Performance of a novel protease-activated fluorescent imaging system for intraoperative detection of residual breast cancer during breast conserving surgery

Intraoperative evaluation of surgical margins in breast cancer

Achieving clear resection margins at the time of lumpectomy is essential for optimal patient outcomes. Margin status is traditionally determined by pathologic evaluation of the specimen and often is difficult or impossible for the surgeon to definitively know at the time of surgery, resulting in the need for re-operation to obtain clear surgical margins. Numerous techniques have been investigated to enhance the accuracy of intraoperative margin and are reviewed in this manuscript.

Intraoperative Imaging Techniques in Oncology

Imaging-based procedures have become well integrated into the diagnosis and management of oncological patients and play a significant role in reducing morbidity and mortality rates. Here we describe the established and upcoming surgical oncological imaging techniques and their impact on cancer management.

Chemical Tools to Image the Activity of PAR-Cleaving Proteases

Protease-activated receptors (PARs) comprise a family of four G protein-coupled receptors (GPCRs) that have broad functions in health and disease. Unlike most GPCRs, PARs are uniquely activated by proteolytic cleavage of their extracellular N termini. To fully understand PAR activation and function in vivo, it is critical to also study the proteases that activate them. As proteases are heavily regulated at the post-translational level, measures of total protease abundance have limited utility. Measures of protease activity are instead required to inform their function. This review will introduce several classes of chemical probes that have been developed to measure the activation of PAR-cleaving proteases. Their strengths, weaknesses, and applications will be discussed, especially as applied to image protease activity at the whole organism, tissue, and cellular level.

Intraoperative Fluorescence Guidance for Breast Cancer Lumpectomy Surgery

BACKGROUND: Although lumpectomy and mastectomy provide equivalent survival for patients with breast cancer, local recurrence after lumpectomy increases breast cancer mortality. Positive lumpectomy margins, which imply incomplete tumor removal, are the strongest predictor of local recurrence and are identified days after surgery, necessitating a second surgery. METHODS: In this prospective trial, we assessed margin status with or without pegulicianine fluorescence-guided surgery (pFGS) for stages 0 to 3 breast cancers. To prevent surgeons from performing smaller than standard lumpectomies in anticipation of pFGS assistance, patients were randomly assigned 10:1 to pFGS or control groups, thus randomization was not designed to provide a control group for evaluating device performance. In patients undergoing pFGS, additional pFGS-guided cavity margins were excised at sites of pegulicianine signal. We evaluated three coprimary end points: the percentage of patients for whom pFGS-guided margins contained cancer, sensitivity, and specificity. RESULTS: Overall, 406 patients received 1.0 mg/kg intravenous pegulicianine followed by lumpectomy. Among 392 patients randomly assigned, 316 had invasive cancers, and 76 had in situ cancers. In 27 of 357 patients undergoing pFGS, pFGS-guided margins removed tumor left behind after standard lumpectomy, 22 from cavity orientations deemed negative on standard margin evaluation. Second surgeries were avoided by pFGS in 9 of 62 patients with positive margins. On per-margin analysis, pFGS specificity was 85.2%, and sensitivity was 49.3%. Pegulicianine administration was stopped for adverse events in six patients. Two patients had grade 3 serious adverse events related to pegulicianine. CONCLUSIONS: The use of pFGS in breast cancer surgery met prespecified thresholds for removal of residual tumor and specificity but did not meet the prespecified threshold for sensitivity. (Funded by Lumicell, Inc. and the National Institutes of Health; Clinicaltrials.gov number, NCT03686215.)

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.

Cysteine Cathepsins in Breast Cancer: Promising Targets for Fluorescence-Guided Surgery

The majority of breast cancer patients is treated with breast-conserving surgery (BCS) combined with adjuvant radiation therapy. Up to 40% of patients has a tumor-positive resection margin after BCS, which necessitates re-resection or additional boost radiation. Cathepsin-targeted near-infrared fluorescence imaging during BCS could be used to detect residual cancer in the surgical cavity and guide additional resection, thereby preventing tumor-positive resection margins and associated mutilating treatments. The cysteine cathepsins are a family of proteases that play a major role in normal cellular physiology and neoplastic transformation. In breast cancer, the increased enzymatic activity and aberrant localization of many of the cysteine cathepsins drive tumor progression, proliferation, invasion, and metastasis. The upregulation of cysteine cathepsins in breast cancer cells indicates their potential as a target for intraoperative fluorescence imaging. This review provides a summary of the current knowledge on the role and expression of the most important cysteine cathepsins in breast cancer to better understand their potential as a target for fluorescence-guided surgery (FGS). In addition, it gives an overview of the cathepsin-targeted fluorescent probes that have been investigated preclinically and in breast cancer patients. The current review underscores that cysteine cathepsins are highly suitable molecular targets for FGS because of favorable expression and activity patterns in virtually all breast cancer subtypes. This is confirmed by cathepsin-targeted fluorescent probes that have been shown to facilitate in vivo breast cancer visualization and tumor resection in mouse models and breast cancer patients. These findings indicate that cathepsin-targeted FGS has potential to improve treatment outcomes in breast cancer patients.

Fluorescence probes for lung carcinoma diagnosis and clinical application

This review provides an overview of the most recent developments in fluorescence probe technology for the accurate detection and clinical therapy of lung carcinoma.

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.

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.

Clinical Impact of Intraoperative Margin Assessment in Breast-Conserving Surgery With a Novel Pegulicianine Fluorescence-Guided System: A Nonrandomized Controlled Trial

Importance

Positive margins following breast-conserving surgery (BCS) are often identified on standard pathology evaluation. Intraoperative assessment of the lumpectomy cavity has the potential to reduce residual disease or reexcision rate following standard of care BCS in real time.

Objective

To collect safety and initial efficacy data on the novel pegulicianine fluorescence-guided system (pFGS) when used to identify residual cancer in the tumor bed of female patients undergoing BCS.

Design, Setting, and Participants

This prospective single-arm open-label study was conducted as a nonrandomized multicenter controlled trial at 16 academic or community breast centers across the US. Female patients 18 years and older with newly diagnosed primary invasive breast cancer or ductal carcinoma in situ DCIS undergoing BCS were included, excluding those with previous breast cancer surgery and a history of dye allergies. Of 283 consecutive eligible patients recruited, 234 received a pegulicianine injection and were included in the safety analysis; of these, 230 were included in the efficacy analysis. Patients were enrolled between February 6, 2018, and April 10, 2020, and monitored for a 30-day follow-up period. Data were analyzed from April 10, 2020, to August 5, 2021.

Interventions

Participants received an injection of a novel imaging agent (pegulicianine) a mean (SD) of 3.2 (0.9) hours prior to surgery at a dose of 1 mg/kg. After completing standard of care (SOC) excision, pFGS was used to scan the lumpectomy cavity to guide the removal of additional shave margins.

Main Outcomes and Measures

Adverse events and sensitivity, specificity, and reexcision rate.

Results

Of 234 female patients enrolled (median [IQR] age, 62.0 [55.0-69.0] years), 230 completed the trial and 1 patient with a history of allergy to contrast agents had an anaphylactic reaction and recovered without sequelae. Correlation of pFGS with final margin status on a per-margin analysis showed a marked improvement in sensitivity over standard pathology assessment of the main lumpectomy specimen (69.4% vs 38.2%, respectively). On a per-patient level, the false-negative rate of pFGS was 23.7% (9 of 38), and sensitivity was 76.3% (29 of 38). Among 32 patients who underwent excision of pFGS-guided shaves, pFGS averted the need for reexcision in 6 (19%).

Conclusions and Relevance

In this pilot feasibility study, the safety profile of pegulicianine was consistent with other imaging agents used in BCS, and was associated with a reduced need for second surgery in patients who underwent intraoperative additional excision of pFGS-guided shaves. These findings support further development and clinical performance assessment of pFGS in a prospective randomized trial.

Trial Registration

ClinicalTrials.gov Identifier: NCT03321929.

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.

Fluorescence Molecular Targeting of Colon Cancer to Visualize the Invisible

Colorectal cancer (CRC) is a common cause of cancer and cancer-related death. Surgery is the only curative modality. Fluorescence-enhanced visualization of CRC with targeted fluorescent probes that can delineate boundaries and target tumor-specific biomarkers can increase rates of curative resection. Approaches to enhancing visualization of the tumor-to-normal tissue interface are active areas of investigation. Nonspecific dyes are the most-used approach, but tumor-specific targeting agents are progressing in clinical trials. The present narrative review describes the principles of fluorescence targeting of CRC for diagnosis and fluorescence-guided surgery with molecular biomarkers for preclinical or clinical evaluation.