A Protease-Activated Fluorescent Probe Allows Rapid Visualization of Keratinocyte Carcinoma during Excision

Acidic tumor microenvironment-activatable fluorescent diagnostic probe for the rapid identification and resection of human tumors via spraying

A fluorescent diagnostic probe for real-time intraoperative image-guided tumor resection can significantly improve the efficiency and quality of oncological therapy, but their development is challenging. Herein, a novel fluorescent diagnostic probe called HLTC based on β-carboline was designed and synthesized. HLTC was found to show a ∼10-fold enhancement of fluorescence quantum field with pH from 7.4 to 4.0, indicating its imaging potential in acid environment which is a typical hallmark of the tumor microenvironment (TME). Following fluorescence microscopy imaging showed HLTC could emit specific signals in cancer cells and sections, by both one-photon excitation and two-photon excitation. Importantly, HLTC enabled the precise and rapid delineation of both transplanted tumor and clinical tumor tissues within several minutes of simple topical spray. The tumor-to-background ratio (TBR) was up to 10.2 ± 1.0 at clinical liver cancer tissues and 9.9 ± 0.3 at clinical colon cancer tissues, allowing precise tumor margin identification and the effective guidance of surgical tumor resection. Furthermore, CCK8 assay, pharmacokinetic evaluation, blood analysis and H&E staining were performed, which verified high biocompatibility and biosafety of HLTC at working concentration. These results reveal the exciting potential of this small-molecule fluorescent diagnostic probe for real-time fluorescence-based navigation during surgical tumor resection.

Protease-activated indocyanine green nanoprobes for intraoperative NIR fluorescence imaging of primary tumors

Tumor-targeted fluorescent probes in the near-infrared spectrum can provide invaluable information about the location and extent of primary and metastatic tumors during intraoperative procedures to ensure no residual tumors are left in the patient's body. Even though the first fluorescence-guided surgery was performed more than 50 years ago, it is still not accepted as a standard of care in part due to the lack of efficient and non-toxic targeted probes approved by regulatory agencies around the world. Herein, we report protease-activated cationic gelatin nanoparticles encapsulating indocyanine green (ICG) for the detection of primary breast tumors in murine models with high tumor-to-background ratios. Upon intravenous administration, these nanoprobes remain optically silent due to the energy resonance transfer among the bound ICG molecules. As the nanoprobes extravasate and are exposed to the acidic tumor microenvironment, their positive surface charges increase, facilitating cellular uptake. The internalized nanoprobes are activated upon proteolytic degradation of gelatin to allow high contrast between the tumor and normal tissue. Since both gelatin and ICG are FDA-approved for intravenous administration, this activatable nanoprobe can lead to quick clinical adoption and improve the treatment of patients undergoing image-guided cancer surgery.

A Cathepsin-Targeted Quenched Activity-Based Probe Facilitates Enhanced Detection of Human Tumors during Resection

PURPOSE

Fluorescence-guided surgery using tumor-targeted contrast agents has been developed to improve the completeness of oncologic resections. Quenched activity-based probes that fluoresce after covalently binding to tumor-specific enzymes have been proposed to improve specificity, but none have been tested in humans. Here, we report the successful clinical translation of a cathepsin activity-based probe (VGT-309) for fluorescence-guided surgery.

EXPERIMENTAL DESIGN

We optimized the specificity, dosing, and timing of VGT-309 in preclinical models of lung cancer. To evaluate clinical feasibility, we conducted a canine study of VGT-309 during pulmonary tumor resection. We then conducted a randomized, double-blind, dose-escalation study in healthy human volunteers receiving VGT-309 to evaluate safety. Finally, we tested VGT-309 in humans undergoing lung cancer surgery.

RESULTS

In preclinical models, we found highly specific tumor cell labeling that was blocked by a broad spectrum cathepsin inhibitor. When evaluating VGT-309 for guidance during resection of canine tumors, we found that the probe selectively labeled tumors and demonstrated high tumor-to-background ratio (TBR; range: 2.15-3.71). In the Phase I human study, we found that VGT-309 was safe at all doses studied. In the ongoing Phase II trial, we report two cases in which VGT-309 localized visually occult, non-palpable tumors (TBRs = 2.83 and 7.18) in real time to illustrate its successful clinical translation and potential to improve surgical management.

CONCLUSIONS

This first-in-human study demonstrates the safety and feasibility of VGT-309 to label human pulmonary tumors during resection. These results may be generalizable to other cancers due to cathepsin overexpression in many solid tumors.

Formulation of a Thermosensitive Imaging Hydrogel for Topical Application and Rapid Visualization of Tumor Margins in the Surgical Cavity

Simple Summary

We have developed a formulation for an innovative, quenched, cathepsin-targeted, fluorescent molecular probe to enhance resection quality for several solid-tumor cancers. Unlike other formulations for imaging probes or tracers in development and entering the clinic, which require systemic administration hours before the procedure, this current formulation is applied topically into the surgical cavity immediately after a standard of care resection. Within minutes of application, the probe activates in the presence of residual cancer in the surgical wound and provides a strong fluorescent signal that precisely delineates any remaining cancer, enabling a more complete resection. Utilization of this imaging gel formulation for topical application to detect breast cancer in the surgical cavity during surgery has the potential to reduce re-excisions, with consequent savings in healthcare costs and enhancement in patient quality of life.

Abstract

Background: Tumor-positive surgical margins during primary breast cancer (BCa) surgery are associated with a two-fold increase in the risk of local recurrence when compared with tumor-negative margins. Pathological microscopic evaluation of the samples only assesses about 1/10 of 1% of the entire volume of the removed BCa specimens, leading to margin under-sampling and potential local recurrence in patients with pathologically clean margins, i.e., false negative margins. In the case of tumor-positive margins, patients need to undergo re-excision and/or radiation therapy, resulting in increases in complications, morbidity, and healthcare costs. Development of a simple real-time imaging technique to identify residual BCa in the surgical cavity rapidly and precisely could significantly improve the quality of care. Methods: A small-molecule, fluorescently quenched protease-substrate probe, AKRO-QC-ICG, was tested as part of a thermosensitive imaging gel formulated for topical application and imaging of the BCa surgical cavity. Results: More than forty formulations of gel mixtures were investigated to enable easy fluid application and subsequent solidification once applied, preventing dripping and pooling in the surgical cavity. The final formulation was tested using human BCa orthotopic implants in nude and NSG patient-derived xenografts (PDX) mice. This formulation of Pluronic F-127/DMSO/AKRO-QC-ICG imaging gel was found to be a good solvent for the probe, with a desirable thermo-reversible solid–gel transition and mechanical strength for distribution of AKRO-QC-ICG on the surfaces of tissue. It demonstrated excellent ability to detect BCa tissue after 10 min exposure, with a high signal-to-noise ratio both in mouse xenografts and freshly excised human lumpectomy tissue. The in vivo efficacy of the AKRO-QC-ICG imaging gel to detect BCa revealed the levels of sensitivity/specificity = 0.92/1 in 12 nude mice, which was corroborated with the sensitivity/specificity = 0.94/1 in 10 PDX mice. Conclusions: Utilization of Pluronic F-127/DMSO/AKRO-QC-ICG imaging gel for topical application to detect BCa in the surgical cavity during surgery has the potential to reduce re-excisions, with consequent savings in healthcare costs and enhancement in patient quality of life.

Preclinical Evaluation of an Activity-Based Probe for Intraoperative Imaging of Esophageal Cancer

Background

Early detection and complete resection are important prognostic factors for esophageal cancer (EC). Intraoperative molecular imaging (IMI) using tumor-targeted tracers is effective in many cancer types. However, there are no EC-specific IMI tracers. We sought to test a cathepsin activity-based tracer (VGT-309) for EC resection.

Methods

Murine (AKR, HNM007) and human (OE19) EC cell lines were screened for cathepsin expression by western blotting. In vitro binding affinity of VGT-309 was evaluated by fluorescence microscopy. Flank tumor models were developed by injecting EC cells into the flanks of BALB/c or athymic nude mice. Mice pretreated with a cathepsin inhibitor (JPM-OEt) were used to confirm on target binding. Animals were injected with 2 mg/kg VGT-309, underwent IMI, and were sacrificed 24 hours after injection.

Results

Cathepsins B, L, S, and X were expressed by EC cell lines, and all cell lines were labeled in vitro with VGT-309. Fluorescent signal was eliminated when cells were pretreated with JPM-OEt. On biodistribution analysis, VGT-309 accumulated in the liver, kidneys, and spleen without other organ involvement. VGT-309 selectively accumulated in flank allografts and xenografts, with mean signal-to-background ratio of 5.21 (IQR: 4.18-6.73) for flank allografts and 4.34 (IQR: 3.75-5.02) for flank xenografts. Fluorescence microscopy and histopathological analysis confirmed the selective accumulation of the tracer in tumors compared to background normal tissues.

Conclusions

VGT-309 is an effective tracer for IMI of esophageal cancer. There is potential for clinical translation both as an adjunct to endoscopic detection and for complete removal of disease during esophagectomy.

Peptide probes for proteases - innovations and applications for monitoring proteolytic activity

Proteases are excellent biomarkers for a variety of diseases, offer multiple opportunities for diagnostic applications and are valuable targets for therapy. From a chemistry-based perspective this review discusses and critiques the most recent advances in the field of substrate-based probes for the detection and analysis of proteolytic activity both in vitro and in vivo.

Fundamentals and developments in fluorescence-guided cancer surgery

Fluorescence-guided surgery using tumour-targeted imaging agents has emerged over the past decade as a promising and effective method of intraoperative cancer detection. An impressive number of fluorescently labelled antibodies, peptides, particles and other molecules related to cancer hallmarks have been developed for the illumination of target lesions. New approaches are being implemented to translate these imaging agents into the clinic, although only a few have made it past early-phase clinical trials. For this translational process to succeed, target selection, imaging agents and their related detection systems and clinical implementation have to operate in perfect harmony to enable real-time intraoperative visualization that can benefit patients. Herein, we review key aspects of this imaging cascade and focus on imaging approaches and methods that have helped to shed new light onto the field of intraoperative fluorescence-guided cancer surgery with the singular goal of improving patient outcomes.

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.

Low-Field NMR Relaxometry for Intraoperative Tumour Margin Assessment in Breast-Conserving Surgery

Simple Summary

Breast cancer is the most diagnosed cancer for women, and clear surgical margins in breast-conserving surgery (BCS) are essential for preventing recurrence. In this study, the potential of fast field-cycling ¹H-NMR relaxometry as a new tool for intraoperative margin assessment was evaluated. The technique allows the determination of the tissue proton relaxation rates as a function of the applied magnetic field on small tissue samples excised from surgical specimens, at the margins of tumour resection, prior to histopathological analysis. It was found that a good accuracy in margin assessment, i.e., a sensitivity of 92% and a specificity of 85%, can be achieved. The discriminating ability shown by the relaxometric assay relies mainly on the difference of fat/water content between healthy and tumour cells. The information obtained has the potential to support the surgeon in real-time margin assessment during BCS.

Abstract

As conserving surgery is routinely applied for the treatment of early-stage breast cancer, the need for new technology to improve intraoperative margin assessment has become increasingly important. In this study, the potential of fast field-cycling ¹H-NMR relaxometry as a new diagnostic tool was evaluated. The technique allows the determination of the tissue proton relaxation rates (R₁), as a function of the applied magnetic field, which are affected by the changes in the composition of the mammary gland tissue occurring during the development of neoplasia. The study involved 104 small tissue samples obtained from surgical specimens destined for histopathology. It was found that a good accuracy in margin assessment, i.e., a sensitivity of 92% and a specificity of 85%, can be achieved by using two quantifiers, namely (i) the slope of the line joining the R₁ values measured at 0.02 and 1 MHz and (ii) the sum of the R₁ values measured at 0.39 and 1 MHz. The method is fast, and it does not rely on the expertise of a pathologist or cytologist. The obtained results suggest that a simplified, low-cost, automated instrument might compete well with the currently available tools in margin assessment.

Molecular probes for selective detection of cysteine cathepsins

Cysteine cathepsins are proteases critical in physiopathological processes and show potential as targets or biomarkers for diseases and medical conditions. The 11 members of the cathepsin family are redundant in some cases but remarkably independent of others, demanding the development of both pan-cathepsin targeting tools as well as probes that are selective for specific cathepsins with little off-target activity. This review addresses the diverse design strategies that have been employed to accomplish this tailored selectivity among cysteine cathepsin targets and the imaging modalities incorporated. The power of these diverse tools is contextualized by briefly highlighting the nature of a few prominent cysteine cathepsins, their involvement in select diseases, and the application of cathepsin imaging probes in research spanning basic biochemical studies to clinical applications.

Recent advances in activity-based probes (ABPs) and affinity-based probes (AfBPs) for profiling of enzymes

Activity-based protein profiling (ABPP) is a technique that uses highly selective active-site targeted chemical probes to label and monitor the state of proteins. ABPP integrates the strengths of both chemical and biological disciplines. By utilizing chemically synthesized or modified bioactive molecules, ABPP is able to reveal complex physiological and pathological enzyme-substrate interactions at molecular and cellular levels. It is also able to provide critical information of the catalytic activity changes of enzymes, annotate new functions of enzymes, discover new substrates of enzymes, and allow real-time monitoring of the cellular location of enzymes. Based on the mechanism of probe-enzyme interaction, two types of probes that have been used in ABPP are activity-based probes (ABPs) and affinity-based probes (AfBPs). This review highlights the recent advances in the use of ABPs and AfBPs, and summarizes their design strategies (based on inhibitors and substrates) and detection approaches.

Development of near-infrared imaging agents for detection of junction adhesion molecule-A protein

•

Anti-junctional adhesion molecule-A (JAM-A) monoclonal antibodies (mAb) conjugated with near infra-red fluorescent dye, IR700 – as a JAM-A mAb/IR700 agent was developed.

•

An in vivo JAM-A mAb/IR700-specific near infra-red imaging of human-derived prostate and breast cancer xenograft is presented.

•

A single injection of the agent is diminished number of mitotic cells in cancerous tissue of mice bearing heterotopic tumors.

•

Since, our agent depicts the specific accumulation within the targeted tumors, this agent may be adapted to solid tumor targeted photoimmunotherapy.

Introduction

Prostate and breast cancer are the most prevalent primary malignant human tumors globally. Prostatectomy and breast conservative surgery remain the most common definitive treatment option for the >500,000 men and women newly diagnosed with localized prostate and breast cancer each year only in the US. Morphological examination is the mainstay of diagnosis but margin under-sampling of the excised cancer tissue may lead to local recurrence. In despite of the progress of non-invasive optical imaging, there is still a clinical need for targeted optical imaging probes that could rapidly and globally visualize cancerous tissues.

Methods

Elevated expression of junctional adhesion molecule-A (JAM-A) on tumor cells and its multiple pro-tumorigenic activity make the JAM-A a candidate for molecular imaging. Near-infrared imaging probe, which employed anti-JAM-A monoclonal antibody (mAb) phthalocyanine dye IR700 conjugates (JAM-A mAb/IR700), was synthesized and used to identify and visualize heterotopic human prostate and breast tumor mouse xenografts in vivo.

Results

The intravenously injected JAM-A mAb/IR700 conjugates enabled the non-invasive detection of prostate and breast cancerous tissue by fluorescence imaging. A single dose of JAM-A mAb/IR700 reduced number of mitotic cancer cells in vivo, indicating theranostic ability of this imaging agent. The JAM-A mAb/IR700 conjugates allowed us to image a specific receptor expression in prostate and breast tumors without post-image processing.

Conclusion

This agent demonstrates promise as a method to image the extent of prostate and breast cancer in vivo and could assist with real-time visualization of extracapsular extension of cancerous tissue.