Paired-Agent Fluorescence Molecular Imaging of Sentinel Lymph Nodes Using Indocyanine Green as a Control Agent for Antibody-Based Targeted Agents

Shortwave Infrared Fluorofluorophores for Multicolor In Vivo Imaging

Developing chemical tools to detect and influence biological processes is a cornerstone of chemical biology. Here we combine two tools which rely on orthogonality- perfluorocarbons and multiplexed shortwave infrared (SWIR) fluorescence imaging- to visualize nanoemulsions in real time in living mice. Drawing inspiration from fluorous and SWIR fluorophore development, we prepared two SWIR-emissive, fluorous-soluble chromenylium polymethine dyes. These are the most red-shifted fluorous fluorophores- "fluorofluorophores"-to date. After characterizing the dyes, their utility was demonstrated by tracking perfluorocarbon nanoemulsion biodistribution in vivo. Using an excitation-multiplexed approach to image two variables simultaneously, we gained insight into the importance of size and surfactant identity on biodistribution.

Real-time tissue perfusion assessment using fluorescence imaging topography scanning system: A preclinical investigation

BACKGROUND AND OBJECTIVES

We previously developed a real-time fluorescence imaging topography scanning (RFITS) system for intraoperative multimodal imaging, image-guided surgery, and dynamic surgical navigation. The RFITS can capture intraoperative fluorescence, color reflectance, and surface topography concurrently and offers accurate registration of multimodal images. The RFITS prototype is a promising system for multimodal image guidance and intuitive 3D visualization. In the current study, we investigated the capability of the RFITS system in intraoperative fluorescence vascular angiography for real-time assessment of tissue perfusion.

STUDY DESIGN/MATERIALS AND METHODS

We conducted ex vivo imaging of fluorescence perfusion in a soft casting life-sized human brain phantom. Indocyanine green (ICG) solutions diluted in dimethyl sulfoxide (DMSO) and human serum were injected into the brain phantom through the vessel simulating tube (2 ± 0.2 mm inner diameter) by an adjustable flow peristaltic pump. To demonstrate the translational potential of the system, an ICG/DMSO solution was perfused into blood vessels of freshly harvested porcine ears (n = 9, inner diameter from 0.56 to 1.27 mm). We subsequently performed in vivo imaging of fluorescence-perfused vascular structures in rodent models (n = 10). 5 mg/ml ICG solutions prepared in sterile water were injected via the lateral tail vein. All targets were imaged by the RFITS prototype at a working distance of 350-400 mm.

RESULTS

3D visualization of 10 µg/ml ICG-labeled continuous moving serum in the brain phantom was obtained at an average signal-to-background ratio (SBR) of 1.74 ± 0.03. The system was able to detect intravenously diffused fluorescence in porcine tissues with an average SBR of 2.23 ± 0.22. The RFITS prototype provided real-time monitoring of tissue perfusion in rats after intravenous (IV) administration of ICG. The maximum fluorescence intensity (average SBR = 1.94 ± 0.16, p < 0.001) was observed at T_peak of ~30 seconds after the ICG signal was first detected (average SBR = 1.19 ± 0.13, p < 0.01).

CONCLUSIONS

We have conducted preclinical studies to demonstrate the feasibility of applying the RFITS system in real-time fluorescence angiography and tissue perfusion assessment. Our system provides fluorescence/color composite images for intuitive visualization of tissue perfusion with 3D perception. The findings pave the way for future clinical translation.

First Clinical Results of Fluorescence Lifetime-enhanced Tumor Imaging Using Receptor-targeted Fluorescent Probes

PURPOSE

Fluorescence molecular imaging, using cancer-targeted near infrared (NIR) fluorescent probes, offers the promise of accurate tumor delineation during surgeries and the detection of cancer specific molecular expression in vivo. However, nonspecific probe accumulation in normal tissue results in poor tumor fluorescence contrast, precluding widespread clinical adoption of novel imaging agents. Here we present the first clinical evidence that fluorescence lifetime (FLT) imaging can provide tumor specificity at the cellular level in patients systemically injected with panitumumab-IRDye800CW, an EGFR-targeted NIR fluorescent probe.

EXPERIMENTAL DESIGN

We performed wide-field and microscopic FLT imaging of resection specimens from patients injected with panitumumab-IRDye800CW under an FDA directed clinical trial.

RESULTS

We show that the FLT within EGFR-overexpressing cancer cells is significantly longer than the FLT of normal tissue, providing high sensitivity (>98%) and specificity (>98%) for tumor versus normal tissue classification, despite the presence of significant nonspecific probe accumulation. We further show microscopic evidence that the mean tissue FLT is spatially correlated (r > 0.85) with tumor-specific EGFR expression in tissue and is consistent across multiple patients. These tumor cell-specific FLT changes can be detected through thick biological tissue, allowing highly specific tumor detection and noninvasive monitoring of tumor EFGR expression in vivo.

CONCLUSIONS

Our data indicate that FLT imaging is a promising approach for enhancing tumor contrast using an antibody-targeted NIR probe with a proven safety profile in humans, suggesting a strong potential for clinical applications in image guided surgery, cancer diagnostics, and staging.

Intraoperative Detection of Micrometastases in Whole Excised Lymph Nodes Using Fluorescent Paired-Agent Imaging Principles: Identification of a Suitable Staining and Rinsing Protocol

PURPOSE

Correctly identifying nodal status is recognized as a critical prognostic factor in many cancer types and is essential to guide adjuvant treatment. Currently, surgical removal of lymph nodes followed by pathological examination is commonly performed as a standard-of-care to detect node metastases. However, conventional pathology protocols are time-consuming, yet less than 1 % of lymph node volumes are examined, resulting in a 30-60 % rate of missed micrometastases (0.2-2 mm in size).

PROCEDURES

This study presents a method to fluorescently stain excised lymph nodes using paired-agent molecular imaging principles, which entail co-administration of a molecular-targeted imaging agent with a suitable control (untargeted) agent, whereby any nonspecific retention of the targeted agent is accounted for by the signal from the control agent. Specifically, it was demonstrated that by dual-needle continuous infusion of either an antibody-based imaging agent pair (epidermal growth factor receptor (EGFR) targeted agent: IRDye-800CW labeled Cetuximab; control agent: IRDye-700DX-IgG) or an Affibody-based pair (EGFR targeted Affibody® agent: ABY-029; control agent IRDYe-700DX carboxylate) at 0.3 ml/min.

RESULTS

The results demonstrated the possibility to achieve >99 % sensitivity and > 95 % specificity for detection of a single micrometastasis (~0.2 mm diameter) in a whole lymph node within 22 min of tissue processing time.

CONCLUSION

The detection capabilities offer substantial improvements over existing intraoperative lymph node biopsy methods (e.g., frozen pathology has a micrometastasis sensitivity <20 %).

Paired Agent Fluorescence Imaging of Cancer in a Living Mouse Using Preassembled Squaraine Molecular Probes with Emission Wavelengths of 690 and 830 nm

New methods are described for the construction of targeted fluorescence probes for imaging cancer and the assessment of tumor targeting performance in a living mouse model. A novel noncovalent assembly process was used to fabricate a set of structurally related targeted fluorescent probes with modular differences in three critical assembly components: the emission wavelength of the squaraine fluorochrome, the number of cRGDfK peptide units that target the cancer cells, and the length of the polyethylene glycol chains as pharmacokinetic controllers. Selective targeting of cancer cells was proven by a series of cell microscopy experiments followed by in vivo imaging of subcutaneous tumors in living mice. The mouse imaging studies included a mock surgery that completely removed a fluorescently labeled tumor. Enhanced tumor accumulation due to probe targeting was first evaluated by conducting Single Agent Imaging (SAI) experiments that compared tumor imaging performance of a targeted probe and untargeted probe in separate mouse cohorts. Although there was imaging evidence for enhanced tumor accumulation of the targeted probe, there was moderate scatter in the data due to tumor-to-tumor variability of the vasculature structure and interstitial pressure. A subsequent Paired Agent Imaging (PAI) study coinjected a binary mixture of targeted probe (with emission at 690 nm) and untargeted probe (with emission at 830 nm) into the same tumor-burdened animal. The conclusion of the PAI experiment also indicated enhanced tumor accumulation of the targeted probe, but the statistical significance was much higher, even though the experiment required a much smaller cohort of mice. The imaging data from the PAI experiment was analyzed to determine the targeted probe's Binding Potential (BP) for available integrin receptors within the tumor tissue. In addition, pixelated maps of BP within each tumor indicated a heterogeneous spatial distribution of BP values. The results of this study show that the combination of fluorescent probe preassembly and PAI is a promising new way to rapidly develop targeted fluorescent probes for tumors with high BP and eventual use in clinical applications such as targeted therapy, image guided surgery, and personalized medicine.

Effect of nonspecific binding of imaging agents to plasma protein in the paired-agent imaging for resection during surgery (PAIRS)

Long-term survival of head and neck squamous cell carcinoma (HNSCC) patients have proven to be correlated with negative surgical margins. Paired-Agent Imaging for Resection during Surgery (PAIRS) is capable of drawing the fine line between tumor and normal tissue by employing a control imaging-agent, which is co-administered with the targeted imaging agent to account for nonspecific signal. PAI is highly dependent on the parallel paired-agent delivery and static quantum yield of the agent to trace the molecular concentration. However, it is well known that nonspecific binding of fluorescence probes to plasma proteins can change its delivery, dissociation constant, and quantum yield. A thorough evaluation of the effect of plasma protein binding in the estimation of receptor concentration was performed for the paired-agents in this study. We are planning to evaluate ABY-029, an anti-epithelial growth factor receptor (EGFR) Affibody, and IRDye 700DX as a control agent. The plasma-dependent change in fluorescence intensity, percent binding, and in vivo distribution kinetics will be studied for each agent alone, and in combination. In this proceeding, the absorption, emission patterns for the targeted agent, ABY-029, measured by UV-Vis, fluorometer, and Pearl were shown. Initial studies indicate that binding to Bovine serum albumin (BSA), human serum albumin (HSA) and EGFR can introduce the Solvatochromic shift, which will change the absorption and emission pattern for ABY-029. Computational modeling will be performed to determine how each of these changes will affect the determined BP, and thus detection of tumors from normal tissue.

Monoclonal antibody-based molecular imaging strategies and theranostic opportunities

Molecular imaging modalities hold great potential as less invasive techniques for diagnosis and management of various diseases. Molecular imaging combines imaging agents with targeting moieties to specifically image diseased sites in the body. Monoclonal antibodies (mAbs) have become increasingly popular as novel therapeutics against a variety of diseases due to their specificity, affinity and serum stability. Because of the same properties, mAbs are also exploited in molecular imaging to target imaging agents such as radionuclides to the cell of interest in vivo. Many studies investigated the use of mAb-targeted imaging for a variety of purposes, for instance to monitor disease progression and to predict response to a specific therapeutic agent. Herein, we highlighted the application of mAb-targeted imaging in three different types of pathologies: autoimmune diseases, oncology and cardiovascular diseases. We also described the potential of molecular imaging strategies in theranostics and precision medicine. Due to the nearly infinite repertoire of mAbs, molecular imaging can change the future of modern medicine by revolutionizing diagnostics and response prediction in practically any disease.

Optical molecular imaging can differentiate metastatic from benign lymph nodes in head and neck cancer

Identification of lymph node (LN) metastasis is essential for staging of solid tumors, and as a result, surgeons focus on harvesting significant numbers of LNs during ablative procedures for pathological evaluation. Isolating those LNs most likely to harbor metastatic disease can allow for a more rigorous evaluation of fewer LNs. Here we evaluate the impact of a systemically injected, near-infrared fluorescently-labeled, tumor-targeting contrast agent, panitumumab-IRDye800CW, to facilitate the identification of metastatic LNs in the ex vivo setting for head and neck cancer patients. Molecular imaging demonstrates a significantly higher mean fluorescence signal in metastatic LNs compared to benign LNs in head and neck cancer patients undergoing an elective neck dissection. Molecular imaging to preselect at-risk LNs may thus allow a more rigorous examination of LNs and subsequently lead to improved prognostication than regular neck dissection.