantages of each method. Taking into consideration the recent advances in analyzing pathologic data from breast cancer tissue with AI, the combined use of new technologies with AI algorithms is proposed, and future directions for real-time intraoperative margin assessment in BCS are discussed.

Fluorescein- and EGFR-Antibody Conjugated Silica Nanoparticles for Enhancement of Real-time Tumor Border Definition Using Confocal Laser Endomicroscopy in Squamous Cell Carcinoma of the Head and Neck

Intraoperative definition of tumor free resection margins in head and neck cancer is challenging. In the current proof-of-principle study we evaluated a novel silica nanoparticle-based agent for its potential use as contrast enhancer. We synthesized silica nanoparticles with an average size of 45 nm and modified these particles with the fluorescence stain fluorescein isocyanate (FITC) for particle detection and with epidermal growth factor receptor (EGFR)-targeting antibodies for enhanced tumor specificity. The nanoparticles exhibited good biocompatibility and could be detected in vitro and in vivo by confocal laser scanning microscopy. Additionally, we show in an ex vivo setting that these modified nanoparticles specifically bind to tumor samples and could be detected using a handheld confocal fluorescence endomicroscope. From a clinical point of view, we believe that this method could be used for tumor border contrast enhancement and for better intraoperative definition of R-0 tumor resection.

A novel method for rapid detection of a Helicobacter pylori infection using a γ-glutamyltranspeptidase-activatable fluorescent probe

A γ-glutamyl hydroxymethyl rhodamine green probe (gGlu-HMRG) reacts with γ-glutamyltranspeptidase (GGT) and immediately produces fluorescence, is clinically applied for real-time cancers' visualization. Since Helicobacter pylori produces GGT, this study aimed to investigate whether gGlu-HMRG can be used to detect H. pylori infections. A wild-type H. pylori strain and the ggt gene-disrupted mutant were cultured and treated with gGlu-HMRG. This fluorescent probe assay was used to quantify GGT activity of H. pylori ex vivo using gastric biopsy specimens. The H. pylori diagnostic capabilities of the assay were determined from altered fluorescence intensity (FI) values at 5 min (FIV-5) and 15 minutes (FIV-15). Distinct fluorescence was identified in wild H. pylori strain, using gGlu-HMRG, whereas no fluorescence was observed in ggt gene-disrupted mutant strain. On ex vivo imaging of gGlu-HMRG, fluorescence intensity increased markedly with time in H. pylori-positive specimens; however, the H. pylori-negative specimens displayed a slight increase in FI. FIV-5 and FIV-15 differed significantly between H. pylori-positive and -negative specimens. FIV-15 differed significantly between H. pylori-positive and -eradicated group. This assay sensitivity and specificity were 75.0% and 83.3% in the antrum and 82.6% and 89.5% in the stomach body. GGT-activatable fluorescence probe is applicable for rapid diagnosis of H. pylori.

Emerging Fluorescent Molecular Tracers to Guide Intra-Operative Surgical Decision-Making

Fluorescence imaging is an emerging technology that can provide real-time information about the operating field during cancer surgery. Non-specific fluorescent agents, used for the assessment of blood flow and sentinel lymph node detection, have so far dominated this field. However, over the last decade, several clinical studies have demonstrated the great potential of targeted fluorescent tracers to visualize tumor lesions in a more specific way. This has led to an exponential growth in the development of novel molecular fluorescent contrast agents. In this review, the design of fluorescent molecular tracers will be discussed, with particular attention for agents and approaches that are of interest for clinical translation.

Red-emitting FIT-PNAs: "On site" detection of RNA biomarkers in fresh human cancer tissues

To date, there are limited approaches for the direct and rapid visualization (on site) of tumor tissues for pathological assessment and for aiding cytoreductive surgery. Herein, we have designed FIT-PNAs (forced-intercalation-peptide nucleic acids) to detect two RNA cancer biomarkers. Firstly, a lncRNA (long noncoding RNA) termed CCAT1, has been shown as an oncogenic lncRNA over-expressed in a variety of cancers. The latter, an mRNA termed KRT20, has been shown to be over-expressed in metastases originating from colorectal cancer (CRC). To these FIT-PNAs, we have introduced the bis-quinoline (BisQ) cyanine dye that emits light in the red region (605-610 nm) of the visible spectrum. Most strikingly, spraying fresh human tissue taken from patients during cytoreductive surgery for peritoneal metastasis of colon cancer with an aqueous solution of CCAT1 FIT-PNA results in bright fluorescence in a matter of minutes. In fresh healthy tissue (from bariatric surgeries), no appreciable fluorescence is detected. In addition, a non-targeted FIT-PNA shows no fluorescent signal after spraying this FIT-PNA on fresh tumor tissue emphasizing the specificity of these molecular sensors. This study is the first to show on-site direct and immediate visualization of an RNA cancer biomarker on fresh human cancer tissues by topical application (spraying) of a molecular sensor.

Red Fluorescence Probe Targeted to Dipeptidylpeptidase-IV for Highly Sensitive Detection of Esophageal Cancer

We have developed an activatable red fluorescence probe for dipeptidylpeptidase-IV (DPP-IV) by precisely controlling the photoinduced electron transfer (PeT) process of a red fluorescent scaffold, SiR600. The developed probe exhibited an extremely low background signal and showed significant fluorescence activation upon reaction with DPP-IV, enabling sensitive detection of esophageal cancer in clinical specimens from cancer patients.

Detection of Sentinel Lymph Nodes with Near-Infrared Imaging in Malignancies

Optical molecular imaging, a highly sensitive and noninvasive technique which is simple to operate, inexpensive, and has the real-time capability, is increasingly being used in the diagnosis and treatment of carcinomas. The near-infrared fluorescence dye indocyanine green (ICG) is widely used in optical imaging for the dynamic detection of sentinel lymph nodes (SLNs) in real time improving the detection rate and accuracy. ICG has the advantages of low scattering in tissue absorbance, low auto-fluorescence, and high signal-to-background ratio. The detection rate of axillary sentinel lymph nodes biopsy (SLNB) in breast cancers with ICG was more than 95 %, the false-negative rate was lower than 10 %, and the average detected number ranged from 1.75 to 3.8. The combined use of ICG with nuclein or blue dye resulted in a lower false-negative rate. ICG is also being used for the sentinel node detection in other malignant cancers such as head and neck, gastrointestinal, and gynecological carcinomas. In this article, we provide an overview of numerous studies that used the near-infrared fluorescence imaging to detect the sentinel lymph nodes in breast carcinoma and other malignant cancers. It is expected that with improvements in the optical imaging systems together with the use of a combination of multiple dyes and verification in large clinical trials, optical molecular imaging will become an essential tool for SLN detection and image-guided precise resection.

Cascade Reaction in Human Live Tissue Allows Clinically Applicable Diagnosis of Breast Cancer Morphology

Clean operating margins in breast cancer surgery are important for preventing recurrence. However, the current methods for determining margins such as intraoperative frozen section analysis or imprint cytology are not satisfactory since they are time-consuming and cause a burden on the patient and on hospitals with a limited accuracy. A "click-to-sense" probe is developed based on the detection of acrolein, which is a substance released by oxidatively stressed cancer cells and can be visualized under fluorescence microscopy. Using live breast tissues resected from breast cancer patients, it is demonstrated that this method can quickly, selectively, and sensitively differentiate cancer lesion from normal breast gland or benign proliferative lesions. Since acrolein is accumulated in all types of cancers, this method could be used to quickly assess the surgical margins in other types of cancer.

Rapid detection of metastatic lymph nodes of colorectal cancer with a gamma-glutamyl transpeptidase-activatable fluorescence probe

Rapid diagnosis of metastatic lymph nodes (mLNs) of colorectal cancer (CRC) is desirable either intraoperatively or in resected fresh specimens. We have developed a series of activatable fluorescence probes for peptidase activities that are specifically upregulated in various tumors. We aimed to discover a target enzyme for detecting mLNs of CRC. Among our probes, we found that gGlu-HMRG, a gamma-glutamyl transpeptidase (GGT)-activatable fluorescence probe, could detect mLNs. This was unexpected, because we have previously reported that gGlu-HMRG could not detect primary CRC. We confirmed that the GGT activity of mLNs was high, whereas that of non-metastatic lymph nodes and CRC cell lines was low. We investigated the reason why GGT activity was upregulated in mLNs, and found that GGT was induced under conditions of hypoxia or low nutritional status. We utilized this feature to achieve rapid detection of mLNs with gGlu-HMRG. GGT appears to be a promising candidate enzyme for fluorescence imaging of mLNs.

Rapid detection of papillary thyroid carcinoma by fluorescence imaging using a γ-glutamyltranspeptidase-specific probe: a pilot study

Background

Nodular lesions of the thyroid gland, including papillary thyroid carcinoma (PTC), may be difficult to diagnose by imaging, such as in ultrasonic echo testing, or by needle biopsy. Definitive diagnosis is made by pathological examination but takes several days. A more rapid and simple method to clarify whether thyroid nodular lesions are benign or malignant is needed. Fluorescence imaging with γ-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG) uses γ-glutamyltranspeptidase (GGT), a cell-surface enzyme, to hydrolyze the γ-glutamyl peptide and transfer the γ-glutamyl group. GGT is overexpressed in several cancers, such as breast, lung, and liver cancers. This imaging method is rapid and useful for detecting such cancers. In this study, we tried to develop a rapid fluorescence detection method for clinical samples of thyroid cancer, especially papillary carcinoma.

Methods

Fluorescence imaging with gGlu-HMRG was performed to detect PTC using 23 surgically resected clinical samples. A portable imaging device conveniently captured white-light images and fluorescence images with blue excitation light. Hematoxylin-eosin (HE) staining was used to evaluate which fluorescent regions coincided with cancer, and immunohistochemical examination was used to detect GGT expression.

Results

All 16 PTC samples exhibited fluorescence after topical application of gGlu-HMRG, whereas the normal sections of each sample showed no fluorescence. HE staining revealed that each fluorescent region corresponded to a region with carcinoma. The PTC samples also exhibited GGT expression, as confirmed by immunohistochemistry.

Conclusions

All PTC samples were detected by fluorescence imaging with gGlu-HMRG. Thus, fluorescence imaging with gGlu-HMRG is a rapid, simple, and powerful detection tool for PTC.

Pitfalls on sample preparation for ex vivo imaging of resected cancer tissue using enzyme-activatable fluorescent probes

In vivo and ex vivo fluorescence imaging-assisted surgery can aid in determining the margins of tumors during surgical resection. While a variety of fluorescent probes have been proposed for this task, small molecule enzyme-activatable fluorescent probes are ideal for this application. They are quickly activated at tumor sites and result in bright signal with little background, resulting in high sensitivity. Testing in resected specimens, however, can be difficult. Enzymes are usually stable after freezing and thawing but catalytic reactions are generally temperature-dependent. Therefore, tissue sample temperature should be carefully considered. In this study two enzyme activatable probes, γ-glutamylhydroxymethyl rhodamine green (gGlu-HMRG) that reacted with γ-glutamyltransferase and SPiDER-βGal that reacted with β-galactosidase, were employed to determine the effects of temperature on fluorescence signal kinetics in both fresh and frozen and then thawed ex vivo experimental ovarian cancer tissue samples. The results suggest γ-glutamyltransferase was less sensitive to temperature than β-galactosidase. Fresh samples showed higher fluorescence signals of gGlu-HMRG compared with thawed samples likely because the freeze-thaw cycle decreased the rate of internalization of the activated probe into the lysosome. In contrast, no significant difference of SPiDER-βGal fluorescence signal was observed between fresh and frozen tissues. In conclusion, although imaging of fresh samples at 37°C is the best condition for both probes, successful imaging with gGlu-HMRG could be achieved even at room temperature with thawed samples. We demonstrate that temperature regulation and tissue handling of resected tissue are two pitfalls that may influence ex vivo imaging signals with enzyme-activatable fluorescent probes.

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.

In Vivo Molecular Imaging for Biomedical Analysis and Therapies

In vivo molecular imaging is a powerful tool to analyze the human body. Precision medicine is receiving high attention these days, and molecular imaging plays an important role as companion diagnostics in precision medicine. Nuclear imaging with PET or SPECT and optical imaging technologies are used for in vivo molecular imaging. Nuclear imaging is superior for quantitative imaging, and whole-body analysis is possible even for humans. Optical imaging is superior due to its ease of use, and highly targeted specific imaging is possible with activatable agents. However, with optical imaging using fluorescence, it is difficult to obtain a signal from deep tissue and quantitation is difficult due to the attenuation and scattering of the fluorescent signal. Recently, to overcome these issues, optoacoustic imaging has been used in in vivo imaging. In this article, we review in vivo molecular imaging with nuclear and optical imaging and discuss their utility for precision medicine.

A topically-sprayable, activatable fluorescent and retaining probe, SPiDER-βGal for detecting cancer: Advantages of anchoring to cellular proteins after activation

SPiDER-βGal is a newly-developed probe that is activated by β-galactosidase and is then retained within cells by anchoring to intracellular proteins. Previous work has focused on gGlu-HMRG, a probe activated by γ-glutamyltranspeptidase, which demonstrated high sensitivity for the detection of peritoneal ovarian cancer metastases in an animal model. However, its fluorescence, after activation by γ-glutamyltranspeptidase, rapidly declines over time, limiting the actual imaging window and the ability to define the border of lesions. The purpose of this study is to compare the fluorescence signal kinetics of SPiDER-βGal with that of gGlu-HMRG using ovarian cancer cell lines in vitro and ex vivo tissue imaging. In vitro removal of gGlu-HMRG resulted in a rapid decrease of fluorescence intensity followed by a more gradual decrease up to 60 min while there was a gradual increase in fluorescence up to 60 min after removal of SPiDER-βGal. This is most likely due to internalization and retention of the dye within cells. This was also confirmed ex vivo tissue imaging using a red fluorescence protein (RFP)-labeled tumor model in which the intensity of fluorescence increased gradually after activation of SPiDER-βGal. Additionally, SPiDER-βGal resulted in intense enhancement within the tumor due to the high target-to-background ratio, which extended up to 60 min after activation. In contrast, gGlu-HMRG fluorescence resulted in decreasing fluorescence over time in extracted tumors. Thus, SPiDER-βGal has the advantages of higher signal with more signal retention, resulting in improved contrast of the tumor margin and suggesting it may be an alternative to existing activatable probes.