Near infrared fluorescence imaging of EGFR expression in vivo using IRDye800CW-nimotuzumab

Visualizing the cellular internalization of therapeutic antibodies via pH-sensitive release of AIEgen

Among the fastest-growing bio-pharmaceuticals, therapeutic antibodies have achieved unprecedented success in treating various diseases. Though powerful, issues such as inefficacy or acquired resistance are waiting to be addressed to benefit more patients with improved therapeutic outcomes. In addition to in vivo distribution, the cellular spatiotemporal information including the antibody-antigen interaction and subsequent internalization is found to be important for the therapeutic effects. To better understand the cellular fate of therapeutic antibodies, especially the cellular internalization process, we employed a pH-sensitive linker to attach a red-emissive AIEgen onto the antibody. The resulting antibody conjugate will undergo AIEgen release to liberate brilliant fluorescence inside acidic endo/lysosomes, allowing wash-free visualization of the internalization process and facilitating the evaluation of antibody-drug efficacy.

Evaluation of nimotuzumab Fab2 as an optical imaging agent in EGFR positive cancers

Molecular-targeted imaging probes can be used with a variety of imaging modalities to detect diseased tissues and guide their removal. EGFR is a useful biomarker for a variety of cancers, because it is expressed at high levels relative to normal tissues. Previously, we showed the anti-EGFR antibody nimotuzumab can be used as a positron emission tomography and fluorescent imaging probe for EGFR positive cancers in mice. These imaging probes are currently in clinical trials for PET imaging and image-guided surgery, respectively. One issue with using antibody probes for imaging is their long circulation time and slow tissue penetration, which requires patients to wait a few days after injection before imaging or surgery, multiple visits and longer radiation exposure. Here, we generated a Fab2 fragment of nimotuzumab, by pepsin digestion and labeled it with IRDye800CW to evaluate its optical imaging properties. The Fab2 had faster tumor accumulation and clearance in mice relative to the nimotuzumab IgG. The fluorescent signal peaked at 2 h post injection and remained high until 6 h post injection. The properties of the Fab2 allow a higher signal to background to be obtained in a shorter time frame, reducing the wait time for imaging after probe infusion.

Development of a new minimally invasive phototherapy for lung cancer using antibody-toxin conjugate

BACKGROUND

Photodynamic therapy (PDT) is a cancer-targeted treatment that uses a photosensitizer (PS) and laser irradiation. The effectiveness of current PDT using red light for advanced cancers is limited, because red light can only reach depths within a few millimeters. To enhance the antitumor effect for lung cancers, we developed a new phototherapy, intelligent targeted antibody phototherapy (iTAP). This treatment uses a combination of immunotoxin and a PS, mono-L-aspartyl chlorin e6 (NPe6).

METHODS

We examined whether cetuximab encapsulated in endosomes was released into the cytosol by PS in PDT under light irradiation. A431 cells were treated with fluorescein isothiocyanate-labeled cetuximab, NPe6, and light irradiation and were observed with fluorescence microscopy. We analyzed the cytotoxicity of saporin-conjugated cetuximab (IT-cetuximab) in A431, A549, and MCF7 cells and the antitumor effect in model A549-bearing mice in vivo using the iTAP method.

RESULTS

Fluorescent microscopy analysis showed that the photodynamic effect of NPe6 (20 μM) and light irradiation (37.6 J/cm² ) caused the release of cetuximab from the endosome into the cytosol. In vitro analysis demonstrated that the iTAP method enhanced the cytotoxicity of IT-cetuximab by the photodynamic effect. In in vivo experiments, compared with IT-cetuximab alone or PDT alone, the iTAP method using a low dose of IT-cetuximab showed the greatest enhancement of the antitumor effect.

CONCLUSIONS

Our study is the first report of the iTAP method using NPe6 for lung cancer cells. The iTAP method may become a new, minimally invasive treatment superior to current PDT methods.

Near-Infrared Fluorescence Imaging of EGFR-Overexpressing Tumors in the Mouse Xenograft Model Using scFv-IRDye800CW and Cetuximab-IRDye800CW

EGFR (epidermal growth factor receptor) is overexpressed in a variety of human cancers (including squamous cell carcinoma of head and neck, colon cancer, and some breast cancers) and therefore is regarded as an ideal target for cancer therapy or imaging purposes. In the current study, we produced a scFv-based near-infrared probe (called cet.Hum.scFv-IRDye-800CW) and evaluated its ability in recognizing and imaging of EGFR-overexpressing tumors in a mouse model. Like the molecular probe consisting of its parental antibody (cetuximab, an FDA-approved monoclonal antibody) and IRD800CW, cet.Hum.scFv-IRDye-800CW was able to recognize EGFR-overexpressing tumors in mice. cet.Hum.scFv-IRDye-800CW was found to be superior to the cetuximab-based probe in imaging of mouse tumors. The tumor-to-background ratio and blood clearance rate were higher when cet.Hum.scFv-IRDye-800CW was used as an imaging probe.

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.

Imaging Immune Cells Using Fc Domain Probes in Mouse Cancer Xenograft Models

Simple Summary

The immune system responds to abnormal cell growth by sending immune cells to kill them. The immune cell response is very important since it can usually stop abnormal cells from growing and spreading. Immuno-therapeutics used to treat cancer require help from the immune system to be effective. A biopsy is typically performed to determine the therapeutic efficacy of cancer treatment which is invasive and difficult. A simpler and less invasive way to monitor therapeutic efficacy is needed. Here, we show a molecule that can be used as an imaging agent to determine immune cell recruitment to tumors.

Abstract

Tracking immune responses is complex due to the mixture of cell types, variability in cell populations, and the dynamic environment. Tissue biopsies and blood analysis can identify infiltrating and circulating immune cells; however, due to the dynamic nature of the immune response, these are prone to sampling errors. Non-invasive targeted molecular imaging provides a method to monitor immune response, which has advantages of providing whole-body images, being non-invasive, and allowing longitudinal monitoring. Three non-specific Fc-containing proteins were labeled with near-infrared dye IRDye800CW and used as imaging probes to assess tumor-infiltrating immune cells in FaDu and A-431 xenograft models. We showed that Fc domains localize to tumors and are visible by fluorescent imaging. This tumor localization appears to be based on binding tumor-associated immune cells and some xenografts showed higher fluorescent signals than others. The Fc domain alone bound to different human immune cell types. The Fc domain can be a valuable research tool to study innate immune response.

Functional in vitro assessment of modified antibodies: Impact of label on protein properties

Labelling of therapeutic antibodies with radionuclides or fluorophores is routinely used to study their pharmacokinetic properties. A critical assumption in utilizing labelled therapeutic antibodies is that the label has no unfavourable effects on antibody charge, hydrophobicity, or receptor affinity. Ideally, the labelled protein should not have any significant deviations from the physiological properties of the original molecule. This article describes an established quality in vitro assessment workflow for labelled antibodies that ensures better prediction of changes in antibody pharmacokinetic (PK) properties after modifications. This analysis package considers degradation and aggregation analysis by size-exclusion chromatography, changes in neonatal-Fc-receptor (FcRn) affinity, and heparin interaction. FcRn binding is important for antibody recycling and half-life extension, whereas heparin affinity provides estimates on the rate of endocytosis through unspecific cell surface binding. Additionally, mass spectrometric analysis to determine the degree of labelling (DoL) completes the package and the combined analysis data allow to predict the label contribution to the PK properties of the modified antibody. This analytical strategy for labelling 11 IgGs has been investigated using 2 different IgG₁ constructs and applying 7 different types of labels. Each labelling resulted in a change in the physicochemical properties of the protein. Not only can the DoL of modified IgGs lead to a change in protein properties, but the type of label also can. Furthermore, it was demonstrated that the labelling process can also influence the behaviour of labelled mAbs. An identical label on different constructs of IgG₁ can cause different affinities for FcRn and heparin. Considering the assessment data, only 6 of the 11 modified antibodies from this study can be recommended for subsequent experiments. In conclusion, a suitability assessment of labelled antibodies prior to any pharmacokinetic studies is essential to reduce cost, allocate resources and reduce the number of animal experiments during pre-clinical drug development.

Pre-clinical study of IRDye800CW-nimotuzumab formulation, stability, pharmacokinetics, and safety

Background

Epidermal growth factor receptor (EGFR) is a target for cancer therapy as it is overexpressed in a wide variety of cancers. Therapeutic antibodies that bind EGFR are being evaluated in clinical trials as imaging agents for positron emission tomography and image-guided surgery. However, some of these antibodies have safety concerns such as infusion reactions, limiting their use in imaging applications. Nimotuzumab is a therapeutic monoclonal antibody that is specific for EGFR and has been used as a therapy in a number of countries.

Methods

Formulation of IRDye800CW-nimotuzumab for a clinical trial application was prepared. The physical, chemical, and pharmaceutical properties were tested to develop the specifications to determine stability of the product. The acute and delayed toxicities were tested and IRDye800CW-nimotuzumab was determined to be non-toxic. Non-compartmental pharmacokinetics analysis was used to determine the half-life of IRDye800CW-nimotuzumab.

Results

IRDye800CW-nimotuzumab was determined to be non-toxic from the acute and delayed toxicity study. The half-life of IRDye800CW-nimotuzumab was determined to be 38 ± 1.5 h. A bi-exponential analysis was also used which gave a t_1/2 alpha of 1.5 h and t_1/2 beta of 40.8 h.

Conclusions

Here, we show preclinical studies demonstrating that nimotuzumab conjugated to IRDye800CW is safe and does not exhibit toxicities commonly associated with EGFR targeting antibodies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08003-3.

Recent progress in the molecular imaging of therapeutic monoclonal antibodies

Therapeutic monoclonal antibodies have become one of the central components of the healthcare system and continuous efforts are made to bring innovative antibody therapeutics to patients in need. It is equally critical to acquire sufficient knowledge of their molecular structure and biological functions to ensure the efficacy and safety by incorporating new detection approaches since new challenges like individual differences and resistance are presented. Conventional techniques for determining antibody disposition including plasma drug concentration measurements using LC-MS or ELISA, and tissue distribution using immunohistochemistry and immunofluorescence are now complemented with molecular imaging modalities like positron emission tomography and near-infrared fluorescence imaging to obtain more dynamic information, while methods for characterization of antibody's interaction with the target antigen as well as visualization of its cellular and intercellular behavior are still under development. Recent progress in detecting therapeutic antibodies, in particular, the development of methods suitable for illustrating the molecular dynamics, is described here.

Comparison of Panitumumab-IRDye800CW and 5-Aminolevulinic Acid to Provide Optical Contrast in a Model of Glioblastoma Multiforme

Maximal safe resection of malignant tissue is associated with improved progression-free survival and better response to radiation and chemotherapy for patients with glioblastoma (GBM). 5-Aminolevulinic acid (5-ALA) is the current FDA-approved standard for intraoperative brain tumor visualization. Unfortunately, autofluorescence in diffuse areas and high fluorescence in dense tissues significantly limit discrimination at tumor margins. This study is the first to compare 5-ALA to an investigational new drug, panitumumab-IRDye800CW, in the same animal model. A patient-derived GBM xenograft model was established in 16 nude mice, which later received injections of 5-ALA, panitumumab-IRDye800CW, IRDye800CW, 5-ALA and IRDye800CW, or 5-ALA and panitumumab-IRDye800CW. Brains were prepared for multi-instrument fluorescence imaging, IHC, and quantitative analysis of tumor-to-background ratio (TBR) and tumor margin accuracy. Statistical analysis was compared with Wilcoxon rank-sum or paired t test. Panitumumab-IRDye800CW had a 30% higher comprehensive TBR compared with 5-ALA (P = 0.0079). SDs for core and margin regions of interest in 5-ALA-treated tissues were significantly higher than those found in panitumumab-IRDye800CW-treated tissues (P = 0.0240 and P = 0.0284, respectively). Panitumumab-IRDye800CW specificities for tumor core and margin were more than 10% higher than those of 5-ALA. Higher AUC for panitumumab-IRDye800CW indicated strong capability to discriminate between normal and malignant brain tissue when compared with 5-ALA. This work demonstrates that panitumumab-IRDye800CW shows potential as a targeting agent for fluorescence intraoperative detection of GBM. Improved margin definition and surgical resection using panitumumab-IRDye800 has the potential to improve surgical outcomes and survival in patients with GBM compared with 5-ALA.

Image-guided mathematical modeling for pharmacological evaluation of nanomaterials and monoclonal antibodies

While plasma concentration kinetics has traditionally been the predictor of drug pharmacological effects, it can occasionally fail to represent kinetics at the site of action, particularly for solid tumors. This is especially true in the case of delivery of therapeutic macromolecules (drug-loaded nanomaterials or monoclonal antibodies), which can experience challenges to effective delivery due to particle size-dependent diffusion barriers at the target site. As a result, disparity between therapeutic plasma kinetics and kinetics at the site of action may exist, highlighting the importance of target site concentration kinetics in determining the pharmacodynamic effects of macromolecular therapeutic agents. Assessment of concentration kinetics at the target site has been facilitated by non-invasive in vivo imaging modalities. This allows for visualization and quantification of the whole-body disposition behavior of therapeutics that is essential for a comprehensive understanding of their pharmacokinetics and pharmacodynamics. Quantitative non-invasive imaging can also help guide the development and parameterization of mathematical models for descriptive and predictive purposes. Here, we present a review of the application of state-of-the-art imaging modalities for quantitative pharmacological evaluation of therapeutic nanoparticles and monoclonal antibodies, with a focus on their integration with mathematical models, and identify challenges and opportunities. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Near-Infrared Molecular Imaging of Glioblastoma by Miltuximab®-IRDye800CW as a Potential Tool for Fluorescence-Guided Surgery

Glioblastoma (GBM) is one of the most aggressive tumors and its 5-year survival is approximately 5%. Fluorescence-guided surgery (FGS) improves the extent of resection and leads to better prognosis. Molecular near-infrared (NIR) imaging appears to outperform conventional FGS, however, novel molecular targets need to be identified in GBM. Proteoglycan glypican-1 (GPC-1) is believed to be such a target as it is highly expressed in GBM and is associated with poor prognosis. We hypothesize that an anti-GPC-1 antibody, Miltuximab^®, conjugated with the NIR dye, IRDye800CW (IR800), can specifically accumulate in a GBM xenograft and provide high-contrast in vivo fluorescent imaging in rodents following systemic administration. Miltuximab^® was conjugated with IR800 and intravenously administered to BALB/c nude mice bearing a subcutaneous U-87 GBM hind leg xenograft. Specific accumulation of Miltuximab^®-IR800 in subcutaneous xenograft tumor was detected 24 h later using an in vivo fluorescence imager. The conjugate did not cause any adverse events in mice and caused strong fluorescence of the tumor with tumor-to-background ratio (TBR) reaching 10.1 ± 2.8. The average TBR over the 10-day period was 5.8 ± 0.6 in mice injected with Miltuximab^®-IR800 versus 2.4 ± 0.1 for the control group injected with IgG-IR800 (p = 0.001). Ex vivo assessment of Miltuximab^®-IR800 biodistribution confirmed its highly specific accumulation in the tumor. The results of this study confirm that Miltuximab^®-IR800 holds promise for intraoperative fluorescence molecular imaging of GBM and warrants further studies.

High-quality quantum dots for multiplexed bioimaging: A critical review

Bioimaging done using two or more fluorophores possessing different emission wavelengths can be termed as a multicolor/multiplexed bioimaging technique. Traditionally, images are captured sequentially using multiple fluorophores having specific excitation and emission. For this purpose, multifunctional nanoprobes, such as organic fluorophores, metallic nanoparticles, semiconductor quantum dots, and carbon dots (CDs) are used. Among these fluorophores, quantum dots (QDs) have emerged as an ideal probe for multiplexed bioimaging due to their unique property of size tunable emission. However, the usage of quantum dots in bioimaging is limited due to their toxicity. Furthermore, the reproducibility of optical properties is cynical. These desirable properties, along with enhancement in quantum efficiency, photostability, fluorescence lifetime, etc. can be achieved by stringent control over synthesis parameters. This review summarizes the desirable properties and synthesis methods of such superior QDs followed by their application in multiplexed imaging.

Systematic comparison of methods for determining the in vivo biodistribution of porous nanostructured injectable inorganic particles

With a wide variety of biodistribution measurement techniques reported in the literature, it is important to perform side-by-side comparisons of results obtained with different methods on the same particle platform, to determine differences across methods, highlight advantages and disadvantages, and inform methods selection according to specific applications. Inorganic nanostructured particles (INPs) have gained a central role in the development of injectable delivery vectors thanks to their controllable design, biocompatibility, and favorable degradation kinetic. Thus, accurate determination of in vivo biodistribution of INPs is a key aspect of developing and optimizing this class of delivery vectors. In this study, a systematic comparison of spectroscopy (inductively coupled plasma optical emission spectroscopy), fluorescence (in vivo imaging system, confocal microscopy, and plate reader), and radiolabeling (gamma counter)-based techniques is performed to assess the accuracy and sensitivity of biodistribution measurements in mice. Each method is evaluated on porous silicon particles, an established and versatile injectable delivery platform. Biodistribution is evaluated in all major organs and compared in terms of absolute results (%ID/g and %ID/organ when possible) and sensitivity (σ_%). Finally, we discuss how these results can be extended to inform method selection for other platforms and specific applications, with an outlook to potential benefit for pre-clinical and clinical studies. Overall, this study presents a new practical guide for selection of in vivo biodistribution methods that yield quantitative results. STATEMENT OF SIGNIFICANCE: The significance of this work lies in the use of a single platform to test performances of different biodistribution methods in vivo, with a strict quantitative metric. These results, united with the qualitative comparison of advantages and disadvantages of each technique, are aimed at supporting the rational choice of each different method according to the specific application, to improve the quantitative description of biodistribution results that will be published by others in the future.

Fluorescence Lifetime-Based Tumor Contrast Enhancement Using an EGFR Antibody-Labeled Near-Infrared Fluorophore

PURPOSE

Imaging techniques for highly specific detection of cancer cells in vivo can have applications ranging from preclinical drug discovery studies to clinical cancer diagnosis and surgical therapy. Although fluorescence imaging using cancer-targeted antibodies has shown promise, nonspecific probe accumulation in tissue results in significant background fluorescence, reducing detection sensitivity using traditional intensity-based continuous-wave (CW) fluorescence imaging. Here we demonstrate that fluorescence lifetime (FLT) imaging can provide significant tumor contrast enhancement over CW intensity in preclinical models of human breast cancer.

EXPERIMENTAL DESIGN

Mice bearing MDA-MB-231 tumors were injected with anti-EGFR antibody conjugated to the fluorescent dye IRDye 800CW (anti-EGFR-800). Time domain fluorescence imaging was performed in vivo and in situ up to 48 hours after dye injection.

RESULTS

Mice injected with anti-EGFR-800 showed a significantly longer FLT (0.7 ± 0.03 ns) compared with the FLT of nonspecific probe uptake in liver (0.63 ± 0.05 ns), providing a dramatic improvement in sensitivity and specificity compared with CW intensity. IgG antibody-conjugated IRDye 800CW did not show an increased FLT compared with normal tissue, suggesting that the FLT increase of anti-EGFR-800 in tumors was associated with receptor expression. Using serial surgery, we show that FLT allows the detection of smaller residual tumors in the surgical bed than possible using CW intensity.

CONCLUSIONS

Our data suggest that FLT can significantly enhance tumor contrast using fluorescently labeled antibodies, thereby accelerating the efficient clinical application of these probes for margin assessment in image-guided surgery and for highly specific detection of tumor receptors in vivo.

Ultrasound-mediated cavitation enhances the delivery of an EGFR-targeting liposomal formulation designed for chemo-radionuclide therapy

Nanomedicines allow active targeting of cancer for diagnostic and therapeutic applications through incorporation of multiple functional components. Frequently, however, clinical translation is hindered by poor intratumoural delivery and distribution. The application of physical stimuli to promote tumour uptake is a viable route to overcome this limitation. In this study, ultrasound-mediated cavitation of microbubbles was investigated as a mean of enhancing the delivery of a liposome designed for chemo-radionuclide therapy targeted to EGFR overexpressing cancer. Method: Liposomes (¹¹¹In-EGF-LP-Dox) were prepared by encapsulation of doxorubicin (Dox) and surface functionalisation with Indium-111 tagged epidermal growth factor. Human breast cancer cell lines with high and low EGFR expression (MDA-MB-468 and MCF7 respectively) were used to study selectivity of liposomal uptake, subcellular localisation of drug payload, cytotoxicity and DNA damage. Liposome extravasation following ultrasound-induced cavitation of microbubbles (SonoVue®) was studied using a tissue-mimicking phantom. In vivo stability, pharmacokinetic profile and biodistribution were evaluated following intravenous administration of ¹¹¹In-labelled, EGF-functionalised liposomes to mice bearing subcutaneous MDA-MB-468 xenografts. Finally, the influence of ultrasound-mediated cavitation on the delivery of liposomes into tumours was studied. Results: Liposomes were loaded efficiently with Dox, surface decorated with ¹¹¹In-EGF and showed selective uptake in MDA-MB-468 cells compared to MCF7. Following binding to EGFR, Dox was released into the intracellular space and ¹¹¹In-EGF shuttled to the cell nucleus. DNA damage and cell kill were higher in MDA-MB-468 than MCF7 cells. Moreover, Dox and ¹¹¹In were shown to have an additive cytotoxic effect in MDA-MB-468 cells. US-mediated cavitation increased the extravasation of liposomes in an in vitro gel phantom model. In vivo, the application of ultrasound with microbubbles increased tumour uptake by 66% (p<0.05) despite poor vascularisation of MDA-MB-468 xenografts (as shown by DCE-MRI). Conclusion: ¹¹¹In-EGF-LP-Dox designed for concurrent chemo-radionuclide therapy showed specificity for and cytotoxicity towards EGFR-overexpressing cancer cells. Delivery to tumours was enhanced by the use of ultrasound-mediated cavitation indicating that this approach has the potential to deliver cytotoxic levels of therapeutic radionuclide to solid tumours.

Near infrared imaging of epidermal growth factor receptor positive xenografts in mice with domain I/II specific antibody fragments

Epidermal growth factor receptor (EGFR) is a transmembrane cell surface receptor that is frequently overexpressed and/or mutated in many cancers. Therapies targeting EGFR have poor outcomes due to the lack of reliable diagnostic tests to monitor EGFR. Current in vitro EGFR diagnostic methods are invasive, requiring biopsies, which limits tumor sampling and availability. EGFR molecular imaging provides non-invasive whole-body images capable of detecting primary tumors and metastases, which can be used to diagnose and monitor response to therapy. Methods: We evaluated properties of two anti-EGFR fragments, 8708 and 8709, as molecular-targeted imaging probes. 8708 and 8709 are anti-EGFR antigen binding fragments (Fabs) that recognize domain I/II of EGFR, which is distinct from epitopes recognized by current anti-EGFR therapeutic antibodies. We used complementarity determining region sequences from 8708 and 8709 Fabs to generate an anti-EGFR IgG and (scFv)2 and scFv-Fc antibody fragments. We expressed, purified, and labeled the IgG and fragments with IRDye800CW and used them to image EGFR-positive and -negative xenografts in CD-1 nude mice. 8709 scFv-Fc was also tested for competitive binding with the therapeutic anti-EGFR antibody nimotuzumab and for quantifying ratios of EGFR and EGFRvIII deletion mutant. Results: IRDye800CW-labeled 8708 (scFv)2 and 8709 scFv-Fc imaging probes showed high levels of accumulation and good retention in EGFR-positive xenografts, with peak accumulation occurring at 24 and 48 hours post injection, respectively. IRDye680RD-labeled 8709 scFv-Fc did not compete with IRDye800CW-labeled nimotuzumab for EGFR binding as assayed by flow cytometry using an EGFR-positive cell line. IRDye680RD-labeled 8709 scFv-Fc and IRDye800CW-labeled nimotuzumab used in combination were able to determine the ratio of cells expressing EGFR and a deletion mutant EGFRvIII. Conclusion: IRDye800CW-labeled 8708 (scFv)2 and 8709 scFv-Fc had desirable binding affinities, clearance times, and tumor accumulation to be used for imaging in combination with current EGFR targeted therapies. This study highlights the potential for using 8708 (scFv)2 and 8709 scFv-Fc as EGFR diagnostic and therapy monitoring tools.

99mTc(CO)3+ labeled domain I/II-specific anti-EGFR (scFv)2 antibody fragment for imaging EGFR expression

Bifunctional chelators (BFCs) are covalently linked to biologically active targeting molecules and radiolabeled with radiometals. Technetium-99 m (^99mTc) is the most widely used isotope in nuclear medicine because of its excellent physical properties. The objective of this study was to synthesize and characterize a novel BFC that allows for the labeling of antibodies and antibody fragments using the ^99mTc(CO)₃⁺ core which forms a very stable complex with ^99mTc in the +1 oxidation sate. This study reports the synthesis of a BFC 1-pyrrolidinyl-2,5-dione-11-(bis((1-(carboxymethyl)-1H-imidazol-2-yl)methyl)amino)undecanoic acid (SAAC-CIM NHS ester), and the in vitro and in vivo evaluation of ^99mTc(CO)₃-SAAC-CIM-DLO6-(scFv)₂ (^99mTc(CO)₃-DLO6-(scFv)₂), a domain I/II-specific anti-epidermal growth factor receptor I (anti-EGFR) antibody fragment. The chelator allowed radiolabeling the (scFv)₂ antibody fragment in very mild conditions with no significant decrease in binding to EGFR. Radiochemical yields of >50% (radiochemical purity > 95%) of the resulting anti-EGFR (scFv)₂ immunoconjugate ^99mTc(CO)₃-DLO6-(scFv)₂ was obtained. The radioimmunoconjugate was stable in histidine challenge experiments with less than 20% transchelation at 24 h after challenge in the presence of a 1500-fold excess of histidine. In vivo biodistribution of ^99mTc(CO)₃-DLO6-(scFv)₂ indicates that the tracer was mainly cleared via renal excretion and to a lesser extent via the hepatobiliary pathway. The microSPECT imaging studies performed in mice confirmed the in vitro affinity results. The ^99mTc(CO)₃-DLO6-(scFv)₂ shows some promising properties and warrants further investigation for imaging EGFR.