Improved Debulking of Peritoneal Tumor Implants by Near-Infrared Fluorescent Nanobody Image Guidance in an Experimental Mouse Model

Promising Diagnostic and Therapeutic Approaches Based on VHHs for Cancer Management

The discovery of the distinctive structure of heavy chain-only antibodies in species belonging to the Camelidae family has elicited significant interest in their variable antigen binding domain (VHH) and gained attention for various applications, such as cancer diagnosis and treatment. This article presents an overview of the characteristics, advantages, and disadvantages of VHHs as compared to conventional antibodies, and their usage in diverse applications. The singular properties of VHHs are explained, and several strategies that can augment their utility are outlined. The preclinical studies illustrating the diagnostic and therapeutic efficacy of distinct VHHs in diverse formats against solid cancers are summarized, and an overview of the clinical trials assessing VHH-based agents in oncology is provided. These investigations demonstrate the enormous potential of VHHs for medical research and healthcare.

The GEM-handle as convenient labeling strategy for bimodal single-domain antibody-based tracers carrying 99mTc and a near-infrared fluorescent dye for intra-operative decision-making

Intra-operative fluorescence imaging has demonstrated its ability to improve tumor lesion identification. However, the limited tissue penetration of the fluorescent signals hinders the detection of deep-lying or occult lesions. Integrating fluorescence imaging with SPECT and/or intra-operative gamma-probing synergistically combines the deep tissue penetration of gamma rays for tumor localization with the precision of fluorescence imaging for precise tumor resection. In this study, we detail the use of a genetically encoded multifunctional handle, henceforth referred to as a GEM-handle, for the development of fluorescent/radioactive bimodal single-domain antibody (sdAb)-based tracers. A sdAb that targets the urokinase plasminogen activator receptor (uPAR) was engineered to carry a GEM-handle containing a carboxy-terminal hexahistidine-tag and cysteine-tag. A two-step labeling strategy was optimized and applied to site-specifically label IRDye800CW and 99mTc to the sdAb. Bimodal labeling of the sdAbs proved straightforward and successful. 99mTc activity was however restricted to 18.5 MBq per nmol fluorescently-labeled sdAb to prevent radiobleaching of IRDye800CW without impeding SPECT/CT imaging. Subsequently, the in vivo biodistribution and tumor-targeting capacity of the bimodal tracer were evaluated in uPAR-positive tumor-bearing mice using SPECT/CT and fluorescence imaging. The bimodal sdAb showed expected renal background signals due to tracer clearance, along with slightly elevated non-specific liver signals. Four hours post-injection, both SPECT/CT and fluorescent images achieved satisfactory tumor uptake and contrast, with significantly higher values observed for the anti-uPAR bimodal sdAb compared to a control non-targeting sdAb. In conclusion, the GEM-handle is a convenient method for designing and producing bimodal sdAb-based tracers with adequate in vivo characteristics.

Nanobodies: Robust miniprotein binders in biomedicine

Variable domains of heavy chain-only antibodies (VHH), also known as nanobodies (Nbs), are monomeric antigen-binding domains derived from the camelid heavy chain-only antibodies. Nbs are characterized by small size, high target selectivity, and marked solubility and stability, which collectively facilitate high-quality drug development. In addition, Nbs are readily expressed from various expression systems, including E. coli and yeast cells. For these reasons, Nbs have emerged as preferred antibody fragments for protein engineering, disease diagnosis, and treatment. To date, two Nb-based therapies have been approved by the U.S. Food and Drug Administration (FDA). Numerous candidates spanning a wide spectrum of diseases such as cancer, immune disorders, infectious diseases, and neurodegenerative disorders are under preclinical and clinical investigation. Here, we discuss the structural features of Nbs that allow for specific, versatile, and strong target binding. We also summarize emerging technologies for identification, structural analysis, and humanization of Nbs. Our main focus is to review recent advances in using Nbs as a modular scaffold to facilitate the engineering of multivalent polymers for cutting-edge applications. Finally, we discuss remaining challenges for Nb development and envision new opportunities in Nb-based research.

Near-Infrared Fluorescence Imaging of Pancreatic Cancer Using a Fluorescently Labelled Anti-CEA Nanobody Probe: A Preclinical Study

Molecular fluorescence-guided surgery using near-infrared light has the potential to improve the rate of complete resection of cancer. Typically, monoclonal antibodies are being used as targeting moieties, however smaller fragments, such as single-domain antibodies (i.e., Nanobodies®) improve tumor specificity and enable tracer injection on the same day as surgery. In this study, the feasibility of a carcinoembryonic antigen-targeting Nanobody (NbCEA5) conjugated to two zwitterionic dyes (ZW800-1 Forte [ZW800F] and ZW800-1) for visualization of pancreatic ductal adenocarcinoma (PDAC) was investigated. After site-specific conjugation of NbCEA5 to the zwitterionic dyes, binding specificity was evaluated on human PDAC cell lines with flow cytometry. A dose escalation study was performed for both NbCEA5-ZW800F and NbCEA5-ZW800-1 in mice with subcutaneously implanted pancreatic tumors. Fluorescence imaging was performed up to 24 h after intravenous injection. Furthermore, the optimal dose for NbCEA5-ZW800-1 was injected in mice with orthotopically implanted pancreatic tumors. A dose-escalation study showed superior mean fluorescence intensities for NbCEA5-ZW800-1 compared to NbCEA5-ZW800F. In the orthotopic tumor models, NbCEA5-ZW800-1 accumulated specifically in pancreatic tumors with a mean in vivo tumor-to-background ratio of 2.4 (SD = 0.23). This study demonstrated the feasibility and potential advantages of using a CEA-targeted Nanobody conjugated to ZW800-1 for intraoperative PDAC imaging.

Splenectomy in epithelial ovarian cancer surgery

OBJECTIVE

Splenectomy is performed in 4-32% of cytoreductive surgeries for ovarian cancer. The objective of our study was to assess splenectomy and evaluate its impact on overall and disease-free survival.

METHODS

We conducted a retrospective single-center study between January 2000 and December 2016. Patients who underwent a cytoreduction for epithelial ovarian cancer, regardless of stage and surgical approach, were eligible for the study. Patients deemed not operable were excluded from the study. Patients were stratified into two groups, splenectomy or no splenectomy. A univariate analysis followed by a multivariate analysis was conducted to evaluate the postoperative complications after splenectomy and the overall and disease-free survival.

RESULTS

This cohort included 464 patients. Disease stages, peritoneal carcinomatosis scores, and the rate of radical surgery (Pomel classification) were significantly higher in the splenectomy group, p=0.04, p<0.0001, and p<0.001, respectively. However, no significant difference was found in the rate of complete cytoreduction between the two groups (p=0.26) after multivariate analysis. In univariate analysis, splenectomy was significantly associated with extensive surgical procedures. In multivariate analysis, the two more prevalent complications in the splenectomy group were the risk of abdominopelvic lymphocele (overall response (OR) =4.2; p=0.01) and blood transfusion (OR=2.4; p=0.008). The average length of hospital stay was significantly longer in the splenectomy group, 17.4 vs 14.6 days (p<0.0001). The delay in adjuvant chemotherapy was longer in the splenectomy group (p=0.001). There was no significant difference in overall and disease-free survival (p=0.09) and (p=0.79), respectively.

CONCLUSION

Splenectomy may be considered an acceptable and safe procedure; however, with no impact on overall or disease-free survival. In addition, it is associated with longer hospital stay and longer time to chemotherapy.

Near-infrared-dye labeled tumor vascular-targeted dimer GEBP11 peptide for image-guided surgery in gastric cancer

Introduction

Positive resection margins occur in about 2.8%-8.2% gastric cancer surgeries and is associated with poor prognosis. Intraoperative guidance using Nearinfrared (NIR) fluorescence imaging is a promising technique for tumor detection and margin assessment. The goal of this study was to develop a tumor-specific probe for real-time intraoperative NIR fluorescence imaging guidance.

Methods

The tumor vascular homing peptide specific for gastric cancer, GEBP11, was conjugated with a near-infrared fluorophore, Cy5.5. The binding specificity of the GEBP11 probes to tumor vascular endothelial cells were confirmed by immunofluorescent staining. The ability of the probe to detect tumor lesions was evaluated in two xenograft models. An orthotopic gastric cancer xenograft model was used to evaluate the efficacy of the GEBP11 NIR probes in real-time surgical guidance.

Results

In vitro assay suggested that both mono and dimeric GEBP11 NIR probes could bind specifically to tumor vascular epithelial cells, with dimeric peptides showed better affinity. In tumor xenograft mice, live imaging suggested that comparing with free Cy5.5 probe, significantly stronger NIR signals could be detected at the tumor site at 24-48h after injection of mono or dimeric GEBP11 probes. Dimeric GEBP11 probe showed prolonged and stronger NIR signals than mono GEBP11 probe. Biodistribution assay suggested that GEBP11 NIR probes were enriched in gastric cancer xenografts. Using dimeric GEBP11 NIR probes in real-time surgery, the tumor margins and peritoneal metastases could be clearly visualized. Histological examination confirmed the complete resection of the tumor.

Conclusion

(GEBP11)2-ACP-Cy5.5 could be a potential useful probe for intraoperative florescence guidance in gastric cancer surgery.

Emerging applications of nanobodies in cancer therapy

Cancer is a heterogeneous disease, requiring treatment tailored to the unique phenotype of the patient's tumor. Monoclonal antibodies (mAbs) and variants thereof have enabled targeted therapies to selectively target cancer cells. Cancer cell-specific mAbs have been used for image-guided surgery and targeted delivery of radionuclides or toxic agents, improving classical treatment strategies. Cancer cell-specific mAbs can further inhibit tumor cell growth or can stimulate immune-mediated destruction of cancer cells, a feature that has also been achieved through mAb-mediated manipulation of immune cells and pathways. Drawbacks of mAbs and their variants, together with the discovery of camelid heavy chain-only antibodies and the many advantageous features of their variable domains, referred to as V_HHs, single domain antibodies or nanobodies (Nbs), resulted in the exploration of Nbs as an alternative targeting moiety. We therefore review the state-of-the-art as well as novel exploitation strategies of Nbs for targeted cancer therapy.

Fluorescent Anti-CEA Nanobody for Rapid Tumor-Targeting and Imaging in Mouse Models of Pancreatic Cancer

Tumor-specific targeting with fluorescent probes can enhance contrast for identification of cancer during surgical resection and visualize otherwise invisible tumor margins. Nanobodies are the smallest naturally-occurring antigen-binding molecules with rapid pharmacokinetics. The present work demonstrates the efficacy of a fluorescent anti-CEA nanobody conjugated to an IR800 dye to target and label patient derived pancreatic cancer xenografts. After intravenous administration, the probe rapidly localized to the pancreatic cancer tumors within an hour and had a tumor-to-background ratio of 2.0 by 3 h. The fluorescence signal was durable over a prolonged period of time. With the rapid kinetics afforded by fluorescent nanobodies, both targeting and imaging can be performed on the same day as surgery.

Engineering nanobodies for next-generation molecular imaging

In recent years, nanobodies have emerged as ideal imaging agents for molecular imaging. Molecular nanobody imaging combines the specificity of nanobodies with the sensitivity of state-of-the-art molecular imaging modalities, such as positron emission tomography (PET). Given that modifications of nanobodies alter their pharmacokinetics (PK), the engineering strategies that combine nanobodies with radionuclides determine the effectiveness, reliability, and safety of the molecular imaging probes. In this review, we introduce conjugation strategies that have been applied to nanobodies, including random conjugation, ^99mTc tricarbonyl chemistry, sortase A-mediated site-specific conjugation, maleimide-cysteine chemistry, and click chemistries. We also summarize the latest advances in nanobody tracers, emphasizing their preclinical and clinical use. In addition, we elaborate on nanobody-based near-infrared fluorescence (NIRF) imaging and image-guided surgery.

Nanobodies as molecular imaging probes

Camelidae derived single-domain antibodies (sdAbs), commonly known as nanobodies (Nbs), are the smallest antibody fragments with full antigen-binding capacity. Owing to their desirable properties such as small size, high specificity, strong affinity, excellent stability, and modularity, nanobodies are on their way to overtake conventional antibodies in terms of popularity. To date, a broad range of nanobodies have been generated against different molecular targets with applications spanning basic research, diagnostics, and therapeutics. In the field of molecular imaging, nanobody-based probes have emerged as a powerful tool. Radioactive or fluorescently labeled nanobodies are now used to detect and track many targets in different biological systems using imaging techniques. In this review, we provide an overview of the use of nanobodies as molecular probes. Additionally, we discuss current techniques for the generation, conjugation, and intracellular delivery of nanobodies.

Use of an antagonist of HMGB1 in mice affected by malignant mesothelioma: a preliminary ultrasound and optical imaging study

Background

Malignant mesothelioma (MM) is an aggressive tumor, with a poor prognosis, usually unresectable due to late diagnosis, mainly treated with chemotherapy. BoxA, a truncated form of “high mobility group box 1” (HMGB1), acting as an HMGB1 antagonist, might exert a defensive action against MM. We investigated the potential of BoxA for MM treatment using experimental 40-MHz ultrasound and optical imaging (OI) in a murine model.

Methods

Murine MM cells infected with a lentiviral vector expressing the luciferase gene were injected into the peritoneum of 14 BALB/c mice (7 × 10⁴ AB1-B/c-LUC cells). These mice were randomized to treatment with BoxA (n = 7) or phosphate-buffered saline (controls, n = 7). The experiment was repeated with 40 mice divided into two groups (n = 20 + 20) and treated as above to confirm the result and achieve greater statistical power. Tumor presence was investigated by experimental ultrasound and OI; suspected peritoneal masses underwent histopathology and immunohistochemistry examination.

Results

In the first experiment, none of the 7 controls survived beyond day 27, whereas 4/7 BoxA-treated mice (57.1%) survived up to day 70. In the second experiment, 6/20 controls (30.0%) and 16/20 BoxA-treated mice (80.0%) were still alive at day 34 (p = 0.004). In both experiments, histology confirmed the malignant nature of masses detected using experimental ultrasound and OI.

Conclusion

In our preclinical experience on a murine model, BoxA seems to exert a protective role toward MM. Both experimental ultrasound and OI proved to be reliable techniques for detecting MM peritoneal masses.

Fundamentals and developments in fluorescence-guided cancer surgery

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

Design and Validation of Site-Specifically Labeled Single-Domain Antibody-Based Tracers for in Vivo Fluorescence Imaging and Image-Guided Surgery

Near-infrared fluorescence molecular imaging has become an established preclinical technique to investigate molecular processes in vivo and to study novel therapies. Furthermore, fluorescence molecular imaging is gaining significant interest from clinicians as an intra-operative guidance tool. This technique makes use of targeted fluorescent tracers as contrast agents that recognize specific biomarkers expressed at the site of disease. Single-domain antibodies have shown to possess excellent properties for in vivo imaging in comparison to conventional antibodies. In this chapter, we describe a method for site-specific conjugation of a near-infrared fluorophore to single-domain antibodies by exploiting cysteine-maleimide chemistry. As opposed to random conjugation, site-specific conjugation results in a homogenously labeled fluorescent tracer and avoids inference with antigen binding.

Lyophilization of NOTA-sdAbs: First step towards a cold diagnostic kit for 68Ga-labeling

Lyophilization is commonly used in the production of pharmaceutical compounds to increase the stability of the Active Pharmaceutical Ingredient (API) by removing solvents. This study investigates the possibility to lyophilize an anti-HER2 and an anti-MMR single-domain antibody fragment (sdAb)-based precursor as a first step in the development of a diagnostic kit for PET imaging.

METHODS

NOTA-sdAb precursors have been lyophilized with the following formulation: 100 µg NOTA-sdAb in 0.1 M NaOAc (NaOAc), 5% (w/v%) mannitol-sucrose mix at a 2:1 ratio and 0.1 mg/mL polysorbate 80. During development of the formulation and drying cycle, factors such as cake appearance, glass transition temperature and residual moisture were analyzed to ensure qualitative and stable lyophilized samples. Stability studies of lyophilized precursor were conducted up to 18 months after storage at 2-8 °C by evaluating the precursor integrity, aggregation, functionality and ⁶⁸Ga-labeling efficiency. A comparative biodistribution study (lyophilized vs non-lyophilized precursor) was conducted in wild type mice (n = 3) and in tumor bearing mice (n = 6).

RESULTS

The lyophilized NOTA-anti-HER2 precursor shows consistent stability data in vitro for up to 12 months at 2-8 °C in three separate batches, with results indicating stability even for up to T18m. No aggregation, degradation or activity loss was observed. Radiochemical purity after ⁶⁸Ga-labeling is consistent over a period of 12 months (RCP ≥ 95% at T12m). In vivo biodistribution analyses show a typical [⁶⁸Ga]Ga-NOTA-anti-HER2 sdAb distribution profile and a comparable tumor uptake for the lyophilized compound vs non-lyophilized (5.5% vs 5.7 %IA/g, respectively). In vitro results of lyophilized NOTA-anti-MMR precursor indicates stability for up to 18 months, while in vivo data show a comparable tumor uptake (2.5% vs 2.8 %IA/g, respectively) and no significant difference in kidney retention (49.4% vs 47.5 %IA/g, respectively).

CONCLUSION

A formulation and specific freeze-drying cycle were successfully developed to lyophilize NOTA-sdAb precursors for long-term storage at 2-8 °C. In vivo data show no negative impact of the lyophilization process on the in vivo behavior or functionality of the lyophilized precursor. These results highlight the potential to develop a kit for the preparation of ⁶⁸Ga-sdAb-based radiopharmaceuticals.

Camelid Single-Domain Antibodies for the Development of Potent Diagnosis Platforms

The distinct biophysical and pharmaceutical properties of camelid single-domain antibodies, referred to as VHHs or nanobodies, are associated with their nanometric dimensions, elevated stability, and antigen recognition capacity. These biomolecules can circumvent a number of diagnostic system limitations, especially those related to the size and stability of conventional immunoglobulins currently used in enzyme-linked immunosorbent assays and point-of-care, electrochemical, and imaging assays. In these formats, VHHs are directionally conjugated to different molecules, such as metallic nanoparticles, small peptides, and radioisotopes, which demonstrates their comprehensive versatility. Thus, the application of VHHs in diagnostic systems range from the identification of cancer cells to the detection of degenerative disease biomarkers, viral antigens, bacterial toxins, and insecticides. The improvements of sensitivity and specificity are among the central benefits resulting from the use of VHHs, which are indispensable parameters for high-quality diagnostics. Therefore, this review highlights the main biotechnological advances related to camelid single-domain antibodies and their use in in vitro and in vivo diagnostic approaches for human health.

Nanobodies: new avenue to treat kidney disease

Current therapeutic options for renal diseases are limited, and the search for disease-specific treatments is ongoing. Nanobodies, single-domain antibodies with many advantages over conventional antibodies, provide flexible, easy-to-format biologicals with many possible applications. Here, we discuss the potential use of nanobodies for renal diseases.

The feasibility of folate receptor alpha- and HER2-targeted intraoperative fluorescence-guided cytoreductive surgery in women with epithelial ovarian cancer: A systematic review

BACKGROUND

Epithelial ovarian cancer (EOC) is often diagnosed late, with a 5-year relative survival of 30.2% for patients with metastatic disease. Residual disease following cytoreductive surgery is an important predictor for poor survival. EOC is characterized by diffuse peritoneal metastases and depositions of small size, challenging a complete resection. Targeted fluorescence imaging is a technique to enhance tumor visualization and can be performed intraoperatively. Folate receptor alpha (FRα) and human epidermal growth factor receptor 2 (HER2) are overexpressed in EOC in 80% and 20% of the cases, respectively, and have been previously studied as a target for intraoperative imaging.

OBJECTIVE

To systematically review the literature on the feasibility of FRα and HER2 targeted fluorescence-guided cytoreductive surgery (FGCS) in women with EOC.

METHODS

PubMed and Embase were searched for human and animal studies on FGCS targeting either HER2 or FRα in either women with EOC or animal models of EOC. Risk of bias and methodological quality were assessed with the SYRCLE and MINORS tool, respectively.

RESULTS

All animal studies targeting either FRα or HER2 were able to detect tumor deposits using intraoperative fluorescence imaging. One animal study targeting HER2 compared conventional cytoreductive surgery (CCS) to FGCS and concluded that FGCS, either without or following CCS, resulted in statistically significant less residual disease compared to CCS alone. Human studies on FGCS showed an increased detection rate of tumor deposits. True positives ranged between 75%-77% and false positives between 10%-25%. Lymph nodes were the main source of false positive results. Sensitivity was 85.9%, though only reported by one human study.

CONCLUSION

FGCS targeting either HER2 or FRα appears to be feasible in both EOC animal models and patients with EOC. FGCS is a promising technique, but further research is warranted to validate these results and particularly study the survival benefit.

Decorating sdAbs with Chelators: Effect of Conjugation on Biodistribution and Functionality

Single domain antibodies (sdAbs) have proven to be valuable probes for molecular imaging. In order to produce such probes, one strategy is the functionalization of the reactive amine side chain of lysines with a chelator, resulting in a mixture of compounds with a different degree of conjugation. In this study, we implemented anion exchange chromatography (AEX) to separate the different compounds or fractions that were further characterized and evaluated to study the impact of the conjugation degree on pharmacokinetic properties and functionality. Anti-HER2 and anti-MMR sdAbs were functionalized with NOTA or DTPA chelator. Anion exchange chromatography was performed using 0.02 mol/L Tris pH 7.5 as the first solvent and 0.25 M or 0.4 M NaCl (in case of NOTA chelator or DTPA chelator, respectively) as the second solvent applied as a gradient. The fractions were characterized via mass spectrometry (MS), surface plasmon resonance (SPR), and isoelectric focusing gel electrophoresis (IEF), while in vivo studies were performed after radiolabeling with either ⁶⁸Ga (NOTA) or ¹¹¹In (DTPA) to assess the impact of the conjugation degree on pharmacokinetics. AEX could successfully be applied to separate fractions of (chelator)_n-anti-HER2 and (chelator)_n-anti-MMR sdAb constructs. MS confirmed the identity of different peaks obtained in the separation process. SPR measurement suggests a small loss of affinity for (chelator)₃-anti-sdAb, while IEF revealed a correlated decrease in isoelectric point (pI) with the number of conjugated chelators. Interestingly, both the reduction in affinity and in pI was stronger with the DTPA chelator than with NOTA for both sdAbs. In vivo data showed no significant differences in organ uptake for any construct, except for (DTPA)_n-anti-MMR, which showed a significantly higher liver uptake for (DTPA)₁-anti-MMR compared to (DTPA)₂-anti-MMR and (DTPA)₃-anti-MMR. For all constructs in general, high kidney uptake was observed, due to the typical renal clearance of sdAb-based tracers. The kidney uptake showed significant differences between fractions of a same construct and indicates that a higher conjugation degree improves kidney clearance. AEX allows the separation of sdAbs with a different degree of conjugation and provides the opportunity to further characterize individual fractions. The conjugation of a chelator to sdAbs can alter some properties of the tracers, such as pI; however, the impact on the general biodistribution profile and tumor targeting was minimal.

Nanobodies as in vivo, non-invasive, imaging agents

In vivo imaging has become in recent years an incredible tool to study biological events and has found critical applications in diagnostic medicine. Although a lot of efforts and applications have been achieved using monoclonal antibodies, other types of delivery agents are being developed. Among them, VHHs, antigen binding fragments derived from camelid heavy chain-only antibodies, also known as nanobodies, have particularly attracted attention. Indeed, their stability, fast clearance, good tissue penetration, high solubility, simple cloning and recombinant production make them attractive targeting agents for imaging modalities such as PET, SPECT or Infra-Red. In this review, we discuss the pioneering work that has been carried out using VHHs and summarize the recent developments that have been made using nanobodies for in vivo, non-invasive, imaging.

The Design and Preclinical Evaluation of a Single-Label Bimodal Nanobody Tracer for Image-Guided Surgery

Intraoperative guidance using targeted fluorescent tracers can potentially provide surgeons with real-time feedback on the presence of tumor tissue in resection margins. To overcome the limited depth penetration of fluorescent light, combining fluorescence with SPECT/CT imaging and/or gamma-ray tracing has been proposed. Here, we describe the design and preclinical validation of a novel bimodal nanobody-tracer, labeled using a “multifunctional single attachment point” (MSAP) label, integrating a Cy5 fluorophore and a diethylenetriaminepentaacetic acid (DTPA) chelator into a single structure. After conjugation of the bimodal MSAP to primary amines of the anti-HER2 nanobody 2Rs15d and ¹¹¹In-labeling of DTPA, the tracer’s characteristics were evaluated in vitro. Subsequently, its biodistribution and tumor targeting were assessed by SPECT/CT and fluorescence imaging over 24 h. Finally, the tracer’s ability to identify small, disseminated tumor lesions was investigated in mice bearing HER2-overexpressing SKOV3.IP1 peritoneal lesions. [¹¹¹In]In-MSAP.2Rs15d retained its affinity following conjugation and remained stable for 24 h. In vivo SPECT/CT and fluorescence images showed specific uptake in HER2-overexpressing tumors with low background. High tumor-to-muscle ratios were obtained at 1h p.i. and remained 19-fold on SPECT/CT and 3-fold on fluorescence images over 24 h. In the intraperitoneally disseminated model, the tracer allowed detection of larger lesions via nuclear imaging, while fluorescence enabled accurate removal of submillimeter lesions. Bimodal nuclear/fluorescent nanobody-tracers can thus be conveniently designed by conjugation of a single-molecule MSAP-reagent carrying a fluorophore and chelator for radioactive labeling. Such tracers hold promise for clinical applications.

Unique Benefits of Tumor-Specific Nanobodies for Fluorescence Guided Surgery

Tumor-specific fluorescence labeling is promising for real-time visualization of solid malignancies during surgery. There are a number of technologies to confer tumor-specific fluorescence. Antibodies have traditionally been used due to their versatility in modifications; however, their large size hampers efficient fluorophore delivery. Nanobodies are a novel class of molecules, derived from camelid heavy-chain only antibodies, that have shown promise for tumor-specific fluorescence labeling. Nanobodies are ten times smaller than standard antibodies, while maintaining antigen-binding capacity and have advantageous features, including rapidity of tumor labeling, that are reviewed in the present report. The present report reviews special considerations needed in developing nanobody probes, the status of current literature on the use of nanobody probes in fluorescence guided surgery, and potential challenges to be addressed for clinical translation.

The Next-Generation Immune Checkpoint LAG-3 and Its Therapeutic Potential in Oncology: Third Time's a Charm

The blockade of immune checkpoints (ICPs), such as cytotoxic T lymphocyte associated protein-4 (CTLA-4) and programmed death-1 (PD-1) and its ligand (PD-L1), has propelled the field of immuno-oncology into its current era. Drugs targeting these ICPs have improved clinical outcome in a number of patients with solid and hematological cancers. Nonetheless, some patients have no benefit from these ICP-blocking therapies. This observation has instigated research into alternative pathways that are responsible for the escape of cancer cells from anti-cancer immune responses. From this research, a number of molecules have emerged as promising therapeutic targets, including lymphocyte activating gene-3 (LAG-3), a next-generation ICP. We will review the current knowledge on the biological activity of LAG-3 and linked herewith its expression on activated immune cells. Moreover, we will discuss the prognostic value of LAG-3 and how LAG-3 expression in tumors can be monitored, which is an aspect that is of utmost importance, as the blockade of LAG-3 is actively pursued in clinical trials.

Nanobodies as Versatile Tool for Multiscale Imaging Modalities

Molecular imaging is constantly growing in different areas of preclinical biomedical research. Several imaging methods have been developed and are continuously updated for both in vivo and in vitro applications, in order to increase the information about the structure, localization and function of molecules involved in physiology and disease. Along with these progresses, there is a continuous need for improving labeling strategies. In the last decades, the single domain antigen-binding fragments nanobodies (Nbs) emerged as important molecular imaging probes. Indeed, their small size (~15 kDa), high stability, affinity and modularity represent desirable features for imaging applications, providing higher tissue penetration, rapid targeting, increased spatial resolution and fast clearance. Accordingly, several Nb-based probes have been generated and applied to a variety of imaging modalities, ranging from in vivo and in vitro preclinical imaging to super-resolution microscopy. In this review, we will provide an overview of the state-of-the-art regarding the use of Nbs in several imaging modalities, underlining their extreme versatility and their enormous potential in targeting molecules and cells of interest in both preclinical and clinical studies.

Nanobodies in cancer

For treatment and diagnosis of cancer, antibodies have proven their value and now serve as a first line of therapy for certain cancers. A unique class of antibody fragments called nanobodies, derived from camelid heavy chain-only antibodies, are gaining increasing acceptance as diagnostic tools and are considered also as building blocks for chimeric antigen receptors as well as for targeted drug delivery. The small size of nanobodies (∼15 kDa), their stability, ease of manufacture and modification for diverse formats, short circulatory half-life, and high tissue penetration, coupled with excellent specificity and affinity, account for their attractiveness. Here we review applications of nanobodies in the sphere of tumor biology.

The Emerging Role of CD24 in Cancer Theranostics-A Novel Target for Fluorescence Image-Guided Surgery in Ovarian Cancer and Beyond

Complete cytoreductive surgery is the cornerstone of the treatment of epithelial ovarian cancer (EOC). The application of fluorescence image-guided surgery (FIGS) allows for the increased intraoperative visualization and delineation of malignant lesions by using fluorescently labeled targeting biomarkers, thereby improving intraoperative guidance. CD24, a small glycophosphatidylinositol-anchored cell surface receptor, is overexpressed in approximately 70% of solid cancers, and has been proposed as a prognostic and therapeutic tumor-specific biomarker for EOC. Recently, preclinical studies have demonstrated the benefit of CD24-targeted contrast agents for non-invasive fluorescence imaging, as well as improved tumor resection by employing CD24-targeted FIGS in orthotopic patient-derived xenograft models of EOC. The successful detection of miniscule metastases denotes CD24 as a promising biomarker for the application of fluorescence-guided surgery in EOC patients. The aim of this review is to present the clinical and preclinically evaluated biomarkers for ovarian cancer FIGS, highlight the strengths of CD24, and propose a future bimodal approach combining CD24-targeted fluorescence imaging with radionuclide detection and targeted therapy.

Cyanine Conjugate-Based Biomedical Imaging Probes

Cyanine is a class of fluorescent dye with meritorious fluorescence properties and has motivated numerous researchers to explore its imaging capabilities by miscellaneous structural modification and functionalization strategies. The covalent conjugation with other functional molecules represents a distinctive design strategy and has shown immense potential in both basic and clinical research. This review article summarizes recent achievements in cyanine conjugate-based probes for biomedical imaging. Particular attention is paid to the conjugation with targeting warheads and other contrast agents for targeted fluorescence imaging and multimodal imaging, respectively. Additionally, their clinical potential in cancer diagnostics is highlighted and some concurrent impediments for clinical translation are discussed.

Indocyanine green fluorescence-guided intraoperative detection of peritoneal carcinomatosis: systematic review

Background

To review the available clinical data about the value of Indocyanine Green (ICG) fluorescence imaging for intraoperative detection of peritoneal carcinomatosis.

Methods

We conducted a systematic review, according to the PRISMA guidelines, for clinical series investigating the possible role of ICG fluorescence imaging in detecting peritoneal carcinomatosis during surgical treatment of abdominal malignancies. With the aim to analyze actual application in the daily clinical practice, papers including trials with fluorophores other than ICG, in vitro and animals series were excluded. Data on patients and cancer features, timing, dose and modality of ICG administration, sensitivity, specificity and accuracy of fluorescence diagnosis of peritoneal nodules were extracted and analyzed.

Results

Out of 192 screened papers, we finally retrieved 7 series reporting ICG-guided detection of peritoneal carcinomatosis. Two papers reported the same cases, thus only 6 series were analyzed, for a total of 71 patients and 353 peritoneal nodules. The investigated tumors were colorectal carcinomas in 28 cases, hepatocellular carcinoma in 16 cases, ovarian cancer in 26 cases and endometrial cancer in 1 case. In all but 4 cases, the clinical setting was an elective intervention in patients known as having peritoneal carcinomatosis. No series reported a laparoscopic procedure. Technical data of ICG management were consistent across the studies. Overall, 353 lesions were harvested and singularly evaluated. Sensitivity varied from 72.4 to 100%, specificity from 54.2 to 100%. Two series reported that planned intervention changed in 25 and 29% of patients, respectively.

Conclusion

Indocyanine Green based fluorescence of peritoneal carcinomatosis is a promising intraoperative tool for detection and characterization of peritoneal nodules in patients with colorectal, hepatocellular, ovarian carcinomas. Further prospective studies are needed to fix its actual diagnostic value on these and other abdominal malignancies with frequent spread to peritoneum.

CD24-targeted fluorescence imaging in patient-derived xenograft models of high-grade serous ovarian carcinoma

BACKGROUND

The survival rate of patients with advanced high-grade serous ovarian carcinoma (HGSOC) remains disappointing. Clinically translatable orthotopic cell line xenograft models and patient-derived xenografts (PDXs) may aid the implementation of more personalised treatment approaches. Although orthotopic PDX reflecting heterogeneous molecular subtypes are considered the most relevant preclinical models, their use in therapeutic development is limited by lack of appropriate imaging modalities.

METHODS

We developed novel orthotopic xenograft and PDX models for HGSOC, and applied a near-infrared fluorescently labelled monoclonal antibody targeting the cell surface antigen CD24 for non-invasive molecular imaging of epithelial ovarian cancer. CD24-Alexa Fluor 680 fluorescence imaging was compared to bioluminescence imaging in three orthotopic cell line xenograft models of ovarian cancer (OV-90^luc+, Skov-3^luc+ and Caov-3^luc+, n = 3 per model). The application of fluorescence imaging to assess treatment efficacy was performed in carboplatin-paclitaxel treated orthotopic OV-90 xenografts (n = 10), before the probe was evaluated to detect disease progression in heterogenous PDX models (n = 7).

FINDINGS

Application of the near-infrared probe, CD24-AF680, enabled both spatio-temporal visualisation of tumour development, and longitudinal therapy monitoring of orthotopic xenografts. Notably, CD24-AF680 facilitated imaging of multiple PDX models representing different histological subtypes of the disease.

INTERPRETATION

The combined implementation of CD24-AF680 and orthotopic PDX models creates a state-of-the-art preclinical platform which will impact the identification and validation of new targeted therapies, fluorescence image-guided surgery, and ultimately the outcome for HGSOC patients.

FUNDING

This study was supported by the H2020 program MSCA-ITN [675743], Helse Vest RHF, and Helse Bergen HF [911809, 911852, 912171, 240222, HV1269], as well as by The Norwegian Cancer Society [182735], and The Research Council of Norway through its Centers of excellence funding scheme [223250, 262652].

Tumor-specific near-infrared nanobody probe rapidly labels tumors in an orthotopic mouse model of pancreatic cancer

BACKGROUND

Nanobodies, derived from camelid antibodies made of only heavy chains, are the smallest, biologic, antigen-binding fragments (~15kDa) with faster pharmacokinetics and better tumor penetration efficiency than standard antibodies. The present study evaluates the efficacy of a fluorescent, anti-carcinoembryonic antigen (CEA) nanobody for rapid tumor labeling in an orthotopic mouse model of pancreatic cancer.

METHODS

Anti-CEA or control nanobodies were conjugated with the near-infrared fluorophore IRDye 800CW. Fragments of BxPC-3 (high-CEA expressing) or MiaPACA-2 (low-CEA expressing) human pancreatic cancer cell lines were orthotopically implanted into the pancreatic tail of nude mice. After tumors reached 7 to 10 mm in size, 2 nmol anti-CEA or control nanobody-IRDye800CW were injected intravenously. Mice were imaged at various time points hours post-injection.

RESULTS

Anti-CEA nanobodies clearly labeled BxPC3 orthotopic pancreatic tumors 3 hours after injection. The signal was present as early as 15 minutes after injection and was robust at 1 to 3 hours after injection with a tumor-to-background ratio of 2.66. In contrast, there was very low accumulation in the low CEA-expressing, MiaPACA2 pancreatic orthotopic tumors. The fluorophore-conjugated nanobody was specific for CEA-expressing tumors, while the control nanobody did not show any tumor-specific signal. Both nanobodies had strong kidney uptake as expected for small-molecule probes. The fluorescence signal was detectable using 2 clinical, Food and Drug Administration-approved, 800 nm imaging devices as well as small animal imaging systems.

CONCLUSION

This anti-CEA, nanobody-based, fluorescent probe labeled pancreatic orthotopic tumors within 15 minutes of intravenous injection. Fluorescent anti-CEA nanobodies have labeling kinetics that approach the speed of nonspecific dyes such as indocyanine green but with the specificity of antibodies. The use of fluorescently-labeled, intact antibodies leads to a labeling delay of 48 to 96 hours between probe administration and the necessarily delayed time of operation, which can be avoided with nanobodies. The kinetics of a nanobody-based probe makes it a practical agent for same-day, patient administration and fluorescence-guided surgery.

Nanobody-targeted photodynamic therapy induces significant tumor regression of trastuzumab-resistant HER2-positive breast cancer, after a single treatment session

Rationale

A substantial number of breast cancer patients with an overexpression of the human epidermal growth factor receptor 2 (HER2) have residual disease after neoadjuvant therapy or become resistant to trastuzumab. Photodynamic therapy (PDT) using nanobodies targeted to HER2 is a promising treatment option for these patients. Here we investigate the in vitro and in vivo antitumor efficacy of HER2-targeted nanobody-photosensitizer (PS) conjugate PDT.

Methods

Nanobodies targeting HER2 were obtained from phage display selections. Monovalent nanobodies were engineered into a biparatopic construct. The specificity of selected nanobodies was tested in immunofluorescence assays and their affinity was evaluated in binding studies, both performed in a panel of breast cancer cells varying in HER2 expression levels. The selected HER2-targeted nanobodies 1D5 and 1D5-18A12 were conjugated to the photosensitizer IRDye700DX and tested in in vitro PDT assays. Mice bearing orthotopic HCC1954 trastuzumab-resistant tumors with high HER2 expression or MCF-7 tumors with low HER2 expression were intravenously injected with nanobody-PS conjugates. Quantitative fluorescence spectroscopy was performed for the determination of the local pharmacokinetics of the fluorescence conjugates. After nanobody-PS administration, tumors were illuminated to a fluence of 100 J∙cm^-2, with a fluence rate of 50 mW∙cm^-2, and thereafter tumor growth was measured with a follow-up until 30 days.

Results

The selected nanobodies remained functional after conjugation to the PS, binding specifically and with high affinity to HER2-positive cells. Both nanobody-PS conjugates potently and selectively induced cell death of HER2 overexpressing cells, either sensitive or resistant to trastuzumab, with low nanomolar LD₅₀ values. In vivo, quantitative fluorescence spectroscopy showed specific accumulation of nanobody-PS conjugates in HCC1954 tumors and indicated 2 h post injection as the most suitable time point to apply light. Nanobody-targeted PDT with 1D5-PS and 1D5-18A12-PS induced significant tumor regression of trastuzumab-resistant high HER2 expressing tumors, whereas in low HER2 expressing tumors only a slight growth delay was observed.

Conclusion

Nanobody-PS conjugates accumulated selectively in vivo and their fluorescence could be detected through optical imaging. Upon illumination, they selectively induced significant tumor regression of HER2 overexpressing tumors with a single treatment session. Nanobody-targeted PDT is therefore suggested as a new additional treatment for HER2-positive breast cancer, particularly of interest for trastuzumab-resistant HER2-positive breast cancer. Further studies are now needed to assess the value of this approach in clinical practice.

Size and affinity kinetics of nanobodies influence targeting and penetration of solid tumours

A compound's intratumoural distribution is an important determinant for the effectiveness of molecular therapy or imaging. Antibodies (Abs), though often used in the design of targeted compounds, struggle to achieve a homogenous distribution due to their large size and bivalent binding mechanism. In contrast, smaller compounds like nanobodies (Nbs) are expected to distribute more homogenously, though this has yet to be demonstrated in vivo at the microscopic level. We propose an intravital approach to evaluate the intratumoural distribution of different fluorescently labeled monomeric and dimeric Nb tracers and compare this with a monoclonal antibody (mAb). Monomeric and dimeric formats of the anti-HER2 (2Rb17c and 2Rb17c-2Rb17c) and control (R3B23 and R3B23-R3B23) Nb, as well as the dimeric monovalent Nb 2Rb17c-R3B23 were generated and fluorescently labeled with a Cy5 fluorophore. The mAb trastuzumab-Cy5 was also prepared. Whole-body biodistribution of all constructs was investigated in mice bearing subcutaneous xenografts (HER2+ SKOV3) using in vivo epi-fluorescence imaging. Next, for intravital experiments, GFP-expressing SKOV3 cells were grown under dorsal window chambers on athymic nude mice (n = 3/group), and imaged under a fluorescence stereo microscope immediately after intravenous injection of the tracers. Consecutive fluorescence images within the tumour were acquired over the initial 20 min after injection and later, single images were taken at 1, 3 and 24 h post-injection. Additionally, two-photon microscopy was used to investigate the colocalization of GFP (tumour cells) and Cy5 fluorescence (tracers) at higher resolution. Whole-body images showed rapid renal clearance of all Nbs, and fast tumour targeting for the specific Nbs. Specific tumour uptake of the mAb could only be clearly distinguished from background after several hours. Intravital imaging revealed that monomeric Nb tracers accumulated rapidly and distributed homogenously in the tumour mere minutes after intravenous injection. The dimeric compounds initially achieved lower fluorescence intensities than the monomeric. Furthermore, whereas the HER2-specific dimeric bivalent compound remained closely associated to the blood vessels over 24 h, the HER2-specific dimeric monovalent tracer achieved a more homogenous tumour distribution from 1 h post-injection onwards. Non-specific tracers were not retained in the tumour. Trastuzumab had the most heterogenous intratumoural distribution of all evaluated compounds, while -due to the long blood retention- achieving the highest overall tumour uptake at 24 h post-injection. In conclusion, monomeric Nbs very quickly and homogenously distribute through tumour tissue, at a rate significantly greater than dimeric Nbs and mAbs. This underlines the potential of monomeric Nb tracers and therapeutics in molecular imaging and targeted therapies.

Radiometal-labeled anti-VCAM-1 nanobodies as molecular tracers for atherosclerosis - impact of radiochemistry on pharmacokinetics

Radiolabeling of nanobodies with radiometals by chelation has the advantage of being simple, fast and easy to implement in clinical routine. In this study, we validated 68Ga/111In-labeled anti-VCAM-1 nanobodies as potential radiometal-based tracers for molecular imaging of atherosclerosis. Both showed specific targeting of atherosclerotic lesions in ApoE-/- mice. Nevertheless, uptake in lesions and constitutively VCAM-1 expressing organs was lower than previously reported for the 99mTc-labeled analog. We further investigated the impact of different radiolabeling strategies on the in vivo biodistribution of nanobody-based tracers. Comparison of the pharmacokinetics between 68Ga-, 18F-, 111In- and 99mTc-labeled anti-VCAM-1 nanobodies showed highest specific uptake for 99mTc-nanobody at all time-points, followed by the 68Ga-, 111In- and 18F-labeled tracer. No correlation was found with the estimated number of radioisotopes per nanobody, and mimicking specific activity of other radiolabeling methods did not result in an analogous biodistribution. We also demonstrated specificity of the tracer using mice with a VCAM-1 knocked-down phenotype, while showing for the first time the in vivo visualization of a protein knock-down using intrabodies. Conclusively, the chosen radiochemistry does have an important impact on the biodistribution of nanobodies, in particular on the specific targeting, but differences are not purely due to the tracer's specific activity.

Fluorescence Guidance in Surgical Oncology: Challenges, Opportunities, and Translation

Surgical resection continues to function as the primary treatment option for most solid tumors. However, the detection of cancerous tissue remains predominantly subjective and reliant on the expertise of the surgeon. Surgery that is guided by fluorescence imaging has shown clinical relevance as a new approach to detecting the primary tumor, tumor margins, and metastatic lymph nodes. It is a technique to reduce recurrence and increase the possibility of a curative resection. While significant progress has been made in developing this emerging technology as a tool to assist the surgeon, further improvements are still necessary. Refining imaging agents and tumor targeting strategies to be a precise and reliable surgical strategy is essential in order to translate this technology into patient care settings. This review seeks to provide a comprehensive update on the most recent progress of fluorescence-guided surgery and its translation into the clinic. By highlighting the current status and recent developments of fluorescence image-guided surgery in the field of surgical oncology, we aim to offer insight into the challenges and opportunities that require further investigation.

NIRF-Molecular Imaging with Synovial Macrophages-Targeting Vsig4 Nanobody for Disease Monitoring in a Mouse Model of Arthritis

Nanobody against V-set and Ig domain-containing 4 (Vsig4) on tissue macrophages, such as synovial macrophages, could visualize joint inflammation in multiple experimental arthritis models via single-photon emission computed tomography imaging. Here, we further addressed the specificity and assessed the potential for arthritis monitoring using near-infrared fluorescence (NIRF) Cy7-labeled Vsig4 nanobody (Cy7-Nb119). In vivo NIRF-imaging of collagen-induced arthritis (CIA) was performed using Cy7-Nb119. Signals obtained with Cy7-Nb119 or isotope control Cy7-NbBCII10 were compared in joints of naive mice versus CIA mice. In addition, pathological microscopy and fluorescence microscopy were used to validate the arthritis development in CIA. Cy7-Nb119 accumulated in inflamed joints of CIA mice, but not the naive mice. Development of symptoms in CIA was reflected in increased joint accumulation of Cy7-Nb119, which correlated with the conventional measurements of disease. Vsig4 is co-expressed with F4/80, indicating targeting of the increasing number of synovial macrophages associated with the severity of inflammation by the Vsig4 nanobody. NIRF imaging with Cy7-Nb119 allows specific assessment of inflammation in experimental arthritis and provides complementary information to clinical scoring for quantitative, non-invasive and economical monitoring of the pathological process. Nanobody labelled with fluorescence can also be used for ex vivo validation experiments using flow cytometry and fluorescence microscopy.

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

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

Targeted Nanobody-Based Molecular Tracers for Nuclear Imaging and Image-Guided Surgery

Molecular imaging is paving the way towards noninvasive detection, staging, and treatment follow-up of diseases such as cancer and inflammation-related conditions. Monoclonal antibodies have long been one of the staples of molecular imaging tracer design, although their long blood circulation and high nonspecific background limits their applicability. Nanobodies, unique antibody-binding fragments derived from camelid heavy-chain antibodies, have excellent properties for molecular imaging as they are able to specifically find their target early after injection, with little to no nonspecific background. Nanobody-based tracers using either nuclear or fluorescent labels have been heavily investigated preclinically and are currently making their way into the clinic. In this review, we will discuss different important factors in nanobody-tracer design, as well as the current state of the art regarding their application for nuclear and fluorescent imaging purposes. Furthermore, we will discuss how nanobodies can also be exploited for molecular therapy applications such as targeted radionuclide therapy and photodynamic therapy.

The development of fluorescence guided surgery for pancreatic cancer: from bench to clinic

INTRODUCTION

Surgeons face major challenges in achieving curative R0 resection for pancreatic cancers. When the lesion is localized, they must appropriately visualize the tumor, determine appropriate resection margins, and ensure complete tumor clearance. Real-time surgical navigation using fluorescence-guidance has enhanced the ability of surgeons to see the tumor and has the potential to assist in achieving more oncologically complete resections. When there is metastatic disease, fluorescence enhancement can help detect these lesions and prevent unnecessary and futile surgeries. Areas covered: This article reviews different approaches for delivery of a fluorescence signal, their pre-clinical and clinical developments for fluorescence guided surgery, the advantages/challenges of each, and their potential for advancements in the future. Expert commentary: A variety of molecular imaging techniques are available for delivering tumor-specific fluorescence signals. Significant advancements have been made in the past 10 years due to the large body of literature on targeted therapies and this has translated into rapid developments of tumor-specific probes.