Toxicity and Pharmacokinetic Profile for Single-Dose Injection of ABY-029: a Fluorescent Anti-EGFR Synthetic Affibody Molecule for Human Use

Predicting head and neck tumor nodule responses to TLD1433 photodynamic therapy using the image-guided surgery probe ABY-029

Incomplete surgical resection in head and neck cancer can lead to locoregional recurrence in >35% of patients. Approaches such as image-guided surgery (IGS) and post-operative photodynamic therapy (PDT) have been proposed to reduce recurrence rates. However, the PDT doses needed to eliminate all unresected diseases are not established. This in vitro proof-of-concept study aims to predict head and neck tumor nodule viability in vitro following PDT with TLD1433 using the IGS probe ABY-029. ABY-029 is an EGFR-specific affibody-IRDye800CW conjugate that has undergone Phase 0 evaluation studies in head and neck cancer, among others. TLD1433 is a ruthenium-based photosensitizer in a Phase II trial for non-muscle invasive bladder cancer. Here, we demonstrate that decreases in fluorescence emission of ABY-029 bound to MOC1 mouse head and neck cancer nodules in vitro can be predictive of TLD1433 PDT responses. Results show that photoactivation of TLD1433 produces reactive oxygen species (ROS) that reduce MOC1 nodule fractional viability in a manner that is inversely correlated with ABY-029 fluorescence intensity (Pearson's r = -0.9148, R2 = 0.8369, p < 0.0001). We hypothesize that this is due to ROS-mediated degradation of IRDye800CW. The findings warrant further studies using head and neck cancer nodules with heterogenous PDT responses and EGFR expression levels. If successful, the future goal would be to use ABY-029 to guide the dosimetry of intraoperative PDT of the surgical bed after IGS to eliminate all microscopic diseases, reduce recurrence rates, and prolong survival.

Dynamic Tracking of In Vivo Receptor Availability in Tumor Using Paired-Agent Imaging

Quantitative assessment of receptor availability (RA) provides valuable insight into therapeutic outcomes in drug development and clinical practice. Here, paired-agent imaging (PAI) is used to dynamically track the availability of the epidermal growth factor receptor (EGFR) in response to in vivo ligand or inhibitor binding in individual mice with head and neck cancer (HNC). Naïve (n = 3) or xenograft HNC tumor-bearing (n = 21) mice were coadministered 0.15, 0.3, or 0.9 nmol ABY-029, and 2.5 nmol of IRDye 700DX. Fluorescence images were acquired for 300 min and then for an additional 60 min after administration of Z03115 (test group), human EGF (positive control), or PBS (vehicle control). Kinetic fluorescence and PAI curves were evaluated to determine the effects of the ABY-029 dose and EGFR blocking on tumor RA estimation. Nonquantifiable increases in ABY-029 fluorescence in tumor and muscle were observed after in vivo blocking, while PAI produced the expected decrease in RA. No statistically significant difference in preblocking RA was observed with different doses of ABY-029. RA decreased in response to blocking in positive control and test group animals, while the vehicle group exhibited no significant change in RA. This study demonstrated that RA can be monitored dynamically in individual animals using PAI regardless of imaging agent dose, while fluorescence from the receptor-targeted imaging agent alone could not. These results demonstrate PAI as a simple imaging strategy that could allow dose optimization in pharmaceutical development and patient-specific dosing for molecular therapeutics.

Agents for Fluorescence-Guided Glioblastoma Surgery

Glioblastoma (GBM) is the most aggressive primary brain tumor, characterized by rapid progression and a median survival of no more than 12-18 months. Fluorescence-guided surgery is crucial, as it allows for tumor visualization and aids in its complete removal, which is essential for improving survival rates. We conducted a literature review to identify fluorescent agents that have been utilized in the removal of GBM and to assess their benefits in achieving maximum tumor resection. Our analysis focuses on their advantages, limitations, and potential impact on improving surgical precision and patient outcomes. We searched the PubMed database for studies published on fluorescence-guided resection of GBM and evaluated the utility of each agent in terms of outcomes, gross total resection (GTR), and their sensitivity and specificity for the tumor. The literature review revealed that the three agents successfully utilized are 5-aminolevulinic acid (5-ALA), sodium fluorescein, and indocyanine green. In addition to these, a variety of dyes have been investigated in studies, including peptides, lipids, and nanosystems, which appear to be very promising. To date, numerous fluorescent agents have been proposed for the surgical resection of GBM. However, 5-aminolevulinic acid (5-ALA) remains the only agent widely adopted in clinical practice, as its safety and efficacy have been well-established. Further clinical trials and studies are necessary to assess the utility, effectiveness, and potential advantages of emerging fluorescent dyes in enhancing GBM resection and improving patient outcomes.

First-in-Human Study of ABY-029, a Novel Fluorescent Peptide that Targets EGFR, Applied to Soft-Tissue Sarcomas

ABY-029, an anti-EGFR Affibody molecule conjugated to IRDye 800CW, recently underwent first-in-human testing in soft-tissue sarcoma. The FDA Exploratory Investigational New Drug status was obtained for the phase 0 clinical trial in which study objectives were to determine whether a biological variance ratio (BVR) of 10 was achievable, whether fluorescence intensity correlated with EGFR expression, and whether doses were well tolerated. Patients (N = 12) with soft-tissue sarcoma were recruited based on positive EGFR IHC staining of diagnostic biopsies. ABY-029 was administered at a microdose (30 nmol, n = 3), medium dose (90 nmol, n = 3), or high dose (171 nmol, n = 6) 1 to 3 hours prior to surgery. Following tumor resection, ex vivo tissue was imaged to determine the mean fluorescence intensity, BVR, and other contrast measures. EGFR expression was correlated with IHC. For micro, medium, and high doses, mean BVR (SD) values in cross-sectional slices were 4 (4), 10 (6), and 7 (8) for the whole tumor region and 6 (5), 13 (11), and 8 (6) for pathology-confirmed regions of interest, respectively. Strong linear correlations were found between all ABY-029 contrast metrics and total EGFR (r≥ 0.86; P < 0.029) in cross-sectional tissue slices and between mean fluorescence intensity and EGFR percent area (r = 0.63; P < 0.0001) in excised region-of-interest tissue sections. No ABY-029-related adverse events were observed. When administered above the microdose, ABY-029 demonstrated a high correlation with EGFR expression and contrast values that were encouraging for translation to clinical practice. Contrast values were similar to those observed with antibody agents but with a substantially reduced imaging-to-resection time and no drug-related adverse events.

Dual-channel pulse-dye densitometry can enable correction of fluorescent targeted and control agent plasma input function differences for quantitative paired-agent molecular imaging: a simulation study

Significance

Paired-agent fluorescent molecular imaging approaches involve co-administration of a control (untargeted) imaging agent with a molecularly targeted agent to account for non-specific effects and quantify binding potential (BP)-a parameter proportional to the concentration of the targeted biomolecule. Accurate BP estimation often requires correction for differences in targeted and control agent plasma input functions (PIFs).

Aim

We provide a simulation-based evaluation of whether dual-channel pulse dye densitometry (PDD) can be used to measure the PIFs of co-administered targeted and control imaging agents, to enable accurate BP estimation.

Approach

Monte-Carlo simulations of light propagation were carried out using the anatomy and optical properties of a finger, as well as experimentally measured PIFs of co-administered anti-epidermal growth factor receptor fluorescent affibody, ABY-029, and IRDye 680LT, a control imaging agent from past mouse experiments. The accuracy of PIF shape estimation from PDD and PIF difference correction was evaluated by assessing BP estimation accuracy in a simulated "tumor" tissue.

Results

"Tumor" BP measurements using deconvolution correction with noise-free PIFs versus PDD-measured PIFs were compared. The relative error in PDD PIF deconvolution BP estimation was 2 ± 1 % . No statistical difference was found between the estimated BP via deconvolution correction with true PIFs and the estimated BP via the reconstructed PIFs using the proposed PAF-PDD methodology.

Conclusions

These results highlight the potential for developing a PDD instrument that can directly measure targeted and control agent PIFs and be used to correct for any PIF differences between agents for more quantitative estimates of BP in paired-agent imaging studies.

Nerve-Sparing Gynecologic Surgery Enabled by A Near-Infrared Nerve-Specific Fluorophore Using Existing Clinical Fluorescence Imaging Systems

Patients undergoing gynecological procedures suffer from lasting side effects due to intraoperative nerve damage. Small, delicate nerves with complex and nonuniform branching patterns in the female pelvic neuroanatomy make nerve-sparing efforts during standard gynecological procedures such as hysterectomy, cystectomy, and colorectal cancer resection difficult, and thus many patients are left with incontinence and sexual dysfunction. Herein, a near-infrared (NIR) fluorescent nerve-specific contrast agent, LGW08-35, that is spectrally compatible with clinical fluorescence guided surgery (FGS) systems is formulated and characterized for rapid implementation for nerve-sparing gynecologic surgeries. The toxicology, pharmacokinetics (PK), and pharmacodynamics (PD) of micelle formulated LGW08-35 are examined, enabling the determination of the optimal imaging doses and time points, blood and tissue uptake parameters, and maximum tolerated dose (MTD). Application of the formulated fluorophore to imaging of female rat and swine pelvic neuroanatomy validates the continued clinical translation and use for real-time identification of important nerves such as the femoral, sciatic, lumbar, iliac, and hypogastric nerves. Further development of LGW08-35 for clinical use will unlock a valuable tool for surgeons in direct visualization of important nerves and contribute to the ongoing characterization of the female pelvic neuroanatomy to eliminate the debilitating side effects of nerve damage during gynecological procedures.

In Vivo Labeling and Detection of Circulating Tumor Cells in Mice Using OTL38

PURPOSE

We recently developed an optical instrument to non-invasively detect fluorescently labeled circulating tumor cells (CTCs) in mice called 'Diffuse in vivo Flow Cytometry' (DiFC). OTL38 is a folate receptor (FR) targeted near-infrared (NIR) contrast agent that is FDA approved for use in fluorescence guided surgery of ovarian and lung cancer. In this work, we investigated the use OTL38 for in vivo labeling and detection of FR + CTCs with DiFC.

PROCEDURES

We tested OTL38 labeling of FR + cancer cell lines (IGROV-1 and L1210A) as well as FR- MM.1S cells in suspensions of Human Peripheral Blood Mononuclear cells (PBMCs) in vitro. We also tested OTL38 labeling and NIR-DIFC detection of FR + L1210A cells in blood circulation in nude mice in vivo.

RESULTS

62% of IGROV-1 and 83% of L1210A were labeled above non-specific background levels in suspensions of PBMCs in vitro compared to only 2% of FR- MM.1S cells. L1210A cells could be labeled with OTL38 directly in circulation in vivo and externally detected using NIR-DiFC in mice with low false positive detection rates.

CONCLUSIONS

This work shows the feasibility of labeling CTCs in vivo with OTL38 and detection with DiFC. Although further refinement of the DiFC instrument and signal processing algorithms and testing with other animal models is needed, this work may eventually pave the way for human use of DiFC.

Quantifying Imaging Agent Binding and Dissociation in 3-D Cancer Spheroid Tissue Culture Using Paired-Agent Principles

Binding kinetics play an important role in cancer diagnosis and therapeutics. However, current methods of quantifying binding kinetics fail to consider the three-dimensional environment that drugs and imaging agents experience in biological tissue. In response, a methodology to assay agent binding and dissociation in 3-D tissue culture was developed using paired-agent molecular imaging principles. To test the methodology, the uptakes of ABY-029 (an IRDye 800CW-labeled epidermal growth factor receptor (EGFR)-targeted antibody mimetic) and IRDye-700DX carboxylate in 3-D spheroids were measured in four different human cancer cell lines throughout staining and rinsing. A compartment model (optimized for the application) was then fit to the kinetic curves of both imaging agents to estimate binding and dissociation rate constants of the EGFR-targeted ABY-029 agent. A statistically significant correlation was observed between apparent association rate constant (k3) and the receptor concentration experimentally and in simulations (r = 0.99, p < 0.05). A statistically significant difference was found between effective k3 (apparent rate constant of ABY-029 binding to EGFR) values for cell lines with varying levels of EGFR expression (p < 0.05), with no significant difference found between cell lines and controls for other fit parameters. Additionally, a similar binding affinity profile compared to a gold standard method was determined by this model. This low-cost methodology to quantify imaging agent or drug binding affinity in clinically relevant 3-D tumor spheroid models can be used to guide timing of imaging in molecular guided surgery and could have implications in drug development.

Neoadjuvant Therapies Do Not Reduce Epidermal Growth Factor Receptor (EGFR) Expression or EGFR-Targeted Fluorescence in a Murine Model of Soft-Tissue Sarcomas

PURPOSE

ABY-029, an epidermal growth factor receptor (EGFR)-targeted, synthetic Affibody peptide labeled with a near-infrared fluorophore, is under investigation for fluorescence-guided surgery of sarcomas. To date, studies using ABY-029 have occurred in tumors naïve to chemotherapy (CTx) and radiation therapy (RTx), although these neoadjuvant therapies are frequently used for sarcoma treatment in humans. The goal of this study was to evaluate the impact of CTx and RTx on tumor EGFR expression and ABY-029 fluorescence of human soft-tissue sarcoma xenografts in a murine model.

PROCEDURES

Immunodeficient mice (n = 98) were divided into five sarcoma xenograft groups and three treatment groups - CTx only, RTx only, and CTx followed by RTx, plus controls. Four hours post-injection of ABY-029, animals were sacrificed followed by immediate fluorescence imaging of ex vivo adipose, muscle, nerve, and tumor tissues. Histological hematoxylin and eosin staining confirmed tumor type, and immunohistochemistry staining determined EGFR, cluster of differentiation 31 (CD31), and smooth muscle actin (SMA) expression levels. Correlation analysis (Pearson's correlation coefficients, r) and linear regression (unstandardized coefficient estimates, B) were used to determine statistical relationships in molecular expression and tissue fluorescence between xenografts and treatment groups.

RESULTS

Neoadjuvant therapies had no broad impact on EGFR expression (|B|≤ 7.0, p ≥ 0.4) or on mean tissue fluorescence (any tissue type, (|B|≤ 2329.0, p ≥ 0.1). Mean tumor fluorescence was significantly related to EGFR expression (r = 0.26, p = 0.01), as expected.

CONCLUSION

Results suggest that ABY-029 as an EGFR-targeted, fluorescent probe is not negatively impacted by neoadjuvant soft-tissue sarcoma therapies, although validation in humans is required.

Nerve Visualization using Phenoxazine-Based Near-Infrared Fluorophores to Guide Prostatectomy

Fluorescence-guided surgery (FGS) is poised to revolutionize surgical medicine through near-infrared (NIR) fluorophores for tissue- and disease-specific contrast. Clinical open and laparoscopic FGS vision systems operate nearly exclusively at NIR wavelengths. However, tissue-specific NIR contrast agents compatible with clinically available imaging systems are lacking, leaving nerve tissue identification during prostatectomy a persistent challenge. Here, it is shown that combining drug-like molecular design concepts and fluorophore chemistry enabled the production of a library of NIR phenoxazine-based fluorophores for intraoperative nerve-specific imaging. The lead candidate readily delineated prostatic nerves in the canine and iliac plexus in the swine using the clinical da Vinci Surgical System that has been popularized for minimally invasive prostatectomy procedures. These results demonstrate the feasibility of molecular engineering of NIR nerve-binding fluorophores for ready integration into the existing surgical workflow, paving the path for clinical translation to reduce morbidity from nerve injury for prostate cancer patients.

Quantitative pharmacokinetic and biodistribution studies for fluorescent imaging agents

Pharmacokinetics and biodistribution studies are essential for characterizing fluorescent agents in vivo. However, few simple methods based on fluorescence imaging are available that account for tissue optical properties and sample volume differences. We describe a method for simultaneously quantifying mean fluorescence intensity of whole blood and homogenized tissues in glass capillary tubes for two fluorescent agents, ABY-029 and IRDye 680LT, using wide-field imaging and tissue-specific calibration curves. All calibration curves demonstrated a high degree of linearity with mean R2 = 0.99 ± 0.01 and RMSE = 0.12 ± 0.04. However, differences between linear regressions indicate that tissue-specific calibration curves are required for accurate concentration recovery. The lower limit of quantification (LLOQ) for all samples tested was determined to be < 0.3 nM for ABY-029 and < 0.4 nM for IRDye 680LT.

Subsurface fluorescence time-of-flight imaging using a large-format single-photon avalanche diode sensor for tumor depth assessment

Significance

Fluorescence guidance is used clinically by surgeons to visualize anatomical and/or physiological phenomena in the surgical field that are difficult or impossible to detect by the naked eye. Such phenomena include tissue perfusion or molecular phenotypic information about the disease being resected. Conventional fluorescence-guided surgery relies on long, microsecond scale laser pulses to excite fluorescent probes. However, this technique only provides two-dimensional information; crucial depth information, such as the location of malignancy below the tissue surface, is not provided.

Aim

We developed a depth sensing imaging technique using light detection and ranging (LiDAR) time-of-flight (TOF) technology to sense the depth of target tissue while overcoming the influence of tissue optical properties and fluorescent probe concentration.

Approach

The technology is based on a large-format (512 × 512   pixel ), binary, gated, single-photon avalanche diode (SPAD) sensor with an 18 ps time-gate step, synchronized with a picosecond pulsed laser. The fast response of the sensor was developed and tested for its ability to quantify fluorescent inclusions at depth and optical properties in tissue-like phantoms through analytical model fitting of the fast temporal remission data.

Results

After calibration and algorithmic extraction of the data, the SPAD LiDAR technique allowed for sub-mm resolution depth sensing of fluorescent inclusions embedded in tissue-like phantoms, up to a maximum of 5 mm in depth. The approach provides robust depth sensing even in the presence of variable tissue optical properties and separates the effects of fluorescence depth from absorption and scattering variations.

Conclusions

LiDAR TOF fluorescence imaging using an SPAD camera provides both fluorescence intensity images and the temporal profile of fluorescence, which can be used to determine the depth at which the signal is emitted over a wide field of view. The proposed tool enables fluorescence imaging at a higher depth in tissue and with higher spatial precision than standard, steady-state fluorescence imaging tools, such as intensity-based near-infrared fluorescence imaging, optical coherence tomography, Raman spectroscopy, or confocal microscopy. Integration of this technique into a standard surgical tool could enable rapid, more accurate estimation of resection boundaries, thereby improving the surgeon's efficacy and efficiency, and ultimately improving patient outcomes.

An efficient site-selective, dual bioconjugation approach exploiting N-terminal cysteines as minimalistic handles to engineer tailored anti-HER2 affibody conjugates

Site-selective, dual-conjugation approaches for the incorporation of distinct payloads are key for the development of molecularly targeted biomolecules, such as antibody conjugates, endowed with better properties. Combinations of cytotoxic drugs, imaging probes, or pharmacokinetics modulators enabled for improved outcomes in both molecular imaging, and therapeutic settings. We have developed an efficacious dual-bioconjugation strategy to target the N-terminal cysteine of a chemically-synthesized, third-generation anti-HER2 affibody. Such two-step, one-purification approach can be carried out under mild conditions (without chaotropic agents, neutral pH) by means of a slight excess of commercially available N-hydroxysuccinimidyl esters and maleimido-functionalized payloads, to generate dual conjugates displaying drugs (DM1/MMAE) or probes (sulfo-Cy5/biotin) in high yields and purity. Remarkably, the double drug conjugate exhibited an exacerbated cytoxicity against HER2-expressing cell lines as compared to a combination of two monoconjugates, demonstrating a potent synergistic effect. Consistently, affibody-drug conjugates did not decrease the viability of HER2-negative cells, confirming their specificity for the target.

Safety assessment of fluorescently labeled anti-EGFR Nanobodies in healthy dogs

Introduction: Surgical resection is one of the main treatment options for several types of cancer, the desired outcome being complete removal of the primary tumor and its local metastases. Any malignant tissue that remains after surgery may lead to relapsing disease, negatively impacting the patient's quality of life and overall survival. Fluorescence imaging in surgical oncology aims to facilitate full resection of solid tumors through the visualization of malignant tissue during surgery, following the administration of a fluorescent contrast agent. An important class of targeting molecules are Nanobodies® (Nbs), small antigen-binding fragments derived from camelid heavy chain only antibodies. When coupled with a fluorophore, Nbs can bind to a specific receptor and demarcate tumor margins through a fluorescence camera, improving the accuracy of surgical intervention. A widely investigated target for fluorescence-guided surgery is the epidermal growth factor receptor (EGFR), which is overexpressed in several types of tumors. Promising results with the fluorescently labeled anti-EGFR Nb 7D12-s775z in murine models motivated a project employing the compound in a pioneering study in dogs with spontaneous cancer. Methods: To determine the safety profile of the study drug, three healthy purpose-bred dogs received an intravenous injection of the tracer at 5.83, 11.66, and 19.47 mg/m2, separated by a 14-day wash-out period. Physical examination and fluorescence imaging were performed at established time points, and the animals were closely monitored between doses. Blood and urine values were analyzed pre- and 24 h post administration. Results: No adverse effects were observed, and blood and urine values stayed within the reference range. Images of the oral mucosa, acquired with a fluorescence imaging device (Fluobeam®), suggest rapid clearance, which was in accordance with previous in vivo studies. Discussion: These are the first results to indicate that 7D12-s775z is well tolerated in dogs and paves the way to conduct clinical trials in canine patients with EGFR-overexpressing spontaneous tumors.

Dual probe difference specimen imaging for prostate cancer margin assessment

Significance

Positive margin status due to incomplete removal of tumor tissue during radical prostatectomy for high-risk localized prostate cancer requires reoperation or adjuvant therapy, which increases morbidity and mortality. Adverse effects of prostate cancer treatments commonly include erectile dysfunction, urinary incontinence, and bowel dysfunction, making successful initial curative prostatectomy imperative.

Aim

Current intraoperative tumor margin assessment is largely limited to frozen section analysis, which is a lengthy, labor-intensive process that is obtrusive to the clinical workflow within the operating room (OR). Therefore, a rapid method for prostate cancer margin assessment in the OR could improve outcomes for patients.

Approach

Dual probe difference specimen imaging (DDSI), which uses paired antibody-based probes that are labeled with spectrally distinct fluorophores, was shown herein for prostate cancer margin assessment. The paired antibody-based probes consisted of a targeted probe to prostate-specific membrane antigen (PSMA) and an untargeted probe, which were used as a cocktail to stain resected murine tissue specimens including prostate tumor, adipose, muscle, and normal prostate. Ratiometric images (i.e., DDSI) of the difference between targeted and untargeted probe uptake were calculated and evaluated for accuracy using receiver operator characteristic curve analysis with area under the curve values used to evaluate the utility of the DDSI method to detect PSMA positive prostate cancer.

Results

Targeted and untargeted probe uptake was similar between the high and low PSMA expressing tumor due to nonspecific probe uptake after topical administration. The ratiometric DDSI approach showed substantial contrast difference between the PSMA positive tumors and their respective normal tissues (prostate, adipose, muscle). Furthermore, DDSI showed substantial contrast difference between the high PSMA expressing tumors and the minimally PSMA expressing tumors due to the ratiometric correction for the nonspecific uptake patterns in resected tissues.

Conclusions

Previous work has shown that ratiometic imaging has strong predictive value for breast cancer margin status using topical administration. Translation of the ratiometric DDSI methodology herein from breast to prostate cancers demonstrates it as a robust, ratiometric technique that provides a molecularly specific imaging modality for intraoperative margin detection. Using the validated DDSI protocol on resected prostate cancers permitted rapid and accurate assessment of PSMA status as a surrogate for prostate cancer margin status. Future studies will further evaluate the utility of this technology to quantitatively characterize prostate margin status using PSMA as a biomarker.

Paired-agent imaging as a rapid en face margin screening method in Mohs micrographic surgery

Background

Mohs micrographic surgery is a procedure used for non-melanoma skin cancers that has 97-99% cure rates largely owing to 100% margin analysis enabled by en face sectioning with real-time, iterative histologic assessment. However, the technique is limited to small and aggressive tumors in high-risk areas because the histopathological preparation and assessment is very time intensive. To address this, paired-agent imaging (PAI) can be used to rapidly screen excised specimens and identify tumor positive margins for guided and more efficient microscopic evaluation.

Methods

A mouse xenograft model of human squamous cell carcinoma (n = 8 mice, 13 tumors) underwent PAI. Targeted (ABY-029, anti-epidermal growth factor receptor (EGFR) affibody molecule) and untargeted (IRDye 680LT carboxylate) imaging agents were simultaneously injected 3-4 h prior to surgical tumor resection. Fluorescence imaging was performed on main, unprocessed excised specimens and en face margins (tissue sections tangential to the deep margin surface). Binding potential (BP) - a quantity proportional to receptor concentration - and targeted fluorescence signal were measured for each, and respective mean and maximum values were analyzed to compare diagnostic ability and contrast. The BP and targeted fluorescence of the main specimen and margin samples were also correlated with EGFR immunohistochemistry (IHC).

Results

PAI consistently outperformed targeted fluorescence alone in terms of diagnostic ability and contrast-to-variance ratio (CVR). Mean and maximum measures of BP resulted in 100% accuracy, while mean and maximum targeted fluorescence signal offered 97% and 98% accuracy, respectively. Moreover, maximum BP had the greatest average CVR for both main specimen and margin samples (average 1.7 ± 0.4 times improvement over other measures). Fresh tissue margin imaging improved similarity with EGFR IHC volume estimates compared to main specimen imaging in line profile analysis; and margin BP specifically had the strongest concordance (average 3.6 ± 2.2 times improvement over other measures).

Conclusions

PAI was able to reliably distinguish tumor from normal tissue in fresh en face margin samples using the single metric of maximum BP. This demonstrated the potential for PAI to act as a highly sensitive screening tool to eliminate the extra time wasted on real-time pathological assessment of low-risk margins.

Fluorescence molecular optomic signatures improve identification of tumors in head and neck specimens

Background

Fluorescence molecular imaging using ABY-029, an epidermal growth factor receptor (EGFR)-targeted, synthetic Affibody peptide labeled with a near-infrared fluorophore, is under investigation for surgical guidance during head and neck squamous cell carcinoma (HNSCC) resection. However, tumor-to-normal tissue contrast is confounded by intrinsic physiological limitations of heterogeneous EGFR expression and non-specific agent uptake.

Objective

In this preliminary study, radiomic analysis was applied to optical ABY-029 fluorescence image data for HNSCC tissue classification through an approach termed "optomics." Optomics was employed to improve tumor identification by leveraging textural pattern differences in EGFR expression conveyed by fluorescence. The study objective was to compare the performance of conventional fluorescence intensity thresholding and optomics for binary classification of malignant vs. non-malignant HNSCC tissues.

Materials and Methods

Fluorescence image data collected through a Phase 0 clinical trial of ABY-029 involved a total of 20,073 sub-image patches (size of 1.8 × 1.8 mm2) extracted from 24 bread-loafed slices of HNSCC surgical resections originating from 12 patients who were stratified into three dose groups (30, 90, and 171 nanomoles). Each dose group was randomly partitioned on the specimen-level 75%/25% into training/testing sets, then all training and testing sets were aggregated. A total of 1,472 standardized radiomic features were extracted from each patch and evaluated by minimum redundancy maximum relevance feature selection, and 25 top-ranked features were used to train a support vector machine (SVM) classifier. Predictive performance of the SVM classifier was compared to fluorescence intensity thresholding for classifying testing set image patches with histologically confirmed malignancy status.

Results

Optomics provided consistent improvement in prediction accuracy and false positive rate (FPR) and similar false negative rate (FNR) on all testing set slices, irrespective of dose, compared to fluorescence intensity thresholding (mean accuracies of 89% vs. 81%, P = 0.0072; mean FPRs of 12% vs. 21%, P = 0.0035; and mean FNRs of 13% vs. 17%, P = 0.35).

Conclusions

Optomics outperformed conventional fluorescence intensity thresholding for tumor identification using sub-image patches as the unit of analysis. Optomics mitigate diagnostic uncertainties introduced through physiological variability, imaging agent dose, and inter-specimen biases of fluorescence molecular imaging by probing textural image information. This preliminary study provides a proof-of-concept that applying radiomics to fluorescence molecular imaging data offers a promising image analysis technique for cancer detection in fluorescence-guided surgery.

Rapid and Quantitative Intraoperative Pathology-Assisted Surgery by Paired-Agent Imaging-Derived Confidence Map

PURPOSE

In nonmetastatic head and neck cancer treatment, surgical margin status is the most important prognosticator of recurrence and patient survival. Fresh frozen sectioning (FFS) of tissue margins is the standard of care for intraoperative margin assessment. However, FFS is time intensive, and its accuracy is not consistent among institutes. Mapping the epidermal growth factor receptor (EGFR) using paired-agent imaging (PAI) has the potential to provide more consistent intraoperative margin assessment in a fraction of the time as FFS.

PROCEDURES

PAI was carried out through IV injection of an anti-epidermal growth factor receptor (EGFR) affibody molecule (ABY-029, eIND 122,681) and an untargeted IRDye680LT carboxylate. Imaging was performed on 4 µm frozen sections from three oral squamous cell carcinoma xenograft mouse models (n = 24, 8 samples per cell line). The diagnostic ability and tumor contrast were compared between binding potential, targeted, and untargeted images. Confidence maps were constructed based on group histogram-derived tumor probability curves. Tumor differentiability and contrast by confidence maps were evaluated.

RESULTS

PAI outperformed ABY-029 and IRDye 680LT alone, demonstrating the highest individual receiver operating characteristic (ROC) curve area under the curve (PAI AUC: 0.91, 0.90, and 0.79) and contrast-to-noise ratio (PAI CNR: 1, 1.1, and 0.6) for FaDu, Det 562, and A253. PAI confidence maps (PAI CM) maintain high tumor diagnostic ability (PAI CMAUC: 0.91, 0.90, and 0.79) while significantly enhancing tumor contrast (PAI CMCNR: 1.5, 1.3, and 0.8) in FaDu, Det 562, and A253. Additionally, the PAI confidence map allows avascular A253 to be differentiated from a healthy tissue with significantly higher contrast than PAI. Notably, PAI does not require additional staining and therefore significantly reduces the tumor delineation time in a 5 [Formula: see text] 5 mm slice from ~ 35 min to under a minute.

CONCLUSION

This study demonstrated that PAI improved tumor detection in frozen sections with high diagnostic accuracy and rapid analysis times. The novel PAI confidence map improved the contrast in vascular tumors and differentiability in avascular tumors. With a larger database, the PAI confidence map promises to standardize fluorescence imaging in intraoperative pathology-assisted surgery (IPAS).

Identification of a Suitable Untargeted Agent for the Clinical Translation of ABY-029 Paired-Agent Imaging in Fluorescence-Guided Surgery

PURPOSE

Non-specific uptake and retention of molecular targeted agents and heterogeneous tissue optical properties diminish the ability to differentiate between tumor and normal tissues using molecular targeted fluorescent agents. Paired-agent imaging (PAI) can increase the diagnostic ability to detect tumor tissue by mitigating these non-specific effects and providing true molecular contrast by co-administration of an untargeted control imaging agent with a targeted agent. This study evaluates the suitability of available clinically translatable untargeted agents for the translation of PAI in fluorescence-guided surgery using an affibody-based targeted imaging agent (ABY-029).

EXPERIMENTAL

DESIGN: Three untargeted agents that fluoresce near 700 nm and exhibit good clinical safety profiles (methylene blue, IRDye 700DX, and IRDye 680LT) were tested in combination with the clinically tested IRDye 800CW-labeled anti-epidermal growth factor receptor (EGFR) affibody molecule, ABY-029 (eIND 122,681). Properties of the untargeted agent important for human use and integrity of PAI were tested: (1) plasma protein binding; (2) fluorescence signal linearity in in vitro whole blood dilution; (3) in vivo pharmacokinetic matching to targeted agent in negative control tissue; and (4) in vivo diagnostic accuracy of PAI vs single agent imaging (SAI) of ABY-029 alone in orthotopic oral head and neck squamous cell carcinomas.

RESULTS

IRDye 680LT outperformed IRDye 700DX and methylene blue with the highest signal linearity (R² = 0.9998 ± 0.0002, 0.9995 ± 0.0004, 0.91 ± 0.02, respectively), the highest fluorescence yield in whole blood at 1 μM (10^{4.42 ± 0.05}, 10^{3.68 ± 0.09}, 10^{1.9 ± 0.2}, respectively), and the most closely matched ABY-029 pharmacokinetics in EGFR-negative tissues (binding potential error percentage = 0.31% ± 0.37%, 10.25% ± 1.30%, and 8.10% ± 5.37%, respectively). The diagnostic ability of PAI with ABY-029 and IRDye 680LT outperformed conventional SAI with an area-under-the-receiver-operating-characteristic curve (AUC) value of 0.964 vs. 0.854, and 0.978 vs. 0.925 in the Odyssey scanning system and Pearl wide field imaging system, respectively.

CONCLUSION

PAI is a highly promising methodology for increasing detection of tumors in fluorescence-guided surgery. Although not yet clinically approved, IRDye 680LT demonstrates promise as an untargeted agent when paired with ABY-029. The clinical translation of PAI to maximize tumor excision, while minimizing normal tissue removal, could improve both patient survival and life quality.

Improved Discrimination of Tumors with Low and Heterogeneous EGFR Expression in Fluorescence-Guided Surgery Through Paired-Agent Protocols

PURPOSE

The goal of fluorescence-guided surgery (FGS) in oncology is to improve the surgical therapeutic index by enhancing contrast between cancerous and healthy tissues. However, optimal discrimination between these tissues is complicated by the nonspecific uptake and retention of molecular targeted agents and the variance of fluorescence signal. Paired-agent imaging (PAI) employs co-administration of an untargeted imaging agent with a molecular targeted agent, providing a normalization factor to minimize nonspecific and varied signals. The resulting measured binding potential is quantitative and equivalent to in vivo immunohistochemistry of the target protein. This study demonstrates that PAI improves the accuracy of tumor-to-healthy tissue discrimination compared to single-agent imaging for in vivo FGS.

PROCEDURES

PAI using a fluorescent anti-epidermal growth factor receptor (EGFR) affibody molecule (ABY-029, eIND 122,681) with untargeted IRDye 700DX carboxylate was compared to ABY-029 alone in an oral squamous cell carcinoma xenograft mouse model at 3 h after dye administration (n = 30).

RESULTS

PAI significantly enhanced tumor discrimination, as compared to ABY-029 alone in low EGFR-expressing tumors and highly heterogeneous populations including multiple cell lines with varying expression (diagnostic accuracy: 0.908 vs. 0.854 and 0.908 vs. 0.822; and ROC curve AUC: 0.963 vs. 0.909 and 0.957 vs. 0.909, respectively) indicating a potential for universal FGS image thresholds to determine surgical margins. In addition, PAI achieved significantly higher diagnostic ability than ABY-029 alone 0.25-5-h post injection and exhibited a stronger correlation to EGFR expression heterogeneity.

CONCLUSION

The quantitative receptor delineation of PAI promises to improve the surgical therapeutic index of cancer resection in a clinically relevant timeline.

Current and Future Applications of Fluorescence Guidance in Orthopaedic Surgery

Fluorescence-guided surgery (FGS) is an evolving field that seeks to identify important anatomic structures or physiologic phenomena with helpful relevance to the execution of surgical procedures. Fluorescence labeling occurs generally via the administration of fluorescent reporters that may be molecularly targeted, enzyme-activated, or untargeted, vascular probes. Fluorescence guidance has substantially changed care strategies in numerous surgical fields; however, investigation and adoption in orthopaedic surgery have lagged. FGS shows the potential for improving patient care in orthopaedics via several applications including disease diagnosis, perfusion-based tissue healing capacity assessment, infection/tumor eradication, and anatomic structure identification. This review highlights current and future applications of fluorescence guidance in orthopaedics and identifies key challenges to translation and potential solutions.

Use of Freshly Amputated Human Limbs for Pre-Clinical Evaluation of Molecular-Targeted Fluorescent Probes

We have co-developed a first-in-kind model of fluorophore testing in freshly amputated human limbs. Ex vivo human tissue provides a unique opportunity for the testing of pre-clinical fluorescent agents, collection of imaging data, and histopathologic examination in human tissue prior to performing in vivo experiments. Existing pre-clinical fluorescent agent studies rely primarily on animal models, which do not directly predict fluorophore performance in humans and can result in wasted resources and time if an agent proves ineffective in early human trials. Because fluorophores have no desired therapeutic effect, their clinical utility is based solely on their safety and ability to highlight tissues of interest. Advancing to human trials even via the FDA's phase 0/microdose pathway still requires substantial resources, single-species pharmacokinetic testing, and toxicity testing. In a recently concluded study using amputated human lower limbs, we were able to test successfully a nerve-specific fluorophore in pre-clinical development. This study used systemic administration via vascular cannulization and a cardiac perfusion pump. We envision that this model may assist with early lead agent testing selection for fluorophores with various targets and mechanisms.

Quantifying imaging agent binding and dissociation in 3D cancer spheroid tissue culture using paired-agent principles

Binding kinetics play an important role in cancer diagnosis and therapeutics. However, current methods of quantifying binding kinetics fail to consider the three-dimensional environment that drugs and imaging agents experience in biological tissue. In response, a methodology to assay agent binding and dissociation in 3D tissue culture was developed using paired-agent molecular imaging principles. To test the methodology, the uptakes of ABY-029 (an IRDye 800CW-labeled epidermal growth factor receptor (EGFR)-targeted antibody-mimetic) and IRDye 700DX-carboxylate in 3D spheroids were measured in four different human cancer cell lines throughout staining and rinsing. A compartment model (optimized for the application) was then fit to the kinetic curves of both imaging agents to estimate binding and dissociation rate constants of the EGFR targeted ABY-029 agent. A linear correlation was observed between apparent association rate constant (k 3 ) and the receptor concentration experimentally and in simulations (r = 0.99 , p < 0.05 ). Additionally, a similar binding affinity profile compared to a gold standard method was determined by this model. This low-cost methodology to quantify imaging agent or drug binding affinity in clinically relevant 3D tumor spheroid models, can be used to guide timing of imaging in molecular guided surgery and could have implications in drug development.

Progresses in Fluorescence Imaging Guidance for Bone and Soft Tissue Sarcoma Surgery

R0 surgical resection is the preferred treatment for bone and soft tissue sarcoma. However, there is still a lack of precise technology that can visualize bone and soft tissue sarcoma during surgery to assist the surgeon in judging the tumor surgical boundary. Fluorescence imaging technology has been used in the diagnosis of cancer. It is a simple and essentially safe technique that takes no additional time during the operation. Intraoperative fluorescence imaging has potential application prospects in assisting the surgeons in judging the tumor boundary and improving the accuracy of surgical resection. This review mainly starts with clinical studies, animal experimentation, and newly designed probes of intraoperative fluorescence imaging of bone and soft tissue sarcoma, to appraise the application prospects of fluorescence imaging technology in bone and soft tissue sarcoma.

Intraoperative Real-Time Near-Infrared Image-Guided Surgery to Identify Intracranial Meningiomas via Microscope

Meningiomas are a common pathology in the central nervous system requiring complete surgical resection. However, in cases of recurrence and post-irradiation, accurate identification of tumor remnants and a dural tail under bright light remains challenging. We aimed to perform real-time intraoperative visualization of the meningioma and dural tail using a delayed-window indocyanine green (ICG) technique with microscopy. Fifteen patients with intracranial meningioma received 0.5 mg/kg ICG a few hours before observation during the surgery. We used near-infrared (NIR) fluorescence to identify the tumor location. NIR fluorescence could visualize meningiomas in 12 out of 15 cases. Near-infrared visualization during the surgery ranged from 1 to 4 h after the administration of ICG. The mean signal-to-background ratio (SBR) of the intracranial meningioma in delayed-window ICG (DWIG) was 3.3 ± 2.6. The ratio of gadolinium-enhanced T1 tumor signal to the brain (T1BR) (2.5 ± 0.9) was significantly correlated with the tumor SBR (p = 0.016). K^trans, indicating blood–brain barrier permeability, was significantly correlated with tumor SBR (p < 0.0001) and T1BR (p = 0.013) on dynamic contrast-enhanced magnetic resonance imaging (MRI). DWIG demonstrated a sensitivity of 94%, specificity of 38%, positive predictive value (PPV) of 76%, and negative predictive value (NPV) of 75% for meningiomas. This is the first pilot study in which DWIG fluorescence-guided surgery was used to visualize meningioma and dural tail intraoperatively with microscopy. DWIG is comparable with second-window ICG in terms of mean SBR. Gadolinium-enhanced T1 tumor signal may predict NIR fluorescence of the intracranial meningioma. Blood–brain barrier permeability as shown by K^trans on dynamic contrast-enhanced MRI can contribute to gadolinium enhancement on MRI and to ICG retention and tumor fluorescence by NIR.

Refining Glioblastoma Surgery through the Use of Intra-Operative Fluorescence Imaging Agents

Glioblastoma (GBM) is the most aggressive adult brain tumour with a dismal 2-year survival rate of 26-33%. Maximal safe resection plays a crucial role in improving patient progression-free survival (PFS). Neurosurgeons have the significant challenge of delineating normal tissue from brain tumour to achieve the optimal extent of resection (EOR), with 5-Aminolevulinic Acid (5-ALA) the only clinically approved intra-operative fluorophore for GBM. This review aims to highlight the requirement for improved intra-operative imaging techniques, focusing on fluorescence-guided imaging (FGS) and the use of novel dyes with the potential to overcome the limitations of current FGS. The review was performed based on articles found in PubMed an.d Google Scholar, as well as articles identified in searched bibliographies between 2001 and 2022. Key words for searches included 'Glioblastoma' + 'Fluorophore'+ 'Novel' + 'Fluorescence Guided Surgery'. Current literature has favoured the approach of using targeted fluorophores to achieve specific accumulation in the tumour microenvironment, with biological conjugates leading the way. These conjugates target specific parts overexpressed in the tumour. The positive results in breast, ovarian and colorectal tissue are promising and may, therefore, be applied to intracranial neoplasms. Therefore, this design has the potential to produce favourable results in GBM by reducing the residual tumour, which translates to decreased tumour recurrence, morbidity and ultimately, mortality in GBM patients. Several preclinical studies have shown positive results with targeted dyes in distinguishing GBM cells from normal brain parenchyma, and targeted dyes in the Near-Infrared (NIR) emission range offer promising results, which may be valuable future alternatives.

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.

Clinically translatable formulation strategies for systemic administration of nerve-specific probes

Nerves are extremely difficult to identify and are often accidently damaged during surgery, leaving patients with lasting pain and numbness. Herein, a novel near-infrared (NIR) nerve-specific fluorophore, LGW01-08, was utilized for enhanced nerve identification using fluorescence guided surgery (FGS), formulated using clinical translatable strategies. Formulated LGW01-08 was examined for toxicology, pharmacokinetics (PK), and pharmacodynamics (PD) parameters in preparation for future clinical translation. Optimal LGW01-08 imaging doses were identified in each formulation resulting in a 10x difference between the toxicity to imaging dose window. Laparoscopic swine surgery completed using the da Vinci surgical robot (Intuitive Surgical) demonstrated the efficacy of formulated LGW01-08 for enhanced nerve identification. NIR fluorescence imaging enabled clear identification of nerves buried beneath ~3 mm of tissue that were unidentifiable by white light imaging. These studies provide a strong basis for future clinical translation of NIR nerve-specific fluorophores for utility during FGS to improve patient outcomes.

Receptor-Targeted Fluorescence-Guided Surgery With Low Molecular Weight Agents

Cancer surgery remains the primary treatment option for most solid tumors and can be curative if all malignant cells are removed. Surgeons have historically relied on visual and tactile cues to maximize tumor resection, but clinical data suggest that relapse occurs partially due to incomplete cancer removal. As a result, the introduction of technologies that enhance the ability to visualize tumors in the operating room represents a pressing need. Such technologies have the potential to revolutionize the surgical standard-of-care by enabling real-time detection of surgical margins, subclinical residual disease, lymph node metastases and synchronous/metachronous tumors. Fluorescence-guided surgery (FGS) in the near-infrared (NIRF) spectrum has shown tremendous promise as an intraoperative imaging modality. An increasing number of clinical studies have demonstrated that tumor-selective FGS agents can improve the predictive value of fluorescence over non-targeted dyes. Whereas NIRF-labeled macromolecules (i.e., antibodies) spearheaded the widespread clinical translation of tumor-selective FGS drugs, peptides and small-molecules are emerging as valuable alternatives. Here, we first review the state-of-the-art of promising low molecular weight agents that are in clinical development for FGS; we then discuss the significance, application and constraints of emerging tumor-selective FGS technologies.

Recent Advances in the Scaffold Engineering of Protein Binders

In recent years, extensive attention has been given to the generation of new classes of ligand- specific binding proteins to supplement monoclonal antibodies. A combination of protein engineering and display technologies has been used to manipulate non-human antibodies for humanization and stabilization purposes or even the generation of new binding proteins. Engineered protein scaffolds can now be directed against therapeutic targets to treat cancer and immunological disorders. Although very few of these scaffolds have successfully passed clinical trials, their remarkable properties such as robust folding, high solubility, and small size motivate their employment as a tool for biology and applied science studies. Here, we have focused on the generation of new non-Ig binding proteins and single domain antibody manipulation, with a glimpse of their applications.

Fluorescence-Guided Surgery: A Review on Timing and Use in Brain Tumor Surgery

Fluorescence-guided surgery (FGS) allows surgeons to have improved visualization of tumor tissue in the operating room, enabling maximal safe resection of malignant brain tumors. Over the past two decades, multiple fluorescent agents have been studied for FGS, including 5-aminolevulinic acid (5-ALA), fluorescein sodium, and indocyanine green (ICG). Both non-targeted and targeted fluorescent agents are currently being used in clinical practice, as well as under investigation, for glioma visualization and resection. While the efficacy of intraoperative fluorescence in studied fluorophores has been well established in the literature, the effect of timing on fluorophore administration in glioma surgery has not been as well depicted. In the past year, recent studies of 5-ALA use have shown that intraoperative fluorescence may persist beyond the previously studied window used in prior multicenter trials. Additionally, the use of fluorophores for different brain tumor types is discussed in detail, including a discussion of choosing the right fluorophore based on tumor etiology. In the following review, the authors will describe the temporal nature of the various fluorophores used in glioma surgery, what remains uncertain in FGS, and provide a guide for using fluorescence as a surgical adjunct in brain tumor surgery.

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 %).

Candidate Biomarkers for Specific Intraoperative Near-Infrared Imaging of Soft Tissue Sarcomas: A Systematic Review

Simple Summary

Near-infrared imaging of tumors during surgery facilitates the oncologic surgeon to distinguish malignant from healthy tissue. The technique is based on fluorescent tracers binding to tumor biomarkers on malignant cells. Currently, there are no clinically available fluorescent tracers that specifically target soft tissue sarcomas. This review searched the literature to find candidate biomarkers for soft tissue sarcomas, based on clinically used therapeutic antibodies. The search revealed 7 biomarkers: TEM1, VEGFR-1, EGFR, VEGFR-2, IGF-1R, PDGFRα, and CD40. These biomarkers are abundantly present on soft tissue sarcoma tumor cells and are already being targeted with humanized monoclonal antibodies. The conjugation of these antibodies with a fluorescent dye will yield in specific tracers for image-guided surgery of soft tissue sarcomas to improve the success rates of tumor resections.

Abstract

Surgery is the mainstay of treatment for localized soft tissue sarcomas (STS). The curative treatment highly depends on complete tumor resection, as positive margins are associated with local recurrence (LR) and prognosis. However, determining the tumor margin during surgery is challenging. Real-time tumor-specific imaging can facilitate complete resection by visualizing tumor tissue during surgery. Unfortunately, STS specific tracers are presently not clinically available. In this review, STS-associated cell surface-expressed biomarkers, which are currently already clinically targeted with monoclonal antibodies for therapeutic purposes, are evaluated for their use in near-infrared fluorescence (NIRF) imaging of STS. Clinically targeted biomarkers in STS were extracted from clinical trial registers and a PubMed search was performed. Data on biomarker characteristics, sample size, percentage of biomarker-positive STS samples, pattern of biomarker expression, biomarker internalization features, and previous applications of the biomarker in imaging were extracted. The biomarkers were ranked utilizing a previously described scoring system. Eleven cell surface-expressed biomarkers were identified from which 7 were selected as potential biomarkers for NIRF imaging: TEM1, VEGFR-1, EGFR, VEGFR-2, IGF-1R, PDGFRα, and CD40. Promising biomarkers in common and aggressive STS subtypes are TEM1 for myxofibrosarcoma, TEM1, and PDGFRα for undifferentiated soft tissue sarcoma and EGFR for synovial sarcoma.

The Neurosurgeon's Armamentarium for Gliomas: An Update on Intraoperative Technologies to Improve Extent of Resection

Maximal safe resection is the standard of care in the neurosurgical treatment of high-grade gliomas. To aid surgeons in the operating room, adjuvant techniques and technologies centered around improving intraoperative visualization of tumor tissue have been developed. In this review, we will discuss the most advanced technologies, specifically fluorescence-guided surgery, intraoperative imaging, neuromonitoring modalities, and microscopic imaging techniques. The goal of these technologies is to improve detection of tumor tissue beyond what conventional microsurgery has permitted. We describe the various advances, the current state of the literature that have tested the utility of the different adjuvants in clinical practice, and future directions for improving intraoperative technologies.

Noninvasive quantification of target availability during therapy using paired-agent fluorescence tomography

Immuno-oncological treatment strategies that target abnormal receptor profiles of tumors are an increasingly important feature of cancer therapy. Yet, assessing receptor availability (RA) and drug-target engagement, important determinants of therapeutic efficacy, is challenging with current imaging strategies, largely due to the complex nonspecific uptake behavior of imaging agents in tumors. Herein, we evaluate whether a quantitative noninvasive imaging approach designed to compensate for nonspecific uptake, MRI-coupled paired-agent fluorescence tomography (MRI-PAFT), is capable of rapidly assessing the availability of epidermal growth factor receptor (EGFR) in response to one dose of anti-EGFR antibody therapy in orthotopic brain tumor models.

Methods: Mice bearing orthotopic brain tumor xenografts with relatively high EGFR expression (U251) (N=10) or undetectable human EGFR (9L) (N=9) were considered in this study. For each tumor type, mice were either treated with one dose of cetuximab, or remained untreated. All animals were scanned using MRI-PAFT, which commenced immediately after paired-agent administration, and values of RA were recovered using a model-based approach, which uses the entire dynamic sequence of agent uptake, as well as a simplified “snapshot” approach which requires uptake measurements at only two time points. Recovered values of RA were evaluated between groups and techniques. Hematoxylin & eosin (H&E) and immunohistochemical (IHC) staining was performed on tumor specimens from every animal to confirm tumor presence and EGFR status.

Results: In animals bearing EGFR(+) tumors, a significant difference in RA values between treated and untreated animals was observed (RA = 0.24 ± 0.15 and 0.61 ± 0.18, respectively, p=0.027), with an area under the curve - receiver operating characteristic (AUC-ROC) value of 0.92. We did not observe a statistically significant difference in RA values between treated and untreated animals bearing EGFR(-) tumors (RA = 0.18 ± 0.19 and 0.27 ± 0.21, respectively; p = 0.89; AUC-ROC = 0.55), nor did we observe a difference between treated EGFR(+) tumors compared to treated and untreated EGFR(-) tumors. Notably, the snapshot paired-agent strategy quantified drug-receptor engagement within just 30 minutes of agent administration. Examination of the targeted agent alone showed no capacity to distinguish tumors either by treatment or receptor status, even 24h after agent administration.

Conclusions: This study demonstrated that a noninvasive imaging strategy enables rapid quantification of receptor availability in response to therapy, a capability that could be leveraged in preclinical drug development, patient stratification, and treatment monitoring.

Phase 0/microdosing approaches: time for mainstream application in drug development?

Phase 0 approaches - which include microdosing - evaluate subtherapeutic exposures of new drugs in first-in-human studies known as exploratory clinical trials. Recent progress extends phase 0 benefits beyond assessment of pharmacokinetics to include understanding of mechanism of action and pharmacodynamics. Phase 0 approaches have the potential to improve preclinical candidate selection and enable safer, cheaper, quicker and more informed developmental decisions. Here, we discuss phase 0 methods and applications, highlight their advantages over traditional strategies and address concerns related to extrapolation and developmental timelines. Although challenges remain, we propose that phase 0 approaches be at least considered for application in most drug development scenarios.

Dual-agent fluorescent labeling of soft-tissue sarcomas improves the contrast based upon targeting both interstitial and cellular components of the tumor milieu

BACKGROUND

Current practices for fluorescence-guided cancer surgery utilize a single fluorescent agent, but homogeneous distribution throughout the tumor is difficult to achieve. We hypothesize that administering a perfusion and a molecular-targeted agent at their optimal administration-to-imaging time will improve whole-tumor contrast.

EXPERIMENTAL DESIGN

Mice bearing subcutaneous xenograft human synovial sarcomas were administered indocyanine green (ICG) (3 mg/kg) or ABY-029 (48.7 μg/kg)-an epidermal growth factor receptor-targeted Affibody molecule-alone or in combination. Fluorescence contrast and signal distribution were compared between treatment groups. Two commercial fluorescence imaging systems were tested for simultaneous imaging of ICG and ABY-029.

RESULTS

ABY-029 has a moderate positive correlation with viable tumor (ρ = 0.2 ± 0.4), while ICG demonstrated a strong negative correlation (ρ = -0.6 ± 0.1). The contrast-to-variance ratio was highest in the ABY-029 +ICG (2.5 ± 0.8), compared to animals that received ABY-029 (2.3 ± 0.8) or ICG (2.0 ± 0.5) alone. Moreover, the combination of ABY-029 + ICG minimizes the correlation between viable tumor and fluorescence intensity (ρ = -0.1 ± 0.2) indicating the fluorescence signal distribution is more homogeneous throughout the tumor milieu.

CONCLUSION

Dual-agent imaging utilizing a single channel in a commercial fluorescence-guided imaging system tailored for IRDye 800CW is a promising method to increase tumor contrast in a clinical setting.

Near-infrared nerve-binding fluorophores for buried nerve tissue imaging

Nerve-binding fluorophores with near-infrared (NIR; 650 to 900 nm) emission could reduce iatrogenic nerve injury rates by providing surgeons precise, real-time visualization of the peripheral nervous system. Unfortunately, current systemically administered nerve contrast agents predominantly emit at visible wavelengths and show nonspecific uptake in surrounding tissues such as adipose, muscle, and facia, thus limiting detection to surgically exposed surface-level nerves. Here, a focused NIR fluorophore library was synthesized and screened through multi-tiered optical and pharmacological assays to identify nerve-binding fluorophore candidates for clinical translation. NIR nerve probes enabled micrometer-scale nerve visualization at the greatest reported tissue depths (~2 to 3 mm), a feat unachievable with previous visibly emissive contrast agents. Laparoscopic fluorescent surgical navigation delineated deep lumbar and iliac nerves in swine, most of which were invisible in conventional white-light endoscopy. Critically, NIR oxazines generated contrast against all key surgical tissue classes (muscle, adipose, vasculature, and fascia) with nerve signal-to-background ratios ranging from ~2 (2- to 3-mm depth) to 25 (exposed nerve). Clinical translation of NIR nerve-specific agents will substantially reduce comorbidities associated with surgical nerve damage.

Repurposing Molecular Imaging and Sensing for Cancer Image-Guided Surgery

Gone are the days when medical imaging was used primarily to visualize anatomic structures. The emergence of molecular imaging (MI), championed by radiolabeled ¹⁸F-FDG PET, has expanded the information content derived from imaging to include pathophysiologic and molecular processes. Cancer imaging, in particular, has leveraged advances in MI agents and technology to improve the accuracy of tumor detection, interrogate tumor heterogeneity, monitor treatment response, focus surgical resection, and enable image-guided biopsy. Surgeons are actively latching on to the incredible opportunities provided by medical imaging for preoperative planning, intraoperative guidance, and postoperative monitoring. From label-free techniques to enabling cancer-selective imaging agents, image-guided surgery provides surgical oncologists and interventional radiologists both macroscopic and microscopic views of cancer in the operating room. This review highlights the current state of MI and sensing approaches available for surgical guidance. Salient features of nuclear, optical, and multimodal approaches will be discussed, including their strengths, limitations, and clinical applications. To address the increasing complexity and diversity of methods available today, this review provides a framework to identify a contrast mechanism, suitable modality, and device. Emerging low-cost, portable, and user-friendly imaging systems make the case for adopting some of these technologies as the global standard of care in surgical practice.

Effect of preoperative cancer treatment on epidermal growth factor receptor (EGFR) receptor expression level in ABY-029 guided sarcoma surgery

Surgical excision via wide local excision (WLE) of the primary sarcoma tumor is a mainstay of treatment due to the limited effectiveness of chemotherapy and radiation. Even with attempts at WLE, 22-34% of the patient will be diagnosed with a positive margin by the pathologist, necessitating additional radiation or surgery. Recent studies have demonstrated reduced local recurrence when using fluorescence-guided surgery (FGS) to detect residual sarcoma following attempted WLE. ABY-029 is an anti-EGFR Affibody® molecule labeled with IRDye800CW that is currently under Phase 0 human trial for FGS. To date, several studies have been performed to evaluate ABY-029 signal intensity in untreated human sarcoma xenografts; however, many patients undergoing cancer surgery have received pre-operative radiation and/or chemotherapy, which can affect tissue properties and tumor molecule expression level. Determining the effects of radiation and chemotherapy exposure on fluorophore binding in sarcomas may influence best practices in implementing FGS for sarcoma. In this project, fluorophore signal intensities in tumor and surrounding tissue were measured and compared to the receptor concentration determined by immunohistochemistry. Here, we report the result for one EGFR positive synovial sarcoma cell lines, SW982. Four groups of human dose equivalent therapies - control, radiation, chemotherapy (Doxorubicin) and radiation followed by chemotherapy - were given to the tumor-bearing mice. The difference between groups can be used to determine the effects of preoperative sarcoma therapies on EGFR expression, ABY-029 uptake, and optical properties of tissues.

Task-based evaluation of fluorescent-guided cancer surgery as a means of identifying optimal imaging agent properties in the context of variability in tumor- and healthy-tissue physiology

Fluorescent molecular-guided surgery (FGS) is at a tipping point in terms of clinical approval and adoption in a number cancer applications, with ongoing phase 0 and phase 1 clinical trials being carried out in a wide range of cancers using a wide range of agents. The pharmacokinetics of each of these agents and the physiology of these cancers can differ vastly on a patient-to-patient basis, bringing to question: how can one fairly compare different methodologies (defined as the combination of imaging agent, system, and protocol) and how can existing methodologies be further optimized? To this point, little methodology comparison has been carried out, and the majority of FGS optimization has concerned system development-on the level of maximizing signal-to-noise, dynamic detection range, and sensitivity-independently from traditional agent development-in terms of fluorophore brightness, toxicity, solubility, and binding affinity and specificity. Here we propose an inclusion of tumor and healthy tissue physiology (blood flow, vascular permeability, specific and nonspecific binding sites, extracellular matrix, interstitial pressure, etc…) variability into the optimization process and re-establish well-described task-based metrics for methodology optimization and comparing quality of one methodology to another. Two salient conclusions were identified: (1) contrast-to-background variability is a simple metric that correlates with difficult-to-carry-out task-based metrics for comparing methodologies, and (2) paired-agent imaging protocols offer unique advantages over single-imaging-agent studies for mitigating confounding tumor and background physiology variability.

Perspectives on the Phase 0 clinical trial of microdose administration of ABY-029 for fluorescence guided surgery: Stability testing

ABY-029, an anti-epidermal growth factor receptor (EGFR) Affibody molecule labeled with IRDye 800CW, has been used in three Phase 0 microdosing clinical trials for fluorescence guided surgery. In May of 2019, the clinical trials were put on hold because the ABY-029 produced under Good Manufacturing Practices (GMP) for human administration had come to the end of term in which the drug product was known to be stable. Stability testing was halted due to limitations in supply of a suitable reference standard and a required test product being discontinued from commercial sale. In order to complete the remaining patients in the three clinical trials, new stability tests were developed and the GMP batch of ABY-029 drug product tested under the new protocols. The GMP batch of ABY-029 passed all stability tests under the new protocols and the Federal Drug Administration (FDA) has given permission to complete the remaining patients with stability testing of ABY-029 performed for each patient. The tests developed and used to test ABY-029 drug product stability are described here.

Fluorescence Image-Guided Surgery - a Perspective on Contrast Agent Development

In the past several decades, a number of novel fluorescence image-guided surgery (FGS) contrast agents have been under development, with many in clinical translation and undergoing clinical trials. In this review, we have identified and summarized the contrast agents currently undergoing clinical translation. In total, 39 novel FGS contrast agents are being studied in 85 clinical trials. Four FGS contrast agents are currently being studied in phase III clinical trials and are poised to reach FDA approval within the next two to three years. Among all novel FGS contrast agents, a wide variety of probe types, targeting mechanisms, and fluorescence properties exists. Clinically available FGS imaging systems have been developed for FDA approved FGS contrast agents, and thus further clinical development is required to yield FGS imaging systems tuned for the variety of contrast agents in the clinical pipeline. Additionally, study of current FGS contrast agents for additional disease types and development of anatomy specific contrast agents is required to provide surgeons FGS tools for all surgical specialties and associated comorbidities. The work reviewed here represents a significant effort from many groups and further development of this promising technology will have an enormous impact on surgical outcomes across all specialties.

Fluorescence molecular imaging for identification of high-grade dysplasia in patients with head and neck cancer

OBJECTIVE

High-grade dysplasia is associated with a risk of malignant transformation, and it is necessary to distinguish from normal epithelium or low-grade dysplasia, especially in the intraoperative setting. We hypothesize that an anti-epidermal growth factor receptor (EGFR) contrast agent can be used to differentiate high-grade dysplasia from low-grade dysplasia and normal epithelium.

MATERIALS AND METHODS

Patients with biopsy proven head and neck squamous cell carcinoma (HNSCC) were enrolled in a clinical trial using systemically injected fluorescently labeled anti-EGFR antibody (panitumumab-IRDye800CW) (NCT02415881). Paraffin embedded tumor specimens from 11 patients were evaluated by fluorescence histopathology. Hematoxylin and eosin (H&E) slides were reviewed by a board-certified pathologist, and regions of invasive squamous cell carcinoma, high-grade dysplasia and low-grade dysplasia were delineated. EGFR expression was assessed for each patient by way of immunohistochemistry.

RESULTS

11 patients were included in the study with a total of 219 areas on tissue sections analyzed; 68 normal epithelium, 53 low-grade dysplasia, 48 high-grade dysplasia, and 50 malignant regions. The signal-to-background ratio (SBR) increased proportionally with increasing grade of dysplasia; normal epithelium (1.5 ± 0.1), low-grade dysplasia (1.8 ± 0.1), high-grade dysplasia: (2.3 ± 0.2). High-grade dysplasia had a significantly higher SBR when compared to normal or low-grade dysplasia (p < 0.05). Fluorescence histopathology positively correlated with EGFR expression by immunohistochemistry, which also increased proportionally with increasing degree of dysplasia.

CONCLUSION

Molecular imaging with an anti-EGFR agent can successfully discriminate high-grade dysplastic lesions from low-grade dysplasia and normal epithelium.

Elucidating the kinetics of sodium fluorescein for fluorescence-guided surgery of glioma

OBJECTIVE

The use of the optical contrast agent sodium fluorescein (NaFl) to guide resection of gliomas has been under investigation for decades. Although this imaging strategy assumes the agent remains confined to the vasculature except in regions of blood-brain barrier (BBB) disruption, clinical studies have reported significant NaFl signal in normal brain tissue, limiting tumor-to-normal contrast. A possible explanation arises from earlier studies, which reported that NaFl exists in both pure and protein-bound forms in the blood, the former being small enough to cross the BBB. This study aims to elucidate the kinetic binding behavior of NaFl in circulating blood and its effect on NaFl accumulation in brain tissue and tumor contrast. Additionally, the authors examined the blood and tissue kinetics, as well as tumor uptake, of a pegylated form of fluorescein selected as a potential optical analog of gadolinium-based MRI contrast agents.

METHODS

Cohorts of mice were administered one of the following doses/forms of NaFl: 1) high human equivalent dose (HED) of NaFl, 2) low HED of NaFl, or 3) pegylated form of fluorescein. In each cohort, groups of animals were euthanized 15, 30, 60, and 120 minutes after administration for ex vivo analysis of fluorescein fluorescence. Using gel electrophoresis and fluorescence imaging of blood and brain specimens, the authors quantified the temporal kinetics of bound NaFl, unbound NaFl, and pegylated fluorescein in the blood and normal brain tissue. Finally, they compared tumor-to-normal contrast for NaFl and pegylated-fluorescein in U251 glioma xenografts.

RESULTS

Administration of NaFl resulted in the presence of unbound and protein-bound NaFl in the circulation, with unbound NaFl constituting up to 70% of the signal. While protein-bound NaFl was undetectable in brain tissue, unbound NaFl was observed throughout the brain. The observed behavior was time and dose dependent. The pegylated form of fluorescein showed minimal uptake in brain tissue and improved tumor-to-normal contrast by 38%.

CONCLUSIONS

Unbound NaFl in the blood crosses the BBB, limiting the achievable tumor-to-normal contrast and undermining the inherent advantage of tumor imaging in the brain. Dosing and incubation time should be considered carefully for NaFl-based fluorescence-guided surgery (FGS) of glioma. A pegylated form of fluorescein showed more favorable normal tissue kinetics that translated to higher tumor-to-normal contrast. These results warrant further development of pegylated-fluorescein for FGS of glioma.